May 10, 2009 at 4:45 pm (Advanced Laboratory, Life as a grad student, Movie, Physics)
Tags: Diet, Food Diary, Movie, Physics, Slice of life, Star Trek, Weigh-In
I return! Somewhat alive. I haven’t been posting lately because finals have been dragging me down. I took what is (in grad school at least) a really heavy load and I got bitten hard by that last week. I had so much to do. I had to grade papers for the advanced lab, I had to get two general relativity homework assignments done, I had to get a general relativity final done, and I had to get the statistical thermodynamics final done. That last one was especially rough, I spent almost 30 hours on it. YUCK.
Anyways rather than trying to post a bunch of back dated articles, I will simply summarize the results here.
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April 22, 2009 at 8:42 pm (Advanced Laboratory, Exercise, Life as a grad student, Physics)
Tags: Advanced Lab, Exercise, Physics
So as it says at the top of my blog I am a graduate student in physics. To earn my keep until I can become a research assistant I am a teaching assistant. In my case I am the TA for the graduate lab. This is a lab that almost all first year grad students must take. It gives them experience with experimental methods and paper writing. Additionally, I figure it makes the theorists have a little more respect for us grubby experimentalists.
We use a lot of radioactive sources in the lab, the are useful for any number of experiments both those involving nuclear physics and those on things like atomic physics, condensed matter physics and basic quantum mechanical things like the statistics of spin. Anyways, we have an experiment called ACAR, short for Angular Correlation of Annihilation Radiation, I won’t get into what the experiment is about beyond this: It uses a Na-22 source which is a positron emitter. Yes I said positron. The proton rich nucleus emits anti-electrons to get rid of some of its excess positive charge. Anyways this source is quite hot. We have it shielded so that the radiation dose rates are quite low (almost lower than the increased cosmic ray dose rate that you receive in an airplane trip). But nonetheless it is quite hot.
This source is hot enough that 30 feet away we can pick up the characteristic gamma rays of the source, despite the shielding. This made us decided that the source needed yet more shielding. As it is the dose rate to students and people working on it is fairly low but the fact that we can pick it up means that it might interfere with other experiments.
“What does all this have to do with moving heavy things?” you may be asking. There is one material that physicists favor for building gamma radiation shields, lead bricks (or sometimes solid chunks of lead if need be). Unfortunately the lead bricks are stored in the Nuclear Science Lab in Neiuland Science Hall, we needed them in Jordan Hall of Science. Even worse, the bricks are stored in the room that holds the Read the rest of this entry »
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April 20, 2009 at 9:24 pm (Diet, Exercise, Physics)
Tags: Diet, Exercise, Physics
It was an interesting experience, walking all day with the weights. They certainly let me know how important flexing at the ankle is. Proper padding as well.
Going up stairs in them isn’t so bad. It appears that knowing how much to raise your foot is governed by proprioception (sensing muscle and joint position) not by, how much force for how long does it take to move this. The problem is going DOWN the stairs. The foot tries to decrease the angle between its top and the shin, unfortunately the weight impairs this so going down stairs is a bit of a chore.
Anything faster than a walk with 20 pounds on each ankle is a bit of a chore. Interestingly enough it is not the increase mass disrupting the system that makes it bad (though I imagine that would come into play quickly if one actually started running / jogging properly). Nope it is the restricted play the ankle has. Once again the weights block the ankle from decreasing the angle between foot top and shin, which it turns out is CRITICAL for anything more than a walk. Maybe if I can get my hands on some sort of high friction material that also can act as a padding I can have them higher than right against my ankle, allowing the movement I desire.
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April 16, 2009 at 11:49 pm (Physics, Programming)
Tags: Code, Physics, Programming
Yesterday I discovered why so many scientists write their own code for things despite there being other code already out there. The code already out there stinks. It is filled with bad practices, spaghetti code, idiosyncrasies and poor design choices.
In my last non diet post I spoke of helping a friend debug a data analysis program. It was horrible. Every function and variable name started with the letter z. The variable names did not make their usage clear. At least 95% of the variables were declared in a global fashion. There were gotos everywhere, all with nonobvious names. There were while statements and if statements that would always evaluate to true. Not once did the programmer free any memory that they had allocated with malloc. No array boundaries were ever checked. Chunks of memory that were not large enough for the array desired were allocated and the programmer just read past the end of the arrays (and got away with it in an ancient solaris machine). It was unpleasant.
Oh did I mention the whole thing was written in c? c is an evil evil programming language. Lacking any object oriented paradigms it lets bad programmers to some truly horrible things, with all the functions coming out of nowhere and no real indication of what they are operating on or why, trying to read code like that is a nightmare. Of course my personal language c++ lets bad programmers construct some REAL atrocities so I shouldn’t say to much there.
I think there should be some sort of scientist programming license, you have to take a couple courses on programming and good programming practices. Then you have to pass a test on those practices and certain system headers that many seem to reinvent bits of. Then and only then can you get your scientific programming license.
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April 13, 2009 at 9:36 pm (Life as a grad student, Nuclear Science Laboratory, Physics)
Tags: NSL, Physics
We use many types of detectors in nuclear physics, each can do different things well and each has its own downsides. Take the germanium detector a type of detector for gamma rays that has excellent resolution in the energy spectrum (it makes very sharp peaks).
In the old days these came in a form called Ge(Li) (pronounced jelly) detector. These detectors were solid crystals of germanium (a semi conductor like silicon) with lithium atoms dispersed through the crystal. I won’t get into why the lithium was there except to say that it compensated for other impurities in the crystal. These detectors ABSOLUTELY must be kept cold (liquid nitrogen cold in fact (77 K, -196.15 C, -321.07 F)), if they are not kept cold then the lithium could move out of position and destroy the crystals usefulness as a high resolution detector of gamma rays.
In modern times we have developed a much less finicky form of germanium detector called HP-Ge of High Purity Germanium, rather than have lithium atoms scattered throughout the crystal to compensate for the other impurities they simply make the crystal so it has no impurities. Unlike Ge(Li) detectors, HP-Ge detectors can be allowed to come to room temperature when they are not being operated; however, they must be cooled to liquid nitrogen temperatures while they operate (if you really want to know why, ask in the comments) and cycling them down to LN2 temperatures and then back to room temperature repeatedly is not great for them.
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