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Superconductivity at room temperature?

LFC's Photo LFC 13 September 2018 - 09:13 AM

Sounds like two somebodies still got some serious splainin' to do.
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D. C. Sessions's Photo D. C. Sessions 14 September 2018 - 09:30 AM

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If superconductivity could be harnessed at room temperature, it would allow for the free transport of energy, wildly faster computers, and incredibly precise sensors. Indeed, it would fundamentally change the world.

Mmmmm ... not quite. There are two obstacles to long-range power distribution with superconductors, and temperature is only one of them -- arguably the lesser.

The other is that superconduction is incompatible with magnetic fields. For weak fields, the superconductor excludes the field; that's how you get the liquid-nitrogen cooled [1] object floating above a magnet. Stronger fields, like in medical instruments, the LHC, and power systems kills the superconductivity. The consequences can be can be pretty spectacular. Every superconductor has what's called its "critical field" where the superconductor "goes normal." So if these folk have demonstrated superconductivity on the small scale at temperatures above 273 K, they still have to demonstrate it at high current densities.

[2] Superconductivity at LN2 temperatures is pretty recent itself.
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baw1064's Photo baw1064 14 September 2018 - 05:03 PM

 D. C. Sessions, on 14 September 2018 - 09:30 AM, said:

Mmmmm ... not quite. There are two obstacles to long-range power distribution with superconductors, and temperature is only one of them -- arguably the lesser.

The other is that superconduction is incompatible with magnetic fields. For weak fields, the superconductor excludes the field; that's how you get the liquid-nitrogen cooled [1] object floating above a magnet. Stronger fields, like in medical instruments, the LHC, and power systems kills the superconductivity. The consequences can be can be pretty spectacular. Every superconductor has what's called its "critical field" where the superconductor "goes normal." So if these folk have demonstrated superconductivity on the small scale at temperatures above 273 K, they still have to demonstrate it at high current densities.

The transition temperature which is normally reported is the one at zero magnetic field. The more one lowers the temperature from there, the higher magnetic field the material can support and remain superconductive. But a zero field transition temperature of 273K would mean you can support a very large magnetic field at 77K (liquid nitrogen temperature) and remain superconductive. So not all bad.
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George Rowell's Photo George Rowell 18 October 2018 - 05:00 AM

I wonder if there is an upper limit to magnetic field intensity set by space itself or dark matter. Similarly might gravity have an upper limit.
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D. C. Sessions's Photo D. C. Sessions 18 October 2018 - 07:28 AM

 George Powell, on 18 October 2018 - 05:00 AM, said:

I wonder if there is an upper limit to magnetic field intensity set by space itself or dark matter. Similarly might gravity have an upper limit.

It's ... high. Very, very, very high. 1 Tesla is a pretty strong field: it's more than the saturation field for most ferromagnetic materials.

A neutron star's magnetic field is high enough that you're better off using exponential notation for it rather than writing zeros.

A lithium atom, thanks to the orbital moment of the single electron in the P shell, has a field near the nucleus of (IIRC) something like 10^18 Tesla. So there's lots of room to improve technology before the Universe gets upset.
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George Rowell's Photo George Rowell 18 October 2018 - 01:48 PM

 D. C. Sessions, on 18 October 2018 - 07:28 AM, said:

It's ... high. Very, very, very high. 1 Tesla is a pretty strong field: it's more than the saturation field for most ferromagnetic materials.

A neutron star's magnetic field is high enough that you're better off using exponential notation for it rather than writing zeros.

A lithium atom, thanks to the orbital moment of the single electron in the P shell, has a field near the nucleus of (IIRC) something like 10^18 Tesla. So there's lots of room to improve technology before the Universe gets upset.
If the upper limit is very, very, very high then that would/could make all observations very, very linear. I am not thinking of improving technology so much as getting a general theory. Switching to gravity as a basic force we assume that a huge mass added to another huge mass will be m1 + m2, but it might be very slightly less, depending on what causes gravity.

I believe gravity could be extra-terrestrial, a minor effect of dark matter. Why should gravity suck, why cannot we be pushed down from above. If we have two bodies close to each other and dark matter interacting at a phenomenally low rate, but with incredibly huge numbers of 'gravitons', then it will leave a graviton vacuum in between. The two masses will be PUSHED together by a seemingly weak force. I looked at this once before and concluded that the force between the two would be to the square of the interactions, making a weak force a very very weak force.

Meanwhile far apart bodies would be pushed apart by the same dark matter. If we conclude that there is limited dark matter then it is also reasonable to assume that it would thin out at the edges of the universe and gravity might even become less, not universally the same.
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D. C. Sessions's Photo D. C. Sessions 18 October 2018 - 02:14 PM

I don't think that squares very well with the fact that gravity is a function of density in a Newtonian sense. Also, obviously, not really easy to square with that (quite a few by now) experimental tests of General Relativity and the Equivalence Principle.

In any case, electromagnetism is rather useful from galactic to subnuclear particles so the "limits of magnetic field strength" thing is going to be quite a ways from anything we're likely to run into in the lifetimes of those now living.
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George Rowell's Photo George Rowell 19 October 2018 - 09:30 AM

If gravity or magnetism is ever show to have an upper limit then things could get interesting. In the mean time I will continue to believe that gravity is extra-terrestrial and that we are pushed down from above. It is one of my foibles.
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George Rowell's Photo George Rowell 25 November 2018 - 05:17 AM

 AnBr, on 13 September 2018 - 01:15 AM, said:


And in windmills - but not quite at room temperature.

https://www.engadget...wer/?yptr=yahoo
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