Some schools call pre-algebra, discrete math, which is a huge injustice to the name of the more difficult course. So I think you're right, discrete is a weed out for CS
That's a good strategy, taking courses outside your major that is. I took a couple of minors to even out my education, it also kept me sane during hours or math, advanced physics, etc. If you find you don't like engineering after your junior year, I'd stick with it just to get the degree. Should you want to go to grad school, you can always switch your curriculum to what you want to study. Usually a department would just make you take remedial courses in that major to "catch up" to their traditional students. Keep in mind that a bachelors in engineering just shows that you can do the basics (meaning you can pass the FE exam without too much trouble if you want the grad school route). A bachelors won't make you an expert in the field or a definitive source of all things related to that field, but it shows that you have a good base in the fundamentals and a capacity for future study or field work. Keep up with the extra classes, they'll pay off
In my field, we've seen almost a 40% increase in undergrad enrollment over the past few years, so I doubt that it's every engineering field that's losing students. Sure since the tech bubble burst, students that would have studied a CS or related field might rethink their plans and pick a different major, but that's not every field. Nuclear, Mechanical, Chemical, Civil, etc etc have all seen steady increases in enrollment. It's most likely just students forecasting what field they think they can get a job in based on the current day demand.
Fingerprints are currently stored in the FBI database for all arrests, which means it doesn't matter if you're innocent or guilty because it's the arrest record that contains your fingerprints, not the court decision. My one worry is that since we enabled the PATRIOT act to supercede due process and individual rights in many cases, how long before a person could be detained as a threat just to have their DNA sampled if they are just an political undesirable? DNA should only be kept for convicted felons of violent crimes, as it currently is in most states. There is no reason why this should be changed.
If your only use for a computer was checking email, browing websites, and basic time management stuff. For those of use to do actual work on our PC's, with larger programs, a la matlab, etc etc, a cell phone just doesn't have the same functionality of a pc. To have comparable speed, screen size, and input capability, a PC is still unmatched. I've seen tons of nifty apps for the treo and hiptop platforms, but for the large part, I still need to sit in front of a full size screen and get work done. If I want to check the news, weather, email, etc, I could use a phone and that would work just fine, but I'll stick with my monolithic pc for when I need to do some work.
That's true with the "free" initial cell phone. It isn't free because if they were to allow the sale of just service without selling a phone, the price per month would be a few bucks less since they use that bump in pricing to pay for the phones (obviously they get bulk discounts so their prices are less than ours would be). The contract period usually covers their loss and then some, especially if you have a 2 year agreement as with most providers. That way, at the end of your contract, you've overpaid for a phone that wasn't worth nearly as much as you paid, yet you still think you got a deal because it was "free" at the beginning.
I'm curious to see how Tivo will do this though, if they offer discounts initially, but overcharge for service and lock users into a contract, what will happen to their business if they change their software to allow DRM that will prohibit users from recording certain shows? Why not just make the user pay full price up front and provide damn good service so the user won't want to change?
Bombing a military target that was far removed from the eyes of the population wouldn't have been nearly as effective of changing the image of the war in the eyes of the average joe. The state controlled media simply wouldn't report the bombing to the populace and would have basically said exactly what that iraqi minister said, that Saddam had the Americans on the run, when the war was over in under 3 weeks. Since the US bombed industrial centers that were full of people, the knowledge of the bombings couldn't be concealed, and therefore the information would spread outwards uncontrollably, thus changing the population's will to fight. Had the multitude still had the will to fight, the war would have dragged on for a whole lot longer, but the US made great use of some military "strategery" and psychological warfare to end the war early. I'm glad my grandfather came home from the pacific in '45. In short, I'm trying to support what you said;-)
"Looks to me like more and more people are going to gt into wireless mesh networks and pgp/gpg just to avoid big brother."
If only people would take that much of an active approach to conceal their privacy. In practice, people are lazy. With the exception of a few groups of people, the vast majority of people on the internet in the US hold the idea that "I have nothing to hide, so why not?". That is very unsettling to me and probably everyone else on/. People already don't conceal their privacy offline. If you want to shat yourself, try looking up yourself/friends/family on www.zabasearch.com and you'll see what I mean. Privacy is unfortunately becoming less and less and the vast majority of people don't care because the invasions of privacy are relatively transparent. If the FBI viewing their entire internet habits/emails doesn't interfere with their daily lives, then they won't complain so long as they're told that it's being done to "stop the terrorists." This is becoming more and more an invisible war where the enemy is the ideal of freedom.
Take your pick, that's why I said "any undergraduate engineering thermodynamics textbook." Try looking up the Moran and Shapiro, latest edition is the 5th I believe, if that doesn't work, look up Nuclear Systems I by Todreas and Kazimi, both are undergrad texts that can be found in most mechanical engineering school's libraries
High temperature systems are very efficient as the HTGR's used in some countries, you're right. Problem is that with high temperatures come weaker materials, making the capacity factor less than that of a lower temperature plant. Not to mention the lower power output. I'm very familiar with this, but if you think that these plants with a 50% capicty factor take the place of a 90% capacity factor plant that yields a 40% efficiency with a much higher power output, you're very wrong. So why not open a textbook and look at underlying reasons before criticizing. Reading an article on slashdot doesn't make you an expert scooter.
I'd imagine the same way propane or any natual gas could be stored, that is in a steel reinforced tank capable of a hundred psi or so. That would hold a decent amount of H-2 gas.
As a person that designs power plants, I'm wondering what design you're working with where a coal plant reaches 50% efficiency. The best efficiency I've seen for most plants is getting close to 40% and that's with a nuclear plant (APWR) The best designed coal plant I've seen had nearly 37% efficiency but a capacity fact of around 60% (meaning they don't have it turned on all the time). Whenever you create your electricity by boiling water with a few regenerative or reheat cycles, your efficiency probably won't ever top the current efficiencies. You can get my numbers from any undergraduate engineering thermodynamics textbook.
The problem with putting the fuel in the middle of the tokamak is that it's very dense in there. The toroidal and poloidal magnets, inner shielding, cooling units, and related cabling/equipment take up much if not all of the room in the inner ring so putting fuel and related cooling in the center is one of those things that was ruled out after some research. So the only place you can really put the fuel is in the outermost portion, within the magnets but outside the pressure vessel (the magnets being more D-shaped and the plasma chamber being a deformed oval leaves some room to the outermost). Lithium doesn't make a very good moderator though, better than most since it's low-Z but it would still take quite a few interactions to slow down a 14 MeV neutron down to the energy that U-238 would absorb. U-238 absorbs most in the 1/v range (low energy from about.1eV to.00253eV/thermal range), so you'd really have to slow down the neutrons to get to that range, and when slowing down neutrons, every collision matters to decrease the possibility of leakage. Hence it's much better to use fast spectrum actinides like Np, Pu, Am, and Cm for a fusion neutron source. As for the neutron flux distribution, it's pretty strong all over, except it's the strongest on the outside of the toroid since that's where the plasma density is the greatest so the majority of neutrons are slung outwards due to some of the more enjoyable aspects of plasma physics (drift motions and whatnot). So the best place to collect the neutrons is on the outside. Using different sizes of tokamaks is possible, but actually achieving fusion requires certain geometry constraints. Since the plasma is pulsed, the field is constantly changing and that relates directly with the plasma temperature. So you can't make it too small otherwise you can't reach ignition temperatures (~5keV for most). If you're still curious about some of the cross sections, there's an online plotting cgi gateway at the Korean Atomic Energy Research Institute (http://atom.kaeri.re.kr/). Cool stuff but not doppler broadened for the range used in fusion reactors.
The neutron wasn't discovered until well after the periodic table was created though so neutrons had no effect on the makeup of the periodic table other than screw with scientists minds over why the weights don't match up to their theory. If you want to look at isotope/isotone differences, then you'd be using a chart of the nuclides.
I think he means something like the Seebeck effect which is the reverse of the Peltier effect, meaning you get energy and electrons are pushed through the npn junction when going from the hot side to the cold side. Obviously you'd lose efficiency when it's a hot to warm conversion because of the lower gradient. It's not a perpetual motion machine, it's been around for almost 200 years and is probably most famously used on modern satellites and probes in the form of RTG's (radioisotope thermal generators).
How would you get a.99 k-effective out of U-238? Even with fuel lumping I don't see it. Unless you're already including the neutrons provided by the fusion reaction, but the problem with that is that a tokamak is a pulsed device which rules out normal k-effective equations so you can't assume steady state of the neutron flux but rather a sinusoidal which if you try to "fix" the flux it would balance out much lower than expected for a steady state beam. Also looking at the first, second, and third chance fission cross sections for U-238 I'm not seeing how that would even be possible for a natural uranium blanket would absorb the neutrons at that high of energy even with the doppler broaded cross sections at the high temperatures in a standard core. I'd check with MCNPX if you have access to it and use the added neutron physics and do a simple kcode to check this, but make sure you have doppler broadened and unresolved region linearized cross sections since you're dealing with high energies (although that might skew it a little, but it's a rough estimate afterall). The U-238 is on the order of 10^-4 barns for the highest fission XS. Also how could you get that much uranium inside the magnets? It's a very tight fit between the magnets and the actual fission chamber. Also rarely is pure uranium metal ever used except for in a godiva sphere setup or other experiments, but never in an actual setting. The reason for that being twofold, first for structural support and second for moderating effects. Most likely this fuel would have to be a carbide, oxide, or possibly even a nitride. You're right about the actinide burner. I've read a few papers (Fusion Science from this past May I believe and some a few years back) written on using a tokamak as a MA transmutation reactor which said that the outer core wouldn't be anywhere near critical though, which considering that the minor actinides used would be mostly Pu-239, as expected, which has a rather high cross sections (10^7 higher than the U-238 for fission) only reached a k-effective of ~.4 or so for a fusion reactor with ITER's dimensions. So I'm not so sure about using a blanket of U238.
Kravlor, You're right on the money, and I couldn't have said it better myself. Politics is one of the ultimate limiters of science. The biggest fight of ITER for the past 15 years was where is it going to be? Not who's going to spend the most on it or any other matter, but rather like a one-upsmanship game where whoever hosts it gets bragging rights. Politicians love that kind of thing and that's why I think it wasn't started any sooner. Sure we could've broken ground on the foundation and started manufacturing the structure on the main and supporting buildings, while waiting on newer, more resilient superconductors for the magnets, along with other bits and pieces. Then just piece it together as things become available. But you can see that it's the politicians holding back the engineering, not a lack of testing, theory, or engineering ability. So the old addage of 50 years until fusion is a great injustice since it's not a fault of the engineers at this point. I'd give it 10-15 after the second ITER test facility in Japan is built before we see fusion as a viable option for commercial power (and that's a somewhat conservative estimate since we don't quite know how long it will be between the first and second facilities are built). Second comes the materials issues. I can't wait to see what alloy they end up using for the divertor plate (this coming from a guy who spent many a sleepless nights modeling these things in Fluent for part of a degree).
I'm not so sure what is meant by a hybrid though. If you mean using a simple neutron source as a supplement to the neutron economy within the commercial reactor, then I'd say that you'd be wasting your time. The limiting factor in commercial plants is the rising levels of neutron poisons within the fuel that steal away neutrons that could be used to produce fission, but are left to be absorbed into xenon or numerous other poisons. AmBe or PuBe sources are already present in most commercial plants as a means to jump start the initial k-effective. You might be able to expand the length of a once-through cycle by a few days or so with a really powerful source, but if you're talking a little table-top fusion device, then I doubt the materials these guys are using to build those would be able to stand up to the conditions inside a commercial reactor. The corrosive properties of water at the high pressures and temperatures, along with kerma effects will destroy just about anything after some time. This little fusion neutron source would have to be inside the plenum and very close to, if not in the middle of, the core if it will make any dent in the k-effective. So I think you'd be much wiser to just go to reprocessing and put the remaining U, Pu, Am, and Cm back into the reactor for a few more go-rounds, also you'd cut way down on the repository needs. But that's a whole other can of worms. But once again I agree with kravlor there, moving towards the AP-1000's or even the older AP-600 design (but why the 600 when you can have the 1000 unless it's declined by the NRC?) would be a much better use of fuel than many subcritical assemblies. Unless you're into BWRs in which case I have very little clue on what route you would go for future plants since those are well outside my scope.
Now, if this little device can prove itself, then hospitals may have a nice new, controllable neutron source for irradiating tracer isotopes. So there's something this could be useful for that would make sense.
I wouldn't toss ITER aside before I get to at least read the journal article on a few of these desktop setups. I'd still like to see what pressure they're operating at, temperature ranges, D/T enrichment, reaction rate, bubble size, mcnp models (a vised geometric plot at the least), fluent models, etc. I just don't trust science magazine or a run of the mill newspaper to publish groundbreaking science that's on par for an engineer to read, since those cater to people without much knowledge of the engineering feat discussed in the article. But that's the nuclear field (or any engineering for that matter), we're supposed to be skeptical as hell until it's widely duplicated. If I can do it in my lab, then I'll believe it. Or at least see it in someone else's lab who built it from scratch from nothing but the other researcher's blueprints. And controlling plasma with magnets isn't too hard, in fact it's down to nearly an exact science where only a few unknowns remain, mainly the occurance of MARFE's, diverter material protection, and so forth. The largest problem lies with protecting the magnets from the 14-MeV neutron flux exiting the core. But still, I wouldn't toss aside ITER just yet. It's got some work to do, but it's a pretty sound model for a large scale fusion power plant.
That and reclaimation of materials from the batteries has improved as well. So you could reprocess the material and remake batteries from old ones, some waste product is to be expected of course. Still, battery technology is a whole lot more efficient than hydrogen. Using straight electrical power instead of a combustible mass to heat, electricity, and motion means a much, much greater efficient. Tack on a few regenerative cycles to recharge that battery and we'd be set. I change my car battery every 5 or 6 years out of habit, not necessity, so I think battery packs might be a whole lot more reliable than a large tank of explosive material. Maybe it's just me, but I wouldn't want my car to explode like a Pinto from a fender bender on the freeway. As much as I'm for new energy methods, I'd still like to see the journal article on this method before I believe it's the next big thing. Somehow I'm doubting efficient conversion using a silica gel and sodium.
Kill the hacker but let the rapists and murderers go free after only serving a few years, yeah that makes sense. I guess this is what we can expect from a legal system that took away the right to own property.
The reactors used on submarines are a very special case though. Firstly, they use highly enriched which isn't good for public consumption because runaway reactors with HEU would be very, very bad. Second, since a submarine has the requirement that is has to go from no power to full power in seconds, it has a very, very, very large, active neutron source (on the order of a few curies if memory serves correctly, but it's been quite a while since I worked on anything nuclear that ran on earth;-) ). The k-effective of a nuclear sub that isn't "on" is usually at about.90~.95. Which means that all it needs is to remove the control rods ever so slightly to start producing power. Also the cooling mechanism of nuclear subs uses seawater as a secondary coolant since it's so abundant. The primary coolant doesn't leave the core obvious, but it's the secondary which directs where that heat will go. So for a small scale reactor, this isn't the way to go, but more towards an RTG, which is what's used in satellites. They aren't exactly small, but they run on the Seebeck effect (reverse of the peltier effect for you computer people). The fuel in an RTG doesn't create the heat/energy by fissioning, but rather by natural alpha decay (heavy,unstable isotope releasing ionized helium atom). The helium atom has a certain amount of energy, usually in the 5+MeV range since the fuel is usually a plutonium isotope. So with that amount of energy being released at a near-constant amount for 25+ years, the benefit would be great; however, shielding and non-proliferation issues persist and render using this as a mainstream, use-at-home reactor as impossible. But one of the things beind worked on by the IAEA along with a few of the US nat'l labs and other is a large RTG that can be safely deployed to areas to use as a portable power plant. It'd be cool, but huge, and expensive until better materials are worked out for shielding.
Very true. Nuclei contain far greater amounts of energy than any exothermic chemical reaction. But if you ask me, all large-scale power generation has crawled forward because it all still depends on massive reheat cycles and steam turbines. The only way to make a better power conversion system is through massive amounts of research into materials capable of more efficient energy transfer such as those found in the newer generations of RTG's and solar panels as a quick example (obviously not large scale generation but big projects stem from small projects in engineering). Much of this research couldn't be done 30-40 years ago since it takes massive amounts of computing power to design and model the systems under all sorts of conditions. Also the leaps and bounds in terms of MEMS technology, miniaturization of transistors, plastics and fiber, etc has led to greater knowledge of nuclear processes that will start to lead towards better power generation. So I don't think it's a lack of research into nuclear power generation at all, but rather a lack of prerequisite knowledge to advance such a dependent technology such as this.
Banning the SSN won't help because that's counter to what needs to be done. The fix is that a social security number should be used for things pertaining to social security only. Meaning that you put it on your W-4 at your place of work, then your boss uses a different number to identify you as an employee. Your credit history can be another personal identifying number non-related to the SSN. Health care providers should do the same. The policy number already links the eligible patients in the family to whatever personal information the policy holds. Do they really need to rely on the SSN for that? Of course not, but because it's their database and they are completely free to designate whatever number to you the damned well please, which is the usual gist of every TOS agreement you sign with a provider. A good example is that colleges have already started switching their student information databases from being SSN-centric to a school assigned ID# that looks like a SSN, but isn't, so this could be a definite way to go. Numerical identifiers shouldn't be outlawed, because it's a very good way to organize and collect data from that perspective; however, the sharing of that data among different sources is another thing. To me, this is very much like using the same username/password combination on every system you frequent, it's just a bad idea if you want to keep some information private. So banning the SSN outright isn't the way to go, but limiting the use of the SSN/personal ID# in other services should be the way to go.
All of Greenpeace may not be against it. One of the founders, Patrick Moore, had an article about his supporting nuclear power in the June 2005 issue of Nuclear News (traditional fission power, fusion not mentioned). I think it was a transcript of testimony in front of one of the numerous energy committees in the House back in April if you don't have access to this periodical. But he makes the case for nuclear being the only rational option for long term energy production. So if not all of Greenpeace is made of the "anti-human," "environmental extremists" (his words) then perhaps they might start to make the case, en masse, that nuclear is a better option than fossil fuels (of course everyone in the nuclear industry is saying "duh" at this point)
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Some schools call pre-algebra, discrete math, which is a huge injustice to the name of the more difficult course. So I think you're right, discrete is a weed out for CS
That's a good strategy, taking courses outside your major that is. I took a couple of minors to even out my education, it also kept me sane during hours or math, advanced physics, etc. If you find you don't like engineering after your junior year, I'd stick with it just to get the degree. Should you want to go to grad school, you can always switch your curriculum to what you want to study. Usually a department would just make you take remedial courses in that major to "catch up" to their traditional students. Keep in mind that a bachelors in engineering just shows that you can do the basics (meaning you can pass the FE exam without too much trouble if you want the grad school route). A bachelors won't make you an expert in the field or a definitive source of all things related to that field, but it shows that you have a good base in the fundamentals and a capacity for future study or field work. Keep up with the extra classes, they'll pay off
Nuclear engineering.... yeah, still engineering, but just had to say it, $65k was my senior class's avg starting salary
In my field, we've seen almost a 40% increase in undergrad enrollment over the past few years, so I doubt that it's every engineering field that's losing students. Sure since the tech bubble burst, students that would have studied a CS or related field might rethink their plans and pick a different major, but that's not every field. Nuclear, Mechanical, Chemical, Civil, etc etc have all seen steady increases in enrollment. It's most likely just students forecasting what field they think they can get a job in based on the current day demand.
Fingerprints are currently stored in the FBI database for all arrests, which means it doesn't matter if you're innocent or guilty because it's the arrest record that contains your fingerprints, not the court decision. My one worry is that since we enabled the PATRIOT act to supercede due process and individual rights in many cases, how long before a person could be detained as a threat just to have their DNA sampled if they are just an political undesirable? DNA should only be kept for convicted felons of violent crimes, as it currently is in most states. There is no reason why this should be changed.
If your only use for a computer was checking email, browing websites, and basic time management stuff. For those of use to do actual work on our PC's, with larger programs, a la matlab, etc etc, a cell phone just doesn't have the same functionality of a pc. To have comparable speed, screen size, and input capability, a PC is still unmatched. I've seen tons of nifty apps for the treo and hiptop platforms, but for the large part, I still need to sit in front of a full size screen and get work done. If I want to check the news, weather, email, etc, I could use a phone and that would work just fine, but I'll stick with my monolithic pc for when I need to do some work.
That's true with the "free" initial cell phone. It isn't free because if they were to allow the sale of just service without selling a phone, the price per month would be a few bucks less since they use that bump in pricing to pay for the phones (obviously they get bulk discounts so their prices are less than ours would be). The contract period usually covers their loss and then some, especially if you have a 2 year agreement as with most providers. That way, at the end of your contract, you've overpaid for a phone that wasn't worth nearly as much as you paid, yet you still think you got a deal because it was "free" at the beginning.
I'm curious to see how Tivo will do this though, if they offer discounts initially, but overcharge for service and lock users into a contract, what will happen to their business if they change their software to allow DRM that will prohibit users from recording certain shows? Why not just make the user pay full price up front and provide damn good service so the user won't want to change?
Bombing a military target that was far removed from the eyes of the population wouldn't have been nearly as effective of changing the image of the war in the eyes of the average joe. The state controlled media simply wouldn't report the bombing to the populace and would have basically said exactly what that iraqi minister said, that Saddam had the Americans on the run, when the war was over in under 3 weeks. Since the US bombed industrial centers that were full of people, the knowledge of the bombings couldn't be concealed, and therefore the information would spread outwards uncontrollably, thus changing the population's will to fight. Had the multitude still had the will to fight, the war would have dragged on for a whole lot longer, but the US made great use of some military "strategery" and psychological warfare to end the war early. I'm glad my grandfather came home from the pacific in '45. In short, I'm trying to support what you said ;-)
"Looks to me like more and more people are going to gt into wireless mesh networks and pgp/gpg just to avoid big brother."
/. People already don't conceal their privacy offline. If you want to shat yourself, try looking up yourself/friends/family on www.zabasearch.com and you'll see what I mean. Privacy is unfortunately becoming less and less and the vast majority of people don't care because the invasions of privacy are relatively transparent. If the FBI viewing their entire internet habits/emails doesn't interfere with their daily lives, then they won't complain so long as they're told that it's being done to "stop the terrorists." This is becoming more and more an invisible war where the enemy is the ideal of freedom.
If only people would take that much of an active approach to conceal their privacy. In practice, people are lazy. With the exception of a few groups of people, the vast majority of people on the internet in the US hold the idea that "I have nothing to hide, so why not?". That is very unsettling to me and probably everyone else on
Take your pick, that's why I said "any undergraduate engineering thermodynamics textbook." Try looking up the Moran and Shapiro, latest edition is the 5th I believe, if that doesn't work, look up Nuclear Systems I by Todreas and Kazimi, both are undergrad texts that can be found in most mechanical engineering school's libraries
High temperature systems are very efficient as the HTGR's used in some countries, you're right. Problem is that with high temperatures come weaker materials, making the capacity factor less than that of a lower temperature plant. Not to mention the lower power output. I'm very familiar with this, but if you think that these plants with a 50% capicty factor take the place of a 90% capacity factor plant that yields a 40% efficiency with a much higher power output, you're very wrong. So why not open a textbook and look at underlying reasons before criticizing. Reading an article on slashdot doesn't make you an expert scooter.
I'd imagine the same way propane or any natual gas could be stored, that is in a steel reinforced tank capable of a hundred psi or so. That would hold a decent amount of H-2 gas.
As a person that designs power plants, I'm wondering what design you're working with where a coal plant reaches 50% efficiency. The best efficiency I've seen for most plants is getting close to 40% and that's with a nuclear plant (APWR) The best designed coal plant I've seen had nearly 37% efficiency but a capacity fact of around 60% (meaning they don't have it turned on all the time). Whenever you create your electricity by boiling water with a few regenerative or reheat cycles, your efficiency probably won't ever top the current efficiencies. You can get my numbers from any undergraduate engineering thermodynamics textbook.
The problem with putting the fuel in the middle of the tokamak is that it's very dense in there. The toroidal and poloidal magnets, inner shielding, cooling units, and related cabling/equipment take up much if not all of the room in the inner ring so putting fuel and related cooling in the center is one of those things that was ruled out after some research. So the only place you can really put the fuel is in the outermost portion, within the magnets but outside the pressure vessel (the magnets being more D-shaped and the plasma chamber being a deformed oval leaves some room to the outermost). Lithium doesn't make a very good moderator though, better than most since it's low-Z but it would still take quite a few interactions to slow down a 14 MeV neutron down to the energy that U-238 would absorb. U-238 absorbs most in the 1/v range (low energy from about .1eV to .00253eV/thermal range), so you'd really have to slow down the neutrons to get to that range, and when slowing down neutrons, every collision matters to decrease the possibility of leakage. Hence it's much better to use fast spectrum actinides like Np, Pu, Am, and Cm for a fusion neutron source. As for the neutron flux distribution, it's pretty strong all over, except it's the strongest on the outside of the toroid since that's where the plasma density is the greatest so the majority of neutrons are slung outwards due to some of the more enjoyable aspects of plasma physics (drift motions and whatnot). So the best place to collect the neutrons is on the outside. Using different sizes of tokamaks is possible, but actually achieving fusion requires certain geometry constraints. Since the plasma is pulsed, the field is constantly changing and that relates directly with the plasma temperature. So you can't make it too small otherwise you can't reach ignition temperatures (~5keV for most). If you're still curious about some of the cross sections, there's an online plotting cgi gateway at the Korean Atomic Energy Research Institute (http://atom.kaeri.re.kr/). Cool stuff but not doppler broadened for the range used in fusion reactors.
The neutron wasn't discovered until well after the periodic table was created though so neutrons had no effect on the makeup of the periodic table other than screw with scientists minds over why the weights don't match up to their theory. If you want to look at isotope/isotone differences, then you'd be using a chart of the nuclides.
I think he means something like the Seebeck effect which is the reverse of the Peltier effect, meaning you get energy and electrons are pushed through the npn junction when going from the hot side to the cold side. Obviously you'd lose efficiency when it's a hot to warm conversion because of the lower gradient. It's not a perpetual motion machine, it's been around for almost 200 years and is probably most famously used on modern satellites and probes in the form of RTG's (radioisotope thermal generators).
How would you get a .99 k-effective out of U-238? Even with fuel lumping I don't see it. Unless you're already including the neutrons provided by the fusion reaction, but the problem with that is that a tokamak is a pulsed device which rules out normal k-effective equations so you can't assume steady state of the neutron flux but rather a sinusoidal which if you try to "fix" the flux it would balance out much lower than expected for a steady state beam. Also looking at the first, second, and third chance fission cross sections for U-238 I'm not seeing how that would even be possible for a natural uranium blanket would absorb the neutrons at that high of energy even with the doppler broaded cross sections at the high temperatures in a standard core. I'd check with MCNPX if you have access to it and use the added neutron physics and do a simple kcode to check this, but make sure you have doppler broadened and unresolved region linearized cross sections since you're dealing with high energies (although that might skew it a little, but it's a rough estimate afterall). The U-238 is on the order of 10^-4 barns for the highest fission XS. Also how could you get that much uranium inside the magnets? It's a very tight fit between the magnets and the actual fission chamber. Also rarely is pure uranium metal ever used except for in a godiva sphere setup or other experiments, but never in an actual setting. The reason for that being twofold, first for structural support and second for moderating effects. Most likely this fuel would have to be a carbide, oxide, or possibly even a nitride. You're right about the actinide burner. I've read a few papers (Fusion Science from this past May I believe and some a few years back) written on using a tokamak as a MA transmutation reactor which said that the outer core wouldn't be anywhere near critical though, which considering that the minor actinides used would be mostly Pu-239, as expected, which has a rather high cross sections (10^7 higher than the U-238 for fission) only reached a k-effective of ~.4 or so for a fusion reactor with ITER's dimensions. So I'm not so sure about using a blanket of U238.
Kravlor, You're right on the money, and I couldn't have said it better myself. Politics is one of the ultimate limiters of science. The biggest fight of ITER for the past 15 years was where is it going to be? Not who's going to spend the most on it or any other matter, but rather like a one-upsmanship game where whoever hosts it gets bragging rights. Politicians love that kind of thing and that's why I think it wasn't started any sooner. Sure we could've broken ground on the foundation and started manufacturing the structure on the main and supporting buildings, while waiting on newer, more resilient superconductors for the magnets, along with other bits and pieces. Then just piece it together as things become available. But you can see that it's the politicians holding back the engineering, not a lack of testing, theory, or engineering ability. So the old addage of 50 years until fusion is a great injustice since it's not a fault of the engineers at this point. I'd give it 10-15 after the second ITER test facility in Japan is built before we see fusion as a viable option for commercial power (and that's a somewhat conservative estimate since we don't quite know how long it will be between the first and second facilities are built). Second comes the materials issues. I can't wait to see what alloy they end up using for the divertor plate (this coming from a guy who spent many a sleepless nights modeling these things in Fluent for part of a degree).
I'm not so sure what is meant by a hybrid though. If you mean using a simple neutron source as a supplement to the neutron economy within the commercial reactor, then I'd say that you'd be wasting your time. The limiting factor in commercial plants is the rising levels of neutron poisons within the fuel that steal away neutrons that could be used to produce fission, but are left to be absorbed into xenon or numerous other poisons. AmBe or PuBe sources are already present in most commercial plants as a means to jump start the initial k-effective. You might be able to expand the length of a once-through cycle by a few days or so with a really powerful source, but if you're talking a little table-top fusion device, then I doubt the materials these guys are using to build those would be able to stand up to the conditions inside a commercial reactor. The corrosive properties of water at the high pressures and temperatures, along with kerma effects will destroy just about anything after some time. This little fusion neutron source would have to be inside the plenum and very close to, if not in the middle of, the core if it will make any dent in the k-effective. So I think you'd be much wiser to just go to reprocessing and put the remaining U, Pu, Am, and Cm back into the reactor for a few more go-rounds, also you'd cut way down on the repository needs. But that's a whole other can of worms. But once again I agree with kravlor there, moving towards the AP-1000's or even the older AP-600 design (but why the 600 when you can have the 1000 unless it's declined by the NRC?) would be a much better use of fuel than many subcritical assemblies. Unless you're into BWRs in which case I have very little clue on what route you would go for future plants since those are well outside my scope.
Now, if this little device can prove itself, then hospitals may have a nice new, controllable neutron source for irradiating tracer isotopes. So there's something this could be useful for that would make sense.
I wouldn't toss ITER aside before I get to at least read the journal article on a few of these desktop setups. I'd still like to see what pressure they're operating at, temperature ranges, D/T enrichment, reaction rate, bubble size, mcnp models (a vised geometric plot at the least), fluent models, etc. I just don't trust science magazine or a run of the mill newspaper to publish groundbreaking science that's on par for an engineer to read, since those cater to people without much knowledge of the engineering feat discussed in the article. But that's the nuclear field (or any engineering for that matter), we're supposed to be skeptical as hell until it's widely duplicated. If I can do it in my lab, then I'll believe it. Or at least see it in someone else's lab who built it from scratch from nothing but the other researcher's blueprints. And controlling plasma with magnets isn't too hard, in fact it's down to nearly an exact science where only a few unknowns remain, mainly the occurance of MARFE's, diverter material protection, and so forth. The largest problem lies with protecting the magnets from the 14-MeV neutron flux exiting the core. But still, I wouldn't toss aside ITER just yet. It's got some work to do, but it's a pretty sound model for a large scale fusion power plant.
That and reclaimation of materials from the batteries has improved as well. So you could reprocess the material and remake batteries from old ones, some waste product is to be expected of course. Still, battery technology is a whole lot more efficient than hydrogen. Using straight electrical power instead of a combustible mass to heat, electricity, and motion means a much, much greater efficient. Tack on a few regenerative cycles to recharge that battery and we'd be set. I change my car battery every 5 or 6 years out of habit, not necessity, so I think battery packs might be a whole lot more reliable than a large tank of explosive material. Maybe it's just me, but I wouldn't want my car to explode like a Pinto from a fender bender on the freeway. As much as I'm for new energy methods, I'd still like to see the journal article on this method before I believe it's the next big thing. Somehow I'm doubting efficient conversion using a silica gel and sodium.
Kill the hacker but let the rapists and murderers go free after only serving a few years, yeah that makes sense. I guess this is what we can expect from a legal system that took away the right to own property.
The reactors used on submarines are a very special case though. Firstly, they use highly enriched which isn't good for public consumption because runaway reactors with HEU would be very, very bad. Second, since a submarine has the requirement that is has to go from no power to full power in seconds, it has a very, very, very large, active neutron source (on the order of a few curies if memory serves correctly, but it's been quite a while since I worked on anything nuclear that ran on earth ;-) ). The k-effective of a nuclear sub that isn't "on" is usually at about .90~.95. Which means that all it needs is to remove the control rods ever so slightly to start producing power. Also the cooling mechanism of nuclear subs uses seawater as a secondary coolant since it's so abundant. The primary coolant doesn't leave the core obvious, but it's the secondary which directs where that heat will go. So for a small scale reactor, this isn't the way to go, but more towards an RTG, which is what's used in satellites. They aren't exactly small, but they run on the Seebeck effect (reverse of the peltier effect for you computer people). The fuel in an RTG doesn't create the heat/energy by fissioning, but rather by natural alpha decay (heavy,unstable isotope releasing ionized helium atom). The helium atom has a certain amount of energy, usually in the 5+MeV range since the fuel is usually a plutonium isotope. So with that amount of energy being released at a near-constant amount for 25+ years, the benefit would be great; however, shielding and non-proliferation issues persist and render using this as a mainstream, use-at-home reactor as impossible. But one of the things beind worked on by the IAEA along with a few of the US nat'l labs and other is a large RTG that can be safely deployed to areas to use as a portable power plant. It'd be cool, but huge, and expensive until better materials are worked out for shielding.
Very true. Nuclei contain far greater amounts of energy than any exothermic chemical reaction. But if you ask me, all large-scale power generation has crawled forward because it all still depends on massive reheat cycles and steam turbines. The only way to make a better power conversion system is through massive amounts of research into materials capable of more efficient energy transfer such as those found in the newer generations of RTG's and solar panels as a quick example (obviously not large scale generation but big projects stem from small projects in engineering). Much of this research couldn't be done 30-40 years ago since it takes massive amounts of computing power to design and model the systems under all sorts of conditions. Also the leaps and bounds in terms of MEMS technology, miniaturization of transistors, plastics and fiber, etc has led to greater knowledge of nuclear processes that will start to lead towards better power generation. So I don't think it's a lack of research into nuclear power generation at all, but rather a lack of prerequisite knowledge to advance such a dependent technology such as this.
Banning the SSN won't help because that's counter to what needs to be done. The fix is that a social security number should be used for things pertaining to social security only. Meaning that you put it on your W-4 at your place of work, then your boss uses a different number to identify you as an employee. Your credit history can be another personal identifying number non-related to the SSN. Health care providers should do the same. The policy number already links the eligible patients in the family to whatever personal information the policy holds. Do they really need to rely on the SSN for that? Of course not, but because it's their database and they are completely free to designate whatever number to you the damned well please, which is the usual gist of every TOS agreement you sign with a provider. A good example is that colleges have already started switching their student information databases from being SSN-centric to a school assigned ID# that looks like a SSN, but isn't, so this could be a definite way to go. Numerical identifiers shouldn't be outlawed, because it's a very good way to organize and collect data from that perspective; however, the sharing of that data among different sources is another thing. To me, this is very much like using the same username/password combination on every system you frequent, it's just a bad idea if you want to keep some information private. So banning the SSN outright isn't the way to go, but limiting the use of the SSN/personal ID# in other services should be the way to go.
All of Greenpeace may not be against it. One of the founders, Patrick Moore, had an article about his supporting nuclear power in the June 2005 issue of Nuclear News (traditional fission power, fusion not mentioned). I think it was a transcript of testimony in front of one of the numerous energy committees in the House back in April if you don't have access to this periodical. But he makes the case for nuclear being the only rational option for long term energy production. So if not all of Greenpeace is made of the "anti-human," "environmental extremists" (his words) then perhaps they might start to make the case, en masse, that nuclear is a better option than fossil fuels (of course everyone in the nuclear industry is saying "duh" at this point)