Tracking Monte Carlo particles (or in this case, ray traces) through a geometry can be tricky because of the subtlety of edge cases. Today I discovered that my tracking routine failed when given a direction of −0.0 . I never imagined that the existence of signed zeroes in IEEE floating point arithmetic could ever bite me.
Showing posts with label work. Show all posts
Showing posts with label work. Show all posts
23 February 2011
02 December 2010
MC2011 proceedings bibliography style
In case anyone out there hasn't yet submitted their paper for the upcoming M&C conference, I have cooked up a BibTeX bibliography style file for the International Conference on Mathematics and Computational Methods that accurately reproduces their example references in the provided LaTeX template. Download it to save yourself the trouble of manually formatting your citations.
10 August 2007
Nuclear data, of a sort
Your exercise of the day is to show with trigonometry and geometry that lim(n*tan(pi/n), n→∞) = pi. (I got this while playing around at work with finding the equivalent area of a circle and a polygon with n sides.)
My landlady gave me, at my request, a bunch of pamphlets I discovered lying around. They're educational booklets published in the mid-'60s by the U.S. Atomic Energy Commision, printed right here in Oak Ridge. They're really cool -- they vary in subject matter from space nuclear power to physical attributes of plutonium to medical uses of radioisotopes. It provides a fascinating look into the past. For example, one of the medical uses was injecting [Na-24]Cl into a patient's bloodstream and placing shielded detectors at points in his body, using the intensity to calculate where flow constrictions might be. I really doubt they do that nowadays. (I assume it was superseded by MRI.)
I was curious to see if any of that detailed information on plutonium had been reclassified, so I did a little googling and came up with this interesting site. There is some really cool (and some useful) information there, but the organization that hosts it seems kind of questionable. Do they think that by posting a bunch of that kind of information, they'll make the US decide to release all of its nuclear secrets into the public domain and simultaneously cease development of advanced nuclear weapons? I hope not.
My landlady gave me, at my request, a bunch of pamphlets I discovered lying around. They're educational booklets published in the mid-'60s by the U.S. Atomic Energy Commision, printed right here in Oak Ridge. They're really cool -- they vary in subject matter from space nuclear power to physical attributes of plutonium to medical uses of radioisotopes. It provides a fascinating look into the past. For example, one of the medical uses was injecting [Na-24]Cl into a patient's bloodstream and placing shielded detectors at points in his body, using the intensity to calculate where flow constrictions might be. I really doubt they do that nowadays. (I assume it was superseded by MRI.)
I was curious to see if any of that detailed information on plutonium had been reclassified, so I did a little googling and came up with this interesting site. There is some really cool (and some useful) information there, but the organization that hosts it seems kind of questionable. Do they think that by posting a bunch of that kind of information, they'll make the US decide to release all of its nuclear secrets into the public domain and simultaneously cease development of advanced nuclear weapons? I hope not.
28 June 2006
Updates
Today's stupid mistake was not remembering that MCNP's energy bins are described in units of MeV, not eV like those in SCALE are. I was confused why the flux above 20 eV was zero, and I even went and asked two people and was about to forward them my input file before I realized my mistake.
I usually have a hard time being coherent. If I have time to think about something and write it down, and I don't have to write it down very precisely, I'm ok. More formal papers and the like are pretty difficult because one can't get away with the stream-of-thought and highly parentheticalized stuff that I usually write. As far as just talking to my mentor out of the blue, unless I'm prepared with notes, I probably sound like a lunatic.
There have been several seminars that the NSTD puts on; today's was on the ENDF libraries. I don't think any of our classes at school have mentioned the effort that goes into evaluated nuclear data files, or most of the details of resonances and self-shielding and so forth. It was really insightful, and would've been nice to have had at the beginning of the summer instead of now when I'd already learned by trial and error and asking questions what most of the details about the resonance processing code that SCALE uses are.
Ultimate today definitely made up for Monday's. On Monday, there were maybe 20 people there, most of whom didn't seem to enjoy the game. Today, though, there were ten of us at first, with the final head count being 16 by the end of the game. That's the right number so that everyone can stay involved and needs to be involved in order for the game to be good; the field isn't so dense with people that all throwing is unreasonable. It's fun to hit the ground running all-out. And by hit the ground, I mean fall down and slide and look awesome. Not awesome is other people getting confused by thinking my glasses are the frisbee and knocking them off my face. But they're still ok.
And I'm irritated that sonic charges $.30 for a cup of tap water. Pft.
I usually have a hard time being coherent. If I have time to think about something and write it down, and I don't have to write it down very precisely, I'm ok. More formal papers and the like are pretty difficult because one can't get away with the stream-of-thought and highly parentheticalized stuff that I usually write. As far as just talking to my mentor out of the blue, unless I'm prepared with notes, I probably sound like a lunatic.
There have been several seminars that the NSTD puts on; today's was on the ENDF libraries. I don't think any of our classes at school have mentioned the effort that goes into evaluated nuclear data files, or most of the details of resonances and self-shielding and so forth. It was really insightful, and would've been nice to have had at the beginning of the summer instead of now when I'd already learned by trial and error and asking questions what most of the details about the resonance processing code that SCALE uses are.
Ultimate today definitely made up for Monday's. On Monday, there were maybe 20 people there, most of whom didn't seem to enjoy the game. Today, though, there were ten of us at first, with the final head count being 16 by the end of the game. That's the right number so that everyone can stay involved and needs to be involved in order for the game to be good; the field isn't so dense with people that all throwing is unreasonable. It's fun to hit the ground running all-out. And by hit the ground, I mean fall down and slide and look awesome. Not awesome is other people getting confused by thinking my glasses are the frisbee and knocking them off my face. But they're still ok.
And I'm irritated that sonic charges $.30 for a cup of tap water. Pft.
27 July 2005
Nuclear weapons and ball lightning
Today I attended a very interesting lecture (and a free, very tasty lunch) given by the vice president of our branch of the Sandia org chart who just retired two weeks ago.
He started the lecture by discussing the prisoner's dilemma, and noting that traditionally the most effective method is that of "tit-for-tat," where responses are based on previous actions. He said that once 40% of a population uses this method, a stable system develops where 7% always rat out/trade a null bag and the remainder always cooperate. This led into him talking about wars and how that method no longer works when "tit" means the destruction of both entities.
Last year, the PRC launched its first of a new class of nuclear missile submarines. They are also, apparently, in the process of constructing two more, a fact that didn't make any major news source (according to him) because of our close trade relationship with China. Not good, especially when they're making crazy threats about nuking the U.S. if we get involved in a war between them and Taiwan.
He also believes that within the next 3-5 years, another country will give an Islamic terrorist organization a ~6 kiloton nuke which they will detonate above the Pentagon, causing the U.S. to withdraw completely from the Middle East.
Among other things, the vice-pres mentioned an interesting study correlating the ratio of males over 18 to males under 18 and a nation's willingness to go to war and sacrifice larger numbers of the male population.
Most of that, along with some stuff about needing more energy, was given as reasons that Sandia exists and needs to continue to exist. He talked a lot about the future of pulsed power as the only feasible fusion energy source, as economically, laser-induced ICF and Tokomak as producers of energy won't happen. I'm personally dubious that they'll be able to get pulsed power ICF to work reliably and continuously, but that's beside the point.
Then he went totally off-topic to talk about a research project he's been pursuing in his own time. He's interested in the kind of ball lightning that doesn't happen anytime near a lightning strike (though usually sometime around a storm). There are stories of this kind hovering around for 20 minutes, doing all sorts of crazy things. One account took place 130 years ago in Ireland, witnessed by one Fitzgerald, of a "lightning ball" about 5 feet in diameter. It moved about a meter per second down a hill, and went into and out of the ground, finally going into a stream and exhausting itself after running into the bank. The crazy part is, everywhere it touched the ground (which was peat) left a huge hole about 4 feet (or meters, I can't remember) deep, so it carved huge tracks in the ground and in the bank near the stream. No mention in the account was made of piles of ground where it might've dug it up, or of steam rising from the ground. I wouldn't believe this at all, but the vice-pres actually went to Ireland and found the place where it happened. Since peat grows so slowly, the holes it allegedly carved in the bank were still there.
Another extraordinary anecdote was in the '70s in England. A lady was in her house when a 6 inch diameter ball hovered up to her and contacted her polyester miniskirt and the underwear underneath it, which a part of vaporized or vanished. She had swatted at it with a hand with a ring on it, and in the moment of time where her hand passed through it, the ring was heated to "scalding temperatures." The vice-pres calculated that if this were due to a powerful RF source, it would have to be outputting about a gigawatt of power. And, since she wasn't vaporized or heated up in contact with it, the band in which it emitted would have to be significantly less than the 2GHz water dipole resonance frequency like in microwave ovens. A physicist allegedly examined the portion of her dress that disappeared, and didn't see any singing or melting or anything. It didn't burn the woman, either.
One thing he's done recently is, using his powers as vice-president, obtained satellite data from Los Alamos of low microwave band emissions over the last several years. There are some anomalies in the data, one of which is a signal that translates to at least a 500MW output in the ~130MHz band over several minutes. He's hoping to use radio towers located all over the U.S. to triangulate a signal such as that if it ever comes around.
Now, personally, I don't know what to believe about those stories. A ball of hovering, glowing substance that emits power in the megawatts per cubic centimeter range for minutes at a time and can mysteriously make huge amounts of mass just disappear? Sounds impossible. My best guess? Demons, because I doubt even aliens could even pull these ridiculous stunts.
He started the lecture by discussing the prisoner's dilemma, and noting that traditionally the most effective method is that of "tit-for-tat," where responses are based on previous actions. He said that once 40% of a population uses this method, a stable system develops where 7% always rat out/trade a null bag and the remainder always cooperate. This led into him talking about wars and how that method no longer works when "tit" means the destruction of both entities.
Last year, the PRC launched its first of a new class of nuclear missile submarines. They are also, apparently, in the process of constructing two more, a fact that didn't make any major news source (according to him) because of our close trade relationship with China. Not good, especially when they're making crazy threats about nuking the U.S. if we get involved in a war between them and Taiwan.
He also believes that within the next 3-5 years, another country will give an Islamic terrorist organization a ~6 kiloton nuke which they will detonate above the Pentagon, causing the U.S. to withdraw completely from the Middle East.
Among other things, the vice-pres mentioned an interesting study correlating the ratio of males over 18 to males under 18 and a nation's willingness to go to war and sacrifice larger numbers of the male population.
Most of that, along with some stuff about needing more energy, was given as reasons that Sandia exists and needs to continue to exist. He talked a lot about the future of pulsed power as the only feasible fusion energy source, as economically, laser-induced ICF and Tokomak as producers of energy won't happen. I'm personally dubious that they'll be able to get pulsed power ICF to work reliably and continuously, but that's beside the point.
Then he went totally off-topic to talk about a research project he's been pursuing in his own time. He's interested in the kind of ball lightning that doesn't happen anytime near a lightning strike (though usually sometime around a storm). There are stories of this kind hovering around for 20 minutes, doing all sorts of crazy things. One account took place 130 years ago in Ireland, witnessed by one Fitzgerald, of a "lightning ball" about 5 feet in diameter. It moved about a meter per second down a hill, and went into and out of the ground, finally going into a stream and exhausting itself after running into the bank. The crazy part is, everywhere it touched the ground (which was peat) left a huge hole about 4 feet (or meters, I can't remember) deep, so it carved huge tracks in the ground and in the bank near the stream. No mention in the account was made of piles of ground where it might've dug it up, or of steam rising from the ground. I wouldn't believe this at all, but the vice-pres actually went to Ireland and found the place where it happened. Since peat grows so slowly, the holes it allegedly carved in the bank were still there.
Another extraordinary anecdote was in the '70s in England. A lady was in her house when a 6 inch diameter ball hovered up to her and contacted her polyester miniskirt and the underwear underneath it, which a part of vaporized or vanished. She had swatted at it with a hand with a ring on it, and in the moment of time where her hand passed through it, the ring was heated to "scalding temperatures." The vice-pres calculated that if this were due to a powerful RF source, it would have to be outputting about a gigawatt of power. And, since she wasn't vaporized or heated up in contact with it, the band in which it emitted would have to be significantly less than the 2GHz water dipole resonance frequency like in microwave ovens. A physicist allegedly examined the portion of her dress that disappeared, and didn't see any singing or melting or anything. It didn't burn the woman, either.
One thing he's done recently is, using his powers as vice-president, obtained satellite data from Los Alamos of low microwave band emissions over the last several years. There are some anomalies in the data, one of which is a signal that translates to at least a 500MW output in the ~130MHz band over several minutes. He's hoping to use radio towers located all over the U.S. to triangulate a signal such as that if it ever comes around.
Now, personally, I don't know what to believe about those stories. A ball of hovering, glowing substance that emits power in the megawatts per cubic centimeter range for minutes at a time and can mysteriously make huge amounts of mass just disappear? Sounds impossible. My best guess? Demons, because I doubt even aliens could even pull these ridiculous stunts.
05 July 2005
Popsicle sticks
This (creating spring-loaded but stable configurations of popsicle sticks without adhesives or glue) is one thing I did today.
01 July 2005
Z tour
I got to tour the Z machine today. It turns out that the fusion experiments that they do are based on high-pressure plasma uniformly ablating the outside of a deuterium pellet (wait, how can deuterium be a pellet? a good question to ask). I think they said they only need to increase the current input by only a factor of 4 or so to reach the fusion break-even point. This only takes raw energy into account; it doesn't factor in thermodynamic inefficiencies or even the possible increase in energy they might get from using, say, a material that has an exothermic reaction with neutrons in the coolant.
The most interesting part was watching the assembly of the wires. They vary in size from 4 to 11 microns, and they (up to 600) must be assembled/threaded by hand (up to a 11 hour process). Apparently men don't have the patience/coordination to do it.
Each shot (about 220 a year) costs about $100 000 in people/equipment. Crazy.
The most interesting part was watching the assembly of the wires. They vary in size from 4 to 11 microns, and they (up to 600) must be assembled/threaded by hand (up to a 11 hour process). Apparently men don't have the patience/coordination to do it.
Each shot (about 220 a year) costs about $100 000 in people/equipment. Crazy.
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