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bio website sjbyrnes.com
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Mar
16
reviewed Approve suggested edit on When I stretch a rubber band, it breaks. When I hold the broken ends together, why doesn't it join again?
Mar
16
reviewed Approve suggested edit on Why does a candle blow out when we blow on it? Our breath is 16% oxygen and only 4% CO2
Mar
16
comment Is there a sound theoretical argument against inner-shell induced nuclear chain reactions?
In the mechanism under discussion, the (alleged) inner-shell holes are created not by x-rays but by fast charged particles. A 20MeV alpha could theoretically create a hundred 20keV deuterons by slamming into them all almost dead-on, but this is extraordinarily unlikely. OTOH, if the alpha is traveling through Pd, it can quite frequently create a hundred inner-shell holes. ALSO, this is allegedly a three-body fusion process where the palladium atom is one of the bodies. So in summary I don't know how you could say that the palladium lattice is not helping ... it's critical!
Mar
16
comment Is there a sound theoretical argument against inner-shell induced nuclear chain reactions?
A deuteron cannot just absorb an x-ray and wind up with extra kinetic energy. Such a process cannot satisfy energy-momentum conservation. (Proof: Think about it in the center-of-mass frame.) That's why your description of ordinary Auger emission -- first an x-ray is literally emitted, then another electron absorbs it -- cannot be correct, even if you found a book that says it. The book is wrong, it's electrostatic. If you look at theoretical papers calculating Auger rates and shifts you'll find that specialists agree it's electrostatic.
Mar
14
awarded  Investor
Mar
11
comment Getting nonphysical results when solving for the index of refraction of a slab?
@YungHummmma -- No, I don't know what he was talking about. This is not a near-field measurement. The light source and detector are both many many wavelengths away from the sample.
Mar
11
comment Getting nonphysical results when solving for the index of refraction of a slab?
I suspect that you're taking your data too literally. It would not be at all surprising for this kind of data to be systematically shifted up or down a bit compared to reality. Mirrors may not be perfectly reflective, samples can scatter some light, optics may not be perfectly aligned, some light might hit the non-suspended part of your sample, etc. You need more constraints in your fitting -- not only $n_r > 0$ but also assuming some functional form consistent with kramers-kronig.
Mar
11
comment Getting nonphysical results when solving for the index of refraction of a slab?
Plane wave model is fine. For example, in ellipsometry, you use a plane wave model to characterize oxide layers that are one or two atoms thick!
Mar
11
revised Phonon scattering process in raman spectroscopy
deleted 11 characters in body
Mar
11
revised Phonon scattering process in raman spectroscopy
added 171 characters in body
Mar
11
comment Getting nonphysical results when solving for the index of refraction of a slab?
How thick is it? How did you measure the thickness? What wavelengths are these? Your experiment was actually measuring a slab with air on both sides, just like how you simulated it, right?
Mar
11
answered Phonon scattering process in raman spectroscopy
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.