fraserphysics (u/fraserphysics)

fraserphysics commented on Google's Liquid Cooling chipsandcheese.com/p/goog... · Posted by u/giuliomagnifico

foota · a day ago

Hm... but in the case when the chips are in serial, the heat transfer from the last chip will be less than when the chips are in parallel, because the rate of heating is proportional to the difference in temperature, and the water starts at a lower temperature for the parallel case for this last theoretical chip.

fraserphysics · a day ago

One way to characterize the cost of cooling is entropy production. As you say, cooling is proportional to difference in temperature. However, entropy production is also proportional to temperature difference. It's not my field, but it looks like an interesting challenge to optimize competing objectives.

fraserphysics commented on Why Hasn't Medical Science Cured Chronic Headaches? newyorker.com/magazine/20... · Posted by u/fortran77

fraserphysics · 13 days ago

I started getting migraines in the 1960s. Thanks for the link.

While a cup of coffee often helped me feel better in years past, I've found eliminating coffee from my diet has reduced my headache frequency. Triptans help when I get the occasional headache now.

I was disappointed that the article didn't talk about the variety of migraine manifestations. Some of the manifestations can be confused with transient ischemic attacks.

fraserphysics commented on New sphere-packing record stems from an unexpected source quantamagazine.org/new-sp... · Posted by u/pseudolus

meindnoch · 2 months ago

That's in Z_{2}^n, not in R^n.

fraserphysics · 2 months ago

I think the result for Gaussian channels is in R^n.

fraserphysics commented on New sphere-packing record stems from an unexpected source quantamagazine.org/new-sp... · Posted by u/pseudolus

fraserphysics · 2 months ago

Don't Shannon's channel coding theorem and rate-distortion theorem establish bounds on possible sphere packing?

fraserphysics commented on How to get my ECG data? · Posted by u/fraserphysics

Bender · 2 months ago

I do not know the answer to your specific question but I do know there are consumer 6 lead ECG's that one can purchase [1] for much less than the amounts you are talking about. Some of them are stand-alone [2] and some require a cell phone.

For 10 minutes in April I was seeing double.

There are many things that can cause this unrelated to the heart and should be looked into by a doctor. I am not a doctor and this is not medical advice. Even staring at a screen too long can cause temporary diplopia and there are nutrient/mineral deficiencies that can exacerbate this unless you mean you were going cross-eyed and there are multiple things that can cause that. Don't panic, talk to professionals. I personally would start with an ophthalmologist and nervous system specialist (that is one person).

just an example, there are many of these, not medical grade but don't need to be for your doctor to see if something is off.

[1] - https://www.amazon.com/KardiaMobile-Personal-Device-Heart-Mo...

[2] - https://www.amazon.com/EMAY-Portable-Channels-Compatible-Sma...

fraserphysics · 2 months ago

Thank you for your reply.

I am also not a doctor. I have an appointment with a specialist MD. My PCP was initially alarmed, but after some research and consultations believes that I am not in immediate peril.

Unfortunately the devices that those links point to would not provide 24 hours of continuous data. The data that Phillips won't give me is a continuous record of about 720 hours with a few small breaks. The interesting event was one 2 second interval in the middle of one night.

fraserphysics commented on Infinite Grid of Resistors mathpages.com/home/kmath6... · Posted by u/niklasbuschmann

bgnn · 2 months ago

People think this is not relevant to real world problems but it actually is, albeit all the calculations aren't that relevant. Silicon substrate's resistance is basically an infinitely large grid of unut resistances at the distances relevant for a local point of an IC. Note that silicon substrate is often heavily doped (p-type) and all info you get from the fab is it's resistivity (often somewhere between 1 to 100 ohm per cm). For the most advanced tech nodes its often 10 ohm/cm. If you need to develop some intuition about noise coupling via the substrate you have to think that it's a grid instead of just calculating the resustance between point A and B. We need to distribute a grid of substrate contacts to collect the noisy currents too. So the grid shows up again!

fraserphysics · 2 months ago

The units of resistivity are ohm * cm not ohm/cm. (I worked at Fairchild a long time ago.)

fraserphysics commented on Dr John C. Clark, a scientist who disarmed atomic bombs twice daxe.substack.com/p/disar... · Posted by u/vinnyglennon

fraserphysics · 3 months ago

Here are a couple of related jobs that could be in a movie:

1. Disabling a terrorist weapon. When you find a mysterious box in NYC making ticking noises and emitting radiation, who you gonna call?

2. Forensics and attribution. When 1 fails how do you figure out what happened and who is responsible?

fraserphysics commented on Excitable cells jenevoldsen.com/posts/exc... · Posted by u/johannes_ne

johannes_ne · 5 months ago

Thank you for all the kind responses.

I also want to make a similar article, where I calculate an ECG for the simulation, and then make and explain the changes necessary to make the ECG look realistic. A main challenge will be that the depolarization has to happen very fast relative to the repolarization, which may be computationally difficult for a cell-based simulation.

fraserphysics · 5 months ago

Also cool would be the inverse. Going from ECG to plausible simulated RD dynamics.

fraserphysics commented on Excitable cells jenevoldsen.com/posts/exc... · Posted by u/johannes_ne

fraserphysics · 5 months ago

I am reworking the analysis of ECGs from an old contest, and I want help from an expert.

In 2000 the Computers in Cardiology challenge (CINC2000) provided ECGs from sleep studies of 70 patients and asked contestants to identify obstructive sleep apnea based on those ECGs. I was on the team that won.

Now I am reworking the problem for the second edition of a book (see https://www.fraserphysics.com/book.pdf), and I see great variety in those ECGs (see https://www.fraserphysics.com/all_ecgs.pdf). I suspect that some of that variety is due to lead placement, and some is due to pathology, but I'm not sure.

Is anyone here willing to help me out?