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bio website sjbyrnes.com
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visits member for 3 years, 2 months
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Apr
27
revised Why do tunneling photons outrace their non tunneling counterparts in vacuum?
added 9 characters in body
Apr
27
answered Why do tunneling photons outrace their non tunneling counterparts in vacuum?
Apr
25
awarded  Nice Answer
Apr
25
comment Why use lasers for intense, localized heat instead of some other light source?
@BenRW -- You're right, I should have said "on the surface of the sun with a mirror overhead", for the maximum theoretically-possible intensity. I was wrong by a factor of two. However, if we're talking about laser cutters, you can't usually heat an object by illuminating it from all directions at once. If it's the surface of an object, you can only access it from one hemisphere obviously. And usually you illuminate it from a much smaller angular range than that. (A high-numerical-aperture lens would be impractical in a laser cutter for many reasons!)
Apr
25
comment Why use lasers for intense, localized heat instead of some other light source?
@BlackbodyBlacklight -- Yes, various flashtubes and discharge and arc lights have much higher intensity than focused sunlight (although still not nearly as much as a powerful laser). These have plenty of applications. But lasers are much more diverse. For example, for thermal emission, you get higher intensity by increasing temperature, but that also tends to decrease the wavelength towards UV. But lasers can also give you high-intensity infrared light, if that's what you want. And lasers can be solid, liquid, gas, low-voltage, high-voltage, ...
Apr
24
answered Why use lasers for intense, localized heat instead of some other light source?
Apr
22
answered Franck and Hertz graph function
Apr
22
comment Dielectric constant of water
At low frequencies you can bet that the conductivity is independent of frequency. But that means that the imaginary part of permittivity is inversely proportional to frequency, i.e. goes to infinity as the frequency approaches zero. en.wikipedia.org/wiki/Mathematical_descriptions_of_opacity
Apr
16
comment Why isn't there a potential difference across a disconnected diode?
Related (possible duplicate): physics.stackexchange.com/questions/86843/…
Apr
3
comment What does a $SU(2)$ doublet really mean?
I wrote up a pretty basic explanation on wikipedia a while ago: en.wikipedia.org/w/…
Apr
3
comment Why is cold fusion considered bogus?
UPDATE (via email): Ron sees now that the Hagelstein bound forbids an incoherent reaction. This rules out the incoherent process he proposed as the explanation for the excess heat experiments, the radiation observed is too low. This points to coherent processes, and he is now exploring coherent versions of the same process, to complete Hagelstein's model, which he believes is entirely sound, and if the appropriate modes are identified, should explain the phenomenon.
Apr
2
comment Could one measure a stick to an arbitrary precision by having its length estimated by enough people?
@ParthVader : Optical illusions are a reasonable way to talk about observational bias in the context of visually estimating lengths -- which is what this question is about. But yes, observational bias comes in many forms.
Apr
1
answered Could one measure a stick to an arbitrary precision by having its length estimated by enough people?
Mar
28
comment Can a burning laser be directed through fiber optics?
If the beam is too powerful and the fiber is too long (e.g. a kilowatt traveling a kilometer), the beam will lose intensity due to stimulated Brillouin scattering. Normally there's no reason to bring a laser beam such a long distance ... except in the oil industry. foroenergy.com/technology
Mar
28
comment The value of one atomic mass unit
$1.66\times 10^{-27} = (6.02\times 10^{26})^{-1}$ :-D
Mar
28
asked Why doesn't Fermi's golden rule distinguish attraction from repulsion?
Mar
26
answered Does optical fiber preserve the angles of incoming light?
Mar
22
comment Is there a sound theoretical argument against inner-shell induced nuclear chain reactions?
For example, the question asserts that Auger deuteron emission is far more likely than Auger electron emission. Therefore, the fact that X-ray emission is likelier than electron emission, as you say, does not preclude the possibility that deuteron emission is more likely than either. You are entitled to argue that the question's assertion is wrong, but that's not what you did. You just ignored the assertion ... as if you hadn't even read the question.
Mar
22
comment Is there a sound theoretical argument against inner-shell induced nuclear chain reactions?
@DavePhD -- The muon is a postulated seed -- the main question is about the chain reaction, not the seed. The chain reaction is indeed supposed to involve fast charged alpha particles, not x-rays. The fusion chain reaction is supposed to happen in a room-temperature tabletop apparatus, not in a billion-dollar facility like NIF or ITER. (Have you heard of cold fusion? You need to look it up if you want to understand the question.) Anyway, from everything you've written, I get the strong impression that you don't understand the question being asked. You should re-read the question.
Mar
20
comment Band gaps: are they at the centre or at the edge of the Brillouin zone?
If I have a transition from the center of the first BZ, to the boundary between the second and third BZ, I would NOT describe this transition as a "band gap ... at the edge of the BZ".