Enthalpy

At 1 atm, coffeine sublimates at +178°C instead of melting at +230°C, apparently without decomposition. You still have 20hPa vapour pressure at only +80°C. http://fr.wikipedia.org/wiki/Caf%C3%A9ine http://de.wikipedia.org/wiki/Coffein (sorry, no such data in the English article) - BUT - You won't keep the air hot right to the nose, nor will the nose be warmer than +37°C (and even less, since +37°C is deep in the body). So the vapour formed at +80°C would condense on the way or at the nose, yuk. The molecule looks also pretty flammable. Can a lower temperature work? For the above reason, coffein should be vaporized at <35°C. Extrapolated from 1000hPa @+178°C and 20hPa @+80°C, it leaves 330Pa @+35°C or 0.3% in air. Inhaling 40mg needs to breathe 1.6dm3 only which I strongly doubt. Maybe someone else could check this? Such an effect would be long observed. Maybe the 20hPa from de.wiki are wrong. Then, it needs caffeine to work through the nose, which I can't tell. If you make the experiment, please remember caffeine is a poison and a drug. To the very least, start at a lower temperature and have friends with you. Compute also the lower explosible concentration and keep the solid temperature low enough not to reach this concentration.

The working theories agree to say that the warmer black sides heat air more, which is accelerated and pushes the vanes. Apparently it needed big science names to find out that air has to converge to the warmer area in order to be pushed away from there... But remember that before 1900, very little was known about fluid dynamics. Eiffel experimented from his tower built in 1899. I'd say this part doesn't need a long explanation nowadays. And we better avoid the word "transpiration" which I feel misleading; it's a flow with nothing special. Is air heated by direct contact or, as the OP suggests, by conduction? This is just a matter of gas density. The mean free path of gas molecules is said to be ~ 1mm, so conduction is more important - by little. Operation with 10 times less pressure and 10mm ean free path would make heating by direct contact predominant. OP, my feeling is that you have all to understand it. Add "air comes from the sides" to your explanation - done. Fun to see that ol' James Clerk approved an explanation that obviously rotates in the wrong direction... To keep in mind when, for instance, referring to Helmholtz about sound quality and "harmonic" spectrum.

D-Li does not produce the proper energetic particles for a booster. D-3He is doubtful as it expels less favourable protons. http://en.wikipedia.org/wiki/Nuclear_fusion#Criteria_and_candidates_for_terrestrial_reactions http://en.wikipedia.org/wiki/Aneutronic_fusion Produce 3He... only in faint amounts, and using much energy. p-Li looks like a candidate for a beam+target apparatus. D-D is much more easily conduced, it produces 3He and 3H that decays to 3He over decades. D is available commercially in big amounts, and D-D is readily conduced in a fusor: http://en.wikipedia.org/wiki/Fusor "just" a matter of produced amounts and consumed energy... Powerful long-term operation would also pollute through neutron activation.

That the BBD works isn't obvious; here's the mode of operation that has convinced me. Take identical temperatures at the input and output. Drive the electrodes slowly enough that the internal temperature differences are small. Then, the effect of varied electrical field at different buckets is to change the individual amounts of stored heat. As the pattern of individual electric fields is propagated, so does the pattern of stored heat among the buckets. Considering slices of the adequate number of buckets, combined with the proper spatial period in the pattern of electric field, one gets a stored heat per slice that increases at an instant of the period while only the preceding slice, not the following, loses heat - that is, heat propagates. ---------- 10µm is a usual insulator thickness at capacitors, both with plastic films and ceramic - thinner exists as well and would improve further the voltage and throughput. With 1800kg/m3, 1500J/kg/K and 0.2W/m/K, 1ms suffices to equalize well the temperatures of adjacent buckets after their heat capacities were changed. Depending on the pattern period, this thickness permits operation around 200Hz, to transport several 100W over 1dm2. Smooth field transitions over time would improve efficiency; the transitions can also spread over several buckets. (Please remember each bucket receives a potential difference, and adjacent buckets can alternate the field direction to limit the voltage across the stack). Because the buckets store much capacitive energy and the electrocaloric effect is only a fraction of it, the drive electronics shall better regain the capacitive energy during discharge than dissipate it. Marc Schaefer, aka Enthalpy

Masses are positive but their acceleration are opposite here. If an accelerating mass radiates, conservation of momentum alone wouldn't suffice to cancel out dipolar radiation, thanks to the phase lag between the radiation by each mass.

Hi! I understand that conservation of the moment implies that for a system of two bodies, for instance a pair of neutron stars, when one mass moves or accelerates in one direction, the other moves or accelerates in the opposite direction, which cancels out. Though... Referring to this file pinched at Wiki http://en.wikipedia.org/wiki/Gravitational_wave the speeds and accelerations of both masses shouldn't attain the observer at the same time, if (not the case of the picture) the observer is in the orbital plane! When the masses are at 45° to the observer, both have a speed and an acceleration, and the effect of the nearest mass should attain the observer first, so they don't cancel out. At least for electromagnetic waves, it would hold. It's a usual way to build antennas. But not for gravitation? No dipolar, far-reaching wave through this phase lag? Thank you!

10% is far more than other known methods... I had read 100%, which must be false. If 10% are radiated and 90% add to the hole, everything is fine.

Hello dear friends! I've read somewhere that mass falling in a black hole (...other compact massive objects should behave about the same way) adds to the mass of the hole AND is fully converted into radiated energy. Is that correct? As mass falls into the gravity field, it loses potential energy so it should get lighter. Also: if the masses of the hole and the falling object have their sum conserved, and light is created at the same time, which I believe is also a source of gravitation, would this create an abnormal gravitational wave: not quadripolar, not even transverse dipolar, but axial? The observer should "feel" (if sensitive enough) a slight added pull at the same time as he sees the light emitted by the event. In case there's a trick with light propagating together with gravitation, we could imagine light being slowed down or deviated on its way to the observer, as opposed to gravitation. Ideas? If possible in simple wording... Thank you!

Caution with variations in the gravity field. Conservation of mass means that the mass of the Sun won't disappear, so no such effect will propagate. Conservation of linear momentum implies that a mass won't suddenly move sidewise, so one won't see a dipole gravitation wave neither. When one mass accelerates in one direction, an other mass does it in the opposite direction. The biggest change that may happen hence be observed is that two masses change their relative distance or positions, for instance if they orbit an other. As a consequence, gravitation waves are at least quadripolar. As well (don't ask me why, but others here may know) the gravitation field we experience from a travelling mass points to the present position of this mass, not to the position where the mass was one propagation time before. It's the same for the electric field of a charged particle. This is a condition for the orbit stability of planets.

AtomicMaster: "you first have to code the number as two's complement" => How complicated and lengthy do you imagine this operation is? To convert an unsigned number into a 2's complement signed one: do nothing at all. To convert a signed number into a 2's complement: it's already done! Apart in IEEE488 floats, do you see places in a computer where signed numbers are not already coded as 2's complement? ----------------------------------------- One credible reason why IEEE488 defines the mantissa of floats as 1's complement: it's because the mantissa's heaviest bit must always be 1 in order to be implicit. According to the standard, this heaviest bit is not represented in the number since it's known to be 1. Every float except zero begins with "zero dot one" which are implicit, only the following bits are explicit in the IEEE representation. This gives one bit accuracy more with the same format width.

Hello you all! Electrocaloric materials are commonly ferroelectric materials like Pzt, BaTiO3, Pvdf... that comprise charged atoms capable to move a bit in the solid, for instance between two places, easily enough to respond to a strong electric field. In the electrocaloric effect, the mobile atoms store heat as they vibrate, but a strong electric field can freeze them in one position, which reduces the material's heat capacity. Resulting temperature changes of a few Kelvin are typical. The use as a cooling machine is investigated of course, one setup being called "Electrocaloric Oscillatory Refrigeration", which has a magnetocaloric material for one part where electrodes control the heat capacity, and an other part called "regenerator" to store heat. The parts move mechanically along an other, come in thermal contact at some moments, heat capacity is changed within the same cycle, and so the magnetocaloric material takes heat at some points from the regenerator at restores it a bit further, where the temperature is higher, hence "pushing" heat. Both parts can be thin and interleaved to work more quickly, and more refinements - people invent. I believe a different device with static operation is possible and, in case it's not already known, wish to call it "Electrocaloric Bucket Brigade Device" since it resemble what electronics called a BBD, and whose present version is a CCD, a charge-coupled device. Like a CCD, the device defines zones of bigger capacity (for heat instead of electric charges) by fields applied through many electrodes. It also moves these zones by defining a pattern of electric potentials among the electrodes and "propagating" this pattern (steering in fact) over the set of electrodes. The similarity has limits: The electrode potential steers the capacity in a CCD, here it's the difference of potential between neighbour electrodes. The potentials can alternate to avoid an impractical potential buildup, they can also reverse regularly over time if healthier for the material. The relative change in capacity is smaller here. Perhaps the best way to understand the pumping effect is to imagine heat transported at uniform temperature, then realize that a limited temperature difference only superposes a limited leak, allowing pumping. In the CCD, the potential controls the charge; a perfect analogy would let the temperature control the heat amount - but here the field controls the heat capacity to make buckets. The temperature drop isn't essential and results just from the locally increased capacity, though my simplified sketch shows only the drop in temperature. As in a CCD, the lowered buckets can be defined at regular intervals, so that the electrodes connect in a periodic manner to a limited set of control inputs. The next bucket is "lowered" (increased heat capacity) before one is raised. A magnetocaloric material could build the same device but is less convenient: the electrocaloric material and its electrodes can easily be thin and stacked in a wide and short device that transports much heat. Material operation near the Curie temperature has been reported, where the electrocaloric effect makes a bigger temperature change. This should work with magnetocaloric materials as well, as I suggested elsewhere. Though, I'd prefer instead to leave in the material for the high-capacity state a smaller non-zero electric field that the thermal energy can more or less overcome, with the hope that more heat is then absorbed at the mobile atoms - this heat being stored in the external electric circuit. That's similar to the pyroelectric operation of the material, and should work at varied temperatures, even cold if adapting there the smaller field. A quick AC field superimposed to the small field that absorbs energy can help the pyroelectric operation at low temperature. Marc Schaefer, aka Enthalpy

http://en.wikipedia.org/wiki/Helium-3 obtained from decay of tritium, produced itself in nuclear reactors by neutron irradiation of lithium. Shortage of both tritium and helium-3 in sight, so new sources are sought by the nuclear industry, despite the present thread looking unprofessional. The Wiki articke cites existing and prospective uses but doesn't tell what the main ones are. Fusion in tokamaks and laser reactors is out of reach; capabilities of the Z-machine aren't widely public. I'd imagine that research tries to replace tritium with stable helium-3 in the boosters of nuclear bombs - I had suggested lithium but igniting D-Li is more difficult.

I'd bet entanglement among 3 particles is possible and even common. Imagine an idealized case where two successive transitions 3s -> 2p -> 1s of an atom emit a pair of photons. The orientation of the intermediate 2p state (between the spherical 3s and 1s) defines the polarization and direction of both photons, but loosely so - as much as an atom is directional, and it's as little directional as a small antenna, with an E pattern as a cosine of the elevation versus the first photon direction. The path of the second emitted photon won't be perpendicular to the first one, but it can have an angle. The pair of photons cumulate a net recoil, which is compensated by the movement of the emitting atom. In this case, the sum of momentums of two photons and an atom is zero, but the directions of both photons is largely undetermined - I'd say that two photons and an atom are entangled. Depending on the situation, one or two constraints could limit the possible behaviours of three particles. ----- What about quantum cascade lasers? They rely on a superlattice in a semiconductor to offer many energy levels to electrons, spaced precisely equal so that every transition can lase in the unique cavity and in accord with the other transitions. That way, one single electron from the power supply injected in the diode makes some 20 transitions, to emit ideally 20 infrared photons. The photons are linked in some way, for instance through the momentum of the electron in the intermediate levels. If (unsure!) the electron isn't much pushed when in the intermediate levels, you get 20 photons linked somehow, say in their direction. The intermediate levels have some width in a superlattice, so the energies of the photons are somewhat fuzzy, but their sum is constrained by the total energy height of the superlattice - again an entanglement, this time on energy. Even partial sums of energy are constrained, but with a tolerance. This supposes that the crystal keeps the electron's energy untouched for long enough. ----- Please take with caution.

An aeroplane crash doesn't need to evacuate a province for centuries. The designers at Westinghouse (Fukushima's technology) did not forget the dangers; it's nuclear power that's inherently too dangerous. We have cheaper power sources, so "not forget the danger" means "don't make it".

Directed radiowaves need the antenna size of a radar or of a radioastronomy receiver. It gets worse with longer waves. An "X ray" laser has been demonstrated... it's X in the sense that it uses a transition between nucleus' states. But the energy of this transition is ultraviolet. Sort of cheating. Gamma lasing at 511keV is reported by using a positron beam impacting matter. Positron-negaton pair exist for some time and are said to lase. With a short pulse, some superradiance allegedly occurred. I suggested (as a message in a box on a forum, as usual) to sweep the impact spot at light speed (by steering the positron beam) to get a directional gamma emission, as pairs would be produced just where the propagating gamma pulse passes. Read no reaction up to now.

AC also attracts ferromagnetic metal. On one induction cooker I can feel it. It's weak because the induction is weak. I looked at the power electronics of this particular cooker: mains enters on a single-phase rectifier without filtering inductor nor capacitor, so it still wobbles at 100Hz here, and this wobbling DC is chopped around 40kHz by semiconductors and sent to the coil, which has flat braided copper and ferrite bars below, while the pan closes the magnetic path above.

What you describe: Fourier, then discard small components, and encode, resemble so much Jpeg...

When coded as two's complement, negative and positive signed numbers add and multiply exactly like unsigned ones. Strictly the same hardware. Only the detection of overflow differs. Though, for some reason I can't grasp, the IEEE488 format for floating point defines the mantissa as one's complement. Multiplier trees can use binary single-bit full adders or half adders. They can also pre-code bit pairs of the multiplier as -2, -1, 0, +1, +2 which has some advantages. See "seminumerical algorithms". Smaller processors save hardware by cabling ony 4*32 bits for instance, or even just one add-and-shift, but presently a full multiplier isn't such a big chunk any more. One 64bit*64bit takes around 1.5*100*64*64=0.6 million transistors "only", which is far less than any cache memory. A typical PC processor has 2-4 cores of each one multiplier and one adder, each floating on 2*64 bits (SSE) or 4*32 bits etc - that's already 8 full float multipliers of 64*64 on a chip, which crunch numbers at one cycle throughput on a Core 2. The AVX hardware passes from 128 bits to 256 bits. Integer division uses a slow method because it doesn't tolerate the residual approximation of Newton-Raphson used for floats, so it's ususally faster if the programmer converts to floats, then back to integers. Intel claims to have speeded up the integer division on recent processors.

Adding some extra weight the buoy will sink. You could go with a boat to a place as deep as your target location, sink there the buoy+weight with a line, and measure the weight-minus-buoyancy with a dynamometer as the composite sinks. This will tell you by how much the buoyancy drops, and thus if the buoy is good enough to keep the hook as desired.

Instead of individual particles that collide sometimes, like molecules in a gas, electrons in a metal could form well-ordered chunks, and these chunks move against the others. This would explain that: - many electrons move as the Hall effect tells; - but electrons store little heat, as they are immobile within a chunk; - conductivity increases at cold, as chunks grow, and losses occur at their boundaries only, since individual electrons have stiff "positions within" (rather: sets of eigenfunctions) a chunk - the heat capacity increases near the transition, as chunks coalesce. Weaknesses: - No isotopic effect! - Chunks should be very stiff to store no heat - The heat capacity would increase over a rather broad temeprature range Strengths: - Explains why high carrier concentration eases superconductivity. Silicon becomes a superconductor with difficulty, and only at huge doping. - Favours superconductivity in 2D atom sheets - Electrostatic repulsion is much stronger than spin coupling invoked by BCS, so it must have some role. BEWARE this is extremely speculative to say the least. I haven't even checked if this idea was already proposed (it resembles coupling through the magnetic moment) and refuted. Marc Schaefer, aka Enthalpy

Hello you all! Weakly Interacting Sub-eV Particles (WISP) are proposed as a dark mass candidate - similar to WIMP but lighter, from the very little I've read. Though, I don't see how they could concentrate at galaxies to explain the missing galactic mass. Even if they're 3K cold (6e-23 J) and 1eV massive (2e-36 kg), their mean speed is ~8000km/s, much more than a galactic escape speed. Would you know more? Like: - Candidate as dark mass elsewhere, not concentrated at galaxies ? - Subject to forces other than gravitation that confine them in galaxies ? - Colder than the electromagnetic background ? - Other ideas ? Thanks!

To paraphrase: Earth already follows the pull by Sun and Moon. What you feel with the accelerometer is only how much this pull differs where you are from the mean pull averaged over Earth's volume - which is nearly the pull at Earth's center.

The Bullet cluster is an evidence for dark matter, against modified gravitation. Though, dark matter isn't necessarily particles. Other constituents have been proposed and aren't completely abandoned as far as I know. Brown dwarves are strongly disfavoured presently, as are cold star remnants, but others may still be possible. Fun: at the bullet cluster, ordinary matter is observed where it is expected after a collision of two galaxies, and so is weakly interacting dark matter... But meanwhile 2-3 more galactic collision remnants were observed for the same microgravitational lenses, and there the dark matter was NOT where expected... Men think and God laughs. At least, this was a disappointment to people who already hoped to have a complete explanation through weakly interacting dark matter. But certainly not an argument in favour of modified gravitation, since microlensing is seen in every case.

A few approximations that can mislead you... Pauli's exclusion principle is not a physical force that repels particles. It's a mathematical impossibility. In a metal, the accessible states for valence electrons occupy the whole crystal. "Overlap" if you wish, but that's an understatement... Every single state is at the same place as any other, with minor variations in the phase or local nodes and antinodes. Take a 1D crystal of 30 atoms: the wavefunctions with 5 and with 6 nodes over this crystal superimpose but are orthogonal, as their signs add over some places and subtract over others, the sum of the product being zero. Electrons do repel an other by electrostatic repulsion, which is not Pauli's principle. But protons attract electrons, which makes atoms. Then, atoms assemble in molecules - like a piece of metal - because this permits electrons to share their room, and as more room means a longer wavelength, the electrons' kinetic energy decreases. The limit to it is Pauli's principle which prevents putting all electrons in the most favourable state, but two electrons can, which is already a covalent bond. A stationary state is not necessarily the wavefunction of a particle. When an electron is trapped at one nucleus, in a metal... then its wavefunction is a weighed sum of stationary states which are orthogonal. This wavefunction is rarely stationary. When an electron is trapped in a small room like one atom, the stationary states' energies are well spaced, often by many kT. This implies that, at thermal equilibrium (not during the absorption or emission of a photon for instance), all electrons occupy the lowest possible states, within the limit of Pauli's exlusion. Though, as particles aren't discernable, we can only tell "these states are occupied, and these are free". In a metal, states' energies are extremely close to an other - very much closer than kT. (The size limit to separated energies is near "quantum dots", which are just few atoms wide). At thermal equilibrium, states clearly lower than the occupation limit (=Fermi's level) are full, those clearly above are empty - and only those few kT away from Fermi's level have an occupation probability perceptibly different from zero or one. At this small energy range, some states are occupied and others are free, with some probability. Though, we can't easily tell if one particular electron combines these states or others, because of lack of discernability. What we can tell is that if one electron has been spotted around one place with about that speed (remember Heisenberg) then we have this many chances of seen it again at that other place with that speed after that time; the few kT width of the uncertain occupation energy range tell that such electrons are broadly delocalized, because confinement in one atom size means an electron kinetic energy of several eV but kT is only 26meV at 300K. And soon, we can't tell where the spotted electron has gone, as its wavefunction is fuzzy, and we mistake it with others. -------------------------------- Our representations of electrons in metals claim they're indepedent, and this is grossly false, obviously - I do agree. Though, better representations are hard to use... Metals have about one (a bit less or few more) valence electron per atom, delocalized to the whole crystal, so the mean distance between electrons is one atom size. This implies that the mean eletrostatic repulsion between two electrons is the same as the attraction by hydrogen nucleus, like 10eV - hugely more than kT. This energy is about isotropic because every electron has neighbours in all directions, but even the variation of this repulsion energy over distance (= the force) is very steep. It does not confine electrons irremediably, because tunnel effect permits them to pass by; in fact, tunnel effect by electrons is what defines an atomic radius (electrons tunnel to the "edge" of the orbital), so at similar distance and energy, electrons can tunnel by an other. But because of this strong repulsion, the proper way would be to write one single psi wavefunction resulting from the positions of all the 1023 electrons, NOT one wavefunction for individual electrons as we do. This is presently done (sometimes) with the (most external) electrons of one atom or a small molecule, where electrostatic repulsion is computed for all the positionS of the electronS. Though, the result is a computer drawing instead of a usable mental representation, and isn't generalized to 1023 electrons. I have the intuition that non-individual electrons (hence opposed to the electron gas mental representation) that repel an other are the key to - All valence electrons mobile in the Hall effect, but very few mobile in the thermal capacity of metals, which is a paradox to my understanding; - Superconductivity. Again, this is only an intuition.

No, because they have no charge. Though, neutrons do have a magnetic momentum, but they're composite particles.