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Twisted graphene has become the big thing in physics

quantamagazine.org

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Re: Twisted graphene has become the big thing in physics

#71

Post by garmaine »

soulofmischief wrote: post #65
ouid wrote: post #36

Earlier quoted context omitted.

no, what I'm talking about is more like a perfectly circular orbit around the sun, where the direction of the acceleration is always exactly perpendicular to the motion.

But there is no perfectly circular orbit around the sun. The mass of the two bodies causes the center of mass to be slightly off center from the sun, and both the sun and earth orbit around this center of mass in a fashion that AFAIK loses energy.

If the two objects were either perfect spheres or tidally locked, then a circular orbit would continue forever. There are no losses due to pure motion in a vacuum.

Re: Twisted graphene has become the big thing in physics

#72

Post by eleitl »

YorkshireSeason wrote: post #55
georgeburdell wrote: post #47

Earlier quoted context omitted.

Pretty typical of academia. Grad students also don't normally get Nobels

And for good reason. A responsible supervisor will typically give PhD students tasks that he has already "kind-of / sort-of" worked out as feasible. I once read the following recommendation for how to set dissertation subjects, I can't recall by whom. - BSc thesis: what I can do over lunch - Master thesis: what I could do in an afternoon - PhD thesis: what I could do in a week (Here the figures don't mean typing, pro…

None of this applicable for hard experimental sciences like physics and chemistry. You can't shortcut bench time, especially since it involves a lot of trial and error. And sometimes it doesn't work out, at all.

Re: Twisted graphene has become the big thing in physics

#73

Post by mikhailfranco »

fsh wrote: post #64
m12k wrote: post #63

Earlier quoted context omitted.

Yeah, imagine if we could more or less losslessly transfer electricity over vast distances. Massive renewable energy farms could be built wherever there was sun/wind/rivers whether the energy consumers are close or not. Energy could be sent to pump water into reservoirs as huge centralized batteries. The problem with 'what happens when the sun isn't shining/the wind isn't blowing' could be sidestepped because it's al…

People seem to underestimate how efficient regular power lines are. The continent-spanning european power grid has a total transmission loss of about 6% using 19th century technology (transformers and copper wires). Modern high voltage DC lines can perform even better. The main limitation seems to be that people don't want to have power lines in their back yard. Not something that superconductors are going to sove.

Interesting video on Chinese 'supergrid' from coal plants in the west, to the population centers in the east, a total length of 3,324 km (2,065 miles):

https://www.youtube.com/watch?v=wfG0USvDTew&t=686s

To increase efficiency, they are increasing the voltage to 1.1 MV:

https://www.youtube.com/watch?v=wfG0USvDTew&t=780s

Re: Twisted graphene has become the big thing in physics

#74

Post by londons_explore »

fsh wrote: post #64
m12k wrote: post #63

Earlier quoted context omitted.

Yeah, imagine if we could more or less losslessly transfer electricity over vast distances. Massive renewable energy farms could be built wherever there was sun/wind/rivers whether the energy consumers are close or not. Energy could be sent to pump water into reservoirs as huge centralized batteries. The problem with 'what happens when the sun isn't shining/the wind isn't blowing' could be sidestepped because it's al…

People seem to underestimate how efficient regular power lines are. The continent-spanning european power grid has a total transmission loss of about 6% using 19th century technology (transformers and copper wires). Modern high voltage DC lines can perform even better. The main limitation seems to be that people don't want to have power lines in their back yard. Not something that superconductors are going to sove.

Since the population and the generation is intermingled, the average joule of energy actually doesn't travel far. Perhaps only a few hundred km.

Re: Twisted graphene has become the big thing in physics

#75

Post by Arbalest »

garmaine wrote: post #71
soulofmischief wrote: post #65

Earlier quoted context omitted.

But there is no perfectly circular orbit around the sun. The mass of the two bodies causes the center of mass to be slightly off center from the sun, and both the sun and earth orbit around this center of mass in a fashion that AFAIK loses energy.

If the two objects were either perfect spheres or tidally locked, then a circular orbit would continue forever. There are no losses due to pure motion in a vacuum.

I thought the theme of my reply is that we're not talking about theoretical constructs, but instead reality... Space is not a vacuum, just much lower pressure than on earth.

Re: Twisted graphene has become the big thing in physics

#78

Post by londons_explore »

kingkongjaffa wrote: post #67
fsh wrote: post #64

Earlier quoted context omitted.

People seem to underestimate how efficient regular power lines are. The continent-spanning european power grid has a total transmission loss of about 6% using 19th century technology (transformers and copper wires). Modern high voltage DC lines can perform even better. The main limitation seems to be that people don't want to have power lines in their back yard. Not something that superconductors are going to sove.

Also the cost of a equivalent superconductor network would be an order of magnitude more expensive that what is essentially room temperature metal cables with very basic technology - transformers, insulation, and switchgear.

A superconducting power network could be built today - it would consist of a pair of ceramic superconductors suspended in a liquid helium pipe, wrapped with 3 feet of insulation.

Every few kilometers, one would need liquid helium pumping and chilling plants.

Total helium losses to leakage wouldn't be too big. Electricity transmission efficiency would be reduced by all the chilling gear running, but still better than regular conductors.

The only real barrier is cost. Not even the cost of the superconducting material. You can't hang a 6 feet diameter pipe on pylons across the nation - you're going to have to bury it, and that's going to get exxxxxpensive fast!

Re: Twisted graphene has become the big thing in physics

#79

Post by ekingr »

ezequiel-garzon wrote: post #76

Does anybody know if the environmental impact of graphene is supposed to be any better than that of plastic? Does it break down more easily as it is so thin? I’m worried we may outdo ourselves with the magic compound of the century...

Another major 'environmental' impact that may be very nefarious is the health effect of such nano-materials.

We don't want to re-create all the mess that we have today form asbestos -- which was also a wonder-material at the time.

Re: Twisted graphene has become the big thing in physics

#80

Post by phkahler »

rezeroed wrote: post #77

Is this a bigger thing than borophene which was a big thing a few weeks ago?

I'm gonna say "no". This is only relevant in that it might lead to better understanding of superconductivity. When the models can predict this, they will have made progress.
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