498 karma · joined April 17, 2010
Personally, I've often been annoyed with Processing's generic name, as it can make searching for solutions for specific issues in Processing difficult, unless there happens to be a solution on the Processing fora.
My CS professor has published papers that are solutions to exercises in The Art of Computer Programming. It's sort of a fact of life for computer scientists that whatever you're doing has probably already been done by Knuth.
The moderator is the substance which slows down the neutrons to a speed where they're likely to fission with the Uranium-235 in the fuel. This is typically water. Water can also absorb neutrons, so it has a poison effect as well. When the moderating effect of the water dominates its poison effects, the reactor is said to be under-moderated. When the moderator is reduced (for example, when it boils away), the reactor becomes less efficient, so it reduces power. This is called a negative temperature coefficient.
The Soviets, however, designed their reactors to be over-moderated, for efficiency. Thus, when the water heated up, and started boiling away, the net result was to increase the efficiency of the reactor (a positive temperature coefficient), since the water was more of a poison than a moderator. Because the reactor is now more efficient, it got even hotter, and boiled more water away. You know the rest.
We've learned a lot about designing safe reactors since Chernobyl, and it's extremely unlikely that an accident on the scale of Chernobyl will happen again (not only because of the moderation issue).
I hope this helps to alleviate your concerns. If you have any further questions, please feel free to ask me.
ii) I falsely conflated uncontrolled fission with meltdown in my explanation. Meltdown is when the core reaches a temperature at which the control rod cladding (which is probably stainless steel, though I can't confirm that) melts. Uncontrolled fission will result in a spectacular meltdown, as happened at Chernobyl. So, being shutdown is not a guarantee against melting down. However, as long as the core stays submerged, then it should stay cool enough to avoid melting down. I haven't read any reports that the operators are concerned about water level in the core, so a meltdown is unlikely. Worst case, you could open up a valve on the primary and stick a hose in it.
The main concern at this point is definitely the steam pressure.
IAANRO (I Am A Nuclear Reactor Operator. I work part-time at my college's research reactor[1])
Nuclear power reactors are of two main varieties: Pressurized Water Reactors, and Boiling Water Reactors[2]. The plant in question is a Boiling Water Reactor (BWR). BWRs work by using the core's thermal energy to boil the cooling water into steam, and then channelling the steam in order to turn a steam turbine. After it exits the turbine, the steam is cooled in a condenser, where it turns back to water, and then is sent back into the core. The condenser requires cool water to be actively pumped through it, to keep the pipes upon which the steam condenses from becoming too hot. The water/steam that runs through the core and the turbine is referred to as the "primary cooling system", and the water running through the condenser is the "secondary cooling system." The primary is assumed to be contaminated (that is, it is measurably radioactive), whereas the secondary system is not, since it is isolated from the primary.
As far as I can tell, the chain of events for this particular plant went something like this:
Shortly after the quake, the reactor successfully shut down in anticipation of the tsunami. This means that no more fission is occurring in the core. Since a core meltdown is a result of uncontrolled fission, this means that the reactor is now incapable of melting down. This will not be another Chernobyl. However, just because U-235 is no longer fissioning, doesn't mean that the core isn't producing heat. The fission fragments (those isotopes produced as a result of the U-235 fissioning) will continue to decay through alpha, beta, or gamma emission, until stable elements at the bottom of the decay chain are reached. The decay of these fission fragments and their decay products will cause the core to continue to produce heat for some time after shutdown.
Presumably due to the fact that every reactor near the east coast of Japan was being shutdown, offsite power for the secondary cooling system was unavailable, so the power plant had to rely on onsite backup power, but the onsite power only lasted for 8 hours. After that, the secondary cooling system failed, which is what triggered the declaration of the Nuclear Emergency, and evacuation of those living within 3Km of the plant.
Since the core is continuing to produce heat, and consequently steam, the steam pressure inside the primary system is rising above normal levels. They are hesitant to bleed off steam into the containment dome, since the dome was probably damaged in the quake, but obviously bleeding off some steam is better than having the primary system rupture. Thankfully, most of the really nasty decay products have a relatively short half-life. In particular, Nitrogen-16, which gives off pretty high energy betas when it decays, has a half-life of 7.2 seconds.
Therefore, releasing the steam is undesirable, but not catastrophic, and probably not even particularly hazardous. The radioactive materials in the cloud will be longer-lived decay products of hydrogen and oxygen in, and as far as I'm aware none of those are particularly active. The cloud will be dilute itself after release, which will lower the intensity of the radiation field significantly. Therefore, the total radioactivity release will be many orders of magnitude lower than that of Chernobyl or Three Mile Island. The media is playing this up to be bigger than it is, because nuclear power still carries a stigma.
[1]: Reed Research Reactor: http://reactor.reed.edu/
[2]: Wikipedia Article on Boiling Water Reactors: http://en.wikipedia.org/wiki/Boiling_water_reactor
[1] http://wiki.osx86project.org/wiki/index.php/Main_Page [2] http://tonymacx86.blogspot.com/2010/04/iboot-multibeast-inst...
That barcode has a persistent pattern in its lower part: every once and a while, there's the same four light blue lines straddling three sets of light grey lines. That movie is about a contestant on the Indian version of "Who Wants to Be a Millionaire". For reference, I found a screencap of the show on Wikimedia[2]. You'll notice that the location and pattern of the lines in the barcode correspond with the location and form of the question boxes in the show. The light blue lines are the outlines of the boxes, and the light grey ones are the text. I don't have a copy of the movie with me, but I suspect that if you linearly interpolate between horizontal position in the barcode and temporal position in the movie, then the scenes where the question boxes are on the screen will correspond with the locations in the barcode where the pattern appears.
As to whether the frame is cropped or resized to be 1-pixel wide, my guess is that they are resized. My reasoning is that if the frame were cropped, then you might not always see the light grey lines along with the light blue lines in the barcode, since you might take a slice of the frame that falls along spaces between words in the questions and answers. Since the appearance of the question box pattern is pretty much uniform, it's probable that the entire frame is resized, so each pixel in each slice corresponds to the "average" color value of pixels at that height in the sampled frame (I say "average" because I don't really know how downscaling algorithms work).
[1]: http://s3.amazonaws.com/data.tumblr.com/tumblr_lh9wkoPf5s1qh... [2]: http://upload.wikimedia.org/wikipedia/en/thumb/a/a4/Ken_Basi...
The runtime of that movie is 148 minutes-almost two and a half hours. Yet it doesn't feel that long. It also manages to have three different groups of characters doing separate things, without confusing the audience. The last move I can recall trying to do that level of simultaneity was The Phantom Menace, which failed horribly at that task. Therefore, I find Inception to be a very interesting movie intellectually, because I think it's fun to think about the techniques that Nolan uses to make a 2.5 hour, multithreaded movie so entertaining.
What if Google started offering, say, free Google Coupons (assuming they roll their own groupon) in exchange for befriending them on FaceTorrent? Not all of my friends and relatives value privacy as much as I do.
[1]:http://edition.cnn.com/2010/TECH/gaming.gadgets/10/21/macboo...
I've graded and TA'd the course for two years, and I think his approach works extremely well. It lets you filter out the people who really get it from the people who are just pattern matching from previous experience.
Really? That's the first time I've heard about it. Do you mind going into more detail, or sharing links? It's not at all obvious to me why the two skills would be correlated (perhaps because my only musical skill is completely average ability to play the guitar).
The problem, I think, is that the spaces between letters are much smaller than the internal negative spaces of the letters. The little horizontal flairs on the sides of many letters in Museo exacerbate this issue. This ends up making it really hard for me to recognize the letters which have no internal negative space, most notably i, t, and r, since they tend to bleed into their neighboring letters at this small size.
It's also good to familiarize yourself with the distinctions between detention and arrest.
In the United States, "detention" is whenever police temporarily restrict someone's rights based on an "articulable" suspicion that a crime has occurred. Police can detain anyone at any time if they have an articulable suspicion, but only for a short period of time, and they cannot search the belongings or vehicles of people in detention without consent (many cops will try to obtain consent by saying things like "let me see what's in your bag," but you are well within your rights to verbally deny consent). A good way to establish if you're being detained is to ask the officer if you're free to go. If not, you should then ask why you're being detained, and memorize the response. This is the "articulable suspicion" that the officer is supposed to have before detaining you.
"Arrest" occurs when "any reasonable person" would feel that they are not free to leave. The distinction between detainment and arrest is subtle, but if you're being handcuffed or put into a police vehicle, your belongings or vehicle are being searched after you have denied consent, or you are detained for an extended period of time, then you're under arrest. Crucially, police are not required to make any formal declaration of your arrest, nor are they required to read you your Miranda rights (though they are required to read them if they wish to question you). If you feel that you're under arrest, your best course of action is to state that you refuse to speak and wish to see an attorney. You can repeat this as often as is necessary. They're not allowed to question you after you say this, but only if don't say anything else. If you do, then you've waived your right to silence. The only exception is that you are allowed to give your name and address in order to be released with a promise to appear in court. If you do give that information, immediately follow it by repeating that you will remain silent until an attorney is present.
Again, I Am Not A Lawyer, although all of this information does come from lawyers who give talks about civil liberties. None of these talks are online, but most of the above is explained in more detail on an actual lawyer's website[1].
[1]: http://www.williamweinberg.com/lawyer-attorney-1127658.html
Here's a video demo: http://www.youtube.com/watch?v=x7VTo0656Rc
"Hi, my name is Aperiodic, and I'm... a mathematician."
"Hi Aperiodic."
"It all started out so easily; you know, a few lemmas with the boys in the evenings. But before I knew it, I was picking up Bourbaki as soon as I got home from work. I would wake up in the mornings, surrounded loose sheets of paper covered in commutative diagrams, without a clear idea of what I did last night..."
This is clearly the case for f(n) = 1, g(n) = lg(n), hence the constant function is O(lg(n)).
An algorithm can be O of different g(x)s, depending on the properties of the input. For example, the runtime of a naive quicksort implementation (which always chooses the leftmost value as a pivot) is O(n^2) if the input list is sorted, while it has runtime O(n*lg(n)) on average and in the best case (where the pivot is always the median of the section of the list being partitioned).
The question is not whether it's possible, but whether it's common.
Regardless, I think it would be particularly illuminating if there <i>were</i> false positives. Why not have employees who are concerned wear dosimeters constantly, and at the same time stick reference dosimeters near where they usually stand while a scanner is in operation. If their dose is roughly the same as that of the reference dosimetry, there's not much room to complain about the scanners.
The fact is we are being constantly bombarded by low-level radiation from cosmic rays and radon gas simply by virtue of standing on the surface of the earth. The level of radiation these scanners output is much smaller than that. Wikipedia[2] cites an article in the European Journal of Radiology that gives a dose range for backscatter machines of between 0.07 and 6 micro-Sieverts. For reference, the National Council on Radiation Protection and Measurements reports that the annual radiation dose from naturally occurring radiation is on the order of several hundred micro-Sieverts [3].
TSA employees have a right to be concerned, because they are involuntarily being exposed to it as a course of their job, without this being made clear to them when they were hired. If you're a traveler, you should be much more concerned about the radiation dose you receive on the plane than the one you receive from the scanner.
[1] Health Physics Society page on radiation exposure on commercial airflights: http://hps.org/publicinformation/ate/faqs/commercialflights..... [2] https://secure.wikimedia.org/wikipedia/en/wiki/Backscatter_X... [3] http://hps.org/documents/environmental_radiation_fact_sheet....