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Enthalpy

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Everything posted by Enthalpy

  1. One common example is natural rubber. It's just poly-isoprene, chemistry knows to make poly-isoprene, but Nature does it better (see Wiki) and on a huge scale. Natural rubber bounces better than artificial one. We still use some in car tyres. A general case is chiral compounds. Biology produces them efficiently, often at 100% left-handed or 100% right-handed, while chemistry tends to make 50-50% mixtures because the enantiomers have the same properties. Drugs are difficult to make partly because only one enantiomer is desired. Also think of extremely cheap materials: petrol, sugar, wheat, ethanol, glass, concrete... We can grow, exploit or transform these for little money, and more elaborate processes can't compete. Here new organic compounds will more likely result from genetic engineering than chemistry.
  2. Where the electrostatic force comes from? From nowhere if you consider it to be fundamental. That's linguistics or logic more than physics. Now one (several) more general theory exists that unifies electric and magnetic forces with the weak force and possibly the strong force, but it won't give you the sort of explanation you seek, probably... Just like electromagnetism, they tell how to compute a force, and nothing more. So you'll get no better answer than a formula. No tiny springs between the particles, no streams flowing between... Because this force is fundamental: it explains other things and is not explained by others. Think of taste: bacon tastes salty (and more), but how does salt taste? Just, well, salty - because it's a fundamental flavour. ----- Why do charges of same sign repel an other? That's observation. It does not result from a theory. The theory is elaborated to fit the observation.
  3. Did we meet on another forum? Same answer here: find where the internal energy has gone, since energy can't disappear. Expansion through a porous material is not an isentropic expansion.
  4. Since energy is conserved, any efficiency would be 100%. Which means that efficiency is not a ratio between output and input energy, but between energy useful to us and energy costly to us. By that definition, heat pumps have an efficiency well over 1, for instance 3. But this is not a net creation of energy: the produced useful heat exceeds the electricity consumed because much heat comes from the cold source, but if said produced heat were used to re-create electricity, one would obtain (far) less than first invested.
  5. "Sometimes" energy is not linked with objects, for instance the light we receive from a star, a galaxy, or particles, disappeared for a long time. As well, in a capacitor, electric energy is not stored in the electrodes but between them, possibly in vacuum. Same for magnetic energy. The electrodes, windings, cavity walls... are only a way to dump or recollect energy in vacuum.
  6. Solids use to be slightly denser than liquids but seriously stiffer (bulk modulus), and this makes for faster sound. For one same compound, all those I can think of are stiffer when solid. Even with different compounds: few liquids are stiffer than some solids. I spent weeks searching both for technological uses, and they're scarce. You get ~4GPa from liquid glycerine if not too hot nor wet and ~0.7GPa from some silicone rubbers, while (solid) ceramics achieve 500GPa. This is at 1 atm pressure. Stiffness increases with pressure, logically enough - as you don't expect shrinkage to zero volume at a finite pressure. 300b, a typical pressure for hydraulics circuitry, are enough to raise the bulk modulus by 30% for instance. Temperature and impurities matter also, like salt in sea water (important for the path of sonar waves due to refraction), and of course bubbles.
  7. Without water, ethylene glycol is seriously viscous, which makes it a much worse coolant than water. Because turbulence is essential to heat transfer, and also because more pressure is lost. As well, the heat capacity is worse than water. It's also hygroscopic, so you end with some water in the fluid, making it corrosive as well. In short: poor coolant. Less efficient at 120°C than water at 70°C, and your device now runs hot. And I really don't see why one should search for a coolant better than water. Many thousand people have already tried and failed. You probably won't get a better answer from a forum.
  8. Blue sky on Earth results from scattering, not absorption. Expect this to happen on any planet without absorbers. The colour of the sky could result from microbes living there in great quantity. Or from dust in the air like on Mars.
  9. Orbits around our Moon are said to be unstable and crash or escape within one year. The difficulty with our own particular Moon is that its trajectory is very complicated. Its orbital plane is very tilted versus the ecliptic, and its big orbit radius makes it quite sensitive to the changes of the Sun's gravitation with distance, and to the change of centrifugal force as well. As a consequence, Earth-Moon distance changes a lot, like +-20,000km over 380,000. The direction of the Moon's orbital plane also changes quickly versus the distant stars. To this, you must add that Earth's field changes a lot along an orbit around the Moon, as does the centrifugal force. All added, a trajectory around our Moon is anything but a calm ellipse. ----- Could an object be captured by the Moon in the first place? That's not very easy, because the object must lose energy (kinetic+gravitational) versus the Moon. The simpler case is when the Moon's gravity brakes an object, permitting it to be captured by Earth. A slingshot suffices; the objet can't arrive too quickly because our Moon is a weak attractor. Much easier at Saturn or Jupiter, where man-made probes could use massive and fast moons to brake at little expense. An immediate capture by the Moon would need some very lucky combination where Earth and the Sun influence the object and, once a time window has passed, the object that coud approach the Moon with some excess energy stays with a binding energy. Intuitively, it must be improbable for an object already captured by Earth, and impossible for any reasonable speed of a object coming from, say, the Asteroid Belt. A delayed capture must be possible with luck: a Moon slingshot permits capture by Earth, and later the Moon captures the object. Until it loses it.
  10. Polyethylene glycol is used mixed with water. It's a standard hydraulic fluid, also used frequently as a coolant.
  11. It is sometimes useful to suppress IF, and is accordingly already done. Essentially in vector processors, which have one instruction unit hence can't reasonably branch depending on tests on every data processed in parallel. Programmers used similar tricks very early, but now these processors have conditional instructions, dispatched once by the single instruction unit to all processing units, to act differently on data based on idividual conditions. A typical such instruction is a conditional store.
  12. In order to offer Fresh the opportunity of a class-action. But for that, he needs some credible story and can't find it by himself.
  13. Maybe you could detail more what you call a "research paper". Most people here understand "a paper describing the achievements of your research", but you more likely mean "a report about the current state of research by other people".
  14. From Google: "phase-transfer catalyst for epoxy resins"
  15. Just make the experiment with a light bulb. Preferibly small and round, like a halogen lamp. Did I see rainbows made by car lamps? I believe so. Intuitively, our eyes have such a dynamic range that replacing the strong Sunlight by a less strong flame light is acceptable, provided the surroundings are dark enough. It can require to intercept as well all indirect light from the flame diffused by the surroundings.
  16. Shape memory alloys are used the big way! They make surgical implants, superelastic frames for glasses, actuators to release satellites from launchers... If you mean specifically the thermal engine: it's not used because of its horrible efficiency of ~1% at best. Gas or vapour engines achieve commonly 30-40% efficiency. This is essentially because E is a few times PV in a gas while it's many times PV in a solid. In other words, a gas expands a lot at heat, so mechanical work can be harvested, while you invest much heat for nothing in a solid. A competitor to shape memory materials is the "wax thermostat" (search keywords), far cheaper and with similar (in)efficiency and force vs move, usable over a smaller temperature range. Shape memory engines can be imagined where efficiency isn't essential but simplicity is. One attempt was to produce electricity from the residual heat of car exhausts - not to make substantial propulsion power, but to replace the alternator. Smaller temperature difference: is there enough pressure from potential users on manufacturers? For electricity-driven actuators it's not so important. For surgery it could be, but bio-compatibility is the absolute criteria there.
  17. It's because the temperature profile during cooling (possibly quenching) depends on the shape.
  18. SpaceX sells its Falcon 9 for some 80M$ presently. Two more boosters won't make it cheaper, so 32,000kg in Leo would cost >>2500$/kg. Then going from Leo to an asteroid and braking there means >3+3km/s. Even with hydrogen, the instruments put there must be >4 times lighter. After what you must consider the mass of the machines needed to extract a single kg of precious metal. The excavator isn't all: metals must be reduced and separated. Even the way back costs some mass, because the transport vessel needs some communications, trajectory control... Which won't be much lighter than the smallest probes sent to other worlds, like 200kg, whose 600kg including fuel must first be landed smoothly on the asteroid. ----- You can compare with materials made in Leo, which is easier to attain and come back from. People wanted to grow protein crystals and semiconductor crystals, both being more expensive than platinum, and needing no multiton machines for one kilogram. Economic fiasco. ----- Besides the many technical issues which let the attempts look to my eyes like a target for a governmental research project rather than an industrial development, I fear the initiative comes from people who don't know how to begin with the task. For sure, I've read strictly none of the many and very exotic breakthrough demanded by the enterprise. The general scheme must be: find an exotic idea that bears huge promises, sell it to a billionaire, then ask on Internet forums how to give the customer a few scientific-looking arguments. And... Did I meet these guys on an other forum? Reminds me of the ones who sold breeder reactors to Bill Gates. Everyone knows what breeders would solve, that no really good design exists, and that breeders have inherent huge drawbacks - but they came with a much more difficult design, which was certainly impossible, full of gross mistakes, and they managed to sell it. Meanwhile they seem to have hired a few pople who understand something about reactors, but well, that can't possibly suffice.
  19. There's a lot of wishful thinking here. Now I know why US researchers are so hyperbolic when communicating results to the public, and newspapers so uncritical: it's because some readers believe them. Graphite is not graphene, graphene is not graphite. Whether you have a single uninterrupted atomic layer or a disordered bunch makes the whole huge difference. Conductivity is not the ability to conduct a significant current. Depositing an ink that contains graphene does not make one sheet of graphene. The demo with alleged "nanotube thread" shows the same mechanical and electrical properties as graphite fibre. ========================================== Some more upstream data sources about what Rice University achieved: http://news.rice.edu/2013/01/10/new-nanotech-fiber-robust-handling-shocking-performance-2/ http://www.sciencemag.org/content/339/6116/182.abstract some hype less than in general newspapers, but still a bit... 10 times more electrically conductive than graphite - which is much worse than a metal. No single figure about mechanical strength, so bad figures would be a reasonable assumption. "Graphite fibres are brittle but our nanotube fibre can be bent" => A graphite fibre bends very well because it's thin too. Then you can add all the inaccuracies added by newspapers, like Teijin being an Israeli company... The researchers have improved the process to make a thread out of nanotubes. This is a nice result, and the thread they chose to show looks good. Gratulations. Everything else is hype. I should like to exhort you to use caution when reading such reports, even in peer-reviewed science papers. Authors write purposely "graphene conducts well and we've printed with an ink that contains it" but it is your duty not to understand "we've printed a good conductor". Authors write purposely "nanotubes are strong and we've made threads of it" but you reader shall not understand "we've made strong threads".
  20. And these waves define the position and moment with some precision, even before humans attempt to make a measure, or other objects modify their behaviour according to this precision. But: what's the difference? Why should you get interested in something you don't observe? Would it make any difference to you? That's not just a joke. It's a very frequent answer by quantum mechanics. Disturbing maybe at the beginning, but reasonable.
  21. It doesn't need a heatshield. Splash 1kg or 1t of platinum in the Ocean or the Antarctica or the Sahara. The atmosphere won't do any harm to a piece of solid metal. Finding the collision debris is less easy. The real limit is: putting anything on an asteroid, and much worse bringing it back, costs more than platinum's value. I consider the varied attempts as obviously hopeless from the beginning. But never mind, those who funded them can live with a few millions less.
  22. Graphite is not graphene. Have you seen any significant current conducted in graphene? Incidentally, nobody can produce a printed circuit from graphene. Nor can nanotubes make a rope. Sorry, this is not technology presently. Some day maybe, or maybe not. The uses will probably be ones we don't imagine, and I'd say: not to replace metals.
  23. Leather is, for most species, a by-product of meat. So to avoid cruelty, I'd prefer a fur substitute. Though, there might be some species grown for their leather only. Does you pseudo-leather have special properties? Exotic materials find uses! You dont' have to replace leather in every aspect, nor do you need to find by yourself the uses of a new material - designers will. Just find and tell what makes it special! Find a dozen imaginative people around you, ask what they would do with the stuff, that will be a first glimpse. For instance, do object bounce very little back on it? Are shocks against it silent? Does it stay flexible in liquid nitrogen? Is it impossible to light, or if it burns, produces no toxic fumes? Does it float on water? Resist UV light, seawater? Biodegrade quickly, or not at all? Smell good, or repel insects? Is it fluorescent, phosphorescent? Does it concentrate some minerals from the soil? Even better, as it comes from a mushroom: is it antibiotic, or does it repel other fungi? You could then make shoe insoles of it, or carpets, air filters, beds, seats, additional bark for sound or ill trees, fruit baskets, paper sheet replacement... You wanted a fur, maybe it just needs some different processing. Say, the separated fibres are in some liquid. You can evaporate the liquid and get a leather-like agglomerate, but if you pull fibres from the liquid and twist them, do you get a yarn? Or if you evaporate the liquid in a fluidized bed instead, is the result as fluffy as fur? A sticky impregnation may suffice.
  24. Resistors have been printed of graphite directly on circuit boards. At that time we had hybrid circuits with good resistors (ceramic, thin metal...) but graphite provided cheap inaccurate resistors for digital circuits and accepted low-temperature processes compatible with epoxy. Now that we have SMD resistors, I don't see why we should bother to print resistors. As for conductors, graphite is too bad. Use a metal.
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