Wikipedia:Reference desk/Archives/Science/2009 December 31

= December 31 =

drinking rubbing alcohol
the effects of doing so are listed by this site as the same as regular booze only stronger. because of this i think it is safe to have 1 or 2 shots of rubbing alcohol safely. obviously more could be dangerous. —Preceding unsigned comment added by Thekiller35789 (talk • contribs) 03:48, 31 December 2009 (UTC)
 * Not if it's isopropyl alcohol, which is often sold as "rubbing alcohol" in the States. Even if it's ethyl alcohol, it's not going to do the lining of your throat any good at 98% abv.  In general, it's not a good idea to drink anything that's not designed to be drunk, especially anything that says "EXTERNAL USE ONLY" in large capital letters on the bottle... Tevildo (talk) 04:14, 31 December 2009 (UTC)
 * If you drink a shot of rubbing alcohol, you will die or at least go blind. Edison (talk) 04:28, 31 December 2009 (UTC)
 * True for methyl alcohol, but isoprop isn't as bad. However, I would certainly recommend the OP to stick to cheap vodka; it tastes (marginally) better, and won't kill them as quickly. Tevildo (talk) 04:33, 31 December 2009 (UTC)
 * If you drink rubbing alcohol, which is isopropyl alcohol in the US, and possibly denatured alcohol in the UK, you will die or at least go blind or damage internal organs. See Rubbing alcohol and . Cheap wine (3 buck Chuck) goes for under $4 per bottle. $2 in some states. Edison (talk) 04:28, 31 December 2009 (UTC)
 * It does not appear that pure isopropyl alcohol causes blindness. --Sean 15:09, 31 December 2009 (UTC)

Symptoms of isopropyl alcohol poisoning include flushing, headache, dizziness, CNS depression, nausea, vomiting, anesthesia, and coma. THESE ARE THE SAME SYPTOMS OF BOOZE. your not going blind and u can dilute it so it wont burn--Thekiller35789 (talk) 05:11, 31 December 2009 (UTC)


 * If you insist on asserting the untrue claim that it's safe to drink, consider why every wino and bum in the world doesn't drink it. They would if it were healthy, because it's dirt cheap.  Comet Tuttle (talk) 06:19, 31 December 2009 (UTC)
 * Just to clarify. Drinking _isopropyl_ alcohol is very harmful to your health (not as bad as methyl alcohol, but still definitely "toxic"), and two shots (~50 cc) is probably enough to kill you.  However, "rubbing alcohol" can be either _isopropyl_ or _ethyl_ alcohol.  Drinking _ethyl_ alcohol that's been sold as rubbing alcohol (or mouthwash, or hand sanitizer) isn't going to kill you immediately, although it's still advisable to stick to alcohol that's intended to be drunk. Tevildo (talk) 10:20, 31 December 2009 (UTC)
 * Tevildo, while I certainly don't want to encourage anyone to drink isopropyl alcohol, I'm curious where you get your info. This page doesn't seem to back you up.  It doesn't show a lethal dose for humans (only a "lowest published toxic dose" &mdash; not clear how bad symptoms need to be to qualify as "toxic" but I assume it's well short of death).  However it shows LD50s for rats and mice (oral) and dogs (intravenous); these are all above 3.5 g per kg of body weight.  For a 50-kilogram person that's 175 g of the stuff. --Trovatore (talk) 21:09, 2 January 2010 (UTC)


 * Especially since most non-food-use ethanol has been denatured - that is, mixed with toxic substances such as methanol or benzene, or with substances which make it disgusting to drink. The reason for this is that there is usually a heavy tax on alcoholic drinks, which solvent and rubbing alcohol manufacturers can avoid by rednering their product "unfit for human consumption". If you're looking at ethanol-based rubbing alcohol because it's cheap, you can bet your continued good health that it's going to be denatured, precisely to prevent people from drinking it. -- 128.104.50.17 (talk) 15:51, 31 December 2009 (UTC)

The main problems of isopropanol (as opposed to ethanol) are twofold. Firstly, rubbing alcohol isn't food grade. So this means it contains a wide range of impurities ... heavy metals, benzene (from chemical production), so and so forth. It's often denatured with bitterants, but the denaturants can in turn poison you much more acutely. Also, isopropanol is a secondary alcohol, which means it can't be easily metabolised into a carboxylic acid and remains in the blood as acetone. John Riemann Soong (talk) 06:58, 31 December 2009 (UTC)

See Surrogate alcohol. Drinking anything like this is potentially very dangerous. To do so would be extremely irresponsible and idiotic. There's no reason or need for anybody to drink these things. The dangers are well documented. 194.221.133.226 (talk) 12:26, 31 December 2009 (UTC)

I've often read news items where people at parties in 3rd world countries drink this kind of alcohol mixed in with sodas or pop and go blind as a result, and have other damage also. Do not drink it - it is poisonous! 78.151.128.34 (talk) 13:25, 31 December 2009 (UTC)

Don't feed the trolls, people. Matt Deres (talk) 15:52, 31 December 2009 (UTC)


 * Please do not provide medical advice. ~ A H  1 (TCU) 23:58, 31 December 2009 (UTC)

Reference desk
how can i see and answer people's questions on wikipedia? can i help others by answering them? —Preceding unsigned comment added by Priyankachopra01 (talk • contribs) 04:29, 31 December 2009 (UTC)
 * You're in the right place. :) If you'd like to answer some questions, please feel free - remember to sign your posts with four tildes ( ~ ), and, if possible, include a link to the relevant article in your answer. Tevildo (talk) 04:33, 31 December 2009 (UTC)
 * And click the edit link next to the question to provide your answer! Graeme Bartlett (talk) 11:57, 31 December 2009 (UTC)
 * Remember not to do homework for somebody else, as indicated by the header, and try to link to external sources if you got the information outside of Wikipedia if you think the link will be helpful. There are also other reference desks where you can ask and answer questions, and another way to help is to get the information into articles on Wikipedia. Have fun! ~ A H  1 (TCU) 21:53, 31 December 2009 (UTC)

Sky
Does the sky begin at the interface with the ground? Even though we perceive extremely tall buildings as "sky scrapers" (spacing intentional), a being 1000 ft tall (making his or her height exceed 100 stories, let's say) would not think such a building was anywhere near they sky. So for an earwig or something of the like, wouldn't sky begin lower?  DRosenbach  ( Talk 05:56, 31 December 2009 (UTC)


 * There is no such thing as "the sky". The sky is the name we give to the concept invented by ancient people who thought the stars were hung above the earth in giant rotating glass spheres, or who spent time pondering what the turtles stood on.  The atmosphere is all of the gas gravitationally bound to the Earth, and it does indeed start right at ground level.  The sky is not a concrete, scientifically definable concept, beyond "What I see when I look up".  -- Jayron  32  06:03, 31 December 2009 (UTC)


 * Come, now. I think DRosenbach was talking about the visuals.  You know &mdash; the blue stuff.  The answer is yes.  The sky "begins lower" for the earwig in the sense that the earwig sees less of the land around him, due to the curvature of the earth, than the 1000-foot fire giant sees around him, so the earwig actually sees fewer square inches of sky as he looks around than does the fire giant.  Comet Tuttle (talk) 06:17, 31 December 2009 (UTC)


 * Obviously, the taller you stand the further you see, unless there is something in the way :) . The distance to the true horizon, as a function of height, is given in the article Horizon; it is roughly proportional to the square root of height. However, there is a caveat: further does not mean lower. We may or may not perceive the true horizon to be a certain distance away; but I do not think we ever perceive a clear sky to be of a particular height. And clouds are a different story altogether. --Dr Dima (talk) 08:47, 31 December 2009 (UTC)


 * OK I guess what I said is not particularly clear. Let me say it again more clearly. The distance to the true horizon is an actual measurable quantity (as opposed to a perceived illusory one), and it increases with the height of the observer. An observer 1000 ft tall (or high) can, under ideal conditions, see roughly 32 times further than an observer 1 ft high. We may or may not perceive the distance to the horizon as finite and well defined, even though it is well defined in reality. However, distance to the horizon is not equivalent to the "height of the sky" (which in reality is not defined at all, as there is no firmament above). And I do not think we ever perceive a clear sky to be of a particular height. --Dr Dima (talk) 09:10, 31 December 2009 (UTC)


 * You may also like this paper. Your mileage may vary :) --Dr Dima (talk) 09:23, 31 December 2009 (UTC)
 * Celestial sphere. ~ A H  1 (TCU) 21:48, 31 December 2009 (UTC)

The sky is a set of angles in two dimensions, those angles which do not end at an opaque object within the atmosphere, from a given location. See steradian. - Craig Pemberton 22:33, 31 December 2009 (UTC)

Calculating radioactive decay
Given the number of protons and neutrons in an atom, is there a formula (or a way of computing) the half-live, decay mode and energy? 95.115.191.19 (talk) 12:22, 31 December 2009 (UTC)


 * No, not as asked. There is no direct, simple, correlation between the number of nucleons and decay half-life.  Predicting the half-life is a complex quantum mechanical problem which has by no means been fully solved.  See nuclear structure and nuclear shell model.  Sp in ni  ng  Spark  12:35, 31 December 2009 (UTC)


 * There isn't a theoretical formula, but you could probably produce a ballpark function by regression analysis. You'd be better off looking up the measured result though. Noodle snacks (talk) 13:38, 31 December 2009 (UTC)


 * Thank you for your answers. Now I am wondering why this is so. As I understand, the standard model of quantum physics is solid and well tested. So there should be a way of computing decay modes and half-life times. Are those subjects outside the reach of the standard model (due to relativistic effects?), is it "only" a matter of exploding computation complexity or are there principal computational issues (as in the three-bodies problem of classical mechanic)? 95.115.160.26 (talk) 15:39, 1 January 2010 (UTC)

Asbergers versus Williams syndrome
If Asbergers Syndrome is defined as an "extreme male brain" could Williams Syndrome be described as an "extreme female brain?" Trevor Loughlin80.0.104.152 (talk) 12:38, 31 December 2009 (UTC)


 * Having just read the first paragraph of Williams Syndrome, it doesn't sound particularly female to me. I would also question Aspergers being an extreme of male characteristics. Aspergers is characterised largely by a difficulty in empathising. Is there any evidence (beyond anecdotal evidence) that men are worse at empathising than women? I think it is more likely that men are just as good as women at working out how another personal feels emotionally but give those emotions a lower importance. I also wouldn't be surprised if that was entirely to do with the society they were brought up in rather than anything physiological. --Tango (talk) 13:28, 31 December 2009 (UTC)
 * Science does not have an answer to your question. Noodle snacks (talk) 13:34, 31 December 2009 (UTC)


 * (Edit Conflicts)Leaving aside the question of whether characterising Asbergers syndrome as "extreme male brain" is actually valid as either a literal description or a metaphor of coincidentally expressed behavior, I would say no, because (i) Asbergers syndrome is not significantly 'disabling' mentally and has no physical signs or symptoms that I know of (though Steve or others may correct me here); (ii) it appears to be part of a "continuous spectrum" of naturally occuring mental characteristics, and (iii) it has no root in any obvious genetic 'fault' (while its cause may be genetic, it's sufficiently obscure that we haven't discovered it yet).
 * There are a few physical manifestations - one that I'm familiar with is a tendency for Asperger's children to walk on the balls of their feet without their heels touching the ground. When I was diagnosed, my mother was amazed that this peculiarity of the way I walked as a kid had an actual explanation.  But these symptoms are not very noticable - and not generally carried through into adulthood. SteveBaker (talk) 04:07, 1 January 2010 (UTC)
 * "Asperger and autistic individuals also exhibit motor control abnormalities such as impaired gait, balance, manual dexterity and grip" . "Subjects with AS were found to perform more poorly than controls on tests of apraxia, one-leg balance with eyes closed, tandem gait, and repetitive finger-thumb apposition" . --Mark PEA (talk) 15:33, 1 January 2010 (UTC)
 * I'm not aware of having poor one-leg balance - but I'm utterly useless at throwing and catching things - my kid says that I'm "ballistically challenged". SteveBaker (talk) 02:33, 2 January 2010 (UTC)
 * By contrast, Williams syndrome, in which the "female" characteristics it appears to exaggerate are (I would argue) likely more cultural than innate to the female sex, (i) is both significantly 'disabling' mentally and has marked physiological effects; (ii) is not part of a "behavioural spectrum", but a one-off condition; and (iii) is caused by a significant known genetic defect which the article details. 87.81.230.195 (talk) 13:45, 31 December 2009 (UTC)
 * Sorry to contradict the politically correct brigade who always want to insist there is no fundamental difference between male and female, but you are not supported by scholarly research. Asperger's and autism are well known to be strongly biased towards male sufferers and there are plenty of academic papers making the link between these conditions and extreme forms of male behaviour, see this for instance.  I don't know the answer on Williams syndrome, but it is at least a reasonable question to ask.  Sp in ni  ng  Spark  16:51, 31 December 2009 (UTC)
 * And it would appear that the claim that Williams syndrome is the "extreme female brain has at least been suggested (search document for "Williams") although the claim is disputed. What is not disputed is that there is strong difference between male and female brains, eg this paper along the lines of systemizing/empathising split.  Sp in ni ng  Spark  17:18, 31 December 2009 (UTC)
 * I didn't mean to be politically correct, I just hadn't seen empathy described (by scientists) as a female trait (and the paper you link to is a recent paper that says it hasn't been discussed much, so it's not surprising I haven't seem any discussion on it). --Tango (talk) 01:48, 1 January 2010 (UTC)


 * Asperger's does not seem extremely "male." It seems more nerdish. An "extremely male" attitude would be "Bah! I've no time for boring details. Out of my way. Let's just forge ahead from point A to point B, without getting tripped up by trivial details." A "typical male" does not stop to get directions in a journey. A typical Asperger's would stop and research all historical details about the location, and all of its notable inhabitants throughout history, then create a Wikipedia article, then talk about it on the Ref Desk, if it caught his fancy. Edison (talk) 03:22, 1 January 2010 (UTC)
 * You should take a look at Simon Baron-Cohen's Empathizing–systemizing theory and his book The Essential Difference before so quickly dismissing the idea of autism as 'extreme maleness'. Fences  &amp;  Windows  04:09, 1 January 2010 (UTC)

I want to make my own battery-powered heating pad.
A proper heated gilet (the kidneys are the most appropriate section to heat due to blood throughput and proximity to surface) is too expensive and also bulky and not possible to wear underneath normal clothing. I want to make a battery-powered pad that can be strapped around one's trunk via an elastic strap. My diagram attempts to show my plan. I can take a peice of felt, sew loops onto the felt and thread nichrome wire through the loops. I can then sew another peice of felt over the first, sandwiching the nichrome wire in between. The wire can then be connected to a battery pack, possibly with a switch. The questions I have now are,

a) how many watts of heat would I want to produce over an area of about half a square foot (450 cm2)? b) which nichrome wire should I buy? ebay has wire at 10, 20, 50 ohm/m and probably many outside and inbetween. I expect to be able to loop around 4 m of nichrome wire (15 rows of 25 cm stretches) c) what voltage should I use? I need most of the resistance to be in the wire.

I guess if I have a), I can figure out b) and c). Am I overlooking something that makes this idea stupid? Seems simple enough to me. I wonder though, since the nichrome wire is often used to make something very hot, if the resistance wont be a lot lower than that stated.. take this one for example; how much around 50 ohm/m will this vary, depending on temperature? Seans Potato Business 13:20, 31 December 2009 (UTC)
 * Well, felt is flammable... I would put something flame resistant (but not heat resistant) in-between the wire and the felt. I'm also not sure about your assertion that the kidneys are the most appropriate body part to heat. You have to be in real trouble before your core body temperature starts to drop, it is the extremities that get cold. One of the main reasons the extremities get cold is because the body cuts off most of their blood supply to preserve heat, but I'm not sure how it knows when it needs to. If it does so based on the skin temperature of the extremities themselves then heating your trunk won't actually have much benefit, other than possibly making your trunk uncomfortably hot. Personally, I prefer wearing well insulating clothes (layers that trap air in-between are usually best). --Tango (talk) 14:35, 31 December 2009 (UTC)


 * (ec) How much heat you need depends on how you are going to use it. Heated jackets are typically 50-100 watts.  If you want to do some calculations, the first thing you need to know is the thermal resistance of the garment you are sewing this into.  Next you need the temperature difference (body heat to ambient temperature) of the intended use (obviously a walk in the New Forest is a completely different requirement to a walk in Antarctica).  You can now calculate how many watts you are going to be losing.  Most of this will be made up by normal body heat, but the difficult part here is that body heat generation is related to activity.  If you are intending to sit motionless in a hunting hide in a snowstorm you are liable to need more heat than if you are hiking.  You really need a thermostat or other form of regulator in this because as activity changes, the temperature inside the jacket will change.  The power you wish to generate along with the battery voltage will yield the resistance you need.  You will need to make the battery at least 12 volts (24 would be better) otherwise the resistance is going to be too low compared with the battery internal resistance, unless you are aiming for a very low amount of heat.  NiChrome resistance will only change by a few percent over the temperature range of interest so that is not an issue.  The stupid thing that you have not considered is how are you going to protect the nichrome wires from the wet? Also, care that short-circuits can't happen is a good idea, a short piece of wire finding itself directly across the battery could get red-hot.  Another thing to think about is that while the garment needs to a high thermal resistance, there also needs to be a lining of some low thermal resistance material to spread the heat from the wires evenly.  All in all, I'm guessing that buying a heated jacket is going to be a lot easier and probably not much more expensive (possibly cheaper once failed prototypes are taken into account).  Sp in ni  ng  Spark  14:40, 31 December 2009 (UTC)
 * One point that hasn't been mentioned - you're going to need a fairly substantial battery. A medium-sized 12V gel cell will have about 5 Ah capacity - so it'll run a 60 W heater (a typical electric blanket is about 150 W, but you won't need as much power for a heating pad) for about 1 hour. Will that be enough for your planned recreational activities?  You might want to consider the chemical-based hand warmers you can get from camping shops as an alternative. Tevildo (talk) 15:16, 31 December 2009 (UTC)
 * Li-ion batteries may be better than industrial lead-acid gels for this application for weight and power density reasons.  Sp in ni ng  Spark  16:34, 31 December 2009 (UTC)


 * I would have thought that it's going to be really difficult to make this any better than a decent warm jacket. I've ridden my motorcycle for hours in sub-zero temperatures, ski-ed at minus 20&deg;C and walked on the antarctic, and the only things that got cold were my extremities (my hands, feet and face) and that's mainly because it's impossible to get enough insulation on them.  What's wrong with a few layers of inner clothing and then a decent coat?  --Phil Holmes (talk) 17:49, 31 December 2009 (UTC)


 * You'd probably also want some kind of safety cutoff, probably in the form of a temperature sensor. If you forgot to turn it off and left it in a heap somewhere, it might catch fire and/or melt...  TastyCakes (talk) 17:57, 31 December 2009 (UTC)

How did the church sign know the temperature?
Tuesday a sign in front of a church had details about the church in what I assume was a rotating series of messages. The time and temperature were also displayed, which reminds me of my savings and loan which still has the time and temperature sign with incandescent light bulbs forming the numbers in the time and the temperature. The church sign was a newer technology, but maybe the science is the same. How do these signs know the temperature and convert it to a group of bulbs? Vchimpanzee ·  talk  ·  contributions  · 17:32, 31 December 2009 (UTC)


 * Interestingly, Wikipedia needs an article on electric signs in general. I can't find one other than Neon sign, which is about the neon tube variety only; there's one on Westinghouse Sign, which was one particular sign; but surely the topic is interesting and notable enough for an article.  The evolution from neon bulb controllers to the current crazy gigantic video screens in Las Vegas would be a good read.  Comet Tuttle (talk) 18:05, 31 December 2009 (UTC)
 * Well it's probably a type of matrix display like an LED display. Each of the lights can be turned off and on by a microcontroller or computer.  The controller has routines programmed into it that know what lights to turn on to display particular letters and numbers.  Originally someone must have gone and made computer functions saying "for an A, turn on this, this this and this", and so on, but this is all removed from the usual operation of the thing, where the user will just send it a string of letters or numbers and it'll display them.  You can read some nuts and bolts on an LCD display connected to an arduino in this tutorial.  And here is a guy that turned a gameboy display into a LED matrix which probably uses a similar idea.  As far as getting the temperature, that would be a simple matter with a thermistor or simply getting retrieving it every so often from the internet.  TastyCakes (talk) 18:09, 31 December 2009 (UTC)
 * We also have Variable-message sign, but that's a specific application despite its generic name. DMacks (talk) 18:25, 31 December 2009 (UTC)
 * HD44780 Character LCD is probably worth a look for a defacto industry standard for character displays. The computer functions that convert characters to letters are probably not really subroutines in some program. It is more likely that they are implemented with a programmable logic device. The data is usually sent in a serial manner. Noodle snacks (talk) 01:29, 1 January 2010 (UTC)
 * I was really wondering where the temperature comes from. The savings and loans had these signs before the Internet, though there are surely other sources. My question was really whether the sign could update without human intervention. It would be on after the savings and loan closed. Vchimpanzee ·  talk  ·  contributions  · 18:24, 31 December 2009 (UTC)
 * Building a temperature sensor into a large sign is a fairly trivial piece of electronics nowadays. You can buy such signs off-the-shelf (example).  Sp in ni  ng  Spark  18:59, 31 December 2009 (UTC)


 * Thermistor may be the old type - resistance changes as temperature changes. (Beware - the article seems to be 95% aimed at electronics nerds.)  Comet Tuttle (talk) 19:41, 31 December 2009 (UTC)
 * 95% of all the science articles on WP are aimed at nerds of one type or another. Telling a layman to read the article on "such'n'such" just serves to confuse and bury the person in technical jargon.  This is one area where Wikipedia needs a Layman's Wikipedia.  It's not so simple as to belong on the Simple English WP but not so complex that the average person can't even get through the introduction without having to look up at least five other terms or principles.  Dismas |(talk) 22:13, 31 December 2009 (UTC)
 * Calling people nerds is offensive and in my experience is an insult used by the educationally sub-normal against anyone who has an understanding or an interest in a subject which goes beyond their own pathetically limited understanding. It seems in the US a desire to learn is to be despised.  Sp in ni  ng  Spark  23:31, 31 December 2009 (UTC)
 * Dismas I don't think you mean to be offensive but this is not the place to launch a discussion about Wikipedia's complexity level. It seems that you partition readers as either laypersons or specialists and that is a patronising attitude. The formal purpose of the Ref Desk is indeed to tell an OP where to read more. If the subject is abstruse then it does the OP no good to pretend that some underlying concepts don't need to be understood first. Pointing someone in the right direction is more important that careless name-calling like nerd (Wikipedia has an article on that word) or taking a pot shot at education in the US. Neither of the "95%" figures quoted by Comet Tuttle or Dismas have any more than rhetorical significance. Cuddlyable3 (talk) 00:02, 1 January 2010 (UTC)
 * A) I would call myself a nerd. B) You both missed my point.  C) thank you for having some good faith and assuming (correctly) that I didn't mean to offend.  And D) I find it hypocritical that S. Spark would first say how offensive the word "nerd" is and then make a harsh generalization about people in the US.  But you're right... this isn't the place.  Dismas |(talk) 00:26, 1 January 2010 (UTC)


 * (EC) I can't speak with certainty for Dismas, but I self-identify as a geek and haven't heard 'nerd' or 'geek' used perjoratively somewhere like this: surely everyone on this desk is a geek (or nerd)? As a geek, or nerd, I find it far more offensive that someone would use 'educationally sub-normal' as an insult: not cool.


 * Most of Wikipedia's articles on mathematics and science topics are inaccessible for anyone who actually wants to learn from them, and this is a recognised problem that many editors have been working on for a long time. The problem is that most editors who know a lot about the topics (particularly more casual editors) get caught up in being precise and complete, at the expense of being accessible or even readable to most readers. I'm a geek, and if I were writing an article on certain topics that I am particularly geeky about I would have to constantly check it with editors who are less familiar with the topics to keep it readable. Mentioning this here increases the chances of interested editors taking a look at those articles and improving them, even if that requires making parts of them less accurate or complete. 86.176.48.114 (talk) 00:38, 1 January 2010 (UTC)
 * Can we go back to discussing how the church sign measures temperature? I'm interested in knowing the answer myself.  --99.237.234.104 (talk) 03:31, 1 January 2010 (UTC)
 * It may be a Church of God with Signs Following. Cuddlyable3 (talk) 19:00, 1 January 2010 (UTC)
 * There are plenty of ways for electronics to measure temperature. There are electrical components called "thermistors" who's electrical resistance varies with temperature.  The computer inside the sign could measure the resistance of the thermistor and thereby infer the temperature.  Displaying that on the sign is then a simple matter.  Another way to do it would be to measure the deflection of a 'bi-metallic strip' - two strips of metal with different rates of thermal expansion that are glued together - when the strip get warmer, one metal expands by more than the other causing the strip to bend.  The computer could use all sorts of ways to measure the amount of bend.  There are LOTS of ways this could be done.  Which specific method is being used by a particular kind of signboard is hard to say - that would probably require calling the manufacturer. SteveBaker (talk) 03:57, 1 January 2010 (UTC)

Flower identification
Hello. I'd be very appreciative if someone could give me a species name, or at least a genus, for the following images: 1, 2, 3. Thanks for the help. — Anonymous Dissident  Talk 21:55, 31 December 2009 (UTC)
 * Dahlia sp.? - Craig Pemberton 22:14, 31 December 2009 (UTC)
 * Also, the third could be Impatiens sp. but don't take my guess at face value. Plants can be tricky. - Craig Pemberton 22:27, 31 December 2009 (UTC)


 * 1 and 2. Zinnia. 3. Petunia.--Eriastrum (talk) 23:33, 31 December 2009 (UTC)
 * Thanks a lot, both of you. — Anonymous Dissident  Talk 03:34, 1 January 2010 (UTC)