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  1. E

    Chinese fuel reprocessing plant, store Kr-85

    Hello everybody! Areva is supposed to build a plant in China to reprocess spent nuclear fuel (agreement hoped in Spring 2018). I should like to remind that the radioactive 85Kr fission product, which stays in the fuel rods until they're opened, can be stored easily until it has decayed, as I...
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    Gravitational Interferometer and Kalman

    Hi Drakkith and the other, thanks for your interest! Well, if someone has already seen a Kalman filter at a gravitational wave interferometer, or knows the function of the auxiliary mirror of Kagra, or knows a better reason why Kagra's chamber will be so cold, or has seen light cooling...
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    Gravitational Interferometer and Kalman

    Cooling by light needs the de-excitation to be almost always radiative, and meanwhile I doubt that shallow acceptors in a semiconductor de-excite radiatively: angular momenta may well forbid it. A three-level scheme should be better, where heat populates partly a shallow acceptor level, light...
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    Gravitational Interferometer and Kalman

    Kagra's main Fabry-Perot mirrors absorb 400mW of the light, to be evacuated from 20K where radiation would be difficult. Kagra foresees several wires of pure aluminium, thin and long so their thermal noise shakes the mirrors very little. Far less simple, but it should be quieter: I suggest to...
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    Gravitational Interferometer and Kalman

    The Kagra or Lcgt project, a cryogenic gravitational wave interferometer being built at the Kamioka mine in Japan shows a secondary mirror and beam in but-last position of the suspension chain, resembling much what I describe. See figure 4 of: "Present status...
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    Gravitational Interferometer and Kalman

    The D=1.25m vacuum tube of Ligo is made of 3mm 304L stainless steel with stiffeners and perhaps maybe 4mm of aluminium extrusion are cheaper. Whether the longer weld seams are affordable is unclear. Also, the steel was baked at 444°C to desorb...
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    Gravitational Interferometer and Kalman

    The Kálmán filter doesn't need a second tube - good, since the tubes make much of the observatory's cost. Movements assessed at each end of the tubes can feed the filter. I propose here to keep the observation of noise by light and deep at the suspension chain, as this is cleaner than an...
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    Gravitational Interferometer and Kalman

    Hello everybody! Extreme interferometers like Ligo, Virgo, Leo600, Tama300 try to detect gravitational waves and ground movements are one difficulty for them. The mirrors are suspended in several stages to insulate them, sometimes...
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    Train brakes by lack of pressure?

    The pressure in the reserve brakes when there is no pressure in the brake pipe. This is intended, so that uncoupling the wagons from the locomotive let's them brake automatically. To move the uncoupled wagons, one has to manually purge the reserve.
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    Train brakes by lack of pressure?

    I check this point precisely because I won't take as secure information what the train company tells and the Press repeats. Here's a doc telling that automatic air brake is the standard in Canada, and that brakes apply by decreasing pressure in the brake pipe...
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    Train brakes by lack of pressure?

    Thank you! The patent claimed and exploited by Mr Westinghouse in the US describes a brake that releases by pressure and brakes by pressure drop. He sold enough of them to grow a big company. When was that abandoned? Sorting out wagons by a hill is done in Europe as well, so there is some...
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    Train brakes by lack of pressure?

    Hi! An attempted explanation for the tragedy of Lac-Megantic is that the only running locomotive was shut down by the fire brigade when extinguishing it, and as this locomotive stopped to provide pressurized air to the train, the wagon's brakes opened and the train ran away. Which I can't...
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    External Torque-Force Relation of Bolt

    Agree with 10.2kN. For that force, a 30mm bolt is hugely oversized, requiring too much torque. The fine pitch needs too many turns but doesn't reduce the torque. For comparison, an M16 10.9 pulls 100kN at usual pre-tension. The torque results essentially from friction at the screw: - At the...
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    Assistance needed with Paraplegic Wheelchair Design

    You can put force sensors at varied chair locations in contact with the body: buttock, back, shoulder blades... The biggest difficulty I see, independently of where and how, is that the user wants to do more in the chair than move. You need some way to tell the chair not to interpret every...
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    Solar Thermal Rocket Engine

    I have such mission designs in the pipe, sure... I had investigated them in 2010 but with a wrong isp. Now with isp=1267 by a more detailed design, they still look interesting, including a Mars scenario where both the transit and the stay are short. Preset much in Martian orbit. I considered...
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    Physical basis for high-bypass turbofans

    Agreed. Accelerate much air a bit consumes less than accelerate little air a lot. Hence by-pass. If the aeroplane speed allows it, prefer even wider turboprops. And for a helicopter, take a huge rotor.
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    Turbochargers, what's the diffrence between the turbine and compressor

    Hi James125! Some photographs show a larger compressors, others not - comparison not obvious. Gas speed determines the tip speed of the wheels, not the (marginally different) mass flow. On a centrifugal compressor, gas speed is a bit lower than metal speed, with the blades curved...
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    Acceleration effect on buckling?

    Ariane 5's core is pulled by its boosters, not pushed. This avoids buckling and saves dry mass. Pushing it means a redesign. Doubling a wall thickness: - Doubles Euler's buckling force, for the stage buckling globally in flexion as a beam, which is rarely dimensioning; - Quadruples the local...
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    Notional passenger electric aircraft from EADS: Ceiling?

    Eads' concept gets power from the gas turbine and transmits it electrically to the fans. Batteries serve for short thrust increase at take-off, and to store regenerative "braking" (descent). Its ceiling is hence the same as other jets, resulting from the gas turbine and the wing. Getting...
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    Acceleration effect on buckling?

    Hi, buckling is evaluated (and avoided) by considering stress, but in an in-line launcher, a constant thrust can produce locally increasing stress as the tanks deplete and the acceleration increases. ----- In a upper stage or a payload, the stronger acceleration provided by the lighter...
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    Solar Thermal Rocket Engine

    Hi RGClark, nice to meet you here! The biggest advantage I see to the Solar thermal engine is its moderate collector area. It results from: - The intermediate isp (specific impulse, similar to the ejection speed). More than a chemical rocket, enabling high-energy missions (I haven't detailed...
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    Solar Thermal Rocket Engine

    A Falcon-9 shall illustrate the transfer from Leo to Gso (log into magnify the sketch). Starting from Cape Canaveral, the launcher puts 10,0t on a 28,5° 400km orbit. The Falcon may need reinforcement for the longer fairing. Minus the adapter, the transfer stage starts with 9350kg. To provide...
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    Solar Thermal Rocket Engine

    To bring a payload from Low-Earth- (Leo) to a Geosynchronous Orbit (Gso), a Solar thermal rocket would use its small push all the way to save time, but this takes more performance than the usual very elliptical transfer (Gto). From an equatorial Leo (sea launch, Alcantara...) the required...
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    Solar Thermal Rocket Engine

    The attached sketch suggests how the chamber could be made, I believe. It's a bit exotic in 2013, as Solar thermal rocket engines still don't exist, so more brainwork is needed between this description and an operating engine. It's made primarily of tungsten, probably alloyed with some...
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    Solar Thermal Rocket Engine

    Much Sunlight is needed, so the launcher's fairing limits the concentrators, say to D=4.4m, and most uses will have several concentrators. They can consist of metal honeycomb, similar to satellite antennas, with an improved reflecting surface. One chamber per concentrator gives redundancy and...
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    Solar Thermal Rocket Engine

    Dear visionary inventors, megalomaniac engineers and audacious explorers, Chemical rocket engines aren't up to our desire to hop in the Solar system: go quickly to Mars, deviate Earth-threatening objects, and so many more missions. We need a higher ejection speed to save propellant mass, but...
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    Will increase in order bessel filter in any way contribute to noise?

    Hey, one first subject where I disagree, although only partially, with Sophiecentaur! :biggrin: As EEG signals are at low frequency, I prefer to pass the full DC up to the digital signal. Digital processing can remove the DC component and still react quickly, while analogue circuits that cut...
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    How to find impulse response.

    The output is the convolution of the impulse response by the input. So if having the input and output, you "could" de-convolve the output by the input to deduce the impulse response. Though, this is an inverse problem! The equations may look good, but the precision of the result may be...
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    Can someone explain the operation of this NAND TTL

    The logic function results perfrectly from a two-diode approach. So much so, that LS-TTL and ALS-TTL do use Schottky diodes instead of multi-emitter transistors. When having no fabrication process with Schottky junctions, the multi-emitter design had some advantages for the desaturation time...
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    Ferrite bead usage

    EMI is difficult and very much experimental, so what one designer does results primarily from his habits. Because EMI worries take so long to solve, and a ferrite bead or decoupling capacitor or voltage regulator is cheap, experimented designers use to put more than strictly needed, in...
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    How much rocket fuel is burned in the first mile/kilometer?

    Single stage launchers to orbit have not been done. Performance would suffice easily since several decades ago, but an SSTO wouldn't be very efficient. Additionally, it would need an engine that throttles much stronger than they presently do, so the acceleration remains bearable at the end, adn...
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    Steam Turbine (SST-9000)

    The steel for blades of steam turbines is a martensitic stainless. It's similar to the common X20Cr13 or 1.4021 or Aisi420 (0.2%C, 13%Cr) with slight improvements. I've forgotten the details, but expect a little bit of Mo and V - possibly Ni as in Pelton water turbines but not necessarily...
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    Steam Turbine (SST-9000)

    25Hz or 30Hz is the usual rotation frequency for a steam turbine in a big power plant. One limit to the tip speed is the material's strength, but it's more relevant to gas turbines where power vs mass counts, that is on aeroplanes. In a power plant, efficiency is more important, and it tells...
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    Forumlae for delay in pair-wise twisted single conductors for frequencies>10MHz

    What distance! And what insulator, shape, size... Depending on that, you can receive a delayed pulse, or more often, a thing hard to recognize, because of dispersion.
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    Induction oven, ferromagnetic

    Possible explanations: - Wiki botched it. It does happen. - Losses result from induced current, but only because the skin effect increases the resistance, and the skin is made much thinner in ferromagnetic materials. Why shouldn't you try to put some figures at it? Search for "Kelvin...
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    Why is there no fibre for microwave (or other) frequencies?

    At THz frequencies, metals are too lossy to make a line or a guide, and researchers use dieletric guides and antennas. Use at lower frequencies is uncommon just because of the dimensions. But "cigar antennas" are dielectric guides, of reduced diameter so they radiate. A few materials (PS, PP...
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    Induction oven, ferromagnetic

    An induction cooker for instance creates losses by magnetic hysteresis. It works only with iron pans, not copper. Some other induction heaters are designed for other materials, work at other frequencies, and prefer simple conductive material.
  38. E

    Differential BJT

    Because Q1 pulls the emitters to +0.3V while Q2 can't sink the voltage. It results from the non-linear behaviour of bipolar transistors, whose emitter current increases brutally if the base-emitter voltage exceeds the threshold. By the way, 0.7V is not a universal value. A low-power bipolar...
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    Energy required to demagnetize Iron.

    It depends fundamentally on the alloy and its history (cold work, temper...). Between steel magnetically hard and a very soft alloy, the energy varies by >1,000,000. Then, this energy can be computed from B and H but it's a minimum value that won't reflect the true expense. The minimum...
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    Good ideas concerning shortening and lengthening electrical impulses

    Same reaction: add the circuitry, if it's a matter of 5ns. Things like pulse compression exist, but are meant for very short pulses or for very high energy. As well, users don't expect nice waveforms from these circuits.
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    Phased Array Radar

    "Objects in space" sounds like "big distance"... People use to search for orbital debris to avoid collisions, and at a few 1000km range, 5cm tends to be the absolute lower limit. Did you already check if you can detect one single object within a single pass? At 800km altitude, objects appear...
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    Oscillator with third and fifth order terms?

    Added even terms would let oscillate as well. They are negligible if your system has an odd response, that is, its transfer function is odd, and then the even components of the series expansion are zero. Many materials behave symmetrically hence build an odd transfer function, but this...
  43. E

    Measuring the permeability of metallic objects

    Permeability of materials is normally measured on purposely-made toroidal cores, to get sensible values. In normal life, if these objects are undesired, they have unit of infinite permeability. Often accurate enough, because air gaps rather than metals determine the flux. Or take 1000, then...
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    Conductivity of metals at 0 kelvin?

    If you measure conductivity, you apply a voltage that moves electrons. No need for entropy. Beyond this, experimental data exists for very low temperature.
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    Escape velocity from solar system

    Agree with answer #5. To add my 2 cents worth: - 42.1km/s is sqrt(2) times 29.8km/s (circular orbit) - The effect of Earth's attraction IS the 11.2km/s escape speed - The real cost for a launcher depends on if it launches eastward to take advantage of Earth's spin, how strong it...
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    Throttling Ideal Gas

    Even with an ideal gas, this sort of thought experiment is very misleading and about impossible to make in practice... First, the gas would take the temperature of the capillary. Then, the gas that at some time remains in the bottle pushes the gas that goes out, gives a work, and loses...
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    How much circuits knowledge is required for device physics?

    Knowing circuitry would be very useful. Though, this doesn't meana course. Reading papers like Elektor would be at least as good (well, I mean, far better). Books for amateurs exist as well, also better than a course.
  48. E

    Bending of antenna

    In parallel wires, the curernt would flow in opposite directions, cancelling their radiation effect. The V antenna has nearly-parallel wires, but they are not parallel, and the small angle makes the radiation.
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    OP amp configuration?

    This circuit is used to create an equivalent feedback resistor bigger than the values available. Say, with 10Mohm feedback and a divider by 100, you have the equivalent of 1Gohm. Useful to improve the low-frequency response with your capacitive source. Though, one should be aware of the...
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    Warming a laser diode using a thermistor

    I didn't expect a laser diode to bet less efficient at cold. Could it be the battery that weakens at cold? They are known for that.