Enthalpy

I've checked recently for other purposes what plain bearings can do or not, here and there http://www.ggbearings.com/ http://www.igus.eu/iglidur and: None wants plastic to rub against the bushes. All suppliers demand metal with a minimum hardness and a grinded surface. PP is not a material for bushes suppliers. Though, I know it does work, with less good performance. The best plastic bearings accept 120MPa or 2m/s but not both: their product must be P*V<1.5MPa*m/s. The best metal bearings accept more pressure but less P*V product. This is for contact bearings. Hydrostatic and hydrodynamic bearings offer other possiblities. The P*V limit is very low and it's a hard limit. Expect quick destruction if exceeded. So I'd recommend to check: If P*V>1.5MPa*m/s, redesign. Forget plain bearings, it's just impossible. Most frequent case. If P*V<1.5MPa*m/s, retry with the best plastic bushes againt metal. If <<1.5 you may try with PP and metal. ABS is probably a bad choice whatever the speed and contact pressure. I know it's annoying... Many designs start with a P*V that no material can accept and must later be improved.

Ahum. Symmetry breaking is not my field, but antennas are, and, how to say... That paper starts very badly. The part about transmission lines not radiating uses formulas established for DC currents in infinite wires - exactly what cannot work for antennas. Then this author "prooves" that two parallel wires can't radiate, despite such antennas have been working for a century. Sorry, that research paper contains nonsense that would not be accepted from an electromagnetism student. Then the paper swiftly switches to Noether's theorem, symmetry breaking and other things. I fear this parts makes as little sense as the one on electromagnetism, and even, that the reviewers let the paper through, not because they understood and approved the simple part, but because they got impressed by the complicated one and by the prestigious university. ---------- About the radiation by dielectric polarization current, there isn't so much of a "mystery"... Vacuum polarization is not a movement of accelerating real charges hence it doesn't radiate. The added permittivity (relative epsilon minus one) is a charge movement and does radiate. The maths behind it may be horribly obscure if starting from Maxwell's equations, and I never saw it done, but the concept is simple. ---------- Their piezo antenna uses a mechanical resonance to let many electric charges move a lot, in an attempt to let a small antenna be efficient. That's the interesting and sensible part of the paper, if the uses accept a narrow bandwidth. ---------- To my opinion, the paper's part about electromagnetism and symmetry should not have been written nor accepted for publication.

Because these thread and subforum deal about physics and hard science, but I want to address some other legitimate queries by forum members, I put there http://www.scienceforums.net/topic/90014-why-do-i-say-the-french-spooks/ a first set of reasons to be surrounded by the French secret services. ---------- Fun: since I described the suppsoed UV camera here, a blossom of questions appeared elsewhere on the Web about how to make a fluorescent dye with UV absorption as narrow as possible. Under varied usernames, with indirect questions. I can't exclude that other groups want such cameras.

Hi dear friends! I mentioned elsewhere that the French secret services are my long-time enemies and got questions on that. In threads and subforums about physics it wasn't the proper place to answer, but here I wish to give some explanations, hints, observations, context. As a first reason for spook presence, my father had several jobs where secrecy matters, with clearances delivered by the spooks. As a French officer during the Algerian independence war, he worked at the military intelligence. What he did previously during the Vietnam war, he wouldn't detail. Later he was the deputy military attaché at the embassy in Germany, and then he worked at NATO's operations headquarters for center-Europe in Brunsum - he only said "liaison officer" - after which he retired from the armed forces and went back to the embassy in Germany. He and we had several accidents, sicknesses and problems then, especially during the NATO period. Like everybody in such positions, he was perfectly aware that secret services surrounded him, and also felt he had trouble too often, but he stopped short of realizing the French spooks made him the problems - he imagined some individuals or groups were after him, or the KGB, or whoever. I won't blame him for that, since most people don't understand it better, and the French spooks give false hints towards false enemies to hide their crimes. Imagine the atmosphere at NATO or the embassy, where most people feel persecuted, where the spooks spy on the workers to let colleagues reveal private information gathered everywhere, pick documents from the trash bins to expose them, spark animosity among workers - and basically do themselves everything that the enemy's spooks might do some day, to test the workers and raise their disconfidence. And then, at the embassy, spooks or "retired" ones, protected by their diplomatic status, would openly reveal their employer (implying that the enemy would know it too) and socialize with the colleagues, with the embassy's contacts in the country, with people from other embassies. The employees would say "O yes, the former DST agent" or "the SDECE officer" very naturally - and I claim: these were the very same spooks who created problems to everyone. I too had several jobs needing a security clearance delivered by the spooks, among other reasons for being surrounded. More later.

Hello everybody! In June 2015, the European Patent Office (EPO) awarded their European Inventor Award. Franz Amtmann and Philippe Maugars winned the "industrial" category for their contribution to the near-field communication (NFC) technology, and while the EPO's wording was still careful, in the Press it naturally became "they invented the NFC"... So here is my own compilation of some contributors I know of, where logically I'm not forgotten. ---------- Nikola Tesla made experiments and had big ambitions. He may have been the first (or not) as he had invented many more machines based on induction and RF. Though, the uses of electricity then, essentially for power, didn't fit the technology well. It didn't succeed commercially and little happened for decades. Later with electronics, new uses appeared where low power and imperfect efficiency are acceptable, especially identification tags. I ignore who developed them, but at least these existed in 1988: Inductive coupling around 200kHz, feeding a card at few mm range; Electromagnetic waves around 500MHz and few GHz to detect a passive card or sometimes feed an active card at several meters. And of course, cards with batteries existed - not the topic here. Electromagnetic waves need to radiate tens of watts to feed an active card with tens of milliwatts at several metres. Health and radiocomm regulations limit their use, among other drawbacks, but they did find early uses to pay at highways for instance. ---------- Jean Barbéris, a visionary colleague at Schlumberger, knew in 1988 what users would want to have in 2000, and was able to convince the deciders and explain the need to me. I got useful and nice explanations from the radiocomm admnistration about what's allowed or not (datacomm versus ISM), how to read the laws, what's specific to one country or more general, and so on. An other colleague told me what kind of processor and power was necessary for a secured transaction. Rare knowledge then. Marc Schaefer (hey, that's me here!) developed in 1H1989 a technology at 13.56MHz where: Inductive coupling at this better frequency and resonance feed the card at ~15cm; The terminal sends data to the card by modulating the power carrier between 90% and 100% amplitude; The card has a very simple circuit to regulate the power, receive the data and check that enough power will be available to the circuit (microcontroller meant for cryptography) before starting it; The card sends data to the terminal over a 3.58MHz carrier. The company didn't claim patents over that technology, whatever their reasons were. I described properly my circuit (3) in my hand-written report, but in the version someone else typed, the diagram was grossly wrong, intentionally or not. In my absence, the colleagues were unable to understand it, and seemingly didn't look at the physical circuit instead. Nor did anyone ask me when I was back two years later. It was a horrible time for me at Schlumberger because the colleagues, friends, neighbours were separated from me in order to keep something secret. Possibly the contactless card, or the satellite I developed in parallel, or the miltary radar components I made meanwhile. Anyway, I refused to go back to that company, and competitors made the big money. The 3.58MHz carrier (4) wasn't an excellent choice. It makes for simple circuits but the ISM frequencies don't permit datacomms in theory, and the available bandwidth is limited. I ignore who developed where the card-to-terminal datacomm that modulates the card's Q-factor at 13.56MHz. I ignore as well who developed the protocols (I had only RS-422 in both directions and no protection against collisions). An other colleague at Schlumberger took part to a standards committee, didn't detail in his thesis who developed what, and got a physics PhD for it. The ISO 14443 includes: Power feeding as I did it; Terminal-to-card datacomm as I did it; The small circuit no - it shouldn't belong to a standard anyway; Card-to-terminal datacomms at 13.56MHz - not from me; Initialization and anticollision - not from me; Protocols - not from me. https://en.wikipedia.org/wiki/ISO/IEC_14443 The usual name was still RFID despite identification had become a minor use and public transports, with a refined and smart card, the major one. ---------- Other people and companies developed the integration of the card's circuit in a chip. I believe AMS and Mikron did a lot for it early; meanwhile many companies mass-produce such chips. Mikron was bought by Philips which became NXP semiconductors. A decade ago, several labs and companies succeeded in charging a smartphone by induction at small range at 13.56MHz with resonance, and failed at feeding usefully more power at big range by induction. The Press attributed to each of them the invention of power by induction - not to me, not to ol' Nikola, both too old for the news. Meanwhile several people transmitted power by radiowaves (or planned to at satellites); one prototype in km and kW range was leaded by Guy Pignolet (hi!). Technology related to inductive power but distinct. ---------- The Near-field communication (NFC) evolved from the RFID. https://en.wikipedia.org/wiki/Near-field_communication Its name is better. It uses the same physical layer, the secure communication algorithms and protocols were already known, but the NFC committee standardized it properly. This is obviously a paramount work - but standardization is not an innovative work to my eyes. What Franz Amtmann's team did at Mikron isn't clear from the award's text. There was certainly much to do before an HF circuit worked on a chip. Unclear to me is also what Patrice Gamand and Philippe Maugars (and team) did at Philips. The award tells shortly "secure connection", and the patents about power from the magnetic field or the battery are as usual incomprehensible even to the specialist. Hundred more people must be missing here.

And? Many processes exceed the melting point of steel, beginning with the production of pig iron and of steel. Several metals are produced in vapour phase, which advantageously separates them. Yatendrao didn't write: "we have three grams and operate in a kitchen".

To discolour (or remove?) FeCl3 stains (from etching printed circuits), fluoride salts are used, or with fewer drawbacks, oxalic acid. Sound a bit like what you describe, but what is the process?

A few hints: - To observe an interference pattern, which is only a statistics, you need to detect many photons. One photon only gives one spot, in such an experiment. - "Knowing that the other particle etc" means that the experiment discards some observations: the ones when the other particle didn't behave as chosen. - There are uncertainties at entagled particles as well. That is, the observed property at one does not determine exactly the property at the other. - "Wave versus particle" is more a game for newspaper. A photon is both.

Many effects combine in loudspeakers... The designer wants to avoid mechanical resonances by the walls. Odd angles can improve that. Fibrous material is put to attenuate the resonances and does its job. It works through a thermal process rather than on the flow. Not least: acoustics isn't so well established nor understood, the designer does what he believes to be useful, the customer buys what he believes to be best, the sales dept recommends what the buyers are ready to believe - so not every design detail is sensible.

Here's an example of steel toroid lifted by magnets. D=20m d=14m to store significant energy, and 1500MPa resist 364m/s +20%. The gap is 2*e=6mm, the N45 magnets are E-e=15mm W=40mm. 2*75 lanes of mean 53.4m need dangerous 2*2.40m3 costing 3.6M€ at 2kU price, possibly 2.4M€ in that amount. The lifting force is 30MN. It permits 2.0m thick steel at 1.2G, and plain bearings shall act at stronger quakes. 2516t steel store 167GJ = 3h*15MW. 20 tori store 3h*300MW, enough to smoothen the production of a 1,300MW plant, and their magnets cost 50M€. That's not cheap, because the flywheels have other costs, but could be affordable to save 1/4 of a 2G€ plant and improve its efficiency. 1M * 900Wh truck batteries may cost 90M$ but are too inefficient. The thin magnetic gap precludes my flow calmer and imposes costly vacuum. The load hence losses at the radial roller bearings aren't obvious. Magnets must be sorted and laid out to remove short-period fluctuations of the induction. The bare edges or the magnets would induce unbearable eddy currents in the facing magnets, but capping the magnetic lanes with thin, very permeable material solves it. I prefer hydraulic or roller bearings and the flow calmer, but magnets are credible. Marc Schaefer, aka Enthalpy

Some permanent magnets layouts improve thrust bearings and adapt to other bearing forms. The current sheaths make it intuitive: Broadening a pole lane too much doesn't increase the force, since the current sheaths flow only at the inner and outer radii. But splitting the area radially in North and South lanes does increase the number of sheaths and the force. Two current sheaths add at the north-south transitions, both at the stator and the rotor, to quadruple the force. More lanes increase the force up to the point where N-S transitions radially too close interact to reduce the force. The optimum could be magnets 2-3x wider than thick. Some tiny radial spacing between the lanes improves the force slightly. This holds for a small gap. Alternate lanes reduce the force quickly at bigger distance, useful. And if an iron path improves the force already, lanes must gain less. Also, I didn't estimate how unstable the radial position gets with such lanes. It may load the radial bearings, which have to be stiff: rollers, needles. Like for electric motors, cogging will improve by: Skewing the transitions between successive magnets. But alternate the skew direction to minimize axial loads. Taking different numbers of magnets at the rotor and stator, with a small GCD like 1, or for symmetry 2 or 3. Offsetting between the lanes the azimutal magnet transitions. The lanes have different lengths at a thrust bearing. Different numbers of magnets per lane let the cogging torques beat; if needed and when possible, have magnets of varied length, or introduce tiny gaps. Marc Schaefer, aka Enthalpy

Nmos logic has disappeared for the eternity to come, together with depletion loads. It was nearly extinct when I studied 30 years ago. Depleted Mos "saturate" with a big drain-to gate voltage, as opposed to bipolars. Bad wording choice, we must live with that. When the output is high (input low), the load transistor conducts less than its saturation current, hence is not saturated. When the output is low, the load transistor conducts its Idss and is saturated. Well, at least if the circuit was designed normally. If the supply voltage doesn't suffice you'll get bizarre ways of operation. Or if a huge dosis of ionizing rays lets the Vt drift, and so on.

Some elements: I'd take permanent magnets rather than an iron plunger. What matters is the induction at the mobile part, and magnets do that better. Less worries with varying induction too. You need the coils to interfere. They should even overlap partially. Though, you don't necessarily need nice sine drive currents; you can stop the current in one (the induced voltage will exist though) and put power in the other. You need a rather fine sensor for the position. Switching the coils at wrong moments would waste quite a bit. One design example would use flat cylindrical magnets and iron disks, all stacked, to achieve a radial field that alternates NSNS (needs some convincing mechanical means!). The corresponding coils would be solenoids on the stator. Consider 0.3T reasonable with Nd magnets, then v*B*L is an induced voltage and I*B*L a force (L over several turns, where the induction is strong). Many-many other designs are possible and sensible.

Hi David-ps, welcome here! Probably not. Abrasion doesn't relate much with hardness. Polypropylene is known to resist abrasion rather well, including when paired with metals, preferably hard metals. Possible scenarios are that rubbing overheated the plastics, or that these two are not compatible. ABS is not used as a rubbing material, supposedly because it has bad properties. My first suggestion would be to get a doc from a supplier of polymer plain bearings and check the pressure and speed they give for their highly optimized materials. You'll see it's not much. Then check your design, keeping in mind that your materials are bad. In case the design uses reasonable pressure and speed, consider other materials. Especially, replace ABS with something better, preferably a metal. Not all alloys are equal to preserve the plastics; almost smooth surfaces are better. If the design's pressure and speed resembles even remotely what plain bearings do, you need these special materials. If they exceed, make a new design.

Hydrogen can fly aeroplanes at subsonic speed, using fuel cells meant for cars and electric motors. I describe there http://www.scienceforums.net/topic/73798-quick-electric-machines/#entry738806 how to build the tank for liquid hydrogen, which takes little volume thanks to the fuel cells, and give some examples or aeroplanes. Whether the fuel can be cheaper than kerosene... Presently not. Kerosene is dirt-cheap (untaxed, nearly a by-product of gasoline and Diesel oil, and airlines let countries and companies compete for the market), while hydrogen is produced from gas. The smaller hydrogen mass consumption may favour it a bit, but I guess it stays more expensive than kerosene. Through some progress, I don't know. The immediate advantage I see to hydrogen is not cost but silence and range - check the figures I give in the other thread, even before any stretching. Would it fit supersonic transport? I vaguely plan to check that, but I don't know when. Fuels cells powerful enough would be heavy.

They won't separate by melting, but you can separate them by distillation. At 1bar, Ag boils at 2160°C and tin at 2620°C. For 10mbar vapour pressure, Ag needs 1509°C and tin 1834°C.

The antihydrogen has no reason to react with hydrogen rather than other particles. The antielectron would annihilate with some electron from the molecule (electrons don't belong to a specific atom, at least the valence electrons). Then, the antiproton may react with a proton in oxygen for instance. The emitted gammas are not absorbed by the same atoms, with a high probability.

The detectors used in optical astronomy lose the phase information when detecting a photon. Once this information is lost, post-processing is little effective. By superposing successive images, you add the received power only. Adaptive optics corrects the distotion to add all light in phase. This is fundamentally better because the focus adds the received field, and the power is like the squared field. In radar and sonar, the detectors keep the phase information, and data processing keeps the whole sensitivity of a distorted wave and antenna - so much that we built flat hydrophones and radar antennas and compute beams afterwards, in many directions a once. Lidars do that more or less with light, by coherent detection and by heterodynes, but as far as I know (or ignore) they aren't as advanced. We have no many-million-pixel detector with phase detection, and I suspect we wouldn't have the data processing power neither for that frequency bandwidth. Some people think at synthetic beam forming with light (that is, aperture synthesis) but it's still the beginning.

Hey, if you invent a compass that points to Mecca insterad of North, you're rich! OK, OK, joke besides. The cause of the geomagnetic field is so little simple that it was debated few years ago. After all, a piece of copper or iron doesn't produce a magnetic field just because it rotates. An experiment with liquid sodium has settled the debate more or less http://perso.ens-lyon.fr/nicolas.plihon/VKS/index.php Though, the necessity of a liquid core and a few hours rotation doesn't always fit easily with what we observe from other planets. From what I believe (or not) to have grasped: The hot Earth core creates convection, at several places. Iron (conductive, not magnetic at that temperature) traps some pre-existing magnetic flux, just because it's a big chunk where currents take typically 10,000 years to dampen out, that is, the inductance increases with the size but the resistance drops. That's the typical timescale of variations in the geomagnetic field. Several convection chimeys result in a global field that is tilted, excentered, variable and reversible over time. Earth's rotation messes somehow in. As metal ascends in convection and grasps speed, it gets narrower and longer, but the trapped flux being concentrated increases the induction. Non-trivial: the narrower but longer metal creates at some identical distance a stronger induction. R/2 and flux*1 implies B*4 over h*4, resulting from I*16, so I*S gets *4 and this is what determines the remote induction. The ascending chunk of metal can create an induction stronger than the one it experienced before ascending, so the field may amplify and perpetuate. Please take with much mistrust..

Just to remind that I (and others) disagree with that claim. ---------------------- The speed and the acceleration of a particle results from how the waves combine, for instance to produce a maximum of probability density in some region. I have no worry with the particle changing its speed abruptly. In the case of the photon, one should (...I didn't) check what happens with its momentum between both media. For electrons in solids at semiconductor interfaces like heteroepitaxy makes, it's the momentum that has some conservation laws, not the speed.

Discrete photons means that light is absorbed and created in packets. It does not imply that photons have separated positions. Under very special and difficult circumstances, one can distinguish the emission of two photons, their absorption, and tell that the photon absorbed there was the one emitted then and here. Usually, it isn't the case: too many photons make light, are emitted and absorbed too close to an other to tell. An other, more fundamental difficulty is that, as bosons, arbitrarily many photons can be in the same state exactly. Then, telling "I saw the photon 123456" just makes no sense, because they're strictly identical. They just get detected at random times. How to check a distance then? Multi-photon absorption happens as well, and to my understanding several photons disappear exactly at the same time.

Hi LoggerTodd, welcome here! If you input all the energy elevels (there are many!) of an element, just a matrix of the differences will tell you the transitions of this element (in the same state, for instance lone atoms). A spreadsheet can do that. It's rather the other way (spectrum to energy levels) that was historically difficult, hi Bohr and the others. One must add some selection rules to filter out the forbidden transitions. This can be done simply from the quantum numbers of the energy levels. Is that more or less your query? Tables of transitions exist as well. Not for every compound, but for the elements certainly. Maybe in the Handbook of Chemistry and Physics.

If you compute one reflexion from the acoustic impedance (density*velocity) or air compared with a solid, you find that sound should be completely reflected except from the lightest foams. The impedance mismatch is like 104. Though, nothing is simple in acoustics. If the wave arrives at a flat angle, it can pass more easily to the other material - both if the transition is long or short as compared with the quarter wavelength. This is the idea behind pyramids in anechoic chambers. Then, you have multiple reflections, which cumulate losses. As this hall looks like, it has parallel panels at the top, which favour multiple reflections locally and reduce the reflected wave. Finally, our ears and brains are accustomed to echo and reverberation, and we do make a difference between 10 reflections and 100 - corresponding to low losses in both cases. So I wouldn't be surprised if wood - with that particular shape - lets the hall sound differently from ceramic. Just think of an empty room: it does sound very hard with naked plaster or stone walls but far smoother with wood walls. Does it relate with the instruments' material? I suppose not. We can tell where an instrument was played (empty room, room with carpets, room filled with people), be it made of metal or wood.

Most noise comes from the air exhaust and could certainly be reduced. You get an idea of the percussion noise by hearing a hand-held hammer drill (remembering the size ratio) or by hearing distinctly both noises. Could the percussion noise be reduced too? Not so much if the tool must break hard material like concrete, for which peak force is paramount. In a first approximation, the shock of the piston on the hammer must be as hard as the target material. But with an adjustment, less hard parts would be used for asphalt. In countries where jackhammers were recognized as harmful for the workers, disc saws replace jackhammers on most occasions, especially to open asphalt.

Hi, OD=0.6 only means that the power of light passing through is divided by 100.6. You would need the light's path length and some attenuation (possibly by diffusion) properties of these specific bacteria to deduce a concentration, provided nothing else attenuates.