Enthalpy

Entropy.

Provided they're aware of the assertions they make... In the 19th century, no physicist wrote at the beginning of his calculation "we assume time is identical for everyone". This is something I found ridiculous from some physics teachers. "Write down all assumptions you make", they used to say! But well, these were teachers - true physicists didn't tell us such a thing.

I too dislike any added engine... We're not building a steamer here! Alternately, gliders are commonly started with a bungee. The current record is about 100km/h; one was established by a kite surf (youtube at 2m from sand banks...), and did I read that a hydrofoil improved it? I'd like to rescue the rigid sail as it's more efficient and stable. Strong wind might be able to lift one if the sail is high enough above the floating fuselage and the centreboard serves as an anchor - perhaps maybe... Easier start was the goal of the intermediate hull for the crew. A jettisoned lift-off sail, maybe. For sure, if one wants to set an official record, some definitions would need a double-check, like what a sailboat is.

With polarizations like here under, sound uniform metal reflects a signal that the detector attenuates, while a more or less transverse crack in the rail, which reduces the E component parallel to the run, gives a signal favoured by the detector. One interesting location is at the bogies (cut for view), where the vehicle's weight distends the cracks: The antenna example here is a horn with a lens, sketched at a bigger scale than the railway engine. More sensors would avoid false detections; their polarization can be offset if someone expects cracks at 45°. Marc Schaefer, aka Enthalpy

My alternative proposal uses GHz radio waves. Power at 40GHz (7.5mm wavelength) is radiated with linear polarization oriented at +45° versus the rail. A reflector or lens of D~90mm concentrates it on a D=40mm spot at 0.2m down distance on the rail. At the same focus, an other primary source with linear polarization receives the reflected wave; it's oriented at -45°, adjusted to near-zero coupling with the transmitter. Reflection on a smooth sound rail surface keeps the +45° polarization which the detector doesn't sense. Cracks more or less perpendicular to the rail, even if thin, give a signal in the detector. The rail's inner and outer edges would give a signal, but they are smooth, and the illuminated spot avoids them. Post-detection software senses quick variations in the reflected signal, discriminating further the rail's sides. Like: compare the measured value with a reference interpolated from measurements 100mm and 200mm before and after. Possible improvements: Components exist for 94GHz, to reduce the illumination of the rail's sides. A precise smooth illumination function (like Gaussian) reduces reflection by the round rail's sides. Have several detectors and cross-check to avoid unjustified detection. Small and cheap enough to equip one or more railway engine on each line. Marc Schaefer, aka Enthalpy

A few considerations about the design as it is first sketched here... Rail joints will give a much bigger signal than any crack, whatever they look like, for sure. You need software to discard detection at the joints. The joints can be detected automatically by the software if their spacing is regular enough for some travel distance. The described electronics is too rudimentary, but the real challenge is to get initially a clean signal; then, processing it is banal engineering. You would better clean the rail before passing the detector on it. A static or rotating brush before the detector could remove loose object; depending on the induction you desire, you have to remove ferromagnetic dirt as well, which might be done by rotating ferromagnets as in waste sorting - but ferromagnetic dirt stuck at your magnets might always be a worry. I agree the flux path goes through the rail in your design. You can add static wedges around the wheel where the contact with the rail is narrow, or offer a path elsewhere: an airgap can be acceptable if broad and thin. The coils that create the induction would better be a pair near the ends. And to pick a cleaner signal, magnetic designs tend to have symmetric picking coils (or sometimes emitting coils), with the useful signal being a difference between induced voltages. What sort of defect do you want to detect: is it a notch, several millimetres long and rather shallow? Is it a rail-wide and centimetre-deep crack where the butt faces are separated by 100µm? What operation mode do you need: a special waggon added to a commercial train running at its normal speed of 20m/s? Or can you have a special train running much slower? Skin effect is a serious limitation. Imagine the magnetic flux increases over 1m (using very long poles at the air gap), stays for 1m, decreases over 1m, with the waggon running at 20m/s: it correspond roughly to 5Hz. In copper, skin depth would be 30mm, but in steel (take µr=5000) it's only 1mm unless the flux suffices to saturate superficial steel. So apparatus for non-destructive testing use to observe how well metal parts repel the induction, not how well they conduct it. A flux-conducting design would limit the frequency of an AC field even more seriously.

Plus some questions that my sketches above don't answer! Like: how to keep the crew alive when the centreboard hits an obstacle, or loses lift..? We're speaking of speeds like 150km/h, that's why I like to have the crew in a cabin at the sail, so they can control the splash like a glider does. And: how to first let the wing take off? Easy with a flexible kite, less so with a rigid wing, far less so if the crew is on board the sail. Maybe the sail must first take off by external means like a motorized winch. Obviously my proposal is far from a complete concept, not to say a design.

I confirm no relation with NMR. But ferromagnetism - hence at moderate temperature! - does have an influence as it concentrates the induced current at the part's surface, depositing heat there, and increasing the part's electrical resistance, which means more heat at the part and less at the inducing coil. Apart from reactance versus resistance, frequency has a serious effect through the Kelvin effect, that is current flowing only in the part's skin, which helps heating the part more than the inducing coil, but doesn't heat in depth. This IS used for surface treatment of steel parts, where the deep material is and stays tempered by the surface is quenched hence hardened following induction heating.

That maybe ? http://www.ansoft.com/news/press_release/021024.cfm You still haven't told for what OS nor at what price. If you wish a uniform induction, old Helmholtz did a good job with his coils. They can be a starting point to added compensation coils. Often, coil resistance isn't a worry at capacitive discharge, since magnetic energy is the limit. Also, the induction from a single loop can be reasonable computed in 3D, so any coil form with cylindrical symmetry results in a field that a spreadsheet can compute - no special software then. What induction are you seeking? Up to some 10T you have still some freedom about the coil's shape, but at 50T (is the record still at 200T?) mechanical stability imposes everything. At 7T I used copper foil, as broad as the coil's length, wound spirally and insulated with paper, hold in a hole in plywood - but epoxy would improve, with glass fabric as an insulator. Thick aramide fabric would hold the metal in place at higher induction.

Weapons are presently more advanced than your suppositions. Reflective surfaces aren't necessarily the answer since they become absorptive at higher temperature. But at least for slow targets, an ablative protection like at atmospheric re-entry shields must be effective. One design example has tar or some polymer got evaporated into a graphite-loaded plasma in front of the protected surface; this plasma is opaque to laser and thermal light and slows down a lot the ablation of the surface.

Pyrolytic carbon (an other element but not a metal) is more strongly diamagnetic than bismuth http://en.wikipedia.org/wiki/Diamagnetism More generally, magnetism is a molecular property, not an atomic one, so melting changes everything. For instance CrO2 is a permanent magnet and was used on magnetic recording tapes but neither Cr nor O is ferromagnetic. Ferrites used in electrical engineering comprise Zn and Mn to be ferromagnetic. Austenitic stainless steel is not ferromagnetic despite being made of Fe and Ni mainly.

It's because electrons have a negative charge. This megastupid convention was taken as physicists still didn't know about electrons.

You must distinguish internal energy from enthalpy to make a sense of the question. Take 1m3 of an idealized liquid with zero compressibility: if it's in a tank and you push on it to increase the pressure by 1Pa, as your piston doesn't move, it takes zero joule of work - here it's internal energy. But if you push this liquid from one tank to an other tank at 1Pa higher pressure, you piston moves and consumes 1J of mechanical work - here it's enthalpy. One subtlety of enthalpy is that it is not stored fully in the fluid itself; part is energy stored in the surroundings of the fluid (for instance the gas that top the liquid in the tanks at pressures P and P+1Pa). Despite of this, enthalpy is a property of this fluid alone, depending just on the state (pressure, density...) of this fluid, and you need no information about the surroundings (composition, heat capacity...) to compute it. Abstract, isn't it? And very powerful theory. It also means that work does not correspond uniquely to the state of the fluid; in some processes it may correspond nearly to enthalpy changes, in others to changes in ambiant heat... This allows thermal engines to extract a net mechanical work from a fluid making a closed cycle, for instance get more work from an expansion at high temperature than is invested in the compression at low temperature.

I had wondered if the initial optical aberration of Hubble came from its Keyhole (spy satellite) parent design, which has a 250km observation distance. I had tried to put some figures on the resulting aberration if using that optics at infinity observation distance and got a significant aberration... So it could well be that the donated telescopes have that same aberration as initially Hubble had. Time to re-use Hubble's early correction software maybe? As an intervention in orbit must be too costly in the present context.

http://nett21.gec.jp/CTT_DATA/AMON/CHAP_4/html/Amon-054.html NO2 is produced in an excited state, electrons falling to ground state produce light. Visible light needs several eV excitation energy that would destroy the NO2. You better heat a piece of ceramic or tungsten to emit ligh, or use non-thermal processes.

Acetone is a known solvent for epoxies, and would harm the chip little, but it will take long! You might warm it, or circulate its vapour as is done in industrial cleaners. Etching would be less slow, yes, but may corrode the chip's thin and exposed contact pads - a copper alloy since you chips seem to be from the Coppermine series, possibly covered with gold. The underside of the package is welded to the motherboard by hundreds of metal balls. Melting them would destroy the mobo.

Suggestion: as X-rays have a significant momentum, they lose energy to the expelled electron if reflected back, and as this energy loss differs randomly at each electron due to random impact parameter, individual interactions don't sum up coherently so they can't make an efficient reflection. As opposed, grazing reflection loses little momentum and energy so the contributions of all electrons can sum up coherently. Even better if the angle is such that electrons aren't expelled nor excited, in which case the photon loses no energy, and phase is coherent over all events. Hey, this would even sound credible! One more effect is that, as reflection is done over several atomic layers which make several wavelengths at X-rays, light reflected from these layers doesn't add coherently in the 180° direction. It does add up at longer wavelengths or at grazing reflection. Maybe a "crystal" of protons or alphas or stripped ions in an ion trap, preferably neutralized by baryonic antimatter, would make a better X-ray reflector than electrons do. Still far-fetched technology in 2012.

The mushroom builds like in a thunderstorm cloud when the rising air reaches the stratosphere, where convection is blocked by the absence of a temperature gradient.

If antimatter had negative gravitational mass, wouldn't black holes create huge amounts of matter and antimatter, with the latter being expelled towards the exterior of the horizon, that is to the univers we can observe? Hawking radiation is faint because the short-distance tunneling effect following pair creation must take advantage of the tiny gravitation curvature at the black hole so the falling particle loses more potential energy than the expelled one gains - explaining why small holes with a stronger curvature are more efficient. But if antimatter loses potential energy by flying away, then the tunneling effect could take advantage of the gravitation field, not just its tiny curvature, and pair production would be hugely efficient. My guess is that the absence of such an expulsion of antimatter towards our observable universe proves that antimatter has a normal gravitation mass, and even must put bounds over any possible mass difference between normal and antimatter. That would make a funny little physics project for a student. Marc Schaefer, aka Enthalpy

If I understand your quest, you want to evaluate the periodic field very near to the surface and to individual ions. Then, I wouldn't first group ions into planes, hemisphere or cylinders, but just sum up the contributions or all individual ions. This may raise difficulties when integrating potentials in 1/R, but you might first compute the field in 1/R2 and deduce later the potential if needed. Better: you could first couple the ions in pairs, and then the far field will decrease in 1/R3, helping the sum converge. In a real case you would need the precise positions of the ions and their charge (which isn't an integer number of q), and then it would get seriously dificult. Even for a simple cubic crystal like table salt, you could seek help from a computation software like Maple.

And 10% is exactly what one doesn't want when cooling a Cpu.

On gravity? (well, of course on gravity, because electric force has been measured to far smaller distances) I feel this is extremely difficult because interacting masses of D<10µm are so tiny! Do you confirm? Or even, have a link describing the experiment?

JC, I don't recognize you usual style here. As I already explained, this thermal power is given for zero temperature difference, as well in the Pdf you linked. Selling Peltiers for computers on eBay does not mean they're useful. I provided links to user experience telling they're not and why. As I stated, in normal sensible uses - which do not include Cpu cooling - you'd have 3 stages or more, dropping the efficiency to very few %. But if you want to waste money and time to buy and try a Peltier on a Cpu, do so and get disappointed as others did.

Most of your questions are already answered. For instance: I want no hull at the surface; traction is to exceed weight, excluding hydrofoils in the sense they're traditionally understood; one has to put the pilots somewhere; stiff wings are known to be far better that a common kite; "need to control actively and permanently" in my first post and, yes, I know Skysails does somewhat similar things, as I stated in the thread originally linked in http://www.scienceforums.net/topic/65217-rocket-boosters-sail-back/page__p__666596__hl__booster__fromsearch__1#entry666596

At least as soon as you want an interesting temperature difference, say to cool an infra-red imager or a sensitive visible imager, you need several cooling steps. Three steps of 27% efficiency bring you to 2%, and the imager isn't even very cold. Looks like they don't. http://www.heatsink-...com/peltier.htm introduction with figures, consistent with our discussion here http://www.tomshardw...cooling-peltier disappointed experimenter, consumes 100W for a Pentium III http://www.tomshardw...ate-suggestions efficiency problem is known http://www.tomshardw...peltier-cooling efficiency problem is known there as well I've checked in case some advance has been made, but Peltiers are still as limited as for 20 years. Pity.