Wikipedia:Reference desk/Archives/Science/2007 October 18

= October 18 =

sharks
Do jellyfish stings effect sharks? If so where can I locate this answer with more info? —Preceding unsigned comment added by 63.3.17.130 (talk) 00:06, 18 October 2007 (UTC)

This was posted 2-1/2 years ago; are people likely to notice and respond to this now? I also wondered if jellyfish stings affect members of their own species, or other species of jellyfish. I've read sea turtles are immune; what about coral or other species? Is their research being done on why turtles are immune? Thanks.

Kinetic Energy in the Universe
Because all matter in the universe came from the big bang, if we use the velocity of all the mass in the universe just before the bang as a reference frame and all of the matter in the universe, does that mean that the total kinetic energy of the universe is 0? If its true, is this useful to scientists in any way?
 * Statements like "velocity... just before the Big Bang" hold no meaning, as the laws of physics do not hold at the singularity point. So no, you can't derive "total kinetic energy is zero" from that statement.  Besides, "total kinetic energy" is better described as a magnitude than a vector. &mdash; Lomn 01:14, 18 October 2007 (UTC)
 * Right there are at least three things wrong with that statement. Firtstly, there is no "before" when we are talking about the big bang.  Secondly, because kinetic energy is mass times velocity SQUARED, it doesn't have vector component to it.  Two particles with the same mass, moving at the same speed in opposite directions don't have "opposite" kinetic energy - they have identical kinetic energy (Suppose they both have a mass of 2 units and velocities of -3 and +3, then m.v2 is 18 for both of them because 32 is 9 and so is -32).  Thirdly, kinetic energy isn't conserved - it can be converted back and forth into other forms of energy - so even if there were some sense in which all mass/velocity 'things' summed to zero - it wouldn't still be true now.  SteveBaker 04:14, 18 October 2007 (UTC)
 * I'm sure you know this, and almost sure you were understood, but lest there be confusion, one usually writes $$(-3)^2$$: prefix negation has lower precendence (counted as that of multiplication) than exponentiation. --Tardis 20:02, 18 October 2007 (UTC)

Most Popular Health Topics
I am wondering if there is a way to determine which health topics are accessed most frequently on Wikipedia. Is there a list available to the public that displays the number of times a health page is accessed. If not, is there a way to access the top ten health issues viewed through Wikipedia? —Preceding unsigned comment added by 67.172.250.112 (talk) 00:27, 18 October 2007 (UTC)
 * I downloaded the 1500 most popular articles, and grepped for "health" in the category. Results:

Rank Article 359  Sigmund Freud 401  Arnold Schwarzenegger 484  Dog 527  Chernobyl disaster 584  Sexually transmitted disease 590  Pakistan 819  Condom 1064 Heroin 1227 Cancer 1498 Air pollution
 * --Sean 01:42, 18 October 2007 (UTC)


 * "Health Topics"...dog, maybe, but Pakistan? Other high ranking pages in June 2007: Rheumatoid arthritis, Malaria, Coital cephalalgia, Necrotizing fasciitis, Breast cancer, Central obesity, Gastroesophageal reflux disease, Genome project, Lupus erythematosus, Blindness (source). --JWSchmidt 02:44, 18 October 2007 (UTC)


 * Why was Pakistan a grep result if the article has no mention of the word "health"? --Bowlhover 03:30, 18 October 2007 (UTC)
 * Sean didn't grep the article - he grepped the names of wikipedia categories mentioned inside it (presumably hoping to find all of the articles that were inside categories relating to health). There is a [Show] section in the Pakistan article that refers to Category:Healthcare in Pakistan.  Hence he also inadvertently included articles that LINK to health-related categories without being in any way about health themselves.  That probably explains all of the ones that don't seem like they should be there!  I didn't say it was a good technique! SteveBaker 04:03, 18 October 2007 (UTC)

Thank you for answering my question. I was also wondering if and where I could access these stats and how I would do that. —Preceding unsigned comment added by 155.100.78.143 (talk) 20:50, 19 October 2007 (UTC)
 * Take a look at this --JWSchmidt 04:30, 20 October 2007 (UTC)

Medicine = poison?
Who was it -- some ancient Greek thinker? - who said all medicines are actually small doses of poison? Thanks, Adambrowne666 00:45, 18 October 2007 (UTC)


 * Sounds similar to Homeopathy. Some homeopaths think it makes sense to make treatments out of toxins that cause the symptoms found in disease states. --JWSchmidt 00:56, 18 October 2007 (UTC)


 * Try Paracelsus - a Renaissance alchemist. Delmlsfan 00:57, 18 October 2007 (UTC)


 * Makes sense in a way. Antibiotics certainly are poison to the bacteria they are supposed to kill. But the toxicity of something basically lies in its quantity or concentration. Lots of things that the human (or whatever) body needs will be lethal if the dosage is too large. I've even heard a story of someone who swallowed some 'household chemical', and rang the doctor, who advised her to drink loads of water while he was on his way to her. In her panic, she drank so much water that that killed her. Don't know if this is an urban myth, though. Anyway, how much of something you ingest has an effect on the 'balance' in your body. Altering the normal pattern of ingestion may thus be used to treat some disease. That said, a lot of medicines are things that the human body hasn't evolved to deal with (eg because they're synthetic), so any amount could be regarded as poison. DirkvdM 07:54, 18 October 2007 (UTC)


 * In a lecture (actually on psychology, not on medicine) I was told the same thing. For a medicine to work, it must affect the body. Anything that affects the body in any way, can be dangerous to the body when the dosage is not right. Lova Falk 11:26, 18 October 2007 (UTC)
 * That's bullshit. Something could affect the body in some way, but completely taper off after, say, 1 ounce, so that a pound, or 1,000,000 pounds of it, has the same effect.  For example, consider "darknesss" -- having 1 lumen of darkness affects the eyes in a certain way, but going to a million or a billion or a trillion lumens won't adversely affect the body.  Likewise, dropping into a pool of water has an affect on the body, but the efffect won't be different if the amount of water in the pool is trillions of gallons.  So, just two examples of how it's NOT true that " Anything that affects the body in any way, can be dangerous to the body when the dosage is not right", 1) darkness, 2) external amounts of swimming pool water.  —Preceding unsigned comment added by 77.234.80.59 (talk) 12:41, 18 October 2007 (UTC)
 * I disagree. If someone takes 1,000,000 pounds of anything they'll be dead.  There's simply nowhere to store that much mass in their body.  Also, a lumen is not a measure of darkness, but a measure of light.  Darkness is the absence of light, so you can't have a "lumen of darkness."  Furthermore, once you're in complete darkness it just doesn't get any darker than that.  Thus a "million or a billion or a trillion lumens" would probably fry you to a crisp instantly.
 * Similar to your "darkness" example, your water example is comparing apples to oranges. We are talking about dosages here, meaning what you are exposed to, and generally it is taken internally.  Even if you're talking about external exposure, how much other water there is is irrelevant, since in both cases the person's body is touching the same amount of water at the same pressure.  You could be up to your neck in a swimming pool or an ocean of water, in either case you'd be equally wet.
 * Simply put, if you drink too much water, you can suffer water intoxication, hyponatremia, or even die. If you breathe too much oxygen, that too can kill you.  This goes for anything and is why dosage is important.  The "common sense" idea that "if X is good for me then 2X is twice as good" is often simply wrong.
 * Back to the original question though, I guess whether that's true it depends on how you define "poison." Would a vaccine or aspirin be considered poison?  If we define "poison" too broadly then saying "anything = poison" is simply stating the obvious. --  Hi  Ev  14:46, 18 October 2007 (UTC)


 * I think I could survive taking 1,000,000 pounds sterling. DirkvdM 17:50, 20 October 2007 (UTC)

Toxicology points to Celsus who said, "All things are poison and nothing is without poison; only the dose makes a thing a poison." --JWSchmidt 15:31, 18 October 2007 (UTC)

Ah, wonderful - all the answers were very interesting - though I wonder if the guy who started with 'that's bullshit' is a bit toxic himself - thanks especially to JWSchmidt; exactly what I wanted. Adambrowne666 20:34, 18 October 2007 (UTC) -- oh, and Delmlsfan too - sorry, I didn't realise Celsus = Paracelsus.

Harnessing biomath
Humans and other animals can innately do some amazing math, such as calculating where a tennis ball coming at you at 100 mph is likely to end up, in a much shorter time than even the Richard Feynmans of the world could calculate it on paper. I'm wondering if there has been any line of research into using that mathematical ability at the conscious level to do equivalent calculations quickly? Thanks. --Sean 00:45, 18 October 2007 (UTC)


 * I'm not sure what sort of "equivalent calculations" you're going to find. As I see it, "biomath" is either very specific in scope or very approximate in result.  That is, the average person knows about where a tennis ball will end up, but about isn't likely to be of sufficient use to spur serious research.  On the other hand, while Roger Federer may be very precise about determining where a tennis ball will end up, he's probably no better than average at, say, gaging a baseball hit to deep center.  In this case, you might have a viable calculation, but your pool of equivalent calculations will be quite restricted. &mdash; Lomn 01:10, 18 October 2007 (UTC)

Sean, what you're talking about isn't calculation. Calculation is something done with digital representations of numbers, like "16 feet + 29 feet = 45 feet". The intuitive estimates you're talking about involve analog operations, like "<-- THIS far --> plus < THIS far > equals <- THIS far ->". It's a completely different way of thinking.

--Anonymous, <--THIS late--->, October 18, 2007.


 * As I see it, predicting where a ball will end up is based on experience; an experienced tennis player will know what trajectory a ball travelling at a certain speed will follow, after seeing similar situations many times before. I fully agree with Anonymous that this is not math but intuition.  A tennis player on the Moon, for example, will not be able to predict trajectories very accurately even if he knows the strength of the Moon's gravity and the effects of a vacuum.  --Bowlhover 03:19, 18 October 2007 (UTC)


 * That is probably the best answer. If you used a simple table based on estimates you would usually be able to find an approximate answer much faster than you could if you calculated it.  This is sort of what goes on inside of our heads, and why people get better at these things with experience.  Their internal "table" gets more accurate, they can "read" it faster, and they learn how to adjust for other variables and to better cope with errors in the results.  Just because things like your tennis ball trajectory scenario could be done using really fast calculations, does not mean that that's the method people are actually using to achieve the result. --  Hi  Ev  15:01, 18 October 2007 (UTC)


 * There is a sense in which we are innately able to imagine approximate solutions to what would be horribly complex problems if calculated out exactly...but they are very, very approximate. If I ask you to imagine a shelf in your garage or garden shed full of paint cans - and think about what happens if one of the two brackets holding up the shelf were to fail - then in a very tiny fraction of a second - and without any accurate data of any kind - you can envisage the whole business.  One end of the shelf slides downwards - the cans start to accellerate down the shelf - they impact the ground one after another - some of the lids come off, paint runs out and forms a big puddle on the floor.  You can imagine the sounds of the cans sliding and clanging on the ground - and perhaps even have a reasonable stab at the smell of the paint.   That's an AMAZING thing to calculate in such a short time with almost zero data - but is it correct?  Does the twisting of the shelf cause the other bracket to fail?  Do the paint cans land on top of each other or spread out a little?  Do all of the lids come off or just some of them?  Exactly how big a puddle does half a litre of a water-based emulsion paint form?  You really didn't calculate this - you formed some kind of clever approximate simulation by gluing together bits of past experience.   However, it's impressive just how close to reality these things turn out to be.   We'd be very hard pressed to write a computer program that could produce such an accurate prediction - even with all of the initial data and all of the physics envolved.  And if we did, it might take hours to run.  Our brains can do a pretty good job in a small fraction of a second.  It's not even that we've seen this exact thing happen before and we remember it.  I can make up "what if" thought experiments based on combinations of everyday things you've never seen - and you can come up with a similarly reasonable answer in very short order.  SteveBaker 03:53, 18 October 2007 (UTC)


 * Funny, my very first physics teacher could go on and on about how awful these fraction-of-a-second predictions were, before you took his class, of course ;-) Someguy1221 04:57, 18 October 2007 (UTC)


 * Anyways, the Amazon Mechanical Turk is trying tor harness peoples ability to do some things better than computers. The idea has been explored to some degree in the novel The Diamond Age by Neal Stephenson. --Stephan Schulz 20:17, 18 October 2007 (UTC)

I read an article claiming that dogs can solve rudimentary optimization problems. A mathematician was tossing a ball into the ocean for a dog to retrieve. The dog would run along the beach for some time, then turn and swim to the ball. The mathematician showed that the turning point (going from running to swimming) was the optimal turning point for minimizing the time to get to the ball. moink 18:36, 19 October 2007 (UTC)


 * There is a corollary question that has been bugging me. How does an animal know it can do a thing? I saw a lioness (on TV) prowling a ghost town who jumped from one roof to another across a street. She hunkered and wriggled for a bit and then went for it. How did she know how far she could safely leap? I mean, that's a big risk for slight gain; she could have just gone downstairs and crossed the street. We would have some idea of the measured distance and of our capabilities in feet (m). --Milkbreath 18:22, 20 October 2007 (UTC)

Cotton buds/Q-tips
Is this just a false memory on my part or were cotton buds (aka Q-tips) at one point specifically sold (in the UK at least) for the purpose of scraping earwax out of the depths of the ear canal? Now, they always make it clear on the packaging that they should *not* be used in this manner. --Kurt Shaped Box 01:24, 18 October 2007 (UTC)


 * Their original designer Leo Gerstenzang saw his wife wrapping cotton wool around the end of a cocktail stick for the purpose of removing the wax from their babies' ears. Yes. SteveBaker 03:34, 18 October 2007 (UTC)


 * Funny, that. What else would people buy them for? And why are they perfectly shaped and proportioned for that purpose? I occasionally use them to clean tape heads, but that's not what I primarily buy them for. DirkvdM 08:03, 18 October 2007 (UTC)


 * Exactly. I look at them and I struggle to think of many other advantages that a cotton bud has over your standard cotton wool in the home environment. --Kurt Shaped Box 09:42, 18 October 2007 (UTC)


 * All you who answer seem to be men. Cotton buds are perfect for small make-up adjustments. They are also ideal for removing kajal out of your eye (kajal has a nasty habit of slipping into the eye) :) Lova Falk 11:22, 18 October 2007 (UTC)


 * They are also handy for touching up small nicks in your rooms' paint, especially at corners. But "cleaning tape heads" was the first alternate use I flashed on too; 'guess I'm getting old. ;-)


 * Atlant 12:28, 18 October 2007 (UTC)


 * They're also good for cleaning the accumulated fluff and scum from mouse rollers. Still, if it wasn't for people buying them to ream their ears out, I doubt that most shops would even bother stocking them. --Kurt Shaped Box 13:04, 18 October 2007 (UTC)


 * Come to think of it, I've occasionally used cotton buds to brush eyelashes from my corneas. The loose ones are not so bad - it's the ones that fold down under the eyelid whilst still attached that are the real bastards. --Kurt Shaped Box 13:00, 18 October 2007 (UTC)


 * So, besides dripping peroxide in our ears, what's the "safe" way to remove wax from the ear canal? Someguy1221 04:54, 18 October 2007 (UTC)
 * I always used to use them, the idea of it being bad for you is a rather recent one. I spent most of my childhood using them... SGGH speak! 08:37, 18 October 2007 (UTC)


 * I suspect we can blame that idea on a corporate liability lawyer somewhere.


 * Atlant 12:29, 18 October 2007 (UTC)
 * No I'm pretty sure it is ENTs. As an answer to Someguy1221, the general recommendation AFAIK is that you shouldn't need to remove ear wax. Use a tissue to clean the outer ear but that's all. Ear wax is a natural part of the ear and should be left to come out on its own, removing it can often make things worse. While I admit, I usually can't resist cleaning my ears either, it makes sense when you think about it. There is no reason to expect most people would have to clean their ears. It's something that no other animal AFAIK does nor does it seem likely our ancestors would have done it. Nil Einne 15:50, 18 October 2007 (UTC)


 * TBH, I still do. Scraping out earwax and scratching an itch inside the ear at the same time has got to be one of the best sensations possible - only *just* behind orgasm and the relief you feel when taking a slash after holding it in for three hours. --Kurt Shaped Box 09:36, 18 October 2007 (UTC)
 * Kurt, take one bobby pin, snap it in half at the join and discard the 'crinkled' half. You now have a smooth end and a rough hooked end to use as you see fit. Never found anything better. This is not medical advice or indeed advice of any sort, if you perforate your eardrum consult a medical professional and don't mention you are silly enough to do what someone off the internet has recommended. But seriously, it's heaven. Lanfear&#39;s Bane 10:29, 18 October 2007 (UTC)
 * I use a paperclip (somewhat straightened). --Psud 11:57, 18 October 2007 (UTC)
 * I once worked with someone who'd sit at his desk scrubbing out his ear canals with matches (phosphorous end!). That may have been an accident waiting to happen... :) --Kurt Shaped Box 13:06, 18 October 2007 (UTC)
 * I have a mild form of psoriasis. It doesn't affect me at all, except for the fact that earwax doesn't dry up and fall out of my ears, like normal people.  So I end up getting solid earwax plugs after a while.  Apparently, it's common enough that any doctor will be willing to squegee out your ears for you.  Basically, they use the same kind of drops they use to break up poo to break up your earwax.  Then, they use a big snub-nosed needle filled with hopefully warm water to hose it out.  You can buy kits from any pharmacy store and do it from home in the shower.  Two reasons why this is far better than q-tips: 1. You don't have to worry about sticking it in too far and jamming the earwax back or puncturing an ear drum.  2. You're not scraping against the thinnest, most delicate layer of skin on your body.  It's a really easy way to get an ear infection.  --JMC  —Preceding unsigned comment added by 160.10.98.106 (talk) 18:09, 18 October 2007 (UTC)
 * Sort of back on track, those cotton bud/Q-tips are also perfect for cleaning dirty laser lenses. Dip one end in a bit of rubbing alcohol (spectacle cleaning solution works), rub over the lens, wait to dry a bit, then use the dry end of the bud to polish it up. I originally learned that to get my Playstation 2 working again, but it works on anything (assuming you can take it apart safely to get to the lens).  Neil   ☎  14:16, 18 October 2007 (UTC)
 * I used to use them to clean 5 1/4 floppies. I had a floppy drive that had been taken apart but which you could attach to a power supply to spin it so with a cotton bud and alcohol you could clean them, just provided you didn't push too hard so your scratched the floppies. Mold build up is a major problem in Malaysia Nil Einne 15:54, 18 October 2007 (UTC)


 * In art restoration, cotton buds/Q-tips are used in great numbers to clean surfaces over very small areas. I work in a museum where restorers have been cleaning a painted wooden ceiling for years. They have a five-year contract. That said, they make their own cotton buds/Q-tips. Watching them, I wonder how they can stand the tedium! Eriastrum (I forgot to log in)--134.186.103.3 19:34, 18 October 2007 (UTC)


 * Regarding cleaning tape heads (when magnetic tape was still the primary audio/video recording medium), most equipment manufacturers discouraged using consumer-grade cotton swabs (buds) because small fibers could cling to the heads. Thus were created special so-called "electronic swabs" which were a little bit of foam rubber at the end of a small stick to perform the same purpose. — Michael J  20:14, 18 October 2007 (UTC)


 * Hey! You should all know that you should not stick anything into your ear that's smaller than your elbow! If you want to clean out the wax, pour some olive oil in there a few times a week and this will dissolve any earwax. If this doesnt shift it, its time to see the nurse/doctor (who will drill it out with a pneumatic drill) —Preceding unsigned comment added by 88.109.65.125 (talk) 01:57, 19 October 2007 (UTC)


 * Oh yes, just remembered, lots of jaw movements side to side are also recommended for loosening the wax. —Preceding unsigned comment added by 88.109.65.125 (talk) 02:00, 19 October 2007 (UTC)


 * you can buy drops at any pharmacy for like $10 that will greatly soften wax. If it doesnt come out after a day or so, you simple blow water into the air to get it out. Any doctor will do this. If your years are blocked use the drops for at least 24 hours, then goto a doctor and the wax will come out easily. Most wax build up is caused by people putting things in their ears. Qtips etc. are not recommended to be put in the ear because they don't help. wax will naturally travel and fall out of the air, even when it gets wet. Don't put stuff in your ear ever.--Dacium 02:35, 19 October 2007 (UTC)

My stepmother is an audiologist and has been repeatedly observed using objects such as keys to clean out her ears. Who knows, maybe her superior knowledge makes it safer for her. moink 18:39, 19 October 2007 (UTC)


 * An effect called: Cobbler's shoes. Oh we dont have an article yet. How sad —Preceding unsigned comment added by 88.109.246.205 (talk) 22:11, 19 October 2007 (UTC)

Bray-Curtis
What is the Bray-Curtis dendrogram and how does it apply to ecology? —Preceding unsigned comment added by Redrumusic (talk • contribs) 06:17, 18 October 2007 (UTC)
 * This file describes how to calculate Bray-Curtis distances for use in constructing a Dendrogram. This article makes use of Bray-Curtis calculations to study "Recovery of frog and lizard communities following primary habitat alteration in Mizoram, Northeast India". --JWSchmidt 14:25, 18 October 2007 (UTC)

Hairsplitting
Considering how long the hair of humans can get if it is not cut, I used to wonder if that wasn't inconvenient for our ancient ancestors. My first guess was that their lifestyle would cause the hair to get a 'natural cut'. For example, domesticated animals often need to get their nails or hooves cut, which of course doesn't happen in nature. But a while ago someone remarked that I have split ends. About 15 years ago I stopped using shampoo (as a result of which, as planned, my hair stopped falling out - I was already starting to go bold at the age of 30). At around the same time I stopped having my hair cut. But it didn't grow further than my neck. So might that be the cause? Are having split ends and hair of the length I have the natural state of our hair? Also, do other animals have split ends? The article suggests, as many people do, that it is a bad thing, even a 'medical condition'. I claim the opposite. Split ends are healthy. DirkvdM 10:44, 18 October 2007 (UTC) ps, I will put a baldness-spell on anyone who whines about this being a medical question. :) DirkvdM


 * Interesting! How do you keep your hair from looking greasy and dirty? Lova Falk 11:18, 18 October 2007 (UTC)


 * By not using shampoo. :) When you use it, it removes grease from your hair. But hair needs some grease, so the Sebaceous glands in your follicles compensate by producing extra 'grease'. So when you stop, the hair gets greasy very fast, but after a while the glands have 'kicked the habit' so to say, and start producing normal amounts of grease again. Takes about a month. A nasty period you need to go through. DirkvdM 18:15, 18 October 2007 (UTC)


 * 1. Just because 'split ends' have a complicated medical name doesn't make it a medical condition (take my word for it)
 * 2. I've heard about split ends but never been able to see them myself..
 * 3. Is it possible that saying "you have split ends" in another way of saying "go and get a haircut!" - a euphemism - a bit like saying "how do you get your skin so shiny looking" can mean "get a bath you greasy ..." - seriously - look a grizzly bears.. they probably have split ends - but pandas dont87.102.3.9 13:10, 18 October 2007 (UTC)


 * I don't think I'd want to come close enough to a grizzly to find out. :) It wasn't a euphemism - we don't normally talk like that in the Netherlands, and especially not this guy. DirkvdM 18:15, 18 October 2007 (UTC)


 * Hair is dead stuff. Aside from social matters of how it looks/smells/feels - you can't do anything bad to the hair itself - so it splits? - big deal.  We evolved hair that doesn't need shampoo.  Baldness happens down inside the follicules where the hair is formed and it should properly be considered a skin condition.  All else is myths and nonsense put about by shampoo manufacturers.  They put all sorts of delicious, mouthwatering ingredients into shampoo and tell you that you need to "feed" your hair...what a pile of poop!  Really!  In reality the only thing shampoo does that actually matters to your hair is to provide some detergent to let the water remove dirt and excess oils...soap in other words. SteveBaker 18:16, 18 October 2007 (UTC)


 * Those social matters are important though. Don't belittle their importance. Having dirty hair means your pillow will smell bad too. Keeping clean is pretty important. By your logic, we don't need to clean ourselves at all. 64.236.121.129 13:35, 22 October 2007 (UTC)

Split ends are normal (I wouldn't say healthy - just normal)- if they exist at all.. Has anyone got a picture of them - I'm dubious as to whether they really exist?87.102.3.9 18:45, 18 October 2007 (UTC)


 * With split ends, if you look closely at the ends of the hairs you can see that the shaft forks at the end. It will do so to differing degrees depending on the level of splitting. I usually take it as a sign I'm overdue a haircut. Skittle 00:16, 19 October 2007 (UTC)

As I understand it, the 'natural' state of human hair is dreadlocks - they're not just for Rastamen and hippies. If anyone just leaves their hair to grow without combing or brushing it, it will eventually dread naturally, after a period of being a matted, tangly, uneven mess. I'm trying to let my (3-foot-long) hair do that at the moment. Seems to be going pretty well. At the end of it, I'll never need another haircut in my life. --Kurt Shaped Box 21:52, 18 October 2007 (UTC)


 * I've heard that each individual hair grows a certain length, stops growing, than falls out. The result is that if you cut your hair, it appears to grow as fast as the growing ones do, but once it reaches a certain length, it stops. — Daniel 22:34, 18 October 2007 (UTC)


 * That's true, as far as I know. My hairdresser once explained to me that women's hair generally (though not always) grows longer than men's - but that everyone's hair, if left alone will eventually reach a 'maximum length' and stop. I suppose that it's the same with beards. I hardly ever even tidy mine up, yet it's still the same length that it was when I started growing it at the age of 20... --Kurt Shaped Box 22:44, 18 October 2007 (UTC)

Possible to use CGI instead of night vision?
Lets say, we are many many years into the future. 2530 or something. We have super advanced computers, quantum computers perhaps, or better. We have a tank in the middle of the night, and it's pitch black. Is it possible for the tank to send signals (possibly radar or something) to get terrain information, then use that information to generate computer generated images in real time to give the driver detailed information of what is in front of him? Perhaps it can be combined with information from a satelite to give topographical information as well.

So in other words, can an advanced computer generate in real time, what is in front of the tank, and display it as if it were day time, and use that CGI instead of nightvision? 64.236.121.129 13:36, 18 October 2007 (UTC)
 * 500 years into the future? We could do it now, including the combination with known topographic data (aircraft use this all the time).  However, sending signals continuously like that is the military equivalent of screaming "I AM A TARGET SHOOT AT ME".  Night vision goggles, on the other hand, are passive, granting them an enormous tactical advantage. &mdash; Lomn 13:44, 18 October 2007 (UTC)


 * Well I said 2530 because I wanted the CGI to look very advanced. Close to how you would expect the objects and terrain to look in real life. Hmm, that is true about being a huge target. Maybe such technology would be best on a civilian vehicle then. Something like that could be useful in fog or stormy conditions where lights alone don't help much. 64.236.121.129 13:55, 18 October 2007 (UTC)
 * For civilian vehicles, I think it far more likely that automated highway systems will be prevalent. A problem with the fog/storm thing is that radars capable of what you want are subject to similar limitations as the human eye.  Millimeter-wave radars, for example, suffer heavily from rain fade. &mdash; Lomn 14:13, 18 October 2007 (UTC)


 * You still don't need to go that far out. We're able to do that level of quality now, and if computing technology continues to advance at the current rate, it'll be about five years before we're able to do it in realtime. --Carnildo 22:30, 19 October 2007 (UTC)


 * Keep in mind that the virtual view will never be completely realistic. For example, radar, sonar, infra-red, and other such things cannot pick up color, only visible light can do that.  I suppose a super-sophisticated computer could attempt to colorize it, but those colors will often only be best-guesses.  It might see a car driving away, but in complete darkness it would not be able to tell what color the car really was.  Fortunately, since you are rarely in complete darkness, light amplifying techniques (like longer exposure) could help determine the approximate colors, but a white car passing near a red light source might still be interpreted by the computer as being red instead of white.  "Pinging" an object with a variable wavelength laser could provide color and other information (distance, speed, etc.).  Also, computers are better at differentiating shades of black than humans are, so that helps too.  Still, the color of moving objects (or other objects while you are moving) would be more difficult to determine in near-darkness than if everything were standing still.
 * Another problem with an active sensors would be that anything in the shadow of the "lighting" would often be "invisible", unlike under normal lighting. It might seem from the virtual view like you are a light source, since that's effectively what you are when you are actively sending out a radar signal or whatever.  Other old data on the area might compensate for such "shadows" or "gaps", but the data might not still be accurate.  I don't know how sharp the picture could be either with things like radar and sonar.
 * To help compensate for the "I AM A TARGET SHOOT AT ME" effect of using active sensors, the "lighting" source might be from a separate drone or drones (much as people sometimes use flares,) or perhaps only brief flashes could be used from a moving zig-zagging vehicle. The latter would have problems with moving objects, however both might end up providing "lighting" for any enemies as well unless there was some way to make it difficult for others to use.
 * You'd never get a 100% realistic image, but with technology 500 years from now you could probably do a fairly decent job in real time while not moving, with moving objects or seeing things while moving appearing a little less realistic. Hope that helps! --  Hi  Ev  16:09, 18 October 2007 (UTC)


 * Well - they kinda do that some of the time - but it's actually not as useful as it sounds. For example, some F16 fighter aircraft have already replaced their ground-following radar (which screams "I'M HERE!" to anyone with enough technology to listen) with computer-generated maps that simulate the same kinds of information.  (I know for sure that the Dutch F16's that are in actual service are equipped that way because I designed the flight simulators they use to train their pilots to use it.) That's OK for things like not hitting mountains - but the trouble with battlefield conditions is that things change too much.  Your computer data will be out of date as the enemy moves around, buildings are destroyed or defensive structures put up.  For people running around a battlefield on foot or in vehicles - it's utterly hopeless.


 * So whatever is generating this synthetic view would have to gather data from the real world in real-time somehow and add that into the synthetic scene. There are only two ways to do that:


 * By actively 'probing' the world with Radar, Sonar or Lidar or shining a spotlight on them ...or...
 * By passively viewing whatever information is coming from those objects.


 * The active techniques all suffer from the problem that they give away your position - so those aren't really recommended. So now we're down to passive techniques.  This means monitoring the signals the enemy is putting out.  But if he's being as careful as you are - he's not going to have lights turned on, he won't have radars and lidars sweeping the world and he's probably trying to be reasonably quiet.


 * So now you are down to monitoring only those things he absolutely cannot avoid emitting - and which you can measure reasonably well. At night, pretty much the only thing like that is heat.  So this hypothetical computer has to look for IR energy. How?  With an IR camera of course.


 * What this boils down to then is that you are suggesting that the computer should get that data with a camera and somehow convert it into a computer graphic that looks as realistic as the data it's recieving...well, yeah - but what's the point?  You might just as well have piped the image from the camera straight into the end-users' eyes.  Not surprisingly that's exactly what they do.  Night Vision goggles and IR sensors are basically just cameras feeding screens in front of the users' eyes.  The result is much faster, takes vastly less electronics and is nowhere near so error-prone.


 * There are systems that use CGI for things like showing the user what's over the next hill (in terms of terrain, lie of the land, that kind of thing) - but they aren't replacements for night vision, you should think of them more as high-tech maps.


 * SteveBaker 17:32, 18 October 2007 (UTC)

Having trouble understanding how Solar Cells work
I read the article on solar cells, but I'm still not sure if I understand it. So the photons in light strikes silicon and this shakes loose electrons in the silicon and these electrons then travel through a wire into a battery? The electrons are electricity? Can the silicon ever "run out" of electrons? 64.236.121.129 14:35, 18 October 2007 (UTC)
 * The free electrons are indeed electricity. These same electrons end up going back to the silicon at the other end. --Milkbreath 14:49, 18 October 2007 (UTC)
 * Technically, the electrons that come back into the battery are very, very unlikely to be the same ones that went out. (Not that you can tell - electrons all look pretty similar!) The actual rate of flow of electrons is very slow indeed.  But this need is the entire reason that electricity has to run around a loop.  Static electricity is a different matter though.  If you do the trick of standing on an insulated block and putting your hand on the shiney chrome ball of a Van de Graaff generator (so your hair stands on end), the electrons only flowed out from the ball and up into your hair - then they stay there until they either leak slowly off into the air - or someone else touches you and a bunch of electrons flow over to them (and they get a short sharp shock in the process). SteveBaker 17:14, 18 October 2007 (UTC)
 * If it's true they're not the same electrons, I can learn a big thing here. All the electrons in the conductors move, sure, oh. Well, eventually they're the same. --Milkbreath 18:08, 18 October 2007 (UTC)
 * To further clarify, the reason why electricity works is by having electrons travel in a loop (2nd paragraph in electric circuit). Things powered by electricity are kind of like how a waterwheel works, but electrons are used instead of water. What Milkbreath said is that the electrons never run out because the electrons loop back to where they came from. --JDitto 15:35, 18 October 2007 (UTC)
 * Water flow is always a nice analogy for electricity. The solar cell is like a pump that's pushing the electrons around the circuit - and the device it's powering is like a water wheel spinning in the flow - you need to take the water out of the water wheel and put it back into the pump or everything runs dry very quickly. Static electricity is more like syphoning the contents of one bucket into another. SteveBaker  —Preceding comment was added at 17:59, 18 October 2007 (UTC)
 * I see. But what about the large solar cell arrays that are used to power homes? How can they complete a circut with something like that? 64.236.121.129 19:40, 18 October 2007 (UTC)
 * The solar cell array acts as a large battery: two wires run from it to the (rest of the) home, and the current travels down one and back along the other. Within the array, the individual cells are connected (in series or in parallel) with more such wires, and the current flows through the cells as previously discussed.  --Tardis 21:09, 18 October 2007 (UTC)
 * Yea I know that. I was talking about a solar farm. A solar powerplant so to speak. 64.236.121.129 13:14, 19 October 2007 (UTC)
 * Apart from acting like a battery, solar cells on the roof of a house would almost always actually be connected to a bank of batteries. You wouldn't just be using the electricity that's directly coming out of the solar cell because that would vary greatly depending on how sunny it is and more importantly if it is day or night. The solar cells charge the batteries when it is sunny (pulling the electrons from the positive side to the negative side "against their will" so to speak) and you discharge the batteries using electricity in the house, creating a circuit for the electrons to flow from the negative to the positive side through your appliance hence powering it.Vespine 01:39, 19 October 2007 (UTC)

Solar cells are P-N junctions of silicon. The P side has some boron replacing the silicon. If you look at Boron on the periodic table, you see it has one less electron than silicon in it's outer valance shell. The N side has phosphorous which has an extra electron. These are electrically neutral sections but when they are placed next to each other, the difference in electron concentration in the two sections create a "partial pressure" of electrons and they want to flow from high concentration to low concentration. THis is just like in biology where high saline cells absorb water through a semi-permeable membrane to even out the concentration. It also happens with gasses and gas mixing and partial pressures. As the eletrons move from high concentration N silicon to low concentration P, the two sides start to charge up. The P silicon starts to get a negative charge as it accumulates electrons. The N side gets a positive charge because the electrons are now gone while the protons stayed in the atoms. This charge difference creates an electric field that opposes the diffusion of electrons from high to low concentration until an equilibrium is established. This region of electric field (called the space-charge region) is what is exposed to light. When a photon hits an atom in the high electric field space-charge region, an electron can be excited to leave the atom. It is then swept out of the space charge region. This "unbalances" the equation and an electron will go through the circuit to return to donation site. There are other things to consider but this is the basic mechanism. --DHeyward 04:31, 19 October 2007 (UTC)
 * So the oppossing charges resist the natural diffusion of the electron. Does that mean the electron is just floating inbetween the two atoms? So is the space-charge region the space in between the two atoms, or does it include the atoms as well? 64.236.121.129 13:26, 19 October 2007 (UTC)

PKC
if you have a Protein kinase C (PKC) inhibitor, and want to inhibit pkc, how would you use it? —Preceding unsigned comment added by Poppynash (talk • contribs) 17:04, 18 October 2007 (UTC)
 * Historically, such inhibitors have often been used in enzyme assays or on cultured cells where you can add them to the culture medium. Some are starting to be used clinically and administered orally. Example: Enzastaurin (LY317615), a protein kinase Cß inhibitor, inhibits the AKT pathway and induces apoptosis in multiple myeloma cell lines. Note the section of that article called "Enzastaurin Treatment".....it is not unusual to have take special care because of high levels of non-specific binding to surfaces or other components in laboratory PKC assays. --JWSchmidt 22:17, 18 October 2007 (UTC)

When to use the terms proper motion and Improper motion
I think I understand what proper motion and improper motion are -- proper motion is a change in apparent location based on the object's actual motion, and improper motion is change in apparent location based on the observer's actual motion. I'm trying to get a handle on when to use the terms, though. Are they just used for stars? Could one talk about the (im)proper motion of a planet, moon, or artificial satellite? Could one talk about the (im)proper motion of an object on the same body as the observer -- for instance, a jogger as viewed from a moving vehicle? Finally, if (im)proper motion is not the term that is usually used in these instances, what would the correct term(s) be? --M @ r ē ino 17:23, 18 October 2007 (UTC)

Ideal gas law example
It's been a while since I've done Physics and when discussing an ideal gas law question with something came up which I can't remember the answer to. The question was relating to an isobaric process? Specifically, a system where the volume is doubled (pressure remains constant) and with no heat lost or gained by the environment. What is an example of such a system? I know there may not be a perfect example but an approximation. I searched but all I found was examples of Charles' Law setups where they kept the pressure constant but increase the temperature. Cheers Nil Einne 17:41, 18 October 2007 (UTC)
 * Because PV=nRT for the volume to increase but the pressure stay the same - the temperature must increase.. - and so there must be an increase in energy since E = constant x T
 * (((I can't think off hand of a real world example - but this system would make a good "gas thermometer" - since the volume is proportional to temperature.)))
 * One possible example would be a chemical reaction of gases in a isolated or insulated system - if the reaction produces energy then the temperature will rise - causing an increase in volume - for the pressure to remain constant the reaction would have to take place in a piston such that the external pressure on the piston would be constant.. (also note it helps if the reaction is constant in volume eg A+B > C+D and not A+B>C - the second case would complicate things)87.102.3.9 17:49, 18 October 2007 (UTC)
 * Well yes, the internal temperature would change. In case there was any confusion, my point about the Charles law example was that they were heating the system which was obviously not what the question is referring to (since no heat is lost or gained by the surroundings) Nil Einne 17:53, 18 October 2007 (UTC)
 * Was my example any good - if the piston is totally thermally insulated? or did I miss something - if so what - I'll keep thinking..87.102.3.9 18:44, 18 October 2007 (UTC)

rubber bands
How far can a rubber band stretch before it bop? —Preceding unsigned comment added by Coco74 (talk • contribs) 19:53, 18 October 2007 (UTC)


 * Hi. Ok, first you need to understand that how far a rubber band can stretch depends on the size of the rubber band, the texture of the rubber, its stretchiness, etc. I've been able to stretch a single rubber band roughly 1 ft, although it again depends on the rubber band. I'd suggest you read the article rubber band. A rubber band will often rebound violently if stretched enough, for instance it can be used to launch a paper airplane or other projectile at over 70 km/h (roughly 45 mph or 35 kt). If you are conting distance or height, why don't you try it yourself? I've found that a rubber band stretched far enough can go roughly 10 m (~35 ft) forward and 5 m (~15 ft) up. Also, a rubber band that has been dried or repeatedly used and stretched has a higher probability of breaking when stretched before it usually does. Hope this helps. Thanks. ~ A H  1 (TCU) 20:06, 18 October 2007 (UTC)


 * it depends on the rubber band. See Bungee jumping. -Arch dude 21:21, 18 October 2007 (UTC)


 * ...and the temperature. Take two identical rubber bands (this works best with the really fat ones) - pop one into the freezer for a while and drop the other into hot water.  Now *quickly* grab first one, then the other and give it a stretch.  You'll be amazed how different they are!  This was the cause of the space shuttle Atlantis Challenger disaster - cold weather impaired the 'stretchiness' of the rubber in the infamous O-ring seals. SteveBaker 23:59, 18 October 2007 (UTC)


 * Wouldn't that be Space Shuttle Challenger? --Psud 10:05, 19 October 2007 (UTC)
 * Yeah - sorry - brain-fade. SteveBaker 11:11, 19 October 2007 (UTC)


 * This question is like asking how fast cars go. It depends on the manufacturer.  No one is going to spend a lot of money on a rubber band.  Also, ozone really degrades them.  That's why they crack after a few months of use. Delmlsfan 01:39, 19 October 2007 (UTC)

Leaky coax antenna?
What is a leaky coax antenna? What does it do exactly? —Preceding unsigned comment added by 67.127.167.238 (talk) 20:09, 18 October 2007 (UTC)
 * Can you add any context? I assume "coax" means coaxial cable, but the only relevant (I think) items I've found for "leaky antenna" are for getting cell phone and wifi signals in train tunnels, which doesn't seem to relate to coax. &mdash; Lomn 20:27, 18 October 2007 (UTC)


 * Obviously it means that a coax cable is 'leaking' electromagnetic waves and therfor is acting as an antenna. Coax cables aren't supposed to leak though.. Searching for 'leaky coax' turns up a few discussions of this.. So a "leaky coax cable" would be a "leaky coax antenna" I imagine and it's doing what it's not supposed to be doing.. Does that explain?87.102.3.9 20:37, 18 October 2007 (UTC)
 * see http://lists.contesting.com/pipermail/towertalk/1997-August/008139.html


 * Alternatively a leaky coax is "A straight length of coaxial cable with regularly-spaced holes cut in the shielding (aka leaky coax) is treated as a Uniform Line Source antenna" from https://doi.org/10.1007%2F0-306-47046-2_7 - effectively the coaxcable is converted into a lot of little antennas by cutting through the shielding - was that what you were thinkng of?87.102.3.9 20:40, 18 October 2007 (UTC)
 * In this example the coax includes lots of small antenna - it's designed for wireless communication - this http://www.hitachi-cable.co.jp/catalog/EW-204.pdf gives a good clue as to a possible use as well as technical info..87.102.3.9 20:44, 18 October 2007 (UTC)


 * "Leaky Coax" or "leaky line" antennas are used to cover a long skinny area such as a tunnel or the cabin of an airliner, as stated above.-Arch dude 21:16, 18 October 2007 (UTC)


 * When I was in college, we had a student radio station. Our broadcasting license only allowed us to broadcast within the bounds of the college buildings.  The solution was to use leaky coax antennae which allow you to outline the areas where you want the radio to work.  I don't understand the detailed technical stuff - but it was really impressive.  Anywhere inside the residence building, any old Medium wave AM transistor radio could pick up the station with ease. If you were in your car out in the parking lot with the front of the car up against the building - you could pick up the station on your car radio with plenty of signal strength - but as you reversed out of your parking space, the signal would drop off so fast that by the time you were 15 feet from the wall, all you got was static. SteveBaker 23:54, 18 October 2007 (UTC)


 * See Leaky feeder 81.79.75.108 11:30, 19 October 2007 (UTC)

Head polish?
I've heard all the jokes about 'head polish'/'head wax' for bald men (and a quick cursory glance at Google would tell me that such products do seem to exist) but is it actually, *really* a common thing for bald men to buff up their 'domes to a sparkling, shiny finish before they go out in the morning? Is this some sort of really well-kept secret? --Kurt Shaped Box 21:45, 18 October 2007 (UTC)


 * I have seen my roommate do it, but I don't think it is a daily thing. Just when he wants to go out and impress the ladies. It is like a porch light and moths, they all want rub it for "good luck." 161.222.160.8 22:54, 18 October 2007 (UTC)


 * Your roomie's not Fabien Barthez, is he? --Kurt Shaped Box 23:41, 18 October 2007 (UTC)

Electromechnical elevator/lift control equipment
Hi there, not sure if anyone can answer this but I've been wondering how the electromechanical equipment that controlled elevators/lifts prior to the invention of integrated circuits/transistors etc works? I can't find anything on this online. The type of equipment I mean includes selectors and relays and contactors and all that sort of stuff but I don't understand how all those components can do the job of controlling a lift, can anyone explain? Here is an image of the type of equipment I mean.

GaryReggae 22:04, 18 October 2007 (UTC)


 * I guess you understand how a contact on the side of the lift could switch a relay that causes the lift to stop - the real situation will be more complicated than this.
 * The picture looks like a sort of simple electromechanical computer with possibly some analogue parts
 * I'd guess that the motion of the lift can be connected to a chain - and then geared down - to a smaller chain - as this smaller chain moves it can cause the lift to stop at certain points (eg floors).. I'm not an expert on this but it doesn't look beyond the capabilities of most people to understand.
 * Could you split down your question into smaller parts - eg were you interested in how the buttons would cause the lift to stop at certain floors, or how the lift is 'programmed' to stop exactly at a given floor - there's quite a few different things to consider - so splitting the question down might help..87.102.3.9 22:55, 18 October 2007 (UTC)


 * In the meantime since these things have almost certainly patents applying to them a patent search might be a good source of information on them.87.102.3.9 22:57, 18 October 2007 (UTC)


 * It's nothing so complicated. There are simply a series of limit switches in the hoistway and as the elevator car passes by them, they indicate to the control logic where the car is in the hoistway and, often, in which direction the car passed the limit switch.


 * Now, envision the logic that has to exist for each floor. We need a relay that latches when you press the up-going hall-call button, a relay that latches for the down-going hall-call button, and a relay that latches when an occupant of the car presses that floor's destination button. These relays also light the lights in each button and they're cleared when the car stops at that floor going the right way (for the hall-call buttons) or just plain when the car stops on that floor (for the car button). Now, we need a little more logic to record which way the car is presently traveling and make it move to the next "call" in the current direction. When there are no further "calls" in the current direction, reverse direction. If there are no calls in either direction, wait for a call and take that as the new current direction. Finally, we need a block of logic that knows how to do the leveling (fine positioning to line up the car and the floor) and cycle the doors open and then closed.


 * It all comes down to a block of relays for each floor that is repeated over and over again, the direction control block, and the "leveling" and door control block. Elevator control systems just used pre-assemblies of these logic blocks.


 * It gets more complicated with more than one car, of course, but the basic principles remain the same. And note that even computerized controls can't schedule cars perfectly because the "hall-call" buttons don't provide enough information to allow perfect scheduling.


 * Atlant 23:36, 18 October 2007 (UTC)


 * This seems like the sort of subject that you'll find books on if you visit a university engineering library or a large reference library. For example, I just searched the University of Toronto's online library catalog for subject "elevators". The university's Engineering & Computer Science Library has a 1966 book called Electric lifts: a manual on the current practice in the design, installation, working and maintenance of lifts (5th edition) by Reginald Stanley Phillips. Also, the university's Gerstein Science Information Centre has a 1927 book Electric elevators, their design, construction, operation and maintainance [sic] by Fred Anzley Annett: this would presumably be about manual elevators, with simpler control systems. These are just examples of what you might find: try a suitable library near you. --Anonymous, 23:48 UTC, October 18, 2007.

Industrial motor controls and ocmmercial lighting often use electro-mechanical relays as their state elements instead of electronics. If you think of a D latch simply as a level sensitive switch (on when clk is high, off when low), a relay is just a D latch. Another relay completes the state element part. --DHeyward 04:43, 19 October 2007 (UTC)


 * Thanks for your replies, these help a bit, sorry I should have been a bit more specific with the original question as I understand that the relays basically open and close circuits depending on which buttons are pressed and that the lift 'knows' where it is via the floor selector but it's really the mechanics of how the lift decides which way to go...I understand for example that if somebody has pressed the floor 3 button then this would presumably cause a relay to latch and there would also be relays for the up and down buttons on the landing that tells the lift to stop at that floor only if it is going in that particular direction but it's the starting process I don't quite get. Presumably there are additional relays that act as safety interlocks and don't allow current to flow through the circuit until the doors are closed and there must be some sort of timer that causes the doors to close.  Then what happens?  How does the lift controller use the state of the relays to decide which way to turn the motor?  I will have a look in my local city library but they didn't have a lot of engineering stuff last time I looked but the patents thing is certainly a good idea.  Thanks.  —Preceding unsigned comment added by GaryReggae (talk • contribs) 08:46, 19 October 2007 (UTC)


 * My experience of how older lifts decide which way to go suggests pretty simple logic: If they are on a floor, they go in the direction of any floors selected; if none are selected, they wait to be called (perhaps going to a "home" floor) then when called, travel in the direction of the floor calling them; if someone presses a button for a floor in the direction opposite to any already selected floors, it ignores the button press. Buttons in the lift override call buttons, so they never see a choice of directions. --Psud 10:17, 19 October 2007 (UTC)


 * There must be a relay that 'remembers' which way the lift is going then? Otherwise when it stops, it wouldn't know which way to go?  Are there any other relays in the system or just 3 for each floor, a direction state relay and safety interlocks?  —Preceding unsigned comment added by GaryReggae (talk • contribs) 10:23, 19 October 2007 (UTC)


 * In most cases it wouldn't need to remember which way it was going because its direction of travel would be determined by which buttons are lit and which call buttons have been pressed. In fact I can't think of any situation where it would need to remember direction, it seems to me that the lift could work out, with simple logic, which direction to go in any situation where it needs to move.--Psud 13:21, 19 October 2007 (UTC)


 * It's essential that the elevator remember which way it's going or it wouldn't be able to provide the "User Interface" we're all used to: elevators travel in one direction, servicing all the passengers going "that way" until they reach the last call in that direction. Then they reverse direction and service all the passengers going the "other way". Now it turns out that it's actually pretty easy to design logic that determines whether there are any further calls "above" the current position of the elevator or "below" the current position of the elevator, and if we have some logic that remembers the current direction, it's pretty easy to determine whether to continue onwards in the current direction or to reverse direction. The only complexity about this is you need a third state to handle the situation when there are no further calls in the current direction and no calls in the opposite direction. In this situation, the elevator controller may either allow the car simply to become idle or (as someone already observed), it may simulate a call to a "home floor" and then allow the car to become idle.


 * If you ever want to try your hand at this, I'm pretty sure there are "relay logic" simulators that you can download; I thinkwe've even discussed them in the past on one of the Reference Desks.


 * Atlant 16:34, 19 October 2007 (UTC)


 * You guys are not going back far enough. Elevators originally had a human operator. Elevators with operators persisted well into the 1960's. Thus, the "wired-logic" era was a relatively brief transition from the manual era to the microcontroller era. -Arch dude 13:43, 19 October 2007 (UTC)


 * I'm sure we're going back exactly far enough. Earlier - Human operator: Boring - human decides up or down or stop. Later - ICs or computers decide up down, stop. Boring. Wired logic - interesting, simple, understandable. --Psud 14:13, 19 October 2007 (UTC)


 * Thanks again for all your help, I have found some very useful patent diagrams for exactly the type of thing I was on about on Google Patents although the schematics are confusing as it looks as though some of the relays are wired in paralell while I would almost certainly have thought they would have to be in series? Things like door interlocks and safety switches should surely work on an AND basis, where it won't work unless they are all OK?  Anyway, I have also been having fun over the weekend using Logisim, a logic circuit designer I found on Google and have almost managed to create a working lift control system using nothing more than latching gates and ordinary logic gates, it just needs a bit of work to stop the lift when there are no more calls rather than continually going up and down whilst waiting for calls.  I'm sure this can be done easily enough using a NOT or NOR gate...If anyone else is interested in the patent, you can find it on Google Patents by the number: 2330489, look up Otis Elevator Control anywhen between 1920 and 1965 and you should find some more similiar equipment, including some drawings of incredibly complicated looking mechanical floor selector machines...can't remember the number of that one I'm afraid.GaryReggae 14:18, 22 October 2007 (UTC)