Tell us Sherlock, what would transport the heat away from the computer's surface in vacuum?
Radiation would.
However, cooling to 3 degrees isn't quite so straight forward as grandparent makes out. You have to transport the heat from your computer to the radiators, which requires either a temperature gradient or work to pump the heat. If the radiators are at (say) 4 Kelvin, the rate at which they radiate that energy is going to be very slow, so you're going to need a lot of radiator surface area per Watt.
Stefan-Boltzman law: power emitted by a black body is: P = 5.67e-8 A T^4 where P is in Watts, A is surface area in m^2, T in Kelvin. So at T=4K we emit just 1.5e-5 W/m^2. (This isn't accounting for the fact that the background is at 2.7 degrees rather than 0. Accounting for this drops the cooling power by about 3e-6 W/m^2.) The good news is that T^4 means you get huge improvement in power for modest increase in temperature. For example, at T=10K, we get 5e-4 W/m^2, at T=20K, 8e-3W/m^2. At 300K, 460W/m^2.
You can analyse cooling of heat sources in a very similar manner to electricity*. Heat power is analogous to current, temperature to voltage, and we have a heat resistance (degrees/Watt) analogous to electrical resistance (volts/amp). The lower the heat resistance between your heat source and your cold sink, the cooler your heat source. The problem with a 1m^2 radiator is that it has high heat resistance, so you need a huge number in parallel (huge surface area) to cool your source to a few degrees above the cold sink. In this example, the universe is your cold sink. For your computer, the air in the room is your cold sink**.
* in the absence of heat pumps. ** in the vast majority of cases.
The houses may help if the sea rise is less severe. For example, instead of getting flooding once in 5 years, they now get it several times a year, but usually the island is above water. Such flooding will come with cyclones, so the floating houses will need to be well anchored. It is also not clear whether agriculture and fresh water supplies can be maintained in such circumstances.
The simple fact that corral atolls are uniformly just above sea level despite sea level changes due to ice ages etc. shows that they react to and track sea level changes. They will build themselves up in response to rising sea levels, so if the sea rises for a while and then stops, the islands can catch up. I have no idea whether this will occur on a time scale useful to islanders however.
For a main sequence star, the procedure would normally go something like this: From the star's spectrum, you know its temperature. (With a good enough spectrum, you can also confirm that it is main sequence.) From the temperature and the fact it is main sequence you know its intrinsic luminosity pretty well. From its temperature you know its intrinsic colour well. Comparing this to the observed colour, you infer how much dust there is between you and the star. (Dust blocks blue light more strongly than red light, so more dust means redder colour.) Knowing how much dust there is, you know how much its observed brightness has been reduced by the dust. Knowing what its brightness would be without dust and its intrinsic luminosity, you use the inverse square law to figure out how far away it is.
However, this star would have a really weird spectrum. If I recall correctly, hydrogen and helium only show spectral lines in much hotter stars, so presumably the only lines are calcium (the only metal they did detect). I don't know how well they can determine temperature with just calcium lines. I'm also not sure how precise this procedure is on ordinary stars, but I'd guess the uncertainty in distance would be about 10-30%.
IAAFA also, but I've never actually used the procedure I describe above.
"Sanitation, medical science, vaccine research, etc." didn't save us from "Swine flu". It was only the fact that swine flu was no more lethal than ordinary flu that saved us.
We didn't get nothing for our science. Initial quarantine attempts slowed the spread by a little bit, and a vaccine was eventually produced. Had swine flu been as lethal as 1918 flu, the vaccine would have saved many millions, and the slightly delayed spread would have amplified this.
The global infection rate for the 2009 swine flu was 11% to 21% (Kelly H, Peck HA, Laurie KL, et al. PLoS One 2011 Aug 5;6(8)). The mortality rate of the 1918 flu was 10-20%. Had the 2009 flu been this lethal, it would have killed 1% to 4% of the world population, or about 65 to 260 million people. (Although maybe we'd have been able to lower this by a bit, as we'd have fought it harder had it been so lethal. We might also have been able to keep some of the infected people alive better than in 1918, but given how overwhelmed the medical services would have been, I'm not confident on this.)
Connie Willis is my favourite author. Blackout/All Clear did keep me turning the pages, but I felt it was quite a bit short of her best work. It was too long, and I felt didn't have a sufficiently coherent plot. I wish she'd spent those years writing more smaller books, even if the total word count was lower.
I haven't read any of the other Hugo nominees, so I can't compare to them.
My favourite Willis books are To Say Nothing of The Dog, Passage and Bellwether.
Use Google Scholar instead of plain Google. He looks to have plenty of real science to his credit. (Although I'm betting those 1930s papers were someone else...)
Hey, have you heard about the new Cray 2 computer? It is so fast, it can finish an infinite loop in under 10 seconds!
(That is how I heard it. They probably told the same joke about the IBM 360. Modern supercomputers aren't much faster at infinite loops, but they can do 20,000 at once.)
From TFA: "and all the signals are synchronized to within two nanoseconds."
Light travels about 0.6m in 2ns, so this suggests accuracy will be much less than the ~3cm accuracy claimed by the summary. (If you have lots of base stations, you can do rather better than 0.6m, but a factor of 20 would not be feasible.)
Also - I didn't notice anything in the article to support the summary's "to the nearest inch" claim. Did I just miss it, or is this from some other undisclosed source?
Yes, combinations of the above are most likely. Like I said, I was deliberately playing up stereotypes.
Yes, the purported Neandertal gene has been found in Australians (I read the paper.)
No, the Polynesian pacific islanders are not closely related to Australians - linguistic and genetic evidence places their origin in southern Taiwan. I think New Guinea has relatives of the Australians.
It could be a merger, it could be a little bit of gene flow followed by extinction. The data don't say.
A previous result suggested non-African humans have about 4% of their genome descended from Neandertals. For the sake of argument, I'll take that as a fact.
Merger scenario: a big wave of modern humans flow into Neandertal territory, outnumbering them by about 25 to one. They all form one big happy interbreeding population, soon forming a uniform gene pool which is about 4% Neandertal, reflecting the original population proportion, and then go on to colonize the rest of the planet.
Genocide/extinction scenario: Big bad Modern hunts down and kills the poor Neandertals, raping the women as they go. Some of the half-breeds integrate into the Modern population and leave descendants, but the purebred Neandertals all die on the end of a spear. Despite a Modern population rather smaller than the Neandertal population, in the end we have only Moderns left with only 4% of the genes coming from the once more populous Neandertal, and the non-meek inherit the earth.
I suppose we could even go for: Neandertal conquest scenario: Once upon a time there was a large population of peaceful Moderns. The nasty Neandertals fell upon them like a wolf upon the fold, killed all the men and kept the women for their pleasure. The resulting society had a small number of master race Neandertals ruling the Modern peons. But due to the Modern women being hotter than the Neandertals*, the Neandertal bloodline was quickly diluted until they were indistinguishable from the slaves. It is because we lack our Master Race rulers that we're in such a mess today. * Ask anyone you know, they'll agree on this. That proves it!
Note that I've presented exaggerated scenarios for dramatic effect - do not assume they represent my personal opinions. As presented, my genocide scenario does not explain why we see no Neandertal mitochondrial DNA in present populations, but it could be tweaked to account for that.
"...some form of communicable disease that was stressing the dinosaur population..."
Try rewriting that as "...some form of communicable disease that was stressing the mammal population..." - it doesn't really make sense, does it? Dinosaur diversity back then was similar to mammal diversity now* - one disease isn't going to account for all, or even a large fraction, of them.
However, the dinosaurs may well have been stressed by evolving mammal and bird competitors - some think that this was the primary reason for their extinction, with the asteroid impact being secondary or even uninvolved.
* Disclaimer: I'm not an expert on dinosaur or mammal diversity.
Once you can solve a size 4 and size 5 cube, all larger sizes are obvious generalizations of the same algorithm. (At least, for the algorithm I use it is so.) I've seen an edited video of someone solving a (computer simulated) size 100 cube. So the fact of a "general algorithm" is not news.
That it is an efficient algorithm and sets a new* upper bound on how many moves you need is interesting. (This upper bound is proportional to (n^2/log n), not (n/log n) as stated in the summary.)
* I don't follow cubology that closely, so I'm taking their word for it that this is a new upper bound.
There's an energy level in C-12 at just the right 'place' for the cross section of the He-4+Be-8->C-12 reaction to be greatly enhanced. Nobody's ever told me *how much* enhanced it is though. The triple alpha reaction has a rate which goes as density squared * temperature ^ 30, so doubling the temperature raises the rate by about a million. This means that relatively modest temperature increases can compensate for quite a lot of lack-of-resonance. However, Fred Hoyle predicted the resonance before it was observed on the basis that otherwise we'd have no carbon, and I presume he knew at least approximately the temperature/reaction rate relationship.
OK, thanks for the explanation, sorry to misunderstand you.
I suspect I'm only over the heads of 75-90% of the readers - many have science background or self education. (As demonstrated by the fact I've had two people correct me already...)
Well, I was actually saying it was both. (My thoughts moved on a bit as I was composing, and perhaps I should have gone back and edited my heading.)
The Cambridge dictionary defines (nuclear) fission as "the splitting of the nucleus of an atom, which results in the release of a large amount of energy". Similarly, Websters says "the splitting of an atomic nucleus resulting in the release of large amounts of energy." I would not have made energy release part of the definition, but it seems the dictionaries disagree with me.
I think we're in danger of arguing about words (which is boring and pointless) rather than arguing about the world (which is interesting and useful.)
The reaction involves fusion, and is accurately described as 'fusion powered', so I'll accept "fusion thrusters" as a description, but still note that it is odd that more particles come out than went in.
The reaction is 1H + 11B -> 12C -> 4He + 8Be -> 4He + 4He + 4He so there are more output nuclei than input.
However, I suppose it is true that all of the energy is coming from fusion, as 12C -> 4He + 4He + 4He is exothermic. (The reverse reaction is an energy source for stars under some circumstances.)
12C is normally stable, so for this reaction to go as stated the nucleus must be created in some suitable excited state.
I find lots of articles online linking the whales and the algae, which, while much better than the one linked to in the summary, don't say much more about the whale than that it was spotted off the coast of Israel.
Now Photoshop is a tool that can be used to circumvent CMI restrictions. Of course no court would declare Photoshop illegal. But what reasoning would they use?
Most companies don't have "The Feds turn up with search warrants and take all your stuff, including backup tapes" as a threat they plan for in their backup strategy. Off site backup doesn't protect against this.
I don't know what the problem is in this case - whether the backups were also seized, or that they simply lack the hardware to restore on to.
Slashdot Mirror
Tell us Sherlock, what would transport the heat away from the computer's surface in vacuum?
Radiation would.
However, cooling to 3 degrees isn't quite so straight forward as grandparent makes out. You have to transport the heat from your computer to the radiators, which requires either a temperature gradient or work to pump the heat. If the radiators are at (say) 4 Kelvin, the rate at which they radiate that energy is going to be very slow, so you're going to need a lot of radiator surface area per Watt.
Stefan-Boltzman law: power emitted by a black body is:
P = 5.67e-8 A T^4
where P is in Watts, A is surface area in m^2, T in Kelvin. So at T=4K we emit just 1.5e-5 W/m^2. (This isn't accounting for the fact that the background is at 2.7 degrees rather than 0. Accounting for this drops the cooling power by about 3e-6 W/m^2.) The good news is that T^4 means you get huge improvement in power for modest increase in temperature. For example, at T=10K, we get 5e-4 W/m^2, at T=20K, 8e-3W/m^2. At 300K, 460W/m^2.
You can analyse cooling of heat sources in a very similar manner to electricity*. Heat power is analogous to current, temperature to voltage, and we have a heat resistance (degrees/Watt) analogous to electrical resistance (volts/amp). The lower the heat resistance between your heat source and your cold sink, the cooler your heat source. The problem with a 1m^2 radiator is that it has high heat resistance, so you need a huge number in parallel (huge surface area) to cool your source to a few degrees above the cold sink. In this example, the universe is your cold sink. For your computer, the air in the room is your cold sink**.
* in the absence of heat pumps.
** in the vast majority of cases.
The houses may help if the sea rise is less severe. For example, instead of getting flooding once in 5 years, they now get it several times a year, but usually the island is above water. Such flooding will come with cyclones, so the floating houses will need to be well anchored. It is also not clear whether agriculture and fresh water supplies can be maintained in such circumstances.
The simple fact that corral atolls are uniformly just above sea level despite sea level changes due to ice ages etc. shows that they react to and track sea level changes. They will build themselves up in response to rising sea levels, so if the sea rises for a while and then stops, the islands can catch up. I have no idea whether this will occur on a time scale useful to islanders however.
For a main sequence star, the procedure would normally go something like this:
From the star's spectrum, you know its temperature. (With a good enough spectrum, you can also confirm that it is main sequence.) From the temperature and the fact it is main sequence you know its intrinsic luminosity pretty well. From its temperature you know its intrinsic colour well. Comparing this to the observed colour, you infer how much dust there is between you and the star. (Dust blocks blue light more strongly than red light, so more dust means redder colour.) Knowing how much dust there is, you know how much its observed brightness has been reduced by the dust. Knowing what its brightness would be without dust and its intrinsic luminosity, you use the inverse square law to figure out how far away it is.
However, this star would have a really weird spectrum. If I recall correctly, hydrogen and helium only show spectral lines in much hotter stars, so presumably the only lines are calcium (the only metal they did detect). I don't know how well they can determine temperature with just calcium lines. I'm also not sure how precise this procedure is on ordinary stars, but I'd guess the uncertainty in distance would be about 10-30%.
IAAFA also, but I've never actually used the procedure I describe above.
"Sanitation, medical science, vaccine research, etc." didn't save us from "Swine flu". It was only the fact that swine flu was no more lethal than ordinary flu that saved us.
We didn't get nothing for our science. Initial quarantine attempts slowed the spread by a little bit, and a vaccine was eventually produced. Had swine flu been as lethal as 1918 flu, the vaccine would have saved many millions, and the slightly delayed spread would have amplified this.
The global infection rate for the 2009 swine flu was 11% to 21% (Kelly H, Peck HA, Laurie KL, et al. PLoS One 2011 Aug 5;6(8)). The mortality rate of the 1918 flu was 10-20%. Had the 2009 flu been this lethal, it would have killed 1% to 4% of the world population, or about 65 to 260 million people. (Although maybe we'd have been able to lower this by a bit, as we'd have fought it harder had it been so lethal. We might also have been able to keep some of the infected people alive better than in 1918, but given how overwhelmed the medical services would have been, I'm not confident on this.)
Connie Willis is my favourite author. Blackout/All Clear did keep me turning the pages, but I felt it was quite a bit short of her best work. It was too long, and I felt didn't have a sufficiently coherent plot. I wish she'd spent those years writing more smaller books, even if the total word count was lower.
I haven't read any of the other Hugo nominees, so I can't compare to them.
My favourite Willis books are To Say Nothing of The Dog, Passage and Bellwether.
You didn't complete the quote: "people are lying 13% of the time when they say they have to take a cell phone call around you."
I.e. You are the cause of 13% of people faking phone calls.
Use Google Scholar instead of plain Google. He looks to have plenty of real science to his credit. (Although I'm betting those 1930s papers were someone else...)
Hey, have you heard about the new Cray 2 computer? It is so fast, it can finish an infinite loop in under 10 seconds!
(That is how I heard it. They probably told the same joke about the IBM 360. Modern supercomputers aren't much faster at infinite loops, but they can do 20,000 at once.)
From TFA: "and all the signals are synchronized to within two nanoseconds."
Light travels about 0.6m in 2ns, so this suggests accuracy will be much less than the ~3cm accuracy claimed by the summary. (If you have lots of base stations, you can do rather better than 0.6m, but a factor of 20 would not be feasible.)
Also - I didn't notice anything in the article to support the summary's "to the nearest inch" claim. Did I just miss it, or is this from some other undisclosed source?
Yes, combinations of the above are most likely. Like I said, I was deliberately playing up stereotypes.
Yes, the purported Neandertal gene has been found in Australians (I read the paper.)
No, the Polynesian pacific islanders are not closely related to Australians - linguistic and genetic evidence places their origin in southern Taiwan. I think New Guinea has relatives of the Australians.
It could be a merger, it could be a little bit of gene flow followed by extinction. The data don't say.
A previous result suggested non-African humans have about 4% of their genome descended from Neandertals. For the sake of argument, I'll take that as a fact.
Merger scenario: a big wave of modern humans flow into Neandertal territory, outnumbering them by about 25 to one. They all form one big happy interbreeding population, soon forming a uniform gene pool which is about 4% Neandertal, reflecting the original population proportion, and then go on to colonize the rest of the planet.
Genocide/extinction scenario: Big bad Modern hunts down and kills the poor Neandertals, raping the women as they go. Some of the half-breeds integrate into the Modern population and leave descendants, but the purebred Neandertals all die on the end of a spear. Despite a Modern population rather smaller than the Neandertal population, in the end we have only Moderns left with only 4% of the genes coming from the once more populous Neandertal, and the non-meek inherit the earth.
I suppose we could even go for:
Neandertal conquest scenario: Once upon a time there was a large population of peaceful Moderns. The nasty Neandertals fell upon them like a wolf upon the fold, killed all the men and kept the women for their pleasure. The resulting society had a small number of master race Neandertals ruling the Modern peons. But due to the Modern women being hotter than the Neandertals*, the Neandertal bloodline was quickly diluted until they were indistinguishable from the slaves. It is because we lack our Master Race rulers that we're in such a mess today.
* Ask anyone you know, they'll agree on this. That proves it!
Note that I've presented exaggerated scenarios for dramatic effect - do not assume they represent my personal opinions. As presented, my genocide scenario does not explain why we see no Neandertal mitochondrial DNA in present populations, but it could be tweaked to account for that.
"...some form of communicable disease that was stressing the dinosaur population..."
Try rewriting that as "...some form of communicable disease that was stressing the mammal population..." - it doesn't really make sense, does it? Dinosaur diversity back then was similar to mammal diversity now* - one disease isn't going to account for all, or even a large fraction, of them.
However, the dinosaurs may well have been stressed by evolving mammal and bird competitors - some think that this was the primary reason for their extinction, with the asteroid impact being secondary or even uninvolved.
* Disclaimer: I'm not an expert on dinosaur or mammal diversity.
Once you can solve a size 4 and size 5 cube, all larger sizes are obvious generalizations of the same algorithm. (At least, for the algorithm I use it is so.) I've seen an edited video of someone solving a (computer simulated) size 100 cube. So the fact of a "general algorithm" is not news.
That it is an efficient algorithm and sets a new* upper bound on how many moves you need is interesting. (This upper bound is proportional to (n^2/log n), not (n/log n) as stated in the summary.)
* I don't follow cubology that closely, so I'm taking their word for it that this is a new upper bound.
There's an energy level in C-12 at just the right 'place' for the cross section of the He-4+Be-8->C-12 reaction to be greatly enhanced. Nobody's ever told me *how much* enhanced it is though. The triple alpha reaction has a rate which goes as density squared * temperature ^ 30, so doubling the temperature raises the rate by about a million. This means that relatively modest temperature increases can compensate for quite a lot of lack-of-resonance. However, Fred Hoyle predicted the resonance before it was observed on the basis that otherwise we'd have no carbon, and I presume he knew at least approximately the temperature/reaction rate relationship.
http://en.wikipedia.org/wiki/Triple-alpha_process
OK, thanks for the explanation, sorry to misunderstand you.
I suspect I'm only over the heads of 75-90% of the readers - many have science background or self education. (As demonstrated by the fact I've had two people correct me already...)
*facepalm*. You're right, sorry.
Make a substantive criticism, and I'll consider it, as I have for my other responder. Otherwise you're just a source of noise.
Well, I was actually saying it was both. (My thoughts moved on a bit as I was composing, and perhaps I should have gone back and edited my heading.)
The Cambridge dictionary defines (nuclear) fission as "the splitting of the nucleus of an atom, which results in the release of a large amount of energy". Similarly, Websters says "the splitting of an atomic nucleus resulting in the release of large amounts of energy." I would not have made energy release part of the definition, but it seems the dictionaries disagree with me.
I think we're in danger of arguing about words (which is boring and pointless) rather than arguing about the world (which is interesting and useful.)
The reaction involves fusion, and is accurately described as 'fusion powered', so I'll accept "fusion thrusters" as a description, but still note that it is odd that more particles come out than went in.
The reaction is
1H + 11B -> 12C -> 4He + 8Be -> 4He + 4He + 4He
so there are more output nuclei than input.
However, I suppose it is true that all of the energy is coming from fusion, as 12C -> 4He + 4He + 4He is exothermic. (The reverse reaction is an energy source for stars under some circumstances.)
12C is normally stable, so for this reaction to go as stated the nucleus must be created in some suitable excited state.
It didn't happen unless they name the scientists and cite the paper.
That was a terrible article. It has almost no detail. In particular, the only source given for this information is "scientists".
Here's a better reference for the algae.
I find lots of articles online linking the whales and the algae, which, while much better than the one linked to in the summary, don't say much more about the whale than that it was spotted off the coast of Israel.
Now Photoshop is a tool that can be used to circumvent CMI restrictions. Of course no court would declare Photoshop illegal. But what reasoning would they use?
I've been around long enough to remember the Secret Service raid on Steve Jackson Games, which was the triggering event for founding the EFF.
Most companies don't have "The Feds turn up with search warrants and take all your stuff, including backup tapes" as a threat they plan for in their backup strategy. Off site backup doesn't protect against this.
I don't know what the problem is in this case - whether the backups were also seized, or that they simply lack the hardware to restore on to.
You mean :)
At least Parker Bros. were smart enough to imitate sensible currency.
They may be 20 years behind Australia, but on the bright side, they're probably 20 years ahead of the USA.