Enthalpy

The difference in crystal structure is quantitatively important. When you observe the hexagonal planes or the alloy, there is only one way (i.e. all ways are equivalent) to stack a second plane on a first one, but for the third plane there are several locations where you can stack it, and they differ by one atomic distance approximately. The change from one crystal structure to an other can hence make big deformations, like one atomic distance per plane thickness which is as atom diameter too. As I believe to understand it: One crystal structure is a bit more stable than the other, but the small difference permits a deformation to slip the atomic planes and adopt a very different new shape: superelasticity. Heat anneals the crystal, whereby the atomic planes slip back to the more stable structure and macroscopic shape. This is only one effect. Some materials can change the shape several times and reversibly over the temperature.

Hexamethylene tetramine, or hexamine. Widely available.

Ammonium nitrate detonates without any fuel, but then it needs a detonator. Varied impurities make it much more sensitive and capable to detonate from heat without a blast cap; then the spoiled part serves as the detonator to the rest of the ammonium nitrate. I've run Propep on it at arbitrary 10,000 bar, here are the main molar fractions: H2O 0.57 N2 0.29 O2 0.14 HNO3 1ppm OH, NO2, N2O nothing but at 100bar no HNO3 is formed, the rest stays as is. In both cases, the temperature is only 1245K.

I like this experiment! A few thoughts at it: At 49MHz, the photon energy is 3.2e-26J. At 4K, kT is 1.6e-20J. Do you have any trick for the amplifier, the attenuator and the transmitting antenna's losses not to radiate their thermal noise? I know no way to distinguish the radiated thermal noise from the signal. Or can you chill the experiment to <8µK? You need to chill the whole experiment chamber since the receiving antennas pick noise from the surroundings. A capacitive attenuator instead of a resistive one would make very little noise. Or a weak coupler provided you can remove all passive loads that would introduce noise. Then you could have superconductive antennas that make very little thermal noise. I expect a dirty trick with the bandwidth here, becoming very narrow and introducing on the pulse duration a physical limit disguised as a technological one. Dielectric antennas radiate too and have smaller losses hence produce less noise. Why are your antennas so small? <1ohm radiation resistance is a source of worries. Approaching a half-wave would ease the experiment - OK, I understand you seek near-field coupling. Detecting 3.2e-26J received once isn't reasonable but you'll use many pulses. If the receiver noise temperature is 4K=1.6e-20J (is it?), then 2.5e11 pulses let the signal just appear at 1 sigma; a pulse repetition of 1MHz takes 3 days. 3 sigma bring you to 26 days and 5 sigma to 72 days. Nice. Why use such a low frequency? At 49GHz instead, the experiment needs 8mK, much easier than 8µK. Amplifying is still feasible (or 26GHz, more common and easier), a correlation by analog means too, and you can downconvert the frequency to an intermediate frequency limited only by the pulse duration. One tiny diode laser worked at EPFL whose resonator was an LC circuit of proper size for visible or near-IR wavelength instead of the usual cavity. Metals are quite lossy at such frequency but it did resonate. Patterning the transmitting and both receiving antennas on the semiconductor would be easy. Why shouldn't you go to these frequencies? There the photon energy exceeds the ambiant temperature. From the analogy with optics, where coupling by evanescent waves exists too, and these are near-field coupling too or resemble a lot, I'd dare to make a prediction or rather a bet... I expect the signal to be quantized, and one single photon to couple to one receiving antenna OR the other BUT I haven't understood what guarantees in the setup that one single photon is transmitted. Let's forget thermal noise at the transmitter: just with a generator and an attenuator, you get a pulse amplitude smaller than one photon. This does not guarantee that one single photon is transmitted. There can be more, this is just a statistics. The hard part is that, as you supposedly want to see whether both receivers get a signal or not, the probability to emit two photons is exactly the amount you want to exclude from the correlation. SO what you need is a source that guarantees that only one photon is transmitted, and the small pulse power does not do that. The lone photon must result from a lone de-excited electron, not from an attenuator. This is commonly done in optics by using one fluorescent atom, for instance nitrogen in diamond. In case radiowaves are better, something similar can probably be done. Ammonia maser, hydrogen maser, adapted rubidium clock, all with a single molecule...? With the proper cavity they must deexcite more quickly. A big quantum well with one single dopant atom?

I feel the question is rather clear - only the answer isn't to me... I can bring practical considerations quickly: this looks difficult to measure with standard hardware. Transformers with core serve up to 100MHz (and rather less), efficient transformers to 40GHz+ with microstrip lines, but photon noise begins to exceed thermal noise of cooled amplifiers rather above 40GHz. Well, the experiment doesn't need efficient transformer coupling, so it must be feasible by stretching the components a bit. My not quite justified bet is: signal itself is quantized, that's why "photon noise" exists, and the experiment will see this photon noise whether it comes from a transformer, a resistor, an antenna or anything. I don't even know how to relate it firmly with the near field, because a transformer lets many electrons interact.

Momentum and position not quantized for free particles shouldn't be a difficulty, so I guess you ask about entanglement having an uncertainty. Here's a paper about the relation between the precision of momentum entanglement and position precision: http://arxiv.org/ftp/arxiv/papers/0905/0905.4830.pdf the authors compare with Heisenberg's relation. In the situations where the process that creates entangled particles is known, the uncertainty appears logically from the properties (for instance the transverse dimensions) of the source.

Your question isn't perfectly clear... http://www.iue.tuwien.ac.at/phd/entner/node12.html

Tilts the quantum well, sure. The electron's energy depends on the electric potential which the external field lets vary over the position - just as in vacuum, possibly with permittivity somewhere. Change to 3D bulk density: I don't understand. As long as the electron stays trapped, there must be some effect on the state density. But tilting will affect the density of states. ---------- With reference to our other question: in case the well results from a MOS gate, if the gate potential releases the electrons, these get free to move in the bulk where the usual state density applies. It's only that in the usual operation of a normal MOS transistor, the channel's carriers go to the source and gate, at least after some short time. Longer storage in the depth would happen in a CCD device.

If I understand you query properly... Many observations need the particle to have had all the possible states prior to detection. Only this explains the observation. You cite the double slit: a photon must pass through both slits so you get an interference pattern on the screen. Pure state... this is possible to a reasonable extent. But a state pure for one quantity is a mix for an other one. If the energy is certain then it takes time to measure: the instant of the measure is uncertain. So a state can be "pure" but not for all quantities at a time - only for the "compatible" ones. "Observation" is often a process where one of the particle's attributes gets more accurately defined, for instance its position. But better doesn't mean certain: every measure has some incertainty. So it isn't "known" with perfect precision nor certainty. My general suggestion would be: do not concentrate on the double-slit experiment, because it easily suggests false interpretations. You might invest time for instance in pictures of molecular orbitals by the atomic force microscope, as this one refutes many false interpretations. http://education.mrsec.wisc.edu/SlideShow/slides/scanning/pentacene.html http://www.nature.com/nchem/journal/v3/n4/fig_tab/nchem.1008_F3.html for instance, the observed electron has not decided to be at one point just because the microscope observed it. The observed and observing electrons interact permanently over all their possible positions.

One "simple" example is 40K which can decay via beta-plus or beta-minus (or electron capture too), suggesting that decay is not a composite particle splitting into smaller compounds. That is, if the neutron were an electron and a proton close to an other, as wrong theories supposed long ago, then the emission of a positron would be impossible. So, new particles are created from nothing, provided the energy is available and some quantities are conserved. Just like a photon is created or destroyed. I imagine this is because our universe is cold now. If the decay with emission of a neutrino pair takes place, the inverse reaction must be possible too, but it doesn't happen because the random presence of a suitable pair of energetic neutrinos is rare these days. With the proper reformulation, thermodynamics should model that. Put the proper temperature, and you get an equilibrium between the lighter and heavier particle. But at 3K, the equilibrium is so unfavourable to the heavy particle that only one reaction direction is observed.

Ouch! An orbital is a stationary wavefunction, that is, it does not depends on time except for the phase rotation. All the information of a particle resides in its wavefunction. And a measure "at an instant" is impossible to make, so it's of no interest to QM, which does not answer it. The nearest possible experiment is to measure the momentum of an electron over a short time, and then the interaction with the measuring particle is inevitably at high energy and momentum if the interaction happens. This does not require the electron to have this momentum prior to the interaction.

Hi Dim! what I can tell is that the Weber bar isn't capable of producing a detectable wave https://en.wikipedia.org/wiki/Weber_bar the best possible effect is a near-field which isn't a propagating wave. I won't risk an opinion about the orientation in the heavy body's field. Just a guess: both effects being small, I expect them to add linearly.

The same material may be ferromagnetic or, above its Curie temperature, paramagnetic. I doubt a simple law works for ferromagnetic materials. Theories have been tried, but in docs for permanent magnets I've never seen one mentioned, only experimental curves, so simple theories resembling a thermodynamics distribution must fail.

No, that doesn't happen. Because protons are composite particles, because their constituents are not favoured over other elementary particles, and because their constituents can assemble into other composite particles. So at the minimum energy you get many electrons, muons... and their antiparticles but no protons. At higher energy you may get a proton from time to time but more probably mesons, and so many elementary particles, many of them charged, that there is no need to create a proton pair for neutrality.

"how frequency of sound varies in water" is a bit unclear. For instance, the frequency of a sound created in the air keeps the same if it passes to water. The frequency produced by some generators may vary if they're immersed due to the mechanical load by the water's mass. The best frequencies to use in water differ from the atmosphere. For long range, lower frequencies are better, but the gradient of temperature and salinity along the depth create odd effects, with a layer around -800m that guides the sound.

What I do agree with: Impacts from molecules create a small force, momentum, etc This force fluctuates Some converter, for instance piezo, can make electricity of the fluctuation This is confirmed by pressure sensors and microphones. They deliver an electric noise which, if their conversion is efficient like a piezo crystal is, results from the random movements of air molecules. Measurable and measured. Where I disagree: This movement converted to electricity won't heat a connected resistor beyond the gas' temperature. The temperature equilibrium results from the electric power (called thermal noise) produced by the resistor too. The converter (piezo crystal) produces a mechanical noise from it and transfers it to the gas that gets heated too. --------- This is a general, interesting and useful idea - though quite difficult to use - that results from thermodynamics' second law. In the case of a piezo crystal used in the experiment you propose, it implies that the material is as "efficient" in converting work to electricity and electricity to work. It wouldn't be so with a piezoresistive material for instance, which doesn't produce electricity from sound but only modulates the electric power available from a separate source. On such a microphone, you can put electric noise, but it produces no acoustic noise, because it's not a converter.

Your drawing makes the proposal clearer. Unfortunately, the magnetic tube won't shield the effect of the current that flows inside. In this case, the ferromagnetic material increases the induction where the material is, but doesn't reduce it elsewhere. So as seen from Earth and its magnetic field, the current loop is still closed. It creates a torque (used on some satellites) but no net force to a first approximation. In that configuration, thinking at the magnetic field created by the current loop is simpler than thinking at the effect of the tube on the geomagnetic field. The only net force comes from the variation of the geomagnetic field with the position, but this effect is minute. I had checked it. It can't compensate the atmospheric drag at 800km even with strong permanent magnets reoriented over the orbit.

A minute hole will suffice, provided it doesn't get clogged up. I feel the hole for the wick is more of a worry. What can prevent leakage through a small hole is surface tension. https://en.wikipedia.org/wiki/Surface_tension

No. This is not how electrostatic force is computed. https://en.wikipedia.org/wiki/Coulomb%27s_law If you put figures on it, you find a minute force. In addition, it's in the wrong direction.

Propane too is heavier than air. 44g/mol versus mean 29g/mol. Is that much better than butane with 58g/mol?

A flywheel stores energy as the speed of a mass: 0.5*mV2. To limit m, they tend to use a big V, and the flywheel's solution is to rotate the mass quickly, where the limit is the wheel's resistance to the centrifugal force. https://en.wikipedia.org/wiki/Flywheel Some people have proposed graphite composite. The strong and light material attains the highest speed but is expensive. My proposal is strong steel, since it can be cheap http://www.scienceforums.net/topic/59338-flywheels-store-electricity-cheap-enough/ Other people have suggested concrete, with some reinforcement of undisclosed nature.

The vapour pressure and the safety together are an obvious advantage of xenon over cesium for instance. Candidate elements are the ones whose gas is monoatomic. N2 for instance is much more difficult to ionize than N. Ionization is easy with xenon; it results not only from the ionization potential but also from more subtle behaviours. For instance, oxygen can capture lone electrons to quench avalanches efficiently - this reason favours SF6 as an insulator.

And this represents several solar cells in series, here two: where you see that if one cell gets no light and its equivalent curernt generator drops to zero, the current that the other cells would produce can't pass through the internal diode. Similarly, when one cell receives less current, it limits all the series strip. That's why, on satellites, we add diodes that permit the remaining cells to produce power. Apparently it isn't common in terrestrial applications but it should be.

Lightning delivers very little energy. Forget it. Energy storage in superconductors has been prototyped by several companies. Cables are made from filaments for varied reasons and have a good section. Already the magnets at the LHC store a significant energy. Scaling up improves, yes. For a given current density, the achieved induction increases with the section, and even once you've reached the material's maximum induction, the energy increases as the coil volume and its density would be interesting. The next question is: how good, how expensive - and there, for instance a flywheel is better, primarily because of costs. http://www.scienceforums.net/topic/59338-flywheels-store-electricity-cheap-enough/ Don't forget neither that useable superconductors, the ones that accept a significant induction and current density, are of type II, which do have losses - in the MW range at LHC. And then, you need real cold, which is expensive. And you risk huge explosions, see "magnet quenching". All put together, I don't believe it has a future, at least with present materials. But I'd be glad to be wrong.

Hi Soderdahl, nice to see you again! Emissivity isn't the same at 1200°C. It won't be small. Big emissivity is attained by roughening the surface. It provides multipath absorption. 1Pa is still a lot. Resistance to oxidation is essential then. Low emissivity after hours or years at 1200°C implies noble metals. A ceramic would be a more natural choice, but don't expect a low emissivity from it neither. ZrO2 0.25 I have data for short-term 1200°C emissivity of metals... Cr >>0.38 Inconel 0.3-0.6 W ~0.22 Co, Ni >>0.22 Pt 0.18 Mo clean 0.18, polished 0.16 Gold polished 0.03 For some metals, sublimation is already a worry at 1200°C.