# Externet

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2116

1. ## Making an alloy at home ?

Hello. How complex could it be to make a couple of kilos of Gd5(Si2Ge2) plus 1% in volume of Fe added ? What equipment would be needed ? Miguel
2. ## Amount of food and belly size...

Hi. Some societies have the daily habit of eating huge volumes of food, without neccessarily having big bellies (like in Spain:-) ) Some people (like me) habitually eat really small quantities of food. I have read -and seen- that poorly fed kids as in some African nations develop large bellies. What is going on ? Can persons fed in large quantities not develop large bellies because their metabolism is used to count on never a short supply of food ; and people eating very little store reserves as a natural 'defense' mechanism and thus developing large bellies ? Miguel
3. ## Subtended angle...

Hi all. Now i got confused; this site: http://www.mathopenref.com/subtend.html shows the subtended angle for the sun being 32 arc minutes or 0.52 degree. That seems very small. Does it mean that in a 12.0 hour day, the sun path could be drawn as 346 sun disks fitting edge to edge on the sky ? Am trying to create a formula, chart or nomograph to calculate the needed diameter of a distant mirror reflecting the entire sun disk. (As a heliostat of what diameter positioned at a given distance will show the complete sun disk) Miguel
4. ## de-salinastion?

Ok, that means one side of the membrane has 800 psi more than its other side... The top of the membrane would have the ocean column pushing water down, and you have to make vacuum under the membrane to obtain 0 psi for the pressure differential. The pump under the membrane would have to be 800 psi anyway for its outlet to reach the surface. Work on that. Miguel
5. ## Behavior of Tin...

Thanks, fellows. The flux formula is from Kester, and they only reveal being a "modified resin". If Sn has affinity for Au, would explain the fast erosion. I would have no problen in trying Pt but if dissolves as gold there is no point on increasing my frustration. It is plain Sn unleaded solder for electronics, and canot discern what material for the soldering iron tip could handle it without degradation. Suggestions on what to use ? Miguel
6. ## Behavior of Tin...

Hello. Does molten Sn attack 24K gold? Just had my electronics soldering iron tip jacketed in 0.5mm pure gold and eroded in a minute at 800ºF! (There is a chance it was a poorly done job by the goldsmith) What other metals will get wet with 96.5% tin solder and not degrade with oxides, corrosion, staying tinned ? Ag, Pt, Ti,...? Miguel
7. ## Centrifuging for ions...

Thanks, jdurg ! As am not thinking this for a batch type/test tube laboratory centrifuge, but for a continuous-flow industrial type as in: http://www.alfalaval.com/ecoreJava/WebObjects/ecoreJava.woa/wa/showNode?siteNodeID=5381&contentID=-1&languageID=1 [These machines run at 10 thousand G's, I know their performance from the years I worked at a fishmeal plant where these extract oil from fish 'broth'] ---> Can I interpret your answer as... A centrifuge can be used as a desalinator if fed with seawater ? Would ions respond sustantially different to extreme gravity than water itself ? Which would float, ions or water ? Miguel
8. ## Swamps, environment without commercial uses ?

Thanks. Well, but if the swamp is drained, it is no more. I mean as in wetland state, gets ignored and stays undisturbed. Or... is there some crops from such places? Miguel
9. ## Centrifuging for ions...

Hello. Can common salt be separated from brine with a centrifugue? How do Cl- and Na+ ions densities compare to water molecules and are affected by hyper gravitational forces? Miguel
10. ## Swamps, environment without commercial uses ?

Are swamps left alone because are useless for cultivating anything ? Are there any fruit trees, crops or something swamps produce besides mosquitoes ? Miguel
11. ## Which is the most 'intelligent' animal, in your opinion?

Hi. Unsure if this is the best place for the subject, but, which animal shows the most 'intelligent' behavior ? (life, strategies, skills, self-sufficiency, activities... at its animal level) Miguel
12. ## help

Depends on the location of its center of mass. When a plumb line from its center of mass falls outside the base footprint, it will fall... unless it is glued to the soil. Miguel
13. ## Speed of sound

Wrong. The well can be much deeper than the surface of its water. That is not even the distance to the water level in the well. The unknown size of the stone poses a much more complex calculation, as the larger it be in relation to the unknown well pipe diameter, causes more air cushioning its falling velocity. The unknown gap between the stone and the well pipe wall can change calculations considerably. Miguel
14. ## Shallow geothermics in real life...

Shallow geothermics. Always wanted to implement it; now I can and am ready. There is now an unused fresh water well in my backyard, has a suction pump, thus should have a check valve at the bottom of the pipe, then I believe is not 'deep'. Canot be over ~30 feet. (Coastal North Carolina) The well water temperature is somewhere near 60ºF. Inserting an automobile radiator in the return side of the central heating/air conditioner duct, fed by the closed loop from a U in the well with a recirculation pump, should supply the dwelling with ~60ºF air, to the capabilities of BTU exchange minus losses. In summer, for a ~85ºF weather, a delta t of around 25ºF; pretty decent, no airconditioner would be needed. Seems doable. In winter, for a ~35ºF weather, a delta t of around 25ºF ; pretty decent, not much extra heating requiered from the outputted 60ºF to reach 70ºF desired BUT: If the central heating system additional work heats up the house to ~70ºF; about THAT would be the return air temperature; rendering the geothermal plan unuseable, as if the inserted radiator has 60ºF, it would be counteracting and cooling a delta t of 10ºF instead ! Am I wrong somewhere? How could this case be used in winter? Many geothermic sites promote supplementary heating in winter even with not that much delta t. I do not see it possible now:-( . Is it about maintaining the dwelling at 60ºF while nobody is at home, then turning on the standard central heating during occupation hours? (And shutting the geothermal off then ?) D----->R------>Rad----->H----->S----->D For D=dwelling; R=return duct; Rad=radiator; H=heater; S=supply duct Thanks, Miguel
15. ## Parabola equation from dimensions...?

Hi. Too many years since left university, cannot think on how to create the equation. An 8 feet long string, (or rod, or sheet) forming a parabola. The shape will be somewhat like a flattened U. I want the focus at the center between the upper ends of the U. (Or, at the lower tip of the accent on this letter Ú ) How do I come up with the equation? -It's to build a reflector with a 8'x4' sheet and be able to mechanically support the focus between its ends- Miguel
16. ## Lithium

What can be done with a bunch of spent Lithium-ion cells I have ? They are half inch diameter, 3 inches long, out of laptops, should provide a decent amount of Li. Miguel
17. ## High-Sample Rate Oscilloscope or Galvanometer

Hi. I would attempt registering the spin using a storage oscilloscope. Borrow, rent, or... It will keep the waveform for analysis of which sampling approach is more convenient if you still want to involve a PC into it, or if the sensor needs modification to obtain a better amplitude/detail. Miguel
18. ## Why does water 'boil' at room temperature?

Hi. Be careful not to confuse the terms 'vapor' and 'steam', often frequently misused. The second is the one created over 100 ºC. The first happens at any conditions, as clearly, clouds are not at that temperature. Miguel
19. ## Tidal Turbines

They are proposing the same here under the San Francisco Golden Gate bridge; deep enough and massive flows. The problem is reliability and maintenance. Anything submerged in seawater is prone to failure by corrosion and carried debris. Technology and construction must be very reliable for success. Miguel
20. ## Pressure Apparatus

No, but use protection against the soda bottle exploding...
21. ## What prevents FM radio from reaching CD quality?

Truly, envious congratulations CurvKyle on your hearing abilities; but I believe you failed. How do you know the speakers you used for the 'online' hearing test are capable of "24Hz" ? Did you make a mistake meaning 24KHz? Well, 24 Hz is not bad either. herme3: Mostly yes, about 97% of radio stations do it in varied amounts. It is compression, limiting, clipping, multi audio-band equalizing, etc. Soft sounds are pushed up to FCC limits bringing a steady level with little dynamic range (difference between soft passages and loud ones) of about only 7 to 10 decibels. A recognizable extreme example is watching a TV movie, were dialog is at nearly the same level of guns shooting. Yes, sure:rolleyes: . Convincing to those who have never heard a real shot. Of course if the TV speaker was to reproduce the sound level of a shot, it would vomit its guts out at the first .22 cal firing. The specialized audio processing equipment is at: http://www.orban.com. There is some instructive audio articles worth reading, but you have to dig for them at the site. Edit- added : the document is titled "Audio quality in the FM plant" Miguel
22. ## Bats can do it, why can't we

My jaw dropped to the floor last week watching a television documental intervieving two blind kids riding bicycles ! and playing basketball ! self guided by continuosly clacking their tongues and listening to echoes. They are able to discern parked cars, pedestrians, obstacles. Perhaps if you do a deep search of the net, something may be transcribed here. It is well worth the effort to find such article. Miguel
23. ## What prevents FM radio from reaching CD quality?

Hi. I like your question. Perhaps because I can answer. The difference from FM broadcast and CD is barely audible if you can hear over 15 KHz, which I doubt unless you are 10 years old... If you disagree, do not argue and get a hearing test first; then we can discuss the subject. The Federal Communications Commission FCC sets 15 KHz as maximum frequency response for a 200KHz channel bandwidth for FM stereo stations to avoid interference with adjacent channels and limits spurious emissions from overmodulation. There is many CD recordings that are much worse than FM broadcasting, and there is many radio stations that sound much worse than a CD. There is NO norm. And beyond, there is millions of ears each with a different opinion about what sounds better. Radio stations do use audio processing to make their signal louder by compression and other effects to gain dial market competitivity, deviating from flat and realistic audio reproduction. CDs are too often also recorded with coloration and effects to suit producers demands, disrespecting fidelity in an attempt to make more \$ by leaning towards trendy sounds. So, you can't cut all cheeses with the same knife. ALWAYS remember the definition of distortion: Any and all difference from the original sound source. Don't tell me that singer XYZ sounds in front of you the same as in its tricked, equalized CD recording. Miguel Audio-recording engineer -13 years working on audio processing equipment for broadcasting-
24. ## Phospor that glows under infrared exposure ?

Hi. Investigating a little deeper, appears that the compound is ZnS with Cu or other dopants to select the color given off. And seems the nasty habit of naming things wrong as "phosphors" when there is no phosphor at all strikes again. That pisses me off. Misleading information using the word phosphor when they should say plainly luminescent. I do not have a plain old green monitor to aim my IR laser onto it and check if the CRT uses the same compound. But that works with electrons, not photons... I'll try on my oscilloscope. The powder coating inside fluorescent lamp tubes, what is it, exactly? It gives off white light when irradiated with UV, IR, plasma, ions, electrons or by what from inside the tube? EDIT- added- Found this: (Ba,Eu)Mg2Al16O27, blue phosphor for trichromatic fluorescent lamps (Ce,Tb)MgAl11O19, green phosphor for trichromatic fluorescent lamps (Y,Eu)2O3, red phosphor for trichromatic fluorescent lamps (Sr,Eu,Ba,Ca)5(PO4)3Cl, blue phosphor for trichromatic fluorescent lamps (La,Ce,Tb)PO4, green phosphor for trichromatic fluorescent lamps And dopants added to ZnS, what is the doping process; is it just adding a minute amount of what Cu compound and mechanically mixing or something more elaborated? Miguel
25. ## Phospor that glows under infrared exposure ?

Hello What compound would glow when exposed to infrared light? It is used applied as paint on a piece of cardboard to test the illumination from remote controls and infrared beams. Read it is some phosphor compound, but unsure if it is plain white phosphor with something else or not. It is shown here: http://img.alibaba.com/photo/10846815/Infrared__IR__Laser_Test_Card__Anti_stoke_.jpg Thanks, Miguel
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