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Comment Not surprised (Score 2) 181

In high school and college, every now and then someone would have surgery or have a bad injury, and they'd come back from the doctor bragging about the drugs they got. It was like a free pass to get high, and no one was ever concerned that it might lead to addiction because the drugs were prescribed by a doctor, so of course they aren't dangerous. It seems due to a failure to educate young people properly and a success on the drug companies' part to make their product seem like magic.

Comment Which record? (Score 2) 110

Alta devices has a record efficiency of 28.8% (not 24%, as quoted in the article) specifically for a single junction solar cell. This cell technically has four junctions, for which I'm not aware of any world records; however, Boeing spectrolab created a five junction cell with the world record for non-concentrated light (38.8%). I'm not aware of the records for spectrum splitting cells, so it's possible that Alta made a spectrum splitting cell with 24% efficiency and that this is the new world record for such a cell, though it's not particularly ground-breaking in terms of impact since it doesn't solve the major problems that make these high efficiency cells so expensive (the triple junction cell still requires an expensive substrate and an expensive process for depositing the films)

Comment Re:The TSA's math is real wrong. (Score 1) 199

Newton's third law doesn't necessarily mean the same amount of work is done on both objects. For instance, consider a block attached to a spring attached to a wall. With the spring initially compressed, it does work on the block as it moves away from the wall, but the spring does negligible work on the wall because the wall is not moving. Substitute pressurized gas for spring, bullet for block, and rifle for wall. An added complication is that the force on the bullet is actually due to gases in the barrel, so if the gases are accelerating then the rifle will feel a different force than the bullet.

The best way to analyze the situation is using conservation of momentum. Assuming the bullet and rifle are both at rest before firing, total momentum must be zero. Take .01kg for the bullet mass, 1kg for the rifle mass, and 1000 m/s for the muzzle velocity. Then .01kg * 1000 m/s = 1 kg * V_rifle --> V_rifle = 10 m/s. In contrast, the kinetic energy of the bullet is .01kg * (1000 m/s)^2 = 10^4 J versus 1kg * (10 m/s)^2 = 100 J, so I would expect the bullet to have around two orders of magnitude greater energy.

You could check wikipedia for "Free Recoil" and "Muzzle Energy" if you want to see how accurate my approximation is.

Comment Re:The TSA's math is real wrong. (Score 1) 199

The two major flaws in your argument are that radiation doses (in rem or Sv) are calculated using a "quality" factor that takes into account the type of radiation and the tissue that absorbs it, and the fact that the units are in energy/mass so the calculations _should_ already take into account the frequency dependence of photon energy. But I do agree that people should be more clear when they say "radiation"--I get the feeling that people hear x-rays and they think of nuclear decay involving protons and neutrons, when x-rays are just high energy light. And what does "background radiation" really mean? Everything around me is radiating but it's mostly infrared light and I'm not too worried about my exposure to infrared, even cumulatively over a long time period.

Comment Re:Math Math Math (Score 1) 154

The most useful thing I learned in high school chemistry was that units behave like variables. I wouldn't have made it far as a physics major if I didn't recognize when the result of a formula has the wrong units or that you can't add meters to seconds.

Comment Re:Just because the math works doesn't mean it's t (Score 3, Insightful) 650

My understanding of an "entropic force" is that it can be described in terms of fundamental forces. The pressure in an ideal gas, for instance, can be derived by looking at the impulse created by a single molecule, and then extending that to a collection of N molecules. This guy seems to be saying that gravity is an entropic force and therefore NOT a fundamental force, but it seems to me that entropic forces are just an abstraction that allows us to ignore the underlying fundamental forces. Of course, I didn't read the whole article, but what I read was poorly written and that doesn't inspire a lot of confidence. Maybe I'll take another look if it gets published.

Comment Re:Sugar cane not corn (Score 1) 894

According to Wikipedia, as of 2008-04-30, ethanol production is no longer subsidized. Care to provide a source countering that?

And to the people who say that more energy is consumed in producing corn I'd also ask for a source. According to the DOE, has a positive energy balance. (Granted, the source is the government, so I guess they're only saying that because of corn lobbyists)

I'm honestly willing to hear claims to the contrary, but all I see here on slashdot is a bunch of people saying that ethanol is bad without citing any research (even TFA didn't cite any original research)

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"An idealist is one who, on noticing that a rose smells better than a cabbage, concludes that it will also make better soup." - H.L. Mencken