Room-temperature superconductivity?

Point out news stories, on the net or in mainstream media, related to polywell fusion.

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Betruger
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Postby Betruger » Sun Aug 29, 2010 10:30 am

That's a can of worms for sure. Make sure you update Internet Explorer to Internet Explorer 8 if you haven't already. Earlier versions can be as much of a security hole as outdated antivirus software or not-updated Windows.

BenTC
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Postby BenTC » Sun Aug 29, 2010 12:12 pm

The only thing I can think of is that you are not logged in the second time you are trying to edit you post. At the top of each topic, look for whether it says "Login" or "Log out of johanprins" "? At login, do you tick "Log me on automatically each visit" ?

For cleanup, you can't fully trust virus scanners. They just get the easy stuff. Once something is dug in, there are no guarantees it can't lie dormant for a while to evade the virus checking. In addition, there is malware that relies on you accepting their EULA to install it and doesn't self propagate, so technically isn't a virus, so doesn't get picked even though they can cause trouble. So also try running Ad-Aware from http://www.lavasoft.com/ . Also perhaps try http://free.antivirus.com/hijackthis/ lloking particularly at BHOs (Browser Helper Objects) - but for this ask for advice on the associated help site because it doesn't just report problems and blindly removing everythign it notes can break your system.

You might also try Firefox. I've used it for years.
In theory there is no difference between theory and practice, but in practice there is.

ladajo
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Postby ladajo » Thu Sep 02, 2010 5:18 pm


johanfprins
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Postby johanfprins » Thu Sep 02, 2010 7:54 pm

ladajo wrote:Johann,
What do you think of this?
http://nextbigfuture.com/2010/08/superc ... hieve.html


Fascinating. I do not know enough about nano-techniques and cannot make out how they prepared their films. How large is the mesh-size and how do the different regions "mesh"? A nano-mesh seems to me the right direction to go into when taking my model into account. But I will need more information before I put my big foot into it!

ladajo
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Postby ladajo » Thu Sep 02, 2010 8:53 pm

Did you get a look at the pdf?
http://pubs.acs.org/doi/suppl/10.1021/n ... si_001.pdf

I have also invited James Heath to join our discussion here, let's see what happens. IMO it could be very educational for us all.

johanfprins
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Postby johanfprins » Fri Sep 03, 2010 8:29 am

ladajo wrote:Did you get a look at the pdf?
http://pubs.acs.org/doi/suppl/10.1021/n ... si_001.pdf

I have also invited James Heath to join our discussion here, let's see what happens. IMO it could be very educational for us all.


I have downloaded the manuscript and will read it asap. Unfortunately I have a lot f meetings to attend today. What interest me most is why a mesh should affect "pair formation". In my model the charge-carriers are normally stationary and arranged on a lattice (mesh). By improving the quality of the mesh the maximum current does increase. Nontheless, I hope that James Heath will join the discussion.

johanfprins
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Postby johanfprins » Fri Sep 03, 2010 3:02 pm

I will appreciate it if somebody would be kind enough to give me a clear definition of what is meant by a "depairing current" as compared to a "critical current" . Are they they same or are they measured in different ways?

Although the preparation technique used for the nanomesh film can be followed, the results show two curves for Nb bulk film: One for Jc and the other for Jdp.

nogo
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Postby nogo » Fri Sep 03, 2010 4:57 pm

johanfprins wrote:I will appreciate it if somebody would be kind enough to give me a clear definition of what is meant by a "depairing current" as compared to a "critical current" . Are they they same or are they measured in different ways?

Although the preparation technique used for the nanomesh film can be followed, the results show two curves for Nb bulk film: One for Jc and the other for Jdp.


Im not a physicist but this is what I think I know :p and I just hope it helps you some. Excuse the lack of rigour.

"Depairing current" is the theoretically maximum "critical current" that you can achieve on a given superconducting material as per thermodynamics (without losing superconductivity). It is NOT experimentally measurable, you just plug numbers into an equation and solve it.

Critical current can be experimentally measured (naively) by increasing the applied current till the material loses superconductivity. You know this.

Both are temperature dependant among other things (structure and such), hence the graph.

You will notice that there are thus only three experimental measurements, namely Jc for bulk, Jcw for 75 nm mesh and Jcw for 34 nm mesh. and one mathematical "prediction" (Jdp for bulk).

Thus, I realize that, by arranging a given bulk material (or at least Nb) in that particular way we can achieve almost the ideal "critical current" for the bulk material. But what do I know.

I can try to google you some math and references if you need them, but Im not qualified to screen them, just curious.

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Postby johanfprins » Fri Sep 03, 2010 6:10 pm

nogo wrote:"Depairing current" is the theoretically maximum "critical current" that you can achieve on a given superconducting material as per thermodynamics (without losing superconductivity). It is NOT experimentally measurable, you just plug numbers into an equation and solve it.

Thanks, I suspected something like this. Now the "great question": Does this equation come from the Ginzberg-Landau approach or from BCS and its numerous fudge factors?
You will notice that there are thus only three experimental measurements, namely Jc for bulk, Jcw for 75 nm mesh and Jcw for 34 nm mesh. and one mathematical "prediction" (Jdp for bulk).

So this means that the "ideal depairing current" has never been measured for Nb before a mesh of 34 nm was created? Now why do they not tell us how they obtained this current theoretically? This is probably the most important part of the information. They must have "extrapolated" it from measured data; and it is very important to know how and on which assumptions. If it assumes depairing of doubly-charged charge carriers, the model is wrong (according to me :twisted: )

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Postby TallDave » Fri Sep 03, 2010 6:18 pm

This might be helpful to those trying to follow:

http://en.wikipedia.org/wiki/Ginzburg%E ... dau_theory

Things like the nanomesh experiment might be a good opportunity to apply the conflicting theories and see which one comes out better. If you really can explain things better than BCS they can only ignore that for so long...
n*kBolt*Te = B**2/(2*mu0) and B^.25 loss scaling? Or not so much? Hopefully we'll know soon...

nogo
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Postby nogo » Fri Sep 03, 2010 6:44 pm

johanfprins wrote:Thanks, I suspected something like this. Now the "great question": Does this equation come from the Ginzberg-Landau approach or from BCS and its numerous fudge factors?


From Ginzberg-Landau, I believe.

Will dig references and math. No promises.

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Postby johanfprins » Fri Sep 03, 2010 7:33 pm

nogo wrote:
johanfprins wrote:Thanks, I suspected something like this. Now the "great question": Does this equation come from the Ginzberg-Landau approach or from BCS and its numerous fudge factors?

From Ginzberg-Landau, I believe.

Did Ginzberg and Landau know about pairing?

nogo
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Postby nogo » Fri Sep 03, 2010 8:36 pm

Johan, while this is not a substitute for proper references, in the meantime here you got a short pdf with math slides from MIT course on superconductivity talking about Ginzburg-Landay theory + depairing current.

http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-763-applied-superconductivity-fall-2005/lecture-notes/lecture18.pdf

Will post something when I find a proper reference to how the depairing current limit was initially suggested. Im learning on the go, so it will take time.

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Postby johanfprins » Sat Sep 04, 2010 9:07 am

nogo wrote:Johan, while this is not a substitute for proper references, in the meantime here you got a short pdf with math slides from MIT course on superconductivity talking about Ginzburg-Landay theory + depairing current.


Thank you: It gives the derivation of a critical current but does not say why it is called the "depairing current". What "depairs" as far as the Ginzberg-Landau model is describing?

I am of course VERY suspicious of the "order parameter" approach. In effect, it means that we do not know what is going on within a "black box", so we grab a function out of the air, assume that it can be expanded around a "critical temperature" in terms of a series which converges, and then we believe that we are modelling and really understanding what happens within the black box.

Furthermore it is assumed in this case that the order parameter has a phase angle which forms a differentiable scalar field within three-dimensional space, and that the momentum is then magically given by the gradient of this field. The fact is that in terms of its definition, momentum can NEVER constititute a conservative vector field whatsoever. Thus, to me, this is a nonsensical result.

What rattles me even more is that the latter relationship is then used to claim that the circular integral over this conservative vector field can be non-zero; and this "explains" flux trapping!. Any vector field which can be derived mathematically by taking the gradient of a differentiable scalar field MUST be a conservative field. NO circular integral within such a field can EVER be non-zero!

It seems that physicists think it is sufficient just to call he scalar field a phase angle so that the integral must be non-zero around a loop: But mathematics does not care what we call a differentiable scalar field. If it is differentiable, its gradient is a conservative vector field, and since it is a conservative vector field, a loop intergral within it must be always zero.

Furthermore there is no differential wave equation in the world which can generate a harmonic wave with such a spatial dependence for its phase angle. The phse angle of a harmonic wave only changes continiously with position perpendicular to the wave-fronts of a moving coherent wave. AND this change is linear with position. In all other cases the wave angle changes discontinuously and can therefore NOT be differentiated by using a gradient operator.

icarus
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Postby icarus » Sat Sep 04, 2010 11:47 am

jp:
I am of course VERY suspicious of the "order parameter" approach. ...


Inclined to agree.

Any vector field which can be derived mathematically by taking the gradient of a differentiable scalar field MUST be a conservative field. NO circular integral within such a field can EVER be non-zero!


Except in the case where the field contains discontinuous jumps (e.g. branch cuts to a higher plane for the 2-D case, Cauchy residues etc,).

It seems that physicists think it is sufficient just to call the scalar field a phase angle so that the integral must be non-zero around a loop:


Non-zero loop integral scalar fields are easy to interpret as phase angles, because they contain discontinuous jumps producing integral angle residues like pi, n*pi, ...., 2*pi, 2*n*pi, etc.

In all other cases the wave angle changes discontinuously and can therefore NOT be differentiated by using a gradient operator.


Such a function can be treated regularly as long as the singular regions of discontinuity are surgically excluded and treated correctly.


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