Enthalpy

Viscosity results from elastic collisions. Computations from the kinetic theory of gases gives even sensible values, if not accurate. Elastic collisions mean that energy is conserved. Spreading the well-ordered velocity into disordered speed means that flow power converts into heat, through viscosity, and entropy increases.

Galinstan, a gallium alloy, is even liquid at room temperature. Purchasing gallium shouldn't be difficult, but you can't transport it easily by plane (as a leak would dissolve a hole in the fuselage). http://www.webelements.com/gallium/physics.html

Alloys good or bad individually. When two parts rub, both can use the same good material. But if one part is of bad material (chromium layer) the other must be good (bronze), probably hence the false belief. This original opinion is what an alloy producer saw and showed in a report. The chromium and titanium example is one I experimented. They galled horribly. Though, both materials are as different as they could be, with the hard chromium layer free of any titanium, and the Ti-Al6V4 part free of any significant chromium. The chromium layer was hard as desired, and the titanium alloy not really weak. I like this example because it proves that pairing different materials is not the solution. I didn't spend weeks and months on that topic, which popped up as an annoyance to be solved. I designed mechanical functions at that time (for crash-test, fun) so in that occasion, the game was not to understand everything and produce nothing, but rather to achieve something without understanding how. It was enough to see that the doxa in books and courses (pair different materials) is grossly false and that I saw no relationship with documented macroscopic properties. So, no, I didn't investigate the microhardness. I suppose lapping was circumferential at my chromium layer, and I just turned the titanium part, so all grooves were perpendicular to the axial movement I had. But hydraulic pistons are leaped in the axial direction (to reduce wear at polymer sealing rings) and their chromium layer galls against badly chosen materials. [Chromium layer on hydraulic parts has virtually no alternative, to preserve seals and withstand sand dirt, but it galls badly] Corrosion resistance by a spontaneous oxide layer of proper quality is often linked with galling. For instance, Al-Mg galls but Al-Zn doesn't. Though, there are exception again, like Al-Si and Al-MgSi being rather good, or aluminium bronze Cu-Al as well. An other exception is Fe-Mn-C construction steel which galls. And the oxide layer alone won't explain why hardness improves a bit against galling, including through cold work which doesn't need to precipitate any phase. Frankly, this must be re-thought from the beginning, starting from new experience, and with a fresh mind. Useful research topic. Not the worst first degree student, if my intuition works. We meet funny people on Internet forums. One chemist entered University last year, as he had already synthesized all known secondary explosives in his garage. You know, the nitramines, and constrained polycycles of nitrogen with multiple bonds.

At least antennas are easily made for 700 THz with present semiconductor technology. They can be metallic (losses are high) or rather dielectric. Many design attempts at photovoltaic cells embed such antennas in order to concentrate light's electric field. Others make metamaterials with arrays of small antennas. The generator is a completely different worry. To my knowledge, nothing has ever been made at 700 THz that looks like MHz or GHz technology. Semiconductor amplifiers stop to amplify at very few 100 GHz (clean operation at 94 GHz is getting usual), vacuum tubes provide higher power, varactors can double or triple the frequency with losses (astronomers made sensitive receivers at 300 GHz some 20 years ago to detect remote molecules). So-called THz waves use to be under 1 THz (yes) or very little above. Their technology is immature: essentially short pulses of undefined frequency, like spark transmitters did before the vacuum valve was invented. This is still far from visible light, which starts at 370 THz. I believe to have ideas for CW 30 THz but need to clarify my texts and make drawings. Everything above is optical technology, understand: lasers. Including down to 30 THz, which uses quantum cascade lasers or heterodyne of two IR lasers. They work up to 151nm with excimers for semiconductor manufacture, which develops technology for 13.5nm and 11nm presently. Lack of a light source, optics... has stopped semiconductor progress in the last years. These lasers let atoms or molecules radiate directly, though radiation is aided by a resonant cavity (usually much bigger than the wavelength, but tuned to it) and by collective behaviour of the lasing centres. Though, at least one example exists in Switzerland (ETH Zürich I believe) where the lasing medium is tiny (a minute diode if memory serves) and coupled with an L/2 metallic antenna which resonates and radiates as a bigger cavity would have. An other example are simply nanocrystals, whose dimensions resonate as a dielectric antenna, which tunes the colour of their fluorescence. So: resonators and antennas have already joined radio waves and optics, while amplifiers have not.

"VKS experiment" or "expérience VKS" http://perso.ens-lyon.fr/nicolas.plihon/Publis/Aumaitre_CRAS_9.pdf

http://msdssearch.dow.com/PublishedLiteratureDOWCOM/dh_005d/0901b8038005d707.pdf?filepath=plastics_eur/pdfs/noreg/190-00347.pdf&fromPage=GetDoc "Vinylidene chloride Cl2C=CH2 is prepared commercially by the dehydrochlorination of 1,1,2-trichloroethane with lime or caustic in slight excess" Looks alike! Though, I wonder about the flame and its smell. At least PVC burns instably and produces black smoke and a pungent odour - I extrapolate it to PVDC. The polymer I got burned easily, without smoke, and the odour was wax-like. Same Pdf, on page 917: smoke, ignition resistance... PVDC (properly obtained, compact, pure!) has a density of 1.77 and 1,1,1-trichloroethane 1.32 but the polymer I got buoyed. Commercial PVC can be as light as 1.30 and would be lighter if improperly produced.

Hello you all! It's just puzzling me... The Oceanic bed has some rifts and trenches, but these are rather local; on most area, the bed is rather flat. Continents have mountains and valleys, but these are local as well, with most area fitting within 0 to 300m. Now, I wonder: when observed from the Oceanic bed, the Ocean is about 3000m thick, and continents are only 100-200m higher (not thicker). Is that pure chance that lasted for eons? Or is there some deep reason for it? Thanks! Marc Schaefer, aka Enthalpy

After putting some figures at it, injecting a sound pulse in the rod by a magnetic pulse, and detecting the echo by a magnetic or electrostatic microphone would be seriously difficult - if any possible. Both the strong pulse and the faint signal stretch usual engineering values, but above all, both must be at the same end of the rod and operate within a short delay, meaning that the sensor's electronics would be dazzled by the actuator. This is what make the method more suitable to metal sheets, where the sensor can be at the opposite side of the sheet and the fields screened. As a comparison, microtomography was nothing simple to develop, but now it exists. Just buy one. If still considering acoustic methods, piezoelectric actuators and sensors (probably one actuator-sensor) are much more efficient and would reduce the huge factor between the emitted and received electric signals. Coupling with the metal rod could be made with a liquid in vacuum or an elastomer with at least a conical form before pressing it; the gap to the rod being wide and thin would need no seal to transmit pressure.

A better reason to hear the higher frequencies first is that the microphone is far from the the wide-spectrum crack but near to the ice shelf. Not coupling from the shelf to water, but just propagation in the shelf, lets higher frequency arrive first at the microphone. Still a consequence of flexural waves propagating faster at higher frequency.

If D-T power worked some day, it would have to regenerate its tritium that lacks from Nature, needing to multiply neutrons, and this step is as polluting as uranium fission is: http://saposjoint.ne...php?f=66&t=2450 http://www.physicsfo...ad.php?t=422576 A report describing the attempted tritium-breeding blankets at ITER and their neutron multiplier: http://www.iter-indu...on_Poitevin.pdf but it keeps silent about beryllium scarcity and pollution by lead spallation. My argument that beryllium is too scarce, leaving only the polluting lead spallation as a neutron multiplier: http://www.physicsfo...71&postcount=66 I had hoped that 9Be could be replaced by 40K, 13C or 17O but these seem to require too much energy from the neutron. As soon as the neutron brakes a bit from the initial 14MeV it's over. Worse, 40K absorbs thermalized neutrons to make (n,p)40Ar. http://www.nndc.bnl....ndfb7.1⊄=10 (the absent 13C must resemble 17O)

Supernovae brightness is just one part of the picture, the one that suggests an accelerating expansion and possibly dark energy widely taking the place of dark matter. Dark matter is deduced from movements of globular clusters, galaxies clusters and superclusters, gravitational lensing. As for light absorption, already the Herzsprung-Russel diagram compared between the Milky Way and the Magellanic clouds would have told it.

Patents offices accept only solutions, not descriptions of tasks. Their description of an idea is realistic. In other words: please tell what you measure, with what sensor, and what measurement you expect from which source of gravitation waves.

The d=20nm punched spot illuminated by a Dvd laser diode shouldn't overheat. Back to (thicker) gold, deposited on thick silica - for instance because this silica makes the lens. It should withstand 300K heating. The silica (1.3 W.m-1.K-1) hemisphere conducts 370µW from a light spot of D=300nm. Gold reflects >99% (...at least in air! Gold has an index) so the incoming light power can be 37mW. Let's take 20mW as I believe it's a common power for DVD burners; if yours is stronger, reduce the current and gain lifespan; if needed, use a duty cycle at some MHz. The d=20nm hole at the D=300nm spot lets <90µW pass through, which is half the light of an old green LED. No adaptive filter, no multiple sources, no integration time - my preferred version. This power leaves adjustment margin if, for instance, light reflection isn't that good. From varied questions read recently on forums, which relate with this point, it seems that people are developing this idea. Gratulations, fingers crossed . Marc Schaefer, aka Enthalpy

Stronger tides coincide with Earth's inclination with respect to the Sun's direction, primarily. That is, near equinox - and of course, Moon, Earth and Sun must be aligned. Then you can add considerations about perigee. Beware Moon's orbit is very complicated: its mean distance varies over time, as eccentricity does, and rather quicly (within a human life). Even the orbittal plane does rotate and not slowly. It's a horrible mess.

Same process as asbestos?

Protect rubber from Sunlight. Mix into grease. Make Indian ink. Colour aluminium anodization in black. I must forget a few thousand more.

If astronomers missed only 20% mass, they wouldn't bother about it! They're looking for a factor of 20.

The article at Wiki was very presomptuous! Vacuum discharge (which you may call arc or not, I don't care) is known to occur at fields that can't possibly create field emission, and at electrode temperature (even locally) that makes thermoionic emission impossible. In fact, it's still a mystery, and the subject of research. And by the way, vacuum discharge is not just a faint glow, it's an authentic zap.

Dispersion comes here because these are flexural waves. Their equation is like d2u/dt2 = d4u/dx4 (with modulus, density and shape adding proportionality factors) (and add a y direction as needed) which, if writing the solution as cos(w*t)*cos(k*x) gives a dispersion relation like w2 = k4. Because waves leave quick propagation media for slower ones, a plate couples sound into air or water better at higher frequency, which implies that high frequencies, which make the attack of a sound brilliant, disappear earlier. On a string instrument, the string better withstands a tension such that sound is faster in it than in air so you get a nice sound from enduring coupling into air. If not, it makes just ptiong at the beginning, from frequencies high enough that the bending stiffness accelerates them. But getting 340m/s from a tight string needs a high tenacity that few materials achieve. Some alloys do, nylon more or less, catgut certainly - and then you need a good elongation, which only catgut offers; it needs low losses as well. It looks surprising, but in 2012 we have no synthetic material better than catgut... Not just from prejudices, but resulting from very physical reasons, which one also hears very distinctly.

Was the polymer oxygen-free? I doubt now. Hot glue guns melt a copolymer with PVA and it smells paraffinic, so maybe there were oxygen atoms in the links. Could it have any use? Polymer designers are happy when they obtain a strong and stiff fibre that resists heat, but when I'm a mechanical designer I need more varied properties depending on the use: very low density, high or low gas permeance, high volume compressibility, big or small rebound, big deformation and shock absorption... I'm sure many lab creations were abandoned that would have met specific uses.

I suggested four 32-bits floats to compute hash values quickly on all GPU, but if using the SSE, MMX or a wide FPU, two 64-bits floats are as good or better. Convert 32-bits slices of the files to be hashed then.

Alas! A hash value for such purpose is too easy to compute, and already the CPU is faster than any disk. That way : for (a = successive 16-bit slices in a cluster) { f = float32 (a); s1 = f + 0.9990*s1; s2 = f + 0.9991*s2; s3 = f + 0.9992*s3; s4 = f + 0.9994*s4; } The four float32 s1, s2, s3, s4 make the hash value of one 4096B cluster. Good enough to compare files. A GPU with 128 MAC at 1500MHz would have hashed files at 96GB/s but the video Ram limits to some 50GB/s and a Pci-E 2.0 *16 to 8GB/s... One SSE crunches a slice per clock, so a 3GHz quad-core hashes 24GB/s but the Ram limits... And a fast SSD limits to 0.5GB/s, blistering barnacles! So while I'm still interested by the added functions on file explorers like FreeCommander, the task is too easy for a GPU. Obviously, any O(n) computation will stumble at data throughput. Back to the error-correcting codes then... Marc Schaefer, aka Enthalpy

A much simpler project now. I gratefully use a file navigator called FreeCommander which can compare two folders in order to synchronize their contents (and does much more). It tells: these files are identical, others differ, these are missing - and then: which ones do you want to update or copy. I misuse it frequently on huge folders, like collections of graphics drivers, and then it gets slow and the CPU is the bottleneck, not the SSD. Easy to improve with a GPU. Even better: I often rename folders or reorganize them, which makes the answer by FreeCommander little useable. I wish it answers "this file was just renamed" or "this subfolder was moved there". It would need to compute hashes of the files to later compare many ones more quickly, but FreeCommander is slower at computing hashes. If you define your hash algorithm properly, it can be parallel even on one file, and there are several files anyway, so a GPU can improve that. Note: comparing just the very beginning of the files even in a first step won't suffice, since many ones begin with "I'm a Jpeg picture". Note: the hash function must give a unique value but needs no cryptographic strength. Note: on any nVidia or Amd graphics card, not an exotic board - but you might restrict to dX10 hardware and above. Note: you can compute independent hash value for each 512B or 4kiB block and leave the CPU compare the hash. Flexibler for the CPU which can cut unnecessary work, more parallel for the GPU. Many similar navigators and synchronizers exist, FreeCommander is just the one I use. Its author is a nice guy and speaks many languages, so if you develop the file comparison or hash on GPU and take contact with him he might integrate it in FreeCommander. Marc Schaefer, aka Enthalpy

In cold air, you don't need a space suit. You need warm clothes (people live in the Antarctic with clothes, -150°C is only 3 times worse) and a regenerative exchanger to withhold the heat and humidity for the next breathe in - but let the CO2 go. The regenerative heat exchanger from Stirling engines can be an example, as well as the cloth Touareg breathe in to retain humidity. I write only 3 times worse because people use low-tech in the Antarctic, like animal fur, or fabrics. Technology has brutally better insulators, especially multi-layer insulators (MLI) which just need to remain flexible, light and scratch-proof despite having vacuum inside and pressure outside. Very accessible to an individual.

Hi, and welcome here! These are some places where I imagine you could inject some theoretical lubricant in the reasoning... Do the alloys keep a uniform composition when you deform them to measure the properties? Al-Zn, -Cu, -MgSi... are metastable when solution treated, with Al-Zn and Al-Cu transforming even at room temperature. I expect intermetallic phases to precipitate, even if more locally than through ageing, when these alloys are measured. Silicon is a near-metal. Anyway, "metalloid" looks more like a collective property than an atomic one, and pressure can change it. For being a "smaller aluminium" with one proton more, I'd expect silicon to integrate the aluminium matrix smoothly, let the excess electron go away, and leave just one positive charge - just like phosphorus does as a dopant in silicon. Or does it? Typical Al-Si alloys have 7 to 13% Si, which means one Si atom every 2 atoms in each direction (I mean, 1 atom of 8 in volume) so Si atoms aren't really independant. Maybe the effect of Si should be measured at low concentration. ----- If you like metallurgy, I have a personal wish... Galling is not understood up to now. All books and courses allege dissimilar materials cure it, but that's brutally false. Too little experimental data exists and, consequently, theories are bad. Worse: we have no empirical rule neither to predict if an alloys galls easily. From trials published by Allegheny and my limited user's experience: - Hardness improves a bit - Lubricant it very doubtful. But I've found no relationship with: - Material pairing. They're individually good or bad. Ti-Al6V galls horribly against hard Cr layer. - Static, dynamic friction coefficient, ratio of them - Elongation at break, hardening by cold work, breaking energy, UTS to YTS ratio... - Heat conductivity, heat capacity, short-time heat capacity, fusion temperature, annealing temperature, change of YTS with heat, thermal expansion, ratios of them - Precipitates and heterogeneous phases, Bcc-Fcc-Hex, crystal size Maybe a relationship with: - Individual alloying elements! C, P would improve, Cr being very bad, and Mn being a better replacement for Ni. So if some day you choose a research topic: - We know how to make aluminium alloys. A theoretical explanation is intellectually interesting but unlikely to result in better materials. - We ignore how to improve anti-galling alloys because we have no theory, no empirical knowledge, too few experiments. You're more likely to improve knowledge in this less known field, and as an alloy user, I'd badly need it.