Enthalpy

You should have a thought at what means elementary particle. This is not even a matter of quantum mechanics.

What promotes convection is when the densest material is on top and the lightest at the bottom - when material at the bottom expands from heat, be it through Sunlight (our atmosphere), radioactivity or maybe crystallisation (our Earth's core)... The density difference to be injected in Rayleigh's equation, point 2 of the first post of this discussion, is measured horizontally across the convection cell and results from temperature. Though, point 1 of the first post of this discussion injects a density difference computed vertically that results from pressure. I disagree with this use, because hydrostatic pressure alone is not the cause sought for plate tectonics, and because a higher density at the bottom would kill convection instead of promoting it. --------- The situation is slightly more complicated, especially for gases like our atmosphere. Convection needs that an air bubble that ascends continues to do so because it keeps warmer during its trip than the surrounding air, despite the dropping pressure of the bubble cools it as it rises. So the proper condition is that the temperature profile of the surrounding atmosphere drops quicker with altitude than does the temperature of an ascending bubble - where this bubble follows with a good accuracy an adiabatic expansion, telling that P varies as T high Cp/R. This is the case of a hot bottom during a Summer afternoon. Similarly in a planet's interior, the contribution to density resulting from depth cancels out as a convection bubble ascends and keeps the same pressure as its surrounds, with which it must be compared. What stands is the contribution by the temperature gradient within the planet. Solids (and pastes...) are simpler here than gases, as compressing them heats them little; neglecting that completely, the criterium would just be "center warmer than surface" to make convection possible - where "possible" does not mean "efficient" nor "existing". Rayleigh's coefficient just compares how efficiently heat would be conducted away from a hot bubble, impeding its ascent. You also have antagonist forces that block convection, especially the segregation among rocks and between rocks and metals, which have already put deeper the densest materials (resulting from the composition, not pressure nor temperature).

This voice coil motor can move the button that represents the distance. To fit in a narrow long box, it splits the coil in two and the flux path in four, achieving 1.0T at the coils' mean D=20mm. A permanent force of 1N takes only 21mW losses, and accelerates the ~32g mobile mass by 31m/s2. If limiting the acceleration force to 1N and the speed to 0.15m/s, the full 2mm stroke takes 18ms. The full speed and force take (or restore) 150mW, exceeding the losses, which suggests regenerative braking. The voice coil motor permits it; other actuator types need less power or none to keep a constant force, but those who store much reactive energy may complicate regenerative braking. A spring balancing the finger's load would also reduce the permanent force. The small power suggests to recharge the battery by a handle or equivalent. An integrated class D audio amplifier can drive the voice coil motor; it needs output Mos with low resistance to save power when braking or when the button is immobile. I'd make a full servo loop on the button's position, but with force limits clearly felt by the user. If wasting more power, the voice coil motor can be smaller. For instance, one half of the above design would consume 2*21mW for permanent 1N. The loudspeaker's design, wide and short, would require a playless angled lever, or a different orientation of the box. Marc Schaefer, aka Enthalpy

That kinetic energy creates gravity is observed routinely, not needing to experiment purposely - if I interpret it properly despite understanding so little of it. The kinetic energy of electrons makes around 0.28ppm of aluminium's mass, but only 0.12ppm of nitrogen's one (carbon and oxygen about the same) and about 0.015ppm for hydrogen. The kinetic energy of nucleons must make a bigger difference, and of quarks in protons versus neutrons even more, but let's take just the one from electrons. Satellites are widely made of aluminium, while their liquid propellants comprise generally the other mentioned atoms. Let's imagine briefly that kinetic energy increases the inertial mass hence the centrifugal force, but not the gravitation force: in low-Earth-orbit at 6670km from Earth's center, the orbits with the same angular speed would differ by 0.4m altitude (0.05ppm) for the propellants and their tanks - but for decades we know propellants float freely within the tanks. The kinetic energy fraction would be bigger with iron, copper, lead... than aluminium. Leave cautiously a paperclip floating in the space station, observe 3/4h later (half an orbit) that it's still at the same place, and you've made an experiment of general relativity.

Any metal in atomic form is very reactive. I have no doubt with tin, and would expect even atomic gold to react with vapour. Some reactions in liquids can deposit silver, which makes mirrors but not quite good enough for astronomy. Maybe a wet reaction exists to deposit gold of good quality? (Aluminium I guess not, as reactions in water would release hydrogen instead) Now we're typically in a question of chemistry, so someone else should jump in.

Good point, pathologists coroners. But at least these can get strong evidence from the object of their study. That's not the case of a psycho-something who claims to make a diagnosis based on statements in a context he ignores, plus some indirect testimony.

Maybe Caledonia wants to understand it in a historical perspective.

No electronic apparatus can challenge a white stick on battery life, I approve that... But a battery that lasts for instance 16 hours and recharges overnight makes a usable apparatus, and the available power exceeds the expectation. From Conrad's catalogue, Li-FePO4 accumulators used by remote control hobbyists store about 370kJ/kg, so: 500g carried at the vaist provide 3.2W 50g in the hand-held box provide permanent 320mW which is more than enough for a laser, electronics and a well thought actuator. For instance the powerful laser diode in a CD burner makes 20mW light with excellent efficiency - and we need only short light pulses. The power consumption is easier than I feared. I'll give a thought at the actuator.

Fantastic. Any doctor trying a diagnosis on people he never met and are already dead would be laughed at. But not a psycho - whatever. Any claim that brilliant people are mad or handicaped gets immediate public support, whatever unfounded. Could that be simple jealousy? Why does the public lose its judgment as soon as the topic is psycho - anything?

Uh? And about the intensity of gravity waves, several detectors with fabulous sensitivity are operating but are still to detect their first wave...

Yes, just like you expect it.

Hi dear readers! To improve blinds' stick, lasers and previously acoustic sensors seem an obvious choice, to detect and range objects and obstacles sooner. http://www.lac.u-psud.fr/teletact/publications/report_training.htm (among many) Though, the varied designs have not replaced the white stick. One reason could be that the acoustic signal that represents the distance competes with useful surrounding sounds and is difficult to use to make a mental image of the surroundings. It would also have to represent very fast variations: if the user scans 5m width in 1/4s, a 0.1m pole lasts for 5ms only, which is difficult to perceive through a pitch change - such a fast sweep is needed if scanning through height as well. Some designs add a tactile actuator, but from what I've read, only as a warning vibration. I propose (is that new?) to represent the distance by the movement of a part that the user feels with a finger. People are already trained to build mental images from tactile feelings, blinds even more so. Voice coil motors and piezoelectric actuators can be very fast. Tiny movements are easily perceived, quick ones as well. The stick just indicates in real time the distance in front of it. Ergonomics is very hard to predict... Much must be determined experimentally. Whether this idea is useful at all... Whether the part's movement shall be parallel to the distance and in the same direction. What amplitude, reaction time, position relative to a fixed reference. 2mm move in 5ms is feasible but would draw much on the battery; piezo actuators look better for that. Anyway, our tactile sense doesn't react so fast, so I expect the user to detail more slowly a small object once detected, and the actuator needs not be so swift - some reaction as fast as the tactile sense, if not at full amplitude, should suffice. We feel and act much faster than 1/10s, as musicians know, but 1/100s is a wide lower bound. Signal tweaking, like nearer narrow objects being represented a bit longer, looks interesting. A big maximum range would improve over the white stick, say to orient oneself in a road crossing, but short-range accuracy is necessary. The distance measure can be transformed nonlinearly, for instance through a logarithmic compression, for better perception. Several moving actuators, possibly for different fingers, can also work at different ranges. The light shall be broad enough to prevent harm, but diverge rather little. Visible light must be better accepted by surrounding people. Such a "stick" would better fit in the palm. Marc Schaefer, aka Enthalpy

Gaseous aluminium is extremely reactive. It reacts immediately if encountering a molecule of oxygen, or nitrogen, or water vapour. Even dry argon would contain too many impurities that would catch the aluminium atoms.

Information may have an objective definition that allows to evaluate its amount, but only under strict assumptions, like "all combinations of bits are possible and have equal probability", which is not common life. Compression is possible - and often works well - because data is not a set of random bits. But "not random bits" means that one finds a relation of some kind, and this is no more objective theory and methods, it's subjective and intelligence. Imagine you have an executable programme. Zip makes general assumptions and compresses it by a factor of 3. You may see it's written for the i386 and then you can compress it easily by a factor of 10. Or you can recognize that it includes subroutines from the MFC or some other layer, remove them from the programme and replace them with calls, and gain more size. Or you can recognize that the whole programme is just msvcrt.dll, and its description takes 10 letters. Or you can replace hundreds of previously elementary particles by the combinations of a handful of quarks - you may consider that as information compression. Before inventing the quarks, no method, no algorithm would have told that the set of then elementary particles contained less information than thought. Forgive me that drift: I consider the size of its description as a good indicator of how complicated a technical project is, and how many chances it has to work properly.

A power of 7 is not a multiple of 7. They go like: 1, 7, 49, 343...

I can solve it, but its mathematical formulation is a detour for me. Would it be possible to formulate it in physical or engineering terms? Is K from nitrogen at moderate pressure, or at least can I use some mean value for it, as high pressure in hydraulic accumulators makes it non-ideal? What are the indices 0,1,2: full of oil, empty...? Even better, do you have numerical values? Sorry for the unusual query, but I think a little bit differently from usual scientists, and the physical feeling would save me much time. If you don't choose this way: the best method with gases uses to compute temperature differences or ratios, as temperature is so to say the central value, even if you don't need it at the end. Its difference relates easily with work in your adiabatic process, and its ratio relates simply with pressure and volume ratios.

If you know a club for technology, you can get hands-on experience there, better than at a school.

Antares has flown for the first time, congratulations! More capacity would result from a liquid second (and optionally third) stage, with electric pumps easing their development, possibly as a step towards turbopumps. The first stage is kept; side boosters as at Ariane 4 would permit to fill it despite the heavier second stage. The second stage has a common tank head of 3mm plain AA6005 sheet. Four chambers save length hence mass. The rest resembles previous designs. 140b and 1.2m nozzles achieve 400kN and isp=376s . 33.5t propellants and 3.3t dry stage put 8.6t in Leo (=9500m/s). A future turbopump would save 1650kg batteries and add little mass. The optional third stage provides 4520m/s to joint Gso from a Wallops Island Leo. Its structure is the conical payload adapter of AA6005 extrusion (t1=t2=1mm, a=45°, B=22mm) and a truss of AA6082 tubes, D=70mm t=1mm, to the engine. RP-1 fits in a 0.5mm thin half-cylindrical alu torus welded to the cone. O2 has an ellipsoidal tank of 150µm brazed steel, plus foam and multilayer insulation, hold by polymer straps. 50b and four 0.8m nozzles achieve 8.5kN (1m/s2, successive kicks) and isp=401s . A turbopump would hardly challenge the 81kg batteries. 6.0t propellants and 826kg dry stage leave 1.9t in Gso. Marc Schaefer, aka Enthalpy

The example with the star unimpressed by the moving observer (which I do agree) is a bit complicated, because other forces (radiation pressure and so on) keep its size and they change with speed as well, in a difficult way. Could you try with two stars, on circular orbits around their common center of mass, in a plane perpendicular to us moving observer? Their distance to an other keeps the same to us, their mass is bigger, their angular velocity smaller - and then I botched something (as expected) because the centrifugal force would decrease, so I haven't transformed the time derivative properly. ---------- In a course, when evaluating the gravitation field by a reasonable mass, Pascal Picard explicitly rejects the Ricci tensor and takes the full Einstein tensor instead. You may ask why, if you wish, but I won't answer that... ---------- I doubt that we should distinguish between individual kinetic energies of two objects and the kinetic energy of their common center of mass. After all, both add up to give the individual kinetic energy versus us, with which we should be able to make computations. ---------- Does someone want to claim that a spinning object, whose inertial mass increases due to speed, still feels the same gravitation force because gravitation results from rest mass only? - To my eyes, it would allow to distinguish between gravitation and acceleration. - The experiment is easy! Take a toroidal gyroscope of graphite fiber running at 600m/s, its inertial mass increases by 2*10-12. Put it within enough nested boxes that don't rotate quickly, send everything to low-Earth-orbit. After only one month, the gyroscope will float 20mm behind its original position in the boxes. I bet many experiments (like the recent spacecraft that observed frame-dragging) are more sensitive than that. - Worse, the kinetic energy of electrons around heavy nuclei. This kinetic energy makes about 2ppm of lead's mass, but only 0.1ppm of carbon's mass. Since our accelerometers are 2*10-9 accurate, lead falling slower than feathers would be known. - In a proton or neutron, how much could kinetic energy weigh? Half of the total mass? That would make a difference to other particles! So I continue to believe that any energy, including kinetic energy, is also inertial mass, and that inertial mass is passive gravitation mass, which is active gravitation mass as well. To evaluate GMm/R2, where I'm bound to Earth's M hence won't scale G nor R, I take for m the mass, not just the rest mass.

If movement increases the gravity pull, then the fast moving observer will feel the star is heavier, but components of the star - which don't have this fast speed relative to an other - will feel the normal star's gravity and continue their normal life. ----- Is it feasible to express the result in words graspable by an engineer? You seem all to consider that the gravitation force results from the rest mass only, with no contribution from the kinetic energy, right? And what happens if an electric field loses energy by accelerating a charged particle, like in alpha radioactivity or in fission: do the set of resulting fragments suddenly produce a weaker gravity field? And what about the kinetic energy of confined particles? Take the 1s electrons in a lead atom. Their energy is -91keV in the nucleus' potential, with -182keV electric energy and +91keV kinetic energy. The resulting atomic mass (1ppm effect) is measureable in mass spectrometers. Such quick particles, for instance electrons confined by a nucleus' electric field, are more difficult to accelerate because they're already fast. Gravitation resulting only from their rest mass would let lead atoms fall slower in an external gravity field than atoms whose electrons have more room. You can imagine systems (quarks and gluons!) where the kinetic energy makes much more than 1ppm of the mass. Shall the gravitational mass of the composite differ from its inertial mass, as inertial mass includes the component's kinetic energy?

Thanks! This seems to confirm that mass, and not just rest mass, creates gravity. Did I get it properly?

This is the diffusion equation, it applies to heat and more situations. Its solution is like erfc[x/(2*sqrt(t)]. You have to arrange it a bit (replace w by 1-w after solving) because the usual condition is exactly the opposite, with matter having temperature w=0 before t=0 where a constant temperature begins at the surface. Yes, you can solve it by a Laplace transform. It is done, but is uncommon among engineers, because it involves half-integer powers of s (written p in some countries), the formal Laplace variable. Sacadura does it, probably in French only (Initiation aux transferts thermiques). The old Fourier did it with his transform for a finite bar of material, so a Fourier series was enough. A semi-infinite bar would need a Fourier transform instead - which is nearly identical with a Laplace transform for real W. A different way is Green's method, more expressive to engineers, which convolves - a Gaussian function thats starts perfectly sharp (Dirac) and spreads out in the material over time (Gaussian functions are such favourable solutions of the diffusion equation, they extend and decrease as sqrt(t)) - with the proper, user-found function of the position that lets the convolution fit the boundary conditions. The nice part is that at t=0 the convolution of many Dirac functions is trivial... If the initial condition is a known temperature distribution, Green's method boils down to a sum of Gaussian functions. Sometimes you have to distinguish x=0- from x=0+ and t=0- from t=0+. A lot there: http://en.wikipedia.org/wiki/Heat_equation

You didn't mention: pressurize the oxidizer. It's necessary, though. Alcohols are the bad choice. Hydrocarbons are more efficient. Diesel oil or heating oil would be far better in that their vapour doesn't ignite if the liquid is at a reasonable temperature. You don't mention the igniter. In case you imagine contact ignition, just forget it. Keep away from nitrous oxide, as it is a single-component explosive whose detonation has killed a trained professional rocket worker recently. You don't tell how you cool the walls of the combustion chamber. The liquid engine rocket would be very dangerous (a solid one just as badly). From your description, you have zero chance to achieve some propulsion, but every chance to get very badly burnt.

We should survive it.

Could you (or someone else, I like you all!) tell more about this? These notions are unclear to me. Up to now, I consider that light creates a gravitation field, because mass deflects light, which means some momentum change before/after for light, and conservation of momentum demands that the attracting body gets the opposite momentum, which I imagine results from attraction of mass by light, suggesting gravitation. Or doesn't it? Photon energy E=p*c can also be viewed as a kinetic energy. Or is it just a matter or wording? Now with massive particles: energy, for instance an electric field, creates a gravitation field. The electric field can lose energy transferred to a charged particle that gains kinetic energy. This transfer can be snappy and local enough that a remote measure sees the sum of both gravitation fields. In the case where kinetic energy creates no gravitation, would the remote measure see a quick (although faint!) drop in the gravitation field?