Enthalpy

Since I've had worries after thinking at the following, I make it public. Three uneasy processes are known to separate Hf from Zr according to Wiki, for instance the fractional distillation of HfCl4 and ZrCl4. In addition, I propose to separate gaseous HfCl4 from ZrCl4 by centrifugation. ZrCl4 sublimates at 331°C=604K where HfCl4 has 1.7atm vapour pressure. RT=5022J/mol there. A lower pressure improves a bit. A tube of 2000MPa Maraging steel can rotate at 416m/s with 20% margin. Ti-Al6V4 and AA7075 would be good enough too, and graphite fibres much better. Neglecting the isotopes, HfCl4 weighs 87g per mole more than ZrCl4: that's 29* easier than uranium enrichment. The kinetic energy differs by 7528J/mol or 1.50*RT, so after some 10 stages, the metals are pure. Marc Schaefer, aka Enthalpy

Here in old Europe, a wind turbine is paid by the electricity sales in about 10 years, which is an excellent investment. The returns on real estate are slower, on improved bank accounts too. Though, it means a big wind turbine, like 1-3MW, that produces electricity injected in the mains. Smaller investors often join their capital to pay one turbine. They often include farmers for which a wind turbine wastes only a few sqm at one corner of a field.

If the conductor is good enough, maybe you don't need to cut it in sections. Sections would let you observe a potential difference along the length direction, which may be small and uninteresting. That would leave you with a two-dimensional problem, easier to solve. Can you tell us more about the situation: is the current injection in the ground intentional? Is the conductor B a safety against current injection, a measure electrode...? Are you assessing the composition of the ground? Because, for each purpose, there are better electrode configurations, and these use to be easier to compute as well.

I hope nobody feels excluded! Reducing a forum to a dialogue would be missing chances. Baltoche, if you permit, I put here your diagram - ask the moderators to remove it if you don't want it. If the conductors are clearly longer than the depth, consider they're infinitely long. Then a leaked current per unit length I/L gives at radius R a current density I/(L2piR) for the complete cylinder. The voltage gradient is rho times bigger, and a voltage difference is the integral, hence the resistance is Log(Rbig/Rsmall)*rho/(L2pi). This holds for one electrode only that injects current. From where the current returns, you get a similar voltage but with opposite current sign, so the position of the return contact is vital. And for the half-cylinder, double the resistance. The voltage is finite only between two radii. One may take the electrode's radius in some cases, but the quality of the contact makes this doubtful. A better case is the already suggested four-point protocol, which works also with cylindric electrodes, and relieves the dependency on the contact resistance. Are you from a French-speaking country?

I don't hear any strength in this instrument. But blatant weaknesses, a lot. This violonist could conceal more or less the instrument's inability to produce clear attacks, but she will never want to play such a horror. It's unusable. Whether a decent violin can be produced of thermoplastics, I doubt it. The very first step would be to adapt the design to the material, not reproduce the shape of a wooden instrument. But flexural waves are so much slower in thermoplastics than in light wood that the task is probably impossible. Integral stiffeners would improve only the lowest modes. Graphite fibres are a better candidate for the speed of flexural waves, especially as a sandwich. Then, with proper damping and a redesign of the instrument, maybe perhaps. By the way, violin design and craft shouldn't be understood as hideout of conservatism. Many makers experiment, not few of them are excellent on acoustics, sometimes academics (try to) add their knowledge. Aluminium and copper alloys have been tried, graphite too, other shapes as well, so one shouldn't expect success with an attempt as elementary as reproducing the shape out of plastic. The very first difficulty is that light wood has objective and quantifyable physical advantages, the second is that the violin's shape has been optimized over a pair of centuries, far from being a frozen tradition.

I'd find a disk more decent than a circle. This printed violin has objective weaknesses, it's not just a matter of habit. The sound starts slowly and attacks are difficult to play. The strength of nearby notes is uneven. The highest notes are weak. This good violonist could adapt to this particular instrument and cope with its weaknesses to hide them more or less. The piece isn't chosen neither to make the weaknesses apparent. In an other context, the printed violin would show its defects more clearly. It's like a computer screen: at the shop, it displays a nice coloured slowly moving image, and there every screen looks good. But to test it, you must display a uniform steady grey or black, or a sudden change, or sharp contrasts, and then you see the weaknesses - which you would later notice on less artificial pictures too.

Hear a violin 3D-printed of polymer: http://3dprintedinstruments.wikidot.com ... nstruments hosted on it could have sounded worse. But it's very far from a decent violin. Printing a violin or a woodwind's reed is the most difficult challenge and I don't imagine plastic to succeed in that task, especially if the shape is just copied from the wooden parts, which is meant for very different material properties. But for instrument parts that don't essentially vibrate, like the body of a recorder or the mouthpiece of a woodwind, we're on the verge of home-printing them. Which I feel ironic, because chip-making manufacturing processes are obviously cheaper than 3D printing for them. A woodwind mouthpiece is only a part of hard rubber, it has a simple shape except for the reed seat which is just copied automatically by the grinding machine from a pattern. So cheaper home printing just results from the many profits in the sales chain.

You can perfectly run a fan from an electric motor. A fan fits an electric motor even better than a propeller, since it permits a higher peripheral speed. Remember: in an airliner motor, the gas turbine serves just to rotate the fan, which is a propeller design optimized for higher air speed. Batteries or fuel cells are the true limit. Fuel cells improve, so a commmuter plane would fly properly right now, a M0.7 long-hauler soon. http://www.scienceforums.net/topic/73798-quick-electric-machines/#entry738806 (cell mass /2 since that message) As for battery progress: do NOT believe press papers nor science paper. It's charlatanism. To get half-way credible information, go to the science paper and read what has been achieved. It's usually 60dB below what the authors promise as a far result of their research, and press papers report only the promises.

I wonder how objective science is allowed to be in such extremely politically sensitive cases. I'd have prefererd a study by, say, a Danish university, rather than the US army. The row resulted from the very idea of "Native American". Had they arrived second and exterminated previous inhabitants, the presently called Native Americans might have lost some legal status. Making science under these conditions must be almost as difficult as archaeology in Israel. You know, when archaeologists find that for instance the historic Galilea couldn't possibly be where the present province is, the answer is just "shut up", because of the huge political implications. I'd find it quite a natural idea that the Americas were settled several times by varied people. Older remnants have been found in Brazil for instance, and they don't match the native populations neither. Or think of the islands in southern Pacific: every not-too-small one is inhabited, as closely as Easter Island. The continent wasn't much farther and certainly easier to find.

Unintentional existing EMF won't suffice for sure. From a dipole, you get -60dBm (=1nW), in altitude maybe -40dBm, from the FM and TV bands. But radio beams from the ground have already powered aircraft, some two decades ago. The goal was to keep the craft airborne indefinitely in the lower stratosphere and use it as a broadcast antenna. I don't know what happens in a jet stream. Then, one has to ask whether the huge-power ground station is any cheaper than gasoline and a second aircraft.

Not really better algorithms... What runs presently is still the gradient retropropagation (Yann Lecun about 1987) and the random annealing of neural network coefficients (few years later). It's mainly that computers are faster now, and by chance such algorithms fit parallel computers not too badly. You know the proverb: when programming, you can be clever and fast, or you can be dumb and slow so that hardware progress catches up you bad software. But you shouldn't be dumb and fast. (Hum, Yann isn't dumb for sure. Impressive in fact. But I can't resist a silly joke.)

Nice! I had thought the process would need to extract the mineral, recombine it chemically, and put it back in the ground. If injecting just the dioxide suffices, this looks really cheap now. Thanks Ed!

It can't be Earth's composition neither. But maybe Eart's crust, or the top of the crust, plus the atmosphere, the Ocean and all the carbonates in the soil. What does the text say?

Why are the craft displayed so dark? They receive very strong sunlight, more than in any tropical desert at noon on Earth, because they're above the atmosphere.

Protons and neutrons transform in an other rather easily. Look at a table of the isotopes: for 80 protons+neutrons, the number of neutrons can vary by +-3 typically, and beyond that, radioactivity brings the nucleus to the favourable proportion, which is around 1 neutron per proton, or rather 1.5 for heavy nuclei. If the mismatch is big, the decay gets very quick. This kind of transformation happens by electron capture, electron emission or positron emission. 40K does all three. https://en.wikipedia.org/wiki/Potassium-40 An isolated neutron happens to be on the wrong side of the favourable proportion. It's radioactive and decays into a proton. Normally you don't find an isolated neutron. I can't tell whether the neutrons in primordial helium and lithium were formed by proton collision that created these elements or before - nor even if such a question is meaningful. On Earth, about every neutron is in a nucleus that was formed in a previous star and spread in an explosion https://en.wikipedia.org/wiki/Nucleosynthesis so many of these neutrons result from the transformation of a proton, the exception being those from primordial nuclides like helium that were incorporated in said star at its birth.

There are varied designs for electromagnetic guns. A common one indeed has just two rails "shorted" (and this is difficult) by the round. The strong current makes itself the induction as it passes in the rails. The main limit is the quality of the moving contact. It's usually graphite since the rest is worse, and it vaporizes, which contributes by the plasma to a contact, but loses power and erodes the rails and the round, destroying the round if exaggerating. Forces on the rails are bad but easier to cope with. One other design switches many coils after an other, preferibly overlapping, to attract a ferromagnetic round. In both cases, I too fear that superconductors are worse than metals because they limit the induction. Coils could also repel the round acting as a short-circuited loop. As far as I know (and I ignore much) this design is less good as a gun. But it's standard at lithotriptors to repel a conductive membrane as a sound transmitter. An inventor wanted to accelerate D-T rounds that way for fusion, and last time I checked it, the design failed because of superconductor limitations.

If the wires are long as compared with the prospected depth, then the good model is not a hemisphere but a half (conductor A) or full (B, C) cylinder, with field as 1/R and potential as Log(). Don't forget the half or double current. Two different conductivities make everything much more difficult. I'm not sure there is an algebraic solution. If the electrode C isn't parallel to the others, it also gets much worse. On the diagram, the second electrode of the circuit that inject the current is missing. If this circuit injects current elsewhere - here into the soil - this current must come back to the circuit somewhere. The second electrode will change completely the shape of the injected current.

Yes, fMRI (and also MEG and PET) is used to observe the changes of blood supply to the brain according to its activity. It makes maps accurate enough to identify the areas linked to each activity; about 15 years ago, academic research was able to identify zones as small as the ones that drive the movements of every finger. I consider it a part of the explanation for mind-reading. This isn't a natural function but is made by imaging devices, since the experiments by academic research amount to mind-reading. Obviously, fMRI, PET and MEG are too clumsy for street uses, but quick estimates tell that an imaging radar can penetrate deep enough at 1GHz or little above and provide images that distinguish the coarse areas of the brain. Interestingly, I noticed such effects when imaging radars became operational, so the developers can have observed it by chance. Whether observing a coarse area (for instance the one that imagines the syllables) with a good time resolution suffices, that's only my hypothesis. Near-infrared would have some capability to observe the brain too. Already used by emergency services in India to detect blood accidents in the brain, well done. Whether it would work from some distance through the hair without a gel, I doubt it. Tinfoil hats (or better, several plies of space blanket) seem to work against mind-reading machines. As such hats stop many radiation wavelengths, they act without a need to know exactly how the machines work. Electric potentials are just the worst tool to monitor the brain's activity, because the skull insulates and the scalp conducts electricity, so the voltages are tiny, noisy and fuzzy. For a video game, it must be possible to build a near-field "radar" (possibly with one single pixel over the useful location) or an infrared sensor. A helmet (or a net) is much more favourable than a remote sensor, because it could propagate the waves all the way in a medium with a big permittivity like water, so (1) the propagation would be stronger and less blurred (2) the angular and spatial resolution would improve since the wavelength would be reduced over the whole path.

Do NOT use hydrogen peroxide on your teeth. I diffuses to the blood vessels and dissolved oxygen creates emboles at other body locations, for instance in the brain. Peroxide contains a stabilizer to avoid its decomposition, and this stabilizer is unsound.

One difficulty with dark matter is that we need it elsewhere, but not where we live. That is, the fall of apples, the paths of the planets and the space probes exclude additional mass in our solar system to a great accuracy. More accurately, dark matter doesn't concentrate where ordinary matter does. But already at galactic scale, we need additional mass (and not little!) to explain the speed of globular clusters and the strength of gravitational lensing - which also tells that this missing mass isnt' always centered on the visible one. And at the Universe's scale, we need more additional mass, possibly of a different nature from the galactic dark matter. ---------- I wouldn't call tunnelling a "mystery". I pleased with waves to explain, predict and accurately compute it.

Oi! One difficulty is that the expansion coefficient relates to the volume with liquids but to linear dimensions with solids. For the rest, you can take an arbitrary container volume at 10°C, compute the liquid volume and the container volume at 110°C and compare. De nada!

You may understand a static magnetic field in terms of virtual photons (which are then static) but this understanding is sterile. It's more an intellectual game to check that a static magnetic field can be described with photons like a propagating electromagnetic wave usefully is. While it's good to check the consistency and universality of the theory, such explanations bring nothing usable for a static magnetic field. According to models that prevail presently, electric current loops in the conductive Earth core create the geomagnetic field. At the considered temperature, iron isn't ferromagnetic, so it's not a consequence of a permanent magnet, and the core being iron and nickel doesn't change much. Void: yes, it's the nature of the electric and magnetic fields that they need no air, ropes, springs nor other matter between the objects that interact. Which is logical, because the electromagnetic forces operate between elementary particles, and since these particles are elementary, there is no matter between them. Or just photons if you wish. What is the magnetic field? Nothing else than that. It's a fundamental force which isn't explained by an other model like sound is for instance, so we can compute it but not explain it. Well, yes, electromagnetism and the weak interaction have a more fundamental common theory, but it's pretty abstruse and provides no more concrete explanation than electromagnetism alone.

The formula isn't complete (even after the corrections) because the resistivity depends both on the electrode radius and on their distance. If the distance clearly exceeds the diameter, you can model (approximately) the current density like the sum of two point sources at the center of the hemispherical electrodes. Then you write each current density as I/(2piR2), multiply by the resisitivity to get a field, and integrate from the plane of symmetry to the electrode's radius to get a half-voltage, from which a ratio gives a resistance. When the distance clearly exceeds the electrode diameter, the resistance depends essentially on the electrode diameter, a radical drawback to detect deposits in the ground. In a more general situation, perhaps you can offset the virtual point current sources within the hemispherical electrodes so that the voltage resulting from both sources is approximately uniform at the electrodes. This trick is perfect for the capacitance of bifilar lines because the equipotentials between parallel charged thin lines are cylinders, so you get an exact solution. Between points, it must be approximate. The described setup is well-known (and refined) for oil (and water) prospection. Used by the Schlumberger brothers as they founded the company a century ago. Meanwhile little used, because acoustic ("seismic") prospection gives more detailed results and the equipment is mobile. You should be aware that the ground's resistivity varies an awful lot depending on the ground water, and it depends radically on the frequency because water is very capacitive, which imposes strong limits on the frequency depending on what is measured and how. People who measure a resistivity, not only of the ground, don't use two electrodes because of the contact resistance which is big, not reproducible, and masks the target's resistance. The very minimum for such a goal is a "four-point" scheme, where two electrodes wider apart inject a current and two electrodes closer to an other measure the resulting voltage. Compute as previously. Varying the distances make the setup sensitive to varied depths, so to some limited extent, you can reconstruct a profile of the resisitivity versus depth. Because of electrochemical potentials, some sort of modulation is necessary at the injected current, on/off being the minimum.

The stalagmite parts assembled during the construction look more orange or brown than the others. This is attributed to transformation by fire up to now. But could it be that clay or a similar material, that made the hypothetic reservoir watertight, incorporated to the old or new calcite over time? Analysis would tell that.

Referring to the images and drawings, index there http://www.nature.com/nature/journal/vaop/ncurrent/fig_tab/nature18291_ft.html At least now, the construction is at a lower area full of water. This is where I would not settle my camp. http://www.nature.com/nature/journal/vaop/ncurrent/fig_tab/nature18291_SF2.html But the limits of the main construction follow the line of constant altitude rather than a circular or oval shape. Constant altitude makes sense for a reservoir, while a smooth shape is preferred for a tent or a camp. Or possibly, the bottom became flat over a long time when the construction retained water that left sediments. On the magnetic map, the anomalies correspond to the highest artefacts (beware the maps have varied orientations). http://www.nature.com/nature/journal/vaop/ncurrent/fig_tab/nature18291_SF5.html If, as I've seen done in archaeology, the map was acquired by moving the sensor at constant height, the locations of strong anomaly can just result from the artefacts being nearer to the sensor. In both directions of the map, the field gradient increases over 30cm and decreases as quickly, which would fit with a mean sensor altitude of 1m. So maybe the height explains the map, needing no modification in the material. Err, it's very presumptuous to suggest that from an armchair, apologies. One fascinating hypothesis relating fire with a reservoir: mud isn't stable over time in water, so the guys (or the girls) put ceramic instead over the stalagmite structure and fired it in situ. If any necesary, this would explain why the stalagmites are magnetically modified at the highest points: the ceramic was thinner there. The small little difficulty is that the oldest ceramic we know dates 29,000-25,000 BP https://en.wikipedia.org/wiki/Venus_of_Doln%C3%AD_V%C4%9Bstonice corresponding to Sapiens Sapiens era, but, well, you know.