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New Superconductor Found "Immune To Magnetism"
Lisandro sends in news that testing of the new class of superconductors we discussed a while back (compounds of iron, lanthanum, and rare earths) has turned up a major surprise: magnetism doesn't shut off the superconducting state. Magnetic fields represent one of three factors that limit expanded applications for superconductors (the others are current density and temperature dependence.) The research will appear in Nature; here's a preprint (PDF).
I seem to recall that one limit was simply the ceramic nature of most superconductors. If it isn't ductile, you can't use it for wires -- which are kind of important for most superconducting applications. Am I wrong about this?
Make cheese not war 8:)
These are not "HIGH" temp superconductors yet. They are only working at -400F, so I doubt you could run these in your PSP.
But having a new class of super conductors opens up further research into new high temp ones.
Scanning the paper, it seemed to have little bearing on this magnetic field tolerance, but rather talked about the effects of grain boundaries. Did anyone understand how the paper related to the press release?
"Ah Crappp!!!" - Magneto, 2008
Read that preprint, or at least look at the pictures -- specifically Fig. 6. It's a measurement of the upper critical field (i.e. the magnetic field that destroys the superconducting state) versus temperature. The 90% line (where the resistivity is 90% of its normal-state value) does indeed go off the graph at low temperatures; it extrapolates to about 60 T for 5 K.
There's a big difference between "This material has a very high critical field" (which is what the article said) and "This material has no critical field" (which is what the summary said).
Bugrit! Millenium hand and shrimp!
When will people use standard units? I'm sorry it's a particular gripe of mine; kelvin is the universal scale. The sooner we wipe out imperial units the better (unless anyone else wants to convert to a base 12 system?).
Nothing to see here.
That's really neat and all, but please let me know when they find something that's immune to gravity, as it's essential to a project I'm working on. (I have a deadline.)
Ack - looks like caffeinated_bunsen beat me to the punch. But it bears repeating - this paper certainly says nothing like "this superconductor is immune to magnetism". This material has a very high critical magnetic field, and if they figure out how to improve the connectivity then it might even someday be able to carry a current density of engineering significance. But it certainly is not "immune" to magnetism in any qualitatively different way than any other type-II superconductor out there. Still...it's nice to see that high-temperature superconductivity can be observed outside the cuprate family, and this paper (showing that it also has a high critical magnetic field) should spur some serious R&D work outside the theoretical physics community.
Reasoning is never, like poetry, judged from the outside at all.
I am a condensed-matter physicist but not a superconductor specialist.
The article does not say that the material is immune to magnetism.
The data relevant to this discussion is presented in Fig. 6 in the paper, which is a plot of the upper critical field (the maximum field the material can support and still be superconducting) versus temperature. Look at the traces marked with square markers.
Notice that these curves do not diverge to infinity as the summary would have you believe.
Granted, values in the 50's of Tesla seem pretty big, considering that the ambient magnetic field on Earth is about 0.5 Tesla. But note that other superconductors have critical fields in this same range. The famous high-Tc superconductor YBCO has a critical field of 135 Tesla (ref: http://www.springerlink.com/content/j0128jt30843362u/)
Compared to elemental superconductors, whose critical fields are around 1 Tesla or less, this material does indeed support a lot more magnetic field. But it certainly isn't "immune to magnetism"
Internal resistanceless batteries would make any kind of short circuit very exciting.
But useful for McGuyver!
- 1.5 T is what's used in MRIs (people have died when metallic objects fly around in these fields)
- 16 T will levitate a frog
- 45 T is the strongest magetic field continuously produced in a laboratory.
- 10,000 T is instantly lethal to organic life
Basically we're fine levitating frogs, but probably won't be able to use it as part of an instant-death ray.Superconductors that are immune to interference from magnets would get us further towards Bussard Ramjets. There are other hurdles, like the mechanical strength of the magnetic coils themselves. (So the magnetic forces don't wreck them.) Even if we couldn't make practical ramjets, magnetic sails would also benefit, which would make deceleration of interstellar craft almost "free."
http://en.wikipedia.org/wiki/Bussard_ramjet
This isn't a matter of opinion, it's an international standard. There is a reason decimalisation took place; we have a base 10 number system. If everyone uses their own defined set of units then people waste time when we try and cooperate.
Nothing to see here.
I read an article in the last year that talked about using liquid hydrogen to cool super conducting transmission lines and also being used as an infrastructure to distribute hydrogen for use in cars, fuel cells, etc...
Me too. It was this article in Scientific American.
...when you're writing a game...tweak the difficulty of "Easy" to something [your mother] can cope with. -- onion2k
I am a scientist and so work with Kelvin all the time. However, I think that Fahrenheit is actually a more useful temperature scale for humans than Celsius. Basically, 0F is wicked cold and 100F is wicked hot. It makes sense for how _we_ relate to temperature rather than how water relates to temperature.
A somewhat off-topic digression:
The conventional wisdom on Bussard Ramjets (included in the wikipedia article) is that they reach a terminal velocity due to the drag of collecting the fuel - and asymptotically approach their exhaust velocity. IMHO that's incorrect.
The bug is that the calculation assumes that they must accelerate the collected hydrogen to the velocity of the craft before fusing it, then depend on the fusion energy to re-accelerate it as exhaust.
However, as with the collected air in chemical ramjets, the momentum of the collected material does not need to be discarded. It can be fused on the fly through the ramjet, retaining its original momentum along the flight path (relative to the vessel). Thus the energy of fusion can be applied to accelerating the reaction products toward the rear. None is needed to replace the momentum allegedly lost capturing the fuel.
Now SOME of the axial momentum of the incoming fuel is traded for radial momentum to collect it. But the energy of that "lost" momentum is converted to pressure and temperature, compressing the material like any other gas. There is a drag on the scoop field from this. But when the exhaust expands again after the reaction there is a corresponding thrust against the nozzle field, reconverting the radial expansion of the reaction products to rearward velocity and recovering the "lost" momentum.
If this whole process were lossless there would be no top end to the kenetic energy the ramscoop could accumulate. With less than 100% efficiency in reapplying the compression energy to the mass (both from lost energy and lost mass) there is some drag from collection that is not recovered. (For instance: Mass lost as neutrinos is a non-trivial fraction.) So there may still be a speed limit. But it can be far higher than that calculated by assuming you "stopped" the gas when you "caught" it.
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
A more important near term result would be a cheap Bussard Polywell fusion system.
A high temperature superconductor that is resistant to high magnetic fields would allow significant efficiency gains and eventually miniaturization.
Who knows in 40 years every new home might have it's own fusion reactor in the basement because of this material.
...PUNY HUMANS
"And I can never remember how to do it"
Use Google.
e.g. http://www.google.com/search?hl=en&q=0F+in+C
It does other unit conversions kph to mph, US gallon to UK gallons, currency conversion.
And also stuff like how long it takes to transfer 700MB over a 512Kbps link:
http://www.google.com/search?hl=en&q=700+MB%2F+512kbps
http://www.google.com/search?hl=en&q=700+MB%2F+512Kbps+in+seconds
The sooner we wipe out imperial units the better
.1337.
Just don't tell today's kids that the number of cubic feet in a gallon is
Weeks of coding saves hours of planning.