Enthalpy

Gather in an open environment: this is called a liquid or a solid. But with helium, it's damned hard. Worse, solid helium needs a minimum pressure, whatever the low temperature. Then, if willing to float the solid in the room, more tricks are requested.

Temperature won't do anything. A standing wave is immobile for some time limited by loss. Microwaves, not light, can stay indefinitely in a superconductive cavity. However, it won't support any object. Photons have no mass in vacuum. In a medium, their speed depends on frequency, so one can define a non-zero mass. Some materials, especially meta-materials, are very dispersive, so they can slow light down a lot, around specific frequencies. Some papers claim to have "stopped" light, but this involves a conversion into an excited atomic state, and back.

The size of the target makes no important difference to couple with the field. But the field doesn't penetrate water deeply. I didn't find the penetration depth quickly in my doc, but for brain's white matter at 2.45GHz, the relative permittivity is like 40 and the conductivity 1S/m. This would give a depth <1cm. It explains why thick food must cook for longer in an oven, even with microwaves. And because the over-genius designers of Wi-fi and Gprs put their transmission in a band where ISM (ovens and so on) are primary users, and transmissions basically forbidden but meanwhile tolerated, a transmission at 2.45GHz hampered by an oven cannot complain. But if some day the 1MW oven of your neighbour industry were hampered by your 100mW Wi-fi, you would be requested to shut it off.

How common could a point black hole be? I thought for every black hole detected, the horizon has a size, like planet-sized for a stellar black hole, and much bigger for a galactic black hole.

Ordinary (ferritic carbon steel) accepts sharp bends without heating. Depending on the width, you can do it with a hammer in vice.

For the buzzer hypothesis: some integrate the electronics, so their narrow resonant frequency is already well served. I googled: buzzer site:murata.com and got for instance that http://www.murata.com/products/sound/selection_guide/piezo_sound/index.html other manufacturers exist, mainly the ceramic producers like TDK, and once you know what you want, a reseller is a better place to make the final choice, one example being http://www.conrad-electronic.co.uk/ce/

I wouldn't separate the black boxes from the plane. Floating objects drift away quickly. Worse, they would separate, or lose the power supply or data link, when they shouldn't. At the plane's tail, they aren't accessible. A radio transmitter is easily located. It doesn't have to know and tell its position. Argos for instance did it before GPS existed. Impossible to turn off: you've seen one advantage to it in one circumstance. I'm confident it would have drawbacks in many other circumstances. And more generally, aviation relies broadly on humans that are intelligent, responsible, and of good will. This works not too badly up to now. Introducing hardware that resists human intention will probably make things worse. If you want to factor bad intentions in, don't forget it happens often on the ground. What can be done, as I suggested after AF447, is let them emit sound at low frequency, not as a high-pitched sound or ultrasound. Low frequencies propagate better in the Ocean, and a known noise would be detected hundreds or even thousands of km away by submarines. Presently, we ignore where MH370 is. Inhabitants of southern Maldives believe to have seen it. Then it may not be a matter of black boxes at all. Even more than a matter of black boxes, if I were a military in southern Asia, I would worry about radars and air defences. Losing an airliner over an achipelago is a bad sign. The transponder was off: does anyone expect an assailant to wear a transponder? I also doubt that the airliner's track was really lost. For instance, Inmarsat got a last "position" (somewhere on the two arcs), but it got some more every hour before - that should enable to reconstruct a path, shouldn't it? And, yes, spy satellites exist, their performance is hugely better than a few pixels on a 25m object, there are so many that no hole exists in their coverage. Once the commercial sat detected a spot (it looks unconvincing), spy satellites could have made perfect pictures of it, located it exactly, and radar satellites would tell if the object is metallic. I don't buy the story that the Indian Ocean is a terra incognita where one can lose an airliner, sorry.

I understand the colours represent radiation intensity. Our Galaxy makes noises which add to the cosmological background.

It happens with DC or universal motors whose excitation coil is in series with the rotor. Without a mechanical load, the rotor current is small, and so drops the excitation current and resulting field. As a consequence, the rotation speed increases, and is known to potentially explode the rotor. It happened (...to professors) in my engineering school. The rotor didn't explode, but it jumped out of the bearings through the stator. Then, it accelerated on the ground and smashed a hole in a stone wall, whose repairs were still visible (and commented) years later. Similar things can happen on a turbo-alternator if the electrical load is lost and the turbine still receives vapour. Some power plants with several turbo-alternators orient them to minimize damage (think of nuclear reactors) in such an event, older ones don't.

Rainproof is the difficult part of it. Some buzzers draw very little power and are extremely loud. Your bike horn sound should be recognizeable as such: if it sounds like a bus horn, people will search for the bus and not pay attention to you.

Yes, waves are mainly standing in an oven. Anyway, with around 0.1m wavelength, few lengths fit in the oven, so "bouncing" isn't as sharp as light on a mirror. The oven cavity is meant to couple efficiently the wave to the target, and a standing wave helps there, the long wavelength also; especially, thoughts like line-of-sight, familiar with light, don't apply and are not a limit. Not all the power is coupled into the target, sure. The walls are designed to absorb little, and even the door joint as far as possible, which is less easy. The rest would naturally bounce back to the emitting magnetron, but this is not desired, as it would hamper proper operation in extreme cases, especially when the oven is empty. To avoid this back bounce (or "reflected wave"), the feed from the magnetron to the oven cavity includes a special (and a bit tricky) component that absorbs power only from one direction, that is the once bounced back.

It's my guess too. The step or gradient in the line-of-sight attraction by the exploding supernova is not a gravitational wave. Quite simply, it's the attraction by the neutrinos that pass by us. The hairy ball theorem is tricky... "Spherical symmetry" implies that the polarization is uniform in all direction. If this constraint is relaxed, then power can be radiated in all directions without any zero, and even with nearly-uniform distribution. A banal turnstile antenna does it, improvements bring a more unifrm power density. Examples there, just for fun: http://arxiv.org/pdf/physics/0312023v1.pdf the turnstile is on page 6. -------------------- I've tried to put figures on the gravity step produced by the supernova 1987A, a type II in our neighbour galaxy http://en.wikipedia.org/wiki/1987A Computing with Newtonian physics, hence not with waves: A change of 1046J = 1029kg at 168,000 light-years = 1.6*1021m produces at Earth a change in attraction of 2.6*10-24m/s2 and of gravitational energy of 4.7mJ/kg (wow!), which I call "a". If (please correct if I botched it) the effect on lengths and times is like sqrt[1-0.5*a/c2], this amounts to 5*10-20 variation. The neutrino burst lasted "less than 13s" [Wiki], but how short was it? I take these 13s=4Gm. The nasty bit is that wave detectors (provided they're sensitive to such a gradient) would detect variations like 10-21 but they are much shorter than the gradient, like 3km=10µs: http://en.wikipedia.org/wiki/Gravitational_wave_detector http://en.wikipedia.org/wiki/Ligo http://en.wikipedia.org/wiki/GEO_600 http://www.ego-gw.it/virgodescription/pag_1.html http://www.ego-gw.it/virgodescription/pag_10.html that would make a variation about 4*10-26 over the detectors' size, undetectable. Other detectors? I've not found any - unsurprisingly... Independent clocks at Earth's antipodes would shift by 10-22s, unmeasureable. It needs a single clock, but fibre transmission isn't accurate enough, and vacuum already exists, with only 3km length. Our Moon's orbit would change by 10-25m and 10-25m/s, let's forget it. Space probes on the same orbit as Earth but 150Gm=500s apart would span the whole gradient. The phase shift of a 6.8GHz link would be 30nrd, damned little. At 633nm it would be 2mrd, well over the detectors' noise, but how to extract the information from all contributions to the phase variation? Hey, if someone knows how to exploit a radio link (polarization shift?) from 90AU to Earth vicinity, sending a probe there in 10 years is feasible, with my Solar thermal rocket engine.

Thanks for sharing your thoughts! Because I have no chance to understand nor decide an interpretation by myself in this field... How to detect them: an L-shaped interferometer would have a proper arrangement, and show maximum sensitivity at 45° to its both arms, in a dipole radiation pattern. Though, both arms aligned would be more sensitive with the same arm length. That was the idea behind my question about how quickly such a radiation dampens over distance. I vaguely suppose that true (quadripolar transverse) waves have a longer range, that's why experts hunt these. In a Newtonian view. energy would be extractible from the wave front. Have two masses, one nearer to the supernova and the other farther. Have a link and a generator between them. Within the propagation time between both positions, the nearer mass is less attracted, so one can exploit a movement and a force that pushes the masses together. What Relativity says to that, I have not the slightest idea. An inertial mass carrying a charge radiates no electromagnetic field to long distances, hence loses no energy. If one wants to describe it as photons, then as virtual ones, that describe a near field, here electrostatic. Energy can be harvested from a moving charge by an observer, using the proper apparatus, and only then would the moving charge lose energy in the reference frame of this observer - through interaction with the apparatus, not from the near field of the inertial charge alone in space. Though, a difference with the supernova is that it radiates energy (in the form of neutrinos for instance), which reduces the mass+energy there, as opposed to the inertial charge.

That's the wrong direction. Quite the opposite: less pressure builds up inside the bell than outside. The first thing to understand is that the bell is smaller than a wavelength in air. The second thing is that its vibration has opposite antinodes: at least 2 in phase and 2 in antiphase, for the lowest mode - and these antinodes are close together and very well matched. The result is that radiation by a bell is inefficient; not only as a small radiator, but also because radiation by each antinode is widely compensated by its neighbours, whose phase it opposite. This is desired, to a controlled degree, so a bell sounds for long. Now, the antinodes with opposite phase interact inside the bell more easily than outside. That's because the path between them is shorter (straight line) and more open, while outside, the path goes around the bell curvature. As a result, the compensation is more efficient inside the bell than outside. ---------- The other effect is more observational. Near the rim, the inner and outside areas are close to an other, so the air can pass easily, and the pressure is locally small. To get more pressure, you have to hear at a position farther from the rim - but these positions are accessible only outside, not inside. I designed a long-range military sonar. But that was easy, compared with music instruments, which are the difficult part of acoustics.

Please forget (and forgive) my post #25, whose logic only suggests that the gravity step arrives at the same time as the photons (and the neutrinos, said to carry most energy in some types of supernovae). But I'm still interested in the answer: as apparently the energy emission creates a gravity step along the line of sight, is this step called a gravitational wave, despite not being transverse?

Why shouldn't you burn the diethyl ether? The flame products are clean. It depends on the other compounds in your ether. Or?

Unless you have a supercooled liquid. But this exceeds the level of secondary school, sure.

This seems logical, but if we consider the sphere centered on the exploding star, with radius to us, I see this argument against: - Until light from the explosion reaches us, the sphere contains a constant amount of mass+energy - This amount makes a constant flux of gravitational attraction through the sphere's surface - And if the explosion is symmetric, the distribution of the flux must be symmetric too - Which results in a gravitational field constant everywhere, until light from the explosion reaches us. Or is there something wrong in this attempt?

Standing waves do interfere as well. The speed of sound in the metal. It depends on the frequency, because these are bending waves. At higher frequencies, bending waves in the metal are faster than waves in air, so these are transferred efficiently to air. At lower frequencies, the ones that last in a bell, the transfer is less efficient. Studiot, you obviously have had an acoustics course - but acoustics is more varied and subtle than a course. You can do better than polemics.

Freezing takes time because it releases heat, which raises the temperature of the liquid hence prevents further freezing. Time is necessary to remove the heat. A supercooled liquid may be cold enough that a significant portion can freeze before the remaining liquid is too warm to proceed further.

Earth can't be static while the Moon orbits it. Both have to orbit around they common center of mass. Our Moon is interesting because it has an important fraction of its planet's mass: 1.23%. I've taken the ean distance to the Moon, 384Mm, and multiplied by 0.0123, to get 4.7Mm as the radius of Earth's wobble. Anything wrong in that?

You shouldn't try to understand interferences in terms of energy nor power, since this is misleading. Pressure and air velocity are better tools when adding waves. For instance, if an interference in air produces a net zero pressure near a moving solid surface, this surface will transmit zero power to the air. It's all correct, conserves energy and power and whatever you want. These are interesting notions (which mislead some people to imagine "gregarian bosons"), but need quite some time to grasp, and the net result is just that power and energy are inefficient tools at interferences, so they're a bit disappointing. Yes, I mean waves in air. Within the bell, the wave is essentially standing, yes - and this makes analysis in terms of energy little useful. Outside, a big fraction of the wave (fraction of air velocity) is a near-field wave; whether you want to call it a standing wave, I won't argue about it. For all low modes of a bell, the wave is much longer in air than the solid's dimensions. This is why the lower modes decay slowly and the bell sounds for long - in addition to the shape that provides a good holding point. The higher modes radiate efficiently, provide a brilliant attack, and disappear quickly. It's because bending modes propagate faster at higher frequencies, and when the speed in the metal exceeds the speed in air, the wave is emitted efficiently. But as the lower modes are emitted by a small object with a multipolar vibration mode, analysis as a plane wave and power is misleading rather than helpful.

Electric and magnetic fields store energy in vacuum. This is the case as well for a capacitor as for a propagating wave. This propagating energy subsists when the source has disappeared. Many remote stars and galaxies that we observe are already extinct. Whether it's vacuum or the field that stores energy... I fear this question has no answer. How should we measure a difference? Yes, electric and magnetic fields are mysterious, in the sense that we have no direct feeling for them. We have equations to make accurate predictions (...sometimes! When not fooled, which happens often with electromagnetism), and we can try to build mental images like streams, but that's all more or less. Maybe some birds, who have a sense for magnetic field, have a natural comprehension for it, but we don't.

Dissolution of a solid metal into a liquid one must be very little more than individual atoms at the surface that happen to concentrate at one time enough thermal energy to leave the solid. Anyway, these surface atoms already share delocalized electrons with both the solid and the liquid, hence have strong links to both. The vapour pressure of the hot solid, which indicates how strong surface atoms bind with the solid, could suggest which metals dissolve less. That would mean: Mo < Nb < Ta < W. Though, how well the dissolved atom binds (radius? valence?) with the liquid may play a role.

I've read as well that, for charged particles with constant velocity, the electric field points to the direction where they're now, and not where they were one propagation time earlier. Some math is, I believe, on en.wiki. Though, we compute antennas with good results by using delayed (not "retarded" as I wrote) fields, which apparently contradicts the previous statement. One possibility: whether the particle accelerates or not changes everything. In addition to thought experiments, we can check what would happen to our Moon if Earth's gravity there pointed to the direction where Earth was one propagation time earlier. http://en.wikipedia.org/wiki/Moon The Moon is 0.0123 times as heavy as Earth and 384Mm away, so Earth wobbles by R=4.7Mm due to the Moon's attraction; light takes 16ms to cover this distance, and the orbit takes 27.32days=2.36Ms. Pointing to an older position would mean an angle of 42nrd. Earth's gravity lets the Moon orbit at 1022m/s, which reveals an acceleration of 2.72mm/s2. The hypothetical angle would impart an azimutal acceleration of 114pm/s2, which would perturbate the orbit by 1000m/s within 278,000 years, obviously not the case. Besides numbers, we could have a thought experiment here as well, since the Moon and Earth would get energy from nothing.