Enthalpy

Hello dear friends! I'd like the cookers to reduce and adjust their power automatically when the liquid in the pan starts to boil, or the oil in the frying pan. Induction cookers, and some others, react quickly enough for it. Maybe they exist already? I suggested it to a Spanish company in 1996. I imagine the sensor could listen to the noise injected by the pan or frying pan in the cooker. Something like a wire could transmit the mechanical noise from the hot area to the vibration sensor working at cool temperature. Then, electronics could first filter the high frequencies or sharp transitions associated with bubbles, then either count the bubbles per time unit or evaluate the strength of the bubble noise, to inform the regulator circuit. Marc Schaefer, aka Enthalpy

No hope! Complexity has to be proven for individual cases, and there is no general method for the proof. This stands for circuits exactly as for algorithms. Just one example: factorization of big numbers has been investigated since antiquity, is vital to every credit card or https data exchange, but we only suppose that factoring is difficult - no proof exists other than the lack of a good method up to now. This is not just a theoretical question! For instance, multiplication of big numbers seems to be of N^2 complexity, but it can be done by a Fourier transform in N*Log(N) complexity - and is done to compute Pi quickly, for instance by the programme Superpi. Same for convolution, for antivirus parsing... Arithmetic circuits have the added difficulty of being too small for O(something) complexity to be meaningful. Take the lookahead carry of a 16 bit adder for instance: it has 1 level only, sometimes 2. General considerations will be overshadowed by detail considerations. You could read Dijkstra about arithmetic circuits, I think his book is "seminumerical algorithms". Pre-Apollo era but still actual. Some more, in software but transposable, in "numerical reciepes in C". The good side of this: no room for a method means room for intelligence.

Citric acid is known to corrode 304 steel, but I expected 316L to withstand. What you need is a "compatibility list" or "compatibility table" for "Aisi 316". They are huge, you may find citrate and calcium in them. Beware 316 and 316L have different corrosion resistance, especially at the weld seams.

And fusion like ITER would produce as much radioactive waste as fission does, as said above. The time of these brilliant people, and the public money, is better invested elsewhere: renewable energy, electricity storage, maybe hydrogen storage...

Without a core, the electromagnet won't work at all for being too inefficient. Even if huge - which isn't an allmighty solution.

The reeds produce a sound that propagates downward in the pipes (which determine the pitch) and upward in the bag. The downward sound is strong because the pipes couple it efficiently into air by resonance. That is, the reed has a high impedance (= pressure oscillations divided by volume throughput oscillations), the air a low one, and the quarter-wave pipe between them converts the high impedance into a small one; this impedance matching makes the power transfer efficient. The upward sound is weaker for having no such impedance adaptation, but for instance the higher harmonics of the note, which are very important for sound quality, aren't amplified on the downward path neither. So the upward path certainly plays a role. The physical properties of the bag certainly influence how these higher hamonics pass to the surround air. The first being the bag's mass per surface unit, but others must have an effect: the humidity at the inner surface (not easy to explain, few people are aware of, but it seems to act in a clarinette), maybe the sound absorption by the material, the roughness of the inner surface, the speed and attenuation of bending waves travelling in the bag's material... As compared with direct radiation through the bag, I suppose the path further through a moisture absorber and through the player's mouth, throat and chest is less important to the public - but is all important to the player, who perceives the tone via his teeth and skull conducting to the ears, and through his chest for the lowest notes. For instance, a saxophone sounds completely different for the player and for the public; the difference is less important with a bassoon (no hard mouthpiece). So my position is: - Can be explained if needed - but less important than the downward path - Try if the public feels a difference, not just the player - Play a harmonica within bags of said materials, and listeners outside will hear a difference. But this difference contributes less than the strong sound through the downward path of the bagpipe.

The question is imperfectly clear, since most steels are attracted by magnets... Basically, ferromagnetism is a molecular property, not an atomic one. For instance, austenitic stainless steel is non-magnetic. But Mn-Zn makes a ferromagnetic alloy called "ferrite" by thankful electronics engineers. You may understand "molecular property" as "not a result of constituents" if you wish.

Still in the present, temperature on Mars does exceed 0°C from time to time, so liquid water in the past needs a thicker atmosphere, not necessarily warmer temperatures. Only much water flowing frequently needs a warmer planet.

Elastic moduli increase much faster than density, so the effect is bigger than expected from density changes and in the opposite direction. Though, I doubt the effect can be used, because: - Compression or traction at a fault is much smaller tan the hydrostatic pressure - Dislocations at a fault have more influence on sound propagation than density there - You wont' make the difference between a compressed rock and a different chemical composition.

Hello you all! Despite the unusual layout, you may recognize the common Sallen-Key biquadratic cell, here as a low-pass: s is j*2pi*F and A is the attenuation Vin/Vout or 1/H. The low-pass Sallen-Key worsens if the resistors differ, so the Q factor resides in the capacitor ratio only, but precise capacitors are often limited to the E3 series (10-22-47). The modification I used for >20 years improves that by adding one buffer: Now the resistors can usefully differ. Most often, a single capacitor value fits the biquad cell and even the complete filter. Big Q-factors can result from the combined resistor and capacitor ratios, the latter being simple like 1 or 10. Store fewer expensive components. Additionally, the Q-factor accepts component ratios four times lower. This as well helps to keep reasonable capacitances. The main drawback of the Sallen-Key-Schaefer is the 14-lead chip for two biquadratic cells instead of an 8-lead chip. A high-pass can be made this way, but the original Sallen-Key already takes identical capacitors as a high-pass. No band-pass is possible, neither with the modification, and a low-pass with notch neither. The Multiple-Feedback lowpass biquad as well can improve with the added buffer - on the paper, as I haven't tried that one. Marc Schaefer, aka Enthalpy

Technologically achieveable pressure does multiply the viscosity a few times. In case you're thinking at the VKS experiment, a low viscosity only reduces the time constants.

Many solvents and tensides are bad for seal joints.

Solar wind ions are not independent and their trajectory isn't hyperbolic. The density and speed of Solar wind follow a law that proves it. ---------- The original paper about gyrochronology is there: http://arxiv.org/pdf/0704.3068v2.pdf

Primordial nucleosynthesis was not an equilibrium. That's why only light nuclides were produced, instead of just iron. So you can forget all arguments comparing temperature with reaction energy. I suppose the part of the big bang hot enough was too short to achieve any equilibrium - but ask a specialist. Fusion from helium to carbon and oxygen does not pass through lithium in stars. There are easier paths. Fusion happens widely before 2 MeV in stars. 15 MK in a normal yellow star makes 1.3 keV.

The paragraph about energy was just a side remark for people wondering if some physics law prevents the buildup of a voltage. The aim here is not to produce power, but to measure effective masses. My language mistake: instead of "extraction potential", please read "electron work function".

Hello everyone and everybody! What about a slightly exotic idea? Here I propose to measure the "effective" mass of charge carriers by centrifugal force. Electrons in vacuum have a mass, and when moving in a solid an other mass, often called "effective" (as if the vacuum mass were ineffective). Centrifugal force creates unequal voltages across dissimilar materials that give a different mass to electrons, and with a proper setup, this voltage seems measurable - which I feel funny. Along a radial leg, the centrifugal force creates a voltage of mA * 0.5*(V2-v2) /q in the material A, or mB etc in the material B, with V the outer speed and v the inner one. By making the odd legs of material A and even legs of material B, and putting many leg pairs in series, we get a significant voltage. At least with metals, the extraction potential won't vary with the minute amount of electrons added or subtracted, and nor will the contact potential; other materials need an ohmic contact. And yes, I believe electric power could be harvested, which would be provided mechanically by the shaft, but is technologically uninteresting. One excellent choice for the disk is a silicon wafer; I take D=2 inches here. An other choice would be a platter of a hard disk drive with its spindle already. Silicon can rotate at 600 m/s (and much more); the inner speed shall be 400 m/s. Take materials that give masses of 1.5*m0 and -1.2*m0 for instance, then each pair of legs offers 1.5 µV; a pitch of 100µm permits 1000 pairs of legs (not all drawn here) resulting in 1.5 mV. Metal thermocouples can develop 20 µV/K for instance, so the outer and inner temperatures must be much closer than 0.1K: nothing special within metals or silicon, but it must impose to rotate in vacuum. 1.5 mV DC is easy to measure, but not on a disk rotating at 3800 Hz (226,000 rpm). Capacitive coupling with the stator simplifies it and can serve as a welcome chopper. Take a gap of 0.2mm and an electrode width of 0.5mm between r = 10 mm and R = 15 mm: you can put 2*40 of them, resulting in 4.4 pF /2 and 150 kHz, so the signal is 1.5 mV pk at 150 kHz through -j*480 kohm, so easy. Take a Fet or Mos amplifier, polarize its inputs with 100 Mohm, you get 2.3 kohm noise equivalent from the polarization - or use a pair of diodes for that. The amplifier's noise is similar and the legs can sum to 40 kohm if made of 2 µm thick metal. Noise over a 10 Hz band is 0.1 µV only; with semiconductor legs, shunt the resistance at 150 kHz by a rotating capacitor of few pF on silicon. A 3.5" platter at 7200 rpm would still provide some 15 µV signal. Hydrodynamic bearings of proper dimensions dampen vibrations, see Dubbel for instance. Silicone and fluorosilicone oils have a negligible vapour pressure but beware they're very under-newtonian at high shear. In metals, electron mass may be less exciting, but it is important in semiconductors. Known materials like silicon may serve as an electron standard, possibly with a metal (silver?) as an intermediate mass standard. What about superconductors, where heavy holes are allegedly essential? Or graphene and nanotubes? Or even electrolytes, to determine the degree of solvation? Marc Schaefer, aka Enthalpy

Pity, flexural waves are neither compression nor shear.

The aluminium radiator is protected by its oxide layer as well. Unless the alloy resists corrosion better than the powder - you'd need to know which alloy both are... - any acid would corrode both, at (very) different speeds which are impossible to predict. The necessary amount of strong acid is BIG. It's amazing how much concentrated acid it takes to dissolve a bit of aluminium. I did it previously with FeCl3 (50kg for <1kg) which acts faster than a normal acid and had to complete it with much additional HCl. Other liquids like gasoline or detergents will help strictly nothing. Well, I believe you have to open the circuit and clean it mechanically...

You could get some first impressions, but these are not figures usable in a design. In a helicopter at fixed altitude, air's exit speed multiplied by the mass throughput is the lift. Throughput is the area multiplied by the exit speed and by air density. Though, air speed isn't really uniform... Now, and this is imprecise as well, the inclination of the blades let them cut air more or less flat, so their speed and angle relate with the air exit speed. In fact, air accelerates before entering the rotor mostly. However, blades need some extra angle to accelerate the air.

Found again some material about galling. http://www.nickelins...Steel_9006_.pdf a foundation paper by Schumacher. Before, Harry Tanczyn wrote "Stainless Steel Galling Caracteristics Checked" which is too old to find on the Internet. Some explanation attempts in the "prior art" section of the US Patent 4,039,356 for instance at FreePatentsOnline or where you prefer. I'm not fully convinced that harder precipitates improve, because 17-4 PH has such precipitates and galls horribly. Nor am I convinced by the high work hardening rate, as for instance Al-Mg5 hardens quickly and galls. As for the oxide layer favoured by Si... Cr and Ti make an oxide layer and gall, even as an alloying element, so Si would be different. Additional experimental results in the datasheet of Nitronic 60: http://www.hpalloy.com/alloys/brochures/Nitronic60book.pdf Please remember these papers are old, like 1977. Imaging and analysis weren't as detailed as presently. Galling probably designates several different processes, yes. Refine that as you want... But to be useful, a theory must be applicable by mechanical designers! That is, the recommandations should fit in few lines.

Why shouldn't you ask the manufacturer of the equipment? And: do you want to detect micro-cracks, or get an estimation of the size, or see their shape and exact position? Only the last option needs a wavelength shorter than the crack. The English article at Wiki is useless, but the German one helps: http://de.wikipedia.org/wiki/Akustische_Mikroskopie GHz frequencies penetrate far less than 1mm in solids - they don't tell in which solid. Anyway, if the only manufacturers target semiconductors, you can forget it.

Look at a cathode ray tube. If the image gets proper colours at the edges, it's because relativistic effects on electron deflection are accounted for. They would be several pixels off. At an ion implanter, at an electronic microscope... special relativity makes very significant changes. Not really on your lawn.

Any reactor burning tritium needs to multiply neutrons, a process that creates radioactivity. This would hold for laser fusion, Z-striction or semi-fast compression (development at General Fusion) as well, but maybe the Z-striction will accept other fuels within a reasonable time - something a tokamak like ITER isn't capable of.

The Hertzsprung-Russell diagram relates the absolute luminosity and the colour of a normal (main sequence) star. Individual stars are observed in remote galaxies, so if something absorbs their light, astronomers notice it, as they don't fit on the HR curve any more. There are more tools. Except for some discrete lines, the spectrum of a star resembles the black body. If the continuous spectrum of a remote star differs too much from the black body, astronomers infer absorbing matter on the line of sight. this is an abandoned explanation, because the micro-lensing effect of cold bodies that massive and abundent was searched and not observed.

An electron gas is an extremely primitive model of a metal. MaybeNextTime conducts more subtle modelling than an electron gas. You can forget the hope of getting sensible strength figures of a metal from the electron gas model. Movement of dislocations reduce the strength by a huge factor, like 10 or 10,000 (pure gold, aluminium...). Holes mean only the curvature of bands where some electrons reside. This curvature changes the movement behaviour of these electrons. What relation with the movement of dislocations?