Enthalpy

Polyester (Mylar) isn't bad! I used natural rubber which is way worse, but my balloon had just to climb for 2-3h, burst and fall down. Generally, metal and ceramics are far better than polymers, but a metal layer in polyester is probably too thin to make a difference. At the thickness covering a space blanket, the metal film isn't even continuous. If you give it a try, take a thicker metal layer. You could search for helium diffusivity polymer but few polymers have the other good properties of polyester. A gas lighter than air weighs less than 29g per mole, so a check through the elements tells it... http://www.webelements.com/ http://www.chemicool.com/elements/ Hydrogen (boom and leaks), neon (expensive and lifts little), N2 (lift nothing), CH4 (I used it. Boom, lifts little), NH3 (yuk), H2O (I used it : inconvenient on Earth, keep for Venus), HF (yuk) -> That's all. No discovery possible. So either you accept CH4, Ne, H2 - or you're reasonable and go to He.

In the absorption over a short time, it's the measure that lets atoms decide in which state they are. I can' tell a means to distinguish a "transition" from the change between old and new state, and have no other means to tell a change has occurred than measuring it, then it determines itself. The mathematical modelling of wave theory tells only a superposition of two states, with the probability varying over time from old to new, corresponding to a weighted sum of both waves. I see no reason to imagine a shorter transition between both, as this is not observable - or is it? Unless I get convinced with some means of observing it, I stick to weighted sum of waves. The absorption of a short bunch of radiation is the same reason why photons were introduced: the observation is binary despite light being a wave, that is, a photon is absorbed or not.

Imposing the volume to a bladder at depth means some force and energy, sure. But the solids that shall do it can have the necessary volume. Generally, stiffer materials can provide more force but expand less - but there are exceptions like Invar or Pyrex. So once you have an efficient pair of materials, the shape you design must match the material to the blade's force and displacement - and it must guarantee a quick heat exchange with water. A factor of merit for the expanding solid is E*K2, where E is Young's modulus and K the coefficient of thermal expansion. This characterizes the available mechanical energy per volume unit. You can try a few metals and plastics - plastics look better but must be thin to react quickly. The truss I sketched is an intuitive approach, which needs backing or adjustment by numbers, to matching the bladder's behaviour. It is stiffer than the bimetal you linked in order to, as you told, give more force. The angle of the truss adjusts this; stack seeral ones if needed. Tubes react to heat more quicky and resist buckling better. ----- A rough first glimpse, without the factors of 2 and 3: Imagine a 10dm3 change bladder that works between 0m and 30m: it absorbs 3kJ if gas pressure varies little. Aluminium (70GPa, 24ppm/K) provides 8kJ/m3 so you need 0.4m3 or 1000kg of it, plus the other metal, not very good. A plastic (2GPa, 200ppm/K, must withstand 12MPa for long!) needs 0.18m3 or 180kg, better. Consider polypropylene. At 20K*200ppm/K, a truss of 200mm length and 40mm height moves by 3.7mm which would fit a D=1.8m bladder, so a flater truss or several stages are better. You must also fit the 0.18m3 somewhere. Levers and pulleys can contribute to the design. ----- The design I heard of long ago used the expansion of a liquid in a cylindre instead of plastic parts. A liquid would need a good heat exchanger with water, like water tubes passing through the cylinder, or many liquid tubes in water making the tank (converging to one single piston). If you find a strongly expanding liquid, fine. The ones I know (petrol) are somewhat better than plastics but polluting. Marc Schaefer, aka Enthalpy

I haven't played with them but read the description on commercial ones, and they mentioned only iron, water and salt. To make the reaction fast, I'd say it takes enough salt and a well-rusting iron, not too pure, with little chromium, aluminium and silicon. But that's just a guess.

The transition gets faster, and equivalently the excited state's lifetime shorter, because it's a maser, that is, a stimulated emission. Both the cavity and the number of coupled molecules reduce the time. How would you tell the transition duration from the lifetime? I mean, between just two states, old and new. Being unable to tell better than "it's in the old state" or "it's in the new one" I can't imagine a way to distinguish both times.

Discrete energies are for the stationary (=non-evolving) states only. ========================================================================================== PaulMuaddib: "When the electron makes a quantum leap, it suddenly changes not only its orbit, but also its energy. In doing that, it emits a burst of light." [Emphasis by Enthalpy] We have no means to know if the change is sudden. The (proton) transition that emits radiowaves at 21cm wavelengths to the delight of radioastronomers takes many years to happen. But if we try to determine if the emitting atom is in the old, the new or an intermediate state, we get a binary answer. As we observe many atoms, we get a statistical answer, hence the "many years". If we observe the emitted photons, we can detect them over a short time, but our receivers are more sensitive if observing them over hours. Other transitions take <1fs. ========================================================================================== PaulMuaddib: "[it seems that the electron] is disappearing from one orbit and reappearing elsewhere in another orbit" An electron is not "in" an orbit. An electron is a wave that occupies some volume, has some energy, momentum... This wave is called an orbital when the electron is trapped around a nucleus. http://winter.group.shef.ac.uk/orbitron/ During a transition, the wave is a combination of the old and the new orbital. While the orbitals are stationary and don't emit light, their combination evolves over time, at a frequency equal to the difference of energy between the orbitals. Better: this evolution over time is a wobble of the charged electron, at the frequency of the might emitted or absorbed, which is perfectly similar to an antenna radiation. The tricky part of the quantum process is that you can detect the emitted photon over a short time (though with a smaller probability) and it will have its full energy.

- There are no valence and conduction electrons in a metal, as no separated bands exist. - If separating the atoms, this is not a metal any more. A metal is a lot of atoms, adn is defined by the metallic bond, which is delocalized. - "Jump between the atoms" is not the same as "shared among all atoms". The electrons are shared among all atoms of a metal, and need no minimum energy added by the external field to move. Nor are electrons local to one atom. Each and every state is global to the whole metal, over many 1000km in a power grid for instance.

The behaviour of gas in the bladder alone would go indeed in the wrong direction, contracting at depth. That's why I have solids, like the truss of two different metals, that impose their behaviour to the bladder. Provided that the solids are properly combined, they let the bladder expand at cold and contract at warmth. To obtain the depth oscillation, it also needs hysteresis, here provided by the controlled brake to let the bladder's volume change only at the surface and full depth. Combining both, the bladder's volume shrinks at once at the warm surface, letting the glider sink, and expands at once at the cold depth, letting the glider rise again.

Electrolysis produces gas amounts that are always very disappointing. Even more so with weak photovoltaic cells and if needing volume at depth to make buoyancy. My intuition shouts: no hope. Use the temperature difference. If the bladder is located before the wings, its volume change will not only provide the net up or down force, it will also put the nose up or down. For pitch stability, you have to adapt the stabilizer setting: it must pull the nose up during descent and down during ascent. Or adapt the wing's setting and keep the stabilizer immobile: this would keep the body parallel to the flow, reducing drag. The bladder's movement might set the wing, perhaps - but this lacks flexibility, so I prefer an electric motor. For roll stability, since the wing can't be V-shaped, the centre of gravity must be low. A different design would put the submarine on its back during ascent. Then the stabilizer can be immobile and the wing V-shaped. An eccentric bladder, near the belly, would do it. Less convenient for data comms etc. In all cases, you need a brake that stops the bladder's movements during descent and ascent, to release it only at the desired depth, to change the direction. Say, a slit ring can block a rod: an electric motor +gear +screw tightens the slit ring at will. ============================================================ Three design families for the bladder that expands at cold: Solids give great forces to contract or expand the bladder despite water's pressure; their thermal expansion is amplified by the dimensions or the shape. I prefer solids to an expanding liquid: no seal, easier thermal contact with water. All designs need a brake, though displayed only at the left design. The piston's seal must work between two liquids for long-term tighness, so the gas is in an elastomer bladder (not displayed!) within the cylinder, the rest being filled with a liquid. The left design gives the necessary engineering flexibility (consider e-beam to weld different alloys), the others are very doubtful. The two holed cylinders at the middle design would have to be long, even with a polymer; pendulum clocks had several parallel rods in series, but this gets boring if exaggerated. The right design would need many trials and isn't adjustable. Marc Schaefer, aka Enthalpy ============================================================ And this is how the oceanic glider can look like: Here a fixed stabilizer and an oriented wing, so the body is always parallel to the flow. The wing orients by flaps, better for the curvature and against algae. Sweep the wing. The center of mass is always low, but goes to the prow for descend and to the aft for ascend. It's important that the wing orients at the same time as the center of mass moves, so maybe the bladder should better control the flaps; elastic coupling and stops to define precise positions? Produce some electricity from the bladder's actuator, when the brake is released. Or from a water turbine. Or have magnesium+seawater batteries if possible. The glider needs a safeguarding ballast, as every submarine, to be thrown away in a situation of uncontrolled sinking. Marc Schaefer, aka Enthalpy

This gliding submarine does exist and is put at work for oceanic research.It does not need an engine because differences in water temperature between depth and surface bring the energy. I read a report several years ago. Though, its design is a little bit tricky, because warmer temperature must reduce its total volume, as opposed to what thermal expansion uses to do. If I remember properly, it has one working volume full of liquid or solid, that expands little but delivers much pressure and force, to forcibly change the volume of a bladder that reacts with less pressure and force than a solid does. And this, despite depth changes the pressure on the bladder... Maybe a void ellipsoid made of bimetallic spring would suffice. Or even, a dome of one metal sitting at a circle of a different metal. Or a bimetallic truss: combines well with a piston, classical engineering then, done. Or put the solid/liquid "in series" with the bladder, and both in a frame that expands little. There are also a few materials that contract at heat, at least in one direction: carbon fibre, latex, many high-perf polymer fibres... And of course, it needs something to stop the submarine diving, at a convenient depth. ----- One fascinating aspect is that it's the first object that can really produce some meaningful work from the Oceanic thermal gradient. Many attempts want to make electricity and sweet water from the temperature gradient, but this challenge is very difficult, and both designs and results aren't fully convincing. Though, I doubt a big wheel with wany submarines attached is a better design...

Mamma mia! Electromagnetic waves are to harm the motherboard? Why tell publicly things you obviously ignore?

One known limit of controlling natural disasters is not technology, but lawyers. That is, if a politician agrees to act against a disaster, he'll get little recognition for the houses he helped save, but gets lawsuits for the houses destroyed because of the action. This happened in Italy where trenches were successfully digged to deviate lava flows. They work, but politicians now dislike to order them.

You have observed eddy currents in the metal. They result from conductivity and are used to build truck brakes for instance, and can be felt by hand under favourable conditions. You didn't observe them in graphite because of the smaller conductivity. DIamagnetism is fainter and can't normally be felt by hand. More, it does not depend on movement.

No. Conduction electrons are delocalized to the complete piece of metal. They don't belong to one atom. That's a metallic bond.

Interesting! Carbon fibres are anyway the material of choice to make strong, stiff and light. Aluminium extrusion has the advantage of classical low-tech. Cheap investment, since extrusion on demand can even be contracted to a supplier, and welding needs a machine meanwhile banal. Carbon fibres were proposed by MAN GmbH to replace a difficult steel process for the casings of Ariane V's solid boosters. Presently, forged rings of austenitic steel are brutally cold-rolled on a specially-made machine to make high-strength thinner cylinders whose welded ends are thicker. Carbon spinning would have been cheaper and lighter, but wasn't accepted for Ariane V. It's used on Vega now and was already common on high-pressure liquid tanks that transmitted no thrust. Then, one has to check if the desired shape and strength can be achieved: fibres work best if spun, and aligned in the stress directions, up to the locations where forces apply. Easy for a pressure vessel, less so for a tank with moderate pressure but compressive axial load. Here stiffness demands a non-uniform thickness, or hollow materials. This is the reason for the sandwich walls and rods described here on 29 December 2012. If the new laser process can help it, it's of course highly welcome!

Well done! Many thanks for sharing!

Such paint is used to make electrolytic layers on insulating substrates. Initially, the conductivity of carbon is feeble, but as copper, nickel or other growths, the current can be increased.

In case somebody is tempted by experiments with black powder: beware, it's one among the most treacherous explosives. Sometimes it detonates, sometimes it burns out, under conditions seemingly identical.

A pre-requisite would be to first synchronize the years with the days. Someone will certainly come with an easy method here.

SamBridge, you're messing up heat with chain reaction, absorber with moderator...

Pardon again? A Fukushima, the reactors were properly stopped for hours thanks to the neutron absorbers every reactor uses, with negligible neutron emission at that time, when heat from fission products' radioactivity put the cores out of control. And if someone could have had access to the cores, controlling them would have been easy. After the tsunami, workers had zero mean of action. If you're interested in such topics, Wikipedia is generally a good introduction: nuclear reactors, control rods, residual heat...

"Transmittance is actually just absorbance ...and synchronised emittance (that is why light travels more slowly through glass)" => Beware this explanation, found everywhere because a stupid book teaches it, is false. You may understand propagation as absorption and emission if you like, and vacuum does it just as good as matter, BUT emission occurs with zero delay. Any delay at emission would imply an attenuation of light, as the delayed wave add less efficiently with the wave not absorbed. Refractive index results from permittivity (and rarely permeability) which is the instantaneous polarisation of matter in the electric field. ------------------------------------------------- Frequency doubling, tripling, mixing... is done commonly but only at a field intensity that lets matter behave nonlinearly - something inaccessible to thermal radiation. It's the kind of peak power accessible to YAG lasers, preferably with a Q-switch, whose pulse is <1ns. Works great then. With a continuous wave instead of pulses, it demands a laser to focus light tightly enough that matter (some very specific crystals in fact) behaves non linearly. Say, with much power in a monomode fibre, fine. If using a CW laser outside a fibre, just with focussing optics, it's better to have a pair of resonators -preferably use the laser cavity itself - to increase the field at the fundamental frequency and let only the harmonic out.

A nuclear bomb diverges within a matter of nanoseconds. Light propagates over 3m in 10 nanoseconds, other things are slower. So any action taken after the chain reaction has started must be made from within 1.5m - which doesn't make it easier. A neutron absorber (on fast neutrons) would have been great, but shipment methods are too slow. You better destroy the bomb before the chain reaction starts. Please remember that there is no relationship whatsoever between nuclear bombs and missiles.

Von Braun used internal truss when he was young. It would still work, but there are limits: - A strong skin is nice to fly quickly through air. To resist impacts of rain, birds, chunks of ice detaching from the cold tanks... And to avoid air flow instabilities at the skin. It's already few mm thin, saving more is difficult. - A tank must be pushed at its base, over the whole lower head. This combines less well with a thrust concentrated in a truss. - The truss and the skin must have the same temperature at every time. Nothing damning, but one difficulty more. What does exist: upper stages (modern Centaur) that are fully enclosed in the payload's fairing at low altitude. They have an external truss, and the tanks are ultra-thin "balloon tanks" of best steel, enough to hold the small pressure but not transmit any thrust. The combination is light. The older Centaur described there http://en.wikipedia.org/wiki/Centaur_(rocket_stage) stands up thanks to internal pressure; this risky design is oldfashioned now. On a lower stage, I considered a structural oxygen tank surrounded by balloon hydrogen tanks that lift nothing beyond their contents, but frankly, I dislike such thin skins exposed to the wind. With extruded aluminium I regularly compute 30-40kg/t with hydrogen+oxygen, already excellent, and with outstanding stiffness and resistance.

attriti0n, on 03 Jan 2013 - 20:08, said: Large kinetic penetrators (tungsten or DU) are heavy and certainly difficult to orbit in one piece, but given time, perhaps this could be done in pieces. --------------- Easy. Shoot many smaller penetrators, kept individual from the beginning to the end. Say, 20t at launch so they fit on a truck, 5t and 5km/s at impact. Then, each pierces like 20m rock depth. Makes a cylindrical hole that moves less material. You'll need quite a few penetrators, especially since they won't fit in the existing hole over several km depth. Such weapons are perfect against big warships, whose era is hence over. Against nuclear power plants, as well. To reach a magna chamber, I suppose other methods are more effective. Shoot a round (not that size nor speed) down the hole, remove the debris? The limit is that you have to cement the hole or it collapses. --------------- Nizmo, did you put some figures on the amount of material to be removed, and if melting it, the amount of heat? This would bring us further. Comparison with energies available to Mankind would sort away many methods.