Sorry, I meant Co-60, I just remembered I was wrong and was going to post a correction, but you beat me to it. Co-60 of course, with half life of about 5.27 years.
Seeing as how this stuff is lethal for periods of time much longer than humanity has even existed as a SPECIES let alone a civilization, and seeing as how the OLDEST structures we've ever created...
Fission byproducts activity decrases to below the level of activity of uranium ore in a period of 700 years (or less, depending on reactor design). 700 years is a manageable period of time, and much shorter than humanity has existed as species. I got this number from the book Intro to Nuclear Engineering by Lamarsh. BTW, the great pyramid in Egypt is estimated to last a million years, even at the current level of erosion, so don't underestimate our ability to build strong structures.
Back when I was in high school, I got a summer internship down the road from Ottawa at a place called Chalk River Nuclear Laboratories
Hey is that where they make Cobalt-50? I know my school imports Co-50 from Canada for the gamma cell in our nuclear lab. (About 10000 Curies' worth every 10 years or so!).
You cannot get a nuclear blast from the fuel used in power plants because the concentration of U-235 is only about 4%. For weapons grade, concentrations of 98% and above are used. Many research reactors that use U-235 can be pulsed for a short time (since they use more enriched Uranium than power plants), which is essentially a runaway reaction, but this reaction stops when tempearture of the neutrons reaches the resonance frequencies of U-238 and absorption crossection increases a lot. You are no physicist if you didn't know that.
Hmm, may be my university nuclear engineering class is not enough to teach me that when people say exponential decay, it means "e to the negative constant times time". Anyway, if fuel is not reprocessed, Plutonium-239 remains in the waste and it does have a long half-life (24000 years). If the fuel is reprocessed and only the fission products are left, the activity falls down to below the level of uranium ore in about 700 years, but this number depends on the exact fuel cycle and reactor design. The activity of uranium ore, while high, is not that dangerous. People used to use some kinds of uranium ore as paint (color was orange). I got those numbers from Intro to Nuclear Engineering by Lamarsh.
We need to know if species can evolve to withstand high levels of radiation, or at least want to know if only it didn't mean loss of some lives along the way
From what I've read, a cockroach (and some other insects) can take as much as 10000 rads body dose and just shake it off. The LD50 dose for humans is about 500 rads. That's whole body dose though. So guess who'll be left after WW3 is over...
You can reprocess spent fuel, thus minimizing the waste. There will still be waste, but not a large volume, so it can be contained easily. IIRC all the nuclear waste ever produced can be stored in a building the size of a football stadium, where if the waste was put so that it covers the football pitch, it would be 1 meter high. Also, waste radioactivity will decay exponentially, so it will not be a hazard in about 100 years after disposal.
You mean FUSION. But as a previous poster mentioned, fusion produces huge quantities of gamma rays and X-rays, which are the most penetrating radiation.
They didn't really say how they got these clock frequencies
Pretty easy I assume, given that Josephson junctions oscillate at frequency dependent on the applied voltage. (In fact Josephson junctions are used for calibration of voltage meters since we can measure frequency to extreme precision). 750 GHz corresponds to EM radiation with wavelength of 0.4mm that will be given off by the circuit and can be observed.
Actually, the resistance of a superconductor is estimated to be truly zero, because smaller and smaller measurements are made all the time and there has not been observed a finite convergence value. Also, you can have an eternal magnetic field by setting up a current loop in any superconducting ring, and the beauty of the thing is that you don't need to input energy once you set up the loop. Since it has no resistance a current loop in a superconductor would last forever. I've heard of an experiment in England by S.Collins where they set up such a current loop and it lasted for years until a trucking strike delayed the delivery of liquid helium.:-)
This cracked me up, man. IIRC a couple of years ago people used to write a whole kernel in 415. Of course I never took that since I took 414 over the summer and 415 wasn't offered.
Both ramjets and scramjets have no moving parts. The difference is that in ramjets the inflow is decelerated to subsonic speeds. However at some high Mach number the pressure loss due to deceleration becomes too high and the combustion product (water) might actually ionize due to intense heating. In that case, scramjets become feasible, where the flow remains supersonic during combustion (SCRAMjet == Supersonic Combustion ramjet). There are meny problems with scramjets which have yet to be researched (like the need to mix the fuel with the intake air REALLY quickly). The SR-71 engine does have moving parts because it is a mix between a turbojet and a ramjet. It operates as a regular turbojet at low speeds. Ramjets have been used in Surface-Air and Air-Surface missiles (eg. C-101, C-301.)
its fuel tanks leak like crazy when it's cooled off on the ground.
Hence the jelo fuel, so that it leaks less.:-) Anyway, ramjets have been used for other applications too (missiles), so they are not unique to the SR-71. Besides, a ramjet is the simplest possible engine, because it has no moving parts: just an inlet and a combustion chamber. A turbofan is much more complicated, because it has a ridiculous number of precisely engineered fanblades, gear assembly, a compressor, etc.
I'm much more impressed by the Concorde. Cruises at Mach 2 only(!), but while carrying 100 passsengers. People who know, say that its engines are the most complicated piece of engineering in the world. Plus, it is really amazing that it actually performs decently aerodynamics-wise at both sub and supersonic speeds. The SR-71 is *horrible* until it reaches cruising altitude and speed. It actually has to take off and then fuel up in the air!
Keep in mind that Pioneer is being kept cryogenically cooled at 3.2K in a hard vacuum and far away from most sources of ionizing radiation. It's not exactly hard to keep tech operating in those kinds of optimal conditions.
Not quite. Pioneer 6 orbits at about the same distance from the Sun as Earth and so half of it is always exposed to the Sun getting 1360 Watts/sq.meter of solar power. However, it is covered with solar arrays, so the inside is in shadow. Solar arrays, have at most 15% efficiency (probably a lot less after 35 years of operation), the rest is thermal power which heats up the spacecraft and has to be dissipated. There can be some very intense temperature differences in different parts of the craft. In fact cooling is often a big problem because there are no convective air currents. CCD cameras are such a problem in newer spacecrafts, because they have a very small operating temperature range (20 Celsius being optimal). Also, the rotation of the craft means that different parts are exposed to the Sun constantly and thermal expansion and contraction also results in fatigue of the materials.
In addition, there are a lot of high-enegy particles hitting the craft constantly, since there is no atmosphere to protect it.
About the SR-71: It is a great craft, but I wouldn't say it symbolizes the pinnacle of technological progress. It's just a rocket with small wings, made from titanium, using jelo as fuel.
Back in the 60s and 70s, probes were over-engineered with triply and quadruply redundant systems at great costs (back then nobody cared about costs). The last probes of that hardcore design are Cassini and Galileo. You know how resilient Galileo turned out. Also, the Vikings and the Voyagers, which cost shitloads of money and were very successful.
Plutonium power generators have 87 year halflife, so power decreases by a factor of 2 every 87 years. So power would probably not be the limiting factor there, like in the case of Galileo for example.
The thing is that there are such things as reprocessing plants that take spent fuel and make new fuel from it. The US refuses to recycle fuel, because recycling separates Plutonium out, which the US says is dangerous to do. Other countries do recycle. All I was saying is that if you are careful about it, nuclear power is much cleaner that most other methods of power generation. Also, there will always be waste in the end, so it has to be stored somewhere in the end. This is the major problem. However, most fission byproducts will decay with half lives much less than 25 years (except Sr-90), so their activity will be basically down to 0 in about 50 years, as evidenced by radiation levels on the Bikini atoll and other test sites. If reasonable measures are taken as storage, there would not be danger, but people still would not have it near them, even though 1 meter thick concrete would be enough. BTW fusion requires sustained temperature of at least 40 million degrees Kelvin. That is why the major problem is containment of the plasma that fusions. There is no material that can withstand that, so some ridiculous things like superconducting magnets etc. must be made to suspend the plasma in "thin air". Imagine the technological challenge in keeping a supercooled magnet next to a 40 million degree plasma!
People are afraid of what they don't understand. Most people do not understand nuclear power and the first thing they associate with the word "nuclear" is a mushroom cloud. Hence the fear that a reactor can somehow explode like an A-bomb, which is in practice impossible.
In fact a coal power plant releases more radioactive stuff than a nuclear plant, because there is a lot of uranium in coal, that gets released as soot after burning the coal. During normal operation a nuclear plant releases only heat that escapes from the heat exchangers and may be some water vapor. Of course there is spent fuel that has to be taken care of after it's been used, but this is much better than carbon dioxide that is released by coal and petroleum and causes greenhouse effect.
I agree with what you say. When I was posting originally I was in a hurry so I worded my post really carelessly so it says that there is a quantum theory for gravity, while there actually isn't. Also, about QCD, I got it backwards, but don't blame me, we just did this in class last week and I haven't studied for it yet:-). Apparently the coupling constant decreases below 1 at high enough energies so that perturbation theory sort of starts to work. The professor also said that the coupling constants converge to some common value at about 1e15 GeV.
While quantum physics give us signifigantly better results for smaller (sub-atomic) physical systems, it hasn't been proven correct by any stretch of the imagination, and there are still an unknown number of forces we have yet to isolate, let alone understand
Quantum mechanics is a theory. You cannot prove a theory correct. You can only prove it wrong by supplying a counter-example. Quantum Mechanics has been confirmed time and time again in many, many experiments and I think that QM is now a generally accepted theory. There are quantum theories for each of the fundamental forces, which are only three (gravity, strong, electroweak) i.e. all interactions of matter are explained by those forces. Let's just say it would be extremely surprising if there were other forces. Another point, IIRC, Quantum Chromodynamics (the strong force theory) has a problem at high energies, but is still accepted as good prediction model for low energies.
I think they also installed a big inertial stabilizer on the top floor of the building. It might not be the same building though. Also, IIRC, the Hancock building in Boston had problems with windows falling down from the external walls and for years the pedestrian areas under the building had to have protective ceilings installed.
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Sorry, I meant Co-60, I just remembered I was wrong and was going to post a correction, but you beat me to it. Co-60 of course, with half life of about 5.27 years.
Seeing as how this stuff is lethal for periods of time much longer than humanity has even existed as a SPECIES let alone a civilization, and seeing as how the OLDEST structures we've ever created ...
Fission byproducts activity decrases to below the level of activity of uranium ore in a period of 700 years (or less, depending on reactor design). 700 years is a manageable period of time, and much shorter than humanity has existed as species. I got this number from the book Intro to Nuclear Engineering by Lamarsh. BTW, the great pyramid in Egypt is estimated to last a million years, even at the current level of erosion, so don't underestimate our ability to build strong structures.
Back when I was in high school, I got a summer internship down the road from Ottawa at a place called Chalk River Nuclear Laboratories
Hey is that where they make Cobalt-50? I know my school imports Co-50 from Canada for the gamma cell in our nuclear lab. (About 10000 Curies' worth every 10 years or so!).
You cannot get a nuclear blast from the fuel used in power plants because the concentration of U-235 is only about 4%. For weapons grade, concentrations of 98% and above are used. Many research reactors that use U-235 can be pulsed for a short time (since they use more enriched Uranium than power plants), which is essentially a runaway reaction, but this reaction stops when tempearture of the neutrons reaches the resonance frequencies of U-238 and absorption crossection increases a lot. You are no physicist if you didn't know that.
Hmm, may be my university nuclear engineering class is not enough to teach me that when people say exponential decay, it means "e to the negative constant times time". Anyway, if fuel is not reprocessed, Plutonium-239 remains in the waste and it does have a long half-life (24000 years). If the fuel is reprocessed and only the fission products are left, the activity falls down to below the level of uranium ore in about 700 years, but this number depends on the exact fuel cycle and reactor design. The activity of uranium ore, while high, is not that dangerous. People used to use some kinds of uranium ore as paint (color was orange). I got those numbers from Intro to Nuclear Engineering by Lamarsh.
We need to know if species can evolve to withstand high levels of radiation, or at least want to know if only it didn't mean loss of some lives along the way
From what I've read, a cockroach (and some other insects) can take as much as 10000 rads body dose and just shake it off. The LD50 dose for humans is about 500 rads. That's whole body dose though. So guess who'll be left after WW3 is over...
You can reprocess spent fuel, thus minimizing the waste. There will still be waste, but not a large volume, so it can be contained easily. IIRC all the nuclear waste ever produced can be stored in a building the size of a football stadium, where if the waste was put so that it covers the football pitch, it would be 1 meter high. Also, waste radioactivity will decay exponentially, so it will not be a hazard in about 100 years after disposal.
You mean FUSION. But as a previous poster mentioned, fusion produces huge quantities of gamma rays and X-rays, which are the most penetrating radiation.
They didn't really say how they got these clock frequencies
Pretty easy I assume, given that Josephson junctions oscillate at frequency dependent on the applied voltage. (In fact Josephson junctions are used for calibration of voltage meters since we can measure frequency to extreme precision). 750 GHz corresponds to EM radiation with wavelength of 0.4mm that will be given off by the circuit and can be observed.
Actually, the resistance of a superconductor is estimated to be truly zero, because smaller and smaller measurements are made all the time and there has not been observed a finite convergence value. Also, you can have an eternal magnetic field by setting up a current loop in any superconducting ring, and the beauty of the thing is that you don't need to input energy once you set up the loop. Since it has no resistance a current loop in a superconductor would last forever. I've heard of an experiment in England by S.Collins where they set up such a current loop and it lasted for years until a trucking strike delayed the delivery of liquid helium. :-)
I have a PII/233, 256M RAM, Win2K. The Open dialogue on Media Player appears almost instantaneously, but I'm assuming it's been cached from yesterday.
This cracked me up, man. IIRC a couple of years ago people used to write a whole kernel in 415. Of course I never took that since I took 414 over the summer and 415 wasn't offered.
The submittor of the article was wrong. 30 nanometers is 300 angstroms, which means the transistors are about 100 atoms across.
Both ramjets and scramjets have no moving parts. The difference is that in ramjets the inflow is decelerated to subsonic speeds. However at some high Mach number the pressure loss due to deceleration becomes too high and the combustion product (water) might actually ionize due to intense heating. In that case, scramjets become feasible, where the flow remains supersonic during combustion (SCRAMjet == Supersonic Combustion ramjet). There are meny problems with scramjets which have yet to be researched (like the need to mix the fuel with the intake air REALLY quickly).
The SR-71 engine does have moving parts because it is a mix between a turbojet and a ramjet. It operates as a regular turbojet at low speeds.
Ramjets have been used in Surface-Air and Air-Surface missiles (eg. C-101, C-301.)
its fuel tanks leak like crazy when it's cooled off on the ground.
:-) Anyway, ramjets have been used for other applications too (missiles), so they are not unique to the SR-71. Besides, a ramjet is the simplest possible engine, because it has no moving parts: just an inlet and a combustion chamber. A turbofan is much more complicated, because it has a ridiculous number of precisely engineered fanblades, gear assembly, a compressor, etc.
Hence the jelo fuel, so that it leaks less.
Sounds like my mom.
I'm much more impressed by the Concorde. Cruises at Mach 2 only(!), but while carrying 100 passsengers. People who know, say that its engines are the most complicated piece of engineering in the world. Plus, it is really amazing that it actually performs decently aerodynamics-wise at both sub and supersonic speeds. The SR-71 is *horrible* until it reaches cruising altitude and speed. It actually has to take off and then fuel up in the air!
Keep in mind that Pioneer is being kept cryogenically cooled at 3.2K in a hard vacuum and far away from most sources of ionizing radiation. It's not exactly hard to keep tech operating in those kinds of optimal conditions.
Not quite. Pioneer 6 orbits at about the same distance from the Sun as Earth and so half of it is always exposed to the Sun getting 1360 Watts/sq.meter of solar power. However, it is covered with solar arrays, so the inside is in shadow. Solar arrays, have at most 15% efficiency (probably a lot less after 35 years of operation), the rest is thermal power which heats up the spacecraft and has to be dissipated. There can be some very intense temperature differences in different parts of the craft. In fact cooling is often a big problem because there are no convective air currents. CCD cameras are such a problem in newer spacecrafts, because they have a very small operating temperature range (20 Celsius being optimal).
Also, the rotation of the craft means that different parts are exposed to the Sun constantly and thermal expansion and contraction also results in fatigue of the materials.
In addition, there are a lot of high-enegy particles hitting the craft constantly, since there is no atmosphere to protect it.
About the SR-71: It is a great craft, but I wouldn't say it symbolizes the pinnacle of technological progress. It's just a rocket with small wings, made from titanium, using jelo as fuel.
Back in the 60s and 70s, probes were over-engineered with triply and quadruply redundant systems at great costs (back then nobody cared about costs). The last probes of that hardcore design are Cassini and Galileo. You know how resilient Galileo turned out. Also, the Vikings and the Voyagers, which cost shitloads of money and were very successful.
Plutonium power generators have 87 year halflife, so power decreases by a factor of 2 every 87 years. So power would probably not be the limiting factor there, like in the case of Galileo for example.
The thing is that there are such things as reprocessing plants that take spent fuel and make new fuel from it. The US refuses to recycle fuel, because recycling separates Plutonium out, which the US says is dangerous to do. Other countries do recycle. All I was saying is that if you are careful about it, nuclear power is much cleaner that most other methods of power generation. Also, there will always be waste in the end, so it has to be stored somewhere in the end. This is the major problem. However, most fission byproducts will decay with half lives much less than 25 years (except Sr-90), so their activity will be basically down to 0 in about 50 years, as evidenced by radiation levels on the Bikini atoll and other test sites. If reasonable measures are taken as storage, there would not be danger, but people still would not have it near them, even though 1 meter thick concrete would be enough.
BTW fusion requires sustained temperature of at least 40 million degrees Kelvin. That is why the major problem is containment of the plasma that fusions. There is no material that can withstand that, so some ridiculous things like superconducting magnets etc. must be made to suspend the plasma in "thin air". Imagine the technological challenge in keeping a supercooled magnet next to a 40 million degree plasma!
People are afraid of what they don't understand. Most people do not understand nuclear power and the first thing they associate with the word "nuclear" is a mushroom cloud. Hence the fear that a reactor can somehow explode like an A-bomb, which is in practice impossible.
In fact a coal power plant releases more radioactive stuff than a nuclear plant, because there is a lot of uranium in coal, that gets released as soot after burning the coal. During normal operation a nuclear plant releases only heat that escapes from the heat exchangers and may be some water vapor. Of course there is spent fuel that has to be taken care of after it's been used, but this is much better than carbon dioxide that is released by coal and petroleum and causes greenhouse effect.
I agree with what you say. When I was posting originally I was in a hurry so I worded my post really carelessly so it says that there is a quantum theory for gravity, while there actually isn't. Also, about QCD, I got it backwards, but don't blame me, we just did this in class last week and I haven't studied for it yet :-). Apparently the coupling constant decreases below 1 at high enough energies so that perturbation theory sort of starts to work. The professor also said that the coupling constants converge to some common value at about 1e15 GeV.
While quantum physics give us signifigantly better results for smaller (sub-atomic) physical systems, it hasn't been proven correct by any stretch of the imagination, and there are still an unknown number of forces we have yet to isolate, let alone understand
Quantum mechanics is a theory. You cannot prove a theory correct. You can only prove it wrong by supplying a counter-example. Quantum Mechanics has been confirmed time and time again in many, many experiments and I think that QM is now a generally accepted theory. There are quantum theories for each of the fundamental forces, which are only three (gravity, strong, electroweak) i.e. all interactions of matter are explained by those forces. Let's just say it would be extremely surprising if there were other forces. Another point, IIRC, Quantum Chromodynamics (the strong force theory) has a problem at high energies, but is still accepted as good prediction model for low energies.
I think they also installed a big inertial stabilizer on the top floor of the building. It might not be the same building though. Also, IIRC, the Hancock building in Boston had problems with windows falling down from the external walls and for years the pedestrian areas under the building had to have protective ceilings installed.