Plus, it is generally one size fits all. And, most of the time that means running. Which I was never very good at either, though not quite 10:30 bad. But, I had no problem with water sports. So, I got graded on how fast I can run, while heading to 1.5 hour swim practices every afternoon in high school.
Actually, I have a little trouble with DDR now due to two things:
1) Being out of shape and over weight. 2) Too many years in water sports developing the wrong muscles for high impact actvity.
Well, smallfurrycreature answered it, but I didn't see any taking sides. It was truth. There was little denigration that Swedes made a choice that was different from the one America made, and that some americans may not liek that choice and therefore should think carefully before moving their.
Mayeb using pinko socialist through you off. I took it for the self deprecating joke that it was.
That is one hockey stick. The green house gas hockey stick is not subject to that sort of reinterpretation. The trick is of course how will planetary climate react to the tremendous increase in greenhouse gases over the last century? A delay between greenhouse gas increase and temperature increase is to be expected given the large thermal mass of the entire planet. But, trying to align that information with global average temperature, and then align that with climate is nearly intractable, there are so many variables. But, do we really want to keep doing something that the laws of physics suggest will be very disruptive to human civilization in the hope that something we do not know about will magically prevent significant problems?
A fundimental property of a black hole (as we understand it) is that everything beyond its event horizon is never emitted.
Correct, except this in itself provides a means to differentiate a black hole from something with a surface in the case where the black hole has a companion star. Material from the companion is pulled towards the black hole. If there were a surface the material hits the surface and releases a burst of X-rays periodically. A black hole will never have these burst since it does not have a surface. A recent study of blackhole candidates and neutron stars with companions has shown just this difference.
Now, this doesn't help much with supermassive black holes in the center of galaxies. But, if you prove the existence of black holes and the mass in a small area at the center of a galaxy is so large that it could only be a black hole, then I would call that sufficient proof for a black hole.
Yes, it is indirect, but rather than being a measurement of the mass of an object and likely radius, which could be something very massive that is not a black hole (no idea what) it actually measure a property unique to black holes vs some other very dense object with a surface. Although, I guess hypothetically it could be something extremely exotic that just absorbs everything that hits it, but has a solid surface. Then, again I would still call that a black hole.
Yes, the moderator has now stopped absorbing fast neutrons. This will in turn lead to a temperature rise in the reactor. Loss of moderator was a contributing factor to the Chernobyl explosion. Slowing down those neutrons keeps the reactor cool. If the graphite burns away, the sudden increase in temperature will fuel the fire.
Ummm... No, that would involve destroying energy. Slowing down a neutron converts the neutron's energy to heat. So, the heat is deposited in the moderator. Now in Chernobyl losing the moderator may result in extra energy being deposited in the coolant water causing the water to vaporize explosively. As there is no liquid in a pebble bed this cannot happen. And, the neutrons are no longer fueling the nuclear reactions resulting in a reduction in heat and neutrons. Oh and the Helium is already at 400-900C therefore increasing the heat to 1800C or even 2700C gets at most a 3-4x increase in pressure, this would typically be non-explosive. (actually less since I did not convert to Kelvin) Liquid to gas conversion increases pressure a lot more than simply increasing the temperature of a gas.
Actually, if you think of it the graphite in a pebble bed is the fission heat exchanger as I suspect helium does not absorb much energy from neutrons. So, the graphite slows the neutrons and absorbs energy from the fission products thereby getting hot and transferring that heat to the helium.
And, I will agree fire is bad, I just see some trouble in sustaining that chemical reaction in the face removal of the fission heat source. Still, since it would not be explosive the problem with a fire would be much more local than Chernobyl was.
listen to yourself... "no chance". you mean "less chance, as far as we can estimate".
No, generally it means physically impossible. At least that is the goal use the laws of physics themselves to make a catastrophic accident impossible.
#1 Don't use water. The potential for rapid conversion of a liquid into a gas is what creates and explosion risk. Consider the helium in a pebble bed reactor running at say 200C (i think it is hotter) and 1atm. At 400C it is 2atm at 800C 4atm, 1600C 8atm. Not even close to enough to cause an explosion. Water vaporized at 800C will explose.
#2 Make sure heat poisons the reaction. Another pebble bed feature when it gets too the reaction slows and eventually settles at a relatively low temperature.
#3 Make sure a fire doesnt release significant radioactive material. Fire is a pebble bed risk, but it looks like a fire could not result in a fuel release. And, again poisons the nuclear reaction by removing the graphite moderator.
Have you considered the fact that nuclear waste disposal requires that the stuff be stored for 10,000 years or more?
This is because we only use 1% of the energy avilable in uranium ore. Increase that to 99% which is well within current technology and first, the waste mass per unit energy is reduced because we are not treating fissionables as waste. Second, while the waste is highly radioactive it reaches the radioactivity of the original ore in 1,000 years, instead of 10,000 years.
Oh and if the reprocessing is done on-site there is limited transportation of plutonium.
Can you guarantee that there won't be geological shifts or that somebody won't dig it up during that time?
Nope, but much less likely in 1,000 years than 10,000 years.
Can you even design a sign that is absolutely certain to communicate to your descendants 50 or 60 centuries hence, "Don't excavate here, what you dig up can kill you and everybody in your vicinity and make it uninhabitable for generations"?
Shouldn't be a problem for a thousand year. As we a re quite capable of reading signs from over 2000 years ago.
Yes! Think of all the things that are not feasible because they use a lot of energy, but would be really good over all. You listed a few.
Like you said energy, good. Getting it from fossil fuels, bad. So, waste is created by nuclear fission. But, the energy generated is about a million times per gram of fuel consumed than chemical energy. But, one problem is that we only use about 1% of the available energy in uranium ore. Even though the technology exists to use 99% of that energy.
Think of all the pollution control processes that become feasible when energy is abundant. What sort of things can be done with garbage if energy were not a limitation?
Increasing the ability to harness energy is the goal period end of story. If we don't do it the entirity of human civilzation is guaranteed to be doomed. Energy is what holds the entirity of civilization back, and your proposal is that everyone should sit back and wait for the inevitable end. Well, I refuse, when energy is abundant anything is possible, including getting out of this galactic backwater before the oceans evaporate due to the continued increase in solar temperature.
The first step is the ability to harness the available energy of the entire planet. This does not necessarily mean depleting the planet, but means harnessing the same amount of energy. My guess is this requires space based acquisition and transport of solar energy. Fusion is another alternative, but the giant fusion reactor in the sky is already running. Still, fusion allows for possibly portable energy. And, portable energy on that scale opens up the stars.
So, maybe we shoud slow down energy use a little until the energy technology catches up, but the ultimate goal has to be to go way beyond todays energy use.
The situation you are describing is why there is work going on to trade efficiency for cost. A solar panel today I believe, converts about 15% of incident light to electricity. And, about 2kW can be generated on about half of a south facing home roof (330sqft). Now let's say a module can be made that costs 1/8th as much but at half the efficiency. You would need 2x the area, but would pay 1/4 of the price.
The otherway can also work, but appears to be much more difficult. i.e increase efficiency at the same price.
The article assumes PUREX processing which can create weapons grade Plutonium from the spent fuel. Pyroprocessing extracts the Uranium and transuranics all together resulting in a output that would require a lot of further processing to become weapons grade, but is very good power plant fuel. Ideally, the processing should occur at the power plant site thereby reducing the need to move plutonium around. And, any that woudl be moved around would be mixed with U-238 and a bunch fo other stuff that would make it unsuitable for a nuclear weapon.
And, I question the 84% of the procesing needed for weapons grade uranium. Fuel is 3-7% U-235 weapons grade is something like 90+% U-235. Not sure where 84% of the enrishment necessary is reached from that.
Graphite burns. Shit, there goes the reaction moderator. Oops. What's that you say? The temperature is now over 1100 degrees centigrade. Darn! That's the melting point of uranium. Looks like the balls, already disinegrating, will now all flow into a big puddle at the bottom of the reactor. Reaching... critcal mass? Will there be an explosion now? I'm not nuclear physisist, but this all seems so potentially..... unsafe....
YES! The moderator is gone! Oh, wait you apparently don't know what a moderator is for. It is there to slow down the neutrons, so they can initiate another fission reaction if the neutrons are not slowed down the U-235 doesn't absorb them, resulting in a halting of the fission reaction. So, burning off the graphite moderator will halt the fission reaction. Melting the Uranium together will also halt the fission reaction for the same reason.
Oh, and the fuel is not metallic uranium it is uranium oxide with a melting point of 2800C. Not likely to happen. Oh and if you read more of the wikipedia entry you would have noted the layer of inflammable silicon carbide in the pebble that is not flammable, and thus acts as a fire break.
So, basically the entire danger in the pebble bed reactor is a chemical fire. And, said fire would occur on the outside of the pebbles, the pebbles and the grains within them would likely be mostly intact due to the silicon carbide layer. Even if the pebbles broke down the grains inside would not leave the reactor as they are too big to float on air. And, have not melted let alone vaporized. And, the loss of the graphite results in the halting of the fission reactions. So, basically a chemical fire near radioactive material, which while extinguishing by menas other than waiting for the fuel to burn off may be difficult does not result in the release of radioactive material... Well no more radioactive material than any other fire.
This is the key to newer reactor designs. The goal is to require constant intervention to keep a reaction going, if any or every human intervention is removed (moderators, coolants, etc...) there is no reaction.
The technology is available to use multi-kilometer deep holes. So, you are talking about the top barrel being worst case 100m below the ocean floor. The barrels are spaced with ocean silt/clay in between. The assumption is that the barrels will leak. The analysis shows in 10,000 years the leaked material will have spread a few meters into the surrounding silt/clay. Remember, the top barrel is 100 meters down. The nuclear material never hits free flowing ocean water.
That's why we shouldn't be building old-style slow reactors that do only a single reaction on the fuel. The US government has been against breeder reactors because they can be used to generate munitions-grade plutonium, but there are newer types of breeder reactors which generate contaminated plutonium, perfectly useful for continuing the reaction, but not for building bombs. And re-reacting the fission products will get rid of long-lived nuclear waste, which means less uranium is needed to begin with, and there is no need for 10,000-year waste dumps when you have waste half-lives measured in decades.
Yes. Just one point breeder reactors do not generate munitions grade plutonium current reporcessing technology (PUREX?) creates munitions grade plutonium. If the reprocessing simply stripped the fission products out and left the U-238, PU, and U-235 alone the resulting output is nto even close to munitions grade.
A recent article I read proposed fast neutron reactors as the way to go. Then, reprocessing spent fuel onsite to extract the fission byproducts as waste and the U-235, U-238, and Plutonium as fresh fuel. Note, the reprocessing technology described was different from current reprocessing that basically purifies Plutonium which scares the crap out of pepople. This takes care of a few problems.
First, the fission byproducts have much shorter half lives than heavy elements and therefore do not require a waste storage facility good for 10,000 year, but more like 1,000 year to reach radiation levels of the original ore.
Second, it halts the tremendous waste of useful energy in the current nuclear cycle. Something like less than 1% of the available nuclear energy is extracted in current slow beutron nuclear power generation. Fast neutron reactors with reprocessing would push that number to nearly 99%.
Third, the risk of plutonium proliferation is significantly reduced. The reprocessing technology proposed is does not result in Plutonium fuel, but a mixture of PU, U-238, U-235 which is pretty useless for weapons without massive purification. And, because it is reprocessed on-site for use onsite the amount of material tranported to waste storage is significantly reduced. Assuming 1% of the original fuel is used at each reprocessing cycle it means only 1% of the resulting mass is sent out as waste each refueling cycle. Basically the 540 tons of nuclear fuel used in a single year right now results in pretty much 540 tons of waste, reprocessing that 540 tons means only 5.4 tons of waste.
Keep in mind that the individual who offered to work for $7/hr was willing to work for that rate. He/she was not forced or lied to in order to work for that rate. You may say, "But you were originally willing to spend $10/hr!". That would only be true if that's what I thought the going rate for the particular skillset was. Suppose you wanted to buy a DVD player and planned to spend $40 for it. Then you see an ad that was selling it for $30. Would you go for the lower price, or would go buy the one that had the price that you were "originally willing" to spend? Remember: retailers have hopes, cares, concerns, and families, too! Are you going to deprive them of those things just because someone else has a sweeter distribution deal?
This is a bad example due to the imbalance of information and power between the employer and the employee. Therefore it cannot be called capitalism, well more accurately it is not a fair market price. A fair market price could happen if the employee knew what all employers were willing to pay for his service and the employers knew what all employee were willing to work for. The result would be a fair market price.
Of course we don't live in a true capitalist economy where prices are dictated completely by the market. First, there is a minimum wage and other government intervention. Second, in general employers have much more information than employees about market pay rates, and what is others are paying. Not to mention most employers will immediately drop a prospective employee who answers "How much are you willing to work for?" with the question "How much are you willing to pay?" Thereby exacerbating the information imbalance.
What you didn't mention was that this was proven with the opening of the Millenium Bridge in Londom where hundreds of people walking across it caused it to sway by several metres.
Umm... Did you bother to even watch that episode? They showed the Millenium bridge as well as Tacoma narrows as examples of how resonances can cause bridges to sway or fail. The millenium bridge was particularly interesting because it was actually a breeze that caused the initial swaying and they found that the people walking across it would subconsciously sway in unison with the bridge amplifying the swaying.
Yeah, once you prove a shark the size of the one in Jaws cannot exist what is the point of going any further. It would have been more interesting to experiment using a shark the size of the one in Jaws.
Re:Your show is great fun to watch and all, but...
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First, most pickup trucks have box beds, not flat beds, and second, the design of the cab determines the airflow pattern over the whole vehicle, not the bed.
I have to disagree here. The rear of a vehicle has a huge impact on the aerodynamics. A round blunt front with a pointy back end is the ideal aerodynamic shape i.e. teardrop. It is most important to bring the air together smoothly at the rear than it is to split it smoothly at the front (subsonic). Real world examples... Airplanes, bicycle farings, Prius. Knowing this take a look at a lot of cars, and note how many would be more aerodynamic driven backwards.
That is not to say the front is irrelevant, just that the back has much more relvance than you ascribe to it. Oh and the tailgate up is perfectly reasonable. It is a two steps to the point at the rear is smoother than one step.
I agree Memory. More specifically, large quantities of DRAM. This is more a result of the decreasing size and trying to figure out what to do with all the additional transistors available. The GPU is an interestign idea, but I think DRAM is easier solely because the heat densities on GPU and CPU are so high that the lower heat density of DRAM would make it easier to add to a CPU. In all likelyhood the DRAM will actually act more like a gigantic exclusive L3 cache, of course with the option of having no offboard memory. At 45nm I bet they could fit the equivalent of an 8Gbit DRAM chip, getting 1GB of memory before adding any external memory.
That was my immediate thought. One fact may show a theory is off. But, whatever new theory appears has to explain all the old experiemental data and the one new piece of data. There seems to be two paths this typically goes. A modficiation to the original theory, or a brand new theory that also emcompasses the old theory under certain conditions. Evolution seems to take the first path where new information moves the theory forward while keeping the fundamental premise. The Newtonian gravity to General Relativity is more liek the second where the entire theory was redone, but with relatively small gravitational fields Newtonian Grvaity and General Relativity are essentially equal to a lot of decimal places.
If we are talking about hte transport car becoming detached in atmosphere it would fall like anything else. Outside atmosphere it would depend on where o the trip and whether the perigee of its orbit were in atmosphere.
If we are talking about the structure itself that is where things get weird, and some one who know more about orbital mechanics can correct me.
Assuming it were severed low to the ground the center of gravity would move up. Causing the hanging portion to move relative to the atmosphere. Air friction would bleed off some of the energy and the structure would gradually descend as it moved. The center of gravity would eventually reach geosynch orbit again and the bottom would stop moving relative to the earth. Not sure what happens to an object with a center of gravity in geostationary orbit and a portion hanging in the atmosphere.
Higher up is more dangerous I suspect because the portion still attached to the Earth falls. And, then we have to deal with whatever it falls on. Not sure enough relative motion would exist between the air and the falling portion to result in burning. So, watch out below. In this case if the upper portion does not extend into atmosphere it would start moving relative to the ground. Ideally, the crew at the top station could move the counter weight to restore geosynch orbit, and eventually restore the connection to ground.
The paper seesm to focus on the fact that small sample size and limited true statistical significance of study results is the reason.
My argument would be of course most studies have small sample sizes and somewhat tenuous statistical significance. Large studies cost large amounts of money. If there were no small studies that published with small amounts of statistical significance how would larger studies get funded? You have to start small in order to figure out whether it is worthwhile funding a larger study in the first place.
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Plus, it is generally one size fits all. And, most of the time that means running. Which I was never very good at either, though not quite 10:30 bad. But, I had no problem with water sports. So, I got graded on how fast I can run, while heading to 1.5 hour swim practices every afternoon in high school.
:)
Actually, I have a little trouble with DDR now due to two things:
1) Being out of shape and over weight.
2) Too many years in water sports developing the wrong muscles for high impact actvity.
Or, as I like to say... Land sports BAD.
Well, smallfurrycreature answered it, but I didn't see any taking sides. It was truth. There was little denigration that Swedes made a choice that was different from the one America made, and that some americans may not liek that choice and therefore should think carefully before moving their.
Mayeb using pinko socialist through you off. I took it for the self deprecating joke that it was.
That is one hockey stick. The green house gas hockey stick is not subject to that sort of reinterpretation. The trick is of course how will planetary climate react to the tremendous increase in greenhouse gases over the last century? A delay between greenhouse gas increase and temperature increase is to be expected given the large thermal mass of the entire planet. But, trying to align that information with global average temperature, and then align that with climate is nearly intractable, there are so many variables. But, do we really want to keep doing something that the laws of physics suggest will be very disruptive to human civilization in the hope that something we do not know about will magically prevent significant problems?
A fundimental property of a black hole (as we understand it) is that everything beyond its event horizon is never emitted.
Correct, except this in itself provides a means to differentiate a black hole from something with a surface in the case where the black hole has a companion star. Material from the companion is pulled towards the black hole. If there were a surface the material hits the surface and releases a burst of X-rays periodically. A black hole will never have these burst since it does not have a surface. A recent study of blackhole candidates and neutron stars with companions has shown just this difference.
Now, this doesn't help much with supermassive black holes in the center of galaxies. But, if you prove the existence of black holes and the mass in a small area at the center of a galaxy is so large that it could only be a black hole, then I would call that sufficient proof for a black hole.
Yes, it is indirect, but rather than being a measurement of the mass of an object and likely radius, which could be something very massive that is not a black hole (no idea what) it actually measure a property unique to black holes vs some other very dense object with a surface. Although, I guess hypothetically it could be something extremely exotic that just absorbs everything that hits it, but has a solid surface. Then, again I would still call that a black hole.
Not to mention it seems the AMD parts tend to retail for closer to or less than the 1000 unit price than Intel.
Yes, the moderator has now stopped absorbing fast neutrons. This will in turn lead to a temperature rise in the reactor. Loss of moderator was a contributing factor to the Chernobyl explosion. Slowing down those neutrons keeps the reactor cool. If the graphite burns away, the sudden increase in temperature will fuel the fire.
Ummm... No, that would involve destroying energy. Slowing down a neutron converts the neutron's energy to heat. So, the heat is deposited in the moderator. Now in Chernobyl losing the moderator may result in extra energy being deposited in the coolant water causing the water to vaporize explosively. As there is no liquid in a pebble bed this cannot happen. And, the neutrons are no longer fueling the nuclear reactions resulting in a reduction in heat and neutrons. Oh and the Helium is already at 400-900C therefore increasing the heat to 1800C or even 2700C gets at most a 3-4x increase in pressure, this would typically be non-explosive. (actually less since I did not convert to Kelvin) Liquid to gas conversion increases pressure a lot more than simply increasing the temperature of a gas.
Actually, if you think of it the graphite in a pebble bed is the fission heat exchanger as I suspect helium does not absorb much energy from neutrons. So, the graphite slows the neutrons and absorbs energy from the fission products thereby getting hot and transferring that heat to the helium.
And, I will agree fire is bad, I just see some trouble in sustaining that chemical reaction in the face removal of the fission heat source. Still, since it would not be explosive the problem with a fire would be much more local than Chernobyl was.
listen to yourself... "no chance". you mean "less chance, as far as we can estimate".
No, generally it means physically impossible. At least that is the goal use the laws of physics themselves to make a catastrophic accident impossible.
#1 Don't use water. The potential for rapid conversion of a liquid into a gas is what creates and explosion risk. Consider the helium in a pebble bed reactor running at say 200C (i think it is hotter) and 1atm. At 400C it is 2atm at 800C 4atm, 1600C 8atm. Not even close to enough to cause an explosion. Water vaporized at 800C will explose.
#2 Make sure heat poisons the reaction. Another pebble bed feature when it gets too the reaction slows and eventually settles at a relatively low temperature.
#3 Make sure a fire doesnt release significant radioactive material. Fire is a pebble bed risk, but it looks like a fire could not result in a fuel release. And, again poisons the nuclear reaction by removing the graphite moderator.
Have you considered the fact that nuclear waste disposal requires that the stuff be stored for 10,000 years or more?
This is because we only use 1% of the energy avilable in uranium ore. Increase that to 99% which is well within current technology and first, the waste mass per unit energy is reduced because we are not treating fissionables as waste. Second, while the waste is highly radioactive it reaches the radioactivity of the original ore in 1,000 years, instead of 10,000 years.
Oh and if the reprocessing is done on-site there is limited transportation of plutonium.
Can you guarantee that there won't be geological shifts or that somebody won't dig it up during that time?
Nope, but much less likely in 1,000 years than 10,000 years.
Can you even design a sign that is absolutely certain to communicate to your descendants 50 or 60 centuries hence, "Don't excavate here, what you dig up can kill you and everybody in your vicinity and make it uninhabitable for generations"?
Shouldn't be a problem for a thousand year. As we a re quite capable of reading signs from over 2000 years ago.
Yes! Think of all the things that are not feasible because they use a lot of energy, but would be really good over all. You listed a few.
Like you said energy, good. Getting it from fossil fuels, bad. So, waste is created by nuclear fission. But, the energy generated is about a million times per gram of fuel consumed than chemical energy. But, one problem is that we only use about 1% of the available energy in uranium ore. Even though the technology exists to use 99% of that energy.
Think of all the pollution control processes that become feasible when energy is abundant. What sort of things can be done with garbage if energy were not a limitation?
Increasing the ability to harness energy is the goal period end of story. If we don't do it the entirity of human civilzation is guaranteed to be doomed. Energy is what holds the entirity of civilization back, and your proposal is that everyone should sit back and wait for the inevitable end. Well, I refuse, when energy is abundant anything is possible, including getting out of this galactic backwater before the oceans evaporate due to the continued increase in solar temperature.
The first step is the ability to harness the available energy of the entire planet. This does not necessarily mean depleting the planet, but means harnessing the same amount of energy. My guess is this requires space based acquisition and transport of solar energy. Fusion is another alternative, but the giant fusion reactor in the sky is already running. Still, fusion allows for possibly portable energy. And, portable energy on that scale opens up the stars.
So, maybe we shoud slow down energy use a little until the energy technology catches up, but the ultimate goal has to be to go way beyond todays energy use.
The situation you are describing is why there is work going on to trade efficiency for cost. A solar panel today I believe, converts about 15% of incident light to electricity. And, about 2kW can be generated on about half of a south facing home roof (330sqft). Now let's say a module can be made that costs 1/8th as much but at half the efficiency. You would need 2x the area, but would pay 1/4 of the price.
The otherway can also work, but appears to be much more difficult. i.e increase efficiency at the same price.
The article assumes PUREX processing which can create weapons grade Plutonium from the spent fuel. Pyroprocessing extracts the Uranium and transuranics all together resulting in a output that would require a lot of further processing to become weapons grade, but is very good power plant fuel. Ideally, the processing should occur at the power plant site thereby reducing the need to move plutonium around. And, any that woudl be moved around would be mixed with U-238 and a bunch fo other stuff that would make it unsuitable for a nuclear weapon.
And, I question the 84% of the procesing needed for weapons grade uranium. Fuel is 3-7% U-235 weapons grade is something like 90+% U-235. Not sure where 84% of the enrishment necessary is reached from that.
Graphite burns. Shit, there goes the reaction moderator. Oops. What's that you say? The temperature is now over 1100 degrees centigrade. Darn! That's the melting point of uranium. Looks like the balls, already disinegrating, will now all flow into a big puddle at the bottom of the reactor. Reaching... critcal mass? Will there be an explosion now? I'm not nuclear physisist, but this all seems so potentially..... unsafe....
YES! The moderator is gone! Oh, wait you apparently don't know what a moderator is for. It is there to slow down the neutrons, so they can initiate another fission reaction if the neutrons are not slowed down the U-235 doesn't absorb them, resulting in a halting of the fission reaction. So, burning off the graphite moderator will halt the fission reaction. Melting the Uranium together will also halt the fission reaction for the same reason.
Oh, and the fuel is not metallic uranium it is uranium oxide with a melting point of 2800C. Not likely to happen. Oh and if you read more of the wikipedia entry you would have noted the layer of inflammable silicon carbide in the pebble that is not flammable, and thus acts as a fire break.
So, basically the entire danger in the pebble bed reactor is a chemical fire. And, said fire would occur on the outside of the pebbles, the pebbles and the grains within them would likely be mostly intact due to the silicon carbide layer. Even if the pebbles broke down the grains inside would not leave the reactor as they are too big to float on air. And, have not melted let alone vaporized. And, the loss of the graphite results in the halting of the fission reactions. So, basically a chemical fire near radioactive material, which while extinguishing by menas other than waiting for the fuel to burn off may be difficult does not result in the release of radioactive material... Well no more radioactive material than any other fire.
This is the key to newer reactor designs. The goal is to require constant intervention to keep a reaction going, if any or every human intervention is removed (moderators, coolants, etc...) there is no reaction.
The technology is available to use multi-kilometer deep holes. So, you are talking about the top barrel being worst case 100m below the ocean floor. The barrels are spaced with ocean silt/clay in between. The assumption is that the barrels will leak. The analysis shows in 10,000 years the leaked material will have spread a few meters into the surrounding silt/clay. Remember, the top barrel is 100 meters down. The nuclear material never hits free flowing ocean water.
That's why we shouldn't be building old-style slow reactors that do only a single reaction on the fuel. The US government has been against breeder reactors because they can be used to generate munitions-grade plutonium, but there are newer types of breeder reactors which generate contaminated plutonium, perfectly useful for continuing the reaction, but not for building bombs. And re-reacting the fission products will get rid of long-lived nuclear waste, which means less uranium is needed to begin with, and there is no need for 10,000-year waste dumps when you have waste half-lives measured in decades.
Yes. Just one point breeder reactors do not generate munitions grade plutonium current reporcessing technology (PUREX?) creates munitions grade plutonium. If the reprocessing simply stripped the fission products out and left the U-238, PU, and U-235 alone the resulting output is nto even close to munitions grade.
A recent article I read proposed fast neutron reactors as the way to go. Then, reprocessing spent fuel onsite to extract the fission byproducts as waste and the U-235, U-238, and Plutonium as fresh fuel. Note, the reprocessing technology described was different from current reprocessing that basically purifies Plutonium which scares the crap out of pepople. This takes care of a few problems.
First, the fission byproducts have much shorter half lives than heavy elements and therefore do not require a waste storage facility good for 10,000 year, but more like 1,000 year to reach radiation levels of the original ore.
Second, it halts the tremendous waste of useful energy in the current nuclear cycle. Something like less than 1% of the available nuclear energy is extracted in current slow beutron nuclear power generation. Fast neutron reactors with reprocessing would push that number to nearly 99%.
Third, the risk of plutonium proliferation is significantly reduced. The reprocessing technology proposed is does not result in Plutonium fuel, but a mixture of PU, U-238, U-235 which is pretty useless for weapons without massive purification. And, because it is reprocessed on-site for use onsite the amount of material tranported to waste storage is significantly reduced. Assuming 1% of the original fuel is used at each reprocessing cycle it means only 1% of the resulting mass is sent out as waste each refueling cycle. Basically the 540 tons of nuclear fuel used in a single year right now results in pretty much 540 tons of waste, reprocessing that 540 tons means only 5.4 tons of waste.
Dastardly
Keep in mind that the individual who offered to work for $7/hr was willing to work for that rate. He/she was not forced or lied to in order to work for that rate. You may say, "But you were originally willing to spend $10/hr!". That would only be true if that's what I thought the going rate for the particular skillset was. Suppose you wanted to buy a DVD player and planned to spend $40 for it. Then you see an ad that was selling it for $30. Would you go for the lower price, or would go buy the one that had the price that you were "originally willing" to spend? Remember: retailers have hopes, cares, concerns, and families, too! Are you going to deprive them of those things just because someone else has a sweeter distribution deal?
This is a bad example due to the imbalance of information and power between the employer and the employee. Therefore it cannot be called capitalism, well more accurately it is not a fair market price. A fair market price could happen if the employee knew what all employers were willing to pay for his service and the employers knew what all employee were willing to work for. The result would be a fair market price.
Of course we don't live in a true capitalist economy where prices are dictated completely by the market. First, there is a minimum wage and other government intervention. Second, in general employers have much more information than employees about market pay rates, and what is others are paying. Not to mention most employers will immediately drop a prospective employee who answers "How much are you willing to work for?" with the question "How much are you willing to pay?" Thereby exacerbating the information imbalance.
What you didn't mention was that this was proven with the opening of the Millenium Bridge in Londom where hundreds of people walking across it caused it to sway by several metres.
Umm... Did you bother to even watch that episode? They showed the Millenium bridge as well as Tacoma narrows as examples of how resonances can cause bridges to sway or fail. The millenium bridge was particularly interesting because it was actually a breeze that caused the initial swaying and they found that the people walking across it would subconsciously sway in unison with the bridge amplifying the swaying.
Yeah, once you prove a shark the size of the one in Jaws cannot exist what is the point of going any further. It would have been more interesting to experiment using a shark the size of the one in Jaws.
First, most pickup trucks have box beds, not flat beds, and second, the design of the cab determines the airflow pattern over the whole vehicle, not the bed.
I have to disagree here. The rear of a vehicle has a huge impact on the aerodynamics. A round blunt front with a pointy back end is the ideal aerodynamic shape i.e. teardrop. It is most important to bring the air together smoothly at the rear than it is to split it smoothly at the front (subsonic). Real world examples... Airplanes, bicycle farings, Prius. Knowing this take a look at a lot of cars, and note how many would be more aerodynamic driven backwards.
That is not to say the front is irrelevant, just that the back has much more relvance than you ascribe to it. Oh and the tailgate up is perfectly reasonable. It is a two steps to the point at the rear is smoother than one step.
Yes, despite their claims of "busting myths", that obviously is there to have a unique show idea, rather than to say everyone else is wrong.
More importantly whether the myth is busted or not,there is usually really cool stuff that goes on. (aka. blowed up stuff)
I agree Memory. More specifically, large quantities of DRAM. This is more a result of the decreasing size and trying to figure out what to do with all the additional transistors available. The GPU is an interestign idea, but I think DRAM is easier solely because the heat densities on GPU and CPU are so high that the lower heat density of DRAM would make it easier to add to a CPU. In all likelyhood the DRAM will actually act more like a gigantic exclusive L3 cache, of course with the option of having no offboard memory. At 45nm I bet they could fit the equivalent of an 8Gbit DRAM chip, getting 1GB of memory before adding any external memory.
That was my immediate thought. One fact may show a theory is off. But, whatever new theory appears has to explain all the old experiemental data and the one new piece of data. There seems to be two paths this typically goes. A modficiation to the original theory, or a brand new theory that also emcompasses the old theory under certain conditions. Evolution seems to take the first path where new information moves the theory forward while keeping the fundamental premise. The Newtonian gravity to General Relativity is more liek the second where the entire theory was redone, but with relatively small gravitational fields Newtonian Grvaity and General Relativity are essentially equal to a lot of decimal places.
How would a space elevator fall?
If we are talking about hte transport car becoming detached in atmosphere it would fall like anything else. Outside atmosphere it would depend on where o the trip and whether the perigee of its orbit were in atmosphere.
If we are talking about the structure itself that is where things get weird, and some one who know more about orbital mechanics can correct me.
Assuming it were severed low to the ground the center of gravity would move up. Causing the hanging portion to move relative to the atmosphere. Air friction would bleed off some of the energy and the structure would gradually descend as it moved. The center of gravity would eventually reach geosynch orbit again and the bottom would stop moving relative to the earth. Not sure what happens to an object with a center of gravity in geostationary orbit and a portion hanging in the atmosphere.
Higher up is more dangerous I suspect because the portion still attached to the Earth falls. And, then we have to deal with whatever it falls on. Not sure enough relative motion would exist between the air and the falling portion to result in burning. So, watch out below. In this case if the upper portion does not extend into atmosphere it would start moving relative to the ground. Ideally, the crew at the top station could move the counter weight to restore geosynch orbit, and eventually restore the connection to ground.
The paper seesm to focus on the fact that small sample size and limited true statistical significance of study results is the reason.
My argument would be of course most studies have small sample sizes and somewhat tenuous statistical significance. Large studies cost large amounts of money. If there were no small studies that published with small amounts of statistical significance how would larger studies get funded? You have to start small in order to figure out whether it is worthwhile funding a larger study in the first place.