The h Bar

4:52 AM

a partial lunar eclipse will occur at 21:38 UTC today earthsky.org/tonight/partial-lunar-eclipse-on-july-16-17, but I guess it can't be seen here because it will have been 5: 38 am on July 17 here, when it may have been at dawn here.

Captain Bohemian

5:25 AM

maybe peanuts really have particular lasting function of curing hunger. Yesterday afternoon I ate a cup of peanut ice cream after a meal and didn't feel so hungry until wee hours. Usually the hunger curing function of that kind of meal can't last that long.

but now I am hungry again, needing to look for food to cure hunger again. If I can find cheap food which can stave off hunger over 24 hours, that will be nice.

John Rennie

5:59 AM

@NicHartley I would have guessed anything thicker than a few microns would do. EM waves are absorbed pretty effectively by conductors.

Gyromagnetic

6:35 AM

@NicHartley , check out the wikipedia article on "skin depth", then you can calculate the thickness you need for a given attenuation

unless were talking about a mesh, then stuff probably gets more involved haha

Skin effect

Skin effect is the tendency of an alternating electric current (AC) to become distributed within a conductor such that the current density is largest near the surface of the conductor, and decreases with greater depths in the conductor. The electric current flows mainly at the "skin" of the conductor, between the outer surface and a level called the skin depth. The skin effect causes the effective resistance of the conductor to increase at higher frequencies where the skin depth is smaller, thus reducing the effective cross-section of the conductor. The skin effect is due to opposing eddy currents...

kyle campbell

@NicHartley phas.ubc.ca/~phys409/manuals/skindepth.pdf cf. pp.14-18 may be useful

Gyromagnetic

6:59 AM

@NicHartley Happy to help ;)

uhoh

7:28 AM

2

Q: Difference between relaxation and resonance leading to an absorption spectral feature?

I need help understanding the physics behind this insightful comment below the question Does water really have strong EM absorption at 3 kHz in solid and 2 GHz in liquid? Why the huge shift?: Please note: This is a relaxation spectrum. The transitions do not come from a resonance (absorption,...

Slereah

8:42 AM

120

Q: What makes four dimensions special?

Do you know properties which distinguish four-dimensional spaces among the others? What makes four-dimensional topological manifolds special? What makes four-dimensional differentiable manifolds special? What makes four-dimensional Lorentzian manifolds special? What makes four-dimensional Riema...

dg.differential-geometry mp.mathematical-physics differential-topology big-list big-picture

why do we always live in the worst possible dimension

Gyromagnetic

12:38 PM

Dear hbars, anyone know of a quick n dirty way of simulating a wave with finite phase coherence?

I tried making a string of random numbers from 0 to pi, and then convoluting it with the memory kernel I want as a phase autocorrelation function (exp(-t/T_coh))

and then adding this as a phase argument

but I think I'm doing it wrong, because by doing this, I get more phases close to zero (effectively doing a weighted moving average)

Not sure if I should open a legit question

string -> array, pi -> 2pi

Physics Meta

1:05 PM

0

Q: My question was downvoted without a reason

Does Fisher Information quantify only the precision of the instrument? I had asked a question recently. There were some comments by someone named Solar Mike. On repeatedly asking him/her on elaborating what he meant, there was no proper reply. I realized most of his answers are similar, on phys...

discussion specific-question down-votes community-moderation

Jake Rose

3:35 PM

@Gyromagnetic is skin depth all that relevant to how thick steel needs to be to stop the waves? I’d have thought the amplitude decay coefficient would have been more useful, and as such the relative permeability etc

Gyromagnetic

@JakeRose , skin depth takes relative permeability into account. And in some ways, can be thought of as an "amplitude decay coefficient". Can you send me a link of what you're thinking of? maybe we are talking about the same thing.

thermomagnetic condensed boson

4:12 PM

@knzhou sup man. i've quickly checked some of your PDF, about solid state. page 9 at some point , it's written "photon" but I think you meant "phonon"

knzhou

4:39 PM

@thermomagneticcondensedboson Thanks for the catch, I'll fix it!

Also I apologize in advance for future issues, these notes are all very rough and Solid State is the roughest of all.

Jake Rose

5:30 PM

@Gyromagnetic but he’s talking about waves. With skin depth the waves still propagate into the material. The currents and the waves are not the same phenomena.

Mo_

@JakeRose Skin depth can be obtained from the amplitude decay coefficient.

@ACuriousMind Hi!
Ever heard of [this](https://de.wikipedia.org/wiki/Lavaschak)? In Germany?

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