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visits member for 3 years, 3 months
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Mar
9
comment Photovoltaic IV data
Everything you're trying to calculate is very straightforward math. For example, for maximum power, you multiply I and V at each point and look for the maximum. For open-circuit voltage, you look at where the IV curve crosses I=0. So you're actually just trying to check whether or not you made a dumb programming error. Made-up data is perfectly adequate for this purpose.
Mar
5
comment Is “dark clothes for winter, light for summer” relevant?
(1) In cold weather, if thermal isolation keeps you warm, then thermal isolation plus sunlight absorption will keep you even warmer. (2) Emissivity is a function of wavelength. Something that looks black is highly emissive for wavelengths around 400-700nm, but not necessarily for wavelengths around 10 microns which is where thermal emission happens. Likewise, something that is visibly white does not necessarily have low emissivity around 10 microns.
Mar
3
answered Physics textbooks that distinguish between laws and definitions?
Feb
28
revised Why viscosity is diffusive?
add context to quote
Feb
28
awarded  Nice Question
Feb
26
comment Is “dark clothes for winter, light for summer” relevant?
If you want to keep warm in the winter, wouldn't it be better to wear black clothes that absorb a higher fraction of the sunlight?
Feb
26
comment Is “dark clothes for winter, light for summer” relevant?
But the biggest problem with this answer is that emissivity is in practice almost always a tiny contribution to heat loss (much less than convection, conduction, evaporation). Even in the shade during daytime, there is plenty of visible light around for a black T-shirt to absorb. I think those silver blankets are designed to be very lightweight and totally impermeable to air and moisture; low IR emissivity is nice but not critically important.
Feb
26
comment Is “dark clothes for winter, light for summer” relevant?
@AlanSE - Even if IR emissivity varies a lot, there is no reason to expect that a white T-shirt would be more "white" in the mid-infrared than a black T-shirt. It could equally likely be the reverse.
Feb
23
answered Why viscosity is diffusive?
Feb
23
answered Continuum limit for solid mechanics
Feb
12
answered Is crystal momentum an operator?
Feb
12
answered Classical and quantum probabilities in density matrices
Feb
9
comment Are the recently observed Dirac monopoles separable?
In a true magnetic monopole, the Dirac string is completely unobservable, even in theory. The string is not a real thing, just a way of describing some of the mathematical manipulations. Is that the case here too?
Feb
8
comment Maxwell equations and symmetry
Don't forget about vectors versus pseudovectors, when you're doing the P transformation.
Feb
1
comment About partially polarized light and the degree of polariztion
#3 - No. For example, if you mix 1 watt of circularly polarized light with 1 watt of unpolarized light.
Jan
30
comment Do holes have wavefunctions?
Normally people bypass the whole discussion by making the single-particle approximation, i.e. not talking about Slater determinants in the first place, but instead treating each electron or hole as an independent particle. Many-particle-effects are taken into account semi-heuristically (if you need higher accuracy) by "exchange forces" and "pauli blocking" etc. etc. (You asked about Slater determinants, so I answered, but this whole topic is not the usual approach.)
Jan
30
comment Do holes have wavefunctions?
An electron-hole excitation is another way to say "move an electron from the valence band to the conduction band". So you would replace one of the valence-band wavefunctions with a conduction-band wavefunction in the Slater determinant.
Jan
29
answered Do holes have wavefunctions?
Jan
29
answered Maximising entropy when energy is shared between systems
Jan
29
comment Why does $E=\nabla\phi$ follow from $\nabla\times E=0$?
en.wikipedia.org/wiki/… - click "show" in the gray box to see a proof