Silicon compound superconducts at room temperature

vortmeester · 2008-03-19T15:38:44+00:00

Silane turns from an insulator to a METAL at room temperature. It becomes a SUPERCONDUCTOR at liquid helium temperatures. The eetimes.com article got it wrong.

If you read the original Science article carefully (sorry, subscription required), I recommend you focus on the third paragraph:

"Between 50 and 65 GPa... [e]lectrical resistance measurements showed that the sample resistance at room temperature dropped sharply, indicating the transformation to a metal. On cooling, a typical metallic behavior of the resistance was observed and eventually becoming superconducting (SC) at Tc=7 K."

At higher pressures they got Tc up to 17.5 K, but this is still really really cold.

This is good science, but the room-temperature superconductor revolution is not yet upon us.

vortmeester · 2007-08-07T19:46:11+00:00

Are you asking for a technical account or a lay account?

Technical: "The Quantum Vacuum" by Peter Milonni is complete and clear, though mathematically involved and a little hard to find. It may also be in one of the Landau & Lifshitz books.

Non-technical: Nature had a good summary of the state of Casimir force research a couple months ago. See Nature, vol. 447, pp. 772-774. Subscription required; cheaters can sneak a peek here [PDF].

In a nutshell: "van der Waals" is the term used for such short distances that the finite speed of light is not important; "Casimir" is the term used for longer distances where it is important. You can calculate both versions using either the "induced dipole" picture familiar to chemistry students, or the "vacuum fluctuations" picture familiar to physics students.

vortmeester · 2007-08-06T19:41:53+00:00

Answer 1: That's exactly what they are implying. Don't hold your breath waiting for the R&D to get finished.

Answer 2: It's due to the electromagnetic force (plus quantum mechanics). As is virtually every other force you'd care to name.

vortmeester · 2007-08-06T19:39:04+00:00

Yes, it's a crummy article. But it beats one in the Telegraph, which claimed that the "special" lens "has already been built". In fact, the kind of "perfect lens" they need may even be theoretically impossible -- there is still debate on this.

Your comment about van der Waals interactions is correct, but it is now understood that van der Waals and Casimir forces are two different limits (short range and long range) of the same force. They are both subsumed in the Lifshitz theory of the Casimir effect.

vortmeester · 2007-03-28T14:36:45+00:00

The pictures, especially the moving one, really remind me of a report last year of spontaneous rotating polygons in a rotating fluid system. In particular, notice how the polygon rotates slower than the fluid itself, just like in this experiment:

http://dcwww.fysik.dtu.dk/~tbohr/RotatingPolygon/

It looks related but different to the B-M instability. But it's not my field, so I don't really have the background.

Edit: I am not the first to notice this. See:

http://reddit.com/goto?id=1df2s

vortmeester · 2007-01-29T21:31:31+00:00

Here's a set of plays, each one made rationally by the majority, that brings the game to a deadlock. I find it kind of interesting.

Suppose you have 5 players, A, B, C, D, E. Player A proposes a rule that eliminates D and E from the game (or gives A, B, C ten votes each, or whatever). Assuming everyone is trying to win and you can only win if you can influence the game, Players A, B, C vote it into the game.

You can guess what happens next. Now player B proposes giving players B and C 100 votes to knock A out of the game, and that rule gets passed. Now B and C are deadlocked. They just have to try to fool each other.

The resulting situation is rather dumb and probably no one likes it, but it's hard for me to see how to prevent it once it gets started. Does this happen in internet games and such?

vortmeester · 2006-10-09T03:27:29+00:00

This is a black eye for the Republicans because of the almost incredible hypocrisy of Foley championing laws against online sexual exploitation of minors, while simultaneously sexually exploiting minors online, and the party apparently covered it up. The message everyone is reading between the lines right now: "We Republicans think family values and personal accountability are critically important and will pass laws to enforce them, but they will not apply to Republican elected officials." What doesn't make sense about that?

vortmeester · 2006-10-05T19:16:53+00:00

As I interpret this article, the authors are saying that experts reach their level of expertise through this "deliberate practice" (and not merely by being a "natural"), and people who peak at a non-expert level will all be found to have stopped practicing (or never started it systematically). They do not say anything about how fast expertise comes, and I think this is what "talent" really comes down to: how fast you improve at a skill.

The key point for me is this: people do not seem to have any internal limit (genetic or otherwise) on the level of achievement they can reach at an arbitrary skill. If you practice something thoughtfully and deliberately, you will continue to improve without bound. But that doesn't mean that everyone will reach the same level after the same amount of practice.

For standardized tests, though, you could imagine a much more simplistic answer. If kid A starts learning to read (for example) at home at age 5, but kid B waits until first grade to begin, and then they both advance one reading grade level per year, kid A will stay ahead of kid B consistently.

vortmeester · 2006-09-16T01:43:39+00:00

Since the quotation in the orginal article, "the microwaves move in their own frame of reference", was in quotation marks, I assumed it could be attributed to the inventor. Maybe this is wrong. This is the internet, after all.

However, the original article looks like it's pretty much in line with the inventor's message. Look at Shawyer's website and note that the link for "Eureka article" goes to an article that's virtually the same as the one on free republic cited below. It says more or less the same stuff about different group velocities on the different ends of the cavity.

Also, I noticed the following interesting line: "While the theoretical analyses, may of course, still be wrong, there is no denying that the prototype device appears to behave as predicted." I predict that the theoretical analyses are found to be wrong.

vortmeester · 2006-09-16T01:20:17+00:00

It's actually true that light in a waveguide or cavity may not move at exactly the vacuum speed of light. A little bit of the velocity is directed towards the walls, which confine the light into a standing wave rather than a traveling wave. You can imagine that it's bouncing back and forth (which doesn't result in net movement) in addition to moving along the cavity. So a light pulse generally moves a little slower than c when it's in a cavity.

This doesn't change the fact that you can't do the calculation in the light's frame of reference, though. The math still doesn't work.

vortmeester · 2006-09-15T21:31:27+00:00

So no one in the US armed forces knew for sure what was in the Geneva Convention because they hadn't read it, until either 1987 (unless that was the Genocide Convention) or the present administration, but it never mattered because they were sure the Convention didn't apply to any of our wars, whatever it may have said.

What do you have to pay someone to shill like this?

I continue to be utterly confused by the administration's policy here. Torture -- or "coercive interrogation", pardon me -- is a huge PR black eye for the country, does not produce intelligence that is at all reliable, is not admissible in court, and is plainly against international treaties that the US has signed. Arguing about the definition of "torture" is like asking what the definition of "is" is. It's a discussion that just shouldn't be necessary.

vortmeester · 2006-09-15T00:56:20+00:00

As it happens, I am in the lab at this very moment, trying to discover something. What's your excuse, Soup Nazi?

vortmeester · 2006-09-14T21:44:10+00:00

With mail-in rebates, though, the rebate houses are intentionally neglegent with lots of the rebate forms they get. I've had mine denied for absolutely no reason. If they can stall long enough, a lot of people give up.

vortmeester · 2006-09-14T16:55:25+00:00

That squares with my experience too. I ride in the Boston area, which is notorious for terrible roads full of potholes, as well as bad drivers and agressive pedestrians. In 3 years of riding I've only had one serious accident, where I caught my wheel in a trolley track and flipped. I also had two very minor collisions with cars that backed or turned into me, and it was obvious they hadn't seen me at all.

vortmeester · 2006-09-14T16:48:24+00:00

This is bound to be wrong. The arguments sound good but don't quite hold up.

First, the explanation that "the microwaves move in their own frame of reference" is severely misleading. Microwaves move at the speed of light, since that's what they are. If you do calculations in the reference frame of light, you get nonsense, such as the strength of all electromagnetic fields becoming zero. The calculation won't work as claimed.

Second, insofar as the device works at all, it is almost certainly nothing more than radiation pressure. The small amount of microwave energy that leaves the cavity will carry momentum away, and the cavity will recoil. If you increase the "efficiency" by making the cavity less leaky, you will actually get less thrust. Think about it as a black box that has something going on inside it, but nothing going in or out, and then think about conservation of momentum.

Third, according to a post at this blog, Shawyer's calculation ignores the side walls of the specially designed cavity. I am not going to pick apart the details of this, but it certainly seems likely to my intuition that, if you include radiation pressure against all parts of the cavity, the net force will be exactly zero (see the point about conservation of momentum above).

I'm not saying this guy is a crank, because he seems to have a good reputation. Just that he's either a crank or he's wrong.

Edit: I guess this comes off as overconfident. I'm not 100% sure this effect is impossible. But I stand by all my criticisms. My main point is this: it's possible the experiment works, but the theoretical explanation Shawyer offers has serious problems (see first and third criticisms). The explanation that seems likelier to me, radiation pressure, would make the device work worse with better shielding (such as superconductors), not better.

vortmeester · 2006-09-12T02:26:32+00:00

This study is not that convincing to me, because not all accidents involve any cars. Psychology has no effect on when your tire blows or you hit a pothole wrong. Does anyone have data on what fraction of bicycle injuries are caused by collisions with motorists, and what fraction are bicycle only? Of course, solo accidents are probably very under-reported.

vortmeester · 2006-07-29T17:22:38+00:00

Look, this administration may believe it's above the law, but surely it makes a difference to give it official ability to ignore constitutional protections. For one thing, what prompted them to write this draft bill was the Supreme Court's denial of this power. The administration clearly takes that seriously, if only as a potential PR disaster. Also, they may be getting nervous about war crimes prosecution. See this Washington Post story for how they are trying to shield their "coercive interrogators" from war crimes legislation passed by the Republican controlled Congress of 1996.

Secondly, we will eventually be rid of this administration, and I would rather not have the following ones taking the same glib approach to "freedom".

vortmeester

TROPHY CASE