Enthalpy

The atmosphere stops the ionizing rays. But without a magnetic field, an atmosphere won't stay. What would be the most practical at this time -> None. A friend of mines suggested to bring water by pulling an asteroid out of its way to collide with Mars. Not even this small deviation is presently feasible.

Different points: Ferromagnetic materials will feel a big force in a strong field like 1T, but you can reduce the field! So much easier. Para and diamagnetic materials, as opposed, feel a very weak force, observable only if you hold them under a wire. And then you'd need a strong field, which is inherently dangerous. Ferromagnetic materials can keep a very weak magnetization. Such materials are called "soft" ferromagnetic. Very common, because they were developed for transformers, electric machines, shielding, measurement instruments... Pure iron is one but has drawbacks; less pure iron with added silicon makes the common transformer laminations, cheap and easy to buy, hence I recommend it combined with a weak field; special alloys like Permalloy are extremely soft, characterized by the small coercive field in A/m. You want as well your electromagnets to keep a very small magnetization! So they must be made of soft material as well. Or use coils without a nucleus, as the effect is already very clear. Ferromagnetism is a molecular property, not an atomic one. Some stainless steels are non-magnetic, while Mn-Zn is a commonly used ferromagnetic material and CrO2 a permanent magnet. Forget about tungsten and terbium, that's the wrong direction. Anyway, rare earth are used in permanent magnets but are only one element of the molecule, like Nd-Fe-B or Sm-Co. The pure element won't give anything interesting. Wikipedia has certainly good articles.

The majority of cosmologists (short of a real consensus) chose for dark matter against modified gravitation when Hubble saw gravitational lensing around zones of a galactic collision where normal matter wasn't seen. More precisely, models of a galactic collision would tell that - normal matter would be at the places where it was actually observed, and - dark matter feeling only gravitation would be where lensing was observed. Though... More recently, other galactic collisions showed lensing where it wasn't suposed to be. And wimps (which are only one class of candidates to constitute dark matter) still elude our detection. So this position is less comfortable now. An other element is that the fraction of the mass we don't connect with ordinary matter varies with the object, with some galaxies showing very little normal matter. This makes modified gravitation more difficult. Anyway, cosmologists keep changing their mind about everything within a decade, so just wait a little bit.

What about re-writing the message so we can understand it?

Do you mean k=2*pi/lambda and omega=2*pi*frequency? The only explanation I see is they provide convenient writing and reading.

At a small rocket like Vega, the atmospheric drag consumes 100m/s or less. At a bigger rocket, it's under 50m/s. Compare with some 8200m/s minimum to reach orbit in a theoretical transfer, or rather 9500m/s because you want to accelerate moderately so the payload survives. That's why rockets are not given nice smooth shapes. Any launcher has a fairing with short conical shapes to save height and mass, not streamlined shapes like an airglider. Thinner atmosphere, or none at all, would bring additional advantages, though. First, it would allow a better trajectory that gets earlier inclined. Second, it would allow bigger nozzles (...when feasible!) that expand to less than 1 bar and make the rocket engine more efficient - and this brings a bigger advantage than the reduced atmospheric drag. But this can be obtained through other means. A few launchers ignite at altitude, being dropped from an aeroplane. The main advantage is to save a spaceport and launch from any place, especially outside national territory and its regulations. But it does not justify the development of an aircraft, so current designs take an existing B-52, White Knight or F-4; as well, a big launcher is just too heavy for an aircraft (Ariane V: 800t, Airbus 380: 650t max take-off.

And one electron.

I believe to understand that big-scale gravitational lensing is detected by observing collections of same objects on both sides of the supposed big mass. "Same object" meaning the same redshift and about the same luminosity. I also imagine that gravitational lensing is distinguished from refraction lensing because it's achromatic. So this method should give conclusive evidence of a lot of mass bending light. Or doesn't it? Then one should determine if this mass is banal nature, for instance cold hydrogen clouds which are difficult to observe. This must be why the authors checked that little X-rays are emitted from the massive region, which I suppose would fluoresce due to some nearby objects if it were mainly hydrogen. Is that it? Seing mass but no stars nor gas, they deduce the presence of dark matter (which isn't a synonym for new particles). Did I get it properly, and where would then be more weaknesses in the reasoning? Thanks!

Some directions : - Find a methanol-fuelled cell. - See what drones use. Many ones fly on fuel cells but they're bigger. - Check the minimum weight of a hydrogen tank (don't store oxygen, use air) and compare it with a lithium battery. I bet hydrogen is worse. - Store liquid hydrogen instead. Polystyrene foam is light. Some hydrides and chemical reactions release hydrogen but I expect them all to weigh more than a lithium battery.

The throughput would be very low if resulting only from the temperature difference. But wind impinging at the roof would change it a lot. Some very open buildings use natural convection - seen one at the 1992 universal expo - and they achieve a wind of around 0.1m/s; friction in a pipe would reduce this speed to nothing and the small section would cut the throughput to zero. If you weren't convinced, you can compute the pressure difference from the density difference, then estimate the speed versus pressure in the pipe from experimental relationships - or even from laminar regime computation, as speed will be so low. Even neglecting all angles will tell you "too slow". Or consider a flame or a chimney: with several 100K temperature difference they achive only 1m/s. An excellent book is "Technische Fluidmechanik" bei Herbert Sigloch but it's in German and I don't have mine here. http://www.amazon.de/Technische-Fluidmechanik-Herbert-Sigloch/dp/3540220089

I don't see a chance that galvanized steel resists electrolysis. As an anode less than as a container. It's nothing more than zinc.

Hi Bob, my two cents worth of comments... You know we agree about the ease of SSTO (and less so about their usefulness). Falson 9's mass ratio can be improved with a small effort. Their tank design with plain metal sheet is meant to save money more than weight. Even with hydrogen, Ariane 5 achieves 100kg of dry mass (all included for that stage) per ton of propellants, and the Shuttle's external tank (without engines nor anything) 36kg/t. With kerosene+oxygen, a tank mass around 12kg/t is obtained just by the better propellant density. My extruded tank construction may improve further. In the atmosphere, recent kerosene engines aren't better than 307s (RD-170). They improve in vacuum (338s). The other difficulty of an SSTO design is the deep throttling needed to keep the acceleration bearable (or even at 1G for vertical landing) as the tanks go empty. Kerosene, which needs a higher mass ratio than hydrogen to achieve orbit, needs an even deeper throttling which no kerosene engine has yet demonstrated - as opposed, the RL-10 has proven it can. But if an SSTO stage has 9 kerosene angines and can shut off all but one, the acceleration is reasonable. If the remaining engine can throttle to 1/3 it can land vertically. Or if this first stage doesn't reach orbit, throttling gets easy.

Yes, there are other means! Which are used. Chemical explosives can squeeze electrical conductors in a magnetic field. Sakharov developed it, and such bombs were used, especially against Al Jezeera's transmitter in Bagdad at the beginning of the latest war. A capacitor discharge in an antenna creates an EMP. Credible figures are: luggage sized, destroys electronics at 10m, disables it temporarily at 100m. I expect effects on the brains as well. A Blumline can switch this energy fast enough, and present electronic switches like high-frequency MOS as well. http://en.wikipedia.org/wiki/Blumlein_transmission_line I believe such an EMP source was used in two Italian cities, as the observations match precisely. Amateurs proposed and demonstrated such weapons for use by police patrols against cars. Directing the effect is just a matter of antenna design - keeping in mind it must withstand high voltage. I urge all airliner designers to harden their designs against these small weapons, easy to conceal and efficient at landing.

Guys, peroxide is dangerous. At 20% concentration it's bad for your skin. At 70% concentration it's a brutal explosive, quite unpredictable, and it lights most materials like gloves and clothes. Do NOT concentrate it by distillation, as you're likely to let it detonate. People telling "90% by freezing" didn't try by themselves. There is a eutectic that prevents reaching this concentration.

First, put a string of resistors in parallel with your capacitors if you connect them in series, so the resistors will share the voltage equally, or it's guaranteed to end in a bang. Then, you need something to discharge the capacitors automatically, for safety. Don't forget that chemical capacitors have a memory effect: some charge (like 10% of the voltage) reappears slowly after you discharged them and open the circuit. And finally, you should have a look at the energy and capacitor size needed to make even a miniature coil gun.

A different method was investigated maybe two decades ago, where the impulse response of the room between a loudspeaker and the person's ears was precisely measured and a "decorrelation" function optimized by a Calman filter (=the known method to implement an autoadaptive filter). Then, this "deconvolution" sequence gives a pulse near the desired location but little elsewhere, as the room's response differs there. Of course, it needs the subject to be immobile, since his position influences badly the room's response, and the response where the subject is. I feel easier to create the sound where desired by optical means.

If all electrical power transform ultimately into heat - even the useful output of the machines - then the total consumption equals the radiation by the sphere which can be computed if you know its emissivity. It's proportional to T^4. This problem is totally artificial, since electrical machines use to burn before 180°C, hence cooling will be by convection, not radiation.

I did similar things and got mainly vapour. But, yes, chemical reactions happen. One would have expected a production of hydrogen and chlorine, but even with DC they readily combine and produce sodium hypochlorite - this will happen even more with AC. Beware hypochlorite - the very one used in household - is a poison. It's the one poison that kills most people in Europe. But when you smell it you have still time to vent the room. In addition, electrodes react heavily with evolving gas, because they ions and single atoms right in contact with the electrodes are very corrosive. You normally get some little soluble copper compound in the liquid after some time, green or blue depending on luck. Electrodes that resist these conditions are difficult to choose, with graphite being more affordable than precious metals like platinum.

Trying to check how probable it was to observe such a collision... From a list of 900 stars which had a debris disk in 2002: http://www.roe.ac.uk...tification.html I assume that 1000 stars have a circumstellar disk which is monitored every few years, a first bold assumption. Let's say this phase of the star evolution lasts for 10 million years. Then, I suppose that (no reason for it!) 30 collisions between gas and the circumstellar disk happen and end in that time, or one in 300,000 years. The 1000 stars would let one such event end every 300 years. If precise infra-red surveys have been made over the last 30 years, astronomers had 1 chance in 10 to see one collision end. Similarly, if each collision lasts for 30 years, astronomers had 1 chance in 10 to see one in action (V488 Per). Not bad. So many figures here are unknown and can be twisted that the desired probability is easily cheated.

The necessary amount of gas can't be a comet tail, but a mass equivalent to a planet may fit. As the disk was active, it radiated 0.3 Jy (0.3*10-26 W/m2/Hz) between roughly 6 µm and 20 µm (or 35 THz) at a distance of 456 L-y (4.3*1018 m, surface 2.3*1038 m2), or a power of 2.4*1025 W. This power was observed for 25 years; let's imagine it lasted for 40 years, then the emitted energy equals 3.0*1034 J. As a circumstellar disk is an early phase of a planetary system, I imagine many objects are still out of the equatorial plane, even massive ones and rather near to the star. Let's say the heavy disk had 30km/s where the collision happened, and the gas 30km/s as well but 30° out-of-plane. Then, it takes 2.7*1026 kg of gas to bring the kinetic energy that heats the disk: that's half a Saturn - remember planets still aren't formed, so these amounts of gas are available. But if the gas orbits at 30km/s and 90° out-of-plane, then 3.3*1025 kg suffice, or half a Uranus. And if the gas had 15km/s above the star's gravitation well and 180° inclination, then 1.1*1025 kg suffice or two Earths. Such an event wouldn't be anecdotal. It would be an important step in the formation of a planetary system - a step needed, by the way. Which implies it wouldn't happen often - not necessarily a bad thing, since many circumstellar disks are observed and TYC 8241 2652 is the first showing this behaviour. Marc Schaefer, aka Enthalpy Thanks D H! From that paper: - The disk emitted 11% as much infrared power as its star over the total spectrum. This is more than usual, with only V488 Per exceeding it; - It emitted at a wavelength around 11µm when it was active, but 22µm now. Both are compatible with a disk heated by collision. Should they observe V488 Per over time?

Please tell us what LFTR has ever run.

A surprise to astronomers... The young star TYC 8241 2652 is considered to have a circumstellar disk that radiates the observed thermal infrared. This IR radiation uses to vary moderately and slowly, but not so TYC 8241 2652 : between 1983 and 2009 it fluctuated by a factor of 3, but then it dropped by a factor of 10 within two years though the star remained quiet. A general-press paper: http://www.gemini.edu/node/11836 The science paper (30€): http://www.nature.co...re11210.html#t2 Free excerpts: one figure, two tables and a rationale that dismisses usual explanations http://www.nature.co...re11210_F1.html http://www.nature.co...re11210_T1.html http://www.nature.co...re11210_T2.html http://www.nature.co...ure11210-s1.pdf Not a coalescence, not a collapse, not blown away nor molten. ----------------- I'd like to suggest a different scenario. The disk has not changed in the event, but its heat source did, which is not mainly the star. A cloud of gas impinging on the disk (or maybe very fine dust) could heat it and explain the previous luminosity. When this source disappears, the disk cools down quickly. A local gas cloud may not be exceptional in a stellar system, even old. I feel it's an explanation to our comet 17P/Holmes, which increased its luminosity by 15 magnitudes without breaking apart. http://en.wikipedia....ki/Comet_Holmes The disk, cooler under normal circumstances, would only need to reside farther from the star. I suppose its diameter is not observed: the authors suggest 0.4 AU diameter at a distance of 456 L-y, converting to 0,0015" apparent radius. A 2m telescope observing at 10µm has its first diffraction zero at 2*1.2" and a 10m telescope observing at 1µm has them at 2*0.025". Marc Schaefer, aka Enthalpy

Nice toys, sure. But I'd prefer semiconductor research to concentrate on connection lines instead of transistors. Because since the Core 2, clock frequency hasn't improved. MOS transistors are perhaps faster at 22nm than 65nm - and perhaps not - but connection lines get slower as processes shrink and they're the limiting factor since the Core 2. Faster methods are needed within the chips! Perhaps by light, by electron beams, by spin waves or with radically better materials (YBaCuO in moderate cold?) but this is where progress is badly needed.

A 2.5t impactor is small, for instance a cone of D=0.5 and L=5m. The reactor's parts not touched directly by the impactor would be pushed to the sides, at a serious speed, for instance 1000m/s. Found data for liquid sodium at +145°C : 917kg/m3 and 2500m/s sound velocity, so a shock wave of 1000m/s would induce at least 2.3GPa and the bulk modulus at 1b is 5.7GPa - just to give a sense of the density increase. Water near its critical point is highly compressible as well. The Mark-1 has its control rods at the bottom, a criticized design. I feel the power spike is an added worry. It wouldn't produce much more radioactivity than normal operation has acumulated, but since only the core's vaporization ends the supercriticality, it would spread elements that other accidents keep solid hence disperse little, for instance plutonium. At Fukushima yes, because the thermal neutron reactors (almost) "need" their moderating water to sustain a chain reaction. At a fast-neutron reactor, the coolant is a hindrance to the reaction. Losing it, and much worse, concentrating the fuel at the bottom of the vessel increases the reactivity a lot. Neutron losses at the core's surface limits much the reactivity of a fast-neutron reactor. Hence I maintain: the same situation, with fuel fallen down in the vessel, would be much worse with a FNR - in fact, it couldn't even reach that point. The mechanical impact of 30GJ (a bit less energy than the 20t of propellants) melts a part of the core and the debris with a high melting point stay in the vicinity. As opposed, prompt criticality (typical time constant 100ns) induces a huge temperature (a nuclear one, not chemical) before various kinds of pressure disperse the reacting components. This means that all elements, including refractory ones like plutonium, are widely dispersed. Without the prompt criticality, things like iodine and caesium fly away. Fast neutrons reactors lose many neutrons at their surface, thermal neutrons reactors few. So density is more important to FNR. And in the case of a battletank impactor, loss of coolant stops the water-cooled reactor but brings the sodium-cooled one into prompt criticality. 30,000 degrees: hey, I wrote "similar". This figure isn't accurate neither. Take the extreme case of France with >50 reactors: bursting them would make the country about unusable. In constrast, dam bursts would make permanent total damage to very few cities. Paris for instance would be partly evacuated for some days after a dam break, then cleaned and inhabitated back. I really dislike the deterrent-type threat by weapons not very difficult nor expensive to build, whose launchers can be banal and located quite far.

For instance because they don't have this capability and because they don't exist?