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bio website sjbyrnes.com
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visits member for 3 years, 4 months
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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.
Oct
22
comment How to distinguish between the spectrum of an atom in motion and the one of a scaled atom?
Can you be more specific? Don't forget, the question is "if we decrease all the masses, does it result in decreasing all the emitted photon frequencies by the same ratio?" So the energy levels are supposed to be proportional to the masses. When you say that the hyperfine structure is proportional to me/mp, are you sure you're talking about the absolute energy level differences, rather than some ratio of splittings?
Oct
12
comment Experimentally diminishing random errors for low wavelength UV observations
It's not just photon shot noise right?
Oct
9
comment What challenges needed to be overcome to create (blue) LEDs?
Oops, maybe my info is out of date. Last I heard they could only make bluish-green. :-P
Oct
2
comment Spin via Change of Phase
Are you familiar with this stuff -- en.wikipedia.org/wiki/… ? Your question is very hard to understand. Why do you say "ϕ should remain as ϕ"? What can "happen in two ways"?
Sep
11
comment Definition of mean free time in the Drude model
"Duration" is not a technical jargon term, it's just a word that means "length of time".
Jul
18
comment Total internal reflection and waveguides
Could you clarify, either (1) You want to learn how to derive the Fresnel equations, or (2) You want to know how you can calculate the angle-dependent phase shift starting from the Fresnel equations, or (3) Both.
Jul
14
comment How can molecule of a few angstroms absorb visible light of a few hundred nanometers?
If you want to understand the cross-section or linewidth of an atomic absorption line, then it is not a mistake to compare the size of the molecule to the wavelength of the photon.
Jul
14
comment How can molecule of a few angstroms absorb visible light of a few hundred nanometers?
I disagree. You can learn many interesting things by learning the classical theory of electrically-small antennas (e.g. en.wikipedia.org/wiki/Chu%E2%80%93Harrington_limit ), and applying those principles to atoms interacting with light.
Jul
14
comment How can molecule of a few angstroms absorb visible light of a few hundred nanometers?
I made an animation illustrating how an electron in a superposition state moves back and forth, just like you say in the first paragraph. See en.wikipedia.org/w/…
Jun
18
comment What could magnetic monopoles do that electrically charged particles can't?
There are two good questions here, incoherently mixed together. The first is: "What applications would a real magnetic monopole have?" The second is: "What applications do the magnetic monopole quasiparticles in spin ice have?" But these two questions are unrelated, see en.wikipedia.org/wiki/…
Jun
18
comment What could magnetic monopoles do that electrically charged particles can't?
Your first paragraph is describing the magnetic monopole analogue of a capacitor.
Jun
18
comment What could magnetic monopoles do that electrically charged particles can't?
The Particle Data Group article is about real magnetic monopoles (elementary particles); the ScienceDaily article is about magnetic monopole quasiparticles. They are unrelated, and it is misleading for you to suggest that they are the same thing. See en.wikipedia.org/wiki/…
Jun
18
comment What could magnetic monopoles do that electrically charged particles can't?
@WetSavannaAnimalakaRodVance -- You are misunderstanding Duality Transformations. Magnetic monopoles would behave differently than electric charges because the world is full of electrically-charged protons and electrons, which the magnetic monopoles would inevitably be interacting with. (Among other things.)
Jun
4
comment Why is the phase velocity used in the definition of the refractive index?
No. You cannot define index of refraction using group velocity. "Index of refraction" has a specific meaning in physics. It is a meaning that everybody learns and uses -- 100% of people, not 99%. Likewise, "group index" has a specific (different) definition. Let me ask you: "Why does the word 'velocity' always refer to the time-derivative of position, and never refers to the mass of Jupiter?" The answer is, because it's the way language works. Words have definitions. Otherwise communication would be impossible!
Jun
4
comment Why is the phase velocity used in the definition of the refractive index?
This is a strange question. If you want to talk about "c / group velocity", you call it "group index". If you want to talk about "c / phase velocity", you call it "index of refraction". It's just terminology! Those terms are as good as any. I think what you're really wondering is: "Why are there zillions of formulas that involve index of refraction, and very few formulas that involve group index?"
May
28
comment total noise power of a resistor (all frequencies)
@endolith -- Yes, I just said it was shorted because I wanted my question to be very concrete and specific. If you have a transmission line, it has a series of modes (standing waves), and in thermal equilibrium each mode has kT of energy (or less at high frequency). These modes exchange energy with a resistor: They give energy via joule heating, and get energy via johnson noise. This quantity 1.893E-12W/K2 is related to how fast the energy is exchanging. But, depending on what exactly you're calculating, you may need to take into account impedance matching etc.
May
13
comment Homemade salad dressing separates into layers after it sits for a while. Why doesn't this violate the 2nd law of thermodynamics?
Yes, heating a system increases its entropy largely because the velocity of each molecule has a greater range of possible values. There are other effects too: At higher temperatures, there is more uncertainty in how fast each molecule is rotating, and how much it is stretching or contorting...
May
12
comment Homemade salad dressing separates into layers after it sits for a while. Why doesn't this violate the 2nd law of thermodynamics?
The process creates heat. Wherever the heat goes, that's where the entropy increases. If the salad dressing is thermally insulated, the heat stays there, increasing the temperature and (thus) entropy. That's what user26866 is imagining. In the opposite extreme, the salad dressing might have negligible heat capacity compared to the surroundings, in which case all the heat spreads into the surroundings, so the entropy increase would occur in the surroundings. That's what Art Brown is imagining.
May
9
comment Homemade salad dressing separates into layers after it sits for a while. Why doesn't this violate the 2nd law of thermodynamics?
you mean exothermic