...the problem is that many companies/institutions close the pay period and issue pay stubs well in advance of the pay date. For example, I'm paid on the 1st of the month, but my January 1 pay check is for a pay period that ends December 22 (this Thursday), and by the evening of December 23 I will have an electronic pay stub waiting for me that shows my Social Security deduction for January 1. If Congress extends the tax holiday on, say, December 27, that doesn't leave much time to update the system, re-issue all the pay stubs, and change all the direct deposit information with the banks. Not impossible, but not a real friendly after-Christmas gift to throw to all the HR departments all across the country. And it's no way to run the world's largest economy.
Since flowing current creates a magetic field, you can't use cuprate superconductors to carry large currents. Don't confuse critical fields with critical currents. This paper is talking only about critical fields - it is not trying to describe the amount of current that this material might eventually carry.
You're right that electric current creates a magnetic field. In a type-II superconductor (like the cuprates and these new FeAs materials), this is managed by introducing defects in the material (grain boundaries, inclusions, etc.) that "pin" the quantitized magnetic flux vortices and prevent them from moving through the material and destroying superconductivity. So it's not fair to say that you CAN'T use cuprates to carry large currents - it's just an engineering problem that has to be dealt with by clever manipulation of the structure of the materials.
So here's the short version:
Critical field = intrinsic property of the material.
Critical current = extrinsic property that depends on critical field, grain structure, presence of second phases, etc.
There are a variety of techniques (depending on the application) that manufacturers use to overcome the inherent brittle nature of most superconductors.
For magnet windings, the preferred technique is to fabricate the wire from ductile precursors, draw to final size, wind the coil, and then perform a heat treatment to react the precursors and form the brittle, superconducting phase. This, for example, will be the technique used when brittle Nb3Sn is used in the magnets for the ITER project.
A related solution is to grind the brittle superconductor into powder, insert it into a tube, and use the natural rolling and sliding action of the particles to draw the material into a fine wire that can be subsequently wound into a magnet, with a heat treatment employed to sinter the powder particles back together to form a continuous superconducting path. This is a common technique for MgB2 superconductors.
For non-magnet applications (like power transmission), the preferred technique is to make a tape (e.g. YBCO) that has only a very thin layer of brittle superconductor. Just like a glass fiber, this very thin layer has a very small bending moment in one direction, and so can be spooled (and unspooled) in this direction, allowing you to manage long lengths.
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.
Dude, forces are so boring. I'd much rather explain it in terms of energy.
Clearly, the rocks slide because the total free energy of the system (rock + ground + atmosphere) at the final position is lower than the total free energy at the initial position. Oh, and there is sufficient perturbative energy in the system to overcome any kinetic barriers that might exist during the state-transition process.
That should do it.
Good question - and the answer is superconductors. Conventional electromagnets will consume power at a rate of I^2/R, which gets unmanageable pretty quickly. But superconducting magnets can flow current without any resistive loss, so the energy savings are enormous. Yes, you need to cool the superconductor - but for magnets exceeding ~1 Tesla it's worth it.
IIRC (can't find the study right now...sorry), one of the concerns about the Freakonomics study was that it didn't work across the pond, i.e. the same abortion legalization/crime drop correlation was not seen in Great Britain and other western European countries. It would be interesting if the authors of this study would do a similar analysis with their lead paint/crime drop correlation.
I think partly this is selection bias. I don't know where you live, but even here in the Bible belt (Tallahassee, FL), for every mammoth brick-and-glass sanctuary, there are three dozen little storefront churches and modest 1,500 sq. foot buildings. It's just that you don't notice those when you drive down the street. I'm not standing up for those that do squander vast sums of money on buildings - I'm just saying there are a lot more humble, thrifty congregations than most people realize.
Slashdot Mirror
800 kg must be a typo...the paint alone supposedly weighs 350 kg.
...the problem is that many companies/institutions close the pay period and issue pay stubs well in advance of the pay date. For example, I'm paid on the 1st of the month, but my January 1 pay check is for a pay period that ends December 22 (this Thursday), and by the evening of December 23 I will have an electronic pay stub waiting for me that shows my Social Security deduction for January 1. If Congress extends the tax holiday on, say, December 27, that doesn't leave much time to update the system, re-issue all the pay stubs, and change all the direct deposit information with the banks. Not impossible, but not a real friendly after-Christmas gift to throw to all the HR departments all across the country. And it's no way to run the world's largest economy.
You're right that electric current creates a magnetic field. In a type-II superconductor (like the cuprates and these new FeAs materials), this is managed by introducing defects in the material (grain boundaries, inclusions, etc.) that "pin" the quantitized magnetic flux vortices and prevent them from moving through the material and destroying superconductivity. So it's not fair to say that you CAN'T use cuprates to carry large currents - it's just an engineering problem that has to be dealt with by clever manipulation of the structure of the materials.
So here's the short version:
Critical field = intrinsic property of the material.
Critical current = extrinsic property that depends on critical field, grain structure, presence of second phases, etc.
There are a variety of techniques (depending on the application) that manufacturers use to overcome the inherent brittle nature of most superconductors.
For magnet windings, the preferred technique is to fabricate the wire from ductile precursors, draw to final size, wind the coil, and then perform a heat treatment to react the precursors and form the brittle, superconducting phase. This, for example, will be the technique used when brittle Nb3Sn is used in the magnets for the ITER project.
A related solution is to grind the brittle superconductor into powder, insert it into a tube, and use the natural rolling and sliding action of the particles to draw the material into a fine wire that can be subsequently wound into a magnet, with a heat treatment employed to sinter the powder particles back together to form a continuous superconducting path. This is a common technique for MgB2 superconductors.
For non-magnet applications (like power transmission), the preferred technique is to make a tape (e.g. YBCO) that has only a very thin layer of brittle superconductor. Just like a glass fiber, this very thin layer has a very small bending moment in one direction, and so can be spooled (and unspooled) in this direction, allowing you to manage long lengths.
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.
Dude, forces are so boring. I'd much rather explain it in terms of energy. Clearly, the rocks slide because the total free energy of the system (rock + ground + atmosphere) at the final position is lower than the total free energy at the initial position. Oh, and there is sufficient perturbative energy in the system to overcome any kinetic barriers that might exist during the state-transition process. That should do it.
Good question - and the answer is superconductors. Conventional electromagnets will consume power at a rate of I^2/R, which gets unmanageable pretty quickly. But superconducting magnets can flow current without any resistive loss, so the energy savings are enormous. Yes, you need to cool the superconductor - but for magnets exceeding ~1 Tesla it's worth it.
March 11 - Sir Richard Sharples, Governor of Bermuda, was assassinated in Government House. This seems to be related to violent behavior...
IIRC (can't find the study right now...sorry), one of the concerns about the Freakonomics study was that it didn't work across the pond, i.e. the same abortion legalization/crime drop correlation was not seen in Great Britain and other western European countries. It would be interesting if the authors of this study would do a similar analysis with their lead paint/crime drop correlation.
I think partly this is selection bias. I don't know where you live, but even here in the Bible belt (Tallahassee, FL), for every mammoth brick-and-glass sanctuary, there are three dozen little storefront churches and modest 1,500 sq. foot buildings. It's just that you don't notice those when you drive down the street. I'm not standing up for those that do squander vast sums of money on buildings - I'm just saying there are a lot more humble, thrifty congregations than most people realize.