Enthalpy

As shorter pulse times reduce the induction far below the present 1-2T, a ferrite core gets possible. Only outside the skull, but it can cut by two the magnetic path length and the current needed. Smaller current and induction also enable coil shapes not circular. Though, neither induction nor the vector potential can be focussed at distance; at best, a subtractive pattern of currents could make the vector potential sharper. As creating the desired fields gets easier, we may consider subtractive patterns... In every case (also at 1ms and 10ms), the turns of the coils should be spread apart where a concentrated field is not desired. This reduces the self-inductance hence the necessary voltage - or current if increasing the number of turns. Marc schaefer, aka enthalpy ============================================= Even shorter pulse times seem possible. With a single thick turn, an 8-shaped coil with both D=70mm loops in series shows about 240nH. It still needs about 200V per turn, but limiting this to 5ns reduces the peak current to 4A approximately, and this is accessible to some RF transmitter transistors. Or have on transistor per loop, at 100V and 4A each. Then, the transistor(s), capacitor (or a cable´s capacity) and flywheel can sit in the coil head, and the cable transmit DC power instead of the strong pulse. Much gets simpler. Can we exaggerate the pulse duration further? Yes, but with an electromagnetic pulse then, not just magnetic. It must have unsymmetric durations if my explanation holds. This one would fully enable to concentrate the field. More later, maybe. Marc Schaefer, aka Enhalpy

I wrote "Newton" preferred to "Force", I see these advantage: If the user means a force but uses kg instead of N, the software will detect it. The software might also check if MPa are used together with mm2, not m2. As a diagnostic, I prefer a synthetic answer like "discrepancy by one pressure", not its equivalent in kg, m and s.

As a sensor for boiling water or oil, I thought naturally of piezo sensors for acceleration or force, but a pickup microphone as on an electric guitar is an interesting option.

My own guts feelings: 20mm diameter needs little blowing pressure, intuitively less than blowing through fine charcoal and ore, and far less than blowing through molten iron. A few big stones at the pipe's outlet, followed by smaller ones (as roads are made), would spread the throughput and reduce the speed, adequate to blow through charcoal. Not so good to harvest molten iron. I doubt about bones. They don't withstand molten iron's temperature and are known to make steel brittle through phosphorus. You can take a few times (3 times?) 0.5*rho*V^2 pressure drop, in pascal, with rho=1.225 kg/m^3, and V in m/s, with throughput=S*V and S=0.0003 m^2 for D=20mm. - With our lungs, 1000 Pa is easy, 5000 Pa is an effort. 1000 Pa would then give 20 m/s or 7 dm^3/s, too much thoughput for our lungs (5 dm^3). Hence D=20mm isn't the limit. One can't blow strongly for half an hour anyway. - With two bags (peritoneum? make the valves of the same stuff) pressed alternately by the hands: press 1kg on 2dm^2 down 0.3 m in 1s, it makes 500 Pa and 6 dm^3/s. That's more or less what fits the nozzle alone, but I expect charcoal and ore to drop more pressure. - Or operate the bags with the feet. 20mm against 23mm up or down won't make a difference for air pressure. The direction of the cone can result from the end where the boring tool was introduced, or where it was removed if the pipe material was clay. Or maybe, if pieces of solid dirt passed the small end, they could remove them from the bigger end. I have on TV seen similar furnaces in operation in remote parts of Africa (as a tourist attraction?). Maybe people could tell you from direct experience?

Hello nice people! Here a bizarre idea to let liquids and gas react together: It's essentially the same hardware used to humidify air: many disks soaked partially in a liquid are rotated; they shall be wetted at each turn to expose a big area of liquid to the gas and promote the reaction. The (better detachable) disks surface is close to the liquid-gas interface and can also be a catalyst, or be itself a reagent, for instance copper-activated zinc. This must be an advantage over other processes, like a mist or bubbles. The gas could also be an other liquid if it's hard to mix - in case no better method exists. One could even superimpose several liquids and a gas, for instance to expose a single-molecular layer of liquid to the gas. It resembles also the heart-lung machine, where rotating disks put blood in contact with air to remove carbon dioxide and bring oxygen: www.ncbi.nlm.nih.gov/pmc/articles/PMC2028454 http://www.ncbi.nlm....j03398-0009.pdf Sub-sub-details: The vessel would better withstand pressure and vacuum. You can fit pumps compressors heater coolers exchangers separators and all that stuff. Screws around the shaft between the disks and the bearings can prevent liquid wetting the shaft from seeping into the bearings - but they won't stop the gas... You can try to inject grease at high pressure in the bearing to prevent leaks there, as usual. At least no chemical has to be pumped to mix in this reactor. You can vary the rotation speed to adjust the thickness of the liquid film. If the disk surface must be exposed to the gas close to the liquid, it could be made hydrophobic from place to place. Corrugations at the disk could even, as the disk rotates, pour the liquid at places that were in contact with the gas. Marc Schaefer, aka Enthalpy ================================== The liquid has its biggest contact area with the rotating disks. This will drag the liquid to make a loop, along the disks at the upper part of the bath, and returning at the lower part. This mixes the liquid in the rotation plane, and as the disks can be thin, diffusion across a few mm can be efficient enough in many cases. The axial direction is less favourable to mixing, with no natural flow there. I imagine the tank's inner face can have fins that take advantage of the loop to create some axial movement as well. A different approach would replace the many disks by a helix, which achieves an additional global axial flow. Or, as disks are simpler to produce and fit, especially if they're consumed by the reaction, a durable helix could occupy the smaller radii near the shaft, and the consumed disks the bigger radii. Or keep individual disks, but cut and warp some fins in them to get an axial flow component. Marc Schaefer, aka Enthalpy

To get the imaginary part of the complex logarithm, which is the argument of the input complex, one can take advantage of the same successive squarings used tio compute the real part. When you square a complex, its argument (its angle, in polar coordinates) doubles, but modulo one turn. So on successive squarings, the sign of the imaginary part gives one bit of the argument at each step. You get the argument in units of turns. This method looks more interesting now. Usable for atan2(r,i) as well but probably less interesting if you don't need a log. Marc Schaefer, aka Enthalpy

The best material is vacuum, and then you've made a Thermos cup. Aid it if needed (not for a cup) by several layers of sheet with low infrared emissivity, in which case it's a multiplayer insulation (MLI). Other possibilities are less efficient. Avoid metals, choose the plastic or ceramic properly, but the good ones are nearly identical. No magic through the material, only the shape. An intermediate method, neither solid nor vacuum, is a foam. Choose a rigid non-toxic one that withstands heat (dishwasher), enclose it between hard protective layers. Something like microballoons in a ceramic might work.

Seen and used some with 3m diameter at La Villette. It works very well, fun and convincing. Do it. Only one person can speak and one listen at a time because the focus is narrow. At La Villette they had sorts of crosshair rings at both parabolas, copy that. But maybe D=15m isn't mandatory for 200m range? Sound quality is perfect, no special noise, BUT I expect wind may bring the sound wave of-axis and then the receiver won't focus any more. Try to put figures on wind shear near the ground. Also, the temperature gradient near the warm daily ground lets sound go up and lost. Maybe it'll work only on calm night, as you can experiment without parabolas: you hear a source from a longer range at night. One more attenuation is when wind blows against the propagation direction. This has nothing to do with a longer path. It's the wind shear near the ground that lets sound go up and lost. Instead of making the reflectors yourself, I suggest to use (borrow!) existing radio dish antennas without their primary source. Usually metallic, stiff and smooth, heavy enough for sound, of precise shape... Perfect. You may assemble D=15m from seven smaller D=5m. You can make the first experiments at D=60cm with satellite TV dishes. One manageable method to produce your own dishes (not my preferred choice) is to make a horizontal shape in sand using a rotated profile, and put fibreglass-epoxy on it. To check material density (kg/m2), compare it with a half-wave of air. It must be significantly heavier. Mind the precision of the shape!

The pressure changes meanwhile. The turbine can harvest PV at most. In a turbine, the transformation into shaft power involves steps where pressure converts into speed - which does mean a change of section, locally where the blades are and the flow direction changes.

In my modernized Apollo scenario, the Leo performance is about 77t from memory. It does need new cryogenic stages but with existing and realatively cheap engines - while the SLS uses new stages with many SSME on some designs. Liquid boosters for SLS: they think of it the wrong way, from the proposals I've seen. They keep the huge expensive central stage with many engines that ignite before launch and just replace the solid boosters with liquid ones at equal performance. The real gain is when you reduce the number of cryogenic engines because liquid boosters bear a bigger share of the performance, resulting in a lighter central cryogenic stage and a weaker acceleration there.

Hi Fizfiz! I must come too late, and this isn't database engineering but numerical analysis, sorry for that... But maybe it serves your later, or someone else. It might be possible - perhaps - to improve the math function library for complex numbers. The libraries I've seen add their layer to functions libraries on real numbers. This can be very inefficient: see how complicated it is to prevent all undue overflow errors in the complex division function given in "numerical receipes in C", a full page of tests and divisions. It is also indirect. For the functions whose real version is not hard-wired but programmed or micro-programmed, maybe the algorithm can be adapted directly to complex numbers. ----- Example: the real division is a multiplication by the reciprocal which is computed by an iterative algorithm, of numerical analysis type, often Newton-Raphson http://en.wikipedia....aphson_division and this algorithm may well fit complex numbers with little effort. ----- Example: the real square root is an iterative algorithm of numerical analysis type, like these http://en.wikipedia....terative_method http://en.wikipedia....al_square_roots again, such a method could run on complex numbers. Here Wiki seems to suggest the standard method http://en.wikipedia...._complex_square which would be pretty inefficient as the moduli demand already a square root. ----- Example: the logarithm. It is computed on real numbers in base 2 using the floating point processor's normalisation. The exponent gives the heaviest bits and is discarded, then the mantissa is repeatedly squared and the exponent gives more bits and is discarded. Could it work on complex numbers? Harvest the biggest exponent of real or imaginary parts, subtract it from both. Iterate: square the complex, again harvest the biggest of both exponents, subtract from both. On complex numbers, I vaguely suppose that the bits of the next iteration's harvested exponent can overlap with the ones already obtained, but if you add the (shifted) contributions instead of concatenating them it may be exact and with no time penalty. By this way you obtain the logarithm of the modulus, which is the real part of the logarithm. ----- There may be other candidate functions: trigo, hyperbolic, exponential... More complicated and less frequent, most special functions are complex by nature. I suppose the Newton-Raphson methods would transpose directly, but for a library, you have to check if they can underflow, overflow, how to minimise rounding errors... Maybe a mere normalisation at the beginning protects the whole function, which would again save time against a complex layer on real functions. Beware I didn't review all existing libraries. Hardware (hi there) able to normalize two floats according to the biggest of both exponents (here considered the real and imaginary parts) would speed up the functions. It should bring the biggest part between 0.5 and 1, scale the other part identically, and return the exponent of the scaling factor. No idea if it's already available. Marc Schaefer, aka Enthalpy

I come too late, sorry for that... but maybe this idea serves someone else - or you for a later project. A piece of software could check that the units of an equation fit together, like: a pressure equals a force per surface unit, not per volume unit. Such an application needs a decent user interface, preferably where the inputted equation can be read permanently. But the input can be made by menus if they're fast and convenient; you don't have to interpret an equation typed as a text by the user. You need to process +-*/^ which includes sqrt(). Users shall know what to do with sin(). I want the application to know constants like µ or h or flux quantum to limit user errors, and I'd prefer to click on "newton" instead of "force". The application can be limited to SI units, but it must know less frequent units like Jansky or Eötvös, and of course optics and radioactivity units. A user will typically launch the application in areas he's less easy with. This is where the application improves over hand-checking. Possible refinements, not urgent: - Other unit systems, especially CGS - Unit systems that take c=1, h/2pi=1, µ=eps=1... Nice small project, and it would be really useful to many people from time to time. Marc Schaefer, aka Enthalpy

Here are eventually some wave forms, click to magnify: I've sketched N=5 for clarity, but real apparatus will probably use a bigger N. Wave forms are idealized; natural ones are smoother, and shall be to protect the components.

Charges added or subtracted to this insulator. Insulator means only that said charges will have difficulties to move.

Up to now, supplied power increases the current quickly in a TMS coil, which must be the neuro-active phase when the induced electric potential gradient is strong, and a passive circuit lets the current decrease more slowly, in which phase I postulate the electric potential gradient must be below a threshold so it doesn't cancel out the effect obtained in the active phase. If this model holds, an other operation mode must produce the same result, where the powered phase increases the current slowly in the TMS coil, inducing a limited electric potential gradient, and the neuro-active phase brakes the coil current quickly to induce a strong electric potential gradient. (This must apply as well when the pulse is not split.) In this other operation mode, the circuitry first supplies a moderate voltage to the coil to accelerate the current, then interrupts the current brutally, which results in a strong electric potential in the coil as well. Very similar to an engine's spark ignition circuit. This operation mode seems advantageous: The smaller electric potential gradient, which I suppose is the more delicate phase, is better controlled as it results from the supplied voltage; The brutal phase, when both U and I are strong, can flow in the circuitry through a diode, which is more robust than a transistor; The circuit example here is simpler. The diodes and transistors must withstand the inductive overvoltage when cutting the current; the supply voltage is much lower, roughly in the same ratio as current fall and rise times in the TMS coil, for instance 10 times lower. The inductive overvoltage is defined through the brake voltage in this example. The power supply provides less peak power now, but the brake circuit absorbs more, and the transistors must cut the full I at full U, uncomfortable. If the brake windings have as many turns as the accelerating windings, these windings can be coupled very closely to protect the transistors, and can even be the same winding - but with the same number of turns, the brake voltage is much bigger than the supply voltage. A different choice uses fewer turns at the brake windings, and injects the brake current directly in the supply. This limits to a fixed ratio between the current rise and fall time, which can be switched if additional brake windings provide different numbers of turns. The transistors demand a separate protection then. Anyway, circuitry to protect the components (and preferably soften the transitions) is necessary, though not drawn on the sketch. Marc Schaefer, aka Enthalpy

If you know TMS apparatus that already work like this, don't hesitate to tell. Or if you know reasons why the brains shouldn't react the same way when the pulse is split. Just as examples of discussion subjects.

Electrons are waves. In an atom, they are the orbitals (at least, pairs of electrons are). 'Point-like" only means that if one uses a very localized particle to sense an electron, he doesn't find a sub-structure to the electron. According to the probability density, sensing for the electron in a smaller volume results in a smaller probability of the electron to interact with the sensing particle (...if no other factor influenced their probability!) but the whole electron interacts then. "Point-like" does not mean that the electron is a point located somewhere randomly in the orbital.

Do you have two successive gaps of 0.5mm each? Then they share the 100V equally, so you can deduce the field. For the charge, you need the capacitance, which results from the area and the gap. Air has nearly the same permittivity as void (a few 10-4 more).

Hi Bob! Nice big way to do it. 5 years are a short delay, but hey, Apollo didn't have much more and it was the first time. This scenario exposes astronauts to long transit times, a drawback. I've put a very different scenario, nearly identical to Apollo, at SaposJoint. Far less ambitious.

Cotton wool should be a good candidate provided it absorbs IR well. Its filaments' heat inertia is tiny, and the autoignition temperature is low. Protect well from wind. Possibly better than tinder. I used cotton wool as a child (a long long time ago!) to make fire when my mom hid the matches for incomprehensible reasons.

A well designed TMS coil can have 1ms time constant, real ones have a bit less, but operation at N=10 or N=100, with fall time shortened accordingly, needs to brake the current actively. The brake circuitry (a lossy freewheel if you wish) is less than obvious, because the brake voltage is (say 10 times) less than the supply voltage, and the brake circuitry shall not misfire during pulse rise, despite users want pulses of both polarities with few ms between inversions. Here's a circuit example: An IGBT opened long before the pulse decides the polarity. The TMS coil could have been connected between these collectors, but the second transformer insulates the TMS coil and permits a direct gate control. A big E ferrite core suffices for such a transformer, so I feel this combination easier. The left IGBT defines the rise time of the current pulse, and the supply voltage defines the rise rate. On this sketch the resistor sets the current fall time in the coil. Operation at big N is meant to reduce losses in the TMS coil, but here most supply power is dissipated in the resistor. While this power is smaller than at N=1, and the resistor easier to cool than the TMS coil, one may prefer to reinject the energy in the supply. A third winding can help this, but since the voltage and current must already challenge the existing main switch technology, this winding shouldn't step up the voltage, so the power dump rail must have a lower voltage than the supply. An adjustable power dump rail would control the fall time independently, and a braking voltage constant over the pulse may improve the TMS operation by limiting to a uniform plateau the induced electric potential gradient. The rail must accept and transform power but be pre-loaded before the first pulse. Several braking windings of different voltage ratios may help. I preferred to draw a resistor on the sketch At high N operation, hence with shorter commutation of a smaller current, MOS must be better than IGBT. Soft commutation (resonance) would be nice, except for the clarity of the sketch Marc Schaefer, aka Enthalpy

A mineral much more magnetic than we have isn't expected (at least from me...) because iron, neodymium magnets... show a significant fraction of the strength electrons can produce.

Hello everybody! Neurology uses Transcranial Magnetic Stimulation (TMS) for research and sometimes diagnostic and treatment. Introduction there: http://en.wikipedia....tic_stimulation Some documentation there, but other manufacturers exist: http://www.magstim.com/ As I understand it (but beware I'm bad on biology and neurology), not the magnetic field, but the gradient of electric potential and current it induces, creates the desired effect on the brains. The action resembles partially an electro-shock, but: The skull is tranparent to the magnetic field, while it hampers the electro-shock's current; Hence the skin isn't as brutalized by TMS; The path of the current and the intensity are better controlled; This lets concentrate the effect to some cm2. Since the gradient of electric potential is the time derivative of the magnetic vector potential A, the average of the gradient over a cycle is zero; I understand a net electrochemical effect is obtained because electrochemical reactions are non-linear (they often show a threshold to voltage) and the pulse is made asymmetric, with a sharp current rise that induces a strong short gradient, and a long current tail that induces a weak long gradient. A pulse can have 100µs rise time and 1ms fall time. Series of pulses are also used, sometimes of alternate polarity, but always with pulses of asymmetric transition times. A good gradient of electric potential needs a strong magnetic induction, and in these non-permeable materials, this means kA in a coil, many kW pulse power, and as a result, the coil is very loud and gets warm, which limits the duration of a session or demands active cooling. ----- I propose to split each pulse into N shorter ones, scaling like that for understanding: Individual pulses are N times shorter, both at rise and fall time; The reactive volts per coil turn are kept the same; Hence the rate: amps*turns per time unit is unchanged; And the amps*turns are divided by N. The effect on the brains should keep unchanged when introducing N, because: The electric potential gradient, which results from the rate of change of the magnetic potential, is unchanged; (if you prefer, it varies as the volts per coil turn, which are unchanged) The cumulated duration of the electric potential gradient is unchanged; The proportion between rise and fall time, hence the ratio of electric potential gradient is unchanged. Beware a few things can go wrong here... For instance if some electrochemical reaction needs a consolidation time before it withstands the inversion of polarity of the electric potential gradient. As usual, I didn't check if this was proposed, tried and possibly abandoned - sorry for that - so interested readers should. Provided the desired effect is still present, splitting the pulse provides big advantages to the apparatus: The current is divided by N, but the duration remains; Consequently, forces in the coil are divided by N2; The coil's deformation speed after N shorter pulses is divided by N, and the noise power by N2; The energy dissipated in the coil is lowered. By less than N2 because losses increase with frequency; Electronics can deliver N times less current if the voltage is kept, and the energy is N times smaller. Transition times divided by N may cool down the enthusiasm of electronics designers. As well, it requires probably to brake the coil current actively, for instance with an H bridge, or braking diodes reinjecting current in the power supply, possibly by a secondary winding somewhere. A transformer before the coil can bring advantages: match the cable's and coil's impedance to the power supply and switching components' possibilities; have a separate winding to brake the current; produce inverted pulses by an other primary winding and two switches instead of an H-bridge. Coils should be made of so-called Litz wire (probably a wrong translation for "braided wire"). In fact, if this isn't already done with 100µs pulses, it should have been: this limits the heat in the coil but may demand a current braker. The current braker could even be a series resistor, easier to cool than the coil. Shorter pulses demand wire braided more finely, which reduce the wire's section filled by copper, so the energy lost in the coil is divided not quite as quickly as N2. Marc Schaefer, aka Enthalpy

Casing and cementing applies only locally to the bore. In a traditional reservoir, hydrocarbons have been held in place for millions of years by a tight capping geological layer, which is not the case in shale. Without the natural cap, and if fracturing the rock, casing and cementing won't help a bit. I'm fully confident that fracturing, which is conducted from kilometres distance, without sight, in an imprecisely known terrain, will sometimes extend beyond the compact rock into permeable terrain, letting hydrocarbons leak. Even if oil companies were Nature-minded (History shows, err, exceptions) errors do happen, and they are logically more probable - understand, more frequent - with shale oil.

You don't have to theorize it because many people have done it, especially for fun. Spectacular, but little happens with nitrogen. The heat source for evaporation is not the atmosphere but the much bulkier ground. It evaporates nitrogen in few seconds or less if you disperse it properly. 27m3 air in the room weigh already 30kg of which 25kg are nitrogen so 1kg nitrogen isn't a radical change. The resulting mix after some time, as evaporated nitrogen would cease to pick heat from the ground as a gas at -196°C, would be some 6K colder than initially. After much longer, the walls will bring the air back to temperature. The overpressure would correspond to 1/30 more moles but brought in at 1/4 of 300K, so about 1/120 more pressure or 8mb, climbing to 1/30, hours after. If the room were completely hermetic, you would feel it in the ears. I suppose the walls and windows resist, but I'd open a window in advance. I strongly recommend NOT to do it with liquid oxygen. This is a seriously dangerous stuff.