6,129 reputation
928
bio website sjbyrnes.com
location Massachusetts
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visits member for 3 years, 1 month
seen 21 hours ago

May
30
accepted Formalism for BEC with short-distance sub-structure “corrections”
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
28
asked Formalism for BEC with short-distance sub-structure “corrections”
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
11
awarded  Nice Answer
May
9
revised What is happening to the electrons, and E & H fields, in an antenna with a standing wave inside?
added 73 characters in body
May
9
revised What is happening to the electrons, and E & H fields, in an antenna with a standing wave inside?
added 37 characters in body
May
9
answered What is happening to the electrons, and E & H fields, in an antenna with a standing wave inside?
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
May
9
answered Homemade salad dressing separates into layers after it sits for a while. Why doesn't this violate the 2nd law of thermodynamics?
Apr
27
comment Why do tunneling photons outrace their non tunneling counterparts in vacuum?
You can calculate the group delay (aka "phase time") easily, e.g. using the classical transfer matrix method. And when you calculate the group delay, you'll find that sometimes it happens to be less than the speed of light over the thickness. So that is already a "theory that explains it", if you ask me.
Apr
27
comment Why do tunneling photons outrace their non tunneling counterparts in vacuum?
When they say "no one has any explanation", they mean "no one has any intuitive explanation". Even more accurate: "no one has any explanation that I personally find to be sufficiently intuitive". There is no scientific mystery here: The math and physics of light propagation through multilayer coatings is extremely straightforward and well understood. They are stating a subjective judgment related to pedagogy. (A judgment which I would disagree with.)
Apr
27
comment Why do tunneling photons outrace their non tunneling counterparts in vacuum?
@user45342 -- Yes, I agree with all that.
Apr
27
revised Why do tunneling photons outrace their non tunneling counterparts in vacuum?
added 16 characters in body
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, ...