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Hi Matt. That has nothing to do with my question. What is the shape of the focus on a catenary reflector? It should not be a point. Is it a line, is it a circle, or...? Miguel

Hello. It's been over 30 years since my days at the university and have trouble thinking... I believe a catenary reflector has a focal area -locus?- instead of a focus point as a parabolic reflector has. Is it a circle ? The intention is to place a pipe of the same section at the locus of a catenary reflector trough, to be insolated and boil water circulating in it. The center of the locus must be centered between the ends of the catenary. The catenary lenght is 4 feet. What would be the correct catenary span or depth? Thanks, Miguel

Same as the net force acting on the water. Will not be buoyant, will not sink. Miguel

Hi. Stolen from http://groups-beta.google.com/group/sci.chem/browse_thread/thread/e953efcde574ddf/dfadde77d600eed7 : The reason that stainless steels are corrosion resistant, even though they consist mainly of iron, is because they contain a minimum of 12% chromium, usually along with some other metals. Ordinary iron and steel alloys rust quickly because atomic iron is much smaller than oxides formed by interacting with atmospheric oxygen and/or oxygen dissolved in water. The oxides formed during rusting create a loose layer that flakes away, exposing fresh metal to the corrosion. Chromium, along with other metals ( such as nickel ), are added to stainless steel alloys to help improve physical propeties and corrosion resistance. The chromium in the stainless steel combines with oxygen, forming a very thin passive film of chromium-containing oxides. The sizes of chromium atoms and their oxides are similar, so they bind together on the surface of the metal, producing a thin oxide layer only a few atoms thick. If the surface is rubbed or damaged and the passive film is broken in air or water, more chromium oxides will immediately form and recover the exposed metal substrate surface, protecting it from further oxidative corrosion. Note that the oxide film is not physically strong, it just forms rapidly, and weakly adheres to the alloy, thus protecting the metal below from further corrosion. It can be disrupted and displaced easily by abrasion, so many common stainless steels aren't suitable for corrosive situations where the surface is continually swept, and special alloys, with other elements are used.. The passive film requires oxygen to self-repair, so stainless steels can have poor corrosion resistance in situations where there is limited oxygen or other elements or species will compete with the oxygen. The smelly active sulphur species in garlic and onions; the volatile selenides in garlic, cabagge, and broccili; and also the chlorides in salty water will all attack and destroy the passive film of most stainless steels more quickly than the film can be repaired in a low oxygen environment. Some of the smelly compounds will bind to your hands ( onto proteins, lipids etc ) and will become non-volatile ( non-smelly ), but the number of binding sites is limited, hence any excess of smellies results in smelly hands. By binding to the metals in the stainless steel bar, the unbound smelly compounds on the surface your hands are transformed into non-volatile ( and thus non-smelly) compounds and complexes on the surface of the stainless. The new surface layer, which is weakly adhering and fragile, will be continuously abraded off by the active rubbing of the bar and replaced by oxides using oxygen from air or water. For many stainless steel items, especially those in contact with chemicals or water, passivating metal finishing processes are applied ( such as treatment with nitric acid ) when fabrication is complete. This ensures they start life with a good, thick layer of oxide. Otherwise corrosion may start in any crevices, scratches, or heat-affected areas ( welding ), and unprotective deposits ( eg smutty black sulphur layers ) may form in low oxygen environments, such as water. I hope the above is more understandable, and addresses your questions. (by Bruce Hamilton)

Hi. At least this will be good for science fiction... The earth and our moon are in a very delicate and precise balance of speed and interacting gravity maintaining their position. In theory¿? any force applied to the moon can change its orbit a given amount. Assumming feasability of assembling a large enough upside down propulsion rocket on the visible side of our moon (or a smaller one for long enough time) and pushing it out of orbit until it is gone, gone...spiraling out no longer on earth's orbit. Yes, many catastrophic consequences implied here, but keep the imagination on. Doing the same with Titan, if a convenient atmosphere and water and other amenities are found there, bring it aiming precisely to start orbiting the earth as replacement. Well, another place to overpopulate and pollute would be available. With proper technology, time and calculus; is there any tiny chance for this to be not fiction some day ? Miguel

I have deleted my own poorly expressed post, where I should had said the atomic clocks are less related to earth's rotation now after the Ninetyeast ridge quake. Miguel

Yes, you are lighter at equator; by two reasons; the increased distance from the center of earth gravity and the centrifugal force. http://www.madsci.org/posts/archives/mar97/857469722.Ph.q.html http://www.madsci.org/posts/archives/mar97/857469722.Ph.r.html What I don't get is if an object on top of a scale at equator determines the force of gravity there or the force of gravity less the centrifugal force. By figures from a post above, 9.78 = G(eq) minus 0.0337 In other words, the weight of a body at the equator does not obey only to the gravity constant there but also the centrifugal force; then the pure gravity constant figure measured at the equator is inexact because the centrifugal force was not taken in account.... I think... Miguel

Hello everyone... Sound propagates in air at 340m/s by the sucessive compression/expansion of the highly compresible gas medium due to soundwaves; ¿ How do solids propagate sound with such diminished compressibility ? ¿ What is the typical range of sound progagation speed in plain soils ? Much faster ? And further ? and with less attenuation ? ¿ Are earthquakes detected by microphony or motion transducers or both ? There was once a web site and group dedicated to sense underground noises, I would appreciate any clues to locate it. Thanks, Miguel

Hi. Trying to learn on the subject, found some good literature and principles of the process but I have this doubt: -Assuming plain water and not extreme vacuum ; the vacuum pump creates 24 inches of mercury, enough heat supplied to the liquid. The vapor starts filling the vacuum above the liquid surface, decreasing the vacuum reading or not? In other words, the vacuum pump must operate constantly and not only to achieve an initial amount? If the vacuum has to suction all the time to maintain said 24"Hg , why is an internal condenser used inside the distillation chamber ? The condensation could be collected at the vacuum pump discharge. Thanks for the light. Miguel

Hi. From my poor understanding, a cesium clock could then be made to work also at other characteristic transition frequencies ? Hello atinymonkey. The link referred does not work, received this : " Invalid Thread specified. If you followed a valid link, please notify the webmaster " ¿Can you please confirm it was properly copied? Miguel

Hello. Can someone direct me where to look for a list of the characteristic frequency, vibration or oscillation of the elements? From atomic clocks information I was able to collect figures for only 3: Rubidium = 6.834,682,612 GHz Cesium = 9.192,631,770 GHz Hydrogen = 1.420,...,... GHz Am looking for the rest, or whatever is known. Thanks, Miguel

Hi everyone. As I am not a thermodynamics guy, but an electronics guy, I beg for your asistance on this forum on my lack of heat transfer thinking. Planning to drill a ~100m deep well in my backyard, it is supposed to reach well beyond a stable ~20°C thermal layer; circulate water trough a long 2" U shaped polyethilene pipe to provide home cooling in ~30°C summers and help warming in ~0°C winters : A convection geothermal heat pump. What are the effects of the water velocity on amount-of-heat transfer ? From analogies on internal combustion engines, the faster the flow the greater the heat transfer - that is why racing engines have high flow coolant pumps- . On the other side, a slow flow speed allows the circulating water to reach the stable temperature and deliver all its potential temperature. What is more convenient ? A small mass flowing at a higher temperature differential or a larger mass flowing at a lesser temperature differential ? Seems to my ignorance that any will work equally, as the amount-of-heat would by Q=mass x (t2-t1) ; leaving good convection radiators, low losses, proper insulation of pipes, system efficiency to determine its effectivity. Is the ideal flow speed the one that will allow the flow to reach within a couple of degrees to ensure there will be heat transfer at all times? Thanks, Miguel

Hello YT2095 Would had been a nice try if some results were obtained. The aperture is narrow, yes. Solar stills with plain flat glass do produce a respectable amount of drinking water with the same temperature differential. No bottlenecks there. The intention is to find a distilling application recycling the zero cost PET disposable beverage bottles, for the third or fourth world to get some drinking water using many of these contraptions. The bottom sun exposed bottle is flat flack, the necks mating has a condensate collection ring and aquarium hose outlet. All that seems fine. Ideas to make the vapors rise to the upper bottle are needed. Maybe venting the top bottle as in distilling colums would help by producing a tiny agitation of the water surface ¿? Miguel

Thanks. I should had said room temperature, about 25°C for the upside-down cool bottle. Miguel

Hello everyone. Simple condensation does not happen : A bottle ¾ filled with water kept hot (~60°C). On top of it, another bottle upside down kept at ambient temperature, coupled neck to neck with adhesive tape, forming a shape sort of an hourglass. No condensation happens in the internal walls of the upside down top cool bottle, even after hours. Why ? What is missing ? How can condensation be achieved ? VERY easy to try and confirm by yourself ! Miguel