Enthalpy

In what profession is the anode defined that way? In electrical engineering, the cathode of a Zener diode is always the same electrode, whatever the current direction. I haven't seen any single exception in 35 years. Same for tunnel diodes, Impatt, Trapatt and the whole and complete zoo. Same for rechargeable batteries in electrical engineering.

An electron produces radiation at the frequency it wobbles. The acceleration influences the emitted power. Sometimes the wobbling frequency isn't well defined, for instance if an energetic electron is deflected when passing near an nucleus; then the emitted radiation contains a broad spectrum of frequencies also.

An EMP weapon would not emit a CW, because this is not necessary and is inefficient. Only the peak power counts to destroy an electronic circuit, and any spark discharge does it far better. Things like a Blumlein circuit are routinely made by good hobbyists and produce 1MW naturally: adapt it as an antenna.

One common detector has nuclei that absorb neutrons and radiate immediately an electron (one gadolinium isotope) or a proton (3He). Then the electron or proton is detected. http://en.wikipedia.org/wiki/Neutron_detection ---------- The magnetic moment of the neutron should radiate when the neutron accelerates. This radiation must be seriously inefficient and unuseable. For instance the spin flip of neutral hydrogen's proton at 21cm takes millions of years instead of nanoseconds, so radiation by the magnetic moment is obviously tiny.

Yes, antennas exist for infrared and visible light, not for gamma wavelength. John D. Kraus proposed it very long ago. Presently, semiconductor technology can easily etch antennas of the proper length to resonate a µm wavelength and little below. Dielectric antennas work properly at visible frequencies. Metal antennas are bad, barely resonating because of big losses, but they do radiate and receive. The signal must be produced or used in the immediate vicinity because a metallic transmission line would loose power within µm; dielectric lines (for instance fibres), as opposed, are good. One example few years ago was a tiny semiconductor laser at ETH Zurich, smaller than a half-wavelength in each direction, that had a radiating resonating circuit instead of a cavity. http://phys.org/news188593304.html You noticed, this is all for very special purposes. Inconvenient for the general uses.

Normal materials and standard hardware withstand it, but you better balance the rotor carefully before running the motor.

One can protect electronic circuits against a nuclear-produced EMP. Military circuits are protected since decades. It doesn't demand very expensive nor heavy hardware: it's more a matter of doing it properly, which isn't obvious. By the way, the pulse produced by a nuclear detonation at altitude isn't necessarily stronger than from other sources, say a flux ciompressor. It harms a larger area.

Here are hints for some components. ---------- Rake I mentioned on Oct 06, 2014 a rake - difficult design at 50m/s. Maybe hard parts with proper wedge shape can rub, near wheels and rails where they would thread in more easily, and using a long slope to linder the contact shock which shouldn't be underestimated. Or these part are put actively in contact when the observed speed has dropped. Instead, the following sketch uses the rubbing of the ropes that retain when desired the catching ring of Oct 06, 2014. On such a winding, similar to a boat's winch, the rope glides if the pulling force exceeds exp(µ*a) times the holding force. If a=1.5*2pi radians and the coefficient of friction µ=0.25, the amplification exceeds 10. As the shuttle pushes the catching ring down, it releases this end of the rope, so the weaker extra bungee at the other end can move the rope untils it's stiff at the low position; there, the extra bungee aided by the multiplication factor holds the ring until a separate mechanism brings the ring and the shuttle to the proper restart position. Before restart, the rake bungee is actively released, the rope actively brought to the wait position, and the rake bungee stretched again. This design isn't easy to adjust, is not fail-safe, but it may work at 50m/s. ---------- Belt The vacuum bubble and the experiment shell must be hermetic but quick to open and close. Better than numerous bolts, they could use a belt as the ones that hold satellites on launchers, here a cut of the right side: The jaws' material must glide well at the lid, cylinder and belt, like polymer bearing material against Cr. A hand wrench can tighten an M16 screw (100kN) to stretch the belt, which then clamps the lid with ~200kN: enough for vacuum inside, enough for air inside up to D~1.3m. As special screw achieves more, but at some point a hydraulic closure is better. ---------- Release mechanism Already proposed there http://www.scienceforums.net/topic/58924-magnetized-target-fusion/ it may release an experiment falling free through vacuum and minimize the side kick. The guided vacuum bubble doesn't need that. 350bar on a nickel membrane rubbing over D=20mm h=40mm on a nickel-coated cone hold safely 1t. 1cm3 releases the pressure much faster than the 5ms to open the valve. The pressure equalizes in 20µs so it's <<0.5% even. The <<0.7N*s side kick lets a 1t*3m experiment rotate at <<1.3mrd/s or <<3*10-7g. Marc Schaefer, aka Enthalpy

There are no free protons in a fuel cell. They're dissolved, for instance in water, or absorbed in a polymer membrane.

Are these bizarre tiny figures for liters of air? Even then, 0.044mol of air, or 0.0093mol of O2, making 0.019mol of H2O, would release 4500J. Anyway, hydrogen cars operate already even if not quite satisfactory, so energy density doesn't rule them out. In fact, if hydrogen is stored as a liquid and used in a fuel cell, it's better than hydrocarbons, both at identical mass and at identical volume.

Common microwave sources wouldn't disable a complete building. Portable EMP generators exist already as weapons and are in use - rather simple technology, accessible to good tinkerers. The effects can be temporary if the power density isn't too high, BUT this depends much on the distance and on how the target electronics is built, so the usual effect is that more electronics is destroyed near the source and more is temporarily hampered farther from the source - if containing software, the recovery is longer. A small EMP generator was used in Aoste and an other Italian city very probably, according to the described observations.

Good idea. Just remember that in such experiments, the pressure is usually very small, so one gets coefficients much larger than at the pressures useful in mechanical engineering. Try to have small contact surfaces, put loads on the parts. If experimenting with glass, don't take flat parts (window glass is very flat), or you'll measure only atmospheric effects: air cushion or suction pad. As a source of data, first check if it indicates at what pressures the coefficients of friction are measured, since the coefficient varies by a factor-of-three with the pressure, and discard the table if no pressure is given. That's a first, very efficient screening. Mechanical design basing of friction, as I did for several years, uses tables that are pages long just for the most common alloys. A table like the extract given in this thread, with one single value per material pair without an indication of the pressure, would definitely not qualify as "reputable" - it would be discarded immediately. A query for a coefficient of friction usually ends with "I measure it by myself to have a credible value".

No, I was responding to some points in the webpage you linked, and didn't realize you were not necessarily the one who wrote the linked webpage. So indeed, it wasn't an answer to the topic you started here, sorry.

For this activity, "explosion" is any combustion including a candle flame, a "deflagration" propagates by the heat or burnt material that ignites still unburnt material at the front, and a "detonation" propagates by the pressure wave. Typically a solid or liquid high explosive detonates. Most gases can either deflagrate or detonate depending on the conditions: mix ratio, initial temperature, also initial pressure, impurities... So do some solids by the way: TNT can burn slowly and badly and needs a blast cap to detonate. In most cases, exploding materials can switch from deflagration to detonation, and without a clearly identified cause, especially if the amount suffices. While methane and natural gas rather easily stay in the deflagration mode, acetylene and more so hydrogen are prone to switch to detonation, so measuring the deflagration speed (only 3m/s for hydrogen in air, 14m/s in oxygen) is dfficult. You can observe a full-size hydrogen boom at the video of reactor #1 at Fukushima dai-ichi (not at #3 which I consider is a vapour expansion). Quite efficient, from a limited amount of hydrogen. To estimate the explosion pressure, a naive approach would consider 300K and 1atm before, roughly 3000K and (in air) as many moles after, to deduce 10atm. Though, it's known to be an underestimation. A first reason is that the gas mix is already compressed by the wave when it ignites; from 300K to 850K, this supposes 38atm at ignition and then T and P *3.5 would result in 135atm - but this one estimate is too high. A further reason is that detonation wavefronts are not plane waves in real situations - only in experimental setups.

And so do I have my doubts, very much so! At least, radiation from a spherical source is impossible as soon as we assume the waves are transverse - be they dipolar or quadripolar. The mere symmetry of the sphere lets locations at right compensate the ones at left. Or for a quadripolar wave, the locations up and down compensate the left and right ones. All at the same distance and propagation time, so that's the easy part. Radiation from a spherical source would be longitudinal. As a sidenote, a hypothetical longitudinal wave would be hard to distinguish from the gravitation resulting from the neutrinos that pass by us. In strong supernovae, neutrinos carry most energy from the explosion, they're nearly as quick as photons and gravitational waves... How to make a difference? It would need an event where much of the released energy stays near the explosion or propagates slowly. I've so big doubts that I wonder (somewhere on ScienceForums) why a binary star shouldn't emit a dipolar gravitational wave. Both stars have a speed and acceleration that vary over time, and if we see their orbit flat and when they're at 45° and 135° from our direction, their opposed acceleration should have produced waves that we receive with different delays hence shouldn't compensate an other. Very similar to the spherical explosion, isn't it? I vaguely suppose that the retarded potentials don't apply here neither. It's a clear case where the source is much smaller than the wavelength, and then retarded potentials are often misleading. The step "we observe earlier the influence of nearer parts" would be where gravitation behaves unexpectedly. For instance in acoustics, near a spherical source or the apex of a cone, the pressure and the speed are out of phase (pressure rises as air accumulates through speed), while they're in phase in a plane wave far from the source, so retarded potentials fail, here in the first geometric half-wave. Similar things happen in electromagnetism, just more complicated. There must be very few dozen people on Earth who have a rational and critical understanding of gravitational waves. I definitely don't belong to them, so I can only stick to what I read - hoping that these indirect sources make sense and that I read the material properly and that I apply it as it should - which states "transverse quadripolar".

The random motion of atoms, electrons and so on, lets them radiate even at room temperature, then in the far infrared around 10µm. The emitted power is drawn from the heat stored in the body; particles that emit photons in a shock rebound less strongly. In space in shadow, a body cools down through radiation. In a lukewarm environment, the body that radiates due to its temperature also receives heat from the environment, in the form or thermal radiation. Because heat doesn't move spontaneously between bodies at the same temperature, this implies that a body at the same temperature as its environment receives as much thermal radiation as it emits. A consequence is that the body's ability to emit thermal radiation (the emissivity) equals its ability to absorb it (absorptivity), for any given wavelength, polarization - for any attribute that permits to filter the radiation. Though, the emissivity and absorptivity do differ at varied wavelength, so copper that absorbs some visible light but emits little infrared gets hot at sunlight (especially without atmosphere) while glass that absorbs little sunlight but emits infrared well gets cold.

Already a few elements - without having put the necessary time into the linked page, sorry for that... It's the enthalpy that matters in the propagation equation, not the internal energy. The enthalpy variation tells the work in an adiabatic transformation, and this woks converts to and from kinetic energy in a wave. Neither the internal energy would be entirely kinetic.For a monoatomic gas yes, but already a diatomic one like air contains more contributions. Rotations can be understood as kinetic energy, vibrations only in part, as the other part is a change in atomic distances or angles. Vapour and carbon dioxide, for instance in air, do contain vibration energy even at room temperature. I don't grasp the difficulty with "entirely kinetic" and "microscopic versus macroscopic". If you mean 1/2µV2 by "macroscopic", this collective oriented movement is not included in the thermodynamic internal energy (nor enthalpy), which accounts for individual unoriented movements (and more) versus the collective one. Did you mean something else?

In contrast to potassium, lithium is said (I didn't try) to react not very brutally with water, and itself and the evolved hydrogen not to ignite usually. This would represent a limited risk in open space. Hard chromium is an other candidate as a liner: big elastic strain, thicker layer easily deposited. Though, because lithium is so soft, I'd prefer an electrodeposited nickel or nickel-cobalt layer, which accepts deformations, over the more brittle chromium and phosporus nickel.

Weighing 534kg/m3, lithium would make a nice float, with a liner to separate it from the water. This sounds a bit bizarre, but after all we have already metallic lithium in batteries all around us. If the float consists of many lined elements, a failure in water wouldn't propagate to the whole float, and would result in a fire if near the surface, and have little consequences at depth. While being lighter than hexane and syntactic foams, lithium is also stiff - much stiffer than water. From 6000m/s sound velocity, the bulk modulus is 19GPa, so 114MPa water pressure shrinks lithium by 0.6%vol or 0.2% in each dimension. The elements can be spherical, without any void: cold isostatic pressing, radiography. They must receive a perfectly conformal coating, for which metal sputtering or evaporation looks feasible. Over this first coating, the liner can be: Malleable, maybe niobium or tantalum. This would resist a finite but big number of cycles, easily experimented on the ground. Hard, with a yield strength exceeding the 0.2% dimension change. At E=200GPa, both electrodeposited nickel-cobalt and electroless phosphorus nickel have margin. Maybe evaporation or sputtering can also make the desired thickness. I'd have a protection against mechanical aggressions, especially if the liner is malleable. Something like strong polymer fibres woven around the liner. While the performance of a lithium float is second to ceramic balls and pressure-aided graphite tanks, it's better than graphite tanks without pressure and syntactic foam, its resistance to pressure gives more confidence, and I prefer the risk of lithium to the one of a vessel with high permanent gas pressure. Marc Schaefer, aka Enthalpy

It's the attraction due to the strong force minus the repulsion between the positive charges. If a nucleus were created from protons and neutrons, the strong force would release energy (and the electric repulsion absorb some), making the nucleus lighter and releasing energy as gammas, expelled quick neutrons, neutrinos... The nucleons are lighter (though it's inherently difficult to attribute energy to one or an other) because of the released energy. This is not restricted to nuclei nor to the strong force. Any form of energy makes objects heavier. Nuclear energy is concentrated enough that its effect on the mass is rather easy to observe and to use in computations.

To evaluate the number of grains, you'd like to compare volumes.

The fields that ionize gases use to be hugely weaker than what would pull an electron away from an atom or a molecule like H2. The field of a proton at 50pm is 600GV/m while excellent solid insulators break at 50MV/m, gases earlier. Only extreme laser pulses, very short, concentrated and energetic achieve to ionize a gas without having a favourable frequency. If it's not the field ripping an electron from a molecule, it needs a more efficient ionizing process, which is impact ionization. Electrons or ions that pre-exist for any reason (radioactivity, cosmic rays and so on) accelerate in the field over a big distance until they hit a molecule. If they have 70nm mean free path to grasp 20eV, a field of 300MV/m suffices now - not perfectly accurate (because the "avalanche" doesn't need an ionization at each impact), but much better than 600GV/m. Also good: for voltages that clearly exceed one ionization potential, it's indeed observed that the breakdown field multiplied by the mean free path is a constant. The too heavy ions are less efficient than electrons to transfer energy to an electron in a molecule and rip it off. Though, electrons alone can't easily sustain a DC discharge, because they can't replenish themselves at the negative electrode where they originate. Only ions arrive there, and at that location, they must rip electrons from gas molecules or from the electrode. This less efficient process determines much the breakdown. AC voltage can stabilize a discharge better than DC does by relieving this dependence on ionization by ions. Then, frequency does have an effect: If the half-period is clearly longer than a few electron flight times, nothing special. At higher frequencies (say GHz), electrons have less time and distance available to accelerate, so they need a stronger field. For instance light never produces an avalanche ionization. Rare gases tend to be easier to ionize than other atoms. Not quite intuitive, but it results from non-rare atoms regrouping in molecules, where electrons are much deeper in the nuclei's field. Other mechanisms quench an avalanche, especially if some atoms can swallow electrons to make negative ions. This tells why the best insulator gases (SF6, CF4) contain electronegative atoms to outperform molecules like N2 that keep their electrons far better; moreover, these gases also reform spontaneously after a breakdown.

Yes, this reasoning puzzles me too, since the beginning of the thread... But I have more confidence in the total flux of gravitational attraction through the sphere depending only on the mass+energy contained in the sphere, and this tells "no effect". The specialists of waves tell that they're transverse, not longitudinal like the implosion would have produced. I can't do better than believe them. The same scenario with electric charges clearly tells "no effect", despite the charges nearer to us apparently should affect us earlier than the ones farther. I've become very cautious with retarded potentials. These are not fundamental physics laws. In electromagnetism, they result sometimes (=for a plane wave, at distance) from Maxwell's laws (which are fundamental) and sometimes not (for instance, the electric field made by a particle with constant speed points to the present position of the particle, not to its position one propagation time ago). The attraction field of a massive particle with constant speed also points to its present position, which can't (and isn't) inferred from retarded potentials. So I vaguely suppose that retarded potentials are what misleads us when considering the star implosion.

It's a help to understand, but this experiment and its description also bear the risk of introducing incorrect comprehension of QM. For instance, the wave function is not only a means to compute a probability of single events. In atomic force microscopes, or at the interaction of two atoms, the same electrons interact all the time, and over the full extension of the wave function. The sole example of the two-slit experiment may let readers get that inaccurately. Readers may also misunderstand that the interaction with the slotted screen is of a different nature than the one with the detector pixels, or that an absorption must be local. So while the double-slit experiment is useful, it must not be the only basis to understand QM.

But when every engineering book gives coefficients like 0.12 to 0.4, when I made measurements dozens of times and got results consistent with engineering books, when a simple inclined surface should have sufficed to everyone to see that metals glide far before 45° - then, a table claiming coefficients like 0.78 or 1 is obviously wrong and to be discarded. Just for comparison, 1 is the kind of coefficient gotten from rubber tyres on a street.