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Electron band structure in germanium, my ass (2001)

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Re: Electron band structure in germanium, my ass (2001)

#331

Post by opello »

hughdbrown wrote: post #330
opello wrote: post #323

Earlier quoted context omitted.

Or even more likely in a lab setting: have another student test your part in their setup for A/B validation testing.

Sort of like the first debugging tip here: https://news.ycombinator.com/item?id=42682602

> 1. Understand the system: Read the manual, read everything in depth, know the fundamentals, know the road map, understand your tools, and look up the details.

Maybe? Although it seems more like it's actually #5:

> 5. Change one thing at a time: Isolate the key factor, grab the brass bar with both hands (understand what's wrong before fixing), change one test at a time, compare it with a good one, and determine what you changed since the last time it worked.

where in my imagined scenario, a student that just finished the lab successfully could pull out their DIP-8 device and swap in the author's to validate that it was possible to make it work in a known good environment.

Re: Electron band structure in germanium, my ass (2001)

#333

Post by saghm »

don-code wrote: post #87
jerf wrote: post #27

One of my Core Memories when it comes to science, science education, and education in general was in my high school physics class, where we had to do an experiment to determine the gravitational acceleration of Earth. This was done via the following mechanism: Roll a ball off of a standard classroom table. Use a 1990s wristwatch's stopwatch mechanism to start the clock when the ball rolls of the table. Stop the stopw…

This is, more or less, exactly what happened when I took Electronics I in college. The course was structured in such a way that you could not move on to the next lab assignment until you completed the one before it. You could complete the lab assignments at your own pace. If you failed the lab, you failed the class, regardless of your grade. The second or third lab had us characterize the response of a transistor in…

> So I made an appointment to see the professor, and his suggestion to me was to drop the class and take it again. Which, of course, would've affected my graduation date.

I would have been tempted to ask him to write me a check for the extra semester of tuition, but I'm sure that wouldn't have made the situation any better (and maybe would have made him more likely to grade strictly).

Re: Electron band structure in germanium, my ass (2001)

#334

Post by smaddox »

For those who are actually interested in this field, the proper way to measure this would be with a four point probe. You do need a constant current source and a high-impedence voltage meter, though.

Also, you don't need to solder wires to the sample. But if you want to measure the hall resistance of a thin film of a semiconductor, you can solder a glob of indium on to four corners of a 1 cm x 1 cm wafer, put it in a magnetic field, and then do basically the same measurement as four point probe, except not inline.

Re: Electron band structure in germanium, my ass (2001)

#335

Post by ForOldHack »

timewizard wrote: post #301
oddmiral wrote: post #210

Earlier quoted context omitted.

Make marks on the thermometer at 0 and 100 degrees C, then project light from a candle to a wall to see these marks with say 5x magnification. Now project marks from the 128 mark ruler to the same wall and align marks from both, then place marks on the thermometer with 5x better accuracy.

A candle is an exceptionally unstable light source. The flame continually moves location as it burns. Any air currents in the room will disturb it and cause flame shadows to be cast. Adding magnification will just make this all worse.

Henry Cavindish used them to measure G. I used lasers and never got even an order of magnitude closer.

Re: Electron band structure in germanium, my ass (2001)

#336

Post by whatshisface »

ethbr1 wrote: post #252
don-code wrote: post #152

Earlier quoted context omitted.

Indeed it could have. I was on a fairly prestigious scholarship; luckily, my marks were good enough that this was a low-risk decision. That said... I graduated with a 3.2 GPA, after being the stereotypical "gifted" student up through high school. A 3.2 is, apparently, still decent. However, I did feel a bit of a twinge seeing my peers walk at graduation with with cords, bents, and other regalia, where I just had my s…

Message for engineering undergraduates: when you have an opportunity to trade great grades for good grades and increased immediate career prospects, take it. Your internship / prospective employer cares way more about the job you're doing for them than +0.5 GPA. (If you're heading right to grad school, obviously different weighting)

If you're heading to grad school, it can be essential to have connections made through UG research. That's a trade that isn't just advised in some fields, but necessary. A letter of recommendation that says you're actually useful as an RA is 1000x more of a direct implication that they would benefit from bringing you on than an A in a few classes. Academics don't like finding out that smart people are impossible to work with any more than industry does, and since they're tied to you for longer, in some ways it's an even bigger deal.

Re: Electron band structure in germanium, my ass (2001)

#337

Post by timewizard »

ForOldHack wrote: post #335
timewizard wrote: post #301

Earlier quoted context omitted.

A candle is an exceptionally unstable light source. The flame continually moves location as it burns. Any air currents in the room will disturb it and cause flame shadows to be cast. Adding magnification will just make this all worse.

Henry Cavindish used them to measure G. I used lasers and never got even an order of magnitude closer.

His measurement apparatus was designed to eliminate air currents was it not? He also had a torsion balance and a vernier to make measurements of the /relative/ changes induced in the apparatus.

I don't see how you're going to use this system to effect repeatable markings on glass tubes.

Re: Electron band structure in germanium, my ass (2001)

#338

Post by kragen »

throwanem wrote: post #329
kragen wrote: post #314

Earlier quoted context omitted.

I've seen an MSDS for sodium chloride USP that recommends against use in food, and says that you should wash your skin with abundant water for 15 minutes if you contact it and seek immediate medical attention if it gets in your eyes (after, of course, spending 15 minutes in the eyewash station). It also warns you to keep it away from sources of ignition, that it should not be released into the environment, and that y…

Fortunately, HF is as safe as NaCl. Or so I take you to suggest, this otherwise totally failing to follow from anything anyone has said...

Sevensor said they would like to make Etsy moms using HF to frost shot glasses reread the MSDS for HF. This would only benefit them if MSDSes were reliable guides to the risks of working with different materials. Unfortunately, as evidenced by my example, they are not. Therefore, the Etsy moms, having reread the MSDS, might reasonably dismiss the information contained in it, unfortunately failing to protect themselves against the very real dangers it poses. Furthermore, given the astounding lack of thought evident in the NaCl MSDS, it is reasonable to guess that many MSDSes you find for HF will propose "safety" measures that are actually counterproductive, such as wearing gloves.

I thought all of this was obvious from my comment.

Re: Electron band structure in germanium, my ass (2001)

#339

Post by malux85 »

BeetleB wrote: post #80
HiPHInch wrote: post #11

I took some effort to change my research interest from computer vision to DFT calculation in quantum chemistry. Honestly, I'm kind of frustrated now, too many work is close-source in this area. The research paper will tell you everything except how to reproduce this work in minimal effort, it's like they are hiding something. They also using a `Origin` to plot and MS Word to write paper, which is also non-free licens…

> The research paper will tell you everything except how to reproduce this work in minimal effort, it's like they are hiding something. They are. I used to work in an adjacent field. Everyone was open about doing it - they're competing with others for grants, and worry that if they reveal the secret sauce, others will move faster than they can. You can say you performed a DFT calculation to get the result, but anyone…

Not only that, but DFT itself has many many different forms. There's DFT that is O(n)^3 and there's DFT that's O(n)^7 in time complexity, the wild variations are due to the different approximations (i.e. algorithm and parameters).

Saying "I used DFT" is like saying "I used a computer", its nowhere near enough info to reproduce the work

Re: Electron band structure in germanium, my ass (2001)

#340

Post by throwanem »

kragen wrote: post #338
throwanem wrote: post #329

Earlier quoted context omitted.

Fortunately, HF is as safe as NaCl. Or so I take you to suggest, this otherwise totally failing to follow from anything anyone has said...

Sevensor said they would like to make Etsy moms using HF to frost shot glasses reread the MSDS for HF. This would only benefit them if MSDSes were reliable guides to the risks of working with different materials. Unfortunately, as evidenced by my example, they are not. Therefore, the Etsy moms, having reread the MSDS, might reasonably dismiss the information contained in it, unfortunately failing to protect themselve…

Many things are obvious from your comment.
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