Enthalpy

Yes: comparing the Sapiens Sapiens' activity 45,000y ago with Neanderthals' 176,500y ago brings little, and the stalagmites as their are arranged obviously didn't serve to support a tent. The orange spots on the nice picture you linked show spots that have been hot. Only the red spot is charred. I suggest that the processing of the stalagmites, especially cutting them, involved heat as a means or a consequence. These stalagmites are 10-20cm diameter stones, so breaking or cutting them needs some doing. A camp fire would not have been made on the stalagmites, and the effect of heat would be observable on the ground too. 20cm spots are also small for a camp fire. By any means, the stalagmites and bones were heated before being assembled.

Meanwhile a giant deposit for used tyres has burnt in Spain. It made smoke.

And if you put a piece of polymer in water, you also get bubbles on it, from the dissolved air. A hint that magnesium doesn't react quickly nor strongly with water is that you can hold it in your hand without getting burns.

No: bonds are attractive, that's why molecules exist. Breaking them absorbs energy. But creation of the new strong bonds, between Mg and Cl, release energy. As a secondary subtlety, a few electrons can be on antibonding molecular orbitals, provided that other electrons on bonding orbitals hold the atoms together, for instance in O2 or in optically excited ethylene. If not, the molecule splits quickly: this happens for instance in excimer lamps, where the excited electronic state holds the atoms together (like Xe2) but the non-excited state, after light emission, lets the atoms repel an other.

The first post is difficult to read. Use a few punctuation marks at the proper places maybe? Many research teams try to control video games through mind reading. Alas, they all try to use the electric voltages on the scalp, which is the wrong way as these are weak, noisy, slow and too little differentiated. Brain imaging techniques achieve mind reading (in academic science) for years, by functional NMR or PET. Check the research papers, that's really convincing. It only needs a brain map for each individual, and a manageable apparatus. Other devices too get a map of the blood throughput in the brains, but by near-infrared imaging. Presently they are slow and of limited resoluton, sufficient for emergency diagnosis of brains accidents, but the budgets of video games could improve them. An other direction is just the brains reflectivity for low-GHz radio waves. The resolution isn't brilliant but the time response is. Imaging radars have sufficed since they were created four decades ago, and their use for mind-reading was probably discovered by chance; this is probably what the secret services use. Adapting them to video games would be decently easy. fRMN sees the intention to move each individual finger, but an imaging radar won't achieve this, I suppose. Recognizing words at the audition or diction areas of the brains must be easier and suffices for a video game.

A cycle where the oxygen-rich preburner heats the fuel in an exchanger to turbine it too would look like this: It needs several flame stages in the preburner to regulate all temperatures, possibly several stages at the exchanger. At least, throttling doesn't make the fuel hotter. I've computed the achievable pressures by expanding the gases at constant Cp: the power differs by 2% only from Propep. I've kept RD-170's 535bar at the prechamber, almost as good as 700bar. 500°C at the turbine resulted from oxidation then; I've also checked at 650°C, where nickel alloys creep little enough. I've also compared with RD-170's known oxygen-rich staged combustion. The hypotheses are arbitrary but the comparison is fair. Unzip the two-sheet xls: HybridStagedExchanger.zip ---------- The heat exchanger gains little performance, some 3s Isp, and only for methane supposed to withstand heat. Accepting 10g decomposition products over 300s in 0.16m3 exchanger and ducts at 535bar permits 710°C for methane, 390°C for cyclopropane and 320°C for spiropentane, according to http://kinetics.nist.gov/kinetics/Detail?id=1956SHA/PAV811:1 http://kinetics.nist.gov/kinetics/Detail?id=1961FAL/HUN609-611:1 http://kinetics.nist.gov/kinetics/Detail?id=1972FLO/GIB548:1 and a low temperature can't pay for pumping the fuel to a higher pressure. Coupling the turbopumps brings very little performance. Safer start maybe. But easier seals are more important. Cyclopropane and spiropentane outperform methane as their density lends to a higher pressure, and they shrink the tanks too. The advantage would be bigger at a gas generator cycle or with electric pumps. Cyclopropane is mass-produced, spiropentane could probably be. Methane with a heat exchanger gains only 3s over cyclopropane without. If a fuel-rich pre-burner accepts methane somehow, this comparison will hold. To my opinion, not worth an exchanger nor a second pre-burner. I've included Pmdeta in the table because it's more common than rocket "kerosene", more efficient, more resistent to fire. Safe and more efficient fuels may be possible http://www.chemicalforums.com/index.php?topic=79637.msg290422#msg290422 ---------- The exchanger is as badly difficult as expected. Spark-gap machining and molybdenum, niobium or tantalum alloys may contribute to a solution. Also, a 3s better 450t first stage gains at its end only 2t, which the exchanger can't squander. I won't put time in it. Would methane soot in a fuel-rich pre-burner? The chemical equilibrium tells yes, so kinematics decides. Maybe little methane can burn with enough oxygen, the combustion get enough time to end (still a small throughput), and only then be quenched quickly with abundent methane. Experiments must decide. Marc Schaefer, aka Enthalpy

Agreed that we can analyze only durable materials. Papers in French too: http://www.lemonde.fr/archeologie/article/2016/05/25/140-000-ans-avant-homo-sapiens-neandertal-s-etait-approprie-le-monde-souterrain_4926458_1650751.html http://www.telerama.fr/monde/grotte-de-bruniquel-c-est-definitif-neandertal-n-etait-pas-la-moitie-d-un-idiot,143045.php#xtor= And in English (complementary information in them): http://www.bbc.com/news/science-environment-36381786 http://www.telegraph.co.uk/news/2016/05/26/mysterious-176000-year-old-rock-formation-discovered-in-france-c/ The paper in Nature: http://www.nature.com/nature/journal/vaop/ncurrent/full/nature18291.html In German: http://www.spektrum.de/news/erstmals-neandertaler-bauwerk-gefunden/1411633 http://www.spiegel.de/wissenschaft/mensch/tropfsteinkreise-von-bruniquel-raetsel-des-hoehlen-funds-a-1094148.html

Human construction 175,000 years ago in Europe, that is, from Neanderthals... http://elpais.com/elpais/2016/05/25/ciencia/1464175777_166364.html 300m away from the entrance of a cave in Bruniquel, France, a wide circle seems to be man-made of broken stalactites and stones. Which changes much knowledge: The oldest constructions known to us were 100,000 years younger They were made by Sapiens Sapiens, never by Neanderthalensis Neanderthals were not known to go deep in caves Of course and obviously, the authors tell "symbolic or ritual use" as usual. An excellent way to avoid contradiction. Well, I do take the risk of proposing a use. It was a reservoir of drinking water. Drinking water did rain from the roof, as it built stalactites - hopefully at that time too. Water is the one wealth for which I'd walk 2*300m and build an artefact. The broken stalactites and stones built a basin, together with mud presently lost to erosion. From a drop every minute you can't drink, but with a basin you can collect water from several stalactites and over more time. This source was fully reliable. Possibly available at every season, not shared with animals, not exposed to damage. Fabulous. Interpretations without human intervention suggest items fallen on the ground, possibly because of an earthquake, and pushed to a circle by a stronger stream at some time. Well, I feel it easy to check: look if the stalactites on the ground are missing from the roof at that place. Marc Schaefer, aka Enthalpy

Hi Simon, welcome here! Even before the heat conductivity, I'd choose the filling gas of a foam to be nonflammable, especially to insulate a house. Something like butane in the walls is excluded. This limits the choice a lot. Then, the molecules shall be heavy, so they move slowly, and carry slowly the heat they receive from the warmer side and store as rotations, vibrations and so on. They should also be big, so they collide often and diffuse slowly between the warmer and colder faces. Though, heavy and big molecules tend to be liquid or solid. To stay gaseous, they need small sticking force between them. Alkanes bring this but are flammable, haloalkanes are heavier and keep the small intermolecular forces. Good combination. The other attempt would take molecules with as few atoms as possible so the vibrations store less heat and the molecules transport less heat. This attempt is limited though, because heavy atoms tend to make solids. It is the solution where haloalkanes are impossible: in filament light bulbs, where only noble gases withstand the heat (excepted halogens which recompose and have other advantages). Heat conducted away from the filament by the gas is the main competitor to light radiation and efficiency. Argon is the standard choice there, but for efficiency, krypton is better. (Xenon lamps are not filament bulbs). At foams, you may also consider that the gas must not react with the foam despite the huge contact area: again in favour of haloalkanes. Neither shall the gas diffuse out of the foam, and this favours big molecules again. There may (must) be other reasons resulting from the fabrication process.

Some fats (triglycerides) melt around +40°C, which makes them bad for cholesterine though edible. Most natural fats are mixes, so their melting point is ill-defined. Among the components of palm oil, you'll find some.

It depends much on the loop current... To shield the geomagnetic field away, a ferromagnetic material was a good start, like mumetal or permalloy.

I have absolutely nothing against calling "vibration" the movement of the electron during the absorption or emission of a photon. In that process, where the wave function is a superposition of two orbitals (which are per definition immobile, or better, stationary), the electron's mean position, speed and acceleration oscillate, which explains that the electron radiates while it doesn't on an orbital. Except for the electron delocalization, this resembles pretty much any vibration.

With pure water, as we used in semiconductor manufacturing, the conduction current is minute, so the current pulse not too long results essentially from water's polarization. Whether the electrodes are insulated will change little. The polarization is mainly the orientation of the molecules in the case of water - or rather, of large groups rather than individual molecules, which explains water's big permittivity. Other compounds have their molecules oriented almost independently, in which case the ambient heat defeats the torque created by the external electric field, or their molecules may be nonpolar, and then the deformation of the molecules (atoms' position, orbitals' shape) is the only response to the external field. And, no, the orientation of the water molecules resulting from the voltage pulse will not split them. For electrolysis, you need preexisting ions that join the electrodes and get neutralized there. First, don't trust dielectric strengths. They are not reproducible, and they decrease (though not quickly) with a bigger distance. They decrease also with the insulator's volume and with time, suggesting that some random process triggers the discharge. I'd have to double-check if heat eases the dielectric breakdown of water. For sure, short pulses don't ease the breakdown, quite the opposite: they help insulators survive the field, and significantly. You don't need short pulses to make sparks in water. Put a needle in deionized water, insulate the electrode everywhere else, put a high DC voltage, zap. I just wonder why one should want a high voltage for electrolysis. The charge makes the produced amount, and to save energy, you want to provide it at a voltage as low as possible. This also implies concentrated solutions, not pure water. And it demands many wide electrodes close to an other, as is done industrially.

-------- Moon to Earth -------- All prospectors bring their samples in hermetic boxes and racks to the ferry. A capsule hosts the racks and is sealed. The prospectors are abandoned and the ferry brings the capsule towards Earth. They separate before reentry, where the ferry burns and the capsule aerobrakes unpiloted, then opens parachutes and lands in a quiet area: Antarctica, central Australia... Little extra hydrogen would leave the ferry in transfer orbit or even in Leo, ready for refuelling. With its Isp=1267s sunheat engine, the ferry accelerates by 455m/s to raise the apoapsis to 20260km. This is 90% efficient because the pushes are long so the operation takes goes in a few months. 11m/s before and 380m/s after periapsis let the ferry leave the Moon on a nearly circular Earth orbit, 300m/s slower than the Moon at apogee. In very few apogee pushes, the ferry brakes by ~550m/s to plunge to Earth. The timing adjusts the landing zone and date for good weather, and 100m/s during the last leg fine-tune the landing point. This sums to equivalent 1547m/s which need a mass ratio of 1.13 thanks to the game changer. The reentry capsule comprises: A structure that resists the aerobraking, the landing and keeps the air out: 29% of the reentry mass. It may have legs that absorb the landing shock. A heat shield: 16%. A parachute: 13%. A battery and electronics that opens the parachute, optionally separates the heat shield and deploys the legs, detaches the parachute after landing, transmits a radio signal: lightweight. This leaves 42% of the reentry mass for the samples in their boxes and racks. The volume of the boxes and racks determines the capsule's size, not the mass nor the heat shield, so it must be optimized. The masses permit 18 half-ton prospectors . Arriving at Lunar orbit: 0.45t 15 sunheat engines 0.32t Tank with foam, Mli, glassfiber truss 0.36t Return leg propellant 0.2t Command and control, robotics 0.05t Capsule adapter 1.3t Empty capsule 1.0t Bus and prospectors adapter 9.0t 18 prospectors ------ 12.7t Fits the 18.8t launch and transfer Standard payload fairings date back to the chemical propulsion era and can't host this full mission, but the Atlas V User's Guide claims : "Longer and wider payload fairings can be developed. Up to D=7.2m and L=32.3m have been considered." Fine, this mission needs just 1/3 more volume. Hey Ariane, Atlas has the same fairing manufacturer as you! These are the masses leaving Lunar orbit: 0.09t 3 sunheat engines, others dropped 0.32t Tank with foam, Mli, glassfiber truss 0.36t Return leg propellant 0.2t Command and control, robotics 0.05t Capsule adapter 2.2t Full capsule ------ 3.2t Fits the return leg mass ratio ---------- Thanks to the sunheat engine, this single mission can bring back 720kg lunar samples from 18 regions . That's twice the mass and three times more sites than we have from Apollo. Better, the prospector robots have months and years to choose the samples over wide and more varied areas, including at the far side. Marc Schaefer, aka Enthalpy

-------- Ascent -------- Each prospector goes once to the Moon' surface and back. Refuelling at the ferry, or even at a later ferry, would have multiplied the landing sites but reduced the samples mass and the reliability. Still for provisional 1000kg leaving the ferry, hence 551kg landed on the Moon, here are rough masses ascending from the surface to the ferry. Before a prospector takes off, it abandons its working and analysis tools on the ground (-20kg). Just after take-off, it separates its legs (-80kg). It keeps the arms and an eye (15kg) to dock at the ferry and transfer the samples. The engine and attitude thrusters (40kg), battery (14kg), tanks (8kg) served for the descent, as well as the bus (60kg), equipment (20kg), undetailed items (20kg). 2215m/s ascent need a mass ratio of 1.75, which permits +119kg samples in 30kg boxes plus rack and 245kg propellants. The craft weighs 571kg without tools nor legs but with samples and propellants and 326kg when docking. Ask geologists: twice as many explored regions and prospectors bringing each one-third the samples mass, or 40kg, should make better science. Each prospector would then weigh 500kg when leaving the ferry. Marc Schaefer, aka Enthalpy

Hey Sensei, you should try once to light a piece of magnesium, so you know how difficult this is. But to extinguish it - provided you achieved to light it - just wait a few seconds, it happens naturally.

Nor is "rubber" accurate enough. Dozens of formulations exist, of very different nature and origin. Most are seriously reactive, especially to oxidizers.

Freezing the glycerol out doesn't work. Its mixes with water just stay liquid at quite cold temperature. Heat or low pressure (takes less energy) is the standard way. Polyethylene glycol, especially tri- and tetra-, are more often used in this application than glycerol, possibly because water separation is a bit easier. Tetra isn't toxic (glycerol neither). To maximize the contact between air and glycerol at moderate power expense, you may consider rotating disks resembling this http://www.scienceforums.net/topic/70340-reactor-for-liquid-and-gas/ which are inspired from an air humidifier anyway. Depending on where you live, you might try to extract humidity from air when it condenses to fog, hopefully every morning as in the Namib. Then a big net suffices to catch and collect the water. Demonstrated in an Andean country, possibly Perú. Hi BabcockHall, nice to see you here!

Just like everyone's magnesium. That's normal life, which differs from YouTube.

The ones designed up to now do reflect sunlight, to Direct the thrust in the desired direction, most often not the one of incoming light Limit the heat, especially if the sail must go nearer to the Sun Increase the thrust when possible Absorbing the incoming light would push always towards the Sun's opposite direction. Reflecting it creates a second push that can be directed, for instance forward on the orbit to brake the craft and let it lose altitude, say to go nearer to the Sun.

I wouldn't put such a shield in the atmosphere but above it, because of the wind. The "casual citizen" doesn't exist. Humans communicate, are fantastically gifted, people are 40dB more clever than politicians, so anything will be noticed. Even if someone thought to have checked all possibilities, other people will find something he hadn't thought at.

Hi acsinuk, many magnetometer types measure permanent fields. The field of atoms is routinely observed and used. A magnetometer won't observe the field of one atom, but of many atoms, yes. At paramagnetic and diamagnetic substances, the atoms orient their fields randomly to an other so the global effect is small, but an external field orients the atoms with a small preference for one direction, and the resulting net field created by the many atoms is measured. It is the cause of the magnetic "susceptibility", perfectly accessible to our instruments. When some very sensitive experiments are made, the response to some para- and diamagnetic materials to the geomagntic field shall even be minimized. Then you have ferri- and ferromagnetic materials, were the atoms orient firmly to an other within a small "Weiss" domain. The result is very strong, either as permanent magnets or as magnetic cores, and reaches 2.2T. No subtle magnetometer is necessary to observe it, since this rotates electric motors. The magnetic field of a single atom is observed, but by less direct means as far as I know. It creates the 21cm radiation of neutral H atoms, the fine and hyperfine structure in atomic light spectra, and so on. Wait... With a Squid we measure less than one field quantum, so we can observe the field of one single unpaired electron at the right place. Direct measure of one atom.

An important message about solar sails is that they exist already. Some have been flown as a propulsion method http://en.wikipedia.org/wiki/Ikaros and many geosynchronous telecom satellites use the radiation pressure to keep their orientation passively and save propellants to extend their life. Explaining... Perhaps interesting is that you can compute the thrust from the photon's momentum (F=P/c where P is the received and the reemitted power) or, as Maxwell did, from the electric currents induced in the mirror and their interaction with the electromagnetic field. Fortunately, both results match - well, sometimes, when there is no mistake, but it already happened, permitting us to tell that theories are consistent. One funny history, very useful for people still learning to doubt, is that ol' James Clerk was so pleased with explaining Crooke's radiometer that way that he completely botched the explanation. Apart from the fully unreasonable orders of magnitude, the explanation would have wanted more push on the clear sides, while in the radiometer, the dark sides trail in the movement. Nevertheless, this frenzy was published in the best peer-reviewed journal and wasn't questioned as it should have been, and still now, you find people who repeat this explanation. Also, other meaningless (but by known people) explanation attempts from early 1900's are still repeated today as plausible possibilities (see Wiki) despite the proper explanation is simple and well established. That's a very nice example showing that even scientists believe an author rather than a theory, that is, they don't behave like scientists. So solar sails are not only possible to build but already in action. Alas, they are small up to now, like 10m*10m, hence they bring only an observable effect, still not a main propulsion method. I suggest there how to build them about 100m*100m big and test them on Earth: http://www.scienceforums.net/topic/78265-solar-sails-bits-and-pieces/#entry763027 http://www.scienceforums.net/topic/78265-solar-sails-bits-and-pieces/#entry857978 that would already provide interesting propulsion, like a few tons to our Moon or to Mercury, and is a step towards real size. The real game changer is rather 1km*1km big, and I have no idea for it. My hope is that, by building one 100m*100m big, we can observe what the difficulties are and find new answers. I really believe this is an enabling technology, to be developed. It's by far not as difficult as it first looks: mechanical engineering, no rare knowledge nor fundamental research needed, just inventions. If I could find good looking ideas for 100m*100m, other people can go on to bigger sizes. Presently, mainly associations put hard work in it, and have very interesting concepts. I feel agencies should develop sails - rather not internally, but rather over some means to tap and help the advance at the associations. Giant mirror... Do you mean, the sail itself, or a giant mirror to concentrate some light on a smaller sail? Because at astronomical distances, concentrated light isn't inside human technology. Sunlight sails at slightly outside the fringe of what we do up to now, but sending 1kW/m2 to just one Sun-Earth distance is very far from anything we do now, and since much effort has already been done, further progress will be slower than on sunlight sails. I know that one project wants to push a tiny sail to a nearby star by concentrating something like 1GW on it, emitted over 1km2. That's a perfect example of a project much exaggerated over many aspects at the same time, expected to cost horribly much for a doubtful result. While its goal is seducing, I radically prefer to develop sunlight sails, something cheaper than most space projects, and which shows a clear usefulness.

It's not only that mass and energy would "convert" in an other. Every energy has mass, if not necessarily rest mass (beware vocabulary difficulties here) - that is, it has inertia, creates gravitation, and is sensitive to gravitation. The usual example of nuclear fission is in fact electrostatic energy (the repulsion among the protons) converted to kinetic energy of the fission fragments. Other energy forms like heat, chemical energy... also have a mass, but as these are less concentrated than nuclear energy, this mass is less obvious.

Simulation software exists for acoustics, and I have little doubt that some works in the time domain rather than frequency domain. The interrogation is rather: what does it bring, how fast and accurate is it? I had considered such a software looong ago for wind music instruments. The design of such instruments takes advantage of software that tells for instance the embouchure impedance over many frequencies, and each frequency demands to solve a huge linear system. My hope was to emit just a pulse, let it propagate (hence no solving of an equation system) with all multiple echoes in the software's instrument model, collect the time response at the embouchure, and fourierize it to a frequency response. Though, it has difficulties. For instance, it takes tiny time steps over a long interval to obtain a frequency response over many octaves. Worse, some processes are dispersive, especially the viscous and thermal losses which are all-important in music instruments, and these don't model naturally with a time-step algorithm - which translates to: complicated and slow. The really bad news, at least for wind instruments, is that strong important losses result from turbulence. Predominant at a bassoon or a saxophone. A frequency-domain analysis doesn't model them properly, but a time-domain analysis could not run once for all frequencies. As well, wind instruments are sometimes nonlinear, as has been shown for the trombone playing ff, and then you can forget any Fourier transform. For easier uses like room acoustics, noise damping and so on, it may be interesting.