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Jun
15
comment What does the work on a current carrying wire in a Magnetic Field?
Related: physics.stackexchange.com/questions/89398/… and links therein.
Jun
6
comment What's the relationship between glow and arc discharge?
Your perceptive question caused me to completely revise my answer (after considering deleting it). Thank you! I think I've got a better handle on things now.
May
22
comment What experiments compete with BICEP 2, and when are their results expected?
@annav: Good luck with your lecture!
May
22
comment What experiments compete with BICEP 2, and when are their results expected?
@annav: I agree that BICEP2's result including foreground model DDM2 is (just) consistent with Planck's upper bound, although BICEP2 still considers it to be in tension with Planck (section 12). The recent criticism of the BICEP2's result is that the DDM2 foreground model's B-mode levels are too low, so the r-range should move lower (improving agreement with Planck), and the 5.9 confidence should drop. (See the link in my previous comment.) In fact, BICEP2 is now waiting for a measured dust map from Planck (due this fall) to replace the DDM2 model. The message is "patience".
May
22
comment What experiments compete with BICEP 2, and when are their results expected?
@annav: BICEP2 claimed $5.9 \sigma$ for a cosmological signal, i.e. after subtracting out the dust. That number is under pressure. All reviewers I have read agree with you that BICEP2 has seen a B-mode signal "in the sky". The question is whether they understand the foreground contributions. (In fact, they have no error bars on their foregrounds!) Again, BICEP2 themselves acknowledge the tension.
May
22
comment What experiments compete with BICEP 2, and when are their results expected?
@annav: As I excerpted above in comments 3-5, the BICEP2 paper itself acknowledges the tension. (After all, it claims a signal at $5.9 \sigma$ confidence, while Planck sees nothing.) By the way, BICEP2's handling of the dust foreground is under intense pressure; see here: pcts.princeton.edu/PCTS/SpecialEventSimplicity2014/…
May
14
comment Child-Langmuir Space Charge Law for Non-Zero Cathode Potential (Non-Zero Initial Electron Velocity)
These formulas might be attempts to combine two effects: 1) the actual anode-to-cathode accelerating voltage potential $V_{AK}$, which can only depend on the difference between the two potentials, 2) an "effective" (e.g. fake) cathode potential $V_{eff}$ that models the initial velocity of the electrons that are "boiling" out of the heated cathode.
May
11
comment Homemade salad dressing separates into layers after it sits for a while. Why doesn't this violate the 2nd law of thermodynamics?
I very much like your approach, and agree with your conclusion, but think one detail is a bit off. See my answer.
May
10
comment What is $vdp$ work and when do I use it?
Nice, thanks. I think the point of the answer by Bryson S. is that $H_{exit}=H_{entry}-W$ for an adiabatic process, where $W$ is the (positive) work output of the shaft, so $H$ decreases as shaft work is performed.
May
7
comment Is there a compound denser than the densest element?
As a rejected edit noted, osmium forms toxic osmium tetroxide when exposed to the oxygen in air (ref wikipedia). Do not suggest it!!!
Apr
28
comment Stability of rotation of a rectangular prism
@dmckee: You may appreciate Terry Tao's answer to this question on Math Overflow: mathoverflow.net/questions/81960/… (also linked at the end of JoeHobbit's answer). I find it quite satisfying (albeit a bit embarrassing to have a mathematician provide such a clear, physical answer). It's a lot of words, but well worth going through!
Apr
28
comment Stability of rotation of a rectangular prism
@fffred: I think Terry Tao's answer on MathOverflow (the one I presume you are referencing) works. For case (1), a displacement of the light masses $m$ out of the plane of rotation would be countered by the centrifugal force. Only in case (3) is this displacement amplified.
Mar
18
comment What experiments compete with BICEP 2, and when are their results expected?
@innisfree: The quote above, from the BICEP paper, shows that BICEP acknowledges tension with other experiments and doesn't currently have a resolution.
Mar
18
comment What experiments compete with BICEP 2, and when are their results expected?
@innisfree: I don't get it: your model would be disproved by the measurements. Are you saying that Planck and/or BICEP2 are misinterpreting their data? That makes sense, but the fact remains that they are now claiming results for r that don't appear to be consistent. That's the tension that needs to be resolved.
Mar
18
comment What experiments compete with BICEP 2, and when are their results expected?
@innisfree: Both experiments reported their results in terms of the same parameter (r), and those results disagree.
Mar
18
comment What experiments compete with BICEP 2, and when are their results expected?
This "most likely" value of r is barely consistent with Planck's upper bound. (Why didn't they report it as the headline number?)
Mar
18
comment What experiments compete with BICEP 2, and when are their results expected?
These high values of r are in apparent tension with previous indirect limits based on temperature measurements and we have discussed some possible resolutions including modifications of the initial scalar perturbation spectrum such as running. However we emphasize that we do not claim to know what the resolution is."
Mar
18
comment What experiments compete with BICEP 2, and when are their results expected?
"Subtracting the various dust models and re-deriving the r constraint still results in high significance of detection. For the model which is perhaps the most likely to be close to reality (DDM2 cross) the maximum likelihood value shifts to r = 0.16 +0.06 -0.05 with r = 0 disfavored at 5.9σ.
Mar
18
comment What experiments compete with BICEP 2, and when are their results expected?
@DavePhD: Interesting. This portion of the conclusion of the BICEP2 "Detection" paper acknowledges the "tension":
Mar
17
comment What was the major discovery on gravitational waves made March 17th, 2014, in the BICEP2 experiment?
Related: resonaances.blogspot.com/2014/03/curly-impressions.html