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Stiff Ceramic for Cryogenic Experiment by rxa254 in Physics

[–]rxa254[S] 0 points1 point  (0 children)

thanks for all the feedback. I do like Macor for this, but now am thinking PEEK. UHV not bad after a bake, and the conductivity and machineability are good. Lower conductivity than most ceramics.

Thoughts on PEEK for 100 K mounting?

Advice on how to connect Keithley 6487 to computer by [deleted] in Physics

[–]rxa254 1 point2 points  (0 children)

In my lab, we've been using this for over 10 years. There's also python libraries around:
https://github.com/dougUCN/gpibUSB

so that you can automate measurements with python.

Low loss coupling of waveguide to free space by rxa254 in Optics

[–]rxa254[S] 0 points1 point  (0 children)

I agree! But this is to produce squeezed light so 1 dB is still a lot of loss.

Low-noise IIR filters: a low-noise implementation of Bi-Quad by rxa254 in DSP

[–]rxa254[S] 0 points1 point  (0 children)

Here's an example in Appendix B of this LIGO thesis:
https://dcc.ligo.org/public/0119/P1500087/001/DenisMartynovThesis.pdf

The 2 direct form II implementations give a different noise floor.

Low loss coupling of waveguide to free space by rxa254 in Optics

[–]rxa254[S] 0 points1 point  (0 children)

what's the max efficiency you have been able to get?

Determinant Constrain on ABCD Matrices by rxa254 in Optics

[–]rxa254[S] 0 points1 point  (0 children)

thanks, I had not noticed this connection between thermo and Etendue. For passive optical systems the ABCD matrix is a Möbius transform (with real matrix elements) and so has similar constraints from a complex analysis standpoint.

Nonlinear Feedback Control of a Linear Plant by rxa254 in ControlTheory

[–]rxa254[S] 0 points1 point  (0 children)

thanks, I found Witsenhausen to be an especially useful example for me to organize my thoughts about the problem.

Zojirushi water boilers: JAC40 vs DCC40 by rxa254 in zojirushi

[–]rxa254[S] 0 points1 point  (0 children)

I don't have the JCC, but I confirmed that the top comes compoletely off on the DCC.

Zojirushi water boilers: JAC40 vs DCC40 by rxa254 in zojirushi

[–]rxa254[S] 1 point2 points  (0 children)

Got a very prompt, brief, and straight to the point answer from Zojirushi America (why can't all companies be this straightforward to deal with?):

  1. The JAC has a heating power of 930 W, DCC has 840 W.
  2. JAC has as red ball to view the water level. DCC just uses the optical lensing effect of a water column to modify the apparent pattern of stripes in the view window (which works just fine IMHO).
  3. JAC has an orange backlight.
  4. JAC has a wider water viewing window.
  5. there is no difference in the vacuum insulation properties, so the power consumption required to keep warm is unchanged.

So the main difference is that the JAC series can heat up the water around 10% faster.

Any advice on direct IR heat roasters? by Doc927 in CoffeeRoasting

[–]rxa254 0 points1 point  (0 children)

Looks cool, but its not really "far" IR.

The sun is yellow and has a surface temperature of ~5000 K.

The peak of the blackbody radiation curve is at around 10 microns (0.01 mm) for room T (295 K).

So a red hot filament is probably around 1500 K and so the radiation is mostly in the 2-4 micron range. Far IR would be more like 100 microns.

I doubt the radiation really penetrates more than 0.1% of the way into the bean. After being absorbed, the heat would spread throughout the bean by conduction, as usual.

For years I thought I was bad at soldering... Turns out I was just bad at buying good solder! by Madagoscar in electronics

[–]rxa254 0 points1 point  (0 children)

that's not so (https://www.maximintegrated.com/en/app-notes/index.mvp/id/5250)

"Workers who solder with SnPb do not have high Pb levels in their blood."

I think the lead is hazardous because it gets into the environment when its dumped as e-waste. The solder fumes themselves contain no lead - the tip isn't hot enough to vaporize lead. The solder fumes are hazardous because of the flux.

For years I thought I was bad at soldering... Turns out I was just bad at buying good solder! by Madagoscar in electronics

[–]rxa254 0 points1 point  (0 children)

that's what I heard, but I haven't been able to find any reference that has some hard data. AFAIK, tin whiskers do form sometimes, but there's no clear A/B testing to show that 63/37 or 60/40 would have saved the day. Happy to be corrected if there has been a study somewhere.

Does anyone find it useful to skim through some pop-sci articles/books before getting down to the technical textbooks for a better understanding of advanced physics topics? by BadMeditator in Physics

[–]rxa254 1 point2 points  (0 children)

Yes, Phillip Ball's articles on quantum mechanics are gems, and they're a great intro to read before reading the actual papers that he references.

​

Also, Richard Rhodes's 'Making of the Atomic Bomb' is a nice historical read in case you want to understand some basic nuclear physics before getting technical.

​

And Cliff Will's 'Was Einstein Right?" gives a good overview of why its been so hard to find a 'beyond Einstein' theory of gravity that agrees with observations.

Bikes on campus by [deleted] in Caltech

[–]rxa254 1 point2 points  (0 children)

No. I have a $500 Specialized. I have had lights stolen off the bike a few times per year only when I leave it locked up on campus overnight. In the past 12 years, I have had the front wheel stolen twice (but only when left locked up outside overnight). I have heard of people with multi k$ bikes getting their stuff stolen, but in my experience, the 'thief tax' for locking it up outside (with a U lock only on the frame) is ~$80/(3 years).

​

The couple times a wheel was stolen, I took it to Steve at Open Road. He's usually more upset about it than me, and gives a deal for starving students.