Electron Band Structure In Germanium, My Ass

http://pages.cs.wisc.edu/~kovar/hall.html

by bootload • 15 years ago

316 97 15 years ago

pages.cs.wisc.edu

jabo3• 15 years ago

I don't understand a wee bit of that, so Go Computer Science! :)

lloeki2• 15 years ago

He's unit-testing Germanium.resistivity(intensity, temperature) like so:

    fixed_i = lambda t: Germanium.resistivity(42, t)
    for t in range(100, 350, step=10):
        assertEqual(fixed_I(t), k*math.expr(t/tref))

Unfortunately fixed_i returns results akin to /dev/urandom because of broken hardware.

jabo3• 15 years ago

Awesome explanation! Thanks.

Groxx2• 15 years ago

That is an absolutely fantastic summary. I upvoted the parent just to get this one more attention :D

jrockway3• 15 years ago

Yeah, I remember a number of labs where I didn't get the data that was expected and had to do the experiment again. Knowing the expected result, producing excellent data was easy; instead of a painstaking data-collection process, I outsourced that to a "function" with "noise". Hey look, r=0.999!

I understand this is the same process by which the top quark was discovered.

starwed3• 15 years ago

Hey look, r=0.999!

I had to grade physics labs one semester -- this was always an instant tell that students were making shit up. :)

jrockway3• 15 years ago

always an instant tell that students were making shit up

Including the correlation coefficient!

5teev• 15 years ago

I wish I'd even once had students who understood the experiment well enough to fabricate data.

linker3000• 15 years ago

I see the test results for germanium but where are the results for his ass?

mikecane• 15 years ago

This pops up every few years. I always forget it and laugh out loud brand new when re-reading it.

joss82• 15 years ago

"Going into physics was the biggest mistake of my life. I should've declared CS. I still wouldn't have any women, but at least I'd be rolling in cash."

This advice should be told to all high schoolers.

Well, at least male ones.

2muchcoffeeman• 15 years ago

Or do both! I always cringe when I meet good programmers that have no understanding of what is going on at the hardware level.

stdbrouw• 15 years ago

Because knowing the hardware is, of course, essential to make a well-functioning CRUD app.

dagw• 15 years ago

A couple of the best programmers I've ever met majored in physics.

aidenn0• 15 years ago

While I would like to think you were talking about myself, I'm guessing you're thinking of people more along the lines of Dennis Ritchie.

berntb2• 15 years ago

Go into chemistry, instead. Lots of nice women. [Edit: It is also a cool subject. And you'll get access to lots of ethanol.]

mikebike• 15 years ago

Aren't they brutal to the grad students working as research assistants in the lab?

rimantas• 15 years ago

Looks like I did well: studied physics and chemistry, got MS in physics and astronomy. Dropped out of PhD in astronomy — was already working as a programmer. To tell the truth I still feel sorry for not getting that PhD, but on the other hand I was not going to be an astronomer anyway, so what's the point.

pbsurf• 15 years ago

There really is no reason to earn an undergraduate degree in physics (as I learned the hard way). It is just as easy to get into a physics graduate program with an ECE or EECS degree plus a couple semesters of upper division quantum mechanics and maybe a semester of stat mech - and you have the option of getting a decent job instead.

toponium2• 15 years ago

Yea perfect case in point. I graduate this Friday with a physics undergrad. Class of 33, 31 males. 2 females :(

JonnieCache3• 15 years ago

Hah, this exactly mirrors my experience in chemistry lessons aged 15. Failing to reproduce experimental results with broken equipment then faking the data with an excel function to get the teachers off my back so I could go back to doing something useful like staring out of the window, or using the magnesium ribbon to heat-seal peoples pencil cases shut.

Good to know that it carries on up to the undergraduate level. And I even managed to associate with women during my eventual CS degree! Feeling pretty smug right now.

yummyfajitas• 15 years ago

Failing to reproduce experimental results with broken equipment then faking the data with an excel function to get the teachers off my back...

I had the exact opposite experience. I once failed to get an experiment working, but kept trying until I was the last person in the lab. Eventually the professor asked why I hadn't finished, and together we discovered the spectrometer was utterly broken.

He gave a a grade of 0-25% to everyone who got the "right" answer, depending on how realistically they faked it (some people didn't bother to add noise or quantize their answers).

alex_c• 15 years ago

Your own example suggests you're in the (vast) minority.

wglb• 15 years ago

My EE professor in Dynamic Fields, halfway through a 3 hour lab, announced to the class "Oh, by the way, anyone who gets a right answer gets an F for the lab." Groans from half the class. "The point of the lab is to show how danged difficult it is to get to the right answer".

I looked at my mess of data and chuckled.

madaxe• 15 years ago

It carries on through undergrad and into post-grad. Even the best funded labs still have mountains of crappy equipment that everyone has to use, and one researcher who keeps everything that works under lock and key.

On the plus side, it's a great way to learn to be really ingenious with limited resources. We figured out how to get accurate hysteresis loops for ferrous samples using a breadboard, an ancient laptop, a few clicks of Cu wire and a bucket of miscellaneous components. That was shortly after we flooded the lab testing Reynold's number for shear-resistant fluids with plumbing parts.

ldite• 15 years ago

Funny as hell when I was a physics undergraduate 10 years ago, and still funny now. I still routinely use the phrase "to first order" when justifying horrific approximations.

nhebb• 15 years ago

This is why the only lab I enjoyed was in Materials Science. The goal of the labs was never to try to get the data to match some pre-defined equation. Instead, the goal was to test materials and interpret the results. Plus, we got to break stuff. :)

schmittz5• 15 years ago

As a materials science major, this comment made me smile. All my labs at Carnegie Mellon were like that, it was(is) great. We just take a bunch of materials and then argue which one would be the best choice. The only time I had to produce results was when we synthesized a known superconducting structure and just had to show that it superconducted (how strongly wasn't important). Good times that sound much better than people's experiences in physics and chemistry. Vindication!

JoeAltmaier• 15 years ago

I had this insight in Junior High - testing friction by putting blocks on top of other blocks, or in a block train, and using a 'force meter' to see how hard I had to pull. The 'force meter' was a piece of spring steel stuck into another block, with a hook on the end.

It was totally non-linear on every surface I tested. The book said it was supposed to be linear. The students were all furtively fudging it, and eventually the teacher said something like "well, its supposed to be linear so do the best you can".

Insight: this was all a bunch of crap. Turns out that friction is totally non-linear anyway, for most materials, but I didn't read that until 20 years later.

Zaak3• 15 years ago

That reminds me of a story about Richard Feynman visiting a physics class outside the US. The diplomat types were very upset with him for pointing out that their books and classes were terrible, teaching things like the energy of a ball going down an incline without taking rotational kinetic energy into account.

tesseract• 15 years ago

http://v.cx/2010/04/feynman-brazil-education

perlgeek2• 15 years ago

He's so totally right about the hand waving approximations used in solid state physics.

All fields of physics need to use some approximations, but those in the solid state were usually the ones with the worst reasons, just things like "it works if we do that" or even "it doesn't if we don't do this".

It went on like that in three courses (two on solid state physics, one on electronics).

Only after that did I happen to come across a decent book which explained some of the approximations in a way that didn't make me cringe, and some of the stuff started to make sense in retrospect. Others are still a mystery to me, and probably always will be.

schmittz5• 15 years ago

It's often poorly explained, I completely agree, but people forget that even Planck introduced his constant just because it made the data fit. It turned out to be arguably the most fundamentally important constant (along with its reduced form) in all of physics.

arethuza2• 15 years ago

Aren't all fundamental physical constants like that - they are essentially meaningless values plugged into theories to make them align with observations?

jodoherty• 15 years ago

Do you remember the title or author of that book?

mechanical_fish• 15 years ago

I don't necessarily know what book he's referring to, but the book that taught me solid state was Ashcroft and Mermin.

That's a book that deliberately starts out with the silliest possible model and then gradually introduces more and more sophisticated models until the book runs out of pages or your head explodes, whichever comes first. ;)

An important insight, however, is that the simple models are incredibly useful. When I was a teenager I used to fret that the teachers were showing me the simple models first because they were fools, or because they thought we were fools. But it turns out that they are doing so to call attention to certain important general features without distracting you with irrelevant detail.

My favorite class in all of science was Roald Hoffman's chemistry class, the highest numbered class in the Cornell chemistry department, a class which represented the point where chemistry and physics merge to become the same subject. And Hoffman deliberately used a relatively simple model of molecule-molecule interactions in a solid, the Hückel model:

http://en.wikipedia.org/wiki/Hückel_method

Moreover, Hoffman would communicate in pictures as much as in math.

perlgeek2• 15 years ago

"Electronic Transport in Mesoscopic Systems" by Supriyo Datta.

It's a very specific book, but it does explain for example why you can assume that only electrons at the Fermi energy contribute to transport phenomena (aka "current").

I guess for somebody not into mesoscopic transport, only the first three or four chapters will be of interested. But for my diploma thesis (which ended too badly to link it here) it was a real live safer.

tzs2• 15 years ago

If anyone needs a refresher in semiconductor physics, there's a good one at this Britney Spears site: http://britneyspears.ac/

edit: how the heck does a link to an excellent introduction to semiconductor physics get voted down in a thread about an article relating to semiconductor physics?

profquail• 15 years ago

You're getting voted down because most people see the domain "britneyspears.ac" and assume you're spamming, without even visiting the link.

That site actually does have some decent articles related to semiconductor physics, the whole "Britney Spears" thing is just a gag to show how simple they've made it (though the humor is likely to be appreciated only by Physics geeks :)

makmanalp• 15 years ago

Sweet jesus, it's true! http://britneyspears.ac/physics/vcsels/vcsels.htm

biot3• 15 years ago

While there does appear to be some physics articles on the site, the whole thing appears to be cloaking itself in legitimacy as a scheme to get inbound links and drive up its page rank score. Their strategy is likely to get people linking for the physics so that they can sell links for heating oil prices, concert tickets, physics help, and so on. It's more about the advertising than the physics.

I'm sure there's a less spammy physics site you could have linked to?

KirinDave• 15 years ago

This is a good joke, but too subtle for most of the people who moderate on HN.

My advice if you care about that sort of thing: link in further, e.g., http://britneyspears.ac/lasers.htm

sliverstorm• 15 years ago

The way I have always approached labs is a thorough report on my procedure, complete results (totally wrong or not) and an analysis of Whether I got good results, Why I got the wrong results, How might one improve the experiment to get better result...

That has always served me well. I don't usually get A+'s on lab reports, but I think that's my fault and for an unrelated reason.

It certainly seems to me reflection on what was done and thoughtful analysis on why it was good/how it could be fixed (with specific statements or suggestions, not general ones)/what went wrong demonstrates understanding of the material that simple results do not. I guess if you are being trained primarily to be a lab worker who's job is to produce accurate numbers, that's important, but if the labs are for learning...

cubicle67• 15 years ago

I read an essay, I think by Isaac Asimov, where he described a graph like this as a "shotgun curve"

elwin• 15 years ago

I sympathize with the horrible equipment. While getting a physics degree, I had a lab where we measured resistivity. My team was the last to succeed in getting numerical data from the 20-year-old oscilloscope via floppy disk. The students scheduled after us had to take a digital photograph of the oscilloscope screen and reconstruct the data from that.

Broken equipment is not confined to undergraduate classes. A few terms later, I had to use the digital photograph method to get data from a spectrometer in a research lab. If my analysis had succeeded, we would likely have published, and the professor would have had a chance at tenure, all on the strength of data obtained by counting pixels.

laeus• 15 years ago

This "lab report" always brings back good memories because it indirectly launched my career in the game industry. I was finishing up my CS degree at UW Madison and working in Mike Gleicher's computer graphics lab in Spring '02. I had previously met Lucas through a fellow CS student (Alex Mohr, now at Pixar). At some point, Lucas was contacted by the AI programmer at Ensemble Studios (Mike Kidd). Mike, a UW alum, had seen the Germanium treatise and wanted Lucas to apply at ES. A month later, knowing how eager I was to join the game industry, Lucas mentioned Mike's email to me and forwarded him my info. Long story short, I got an interview at ES and was hired straight out of college into a dream job.

I look forward to seeing this link pop up again in a few years. :)

wbhart• 15 years ago

Oh, lovely story. I had precisely this happen in Physics at Uni. I wrote down every piece of data, wrote out my computations in full. When I submitted it, I got a D. I challenged my prof to check any one of the data points or computations and exhibit a single error (I knew he wouldn't because I had checked myself). He refused to check even a single one. Every single person for 20 years had fudged the results!!

beefman• 15 years ago

All scientific results should be reported this bluntly.

BrotherSand• 15 years ago

Hilarious! First time I've seen this and I laughed so hard I had tears running down my face. I think it was figure 1 "check this shit out" that made me really lose it. Got some odd looks on the train.

Groxx2• 15 years ago

An oldie, but a goodie. Easily my favorite scientific report paper of all time.

>Banking on my hopes that whoever grades this will just look at the pictures, I drew an exponential through my noise. I believe the apparent legitimacy is enhanced by the fact that I used a complicated computer program to make the fit. I understand this is the same process by which the top quark was discovered.

Absolutely brilliant.

tinyrock• 15 years ago

The crap results were probably due to the soldering messing around with the crystal properties. Using a pressure-contacts approach instead seemed to do the trick:

http://tinyrock.com/resources/4000918/Bandgap-Measurements-I...

Has it really been 10 years!

bluesmoon• 15 years ago

During my physics practicals for my high school final exam, I had to measure the voltage of a Daniel Cell using a Dry Cell (1.5V), a 2metre length of wire and a bunch of other stuff.

The only problem... the dry cell was dead, so only carried 0.8V or something. So, my results consistently showed that the Daniel Cell had a PD of 1.7V (it's supposed to be ~1.1V).

The examiner came up with a brilliant solution to "fix" my data. Switch the labels on the data columns.

Niksko• 15 years ago

Ah, physics, the slower cousin of mathematics. How I weep for you.

Electron Band Structure In Germanium, My Ass

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