Engineering

What are the main reasons centralized electric networks use alternative currents aside the fact AC/AC transformers are cheap and is it guarantied we will never switch to DC in distributed electric systems? Can we design a bipolar DC outlet? What about DC/DC converter prospects?

Krypton-85 85Kr is a beta emitter with 687keV maximum energy and 10.7 year half-life. It's produced by uranium fission with 0.27% yield (137Cs and 90Sr: 6%). Here a report, a bit old and in French, but figures read the same in English anyway. 85KrIpsn.PDF When reprocessing used nuclear fuel rods at La Hague, solid fission products like 137Cs and 90Sr and separated for storage, but 85Kr is just diluted and emitted in the atmosphere. For instance in 1999, La Hague emitted 2.9*1017 Bq of 85Kr, more than the radioactivity of 137Cs and 90Sr released by the Chernobyl disaster. Iodine, caesium, strontium radioisotopes fall on the soil more quickly and locally if emitted…

Hi all. Magnets inside hard drives are bracketed by mu metal. Is the outside plate seen in some hard drive covers also mu metal ? Like the greyish portion on the cover below: The covers without an attached 'plate', are they usually made of mu metal ? Cover alone :

Hello everybody! We read again and again "Face-centered cubic metals are ductile, body-centered are not, while hexagonal close-packed are brittle". Some authors want even to justify it through numbers of slipping planes. Worse, a few ones would curb Nature to their reasoning if only they could, like "Ti-Al5V is brittle because it's a hexagonal alpha alloy" or "Zinc breaks upon bending because hexagonal" - no, I won't tell you who wrote that one. About every metallurgy textbook has a crystallography chapter that reproduces this nonsense, and I'm getting tired of it, so I've just made a table with metals of mechanical use. Most metals go against the claim. Observations…

I would appreciate any advice on finding the best insulation material for my food carrier. I have been testing an insulated reusable/returnable one hand-held carrier design to hold freshly prepared food hot as to be delivered. It works, but the heat retention is insufficient. The temperature is good for 45 minutes. It is made of blow molded polyurethane. I want to improve the heat retention to as long as possible, two hours! I have tested ways to maintain the food for a fresh appearance. Numerous material were tested, money was spent and lessons were learned. High-density Styrofoam, low cost, in different applications had good insulation quality but required too man…

The stem body with the motor, gears and batteries does not counter-spin in this stirrer gadget, it still manages to revolve the thick sauce/soup. How is it achieved ?

I usually sit next to a window at home and I hear that 80% of UVA penetrates glass and UVA is what causes aging. So my skin has been exposed to unecessary aging for years. I bought blackout shades. But I am concerned that they might be facing the wrong way. My question is. If blackout shades/blinds face the wrong way 1)would more UVA penetrate into my apartment than if they faced the right way? 2) IF UVA does penetrate, would it then bounce off the the walls and hit the blackout shades (which are facing the wrong way and which allowed UVA im) and then reflect back onto my skin again - so then my skin would be hit by twice as much UVA than it wo…

I get an increase in payload of ~5% using gravity feed tank to tank, 2 extra bulkheads in the boosters (mass not accounted for), LOX tank at bottom of main core (which may need some extra plumbing – mass not accounted for). Not really worth it? It seems throttling back the core engines to 70% reduces crossfeed advantage, but it seems like throttling back incurs some loss I haven't accounted for? It looks like this - stacks represent core and boosters tank placement. red is RP-1, blue is LOX, green is crossfeed LOX. Main core mass LOX: 243t (always metric tonne) RP-1: 161t Total mass: 404t Booster mass L…

Hi all, Im inventing a new product and need some advice as to what material i should use to create part of it. The goal is for it to be a clear material, thats heat resistant (wont bend or misshape) when a lit cigarette is touching it. Basically i just need to figure out what cheapest compound can be used as an ash tray almost. If i need to provide clearer instructions as to my request, just ask. Thanks!

Good day looking to build a electromagnet that is very powerful and curious as to best power supply(110 or 12 volt) unit will be made from largecopper coil I will source and will have a 24 x 24 inch metal plate on top unit is to attract metal filings from our small milling mill (prototype) that I will attempt to build on our farm with my son unit must be very strong able to pull metal from at least 4 inches away. Any help with materials list greatly apreciated regards steve

Hello all, I'm doing sorption studies of certain heavy metals (Pb, Cu, Zn, Ni, Cd, Cr) in soil (natural clay and kaolinite) with ph as a variable (2,4,7,10,12).On adjusting pH to reach a constant value using NaOH and HCl, my heavy metals in nitrate salts form are getting precipitated. thus unable to maintain the concern concentration (50ppm, 250ppm, 500ppm, 750ppm, 1000ppm). help me out please.. thanks in advance.

Or How To Sail The Cosmos. Any takers?

Want to learn how a 2500 watts PEL Hi-Power electronic stabilizer works? It does not provide 220 volts although values mentioned on it are as: Input = 90V - 250V Output = 220V I opened it and it has two meters which show input and output voltages. It has a transformer (not sure step up or down). It has a circuit which have 2 10A relays. Relays number is H200Fd12-10A. This circuit also have two rotating screw like things which can be adjusted to increase amperes or decrease amperes as one of person while repairing told me. The problem I believe is with this circuit. I am ready to change whole circuit along with relays. The maximum size relay I can get is 30A relay…

Turbofans work by burning jet fuel to spin turbines, ultimately powering the massive fan you see in the front of the engine. Could you substitute the jet fuel with liquid hydrogen and, in theory, make a jet plane that produces no CO2

I have been working on a rocket engine and I have cad models and everything and I am getting ready to build it. Then, I was running over the numbers one more time and I realized that the thrust I was getting was completely different from what I should have been getting. The big problem is the nasa equations. It uses the variables Ttotal and Ptotal. NASA states, "pt is the total pressure in the combustion chamber, Tt is the total temperature in the combustion chamber." However, when I plug in 300 psi and 5742 degrees fahrenheit and the exhaust values for each variable as given by NASA's isentropic equations, I get a thrust of 735 pounds, whereas the first time…

A strange conundrum: nowadays whenever I try to play my Blu-ray edition of 'The Lord of the Rings', I get plenty of video, but no audio. That's to say there's audio throughout the preamble (adverts etc) that comes before the main feature starts. But as soon as the actual cinematic part of the disc begins it goes completely silent. The same problem exists on all three discs - though, interestingly enough, it doesn't occur on any of the special features discs bundled with the boxed edition. They come out loud and clear! No other Blu-ray film or DVD of mine has this weird and wonderful audio issue. They play just fine. It occurs only on the three LOTRs discs - and then it's …

A cool air turbine with a tubular duct that runs from its exhaust to its intake. Would the air speed in the duct be faster due to vacuum force rather than being open ended? Would the turning force on another inline turbine introduced into the duct system be greater or less? Would the air speed decrease after the added inline turbine to the duct system? This is not homework help its things that I have been thinking about due to a hobby project I been woking on but have no way of measuring air speed or turning force. I think it would increase airspeed and turning force on second turbine. I also think once the second turbine has spooled up too spee…

How do they make hydrogen tanks(I also need a oxygen tank, but I assume that it works the same way). If you blow hydrogen into a tank, how would you get the air out? With a gas tank, you're working with a liquid, and a gas, but for gaseous hydrogen, how would you push out the air, and put in hydrogen, without pushing out hydrogen in the tank? Also, how much volume would you need to fit 1 000 000 000 000 H2 or O2.

Hello dear friends! Heterojunctions are produced by deposition (often epitaxy) of a semiconductor on an other to achieve excellent components. Silicon being the most commmon material, Si1-xGex is used as a material with a different bandgap, despite the drawbacks of germanium: lattice constant very mismatched, main electron valley in <111> direction versus <100>... As opposed, the GaP crystal is known to resemble Si closely: same zincblende lattice (called diamond when the atoms are identical), lattice constants matched to 500ppm, main electron valley in <100> direction too. GaP's bandgap is also bigger and differs more from Si, nice. http://www.ioff…

Another (possibly silly) idea for a moonbase habitat, hopefully the last for a while: The latest ideas for moonbase as put forth by ESA is a 3D-printed shell made substantially of lunar regolith. https://www.space.com/19602-moon-colony-3d-printing-lunar-dirt.html Robots would be sent ahead of crew landing to build the base out of material sent from earth with in-situ resources. This seems ambitious to me on the how many things can go wrong front, though I admit it is very cool. So my idea is more pedestrian. In a previous thread I suggested using landed/crashed propellant tanks http://www.scienceforums.net/topic/110982-lithobraking-f…

What is the operating limit for which electronic devices work properly? In the US we see it is 60 Hz and in other parts of the world it is 50 Hz, so what are the upper and lower limits for which a device can operate properly?

How to cheaply and efficiently power a Moon Base. Powering a Lunar Moon Base isn't simple because the moon is in shadow for long periods of time. Solar power must have weeks of backup which would require a lot of batteries or some sort of backup generator that runs on maybe hydrogen and oxygen. Solar panels must be oriented to the sun to maximize efficiency, or more panels must be employed. One idea is to place the solar panels in space, perhaps at EML-1 and beam the power back to the moon. This still requires a very large array to capture the energy on the moon. This idea is similar, it uses a satellite in a polar orbit such that it is always exp…

A rotovator/lunavator with a 200 km long tether rotating in space above the lunar surface drops momentarily to swap a large battery pack (mass of 250 kg) for a depleted one to be charged. Is there a simple and effective mechanism that would do this? If the operation is too fast for a release then a catch, maybe two "bays" could be used. Instead of exchanging position on the tether on route, the base (where the exchange takes place) could coordinate which side or position is open when the exchange happens so that the spent battery can be placed at the correct location. Some king of catch and release mechanism - hook and eye? Ideally, an object in flight could als…

One year roundtrip, 30 day stay to Mars. Is it possible with solar thermal engines instead of nuclear thermal? https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140009587.pdf We can assume Earth and Mars capture orbits for the solar thermal part and chemical rocket to and from capture orbits. Perhaps with slower unmanned propellant drop missions ahead of mission if necessary.

It sounds really stupid at first - a survivable crash landing... The idea is similar to aerobraking where regolith is used to decelerate a space ship. Not one with humans aboard of course, it's a crash landing and bad things can happen. So bring the elliptic orbit of a ship to a grazing height and touch down, then skid along the lunar surface. But what can this get us? A bunch of otherwise useless upper stages of rockets could have their material recycled once dropped onto the lunar surface. If we do this enough times, we might become able to clear out a runway or learn how to do it without much damage, then more sensitive stuff could be "landed" this way. …