Today is the General GRE, more specifically it starts in about 3 hours. Ah well, at least the Physics subject GRE isn’t for 3 weeks.
Apple employee who demands to remain anonymous
Sept. 17, 2014
This better be a fucking joke/rumor.
Apple holds a patent which mentions that its technology could have applications for law enforcement and government security. For example, the patent description notes that covert ‘police or government operations may require complete ‘blackout’ conditions’.
This little tidbit sold me on the Galaxy over the iPhone for my next phone since I’m due for an upgrade.
If true, this is horrifying.
First unwanted U2 albums and now this no thanks
Staying my Black ass with Android, then…
Hah, special relativity is fun. Two ships got where they were going at the same time (by the time observed by an observer at destination or origin) BUT the wall time for the two ships differs by a month because of the differences in their velocities ( one was moving at a constant 0.97 c, the other went 50% at 0.95 c and the other times at 0.99 c)
It makes me happy to know out there in the world is a high-energy radio telescope with the initials OCRAP.
mantoniospam said: For reference’s sake, how efficient are fusion reactors nowadays? How about the fission ones that are actually used?
Best way of comparing efficiencies between disparate reactions in my book is in relation to the complete annihilation of one atom of hydrogen (about as efficient as you can get for energy creation in a nice standard unit size)
In that frame of reference the “pool heater” is around 0.4%, the sun gets 0.7% (so the pool heater is only ~half as efficient, whoops, glad I double checked) and fission gives about 1/9 of that (~0.04%) from what I know of current reactors. As for what the current efficiencies of the research reactors is, damn good question, none of the public ones are power positive yet (so negatively efficient XD) and the one I know of that is power positive currently is under a deep shroud of secrecy (the polywell, the descendant of the stellarator designs).
Special relativity has the best absurd example problems of all the physics I’ve taken thus far, easily
An eccentric billionaire decides to sterilize his 10^6 liter swimming pool by boiling the water in it, For heating purposes he uses the fusion reaction
1^H + 3^H => 4^He + energy
Assuming the heating system is 20% efficient (!), how much does he pay for the Tritium to raise the pool temperature from 20 to 100 C? It takes 4.2 Joules to raise 1 g of water 1 c and Tritium costs $5 per cm^3 of gas at STP.
Atomic Masses :
- 1^H 1.0081 amu
- 3^H 3.0170 amu
- 4^He 4.0039 amu
The answer is $610, but thats only because his “pool heater” is more efficient than the Sun and it only takes .122 liters of Tritium (even for that half olympic sized pool). Try working it out yourself with wolfram alpha’s help, its a great exercise in unit conversions.