Wikipedia:Reference desk/Archives/Science/2006 September 5

= September 5 =

Discovering an alien probe
Let's say an alien robotic probe parachutes down to a suburban area in the U.S. Someone discovers it. What will happen next? Also, ideally, what should happen next? --Bowlhover 01:09, 5 September 2006 (UTC)


 * Our government would take it away. And convince that entire suburban area that the said event never took place. Russian F 01:39, 5 September 2006 (UTC)


 * George Bush would invade a country that wasn't involved. Peter Grey 02:10, 5 September 2006 (UTC)


 * Seriously, although I'm not very happy with the U.S. government, I don't think they're hiding anything about alien probes. They are hiding information about U.F.O.s, but those U.F.O.s are probably either natural phenomena or machines built by humans.  --Bowlhover 03:35, 5 September 2006 (UTC)


 * The reason you don't think the government is hiding information about alien probes is that you do not believe there have been any alien probes. Now, if I were to tell you there have been several, and you believe me, would you still think the government isn't hiding the information? --Lambiam Talk 08:12, 5 September 2006 (UTC)


 * No, but I don't believe that there have been any alien probes. How hard is it to expose the truth if many people took pictures of it?  It would be hard to confiscate all of the evidence, wouldn't it?  --Bowlhover 03:39, 6 September 2006 (UTC)


 * Why specifically the US? Is this meant as a question about US politics (as Peter took it to be)?


 * Given Peter's example, the person who discovers it should idealy inform international organisations first, before the US government finds out. The UN would be a good choice, but they would not have a mandate to claim it. No extra-USian governmental organisation would. So may be he should infomr a private enterprise and get them to transport it to a neutral country. But I don't know which enterprise would be willing or able and what constitutes a neutral country anyway. New Zealand? DirkvdM 09:08, 5 September 2006 (UTC)


 * Tell anyone except your own government first - that way there's less chance that they'd just spirit the thing away, never to be seen again. The UN, international news agencies, the Pope, anyone with a bit of clout. --Kurt Shaped Box 23:53, 5 September 2006 (UTC)


 * Am I the only one who doesn't think the authorities would cover it up? At least not after they confirmed for themselves what it was. freshofftheufo  ΓΛĿЌ  13:49, 5 September 2006 (UTC)


 * Bill Clinton seemed absolutely thrilled to think that discovery of alien life had been done under his term (ALH84001). I think that the assumption that American politicians would be happier hushing something like that up does not take into account the political benefits of being the first president to announce contact with another civilization. --Fastfission 14:49, 5 September 2006 (UTC)


 * In a sense, the probe would have the initiative. If it can communicate, and has a sufficiently advanced artificial intelligence, then we'd be very interested in what it had to say; if it was damaged, then all we could do would be to analyze it.  If it said it would only talk to the UN, we probably wouldn't argue.  There would be a conflict between quarantining it (it could have extraterrestrial bacteria, or it could have become radioactive, etc.) and displaying to the media, given that there would be a natural skepticism about the discovery, especially if it had not previously be detected moving through our solar system. If it appeared in US territory, given that the US has the resources to examine it, they would probably handle it through military channels (because there could be a legitimate worry that it would be dangerous).  A cover-up would probably be impossible. Peter Grey 17:59, 5 September 2006 (UTC)


 * Is it really a good idea to carry the probe away immediately? The aliens who sent it don't even know there's life on Earth, and if somebody takes the probe away, they'll think their mission failed.


 * I picked the U.S. as the landing place because its people know (relatively) a lot about science. If I picked some small community in Africa, where half of the residents are illiterate, they'll think it's a gift from God or something.  And no, this is not a question about U.S. politics.  It's about how we should let the aliens know that life exists on Earth.  --Bowlhover 03:39, 6 September 2006 (UTC)


 * Everyone here is making a mistake. You're taking the viewpoint of the aliens in "knowing" an alien probe has landed.  Now a human would have no such knowledge.  Suppose the thing landed on your own street.  From your point of view a 'thing' (not a probe) has 'appeared' on the ground (and not landed).  Unless the landing was witnessed, and unless it's huge, it would appear to be some kid's weird toy.   How did it get there?  Where did it come from?  If not a toy, then it would look just like a hoax or like a publicity stunt, or like some weird project built by subscribers from [makezine.com].  Wouldn't it take quite a bit to convince you that it wasn't just a toy or a hoax?  That said, I would predict that if it's small enough, one of the neighbors would not recognize it as a probe, but would see it as valuable and unclaimed, and therefore steal it.  Then perhaps they'd diddle with it for awhile, then dump it in their backyard or cellar and eventually forget about it.   Which leads to this conclusion:  several alien probes may have already landed, and they're sitting forgotten in barns, cellars, or weed-filled back yards right this minute.  :) --Wjbeaty 00:23, 9 September 2006 (UTC)


 * Why are you assuming the alien probe lets itself be confiscated and examined? --Proficient 03:46, 6 September 2006 (UTC)


 * If a probe lands in a an inhabited area with artificial structures, it is probably not trying to go undetected. Of course, maybe it's builders just think differently. Peter Grey 13:24, 6 September 2006 (UTC)


 * Kurt, the pope? He'd certainly hush it up. What are the chances the aliens are catholic? And what would the catholics make of that?


 * Why do these things always land in the US in hollywood movies? It has only 2% of the Earth's surface. Then again, the martians in War of the worlds landed in England, which even has less than a promille of the surface. A Luxemburgian SciFi writer would have a serious credibility problem. :) DirkvdM 17:50, 6 September 2006 (UTC)


 * You seem to be assuming they just land somewhere at random (and you even include landing on water, apparently). What if they have been observing us and decide to land in the "center of power".  They might well decide that is the US now, or England back in H. G. Wells' day. StuRat 09:53, 7 September 2006 (UTC)


 * If conquering the Earth is the goal (as was teh case in War of the Worlds) then it wouldn't be smart to land in the lion's den. Especially if that lion is armed to the teeth. Landing on an ocean would make most sense if the goal is to establish a base first. The oceans are barely observed (a problem for meteorologists) and one can go underwater for even better cover. But even if they don't know how to build (u)boats and have to land on ... ehm ... land, a remote piece of land would make a better choice. Like Siberia or the Sahara. The US has some deserts too, but is the most paranoid country on Earth when it comes to attacks (with reason, but that's a different issue), si that would be the most likely place to be detected. So, to come back to the original question, if aliens land in the US they are either incredibly stupid or want to be detected. DirkvdM 18:50, 7 September 2006 (UTC)


 * If they had an overwhelming military superiority, though, it would make sense to defeat the biggest threat first. This seems to be the case (or, at least, the aliens think it's the case) in most movies I see. StuRat 04:22, 10 September 2006 (UTC)


 * If you're paranoid with good reason, well...then...you're not paranoid. The definition of paranoia is the irrational fear that people are out to get you. If people are indeed out to get you, and you're worried about it, then by definition you're not paranoid. Rather, you're just very rationally concerned. Loomis 21:07, 10 September 2006 (UTC)

separation of chemical compounds
How could you separate barium sulfate from ammonium chloride?

How could you separate barium chloride from calcium sulfate?

How could you separate tellurium dioxide from silicon dioxide?

Undesguised homework again? Choose some of the properties and use the most appropriate ones to aid separation.--Light current 02:00, 5 September 2006 (UTC)


 * i'm guessing reading isn't his/her strong point... Xcomradex 03:03, 5 September 2006 (UTC)


 * Mine neither--Light current 05:30, 5 September 2006 (UTC)


 * no for you it's spelling, unless it's all a clever desguise... ;-) (no harm intended). Xcomradex 08:07, 5 September 2006 (UTC)


 * I prefer to call it finger trouble! THe keys are too close on my keyboard 8-)--Light current 08:24, 5 September 2006 (UTC)


 * Salts like the ones you describe are usually separated using precipitation reactions. You need to figure out the rest. - Mgm|(talk) 10:53, 5 September 2006 (UTC)


 * Sulfates of the Alkaline Earth elements are generally insoluble in water. Chlorides are usually very soluble in water.  I do not have a clue about the last one, both are very insoluble in water, but maybe a solvent exists which is good for one but not the other.


 * For the third pair, one of them is twice as dense as than the other. See Silicon dioxide and Tellurium dioxide.  Of course, I'd use a mortar and pestle and my firing oven, but that's just me... -- Fuzzyeric 00:06, 6 September 2006 (UTC)


 * This is a repeat question. I answered it back in February 2006 .  Looks like the teacher is using the same questions.  --Uthbrian (talk) 02:59, 11 September 2006 (UTC)

California Moss Genus/Species
Can someone tell me the taxonomical binomial nomenclature of that common, general greenish moss that is found all over rocks and such on the southern West Coast? Thanks so much, ChowderInopa 01:58, 5 September 2006 (UTC)


 * You mean what its called?--Light current 02:04, 5 September 2006 (UTC)

Yes, I mean the scientific name. ChowderInopa 02:38, 5 September 2006 (UTC)


 * Can you say something more about its appearance? Are these damp habitats? Are you sure it is not lichen? --Lambiam Talk 07:59, 5 September 2006 (UTC)

The southern west coast of what? Oops, missed the header. DirkvdM 09:09, 5 September 2006 (UTC)

satellite imagery maps
I need to know where to look for the satellite imagery maps. I want to see what my home looks like from above and the locations around my home. Please show me how to get there on wikipedia. Floyd —Preceding unsigned comment added by 68.119.96.36 (talk • contribs)


 * I'm too tired to do the whole 'build a satellite' launcher routine, fun as it would be. Google is your friend.  Go there, and punch in your ZIP/postcode.  If necessary, switch from map to satellite view.  --Mnem e son 02:21, 5 September 2006 (UTC)


 * for even more google, try Google Earth. its great. Xcomradex 03:05, 5 September 2006 (UTC)

Do you smell burning toast?
Hey, could anyone settle a debate for me? My friend doesn't believe that smelling burnt toast, when there is no environmental source of the smell, could be a sign of a stroke. Is it a common occurrence, something that happens rarely, or just a myth? Thanks in advance for your input. --Dimblethum 02:52, 5 September 2006 (UTC)


 * It could be a sign that you suffered a stroke, and then tried to toast the same slice of bread 10 times, after which it would smell rather burnt. :-) StuRat 03:02, 5 September 2006 (UTC)


 * It may be a symptom of a stroke. (See for example this case study.)  It may also be indicative of a brain tumour (it is sometimes a sign of brain metastases in advanced cancer), or of some neurological problem, or it could just be a passing random olfactory hallucination.   An odour of 'strawberries' is also reported by some individuals.  Some people have also reported a burnt toast smell immediately before a seizure or migraine.  TenOfAllTrades(talk) 03:04, 5 September 2006 (UTC)
 * Burning rubber is another one. George Gershwin had this symptom before they diagnosed his brain tumour.  Any disturbance to the proper functioning of the brain can produce visual, auditory, olfactory, gustatory, or kinesthetic perceptions of external phenomena that do not objectively exist.  JackofOz 07:13, 5 September 2006 (UTC)


 * So are synesthetics in constant threat of a stroke? DirkvdM 09:19, 5 September 2006 (UTC)
 * I think you can work that one out yourself, Dirk. JackofOz 12:04, 5 September 2006 (UTC)

burnt toast
I've heard that burnt toast has the same calories as regular toast. I believe it has less, but negligably less compared to our caloric intake.

what are th e facts?

Jasbutal 03:52, 5 September 2006 (UTC)


 * That sounds reasonable, but I have no facts. I would guess that if a piece of burnt toast is still palatable enough to swallow, then it can't be too badly burnt after all, and its interior is still perfectly nutritious. Melchoir 03:58, 5 September 2006 (UTC)


 * I dont see how it can have the same, since some of the bread has been reduced to pure carbon. THat is how you tell the calorific value of food- you burn it in pure oxygen till theres only ash Food_energy.--Light current 05:09, 5 September 2006 (UTC)


 * I'd say both statements are probably correct; there isn't necessarily any contradiction between "(approximately) same" and "negligibly less". (Or course, that depends on how burned the toast is — if you burn it all the way down to water, carbon dioxide and ash, it won't have any caloric value left.)  —Ilmari Karonen (talk) 05:23, 5 September 2006 (UTC)


 * Exactly. So how many calories would you like in your toast this morning Sir?--Light current 05:27, 5 September 2006 (UTC)


 * As dry as it may seem, regular toast still contains a considerable amount of water. The overheating that causes the toast to burn also evaporates some of the water. The net effect on the calories per unit weight may initially be an increase. --Lambiam Talk 07:51, 5 September 2006 (UTC)


 * Yes that is why toast racks are used I believe- to let the toast dry out and not go all soggy.--Light current 08:10, 5 September 2006 (UTC)


 * Very interesting. --Proficient 03:48, 6 September 2006 (UTC)

Blindness and circadian rhythm
I recall reading about an experiment where some college students were locked in a windowless suite of rooms without a clock, and were invited to sleep whenever they wished. Many of them began sleeping at unusual times that wouldn't map well to the 24-hour day. However, when they were made aware of the sun's progress, their sleeping patterns began to approximate the day-night cycle. Is anyone else aware of this study? My question is this: do the sleeping habits of blind people tend to be independent of the sun? Presumably the only non-visual distinction between day and night would be one of temperature, and if the person remained inside in a climate-controlled environment, this would not matter. Long question short, is there any record of blind people having trouble casually (i.e. without having to put special effort into it) distinguishing night from day, and experiencing sleeping problems as a result? Is it plausible? I'm not talking about people with jobs and schedules, but people who might not pay close attention to clocks, such as people in hospitals or retirement homes. Bhumiya (said/done) 05:00, 5 September 2006 (UTC)


 * I don't believe your assumption that blind people are less aware of the time of day is correct. They have a variety of ways to check the time, from audio watches, to radio and TV broadcasts, to periodic events, like church bells ringing, etc.  While it's true that a blind person in a coma in a hospital would be unaware of the passage of time, the same is also true of a sighted person in a coma. StuRat 07:12, 5 September 2006 (UTC)


 * Well, that's true, but I didn't mention comas. I only meant patients in general, who would have little to do but lie in bed. Bhumiya (said/done) 03:56, 6 September 2006 (UTC)


 * I believe that a blind person, in any condition short of a coma, would still be aware of the approximate time of day. StuRat 06:44, 7 September 2006 (UTC)


 * Years ago I remember seeing a tv doc about people living in windowless rooms without any time cues. They started to live on a 25 hour cycle, which curiously enough is the same length of day as on MARS!!

I think blind people would take their cues from tv, radio, alarm clocks, and other people.


 * But I think the intresting question is whether you can force your body to physiologically adapt to an arbitrary night/day cycle without the usual help you get from light, which causes your brain to secrete a variety of transmitters that entrain your circadian rhythm. I guess it would depend on what the exact cause of the blindness is. Nrets   16:56, 5 September 2006 (UTC)


 * I think that if anyone is not aware of the sun's changing, then they will have an internal clock that keeps changing and getting off. --Proficient 03:50, 6 September 2006 (UTC)


 * I once heard or read, but cannot confirm, that there are two common circadian patterns among humans, one of which is about 25 hours long, the other 32 hours or something like that. Bhumiya (said/done) 03:56, 6 September 2006 (UTC)


 * I remember hearing, but I also can't remember where, about recent research suggesting that there was some kind of problem with the research that came up with the 25 hour figure, and that more recent research suggests that the free-running cycle in humans is closer to 24 hours. (Our article on circadian rhythm sure needs work.  We also have an article on Free-running sleep, but it seems to use the term to mean sleep that's unaffected by artificial rhythms, while in biology I think "free-running" refers to rhythms unaffected by anything external to the organism, natural or not.)  --Allen 04:15, 6 September 2006 (UTC)


 * I think that we may be proceeding with a false assumption. I also remember hearing, from at least two sources, that the effect of light affecting circadian rythm is not purely visual. The effect of light upon one's skin can also serve as a cue. Even a blind person would have light shining on his/her skin, and this would seem to be an additional cue as to whether it's daytime or nighttime. Loomis 12:46, 7 September 2006 (UTC)

Mantle
Has there ever been an attempt at diging down through the crust to reach the mantle?


 * Yes I think it was called the Mohole project.--Light current 05:29, 5 September 2006 (UTC)


 * ...which failed. The Japanese are going to have another go at this next year. See Chikyu Hakken.--Shantavira 06:06, 5 September 2006 (UTC)


 * At the risk of asking a silly question, wouldn't that cause magma to rise and cause a volcano? I suppose one would have to make sure to drill at the right spot, where the is no magma chamber. Did I just answer my own question? DirkvdM 09:32, 5 September 2006 (UTC)
 * If you'll forgive me for attempting to answer a question that I myself was about to ask: I believe any area that would be in danger of spurting would be doing so already, or at least would be showing some sort of bulge. Any low/thin area of sea bed should conceivably be on top of a relatively inactive section of magma. freshofftheufo  ΓΛĿЌ  13:38, 5 September 2006 (UTC)
 * And yes, I guess you did ^_^ freshofftheufo  ΓΛĿЌ  13:40, 5 September 2006 (UTC)

Awesome.

At the risk of accusation of adding rubbish comments, I would say I tend to agree with the bulging hypothesis--Light current 00:03, 6 September 2006 (UTC).


 * Ah, so that explains the eruptions. This the kind of rubbish comment you were talking about? DirkvdM 09:21, 6 September 2006 (UTC)

Small writing - should it be allowed?

 * Hmmm, I now realise you may not have been thinking about the bulging and eruptions I was thinking of .... DirkvdM 19:16, 6 September 2006 (UTC)
 * Yeah man, that was pretty embarrasing. Maybe if you delete it now, no one will notice. freshofftheufo  ΓΛĿЌ  14:13, 7 September 2006 (UTC)
 * Or maybe if I make myself really really small ... can't get it smaller than 0, though. DirkvdM 18:55, 7 September 2006 (UTC)


 * Psst! do you think you will go unnoticed by writng this small? Some people here have eagle eyes you know!
 * Damn, someone gave this a really big header. We'll be spotted any moment now. DirkvdM 06:55, 8 September 2006 (UTC)


 * Yeah but this is a legitimate discussion of the use of small writing on the Ref desks. And it takes up less room than big writing.--Light current 07:04, 8 September 2006 (UTC)

Is it Bad to run PC without proper Earth supply?
Hi friends!...I've been using pc for a couple of years without supplying earth because in our block we have no earth connection to ground...Now is it ok to proceed so or need to give earth?..however I can feel some earth(mild current shock) passing on me whenever I touch the metal parts in the PC because of no earth..I know why this is,because of the returning current has no path way to ground an hence circulating in the cabinet and in all the metal parts..Some say it will affect HDD or RAM soon...Is it so?..and is it okay to proceed as usual?...or should I take immediate action for earthing?.But until now I haven't gotten any faults in my PC...Please help friends...My advance thanks


 * I'd say if you are feeling any shock at all, then yes, the computer should be grounded, immediately. (It's also a good idea, in any case.) :-) StuRat 07:06, 5 September 2006 (UTC)


 * Do you mean you should be grounded? What naughty things have you been upto this time? DirkvdM 09:36, 5 September 2006 (UTC)


 * "One should be grounded in reality" ... you ought to try it sometime ! :-) StuRat 01:58, 6 September 2006 (UTC)


 * If you have an external AC adapter, you should not be in danger of a serious shock, as it only delivers a low voltage (say 16V) to your PC. With an internal power supply, you might get electrocuted, which is generally not recommended. You could use a voltage meter to check if any metal parts carry an unsafe voltage compared to ground. --Lambiam Talk 07:34, 5 September 2006 (UTC)

Thanks...I recieve some mild shock inside the PC only...Maximum voltage of the SMPS (Internal Power Supply output only) is 12V.So I guess there shouldn't be risk of high volage shock..but say the current rating is as high as 22A..The shock is mild only which is bearable though..My suspect is that if it's gonna affect my hardware parts?...I haven't recieved any complaints yet since from the time I bought I've been using without earthing...


 * Unless this equipment is double insulated (which I doubt, if it has a metal case), it is not only undesirable, it is downright dangerous and even LETHAL. THe fact you are getting shocks should tell you this. Switch off NOW, unplug from the socket, and contact a reliable electricain immediately!--Light current 08:05, 5 September 2006 (UTC)


 * Isn't that last advise a bit over the top? I've connected my computer case to an unpainted part of a radiator. Shouldn't that suffice? DirkvdM 09:36, 5 September 2006 (UTC)

No I dont think so. The BS regualtions state that Any Class 1 equpt should have all exposed conductive materials solidly earthed to the mains earth. Furthermore, there is a requirment that the loop resitance of live and earth shall be less than a certain amount so that the protective device is activated. --Light current 13:22, 5 September 2006 (UTC)
 * The equipment is double insulated (wire casing and psu casing) until it gets to the PSU and after that the voltage and current are whacked down from hairburning to finger tickling levels. so... people should be alright. Philc  TECI 10:44, 5 September 2006 (UTC)


 * In the UK I'm sure it would be illegal to have an electricity supply without an earth. But in America......


 * Still though, most household items dont have an earth, only ones with metal casing do, often they dont even have an earth pin, just a dud plastic one. Philc  TECI 10:44, 5 September 2006 (UTC)

I thing no one here has grasped exactly what I meant.I told you that the shock is not severe at all and it's just a leakage current due to the absence of proper earthing....The shock is bearable only...This shock wasn't observed when I checked it with my friend's house(He has earth in his house)since the PC operates with only 12V,how can it be so lethal and dangerous?..The cause why I recieve shock should be b'coz of leakage current circulating over the panels....It's seems no threat to humans though I suspect if it can be for the Hardware in my PC...If I touch the RAM,HDD it gives me this mild shock still...I really wonder when it will die hard...
 * This is stray voltage, as in this ref It is very bad for cows.  For people, it is not that good, especially if one day you are touching the case, and the water tap at the same time.  You could put on a Residual-current device, or attempt to ground with a pipe.  Most likely, there is a short in the computer that will limit its life. --Zeizmic 12:28, 5 September 2006 (UTC)


 * If youre feeling anything, it means that electric current is flowing from your computer metalwork through your bod and down to earth. THis means that the casing is live and dangerous. I advise you get it looked at! It really sounds as if this eqpt needsan earth. Check the handbook!

THe danger comes from the fact that mains voltages are entering the power supply. If the power supply is faulty, the case can become live. If the case is not earthed, protective devices (fuses, breakers) will not operate and you are in danger of ELECTROCUTION! Please take it from me. I have experience in this field.--Light current 13:31, 5 September 2006 (UTC)


 * The usual phenomenon with lots of big SMPSs is that there's a big RFI filter right at the mains power input; the filter blocks both RFI coming into the supply from the line and power supply hash going back out onto the power line. This filter usually takes the form of an LC "pi" filter on both the neutral (return) and hot (live) lines, usually with pretty substantial capacitors to the safety ground which, of course, is then connected to the chassis of the SMPS and whatever the SMPS itself is then bolted to. If the safety ground lead isn't so hot or is outright disconnected, you find that the capacitors make a voltage divider that puts the chassis at about 50% of the line (mains) voltage, and most people can definitely feel that ;-). Whether or not it's enough current to cause a hazard depends on the design of the specific power supply, but I think that regulatory agencies won't permit such large capacitors in the pi filters as to allow a dangerous amount of leakage for ordinary equippment that is expected to be used in a residential or office environment.


 * At Digital Equipment Corporation (my former employer), because our high-current pi filters had larger capacitors, we had to put warning labels on the power cords of our big commercial equipment warning folks that there was enough leakage capacitance that the safety ground had to be connected to earth; otherwise, unsafe amounts of AC leakage current would occur.


 * So that's one aspect of the problem: ordinary operation. Then there's the question of the various faults that can occur. I'm in complete agreement with the folks above that because certain faults could possibly lead to mains power being connected to the chassis, it's essential that things that have a safety ground pin on their line cord (mains flex) either be connected to an actual safety ground or be connected to the mains through a residual-current device (ground fault circuit interrupter/GFCI). Those two methods are the only way to assure your safety if a worst-case fault occurs in the power supply.


 * And then, of course, there's the question of electrostatic discharge and your computer's ability to resist that. Absent an intended safety ground, you may find that your computer isn't able to resist static discharge (for example, sparks from you) to the degree that you would have expected. But that only endangers your data and your computer, not you.


 * Atlant 00:03, 6 September 2006 (UTC)

Dont forget, Atlant, that we dont know the line voltage at this users house. If its only 120V ac and it is a line RFI filter thing, then he gets 60 vac to ground. However in countries with 240 vac, the volts are definately 'feelable'. The current limiting of course depends upon the capacitor reactance. I had this very problem with an intermittent earth wire (inside the scope case) on a 485 Tek scope - wondered what the hell was going on!--Light current 00:22, 6 September 2006 (UTC)


 * Where do you live, where your entire block isn't electrically grounded?! That floating city from Star Trek? Clarityfiend 04:18, 6 September 2006 (UTC)


 * In the US it would be very strange for the whole block to share an earth ground. Each house should have its own 8 foot (or so) copper rod driven into the ground to provide earth ground. Failing that, you should be able to tie the ground wire of the electrical system to a cold water pipe. Of course if the electrical is old enough, there won't be a ground wire run to every outlet, but its easy enough to ground any new circuits you install. -- 69.106.48.1 05:00, 6 September 2006 (UTC)


 * (Off on a tangent...) In the US, you actually do share earth grounds. Ordinary household split phase utility distribution systems are usually constructed with a grounded neutral, grounded at many points including every distribution step-down transformer. Then, the neutral is grounded one more time at your house's service entrance. All this redendancy of grounding helps assure that the neutral really does stay within a very few volts of the true earth ground potential.


 * Atlant 23:56, 6 September 2006 (UTC)

Make sure electrical modifications are done by a qualified electrician. The ground wire for any new socket must run from the circuit breaker panel or fuse box. It is improper to go around connecting the ground terminal of an outlet to any random cold water pipe near the outlet. One reason for this is that the circuit impedance may be too high to pop a circuit breaker quickly to prevent electricution. The impedance is lower when the ground return is in the same cable as the outgoing hot wire, and higher when it travels a different path. Also the pipe you connect to may be isolated from the main ground by a dielectric fitting, and so a phase to ground short in an appliance would only energize say your bathroom faucet, creating a new shock hazard. Edison 15:06, 6 September 2006 (UTC)

Memory and aging
Can you please find me information about Barnes' 1997 experiment with rats. he tested how the rat's age affected memory.

thank you.


 * Google is your friend. Just search for your key terms such as: Barnes 1997 experiment rats memory.  Dismas|(talk) 07:44, 5 September 2006 (UTC)


 * you won't have luck with rats around here, there are no experts. but if you were to ask about barnes's earlier experiments with seagulls... Xcomradex 08:11, 5 September 2006 (UTC)

ARRRGH--Light current 08:26, 5 September 2006 (UTC)


 * No expert on rats ? That's not fair ! StuRat 23:16, 5 September 2006 (UTC)

Phloretin, phloridzin
According to the literature, both of these chemicals seem to inhibit glucose transport into cells. -idzin has a glucose molecule attached, where -etin is exactly the same molecule, just missing this glucose moiety. Does anyone have any insight into why this is, as it's quite counter-intuitive. I would expect -idzin to be an "invincible substrate" kind of thing, but then how does -etin work?

Thank you very much Aaadddaaammm 09:04, 5 September 2006 (UTC)


 * i guess it shows you the aglycone of phloretin is active piece, not the glucose bit. phloretin is a protein kinase C inhibitor, as well as an inhibitor of a number of transporters, including the glucose transporters. so that's where the effect comes form, it's just coincidence phloridzin has glucose on it. . Xcomradex 10:18, 5 September 2006 (UTC)

How processors work ?
How the control unit of a CPU/PROCESSOR/MICROPROCESSOR works ? I've cearch in wikipedia and in other sites but they all provide me the information that microprocessors are made of transistors ; several electronic gates like and,or,not are described. But i want to know the process by which microprocessors control an electronic devie ; how i/o ports are connected with logic gates ? How logic gates are placed in a microprocessor ?

Is the control unit of embedded system do the same work similarly to the microprocessor of a pc ?

How the architecture of Pentium processor and control unit of an embedded system differs (as i know they do the same work but with different speed)? I want to construct a control unit(something like used in embedded system)using IC/logic gate (no problem if the processing power is low) for experimental purpose ; how the IC/logic gates have to be configured?


 * The information is all in Wikipedia. I doubt whether anyone is going to give you a succinct answer to all your questions here as they involve several different disciplines. Have you looked at transistor, digital circuit, logic gate, and microprocessor? --Shantavira 10:28, 5 September 2006 (UTC)


 * CPUs may be made out of logic gates, but that's like saying DNA is made out of atoms. It's not an explanation.
 * Here's a popular question: "Where is the little man who actually does the work?"   Often that little guy is a binary counter which can turns on various output lines depending on the current count.  The "little man" can also be a ROM and a parallel latch, where the data bits from the ROM are held in the latch and sent back to the ROM's address lines.  In any case, the 'brain' of the CPU is a state machine.  You may be more familiar with a common state-machine everyone uses: the dial on a washing machine.  In fact, it should be possible to use an old washing machine dial as the central mechanism in a very crude electromechanical computer.  (First thing to do would be to change the gearing so that the dial can be rotated fairly rapidly!)  --Wjbeaty 20:03, 6 September 2006 (UTC)

Yes,though most of us know it better,we can't keep typing everything in here.It's practically impossible..My suggestion is to have a good book knowledge first....But we can give some basics what we can....First you must know the internal architechure of any basics Microporcessor atleast like 8085,8086 (x86 series basics is good).Try google search for the architechure 1st.It's quite easy to learn...Your question is multi-directional and it confuses me where to begin with...I'll drop some basics that should be useful...later check the Wikipedia or in google, in detail for learning about transistors in digital circuit and logic circuits that control devices as Shantavira said. 1)Any control unit uses multiplexers(MUX) and DMUX to send signals to the multiple periperals with reduced pins in IC.This helps in reducing the CPU size...These are usually done with the aid of gate combinations eg.,NAND or XOR etc....So to enable a peripheral,all it needs to send is a low or high signal like(READ or WRITE or READY or ACKN or etc)which is an information that can be obtained from reading the instruction stored in RAM with respect to the CPU clock.It has Address Bus and Data Bus inside...Upon executing each instruction step by step,your CPU(Program Counter\Stepper)places the next intruction address and starts fetchin the data from RAM.This process keeps on cycling according to your program....Upon this,instruction is something which has information about the operation type and the Data for that operation written in Machine Language.This is depicted as opcode(operation type) and operand(operation Data) which is a standard format of any instruction. For eg., "INSTRUCTION = (OPCODE+OPERAND)" =   "OUT FFh". Here Out is the OPCODE and FFh is the peripheral address.The data to be sent to this device is stored in one of the data registers.Each instruction is stored in different address in your RAM.So All you gotta do is to write your desire instructions and then store it in RAM and begin executing..There you go.....Here The opcode tells the CPU to send the data in it's default register to the device which is in the address 0xff location....Upon executing this instruction,the CPU 1st reads the Opcode only in it's first clock cycle and then it understands the meaning of that operation and it generates control signal accordingly and clears the pathway to this address and sends the data by reading the Operand in its next clock cycle.By decoding opcode,CPU can determine it's action and it generates the control signal...Provided the CPU has many supporting registers(unit for storing data) for ALU operation....so it can store frequent data up there and refer to it..Note it's only the instruction of your program that makes the CPU to geneate control signals...Your electronic device when connceted to CPU,automatically it must be given as address so that it can be identified uniquely like IP address...as we looked the instructions,just choose the appropriate insturction for controlling the device....For more and detailed information about the generation of control signals,please check out your text books...  2)About the transistors,the ON and OFF state is the only means by which we can store any data digitally.perhaps if one transistor is required for just storing one bit(0 or 1),then 8 transistors are required for 8-bit and so on..Technically they no longer call it as 8 transistor,but simply as Register and they give names like reg A or reg EA or so on....So a 32 bit CPU like any pentium processors has registers of 32-bit lengh,but it can have 16 or 8 bit units still...More the amount of registers,more number of intructions can be executed and stored and hence maintaining parallelism....so more number of transistor,more powerful and faster your CPU is. 3)Since 4004 is the 1st microporcessor(to my knowledge) which just had about 2300 transistors with operating clock of 108 KhHz...It's only a 4-bit processor(Data bus only) compared to any 32/64 bit processor now...So I guess atleast 2300 number of transistors might be required for making a CPU with reduced size(I'm not though sure)  4)Similarly for playing music CD's there are always some default instructions which are stored in your player's memory permanant.They are nothing other than the one that tells your procesor about seeking the CD with spin up and spin down command and also how to control the laser movement in readind the CD directory..You can learn more about this by experimenting with Microprocessor controlled Stepper motor.Once locked to the track in the disc,it keeps the trace and starts moving horizontally hence giving the data(music) from the pits....Apart from this,all user interfaces(Buttons,LCD,etc) are all controlled by microporcessor(Microcontroller is used these days instead) only...Regarding MP3 or other formats of audio,comp/decomp and all kinda processing is done by DSPs only...Besides these there are lot to know....I hope this Basics should help somehow..(Correct me if I'm wrong)


 * You may also want to read and subpages.  (You probably need some knowledge of informatics or electric engineering to understand that.)  &#x2013; b_jonas 21:38, 5 September 2006 (UTC)

Smelling things that aren't there
Ever since high school I have had periods of time where I would occasionally smell what I can most closely call cigarette smoke (although not quite). The whole thing seems to be psychological and fairly random (I'm not sure of any specific triggers), I can go months at a time without smelling it. and I have a friend who has had a similar phenomenon since her uncle died of lung cancer. Strangely enough, another friend has the same situation but with "hospital smell." I don't like cigarette smell and the latter friend doesn't like the smell of hospitals. Is there a term for this? Am I going to die? AEuSoes1 10:03, 5 September 2006 (UTC)
 * Well, I doubt you're dying, but according to Reference_desk/Science it might be a symptom of a stroke. I don't know what smelling things without a source is called, but if you worry about dying, you should see your doctor about it. - Mgm|(talk) 10:50, 5 September 2006 (UTC)
 * That's what made me think of this, but I'm not smelling it constantly, which the case study stated. According to the page on strokes I (a 24 year-old in fit health) am not really at risk for a stroke. AEuSoes1 11:23, 5 September 2006 (UTC)
 * Some more information and links can be found under hallucinations and olfaction. There's also an unreferenced stub article on phantosmia. If you're worried, please go see a doctor. We cannot give medical advice at the reference desk. ---Sluzzelin 12:19, 5 September 2006 (UTC)
 * Is it possible you're actually around people who are smoking? Maybe they're smoking something close to cigarette smoke.--152.163.100.74 12:33, 5 September 2006 (UTC)
 * Intermittent smells can also be a sign of an impending seizure or migraine. See aura. Not common, but certainly possible. InvictaHOG 20:40, 5 September 2006 (UTC)
 * The whole "am I going to die" part was actually a joke. I've already been to a doctor about this and he thought it might be an allergy to something (if it walks like a duck...).  Thanks for the info.  AEuSoes1 21:02, 5 September 2006 (UTC)

Plane speed
If a plane is flying east to west, does it travel faster relative to the ground because of the spin of the earth? Or does the fact that the air it is in also spins cancel that out? Richard Bladen 13:24, 5 September 2006 (UTC)


 * The latter. Consider that at the equator the rotational speed of the Earth is over 1000 miles per hour, faster than the cruising speed of virtually all aircraft.  However, US->Europe flights are usually of shorter duration than Europe->US flights due to prevalent winds. &mdash; Lomn | Talk 14:44, 5 September 2006 (UTC)


 * And for planes that get into the jet stream, the difference in speed is even more dramatic. Planes routinely use both ground speed and air speed to measure their velocity. StuRat 23:10, 5 September 2006 (UTC)


 * Thanks a lot Richard Bladen 00:25, 7 September 2006 (UTC)

Well, first I think you may have your directions mixed up. If you look down at the earth from above the North Pole, you'd see it spinning counter-clockwise. The sun rises in the east and sets in the west. Any "kick-start" you might expect from the earth's rotation would work in the opposite way. The Earth rotates "west to east", and so it would only add to velocity if you took off from the west heading east. Now the rest of you guys may think I'm being silly by talking about the Earth's rotation providing a "kick start". And in the case of planes which remain in the atmosphere you'd be right. The Earth spins, but so does its atmosphere along with it, so the whole "rotation of the Earth" factor wouldn't really have any relevance. However, when it comes to launching spacecraft into orbit, it's no coincidence that NASA chose Florida's Cape Canaveral, or that the French choose to launch their rockets from French Guyana in South America rather than from France. Two elements are at work here. The rotation of the Earth gets faster the closer one gets to the equator. That's why they chose Florida, the most southerly state in the continental US. Also, because the Earth spins "west to east", the best location would be somewhere on the east coast, so that God forbid anything should go wrong, the spacecraft would "splash-land" somewhere in the Atlantic Ocean off the Florida coast, rather than "crash-land" somewhere in Nevada if the launch site was in California. A "splash-land" is much safer for the crew, as the likelihood of their survival is much higher if they would "splash-land" in the sea rather than "crash-land" somewhere east of California. The prospect of debris (or in the case of the space shuttle, it's two booster rockets) falling into the ocean is also obviously much safer than having them land God knows where in some state east of California. And once the craft is up there, it tends maintain a "west to east" orbit of the Earth. Finally, when it is brought back to Earth, it also does so in a "west to east" fashion. Remember how they finally retired the old Russian Mir space station? The thing entered the atmosphere way off somewhere around Australia, and then burned up in the atmosphere over the South Pacific, minimizing the chances that anyone would get hurt by any possible falling debris. Also note the Columbia tragedy. It too was attempting a "west to east" landing in Florida. However as we all know something went wrong and the thing burned up in the atmosphere somewhere around Texas, leading to a great deal of debris landing in those states between Texas and Florida. Thankfully, (aside from the crew of course) I don't believe anyone was harmed on the ground. Sorry for going of on this huge tangent...I just thought it might be interesting for the questioner to know that s/he wasn't all wrong in making the instinctive assumption that the rotation of the Earth actually can be an extremely important factor, perhaps not with regard to air-flight, but definitely with regard to space-flight. Loomis 20:25, 10 September 2006 (UTC)

Keep your bowels fit?
Will your bowels deteriorate if they don't get anything to "work" with, food for instance? I was just wondering, if a person's nutritious requirements were met simply by eating a capsule the size of a walnut once a day (very futuristic), leaving the bowels inactive for most of the day, would the bowels stop working/deteriorate in function? Jack Daw 13:37, 5 September 2006 (UTC)


 * Your body would still need to dispose of bile and dead blood cells - the stuff that makes your poop green or brown (depending on which is in excess). So, even without food, your bowels would continue pushing "stuff" through.  I think the real "victim" would be the population of bacteria in your bowels waiting for something good to eat. --Kainaw (talk) 13:55, 5 September 2006 (UTC)


 * So what about the bacteria then? What would happened to them, and how would that affect us? Jack Daw 14:27, 5 September 2006 (UTC)


 * The bacteria are part of your immune system. Without them, any foreign bacteria that make it to your gut will have an easier time causing disease.  Of course, since you're not eating much, fewer foreign bacteria will make it to the gut in the first place. --Serie 22:41, 6 September 2006 (UTC)


 * I'm actually not sure anybody knows the answer to this, since such a diet does not yet exist. Some information may be gleaned from victims of malnutrition, but the malnutrition itself confounds the observation. In other words, it may not be clear whether a particular intestinal symptom is due to lack of activity in the bowel or to lack of nutrition for the cells. See below. --Ginkgo100 talk · e@ 20:20, 5 September 2006 (UTC)

Actually, the bowel begins to decondition shortly after a person stops eating/drinking. This happens a lot in the ICU setting. As for bypassing the bowel entirely, we don't need pills. We actually routinely completely bypass the bowel by using total parenteral nutrition, which is basically food through the veins. There are people who have lived decades without eating. InvictaHOG 20:42, 5 September 2006 (UTC)


 * So, yes, the bowels will deteriorate without food, perhaps to the point where they become completely unusable, forcing the victim to live the rest of their life getting all their nutrition via an IV. Not a pleasant prospect. StuRat 23:05, 5 September 2006 (UTC)


 * I believe this is an issue for astronaut food - the bowels need something to work on, so just pill food won't do. Strangely I can't find anything on that in Wikipedia. DirkvdM 09:26, 6 September 2006 (UTC)


 * Oh, I should have thought of that. *smacks head* Of course there are ways to provide nutrition besides through the gut. --Ginkgo100 talk · e@ 22:05, 6 September 2006 (UTC)

How does retinol kill?
The retinol article says that retinol can kill you, but How? It doesn't say. Anyone's got an answer?
 * The liver eventually can't store any more retinoids and they enter the blood stream causing a strong and dangerous immunological response called sepsis. See also hypervitaminosis A.---Sluzzelin 14:20, 5 September 2006 (UTC)


 * I see. And why does increased serum retinol cause sepsis? Jack Daw 14:26, 5 September 2006 (UTC)

On a similar subject, said article also states that: "The livers of certain animals, especially those adapted to polar environments, often contain amounts of vitamin A that would be toxic to humans." Why do polar animals have greater hepatic concentrations of retinol? I suppose it helps them in some way, but how? Jack Daw 13:42, 5 September 2006 (UTC)
 * Due to the scarcity of vegetable food, arctic super-predators, such as polar bears, eat a lot of other animals who are also predators. Organic compounds tend to accumulate up the food pyramid. See biomagnification. Higher hepatic concentration of retinol doesn't help the animals directly, some of them have just adapted greater storage capacity for organic compounds, thus avoiding sepsis. ---Sluzzelin 14:20, 5 September 2006 (UTC)


 * Naturally. Thank you. DS

request for location of manuals and papers
Can somebody say me a good website to find detailed and illustrated manuals and papers on any of the following topics : neural network, artificial intelligence, power electronics, power quality, robotics, VLSI, HVDC transmission and electronic topics? thank you for your help.

Start by searching for the terms in Wikipedia, and reading the articles you find. Then read the references in the Wikipedia articles. Then Google the terms and read the websites you find. Then go to a public library and ask the reference librarian to help you find books and magazines on the topics of greatest interest. Edison 20:19, 5 September 2006 (UTC)


 * Edison made some good points. --Proficient 04:05, 6 September 2006 (UTC)

backlog?
Has it ever occured to anyone how much Backlog sounds like B'log? Blog? Backlog? What are the scientific chances that 2 unrelated words would sound so similar--152.163.100.74 14:15, 5 September 2006 (UTC)
 * This is a rather vague question. Anyway, the words are related -- quite closely.  They're two compound words both using "log" plus a leading descriptor.  As for sounding alike... I find that it's fairly hard to confuse a two-syllable word with a one-syllable word, particularly when the extra syllable is the stressed one.  However, languages generally reuse bits of sound (check the Language desk for better explanations).  For example, a word starting with "str" is scientifically unlikely if you just generate character strings, but it's easy to think of a great many English words satisfying the condition. &mdash; Lomn | Talk 14:56, 5 September 2006 (UTC)
 * They're called homophones. JackofOz 00:09, 6 September 2006 (UTC)


 * I see where you're coming from, but I don't quite agree that they sound so similar. --Proficient 04:06, 6 September 2006 (UTC)
 * hahahah what ar ethe scientific chances?!?? omg I love the hubris and faith on this site. I...um...calculated it using computational linguistics. The chance is 1/15212. Jasbutal 04:42, 6 September 2006 (UTC)


 * I recall reading somewhere that there is a tendency for homonymy in languages. Probably has something to do with needing to remember less words with more definitions.


 * Bread and dead sound similar. Fish and dish sound similar, as do bead and freed, boron and boring and any number of other words. Read a rhyming dictionary and see just how many other unrelated words are similar. smurrayinch e  ster( User ), ( Talk ) 15:28, 11 September 2006 (UTC)

Gourami identification needed
I need help identifying which species is in this picture. I own the fish, but I never bothered to ask what species it is. The image is currently on Trichogaster trichopterus because it mentions "golden" varieties, but I'm not sure if that's right (the markings look different). Help would be greatly appreciated. -- Pharaoh Hound  (talk)  14:59, 5 September 2006 (UTC)


 * It is a golden variety of blue gourami (Trichogaster trichopterus) as you thought. --Ginkgo100 talk · e@ 20:08, 5 September 2006 (UTC)


 * Thanks! (sorry I didn't answer sooner, the server was locked for maintenence when I tried yesterday) -- Pharaoh Hound  (talk)  12:43, 6 September 2006 (UTC)

Simple Law of Motion Question
Simply stated, in a practical application, would a ball dropped in a moving train fall directly down, or would it experience some movement towards the back of the train (assuming the train is moving at a constant speed)?

From the pov of someone in the same carriage, the ball would appear to drop vertically to th e floor. From the point of view of someone watching from the trackside, the ball would appear to travel in a parabolic trajectory.--Light current 15:16, 5 September 2006 (UTC)
 * [Edit conflict] (Assuming the train and ball are already travelling at a constant velocity) To a person on the train, the ball falls straight down. To a person obseving from outside the train, the ball falls both down (accelerating at one g) at forward (at the velocity of the train). Raul654 15:17, 5 September 2006 (UTC)


 * Should your train for any reason at all be situated in space, the ball, once dropped, should move alongside you without much trouble at all. :) 81.93.102.45 16:55, 5 September 2006 (UTC)


 * It is accelaration that would cause the ball to fall in a curved path relative to the train, not velocity, assuming the carridge is a sealed capsule, (i.e. if your on a flat bed, the wind would blow it back). Philc  TECI 20:10, 5 September 2006 (UTC)


 * There's always a caveat, so just to ruin the party: if the traincar in question has a lot of open windows, the resulting draft would push the ball towards the back of the train. Melchoir 20:17, 5 September 2006 (UTC)

Also, the ball would only fall straight down if the train is moving at constant speed in a straight direction. StuRat 22:50, 5 September 2006 (UTC)


 * If windows are open, the air current can go in many directions, depending on where you are located. Often, right next to a window, there may actually be a strong forward wind. (btw, is the similarity between 'wind' and 'window' purely coincidental?) DirkvdM 09:31, 6 September 2006 (UTC)


 * Wiktionary claims it isn't, it's actually derived from wind. And there's also "windscreen".  &#x2013; b_jonas 12:14, 6 September 2006 (UTC)


 * Ha! Another thing I make up that turns out to be true. It's a good thing I make up most of the things I say. That way there's a good chance I get it right. :) DirkvdM 17:54, 6 September 2006 (UTC)

Strange insect identification
Hello, can anybody help me identify this strange insect I found in my garden? Thanks in advance. Davide125


 * Froghopper? It looks like the insects that come out of cuckoo spit in my garden, and cuckoo spit redirects to that page. Skittle 17:23, 5 September 2006 (UTC)


 * Froghoppers are rather small. How big is this critter? Also it might help to know which country your garden is in.--Shantavira 17:28, 5 September 2006 (UTC)
 * Me? England. I thought this beastie looked smallish too, given its size against the leaf. Happy to be corrected though. Skittle 17:30, 5 September 2006 (UTC)
 * Thank you for your reply. The insect is pretty small, about 3-3.5 cm including the antennas. The garden is in northern Italy. Davide125 18:21, 5 September 2006 (UTC)

It is some sort of bug - that's as specific as I can be, I'm afraid. You can tell it's a bug by its long ventrally retracted mouthparts, just visible in the photo. BenC7 10:08, 7 September 2006 (UTC)

Just from having a quick browse, it appears to be from one of the families of heteroptera. Maybe a type of leaf-footed bug. BenC7 10:15, 7 September 2006 (UTC)

That's a beautiful picture, whatever it is, maybe you could add it to the article about that type of insect. Gary 02:32, 11 September 2006 (UTC)

Construction of Light Emiting Diodes (LEDs)
I am particularly working on a project whereby I need to construct a 2-Volts-DC LED lighting — 17:38, 5 September 2006 (UTC)17:38, 5 September 2006 (UTC)83.229.66.186


 * Construct from what starting point? Do you have a handful of LEDs and resistors from Radio Shack? Do you have a some PN junctions? Do you have some appropriately-doped pure semiconductors? An undoped Si crystal? A pail of beach sand? DMacks 19:03, 5 September 2006 (UTC)


 * Hehe, I have sometimes thought about how long it would take to, say, build a computer, if all you had to start with was the natural resources. One could imagine that mankind, because of a natural disaster or something, lost all of present technology. Mabye there is only some tenths or hundreds of people left. How many generations would it take to build a computer (or go to the moon, or build a submarine, …)? The first generation would have to try to pass on all their knowledge to the next (a great task in itself), but they hardly know everything, so future generations would have to, well, not reinvent the wheel, but a whole lot of other things. Or could it be accomplished while the starting generation is still alive? —Bromskloss 21:33, 5 September 2006 (UTC)
 * Make sure you download Wikipedia (how is that even possible) before the downfall of civilization. It would give quite a jumpstart. Imagine Michael Faraday or Joseph Henry with a laptop containing all Wkipedia articles, and the jumpstart it would give science and technology.(I chose their era so they could build batteries to power it). Edison 15:11, 6 September 2006 (UTC)


 * Yeah, but when they found out that (on the day of download) "My teacher says that Isaac Newton is soooo gay!", they might not want to work with him anymore. ;-)


 * Atlant 00:06, 7 September 2006 (UTC)

Given that you have the led and a 2 volt light source, the big trick is to connect the led so that it is biased to conduct electricity, and to have a resistance in the circuit to limit the current to an appropriate amount. See LED circuits. An LED connected across a battery without a limiting resistor would generally fry when forward biased. Edison 20:24, 5 September 2006 (UTC)


 * A lot of modern LED flashlights seem to skip the limiting resistor and just count on the battery's internal impedance to limit the current flow. Given the rather small difference between 2V supply and the forward voltage of the diode, the choice of resistor is pretty problematic anyway: the correct value of the resistor would be very sensitive to small variations in the battery voltage and the LED forward voltage. Many modern designs now get around this dilemma by using sophisticated active regulator ICs rather than mere passive resistors. The active regulator also wastes less power than a passive resistor and allows draining the battery further, optimizing its service life.


 * One reference: http://www.elecdesign.com/Articles/ArticleID/13284/13284.html


 * (But Google will find you many more)


 * Atlant 00:11, 7 September 2006 (UTC)

what kind of mirror has best reflection of visible light ?
I want to know how much percent the best mirror for the visible light,reflects ? —The preceding unsigned comment was added by J.hesam (talk • contribs).
 * Maybe spectralon. Its reflectance exceeds 99%.---Sluzzelin 19:07, 5 September 2006 (UTC)


 * The "Technology" section of the Mirrors page has some info. DMacks 19:08, 5 September 2006 (UTC)


 * Dielectric mirrors can reflect >99.999% of a narrow band of wavelengths. In 1998, MIT claimed they had created a so-called perfect mirror that was a "very efficient reflector over a broad range of angles".  I haven't been able to find any exact numbers or more recent details about it, though, so it might not be much more than a research prototype. -- Plutor  talk contribs  19:11, 5 September 2006 (UTC)


 * I found a few (potential) primary citations for that work...see Talk:Perfect mirror). DMacks 19:27, 5 September 2006 (UTC)


 * Sluzzelin: the spectralon article claims that it has a very high diffuse reflection, so it's definitely not a perfect mirror. &#x2013; b_jonas 21:27, 5 September 2006 (UTC)
 * Dielectric mirrors, as mentioned. — [ Mac Davis ] (talk) ( Desk | Help me improve )

See total internal reflection. Of course you have to be inside the high-refractive index medium. --Trovatore 04:54, 6 September 2006 (UTC)


 * ...and you have to be away from perpendicular. List of indices of refraction suggests that 4 is a very large value for n and 1 is smallest. That interface would give a θc of about 14.5 °, meaning there's a ~29-degree cone of non-mirroring. DMacks 05:30, 6 September 2006 (UTC)


 * Is there such a thing as an active (powered) mirror that amplifies the incoming light, thus exceeding 100% reflection? DirkvdM 09:35, 6 September 2006 (UTC)


 * I don't know, but there are shaving mirrors with fluorescent lamps in their frame that illuminates your face. &#x2013; b_jonas 12:02, 6 September 2006 (UTC)


 * Lasers do this (monochromatically). Linear cavity lasers do this by design.  (Ring lasers, ..., not so much.)  There are patents for 3-color image intensifier goggles, but I don't see how one could do this in the form factor of a mirror. -- Fuzzyeric 06:57, 7 September 2006 (UTC)

What would happen
if an unstoppable force collided with an immovable object (assuming it were possible)? A Clown in the Dark 18:22, 5 September 2006 (UTC)
 * Irresistible force paradox ---Sluzzelin 18:51, 5 September 2006 (UTC)

Ah, that was simple. Thanks! A Clown in the Dark 18:52, 5 September 2006 (UTC)


 * I think this is Lambiam's principle of explosion. :) Rentwa 21:11, 5 September 2006 (UTC)


 * I love that paradox. --Proficient 04:07, 6 September 2006 (UTC)


 * Makes me wonder. Is it possible to ask a question that hasn't been asked before? How many people will already have asked that question? (And how many people will already have asked that (and how many ... ok, let's rule out recursion)). DirkvdM 09:37, 6 September 2006 (UTC)

Maybe there should be a continuously updated index of all the questions that have ever been asked on the Ref Desk. Of course, that would require them having meaningful titles, not just things like "Question", or "What would happen". You seem to have a bit of spare time on your hands, Dirk, so why don't you get the indexing project started. Call me if you have any questions. :--) JackofOz 10:19, 6 September 2006 (UTC)


 * What, with all the time I spend on the ref desk, what makes you think I've got spare time on my hands? Or was that your point? Well, it's mine too. (reminds me of the question of whether the presence of a lot of police in a neighbourhood means it's very safe or very unsafe) DirkvdM 18:00, 6 September 2006 (UTC)
 * Well, you tell us you haven't worked in 15 years, and you seem to go travelling around the world at the drop of a hat. Actually, you seem not only to have a lot of spare time on your hands, but a lot of spare cash as well, despite no job for a very long time.  How do you do it?  What is your secret?  JackofOz 21:12, 10 September 2006 (UTC)
 * faqs.org has a quite good index of FAQs in various topics. &#x2013; b_jonas 11:56, 6 September 2006 (UTC)

The unstoppable force would simply change direction - it would 'bounce'' off the immovable object.

In a sense this happens every day, when two objects are in compression against each other - one is an unstoppable force, the other is unmovable.


 * Errr...it would not change direction. For the unstoppable force to change direction, it would have to stop.
 * It would not have to stop if it changed direction instanateously. If for example, you fired a bullet at a heavy steel plate it would not stop but ricochet.

genetically modified foods
what is the mean of genetically modified foods?


 * Basically it is transformation with new DNA, often from an unrelated organism. David D. (Talk) 21:11, 5 September 2006 (UTC)


 * Perhaps typing "genetically modified foods" into the Search box would have been a good place to start learning on your own... DMacks 21:13, 5 September 2006 (UTC)


 * Do you mean what the average genetically modified food is or what the meaning is or why they are mean? Or am I being mean now? (And don't tell me I'm average, or I'll get really mean.) DirkvdM 09:41, 6 September 2006 (UTC)

What is the process of liqiudizing Oxygen?
I just want to ask a question about liquidizing Oxygen. Thank you. --64.180.82.114 21:40, 5 September 2006 (UTC)


 * According to Liquid oxygen, the usual process is fractional distillation. I guess you just condense ordinary air first. Melchoir 21:42, 5 September 2006 (UTC)


 * You would also need to lower the temp quite a bit, wouldn't you ? StuRat 22:51, 5 September 2006 (UTC)


 * Liquid air talks about how to condense ordinary air, including separation of different components by their boiling point. DMacks 23:01, 5 September 2006 (UTC)


 * Ah, there's the money link. I've put it into the See also. Melchoir 23:20, 5 September 2006 (UTC)


 * On a lab scale (do not try this at home!) passing a flow of oxygen gas thorough a liquid nitrogen cooled copper coil gives access to tens of mLs of liquid oxygen terrifyingly quickly. for great fun for those slow fridays, i recommend cotton wool. Xcomradex 02:28, 6 September 2006 (UTC)

How about the Linde process for the liquefaction of air?--Light current 18:05, 6 September 2006 (UTC)


 * Information on the Linde process is currently scattered among Carl von Linde, Liquid air (already mentioned), and Joule-Thomson effect. I'm not sure where the redirect for Linde process should point. Or maybe it should be unified into its own actual page? DMacks 18:12, 6 September 2006 (UTC)

It must be (or have been) an important process: I remember covering it at school! Redirect should point to liquid air--Light current 18:47, 6 September 2006 (UTC)

PV=nRT. Just like air in a can gets cold from the change on volume and pressure sucks out the energy from the surroundings, you would start by making dry ice using compressed Co2 cooling the system down then switch to compressed O2 but it is very very very dangerous!!!! Is you need a heat dump use liquid N2

Reference voltage for decibel measurement
When calculating frequency repsonse on electronic hifi equipment, what is the reference voltage for the decibel measuremnet used in a frequency vs dB graph? Is it the '  perfect ' output voltage?


 * I think its 0 dBm ie 775 mV rms (in a 600R system).--Light current 23:58, 5 September 2006 (UTC)

Many experimenters fail to control impedance in calculating/measuring decibels. And did you mean 600 ohms? Did dBm mean "decibel referenced to a milliwatt across 600 ohms? Edison 15:39, 6 September 2006 (UTC)


 * Yes in 600 ohms (R is the unit for ohms) Try this calc --Light current 17:57, 6 September 2006 (UTC)


 * The graph shows gain, which is output power divided by input power. The reference is therefore the input. There is no need for an arbitrary reference level. See this random example I found on Google. The y axis is marked 'Gain', as it should be. --Heron 22:00, 6 September 2006 (UTC)


 * Remember, all decibels are just a ratio between two values. So when an amplifier states (for example), that it has a frequency response of 20Hz to 20KHz ± 0.1 dB, what that means is that if you plotted the frequency response from 20 Hz to 20 KHz, the line that represents the frequency response would stay within a band that is 0.2 dB high. In this case, the ratio you're measuring is the ratio between the best gain of the amplifier (within our specified frequency band) and the worst gain of the amplifier (within our band).


 * Any time you see dB representing an absolute value, there'll always be some indication of what the value is ratio'd from. For example, the dBm that folks were speaking of above is a ratio from 1 milliwatt. If someone says dBV, then they're expressing a ratio from 1 volt. dbA is a ratio of acoustic power related to a particular absolute value of sound pressure level (the softest sound the average person can hear at 2KHz) and weghted according to an "A" frequency response curve (a particular weighting curve that has something to do with the response of human hearing).


 * Atlant 01:05, 7 September 2006 (UTC)

canine dental
I have a five month old Standard Poodle, that has adult teeth coming in missing enamel on 1/3 to 1/2 of each tooth. I am researching the probability of heredity/genetic traits to notify the breeder of possible health related concerns. All her teeth will have to be capped to prevent decay. I have read many articles suggesting auto-immune issues; and want more information on related documented cases and results. I can send pictures. Thank you. 


 * I'm only familiar with enamel hypoplasia in dogs as related to canine distemper, but according to the Merck Veterinary Manual, it can also be caused by malnutrition and possibly inherited . --Joelmills 01:46, 6 September 2006 (UTC)

Yes, thank you. Dr. Bellows, dentalvet, has the same opinion.

My journey: (1) is to find out if this is related to the 3- series puppy-shot that contain "parvo, influenza, distemper & hep." when administered with an undetected low-grade fever, (2) or, if there is a heredity-gene trait and is there a genetic test available? (3) to answer a question swarming my brain; what could destroy the mineral presentation of "Hydroxyapatite" during the "Odontoblast period" of the "Dentinogenesis" formation?

I am no scientist or practioner....just want answers to why my puppy has permanent damage to all her adult teeth, like a line was drawn and half of each tooth has no enamel. It is suggested that the "leukocyte alkaline phosphatasa" found in white blood cells, could lead my way to more knowlegde. I will have her tested for amenia and hypothyroidism. Perhaps the vaccines, eliminated the part of her immune-system that protects the "Dentinogenesis" formation.