Enthalpy

Japanese electricity producers had bought MOx ("mixture of oxides"), a nuclear fuel that mixes less-enriched uranium with plutonium resulting from the reprocessing of spent nuclear fuel. After the Fukushima disaster, especially as people realized that the higher reactivity of MOx to fast neutrons would let it behave differently if water evaporated from the spent fuel pool #4, and maybe as the Japanese gouvernment understood that other countries could just steal the shipment, the old Japanese government asked to stop all shipments of MOx. These days, Areva wants to ship MOx again to Japan. If we were to believe newspapers, Japanese electricity producers have no use for it (credible with just two reactors active), but Areva doesn't want to store it any longer, so it shall be stored in Japan instead, and the new Japanese government didn't oppose it. The roughly 400kg contained plutonium suffice to make 30 bombs. Areva argue that it's "civilian" plutonium containing much 240Pu that makes it unsuitable for bombs, but this is BS. A standard Pu bomb does detonate with "civilian" plutonium, with a yield on only 500t instead of 15kt - so the devastation radius is 1/3 that at Hiroshima. Worse: every book tells that a so-called booster lets civilian plutonium detonate as efficiently as military one does. It takes a little bit of tritium, which a country controlling a nuclear reactor has. Now, imagine the effort and sacrifices made by, say, North Korea, to have plutonium for its nuclear bombs. The shipment passes by, whose contained plutonium is separated just by chemical means. Stealing the shipment is a much smaller effort! 30 soldiers on board won't stop a country willing to save a decade and hundreds of technicians. The story doesn't tell if a submarine escorts the shipment, but for instance North Korea does have submarines as well. And how much does this escort cost to the French taxpayer, as compared with Areva's sale? I previously thought MOx was a means to destroy the huge amounts of plutonium now available on Earth, but fuel reprocessing to MOx at La Hague and a few others is done only once; the second reprocessing would be too costly, and the new plutonium is left in it. So we still sit on the hundreds of tons of plutonium. That's an insane story... Or could there be an alternative explanation? Japan willing to make quickly from the MOx a few almost-complete nuclear bombs, for balanced deterrence with North Korea?

I believe collisions tend to equalize the energy (as a mean result, sure) rather than the momentum. By the way, "momentum conserved" means the vector sum of the colliding molecules, not the way they share the momentum relative to their common center of mass. The equipartition theorem (wiki article) tells the same as I do, unless I missed something. The mean energy is equally shared among all degrees of freedom, which includes the translation energy of all species. About the thermodynamic isotope effect, this paper seems to understand it the same way as I do: http://old.iupac.org/goldbook/T06319.pdf "zero-point energy difference" on vibration of protium, deuterium and tritium. Looks like this effect has a long name and theory to apply essentially to hydrogen, a tiny bit to carbon, by vibration rather than translation. If I try to put figures, imagine temporarily that thermal equilibrium gives a uniform mean momentum rather than energy. - CH3D (17g) would have 3% less translation energy than CH4 (16g) so it would need 115K to boil instead of 112K @1atm - way overvalued. - H218O would be segregated by several per-cent at each evaporation, but its at most 10-4. - Heavy water separation would also enrich in H218O, but this does not happen.

We don't need to believe or think: they do exist and are used daily. Sha-1, Sha-256 and many more, like the common MD5 still used despite being broken. http://en.wikipedia.org/wiki/Sha-1

DOS allowed the applications to access the Bios interrupts, but also to bypass them. For Windows, beginning with 95 (and maybe Nt3), the OS has its own functions to access the hardware that do not call Bios interrupts. For Windows Nt series, at least from 2000 (and possibly before), the OS prohibits applications to access the Bios interrupts. This is a major step towards safety, but prevents some applications to run, notably the ones dating back to Ms-dos that accessed the Bios interrupts and possibly the hardware directly. For Windows Nt series, one must distinguish the administrator session from power users and normal users. The administrator session (and the system of course) can access the hardware through more direct Windows functions, for instance read a disk sector by its number, instead of a position in a file defined by Windows. This explains why some disk measurement tools can test a disk at locations where files already exist, or a disk where no partition has been created; these need the administrator mode, or rely on a server task in admin mode - while the other test tools create a test file and can run in user mode. The Bios functions evolved little, but as a big benefit, offered a rather uniform interface to varied hardware. Though, they were an awkward limit if some added hardware was not compatible, for instance a disk too big for the CHS mode. Windows not relying on the Bios to access the hardware improved that point but made Win itself less easy to port among different hardwares - and the Bios has first to launch Windows' boot...

Knive alloys are high-carbon martensitic steel, preferably stainless. Known ones: X105CrMo17 or 1.4125, nearly equivalent to Aisi 440C X90CrMoV18 or 1.4112 these are used for the best scissors, razors, surgeon tools... Their heat treatment is more subtle. They would really improve over the common X40Cr13: harder, resist corrosion better. Would rare alloying elements like iridium bring them anything? I suppose you won't find literature on this topic. And since alloys are nearly unpredictable and can be quite sensitive to minor amounts of undesired elements (think of P, S...) I'd stay away from them to avoid brutal degradations like embrittlements or abnormal reactions to heat. The better X105CrMo17 and X90CrMoV18 are said to be unusable by a smith, that's why the X40Cr13 is common. But you can find them as industrial round material, shape them with a grinding wheel, and let a professional harden them.

The outermost electrons define chemical properties (keeping in mind that transition elements mix up their outermost shells) and, at heavier elements, these electrons are on shells less strongly bonded to the nucleus. Heavier elements leave their outer electrons more easily. You can check the ionization energy of the elements, there: http://www.webelements.com/caesium/atoms.html click up right on neighbour elements to compare. "Reactivity" has different meanings... A metal is more reactive when it loses electrons readily, and an oxidizer when it picks electrons readily, so oxidizers (halogens etc) are more reactive when lighter. Chemistry isn't that simple, and the effect is just a general idea with many exceptions. One might expect reactive elements to make strong bases or acids, but HF is weaker than HCl, the next HBr, HI following the expected order. Salt solubility neither is a simple consequence of reactivity. Neither is displacement in a solution a direct consequence of reactivity. So beware of a simplistic representation of reactions that would be determined by reactivity comparisons only: they're not.

All right, helium is the other abnormal element... Just cool it below 2K and the isotopes separate spontaneously. 3He goes in one phase, 4He in the other. Plus many properties that make helium really special. As for the boiling point, the number of neutrons has very little effect, because heat gives a uniform (mean) energy to the molecules rather than a uniform speed, and this kinetic energy compares directly to the sticking energy that keeps the molecules in the liquid. So the isotopic effect if far smaller than the mass ratio - very small in fact. Hydrogen is special in that its chemical bonds depend on the nucleus' mass. Because the proton is not so heavy, it is significantly delocalized (call it ground state vibration energy if you wish), so that the electrons make less strong bonds, because the proton can't be centered precisely at the best possible place that minimizes electrons' energy. Deuterium is heavier, so electron bonds can localize its nucleus better to minimize their energy, and the bonds are stronger. This makes an interesting difference at the Van der Waals' forces which aren't very strong and define the melting and boiling points of many substances. For water, it's a hydrogen bond, which is oriented by the molecular H-O bond, hence sensitive to the diffuse position of the proton. The ease of ionization in acidic conditions is also sensitive to hydrogen's nuclear mass. This is used to separate heavy water using a simple acidic cycle, without first separating hydrogen from oxygen of all water just to keep the deuterium. Thanks to that, heavy water is readily available at moderate price, while other pure isotopes are expensive.

Properties that result from electrons (electronegativity, boiling point...) don't depend significantly on the number of neutrons (hydrogen being the one exception), so you can take the mixture's properties and use them for individual isotopes. Properties that result from the atom's mass (density...) can be scaled for each isotope from its mass compared with the mean mass of the natural mix. So element tables give properties only for the natural mix of the isotopes, to keep the table's size reasonable, and because the rest can be deduced if needed. A nice table there: http://www.webelements.com/ including isotopes when, at the chosen element, you ask for Nuclear properties > Isotopes, example http://www.webelements.com/boron/isotopes.html Most elements have a nearly constant proportion of isotopes on Earth, but because this proportion can be counted down to individual atoms, special uses exploit the tiny difference: 13C datation, origin of uranium ore... The proportions vary a bit with altitude or with depth, and so on. A few natural elements are less constant - generaly when their isotopes result from the radioactive decay of various elements that differ chemically. Artificial elements like the transuraniums vary a lot. The proportion varies a lot among our Sun's planets but is remarkably the same for our Moon.

Hi Elver Loho, welcome here! Oceans contain huge amounts of heat, but this is notoriously difficult to exploit, be the temperature difference with air or, more commonly, with the Ocean's depth, since water is cold already at 30m depth and its heat capacity is more concentrated than air's one. The huge difficulty is the small temperature difference. Carnot's efficiency for a 10K difference around 300K is 10/300 or 3.3% as a theoretical maximum... But the machine must achieve to run in the first place! Imagine a gas turbine: the turbine stage would extract only 3% more work than the compressor takes, and since efficiency is 80% at each, the machine doesn't even rotate! The same holds for any thermal engine. The efficiencies you found are for healthy temperature differences, like 900K hot source and 300K cold sink. The least bad thermal engines for small temperature differences evaporate a compressed liquid to expand the vapour, because the compression of the liquid needs much less work than the expansion of the bulky vapour gives, so the imperfect machine has a chance to run. Forget Seebeck, which is universally bad even under optimum conditions, and Stirling, which is heavy and inefficient as compared with turbines. A lot of creativity was already invested in exploiting the Oceanic thermal gradient - just have a look at the many patents. I did try also. It's a damned hard topic, especially if you remember that seawater dissolves gas (which can't be compressed back to the liquid once evolved) and salts. So "energy is available" is not a new idea; "I know the previous attempts and have arguably found a better method" would be a welcome breakthrough. How many watts, how difficult? A different answer could be: far more expensive than wind power, and we don't know how to do it, while wind power is existing technology.

Piaggio's P180 Avanti is a business aircraft: http://en.wikipedia.org/wiki/Piaggio_P180_Avanti and it could fly right now with fuel cells: - Reported 5.3M€ price allows 2*6 fuel cells from Honda's FCX Clarity, as the whole car is said to cost ~140k$, and this saves the turbines. - 2*6 fuel cells weigh ~1000kg but replace 1200kg kerosene and 2*170kg turbines with light hydrogen and light electric motors. - No more turbine exhaust through the propeller. Swept blade tips should help as well. 2800km cruise at 644km/h and 80% power or 507kW take 2*8GJ, obtained with 60%*95% efficiency from 2*98kg hydrogen carried liquid at 1atm: the tanks are smaller, lighter and supposedly safer than for gas under pressure. Then, hydrogen fits in the volume of the original nacelles, together with the fuel cells, motors and propellers, and can be kept away from the cabin. Hydrogen takes 2*1.4m3, for instance ellipsoids 1m wide and 2.8m long. The nose fairing protects against impacts, with fibre and foam like a bulletproof vest. Adjust the center of mass by the compact fuel cells. Bigger tanks would increase the range. The neodymium electric motors (2*65kg) can drive the propellers directly, resembling the PW127M equivalent already described. Unoptimized, the gap can have 480mm diameter and 105mm length. 30 poles and square wire let lose ~6kW, maybe air-cooled at the spread half-turns of the wires. I propose to hold hydrogen liquid at 20K and 1atm in thin steel, superinsulated and hold in a vacuum vessel by polymer straps; this design may also fit cars and others. Ask your usual satellite designer, or Wiki. Here 200µm Maraging steel (11kg, per nacelle here under), coated with nickel and brazed together, resists 10bar. 30mm foam (10kg) let pass only 1.5kW if vacuum is lost. This leaves 1 hour to reach 10bar, or lets 3.4g/s evaporate. That's only half the engine's consumption, so the plane can go on flying, but it's a strong flame on the ground, so foresee a safe purge. 80 plies multilayer insulation (10kg) in vacuum let 0.6W pass through. That's 3.3kg/month evaporation, which can optionally feed a fuel cell that power a cryocooler keeping hydrogen liquid, as Nasa proposes. Polymer belts (<1kg) hold the steel envelope in all directions. Cumulated 1cm[super]2[/super] are more than enough, 10cm free length leak <0.1W. At the proper (3D!) angle, they let the steel envelope shrink unhindered. Extruded aluminium profile is welded together to constitute the vacuum vessel (74kg). Details there: http://www.scienceforums.net/topic/60359-extruded-rocket-structure/ 1mm walls (less if possible) of AA5083 for 40mm sandwich thickness resist jumping on and offer successive airtight walls. The profile can be round, maybe in the extrusion direction as well. Someone else shall design the airtight opening, preferably as lower and upper half-shells... Marc Schaefer, aka Enthalpy

Fluids can convert pressure to speed and, often less efficiently, speed to pressure. Head expresses the sum of both, with the speed component converted with ideal efficiency to more pressure. Pressure can be given as a water height if this is more expressive.

An electric motor can propel Burt Rutan's LongEZ: the "Long ESA" does it (search keywords). http://en.wikipedia.org/wiki/Rutan_Long-EZ Glider-like aircrafts like Yuneec can fly for an interesting time on battery power, but not the LongEZ meant for general aviation. A 10-week student project at the TU Delft checked hydrogen and fuel cells to supply an electric motor on LongEZ: http://www.tudelft.nl/en/study/undergraduates-bachelors/undergraduate-programmes/aerospace-engineering/degree-programme/third-year/design-synthesis-exercise/ds-exercise-2012/taking-the-next-step-towards-zero-emission-general-aviation/ with excellent flight duration and range. I wanted to check a quick electric motor, but a slow 86kW motor is light and saves the gear. To rotate at 45Hz or 36m/s, its 2mm thin Nd magnets are wrapped with little graphite; they achieve 0.89T in 1mm gap, which is 52mm long and has 260mm diameter. 28 poles contain each 3 slots, 2 being active at any time, each fitting one phase. Each slot contains 2*3 wires of 2mm*2mm, in series for a flat-top 282V drive. The 4,5% losses could improve if wanted, and the wires' spread half-turns dissipate them easily in air. The motor looks similar to the previous APU and weighs 10kg. A single Honda FCX Clarity fuel cell supplies the electricity. Does its price fit this aeroplane? Its mass, plus the motor and the inverter, replaces the original Lycoming O-235's 109kg. 3235km range at 232km/h, or 50,200s (14h!) at 34kW (40% power) need 1.85GJe. That's only 10.7kmol or 21.7kg hydrogen with a 60% efficient fuel cell. At 298K and 300b it takes 1.1m3, light with graphite composite but hard to accommodate. Liquid at 20K and 1b it takes 0.31m3, a D=0.84m sphere or ellipsoid which fits in a longer aft. More later about the insulation. Marc Schaefer, aka Enthalpy

Braking forces: (1) Hysteresis in iron. Force essentially independent of the speed. (2) Eddy currents in iron, magnets... Force proportional to the speed but saturates or could even decrease. (3) Usual rolling resistance. If the wheels of the wall are not smooth, or the wheels eccentric, they may well be the main source of resistance. Hysteresis: you would have needed the magnetic data of the wall's material, which is not usual with normal construction steel. Either take steel for magnetic uses, expensive and mechanically poor, then the coercive force is known (or the energy loss per cycle and per kg) and gives a magnetic energy versus dispacement hence a force, or use normal steel and try to find magnetic properties for it or a similar one, with no guarantee. At reasonable speed like 0.5m/s, eddy currents will create a modest resistance. I suggest to experiment, since predicting that is not very easy nor accurate (it would require a reasonable precision over the field distribution, uneasy with hand computation). In experiments on a horizontal track, swapping between magnets and equivalent weight separates the different forces.

http://stoner.phys.uaic.ro/old/ANALE/Anale_1999_2000/An_Univ_Iasi_1999_2000_17.pdf third hit by Google.

If two orbitals interact weakly (so this is an approximation, because bonds are rather strong interactions) their combination, or molecular orbital, can be a sum or a difference of the atomic orbitals. The sum has a bigger volume, the difference a smaller one. The bigger volume means less kinetic energy, which makes the orbital bonding. The smaller volume makes the anti-bonding orbital. In addition (or even the main reason), the uniform phase over both atomic orbitals means also a longer wavelength (as the phase spreads over two atoms) and a smaller kinetic energy, while the opposite phase means a smaller wavelength.

Power transmission by microwaves is already unreasonable from geosynchronous orbit, or 36,000km away, where is demands square kilometers of antennas both in orbit and on the ground. Forget it for bigger distances. Yes, the produced intensity increases nearly as much as light concentration, as long as the cells don't overheat etc. This is done on Earth to reduce the area of costly Solar cells, but needs cells specially designed and actively cooled. The efficiency even improves a bit because the higher current density means a bigger cell voltage. Do Solar energy, but on Earth. Solar thermal energy and concentrated photovoltaics are economic, while space Solar has big obvious difficulties.

An annulus is used where the stream is expected to have a cylindrical symmetry. Sheets, disks... fit other cases better. Head as a length: in a dam it's more expressive, in a turbofan not.

Fun! It is one solution. I hope no life depends on it, because it might not be perfectly reliable; especially, magnetic attraction decreases quickly over the distance. The metal surface must be ferromagnetic, for instance steel. You will also have looses through eddy currents that will brake the vehicle's movement - unless the metal surface is a very special design. You could split each wheel in two parallel steel disks, close to an other, with a disk magnet between both steel disks. The wall closes the magnetic path - but much flux leaks through the air all around the wheels. One other design decouples the wheels from the magnets. Put the magnets under the car's body, use normal wheels, rather stiff and without susension, so the magnets are always close to the wall. Rubber wheels bring better grip and the magnets leak less. The magnet under the car body could perhaps be an electromagnet: less dangerous, an easier to clean from iron dust. Though, electromagnets are more sensitive to distance, and are not always possible. For the design of an attractive permanent magnet, you can get inspired by ones that hold knifes at kitchen walls, or by magnets that hold steel parts at grinding machines or milling machines. Better: buy one already built.

Don't worry about collisions in the Kuiper belt. Spacecraft already passed through the less faint disks of Neptune and nothing happened. Could you choose a more detailed title for the threads?

Hi Michal, willkommen! You have to decide if you magnetic levitation attracts or pushes. Pulling is done with normal materials (iron, copper...) at room temperature but needs an active feedback (sensors +loop +power electronics) to stabilize the distance. Pushing is naturally stable but uses superconductors (I know no exception, even at the size of a train) hence expensive materials and low temperatures. I regret the bad news... Could you tell more about the wheels? Are these magnetic bearings, for rotating axles and normal wheels? Or just levitating supports - these don't rotate usually, because magnetic levitation makes translation easy. One demo was a skateboard (over a linear and short way, but already fun) in a French university. Available over youTube.

Auxiliary Power Units feed aeroplanes with electricity and traditionally compressed air when the main engines don't do it. This alternator design shall rotate at 813Hz like the gas turbine, suppressing the gear, to provide 1270kW. Click the sketch for full scale. 10m thick Nd-magnets create 0.9T at the gap. 3mm of wound graphite composite hold them at 200m/s. A single strand per output passes once at each of the 6 poles to produce flat ±136V; three 120° outputs in a hexaphased rectifier provides +270Vdc to the aeroplane (the 15kHz filter is not represented). This saves heavy power electronics. A second set of 3 phases share the slots and provides -270Vdc. Or put the second set in distinct slots, or have dodecaphased rectifiers... Six 3.5mm*3.5mm wires make the "Litz" strand. They swap their positions and the ends of the stator, where they spread to dissipate 24W per wire in a strong wind; each wire could be subdivided. The wires evacuate the heat produced at the middle, dropping 54K. Alternately, oil can remove heat at the wires' turns, or (easier to seal?) oil can flow through each wire. I evaluated ohmic losses to 7kW=0.55% with turns too short. Mass is around 16kg but without casing, cooling, shaft... Air cooling conflicts with the slot inductance, and both are marginal here. This lets the +270Vdc and -270Vdc interact if they share the slots. The flux' permanent return path at the rotor is designed too small, and a complementary plunger adjusts the flux and output voltage in real time. Marc Schaefer, aka Enthalpy

Objects going in random directions interact often, be it by shocks or by gravitation, and they lose their random speed through inelastic shocks or - in elastic interactions like gravitation - because some objects acquire energy and leave the galaxy while the others loose energy; that would be the equivalent of evaporation that cools a liquid. Beware this is how I believe to understand it; it may not be standard science. The mean rotation momentum however is preserved as this one creates no collisions, just a general movement, which survives over this evolution and gives the disk its diameter while interactions reduce the thickness. The direction of the initial mean momentum determines the orientation of the disk. I also imagine that small plentiful objects interact often and can also get or loose more energy if meeting heavier objects, so they "condense" faster to the disk than heavier objects do - so you get gas, dust and individual stars in the disk, while heavier objetcs like globular clusters stay for long in the halo. As well, distance is important, with (not too) centrical objects grouping in the plane faster, while more distant ones stay longer at random. Similar to our Solar system and Oort's cloud. Again, I may be horribly wrong. Beware as well that galactic dark matter plays the main role in the formation and evolution of galaxies but its distribution and properties are badly known... Fresh science: small satellite galaxies in our neighbourhood are to be in the plane of giant galaxies, and not at random as previously thought. Did I read that irregular galaxies result from galactic collisions?

Available at Abebook, and used from Amazon.com. You might set an automatic alert from your eBay account if a member sells one.

Hi Axelneo, welcome here! - The photon carries the energy difference between two states. You know the final is the ground state. - You know (or learn it) the energy of hydrogen's ground state. It's called one rydberg. It's also the ionization energy of an isolated hydrogen atom, not molecule. - You're also supposed to know how energy levels go in the hydrogen atom. There is a simple law with integer numbers. - Comparing the photon energy with one rydberg, you can tell what the initial energy was, in rydberg units. Then consider the law with integer numbers, it tells you the initial level.

Cavendish measured directly the force between objects of a size manageable by humans http://en.wikipedia.org/wiki/Cavendish_experiment with an elegant and refined setup (designed by Michell) in 1798. Presently, accelerometers used for geologic prospection detect the presence of a few kg at several metres. http://en.wikipedia.org/wiki/Gravimeter "The superconducting gravimeter achieves sensitivities of one nanogal, one thousandth of one billionth (10-12) of the Earth surface gravity." Gravity gradiometers must be more sensitive to local objects http://en.wikipedia.org/wiki/Gravity_gradiometry At least one detector shown 20 years ago made from 1/2m distance a picture of where mass is in a piece of luggage - at about 3*3 pixels resolution. So it's possible and it's done... but consider that these setups and apparatus are among those that most exaggerate the performance as compared with anything reasonable.