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bio website sjbyrnes.com
location Massachusetts
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visits member for 3 years, 11 months
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Apr
13
comment By what maximum amount can we concentrate sunlight?
The real limit is that you see the sun in every direction, not just the upper hemisphere of directions. Mirrors do exist! The upper hemisphere alone should only give you 25000x, iirc. You must have made an error but I'm not sure what.
Apr
6
comment How to calculate liquid pressure regardless of the gravity?
Two questions: (1) Do you know n (number of air molecules)? (2) Is the balloon made of a stretchy elastic material like rubber? (If so, the rubber provides almost all the pressure and the water outside can be ignored!)
Mar
23
comment Can a nuclear bomb be used as the power source for a laser beam
See en.wikipedia.org/wiki/Nuclear_pumped_laser but I don't know any details
Feb
16
comment What is thermodynamic equilibrium?
@EnochArden - The laws of thermodynamics are not axioms handed down by God. They are consequences of statistical mechanics, just as all macroscopic laws of physics can be derived from microscopic starting points. See any statistical mechanics textbook for detailed derivations.
Feb
16
comment What is thermodynamic equilibrium?
@EnochArden - The velocity distribution of a gas is macroscopically measurable - look at doppler shifts of spectral lines for example - as is whether light satisfies a blackbody distribution etc. I take the Boltzmann distribution as a starting point: P~exp(-E/kT). There's a letter "T" in that formula, it's a parameter, and everybody refers to this parameter as "temperature". That's all I mean by "temperature", there's nothing circular there.
Feb
13
comment Confusing Chemical potential of mixtures
I don't think there is any sensible or useful way to define chemical potential for a liquid mixture. So I would say it has no chemical potential. Lots of things do not have a chemical potential: The color orange, beauty, etc. :-D Chemical potential is a useful concept to the extent that something maintains its identity in different environments, and is usually (or always) conserved, loosely speaking. So it's a very useful concept for atoms or molecules, but not really for a liquid mixture, since the composition can easily and smoothly change.
Feb
12
comment Confusing Chemical potential of mixtures
What is "chemical potential of the total fluid"? I suspect that there is no such thing.
Feb
4
comment Probability of fluorescence: matching of binding energy and incoming radiation energy?
The binding energies are given by the "K edge", "L edge", etc.
Jan
10
comment Local EPR-experiments with photons in vacuum?
Indeed, the line from A to B is something called a "null interval" which is totally entirely completely unrelated to the concept of "empty intervals" of real numbers in high-school math. These two things are just as unrelated as the "intervals" in music theory and in aerobics. That's why I still think you should mentally rename it a "null shminterval".
Jan
9
comment Local EPR-experiments with photons in vacuum?
Indeed, I am saying that the term "null interval" in special relativity has a very very different definition than an "empty interval" in the sense of intervals of real numbers. If you don't believe me, try looking up the former definition in an SR textbook, and then looking up the latter definition in a high school math textbook. You will see that they are completely different and unrelated.
Jan
9
comment Local EPR-experiments with photons in vacuum?
Sometimes words have multiple meanings. You found an article called "Interval (mathematics)" which has a certain definition of "Interval". But you are wrong to conclude that this is the universal and only definition of the word "Interval". The more relevant article is en.wikipedia.org/wiki/Interval , which proves that the word "Interval" has at least 15 different definitions. The word "interval" in the context of special relativity means something different than the the word "interval" in the context of the number line, just as it means something different in music, or in sports. :-D
Jan
9
comment Local EPR-experiments with photons in vacuum?
When you say "all properties of an interval", I think you mean "all the properties that I intuitively expect an interval to have", but your intuition is wrong because your intuition is based on a lifetime of experience with Euclidean geometry. Well, you're entitled to have the opinion: Anything that deserves to be called an interval must certainly have the following properties...!. But you must understand that other people do not feel this way. That's why I suggest that you mentally replace the word "interval" with "shminterval", a made-up word which is therefore free of your preconceptions.
Dec
10
comment Is there a relation between (non-) existence of magnetic monopoles and thermodynamics?
I don't understand what point you're trying to make. Are you trying to prove "If there are magnetic monopoles, nothing is thermodynamically reversible?" Or "If there are magnetic monopoles, then everything is thermodynamically reversible?" Or "If there are magnetic monopoles, the second law of thermodynamics is false"? Or what?
Dec
7
comment What limits the doping concentration in a semiconductor?
Well, you can write it in terms of "enthalpy of mixing" etc. But if you tell me two atoms, I cannot tell you the solubility limit (or the enthalpy of mixing or anything else useful) except by experiment or numerical simulation.
Dec
4
comment Stimulated emission direction
You should look up optical amplifier - scholarpedia.org/article/Optical_amplification en.wikipedia.org/wiki/Optical_amplifier and more specifically gain guiding rp-photonics.com/gain_guiding.html
Dec
4
comment Why does a thermoelectric generator need both p and n elements?
I don't see any reason that ohmic losses are an inevitibly large problem in the design I drew, if you make reasonable choices about geometry etc. I agree that a large voltage is more practically useful in the final output, but it's not a big deal, you can always put a step-up voltage converter at the device output.
Dec
4
comment Why does a thermoelectric generator need both p and n elements?
Copper has 400X larger thermal conductivity than BiTe. So if you compare the heat conductance of a 1-meter-long, 1mm-diameter copper wire with the heat conductance of a 10cm^2, 1mm-thick BiTe, the BiTe will conduct more heat than the copper wire ... by a factor of 2000.
Dec
4
comment Why does a thermoelectric generator need both p and n elements?
You say "heat will be conducted away from the hot junction by the wire itself, so no electricity will flow." (I assume you mean "electrical current" not "electricity".) I don't understand how you reach that conclusion. Some heat will surely flow through the wire, but not all of it, indeed probably almost none of it. A long thin copper wire has a very low thermal conductance. In the design I drew, it is entirely possible to have 99% of the heat flow through the thermoelectric material and 1% flow through the wire. Then why should heat flow through the wire make any difference at all?
Nov
10
comment How to convert RGB values to physical radiometry and/or photometry quantities and back?
A few nitpicks... All modern displays and printers use sRGB, which is gamma-corrected. So you're correct that it's not logarithmic. But it's not linear either. Also, plenty of hardware can provide more accurate colors than 255-255-255, even though not all programs take advantage. See en.wikipedia.org/wiki/Color_depth
Oct
22
comment How to distinguish between the spectrum of an atom in motion and the one of a scaled atom?
OP's description isn't correct, and this is a good proof. Upvoted! However, there is something along those lines that works. If I set hbar = c = 1, I can scale all quantities with units of eV^N by a factor of 10^N. So I would increase masses and energies and frequencies by 10X, I decrease lengths and durations by 10X, etc. That would definitely be a consistent way to scale the wavelength of every spectral line. See my answer.