From neufeld@physics.utoronto.ca Mon Jun 19 16:50:25 EDT 1995 Article: 130 of sci.physics.cond-matter Xref: info.physics.utoronto.ca sci.physics.cond-matter:130 Newsgroups: sci.physics.cond-matter Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: What is a liquid? Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Sun, 18 Jun 1995 19:36:34 GMT References: Status: O In article , Pieter Kuiper wrote: >In article , hrizuk@ptd.net wrote: > >> I've heard many descriptions of liquids, but I've never heard any >> satisfactory definitions of just what a liquid IS. > >Liquids have low viscosity (a somewhat circular definition). > The definition I've always used is that a liquid is a condensed phase which does not produce a restoring force to a shear. In other words, if you have a cube of a liquid, and you slide two opposite faces in their own planes in opposite directions, the liquid does not try to spring back into its original shape. -- Christopher Neufeld....Just a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Mon Jun 19 16:56:10 EDT 1995 Article: 148 of sci.physics.cond-matter Xref: info.physics.utoronto.ca sci.physics.cond-matter:148 Newsgroups: sci.physics.cond-matter Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: What is a liquid? Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Mon, 19 Jun 1995 20:54:27 GMT References: Status: O In article , David Bick wrote: >In article neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) writes: > >> The definition I've always used is that a liquid is a condensed >> phase which does not produce a restoring force to a shear. > >Unfortunately this ignores viscoelastic fluids (such as most polymer >melts). > Well, now we fall into semantics. Any such "adjective-fluids" or "adjective-liquids" I usually think of as being a separate phase from the liquid phase. By analogy with liquid crystals, I would guess that a polymer melt has multiple fluid phases, distinguished by different alignment characteristics among chains. To you, this phase or these phases fall under the category of liquids, and to me it/they don't. As this is a matter of definition, I think we're stuck at this point. -- Christopher Neufeld....Just a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Mon Jun 19 21:35:54 EDT 1995 Article: 19634 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:19634 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Real faster than light Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Tue, 20 Jun 1995 00:34:18 GMT References: <1995Jun19.212639.6312@schbbs.mot.com> Status: O In article <1995Jun19.212639.6312@schbbs.mot.com>, Bronis Vidugiris wrote: >In article , >Erik Max Francis wrote: >)AT&FE1V1X4&C1&D2S0 0S2 43 writes: >) >)> The only explanation to ftl is with negative energy. Neg energy always goes >)> faster than light unless you slow it down, yes its possible! >) >)This is plainly false. Negative energy (i.e., exotic matter) is >)possibly capable of warping spacetime so that other particles will >)travel faster than light, but negative energy itself will not travel >)faster than light anymore than positive energy does. > >I thought I read something on the net about the Casmir effect and >the speed of light increasing in the so-called negative energy >vacuum? > Perhaps. I haven't heard any followup on it since the original paper came out a few years ago. The calculation purported to show that the speed of light in the region between two conducting plates is increased in the direction perpendicular to the plates, and unchanged in the direction parallel to the plates. The increase would be quite small, on part in 1E+36 for reasonably small plate separation (about one micron). I think I can provide the reference for this. I used to know it from memory, but you know how things go. PS: I've been offline a couple of weeks, getting married. Did I miss anything? -- Christopher Neufeld....Just a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Tue Jun 20 11:50:50 EDT 1995 Article: 8430 of comp.os.linux.development.system Xref: info.physics.utoronto.ca comp.os.linux.development.system:8430 Newsgroups: comp.os.linux.development.system Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Error in libc ??? 'atof' does not work Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Tue, 20 Jun 1995 00:29:38 GMT References: <3s42o7$4bj@nyx10.cs.du.edu> <3s4kf8$713@aplatform.com> Status: O In article <3s4kf8$713@aplatform.com>, Gary E. Miller wrote: >Michael Fonte (mfonte@nyx10.cs.du.edu) wrote: > >: Is there a bug in Linux's libc (specifically atof)??? The following >: code works fine on our Sun's but does not work under Linux(486or586 arch). > >: #include >: #include > >: main(int argc, char **argv) >: { >: float f_number; > ^^^^^ >: f_number=atof(argv[1]); > ^^^^ > ANSI C atof() returns a double, not a float! > >: printf("%f\n",f_number); > ^^ ^^^^^^^^ > %f means a double, but f_number is a float >: } > >A float is not a double on just about any CPU ever. > But none of this is responsible for the error. For one thing, floats are treated the same way as doubles in a printf. Try it, I just did, with gcc v2.6.2. Further, it is not necessary to cast a function which returns double to float just to assign it to a float, the compiler is quite capable of inferring the necessity of that. The problem is that atof() is returning something, but the compiler doesn't know what, and is defaulting to integer. People, please, when developing a program, compile with "-Wall -Wmissing-prototypes", you'll save yourself no end of trouble. Get rid of **every** warning message, even the ones which seem unimportant. Nobody wants to see your code compiling with warnings when they try to build it themselves. Anyway, try #include-ing stdlib.h. -- Christopher Neufeld....Just a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Thu Jun 29 22:41:18 EDT 1995 Article: 19816 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:19816 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Influence on gravitation? Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Fri, 30 Jun 1995 02:14:22 GMT References: <3ssgv2$t5n@sulawesi.lerc.nasa.gov> Status: O In article <3ssgv2$t5n@sulawesi.lerc.nasa.gov>, Geoffrey A. Landis wrote: >In article Lance Purple, >lpurple@netcom.com writes: >> Reducing the local gravity is much more difficult. You can briefly >>reduce it > >But the method I like best: > 5: just saturate your body with iron filings, and stand in a *big* >magnetic field... > You don't even need the iron. I received email from somebody in a high field magnet lab who had successfully levitated a live mouse diamagnetically. You need huge field gradients, but the mouse didn't seem any worse for the experience. -- Christopher Neufeld - B.Sc., M.Sc., A.B.D. neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Tue Aug 1 01:19:45 EDT 1995 Article: 28769 of comp.unix.shell Xref: info.physics.utoronto.ca comp.unix.shell:28769 Newsgroups: comp.unix.shell Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: .plan as a pipe Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Tue, 1 Aug 1995 04:03:40 GMT References: <3u5uvo$lq0@newsbf02.news.aol.com> <3uehi4$mvl@hermes.synopsys.com> <3uj8ff$k3m@serve.tech.mis.cfc.com> <3ve6mu$o06@cmcl2.NYU.EDU> Status: O In article <3ve6mu$o06@cmcl2.NYU.EDU>, Hung-Hsien Chang wrote: > >Hi! I recall that there is a trick to make the .plna becomes a pipe >so it would know when people access your .plan. How does it work? >I don't have the procedure and code anymore. > Try the "planner" package, or my more general "runpipe" package. They are both available at FTP from this machine: ftp://caliban.physics.utoronto.ca/pub/planner.tar.Z ftp://caliban.physics.utoronto.ca/pub/runpipe.tar.gz The "runpipe" package has been written on Linux. If anybody ports it to a different O/S (probably just a matter of changing a few #includes), please send me your patches so I can make them part of the standard distribution. -- Christopher Neufeld - B.Sc., M.Sc., A.B.D. Looking for a job in Ottawa Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" neufeld@physics.utoronto.ca From neufeld@physics.utoronto.ca Tue Aug 1 19:37:39 EDT 1995 Article: 20174 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:20174 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: science in ScF (was Re: Butler wins MacArthur! Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Tue, 1 Aug 1995 21:01:23 GMT References: <1995Jul28.221147.29914@den.mmc.com> <3vjvt0$7gv@newsbf02.news.aol.com> <1995Aug1.143916.1752@den.mmc.com> Status: ORS In article <1995Aug1.143916.1752@den.mmc.com>, Wil McCarthy wrote: >In article <3vjvt0$7gv@newsbf02.news.aol.com>, paxd@aol.com (Pax D) writes: >|> >|> This might be possible if a planet has TWO axes of rotation... though I'd > >Again, not possible. You could impart a moment about two separate axes, but >they would sum to a rotation about a single axis. > Yes and no. If the initial angular momentum is not aligned with one of the stable eigenvectors of the moment of inertia tensor the body will precess. Its motion will not be describable by rigid rotation of the body around an axis fixed with respect to the body. One could claim that this is as if the object was rotating about two axes, at least for the purposes of our discussion here. Our planet might have such a precession, with the axis of rotation wandering about five metres from the geographic North Pole with a period of some 427 days, according to an old copy of Goldstein's classical mechanics text. -- Christopher Neufeld - B.Sc., M.Sc., A.B.D. Looking for a job in Ottawa Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" neufeld@physics.utoronto.ca From neufeld@physics.utoronto.ca Tue Aug 1 23:02:05 EDT 1995 Article: 20178 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:20178 sci.misc:9962 Newsgroups: sci.misc,rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: "Waterworld" premise Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Tue, 1 Aug 1995 23:42:18 GMT References: Status: O In article , Richard H Clancey wrote: > > I figured that since the Soviet Union had no port cities, > I believe that the usual analysis says that they had no warm water port cities. This was considered a strategic disadvantage, and was responsible for the Western powers being quite interested in Soviet activities or interests in such areas as India, Turkey, south-east Asia, and the Carribean. -- Christopher Neufeld - B.Sc., M.Sc., A.B.D. Looking for a job in Ottawa Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" neufeld@physics.utoronto.ca From neufeld@physics.utoronto.ca Wed Aug 2 12:17:01 EDT 1995 Article: 20189 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:20189 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: axes of rotation (was Re: science in ScF (was Re: Butler wins MacArthur! Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 2 Aug 1995 16:14:25 GMT References: <1995Jul28.221147.29914@den.mmc.com> <1995Aug1.143916.1752@den.mmc.com> <1995Aug2.143330.28901@den.mmc.com> Status: O In article <1995Aug2.143330.28901@den.mmc.com>, Wil McCarthy wrote: >In article , neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) writes: >|> >|> This might be possible if a planet has TWO axes of rotation... though I'd >|> > >|> >Again, not possible. You could impart a moment about two separate axes, but >|> >they would sum to a rotation about a single axis. >|> > >|> Yes and no. If the initial angular momentum is not aligned with one of >|> the stable eigenvectors of the moment of inertia tensor the body will >|> precess. > >Dynamically unstable, Chris. Like a top that wobbles in wider and wider >circles, the planet's precession will grow until the rotation _does_ fall >into one of the stable dynamic regions, and there the system will stay. > On what time scale? As I mentioned in my posting, the Earth is still precessing, and this precession doesn't seem to be growing at an alarming rate. In fact, it can't grow in the absence of external torques because the moment of inertia about an equatorial axis is slightly less (0.33%) than that about the polar axis, so for a constant angular momentum the equatorial axis rotation has a higher kinetic energy. The system can't decay into a higher energy state. That said, the precession exists for precisely the reason that the moments of inertia are different. The closer the moments of inertia, the lower the precession frequency. The system doesn't really compare with a top, as the precession behaviour is markedly different for a top. In that case, the precession is accompanied by a nutation, due to the external force acting on the top. The wider and wider circles are lower energy configurations, a result of friction in the bearing and with the surrounding air. A planet won't do this if it is oblate and rotating about an axis close to the symmetry axis. >Anyway, a system precessing in such a way has no geosynchronous orbit >around it at all, unless (for an instant!) the precession and rotation >rates match. And _this_ is only possible if the planet is extremely >nonspherical in shape, which kinda moots the whole discussion wrt Earth >and that TNG planet. > I'm not disagreeing with this. I should mention that it isn't possible for the precession and rotation frequencies to be equal, except in the degenerate case, since the ratio of frequencies is equal to (I1 - I3) / I1. In that expression, I1 is the equatorial moment, and I3 the polar moment. Anyway, in my original posting I was merely pointing out that a rigid body in the absence of external torques need not have pure rotations about a single axis. -- Christopher Neufeld - B.Sc., M.Sc., A.B.D. Looking for a job in Ottawa Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" neufeld@physics.utoronto.ca From neufeld@physics.utoronto.ca Mon Aug 7 20:32:30 EDT 1995 Article: 20247 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:20247 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: axes of rotation (was Re: science in ScF (was Re: Butler wins MacArthur! Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Tue, 8 Aug 1995 00:28:53 GMT References: <1995Jul28.221147.29914@den.mmc.com> <1995Aug2.143330.28901@den.mmc.com> <3vs0mm$ov1@bubba.NMSU.Edu> Status: O In article <3vs0mm$ov1@bubba.NMSU.Edu>, David Wayne McKee wrote: >Christopher Neufeld (neufeld@caliban.physics.utoronto.ca) wrote: >: > >: On what time scale? As I mentioned in my posting, the Earth is still >: precessing, and this precession doesn't seem to be growing at an alarming >: rate. In fact, it can't grow in the absence of external torques because >: the moment of inertia about an equatorial axis is slightly less (0.33%) >: than that about the polar axis, so for a constant angular momentum the >: equatorial axis rotation has a higher kinetic energy. > > OK, it may be a bit late to jump in, but I believe that the precession of >the equinoxes *is* caused by an external torque. To whit: tidal forces >on the equitorial bulge. > That's true. The precession I'm talking about is not the precession of the equinoxes, that's an entirely different phenomenon. The precession I wrote about has a period of ~427 days, and is the torque-free precession of the Earth. To quote from a foot note in this Goldstein text: The force-free precession of the earth's axis is not to be confused with its slow precession about the normal to the ecliptic. This *astronomical* precession of the equinoxes is due to the gravitational torques of the sun and the moon which were considered negligible in the above discussion. That the assumption is justified is shown by the long period of the precession of the equinoxes (26000 years) compared to a period of roughly one year for the force-free precession. >: I'm not disagreeing with this. I should mention that it isn't possible >: for the precession and rotation frequencies to be equal, except in the >: degenerate case, since the ratio of frequencies is equal to (I1 - I3) / I1. >: In that expression, I1 is the equatorial moment, and I3 the polar moment. > > To tell the truth, I don't remember this part of classical mechanics. >Does this imply that that where I1 != I3 there will always be a precession? > Not necessarily, but that a precession is one (actually two) of the basis functions which span the space of solutions to the force-free rigid rotating body. According to Euler's equations, one can construct a pure state corresponding to a rotation about the I3 axis, and the system will rotate forever without precession (stability in the presence of some dissipation is another matter, Newton's equations say you can balance an egg indefinitely on a knife blade, too). Euler's equations in omega_x, omega_y, and omega_z for a cylindrically-symmetric problem reduce to a set of three coupled, first order, nonlinear differential equations. Clearly the pure rotation state isn't the only possible solution. We need three solutions to span the space. The precession corresponds to two solutions (an amplitude and a phase), the I3-axis rotation is the third. -- Christopher Neufeld - B.Sc., M.Sc., A.B.D. Looking for a job in Ottawa Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" neufeld@physics.utoronto.ca From neufeld@physics.utoronto.ca Tue Aug 8 13:12:54 EDT 1995 Article: 28946 of comp.unix.shell Xref: info.physics.utoronto.ca comp.unix.shell:28946 Newsgroups: comp.unix.shell Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: sum the sizes of many files Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Tue, 8 Aug 1995 03:30:58 GMT References: <405m2t$pf6@news.ycc.yale.edu> <4065r7$glg@newdelph.cig.mot.com> Status: O In article <4065r7$glg@newdelph.cig.mot.com>, Praveen C. Puri wrote: >In article <405m2t$pf6@news.ycc.yale.edu>, chen@fractal.eng.yale.edu (Q. Richard Chen) writes: >|> For example, I would like to >|> dump all *.bin files to a floppy with 1.44Mb as long as >|> the total sum is less than 1.44Mb. Right now what I do is >|> simply do a >|> ls -l *.bin > >Use this command: > >ls -l *.bin | awk '{sum+=$4} END {print sum}' > I would suggest one modification to this, use "du -a *.bin", rather than "ls". (and of course, the '4' becomes a '1'). You see, you might have files with holes, and assuming that the file system on the 1.44MB floppy supports these, you will get more efficient use of the disk if you base your calculation on the actual physical disk space used, rather than the logical distance between the beginning and end of the file. -- Christopher Neufeld - B.Sc., M.Sc., A.B.D. Looking for a job in Ottawa Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" neufeld@physics.utoronto.ca From neufeld@physics.utoronto.ca Tue Aug 8 13:55:53 EDT 1995 Article: 20259 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:20259 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: axes of rotation (was Re: science in ScF (was Re: Butler wins MacArthur! Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Tue, 8 Aug 1995 17:48:04 GMT References: <1995Jul28.221147.29914@den.mmc.com> <3vs0mm$ov1@bubba.NMSU.Edu> <1995Aug8.142524.4509@den.mmc.com> Status: O In article <1995Aug8.142524.4509@den.mmc.com>, Wil McCarthy wrote: >In article , neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) writes: > >|> dissipation is another matter, Newton's equations say you can balanc an >|> egg indefinitely on a knife blade, too). Euler's equations in omega_x, >|> omega_y, and omega_z for a cylindrically-symmetric problem reduce to a >|> set of three coupled, first order, nonlinear differential equations. >|> Clearly the pure rotation state isn't the only possible solution. We need > >The issue here is one of dynamic stability. It may help to visualize this >situation by thinking of spinning tops. The normal mode for a top is to >spin along the axis with the highest inertia (the one which most of the >mass is furthest from, i.e., the one with the stick sticking out of it). > We're still clearly talking about different things. I am talking about a rigid body in free space, under the influence of no external torques, while you're talking about a spinning top which is fixed at a point, under the influence of an external gravitational field. >If you perturb the top a little bit, you create a precession, or "wobble." >This is _not_ a second axis of rotation, but rather a single axis of >rotation which is moving under the influence of a torque, caused by >unbalanced centrifugal forces. > While I agree that, strictly speaking, a precession does not indicate a second rotational axis, that's not really what we're talking about here. This thread (or at least the part of it to which I've been responding) is concerned with the question: is it possible for a rigid body rotating in free space, in the absence of external torques, to rotate in a way other than a pure rotation at constant angular velocity about a fixed body axis? I claim that it is possible. >In fact, this is a "restoring" torque, >meaning that it pushes the top back toward its original axis, and shrinks >along with the perturbation angle, going exactly to zero once the top has >been righted again. Thus, the precession is dynamically unstable and >quickly damps out. > This, I disagree with. The motion of a heavy symmetrical top fixed at a point does not damp out precession or nutation perturbations. To do so it would have to shed angular momentum preferentially about some axis. Consider that at first I have a symmetric top spinning uniformly about a vertical axis, with no other components to the motion. I walk up to it and give it a slight push at the top, so that the axis is no longer vertical. I have just applied a force with a non-zero perpendicular displacement from the pivot. That means I have applied a torque. That torque was applied for a non-zero time interval, and its time integral gives the change in angular momentum about a horizontal axis. So, the top now has a component of angular momentum about a horizontal axis. There's no escaping that conclusion. In order for it to "damp out" this motion it would have to transfer that angular momentum to something else. Where does it go??? >However, in weightless, vacuum conditions, the tumbling will continue >forever, along a single axis. Again, the precession is short-lived. > No, it is not. All right, here are the equations of motion, I1=I2, the moment of inertia about an equatorial axis, and I3 is the moment of inertia about the polar axis. I1 d/dt(w_x) = (I1 - I3) w_z w_y I1 d/dt(w_y) = -(I1 - I3) w_z w_x I3 d/dt(w_z) = 0 These equations describe the _force-free_ motion of a rigid body with cylindrical symmetry. Where's the damping? You can eliminate w_x or w_y in the first two equations, and you get, for instance: d/dt (d/dt ( w_x )) = - ((I1 - I3) w_z / I1)^2 w_x where w_z is constant. That's a simple harmonic oscillator, no damping. The direction of the vector omega revolves about the z-axis. From the perspective of a fixed observer on the surface of the object, the rotational pole follows a path of constant latitude about the axis of mean rotation. As I mentioned before, on the Earth that path is about five metres south of the North Pole, and completes a revolution about the North Pole about once a year, and so the correction is fairly unimportant. >It is still quite meaningless to speak of a planet, or any other solid >object, having two axes of rotation. > As I said before, I'm not talking about having two axes of rotation, I'm talking about motion which isn't simple rotation about a body-fixed axis. On the Earth is would be possible to put a spacecraft into geostationary orbit over a point up to five metres North or South of the equator, on at least one day of the year. Clearly this is not an exciting refinement on orbital positioning, but it is *possible*. -- Christopher Neufeld - B.Sc., M.Sc., A.B.D. Looking for a job in Ottawa Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" neufeld@physics.utoronto.ca From neufeld@physics.utoronto.ca Wed Aug 9 13:49:46 EDT 1995 Article: 20278 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:20278 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: axes of rotation (was Re: science in ScF (was Re: Butler wins Ma Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 9 Aug 1995 17:46:31 GMT References: Status: O In article , Leonard Erickson wrote: >-=> Quoting Christopher Neufeld to All <=- > > CN> This, I disagree with. The motion of a heavy symmetrical top fixed > CN> at a point does not damp out precession or nutation perturbations. > >Consider the spinning body in *space*. > All right, we're back to rigid body, force-free motion. I feel like I'm trying to track a madly dodging target. >But let us go on. You've induced a precession. As you note, angular >momentum must be conserved. But what you *failed* to note is that the >angular momentums about each of these "axes" can be *summed*, to give >an "effective" axis of rotation. > If you've been reading the other postings I've made in this thread you will realize that I know this. What I'm saying is the following: If the total angular momentum is not exactly aligned with the symmetry axis of the cylindrically-symmetric rotating rigid body, then the (stationary) point on the body which is pierced by a line travelling from the centre of mass and along the angular momentum vector will not be at the pole of the body, where I am defining the pole of the body as a point on the symmetry axis of the body. Right? Right. Now, according to elementary mechanics, that point on the surface of the body is not stationary, but traverses a smooth curve of constant latitude around the pole of the body. This motion of the rotational axis relative to the fixed-body coordinates is called "precession". >This doesn't seem important until you realize that you can get the >*same* TOTAL angular momentum in an infinite number of ways. One is by >having all rotation about the "effective" axis. Another is your >starting situation, with it split between the two axes, and the body >precessing. > Yes, but these ways all have *different energies*. Really and truly, they do, if the body is not spherically symmetric. A rigid body in free space cannot change its energy, so a given angular momentum + energy gives a class of solutions which consist of two disjoint curves of constant and equal latitude. >But for various reasons involving moment of inertia and other dynamical >considerations, the "single axis" setup is the only truly *stable* one. >The others tend to degenerate to it in greater or lesser times >(remember, there is *no* difference in angular momentum between *any* >of these states) > But there's a difference in energy. A water bottle in an Apollo spacecraft will be able to damp out pretty quickly. A rock in the shape of a football will take a very, very long time to damp out. OK, back to what I thought I was talking about. Is it possible for a body in free space, let's say a planet, to precess even a long time after it is formed? I claim it is. Our planet is doing it. I am not talking about precession of the equinoxes, which is an entirely different thing completely unrelated to the phenomenon I'm talking about. -- Christopher Neufeld - B.Sc., M.Sc., A.B.D. Looking for a job in Ottawa Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" neufeld@physics.utoronto.ca From neufeld@physics.utoronto.ca Wed Aug 9 18:51:55 EDT 1995 Article: 20290 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:20290 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: axes of rotation (was Re: science in ScF (was Re: Butler wins MacArthur! Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 9 Aug 1995 22:09:46 GMT References: <1995Aug9.182931.7117@schbbs.mot.com> Status: O In article <1995Aug9.182931.7117@schbbs.mot.com>, Bronis Vidugiris wrote: >In article , >Christopher Neufeld wrote: > >) As I said before, I'm not talking about having two axes of rotation, >)I'm talking about motion which isn't simple rotation about a body-fixed >)axis. On the Earth is would be possible to put a spacecraft into >)geostationary orbit over a point up to five metres North or South of the >)equator, on at least one day of the year. Clearly this is not an exciting >)refinement on orbital positioning, but it is *possible*. > >I think you (Chris) actually did use the rather unfortuante phrase. I >recall wincing at the time. (Check your spool if you have any doubts). > I save all my postings. Here's what I wrote: Newsgroups: rec.arts.sf.science From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: science in ScF (was Re: Butler wins MacArthur! Message-ID: Date: Tue, 1 Aug 1995 21:01:23 GMT In article <1995Aug1.143916.1752@den.mmc.com>, Wil McCarthy wrote: >In article <3vjvt0$7gv@newsbf02.news.aol.com>, paxd@aol.com (Pax D) writes: >|> >|> This might be possible if a planet has TWO axes of rotation... though I'd > >Again, not possible. You could impart a moment about two separate axes, but >they would sum to a rotation about a single axis. > Yes and no. If the initial angular momentum is not aligned with one of the stable eigenvectors of the moment of inertia tensor the body will precess. Its motion will not be describable by rigid rotation of the body around an axis fixed with respect to the body. One could claim that this is as if the object was rotating about two axes, at least for the purposes of our discussion here. Our planet might have such a precession, with the axis of rotation wandering about five metres from the geographic North Pole with a period of some 427 days, according to an old copy of Goldstein's classical mechanics text. [ .sig deleted ] === END OF INCLUDED TEXT === I didn't claim that this was "rotation about two axes", merely that, for the purposes of the discussion in progress, the precession had a similar effect. What I meant was that a precession would have the properties which "Pax D" was looking for in a body with two rotational axes, namely that there exist, at least for short periods of time (possibly on the scale of days), points off the equator which can support a geostationary-like orbit. -- Christopher Neufeld - B.Sc., M.Sc., A.B.D. Looking for a job in Ottawa Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" neufeld@physics.utoronto.ca From neufeld@physics.utoronto.ca Wed Aug 9 19:11:00 EDT 1995 Article: 20292 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:20292 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: axes of rotation (was Re: science in ScF (was Re: Butler wins Ma Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 9 Aug 1995 22:51:45 GMT References: <1995Aug9.184731.26311@den.mmc.com> Status: O In article <1995Aug9.184731.26311@den.mmc.com>, Wil McCarthy wrote: >In article , crystals!f51.n105.z1!Leonard.Erickson@news.pacifier.com (Leonard Erickson) writes: >|> >|> But for various reasons involving moment of inertia and other dynamical >|> considerations, the "single axis" setup is the only truly *stable* one. > >Christopher Neufeld is correct that there are an infinity of possible >states for a spinning system, but he still has not wrapped his head >around the dynamic stability issue. > I thought I had, years ago. I still think I did. Fine, I will now put a direct question to Wil McCarthy: Why is the planet Earth precessing, with its rotational axis wandering about the geographic North Pole at a distance of about five metres, and a period of about 430 days? This is not the lowest energy configuration. The kinetic rotational kinetic energy of the Earth for a constant angular momentum would drop by about 5E+14 joules by my calculations if the rotational axis were to line up with the pole. All right. I think we're almost in agreement, but not everybody realizes it yet. As previously noted, somewhat vociferously of late, a precessing body will, in the presence of dissipation which does not change the angular momentum, settle on a rotation about the highest eigenvalue of its moment of inertia tensor. Wil McCarthy and Leonard Erickson both agree with this statement, as shown by the quoted text. Here's where we disagree: I claim that the time scale for this to occur is fairly long for a solid object similar to, say, the Earth or the Moon. I claim that it is perfectly feasible to find a planet, moon, or asteroid billions of years after its formation which still exhibits a precession. That's it, other than that, we are in complete agreement. So, it's time to plug in numbers. I'm not a materials scientist. Does anybody have values for the dissipation or inelastic response in typical materials under the action of an oscillating applied pressure with a period in the vicinity of one year? Something like: "for low frequencies, a piece of granite which is compressed and released at pressures of Gigapascals returns fraction of the work done to compress it." -- Christopher Neufeld - B.Sc., M.Sc., A.B.D. Looking for a job in Ottawa Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" neufeld@physics.utoronto.ca From neufeld@physics.utoronto.ca Thu Aug 10 18:22:06 EDT 1995 Article: 20345 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:20345 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: axes of rotation (was Re: science in ScF (was Re: Butler wins MacArthur! Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Thu, 10 Aug 1995 21:12:42 GMT References: <1995Aug10.143713.15941@den.mmc.com> Status: O In article <1995Aug10.143713.15941@den.mmc.com>, Wil McCarthy wrote: > >in ascii, but a body rotating on other than its symmetry axes will >produce stabilizing torques. For the extreme case, imagine a spinning >(not tumbling) circular plate. If the spin axis is perpendicular to the >plate, then the plate's mass is distributed as far as possible from the >spin axis, meaning the moment of inertia about the axis is maximized, >meaning the centrifugal force pulling the plate's edge outward (not north >or south) is maximized, meaning the plate is not going anywhere. > >If you introduce a slight wobble, then the centrifugal force no longer >pulls straight along the radius of the plate, but rather straight away >from the spin axis. Here's a crappy diagram: > > spin axis > | > | / --> centrifugal force > | / > |/ (plate) > / > /| > / | > centrifugal force <-- / | > | > spin axis > >It should be obvious that these force vectors will create a torque that >pulls the plate back toward axisymmetric rotation. Furthermore, this >torque goes to zero when the plate and spin axis are once again >perpendicular, so that once again the plate will stay where it is. > Yes, no problem, this is obvious. The plate can lower its total mechanical energy by spinning flat. If there is a bearing there, or a surrounding fluid medium, or the thing has the consistency of pizza dough, or there is some similar source of dissipation then it will do that. But if it's a plate-shaped asteroid spinning in a vacuum, how does it manage it? There's a force on satellites trying to make them hit the Earth. Take a satellite with an elliptical orbit, I can draw all sorts of force vectors showing that it will want to hit the Earth and that at times the satellite is getting closer to the Earth, as if to hit it, but in the absence of a way to carry energy away, the satellite can't fall. To do so would be to violate the law of conservation of energy. If your spinning plate could flatten out its spin in the absence of an energy sink, it would also be violating the law of conservation of energy. It's that simple. Here's how that plate, in the absence of an external source of dissipation, has to flatten out: Imagine I've drawn an ink spot on the rim of your plate, in the upper right. As time goes by, this ink spot will be seen to move around the arc of the plate. That's because the plate is precessing, as we've discussed earlier. Concentrate on the ink spot. At first, it is fairly close to the rotation axis, and feels a fairly small centrifugal pseudo-force. As it migrates down to the "equator" of the rotation, this pseudo-force increases. The material of the plate there stretches somewhat, and the shape of the disk changes subtlely. The moment of inertia tensor also changes, and the disk's rotation becomes a bit more flat because of this. Now, the ink spot continues to the lower-left corner. The pseudo-force on the material there decreases, and the disk distorts back toward its initial shape. Again, the moment of inertia changes, and again the disk's rotation flattens out a bit. In the body-fixed frame the moment of inertia is changing, a deformation has appeared which orbits the circumference of the disk one for every precession period. Material in the plate is deforming, and heating up. Rotational kinetic energy is being transformed to heat, and angular momentum is being strictly conserved. This procedure takes time. For a steel plate rotating at a few hertz I am sure that the flattening-out time can be measured in centuries or longer, probably much longer. I have no gut feel for the time scale involved, but the dissipation can not be very high, the deformation is minute. A satellite (or gyroscope) contains a number of dissipative elements. Perhaps the most important is the bearing connecting the spun and despun buses. If you have a wobble induced it will impart a transverse load on that bearing, and the bearing will dissipate the energy, eliminating the wobble. Even in the absence of a despun section, components like antennae and panels, not to mention the honeycomb and mylar, will all dissipate energy as they are pushed and pulled by the uneven wobble, and the satellite will stabilize itself again. A professor just came in while I was typing that and asked about the diagrams and what I was discussing. I said that I was trying to defend the statement that a steel plate rotating about an axis other than its symmetry axis in a vacuum would not settle down. He said, "Well, unquestionably," and walked away. Fine, proof by anonymous authority. You've got two physicists, three differential equations, and the standard textbook on classical mechanics arguing this case now. -- Christopher Neufeld - B.Sc., M.Sc., A.B.D. Looking for a job in Ottawa Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" neufeld@physics.utoronto.ca From neufeld@physics.utoronto.ca Thu Aug 10 18:26:29 EDT 1995 Article: 20351 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:20351 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: axes of rotation (was Re: science in ScF (was Re: Butler wins Ma Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Thu, 10 Aug 1995 22:21:16 GMT References: <1995Aug9.184731.26311@den.mmc.com> <1995Aug10.150145.18419@den.mmc.com> Status: O In article <1995Aug10.150145.18419@den.mmc.com>, Wil McCarthy wrote: >In article , neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) writes: >|> So, it's time to plug in numbers. I'm not a materials scientist. Does >|> anybody have values for the dissipation or inelastic response in typical >|> materials under the action of an oscillating applied pressure with a >|> period in the vicinity of one year? > >Egad, what does this have to do with anything? The damping of precession >does not have anything to do with oscillating pressure in the spinning >body. I suppose you could disspiate energy in this way, but a rigid body >will also seek axisymmetric rotation, and will do so in fairly short order. >Like, a few hundred revolutions, at most. > No, it has everything to do with it. Maybe we should combine these two parallel-running thread components. Look, the thing has to dissipate energy. It ***must***. It cannot stabilize its rotation without dissipating the energy. For an almost-rigid body in free space this inelastic deformation is the only way it can do it. Really, the only way. A rigid satellite, like, say, the moon, will seek to be on the ground. Why doesn't it? There is one force on it, gravity. It would like to be on the ground. If the moon had zero angular momentum, it would shortly be on the ground. If there were a cloud of gas around the earth extending up to the moon, then eventually the moon would be on the ground. The moon is seeking to be on the ground, but it cannot manage it because to do so it would have to lose angular momentum, energy, or both. >I'm not trying to be snide or anything, but to a rocket jock like me, >everything is vectors and forces and mass. > I'm trying to think of a way to demonstrate this with vectors and forces, leaving out Lagrangians and the like. I am having some difficulty. As I understand it, you believe that Euler's equations do not apply in this case, since you reject the solution. Modelling a rigid body of finite extent in terms of forces on components of the body is extremely awkward. You wind up with a flurry of constraint conditions to define the shape of the body. I'm frankly not clever enough to solve things that way and transcribe it to ASCII. As far as I can tell, you are being thrown off by the fact that the object is spinning. The object behaves like a gyroscope, and that behaviour tends to defeat the intuition of people. Consider from your other posting, the diagram which showed centrifugal "forces" pushing a plate toward flat rotation. Now, if the plate were not rotating, the plate would respond to this applied torque in the way you described in your posting. Consider, now, a gyroscope fixed at a point, spinning but not vertical. The gravitational force provides a torque which the very same argument would say causes the gyroscope to tip onto its side. However, this torque doesn't make the gyroscope tip that way. Rather, the body moves at right angles to the applied force. The larger the force you apply, the more quickly it moves at right angles to that force. Stop the gyroscope from spinning, and it behaves in an intuitive way once more. Please, find a good classical mechanics textbook and read what it says about free-space rotations of non-symmetric bodies. I'm not making this stuff up. -- Christopher Neufeld - B.Sc., M.Sc., A.B.D. Looking for a job in Ottawa Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" neufeld@physics.utoronto.ca From neufeld@physics.utoronto.ca Fri Aug 11 15:41:34 EDT 1995 Article: 20401 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:20401 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: axes of rotation (was Re: science in ScF (was Re: Butler wins Ma Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Fri, 11 Aug 1995 19:33:47 GMT References: <1995Aug10.150145.18419@den.mmc.com> <1995Aug11.143446.27644@den.mmc.com> Status: OR In article <1995Aug11.143446.27644@den.mmc.com>, Wil McCarthy wrote: >In article , neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) writes: >|> Please, find a good classical mechanics textbook and read what it says >|> about free-space rotations of non-symmetric bodies. I'm not making this >|> stuff up. >|> > >Hee hee! I was about to say the same thing to you! ;) > > [ ... ] > >For a discussion of this, see Greenwood: PRINCIPLES OF DYNAMICS, pg. 369, >"Stability of Rotational Motion About a Principal Axis," or somewhat more >obtusely, Kane, Likins, and Levinson, SPACECRAFT DYNAMICS, section 3.1, >"Rotational Motion of a Torque-Free Axisymmetric Rigid Body." > All right, fine. I choose the second, _Spacecraft Dynamics_. The 1983 printing, if you don't mind. Section 3.1, "Rotational Motion of a Torque-Free, Axisymmetric Rigid Body", starting on page 159. When an axisymmetric rigid body B is subjected to the action of forces whose resultant moment about the mass center B* of B is equal to zero, the rotational motion of B in a Newtonian reference frame N can be described in terms of two motions of simple rotation, each performed with an angular velocity of constant magnitude. [ nasty reference frame material deleted ] The associated angular velocities are called the angular velocity of spin and the angular velocity of precession, respectively, and can be expressed as ..... A bunch of math follows, which supports everything which the Goldstein text had to say about this motion, though it handles it in a somewhat different way. There is no mention anywhere in the section (and I've read through the entire section) of stability, damping of precession, or anything like that. See, for instance, the bottom of page 166, or the second paragraph on page 162. Now, let's look at what the book has to say about stability. This appears in section 3.2 "Effect of a Gravitational Moment on an Axisymmetric Rigid Body in a Circular Orbit", where we assume an external torque (moment) on the body. Figure 3.2.5, and the discussion on p. 173 are about this. Stability also appears in section 3.4 "Torque-Free Motion of an Unsymmetric Rigid Body", but in that discussion it does not say that the unstable rotation will degenerate into one of the stable rotation modes. Note that this is not what we were talking about in the case of an oblate planet, I'm just including this for the sake of completeness. If the body starts out in a pure state of one of the stable rotations, and then something bumps it, its subsequent motion does *not* damp out to point along the stable axis again. Rather, it precesses in space, but the body-fixed axis never strays far from its mean value. The smaller the bump, the closer is stays to the mean direction. If the body starts out in a pure state of the unstable rotation, then a small bump causes it to tumble, with the body axis pointing in all directions with time. It will not, however, decay into one of the stable rotations. Look at the math! -- Christopher Neufeld - B.Sc., M.Sc., A.B.D. Looking for a job in Ottawa Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" neufeld@physics.utoronto.ca From neufeld@physics.utoronto.ca Tue Aug 15 10:18:18 EDT 1995 Article: 122362 of rec.arts.sf.written Xref: info.physics.utoronto.ca rec.arts.sf.science:20539 rec.arts.sf.written:122362 sci.space.policy:21101 Newsgroups: sci.space.policy,rec.arts.sf.written,rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Habitable Moons Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Tue, 15 Aug 1995 14:12:03 GMT References: <40pn9o$pp4@panix.com> Status: O In article <40pn9o$pp4@panix.com>, Ian Strock wrote: >In tuff@ellis.uchicago.edu (Geoff Tuffli) writes: > >>I'm a little curious about something here; my understanding was that >>the moon was totally lacking in anything remotely resembling water. > >Actually, 25%-50% of the moon's rock is oxygen, which, when combined with >hydrogen, gives water (and a lot of energy). Thus, one of the near-term >goals is to set up efficient oxygen mining, combined with hydrogen >shipping (FAR cheaper than shipping water--hydrogen is one-ninth the >total mass of water). > A report which I was involved with to the Canadian Space Agency on the applications of a robotic lunar oxygen extractor (described by Mark Loszowski and presented at the CASI conference about four or five years ago) suggested that it might be more efficient to ship methane than to ship hydrogen. Methane is 25% hydrogen by mass, with the rest being carbon, which is itself a fairly useful material not found in bulk in random lunar rock. Also, the cost of lifting materials from the surface of the Earth is not only the mass, but also the bulk. It's much cheaper to lift a tonne of depleted uranium on a small expendable than to lift a tonne of meringue pies. Liquified methane actually has a higher volume density of hydrogen than liquified hydrogen, and is *much* easier to handle and store. -- Christopher Neufeld - B.Sc., M.Sc., A.B.D. Looking for a job in Ottawa Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" neufeld@physics.utoronto.ca From neufeld@physics.utoronto.ca Wed Aug 16 10:07:54 EDT 1995 Article: 122426 of rec.arts.sf.written Xref: info.physics.utoronto.ca rec.arts.sf.written:122426 Newsgroups: rec.arts.sf.written Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Postapocalyptic recommendations wanted Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Tue, 15 Aug 1995 23:05:43 GMT References: <51296.owenc002@gold.tc.umn.edu> <40qlth$fve@clarknet.clark.net> Status: O In article <40qlth$fve@clarknet.clark.net>, Ahasuerus the Wandering Jew wrote: >David Owen-Cruise (owenc002@gold.tc.umn.edu) wrote: >> I'm looking for recommendations for my wife's reading pleasure. Her >> SF preference is for Postapocalyptic/major disaster novels. [snip] > >http://caliban.physics.utoronto.ca/neufeld/postapoc.txt > Hmm, I was wondering why that file was suddenly getting so much attention! ;-) For the web-challenged, the http file tree is a subtree of the anonymous FTP tree, so that file can also be found at: ftp://caliban.physics.utoronto.ca/pub/www/neufeld/postapoc.txt -- Christopher Neufeld - B.Sc., M.Sc., A.B.D. Looking for a job in Ottawa Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" neufeld@physics.utoronto.ca From neufeld@physics.utoronto.ca Tue Aug 22 20:11:52 EDT 1995 Article: 20549 of ont.forsale Xref: info.physics.utoronto.ca ont.forsale:20549 Newsgroups: ont.forsale Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Giving away a single bed Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Tue, 22 Aug 1995 23:50:59 GMT Status: O I've got a single bed with mattress, box spring, and frame on casters. It'll go in the garbage on August 29 unless somebody wants it. It's free to whoever can pick it up from the downtown Toronto area. The frame disassembles into pieces, the longest of which are as long as the matress, about 1.8 or 1.9 metres. -- Christopher Neufeld - B.Sc., M.Sc., A.B.D. neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Fri Aug 25 18:37:35 EDT 1995 Article: 20686 of ont.forsale Xref: info.physics.utoronto.ca ont.forsale:20686 Newsgroups: ont.forsale Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Women's inline skates and a futon for sale Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Fri, 25 Aug 1995 22:05:31 GMT Status: O I have a few items to be disposed of by Tuesday, August 29. Women's size 5, Seneca brand inline skates - $10 Pads to wear while using same - $5 Single-bed sized futon - $15 I also still have a single bed - matress, box, and metal frame, free to anybody who can pick it up from downtown. -- Christopher Neufeld - B.Sc., M.Sc., A.B.D. neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Fri Aug 25 19:12:04 EDT 1995 Article: 127081 of sci.physics Xref: info.physics.utoronto.ca sci.physics:127081 Newsgroups: sci.physics Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Baby has got red eyes... Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Fri, 25 Aug 1995 22:30:12 GMT References: <41kcv4$on0@neptune.ethz.ch> Status: O In article <41kcv4$on0@neptune.ethz.ch>, Nordal Cavadini wrote: >Have you ever noticed these poor pictures taken with your sister's >camera, where nearly everybody (you included!) has got red eyes? > ... >In order to avoid looking like a vampire, you just have not to stare >directly at the camera; thus the effect has to do with reflection, >I suppose. >The question is: in which way? > Well, my eyes are better at it than most. I'm often the only person in the picture with blood-red eyes, and it doesn't help for me to look away >from the camera. I've even got a .GIF of myself (not the one in my home page) looking about 40 degrees off the camera line, and while the blue of my irises is not visible, the red reflections of my retinas stands out beautifully. BTW, the picture of my in my home page doesn't exhibit this effect because it was taken in a photo studio with the flash lamps significantly off the camera-face line, so they weren't reflected right back at the camera. -- Christopher Neufeld - B.Sc., M.Sc., A.B.D. neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Sun Aug 27 14:16:36 EDT 1995 Article: 20799 of rec.arts.sf.science Xref: info.physics.utoronto.ca alt.horror.cthulhu:14860 rec.arts.sf.science:20799 rec.arts.sf.written:124040 Newsgroups: alt.horror.cthulhu,rec.arts.sf.science,rec.arts.sf.written Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: REQ: Need some serious ideas!! Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Sun, 27 Aug 1995 18:15:52 GMT References: <19950826.071656.45@econym.demon.co.uk> Status: O In article <19950826.071656.45@econym.demon.co.uk>, Mike Williams wrote: >In message <41lmp8$rb7@dewey.csun.edu> creatrix wrote: > >> >> Here's one for the Mad Scientist. >> >> 1) steal all the nukes of the world. >> 2) put them all on one side of the earth. >> 3) Set off all nukes at same time, away from Sun. > >(2) The Earth's mass is about 5,976,000,000,000,000,000,000,000,000 kg, and >it's orbital velocity is about 750 metres/sec. > Your mass is too high by a factor of 1000, and the speed too low by a factor of almost thirty. >region of 1e32 Joules, but I think it's unlikely that all the nukes in the >world would generate more than 1e15 Joules. > From which number we immediately conclude that the total global nuclear arsenal amounts to the uninspiring total of 255 kilotons TNT, roughly a dozen Hiroshima bombs, and about one fortieth of the size of a single american city-buster. -- Christopher Neufeld - B.Sc., M.Sc., A.B.D. neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Fri Oct 13 14:16:36 EDT 1995 Article: 14779 of comp.os.linux.development.system Xref: info.physics.utoronto.ca comp.os.linux.development.system:14779 Newsgroups: comp.os.linux.development.system Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: 128 MB Linux? Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Fri, 13 Oct 1995 18:16:19 GMT Status: O Well, this seems the best place to ask around. In my job (not at the university) we need to run a large application. 64 MB isn't enough, so we can't use MS-DOS or Windows. We're somehow crashing the O/S (panic trap, the whole deal) consistently within a couple of hours when we try OS/2. I suggested that we go over to Linux, and after some battling with hardware I got it installed. According to free(1), the kernel is only seeing 64MB of the 128MB on board, though. This is kernel 1.2.1 with the patches to recognize the Adaptec AHA-2940 SCSI card (I couldn't get the SCSI card recognized using the Slackware 3.0 boot disks at tsx-11). Does a 128 MB kernel exist? Is it likely to exist ever? Does anybody need a 128 MB kernel tested? Here's the hardware: Digital Celebris Pentium-90 with 128 MB RAM One IDE controller Adaptec 2940 SCSI controller with 2 GB Seagate drive and a NEC Multispin 6X CD-ROM Colorado 700 tape drive on the floppy disk controller USR 28800 modem for a SLIP connection Please let me know if there's a chance we can convert this operation to Linux. -- Christopher Neufeld - B.Sc., M.Sc., A.B.D. neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed Oct 18 22:58:44 EDT 1995 Article: 10256 of comp.os.linux.development.apps Xref: info.physics.utoronto.ca comp.os.linux.development.apps:10256 Newsgroups: comp.os.linux.development.apps Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Problems profiling Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 18 Oct 1995 22:16:21 GMT Status: O I apologize in advance if this is a FAQ, I haven't been able to keep current on my newsgroups because of network problems. It doesn't seem to have been an FAQ in August. I am trying to compile a medium-sized (approx. 50 source modules, 500 kB stripped executable) application to produce profiling code. I compile each module with "-p", then link them with "-p". However, if I try to compile an a.out executable and link with either "-p" or "-g", the linker reports an error, saying that: "Output file requires shared library `libc.so.4'" and ld ABORTs. This doesn't happen when I try to compile a simple Hello world program for profiling. Without profiling, my application compiles cleanly without warnings, and executes properly. If I compile ELF, the linker doesn't find the profiling subroutines and quits with unresolved references. So, can anybody help me out? Either a clue to what's confusing ld in the a.out case, or a pointer to an ELF debugging and profiling library? I'm using the gcc v2.7.0 ELF on the August Infomagic Linux Developer 4 CD set, and I've already scanned the HOWTOs and FAQs there for a clue to what's going on. This also happened with the 2.6.3 ELF and a.out versions. -- Christopher Neufeld - B.Sc., M.Sc., A.B.D. neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Sat Oct 21 00:29:26 EDT 1995 Article: 10330 of comp.os.linux.development.apps Xref: info.physics.utoronto.ca comp.os.linux.development.apps:10330 Newsgroups: comp.os.linux.development.apps Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Problems profiling Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Fri, 20 Oct 1995 20:18:29 GMT References: Status: O OK, I'll answer my own posting. I was looking for ELF profiling libraries to go with the gcc v2.7.0. I found them in the Redhat distribution, available at mirror sites everywhere. Look in the updates in the redhat v2.0 file tree. Anyway, once I found 'rpm' to extract the libraries (profiling and debugging), I was able to profile programs with "-pg" and "gprof(1)". -- Christopher Neufeld - B.Sc., M.Sc., A.B.D. neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Mon Nov 20 15:55:10 EST 1995 Article: 11564 of comp.os.linux.development.apps Xref: info.physics.utoronto.ca comp.os.linux.development.apps:11564 Newsgroups: comp.os.linux.development.apps Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: How to pipe into an rlogin? Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Mon, 20 Nov 1995 20:39:49 GMT Status: O In my office (not at the university) we are using DHCP for most IP numbers. I managed to get one static IP# for a Linux box, but the others have to get their IP numbers dynamically. I'm trying to set up a user-friendly tape backup across the network to the host with the static IP#. Typically, I do this with scripts which execute something like: afio [options] - | rsh -l tapeuser tapehost dd of=/dev/nrft0 The afio writes to stdout, that goes to the stdin of the rsh, which then feeds through dd, and the files get saved on the remote host's tape drive. The problem is that DHCP and DNS resolution are not compatible, so it is not possible to authenticate a user and machine. I would have to create an .rhosts file which allows universal access to the tapeuser account, and I'm reluctant to do that because of the security issues (though we are behind a firewall, so it's not as bad as it seems). Since I cannot know whether the IP# of the incoming requestor is somebody who is supposed to have access to the account, I created a new "shell" for the tapeuser. A login attempt would produce a menu, options are selected, and the program writes a control file into its own directory and closes the login. A subsequent login attempt within five minutes causes the shell to read instructions from the control file. In this case, among other things it forks, then execs the 'dd' process (statically linked, the shell first chroots to /home/tapeuser and then drops its superuser privileges, so the system libraries and binaries are unavailable to it). By packaging the login in my own C program, and controlling what it does, I hoped to avoid the more obvious security problems. The problem is that the data is not reliably transmitted. I expect that I can do something like this: rlogin -l tapeuser tapehost < largefile and get "largefile" written to tape, or to a disk file if I'm testing it that way. I generally lose twenty bytes or so off the top of the file, and the contents of everything after the last complete 512 byte block (as if the final incomplete block is lost). Often I lose much more, sometimes nothing gets through to the dd process at all. It seems that the data stream from the redirection is going down the pipe before the dd process is ready for it, so I lose the first few bytes. Once the file has been transmitted, it SIGHUPs my "shell" and my 'dd' process. I patched both to ignore SIGHUP, but that didn't fix the problem. I still lose the end of the file. I've come up with a temporary solution, but it requires considerable user intervention. Is there something I'm missing? I've tried using the -E and -8 flags, and setting 'bs=1' on the dd, but nothing has produced a reliable connection. When I test it with "rsh dd ..." it works as I expect it to. What is being done by the "tcsh -c" in the latter case which is not being done by my shell? -- Christopher Neufeld - B.Sc., M.Sc., A.B.D. neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed Dec 6 19:04:20 EST 1995 Article: 17609 of comp.os.linux.development.system Xref: info.physics.utoronto.ca comp.os.linux.development.system:17609 Newsgroups: comp.os.linux.development.system Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Priorities in 1.3.45? Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 6 Dec 1995 23:18:23 GMT Status: O I just realized that the upgrade to v1.3.45 seems to have had an interesting side-effect on my pentium box. All processes are now running at nice level 15, and I can't renice them to anything else. I rebooted with the old 1.3.34 kernel, and the problem went away. Am I the only one who had this happen? The kernel was compiled ELF on gcc 2.7.2. -- Christopher Neufeld - B.Sc., M.Sc., A.B.D. neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Thu Dec 7 13:42:39 EST 1995 Article: 25005 of comp.compression Xref: info.physics.utoronto.ca comp.compression:25005 comp.lang.c:143037 Newsgroups: comp.compression,comp.lang.c Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Need fast in-core compression of ~100 bytes Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Thu, 7 Dec 1995 18:40:58 GMT Status: O For my job (not at the university) I am working on a simulation program in C which is straining our physical memory (128+MB). The model maintains hundreds of thousands of records, each of them either 72 or 104 bytes long. We must be able to access these records randomly, and the records will be read more often than they are written to. At the moment, we carry two vectors of pointers to the memory locations holding these records, and malloc space for the records. What we can do with the simulation is limited by physical memory and real-world elapsed time of the run. I suspect that we can save a lot with an in-core compression routine. I'm wondering if anybody has any experience with compacting such small units of data. The 72 byte records themselves would have to be compressed, rather than a concatenation, if we are to have any hope of efficient random access to the records. Here are some particulars: - the records are bitfields, 32 bit integers (though we typically use only about 20 bits of those), and floats. No text. - we have access to stored records from previous simulations which can be used to build a compression dictionary prior to model run, then read in by the model. We should get fairly good compression using a dictionary from a previous run, rather than building our own, LZW fashion, in the course of the simulation run. - when all the records from a reduced-size run are concatenated into a single 5MB file, it gzips (level 6) down to 1MB. As a crude first estimate, then, we might expect to do not much worse on the individual records, with the right dictionary. Gzip uses an LZ77 algorithm. - whatever we come up with has to be quicker than our swapping to disk, or there's no point doing it. - the model visits and modifies each record at least once per pass through the simulation, and makes 100 or more passes, so there won't be any entries which page out and are never requested. I can handle stuff like memory caching of recently uncompressed records, as the model tends to request the same records several times before moving on to others, but I need a strategy or algorithm for doing the compressions and expansions efficiently. Has anybody come across a problem like this before, and have any suggestions? -- Christopher Neufeld - B.Sc., M.Sc., A.B.D. neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Tue Jan 23 12:32:13 EST 1996 Article: 98857 of comp.os.linux.misc Xref: info.physics.utoronto.ca comp.os.linux.misc:98857 Newsgroups: comp.os.linux.misc Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: How to remove file with name -24831 Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Mon, 22 Jan 1996 21:56:28 GMT References: <30FE50CB.39F8A49D@mail.leidenuniv.nl> <4e0m2d$1dt@dialin120.zdv.Uni-Mainz.DE> In article <4e0m2d$1dt@dialin120.zdv.Uni-Mainz.DE>, Paul Seelig wrote: >In article <30FE50CB.39F8A49D@mail.leidenuniv.nl>, > Ewald de Wit writes: >>There's a file called -24831 on my >>system and everytime i try to rm, mv, cat or do whatever with it, >>the minus sign is interpreted as the beginning of an option. > >I tried it too and found no other way than to invoke emacs with a listing >of the directory and delete it from there. > Well, there is another way. According to the 'rm(1)' man page, do the following: rm -- -24831 Works for me. -- Christopher Neufeld - B.Sc., M.Sc., A.B.D. neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Tue Jan 23 12:34:23 EST 1996 Article: 13898 of comp.os.linux.development.apps Xref: info.physics.utoronto.ca comp.os.linux.development.apps:13898 Newsgroups: comp.os.linux.development.apps Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: GCC: -m486 flag on a Pentium? Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Mon, 22 Jan 1996 22:00:44 GMT References: In article , Randy Chapman wrote: >Oskar Widerberg (oskar@surfchem.kth.se) wrote: >: Does the gcc flag -m486 do anything good on a Pentium-based computer when >: compiling? >Yes. It makes the result bigger and sometimes slower. > Has somebody been overloading the "good" operator again? -- Christopher Neufeld - B.Sc., M.Sc., A.B.D. neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Fri Mar 1 15:30:07 EST 1996 Article: 25897 of comp.security.unix Xref: info.physics.utoronto.ca comp.security.unix:25897 Newsgroups: comp.security.unix Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Fingering command-Need help Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Fri, 1 Mar 1996 20:29:21 GMT References: <4f3rin$d9h@grissom.powerup.com.au> <4h1kij$6di@hp01.redwood.nl> <4h4mg6$p17@clem.mscd.edu> In article <4h4mg6$p17@clem.mscd.edu>, Jon Trulson wrote: >Rob J. Nauta (rob@redwood.nl) wrote: > >: Good passwords are much more useful >: than crippling your machine. An attacker can get full name from sendmail >: (with EXPN and VRFY), while tty location is useless nowadays, no terminals >: are hardwired, everything is a pty (pseudo-tty). > > Yeah, but to my knowlege, one cannot use VRFY to list all the valid >accounts on your machine. finger can. > However, a bit of experimentation can come up with mail aliases set up to make broadcast mail easier. On a machine here you can ask sendmail "expn all_students" and get a list of a large number of user names. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Sun Mar 3 13:12:45 EST 1996 Article: 174575 of rec.arts.sf.tv.babylon5 Xref: info.physics.utoronto.ca ott.general:23280 rec.arts.sf.tv.babylon5:174575 Newsgroups: rec.arts.sf.tv.babylon5,ott.general Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Previous Babylon 5 episodes on videotape in Ottawa area? Distribution: ont Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Sat, 2 Mar 1996 18:52:55 GMT I've been watching Babylon 5 since it started a few years ago. My wife didn't catch the first two seasons, but watches it with me now. She is sometimes at a disadvantage because she doesn't know all of the backplot, so sometimes I'll react with surprise to a single line of dialogue which doesn't affect her the same way, because of her lack of context. Anyway, she'd like to catch up now. We're wondering if anybody in Ottawa has a fairly complete collection they'd be willing to loan out piecemeal for us. I doubt that there are any tapes of the first two seasons for rent anywhere, but it is frustrating for my wife to enter part way into the series. She could catch up some from the Web site, but it's not the same.... Thank you. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Thu Mar 14 10:06:34 EST 1996 Article: 49684 of sci.energy Xref: info.physics.utoronto.ca sci.energy:49684 Newsgroups: sci.energy Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Floating magnets above the north pole? Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Thu, 14 Mar 1996 15:02:12 GMT References: <31455627.6A60@bc.cybernex.net> <1996Mar12.170439.26648@freenet.victoria.bc.ca> In article , John McCarthy wrote: >In article <1996Mar12.170439.26648@freenet.victoria.bc.ca> ug837@freenet.Victoria.BC.CA (Karl F. Johanson) writes: > In a previous article, jhardin@bc.cybernex.net (James Hardin) says: > > >Would it be possible to float a 100Lb. superconducting electromagnet above > >the earths magnetic north pole, by repelling against the earths magnetic > >field, and if so how much power would it take? > > > No, the Earth's magnetic field is far too weak. > >Are you sure it's too weak? > Well, first of all, the earth's magnetic field is pretty well vertical at the north pole, so you wouldn't be able to levitate it there. At the equator, the field is horizontal, and a current carrying wire running parallel to the equator could, in theory, be levitated. A segment of wire can be levitated in a field if the magnetic force per unit area (B*J*A*l) equals the weight (p*g*A*l) where: B = (horizontal) field in tesla (perpendicular to the wire) J = current density in amps/m^2 A = cross-sectional area of wire l = length of wire p = density of wire in kg/m^3 g = gravitational constant, 9.81 m/s^2 For copper, a fairly dense metal, this gives a current density of about 8E+8 A/m^2, or 8E+4 A/cm^2. Such current densities are achievable in conventional superconductors, whose densities do not differ from copper's by a large amount. To go from here to a bulk magnet is a bit tricky, the large current density is really achieved in the vicinity of the surface, to a depth characterized by the London penetration depth, typically several hundred angstroms for the conventional superconductors. The material deeper than that is effectively dead weight. This is one reason that conventional superconducting wire is made from hundreds of micron-scale strands in a copper matrix. Our hypothetical superconducting magnet would have to be similarly fuzzy material. As for "how much power would it take", the answer is approximately zero. There's a startup cost associated with energizing the coils, but we maintain high fields in superconducting coils all the time when the apparatus is completely unplugged from the wall. The field stays up for weeks, with no measurable decrease. This would be true even if the field were being used to levitate objects. There's no power cost associated with levitation (though there may be one related to inefficiencies, if present). -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Thu Mar 21 13:02:06 EST 1996 Article: 158586 of sci.skeptic Xref: info.physics.utoronto.ca alt.alien.visitors:131859 alt.paranet.abduct:6651 alt.paranet.ufo:62927 alt.ufo.reports:7627 sci.skeptic:158586 Newsgroups: alt.ufo.reports,alt.alien.research,alt.alien.visitors,alt.paranet.ufo,sci.skeptic,alt.ufo.reports,alt.paranet.abduct Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: UFO Report?? - Hot off the wire! Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Thu, 21 Mar 1996 17:55:32 GMT References: <4indc4$h4b@nntp.igs.net> <4iqk7o$rrf@texas.nwlink.com> In article <4iqk7o$rrf@texas.nwlink.com>, National UFO Reporting Center wrote: >I just noticed the discussion regarding the alleged sighting at >Waltham, Quebec. > >If anyone can provide the National UFO Reporting Center with >more facts regarding this incident, I would be grateful. > The latest story, this morning on CFRA radio (the station cited in the original posting in this thread), is that the UFO was a St. Patrick's Day balloon that a man was planning to give to his mother. The man has been interviewed, he lost his balloon near there. It was spherical, mylar, green on one side, with a red ribbon attached, and a message referring to his mother (I don't recall the exact wording). Given the original behaviour of the UFO (a sub-metre sized, silent, colourful sphere which floated into the construction site and landed, then flew away again before anybody could get a good look at it) this is a reasonable explanation. >The description of the object is somewhat similar to another >report we received from another part of the North American >continent. > Quite possible, St. Patrick's Day is widely celebrated in North America, and many of the celebrants have mothers. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed Apr 10 13:23:02 EDT 1996 Article: 113472 of comp.os.linux.misc Xref: info.physics.utoronto.ca comp.os.linux.misc:113472 comp.os.linux.networking:39423 Newsgroups: comp.os.linux.networking,comp.os.linux.misc Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Weird samba and lpr problem Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 10 Apr 1996 14:05:55 GMT I've got a strange problem when printing to a Samba networked printer via lpr. At times, the Samba client fails to log in to the printer server. This only happens when it is run by the lpd, not when run in a script such as: /var/spool/samba/postscript/printps < file.ps When problems appear the samba client program reports a failure to connect to the server. It breaks the pipe, and lpd forks a dozen times or so before giving up on the job. If I then kill the original lpd and restart it as root, it works again, at least for a while. I'm wondering if somebody out there can give me a pointer on where to look for the problem. Why does smbclient, when run by the daemon, sometimes fail to be authorized to print (there is no password required for the printer server)? Why does restarting the daemon fix that, since the client is so far removed from the daemon, and only started up when a print job is submitted? lpd -> forked lpd -> bash -> smbclient For the curious, here's the printcap entry: ps|lp|12laser1ps|postscript:\ :lp=/dev/nullpr:\ :sd=/var/spool/samba/postscript:\ :lf=/var/spool/samba/postscript/lp-err:\ :if=/var/spool/samba/postscript/printps:\ :sh:\ :sf:\ :mx#0: and here's the script (with the IP# stripped to satisfy the security-conscious here, I'm working in a government office). #! /bin/sh # ( echo "print -" gs -q -sDEVICE=ljet4 -sOutputFile=- - ) | \ /local/samba/smbclient '\\HQ7\12LASER1' -I -P -N Anyway, when this script is run by the user, in a pipe or with input redirected, it never has this problem. Again, I don't think anybody can give me a quick answer, but just a pointer to what sort of interactions I should be looking for in order to solve this problem myself. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Fri Apr 19 16:45:09 EDT 1996 Article: 163149 of sci.skeptic Xref: info.physics.utoronto.ca sci.skeptic:163149 Newsgroups: sci.skeptic Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Can we travel to the neighboring stars? Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Fri, 19 Apr 1996 14:10:44 GMT References: <4l5vst$6oo@news.uni-c.dk> In article <4l5vst$6oo@news.uni-c.dk>, Stephan Mannstaedt wrote: > > > THE CONCEPT OF THE DEVICE > >The prime part of the device is a superconductor. We are not interested in >the superconductor because it can be used as a conductor, but because it >repels magnetic fields. > More precisely, a superconductor excludes magnetic fields from the superconducting volume. >If you have heard about superconductors before, you may have seen >pictures of magnets hovering above the superconductor. The principle looks >something like this: > >============================================================================= > > SS > SS > NN > NN > > > _________________________________ <--- mirror > sssssssssssssssssssssssssssssssss > > "NN" > >Fig.1: Graphic illustration of the Meissner effect. The SS and NN are the >south and north pole of a normal magnet, the s is the superconductor, and the >"NN" represent the magnetic pole which is generated by the superconductor. >The ____ line represent the surface of the superconductor, and the location >of the "NN" pole can be found by using the __ line as a mirror. > No, actually, as drawn, the system is unstable. A lower energy configuration has the mirror lying horizontally, with the image magnet parallel to it, reflected in the surface of the superconductor. >============================================================================= > >The magnet, illustrated in Fig.1., is hovering above the superconductor due >to the Meissner effect. The important issue in this connection is to notice >that the surface of the superconductor works as a mirror for any magnetic >fields. Due to this, the superconductor actually behaves as a magnetic mono- >pole when it is exposed to a magnetic field (strangely enough, this >observation has been totally ignored in all text books about this subject I >have read). > Absolutely not. If it did behave as a magnetic monopole then there would be magnetic field penetration within the bulk, which you yourself point out does not happen. The spatial dependence of a magnetic monopole's field is different from that of a dipole's field, so you cannot satisfy the boundary condition of zero vertical magnetic field at the surface of the superconductor. The concept involved is described in *all* undergraduate electromagnetism textbooks, though usually in the context of electric charges and conducting surfaces. Look for "the method of images", or simply "image charges". It's covered in undergrad books because this provides an elegant solution for some otherwise quite hairy problems. The math is formally equivalent to the superconducing case, though the sign of the image charges changes from the electrostatic solution because the boundary condition is zero perpendicular field rather than zero transverse field. >The forces in the system can be calculated as the forces between two magnets >which are repulsed by each other. But when a superconductor is exposed to a >magnetic field, part of the surface becomes non-superconducting (there exist >a so-called London penetration depth which describes how deep a given >magnetic field will penetrate the superconductor). The force upon the >superconductor can also be calculated on basis of the volume of the >superconductor which is turned into a non-superconductor. > No, that's not true. The London penetration depth doesn't change with applied field, for instance, but the force does (all other things being constant). The superconductor, in any case, is not repelled by magnetic fields, but rather by magnetic field gradients. A superconductor in a uniform magnetic field will not feel a net force (though it may experience a torque because of shape effects or structural anisotropy). A good way to think of this is in terms of the method of virtual work. If I put a magnet on top of a superconductor (or vice versa, but let me treat this case), the magnetic field lines coming from the magnet are squeezed into a very narrow region between the bottom of the magnet and the first one or two penetration depth thicknesses into the superconductor (in other words, forming a large flux). The magnetostatic energy density in this region is proportional to the square of the magnetic field, and assuming that edge effects are small the flux lines are confined to a volume which is linearly proportional to the height of the magnet above the superconductor. This means that the magnetic energy density is inversely proportional to the square of the height at which the magnet hovers, while the gravitational potential energy is linearly proportional to the height. If the magnetic energy density is high enough in the contact case, then the system can lower its total energy by levitating the magnet. Ultimately, it stops going up, when the energy advantage in magnetic fields is exactly balanced by the penalty in gravitation. Anyway, the fact that there is an energy difference in moving from one place to another determines that there is a force on the object, by the principle of virtual work. If you ask "where does the force really come from", it's best to think of the model of a superconductor as something which produces currents in the region near the surface (that's what the penetration depth really amounts to, the thickness of the super-current carrying region). These currents form a divergenceless flow (no net accumulation of charges at some parts of the superconductor) at all points over a bounded surface. In the presence of a magnetic field gradient, the magnetic force on this current distribution will be different in different places, and the net force will not be zero. This leads to a repulsion of the superconductor by the magnetic field **gradient**. It's easy to see from this analysis that, ignoring shape effects and material anisotropy, a uniform magnetic field doesn't exert any forces on a superconductor. >============================================================================= > > > SPOOL SPOOL > _______SPOOL_________________________________SPOOL_____ <- mirror > SPOOL sssssssssssssssssssssssssss SPOOL > SPOOL s s SPOOL > SPOOL F F SPOOL > SPOOL FFFFFFFFFFFFFFFFFFFFFFFFFFF SPOOL > SPOOL SPOOL > SPOOL SPOOL > > >Fig.2: A cross-section of the device. The SPOOL is a standard electric spool, >s is a superconductor, and F is a ferromagnetic material such as soft iron. >The ___ line represents the surface of the superconductor, and is the line >where the magnetic field which exposes the superconductor is to be mirrored >(when we want to find the location of the magnetic pole generated by the >superconductor). > >============================================================================= > >[ ... ] As there is only 3 objects involved, it is very easy to >visualize the total forces which apply to the device: > >1) The spool versus the ferromagnetic material: [...] > >2) The superconductor versus the ferromagnetic material: [...] > >3) The spool versus the superconductor: > The superconductor is repulsed by the magnetic field. The superconductor > is therefore under influence of a force downward. The spool is influenced > by a magnetic pole generated by the superconductor, which location can be > found by mirroring the spool in the ___ mirror line. As the magnetic pole > generated by the superconductor is located inside the spool, the spool is > not influenced by any force. > It's hard to say what you mean here, since you haven't told us whether the solenoids are applying their fields in the same direction or opposing directions. However, in either case a superconducting image magnet located exactly midway between the solenoids and on their mutual axis would feel no net force. An image magnet off-axis would feel a net force pushing it away from the axis, and the solenoids would feel a reaction force balancing the force on the superconductor. Just because a magnetic source is within the cylinder described by translating the solenoid along its axis does not mean that it cannot exert a force on the solenoid. Again, the magnetic field due to the image magnet is different at different points on the circumference of the solenoid, so the forces don't cancel (the solenoid is another example of a divergence-less current flow), and there is a net force on the solenoid. It is not surprising that the net force on the solenoid system exactly balances the force on the superconductor. >The energy in the system is preserved, but we find that the total momentum of >the system is NOT preserved. > Superconductors obey Maxwell's equations just as anything else we know about. Maxwell's equations are formally proven to conserve momentum. >//////////////////////////////////////////////////////////////////////////// > > > THE MEASUREMENTS I HAVE CONDUCTED > >I have build a small prototype of the device described above. As >superconductor I used a 5x8x22 mm YBa2Cu3O7 crystal. > I wish I'd had crystals like that for my Ph.D. work, mine were typically a couple of cubic millimetres, the biggest we could get! >When I started the measurements (I have a video tape of >it) the system was slightly out of balance and the pointer was slowly >swinging clockwise and counter-clockwise like a pendulum. While the pointer >was in the middle of a counter-clockwise swing, I switched on the power >source and the pointer did immediately start reversing its movement (it >started moving clockwise). The reverse movement was not sudden by nature, but >appeared as a slow acceleration in the clockwise direction. The movement >stopped after a few second, but only after the pointer had passed the >previously most counter-clockwise position. > It does sound like you've made a dandy compass. >I assume that the device stopped >moving because the superconductor got overheated. I switched off the power >source, and I waited about 10 seconds and repeated the sequence. > I don't think that works. The superconductor was in the cryogen, right? As long as there is liquid nitrogen covering it, it will not be overheating. Why don't you try the following test: repeat the experiment but with the superconductor absent. Fill with liquid nitrogen, do everything the same, but don't use an actual superconductor. Further, the measurements seem somewhat subjective, because of the necessity of watching a swinging box and deciding rather it's swinging in a different way. I'd suggest you get a friend to come by and do the experiment several times. Before each attempt, you leave the room, your friend either removes the superconductor or doesn't, then closes the box and leaves the room. You reenter, and perform your measurement, recording the result. Afterwards, get together with your friend and see if you were able to tell which runs had a superconductor in them. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed May 1 13:16:28 EDT 1996 Article: 165655 of sci.skeptic Xref: info.physics.utoronto.ca sci.skeptic:165655 Newsgroups: sci.skeptic Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: The missing force Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 1 May 1996 14:40:04 GMT References: <4m2afs$aa4@news.uni-c.dk> In article <4m2afs$aa4@news.uni-c.dk>, Stephan Mannstaedt wrote: > >- The superconductor is influenced by a magnetic field (B), trivially >calculated as B = \mu NI/\sqrt(4R^2 + l^2), \mu being the permeability, >R the radius of the solenoid (the half distance between the '+' and '*'), >N the number of turns in the solenoid, I the current in the solenoid, l the >hight of the solenoid (the length along the z-axis of the '*' and '+'). > >Due to the Meissner effect, the superconductor will generated a magnetic >field with an equal strength, but with the field lines running in the >exact opposite direction (the surface of the superconductor will have a >zero magnetic field). The superconductor is consequentially repulsed >by the solenoids magnetic field (in an upward direction on the figure). > No, that's not true. The magnetic field lines produced will have no component normal to the surface of the superconductor, but there can be a tangential component. You've discovered the effect which haunts some undergrads when they compute image charges in a conductor system, and forget that it is not the total electric field at the surface which is zero, but the tangential one which is zero, and so they compute that there are no electric fields anywhere in the universe, and become disappointed. You see, one could generalize your analysis to the case where the solenoid is arbitrarily far away, and not necessarily surrounding the superconductor. You would then be forced to conclude that the existence of a superconductor anywhere in the universe prevents any magnetic field lines from existing. This is not true. Once we assume that the magnetic field lines produced by the superconductor in the exclusion of flux (in the type I regime) are not equal in magnitude and direction to that of the surrounding solenoid, the rest of your analysis fails. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed Jul 3 11:00:20 EDT 1996 Article: 54171 of sci.energy Xref: info.physics.utoronto.ca sci.energy:54171 sci.energy.hydrogen:4424 sci.engr:25541 Newsgroups: sci.engr,sci.energy,sci.electrochem,sci.energy.hydrogen Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: super-conductor Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 3 Jul 1996 14:24:44 GMT References: <31D4587C.7533@cadvision.com> <31D82190.37FF@interlog.com> <4rc7oc$hmn@news.hcl.com> In article <4rc7oc$hmn@news.hcl.com>, Robert McDermid wrote: >In message <31D82190.37FF@interlog.com> - Bob Falkiner >Mon, 01 Jul 1996 15:05:52 -0400 writes: >> >>Steve Cummings wrote: >>> >>> Bruce MacNeil wrote: >>> > >>> > My professor has asked me to write a sci-fi story on the premise that room >>> > temp super-conductivity was an everday phenomena. >>> > >>> >>> How about a super conductor electric energy storage system. Let's say a terrorist stores >>> up energy over a month then releases the energy catastrophicaly (as gamma rays) next to a >>> Canadian peace keeping base. >> There's more to this than just a room-temperature superconductor, what you describe would be a superconductor with a ridiculously high critical field, and an astonishing physical strength. Right now, the amount of magnetic energy we can store in a given-sized conventional superconducting coil is a function of two things, the upper critical field and the tensile strength. The design is usually adjusted so that both of these constraints limit you to more or less the same energy storage. Some numbers to play with: In 1968 a large superconducting magnet was built at Brookhaven. It had an outer diameter of 8.9 feet, an inner diameter of 7.9 feet, a length of 7.3 feet, and a central field of 2.5 tesla. The energy stored was 45 megajoules at full field, about the equivalent of 10 kilograms of TNT. The current carried in the coils was 4500 amperes, and the conductor weighed 12 tons. The stress on the coils was 16000 psi, about 1100 atmospheres. The energy stored in a coil goes up as the square of the current. So does the force on the walls. We've had an improperly reinforced magnet coil deform itself into uselessness because the startup manufacturer thought they could provide the mechanical strength with paraffin rather than the fibreglass called for in the original design. Applying the principal of virtual work to calculate the force on a superconductor due to the magnetic field it encloses, one can produce a model of a superconducting bomb in terms of a compressed gas cannister. Both have large amounts of energy to be released in a short time, the energy pushes out on the walls, and the force of that push approximately the same for the same total energy release, whether it be a superconducting coil or compressed gas. So, the superconducting bomb has to have the material strength of a compressed air bomb of similar destructive force. When our hypothetical superconducting bomb goes off, the energy is not released as gamma rays, except the incidental black-body radiation from vaporising the superconductor. The energy is released as resistive dissipation in the coil. If the coil flashes to plasma or something, then it conducts a current and heats up. If the coil is suddenly disassembled, the somewhat surprised unconfined magnetic field takes the oppurtunity to induce monster currents in any conducting materials nearby as it collapses. This would be an expensive EMP bomb. >Larry Niven has used the room temperature superconductor in a >number of his stories/books. One which comes to mind is >Ringworld Engineers. Generally, he makes use of the >interesting property that a superconductor is a conductor >of heat, as well as electricity, and hence will always >be the same temperature throughout. > But this, in fact, is incorrect. A superconductor is a poor conductor of heat, so much so that it is used in low-temperature labs as a heat switch. Typically a demagnetization stage used for refrigeration is attached to a sample by some thin strands of tin. The tin is superconducting at the ambient temperature in the chamber, and conducts little heat from the demagnetization stage to the sample. The stage is magnetized, cooled to ambient, and then demagnetized. The spins in the magnetization stage, being in an entropically unlikely state, aligned in the absence of a field, randomize, and in doing so they cool the demagnetization stage far below ambient. A small coil placed near the tin strands is turned on, applying a field above the critical field for tin, causing it to go normal. It now conducts heat from the sample to the demagnetization stage, cooling the sample. The coil is turned off, thermally isolating the sample, and the procedure repeats. The superconductor is used as a switched thermal conduction path with no moving parts (moving parts would be a major problem in a millikelvin-range experiment). The switching authority is about three hundred for typical setups, the thermal conductivity of the normal-metal state is hundreds of times higher than that in the superconducting state. >Thus, if you make >a suit out of superconductor, with a wire hanging off into >a pot of water, you can stand in the middle of a blast >furnace and never get hotter than the boiling point of water. > For those of you with access to blast furnaces and boiling-water temperature superconductors, and a tailor eager to face new challenges, do *not* try this at home. As outlined in the last paragraph, all of the superconductors we know about would not behave in quite this fashion (though the low thermal conductivity of the suit may help you for a while). -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed Jul 3 12:27:06 EDT 1996 Article: 129534 of comp.os.linux.misc Xref: info.physics.utoronto.ca comp.os.linux.development.apps:21276 comp.os.linux.misc:129534 Newsgroups: comp.os.linux.misc,comp.os.linux.development.apps Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Demand for TPL port? Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 3 Jul 1996 15:23:09 GMT In our office (at work, not the university) we're using TPL for production of tables for modeling work. Our modeling is done in Linux, but the postprocessing into tables is done under DOS, with the 2 GB file system limitations and inability to access our Unix tools when booted there. Further, the requirement to keep such large MS-DOS partitions cuts down on the useable simulation disk space as it's inconvenient to split the output across multiple partitions, some MS-DOS and others Ext2. We have been talking with the folks at QQQ software, makers of TPL, and they are a bit unsure about whether to expend the time and money to do a Linux port. While they do have versions for POSIX Unix, there is the cost of obtaining a test platform machine, getting somebody there to put up a Linux system, and teething themselves on it. This is balanced against the $1500 per copy they charge for TPL. At the moment, they have an expected market of four or five copies, from us and a group associated with us, and have never before had requests for a Linux version. I'm wondering if anybody else thinks that they might be interested in a Linux port. Please let me know in email, preferably with some short description of the application which warrants $1500 for a table-generating program. I'll talk with them again later and might be able to convince them if it looks like there is a significant interest. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Mon Jul 8 11:48:56 EDT 1996 Article: 2755 of alt.books.larry-niven Xref: info.physics.utoronto.ca alt.books.larry-niven:2755 Newsgroups: alt.books.larry-niven Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: "Stealth" Ringworld Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Mon, 8 Jul 1996 13:52:07 GMT References: <4romt7$ci2@news.esslink.com> <836806329snz@npagroup.demon.co.uk> In article <836806329snz@npagroup.demon.co.uk>, Tim Atkinson wrote: >Would an effect of the superconductor grid be to equalize the >temperature of the scrith to avoid or minimize heating problems.... > Lest this misconception become too widespread, I should point out that currently known superconductors are not perfect conductors of heat. Quite the contrary, in fact, they are very poor thermal conductors. I'll include an article I recently posted to another group: === BEGIN TEXT === > [ ... ] But this, in fact, is incorrect. A superconductor is a poor conductor of heat, so much so that it is used in low-temperature labs as a heat switch. Typically a demagnetization stage used for refrigeration is attached to a sample by some thin strands of tin. The tin is superconducting at the ambient temperature in the chamber, and conducts little heat from the demagnetization stage to the sample. The stage is magnetized, cooled to ambient, and then demagnetized. The spins in the magnetization stage, being in an entropically unlikely state, aligned in the absence of a field, randomize, and in doing so they cool the demagnetization stage far below ambient. A small coil placed near the tin strands is turned on, applying a field above the critical field for tin, causing it to go normal. It now conducts heat from the sample to the demagnetization stage, cooling the sample. The coil is turned off, thermally isolating the sample, and the procedure repeats. The superconductor is used as a switched thermal conduction path with no moving parts (moving parts would be a major problem in a millikelvin-range experiment). The switching authority is about three hundred for typical setups, the thermal conductivity of the normal-metal state is hundreds of times higher than that in the superconducting state. >Thus, if you make >a suit out of superconductor, with a wire hanging off into >a pot of water, you can stand in the middle of a blast >furnace and never get hotter than the boiling point of water. > For those of you with access to blast furnaces and boiling-water temperature superconductors, and a tailor eager to face new challenges, do *not* try this at home. As outlined in the last paragraph, all of the superconductors we know about would not behave in quite this fashion (though the low thermal conductivity of the suit may help you for a while). -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Fri Aug 2 11:22:00 EDT 1996 Article: 35004 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:35004 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Diesel-powered spacecraft Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Fri, 2 Aug 1996 15:05:30 GMT References: <4t90lb$7il@gap.cco.caltech.edu> <31FB6C81.6149@drycas.club.cc.cmu.edu> <960801.040941.1J8.rnr.w165w@krypton.rain.com> In article <960801.040941.1J8.rnr.w165w@krypton.rain.com>, Leonard Erickson wrote: >William Timmins writes: > >> That is... have a sphere mounted by electromagnetic repulsion. To turn >> your vessel, have two loops on opposite sides of the sphere spin the >> sphere, and thus the vessel. To halt the sphere & ship, use inductance >> to drain the momentum. >> >> A system that would use up very little energy (mainly in moving the >> sphere when the ship accelerates and efficiency losses in the system), >> and NO reaction mass. > >These are used in many satellites. And they have a *major* flaw. It >turns out that in real life, you don't make the same number of "turns" >in one direction as in another, or at least not in the short run. The >problem this causes is that there is a limit to how fast you can spin >the sphere, and the unmatched turns mean that you *will* reach that >limit sooner or later. At which point you can't manuever anymore. > >So, since you still need attitude jets to "dump" the excess angular >momentum, you might as well just use them exclusively. And attitude >jets will turn you a *lot* faster. > Well, attitude jets are one thing, but a lot of satellites use magnetotorquers. The Hubble Space Telescope, for instance, has five momentum wheels (some may still be down, I don't recall whether the broken ones were replaced in the big Hubble repair). These are gyroscopes which enable the telescope to rotate and hold a bearing. As Leonard (Shadow) Erickson points out, there is always a secular torque on your system, even if you don't know what it is going to be before launch, and so your spacecraft needs some way to shed the angular momentum which builds up. The HST has large loops of current-carrying wire which react against the Earth's magnetic field to perform this "momentum wheel desaturation", shedding angular momentum without expending reaction mass. Nobody wants to run thrusters on the telescope, that would run the danger of contaminating the optics and ruining the satellite. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Fri Sep 6 13:22:55 EDT 1996 Article: 142350 of comp.os.linux.misc Xref: info.physics.utoronto.ca comp.os.linux.misc:142350 Newsgroups: comp.os.linux.misc Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Ghostscript and low resolution on LJ4si Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (Steve Kotsopoulos) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Fri, 6 Sep 1996 16:36:19 GMT I've been searching news spools and web sites, and haven't found any indication of how to fix this problem. I'm trying to print PostScript files to our LaserJet 4si. The input files are greyscale PostScript bitmaps and render very well on the screen with ghostview. When I send one of these pictures to the printer, it is rendered very coarsely. A uniform black field prints out well, but any shade of grey is printed as a checkerboard of black and white squares, with 34 dark squares to the inch. A darker shade of grey has larger black regions, but the white regions always make up at least half of the area. This gives me an effective 34 pixel-per-inch output, each pixel consisting of two dark and two white squares, and never darker than 50% inked. I can't believe that this is the highest resolution which a LaserJet 4si can achieve on bitmapped images. This limit appears when printing PostScript from multiple sources. Am I doing something obviously wrong? The setup: ghostscript version 2.6.2 (GNU) invocation: gs -q -dSAFER -sDEVICE=ljet4 -sOutputFile=- - -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Tue Oct 1 16:11:54 EDT 1996 Article: 208064 of sci.physics Xref: info.physics.utoronto.ca sci.physics:208064 Newsgroups: sci.physics Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Gliding jet (was Re: how bumblebees fly?) Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Tue, 1 Oct 1996 20:09:44 GMT References: <52d552$fra@cantuc.canterbury.ac.nz> <52oltf$984@zeus.orl.mmc.com> <52q4g9$10ua@news.ccit.arizona.edu> In article <52q4g9$10ua@news.ccit.arizona.edu>, Frank Manning wrote: >In article <52oltf$984@zeus.orl.mmc.com> >Doug_Groseclose@ccmail.orl.mmc.com (Doug Groseclose) writes: > >> BTW, a bumblebee >> would have about the same glide path as any modern jet >> airliner-- roughly that of a rock dropped from a >> height. > >Beg pardon? > >[...] A few years back there was a fascinating story about a Boeing >767 or 757 that ran out of gas. The airplane made a pretty good >deadstick landing at a small airfield that one of the pilots happened >to be familiar with from flying there previously (sailplanes, I >think). > This sounds the the "Gimli Glider". On July 23, 1983, Air Canada flight 143, a Boeing 767, ran out of fuel near Winnipeg. The fuel gauge was not working, and a manual measurement of the fuel level ran afoul of a pounds to kilograms conversion, so the tanks were only half full. They landed at an abandoned military base near Gimli, Manitoba, after skipping over many small airfields which would not have allowed a 767 to land without flaps or thrust reversers (flaps were lost when the power went out, and thrust reversers, of course, were not working). The nose gear failed after landing, and a small fire started in the wheel well, but nobody was injured. To this day, the people of Gimli hold parades to commemorate the "discovery" of Gimli by the outside world. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed Nov 6 17:03:36 EST 1996 Article: 154872 of alt.folklore.computers Xref: info.physics.utoronto.ca alt.folklore.computers:154872 Newsgroups: alt.folklore.computers Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: What *exactly* is an Apple IIgs? Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 6 Nov 1996 14:40:16 GMT References: <846068541.19556.0@angel2.cityscape.co.uk> <32791acd.23082631@news.pgh.net> <327BC9B7.713F@rconnect.com> <55jpg1$ejb@jake.probe.net> In article <55jpg1$ejb@jake.probe.net>, Natural Born Cereal Killer wrote: >Clymer's Place said to all and sundry... > >>The Apple ][GS was indeed a 65C816. > > Running at 2.3MHz if memory serves, quite a step up from the 1MHz >65c02 the Apple II users remembered. For an extra $75 or so back in '88 >you could hook in a 7MHz chip via a TransWarp board from Applied Engineering. > It was 2.8 MHz, but with RAM refresh cycles it had an effective clock speed of about 2.5 MHz for purposes of calculating algorithm run time given machine code cycle times. Mine is still running at home, with the ZipGS, the alternative to the TransWarp, at about 8 MHz. Of course, the computer can be toggled into 1MHz mode so that classic video games were still playable. A few programs didn't work on the new hardware, but they were very few. >>The GS had (as I remember ;-? ) a maximum of 4 MB Address space. > > More like 16M, though I think there were some tricks involved to >see that much. 8MB was supposedly directly addressable. > Well, mine's got 4.25MB, so it can address at least that much. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed Nov 6 17:14:25 EST 1996 Article: 56162 of sci.space.policy Xref: info.physics.utoronto.ca alt.alien.visitors:177607 alt.conspiracy:238552 alt.paranet.ufo:90694 alt.ufo.reports:15355 sci.space.policy:56162 Newsgroups: alt.conspiracy,alt.alien.research,alt.alien.visitors,alt.conspiracy.area51,alt.paranet.ufo,alt.ufo.reports,sci.space.policy Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: LANL: Alien Artifacts ?? Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 6 Nov 1996 20:17:28 GMT References: <4il5m6$s3k@news.mcn.net> <327B95CF.2D81@market1.com> <55gj5f$pff@ns2.southeast.net> <55lvqu$gff@starman.rsn.hp.com> In article <55lvqu$gff@starman.rsn.hp.com>, Richard A. Schumacher wrote: > >>>Sensitive Compartmentalized Information Underground Facilities (SCIFs) at >>> Los Alamos National Lab where "Alien" artifacts are kept ?? > >>Many internet users who have gone to http://www.lanl.gov have had >>their ISPs contacted by the federal government with a suggestion of >>account termination. > > >Name two of them. If they're too scared to identify themselves, >tell us _exactly_ what they did to attract such attention. > I suspect that what he's referring to might be the no-robots policy at http://xxx.lanl.gov (and yes, that machine name is blocked by some anti-smut packages that parents can buy for their children's browsers). Anyway, for more information, read: http://xxx.lanl.gov/RobotsBeware.html (I like the comment about the gorillas with photocopiers). I believe that they have at one time or another contacted ISPs to get them to kill a user's robot which was attacking their site, but I'm not sure about that. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed Nov 13 15:19:17 EST 1996 Article: 39112 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:39112 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Relativity and constant subjective acceleration Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 13 Nov 1996 18:55:09 GMT I saw a few postings here about the question of time taken by a person to accelerate to relativistic speeds at constant subjective acceleration, and thought I'd throw a few numbers in. Given more than a piece of lunch hour, I could probably massage these numbers into a more useful form. Anyway, assuming that my math is correct, then if an object is accelerating at rate A' in a frame S' which moves at a speed 'v' with respect to an observer's frame S, then the observer in S measures an acceleration of A = A' / gamma^5 where gamma is the usual 1/sqrt(1-v^2/c^2) >From there, the differential equation gets a bit furry, as I've forgotten the mathematical trick which allows undergrads to do useful work with this. Anyway, a couple of relations which do integrate out without too much difficulty are: 3 A' t / c = (gamma^2 + 2)^2 sqrt(gamma^2 - 1) 3 A' x / c^2 = gamma^3 - 1 From this, it's not difficult to obtain t for a given x in the observer's frame, and so measure the time it takes for the person to reach a given distance. x as a function of t is doable, the first equation can be transformed to a cubic with one real root, and there is an algebraic solution to that. What comes out is pretty nasty-looking. Transforming these to the travelling person's frame will probably take another piece of another lunch hour. I suspect that the equations in that case are significantly simpler. However, there is one result which I do remember, which is fairly non-intuitive. If a person accelerates at a constant subjective acceleration then there is a certain finite head start he can have on a light beam so that the light beam never catches him up in finite time. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Thu Nov 14 10:30:11 EST 1996 Article: 223006 of sci.skeptic Xref: info.physics.utoronto.ca alt.pagan:199934 alt.paranet.paranormal:12724 alt.paranet.psi:7720 alt.paranet.ufo:91203 alt.paranormal:44460 sci.skeptic:223006 Newsgroups: alt.paranormal,alt.paranet.paranormal,alt.paranet.psi,alt.paranet.paranormal,alt.pagan,alt.out-of-body.alt.alien.visitors,alt.paranet.ufo,sci.skeptic Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Program to test psychic ability Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 13 Nov 1996 17:34:30 GMT References: <56395g$jm4@duke.telepac.pt> <32877C74.2781E494@found.com> <56a4ho$3u8@newshost.vvm.com> In article <56a4ho$3u8@newshost.vvm.com>, Dan Pressnell wrote: >mistered@1stresource.com (Edward Keyes) wrote: > >:In article <32877C74.2781E494@found.com>, "Mr. Big" wrote: > >:> Psychic test program >:[snip] >:> number = (rand() % 10) + 0x30; >:[snip] > >:Yikes! This is a common error with random number generators. Typically, >:the low-order bits of a system-supplied random number are much less >:random than the number as a whole. A better construction would be >:something like: > >: number=0x30+10*rand()/(RAND_MAX+1); > >Not only that, but random number generators tend to exhibit a pattern, >regardless of how you manipulate the results. > >I once plotted random (x,y) points on the screen with the Microsoft >BASIC program. After a while the pattern emerged: diagonal stripes >across the screen. Not good "randomness." > That's a flaw of all linear congruential random number generators. There are other ways of generating random numbers which do not produce striping in two dimensions. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Mon Nov 18 10:52:12 EST 1996 Article: 39319 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:39319 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Relativity and constant subjective acceleration Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Mon, 18 Nov 1996 14:20:33 GMT Well, I found a silly sign error in my last derivation of the acceleration transformation. I redid it, and got closed form solutions for all the expressions which have the correct forms in various limiting cases. So, once again. Assuming a magical stardrive which allows you to accelerate continuously at constant subjective acceleration of A', then in the frame of a stationary observer, your acceleration is measured as: A = A' / gamma^3 The integrals are now trivial, and in the stationary observer's frame the following hold: x(t) = c^2 / A' * (sqrt(1 + (A' * t / c)^2) - 1) t(x) = c / A' * sqrt((A' * x / c^2 + 1)^2 - 1) beta(t) = v(t)/c = A' * t / sqrt(c^2 + (A' * t)^2) the accelerating passenger measures an elapsed time of: t'(t) = c / A' ln(A' * t / c + sqrt(1 + (A' * t / c)^2)) To put some numbers on this, for acceleration at one gravity, the time taken to reach various distances is: 0.25 ly: t = 0.74 yr, beta = 0.61, t' = 0.68 yr 0.5 ly : t = 1.10 yr, beta = 0.75, t' = 0.95 yr 1 ly : t = 1.71 yr, beta = 0.87, t' = 1.29 yr 2 ly : t = 2.81 yr, beta = 0.945, t' = 1.73 yr 4 ly : t = 4.87 yr, beta = 0.981, t' = 2.25 yr 10 ly : t = 10.9 yr, beta = 0.9961, t' = 3.02 yr 100 ly : t = 101 yr, beta = 0.99954, t' = 5.17 yr After this, for every 10 fold increase in distance travelled, beta adds two nines, and t' increases by 2.2 years. The fixed-observer time frame remains one year more than the time of light. For a trip which stops at the end, calculate the time to cover half the distance, then double the t and t' variables. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Tue Dec 3 14:24:36 EST 1996 Article: 39854 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:39854 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Strange Matters Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Tue, 3 Dec 1996 14:39:11 GMT References: <57uqgq$qma@news.sas.ab.ca> <57v01q$9tt@news.marcam.com> In article <57v01q$9tt@news.marcam.com>, Phillip Thorne wrote: >blaine@freenet.edmonton.ab.ca () wrote: >> >>Just out of curiosity, how about extending this to forms of matter >>composed of particles other than protons, neutrons, and electrons? >> >>Granted that nearly all particles are notoriously unstable, but so are >>neutrons (with a very long half-life of 1 ks, or ~18 minutes), and they >>are stable in nuclei that do not beta-decay. [SNIP] > >Which leads to the question of: what exactly -is it- about >nuclei that keeps neutrons stable, that is missing when they >go free? Something about the intranuclear strong force, >being mediated by pions (as opposed to the intrahadronic >strong force mediated by gluons)? > >In neutron stars, are the neutrons really stable? >Or do they frequently decay into protons and electrons, >but immediately get inverse beta-decay squished >back together? (speaking imprecisely) > Neutrons in a nucleus are stable because of energetic concerns. Basically, if the neutron were to convert into a proton, electron, and anti-neutrino, you would find that the extra proton in the nucleus increases the total electrostatic energy of the system, and that this increase in energy exceeds the energy released by the conversion of the neutron. This makes stable isotopes truly stable, there is no way for the neutron to decay. Nuclei with an excess of neutrons can beta-decay, sometimes with fairly long time scales, because the energy differences are marginal and the decay mechanism, mediated by the weak force, is inherently slow. Nuclei with an excess of protons can capture an electron from the surrounding shells and convert a proton to a neutron. In a neutron star there can be a fairly large number of protons and electrons as well. A typical neutron star might be ten or twelve percent protons by mass. The electrons fill up a Fermi sea up to very high kinetic energies, while the neutrons fill up a Fermi sea to lower energies (because of their higher masses). It turns out that the neutron star is stable when the most energetic neutron cannot decay into an electron with energy higher than the Fermi energy for the electrons. At that point, the neutron could decay, but the electron would have literally nowhere in phase space to be, so the neutron is unable to decay. Now, in a real neutron star with a fuzzy electron surface (due to finite temperature) you ought to be able to get some decay and recombination, but it is not allowed to talk about "this electron is formed in a decay while that other electron is captured on a proton" in the quantum mechanics of degenerate fermi gases. All you could say is that there is some decay and recombination, with no net transmutation, and the Fermi seas cooled by neutrino energy-shedding. This cooling would be slight, as the Fermi energies in neutron stars are huge (you need a difference in Fermi energies of a couple of MeV to get stability, and 2 MeV is about 24 billion degrees kelvin, so the electron sea would have to be hotter than that for thermal effects to appear). The Fermi surfaces are effectively cold, even in a neutron star. Consequently, the thermally excited region is a very tiny portion of the total available phase space. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed Dec 4 12:47:24 EST 1996 Article: 39874 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:39874 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Vernor Vinge's bobbles (SPOILER) Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 4 Dec 1996 14:47:45 GMT References: <56h1hu$m1t@dfw-ixnews8.ix.netcom.com> <5724t5$5kd@nntp5.u.washington.edu> In article , Jonathan Cunningham wrote: > >When I read about these, I was surprised to learn that there is an >electric field of (IIRC) about 100v/m even on a fine day (actually, >the polarity is reversed from what you get in a thunderstorm, when >the field strength is *much* higher). Weird to think that when I >stand up, my head is 200v different to my feet (approx.) > No, it's not. You are a conductor, and so cannot support an internal electric field. Your head and feet are at the same voltage, and what you've done is to distort the electric field lines in your vicinity so that the 100 V/m doesn't apply where you are. That figure is correct for a place where the ground is locally flat, and there are no conducting objects sticking out of it. Of course, what it does mean is that if you are lying down, and you stand up, there is a motion of charge such that, were the Earth's electric field suddenly to disappear your head would find itself suddenly 200 volts away from your feet, but your body's capacitance is sufficiently low that this is not a health threat. You don't feel the current flow when you stand up. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Thu Dec 5 12:46:46 EST 1996 Article: 39888 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:39888 rec.arts.startrek.tech:67413 Newsgroups: rec.arts.startrek.tech,rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Antimatter rockets: formulas, numbers, Robert L. Forward Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Thu, 5 Dec 1996 14:04:28 GMT References: <57njde$8sq@news.marcam.com> <57npc8$rbr@sloth.swcp.com> <01bbe224$f35d5220$e702a0c0@crunch> In article <01bbe224$f35d5220$e702a0c0@crunch>, Gary L. Krepps wrote: > > >Taki Kogoma wrote in article ><57npc8$rbr@sloth.swcp.com>... >> Phillip Thorne appears to have submitted >> message <57njde$8sq@news.marcam.com> to rec.arts.startrek.tech: >> >From _Indistinguishable from Magic_, Robert L. Forward, >> >1995, Baen Books, ISBN 0-671-87686-4 (non-fiction) >> > >> [...] >> >(2a) Proton plus antiproton produces (on average) two neutral and >> >three charged pions. >> > >> >p+ + p- --> 2 pi0 + 2 pi- + pi+ >> >> Something definitely screwy about this; conservation of charge and all >> that... >> >Yeah, you're getting a negative charge from nowhere. You can't keep that >up for very long, ya know. > I disagree. It is eminently possible to produce two neutral and three charged pions on average. Not in an average interaction, but averaged over a large number of interactions. If you're running an antimatter engine, where the distinction between charged and uncharged pions is quite important, then you want to know the average over all reactions of these individual particle types. If there is more than one common branch, then you can produce an average which is impossible in individual cases. The average state of a bit in a compressed disk file is one half, and the average television station I watch is probably something like 20.1725. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Mon Dec 9 11:16:01 EST 1996 Article: 39941 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:39941 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Antimatter rockets: formulas, numbers, Robert L. Forward Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Mon, 9 Dec 1996 16:05:54 GMT References: <588iq1$ks0@freenet-news.carleton.ca> >>>> >(2a) Proton plus antiproton produces (on average) two neutral and >>>> >three charged pions. >>>> > >>>> >p+ + p- --> 2 pi0 + 2 pi- + pi+ >>>> >>>> Something definitely screwy about this; conservation of charge and all >>>> that... >>>> >>>Yeah, you're getting a negative charge from nowhere. You can't keep >that >>>up for very long, ya know. >>> >> I disagree. It is eminently possible to produce two neutral and three >> charged pions on average. Not in an average interaction, but averaged >> over a large number of interactions. If you're running an antimatter >> engine, where the distinction between charged and uncharged pions is >> quite important, then you want to know the average over all reactions of >> these individual particle types. If there is more than one common >branch, >> then you can produce an average which is impossible in individual cases. >> The average state of a bit in a compressed disk file is one half, and >> the average television station I watch is probably something like >> 20.1725. >> >And the average charge of any large body is essentially zero. Remember, >if you multiply the average by the number of events, you get the total. >If the average reaction produces a net charge of minus-one, then, yes, >you're creating charge from somewhere. > (Curse my 1/2 day expiring news feed! Cutting and pasting from DejaNews...) Perhaps I was reading more into the quoted text than you. I assumed that the original text was "produces an average of two uncharged and three charged pions", and that the reaction was added in by a helpful reader. In that case, one could envision, for example, two paths: p + p_bar -> 4 pi0 + pi+ + pi- (50%) p + p_bar -> 2pi+ + 2pi- (50%) Now, we produce an average of two uncharged and three charged pions per reaction, but no reaction produces exactly two uncharged and three charged pions. That's the point I was trying to make. Now, if Forward's text actually included the reaction as written, then I'd say it was misleading in context, and ought to be written more as: p + p_bar -> 2 pi0 + 3 pi+- (on average) -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed Dec 11 16:06:26 EST 1996 Article: 39993 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:39993 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Realistic colony possibilities Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 11 Dec 1996 17:53:56 GMT References: <58l5f1$g9b@dismay.ucs.indiana.edu> In article <58l5f1$g9b@dismay.ucs.indiana.edu>, eric andrew sonstroem wrote: >> >>We could establish a colony at the Lagrange point behind Mercury, using >> >>the entire planet as a sun-shield. The colony would have to be actively >> >>stabilized, since that Lagrange point is unstable. > >The Lagrange point is *along* Mercury's orbit. It is not behind Mercury >relative to the sun. It wouldn't be shaded at all. > There are five Lagrange points. Two of them are along the orbit, one ahead and one behind. One is on the other side of the primary, one is between the primary and the planet, and one is opposite the primary as seen from the planet. It is this last Lagrange point to which he was referring. The point is actually 2/3 stable, it is unstable against radial perturbations but stable against transverse perturbations. Assuming my calculations are correct, and ignoring the eccentricity of Mercury's orbit, that point is about 90% shaded from sunlight. I get about 221000 km elevation for the outer Lagrange point. At that distance, Mercury's disk is 1.26 degrees across, while the Sun's is 1.33 degrees across. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Tue Dec 17 14:38:18 EST 1996 Article: 40131 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:40131 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: shelf life of simple fission weapons in SF Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Tue, 17 Dec 1996 14:32:11 GMT References: <850158025@sheol.org> <58vdjf$dih@clark.zippo.com> <593h0h$adj@nntp.interaccess.com> In article , Kedamono wrote: > >This reminds me of movies that have A-bombs or H-bombs being used by >terrorist. One in particular, who's name escapes me, had a standard >spherical implosion A-bomb. In fact it have it sitting on the counter, >with all these detonators sticking into pieces of plastique. Real pretty. >So what do our stalwart heroes do? They muck about with the detonating >system, trying to disarm the timer. > "The Manhattan Project", 1986. And don't forget, it wasn't just any plutonium that "Paul Stephens" stole, it was a new super-plutonium invented by "Dr. Mathewson". There was no place isolated enough to put the bomb to let it go off safely. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Tue Dec 17 16:13:43 EST 1996 Article: 40147 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:40147 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Who's dat out dere ? was A VON NEUMAN PARADOX ANSWER Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Tue, 17 Dec 1996 19:44:40 GMT References: <58vt97$37k@li.oro.net> <505@eildon.win-uk.net> <594gko$np@harbinger.cc.monash.edu.au> In article <594gko$np@harbinger.cc.monash.edu.au>, Joseph Askew wrote: > >I'll put good money that the first people to see a pulsar's signal >had to reassure themselves for a moment it couldn't be artificial. > You'd win. The first pulsar was named "LGM-1", in jest. That stood for "Little Green Men". -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed Dec 18 11:17:56 EST 1996 Article: 40188 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:40188 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Strange Matters Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 18 Dec 1996 14:04:00 GMT References: <588jf2$l22@freenet-news.carleton.ca> <58a5rd$pob@cnn.Princeton.EDU> <17860964DS86.C369801@mizzou1.missouri.edu> In article <17860964DS86.C369801@mizzou1.missouri.edu>, Walker on Earth wrote: >In article <58a5rd$pob@cnn.Princeton.EDU> >shocklee@rogue.princeton.edu (Paul D. Shocklee) writes: > >>: > against beta decay is that the electron Fermi sea should be filled up to >>: > a momentum greater than the maximum momentum of the electron emitted in >>: ^^^^^^^^ ^^^^^^^^ >>: > neutron beta decay. [...] >>: > >> >>: Fermi *momentum* or Fermi *energy*? Or is one a shorthand for the other? >>: (*Energy* makes more sense in your argument and given the units you use.) >> >>I probably should have said Fermi energy. This energy corresponds to a >>magnitude of the momentum, which you can call the Fermi momentum. > >In the derivations I have seen, it is more convenient to manipulate >the quantity momentum than the quantity energy, but it is easy enough >to equate one with the other by the relation: p = (2mE)^(1/2). > A couple of quick points. The electrons in a neutron star are relativistic, so p = E / c is a better approximation. Also, the distinction between Fermi momentum and Fermi energy isn't really important in the context of neutron decay within the neutron star. The usual formulation is to say that a neutron within the fuzzy edge (the neutron needs an empty state to land in, too) of its (non-relativistic) Fermi surface emits an electron in the optimal direction, such that little momentum winds up in the neutrino and most of the reaction momentum winds up in the electron, moving in a direction parallel to that of the original neutron. When all of these things happen, if there's still no empty momentum state for the electron to land in, then the reaction is suppressed. You could talk about energies, but it doesn't gain you much because they're not additive in the same way as momentum vectors are. A neutron moving with a kinetic energy of 10 MeV emits a 3 MeV electron in its own rest frame, and a neutrino. The electron's energy is not deducible from this information, though upper and lower limits on it are. From this, you can perform the same analysis as in the momentum case, but the math is a bit messier. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Fri Dec 20 16:08:08 EST 1996 Article: 40221 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:40221 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Weapons - a Catalog Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Fri, 20 Dec 1996 20:09:27 GMT References: <32AC5569.246F@northnet.org> <58j8f2$ikj@news.rain.org> <32AD8976.6B651D0E@alcyone.com> In article , B. Vermo wrote: >In article <32AD8976.6B651D0E@alcyone.com>, >Erik Max Francis wrote: >| >|Gravel or small-arms fire would do certainly do damage to civilian ships, >|but warships armed for bare will stand much better. > >A 10g slug at 0.1c has an impact energy of 301.3 kJ, over a few square >millimeters, which would call for some rather bulky armour. > If it really were only 301.3 kJ, it would not take much to protect against it. A car on city streets carries that much kinetic energy. Admittedly hard to armour against over a surface of square millimetres, but since the actual kinetic energy is 4.5 billion kilojoules, the difficulty is somewhat understated by your response. Hmmm, this is a good example for students having trouble with "precision" versus "accuracy". The 301.3 kJ is quite precise, but not very accurate. The expression you should be using is: E = m * c^2 * (1 / sqrt(1 - v^2/c^2) - 1) >If a gun could boost 1g pellets to 0.5c, the >energy would be 173.1 kJ each for something you could spew out in streams. >If you can manage 0.75c, pellet energy will be 339.9 kJ, which is better than >the 'slow' 10g slug has. > Make these 1.39e+13 joules and 4.61e+13 joules. All these numbers assume that the projectile is completely stopped within the ship, and that the momentum imparted by the particle results in a negligible velocity change. The latter is true in context for target ships larger than about 100 grams, the former is unlikely, even for ships considerably heavier than 100 grams. Note, however, the effects of such a launcher on the ship holding it. If the launcher weighs one ton it will recoil at 340 m/s each time a one gram mass is fired at 0.75c. If the total weight of the ship is one hundred tons, and it fires ten of these a second, then the weapon alone is accelerating the ship at 3.5 gravities. Meanwhile, the onboard power plant is producing a rather stupendous 461 terawatts, plus whatever power is wasted in the launcher. Note that superconductors don't provide impedance-free flow to currents when the currents are not constant, so there are upper limits on the efficiency of the launcher. Assuming only one percent of the energy is wasted in the launcher, your one hundred ton ship is now generating 4.6 terawatts of heat. Assuming that most of the mass of the ship is metal, such as aluminium or iron, then a radiator failure would result in the whole ship heating up at about 200000 degrees per second. If your radiator is a sphere with the area of two football fields, it would have to be heated to 9500 degrees kelvin. From 16 kilometres away this would shine as brightly as the Sun does from Earth orbit, though it would be considerably bluer. Perhaps another approach is to accelerate the whole ship up to relativistic speeds and throw sub-relativistic projectiles at those targets which you can hit (not many, because of the foreshortening). A ship moving at 0.75 c and capable of firing projectiles at 100 km/s relative to itself would deliver those objects at essentially 0.75c to any target it could hit within a cone of 0.3 milliradians (1 minute of arc) as measured in the stationary frame of the targets. From a distance of one astronomical unit, it could hit targets within a cone 90000 kilometres across at the base. That would blanket the Earth out to geostationary orbit if it could get all its projectiles fired before closing within one A.U. Of course, this 100 ton ship is going to take a lot of energy to accelerate up to that speed. The acceleration can be done far away from the targets, in fact it has to be done very far away, and then the ship can coast through with minimal constraints on its energy and heat dissipation requirements. This approach, carried to its logical conclusion, just moves the launcher back one step. Now your attacking force stands way, way, way back, and launches relativistic drones, each of which flies through the target region, firing sub-relativistic particles at objects in its field of view. Ideally, most of the mass of the drone is fired as ammunition, and even better would be to have the empty firing mechanism collide with whatever tempting and static target was along the line of flight. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Mon Dec 23 17:23:29 EST 1996 Article: 61637 of ott.forsale Xref: info.physics.utoronto.ca ott.forsale:61637 Newsgroups: ott.forsale,ott.forsale.computers Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: WTB Applecolor RGB monitor Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Mon, 23 Dec 1996 22:03:29 GMT I'm wondering if anybody has an old 12" Applecolor RGB monitor they'd be willing to sell. If not a 12", I'd consider the larger sizes. Please let me know at neufeld@physics.utoronto.ca. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed Jan 8 09:55:29 EST 1997 Article: 40909 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:40909 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: heat radiation fins for starships Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 8 Jan 1997 14:17:40 GMT References: <961225.235128.9b5.rnr.w165w@krypton.rain.com> <5aahck$hro@sp115.ocs.lsu.edu> <970106.205949.8b6.rnr.w165w@krypton.rain.com> In article <970106.205949.8b6.rnr.w165w@krypton.rain.com>, Leonard Erickson wrote: > >300K is roughly "room temperature". Cooling something to room temp >means that the radiator(s) will be at 300k *or hotter*. This is >elementary thermodynamics. You can't get rid of heat with a radiator >that is *cooler* than whatever you are trying to cool! > I'm afraid I don't agree with this. It's quite possible, if the radiator is large or the thermal insulation between the hot region and the radiator is not too low. In fact, it requires deliberate effort on your part to make the radiator warmer than the contents (you have to run a refrigerator between the contents and the radiator). If the radiator doesn't radiate, it comes into thermal equilibrium with the contents, and everything is at the same temperature. Now, add radiation, and the radiator cools down, more so than the contents. In fact, it is this temperature difference which allows heat to flow from the contents to the radiator (assuming to heat pumping). The RTGs on Cassini will be much warmer inside than outside, and will radiate from the outside only. The thing you can't do is get rid of heat with a radiator which is cooler than the ***surroundings***. That is one reason you might want to heat up your radiator above the temperature of the contents. If you want to maintain 300 K temperatures in a ship which is surrounded by an ambient gas or radiation field at a temperature of 400 K, then you'd better warm up your radiator significantly above 400 K, by pumping heat >from the inside to the radiator. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Mon Jan 13 08:23:20 EST 1997 Article: 163377 of sci.electronics Xref: info.physics.utoronto.ca sci.electronics:163377 Newsgroups: sci.electronics Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Identify flyback transistor in Applecolor monitor? Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Sun, 12 Jan 1997 22:50:27 GMT I'm wondering if anybody can help me to identify the smoked flyback transistor in my Applecolor monitor. The part bears no manufacturer's mark, just two lines of text: D1650 7A The casing is 1.5 by 2.5 centimetres, with a screw hole for mounting to a heat sink. The legs are B C E from left to right. The transistor is part Q502 on the Applecolor RGB monitor, manufactured in 1987. This is the only power transistor in the HV section, the only one which is on a heat sink. Also, if somebody identifies the part, and determines that it is *supposed* to have 0.3 ohm resistance base to emitter, and no measurable diode turn-on voltage between those pins, please let me know so that I can find another possible cause of the monitor failure. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Fri Jan 17 08:35:27 EST 1997 Article: 48696 of sci.electronics.repair Xref: info.physics.utoronto.ca comp.sys.apple2:114289 sci.electronics.repair:48696 Newsgroups: sci.electronics.repair,comp.sys.apple2 Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Identify flyback transistor in Applecolor monitor? Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Thu, 16 Jan 1997 20:32:40 GMT I'm wondering if anybody can help me to identify the smoked flyback transistor in my Applecolor monitor. The part bears no manufacturer's mark, just two lines of text: D1650 7A The casing is 1.5 by 2.5 centimetres, with a screw hole for mounting to a heat sink. The legs are B C E from left to right. The transistor is part Q502 on the PCB of the Applecolor RGB monitor, manufactured in 1987. This is the only power transistor in the HV section, the only one which is on a heat sink. Please, if somebody knows the details I need to buy a replacement component, let me know. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Mon Jan 20 13:12:17 EST 1997 Article: 41274 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:41274 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Detecting the use of an FTL drive... Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Mon, 20 Jan 1997 17:55:03 GMT References: <5bjlmo$9nu@snow.btinternet.com> <32E00334.18EE0D15@alcyone.com> In article <32E00334.18EE0D15@alcyone.com>, Erik Max Francis wrote: >David N. Paterson (Pixi) wrote: > >> Some types of (postulated) drives have the ship travelling FTL, but >> still in our existing space-time universe. To reach that speed, they >> must be accellerated (by some means) from their previous STL speed. >> At some point therefore, they must travel *at* the speed of light, and >> must therefore, for a brief instant, have infinite mass. Also, while >> travelling very close to C, their mass would be *very* large. > >Infinite is infinite, no matter how you cut it, and now matter how briefly >it happens. > I must disagree with this. In the context we are interested in something like the integral of mass(t) * dt. Integrals of functions which become infinite are not required to be infinite themselves. The classic example is the Dirac delta function (watch the mathematicians shudder!), but other examples abound. The integral of 1/sqrt(|x|) from -1 to +1 is perfectly finite, even if the function itself is unbounded above at zero. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed Jan 22 17:28:03 EST 1997 Article: 41377 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:41377 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: So how *do* you get FTL & Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 22 Jan 1997 17:50:05 GMT References: <5bn7mq$3mo$1@gail.ripco.com> <32E1CF8E.1EBF@sk.sympatico.ca> <549@eildon.win-uk.net> <32E39608.5DBF@nada.kth.se> In article <32E39608.5DBF@nada.kth.se>, Johan Forsberg wrote: >Alastair Ward wrote: >> >> I would be grateful if you could explain what is meant by the phrase - >> >> "causality is preserved" >> >> This seems to have a special meaning in Physics and I have been unable >> to find an explanation in any of the books I have access to. Thank you > >If one observer sees event A happening before event B, then *all* observers >must do likewise, no matter where they are, or how they are moving. > No. You have to be a bit more precise than that. If one observer sees event A happening before event B, and event B does not occur before light from event A reaches the position of event B, then all observers agree on this fact and on the ordering, even if they differ as to the lengths and times involved. If event B occurs before light from event A could have reached it, then observers will differ on the ordering of events. Some will see the events as simultaneous, some will see A before B, and some will see B before A. Also, to clear up ambiguity, wherever I say "see event A" I mean that the observer sees the event and *corrects* for the finite time it takes light to reach him from that event. The effect is not a time-of-light effect. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Tue Jan 28 13:40:03 EST 1997 Article: 41591 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:41591 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Preserving causality Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Tue, 28 Jan 1997 18:39:02 GMT References: <5c8j7r$2j53@eccws1.dearborn.ford.com> <32E99F27.9C1BF43@alcyone.com> In article , Andrew Plotkin wrote: >Erik Max Francis (max@alcyone.com) wrote: >> > Finally, there is nothing wrong with preferred reference frames, >> > provided >> > that there is some logical reason for the reference frame to be >> > preferred. > >> And provided you don't mind throwing away special relativity. The first >> postulate of special relativity is the relativity principle, which states >> that there are no special frames. If you allow special frames, what you >> have is not special relativity. > >I think I am going to strenously disagree. (On purely definitional >grounds.) > >That postulate of SR, as I view it, is the claim that there are no >special frames of references *in the laws of physics*. In any particular >situation, there may be a frame of reference which is special *for the >purposes of that situation*. It will not be special for the purposes of >using Maxwell's equations, but it may be special for other reasons. > >The obvious example is the rest frame of the cosmic microwave background >radiation (the frame in which the CMBR is most nearly isotropic.) There >*is* one of these, and presumably it doesn't force us to throw away SR. :) > This is entirely different. Here is a more precise statement of the "no preferred frames" hypothesis. Assuming flat space, the absence of a preferred frame means that if you were sealed inside a box and forbidden interaction with the surroundings, that there is no physical measurement you could possibly perform within the box which would tell you your absolute speed with respect to the universe. A preferred frame FTL drive violates this precept. I could send a small object on an FTL trip within the box, and by careful measurement of the departure and arrival times I could determine my absolute speed with respect to the surrounding universe. Similarly, space defined by Galilean transformations violates this, because the speed of light would necessarily be different for different box speeds. Yes, the cosmic microwave background defines a frame, but it doesn't define a **special** frame. The laws of physics are not different for people moving relative to the CBR from those for people at rest relative to it. All must agree on measurements they perform while sealed within boxes. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Thu Jan 30 09:06:29 EST 1997 Article: 41693 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:41693 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: 'Hardening' asteroids/meson cannon Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Thu, 30 Jan 1997 14:01:10 GMT References: <32E5A593.3BDA0B12@alcyone.com> <32E6C418.2009@ibm.net> <5ci7lk$8in@calvin.st-and.ac.uk> In article <5ci7lk$8in@calvin.st-and.ac.uk>, David Thomas Richard Given wrote: >In article <32E6C418.2009@ibm.net>, Kasey wrote: >>Plus Black holes "evaporate", the smaller they are the faster >>this happens. a black hole the size of Ceres (largest asteraiod in our >>asteroid blet) would "evaporate" explosivesly, on the order of megatons. >[...] > >Nearly right. When a black hole evaporates, *all* its mass/energy is >released. An asteroid the size of Ceres is rather large; that's a lot of >energy. I don't know the exact figures, but put it like this: if Ceres was >turned into a black hole and then evaporated, one hemisphere of the Earth >would get sterilised. > The mass-energy of Ceres, completely converted, is 2.6E+19 gigatons TNT. That's half a million times the gravitational binding energy of the Earth. It would not all get released at once, though. This energy is equivalent to the total solar output for 8600 years. As I recall, an evaporating black hole does not peak quite so early. It would take a long time for that much black hole to disappear. Indeed, if I'm reading the math correctly at: http://www.intelli-net.com/personal/tsmith/cosm.html then a Ceres-mass black hole has a lifetime of 4.9E+43 years. With that much lead time I imagine humans would be able to solve the Great Ceres Time Bomb problem. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Tue Feb 4 09:48:17 EST 1997 Article: 41952 of rec.arts.sf.science Xref: info.physics.utoronto.ca alt.sci.planetary:15671 rec.arts.sf.composition:3813 rec.arts.sf.science:41952 Newsgroups: alt.sci.planetary,rec.arts.sf.composition,rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Fictional planet--weather and climate questions. Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Tue, 4 Feb 1997 14:36:23 GMT References: <01bc0a69$229400e0$d72674cf@default> <01bc1059$7b1ec880$265ee8cd@sal9000> <32F3CCDC.3027BFF6@alcyone.com> <01bc109a$7eaa28a0$295ee8cd@sal9000> In article <01bc109a$7eaa28a0$295ee8cd@sal9000>, John D. Gwinner wrote: >Erik: > >> I haven't read "Rocheworld." There are ways of inventing weird >situations >> where you could get constant torques that just _happen_ to keep the >body's >> second-order rotation in sync with its orbit, but now it's getting a >little >> silly . . . > >I don't have the book on the shelf, but it's an egg shaped moon the size >(roughly) of earth in orbit around a Jovian, *I think*. I believe that the >'point' was pointed at the jovian in some kind of tidal lock, but boy, I >could be wrong. > Not really very close. Rocheworld, as described, consists of two almost equal-sized planets in a very tight orbit, tidally locked to each other. Rotation is in the ecliptic plane, so the pole does not point at the sun. If you want to keep one pole pointing at the sun, you pretty much have to cheat. You can put the object in orbit about a fairly dark source, a Jupiter-sized gas ball. Put this whole thing in a very long orbit around a very bright sun, with its orbital plane perpendicular to that of the gas ball around the sun, and for several years at a stretch the pole will be pointing more or less at the sun. Or, put the planet in orbit around a dark object, put this collection on the edge of a dirty nebula, and put a whole lot of bright nearby stars around the whole thing. The nebula blocks light coming at the planet from one direction. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Tue Feb 4 17:25:28 EST 1997 Article: 41953 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:41953 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Preserving causality Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Tue, 4 Feb 1997 14:46:59 GMT References: <5c8j7r$2j53@eccws1.dearborn.ford.com> <01bc105c$d0638530$265ee8cd@sal9000> In article <01bc105c$d0638530$265ee8cd@sal9000>, John D. Gwinner wrote: >Christopher Neufeld wrote ... > >> A preferred frame FTL drive violates this precept. I could send a >> small object on an FTL trip within the box, and by careful measurement of >> the departure and arrival times I could determine my absolute speed with >> respect to the surrounding universe. > >Good concrete analogy, but somehow I don't see the problem with this. >Saying SR is not consistent with non-causality problematic FTL to me seems >to be a non-issue; as long as the FTL does not violate SR with respect to >NON FTL travel. > On the whole I agree, it's not a logical contradiction. Of course, if there are no preferred frames for causal events, but there is a preferred frame for FTL events, then the universe is edging out of the mysterious and into the perverse. In any case, such behaviour would be inconsistent with special relativity which assumes that the laws of physics are the same in all inertial frames in flat space. I just wanted to point out what the "no preferred frame" assumption actually is. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Fri Mar 7 12:45:15 EST 1997 Article: 116756 of comp.sys.apple2 Xref: info.physics.utoronto.ca comp.emulators.apple2:11329 comp.sys.apple2:116756 Newsgroups: comp.emulators.apple2,comp.sys.apple2 Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: apple2-v003-linux.tar.gz Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Fri, 7 Mar 1997 16:08:03 GMT References: <3318988D.151D12E1@baldmountain.bbn.com> <331C20AC.34EF864E@de.epfl.ch> <331C68E4.4D83@baldmountain.bbn.com> In article <331C68E4.4D83@baldmountain.bbn.com>, Aaron Culliney wrote: >Christian Koechli wrote: >> >> I got the new file from ftp.apple.asimov.net unpacked it >> and tried to compile it on my RedHat 4.1 (kernel 2.0.27) linux box: >> >> # make >> gcc -I/usr/include -Wall -c apple2.S >> /tmp/cca01775.s: Assembler messages: >> /tmp/cca01775.s:2163: Error: register does not match opcode suffix >> /tmp/cca01775.s:2171: Error: register does not match opcode suffix >> make: *** [apple2.o] Error 1 >> > >Someone else reported this problem with RH4.1 and gcc v.2.7.2.1. (I >currently use RH3.0.3, kernel2.0.23, on an i586 with gcc v2.7.2 and >everything works just fine) > Well, I get the problem with gcc 2.7.2.1 on an i586. It's a simple thing to fix, though. Here's the patch: ===== BEGIN PATCH ===== *** apple2.S Tue Mar 4 12:52:38 1997 --- apple2.S~ Sat Mar 1 15:15:25 1997 *************** *** 1572,1590 **** /* ---------------------------------- HANG instruction ---------------------------------- */ op_HANG: ! decw PC_Reg Continue /* ---------------------------------- NOP_2 instruction ---------------------------------- */ op_NOP_2: ! incw PC_Reg Continue /* ---------------------------------- NOP_3 instruction ---------------------------------- */ --- 1572,1590 ---- /* ---------------------------------- HANG instruction ---------------------------------- */ op_HANG: ! decb PC_Reg Continue /* ---------------------------------- NOP_2 instruction ---------------------------------- */ op_NOP_2: ! incb PC_Reg Continue /* ---------------------------------- NOP_3 instruction ---------------------------------- */ ===== END PATCH ===== As you see, the patch looks like it fixes a couple of bugs. The program counter being treated as a byte value when it should be a word. I don't suspect that the HANG and NOP_2 operations are often invoked in real code, so it shouldn't be a big problem. I suspect that it only causes problems on page boundaries in the virtual machine, if the byte-ordering is low-high for the PC. (reminiscent of the 6502 indirect jump bug). Oh, this problem was also in v002, I patched it and kept going. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed Mar 12 17:40:27 EST 1997 Article: 255299 of sci.skeptic Xref: info.physics.utoronto.ca alt.conspiracy:272567 alt.folklore.science:39143 sci.astro:156411 sci.astro.amateur:82389 sci.skeptic:255299 Newsgroups: alt.conspiracy,alt.folklore.science,sci.skeptic,sci.astro,sci.astro.amateur,hsv.general Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: moon landing was FAKE, because 24000km/hr is LESS then 28000km/hr Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 12 Mar 1997 22:31:54 GMT References: <857997396.18421@dejanews.com> In article <857997396.18421@dejanews.com>, Mark Peeters wrote: >On my previous posting >nobody did contradict the numbers > >NASA says that the current SPEED-record for a man-made object of 2 gramms >is 24000km/hr... > (see http://www.wstf.nasa.gov/labs/hypervl/currtest.htm ) > Nope. I looked there, no mention that this was a speed record. In fact, the word "record" does not appear in that document. Objects were fired at speeds of 6.7 km/s at hydrazine tanks to determine whether that would cause them to explode (it didn't). This is consistent with looking at the effect of an impact between a low-earth orbiting object and another one in a high relative inclination, such as an equatorial satellite striking a piece of debris in a polar orbit. Why would NASA care about such information if they didn't actually have such satellites in orbit??? >For space-travel around the earth 28000km/hr is NEEDED... >( see http://www.geocities.com/CapeCanaveral/Lab/1917/proof1.html ) > So your contention is that there are no satellites in orbit right now? Not a single man-made object is circling the Earth? Instead, armies of technicians are striving night and day to maintain the fiction that there are satellites in space: 1) every night flying dozens of planes on courses which appear to be satellites from the ground, at local dusk (I've seen many satellites per evening whenever I was out of doors shortly after sunset). 2) flying thousands or millions of helicopters over every point on the globe where somebody might conceivably turn on a GPS system so as to provide the data the unit requires in the absence of GPS satellites (this means that Radio Shack and Walmart have to be in on the big conspiracy, since a GPS unit couldn't operate as described even with helicopters pretending to be satellites, it would have to be designed with the knowledge that there really are no GPS satellites). 3) Keeping a big coil, about 70000 km in length, either of copper wire or fibre optic, used to introduce the barely perceptible time delays you hear on international calls, and then routing all of those phone calls through this delay line, often twice in each direction. 4) Putting cellular phone relays in all those GPS helicopters. 5) Hiring graphic design artists to make up convincing weather maps for all of the local television stations. 6) Maintaining a secret shuttle base out in the Atlantic somewhere so that when the space shuttle pretends to go on a fifteen day mission it can actually land at this base, the astronauts sipping tropical drinks between their sessions in the ANTI-GRAVITY CHAMBER for the telvision cameras. 7) Paying for the legion of Canadian helicopters which fly over the Earth making RADAR maps for sale to commercial ventures and other countries, so that we can pretend that RADARSAT is actually up there in a polar orbit looking at ice pack flow patterns and other terrain features. 8) Generating all of the fake scientific data which the poor folks at JPL, STScI, ISTS, etc. then analyze, never knowing that they're analyzing something which somebody else made up. 9) Retirement pay for the people who flew the planes which pretended to be Sputnik, all around the world, several times (it couldn't be one plane, no plane in the world can circle the globe in ninety minutes, it would have to be a huge number of planes flying short stretches, close enough together that the lack of continuity wasn't noticed). 10) An agreement with Iraq during the Gulf War that they report to the American government the precise position of every missile launcher each time one is launched. 11) Hush money paid to every American, Canadian, Chinese, Iranian, Briton, Russian, Italian, etc. who owns a television satellite dish, so that they don't reveal that the object actually is nothing more than a giant, expensive, ugly ornamental planter, with an extension cord. Note that the helicopter theory doesn't work here, everybody in a city points their dishes in exactly the same direction, and the parallax difference would be obvious for anything as close as a helicopter. Have you ever seen one of these helicopters, festooned with relay antennas, flying over a major metropolitain area, non-stop, night and day? Get a pair of binoculars, visit a friend with a satellite dish, and stand in front of the dish, then point your binoculars along the axis of the dish. Let us know how many helicopters you see hovering in the field of view of the binoculars, and then go back a few days in a row to see if they are still there. I've never seen them, though I don't use binoculars, I have better than average uncorrected vision. and so on. Note here that I'm only pointing out the things which you could fairly easily verify for yourself, with phone calls and no special equipment, or by talking to people older, and possibly wiser, than you. If you had access to the right electronics you could settle the matter quite quickly with active or passive searching. Really, with the millions of helicopters you'd have us believing are hovering out over our cities, countrysides, and open oceans every minute of the day, it's a wonder we can hear ourselves think! How do the air traffic controllers keep all those fake satellite airplanes from colliding with the myriad fake satellite helicopters? A few years ago it was in the newspapers that the Russian Mir was flying over Canada at dusk in Eastern Canada for several nights. A lot of people went outside and watched it. It crossed the country West to East in about a quarter hour. No airplane could do that, your web page claims that no airplane can possibly fly faster than 2860 km/h (East to West, you claim that the limit is lower but unspecified for the West to East case), and that would not be anywhere near quickly enough to cross the country. People standing out of doors saw the light cross the sky in about two minutes, and maintained view of it while it passed over the fairly heavily populated corridor from Toronto to Montreal. There was no time when there weren't many people looking at it. So, how did a plane, or bunch of planes, simulate flying some 25000 km/h or faster? It was seen simultaneously over Toronto, Ottawa and Montreal, cities 600 km apart. Here's a test for you. Get a couple of friends in cities roughly north or south of you (I find most of the satellites I see are polar orbiters). Make the distance between cities about 50 kilometres. All three of you go outside and look up just when the sky has become black. Make a conference phone call so everyone can talk to everyone else. When one of you sees a bright white spot moving fairly quickly across the sky, maybe flickering, but maybe not, say so on the phone, so everybody else can look for it. Have everybody mark on a sky map the position of the spot. It doesn't have to be very precise, just get an idea of where it is. Wait about thirty seconds, and then mark the position which it has moved to. Do this for a few satellites, before it gets too late and they pass into the shadow of the Earth. Now do some geometry. Calculate, roughly, how far away the objects are that you saw, given the positions of the observers, the perceived position of the object against the background stars, and the assumption that the stars are so very far away that there is no parallax associated with your different locations. If you do the math correctly you should get an answer of between 100 km and 500 km elevation, and I expect you'll have uncertainties of at least twenty kilometres on those numbers. Now, calculate how quickly the helicopter or airplane is moving which all three of you saw. It must have been one helicopter, if it were several different ones then *they* would have to have known exactly where the three of you were, and when you were planning this experiment. And, if you'd added a fourth person at another city without telling *them*, then the whole scheme would have been blown, you would have discovered *their* big secret!!!! If you do this, you should be able to satisfy yourself that you saw something traveling in Earth orbit. The fact that ancient astronomers didn't report hundreds of small moons flying by suggests that this is a recent addition to the sky. I suppose that leaves surveillance devices left by space aliens, but I find the idea that they are surveillance devices left by humans to be less unlikely. In your website you say that you will give your life to anybody who can contradict the speed limit you claim, with a scientific publication. I would suggest that an experiment you can perform yourself with a few trusted friends holds even more value than a publication, since we've already shown that so many people are involved in this conspiracy with the helicopters that involving the editors of PhysRevA is not a big deal. I do not think that I would like your life, though. I've got a perfectly fine one, which I strongly suspect I find much more satisfying than I would find yours. >But most posters did NOT DARE to use their OWN UNDERSTANDING... >and simple said that the moon landing was real, although some of them >admitted that many photo's were and TV-images were faked... > >Do you dare to VISIT the mentioned SITES... > Yes. I dare. Visited. Was impressed by the NASA site (that they plan to make space suits as strong as a good bulletproof vest). Your site seems to say that photons are lighter than a quarter-inch disk of metal (which for some reason you determine must have weighed 0.01 grams even through there is no mention of the weight in the cited Sandia news release, and that seems a bit on the low side). Photons go faster than the fastest human-projected object of this weight. You then find a series of projectiles and "maximum" speeds, and show a decreasing trend. Then, since the space shuttle is heavier than the heaviest such object, you conclude that it must be true that its maximum speed is lower than the speed of the heaviest object. Following your links (strip out those single-quotes, they're confusing Mosaic), I see no claims by any of the cites that the speeds they mention are maximum speeds. They're just speeds of certain objects, in certain situations of interest to the experimenters for reasons other than their speeds, but they never say "nobody has ever made something this big go this quickly before". Only the Sandia press release says that, and their statement does not contradict the position that the space shuttle moves at a lower speed consistent with being in low earth orbit. So, you've got some speeds, not maximum attained speeds, just some numbers which you picked because you felt they would support your position. You obviously have gone to great trouble to locate only those numbers which would support your position, even if in order to support your position you had to prepend the adjectival phrase "maximum ever achieved by humans" to the speeds involved. It must have been difficult, sorting through all of the speeds of objects over history and picking out only those ones which you liked. Be glad you're not working in a field of physics which requires thousands or millions of measurements in order to provide statistically valuable results, it would take you years to pick and choose the measurements you wanted from such a flood of data. The heaviest thing I have ever made move quickly was an automobile, weighing about 1.5 tonnes, at about 140 km/h. Following your reasoning, were I to get behind the wheel of a jumbo jet I would be incapable of flying it faster than that, as this object is heavier than the heaviest thing I've ever caused to move at that speed. The trend is there, I've made electrons move at close to the speed of light by rubbing my feet on the carpet and putting my finger near a doorknob. I've projected air and saliva at supersonic speeds during a sneeze. I've dropped rocks off of cliffs which reached speeds of more than 140 km/h before stopping. You say that it's easier to accelerate a 100 g bullet than a 100 kg cannonball. That's certainly true. And if you put a SSME (space shuttle main engine) and fuel tank on each of them, they'd both wind up going pretty quickly. Probably the same speed, more or less, because of the vastly larger mass of the fuel tank. Now, tell me, which goes faster, a 100 g bullet which Mark Peeters throws from his clenched fist, or a cannonball fired from a real cannon? You seem to feel that whatever technique is used to propel an object, there is some universal scaling law which prevents heavier objects from going more quickly than lighter objects. For each of the situations you mention, it is probably true that replacing the projectile with a lighter one will at least not reduce the speed, though it may for technical reasons not increase the speed. Now, in order for your argument to be valid you would have to compare the final speeds of the following objects: - A photon strapped to three SSMEs, two rocket boosters, and a fuel tank. - An electron strapped ... - A proton strapped ... - A metal disk strapped ... - A two gram weight strapped ... - Ten and seventeen gram weights strapped separately to ... - A one kilogram weight strapped ... - A space shuttle strapped ... In this case, you would find that the space shuttle is the slowest of the bunch. You'd also find that you had shot an electron, a proton, a metal disk, four weights, and 27 Rocketdyne engines into interplanetary space, and put a space shuttle into orbit. The photon, unfortunately, broke loose from your apparatus immediately. >It took me 20 years before I dare to compare 24000km/hr with 28000km/hr.. > The hypervelocity experiments have not been going on for twenty years, but I assume that this was hyperbole. >Do you think that you have MORE COURAGE? > Yep. Took me just a few minutes after reading your message to read the sites, and compare the numbers. I find one number to be somewhat smaller than the other, and neither number is particularly exciting, given that there is no claim that 24000 km/h is the highest achieved speed by a man-made object. If it took me three minutes to do this, and took you twenty years, then I guess I have about three and a half million times your courage (I'll assume a linear response function). For crying out loud, the Netherlands is a member of the ESA (as is Canada), surely you have some exposure to these things out there? ESA ESTEC is centred in your country. You can reach them at +3171 565.6565. The centre is about twenty-five kilometres up the coast >from The Hague. I have heard people claim that the moon landings never happened, but you're the first person I've ever heard claim that there has never been an object sent into space. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Fri Mar 14 23:30:34 EST 1997 Article: 256479 of sci.skeptic Xref: info.physics.utoronto.ca alt.astrology:121303 alt.out-of-body:18365 alt.paranet.paranormal:15950 alt.paranormal:58165 sci.skeptic:256479 Newsgroups: sci.skeptic,alt.paranormal,alt.out-of-body,alt.paranet.paranormal,alt.astrology Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Curley Predictions Stock Market Crash - Exactly to the Day Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Fri, 14 Mar 1997 22:45:09 GMT References: <3328099A.39CF@globalserve.net> In article <3328099A.39CF@globalserve.net>, Earl Curley wrote: >First of all will someone please explain to William Barwell and the rest >the fools in sci.skeptic that the Ides of March is March the 12th. >Thanks. > According to Webster's dictionary, the ides of March is the 15th. Also, the 15th of May, July, and October. The ides of other months are on the thirteenth. So, the ides of March is tomorrow. There is no trading on Saturday. >In November, "The I.R.I.S. Chronicles" ( >http://www.webdesign.ca/iris2.html ) predicted with the following >header: > > "BEWARE THE IDES OF MARCH" > >that stipulated that stock market investors were going to see the Dow >Jones Industrial Average stock market begin and continue to plummet >between 800 and 1000 points within a two week period. > >The prediction was exactly dead on. On Monday and Tuesday (March 10-11) >the Dow Jones reached into record high levels and on Wednesday, March >12th (the Ides of March) the market began it's downward plunge with a 49 >point drop and as of this afternoon (1:59 PM) the market has dropped >over 119 points. > As of 4PM Eastern Time on Friday, March 14, the American stock market has rebounded, the DJIA making back more than a third of what it lost on Thursday, and everybody anticipating a continued climb next week. DJIA up 56.57 points to 6935.46 NYSE composite up 1.83 to 417.70 NASDAQ composite down 0.31 to 1292.97 (that's no change, really) AMEX Market Value up 2.45 to 600.47 Advances lead declines on the NYSE by more than two to one. Basically, the US government's Labor Department did not report serious inflation, calming investor's fears of higher interest rates. Computer trading was not stopped. >I'm really enjoying this. > As are we all. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Sat Mar 15 00:16:00 EST 1997 Article: 44661 of rec.arts.sf.science Xref: info.physics.utoronto.ca alt.folklore.science:39267 rec.arts.sf.science:44661 rec.arts.sf.tv:100148 sci.astro:156797 sci.physics:235413 Newsgroups: rec.arts.sf.science,sci.astro,sci.physics,alt.folklore.science,rec.arts.sf.tv Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Common Sense and Science (was Re: TV Asteroid Science) Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Fri, 14 Mar 1997 22:21:36 GMT References: <5e8nuu$424@access5.digex.net> <5g5gbt$54b@nnrp1.news.primenet.com> <5g8qst$q00@hbu005.ha.uk.sbphrd.com> <5g9bh5$40c@nnrp1.news.primenet.com> In article <5g9bh5$40c@nnrp1.news.primenet.com>, Brian Trosko wrote: >Triple Quadrophenic wrote: >: Of course, he can't travel at c and can't have infinite acceleration. However, >: he can get as close to either as he likes. This means that he can change >: parameters so that a trip of 4 ly takes 730 days (of his time). This means >: that his speed has been 2c. > >: Clearly, he can go just as subjectively fast as he wants to go > >Not that way. To *him*, *his* clocks are running normally. If he travels >for four years, it takes four years of his time. When he reaches >relativistic speeds, it's the rest of the universe* that he sees as having >the slow-running clocks. > >That's why it's called relativity. In his frame, he's at rest, and the >rest of the universe* is moving with respect to him. If he sets out for >a point 4ly away, it will always take more than 4 years *by his own clock* >to get there. > No, Mr. Quadrophenic is correct. A person can accelerate up to relativistic speeds and experience less subjective time to cover a journey than light would take on the same journey as measured in the initial rest frame. If I can accelerate up to 0.9 c very quickly, I can make it to Alpha Centauri in less subjective time than four years. A few months ago I posted some equations of the subjective time to reach distances for a given constant subjective acceleration. At one g, a four light year trip, starting and ending at rest (relative to the frame in which the four light year distance is measured) takes 3.46 years. If you keep accelerating through, rather than turning around and decelerating at the half-way mark, then it takes 2.25 years. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Mon Mar 17 11:38:45 EST 1997 Article: 257944 of sci.skeptic Xref: info.physics.utoronto.ca alt.astrology:121740 alt.out-of-body:18679 alt.paranet.paranormal:16502 alt.paranormal:59077 sci.skeptic:257944 Newsgroups: sci.skeptic,alt.paranormal,alt.out-of-body,alt.paranet.paranormal,alt.astrology Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Curley Predictions Stock Market Crash - Exactly to the Day Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Mon, 17 Mar 1997 15:44:44 GMT References: <3328099A.39CF@globalserve.net> <332B3466.60AA@globalserve.net> In article <332B3466.60AA@globalserve.net>, Earl Curley wrote: >Christopher Neufeld wrote: > >> As of 4PM Eastern Time on Friday, March 14, the American stock market >> has rebounded, the DJIA making back more than a third of what it lost on >> Thursday, and everybody anticipating a continued climb next week. >> >> DJIA up 56.57 points to 6935.46 >> NYSE composite up 1.83 to 417.70 >> NASDAQ composite down 0.31 to 1292.97 (that's no change, really) >> AMEX Market Value up 2.45 to 600.47 >> Advances lead declines on the NYSE by more than two to one. >> >> Basically, the US government's Labor Department did not report serious >> inflation, calming investor's fears of higher interest rates. >> Computer trading was not stopped. > >One would have expected a Canadian to have more sense but I guess the >skeptic rash is catchy. The callors where activiated 20 minutes into >trading on Thursday as was reported in the CNN report located at >http://www.webdesign.ca/stockproofs97.html > I couldn't find this document in your web server, so I went to the CNN source and did an explicit search. I find I must apologize to EGC, as there was, according to CNN, a stop to electronic trading on Friday shortly after the opening bell. This was because the stocks were ***rising*** too quickly. Quoting a tiny part, "...the Dow Jones industrial average burst out of the gate Friday, setting off curbs on electronic trading less than one hour into the session. By noon, the average was up 58.50 points...". I hadn't realized that the electronic limits applied to gains as well as losses. As this happened before I posted the article, I should have noticed it. As of right now, the stock markets are bouncing around in a fairly tame fashion. BTW, it's "collars". I only mention this because I'm not aware of the terminology used in the financial industry, and I actually tried to look up "callors" in the search of the site. Silly me. So, are we to consider your prediction in two parts? "Stocks will fall" and "electronic trading will be suspended every day"? If so, do you claim a 50% hit if the stocks rise so much in the next two weeks that electronic trading is cut off regularly? Anyway, I am one of those people willing to give you the benefit of the doubt. You claim that March 12 is the day the stock market begins its slide, that's quite clear from your articles. So, at the beginning of trading on March 12 the Dow Jones industrial average stood at 7039.37. I will consider your prediction accurate if it is at or below 6239.37 on the 26th of March. Is that fair? Or would you rather I allowed a hit if it ever falls below 6239.37 during that interval? Anyway, it will probably all hinge on the meeting of the U.S. Federal Reserve next week, eh? So, if the stocks go down that much, perhaps we should ask you for more investment advice. What do you think about SmithKline Beecham, makers of chlorpromazine? -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Tue Mar 18 14:35:49 EST 1997 Article: 44918 of rec.arts.sf.science Xref: info.physics.utoronto.ca alt.folklore.science:39426 alt.tv.star-trek.ds9:40507 rec.arts.sf.science:44918 rec.arts.sf.tv:100493 Newsgroups: alt.folklore.science,alt.startrek,alt.tv.star-trek.ds9,rec.arts.sf.science,rec.arts.sf.tv Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Superconductors and zero resistance (was Re: Nanotechnology, Genetic Engineering, ...) Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Tue, 18 Mar 1997 15:57:14 GMT References: <01bc2bd0$4decfca0$154797c2@hoopje-pc.iaehv.iaehv.nl> <01bc30d6$583f2880$cd4e97c2@BZTcomputer.iaehv.iaehv.nl> <5gee1i$1ku@news.jhu.edu> <01bc32db$d1b5a3e0$094797c2@BZTcomputer.iaehv.iaehv.nl> In article <01bc32db$d1b5a3e0$094797c2@BZTcomputer.iaehv.iaehv.nl>, Ben Z.Tels wrote: >Yes, MATHEMATICALLY zero. But that doesn't mean absolutely zero, especially >in a science that can prove that 0.9999999999999999.... etc equals 1. > The resistance of a superconducting loop is absolutely zero. When you have a closed loop of superconductor the boundary conditions on the superconducting wave function require that the total magnetic flux threading the loop be an integer multiple of a discrete quantum. We talk of a certain number flux quanta threading the loop. You can no more have half of a flux quantum than you can have half of an electron in the loop. Any resistance in the superconducting loop requires that the flux decrease by an integer number of these steps. It is possible, then, to perform an experiment which counts the number of flux quanta passing through the loop. An object known as a superconducting quantum interference device (SQUID) can see individual flux quanta entering or leaving the measurement surface. In all experiments of this nature on classic superconductors there is no resistance noticed, and if there were, it would be more in the nature of a "resistive event" rather than a quantity which could be used in the usual terminology of continuous currents, continuous dissipated powers, and so on. Consider a type II superconducting loop of classic materials (HTSC are a bit more complicated for reasons I won't go into here), one millimetre thick, in its normal operating regime (liquid helium temperature, operating in the type II regime of its phase diagram). Statistical fluctuations due to thermal noise could cause the coil to lose a single quantum of flux. In order for that to happen, the fluctuations would have to drive a section of the superconductor normal for at least the length of the superconducting coherence length. Based on statistical arguments, the mean time between such resistive events is, very roughly, 10^(10^10) years. That means that over time scales which dwarf the lifetime of the universe, mathematically, absolutely zero energy is lost by the current in the superconductor. If that's not zero resistance, then what is? -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed Mar 19 10:52:28 EST 1997 Article: 45003 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:45003 rec.arts.sf.written:226547 Newsgroups: rec.arts.sf.written,rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: AI loose on the Internet? Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 19 Mar 1997 14:16:53 GMT References: <5fnsod$mg0@clark.zippo.com> <332EBDCB.9B6B166@alcyone.com> In article , Remus Shepherd wrote: >Erik Max Francis wrote: >> Mark V. Shaney is a Markov chain generator, which outputs words based on >> the probability of finding them together in an input document. > > To give you an example, I piped the above text Erik wrote into the >Perl 'travesty' program, which is, I believe, a Markov chain generator. >(Correct me if I'm wrong. <:) ) > Just a warning to people with the travesty program. I keep all of my old postings in a disk file for reference, so when I wanted an input stream for 'travesty', that was a natural place to look. 100 kB of, presumably, reasonable English. Stripping out the quoted material, and piping through travesty, produced output. Here's the warning: don't do this. There's something very disturbing about reading text which sounds **exactly** like you would sound, if you were insane. Anyone here think Robert McElwaine's writing is invariant over the travesty operator? -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed Mar 19 10:52:31 EST 1997 Article: 45004 of rec.arts.sf.science Xref: info.physics.utoronto.ca alt.folklore.science:39485 alt.tv.star-trek.ds9:40628 rec.arts.sf.science:45004 rec.arts.sf.tv:100585 Newsgroups: alt.folklore.science,alt.startrek,alt.tv.star-trek.ds9,rec.arts.sf.science,rec.arts.sf.tv Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Discovery of High-Tc superconductivity (was Re: Nanotechnology, ...) Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 19 Mar 1997 14:38:59 GMT References: <01bc2c07$9c8cd600$050392cf@default> <01bc32dc$87c59c80$094797c2@bztcomputer.iaehv.iaehv.nl> <5gldrh$7sm@news.ox.ac.uk> <332EDAEA.3F3A@flash.net> In article <332EDAEA.3F3A@flash.net>, Cam Kirmser wrote: > >As an aside, it was IBM that discovered the ceramic SC. > Well, not exactly. Your article makes it sound much more structured and planned than that. Georg Muller was an IBM research scholar. A fairly rare designation granted to people with exceptionally good research records, he basically had carte blanche to research whatever he thought was interesting, and pass the results back to IBM. He had read a report >from years earlier of unusual electrical properties of some rare-earth perovskites, and decided to make a thorough study of them. It was somewhat of a hunch, and it paid off. I believe that the group which originally noticed the strange behaviour of LaCuO was French, not Japanese. Anyway, they didn't have a superconductor in their lab, just an interesting semi-metal, as LaCuO is not superconducting with zero strontium doping. It was Bednorz & Muller's work which included doping the materials with strontium, producing superconductivity at 30 K. >The Japanese took the approach that a SC has to have certain properties, >including color, and that only results that exhibited these qualities >would be tested as a SC. By this method, Japan was able to farm out >research even to those of limited knowledge or ability in the (well >founded) hopes that they would find a SC first. On the other hand, our >labs tested EVERYTHING, a slower but more thorough method. > But there was not a concerted effort going on to find new superconductors. Before Bednorz and Muller's discovery, the field of high-Tc superconductivity was considered a bad thing to be in. The successful BCS theory put an upper theoretical limit on superconductivity of 26 kelvin (based on arguments of the stability of a structure with high deformation-induced polarization). There had been occasional "discoveries" of high temperature superconductivity in the previous years, but they had never panned out. It had been over twenty years since any significant advances in superconducting materials had been made, and those were in the low-temperature superconductors. This wasn't the sort of research you would do if you were a new professor looking for tenure, chances are you'd never get anything worth publishing. This is why, when Bednorz and Muller published, they took a very apologetic, low-key approach, and possibly why they published in "Zeitschrift fur Physik" rather than the more widely read "Physical Review B". Even given Muller's reputation as a solid researcher, the overwhelming reaction of the condensed matter physics community was that it was a mistake. Few people even considered following up on it. One Japanese graduate student who saw the paper went to his graduate supervisor and suggested that he try to reproduce the results. The supervisor read over the paper, saw the mention that it was green, and said that no superconducting material would be green, the fact of the colour suggests tightly bound electrons rather than the shininess you expect of a material with a high density of electrons (believed important for superconductivity to appear). The supervisor recommended to his student that he not waste time on this paper, but the student went ahead and did it anyway. It was his confirmation of the original Bednorz and Muller paper which made people notice it, and start to examine the ceramic superconductors. Then, it was Paul Chu's group in Texas, with the discovery of YBCO, which initiated the bedlam which was to follow. Some details may be incorrect, but this is the way I remember things. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed Mar 19 11:31:37 EST 1997 Article: 258744 of sci.skeptic Xref: info.physics.utoronto.ca sci.skeptic:258744 Newsgroups: sci.skeptic Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Curley Predictions Stock Market Crash - Exactly to the Day Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 19 Mar 1997 15:23:01 GMT References: <3328099A.39CF@globalserve.net> <332B3466.60AA@globalserve.net> <332E854D.7EC5@globalserve.net> In article <332E854D.7EC5@globalserve.net>, Earl Curley wrote: >Christopher Neufeld wrote: >> In article <332B3466.60AA@globalserve.net>, >> Earl Curley wrote: >> > >> >One would have expected a Canadian to have more sense but I guess the >> >skeptic rash is catchy. The callors where activiated 20 minutes into >> >trading on Thursday as was reported in the CNN report located at >> >http://www.webdesign.ca/stockproofs97.html >> > >> I couldn't find this document in your web server, so I went to the CNN >> source and did an explicit search. > >You didn't look hard enough because the article dated March 13, 1997, >courtesy of CNN is and always has been on that web page. > It still doesn't show up. I get "The requested URL /stockproofs97.html was not found on this server." Have you got your httpd set up not to answer requests from Mosaic, because of the lack of frames or tables support? Don't tell me to use Netscape, I avoid it whenever possible. Not just because of the nonsense of redefining HTML every time they want to, but we paid for the program to use in my office, and I got a chance to send in a bug report for 3.01 the other day. Got back a one line reply that I was using an unsupported platform, and they were not interested in hearing about my problems. Fortunately for everyone concerned, their billing department does support the credit card we used, and has little trouble charging the same rate as that for supported platforms. >>This was >> because the stocks were ***rising*** too quickly. Quoting a tiny part, >> "...the Dow Jones industrial average burst out of the gate Friday, setting >> off curbs on electronic trading less than one hour into the session. > >>By >> noon, the average was up 58.50 points...". I hadn't realized that the >> electronic limits applied to gains as well as losses. As this happened >> before I posted the article, I should have noticed it. > >Again, I'm afraid you have a problem reading the articles posted by >CNN. The market started on a downtrend and reached in the higher levels >after 1:27PM on Friday. > Well, if it started on a downtrend, it was a very short downtrend, as CNN reports that it was up 50 points in the first hour. It was up about 80 points by 11:30, then dropped over 40 before 1:30, then rose again. You seem to have picked up on the second rise. The first one was much more dramatic, and started within an hour of opening. >> As of right now, the stock markets are bouncing around in a fairly >> tame fashion. > >Tame Fashion? Do you call a high low of -81 points a tamely fashion and >then a spurt of computer buying in the last five minutes to bring the >market to a +20 point finish? I presume you don't have the resources to >invest in the markets. > Presume what you like, but just because I'm posting from a university account don't assume that I'm a poor, starving graduate student. I don't invest in stocks for the short term, only for long stretches (such as my retirement) so that I don't care what the market does over short periods, and never paid it much attention. Thirty-five years can do a lot to average out fluctuations. >> BTW, it's "collars". I only mention this because I'm not aware of the >> terminology used in the financial industry, and I actually tried to look >> up "callors" in the search of the site. Silly me. > >Learn to look for the term "stop loss" as well. > Nope, no "stop loss" in the CNN archives, but I will continue looking. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed Mar 19 16:16:49 EST 1997 Article: 45021 of rec.arts.sf.science Xref: info.physics.utoronto.ca alt.folklore.science:39503 alt.tv.star-trek.ds9:40662 rec.arts.sf.science:45021 rec.arts.sf.tv:100607 Newsgroups: alt.folklore.science,alt.startrek,alt.tv.star-trek.ds9,rec.arts.sf.science,rec.arts.sf.tv Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Nanotechnology, Genetic Engineering, and whole bunch of other really cool stuff Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 19 Mar 1997 20:51:57 GMT References: <01bc2c07$9c8cd600$050392cf@default> <332EDAEA.3F3A@flash.net> <01bc33e9$b17a2560$400492cf@default> <332F5D90.5C5@flash.net> In article <332F5D90.5C5@flash.net>, Cam Kirmser wrote: >> >> What happens when a SC is exposed to an electromagnet? > >Exposure to an electromagnet >would have no effect because a SC is not Ferric, it has no Iron content. >Now, the little experiment that schools have, spinning a small magnet >held suspended above a SC in a pool of LN, does not depend on Iron >content. > This question should be answered in three parts. What happens when a superconductor is exposed to a magnetic field while above the transition temperature, what happens below the transition temperature, and what happens when there is no applied field? A superconductor exposed to an electromagnet, or any other magnet, while in the superconducting regime will be repelled from the magnet. That's what is seen in those high school science experiments. This is a consequence of the flux exclusion of the superconductor, and the resulting energy cost of forcing magnetic field lines into a smaller volume. One of the new copper-oxide superconductors, when exposed to a magnetic field, will rotate to align the Cu-O planes with the magnetic field. This behaviour is a consequence of the anisotropy of effective electron mass, and is the property I studied to obtain my Ph.D. Other anisotropic superconductors, such as one-dimensional organic superconductors, ought also to exhibit this behaviour in the bulk. A superconductor in the normal regime exposed to a magnetic field will not do anything particularly remarkable which would mark it as a superconductor. It will have some magnetic response, though off-hand I don't know if it would exhibit diamagnetism or paramagnetism, or even if there are possibly multiple phases which would exhibit different magnetic responses. It will look like any other non-ferromagnetic material. In the absence of an applied magnetic field, can a superconductor in the normal regime produce a permanent magnetic field? In other words, can it be a ferromagnet? Until several years ago the answer was an unequivocal no. The inclusion of magnetic ions in a superconductor interferes with the quantum mechanics of superconductivity in such a way as to destroy superconductivity. Less than 1% of magnetic impurity is sufficient to suppress all such behaviour in a superconductor. This is a very general result, believed to be independent of the mechanism involved in superconductivity. Now, some superconductors have been made with, I believe, nickel on some of the sites. The last explanation I heard for this was that the nickel atoms lie exclusively in regions of the material where the superconducting wave function does not penetrate, like the barium atoms in YBCO, staying away from the superconducting sheets. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Thu Mar 20 10:40:49 EST 1997 Article: 45075 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:45075 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Stargates: Please Help! Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Thu, 20 Mar 1997 14:44:38 GMT References: <332E344E.1BBA@nbcc.nb.ca> <3330150D.19CA2B4F@alcyone.com> In article <3330150D.19CA2B4F@alcyone.com>, Erik Max Francis wrote: > >One of my favorite ideas for a fast system is a lightspeed-based stargate >system. By some undisclosed process the transiting ship is converted to a >massless correspondence particle(s) and is transferred to the receiving >gate at c; when it arrives, naturally a related but opposite undisclosed >process converts them back. > > [ ... ] > >And, there's nothing relativistically wrong with the system. > There is something classically wrong, though. The centre of mass of the combined system has been displaced. By our current understanding of physics, this can never happen. Enclose a big box around everything involved in the interaction, and the centre of mass of the box can't move (assuming you're in a frame in which it was originally at rest). This goes right back to action/reaction forces. The way you might fix this is with a "balance mass". Water, rock, whatever's cheap at your broadcast point. When you send the ship, an exactly matching mass is taken out of the bank of balance mass and projected along an opposing path. You might decide that this mass, in the absence of a receiving device to reconstitute it, comes out as gravel, atomic dust, a black hole, or whatever suits your fancy. Clearly you can't have a receiver at the end where the balance mass comes out, it would have to be _exactly_ opposite the destination relative to the starting point, and what with orbital motions, stellar proper motion, and time of light communication delays, you'd have to plan each journey years in advance, and time them very precisely. Of course, if the balance mass is coming out as a kiloton mass black hole, somebody on the opposite end from your destination would be pretty amazed. The chances of being hit are tiny, but with all of the variability involved you could easily imagine a locally compact network of senders and a distant, locally compact network of receivers resulting in a fairly random distribution of black holes around a point in space, all exploding violently about six hours after arriving. Drive the nearby astronomers nuts! -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Fri Mar 21 11:46:08 EST 1997 Article: 45137 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:45137 rec.arts.sf.written:226946 Newsgroups: rec.arts.sf.written,rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: "Mono-wire" Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Fri, 21 Mar 1997 14:44:12 GMT References: <332F546F.3F1C@swipnet.se> <33309892.5DEC@utoronto.ca.> In article <33309892.5DEC@utoronto.ca.>, Rocky Persaud wrote: > >Metals are also not single molecules. They are not molecules in >any sense. They are made of millions of crystal grains, with each >grain a crystal matrix of metallic ions. Grains form when he crystals >are misaligned. The weakest part of a metal are the grain boundaries. >If we had nanatech assemblers, we could make bulk objects out of a >single metal crystal with no grains. It would be much stronger than >contemporary metal because its atoms would be tightly packed, with no >discontinuities, and its strength should be about equal to the bond >strength of the individual ions (I expect it would be exactly equal, >actually). But because there would be no grains, this nano-assembled >metal would not be ductile. > Actually, this is not necessarily true. Bulk metal gets some of its hardness and stiffness from the dislocations in the crystal lattice. A pure crystal can be very easy to deform if sheared along one of its symmetry planes. Crystalline metal is very different from, say, diamond crystals, where the inter-atomic bonding is much stronger. One memory from my graduate school which I doubt I will forget (and which I *know* the student involved will never forget) involved an accident while spark-planing a large single crystal of pure gold for an experiment. The crystal was about sex millimetres on edge, cubic, and was shaped so that one face represented the 1-1-1 axis of the crystal, that means that if you imagine the underlying crystal structure, the bulk crystal presented a face perpendicular to a line drawn from the centre of the cube to one of the corners. Spark planing brings a polished copper electrode down over the sample in a large bath of oil, bringing it almost into contact. Pulses of high voltage are created which tend to jump between the electrode and the sample in those places where the two are closest together. Since the electrode is removed, polished to optical smoothness, and replaced at intervals during this process, the sparks tend to jump to bumps on the surface of the sample, and they obliterate a small amount of material there, smoothing it out. This allows you to get an optically smooth face on a sample which is too delicate to touch, not to mention stick in a milling machine or rub against a diamond stone. Now, on that fateful day, the electrode came down over the sample, the sparks started, then the contact alarm went off, and everything shut down. So, the student made a few adjustments to the parameters governing the motion of the electrode, started it up again, and the contact alarm went off again. After the third time he decided something was really wrong, and hit the electrode retraction switch. When it was about thirty centimetres above the sample, the electrode fell off (it had not been secured properly, and so was sliding down, which is what had set off the alarms earlier). It was like a hammer, with a delicate single crystal of gold playing the part of anvil. The sample, of course, was ruined beyond hope of recovery, so many dislocations had been introduced by the impact that the experiment would not have been able to produce useful data from it. Looking at the sample, it had an interesting surface feature, a V-shaped mark on one of the side faces of the cube at right angles to the face which had been hit. This represented the boundary between two regions, the lower fixed region, and the upper region which had _slid_ down the crystalline planes. The V-shape, a very precise right angle, revealed the underlying crystal structure, which you recall was not in the same direction as the faces of the bulk crystal. It was like a tiny avalanche of metal, quite interesting if you weren't personally involved in the experiment which used a single crystal of gold. An amorphous piece of pure gold would have deformed somewhat, but it would not have sheared like that. The monocrystalline nature significantly reduced its resistance to shear, at least in some directions. The metal was still quite ductile, in any case. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Sat Mar 22 23:02:15 EST 1997 Article: 259815 of sci.skeptic Xref: info.physics.utoronto.ca sci.skeptic:259815 Newsgroups: sci.skeptic Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Curley Predictions Stock Market Crash - Exactly to the Day Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Sun, 23 Mar 1997 00:38:11 GMT References: <3328099A.39CF@globalserve.net> <332E854D.7EC5@globalserve.net> <33326493.4406@globalserve.net> In article <33326493.4406@globalserve.net>, Earl Curley wrote: >Christopher Neufeld wrote: > >> It still doesn't show up. I get "The requested URL /stockproofs97.html >> was not found on this server." > >Chris the URL may have been typed incorrect because it should have read: >http://www.webdesign.ca/stocksproof97.html . I noticed someone >constantly trying to access "stockproofs.html" for the last three days >from your server but since your a newbie to these threads I didn't >recognize your ISP or I would have e-mailed you to advise you to change >the URL. > Umm, I don't think so. You see, when I go looking for web pages, it's not through the physics account. I get mail and read news from the university, but I'm hundreds of kilometres from there, through a telnet session. You see, I work for the government, and for security reasons the network I run is separated from the rest of the office network. This causes some problems, because the people downstream of me don't know how to turn off their firewall, and the people who own our domain don't know how to reconfigure their DNS. As a result, any time I read a web page (from machines on my network), the remote machine __cannot__ do a reverse DNS, we're unlisted (which causes some problems with FTP because some sites don't allow access without reverse DNS resolution). You'll get an IP number only in your access logs, and that IP number has no relation to anything else. Certainly not a physics.utoronto.ca address. Because of the speed of our link, and because of the firewalling problems, I cannot run Mosaic on the physics machine and see it in my office. >> Well, if it started on a downtrend, it was a very short downtrend, as >> CNN reports that it was up 50 points in the first hour. It was up about >> 80 points by 11:30, then dropped over 40 before 1:30, then rose again. >> You seem to have picked up on the second rise. The first one was much >> more dramatic, and started within an hour of opening. > >I'm afraid not. I'm not sure which CNN News broadcast you are watching >because that's wrong again. > I was looking at the news stories on http://cnnfn.com/markets, and the graphs of the DJIA. >> invest in stocks for the short term, only for long stretches (such as my >> retirement) so that I don't care what the market does over short periods, >> and never paid it much attention. Thirty-five years can do a lot to >> average out fluctuations. > >then why even comment on the prediction in the first place? If you >invest in only long term stocks than you have nothing to worry about now >don't you? > Yep, I know. As I said, I was never interested. For that matter, my retirement is mostly in Canadian stocks, obviously, so the DJIA is only of secondary interest (there's about a 70% correlation between Canadian and American stocks, but clearly the DJIA isn't the data to use when checking RRSPs). As for why I would comment, well, why not? Anyway, if you like you can keep track of the DJIA closing price at: http://caliban.physics.utoronto.ca/neufeld/djia.gif updated daily. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Mon Mar 24 10:03:51 EST 1997 Article: 45295 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:45295 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Stargates: Please Help! Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Mon, 24 Mar 1997 13:46:26 GMT References: <5gvmus$7oa@lois.zippo.com> In article <5gvmus$7oa@lois.zippo.com> Tommy the Terrorist writes: >In article Christopher Neufeld, >neufeld@caliban.physics.utoronto.ca writes: >> There is something classically wrong, though. The centre of mass of >>the combined system has been displaced. By our current understanding of >>physics, this can never happen. Enclose a big box around everything >>involved in the interaction, and the centre of mass of the box can't >>move (assuming you're in a frame in which it was originally at rest). >>This goes right back to action/reaction forces. > >"Light pressure" would compensate. In other words, by sending out the >light beam, you're emitting energy (= that same mass as you transmuted) >in a particular direction, generating a reactive force. > Perhaps I misread the original proposal, but I didn't see any mention of a light beam carrying data, just a sort of magical hyperdrive which displaces an object at light speed. So, for a while, the object isn't anywhere, and there is nothing to take its place. Yes, you could propose a recoil at the launch point, but then this object is recoiling in the absence of any obvious extant momentum packet representing the launched device. Now, if we're talking about converting the entire ship into a massless particle and sending it through normal space, then I agree, this is most easily solved by recoil at the launcher, but that wasn't how I read this. Now, while this hypothetical hyperdrive is in operation the ship's mass energy is not present in the universe, that is arguably as bad as an unbalanced momentum. >> The way you might fix this is with a "balance mass". Water, rock, >>whatever's cheap at your broadcast point. When you send the ship, an >>exactly matching mass is taken out of the bank of balance mass and >>projected along an opposing path. > >This is fried. You're demanding an absolute frame of reference at all >times. Travel at a different velocity and it *doesn't* balance out. No >"time of light communication delays" involved - you send a widget to >Sirius, and they either send the "balance mass" or not - and if your >broadcast doesn't go, that's a bit of information. > You clearly did not read what I wrote, so go back and read it again. I said that the balance mass would be sent from the **broadcast** point, not the receiver. Then you bring in velocities and absolute frames? Why? -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Thu Mar 27 11:06:55 EST 1997 Article: 45399 of rec.arts.sf.science Xref: info.physics.utoronto.ca alt.folklore.science:39895 alt.tv.star-trek.ds9:41495 rec.arts.sf.science:45399 rec.arts.sf.tv:101252 Newsgroups: alt.folklore.science,alt.startrek,alt.tv.star-trek.ds9,rec.arts.sf.science,rec.arts.sf.tv Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Superconductors and zero resistance (was Re: Nanotechnology, Genetic Engineering, ...) Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Thu, 27 Mar 1997 14:24:58 GMT References: <01bc2bd0$4decfca0$154797c2@hoopje-pc.iaehv.iaehv.nl> <01bc32db$d1b5a3e0$094797c2@BZTcomputer.iaehv.iaehv.nl> <01bc3a27$fdc960e0$74dc989e@hine.demon.co.uk> In article <01bc3a27$fdc960e0$74dc989e@hine.demon.co.uk>, Nick wrote: >Are you sure you're not talking out of your derriere? > >> The resistance of a superconducting loop is absolutely zero. When you >> have a closed loop of superconductor the boundary conditions on the >> superconducting wave function require that the total magnetic flux >> threading the loop be an integer multiple of a discrete quantum. [...] > Quite certain. If you doubt me, go to a library and look it up. It's really quite straight-forward, basic stuff. I did my Ph.D. on superconductors, and I did not have the liberty of making things up during my oral exams. If you'd like a reference, try: _Introduction to Superconductivity and High-Tc Materials_ by Michel Cyrot and Davor Pavuna. ISBN 9810201435 (9810201443 paperback), 1992 by World Scientific Publishing. You'll find it in a good technical library at QC611.92 C97. Specifically, I refer you to page 39 in my paperback copy, section 2.8, on flux quantization. Posted and emailed. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed Apr 2 12:57:52 EST 1997 Article: 45613 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:45613 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Descriptor Theory?? Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 2 Apr 1997 14:30:12 GMT References: <5hn2gm$mac@netra.montana.edu> <333FE96D.7DC0F851@alcyone.com> <5hqit7$4ft@proxy5.proxy.ozemail.net> In article <5hqit7$4ft@proxy5.proxy.ozemail.net>, Chris Lawson wrote: > >I believe that some labs have already cooled atoms to *less* than zero >Kelvin. I know it sounds absurd, but it relies on a "loophole" in >thermodynamics which actually allows matter to exist in a state of >negative temperature. > Well, depending on how rigorously you want to define temperature, some places have *heated* matter to less than zero Kelvin. It really is somewhat sloppy terminology, though, as temperature is not defined for non-equilibrium systems, such as you would have in this case. Imagine a system of non-interacting, simple atoms. Each atom has two states, a ground state and an excited state. The excited state has an energy "deltaE" higher than the ground state. According to simple thermodynamics, the fractions of atoms in the ground and excited states are: F(ground) = 1 / (1 + exp(-deltaE / k T)) F(excited) = 1 - F(ground) = exp(-deltaE / k T) / (1 + exp(-deltaE / k T)) Now, if T = 0, F(ground) = 1 and F(excited) = 0. As T approaches infinity, F(ground) = 0.5 and F(excited) = 0.5. Plug in negative temperatures, and you get F(excited) > F(ground). This is an inverted population, and corresponds, in the equations, to negative temperature. This is not a stable situation, but inverted populations can be produced, the most obvious location being inside a simple laser. Really, this situation represents a sample more than infinitely hot, it's just that that maps to negative temperatures in the equations. You get such a situation by adding energy to a hot system, not removing energy from a cold one. Personally, I don't call this negative temperature. It's not in equilibrium, so temperature is not well-defined, and if you couple it thermally to a hot system it will heat up that system, not cool it. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Mon Apr 7 10:39:40 EDT 1997 Article: 45778 of rec.arts.sf.science Xref: info.physics.utoronto.ca alt.folklore.science:40171 alt.tv.star-trek.ds9:42416 rec.arts.sf.science:45778 rec.arts.sf.tv:102114 Newsgroups: alt.folklore.science,alt.startrek,alt.tv.star-trek.ds9,rec.arts.sf.science,rec.arts.sf.tv Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Superconductors and zero resistance (was Re: Nanotechnology, Genetic Engineering, ...) Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Mon, 7 Apr 1997 13:52:52 GMT References: <5i2bq2$1dt@lois.zippo.com> In article <5i2bq2$1dt@lois.zippo.com>, Tommy the Terrorist writes: >Just out of curiousity... > >Suppose I have a tube of a high-Tc metal. Right at the middle, a plate >of a low-Tc metal has been melted into place, so that it forms a >seamless, alloyed transition with the high-Tc metal. > Not a far-fetched object, though it would probably be done with alloyed metals, or even just a small heater on the disk. High-Tc is awkward to work with. >The temperature is brought down until the high-Tc metal is >superconducting. A small circular current is induced around the tube; >since the center plate has some resistance, this should be possible. >Then the temperature is decreased until the low-Tc metal is also supposed >to superconduct ... which would displace all the magnetic flux... > >What happens? > What happens is really a function of the energetics. A superconductor is that way because it's an energetically favourable state to be in. A flux line penetrating the material is energetically costly, as it drives a small amount of the material into the normal state. Assuming that there is flux pinning in the disk, that is that the disk contains impurity sites which tend to trap the magnetic flux lines, then the system will find itself in a long-lived metastable state in which the flux quanta which were passing through the disk are still present, sitting in the impurity sites, and driving a small amount of the material normal there. For practical purposes, at low temperatures these flux lines are not going to leave there, and the system will appear stable. If there is no flux pinning, then the flux lines will migrate out of the disk, toward the walls of the cylinder, as this minimizes the sum of phase energy and magnetic energy. As the flux lines approach the cylinder walls, they will bend somewhat so as to enter the walls, and then migrate out of the cylinder by passing the kink at the disk through the cylinder wall, straightening the flux line again. Things get complicated if the cylinder material traps flux and the disk does not, or if the energy cost of supporting a flux quantum in the cylinder is higher than in the disk. In that case, you form another metastable state with flux quanta in the disk tending to form a triangular lattice, and few quanta penetrating the cylinder. Basically, the magnetic field does what you expect it to do. It can't pass through a material unless the energy available to it is sufficient, and so is likely to remain trapped inside the assembly in a metastable state. You can ask what happens if you take a very strong container, put water in it, and then cool it to -1 degrees. At constant pressure it's energetically favourable for the water to freeze, but in doing so it would have to expand, and there's no room for it to do that. So, some of the water freezes, and some remains liquid, and the pressure goes up. Same thing with the superconductor. It would like to go fully superconducting, but the magnetic field prevents that, and it's got nowhere to go (probably), so some of the material has to stay in the normal state. The water bottle is metastable, as it can get to a lower energy state by bursting the container. Similarly, the superconductor is in a metastable state now, it could lower its energy if it could get the flux lines out of it, but there's an energy barrier to get over first. >(more generally, this question is supposed to grope at this: is there >any way, through the creative use of superconductors, to do interesting >things, like move objects at a distance, or transmit information, using >single magnetic flux quanta?) > I can't see any way this could happen. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Thu Apr 10 00:04:45 EDT 1997 Article: 45859 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:45859 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: HELP! URGENT! PLEASE! Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 9 Apr 1997 20:28:20 GMT References: In article , Goggles wrote: > >Hello, I need help in explaining the following sciencefiction ideas. I >need to know if there is any truth to these elements. > >1. Tachyon (spheres?) >2. hyperspace >3. soderstrom radiation >4. luster quarks, lepton matrices > Robert J. Sawyer is a science fiction writer, so don't expect _Starplex_ to be based on anything more than what is convenient to the story. tachyons are hypothetical particles, known for being killed in field theories (as in the exercise called "tachyon killing" to reject those solutions) hyperspace is a common science fiction term with little overlap to any known facts Soderstrom radiation appears only in _Starplex_ Luster quarks, also, appear only in _Starplex_ Lepton matrices could refer to the interaction matrices used to compute numerical results on Feynman diagrams, such as branching ratios, but as such they are just a mathematical representation of a particle's properties -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Mon Apr 14 13:00:56 EDT 1997 Article: 8593 of comp.protocols.time.ntp Xref: info.physics.utoronto.ca comp.protocols.time.ntp:8593 Newsgroups: comp.protocols.time.ntp Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Possible firewall solution? Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Mon, 14 Apr 1997 16:10:33 GMT At my office (not at the university, despite my address), we have a local network which is firewalled by people who don't know how to reconfigure the access lists (that's why I read news and get email at my old account!). Since we have a lot of NFS, and some heavily-used machines which see very large clock interrupt drop rates under peak I/O loads, I've been trying to synchronize the machines using NTP. At first, I had hoped to fix the time to an NTP server in the real world, but the firewall machine won't let me do that, and there is no possibility of reconfiguring it. My next solution was to slave to one machine's clock, a machine which is known to keep fairly accurate time. I figured I could fix things up with known clock drifts, and keep everything precise, if not accurate. So, my preferred time server became 127.127.1.11. Once that was up and running properly, I started playing around a bit. I noticed that ntpdate will run simultaneously with xntpd if ntpdate is asked to use an unprivileged port. Our firewall allows unprivileged UDP traffic, and I was able to set the system clock from the remote site. So, it seems to me that I can do something like the following: 1) In a cron job, run an unprivileged port ntpdate which then sets the system clock from a public access server. 2) Set the minimum polling interval to the hardware clock to be strictly greater than the time between cron job runs. 3) Let this go for a while, and the driftfile should force everything to fit. My question: is there anything wrong with this approach which I'm not aware of? Some assumption I'm making which is invalid? I'd never heard of NTP before three days ago, I hope I'm understanding the documentation. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Mon Apr 14 15:08:35 EDT 1997 Article: 45987 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:45987 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: the length of day for a station in geosychnronous orbit Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Mon, 14 Apr 1997 19:05:40 GMT References: <5isagv$ae3@nntp.seflin.org> <3351D2CC.78D1BE2@alcyone.com> In article <3351D2CC.78D1BE2@alcyone.com>, Erik Max Francis wrote: >Greg Muir wrote: > >> What would be the length of day for a station in geosynchronous orbit? >> I'm assuming it would be much longer given the smaller diameter of the >> umbra's cone at that point. My problem is I'm not sure how to determine >> how much. > >I'm not sure offhand. This is not a trivial calculation, as the Earth's >equatorial plane is inclined to the Earth's orbital plane, at least a >little, as I recall. > It is a great annoyance to the people who design geostationary satellites that there is any "night" at all, since there is so little of it. Basically, in Spring and Autumn there will be a stretch of time when satellites will go into eclipse for an hour each day. The rest of the time the satellite is in sunlight. Nonetheless, heavy storage batteries have to be included in the design for these short blackout periods. Unless my math is off, this occurs for three weeks before, and three weeks after, each equinox, with a maximum eclipse time of one and a quarter hours. The awkwardness of carrying heavy batteries around has led to at least one proposal to run the SPS concept in reverse, beaming power to satellites in Spring and Autumn when they pass into eclipse. This would probably be achieved with lasers, rather than microwaves, just because the solar panels are already in place to receive that energy, and will be pointing right at the Earth (actually, at the Sun, but it's the same thing, obviously). BTW, the umbra is not significantly reduced at GEO altitude. The Earth's disk is 12750 kilometres in diameter. The umbra's disk is 12400 kilometres in diameter, and the penumbra's disk is 13120 kilometres. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed Apr 16 09:13:41 EDT 1997 Article: 266553 of sci.skeptic Xref: info.physics.utoronto.ca alt.alien.visitors:204120 alt.paranet.ufo:108035 sci.skeptic:266553 Newsgroups: alt.alien.research,alt.alien.visitors,alt.paranet.ufo,sci.skeptic Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Scientists Make Frog Float in Mid-Air Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 16 Apr 1997 03:49:59 GMT References: <5iohhu$54f@sun.sirius.com> <01bc4935$f4b61800$b1e32499@pentium-best> <33537D58.46E4@concentric.net> <335399f7.13034702@nntp.ix.netcom.com> In article <335399f7.13034702@nntp.ix.netcom.com>, Badwater Bill wrote: > >Let's get the scientific paper on it >and see what the mechanism is, if in fact they even floated the frogat >all. In my experience, a magnetic field polarizes molecules in the >direction of the field. Every capacitor on Earth that uses organic >matterial between the plates works that way so why would the frog be >different? > These are surprising statements from a nuclear physicist. Your experience of magnetic fields apparently does not include diamagnetic materials. These are materials which, like superconductors, respond to a magnetic field with an opposing magnetic polarization, acting to lower the magnetic field within the bulk of the material. If you can get your hands on the 1989-1990 CRC Handbook, and look on pages E-134 through E-139, you will see a list of organic compounds which react in exactly this way to an applied magnetic field. The category heading is "Diamagnetic Susceptibilities of Organic Compounds", in case you can't find that particular edition of the book. I'll list the first five entries in the list, just so you can get a rough idea of the lexicographic density of such compounds in the CRC: acenaphthanthracene, acenaphthene, acetal, acetaldehyde, acetamide. The materials you are thinking of are paramagnetic or ferromagnetic, and are actually in the minority among organic compounds. Even water is repelled by a magnetic field. One thing which I haven't seen mentioned in the coverage, though, is that it is not strictly the magnetic field intensity which is important, but rather the product of the field and the field gradient, in exerting a force on the levitated object. A uniform magnetic field cannot push a diamagnetic object in any direction, though it can spin things around if they have a non-spherical shape or are anisotropic. As for your capacitor comment, you should be aware that it is not magnetic energy which is stored in a capacitor, but rather electrostatic energy. There is no significant magnetic field inside a capacitor, where would you expect the source terms to come from? A magnetic field is produced by currents, including those contained in the orbitals of ferromagnetic materials, or by time-varying electric scalar potential fields. A capacitor can be charged up, unplugged, and put on a shelf for a year. Nothing inside is changing, there certainly isn't a persistent current running inside the capacitor, and most capacitors do not contain significant amounts of ferromagnetic material (put a magnet near the capacitor to test this) so the capacitor can't be storing energy in the magnetic field. It is inductors which store energy in magnetic fields, not capacitors. > Strong magnetic fields line up the poles of molecules with magnetic >moments in the direction of the field, they don't line up backward and >repel the external field (I'm being redundant). > The effect is not to align molecules with magnetic moments. Those molecules are ferromagnetic, and they are rare indeed inside organic matter (don't forget that the iron in hemoglobin is oxidized, and so does not have a magnetic moment). It is inducing magnetic behaviour in materials which do not have intrinsic magnetic moments. What it comes down to is the following. Consider a material immersed in a magnetic field. If it is paramagnetic then the magnetic response within the material acts to increase the field within the material, and reduce it without. If it is diamagnetic, then the magnetic response within the material acts to decrease the field within the material, and increase it without. Whichever of the two responses results in a lower total energy of the system is the one which will be observed. For most materials, there is a higher energy cost associated with magnetic fields within the material than in the free space around it, and so the material behaves diamagnetically, and so would tend to be levitated by a strong magnetic field which reduces in intensity as you go in the upward direction. I'm leaving the newsgroups line intact, as I don't know where you're reading this thread, but followups might want to consider the relevance of the thread to some groups. Note that I probably won't see them unless they're in sci.skeptic. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Thu Apr 17 10:44:20 EDT 1997 Article: 267006 of sci.skeptic Xref: info.physics.utoronto.ca alt.alien.visitors:204386 alt.paranet.ufo:108133 sci.skeptic:267006 Newsgroups: alt.alien.research,alt.alien.visitors,alt.paranet.ufo,sci.skeptic Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Scientists Make Frog Float in Mid-Air Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Thu, 17 Apr 1997 14:26:18 GMT References: <5iohhu$54f@sun.sirius.com> <5j0nob$8e2@usenet.rpi.edu> <92on2qztwhn.fsf@swallow.eecs.umich.edu> <3354ea6d.487665@news.pacific.net.sg> In article <3354ea6d.487665@news.pacific.net.sg>, Mr. Soon Chen Peng wrote: > >From wht I can recollect is the theory of nmr.... The magnetic field >is to split the individual subatomic level due to the accquired >angular momentum each electron has in orbit...in doing so, by >carefully projectiion of energy phtons to "excited" the electron to >higher energy state.... > Not really. What you're describing is a form of atomic energy level splitting due to an applied field. I believe this one is called Zeeman splitting. NMR involves the magnetic interaction of atomic nuclei, not electrons (though most NMR relies on interactions between nuclei and surrounding electrons in order to work). For instance, in a continuous-wave NMR magnetometer, the nuclei of copper have a resonance at a frequency in the range of several megahertz per tesla of applied magnetic field. If you put a sample of copper powder within a coil suspended in a magnetic field, and then scan in frequency, you find that at one particular frequency there is a sudden increase in the measured resistance of the coil. This is due to an inductive coupling of the nuclei with the coil. The nuclei disperse their energy by interacting with the electrons in the sample, so the net effect is a transfer of energy from the coil to the copper sample within it, which manifests itself as an increase in the resistance of the coil. A properly configured system can detect this small change, and so determine when the frequency has reached that of the resonance of the nuclei within. Knowing the resonance frequency of copper nuclei, it is easily possible to measure the magnetic field to about five digits of precision this way. Pulsed NMR is a bit trickier conceptually. There are a few different variants, depending on what you're trying to measure. If a small DC magnetic field is applied in one direction, and then an alternating magnetic field applied at right angles to it, it can be shown that, in an appropriate rotating reference frame, the nuclei which were formerly aligned with the DC field are rotated down into the plane perpendicular to that field. One can now remove the transverse alternating field, and measure the time it takes for the nuclear spins to re-align themselves with the applied DC field. This relaxation time is generally denoted T1. Because of irregularities in the magnetic fields within an object due to the internal environment, the spins which have been rotated into the perpendicular plane also precess about the applied field at slightly different rates, and so can dephase. The characteristic dephasing time is denoted T2, and can be measured by allowing the system to dephase for a certain fixed time and then applying a second precession pulse to bring the nuclei back to the aligned configuration. How many nuclei are re-aligned is a function of how severely dephased they are. >As for the microwave oven on water molecule... >mainly they absorb to move an atom to its next higher vibrational >state.... > Not really. The vibrational states of water are very far apart, microwaves are not energetic enough to influence them significantly. Contrary to popular belief, microwaves are not tuned to any significant resonances in the water molecule, or in any other molecule. The frequency of microwave ovens was chosen for regulatory reasons, and for reaons of convenience. The frequency band in which microwave ovens work was reserved for scientific and industrial use, and this counted. Moving the frequency 30 or 40 percent one way or the other wouldn't make a very big difference to how a microwave oven works. Lower frequencies would tend to penetrate further, but be less efficiently absorbed, requiring higher power densities within the cavity. Higher frequencies would tend to penetrate less well, and run the risk of drying or charring the surface by depositing all the energy in too small a volume. Large scale microwave ovens for cooking large blocks of food in fact operate at a much lower frequency. Conductors will heat up when exposed to microwaves, as charge carriers move around and then dissipate energy as heat. Dielectrics heat up for a similar reason, involving charge motion on the molecular scale. This is all that's happening inside a microwave oven. It is quite possible to warm up objects in a microwave even if they have no water content, as long as they have suitable dielectric losses at 2.45 GHz. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Thu Apr 24 13:24:06 EDT 1997 Article: 267459 of sci.skeptic Xref: info.physics.utoronto.ca alt.folklore.urban:346410 sci.skeptic:267459 Newsgroups: alt.folklore.urban,sci.skeptic Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: "Cyber"stalker and Toronto family? Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Thu, 24 Apr 1997 15:44:26 GMT References: <5ivj53$fue@fridge-nf0.shore.net> <33558fa5.0@lagoon.idirect.com> <5jh17d$nat$1@nnrp01.primenet.com> >In article <33558fa5.0@lagoon.idirect.com>, >Daniel L. Dreibelbis wrote: >> >>On 15 Apr 1997 09:52:35, Keith D. Tyler wrote: >>>A news brief came through the AP today (cutely headined with 'Cyperpunk >>>[sic] terrorizes Canadian family') regarding the story of an Windsor, >>>Ontario family[1] that is supposedly being terrorized by a >>>"Cyber-stalker"[2]. >>> >>>AP attributed the original to the Toronto Sun, and the original is >>>available in the Tech Talk section of the paper (or at >>>http://www.canoe.ca/CyberTech/apr09_hell.html). >>> >>>Fine and dandy, but its the annoying little details of the story that get >>>me. According to the story, the prankster is: >>>* Tapping into their phone lines >>>* Turning off their power, including turning lights on and off >>>* Changing the channel on their cable box >>> >>>Ignoring the fact that nothing Internet-related is mentioned or inferred >>>by the story, the things being done just seem dubious. >>>Perhaps I dont fully understand the Canadian or Ontario cable and electric >>>systems, but these things happening dont seem very likely. >>> >> Precisely. I've been following the story myself, and a few bells >>have been going off. It seems much of what the "cyberstalker" has been >>doing is very reminiscent of things claimed by those who swear they >>live in haunted houses - and have usually been proven to be perpetrated >>by a member of the family, usually a troubled teenager. I'm quite >>surprised that James Randi, CSICOP, or Toronto's own skeptic Henry >>Gordon haven't commented on this >>>According to the Sun, the power company has no idea how this guy is >>>turning off their power. >>> >>>Conveniently, the stalker called the mother while the Sun was in the house >>>to interview her. >>> >> apparently the family has announced they're moving out of the >>house. Should be interesting to see if the cyberstalker follows them - >>but then that would bring up the obvious. >> Despite the subject line, the incidents occured in Windsor, as quoted in the text above. It was, in the end, all a prank, by the 15 year old son. A professional electronic detection team entered the house, swepth it thoroughly, checked out the wiring, and declared the house clean, save for a microphone they found which turned out to have been left there earlier by a news crew. They reported this to the police, and reported their conviction that there was nothing high-tech going on here, and that perhaps they should have another talk with the young lad in the family, and he confessed. He was switching on and off the power by the simple expendient of manipulating the switches designed for that purpose, and breaking into phone calls by picking up the extension. Canadian cable carries the "Discovery Channel" which includes the show @discovery.ca, an excellent daily one hour science news show. They helped to sponsor the security services firm which performed the sweep of the house. The story can be found on the web, until it gets removed, the current URL is http://www.exn.net/news/0.cfm?ThisStory=19970421-02 -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Mon Apr 28 23:39:50 EDT 1997 Article: 118645 of comp.sys.apple2 Xref: info.physics.utoronto.ca comp.sys.apple2:118645 Newsgroups: comp.sys.apple2 Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: GS/OS and disabled drivers Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Mon, 28 Apr 1997 15:06:13 GMT I'm afraid I'm a bit rusty in the details of my computer's OS now. Years ago I had tuned the OS to where I liked it, and since then I've left it entirely alone. Now I'm not sure what I did, and how to undo it. I didn't want the GNO/ME shell to rattle the 5"1/4 disk drive every time I issued a "df" command, so I disabled the AppleDisk5.25 driver in System/Drivers, since I had little use for the drive in native mode. Now I find I want to do a bit of writing to a 5"1/4 disk under GS/OS, and I can't seem to get the driver enabled. I go into the folder, mark the icon, select Icon Info, click in the box to re-enable the driver, shutdown and power cycle, but the machine still comes up without the 5"1/4 driver installed. I thought that perhaps I had reached some sort of internal limit, with ten devices defined (printers, null device, etc.), so I disabled the System/Drivers/Ram5 driver, but the system still came up without a 5"1/4 disk, and with a RAM disk. This also happens when I shift-boot, so I don't think I installed some Init somewhere once which overrides the status of the driver enabled bit. I'm confused now. How do I re-enable the 5"1/4 driver, and while on the subject, how might I disabled the RAM disk under GS/OS if I ever wanted to do it (aside from setting the size to zero in the control panel)? System: 6.0.1 with HardPressed (no Drivers are compressed), booting into ProSel and executing the Finder from there. Various small inits and DAs from GS+ magazine and other sources. I have two 88 MB cartridges for my hard drive, and this happens with both of them, even though the second one has been much less customized than my primary cartridge. I'll ask that any replies be Cc-ed to my email, we've been having real news problems here with some flaky network cards, and I see only about a tenth of the posted articles in the newsgroups. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Mon Apr 28 23:43:17 EDT 1997 Article: 231774 of rec.arts.sf.written Xref: info.physics.utoronto.ca rec.arts.sf.written:231774 Newsgroups: rec.arts.sf.written Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: constant-thrust ships Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Mon, 28 Apr 1997 17:49:48 GMT References: <33616427.395D@neosoft.com> In article <33616427.395D@neosoft.com>, Jimi Freidenker wrote: > > Suppose you have a spacecraft that travels at a constant acceleration, >say one g so that the passengers can travel in comfort. Stipulating that >this is possible, how would I calculate travel time given interstellar >distance? Of course, such a ship would accelerate to the halfway point, >and then reverse thrust to decelerate at the same rate. It would quickly >reach "relativistic" speeds, but I don't think the Lorenz transforms >apply because of the accelerated frame. It looks like a job for General >Relativity, and I'm a little out of my depth. > Special relativity and the Lorenz transforms work just fine on this problem. Here's part of an old posting of mine from rec.arts.sf.science: ===== [ ... ] So, once again. Assuming a magical stardrive which allows you to accelerate continuously at constant subjective acceleration of A', then in the frame of a stationary observer, your acceleration is measured as: A = A' / gamma^3 The integrals are now trivial, and in the stationary observer's frame the following hold: x(t) = c^2 / A' * (sqrt(1 + (A' * t / c)^2) - 1) t(x) = c / A' * sqrt((A' * x / c^2 + 1)^2 - 1) beta(t) = v(t)/c = A' * t / sqrt(c^2 + (A' * t)^2) the accelerating passenger measures an elapsed time of: t'(t) = c / A' ln(A' * t / c + sqrt(1 + (A' * t / c)^2)) To put some numbers on this, for acceleration at one gravity, the time taken to reach various distances is: 0.25 ly: t = 0.74 yr, beta = 0.61, t' = 0.68 yr 0.5 ly : t = 1.10 yr, beta = 0.75, t' = 0.95 yr 1 ly : t = 1.71 yr, beta = 0.87, t' = 1.29 yr 2 ly : t = 2.81 yr, beta = 0.945, t' = 1.73 yr 4 ly : t = 4.87 yr, beta = 0.981, t' = 2.25 yr 10 ly : t = 10.9 yr, beta = 0.9961, t' = 3.02 yr 100 ly : t = 101 yr, beta = 0.99954, t' = 5.17 yr After this, for every 10 fold increase in distance travelled, beta adds two nines, and t' increases by 2.2 years. The fixed-observer time frame remains one year more than the time of light. For a trip which stops at the end, calculate the time to cover half the distance, then double the t and t' variables. ===== -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Mon May 5 15:29:41 EDT 1997 Article: 46241 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:46241 sci.astro:162767 sci.space.policy:70200 Newsgroups: sci.astro,sci.space.policy,rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Dyson Sphere FAQ (Was: Could intelligent) Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Mon, 5 May 1997 19:21:01 GMT References: <336769EA.587@ias.fr> <336CBDEB.DA5248A@alcyone.com> In article <336CBDEB.DA5248A@alcyone.com>, Erik Max Francis wrote: >Jason Bontrager wrote: > >> smallish Dyson Sphere such that the surface gravity on the outer surface >> is roughly .75g. Then >> you thicken it at 4 points arranged in a tetrahedron (I think thats the >> right shape, an equilateral >> four sided figure). Assuming the 4 points are massive enough, and given >> that they are not >> opposite each other, would their combined gravitational attraction to the >> star in the middle be >> enough to keep everything centered? > >No; a tetradehedral arrangement of bodies would not be stable either. > Just to save people some trouble in thinking of other geometries which might work, let me point out that there are none, assuming the following: the central star has no significant higher mass multipole moments, and the gravitational field strength is small enough that relativistic corrections to gravitation are unimportant. Assuming these to be true, the problem of a stable configuration is equivalent to asking for a configuration of masses which can hold the sun at a particular position in free space (we will assume that the struture itself is not allowed to pass through the bulk of the Sun, otherwise it would be fairly easy to make a stable configuration). Now, construct an imaginary closed surface which divides space into two regions, one region (the inside) contains the star and encloses the desired stable point, the other region (the outside) encompasses everything else. The gravitational potential energy of the star within this surface is given by E = M * phi, where 'phi' is the gravitational potential due to the distribution of other masses. Now, phi has a very useful property, it has a laplacian of zero everywhere inside the volume. If a function has a laplacian of zero everywhere within an enclosed volume, then either the function is a constant, or the extremal values lie on the surface. It is not possible to have a local minimum or maximum within the enclosed volume. The case of a constant is the rigid Dyson sphere, the sun feels no force either pushing it toward the centre nor pulling it toward the edge. According to the above reasoning, any configuration which produces a net force must, of necessity, push the sun toward the imaginary surface. For instance, the ringworld. Make the imaginary surface a sphere around the centre of the ring, with the ring just outside the sphere, like the equator of a globe. The energy maximum is at the north and south poles, the minimum is on the surface nearest the equator. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed May 7 16:41:41 EDT 1997 Article: 46307 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:46307 sci.astro:163016 Newsgroups: sci.astro,rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Dyson Sphere FAQ (Was: Could intelligent) Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 7 May 1997 19:25:44 GMT References: <336CBDEB.DA5248A@alcyone.com> In article , Jason Bontrager wrote: > >I get the impression that you're saying there is no way to construct a rigid >Dyson sphere such that the geometry of the structure creates a suitable >gravitational environment inside the sphere to hold it in place relative to >the star inside. Is that right? > Yes. >If so, then is there *any* passive way to keep the sphere from drifting into >the star if nudged? Possibly a third body in the system, or a combination >the geometry of the sphere, it's rate of spin, and a third body? I'm mostly >interested in a configuration which would allow people to live on the >outside of the sphere in a shirtsleeve environment. >Thanks for your feedback. > I imagine there are a few different ways to maintain feedback without active systems. One thing to mention is that some years ago Paul Dietz and I did some trajectory models for a ringworld, assuming that it was much more massive than the centra sun, and started with the sun out of the plane of the ring. It turns out that there is a horizontal restoring force in some regimes out of the plane of the disk, and a destabilizing force everywhere in the plane. For the correct initial conditions the trajectories of the central sun remained confined to a volume, roughly similar to an hourglass with non-zero waist thickness, as it bounced up and down through the plane of the ring. While there is no stable point, there are bounded trajectories, just as there is no stable point to place a stationary planet in the potential field of the sun, but planets exist because they are not at rest. It is conceivable that something similar could be performed with a Dyson sphere, though I should point out that the stable trajectories for the ringworld required oscillations of the sun along the axis of the ring which exceeded the radius of the ring. One can also conceive of negative feedback systems in a solid Dyson sphere. Let's assume that people are living on the outside of the sphere, in an atmosphere. If the sun moves within the sphere so that it's closer to one part of the sphere, the local air pressure above that point will increase, while the antipodal point will see a decrease in pressure. If regions at low ambient air pressure are made to become transparent, a restoring force is exerted by the photon pressure. This system should even damp out oscillations because of the shift in atmospheric pressure produced by the acceleration of the sphere, rather than oscillating back and forth as some perverse simple harmonic oscillator. Another possibility arises if the sphere is not electrically conducting. Charge up the central star. Assuming that it sheds its charge symmetrically there will be a greater buildup of charge on the parts of the sphere closer to the star than the parts farther away, and there will be a net electrostatic force pushing the sphere back where it belongs. A system of injecting charge back into the central star would probably be required at some point, and if the sphere is conducting then there's a serious problem, the sphere polarizes if the central star is leectrically charged, and produces a destabilizing force. I imagine other people can come up with variants. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Fri May 9 12:49:43 EDT 1997 Article: 46360 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:46360 sci.astro:163179 Newsgroups: sci.astro,rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Dyson Sphere FAQ (Was: Could intelligent) Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Fri, 9 May 1997 13:22:50 GMT References: <5kqn27$57r@masters0.InterNex.Net> <5kqsmg$pb7@epic17.Stanford.EDU> <5kr0kf$gsq@masters0.InterNex.Net> In article <5kr0kf$gsq@masters0.InterNex.Net>, Jeffrey Jacoby wrote: >Ian Burrell (iburrell@leland.Stanford.EDU) wrote: > >> The collectors would be solar sails and act as statites. In other >> words, they would use light pressure to hold themselves above the >> ecliptic. This might not work well for high inclination orbit, but >> the orbit could be synchronized so the nodes were far from the Earth. >> and didn't block illumination. > >OK, I hadn't thought of that one. How high above the ecliptic will >this work? Using this same idea, how far out will the light pressure, >et al, just balance the sun's gravity (thus the collectors don't >even need to be in orbit)? > Well, this one is easy to calculate. Solar radiation pressure falls off as 1/r^2. Gravity falls off as 1/r^2. So, if it works anywhere, it works everywhere. A perfectly reflecting sail of mass approximately 1.5 grams per square metre (averaged over sail and payload) should hold station anywhere in the solar system without requiring heliocentric orbital motion. One problem appears when you put swarms of these in concentric shell orbits, though. The inner shells eclipse the outer shells, and the reflected radiation from the outer shells neutralizes the lift of the sails exposed. For this reason I suspect that orbiting shells are more practical when the total solar coverage becomes large. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Fri May 9 16:13:25 EDT 1997 Article: 46370 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:46370 sci.astro:163195 Newsgroups: sci.astro,rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Dyson Sphere FAQ (Was: Could intelligent) Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Fri, 9 May 1997 17:53:19 GMT References: <5kt6b9$met@tree.Stanford.EDU> In article <5kt6b9$met@tree.Stanford.EDU>, ladasky@leland.Stanford.EDU (John Ladasky) wrote: >In article , Christopher Neufeld wrote: >> One thing to mention is that some years ago Paul Dietz and I did some >>trajectory models for a ringworld, assuming that it was much more massive >>than the centra sun, and started with the sun out of the plane of the >>ring. It turns out that there is a horizontal restoring force in some >>regimes out of the plane of the disk, and a destabilizing force >>everywhere in the plane. > > So if the oscillations are on the order of the radius of the ring, >that means that the apparent position of the sun would travel 45 degrees >to each side of the zenith, and the intensity of sunlight would vary by a >factor of two. Cool. That should emulate seasons somewhat. What kind >of oscillatory periods did you calculate? > Intensity would actually vary by about 30%. For an oscillatory amplitude of 45 degrees, with negligible off-axis displacement, the difference in insolation should be almost the same as the difference between winter and summer which you would get if you lived at 23 degrees north or south latitude (since 45 degrees is almost exactly double the Earth's axial tilt). I don't recall now the period of motion, but it's not difficult to estimate. Assume that the sun remains on axis, linearize the potential field in that neighbourhood, and pretend it's a simple harmonic oscillator. You should get the right answer to within a factor of a few. The answer is: sqrt(G * mass_of_primary / radius_of_ring^3). Some people may recognize that expression. It's the period of a planet orbiting at that distaince. One year, for an Earth-like ring around our sun. Now, in fact, this linearization breaks down when the off-axis displacement is significant on the scale of the radius of the ring, and the correction is to make the period longer. So, for large oscillations along the axis, the period is somewhat longer than one year. Note that seasons would come at twice this frequency, since summer occurs when the star crosses the plane of the ring, not when the star is at one of the peaks. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Mon May 12 12:42:42 EDT 1997 Article: 46461 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:46461 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Dyson Sphere FAQ (Was Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Mon, 12 May 1997 13:46:53 GMT In article <5kukqt$lkl$1@gail.ripco.com> flpalmer@ripco.com (Frank Palmer) writes: >In article: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) writes: >>One can also conceive of negative feedback systems in a solid Dyson >>sphere. Let's assume that people are living on the outside of the sphere, >>in an atmosphere. If the sun moves within the sphere so that it's closer >>to one part of the sphere, the local air pressure above that point will >>increase, while the antipodal point will see a decrease in pressure. If >>regions at low ambient air pressure are made to become transparent, a >>restoring force is exerted by the photon pressure. > >But this is exceded by the difference in weight of air above >the points (AKA air pressure). With an atmosphere, the >system is in positive feedback. > I don't believe that you can say this without knowing the engineering details. You can make the pressure response arbitrarily steep, it's not that there's some physical law connecting the transparency to the amount of pressure difference. The physical effects to keep in mind are things like the maximum speed with which air can move to create these pressure differences. The mass polarization of the sphere is important to keep in mind, though, as it does exert a destabilizing influence. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Fri May 23 14:44:06 EDT 1997 Article: 46991 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:46991 sci.astro:164619 Newsgroups: sci.astro,rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Dyson Sphere FAQ (Was: Could intelligent) Distribution: usa Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Fri, 23 May 1997 13:54:47 GMT References: <5kr0kf$gsq@masters0.InterNex.Net> <3384923C.6560@sdrc.com> In article <3384923C.6560@sdrc.com>, Jim Batka wrote: >Christopher Neufeld wrote: > > >> Well, this one is easy to calculate. Solar radiation pressure falls >> off as 1/r^2. Gravity falls off as 1/r^2. So, if it works anywhere, it >> works everywhere. A perfectly reflecting sail of mass approximately 1.5 >> grams per square metre (averaged over sail and payload) should hold >> station anywhere in the solar system without requiring heliocentric >> orbital motion. > >What about the solar wind pressure? > Insignificant, it's only a couple of percent of the solar pressure, and has some unfortunate properties (no reflection, so the force is radial to the sun rather than normal to the sail, solar magnetic field fluctuations result in variations in solar wind intensity). Averaging out the magnetic field fluctuations, and even given that the solar wind is somewhat concentrated in the equatorial plane, if I remember correctly, you still get a 1/r^2 type force from it, so it does not change the conclusion double-quoted above. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Thu May 29 14:47:05 EDT 1997 Article: 47230 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:47230 rec.arts.sf.written:236421 Newsgroups: rec.arts.sf.written,rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Is it Sci-Fi or Science Fiction? Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Thu, 29 May 1997 14:58:34 GMT References: <862865486.26192@dejanews.com> <338A6F8B.49AE@stud.warande.ruu.nl> <5mhhoq$m3l@proxy5.proxy.ozemail.net> In article <5mhhoq$m3l@proxy5.proxy.ozemail.net>, Chris Lawson wrote: >"S. Wilson" wrote: > >>Say you could hack into the "operating system" of the universe. Say you've >>puzzled out enough of the creators' programming language to change >>universal constants. What would you alter? > >>P.S. My vote is for c. Just for kicks, I'd make it 1000 miles per hour. >>Heh. Relavalistic F-15s. > >And the solar energy output would drop by a factor of gadzillions, >thus freezing the butt off Life on Earth. (E=mc^2, therefore reducing >c reduces E, only more so :-) > I don't think it would be quite that straight-forward. First of all, if you turned off all fusion in the sun right now, you wouldn't even be able to detect it with bolometers for thousands of years. Your tea kettle doesn't freeze solid the moment you unplug it, and the sun will stay nicely warm for some time to come. Reduce the power output of the sun, and as it cools, it contracts, increasing the fusion rate until a new balance is struck. You'd wind up with a more compact, cooler sun, but the power output would still be comparable to the present day output, not "gadzillions" of times lower. Off hand, I don't know if the speed of light is intimately connected to the Stefan-Boltzmann constant, but I rather suspect that it is, so the fact that the sun remains at the same temperature for a long time may not necessarily mean that it keeps radiating the same amount of heat and light. Some other effects, though, would be less pleasant. First, there's the 11 years of darkness. That's the amount of time it takes the slow light leaving the sun to arrive at the Earth after the fast light has already passed us by. Of course, when it's time to reset the speed of light to the familiar value, we get 11 years of sunlight in the space of eight minutes. We're all likely to be somewhat crispy after that. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Mon Jun 2 17:31:34 EDT 1997 Article: 275584 of sci.skeptic Xref: info.physics.utoronto.ca sci.skeptic:275584 Newsgroups: sci.skeptic Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Earl's perfect record intact! Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Mon, 2 Jun 1997 13:56:38 GMT References: <01bc6d13$57e59080$7fd992cf@default> <19970530174001.NAA23569@ladder02.news.aol.com> In article <19970530174001.NAA23569@ladder02.news.aol.com>, LazzWaldo wrote: >Ron Bobo posted > >>Careful, Tony - we wouldn't want you to get caught and lose your computer >>access - you're too great a source of amusement. > >Hey, coward, just post your grades, as you said you would. > >Shakespeare wote a line about you: > >"Full of sound and fury; signifying nothing." > You missed the best part of that quote, the line immediately preceding it (Macbeth, Act 5, Scene V, Macbeth's third recitation in the scene). -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Thu Jun 5 16:58:42 EDT 1997 Article: 247483 of sci.physics Xref: info.physics.utoronto.ca sci.astro:166032 sci.bio.misc:8400 sci.chem:94350 sci.edu:16985 sci.math:180892 sci.med:196792 sci.physics:247483 sci.skeptic:276211 Newsgroups: sci.edu,sci.med,sci.physics,sci.astro,sci.chem,sci.skeptic,sci.math,sci.bio.misc Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Gender Bias in peer review Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Thu, 5 Jun 1997 13:36:37 GMT References: <3394C89C.6225@vasilisa.com> <3395A59B.61C5@elsevier.co.uk> In article <3395A59B.61C5@elsevier.co.uk>, Matthew Flynn wrote: >welshwytch wrote: >> >> Once gender bias in peer review is isolated and made visible through >> rigorous analysis of data -- how does one combat it among >> scientists? How can the anonymity of peer review by preserved >> while making peer reviewers accountable for sexism that permanently >> alters or even destroys the careers of women PhDs in the >> sciences? > >In journal peer review this could be done easily by keeping the authors >of papers, as well as the reviewers, anonymous until the paper had been >accepted or rejected. > This is not so simple in practice. The people chosen to review the paper are intimately familiar with the detailed work in the particular problem studied. I am told that, more often than not, a reviewer can identify the author of a paper solely from the problem which is being examined and the approach being taken. If that is not sufficient, the reference list is almost certainly a dead giveaway, people don't often write papers in isolation, they will have a string of related works, and will refer to their own papers during the analysis. In experimental papers, the apparatus itself might be described in an earlier paper, which at least pins down the lab, if not the particular person who wrote the paper. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Fri Jul 4 17:24:07 EDT 1997 Article: 48246 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:48246 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: O`Neill colonies (was Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Fri, 4 Jul 1997 21:14:59 GMT References: <5pcvad$pnu$1@gail.ripco.com> In article <5pcvad$pnu$1@gail.ripco.com>, Frank Palmer wrote: > * Original msg to: Underdog@silcom.com > > >In article: <5p9iks$cjf@ocean.silcom.com> >underdog@silcom.com (Eric Tolle) writes: > > Un> 2. Rotation. An asteroid rotating on one axis may be dealt with > Un> simply by placing the colony on the axis. The question is, are there > Un> many asteroids with double or triple axis rotation? > >Hardly any. Every rotation of a solid body is around a single >axis. > At the risk of restarting a discussion which I was involved in with Wil McCarthy two summers ago here, free-space rotations of non-spherical solid bodies include the possibility of precession. The rotational axis of the body, defined as a line connecting two points which rotate but do not translate relative to the centre of mass of the body, can itself describe a circular path over the surface of the body around the nominal rotation axis. For instance, the Earth's rotational axis describes a roughly circular path around the North Pole, about five metres south of it, with a period of about 427 days. More irregular objects can have more severe precessions. Note that this is the force-free precession of a body rotating in space, and has nothing to do with precession of the equinoxes caused by external forces. What this means in the context of a rotating asteroid is that the hollowed out region has to have enough clearance to allow for existing precession, or the precession has to be damped out (precession is a higher energy excitation than pure rotation about the axis, so it can be suppressed by damping, even by something as simple as filling it partway with a fluid). -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Tue Jul 8 09:22:02 EDT 1997 Article: 48363 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:48363 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Fail-Safe Beanstalks? Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Tue, 8 Jul 1997 13:20:46 GMT References: <5pc559$khj@universe.digex.net> In article , Toe wrote: >In article <5pc559$khj@universe.digex.net>, nancyl@universe.digex.net >(Nancy Lebovitz) wrote: > >> Are there any theories of how a fail-safe beanstalk could be designed? >> Assuming that a falling beanstalk would be a major diaster, could >> it head for orbit in chunks or crumble to dust if it started to >> fall? Any other solutions? > > >It depends on your definition of "fail-safe." At some point you just have >to accept failure. > >But I say a really close to fail-safe method would be to design a suitable >polymer -- or possibly monomer -- and use nanotech assemblers to extrude it >into a cable. > And yet another extremely useful word gets its meaning popularized out of existence. "Fail-safe" is entirely different from "fail-proof". A fail-proof system tries to avoid failures. A fail-safe system tries to ensure that **when** it fails, it does so in a safe way. For instance, the brakes on modern trains are kept open by pneumatic pressure in tubes running the length of the train. If the train is severed at a point, the cars behind the break lose air pressure, and their wheel brakes activate. Similarly, for elevators, if the tension in the suspension cable is severely reduced, track brakes activate because the tension in the cable is the only thing which prevents the brakes from grabbing the tracks (top marks to "Speed" for this one). People rightly put more faith in fail-safe systems than in so-called fail-proof systems. An example of a fail-safe beanstalk might be one in which sudden changes in tension in the cable cause it to decompose into fluff too small to reach the surface at high speed, though I can't imagine that any system with chemical bonds strong enough to serve the function could be encouraged to simply fall apart under the correct circumstances. Note that putting scuttling charges along the length of the cable doesn't really result in a fail-safe system, unless they are unavoidably detonated by such tension swings, or contact with air at high speeds, or something similar. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed Jul 23 10:21:03 EDT 1997 Article: 286799 of sci.skeptic Xref: info.physics.utoronto.ca alt.atheism:534600 rec.arts.movies.current-films:127596 rec.arts.sf.movies:91328 sci.skeptic:286799 Newsgroups: rec.arts.movies.current-films,rec.arts.sf.movies,alt.atheism,sci.skeptic Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: CONTACT and pi Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 23 Jul 1997 13:56:55 GMT References: <33ADA331.662B@alpha.wcoil.com> <33D14A78.3DBD@cs.ucsd.edu> <33D292F3.448E@email.psu.edu> <33D3059C.788@student.canterbury.ac.nz> In article <33D3059C.788@student.canterbury.ac.nz>, Gareth Wilson wrote: >Evan Blaisdell wrote: >> >> KSG wrote: >> > >> > Gareth Wilson wrote: >> > > >> > > The thing with a circle appearing in pi is a little silly. >> > > Pi contains all possible arrangements of numbers, so the fact that >> > > hidden somewhere inside it is a circle, or "GOD EXISTS", or >> > > "YOU ARE WASTING COMPUTER TIME" isn't really significant. >> > > >> > >> > This is new. When was this proved? >> > >> > -- >> > KSG >> > Bring the Noise on KSDT UCSD >> > KSDT: http://scw.ucsd.edu/ksdt/index.html >> >> It isn't proved, it's from the book "Contact". >Pi has been proven to be an irrational number, which means the string of >digits will be infinitly long and never repeat a sequence. Given those >conditions, it must contain all possible arrangements of numbers. > Base 10: 0.10100100010000100000100000010000000100000000...... -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Thu Aug 7 13:18:28 EDT 1997 Article: 49499 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:49499 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Splitting atoms Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Thu, 7 Aug 1997 13:37:39 GMT References: <5s863c$1sh$1@gail.ripco.com> In article <5s863c$1sh$1@gail.ripco.com>, Frank Palmer wrote: > >Unstable isotopes break down on a timeline which is, as far as >we can discover, neither individually predictable nor >controllable. (The rate is statistically determinate.) > Actually, the rate of decay can be affected. Some isotopes have different decay rates for different _chemical_ environments. The redistribution of the electron shells, with the subsequent change in electron density within the nucleus, affects the energetics or phase space requirements (I don't recall offhand which, but the phase space of electron capture events would be affected). This results in a change in the mean decay time for the isotope, which I understand has been measured. OK, pulling up the sci.physics FAQL, I see that Be-7, which decays by electron capture with a halflife of a bit over 50 days, can show half-life variations of about 0.2% depending on chemical environment, and pressure. Other isotopes are listed which exhibit the effect. Reading that description, it looks like all the measurable effects are due to phase space constraints, not to modification of the coulomb barrier by electron density in the nucleus. Another possibility, observed in the context of atomic transitions but not yet in nuclear transitions, is the quantum Zeno effect. Watch the nucleus closely enough, quickly enough, and it will never decay (transition probability within a fixed time period scales down as 1/(observation rate) once the observation rate is small compared to the time scales involved in the decay). -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Thu Aug 7 13:18:33 EDT 1997 Article: 49500 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:49500 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Buoyancy in zero G (was: Zero-G Swimming Pools) Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Thu, 7 Aug 1997 13:48:03 GMT References: <5ru661$h8c$1@its1.ocs.lsu.edu> <5s43nl$k7j@proxy5.proxy.ozemail.net> <33e7c18b.108795226@news.flash.net> In article <33e7c18b.108795226@news.flash.net>, candid wrote: > >i can't remember all that i read, but i found an interesting book on >physiology in space. > >the interesting things that i remember (i'm in the medical profession, >not the physics profession) are that inertia is essentially anulled if >you are submerged. they did tests where they put people in fluid >filled tanks and accelerated them at tremendous speeds...speeds that >would cause lack of consciousness in a similar "dry" individual. they >did drop tests with mice (poor mice) and the submerged mice survived >like a 100 foot drop while the "dry" mouse was, sadly, smashed. > To clarify this a bit, the inertial effects of deceleration, throwing you against the walls of your container, are largely absent if you are immersed in a medium of equal density. Consider that when you're sitting in a car with a helium balloon, and the car veers right, you fall toward the left side of the car, while the helium balloon moves to the right. So, there must be some intermediate density where nothing much happens. While this technique is useful in the contexts "candid (ns)" mentions, as flight suits for high acceleration maneuvers, it is limited by the fact that the body itself is not of a uniform density. Bones are heavier than muscle tissue, and air-filled lungs are lighter than both. At sufficient acceleration you do not suffer the blunt trauma of hitting the walls, or the strain of being held back only by belts in certain places while the rest of your body tries to pool down in one spot, but you will suffer the effective equivalent of something pulling up on your lungs while pushing down on your bones. I don't know enough of physiology to know if the brain is suspended in a fluid of equal density, it would seem to be a good evolutionary step, but the fact that you can receive a concussion at all suggests that the density matching is not perfect. Other organs are likely not perfectly matched with their surroundings, and blood does not have the average density of a human body, so acceleration effects are still felt. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Fri Aug 15 13:51:47 EDT 1997 Article: 49817 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:49817 rec.games.frp.misc:156134 Newsgroups: rec.games.frp.misc,rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: SF questions (FTL, computer storage devices) Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Fri, 15 Aug 1997 13:44:29 GMT References: <33D496F1.1F1B@stud.uni-hannover.de> <33EE85EC.33F2@here.com> <01bca6f4$a07e6400$7a6d1cce@softdisk.com.softdisk.com> <5sr66e$ich37@cook.dot.gov.au> In article <5sr66e$ich37@cook.dot.gov.au>, Brett Evill wrote: > >In the first place, the Lagrange points are not anomalies in any way. There >existence was calculated by Pierre de Lagrange hundreds of years before >spacetravel. They are simple the points where a light object can orbit in >the join gravity fields of the Earth and the Moon and retain a fixed >relative prosition with respect to both of them. Lagrange Points 1, 2, and 3 >(which are in line with the Earth and Moon) are unstable: the non-stationary >orbits near them lead away. L4 and L5, corresponding to the Moon's leading >and trailing Trojan points are stable: the non-stationary orbits near them >lead toward them. > To be more precise, Lagrange points 1 through 3 are only two-thirds stable. There are two directions, perpendicular to the primary-secondary axis, along which perturbations are corrected by a restoring force, and one direction, along the axis, along which perturbations are amplified. This distinction allows things like satellites in halo orbits around these points, and would be a stabilizing mechanism for a lunar synchronous skyhook passing through the Earth-Moon L1 point (you could make a useful one out of several tons of nylon, though I don't know how nylon takes UV light). >>These points exist all over the place, but are >>normally very small and shift, but the ones I heard refered to as L4 and L5 >>are reasonably large and reasonably stable... > >They are not quite all over the place. There are two associated with each >pair of orbiting bodies. > The L4 and L5 points form potential wells in the rotating coordinate system only when the mass ratio between the two bodies generating the wells is at least 24.960. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed Aug 20 15:18:29 EDT 1997 Article: 49966 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:49966 rec.games.frp.misc:156540 Newsgroups: rec.games.frp.misc,rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: SF questions (FTL, computer storage devices) Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 20 Aug 1997 13:33:27 GMT References: <5t7akm$ntf$1@ramp2.tir.com> In article <5t7akm$ntf$1@ramp2.tir.com>, wrote: > > Something like this is already done with today's chemical rocket >engines. Hydrogen-oxygen engines are typically run at 5 parts oxygen >by mass to 1 part hydrogen, in spite of the fact that 8:1 would be >more efficient. This is because running an 8:1 mixture would result in >temperatures too high for the nozzle and combustion chamber to handle. > Are you sure this is the reason? I was under the impression that there were two reasons. First, that it's difficult to design a motor which works in a hot oxidizing environment, so you want to run fuel-rich to reduce corrosion. Secondly, hydrogen has a much lower molecular weight than water, so Isp is improved by ensuring that some of the exhaust is hot hydrogen rather than hot water (lighter molecules have more momentum per unit mass than heavier molecules at the same temperature). -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed Aug 20 15:18:46 EDT 1997 Article: 49969 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:49969 rec.games.frp.misc:156548 Newsgroups: rec.games.frp.misc,rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: SF questions (FTL, computer storage devices) Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 20 Aug 1997 13:50:42 GMT References: <33D496F1.1F1B@stud.uni-hannover.de> <01bca6f4$a07e6400$7a6d1cce@softdisk.com.softdisk.com> <33F6B8FD.CD73A3@alcyone.com> <01bcab5e$d50e7020$496d1cce@softdisk.com.softdisk.com> In article <01bcab5e$d50e7020$496d1cce@softdisk.com.softdisk.com>, Dagger wrote: >> > As for the information that can give credence to the possibility of >such >> > a >> > gravitational anomally existing, who here has heard of the lagrange >> > points >> > near the moon? >> >> Uh, how could that _possibly_ be relevant to a gravitational beam >> projector to be used as a drive (which wouldn't work anyway)? > >Because it points out that you can have a point that doesn't have any mass >in itself that does have a gravitic attraction. > Actually, those points don't have a gravitational attraction per se. Consider the L4 and L5 points for the Earth-moon system. The moon is orbiting around the Earth, and now imagine that you were a stationary (i.e. non-orbiting) observer in the moon's orbit around the Earth. Perhaps you are a statite being held up by light pressure, or "you" are actually a stream of slow-moving particles crossing that orbit, so that you can examine that position for a long time. As the L4 and L5 points move through and past you, you do not feel a force pulling toward these locations. In other words, for the leading Lagrange point, 60 degrees ahead of the moon in its orbit, a particle stationary in the orbit which is passed by the Lagrange point position does not get first pulled toward the moon along the orbit, and then pushed away along the orbit. It feels merely the slowly increasing gravitational force of a 7.4E+22 kilogram body bearing down on it at almost a kilometre per second. These regions of stability only appear because you are doing the analysis in a rotating coordinate system, and this extra pseudo-force field provides the necessary substrate for the stability regions. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Fri Aug 29 13:52:56 EDT 1997 Article: 50189 of rec.arts.sf.science Xref: info.physics.utoronto.ca alt.gobment.lones:16199 rec.arts.sf.science:50189 Newsgroups: rec.arts.sf.science,alt.gobment.lones Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Worldbuilding Help Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Fri, 29 Aug 1997 13:40:51 GMT References: <5tu2oj$p9$1@gail.ripco.com> In article , Anton Sherwood wrote: > >The description below is incomplete. On a phase diagram whose axes are >temperature and pressure, the boundary between liquid and vapor is a >*curve*, not a point. You could, I imagine, manipulate temperature >and pressure around the triple point to cycle either way: >vapor-solid-liquid-vapor or solid-vapor-liquid-solid. > >Frank Palmer writes >: There is for any liquid, a "critical point." This is the >: combination of pressure and temperature where the density of >: liquid and vapor become the same. (You can cycle around the >: critical point so that the liquid boils, and then boils, and >: then boils again.) >: The critical point for H2O would be quite unpleasantly >: hot, but you could find a more convenient liquid. Then all >: you have to do is explain why that is the type of liquid which >: provides the oceans of your planet. > No, Frank is quite correct. He is not talking about the triple point, but about the critical point. The liquid-vapour coexistance line (or "curve", if you prefer, though the usual term is "line") extends up and to the right on a P vs. T phase diagram. It does not go on forever, though. At the "critical point", the rightmost end of the coexistance line, the latent heat of transition goes to zero. In other words, the phase transition becomes second order there. To the right of this point, it is not formally correct to refer either to liquid or vapour phases, one talks about a "supercritical fluid". What does this mean? Imagine a sample of liquid at a temperature below the critical temperature, and pressure above the critical pressure. Now, we heat this sample at constant pressure to above the critical temperature, lower the pressure to below the critical pressure, then lower the temperature again to below the critical temperature. You now have a sample of vapour. At no time in this sequence was there a clearly defined place where the liquid boiled to vapour, it just sort of diffused outward. In fact, at no time was there a significant presence of two phases. You started out essentially all liquid, and ended essentially all vapour, but you never had a half and half mixture. Now, in contrast, if you'd simply lowered the pressure from your starting point, the liquid would have boiled to vapour exactly as you'd observe in a tea kettle. You would reach the same final state, but you would have crossed the liquid-vapour coexistance line, and the liquid would have undergone a first-order phase transition. Exactly at the critical point, thermodynamic fluctuations have essentially infinite spatial correlation. In the real world, this means that density fluctuations large on the scale of the sizes of the molecules in the material occur. This gives rise to an effect known as "critical opalescence", in which the density fluctutaions in the sample are comparable to the wavelengths of visible light, and the light is scattered in randomly shifting patterns. You can see this, for instance, in carbon dioxide at 73 atmospheres and 31 degrees celcius, where it was first seen by van der Waals in the nineteenth century. So, a sea of liquid above the critical temperature and at the right ambient pressure would have a very ill-defined surface. Under sufficiently large external pressure it would, for all practical purposes, be a liquid. Under low external pressure it would be a vapour. At intermediate pressures it would vary smoothly between these two extremes. Since a sea has a depth-dependent pressure, this would be a natural way to produce a sea with a poorly defined liquid-vapour interface. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Sun Sep 7 16:05:08 EDT 1997 Article: 38074 of ott.general Xref: info.physics.utoronto.ca ott.general:38074 tor.general:112398 Newsgroups: ott.general,tor.general Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Reminder: Babylon 5 reruns Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Sun, 7 Sep 1997 18:52:10 GMT Just a reminder to those people who might be interested in seeing the Babylon 5 series from the beginning, CFMT is carrying the series, starting from the pilot movie and on through seasons 1 through 4, all over Southern Ontario, starting this Monday (September 8). The pilot runs two hours, from 6pm, and after that the series will be shown in original broadcast order Monday to Friday, 7pm. People who came in in the middle of the series can get the backplot, and others can complete their videotape collections. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed Sep 10 09:45:38 EDT 1997 Article: 50487 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:50487 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: small technical nit in G.I. Jane Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 10 Sep 1997 13:43:53 GMT References: <873684254@sheol.org> In article <873684254@sheol.org>, Wayne Throop wrote: > >But one teensy, tiny technical point leaped out at me; in one particular >scene quite far into the movie, they seemed to be discussing how they >had to act lest a plutonium power source from a recently deorbited >satellite would Fall Into the Wrong Hands. Because, the plutonium in >the (presumably thermionic) canister was "weapons grade". > > [ ... ] > >Comments from anybody who remembers details on the isotopes in >termionic power sources? IIRC, they cannot plausibly be used in >weapons, because they have too short a half-life, and any operation >time at all as a heat source would mean only fizzle yields when >attempted in use as an explosive device. > The plutonium used in RTGs is non-fissionable. In fact, having a fissionable isotope would really get in the way of science experiments. A lot of trouble goes into seeing that only plutonium-238 is used in the RTGs because that isotope decays exclusively by alpha emission, easily shielded. A fissionable isotope wouold spray neutrons around which would activate the surrounding structure, and the thing would start spitting gammas and electrons all over the place, which would change the background readings over time. Here, for those interested, is a description of the RTGs used on Galileo and Ulysses, from a 1990 posting by Bill Higgins, then at HIGGINS@FNAL.BITNET but now at higgins@fnald.fnal.gov: --- BEGIN INCLUDED TEXT --- I've summarized what I know about the Ulysses RTG's and the risks posed by its plutonium dioxide fuel. Because of its length, I'm breaking my discussion up into several separate postings. DESIGN OF ULYSSES RTG Ulysses is powered by a particular model of radioisotope thermoelectric generator (RTG) known as a General Purpose Heat Source (GPHS). Galileo had two of these, Ulysses has only one. It is a 55.5-kg device which produces 285 watts of electrical power when its fuel is fresh. The fuel is plutonium-238 (not 239, the fissionable isotope used in bombs) in the form of plutonium dioxide, a ceramic. This isotope decays exclusively by giving off 5.5 MeV alpha particles, and no other radiation. Alpha particles are the easiest kind of radiation to stop. A thin sheet of paper will stop most alphas. The iridium cladding on the plutonium-oxide fuel slugs is more than enough shielding to prevent radiation from escaping. It is also malleable enough to deform under stress without releasing the oxide inside. The fuel pellets are in cylinders, 2.75 cm in diameter by 2.75 cm long. Each pellet yields thermal power of 62.5 watts; the 72 pellets loaded into Ulysses have a total thermal loading of about 4410 watts. Therefore specific power for the GPHS is 5.1 watts/kg, and electrical conversion efficiency is 6.8%. Two cladded pellets go into a cylindrical graphite-epoxy impact shell; this is wrapped in a carbon-bonded carbon fiber insulator. Two impact shells go into a block-shaped graphite-epoxy enclosure called an aeroshell. The aeroshell, measuring 9.7 x 9.3 x 5.3 cm, is the primary re-entry protection for the fuel. The insulators should protect the fuel >from the high temperatures of re-entry, while the impact shells protect it from mechanical impact. Eighteen aeroshell modules are stacked into the aluminum housing of the GPHS, which also contains 576 silicon-germanium thermocouples. In the case of an accidental reentry, the GPHS is designed to separate into separate modules. Between $20 million and $30 million have been spent on a testing program to insure its safety, exposing RTG components to heating, projectile impact, explosions, immersion in water, and fires. --- END INCLUDED TEXT --- -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Fri Nov 7 20:52:05 EST 1997 Article: 51553 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:51553 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!neufeld From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Radioactive antimatter? Message-ID: Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Sat, 8 Nov 1997 01:45:07 GMT References: <63vs9l$smo$1@eskinews.eskimo.com> In article <63vs9l$smo$1@eskinews.eskimo.com>, Tony Zbaraschuk wrote: > >Now, if I'm not mistaken, antimatter _doesn't_ leave radioactive >material behind (matter-antimatter reaction -> gamma rays, not >fragments of atoms). So are these books wrong, or am I missing >something? > Well, a matter-antimatter reaction would probably activate some materials in the vicinity. When a proton meets an anti-proton or anti-neutron, the reaction is messy. One quark hits one anti-quark, things get blown apart, and a spray of pions is the result. Charged pions decay fairly slowly on their own, ultimately to electrons, positrons, and neutrinos, usually via a muon, unless they strike baryonic matter, in which case the charged pions have a tendency to convert to neutral pions and decay quickly. In so doing, they convert a proton to a neutron, or vice-versa. This can lead to activation of the struck nucleus, particularly if the target is a light element. Exaples: carbon-12 could get converted to nitrogen-12 with a half-life of 11 milliseconds, decay is via positron emission possibly with an additional alpha particle. Alternately, it could be converted to boron-12 with a half-life of 20 milliseconds, decay via beta emission possibly with an additional alpha particle. Iron-56 could get converted to manganese-56 with a half-life of 2.579 hours, decay via beta emission. Alternately, it could be converted to cobalt-56 with a half-life of 77.7 days, decay via positron emission or electron capture. High energy gammas themselves can activate a nucleus by spallation, by producing one or more unstable fragments, but I doubt a measly 511 keV would do it. Any nuclear physicists out there to answer my speculation? -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Mon Dec 8 09:42:30 EST 1997 Article: 52323 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:52323 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!caliban.physics.utoronto.ca!not-for-mail From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: SPS aiming Message-ID: <66h0t5$9rf$1@caliban.physics.utoronto.ca> Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Mon, 8 Dec 1997 14:40:37 GMT References: <66dihu$m0k$1@gail.ripco.com> Lines: 37 In article <66dihu$m0k$1@gail.ripco.com>, Frank Palmer wrote: > >Or, you could put up 3 satelites. There are still problems: >Getting 3 ground stations which are close to 120 degrees apart >The aiming problem is greater. >The likelihood of radiation hitting something else is greater. > There's no reason for a solar power satellite to have a danger of hitting an unintended target. The design of the emitter would be a phased array of small radiating elements. Out of phase, they radiate a diffuse, spherical distribution of power which is effectively harmless at distances large compared to the size of the solar panel array. So, in order to prevent accidental radiation excursions into a city if the SPS gets confused or the transmitting array breaks loose and starts to wobble, just don't give the transmitter a local oscillator to synchronize the elements of the phased array. Have the phased array operate as a phase-conjugating mirror, driven off a pilot beam transmitted from the ground station. This actually makes the design much simpler, there's no need to compute the phase difference of the broadcast elements, or correct for atmospheric effects, or anything else. The power beam is required to follow the pilot beam down exactly. With this design, the only thing an SPS could aim at would be a receiving antenna. If it lost touch with its designated receiver, the phased array would dephase, and any power radiated would be in a harmless, undirected pattern. Because the ground station itself would have to be a large phased array, terrorists highjacking the beam into a city would be unlikely, as people are likely to notice the several square kilometres of antenna farm being installed. This leaves only accidental incursions into the space between the ground station and the satellite as potentially dangerous to airplanes, birds, parachuters, and similar flying things. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Tue Dec 9 11:49:48 EST 1997 Article: 52347 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:52347 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!caliban.physics.utoronto.ca!not-for-mail From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Spaceship Gyros Message-ID: <66jkms$d75$1@caliban.physics.utoronto.ca> Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Tue, 9 Dec 1997 14:30:52 GMT References: <971208.023825.9P4.rnr.w165w@krypton.rain.com> <19971209021400.VAA08983@ladder02.news.aol.com> Lines: 48 In article <19971209021400.VAA08983@ladder02.news.aol.com>, Das Miller wrote: > >from sadow@krypton.rain.com (Leonard Erickson) in ><971208.023825.9P4.rnr.w165w@krypton.rain.com> > >>In >>fact, that's how they learned the hard way about the non-uniform >>influences on the satellites. > >Really? I'd have thought it would be obvious . . . of course, maybe it's just >obvious in retrospect. > I can think of a classic example, in one of the first satellites. The Alouette, launched on Sep. 29, 1962. It was a spin-stabilized satellite intended to develop technology and study the ionosphere, and made Canada the third country to build a working satellite. The satellite looked like a big soccar ball with four long antennae, referred to as STEMs, for Storable Tubular Extendable Member. These 1 inch wide hollow whiplike antennae were mounted on the equator of the spinning satellite to form two rigid crossed dipoles, one 150 feet, the other 75 feet from tip to tip. The entire satellite, then, had cylindrical symmetry, at least when averaged over one rotation. Or so they thought. The Alouette spun down, more quickly than could be explained by atmospheric friction in its relatively high orbit. It turned out that Alouette was experiencing a secular torque. As it rotated, parts of the STEMs would pass into the shadow of the satellite, then come out again. The sun would shine on one surface of the STEM but not the other after it came out of eclipse. This differential heating would cause small deflections in the STEMs. This broke the cylindrical symmetry of the satellite, and it experienced a spinning-down torque due to photon pressure on the slightly warped antennae. This was a surprise at the time, and the people I know in Canadian aerospace design, and probably elsewhere, design their spacecraft on the assumption that there will be a limited secular torque of unknown origin on the system, and provide a way of dealing with it. SPAR Aerospace still produces STEMs, but the current designs have perforations along their walls, and the inside surfaces are darkened. These modifications are designed to ensure a uniform heating, so that STEMs don't deform when illuminated from one side. Despite the problem with the spin-down, Alouette collected data for ten years before being turned off by ground commands. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Tue Dec 9 11:52:40 EST 1997 Article: 48499 of comp.mail.sendmail Xref: info.physics.utoronto.ca comp.mail.sendmail:48499 Newsgroups: comp.mail.sendmail Path: info.physics.utoronto.ca!caliban.physics.utoronto.ca!not-for-mail From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Rewriting recipient on attempted relays? Message-ID: <66jsnq$dnd$1@caliban.physics.utoronto.ca> Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Tue, 9 Dec 1997 16:47:54 GMT Lines: 40 I had a problem with my anti-relaying rulesets in sendmail, and somebody in the ameritech.net domain was using my machine to forward his exciting business opportunities all over the world. So, I upgraded everything, rebuilt my sendmail.cf from scratch, and then put in the anti-relay rulesets described in http://www.iav.com/ia/unix/spammer.html. In the past week, this change has blocked 956 further attempts to relay spam, all from dynamic IPs in chicago.il.ameritech.net. The spammer apparently doesn't have error detection in his relaying software. I have sent numerous email messages and faxes to the administrators of ameritech.net, and have received no response. I contacted their upstream provider, ais.net, but they decline to take any responsibility for the silence of the folks to whom they sell the bandwidth. I now have running a perl5 script (available on request) which watches the log file produced by a mail.notice line in my syslog configuration, parses out the denial message, and emails a report to abuse@ameritech.net, giving the source IP number and name, the intended recipient, and an NTP calibrated time stamp of the time of the attempt. As the spammer sends his junk out in batches of fifty at a time, in the space of a couple of minutes, this means that the folks at ameritech are getting fifty automated mail messages at a pop. This has not produced any response. So, my question. Is there a way to modify the anti-relay ruleset to rewrite the recipient? What I'd like to do is, rather than refuse the relay, forward the whole spam to abuse@ameritech.net (only if it came >from a machine in chicago.il.ameritech.net), preferably with some information about the email address of the originally intended recipient. I figure that if the automated abuse reports don't get their attention in the next few days, forwarding the spam directly to them seems the simplest way of disposing of it. It seems only fair, as I got a bounce message in my personal mailbox for every invalid email address the spammer tried to send to before I closed the relaying hole. The fellow did make two relaying attempts from infinet.net, and when I sent the log information to them they immediately wrote back for more information so they could terminate his account. This stands in sharp contrast to the deafening silence from ameritech. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Thu Dec 11 08:52:13 EST 1997 Article: 52406 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:52406 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!caliban.physics.utoronto.ca!not-for-mail From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: colonies Message-ID: <66or3k$j0o$1@caliban.physics.utoronto.ca> Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Thu, 11 Dec 1997 13:50:44 GMT References: <881033971.3038@dejanews.com> <66hdi4$3a$4@bone.globalone.no> <1d0yqgm.r2d9rt13gi9mfN@pm1-41.richmond.infi.net> <348D7CF7.7EA4C773@alcyone.com> Lines: 23 In article <348D7CF7.7EA4C773@alcyone.com>, Erik Max Francis wrote: >Jerry Bryson wrote: > >> Utter speculation here, but I wonder if Mercury once was Venus' moon. > >Very unlikely. Mercury shows no signs of major trauma, as would be >expected if something were ripped out of Venusian orbit and then forced >into a more reasonable orbit around the Sun. > I would condition this a bit, and say "Mercury shows no signs of the sort of major trauma which would be expected..." The planet itself is very dense for a terrestrial planet, leading astronomers to believe that Mercury had most of its mantle blown off in a very high energy collision early in its history. A talk I attended once suggested that the planet was almost completely disrupted, and it lost more than half of its per-collision mass. I'd be pretty traumatized if that happened to me. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Mon Dec 29 14:01:26 EST 1997 Article: 52998 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:52998 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!caliban.physics.utoronto.ca!not-for-mail From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Gravity Wells Message-ID: <688rn0$mtc$1@caliban.physics.utoronto.ca> Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Mon, 29 Dec 1997 18:55:28 GMT References: <681uvm$45h@panix3.panix.com> Lines: 28 In article <681uvm$45h@panix3.panix.com>, Ian Strock wrote: >In <681tgj$krq$2@news.sas.ab.ca> blaine@freenet.edmonton.ab.ca () writes: > >>I am curious. Is it possible to calculate the actual "depth" of the well >>in linear units such as metres? This "depth" is in the 4th dimensional >>axis, and I'm not sure which letter is used to refer to it. (X, Y, and >>Z refer to the three observable spatial dimensions.) > >As I recall, depth of a gravity well is measured in acceleration, so the >unit would be meters per second squared. Thus, Earth's gravitational >attraction of 9.8 m/s^2 means you need to accelerate at least faster than >that to leave Earth. The moon's gravitational attraction of about 1.6 >m/s^2 means it's gravity well is one-sixth as deep as Earth's. > No, that's not the "depth" of the well, it's the steepness or the pitch. The depth is measured in units of energy/mass, the amount of energy which must be added to the object in order to get it out of the well, per unit of mass. The units of this are the same as velocity squared (a scalar, not vector quantity), and, not surprisingly the depth of a well is proportional to the square of the escape velocity in the non-relativistic limit. By this definition, the Moon, with an escape velocity of about 2.4 km/s has a gravity well about 4.5% of the depth of the Earth's (escape velocity 11.18 km/s). -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed Dec 31 08:53:01 EST 1997 Article: 53061 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:53061 rec.arts.sf.written:262484 Newsgroups: rec.arts.sf.science,rec.arts.sf.written Path: info.physics.utoronto.ca!caliban.physics.utoronto.ca!not-for-mail From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Communicating with aliens -- Let me count the ways Message-ID: <68dif3$pl0$1@caliban.physics.utoronto.ca> Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 31 Dec 1997 13:48:19 GMT References: <67ru6d$gl2$1@nntp5.u.washington.edu> <67rvfn$8hr$1@morgoth.sfu.ca> <34A63581.23002861@alcyone.com> Lines: 29 In article <34A63581.23002861@alcyone.com>, Erik Max Francis wrote: >Charles Frederick Goodin wrote: > >> Also, wouldn't the base the aliens count in cause trouble with >> Celsius. > > [ ... ] > >In reality, you'd pick something simple. Say, the liquefaction point of >hydrogen (20 K). That would be one "degree." Simple, easy to use. > This assumes the aliens already know what "1 atmosphere" means, as hydrogen boils at different temperatures depending on the external pressure. Triple points, or some equivalent, are probably easier to communicate. The temperature of the helium-4 lambda point, the triple point of water. Otherwise, a pressure-insensitive temperature, such as the Curie temperature of iron (for "reasonable" pressures). Another possibility for communicating temperature is that the Boltzmann constant would carry the same meaning is whatever units it was measured, so any previously agreed-upon energy standard immediately communicates a temperature standard, by E = k_B T. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed Jan 28 09:21:34 EST 1998 Article: 54096 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:54096 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!caliban.physics.utoronto.ca!not-for-mail From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: 1st Jan 2000 Message-ID: <6ane43$pig$1@caliban.physics.utoronto.ca> Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 28 Jan 1998 14:08:03 GMT References: <990@eildon.win-uk.net> <6a8ff6$kj7@sjx-ixn5.ix.netcom.com> <6aj05v$rlp2@bolt.lakeheadu.ca> <34ce0a8d.6169134@news.dsuper.net> Lines: 21 I propose a simple solution to this entire discussion. One which will, once and for all, quash these discussions which occur every hundred years or so. We'll have two years numbered 1998. To avoid confusion, I propose that next year be denoted "1998b". The year after that will be 1999, and the following year 2000 will start the next millennium, and everybody will be happy. This has an extra advantage of leveling the playing field in the world of computer preparedness. All of these companies out there with an unfair advantage over their competitors because they spent time and money fixing the Y2K bug will get their come-uppance. How many Y2K fixes are going to work seamlessly with "1998b", and the knowledge that "1999" is two years after "1998"? See everybody scrambling to get the "Y1998B" patches done before next January! Watch as databases crumble! -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Tue Feb 24 11:25:40 EST 1998 Article: 282248 of sci.physics Xref: info.physics.utoronto.ca sci.physics:282248 Newsgroups: sci.physics Path: info.physics.utoronto.ca!caliban.physics.utoronto.ca!not-for-mail From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Three points more stable than four? Message-ID: <6csa44$rta$1@caliban.physics.utoronto.ca> Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Mon, 23 Feb 1998 17:03:00 GMT References: <6cpahh$i0n$1@rzsun02.rrz.uni-hamburg.de> <6cptpq$ggl$1@newsd-162.iap.bryant.webtv.net> Lines: 24 In article <6cptpq$ggl$1@newsd-162.iap.bryant.webtv.net>, wrote: >A table with 3 legs will set with all legs touching the floor even if >the legs are uneven or the floor is warped, or both. > >A table with 4 legs requires that all legs are equal and the floor is >level to sit with all its legs on the floor without rocking. > This isn't true. A table with four legs, on a floor surface which is sufficiently smooth (i.e. no sections of the floor which are sufficiently slanted that a leg would slide if resting there, and with surface irregularities smaller than the height of the legs) can always be *rotated* until all four legs are firmly on the ground, even if the floor is not smooth. If the legs are not equal length, the floor must have surface irregularities at least as large as the smallest displacement of a table leg end from the plane passing through the other three legs. Put more concisely, if the floor is bumpy, and you don't care about rotations, you can almost always rotate the table about its vertical axis until it is stable. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Fri Mar 13 08:12:50 EST 1998 Article: 55002 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:55002 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!caliban.physics.utoronto.ca!not-for-mail From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Planet/biosphere killers.... Message-ID: <6e8p6d$48h$1@caliban.physics.utoronto.ca> Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Thu, 12 Mar 1998 13:50:05 GMT References: <6e1rtr$a6p$1@nnrp1.dejanews.com> <350751C3.30232ADC@alcyone.com> Lines: 28 In article <350751C3.30232ADC@alcyone.com>, Erik Max Francis wrote: >cincsac@juno.com wrote: > >> What I'm wondering about is, how could I come up with numbers for >> these (e.g., how much energy is involved, etc.)? > >> 7) If there aren't any oceans, heat up the atmosphere by 500K or so. > >The stratosphere goes up to about 50 km, so its total volume is 2.6 x >10^19 m^3. With a density of 1.29 kg/m^3, this gives a mass of 3.3 x >10^19 kg. Air's specific heat capacity is perhaps 1 kJ/kg/K, so raising >the temperature from 300 K to 500 K corresponds to a massic energy >requirement of 200 kJ/kg, so that means the total energy requirement is >6.6 x 10^24 J. > Nice work on the earlier entries, Erik, but you can do better than this for the mass of air. You're assuming uniform density, which is certainly not true. Atmospheric pressure is 101325 newtons/m^2, and the atmosphere extends over a sufficiently short distance that you can assume gravity is the same over the entire depth, giving a mass of 10330 kg/m^2. Multiply by the surface area of the Earth, and we get a mass of about 5.3E+18 kg. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Fri Mar 27 14:46:22 EST 1998 Article: 55610 of rec.arts.sf.science Xref: info.physics.utoronto.ca rec.arts.sf.science:55610 Newsgroups: rec.arts.sf.science Path: info.physics.utoronto.ca!caliban.physics.utoronto.ca!not-for-mail From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Survey of inefficienc Message-ID: <6fgg7r$a92$1@caliban.physics.utoronto.ca> Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Fri, 27 Mar 1998 15:22:35 GMT References: <6fddgh$mb8$1@gail.ripco.com> <351B1BBA.5A4B761B@alcyone.com> Lines: 72 In article <351B1BBA.5A4B761B@alcyone.com>, Erik Max Francis wrote: >Frank Palmer wrote: >> >> The optimum point in the orbit (I'm assuming that earth is >> near the perihelion) would be at aphelion or about 1/4 of the >> way around the asteroid's orbit from the closest proximity to >> earth's orbit. > >Eh? Aren't impulses more energy-efficient at perihelion? > I can think of a couple of reasons why aphelion would make more sense for deflecting an asteroid. First, the parenthetical assumption in the double-quoted text above. If the Earth orbit is near perihelion, then an impulse at perihelion results in a new orbit which still has a perihelion near Earth orbit, so all you've done is moved the asteroid into a different Earth-crossing orbit, and it is possible that you'll have to do the whole thing again in a few centuries. An aphelion impulse can put the asteroid into an orbit which never comes close to Earth orbit again. Second, the aim of this is not necessarily to produce the greatest change in the orbital energy of the asteroid, but rather to modify the orbital elements most drastically. Here we are implicitly assuming that our capabilities are marginal, so we need all the help we can get from orbital mechanics. An impulse delivered at aphelion results in a larger change in the angular momentum of the orbit than an equal impulse delivered at perihelion. For significantly elliptical orbits the savings can be great. Consider, for example, a satellite which is in a highly elliptic parking orbit, with an apogee speed of 1 km/s and a perigee speed of 8 km/s. If you have a rocket capable of delivering a total delta-v of 1.5 km/s, you can do a 90 degree plane change with an apogee burn, but the effect at perigee is significantly less dramatic. To put in some numbers, my hypothetical Earth-orbiting satellite has a perigee altitude of 1.1E+7 metres (from the centre of the Earth), and an apogee of 8.9E+7 metres. Restricting myself to in-plane maneuvers, now, my 1.5 km/s delta-v rocket causes the orbits to change in the following manner: perigee burn, delta-v positive Satellite goes to escape, hyperbolic excess velocity of 420 m/s perigee burn, delta-v negative R_p: 1.1E+7 V_p: 6500 m/s R_a: 1.6E+7 V_a: 4600 m/s apogee burn, delta-v positive R_a: 2.0E+8 V_a: 1100 m/s R_p: 8.9E+7 V_p: 2500 m/s (note: the old apogee is now the perigee, the orbit is much higher) apogee burn, delta-v negative Satellite can be dropped onto the Earth. So, a perihelion burn is more energy efficient, and is the choice if you want to send the asteroid to solar system escape velocity, but this is probably overkill. An aphelion burn gives you more authority to change the orbital elements, and, for asteroids whose perihelion is close to that of the Earth's orbit, allows an orbit change into a non- Earth-crossing orbit. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Mon Mar 30 14:49:49 EST 1998 Article: 104410 of comp.os.linux.networking Xref: info.physics.utoronto.ca comp.os.linux.networking:104410 Newsgroups: comp.os.linux.networking Path: info.physics.utoronto.ca!caliban.physics.utoronto.ca!not-for-mail From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Transparent port reassigning of UDP on incoming/outgoing packets? Message-ID: <6fof1u$4ha$1@caliban.physics.utoronto.ca> Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Mon, 30 Mar 1998 15:51:26 GMT Lines: 32 It occurred to me recently that it ought to be possible to redirect packets using the firewalling / masquerading rules to avoid problems with an intervening firewall, but I haven't figured out a way to do what I want. Here's the situation: I have a network of machines which is behind a firewall (actually a packet-filtering router), which is completely beyond my control. No changes to the forwarding policy will be made, for any purposes. I control one more machine outside of this firewall (the one I use to post news). The outside machine uses NTP to keep the clock synchronized. The inside network uses NTP, but we cannot synchronize properly to an external source because the firewall blocks the NTP packets on port 123, so we run ntpdate every three hours on the network time master, which works because it can be run with packets on unprivileged ports. What I'd like to do is to leapfrog over the blocked ports on the firewall, by having the outside machine rewrite packets aimed at UDP 123 on the time master into a port which isn't blocked. The time master should then rewrite the incoming packet so that it appears to arrive on UDP 123. This way, without recompiling the NTP sources, I can make the data travel over a channel which isn't blocked by the filtering router. Each machine would know the IP number of the other, and would rewrite only packets directed at the opposite number, or coming in from its opposite number. Meanwhile, the external machine can still act as a standard time server for other computers without confusing them by sending data on the wrong ports. So, is this approach possible in the 2.0.* series of kernels? Thank you for any help. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Thu Apr 2 15:36:13 EST 1998 Article: 104748 of comp.os.linux.networking Xref: info.physics.utoronto.ca comp.os.linux.networking:104748 Newsgroups: comp.os.linux.networking Path: info.physics.utoronto.ca!caliban.physics.utoronto.ca!not-for-mail From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Transparent port reassigning of UDP on incoming/outgoing packets? Message-ID: <6g0pbu$a89$1@caliban.physics.utoronto.ca> Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Thu, 2 Apr 1998 19:36:30 GMT References: <01bd5cc9$e441eeb0$0202010a@groover> Lines: 20 I've had a couple of suggestions, in email and posted, of ways to change the port used by a UDP application on a selectively depending on the target host, without having to recompile the sources, but both solutions do only half the job. It is fairly easy to redirect an incoming packet on one UDP port so that it arrives on the same machine at a different port number, several applications running in user space can do this. The problem is with rewriting the outgoing packet. That has to be done in the kernel space, for obvious reasons. Transparent proxying *almost* works, when combined with udprelay or a hand-written C program which does the appropriate calls to extract the target IP and then forwards it on its way, but proxying doesn't affect locally sourced packets, a capability which I would need for the NTP firewall skipping I'm trying to do. It is an input rule, not an output rule. So, unless anyone can think of something I'm missing, I guess it's time to play with xntpd or kernel sources. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Sat Apr 4 00:22:08 EST 1998 Article: 10339 of comp.protocols.time.ntp Xref: info.physics.utoronto.ca comp.protocols.time.ntp:10339 Newsgroups: comp.protocols.time.ntp Path: info.physics.utoronto.ca!caliban.physics.utoronto.ca!not-for-mail From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Solution for annoying filtering routers (Linux) Message-ID: <6g3m45$cc5$1@caliban.physics.utoronto.ca> Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Fri, 3 Apr 1998 21:59:33 GMT Lines: 30 For those of us living behind firewalls which refuse to pass incoming UDP packets on port 123, I now have a working solution, assuming control of at least one box outside of the firewall. Requires: - kernel support of transparent proxying on the NTP master which is on the wrong side of the firewall, or udprelay to relay the packet to port 123. (I have not tested this with udprelay). - root access to one machine outside of the firewall. It does not require recompiling the xntpd sources, if xntpd is dynamically linked against the C library. The solution I have used is to create a dynamic link library which wraps sendto(). It loads a database of IP numbers and ports which the firewall allows to pass, and rewrites the destination of outgoing packets which match a certain IP#/netmask pair to the appropriate port. The receiver, inside the firewall, then uses transparent proxying or udprelay to put the packet back onto UDP 123. Note that typically only the outside machine has to rewrite packets, as filtering routers are quite happy to let most outgoing traffic alone. I can provide the source code for this kludge to anybody who wants, and I'm also willing to configure my external stratum 3 NTP server to send to the new port number of your choice, if you provide an IP and port number of a machine similarly blocked by an annoying filtering router. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Thu Apr 9 10:29:49 EDT 1998 Article: 55957 of rec.arts.sf.science Xref: info.physics.utoronto.ca alt.tv.babylon-5:80549 alt.tv.star-trek.ds9:67052 rec.arts.sf.science:55957 rec.arts.sf.tv:135360 rec.arts.sf.tv.babylon5:234614 rec.arts.startrek.current:333551 Newsgroups: alt.tv.babylon-5,alt.tv.star-trek.ds9,rec.arts.sf.science,rec.arts.sf.tv,rec.arts.sf.tv.babylon5,rec.arts.startrek.current Path: info.physics.utoronto.ca!caliban.physics.utoronto.ca!not-for-mail From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Star Trek science advisors Message-ID: <6gfre7$9rd$1@caliban.physics.utoronto.ca> Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 8 Apr 1998 12:43:51 GMT References: <350EF96C.5F25@accesspro.net> <6ftn00$mj7@zappa.northnet.org> <87d8f15xcg.fsf@ibm.ne <6g08ft$ohs$2@reader1.reader.news.ozemail.net> Lines: 52 In article <6g08ft$ohs$2@reader1.reader.news.ozemail.net>, Chris Lawson wrote: >tmill06@ibm.net (Timothy J. Miller) wrote: > >>"John D. Gwinner" writes: > >>> So you can have a stationary orbit over the north pole with the right >>> construction. > >> Over the north pole of a star, yes. > >> Over the north pole of a *planet* (per the actual ST:TNG goof), >>good luck. > >Not true. Forward's statite concept was for planetary polar positions. >The solar wind still whizzes past the Earth (causing the aurorae, for >instance) and can be used by a satellite to maintain position above >the Earth's poles (among other positions). > You're mixing two different things. The solar wind, which causes aurorae, is a tenuous plasma moving out from the sun. There is also sunlight. This sunlight embodies a momentum flux hundreds of times larger than the solar wind at our distance from the Sun. One does not make a solid sheet to reflect solar wind, the momentum captured per unit mass of collector makes it impractical. The solar wind momentum transfer devices I've heard of use a magnetic sail, whose mass scales up with the circumference of the intercepted solar wind area, rather than with the area. Then, you just build one of these things really, really big. >(note that this is a slight simplification, as the density of the >solar wind is not perfectly spherically distributed, nor is it >completely constant with time, and also the local gravity of Earth >might affect the critical value of the solar sail density/SA required) > Statites are solar sails, at least as Forward describes them. They hang on sunlight, not solar wind. Sunlight is isotropic to a very good approximation, and time variation is not more than a few percent. Hanging a statite in the vicinity of a planet requires a lower mass per unit area for the sail than hanging one far from other planets. Many years ago I suggested in the newsgroups a device for cleaning debris out of low earth orbit, which involved a statite reflecting sunlight across the limb of the earth to de-orbit small debris by Poynting pressure while leaving essentially unaffected the more important things there, like GPS and other low-orbiting satellites. For a reasonable mass per unit area the sail had to be quite far from the Earth, and then lunar gravity starts to complicate things. Still, perhaps some day... -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Tue Apr 14 16:26:20 EDT 1998 Article: 55981 of rec.arts.sf.science Xref: info.physics.utoronto.ca alt.tv.babylon-5:80589 alt.tv.star-trek.ds9:67108 rec.arts.sf.science:55981 rec.arts.sf.tv:135483 rec.arts.sf.tv.babylon5:234682 rec.arts.startrek.current:333648 Newsgroups: alt.tv.babylon-5,alt.tv.star-trek.ds9,rec.arts.sf.science,rec.arts.sf.tv,rec.arts.sf.tv.babylon5,rec.arts.startrek.current Path: info.physics.utoronto.ca!caliban.physics.utoronto.ca!not-for-mail From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: Re: Star Trek science advisors Message-ID: <6gvqtc$af9$1@caliban.physics.utoronto.ca> Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Tue, 14 Apr 1998 14:13:00 GMT References: <6gn5vm$9lo$1@reader1.reader.news.ozemail.net> Lines: 40 In article <6gn5vm$9lo$1@reader1.reader.news.ozemail.net>, Chris Lawson (claw@ozemail.com.au) wrote: >neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) wrote: > >But the point I was trying to make is that you can effectively place a >statite anywhere in the solar system except in a planetary shadow. > Yes, provided that the sail is light enough, of course. >> Hanging a statite in the vicinity of a planet requires a lower mass >>per unit area for the sail than hanging one far from other planets. > >I assume this is because a near-planet statite must contend with the >planet's gravity without the benefit of any additional sunlight. Am I >correct? > Yes, that's right. >Actually, I imagine a statite of sorts could do OK in one of the >Lagrange points. Even at unstable L points, like L2 and L3, an >effective solar sail could maintain the statite's position with much >greater mass/SA ratios than a free-space statite would need. It might >even be feasible with current material technology. > It wouldn't be a statite at the Earth-Moon Lagrange points, as it wouldn't be stationary. A statite is sort of like a device in a permanent sun-synchronous location. The Earth-Moon Lagrange points move relative to the Earth-Sun line, so what you have is a sail-assisted orbit, rather than a true statite. You could hang one at the Earth-Sun Lagrange points, only one of them is really useful for this, I would think, the intermediate Lagrange point. When I suggested using a solar sail in a hanging orbit to clean debris it was because I wanted to have a 100% duty cycle, so the angle between the Sun, Earth, and sail shouldn't change. This is where a statite works well. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed Apr 15 13:13:22 EDT 1998 Article: 229944 of comp.os.linux.misc Xref: info.physics.utoronto.ca comp.os.linux.misc:229944 Newsgroups: comp.os.linux.misc Path: info.physics.utoronto.ca!caliban.physics.utoronto.ca!not-for-mail From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) Subject: dcron 2.2 and Daylight Savings Time Message-ID: <6h2daa$cde$1@caliban.physics.utoronto.ca> Nntp-Posting-Host: caliban.physics.utoronto.ca Sender: news@info.physics.utoronto.ca (System Administrator) Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Date: Wed, 15 Apr 1998 13:39:22 GMT Lines: 11 I just noticed that my crond didn't make the switch to DST along with the rest of the machine. I've downloaded the 2.3.3 sources, but there's no mention in the CHANGES file of a fix for this, and the bug reporting address doesn't resolve. Those of you with cron jobs might want to check that the daemon is running properly. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Thu Jan 14 15:23:43 EST 1999 Article: 68593 of comp.os.linux.development.system Newsgroups: comp.os.linux.development.system Subject: Strange behaviour in 2.2.0pre7. Netscape freezes locking NFS disk. Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) NNTP-Posting-Host: 128.100.75.114 Message-ID: <369e5121.0@capella.physics.utoronto.ca> Date: 14 Jan 1999 15:18:41 -0500 X-Trace: 14 Jan 1999 15:18:41 -0500, 128.100.75.114 Lines: 29 Path: capella.physics.utoronto.ca!caliban.physics.utoronto.ca!neufeld Xref: capella.physics.utoronto.ca comp.os.linux.development.system:68593 I'm trying out the 2.2.0pre* series on one of my office computers, a dual PPro 200. Right now I have 2.2.0pre6 and 2.2.0pre7, SMP kernels. I notice that software-commanded reboots still don't work, I have to hit the reset button after commanding "shutdown -r". Something else seems to have broken, though, in Netscape 4.5. If you start netscape, then call for the "composer" from the menu, netscape freezes, and seems to be having trouble with file locks. It did not do this with v2.0.33 but does it with both pre6 and pre7. I realize that this is very possibly a bug in netscape, but I offer it up here just in case it isn't. A strace shows that netscape is looping, possibly forever, within: gettimeofday({916344699, 562021}, NULL) = 0 sigreturn() = ? (mask now []) fcntl(23, F_GETLK, {type=F_RDLCK, whence=SEEK_SET, start=0, len=0, pid=0}) = ? ERESTARTSYS (To be restarted) --- SIGALRM (Alarm clock) --- File descriptor 23 is ~/.netscape/custom.dic, which is mounted from an NFS disk served by another Linux box running 2.0.33 and Universal NFS Server 2.2beta37. When the offending file is copied to the local disk and symlinked in the NFS directory, the problem goes away. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Thu Jan 14 17:32:58 EST 1999 Article: 68609 of comp.os.linux.development.system Newsgroups: comp.os.linux.development.system Subject: RealPlayer audio output brittle with 2.2.0pre6 Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) NNTP-Posting-Host: 128.100.75.114 Message-ID: <369e6f71.0@capella.physics.utoronto.ca> Date: 14 Jan 1999 17:28:01 -0500 X-Trace: 14 Jan 1999 17:28:01 -0500, 128.100.75.114 Lines: 47 Path: capella.physics.utoronto.ca!caliban.physics.utoronto.ca!neufeld Xref: capella.physics.utoronto.ca comp.os.linux.development.system:68609 Another thing has turned up in my checking of the 2.2.0pre6 kernel, again with software for which I don't have the source code. RealPlayer version 5.0 Gold (5.0.0.35) can no longer recover from network congestion. It tries to rebuffer the stream, then pops up a window with "Error 1", and indicates that it failed to write the data it was sending (1066 bytes send to write(), return code 844). You then have to restart the audio player manually. The kernel version is 2.2.0pre6 SMP, running on a dual PPro 200. The sound card is a Vibra16 built into the Dell OptiPlex GXPro motherboard, and I'm using the SoundBlaster drivers. The contents of /proc/sound: OSS/Free:3.8s2++-971130 Load type: Driver compiled into kernel Kernel: Linux narn 2.2.0-pre6 #4 SMP Thu Jan 14 15:05:45 EST 1999 i686 Config options: 0 Installed drivers: Type 1: OPL-2/OPL-3 FM Type 26: MPU-401 (UART) Type 2: Sound Blaster Type 29: Sound Blaster PnP Type 7: SB MPU-401 Card config: Sound Blaster at 0x220 irq 5 drq 1,5 SB MPU-401 at 0x330 irq 5 drq 0 OPL-2/OPL-3 FM at 0x388 drq 0 Audio devices: 0: Sound Blaster 16 (4.13) (DUPLEX) Synth devices: 0: Yamaha OPL3 Midi devices: 0: Sound Blaster 16 Timers: 0: System clock Mixers: 0: Sound Blaster -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Tue Mar 2 16:09:56 EST 1999 Article: 71704 of comp.os.linux.development.system Newsgroups: comp.os.linux.development.system Subject: Patch for 2.2.* and some Digital Celebris machines Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) NNTP-Posting-Host: 128.100.75.114 Message-ID: <36dc5222.0@capella.physics.utoronto.ca> Date: 2 Mar 1999 16:03:30 -0500 X-Trace: 2 Mar 1999 16:03:30 -0500, 128.100.75.114 Lines: 139 Path: capella.physics.utoronto.ca!caliban.physics.utoronto.ca!neufeld Xref: capella.physics.utoronto.ca comp.os.linux.development.system:71704 Posted and emailed to Linus. A few of us have noticed problems with the 2.2.* series kernels and some Digital Celebris Pentium boxes. The machines hang before console initialization on 2.2.1 and 2.2.2. In my office we have four such machines, three of which fail on the boot, and the fourth has no trouble at all. The folks at Digital are stumped, the motherboards are the same on all of them. Anyway, the problem is that on the problematic boards, the 82C54 programmable interval timer does not clear its output bit after the countdown is commanded. The result is that a delay loop which is supposed to take 50 milliseconds instead takes effectively zero time. The number of CPU clock cycles spent in this 50 ms loop is then divided into a 64 bit number, with the expectation that a valid 32 bit value will be returned, but because of the short-circuited loop, the resulting quotient overflows on the division, and everything stops with a division error. The following patch fixes the problem by detecting when the loop has been short-circuited, and returning an out-of-bounds value to the calling subroutine. This means that the TSC cannot be calibrated (at least not by this technique), so the kernel falls back on non-TSC behaviour. The patch has been tested, and allows problematical boards to boot into non-TSC mode while still giving correct TSC behaviour for other Digital Celebris machines whose CTC is working properly. *** linux/arch/i386/kernel/time.c.orig Thu Jan 21 09:09:30 1999 --- linux/arch/i386/kernel/time.c Tue Mar 2 16:06:54 1999 *************** *** 587,605 **** --- 587,620 ---- "movl %%eax, %%ebx\n\t" "movl %%edx, %%ecx\n\t" /* Busy wait. Only 50 ms wasted at boot time. */ "0: inb $0x61, %%al\n\t" /* Read Speaker Output Port */ + "incl %3\n\t" /* Add one to loop counter. */ "testb $0x20, %%al\n\t" /* Check CTC channel 2 output (bit 5) */ "jz 0b\n\t" /* And read the TSC. 5 jiffies (50.00077ms) have elapsed. */ "rdtsc\n\t" /* Great. So far so good. Store last TSC reading in * last_tsc_low (only 32 lsb bits needed) */ "movl %%eax, last_tsc_low\n\t" + + /* If the loop counter is zero, then there's a problem with + * the CTC (maybe a Digital Celebris Pentium machine?). + * The calibration fails. */ + "movl %3, %%eax\n\t" + "andl $0xffffffff, %%eax\n\t" + "jz 1f\n\t" /* Bad CTC. Give up on this + * optimization. The '0' in %eax will + * be returned to the caller. */ + + /* Values were OK. Load the %eax again for the + * subsequent math. */ + "movl last_tsc_low, %%eax\n\t" + /* And now calculate the difference between the readings. */ "subl %%ebx, %%eax\n\t" "sbbl %%ecx, %%edx\n\t" /* 64-bit subtract */ /* but probably edx = 0 at this point (see below). */ /* Now we have 5 * (TSC counts per jiffy) in eax. We want *************** *** 613,625 **** "movl %%eax, %%ecx\n\t" "xorl %%eax, %%eax\n\t" "movl %2, %%edx\n\t" "divl %%ecx\n\t" /* eax= 2^32 / (1 * TSC counts per microsecond) */ /* Return eax for the use of fast_gettimeoffset */ ! "movl %%eax, %0\n\t" : "=r" (retval) ! : "r" (5 * LATCH), "r" (5 * 1000020/HZ) : /* we clobber: */ "ax", "bx", "cx", "dx", "cc", "memory"); return retval; } __initfunc(void time_init(void)) --- 628,640 ---- "movl %%eax, %%ecx\n\t" "xorl %%eax, %%eax\n\t" "movl %2, %%edx\n\t" "divl %%ecx\n\t" /* eax= 2^32 / (1 * TSC counts per microsecond) */ /* Return eax for the use of fast_gettimeoffset */ ! "1: movl %%eax, %0\n\t" : "=r" (retval) ! : "r" (5 * LATCH), "r" (5 * 1000020/HZ), "m" (0xffffffff) : /* we clobber: */ "ax", "bx", "cx", "dx", "cc", "memory"); return retval; } __initfunc(void time_init(void)) *************** *** 652,668 **** * moaned if you have the only one in the world - you fix it! */ dodgy_tsc(); ! if (boot_cpu_data.x86_capability & X86_FEATURE_TSC) { #ifndef do_gettimeoffset do_gettimeoffset = do_fast_gettimeoffset; #endif do_get_fast_time = do_gettimeofday; use_tsc = 1; - fast_gettimeoffset_quotient = calibrate_tsc(); /* report CPU clock rate in Hz. * The formula is (10^6 * 2^32) / (2^32 * 1 / (clocks/us)) = * clock/second. Our precision is about 100 ppm. */ --- 667,683 ---- * moaned if you have the only one in the world - you fix it! */ dodgy_tsc(); ! if (boot_cpu_data.x86_capability & X86_FEATURE_TSC && ! (fast_gettimeoffset_quotient = calibrate_tsc()) != 0) { #ifndef do_gettimeoffset do_gettimeoffset = do_fast_gettimeoffset; #endif do_get_fast_time = do_gettimeofday; use_tsc = 1; /* report CPU clock rate in Hz. * The formula is (10^6 * 2^32) / (2^32 * 1 / (clocks/us)) = * clock/second. Our precision is about 100 ppm. */ === CUT HERE === -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Mon Nov 23 11:07:03 EST 1998 Article: 255974 of comp.os.linux.misc Newsgroups: comp.os.linux.misc Subject: Fileutils 4.0 breaks teTeX 0.4 Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) NNTP-Posting-Host: 128.100.75.114 Message-ID: <3659874e.0@capella.physics.utoronto.ca> Date: 23 Nov 1998 11:03:26 -0500 X-Trace: 23 Nov 1998 11:03:26 -0500, 128.100.75.114 Lines: 52 Path: capella.physics.utoronto.ca!caliban.physics.utoronto.ca!neufeld Xref: capella.physics.utoronto.ca comp.os.linux.misc:255974 Status: O A change to the output format of "ls" in the latest fileutils breaks the texhash function of teTeX 0.4, and LaTeX stops working. "texhash" does a recursive ls, with "ls -LRa ./ /dev/null" in /usr/local/teTeX/texmf. It then parses the output to produce a database used by the LaTeX binaries. The change in ls is the following. I created a directory named "aaa", and an empty subdirectory of it, "bbb". I ran "ls -LRa ./ /dev/null" in this directory, once with the new ls, and once with the old. The outputs differed: Old ls: /dev/null ./: . .. bbb ./bbb: . .. New ls: /dev/null .: . .. bbb bbb: . .. The difference breaks the sed script used by texhash to create the database. The following patch will fix texhash for the new fileutils: --- texhash.orig Fri Nov 20 15:29:52 1998 +++ texhash Fri Nov 20 15:32:09 1998 @@ -62,7 +62,7 @@ echo '% This is file ls-R. Maintained by texhash and append_db.' > $db_file_tmp # the main task: -(cd $TEXMF; \ls -LRa ./ /dev/null | sed 's@\.//@./@;/^\.*$/d' ) 2>/dev/null >> $db_file_tmp +(cd $TEXMF; \ls -LRa ./ /dev/null | sed -e 's|^\(.*:\)$|./\1|g' | sed 's@\.//@./@;/^\.*$/d' ) 2>/dev/null >> $db_file_tmp echo "$progname: Done." >&2 rm -f $db_file -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Thu Aug 19 09:17:59 EDT 1999 Article: 70016 of rec.arts.sf.science Newsgroups: rec.arts.sf.science References: <37B8E15C.986FB062@alcyone.com> <37B8ED1E.453B6167@who.net> <37BB4FCB.5E8CAC1A@clark.net> Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Subject: Re: "New spacecraft propulsion method could be out of this solar system" From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) NNTP-Posting-Host: 128.100.75.114 Message-ID: <37bc0286.0@capella.physics.utoronto.ca> Date: 19 Aug 1999 09:11:34 -0500 X-Trace: 19 Aug 1999 09:11:34 -0500, 128.100.75.114 Lines: 36 Path: capella.physics.utoronto.ca!caliban.physics.utoronto.ca!neufeld Xref: capella.physics.utoronto.ca rec.arts.sf.science:70016 Status: O In article <37BB4FCB.5E8CAC1A@clark.net>, Nyrath the nearly wise wrote: > > I have a vague memory of seeing plans for a charged solar > sail. The mirrored surface was accelerated by photons, > and the charged surface was accelerated by solar wind. > Since these two are often at different vectors, > it allowed the charged sail to "tack" into the wind. > This would probably be of fairly limited effectiveness, as the momentum flux carried by the solar wind is about a thousand times lower than the momentum flux in the light. That's why magsails need to extend over much larger areas (though wire-loop magsails have the advantage of requiring a mass along the circumference, not the area). One place that currents in a solar sail might be useful, though, is for attitude control. Run thin wires in a lattice across the sail, with switches at the intersections, and provide a small, distributed torque over the entire structure, rather than trying to pivot the fragile sail with thrusters in a few spots around the circumference, or with payload trim adjustments. In any case, there are better ways to maneuver a solar sail. Remember the 35 degree rule for planar solar sails, they work best when the sunlight hits at about 35 degrees off the normal, maximizing the component of thrust tangential to the orbit, and so changing the energy of the orbit, allowing you to go out from the Sun, or in toward the Sun, with equal ease. If you go to non-planar sails, you can have a focused-beam secondary reflector. The primary reflector is face-on to the sun, and shines the light onto a smaller secondary reflector which can be rotated to provide directional thrust. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Thu Aug 19 13:48:27 EDT 1999 Article: 70025 of rec.arts.sf.science Newsgroups: rec.arts.sf.science Subject: Re: "New spacecraft propulsion method could be out of this solar system" References: <37B8E15C.986FB062@alcyone.com> <37BB4FCB.5E8CAC1A@clark.net> <37bc0286.0@capella.physics.utoronto.ca> <7phavp$4el$1@watserv3.uwaterloo.ca> Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) NNTP-Posting-Host: 128.100.75.114 Message-ID: <37bc4249.0@capella.physics.utoronto.ca> Date: 19 Aug 1999 13:43:37 -0500 X-Trace: 19 Aug 1999 13:43:37 -0500, 128.100.75.114 Lines: 25 Path: capella.physics.utoronto.ca!caliban.physics.utoronto.ca!neufeld Xref: capella.physics.utoronto.ca rec.arts.sf.science:70025 Status: O In article <7phavp$4el$1@watserv3.uwaterloo.ca>, James Nicoll wrote: > > Terrifically stupid question: how opaque are plasmas? It's a >pity that the M2P2 trick can't be used to effectively extend the area >of a light sail. A thousand times 1 cm/s/s is 1 m/s/s, quite a nice >acceleration. > Plasmas are essentially transparent above their cutoff frequencies. The cutoff frequency is a function of the free charge density in the plasma. Metals like aluminum are quite transparent in the ultraviolet because the carrier density is too low to reflect that light. So, naturally, you're looking for a carrier density similar to that of metals in order to obtain optical opacity (in fact, reflectance, which would be even better). Unfortunately, the least mass-intensive way to make a plasma of the required density is ... drum roll please ... to use a piece of metal. The electrons form the plasma without mass loss or confinement issues, and the plasma can be made quite thin by rolling it in a mill or vapour- depositing it on a piece of plastic. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Fri Aug 27 09:10:33 EDT 1999 Article: 70525 of rec.arts.sf.science Newsgroups: rec.arts.sf.science References: <37C59806.30DD62DE@tabletoptelephone.com> <37C6062E.9EB45E24@alcyone.com> Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Subject: Re: L-5 Artsutanov Elevators. From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) NNTP-Posting-Host: 128.100.75.114 Message-ID: <37c68d1a.0@capella.physics.utoronto.ca> Date: 27 Aug 1999 09:05:30 -0500 X-Trace: 27 Aug 1999 09:05:30 -0500, 128.100.75.114 Lines: 32 Path: capella.physics.utoronto.ca!caliban.physics.utoronto.ca!neufeld Xref: capella.physics.utoronto.ca rec.arts.sf.science:70525 Status: O In article <37C6062E.9EB45E24@alcyone.com>, Erik Max Francis wrote: >Hop David wrote: > >> Put a mass at an L equilibrium point. Now there are new equilibrium >> points between the mass and moon and the mass and earth. Put a mass at >> these points. In this fashion could an L-5 colony be built both >> earthward and moonward without causing stress? >> >> I doubt the elevators could touch down but even if they went a >> fraction >> of the distance wouldn't these elevators be a more efficient method of >> moving mass than clawing up a gravity well with rockets? > >But you still have to crawl up the gravity wells, and you still have to >propel yourself back and forth along the new lanes you've just created. >Even if you use some kind of electromagnetic-driven system to get back >and forth along the stalks, you're still going to have to do >stationkeeping on the stalks (since they're simply floating around in >space, with one end in a Lagrange point, but that isn't going to help if >you're using large masses around). > I recall once doing some calculations to show that you could make a tethered lunar skyhook through the Earth-Moon L1 point. In fact, you could make it out of nylon, and still have a useful mass ratio. You might use it to lower things to the moon's surface, since the lack of an atmosphere makes surface launches easier, but landings harder. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed Sep 1 08:19:21 EDT 1999 Article: 70810 of rec.arts.sf.science Newsgroups: rec.arts.sf.science References: <19990831232402.05927.00002441@ng-fv1.aol.com> Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Subject: Re: Unknown TV Show From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) NNTP-Posting-Host: 128.100.75.114 Message-ID: <37cd1891.0@capella.physics.utoronto.ca> Date: 1 Sep 1999 08:14:09 -0500 X-Trace: 1 Sep 1999 08:14:09 -0500, 128.100.75.114 Lines: 14 Path: capella.physics.utoronto.ca!caliban.physics.utoronto.ca!neufeld Xref: capella.physics.utoronto.ca rec.arts.sf.science:70810 Status: O In article <19990831232402.05927.00002441@ng-fv1.aol.com>, Andido wrote: >There was this sci-fi show back in the 80's that I cannot remember the name of. >It was about this guy who was an alien criminal exiled to earth and he had to >find a job and decent living. He was followed around by this cartoonish eyeball >everywhere he went > Probably "Hard Times on Planet Earth". A few details are available in the IMDB. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed Nov 10 09:01:04 EST 1999 Article: 13515 of comp.lang.c.moderated Subject: Re: choose,factorial Approved: clc@plethora.net References: From: Christopher Neufeld Organization: The Puffin Group Return-Path: Reply-To: neufeld@physics.utoronto.ca Newsgroups: comp.lang.c.moderated Message-ID: X-Mailer: Mail User's Shell (7.2.5 10/14/92) Originator: clcm@plethora.net (Comp Lang C'Moderated) Lines: 119 Date: Tue, 09 Nov 1999 18:56:13 GMT NNTP-Posting-Host: 205.166.146.1 X-Complaints-To: abuse@plethora.net X-Trace: ptah.visi.com 942173773 205.166.146.1 (Tue, 09 Nov 1999 12:56:13 CST) NNTP-Posting-Date: Tue, 09 Nov 1999 12:56:13 CST Path: capella.physics.utoronto.ca!utnut!newsflash.concordia.ca!sunqbc.risq.qc.ca!newsfeed.berkeley.edu!hermes.visi.com!news-out.visi.com!ptah.visi.com!not-for-mail Xref: capella.physics.utoronto.ca comp.lang.c.moderated:13515 Status: O In article you write: >What is wrong with the following >code? It gives incorrect (well, different than intended) answers. It's OK >for, say, choose( 25, 0), but try choose( 24, 1). > > >/*******************************************/ >int factorial( int i ) >{ > > > if( i <= 1 ){ > return 1; > } > > return (i * factorial(i-1) ); >} > You have an integer function computing full factorials of numbers around 24 and 25. This is your problem. You're in math, what is that approximate size of 24 factorial? How many bits are in your machine's integers? If you have 32 bit integers, you can represent a number up to 2^31 (one bit is used for the sign), up to about two billions (american billions). You can't represent factorials above 12 (or 12.5 if you're into gamma functions). If your machine has 64 bit integers, you're restricted to about 19 (or 19.98) factorial. You've got three choices. One, is to do the common factor elimination prior to the expansion of the factors. This way, choose(24,1) becomes: 24 / 1 and choose(24, 5) becomes: 24 * 23 * 22 * 21 * 20 / ( 5 * 4 * 3 * 2 * 1 ) Note that this won't save you in some cases. You still won't be able to compute choose(24, 12) this way on a machine with 32 bit integers, as the numerator and denominator are both quite large, even through the answer (2704156) can be represented in an integer. Another way is to multiply out the individual fractions as floats: (24 / 5) * (23 / 4) * (22 / 3) * (21 / 2) * (20 / 1) This works fairly well, though you have rounding error problems, and you're likely to wind up with a number which is almost, but not quite, an integer (so be careful casting it back to your answer, you might truncate a pile of nines and be off by one in the answer). If you want to get sophisticated, write a program which does common factor elimination among the numerator and denominator before multiplying them out. So, it would notice that "24" cancels exactly against (4 * 3 * 2), and 20 cancels against 5 to leave 4, so your computation becomes: 1 * 23 * 22 * 21 * 4 / 1 Note that it is always possible to reduce the denominator to 1, so you can use that as your completion condition for the common factor elimination program. The other way to do it is the way I compute large factorials, using a formula based on the McLaurin series expansion of the log of the gamma function: (z-1)! = e^{-z} z^{z - 1/2} \sqrt{2 \pi} [ 1 + \frac{1}{12z} + \frac{1}{288 z^{2}} - \frac{139}{51840 z^{3}} - \frac{571}{2488320 z^{4}} + \frac{163879}{209018880 z^{5}} + \frac{5246819}{75246796800 z^{6}} ] This gets you a whole bunch of digits. The last two terms took me most of an evening to compute from combinatorics on an old Apple ][, but I'm pretty sure they're correct. Anyway, from this, you can take logs of the numerator and denominator, subtract them, and get the logarithm of the answer. Finally, if you're into black boxes, here's the way I do it in my hp67 emulator program: double factorial(double x) { double wholepart; double fracpart; double fval; fracpart = modf(x, &wholepart); #ifdef HAVE_LONG_DOUBLE_LIBM fval = expl(lgammal(x + 1)); #else #warning Without a libm supporting long doubles your factorial #warning results may be uncertain in the 14th or 15th decimal place fval = exp(lgamma(x + 1)); #endif if (fracpart == 0) /* If the number was an integer, make sure that * the factorial is an integer, too. */ fracpart = modf(fval + 0.5, &fval); return fval; } Posted and emailed to original sender. -- Christopher Neufeld neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" -- comp.lang.c.moderated - moderation address: clcm@plethora.net From neufeld@physics.utoronto.ca Fri Nov 12 15:34:32 EST 1999 Article: 56705 of comp.security.unix Newsgroups: comp.security.unix Reply-To: neufeld@physics.utoronto.ca Organization: The Puffin Group Subject: Sending packets at my lockd From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) NNTP-Posting-Host: 128.100.148.69 Message-ID: <382c7828.0@capella.physics.utoronto.ca> Date: 12 Nov 1999 15:27:20 -0500 X-Trace: 12 Nov 1999 15:27:20 -0500, 128.100.148.69 Lines: 16 Path: capella.physics.utoronto.ca!caliban.physics.utoronto.ca!neufeld Xref: capella.physics.utoronto.ca comp.security.unix:56705 I'm posting this as a bemused administrator. I've got a firewall rule which notifies me when people try things I might not want them to do. One of those things is sending packets at the lockd port, on TCP 4045. Well, I've seen several of those packets come in today. I wouldn't be too surprised, except that the source is really weird. Nov 12 13:28:57 vorlon kernel: Packet log: outside DENY ppp0 PROTO=6 207.25.71.5:80 154.5.69.97:4045 L=60 S=0x00 I=10999 F=0x0000 T=243 (#3) That is, it's coming from the www port on www11.cnn.com. I have a Netscape browser open to cnn.com, but why is their server so interested in my lockd? I got 33 such packets in about 15 minutes. -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Sat Nov 20 23:45:22 EST 1999 Article: 13725 of comp.lang.c.moderated Newsgroups: comp.lang.c.moderated References: Reply-To: neufeld@physics.utoronto.ca Organization: University of Toronto - Dept. of Physics Subject: Re: choose,factorial From: neufeld@caliban.physics.utoronto.ca (Christopher Neufeld) NNTP-Posting-Host: 128.100.148.69 Message-ID: <383774de.0@capella.physics.utoronto.ca> Date: 20 Nov 1999 23:28:14 -0500 X-Trace: 20 Nov 1999 23:28:14 -0500, 128.100.148.69 Lines: 77 Path: capella.physics.utoronto.ca!caliban.physics.utoronto.ca!neufeld Xref: capella.physics.utoronto.ca comp.lang.c.moderated:13725 In article , karmol wrote: >In article , >Christopher Neufeld wrote: >> Another way is to multiply out the individual fractions as floats: >> >>(24 / 5) * (23 / 4) * (22 / 3) * (21 / 2) * (20 / 1) >> >>This works fairly well, though you have rounding error problems, > >A better way is to multiply out the individual fractions as *ints*: > >24/1 * 23/2 * 22/3 * 21/4 * 20/5 > When I first read this, I thought you were implying brackets around those factors, because of the whitespace grouping (and the function which you included below, which does evaluate it as if brackets are around each factor). If this chain of operations is applied from left to right, it will always produce the correct integer value, though overflow is still a danger, as you pointed out. >The probability >of overflow is non-zero, but drastically reduced; (this would also be a >problem for longs, doubles, or long doubles); the only way to fix that >is with arbitrary precision math functions. > One thing about the last method I presented is that you can keep intermediate values as logarithms. You really have to go to pretty big numbers before you start overflowing logarithms. >How about the following (untested) function? > >int choose(int n, int k) >{ > int c = 1; > > if (k > n/2) > k = n - k; > > for (i = 1; i <= k; i++) > c *= n-- / i; > > return c; >} > Well, let's test it, shall we? choose(7,2) = choose(7,3) = choose(7,4) = choose(7,5) = 21 choose(8,3) = choose(8,4) = choose(8,5) = 48 choose(9,3) = choose(9,4) = choose(9,5) = choose(9,6) = 72 it got (7,2) and (7,5) right. This is because of integer division rules in C. The result of the quotient of two positive integers N1 / N2, where N1 and N2 are both in the domain of your integer type, is the largest integer R such that R * N2 is not greater than N1. In your code, first (n-- / i) is evaluated in integer arithmetic, and then the resulting integer is multiplied into 'c'. Some of those ratios are truncated in the process. To use the example above, the function evaluates the following expression: 24 * 11 * 7 * 5 * 4 = 36960 The algorithm you present is properly encoded with the following in the action loop: for (i = 1; i <= k; i++) { c *= n--; c /= i; } -- Christopher Neufeld - Not a graduate student neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Thu Nov 25 09:17:41 EST 1999 Article: 79812 of rec.arts.sf.science Path: news.magma.ca!not-for-mail Newsgroups: rec.arts.sf.science References: <942988690@sheol.org> <38362FAE.3998D7F2@home.com> <81iib901cth@enews4.newsguy.com> Reply-To: neufeld@physics.utoronto.ca Organization: DYNACAN group - Human Resources Development Canada Subject: Re: Zero Point Energy in sci-fi From: neufeld@vorlon.dynacan.org (Christopher Neufeld) Lines: 25 Message-ID: Date: Thu, 25 Nov 1999 14:17:06 GMT NNTP-Posting-Host: 209.217.100.58 NNTP-Posting-Date: Thu, 25 Nov 1999 09:17:06 EDT Xref: news.magma.ca rec.arts.sf.science:79812 Status: O In article <81iib901cth@enews4.newsguy.com>, Tommy the Terrorist wrote: >In article <38362FAE.3998D7F2@home.com> Mark Fergerson, >mfergerson1@home.com writes: >> Robert L. Forward has actually patented a device for extracting ZPE. >>[ ... ] It consists of a bunch of >>tiny "leaves", built of semiconductor, with "motor/generators" >>attaching the leaves to each other. > >I thought there was a law in the U.S. prohibiting the patenting of >a perpetual motion device unless the applicant presented a working >model. > Forward's vacuum energy device is not a perpetual motion machine. It takes advantage of the (experimentally measured) Casimir force between parallel conducting planes. I believe he describes it as a vacuum energy battery. The force is conservative, you charge the battery by applying force to move the plates apart, then you discharge it by allowing the plates to move together, doing work on an appropriate system along the way. -- Christopher Neufeld neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@dynacan.org Wed Dec 1 10:35:23 EST 1999 Article: 2305 of rec.humor.funny Newsgroups: rec.humor.funny From: neufeld@dynacan.org (Christopher Neufeld) Subject: You get a reflective vest, a helmet, and a violin Keywords: smirk, true Approved: funny-request@netfunny.com Path: news.magma.ca!nntp.magma.ca!news1.tor.metronet.ca!news1.mtl.metronet.ca!sunqbc.risq.qc.ca!howland.erols.net!novia!news.netfunny.com!funny-request Followup-To: rec.humor.d Message-id: Date: Tue, 30 Nov 1999 19:30:00 PST Xref: news.magma.ca rec.humor.funny:2305 As one of only three full time employees in my working group, I was required to attend a fire and emergency preparedness seminar, so that I could help others to leave the building in the event of trouble. I work in a federal government building called the "Narono building". The first slide went up, proudly proclaiming this to be the: Narono Emergency Response Organisation It occured to me that, since the primary responsibility of this group is fire evacuation, not much thought had been put into the resulting acronym. -- Selected by Jim Griffith. MAIL your joke to funny@netfunny.com. Join and contribute to the Electronic Frontier Foundation today. \nThis joke's link: http://www.netfunny.com/rhf/jokes/99/Nov/narono.html From neufeld@physics.utoronto.ca Sun Dec 19 19:56:01 EST 1999 Article: 80691 of rec.arts.sf.science Path: news.magma.ca!not-for-mail Newsgroups: rec.arts.sf.science References: <83f137$d8t$1@freenet9.carleton.ca> <385D39EE.F8FAD3B@alcyone.com> <385D670B.4CA1C6DD@alcyone.com> Reply-To: neufeld@physics.utoronto.ca Organization: DYNACAN group - Human Resources Development Canada Subject: Re: EPR Cat paradox? From: neufeld@vorlon.dynacan.org (Christopher Neufeld) Lines: 34 Message-ID: Date: Mon, 20 Dec 1999 00:54:57 GMT NNTP-Posting-Host: 209.217.100.58 NNTP-Posting-Date: Sun, 19 Dec 1999 19:54:57 EDT Xref: news.magma.ca rec.arts.sf.science:80691 In article <385D670B.4CA1C6DD@alcyone.com>, Erik Max Francis wrote: > >Try removing the prearrangement that wavefunction will be collapsed >prior to your observation, and ask yourself what information is >transferred. "Something" is transferred, but it is not information. > Just to reinforce Erik's point a bit, let me wade in with yet another imperfect analogy. Earth founds a colony, let's call it "Sherman's Planet", past Antares, and just as far from Antares as that star is from Earth. Because the star is between Earth and Sherman's Planet, in the event that Antares goes supernova, communications between the two populations might be disrupted. The contingency plan, then, is for Earth to relay communications through another colony if the line of sight is blocked by the glare of the supernova. One day, the people on Sherman's Planet look up and see that Antares has blown up. They instantly know that Earth has seen the same thing, and has redirected their communications array from direct transmission to the one-bounce relay mode. Amazing? No entangled quantum states, purely classical physics. OK, perhaps it would be better to focus the discussion a bit. Let's go back to the Schrodinger's cat thing, and assume I want to send a message at FTL speed. I am permitted to use any number of entangled particles. When the two parties are a light year apart, one of them flips a coin. It comes up heads, and he wants to let the other person know it came up heads (and wants the message to get there in under a year). How does he do it? This is what we mean by transmitting information. I want to send one bit. Show me how. -- Christopher Neufeld neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Sun Dec 19 20:36:09 EST 1999 Article: 80695 of rec.arts.sf.science Path: news.magma.ca!not-for-mail Newsgroups: rec.arts.sf.science Subject: Re: EPR Cat paradox? References: <83f137$d8t$1@freenet9.carleton.ca> <385D670B.4CA1C6DD@alcyone.com> Reply-To: neufeld@physics.utoronto.ca Organization: DYNACAN group - Human Resources Development Canada From: neufeld@vorlon.dynacan.org (Christopher Neufeld) Lines: 37 Message-ID: <5Kf74.1049$B3.3678521@news.magma.ca> Date: Mon, 20 Dec 1999 01:36:01 GMT NNTP-Posting-Host: 209.217.100.58 NNTP-Posting-Date: Sun, 19 Dec 1999 20:36:01 EDT Xref: news.magma.ca rec.arts.sf.science:80695 In article , wrote: >Christopher Neufeld wrote: > >> OK, perhaps it would be better to focus the discussion a bit. Let's go >> back to the Schrodinger's cat thing, and assume I want to send a message >> at FTL speed. I am permitted to use any number of entangled particles. >> When the two parties are a light year apart, one of them flips a coin. It >> comes up heads, and he wants to let the other person know it came up >> heads (and wants the message to get there in under a year). How does he >> do it? This is what we mean by transmitting information. I want to send >> one bit. Show me how. > >Don't flip a coin. Do a measurement of a particle. You do a measurement of >a particle, and it comes up spin-up. You want to let the guy a light year >away know that information as quickly as possible. > No, I'm sorry, I don't care about this information. I want to flip a coin and send a bit based on the outcome. I want to string a bunch of these bits together and use them to send email. The case you mention is uninteresting to me, just as in the supernova example I gave. >Easy. He has the other entangled particle. Right after you measure your >particle, and learn it was spin-up, he measures his, and of course must >find that it was spin-down. He now knows that yours was spin-up. > >Sounds like information to me. > I measure the state of Antares, I see it's spin-supernova. Right after I measure my view of the star, and learn is was spin-supernova he measures his view of the star, and of course must find that it was spin-supernova. He now knows that mine was spin-supernova. Is this information? If it's different, how? -- Christopher Neufeld neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@thepuffingroup.com Mon Dec 20 14:14:51 EST 1999 Article: 336874 of comp.os.linux.misc Path: news.magma.ca!not-for-mail Newsgroups: comp.os.linux.misc,comp.os.linux.networking Reply-To: neufeld@thepuffingroup.com Organization: The Puffin Group Subject: Asking for comments on new HOWTO, setting up a new domain From: neufeld@vorlon.dynacan.org (Christopher Neufeld) Lines: 30 Message-ID: Date: Mon, 20 Dec 1999 19:01:02 GMT NNTP-Posting-Host: 209.217.100.58 NNTP-Posting-Date: Mon, 20 Dec 1999 14:01:02 EDT Xref: news.magma.ca comp.os.linux.misc:336874 comp.os.linux.networking:219333 I just finished moving our office network to a new domain. I figure that my experiences might be helpful to others who want to create a Net presence for their small offices, so I prettied up our internal documentation on the notes and made them into a HOWTO. This is very preliminary, and has pretty heavy emphasis on the particular design choices which I made in setting up my office network. I would like comments and criticisms, in particular any subjects I have left out, or places I provided too much or insufficient detail. For now, the document is available at: http://caliban.physics.utoronto.ca/neufeld/Domain.HOWTO/DOMAIN.HOWTO.html The abstract reads: "This document outlines the things you will probably have to do when you want to set up a network of computers under your own domain. It covers configuration of network parameters, network services, and security settings." The source is in SGML format, so if people would rather see it in some other format, let me know as well, it's easy enough to generate from the SGML. Thank you. Please send any comments to: neufeld@thepuffingroup.com -- Christopher Neufeld neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Tue Dec 21 21:05:02 EST 1999 Article: 80811 of rec.arts.sf.science Path: news.magma.ca!not-for-mail Newsgroups: rec.arts.sf.science Subject: Re: EPR Cat paradox? References: <83f137$d8t$1@freenet9.carleton.ca> <8VB74.966$Ef6.234815@news.shore.net> <_RV74.1086$Ef6.260607@news.shore.net> Reply-To: neufeld@physics.utoronto.ca Organization: DYNACAN group - Human Resources Development Canada From: neufeld@vorlon.dynacan.org (Christopher Neufeld) Lines: 29 Message-ID: Date: Wed, 22 Dec 1999 02:02:16 GMT NNTP-Posting-Host: 209.217.100.58 NNTP-Posting-Date: Tue, 21 Dec 1999 21:02:16 EDT Xref: news.magma.ca rec.arts.sf.science:80811 In article <_RV74.1086$Ef6.260607@news.shore.net>, wrote: >Aaron Bergman wrote: > >> You still haven't accepted the simple fact that this is not a >> message, however. No information is transmitted. > >What is "information?" > >To me, information is the answer to the question: "Did the particle on >Earth that was measured when I was 100 light years out turn out to be spin >up or spin down?" > >The answer to that question is information, by any reasonable sense of the >word. > Let's go back to my supernova example. You're in a spaceship on the far side of Antares, as far from that star as it is from the Sun. Star goes pop. You see the radiation from the supernova, and immediately infer that people on Earth also saw it at exactly the same time, even though there is not enough time for a signal from Earth to get to you telling you that they saw the supernova. If they had promised to kill a cat if the star went supernova before a certain date, then you have instantly deduced the "fact" that the cat is dead. In the same way as in your example. Please, how are these two examples different? -- Christopher Neufeld neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity" From neufeld@physics.utoronto.ca Wed Dec 22 15:12:12 EST 1999 Article: 80829 of rec.arts.sf.science Path: news.magma.ca!not-for-mail Newsgroups: rec.arts.sf.science Subject: Re: D20 "toxicity" question. References: <3861206f.34728526@news.clara.net> Reply-To: neufeld@physics.utoronto.ca Organization: DYNACAN group - Human Resources Development Canada From: neufeld@vorlon.dynacan.org (Christopher Neufeld) Lines: 29 Message-ID: Date: Wed, 22 Dec 1999 20:12:05 GMT NNTP-Posting-Host: 209.217.100.58 NNTP-Posting-Date: Wed, 22 Dec 1999 15:12:05 EDT Xref: news.magma.ca rec.arts.sf.science:80829 In article <3861206f.34728526@news.clara.net>, Andrew Dennis wrote: >Does anyone know (or at least know a good source) for data on how >toxic heavy water - deuterium oxide - is? I've got the New Scientist >piece on what it does to the fluid in your inner ear, thanks, and I've >got a few MSDS that indicate it's dangerous to kidneys and nervous >system in "large quantities". > Go to deja, and read a thread: REQ: inffo on Heavy Water >from 1995. Originally started in groups: sci.physics.accelerators, sci.misc, sci.physics.fusion, sci.med, sci.research, rec.arts.sf.science My contribution to that thread was: a body burden of several percent is usually fatal, deuterium substitution in DNA affects the bonding strength of the "rungs", messing up transcription. There are undoubtably other effects, hydrogen exchange reaction rates get messed up, for example. -- Christopher Neufeld neufeld@physics.utoronto.ca Home page: http://caliban.physics.utoronto.ca/neufeld/Intro.html "Don't edit reality for the sake of simplicity"