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July 24

Mercury Biological Effects

How does mercury interact with the biology of humans? We know that mercury causes problems, and lead causes problems, because lead binds to places calcium would bind to. How about mercury?174.3.103.39 (talk) 00:05, 24 July 2009 (UTC)

I am not sure this is known. Mercury poisoning article says "much remains unknown", either. I'll see if I can find something in the literature, but it won't be right away. Sorry. --Dr Dima (talk) 00:10, 24 July 2009 (UTC)

One theory mentioned in literature is that mercury ion binds to sulfur in cysteine and interferes with activity of proteins, e.g., Thioredoxins. --Dr Dima (talk) 00:23, 24 July 2009 (UTC)

Yeah, that makes sense to me (76.21 posting from a library computer) -- mercury has a high affinity for sulfur in general, so it would tend to irreversibly bind to cysteine. And since neurons in particular have high concentrations of cysteine-containing proteins, it would tend to kill them neurons and (eventually) make you crazy. BTW, I think the reason why organic mercury compounds are so much more poisonous is because they're less polar and thus can more easily go through the blood-brain barrier. FWiW 146.74.230.113 (talk) 00:52, 24 July 2009 (UTC)

The best known example of mercury's ill effect on man is the minamata disease which first was identified in Japan.Due to mercury content in the river water,it passed on into the fish and then into man.The concentration in the rivers though low was dangerous due to phenomenon of "biomagnification".So the people who consumed it ended up accumulating higher concentration of mercury.This severly affected the limbs and the muscles.For more info refer http://en.wikipedia.org/wiki/Minamata_disease —Preceding unsigned comment added by 117.193.130.204 (talk) 13:55, 24 July 2009 (UTC)

See also http://en.wikipedia.org/wiki/Mad_Hatter#.22Mad_as_a_hatter.22 --Phil Holmes (talk) 22:25, 29 July 2009 (UTC)

Intelligence

If I excise my brain by thinking a lot, will i become more intelligent. And what would that mean for me/ —Preceding unsigned comment added by 79.75.60.53 (talk) 00:21, 24 July 2009 (UTC)

It really depends on what you mean by "intelligent". It isn't a well-defined concept. If you want to become knowledgeable, try reading a lot. If you want to become good at solving problems, practice solving problems lots. If you want to understand complicated things, take a course on them. --Tango (talk) 00:24, 24 July 2009 (UTC)

No I want to be more intelligent as in the IQ tests they give you. Also clever (is it the same?). —Preceding unsigned comment added by 79.75.60.53 (talk) 00:30, 24 July 2009 (UTC)

I suggest you start by reading Intelligence quotient and intelligence. If you want to do well on IQ tests, then practicing the sorts of questions found in IQ tests would appear to be indicated. But note that IQ is at best a very poor measure of intelligence; that clever and intelligent are probably not the same thing; and that neither is of much use except in combination with other attributes. The very shortest answer to your first question is "yes", but there's much hidden beneath that answer. As to what that would mean for you, we cannot say. In general, it's a good thing, but effects vary from person to person and from time to time. --Tagishsimon (talk) 00:40, 24 July 2009 (UTC)

Can I reiterate an earlier discussion that learning to think more critically will get you far in this world (and will cure you of your obsession with IQ tests!). If I can recommend a wonderful, fun little book: Thomas Gilovich, How We Know What Isn't So. It's a wonderful little primer on critical thinking and why the general-issue human brain is so poor at it. --98.217.14.211 (talk) 00:44, 24 July 2009 (UTC)

Is it my jeans that say how intelligent I am? —Preceding unsigned comment added by 79.75.60.53 (talk) 01:01, 24 July 2009 (UTC)

See Nature versus nurture and Heritability of IQ. --Tagishsimon (talk) 01:13, 24 July 2009 (UTC)

Please do not attempt to excise your brain at home. Only a qualified surgeon has the necessary skill and tools to perform this operation. Cuddlyable3 (talk) 12:10, 24 July 2009 (UTC)

By which s/he means, the correct word is "exercise". ("wiktionary:Excise" means cut out). Also, "genes", not "jeans". Knowing this doesn't make you any more intelligent, but people might think you are. AlmostReadytoFly (talk) 14:00, 24 July 2009 (UTC)

One might reasonably ask what garments express "I'm intelligent". —Tamfang (talk) 18:57, 2 August 2009 (UTC)

Medicinal use of "Cineraria[e] maritima"

My local museum has an old medicine bottle(I'm not sure of the exact date, but it's early 20th century) labeled "Cinerariae maritima". Apparently "Cineraria maritima" is an alternate name for the dusty miller plant, Senecio cineraria, but what medical use has this plant had? 69.224.113.202 (talk) 02:59, 24 July 2009 (UTC)

It was a old-time "patent medicine" or "herbal medicine" claimed to cure cataracts, advertised to doctors and pharmacists starting in the the 1880's [1] as "Succus cineraria maritima." An 1892 mention suggested it had been tried and rejected in the past as a remedy for something [2]. The plant was also called "Dusty Miller" and was a common ornamental border plant in the 19th century. Showing a great case of seemingly reliable sources not being so, several seemingly mainstream medical journals in the 1890's uncritically reprinted press releases from the nostrum's manufacturer, quoting little-known doctors in faraway countries who had "cured cataracts" with the medicine. Clinical testing, or at least the circa 1900 version where it is tried on a few patients without any control group and with the doctor and patient knowing it was the medicine, found it ineffective [3], [4].. In 1916 the U.S. government shut down one supplier who sold it via circulars claiming amazing cures, with testimonials. But at the time, all they U.S. government could do as a penalyt was fining the company $10. See [5], and [6]. Homeopathic publications still list it. "Toxicity of houseplants" suggests [7] that long term consumption of the plant could be toxic. Edison (talk) 04:09, 24 July 2009 (UTC)

Infections During Pregnancy. — —Preceding unsigned comment added by 117.198.243.37 (talk) 03:45, 24 July 2009 (UTC)

Venus

Hypothetically, if Venus could be moved to a different distance from the Sun, what distance from the Sun would result in Venus achieving an Earth-like temperature, assuming that its atmosphere stays the same? --Shanedidona (talk) 03:33, 24 July 2009 (UTC)

I'm not a planetary physicist (as I said before), but it's clear to me that it would have to move to a distance FARTHER than Earth to achieve the same temperature cause its atmosphere keeps the heat in more. FWiW 98.234.126.251 (talk) 07:16, 24 July 2009 (UTC)

Curiously if it was the same surface temp as the earth the atmosphere would not be the same, as the vapours would condense at the lower temperature. You may need to ask again in another way.83.100.250.79 (talk) 08:59, 24 July 2009 (UTC)

Tough question to answer. 98.234.126.251 is correct, at first guess, Venus would need to be moved further away than the Earth as it has a very thick atmosphere and a powerful greenhouse effect. Unfortunately, reducing the insolation (by moving it further away) will initiate changes in its atmosphere, with components of it precipitating out and changing its composition - therefore changing how much of a greenhouse effect it experiences. You would need to build a more detailed climate model, and considering how hard it is to build a climate model of the Earth, building one of Venus would be even harder. — QuantumEleven 12:48, 24 July 2009 (UTC)

"Unfortunately, reducing the insolation... will initiate changes in [Venus's] atmosphere"... -- I wonder what would be so "unfortunate" about that? 98.234.126.251 (talk) 23:46, 24 July 2009 (UTC)

The atmosphere of Venus is carbon dioxide and nitrogen to better than 99.9%. Neither of these would change state if reduced to Earth-like temperatures. Dragons flight (talk) 01:11, 25 July 2009 (UTC)

Early in Earth's history, its atmosphere was almost entirely CO2 and N2 as well. The rise of unicellular plants converted the CO2 to O2 and gave us an oxygen rich atmosphere. Without life, Earth would likely revert back to an atmosphere similar in composition to that of Venus as well. It is quite likely that if you hooked a tow-cable up to Venus and dragged it to Earth's orbit and gave it time to equilibrate, you would have a planet whose atmosphere would be almost identical to the pre-life Earth's. If you innoculated this relocated Venus with life, you may even be able to closely approximate Earth's modern conditions after a few billion years. The deal with Earth;s atmosphere is that O2 can ONLY exist because plants make it; it is FAR too reactive to exist for even a few thousand years without constantly being replenished. Prelife Earth likely had a greenhouse effect similar to that of Venus. --Jayron32 03:25, 25 July 2009 (UTC)

what is TDSi engine

how does a TDSi engine workSaurabhasks (talk) 06:10, 24 July 2009 (UTC)

You'll want to look at Turbocharged Direct Injection, Diesel engine and Diesel car history. I'm not sure what the 's' will signify - sometimes it means 'sports' and is a reference to the Trim level. 194.221.133.226 (talk) 10:18, 24 July 2009 (UTC)

Mosquito and HIV

Suppose a mosquito bites a person infected with HIV.In this process the mosquito inserts it proboscis into the blood stream of the person.Then again when it bites .i.e.inserts its proboscis into the blood stream of a healthy person ( consider immediately ) the person doesnt contract HIV.how???Is it not the same as two persons using the same syringes or needles where they contract HIV.i.e. comparing the proboscis of mosquito to a syringe or needle. —Preceding unsigned comment added by 117.193.131.167 (talk) 06:59, 24 July 2009 (UTC)

I think it's because the moskeeter sucks the blood out rather than putting it in. FWiW 98.234.126.251 (talk) 07:18, 24 July 2009 (UTC)

As linked from the AIDS article: Why mosquitoes cannot transmit AIDS.--Shantavira|^{feed me} 07:27, 24 July 2009 (UTC)

that website was very informative. thanks —Preceding unsigned comment added by 117.193.142.180 (talk) 10:58, 24 July 2009 (UTC)

In a country where a large percentage of the population is infected and mosquito bites are common, the transmission by squashing a blood-engorged mosquito who is completing his meal on a second victim, with the HIV infected drop of blood deposited on the skin around the bite, followed perhaps by scratching, sounds like the most likely route. A 1 in 10,000,000 chance sounds like it would not happen, but some countries in subsaharan Africa have a high incidence of Aids (over 15% per the Aids article) as well as a high incidence of mosquito bites. The Aids article says that health care workers anywhere must be very careful not to get blood on them, and to cleanse blood from their skin immediately. A drop of blood is a drop of blood, whether from a medical procedure or a splatted mosquito. This route does not require that the virus survive long in the mosquito, or that the mosquito somehow pumps it back into the second person. Edison (talk) 15:03, 24 July 2009 (UTC)

Here's a question. If mosquito enzymes digest the HIV virus, why don't we use those enzymes from mosquito samples to develop a cure for HIV? ~AH1^(TCU) 03:51, 25 July 2009 (UTC)

I think it's a good idea, but we'll have to do a lot more research on what those enzymes are and what exactly do they do. 98.234.126.251 (talk) 05:06, 25 July 2009 (UTC)

Most of the viruses are made up of RNA or DNA as the central core and surrounded by protective protein coat.When this protein coat is digested the virus gets destroyed.Therefore protein digesting enzymes digest the proteins surrounding the virus.Thats what happens to HIV in mosquitoes stomach.Also you asked above, the enzyme cant be used because it is not specific to HIV.It shouldnt end up digesting vital proteins in blood.For the HIV vaccine it needs to be specific against the HIV virus. —Preceding unsigned comment added by 117.193.139.242 (talk) 05:05, 25 July 2009 (UTC)

Well, how about we try chemically modifying the enzyme to make it specific? Or would that be inherently impossible? (I'm just a petroleum chemist, I don't really know exactly how this particular enzyme works, so forgive me if I'm wrong.) 98.234.126.251 (talk) 05:09, 25 July 2009 (UTC)

It is very possible to do that, but that would take a hell of a lot of research.174.3.103.39 (talk) 07:11, 27 July 2009 (UTC)

Plus, as 117.193 pointed out, the same enzyme might not work against different strains of the AIDS virus -- it might have to be specifically modified for each new strain that appears. (In other words, there's also a risk of making it too specific in the process of modification.) FWiW 98.234.126.251 (talk) 22:55, 27 July 2009 (UTC)

Just took it from the topic HIV cure that follows below..just for ur quick reference.here it is "the fact that the virus attacks the very immune system cells targeting it certainly makes things difficult. My understanding too is that the genius of this particular virus is the gp120 glycoproteins which "decorate" the proteins which effect entry of the virus into the cell. To "cure" something, or to make a vaccine against something, you need a target. But gp120 is highly variable, so it's difficult to target, and it hides the less variable proteins underneath that do the dirty work of infecting the T-cells. Any one successfully infecting HIV can produce a million new particles with variant gp120's, and only one of them has to work for the infection to continue. ".....so u see the specific difficulty associated with the menancing HIV.Most of the virus till today dont have a cure.When we can ourselves(I an engineering student) think of so many possibilities scientists who have been researching on HIV still havent hit upon the cure.So hope u get the point —Preceding unsigned comment added by 117.193.128.204 (talk) 04:17, 26 July 2009 (UTC)

Yeah, I see what's the problem with the strategy I suggested. Well, let's all of us keep trying to come up with new ideas till we find something that works. 98.234.126.251 (talk) 22:57, 26 July 2009 (UTC)

temps of stellar objects

hi, where might i find info of the temperatures of various stellar objects, the wiki pages related to the objects don't quote their temperatures/temp range/av temp... also i'm guessing that gas and dust clouds are cooler than debris disks? is that right? thanks! :) —Preceding unsigned comment added by 121.202.252.240 (talk) 07:52, 24 July 2009 (UTC)

Black body provides the temperature for most radiating objects. As for dust clouds vs debris disks, I'm not precisely sure of the distinction you're drawing. There shouldn't be anything inherently warm about either; each will be heated based on proximity to a star or other radiating thing. — Lomn 13:05, 24 July 2009 (UTC)

Does SIMBAD [8] meet your needs? That looks like it gives info on individual objects (Magnitudes, temperatures etc). Also see Category:Astronomical_databases. AlmostReadytoFly (talk) 13:13, 24 July 2009 (UTC)

thanks a LOOOOOOT guyz :)

Animals that eat 'meals'

Most humans will eat a variety of types of food in one sitting/meal - e.g. meat and two-veg. Beyond domestic pets (since we provide their food) is there evidence of other animals eating 'meals'? I.e. do any animals have little food-combos that they put together and eat, much like we do? I don't mean like chopping and preparing - just the idea of saving, say, some berries aside until it finds some nuts and then eating them both together. 194.221.133.226 (talk) 09:11, 24 July 2009 (UTC)

"Hmm," said the cat, "I think I'll save this mouse liver until I can find some fava beans and a nice chianti." I tried researching this but there are too many refs talking about "animal meal" i.e. "ground up animals," to make it easy to find an answer. I've seen various animals combining water and a food in close succession, but not who really collected foods to make a pleasing combination of flavors or colors. Certainly they have p[references for certain food combinations over others, which might be too salty or too sweet, or which might contain ingredients they do not like. They pretty much seem to browse and eat some of this, then later some of that. Chimpanzees eat food where they find it [9] rather than assembling a "meal." Edison (talk) 20:07, 24 July 2009 (UTC)

Availability might be the question, since storage may be difficult. If two varieties of food were available at once, and especially if both were plentiful, I think other forms of life would eat quantities of each, much as humans do, and they might move between the two (or more) items in a way similar to the way we move between types of food in the course of an eating session. Perhaps there have been experimental studies of this, but I don't know. Bus stop (talk) 20:22, 24 July 2009 (UTC)

Parrots may gather and transport food to their mate setting on the eggs, and they eat a varied diet. There is an opportunity to collect and serve a meal of several ingredients. Edison (talk) 20:07, 24 July 2009 (UTC)

Storage is one major drawback to assembling a meal. Availability is the other. Some animals store food for later, others lose what they don't eat now. So, eating various foods in succession is much more prevalent. E.g. a bear may wander away from a stream full of salmon to snack on some berries, a leopard may store a freshly caught gazelle and go off to hunt for smaller prey. Birds are known to rake lots of seeds out of bird feeders to get to some specific ones they like and then snack on the ones from the ground later on, cats or dogs with access to both dry food and wet food may switch between one and the other. Domestic cats are often observed to come in for some pet food after a life catch. Although most animals are specialized as "meateaters" or Herbivores they do consume a little bit of the other as part of their usual diets. Herbivores eat some worms and insects along with the plants they consume. Carnivores get their prey's last meals along with the meat. (They only get the roughage, they usually can't metabolize the nutrients.) Animals have individual tastes along with general preferences. The key problem with your question is that it assumes we can correctly assign purpose to animal behavior. That is dicey. Sometimes observation and analysis help, e.g. parrots were found to eat certain clays to provide needed nutrients for their diets and some birds eat certain herbs for medicinal purposes. But does that sparrow fly away from the seeds to pick up a maggot to "assemble a meal" or to evade being attacked by other birds or a predator. Is there some other reason we haven't thought of, or is there no reason at all? 71.236.26.74 (talk) 21:46, 24 July 2009 (UTC)

I certainly agree that I can't think of any animals other than humans who do this - so the obvious question is not "Why don't animals do this?" - it's "Why do humans do it?" SteveBaker (talk) 23:57, 24 July 2009 (UTC)

Hamsters collect food in their cheek pouches and store it in their larder for later consumption. If any animal collects food for later "meals" they would be a good candidate, having typically a pantry stocked with nuts, seeds, Cheerios, berries, etc. Edison (talk) 03:52, 26 July 2009 (UTC)

Cats purring

Another feline question today!

Somebody told me that female cats are much more inclined to purr than male cats - is this true?b Our article on purring doesn't mention that. —Preceding unsigned comment added by 62.25.96.244 (talk) 10:24, 24 July 2009 (UTC)

OR In my experience it's the other way round! --TammyMoet (talk) 10:44, 24 July 2009 (UTC)

Purring in cats has two sources: contentment and fear. So if you have a male that is happy a lot or a fraidycat he'll purr a lot. Females are less likely to challenge their position in a domestic family "pack". So, on average, they are more likely to be content with their lives and attention from her owners. That doesn't mean the opposite doesn't happen. Cats are individuals with a whole spectrum of personalities. (OR we had a tom that kept getting beaten up by any cat in the neighborhood and even the birds "dive bombed" him. He was the purriest furry I've ever encountered.) 71.236.26.74 (talk) 22:02, 24 July 2009 (UTC)

Electric Shock

What is the range of shock that is dangerous to man?That is the volltage range of shock and the number of amperes of current that is dangerous to man.Is there any animal resistant to electric shock??? —Preceding unsigned comment added by 117.193.142.180 (talk) 11:08, 24 July 2009 (UTC)

It isn’t the voltage per se that’s the problem, it’s the current. Currents approaching 100 mA are lethal if they pass through sensitive portions of the body. See electric shock. Red Act (talk) 11:30, 24 July 2009 (UTC)

Electric eels are presumably resistant to electric shock, since they themselves don’t get electrocuted when they electrocute their prey. Also, something like a turtle with its appendages pulled in would in a way be resistant to electric shock, since I’m pretty sure a turtle’s shell has a very high resistance, compared to flesh. Red Act (talk) 11:51, 24 July 2009 (UTC)

I disagree with the statements about turtles. They have skin which is always exposed to the surrounding water. Edison (talk) 14:38, 24 July 2009 (UTC)

Not all turtles are aquatic. Googlemeister (talk) 15:08, 24 July 2009 (UTC)

Yes, I was assuming the turtle wasn't in water. I should have said that. Red Act (talk) 17:42, 24 July 2009 (UTC)

It is the current that matters, but perhaps an appropriate question would be of the resistivity of the human body, so the OP could figure out an appropriate voltage that would send 100 mA through it. —Akrabbim^talk

The resistance of the human body varies a lot depending on which two parts of the body contact is made with, and how contact is made – touching a wire with a dry finger is a lot different from standing on a metal plate with wet feet. However, the electric shock article says that death has occurred with voltages as little as 32V. Red Act (talk) 12:47, 24 July 2009 (UTC)

Mythbusters thinks that 7mA can kill you if it goes directly through your heart. Not sure exactly where they are getting their info. Googlemeister (talk) 13:03, 24 July 2009 (UTC)

In the 19th century War of the currents experiments were done on a variety of animals, determining the minimum voltages and currents necessary for fatal electrocution. Thomas Edison argued that DC was less lethal than AC. Ultimately, several thousand volts of AC was chosen as the means of execution, first used on muyrderer William Kemmler. Electrocution was widely used from the 1890's through the 1960's. The source impedance of the high voltage AC determined the current rather than the skin of the condemned. The resistance of the human skin for a given electrode placement may suddenly decrease when a sufficient current passes through it, due to disruption of the skin. Dry skin has higher resistance than wet skin, perspiring skin, or bleeding skin. The route of the current has a big factor in determining the danger. The heart or brain are not good places to have current passing. Edison (talk) 14:38, 24 July 2009 (UTC)

BTW, do you know the highest voltage (I mean like from live wires, not lightning and stuff) that a human ever survived? I've heard of one guy who was reported to have survived being zapped with 750V DC (he was bare-handing a live generator in an express diesel, see Pioneer Zephyr), and a few who survived 600-650V DC from touching the electric rail in the subway, but I don't know if any of this is true. 98.234.126.251 (talk) 23:55, 24 July 2009 (UTC)

Did this chap touch the wire?[10] Warning shows man being killed by electricity. —Preceding unsigned comment added by 79.75.60.53 (talk) 23:07, 25 July 2009 (UTC)

That was 1500V DC, and I could see it was almost instantly fatal. What I was asking was, what's the highest voltage electric shock that anyone ever survived? Thanks for the video, though, it was interesting in a scary kind of way. I'll take care not to touch any live wires :-) 98.234.126.251 (talk) 00:52, 26 July 2009 (UTC)

You can survive any voltage as long as you are not in contact with earth and are wearing and equipotential suit. does Live OH line working count?

I've seen the Helicopter Linemen episode on the History Channel, so I know what you're talking about. I'm asking about electric shocks from live wires, though (not from lightning strikes or Tasers or anything like that, but from live wires only). BTW, an equipotential suit is called a Faraday suit cause it acts like a Faraday cage. I've changed the link to point to that article; hope you don't mind. 98.234.126.251 (talk) 02:42, 26 July 2009 (UTC)

The current capability or Coulombs of current stored are more important than the open circuit voltage. School kids routinely touch Van de Graaf generators charged to hundreds of thousands of volts, but without a capacitor or Leyden jar attached up to store a dangerous amount of electricity. A "live wire" likely has tens of thousands of amps of sustained current available until the circuit breaker at the substation opens or a fuse blows. I would expect to die if I touched a live wire at 12kv, 4kv, 2400 volts, 480 volts, or 240 volts. 120 volts could well be lethal, and has been many times, depending on conditions, such as how well grounded the victim is and what path the current follows through the body, and for how long. For lower voltages, there are probably situations where it could be lethal. If a patient is on a grounded metal operating table, for instance, quite a low leakage voltage could be lethal, depending on the route of the current. Cows may refuse to give milk if they feel 1 or 2 volts of stray voltage, and the dairy operator are forced out of business. Prudence dictates observing applicable electrical safety codes. Edison (talk) 03:47, 26 July 2009 (UTC)

"I would expect to die if I touched a live wire at... 240 volts"? I personally survived getting zapped with 240 volts AC, as I said before. I wanted to know if anyone survived touching a live wire at 480 volts or higher. Thanks for that bit about the cows, though. 98.234.126.251 (talk) 23:03, 26 July 2009 (UTC)

The internal resistance of the human body between any two randomly chosen points ( a few inches apart of course) is approximately 700 ohms.

So, what would be the total resistance of the human body (including resistance of the skin, but not of the clothes/shoes) for a same-hand/same-foot pathway (which is, I believe, the pathway of the electric current in the majority of accidental electrocutions, including my own little incident with those Christmas lights)? 98.234.126.251 (talk) 05:50, 30 July 2009 (UTC)

Oh, I see now why somebody can survive getting zapped by 600V DC from an electric rail -- it's the victim's foot that usually touches the rail, and the current flows through the foot to the ground -- so the victim ends up with third-degree burns on the foot, but the heart and the brain remain unaffected. I still don't see how that railroad mechanic could get zapped from a 750V DC generator and still survive, though. 98.234.126.251 (talk) 07:30, 30 July 2009 (UTC)

How dehydrated was I?

Last night I felt really dehydrated and I whipped up a two quart (8 cups) pitcher of (sugar free) iced tea. In the hour before bed I drank it all. This morning I felt really good and barely needed to pee. I did pee, but not a huge pee, just a regular morning pee. Assuming I am not "retaining water", how dehydrated was I? Possibly dangerously so?--70.107.76.121 (talk) 11:34, 24 July 2009 (UTC)

From the dehydration article, the symptoms progress as follows:

Symptoms of mild dehydration include thirst, decreased urine volume, abnormally dark urine, unexplained tiredness, irritability, lack of tears when crying, headache, dry mouth, dizziness when standing due to orthostatic hypotension, and in some cases can cause insomnia.

In moderate to severe dehydration, there may be no urine output at all. Other symptoms in these states include lethargy or extreme sleepiness, seizures, sunken fontanel (soft spot) in infants, fainting, and sunken eyes.

The symptoms become increasingly severe with greater water loss. One's heart and respiration rates begin to increase to compensate for decreased plasma volume and blood pressure, while body temperature may rise because of decreased sweating. Around 5% to 6% water loss, one may become groggy or sleepy, experience headaches or nausea, and may feel tingling in one's limbs (paresthesia). With 10% to 15% fluid loss, muscles may become spastic, skin may shrivel and wrinkle (decreased skin turgor), vision may dim, urination will be greatly reduced and may become painful, and delirium may begin. Losses greater than 15% are usually fatal.

You can judge best, and we cannot offer a diagnosis, but you haven't mentioned any symptoms which would suggest it was anything more than mild. AlmostReadytoFly (talk) 12:36, 24 July 2009 (UTC)

Also note that drinking very large volumes of water can have adverse medical effects (including death). But we cannot offer medical advice. A woman who died in 2007 from participation in a radio station's "water drinking contest" consumed about 4 times the water you did. I would expect that if someone were suffering from severe dehydration, the water would not have to be flavored, like your "sugar free (artificially sweetened?) tea". Maybe you just liked the taste of the tea. Edison (talk) 14:21, 24 July 2009 (UTC)

There's also water loss through sweating & breathing to take into account. Still, it's an interesting question: where did all that water go? --Tagishsimon (talk) 14:33, 24 July 2009 (UTC)

Absorbed by cells perhaps. Googlemeister (talk) 15:06, 24 July 2009 (UTC)

This page linked from one of the wikipedia articles may be interesting in this regard. [11]. There's a lot of water outside of cells. Sweat is taken from the plasma, but that gets replenished to a certain extent from other souces. Our article only has consumption for the resting state which would be about 2.5 qt/day. In actual cases of dehydration it is important to not just replace water, but also electrolytes in the right combination [12]. -- 71.236.26.74 (talk) 20:48, 24 July 2009 (UTC)

Some (myself included) enjoy unsweetened iced tea over the sweetened kind. Doesn't have to be artificially sweetened. —Akrabbim^talk 15:16, 24 July 2009 (UTC)

When I lived in Tucson, I used to come back from summer bike rides and drink more than that, regularly. An ordinary-sized male in good shape needs to be down about two gallons before getting to the point of really serious dehydration. The risk of heatstroke is much higher. Looie496 (talk) 15:43, 24 July 2009 (UTC)

Just because you get away with it doesn't mean it's a good idea, though. Risk of kidney stones goes up if you let the urine in your kidneys get too concentrated. The whole "drink eight glasses a day" fad was probably overblown, but it's good to stay hydrated. --Trovatore (talk) 18:20, 24 July 2009 (UTC)

RE: death by water, see: Water intoxication, hyponatraemia, Leah Betts and Anna Wood (schoolgirl). --Mark PEA (talk) 18:54, 24 July 2009 (UTC)

So, it seems the answer is, I probably wasn't dangerously dehydrated just mildly so (since I had no symptoms other than great thirst) and I probably shouldn't drink much more than that at a single sitting (not that I was planning to). The tea was artificially sweetened but only mildly so. I hate sugary (as in actual sugar) drinks when I'm thirsty. I find them cloying and that they don't really satisfy my thirst deeply. By the way, hydrate is a terrible word in my opinion that is used way too much. Thanks all.--70.107.76.121 (talk) 22:22, 24 July 2009 (UTC)

angular momentum to momentum

What is the equation which converts momentum to angular momentum? -- Taxa (talk) 14:25, 24 July 2009 (UTC)

Have you seen the articles linear momentum and angular momentum? The latter gives:

$L=mvr\sin \theta \;$

where m is the mass, v is the speed (magnitude of the velocity vector), r is the distance from the origin and $\theta$ is the angle between the velocity and the radius vector. So

$L=pr\sin \theta \;$

where p is momentum. Of course, this doesn't apply to all situations (e.g. it wouldn't apply to spinning bodies). AlmostReadytoFly (talk) 15:13, 24 July 2009 (UTC)

Or in other words, L = r X P, where the bold represents vectors and X represents the vector cross product. It should be noted that Angular momentum depends on the origin of coordinates, in addition to the velocity of the reference frame. Rkr1991 (talk) 16:08, 24 July 2009 (UTC)

medicine

what is mesecentric adenitis ? how is caused ? —Preceding unsigned comment added by 117.201.12.2 (talk) 15:47, 24 July 2009 (UTC)

See adenitis. There is not a single cause. There are thousands of possible causes. -- kainaw™ 15:51, 24 July 2009 (UTC)

Perhaps you mean "mesenteric adenitis". If so, you could try this link. Tonywalton ^Talk 15:53, 24 July 2009 (UTC)

Wavelength versus radius

Have any electromagnetic wavelengths been detected which are shorter than the electron radius? -- Taxa (talk) 16:54, 24 July 2009 (UTC)

I'm not sure about shorter, but wavelengths about the same as an electron radius (maybe slightly shorter?) are in some gamma rays.
electron radius: 2.81794 x 10-15 m
gamma rays: around 10-15 m Dogposter (talk) 17:11, 24 July 2009 (UTC)

Gamma rays are often denoted with their energy instead of their wavelength. In the case of photons: E = h * c/wavelength

where:

h = 4.135 × 10−15 eV s

c = 3 * 10^8 m/s

A quick googling find cosmic gamma rays with energies of more than 100 giga eV. So doing the math:

wavelength = 1.24 * 10^-17, far shorter than the classical electron radius. :-) EverGreg (talk) 22:01, 24 July 2009 (UTC)

Electrons are point particles and have no radius, so no. — DanielLC 05:40, 26 July 2009 (UTC)

So what are these point particles made of?

DC vs AC

continuing from the discussion on electrocution etc...which is more dangerous DC current or AC current???If so why??? —Preceding unsigned comment added by 117.193.130.131 (talk) 17:16, 24 July 2009 (UTC)

As our article on electric shock notes, AC and DC have differing effects and thresholds. Additionally, AC's effects are highly dependent on the frequency (at low frequencies, it approaches the behavior of DC). As such, there is no good one-or-the-other answer to which is most dangerous. — Lomn 17:51, 24 July 2009 (UTC)

Sure there is. You're right that there are lots of details you can go into, but the short answer is that for the frequencies and voltages one is likely to encounter, AC is more dangerous. --Trovatore (talk) 17:58, 24 July 2009 (UTC)

Fair point. As an engineer I've perhaps got an unfair standard of "likely to encounter"; I've seen people lock up on HVDC sources several times. — Lomn 18:07, 24 July 2009 (UTC)

Well…sorta. It is more precise and correct to say that in our civilisations, dangerous voltages are oftener present as AC than as DC, and that one doesn't generally encounter DC at dangerously high voltage. However, that doesn't address the question of whether DC or AC is inherently more dangerous. —Scheinwerfermann ^T·_C18:09, 24 July 2009 (UTC)

The same voltage is ordinarily more dangerous as 60-cycle AC than as DC. That's because of the effect on the heart. --Trovatore (talk) 18:15, 24 July 2009 (UTC)

Mr Trovatore U claim that AC is more dangerous.I would like to know the exact detail why it is so.Also your statement on effect on heat is unclear.Please clarify —Preceding unsigned comment added by 117.193.139.242 (talk) 04:46, 25 July 2009 (UTC)

That might be because the peak voltage is higher. e.g. 230V AC has a peak of around 326V (No. of cycles doesn't matter - so long as it is a sine wave). Also ISTR that someone told me that the voltage does not matter that much, it's more where the current flows through - route 15mA across the chest and it's goodbye...  Ronhjones  ^(Talk) 18:52, 24 July 2009 (UTC)

This might be an urban legend, but I've always heard that an AC shock will cause you to grab on to whatever you're holding, but a DC shock will throw you across the room (or maybe the other way around...I'm kinda fuzzy on the details). Is there any truth to this? -RunningOnBrains^(talk) 18:30, 24 July 2009 (UTC)

Electricians or others who work around electricity know not to use their person as a voltage detector, but they still avoid touching a wire with the palm of the hand, for fear the hand would clutch it and be unable to let go, whereas if it contacted the back of the hand the contact would more likely get broken. Of course if a lethal current passes through the back of your hand, you are still dead. (Original research:)In my personal experience, AC or DC can each cause painful shocks and muscle contractions. I've felt 120 VDC and 120VAC from high current sources and cannot recommend either. Radios and TVs used to have high voltage DC B+ supplies for the vacuum tube plate circuit, and shocks from that were painful and dangerous, since they could be a couple of hundred volts. AC or DC voltage sufficiently high can literally burn a hole in the skin, thereby reducing the contact resistance, so only the impedance of the source and the relatively low internal resistance of the body limit the current. In the "War of the Currents," the Champion of Direct Current, Mr. Brown, challenged George Westinghouse to an electrical duel, where each would take a jolt of his favored current, then the voltage increased and the process repeated until one cried "Uncle!" Westinghouse declined to participate. In animal tests done by the DC proponents in the 1880's AC appeared to be lethal at lower voltages than DC. The notion of AC electrocution as capital punishment followed several gruesome and highly public electrocutions of electrical workers atop utility poles, when they encountered the high voltage AC used for arc lighting. The 2400 volt AC then common was clearly more dangerous to pass through the body from inadvertent contact than the 110 volt DC then in use, although I am confident that 110 DC could also cause a fatality, given sufficient contact area or sufficiently low resistance, and current continued for a sufficient time. Edison (talk) 19:28, 24 July 2009 (UTC)

(WP:OR) I don't think 110V (DC or AC) would cause a fatality -- I've personally been zapped with 240V AC, and I'm still alive, as you can see. I can personally testify, though, that it hurts like hell. 98.234.126.251 (talk) 00:08, 25 July 2009 (UTC)

I have actually read in my textbook that an AC shock is always attractive and a DC shock is repulsive. A quick googling gives this, so as Lomm says, there are a whole lot of factors to be taken into account. But, for household frequencies and voltages, an AC shock is definitely more dangerous. Rkr1991 (talk) 03:35, 25 July 2009 (UTC)

So in other words, an AC shock makes you hold on tight to the wire, and a DC shock makes you fly halfway across the room... :-) 98.234.126.251 (talk) 05:12, 25 July 2009 (UTC)

Maybe not halfway across the room, but certainly enough to take your hand off quickly. Rkr1991 (talk) 07:20, 25 July 2009 (UTC)

It's only my personal experience, don't try this at home. AC voltage is definitely repulsive under certain conditions. 120 VAC is good for about 2-3 feet, 240 VAC is good for five feet at least. Whether that's involuntary muscle contraction or instinctive/aversive escape from pain, I dunno - but you definitely fly through the air. I've never deliberately placed my open palm onto a live voltage, so I can't speak to the grasping phenomenon. Actually I have done that, but with an electric fence, which deliberately uses short pulses - and both of a DC and AC fence controller deliver terrific shocks, the difference was that AC could still give you the shock with weeds growing up and touching the fence. Don't know if that helps. Franamax (talk) 08:53, 25 July 2009 (UTC)

And if it illuminates further: electric fencers deliver 400-1200V in the short pulse, but not a lot of current. You get the blinding pain, but you're still standing in the same place after. Contacting household wiring (the discussion about "likely to encounter" above) puts you into contact with a large supply of electrons, so the total power transfer is likely much larger. I think maybe that is what moves you across the room so effectively. I suppose I'm just lucky. Franamax (talk) 09:01, 25 July 2009 (UTC)

Do electromagnetic waves have any width?

The classic diagram of an EM wave shows its oscillating electric and magnetic fields, e.g. this.

Are these E and B vectors actually occupying real 3D space? Is the wave actually wider in places and taller in others?

Or is an EM wave more like an infinitely thin piece of fishing line, with varying E and B intensity along it?

Ben (talk) 17:29, 24 July 2009 (UTC)

Yes, they do. Try reading this. Dogposter (talk) 17:45, 24 July 2009 (UTC)

An electromagnetic wave is not as one-dimensional as that picture suggests. In the simplest case of a plane wave, the entire space is filled with compies of that picture, so to speak. But the E and B vectors themselves do not occupy 3D space, the dimension of their components is not distance or length. —Preceding unsigned comment added by 81.11.170.162 (talk) 17:53, 24 July 2009 (UTC)

We depict the magnitudes of the E and B vectors by their lengths, but that is just to make it easy to draw. They don't really have a length that varies, it is the field strength that is varying. --Tango (talk) 19:30, 24 July 2009 (UTC)

If light has to pass through an aperture or slit, its passage from source to detector is affected in interesting ways. A discussion of how passing through an aperture or slot in a conductive wall affects radio frequency waves would be interesting. FM broadcast, say 100 megaHertz, might be an interesting frequency, or perhaps 900 mHz used for phones. If the receiver is in a Faraday cage,how well will the radio waves pass through a slit of varying proportions, or a small variable aperture? Do any interesting nonintuitive things happen, like diffraction or polarization? Edison (talk) 20:04, 24 July 2009 (UTC)

This sounds rather like a homework type question, but I can help you by pointing out that radio waves are like light waves with a bigger wavelength. Your 100 megahertz wave is about 5000000 times bigger than a light wave, so it will have similar properties but at a different scale. You can read Diffraction, Waveguide, polarization, Slot antenna. A waveguide for a FM radio frequency is a large construction and would not be used in practice. Graeme Bartlett (talk) 22:27, 24 July 2009 (UTC)

I'll take this over as a definitely non-homework question. My FM radio antenna, CB antennas (never had one) and Wi-Fi antennas all have different optimum lengths. This implies a three-dimensional aspect to photons/EM waves, dependent on wavelength/energy. And by imperfect analogy, neutrons and electrons get "smaller" in "cross-section" as they get more energetic (which is why high-energy particles travel farther through matter). So there certainly does seem to be a size aspect, and slits and cages only seem to confirm it. So can we think of actual "wiggles"?

And further, if we shoot polarized photons at a Faraday cage that has a rectangular mesh, can we separate the electric and magnetic fields inside the cage? These questions torment me! :) Franamax (talk) 08:11, 25 July 2009 (UTC)

If you put a radio inside a good Faraday cage you shouldn't get any signal. You can try it: put a radio inside your microwave (which is a Faraday cage). Try putting your cell phone inside and calling it.Computeridiot34 (talk) 18:11, 25 July 2009 (UTC)

I'm thinking more about a "bad" Faraday cage. A microwave oven has apertures much smaller than the radio wavelength. We need a leaky cage to pursue my thoughts. Can we separate the electric and magnetic components of the field leaking through by varying the rectilinear dimensions of the cage? My microwave has round holes in the shielding, so I wasn't able to get just the magnetic bits of the ringtone. ;) Franamax (talk) 01:30, 26 July 2009 (UTC)

A Faraday cage with either round or rectangular holes by definition CANNOT polarize EM waves. To get polarized photons, you need a Faraday cage with long narrow slits in it. 98.234.126.251 (talk) 23:47, 26 July 2009 (UTC)

This is most definitely not a homework question :), just something I have occasionally wondered about. I thought I'd ask any pro physicists out there for the answer, rather than trying to revise Maxwell's equations and work it out from scratch.

I was thinking of a laser pulse - it's clearly a narrow beam, as you can see by flashing a laser pointer at a wall. What's a good way to imagine the photons in such a pulse? Are they like lots of little darts flying along through my living room in a straight line?

Ben (talk) 21:17, 25 July 2009 (UTC)

I saw a Faraday cage used for EEG recording, made of chickenwire, with perhaps a 1 inch mesh. People joked that it would keep out em waves larger than pingpong balls. It seemed to shield against 60 hz electrical interference, and pretty well blocked AM and FM (U.S.). Signals. As the mesh varies down to aluminum screenwire (perhaps 1 mm mesh) or up to fence wire (perhaps 4 inch mesh) what is the effect on the shielding ability of various wavelengths? Edison (talk) 03:34, 26 July 2009 (UTC)

Aluminum screenwire would keep out all radio waves and also all microwaves with a wavelength of more than (I think) 2 mm, which is why it's used for microwave oven windows (to keep the oven from microwaving everyone in the kitchen) and also on the air intakes of the Stealth fighter (to keep radar waves from reflecting off of the turbine blades inside). 98.234.126.251 (talk) 23:43, 26 July 2009 (UTC)

Engines in Space

Does every engine that could move a spaceship have to expel matter or heat or something in the opposite direction to travel? SGGH ^ping! 22:08, 24 July 2009 (UTC)

One engine which could move a spaceship, in space, without having to expel heat or something in the opposite direction would be a winch. As the cable is reeled in the spaceship moves toward the takeup reel. The winch could be mounted on an asteroid. The center of mass of the spaceship and asteroid would remain in the same place, but the the asteroid outweighed the spaceship by a factor of several million, the motion would be mostly on the part of the spaceship. Technically, the asteroid would be moving in the opposite direction to the asteroid, as surely as if you lifted the ship with a long hydraulic jack from an object behind it. The resulting acceleration could be far greater than that due to the gravitational attraction of the small asteroid and the spaceship. A Dean drive or other scifi "reactionless thruster" would seem to violate Newton's laws. Maybe cutting edge physics offers some out via wormholes, string theory, other dimensions, or whatever. Telekinesis seems about as (un)likely a solution to the problem of reactionless thrust. Edison (talk) 22:29, 24 July 2009 (UTC)

Yes. See Newton's third law. APL (talk) 22:30, 24 July 2009 (UTC)

Yep. It's a necessary consequence of the law of conservation of momentum. (The 'something' you expel doesn't have to be material, mind you. Photons will do the job, so you can get a miniscule thrust just from pointing a flashlight behind you.) TenOfAllTrades(talk) 22:35, 24 July 2009 (UTC)

We have a detailed article on Spacecraft propulsion. There is an entire section there discussing the (im)possibility of active propulsion without a reaction mass. There are also hypothetical models of reaction-mass-less drives like the Alcubierre drive, but it is unclear if that model is even consistent with the laws of physics, let alone how to build one. --Dr Dima (talk) 22:46, 24 July 2009 (UTC)

The relevant articles are working mass and Tsiolkovsky rocket equation. Luckily, as KE ∝ mv², if you can accelerate the mass to a very high velocity, you can get lots of reaction while using up only a small amount of working mass; see Hall effect thruster for an example. -- Finlay McWalter Talk 22:53, 24 July 2009 (UTC)

Interestingly, in a curved spacetime, it is possible for a spacecraft to move around without using a reaction mass for propulsion, by “swimming”, i.e., by cyclically adjusting how its weight is distributed in a particular way. However, this effect is vastly too small to be of any practical use in real situations. See the August Scientific American for an interesting article on this. Red Act (talk) 23:04, 24 July 2009 (UTC)

We should of course mention the possibility of using Solar sails - those work without reaction mass - providing there is a nice big source of light nearby. But any kind of "engine" would need to expel reaction mass. The engines that require the least are things like ion thrusters - because the thrust an engine produces is proportional to the momentum of the exhaust jet - and momentum is a product of both the mass of the exhaust and its speed - you can use less reaction mass and get the same amount of thrust if you propel it faster. Ultimately, propelling the exhaust out at close to the speed of light would be good. Additionally, these machines use electrical power to accelerate the exhaust - so they can be powered by solar cells and avoid the need to consume chemical energy. That gives an ion thruster the ability to produce a sustained propulsive force for an extremely long time without running out of either chemical fuel or reaction mass. But ultimately, it'll wear out. Another idea is the Bussard ramjet which is supposed to collect interstellar hydrogen in a magnetic 'scoop' and use that both as fuel and reaction mass. Such a device would have to be moving at an ungodly speed to collect enough of the stuff to be useful though. SteveBaker (talk) 23:45, 24 July 2009 (UTC)

A space elevator would also work without reaction mass (I'm not sure if it would count as a winch, though). 98.234.126.251 (talk) 00:11, 25 July 2009 (UTC)

Now consider how a wench could move a spaceship. Edison (talk) 03:29, 26 July 2009 (UTC)

Yeah, I get the picture! ROFLMAO!!! 98.234.126.251 (talk) 23:06, 26 July 2009 (UTC)

Maybe a magnet attracted to an object might move a ship in zero gravity; super high powered magnet in the future could do the trick —Preceding unsigned comment added by 214.13.64.7 (talk) 08:46, 26 July 2009 (UTC)

Would a railgun (or coilgun) count under this definition? 98.234.126.251 (talk) 23:08, 26 July 2009 (UTC)

Eiffel Tower sticks to the Moon !!!!!!!!!!

I had an argument with my friend and I hope I will be proved correct quickly on this. Could I stick the Eiffel Tower to the Moon with one small piece of bluetac? —Preceding unsigned comment added by 92.18.90.155 (talk) 22:20, 24 July 2009 (UTC)

It depends what you mean by "stick". The moon has gravity (about 1/6 of the Earth's). The Eiffel tower if stood upright would sink right in and stay all on its own unless some force was acting on it to pull it away, and it would have to be a force of some power given the mass of the Eiffel Tower. The way you've asked this question leads me to believe that you thought an object on the moon would simply float away if not stuck or tied down in some way, which is not the case. If you were on the moon next to an Eifell tower, you wouldn't be able to move it with ten elephants. Even if the moon was gravity-less, if the Eiffel Tower was on its surface, and there was no force acting upon it, it would stay; it wouldn't need to be "stuck" at all. If there was a force acting on it, the bluetac would work to the extent of its sticking power combined with the amount you used, that is, whatever extremely small or large power of sticking it had would only "win out" against the force if the force was commensurately larger in degree pulling the Eiffel Tower away. All this is to say that I think your question doesn't really make sense because it assumes facts in error.--70.107.76.121 (talk) 22:31, 24 July 2009 (UTC)

(EC):The Bluetac would seem unnecessary. The Apollo lander stuck to the moon just by landing, since the moon has gravity. Just find a level solid rock for a site and lower the tower gently into position. No wind to blow it over, so no anchoring required. The view would be magnificent! Edison (talk) 22:33, 24 July 2009 (UTC)

But I think it would lack some of the parisienne 'atmosphere' :-) SteveBaker (talk) 23:36, 24 July 2009 (UTC)

groan... --Tango (talk) 23:54, 24 July 2009 (UTC)

Are we certain the Apollo lander did not have Bluetac on the bottom of its legs86.4.181.14 (talk) 14:50, 25 July 2009 (UTC)

Heh, I get it now. When I first read this, I was thinking much more about the "atmosphere" in the public washrooms just near the base of the Tower and how much nicer it would be to smell only yourself in the spacesuit. Ahh, the "atmosphere" of Paris! :) Franamax (talk) 07:13, 25 July 2009 (UTC)

To generalize this, yes and no. You are talking about two different forces, the gravitational and electromagnetic forces. Your little piece of Bluetac exerts both (the "stickiness" is an example of the EM force). Gravitational force acts over long distances and varies with mass. Electromagnetic force acts much more strongly over a much shorter distance and varies with charge. If you could set up a magical situation where both the Eiffel Tower and the Moon were falling through free space with just enough counterforce on them to prevent them "sticking together" gravitationally, then magically place that bit of sticky stuff in between them, the extra mass of the Bluetac would draw the two bodies together and once they all touched, the EM forces (the stickiness of the Bluetac) would possibly speed the bodies up at the last few microseconds, and would hold them together just a little tighter. It would then take just as much force to separate the Tower and the Moon in free space as it would to separate two ashtrays here on Earth. So, in our magic world, yes; in our real world, not even close. Franamax (talk) 07:37, 25 July 2009 (UTC)

I'd like to point out that the Eiffel Tower is made of wrought iron and is electrically conductive, therefore it would not retain static electricity and would not stick to Bluetac. FWiW 98.234.126.251 (talk) 08:47, 25 July 2009 (UTC)

So you're saying that it's not possible to glue metal objects together? It's not the overall static charge, it's the very local distribution of forces that give rise to the effect. Alternatively, it's the overall balance of charge that matters and even single electrons are important. I'd have to check my Feynman to review how few electrons are needed to split the Earth in two. The localization of force becomes very important. Franamax (talk) 09:17, 25 July 2009 (UTC)

Or here's something better: in my magic experiment, I already specified that we had counterforces for gravitational atttraction between the Tower and Moon. We indeed will also need to compensate for net charge. The Moon will have a net electrical charge, either positive or negative. The Eiffel Tower will presumably still have Earth's net negative charge when we tow it out for the experiment. So we will have to magically compensate for that too, using the inverse-square rule.

However, when we introduce the Bluetac, we introduce a new charge (magically). This will cause a redistribution of charge over the entire conducting body of the Eiffel Tower, so the net force will still be the same as our ashtrays. (Static electricity per se has nothing to do with it actually, we are talking about EM forces exchanged between individual molecular bonds) Franamax (talk) 09:29, 25 July 2009 (UTC)

Oh, so Bluetac uses glue. I was under the false impression that it uses static electricity. I stand corrected. 98.234.126.251 (talk) 01:02, 26 July 2009 (UTC)

explanation: in case anyone wonders about the problem, here is my impression of why the OP asked this: both he and the person he "bet" with thinks there is no gravity at all on the moon, that if you placed something there it would just float off. Unless of course you attached it to ANY extent. 82.234.207.120 (talk) 18:00, 25 July 2009 (UTC)

Of course, due to Newton's third law, gravity and the force the ground applies to the tower cancel. Conclusion: the tower isn't stuck to the ground by gravity.

To the OP: if there's no gravity on the moon, how do you explain the Apollo footage? --Bowlhover (talk) 22:08, 25 July 2009 (UTC)

Your post is just an invitation for moon hoax conspiracy idiots to drop a line, and you know what does and should happens to them.--70.107.76.121 (talk) 22:44, 25 July 2009 (UTC)

Good job, Buzz! Now if someone would do the same to the 9/11 conspiracists and the Holocaust deniers... 98.234.126.251 (talk) 00:59, 26 July 2009 (UTC)

I'm looking forward to the circa 2040 footage of old Barack Obama punching a persistent birther in the face. :) --Sean 13:33, 27 July 2009 (UTC)

What do you mean by the term "persistent birther"? 98.234.126.251 (talk) 22:59, 27 July 2009 (UTC)

These idiots. --Sean 13:28, 28 July 2009 (UTC)

Heavy Boots! APL (talk) 17:40, 26 July 2009 (UTC)

E=mc²

In terms of Einstein's equation is the energy "stored" as angular momentum and if not how is it "stored"? -- Taxa (talk) 23:08, 24 July 2009 (UTC)

In terms of E=mc², the energy is "stored" as mass. That equation is the energy something has when it’s not moving, and hence has no momentum or angular momentum. Red Act (talk) 23:13, 24 July 2009 (UTC)

_{I knew someone would answer while I was typing. Grr.}

It's "stored" as mass. For example, if a Uranium 235 nucleus is hit by a neutron and undergoes fission, the products have slightly less rest mass than the U-235 nucleus and the neutron, and the difference becomes energy, in the form of heat and gamma rays.

However, if you think of a moving particle, it also has energy due to linear momentum (energy due to movement i.e. kinetic energy). In this case the total energy E is given by:

$E^{2}=(mc^{2})^{2}+(pc)^{2}\,\!$

So far, I've talked about rest mass, which is the mass a particle has if it's not moving. You can use E=mc² to think of a relativistic mass, which increases if the particle has more linear momentum.

$m_{\mathrm {rel} }={\frac {1}{c^{2}}}{\sqrt {(mc^{2})^{2}+(pc)^{2}}}$

See also Mass in special relativity for a hopefully better explanation, if you haven't already. AlmostReadytoFly (talk) 23:39, 24 July 2009 (UTC)

Impacts into Jupiter

Jupiter had a large impact recently, and another a few years ago. Does this information allow any estimates of the probability of a major impact into Earth? The diameter of Jupiter is 142,984km, the diameter of Earth is 12,756.2km. The cross sectional area of Jupiter is therefore 126 times that of Earth. 78.147.128.100 (talk) 23:41, 24 July 2009 (UTC)

Not really, two impacts is not a statistically significant sample. In fact, you can draw any curve you want through two points. A larger number of known impacts with a distribution of impactor size would be needed to draw any conclusions. Franamax (talk) 23:53, 24 July 2009 (UTC)

Not really - Jupiter is very massive so its gravity tends to pull in asteroids and comets far more than Earth does. In fact, it has been theorised that Jupiter "vacuumed up" lots of debris in the early days of the solar system and without it the Earth would be bombarded far more often (perhaps so much so that life couldn't have evolved, at least not to the extent it has). There are also different amount of debris in different parts of the solar system. There are astronomers searching the sky for Near-Earth objects and they have a pretty good idea of how many there are (by extrapolating from the bits of sky they've searched - there is still plenty of sky to search). --Tango (talk) 23:59, 24 July 2009 (UTC)

Tango, not that I'm saying you're wrong or looking for an argument, but do you have sources on Jupiter actually "sucking in" other bodies? I'd think it more plausible that orbiting bodies would be accelerated far away than actually crashing into the planet. In other words, a near miss is more probable than a direct hit. It does seem that Shoemaker-Levy 9 was gravitationally bound, but was that an exception or a rule? Just asking for my own benefit. Think of this as "Impacts into Jupiter, part the second". :) Franamax (talk) 07:07, 25 July 2009 (UTC)

See Jupiter#Impacts for a mention of the vacuum cleaner metaphor (with a reference). --Tango (talk) 16:48, 25 July 2009 (UTC)

I dont't think Jupiter's gravity played that great a role in the Shoemaker comet hitting it. Perhaps Earth is Doomed. Edison (talk) 03:25, 26 July 2009 (UTC)

wave versus particle

If the alternation between the magnetic filed and the electrostatic field of a light wave were to not propagate by the "leap frog" propagation and remain stationary for only one cycle would that explain the idea of a particle of light some call the Photon? -- Taxa (talk) 23:54, 24 July 2009 (UTC)

I'm not quite sure what you're asking here, but I'm willing to bet the answer is no. A photon isn't a temporary stationary field, and quantum physics can't be explained using classical electrodynamics. AlmostReadytoFly (talk) 00:02, 25 July 2009 (UTC)

A photon is never stationary (it has to travel at the speed of light), so that's certainly not going to work. --Tango (talk) 00:05, 25 July 2009 (UTC)

Do stationary waves propagate? -- Taxa (talk) 00:44, 25 July 2009 (UTC)

Do you mean do standing waves propagate? They do. They propagate back and forth in a defined space. One common model of the electron is to treat it as a standing wave rather than a particle. Indeed, under wave/particle duality; any particle which is localized (not necessarily stationary, just contained in a finite space) is generally held to be a standing wave. The deal with photons is, they cannot be held still, or even confined to a define probability space the way that electrons can; so photons are clearly not "standing waves". --Jayron32 03:13, 25 July 2009 (UTC)

I read somewhere that all photons are at all possible places in the universe at the same time due to their velocity (c). Can this be correct?

That would be the case if photons traveled at an infinite velocity -- but they don't -- they travel at the speed of light -- so this is clearly wrong. If what you read was right, then how come the signals from the Mars Rovers take half an hour to get here? 98.234.126.251 (talk) 05:40, 30 July 2009 (UTC)

July 25

Could a gull lift a cat in its beak?

See here. Sounds unlikely to me, taking into account that most housecats are heavier than most gulls and the wing-loading and compensation for nose-heaviness that would be necessary for such a feat of strength (in human terms, it would be a bit like piggybacking a person twice your weight, then trying to sprint at full speed - or possibly something more difficult than that). Considering that this was a rooftop-nesting gull in the UK, it would likely be a Herring Gull or a Lesser Black-backed Gull (with an outside chance of it being a Great Black-backed Gull). I've personally seen a gull grabbing an adult cat by the scruff of the neck and yanking it from a drainpipe as it tried to climb up and I've seen gulls fighting with cats and winning - but neither of these scenarios involve physically lifting the cat into the air. --Kurt Shaped Box (talk) 04:27, 25 July 2009 (UTC)

Are you asking for the airspeed of an unladen swallow gull? Seriously... It's not a question of where he grips it! It's a simple question of weight ratios! A five ounce bird could not carry a one pound coconut cat. --Jayron32 05:28, 25 July 2009 (UTC)

A lot of cats are more hair than flesh, so they're actually pretty light. And some gulls are pretty big, the ones at my adopted home of Vancouver are much bigger than the ones in Ontario (and they scr-r-ream like humans being murdered, early in the morning). Definitely a large gull could have a go at a small cat - but the weight ratio and nose-down problems would come into play, which I think explains the four-foot extent of the abduction attempt. The more interesting question for me is why a gull would decide to target a cat rather than, say, a discarded hot-dog bun. Maybe its eyesight is failing? Anyway, I'm definitely going to stop putting bread on my pets before letting them out! :) Franamax (talk) 06:00, 25 July 2009 (UTC)

For the gull to lift a cat it'd have to be dead. Getting the "neck grip" right isn't easy and I doubt a gull's beak is suitable. I would have thought it would also have to be a small cat, but then I found that those gulls carry off salmon in the 12 lb. range. So weight wise it might be possible. I'd agree with Framamax that the big question would be "why" and I'd rate such a necessity presenting itself as rather rare. 71.236.26.74 (talk) 21:46, 25 July 2009 (UTC)

If it really happened, it's pretty obvious to me that the gull was planning to kill the cat by flying up and dropping it from a great height. Gulls *really* don't like cats. I've heard of them killing rats and mice for food in that way (they apparently follow the prey down, then strike it beak-first, moments after it hits the ground). I read somewhere (and I *so* wish that I'd seen this myself!) that the gulls will sometimes go into a steep, full-speed dive with the prey in their mouths, then let go of the thing in a similar way to a Stuka dropping a bomb.

So, an approx 3-4lb gull can fly with a 12lb salmon? Really? I didn't know that - sounds amazing, if true... --Kurt Shaped Box (talk) 02:23, 26 July 2009 (UTC)

Reliable source needed for any bird carrying something weighing several times as much. And a cat dropped from a considerable height could survive. Edison (talk) 03:24, 26 July 2009 (UTC)

Indeed, 'extraordinary claims require extraordinary proof' and all that. I know that gulls are strong (if you've ever held one, you'll know how powerful the wings are) but I'd be astounded if they were strong enough to fly with 3x their own bodyweight (at least!) loaded at the front (they can't grip objects with their feet). As for the cat, I don't think it's fair to expect a gull to know that cats always land on their feet... --Kurt Shaped Box (talk) 04:13, 26 July 2009 (UTC)

At closer inspection the source that threw me off my common sense objection turned out to be a "fish story" in every respect of the phrase. Some fishermen apparently were trying to get rid of some presumed competition. A more reliable source says that Great Black-backed Gulls had never been reported to carry off anything heftier than an Eider duck. If those were anything like the ones described here is still pretty impressive,[13] but less than half the fishy tale. That would get us back to a rather small cat. If you'd ever tried to hold on to a cat that didn't want to be held you'd know that they are pretty good at wiggling out of being gripped. That makes the scenario of a conscious life cat being carried off rather impossible. It'd at least have to be stunned or unconscious.71.236.26.74 (talk) 07:09, 26 July 2009 (UTC)

Landing on the feet is NOT going to save the cat, if it's landing at terminal velocity, which I can't calculate off-hand, but can be 120 mph for skydivers, so it not likely to be very slow.

If the bird knows to, or accidentally does, pick up the cat by the scruff of the neck, the cat will dangle in a fairly helpless position, where it can't fight back or wriggle too much.

How much weight a bird can fly with would depend more on the size of its wings, less on its body-weight, as it is the wing-span which gives it the lift for flying. Migrating species often carry 50% more than their "normal" weight in pre-migration fat stores, albeit this weight is well distributed on their bodies, not dangling in a very un-aerodynamic manner from their beaks. - KoolerStill (talk) 14:11, 26 July 2009 (UTC)

Cat't don't typically land on their feet when falling that far. They land upright, but more spread out in a belly-flop formation to lower their terminal velocity. It sometimes works.[14] However, even when it does work, it looks like about 2/3 of them require immediate veterinary attention. (We can assume that the other third is really sore.) So I think that if I were a seagull I would consider this a suitable revenge against a cat who was being a jerk. APL (talk) 17:32, 26 July 2009 (UTC)

I'm having a bit of trouble envisioning how a gull is supposed to hold on to a cat by the scruff and take off. the former would put it's beak at an angle towards the cat's body. Hence it might work for dragging a cat off a pipe as Kurt seems to have observed. In this position I can't quite see how the gull could take off. There seem to be a lot more likely scenarios of what it could do, like throwing the cat or bashing it on to the ground to stun it. Carrying it off while it is still able to struggle and getting the neck grip to work with a beak in close to upright position is just a very unlikely scenario. 71.236.26.74 (talk) 21:08, 26 July 2009 (UTC)

Empirical evidence of a sort: Seagull flies off with cat in beak --Tagishsimon (talk) 09:04, 29 July 2009 (UTC)

HIV cure

why is a cure not yet found for HIV??What are the difficulties faced in finding the cure for HIV??whats so special about HIV?? —Preceding unsigned comment added by 117.193.139.242 (talk) 05:07, 25 July 2009 (UTC)

Mostly because HIV is a virus, and there are no "cures" for viruses. Antiviral drugs do not actually "cure" us of any viruses, merely slow them down so that our own immune systems can keep them contained. This is true of all viruses, not just HIV. Viruses have treatment, but no cures. Either your own immune system adapts to them, and you get better, or your immune system does not, and you die. Since HIV actually infects immune system cells directly, this creates a HUGE problem... --Jayron32 05:24, 25 July 2009 (UTC)

Me personally, I'd define "get better" as being "cured". Franamax (talk) 06:28, 25 July 2009 (UTC)

I think part of this is that HIV doesn't just destroy white cells, it actually uses the T-cells' CD4 receptor (which is the main receptor that they use to identify the virus in the first place) and / or the antigen-antibody complex to assist with binding to the white cells, then reproduces INSIDE those white cells -- so the body's natural immune response not only don't help at all, it actually just makes the infection that much worse. (Which is why I don't think a vaccine can ever work against the AIDS virus.) It might in principle be possible to cure someone with the AIDS virus by taking all the blood outside the body, radiating it to kill all the white cells, and filtering the blood through a nanofilter before returning it to the body -- followed by a complete bone-marrow transplant -- but the problem is, since you killed all the white cells, the patient will have to be confined to a sterile room for several weeks until his / her immune system creates new, clean white cells, cause if the patient gets even the slightest infection during those several weeks, he / she could easily die. FWiW 98.234.126.251 (talk) 05:29, 25 July 2009 (UTC)

I can't find any mention of this in the HIV article - but haven't there been a few tens of people who have completely recovered from HIV infection through means as yet unknown? Or was that all just ill-informed science by press conference stuff? --Kurt Shaped Box (talk) 05:50, 25 July 2009 (UTC)

Well, there's the Daily Mail [15]. I wouldn't exactly put that in the article though... However, I'm pretty sure that there are some tens of people who appear to be completely immune in the first place. Prostitutes in Uganda or something, if I recall. Franamax (talk) 06:28, 25 July 2009 (UTC)

Yes, the fact that the virus attacks the very immune system cells targeting it certainly makes things difficult. My understanding too is that the genius of this particular virus is the gp120 glycoproteins which "decorate" the proteins which effect entry of the virus into the cell. To "cure" something, or to make a vaccine against something, you need a target. But gp120 is highly variable, so it's difficult to target, and it hides the less variable proteins underneath that do the dirty work of infecting the T-cells. Any one successfully infecting HIV can produce a million new particles with variant gp120's, and only one of them has to work for the infection to continue.

And 98.234, your irradiation scheme might work except that HIV can cross the blood-brain barrier, so you'd have to remove and irradiate all the cells in the brain, which might not work so well. ;) And there may also be other undiscovered reservoirs of infection too. Franamax (talk) 06:28, 25 July 2009 (UTC)

I didn't know that it crosses the blood-brain barrier like methylmercury or something! (Ain't there so much new stuff to learn on Wikipedia?) I stand corrected regarding the radiation scheme. And BTW, Kurt Shaped Box, there haven't been "tens of people who completely recovered from HIV infection through means as yet unknown -- there was one man who completely recovered from the AIDS virus after being given a complete bone-marrow transplant (it's not yet clear if his recovery really is "complete" complete, as in NO viruses OR infected cells remaining in the body), but no other miraculous recoveries so far. That Daily Mail article is just plain wrong (well, what do you expect, they're just reporters...) 98.234.126.251 (talk) 08:01, 25 July 2009 (UTC)

This is only partically true... irradiation works similarly to chemotherapy in that it doesn't target specific tissues but is especially toxic to cells that are dividing quickly; this includes many cancers, but also the cells of the bone marrow, digestive tract and hair follicles. While irradiation would kill off a major HIV reservoir in the bone marrow, one major factor that keeps an irradiation approach from working is that HIV can also infect and replicate with macrophages, which don't divide, and therefore typically aren't killed off by irradiation. In addition, macrophages often migrate to and take up long-term (i.e., years) residence within many tissues, including the brain (where they're called microglia) but also many others (see the macrophage article for a short list). So in that respect HIV can cross the BBB, but only by being ferried across by a previously infected macrophage ([16]). HIV, however, can't actually productively infect any of the other cells in the brain though [17], so it's not the crossing of the BBB that keeps irradiation from working, it's the ability of macrophages to find a nice comfortable home, get a cat and a white picket fence, and live there for a looooong time. Another good thorough review: http://www.ncbi.nlm.nih.gov/pubmed/19486514. Cheers! – ClockworkSoul 19:34, 26 July 2009 (UTC)

Okay, fair enough. Thanks. --Kurt Shaped Box (talk) 02:46, 26 July 2009 (UTC)

wavelength distribution

Is there a similar diagram for wavelengths between .000002 and .000006 nanometers? -- Taxa (talk) 14:03, 25 July 2009 (UTC)

If my calculations are correct, those wavelengths correspond to temperatures in the region of 100 billion kelvin, which are associated with Type II supernovae. They emit light over pretty much the entire spectrum, so are easily visible from the Earth's surface. Gamma ray photons of those wavelengths have energies of about 0.6 GeV, which I don't think are quite strong enough to trigger showers of secondary particles when they hit the upper atmosphere (which is how really high energy gamma rays are detected), so they would probably be very difficult to detect from the surface (even if they could penetrate the atmosphere there would be so few of them that you would need an extremely large detector to stand a reasonable chance of one hitting it). You may find our article, Gamma-ray astronomy useful. If you explain why you are interested I might be able to give a more useful answer. --Tango (talk) 15:23, 25 July 2009 (UTC)

Within this range of wavelengths fits the radius and diameter of the electron. I'm curious how such a distribution of electromagnetic waves would look in this range whether produced in a laboratory or observed above the atmosphere. -- Taxa (talk) 15:58, 25 July 2009 (UTC)

Electrons don't really have a diameter, the classical electron radius (which I assume is what you are talking about) is a fairly meaningless concept. There is certainly no connection between electrons and photons of that wavelength. The closest you get to a connection between electrons an a certain wavelength is the de Broglie wavelength, which depends on the electron's speed. I'm not sure what the opacity of the atmosphere has to do distribution of wavelengths - the distribution will depend on what is emitting the radiation (if it is emitted above the atmosphere and detected beneath it then the opacity will be a factor, but it won't be the only factor). --Tango (talk) 16:32, 25 July 2009 (UTC)

I don't think you meant to say that the radius of an electron is smaller than .000002 or larger than .000006. Just in case let's change the wavelengths to between .000001 to .00001. nanometers. Also, lets replace the atmosphere with an electron and see whether there is any difference in the intensity for each wavelength between this range. You may be surprised. -- Taxa (talk) 22:06, 25 July 2009 (UTC)

I meant precisely what I said - electrons don't really have a diameter. In the standard model they are point particles. I don't know what you mean by replacing the atmosphere with an electron or what you want the intensity of. Your question makes no sense. This is a recurring pattern with your questions. Please learn a little more about the subjects that interest you before asking questions like this - your questions are often based on fundamental misunderstandings of the subject matter so cannot be answered. --Tango (talk) 01:34, 26 July 2009 (UTC)

Is this a request for us to perform original research? We don't do that. This self-published and typo-laden physics paper purports to investigate the earth-atmospheric and extraterrestrial absorption of high energy gamma-rays; maybe it can be a starting point for your investigations. The trouble is that not much experimental physics has been done with that range of gamma ray, because it's hard to make in the laborator (due to its very high energy). As such, characterizing the Earth's atmospheric absorption is difficult. I suspect there will be negligible absorption or attenuation, as such high energy waves don't interact with atomic-scale objects; but it sounds like you are proposing that somehow, they will interact with electrons. Take a look at scattering. At present, there are many types of known scattering observed in physics, but as far as I am aware, there is not experimental data for the wavelengths in question. Nimur (talk) 02:03, 26 July 2009 (UTC)

You might also be interested in terrestrial gamma-ray flashes, which until recently ( ~1994) were considered "spurious". They are now an active area of atmospheric and space-physics research. Nimur (talk) 02:05, 26 July 2009 (UTC)

Any charged primary above a few MeV is likely to interact in the atmosphere via pair production, which is the essential mechanism for a shower. The more energy, the larger the shower. Dragons flight (talk) 02:34, 26 July 2009 (UTC)

purpose of neutral wire in household supply

what is the purpose of neutral wire in the domestic electric supply? If the neutral one is provided for earthing then why an extra port is provided for earthing in three pins? —Preceding unsigned comment added by 203.197.117.165 (talk) 14:57, 25 July 2009 (UTC)

See Ground and neutral. It has a section on combining earth and neutral. --Tango (talk) 15:29, 25 July 2009 (UTC)

The neutral must carry the same current, but opposite in phase, to that carried by the hot or "phase" wire. If only one hot wire were connected to a device, and no neutral wire, no current would flow, no power would be drawn, and the device would not light up, heat up, move, or whatever its function is supposed to be. There would be an "open circuit," as surely as if the switch were turned off. The neutral wire is not there for earthing. The ground wire is the safety conductor, so that if a device shorts to the metal case, the current flows to earth on the ground wire and the fuse blows. The earth/ground wire should carry no current in normal operation. The neutral is essential to operation, and the earth/ground is a safety feature.Edison (talk) 03:21, 26 July 2009 (UTC)

Man With 'Two Brains'

I just watched a fascinating documentary about a man who had the two halves of his brain disconnected from each other and this answered some parts of an almost lifelong question I have had. Here is a hypothetical scenario: a person is laid on a track and a circular saw comes along and cuts him exactly in half from head to groin. Besides the obvious pain this person would be in (let's give him some strong painkillers first), what exactly would the two halves be feeling in the few minutes that it would take for the brains to shut down through lack of oxygen? I have thought about this ever since I heard that cutting a worm in half makes two separate worms. OK, it's more complicated with a person, because the two halves of the brain operate differently. Not only that, what would happen to consciousness? Would the person's brain favour the consciousness of one half or the other? Or both? --KageTora - (영호 (影虎)) (talk) 15:45, 25 July 2009 (UTC)

The brain has a tendency not to react well but to react fast to such shock. When people say a loved one died instantly in a crash what they really mean is that the brain shut down instantly. You are unconscious and in the case you have described unlikely to regain consciousness be fore your enter the next world. -- Taxa (talk) 16:07, 25 July 2009 (UTC)

Firstly, you don't get two worms, you get a dead worm in two halves. Occasionally the head end may survive, but what people usually see is just random muscle spasms for a short time after death. With a human being cut in half they would lose conciousness due to pain and blood loss extremely quickly (seconds, not minutes). There wouldn't be time for the two halves of the brain to have independent thought. When someone undergoes a corpus callosotomy it is done very carefully and cleanly. A circular saw would rip the head and brain to shreds. --Tango (talk) 16:08, 25 July 2009 (UTC)

Right, but what if a brain was separated into two halves and kept alive, although operating completely independantly from each other? My real question is where the consciousness would be - of course, it would be in both. But, how would that seem to a brain that originally had the two halves connected and now has two separated? --KageTora - (영호 (影虎)) (talk) 17:04, 25 July 2009 (UTC)

I think the only way you could keep it alive was if you separated them surgically with a corpus callosotomy. The resulting condition is called split-brain, that article will probably answer some of your questions. --Tango (talk) 17:18, 25 July 2009 (UTC)

There is not a clear scientific consensus on the presence or physical manifestation of consciousness in the brain. The OP's queries about "where" the consciousness would be provide an interesting thought-experiment (although the actual method proposed would result in near-instantaneous unconsciousness and death). We have a large number of articles related to consciousness. Some of the better ones, like neural correlates of consciousness, attempt to summarize current scientific understanding about the physiology of consciousness (e.g. where in the brain does it take place). Unfortunately, (as you will discover if you read through these articles), there is not much agreement on basic principles such as the definition (or even the existence) of consciousness, so it is hard to say in which parts of the brain it is residing. For a less biological and more philosophical overview, read mind-body dichotomy. Unfortunately a review of the results at Google Scholar shows a lot of philosophy and preciously little biology. This is a tough research area for real science. Nimur (talk) 02:11, 26 July 2009 (UTC)

Douglas Hofstadter's books discuss this stuff in an entertaining way. He likes he concept - the metaphor - of an anthill having consciousness as the result of the interactions of its individually mindless ants. 213.122.53.30 (talk) 17:16, 27 July 2009 (UTC)

Some of my questions are answered, but I still have one remaining one. What if (by some new method) we were able to keep the two halves alive? What would the person feel, now being two 'people'? This is really the crux of my question. --KageTora - (영호 (影虎)) (talk) 06:41, 26 July 2009 (UTC)

That experiment has never been done, so there are no suitable references to point you toward. The reference desk is not supposed to be the place for wild speculation about hypothetical stuff. Nimur (talk) 16:11, 26 July 2009 (UTC)

Well, the study has been partially done, in the split-brain patients studied by Sperry and others. The general outcome is that only one of the halves is capable of using language, and the language-using half is not aware that it only controls half of the body. The non-language-using half can often express itself to some degree by controlling behaviors such as hand movements, but can't understand or answer questions. (It should be noted though that these brains are not fully split -- there are subcortical connections that remain intact, and allow whole-body behaviors such as walking to be performed.) There have also been patients with massive strokes who to a large degree are left with only half a brain. Looie496 (talk) 17:33, 26 July 2009 (UTC)

You may be interested in a series of papers by Prof Donald Mackay of Keele about dialogue between the right and left half of almost split human brains (try google scholar). Also there is a very funny long poem written about this in 1910 by "APBS": The Amputee: A Forecast Circ AD 1970. There is a long medical history of a car/plane/tram crash then in the middle it goes "Now amputations Hitherto had left it fairly clear, and to causal observers it must obvious appear That it's easy to distinguish which is A the patient and, Which is B the part removed from him, an arm or leg or hand; But a singular dilemma now confronted Dr. P, He was really not quite certain which was A and which was B, For B or what he thought was B had horrified Perowne By indulging in a totally inexplicable groan..." The poem concludes "Some say A was first to die and some say it was B".

See the novel Peace on Earth by Stanislaw Lem. Mikmd (talk) —Preceding undated comment added 18:33, 29 July 2009 (UTC).

Viruses - what's the point?

What's the point of viruses? What's the point of inhabiting a body, killing it, and then dying when it dies? Why not be friendly with it and be a symbiotic bacteria or something? --KageTora - (영호 (影虎)) (talk) 15:49, 25 July 2009 (UTC)

Even in our own DNA are programs which cause death. For instance, the webbing between fingers and other extraneous materials and constructions which benefit us when they are gone. -- Taxa (talk) 16:02, 25 July 2009 (UTC)

True but irrelevant. --Tango (talk) 16:13, 25 July 2009 (UTC)

Most viruses don't kill their host. Take the common cold, for example - it's very mild and the only symptoms are ones that aid it in spreading (coughing and sneezing). Often when a virus is deadly it is because it has crossed over from a different species. It wouldn't kill members of that species, but does kill humans. It won't generally spread for long in humans before killing all its hosts and dying out. Consider Simian immunodeficiency virus, the version of HIV found in other primates. It doesn't do any harm to them, but when it crossed over into humans and became HIV it became deadly. HIV takes a long time to kill you, though, which is why it can spread so effectively. --Tango (talk) 16:13, 25 July 2009 (UTC)

No point. They just are. APL (talk) 16:17, 25 July 2009 (UTC)

Viruses don't have a motivation, or plan a strategy. What's important to think about is what mechanisms have led the virus to continuing to exist and spread. Viruses that fail in that disappear, and viruses that are successful continue on. The way that viruses reproduce is inherently destructive: they trick host cells into producing more viruses at the expense of the cells' normal functions. If that leads the host to eventually die, it's not necessarily a set back for the continuation of the virus if it has a means of spreading to other hosts in the mean time. However deadly viruses don't kill people out of malice, it's just a side-effect of the mechanism they use to effectively stay alive and reproduce. Rckrone (talk) 16:33, 25 July 2009 (UTC)

Exactly, but staying alive and reproducing are two different things. I'd love to be alive in a hundred years' time and with a bunch of kids to look after, but if having kids (through a host - not a nice way of putting it, but this is an analogy, remember) is going to kill me in a few weeks or months, I really wouldn't mind just getting along with the host and looking after each other. I think you see my point. --KageTora - (영호 (影虎)) (talk) 17:10, 25 July 2009 (UTC)

Your survival instinct is because you need to be alive to reproduce again or to look after your children. That doesn't really apply to a virus. Viruses reproduce exponentially, so the original virus still being alive is pretty much irrelevant to the rate the virus can continue to reproduce. --Tango (talk) 17:21, 25 July 2009 (UTC)

As others have mentioned, the virus doesn't care what happens to the host, as long as it's able to reproduce. Certain strategies diseases use to spread (diarrhea for rotavirus, uncontrolled bleeding for ebola, etc.) have very disastrous consequences for the host, but by the time the host dies, the virus has a new host. Your general inclinations are correct, though, that if the infection is too severe the virus may kill the host before it can spread, or reduce the host population to the point where spread is not sustainable. There is usually a tendency for diseases to moderate their lethality toward their native host over time - those viruses which can maintain themselves in a host without killing tend to produce more offspring over the long term than those which move quickly from host to host, leaving dead bodies in their wake. -- 128.104.112.87 (talk) 17:54, 25 July 2009 (UTC)

To add to what Tango said look through the article on Zoonosis, diseases which humans get from animals. Most of the diseases listed there kill us amazingly fast but their vectors are animals, not us. Killing humans really fast doesn't affect its ability to spread itself. They include Anthrax, Cholera (really infectious among us as well though), Hantavirus, Ebola, Marburg Virus, Plague.

Computeridiot34 (talk) 18:05, 25 July 2009 (UTC)

It's of note that cholera is not really that infectious from person-to-person, unless contaminated water supplies are shared. --98.217.14.211 (talk) 18:15, 25 July 2009 (UTC)

And anthrax is not contagious from person to person at all. 98.234.126.251 (talk) 01:07, 26 July 2009 (UTC)

Can we also point out that its not even clear if viruses are technically "alive" or not (see Life#Definitions, subsection on viruses). They aren't acting consciously. They're sort of ideal replicators — they are about one step up from raw DNA. It's like a bug in computer code that happens to perpetuate itself onward. --98.217.14.211 (talk) 18:13, 25 July 2009 (UTC)

That is purely a technicality. How we define life really doesn't make any difference to anything. --Tango (talk) 19:12, 25 July 2009 (UTC)

Except in that giving the virus itself too much autonomy in making its decisions is clearly wrong. --98.217.14.211 (talk) 02:52, 26 July 2009 (UTC)

KageTora also appears to be making a presupposition about self-preservation as an implicit goal for the virus. Self-preservation is present in most species because it has evolved and continues to enhance the capability to proliferate. As an intelligent creature, you can think about survival strategy and choose particular courses of action. However, most "lower forms" of life (and viruses, which are borderline "life") do not strategize. They simply "do". Viruses continue to exist on earth because their method of existence is conducive to reproduction and propagation. Though in some cases this results in catastrophic self-destruction, that is not something which precludes the virus from pursuing its natural course of action. In fact, the virus lacks the physical or biological capability to even be aware that its actions cause any environmental changes that might harm its future survival chances. You might find the articles about symbiosis, parasitism, and predation useful; many organisms participate in such biological coexistence relationships without any awareness that they are part of a multi-organism system. In some cases, this results in the eventual destruction of one or both organisms. Long-term sustainability is less relevant than the prior history here (as Rckrone mentioned). Nimur (talk) 02:21, 26 July 2009 (UTC)

Exactly my point. Viruses seem to have no stimulus whatsoever for self-preservation, but rather a goal for replication regardless of itself. That goes against everything that Darwin said. --KageTora - (영호 (影虎)) (talk) 02:45, 26 July 2009 (UTC)

Except it doesn't actually play out that way. In fact, they're a beautiful example of Darwinism at the extreme, to the point where you can represent their survival very precisely in an abstract way (which is a lot harder to do with, say, lions and tigers). On the one hand, if they killed everything they touched, they wouldn't survive to reproduce another generation. If they tip the "fatal" side too much that way, then they're definitely not going to be that prevalent. If they can get it just right, they thrive and thrive. Consider the common cold, most influenza, and other viruses we are rather familiar with because they don't actually kill most people who get them (any more). They come and go, spreading themselves through the population just fine. As for whether they kill the host organism, it's inadvertent in probably most cases (there are probably some viruses that benefit from death practices in being spread and wouldn't spread if the human was alive), in the same way that human biology starts to rapidly break down once we are past the age in which our health is vital to our reproductive success. --98.217.14.211 (talk) 02:52, 26 July 2009 (UTC)

The point of a virus is that it kills an unhealthy creature. Sickly creatures tend to go around making things unpleasant for more robust individuals, so for a virus to remove them from the ecosystem isn't a wholly bad outcome. Being that viruses are not strictly considered 'life', they don't need to have any higher goal. They just kill. They could perhaps be better considered to be an emergent, temporary aspect of a higher but very ill being, like vomit. What's the point of vomit? There's no point, it's just a disgusting product of a sickly animal. Vranak (talk) 17:27, 26 July 2009 (UTC)

I'm sorry, but that's unhelpful and incorrect. Viruses do more than simply kill; see mitochondrion#origin and Endosymbiotic theory for some interesting theories regarding how other viruses play the game. More generally, viruses are designed simply to reproduce; killing the host organism is only a problem if the virus has been unable to spread past the corpse. It's no different than people consuming corn or chickens - killing the organism during harvest is not the specific intent, but simply a result and a result we don't care about if we can move on to the next corn plant before we starve.

KageTora, you seem to be looking for purpose in nature. There isn't one. Our article on teleological argument is slated toward the religious aspect, but may still be helpful. Viruses don't get to chose their strategy and the one they have now seems to work just fine for them anyway. Matt Deres (talk) 16:21, 27 July 2009 (UTC)

What's the point of "life"? Richard Dawkins would say that it's to propagate DNA. Axl ¤ [Talk] 19:42, 30 July 2009 (UTC)

David Merrell's mouse experiments

where is our article on David Merrell's mouse experiments please? thx 82.234.207.120 (talk) 16:05, 25 July 2009 (UTC)

Try Hopping mouse. -- Taxa (talk) 16:15, 25 July 2009 (UTC)

What does that have to do with the question? --Tango (talk) 16:21, 25 July 2009 (UTC)

We don't seem to have an article. I've found this page via Google, though. I'm not sure it is notable enough to have a Wikipedia article - it is an experiment done by a high school student for a science fair. It got several awards, but I haven't found much independent news coverage or anything else that would make it notable. --Tango (talk) 16:21, 25 July 2009 (UTC)

Are you kidding? It sent shock waves through the UNIVERSE, no tto mention receiving acolade from the Navy and even CIA. It is the most notable thing I've read about in the past 3 weeks. 82.234.207.120 (talk) 16:28, 25 July 2009 (UTC)

thanks for that nice article. —Preceding unsigned comment added by 117.193.129.196 (talk) 19:20, 28 July 2009 (UTC)

If you can find several independent reliable sources about it, then by all means write an article. --Tango (talk) 16:35, 25 July 2009 (UTC)

If you are interested, there are a few articles here on Google News. It seems it did get some coverage, but I don't know if it was really enough to warrant an article. --Tango (talk) 16:40, 25 July 2009 (UTC)

Click "random article" on the bar at the left 20 times. Still feel that way? 82.234.207.120 (talk) 17:14, 25 July 2009 (UTC)

The ref desk isn't here to debate notability. I gave you some advice based on my extensive experience of Wikipedia, if you don't want to take it then write the article and see what happens. --Tango (talk) 17:23, 25 July 2009 (UTC)

I suspect the interest in the story is mostly about a 16 year old coming up with something interesting at a science fair. Would like to see proof of the CIA and Navy accolades. The story is more human interest than hard science (and it sounds like he left the music on while they navigated the mazes, which introduces a lot of question into the findings, in my opinion... I suspect that thumping hard rock music is going to disrupt a mouse's internal navigation a lot more than anything else). It also doesn't in any way actually show that hard rock is negative in humans (mouse models are not exact, especially cognitive models!!). Anyway... I don't see shock waves in the universe, personally. --98.217.14.211 (talk) 18:19, 25 July 2009 (UTC)

"Navy and CIA accolades" could mean that the recruiter who was present at the Science Fair commended the student. (Or it could mean national recognition and a scholarship). The article does not say. Usually, events that are notable enough to merit articles appear in several online and offline sources. If this research was worthy of followup work, eventually a paper would be published somewhere. That might constitute a reliable source, depending on who published it, whether it was peer-reviewed, etc. Nimur (talk) 02:27, 26 July 2009 (UTC)

rabbits and Hopping mouse

Are rabbits related to the Hopping mouse? -- Taxa (talk) 16:19, 25 July 2009 (UTC)

The mice are rodents, which are similar to rabbits (rabbits were once classed as rodents, but not now).83.100.250.79 (talk) 16:23, 25 July 2009 (UTC)

Not closely, no. Hopping mice are rodents, rabbits are lagomorphs. According to that article: "Though these mammals can resemble rodents (order Rodentia), and were classified as a superfamily in that order until the early twentieth century, they have since been considered a separate order. For a time it was common to consider the lagomorphs only distant relatives of the rodents, to whom they merely bore a superficial resemblance." --Tango (talk) 16:24, 25 July 2009 (UTC)

Muad'Dib, the hopping mouse! SGGH ^ping! 20:01, 25 July 2009 (UTC)

Maximum sustainable population

What is the best estimate of the maximum world population that would be environmentally sustainable? NeonMerlin 18:21, 25 July 2009 (UTC)

I don't think there are any particularly good estimates. Improvements in technology can increase agricultural yields and political issues can result in food not getting to where it is needed (or even not being grown in the first place). See Malthusian catastrophe for a discussion of the issue. --Tango (talk) 18:52, 25 July 2009 (UTC)

Considering what was done to people in the movie the Matrix people could be packed together to a degree that I care not to imagine considering the state of all the major cities today. -- Taxa (talk) 18:55, 25 July 2009 (UTC)

The Matrix is a load of nonsense. Humans don't generate energy, they use it. You can't pack people together like that without some kind of food source. --Tango (talk) 19:02, 25 July 2009 (UTC)

You need to define your terms, and you need to decide whether or not to permit technology that has not yet been invented. If we define "sustainable" as using only renewable resources, and you define "renewable" as coming from the sun, then we can compute an upper bound. The earths' diameter is 12,000KM, then the earth has a capture cross section of about 3/4 x 144 million Km^2, or very roughly 100 million million square meters. Each square meter is good for about one KW, and a resting human uses about 125W, so we have energy for 8 humans per square meter of capture cross section, or 800 million million humans. Now pick a technology "discount" based on your own assumptions: let's assume that an acceptable technoligy can practically operate at only one part in 800 "efficiency" in an environmentally sustainable manner. Then, we get one million million humans as an upper bound. Of course, by the time we have this level of technology, we will not need to remain on earth. -Arch dude (talk) 02:35, 26 July 2009 (UTC)

Does this take into account the costs of recycling air and waste products? NeonMerlin 04:28, 28 July 2009 (UTC)

I think so, yes. The energy required to photosynthesis CO2 and water into glucose and oxygen is the same (give or take some inefficiencies) are the energy released by respiring glucose and oxygen into CO2 and water. Ditto for all the other reactions going on in the human body. All you need to do is replace the energy lost as heat, and that is the 125W mentioned. There may be a little more lost by the plants, etc., but plants aren't warm blooded, so there isn't much. --Tango (talk) 20:25, 28 July 2009 (UTC)

Substance Dependence

What mechanism defines the "normal" amount of a particular neurotransmitter? Can this value be altered?—What prevents us from eliminating opiate tolerance, for example, and therefore allowing for an infinite amount of pleasure?

Alfonse Stompanato (talk) 18:55, 25 July 2009 (UTC)

"An infinite amount of pleasure" is an ill-defined concept. Increasing the dose of opiate will have adverse effects, though. Hypersensitivity and pleasure-response are not the only physical responses to opiates. Take a look at the adverse effects in our article. Respiratory depression can occur, which can lead to death, if doses are sufficiently high. Nimur (talk) 02:34, 26 July 2009 (UTC)

The mechanism is homeostasis. The amount of neurotransmitter could theoretically be extremely different in two people but the neurophysiology is near identical, because other factors are involved (number of receptors, receptor modification, enzyme number, et al). The problem at the moment is that agonists at the opioid receptor trigger signalling pathways associated with analgesia/euphoria/etc but also trigger signalling pathways associated with desensitization and tolerance. It may however be possible to trigger only the positive signalling pathways, but it's a relatively new discovery so don't expect any non-tolerant opioids on the market for at least 15 years. I strongly recommend reading these papers (in order):

Galandrin S, Oligny-Longpré G, Bouvier M. (2007). The evasive nature of drug efficacy: implications for drug discovery. Trends in Pharmacological Science. 28(8): 423–430.

Whistler JL, Chuang HH, Chu P, Jan LY, von Zastrow M. (1999). Functional dissociation of mu opioid receptor signaling and endocytosis: implications for the biology of opiate tolerance and addiction. Neuron. 23(4): 737–746.

Bosier B, Hermans E. (2007). Versatility of GPCR recognition by drugs: from biological implications to therapeutic relevance. Trends in Pharmacological Sciences. 28(8): 438-446.

The original question is the topic of a great deal of ongoing research, and the answers are still very unclear. The nature of pleasure in the brain is also still unclear in many respects. As Nimur says, eliminating opiate tolerance certainly wouldn't allow infinite pleasure -- opiates are mainly sedative and only secondarily rewarding. Eliminating dopamine tolerance in certain brain areas would be more effective, but there is probably more to the story. Looie496 (talk) 17:25, 26 July 2009 (UTC)

Thanks! I figured that this question might not have an answer yet—but I didn't necessarily know the reasons for this. —Preceding unsigned comment added by Alfonse Stompanato (talk • contribs) 18:14, 26 July 2009 (UTC)

Mysterious carpark bumps

Please help me identify the function of these mysterious objects found in the carpark of my local Tesco supermarket - context, closeup. Here is all I know about them: there is one in every parking bay, located on the midline of the bay about 1 metre from the end - roughly where the engine-block of a car would be if you were parking nose-in; the bumps have no identifying marks (no manufacturer, no patent number, no serial number, no "property-of" tag); the bumps are attached to the ground, but can be wiggled around - it's probably straightforward to prise them up with a couple of crowbars; there is no evidence of wires running to them; the bumps are made from a dense black plastic (not rubber) - it feels like they're just a shell over something; the carpark in question does not suffer from drainage issues; the bumps are approximately 100mm in diameter and are about 15mm high, with a tapered edge - they are too small to be effective as traffic calming measures; the carpark in question is close to the shopping area of town (and is used by non-tesco shoppers) so Tesco employs a man with a clipboard on Saturdays to police overstayers; the bumps are very robust (they can withstand frequently being driven over) and there is no indication that they have any mechanical aspect (I don't think they're mechanical switches of any kind); I've never seen a store employee or contractor cleaning, touching, or servicing them, and there is no signage suggestive of their purpose; I don't think they're caps for holes one would use to put in parking-prevention bollards - they're at the wrong end of the bays for that.

My guess is that they are related to parking control: that they house a magnetic car sensor and keep track of how long the car above them has been in that bay (resetting when a car leaves). If that's true, they must be battery powered and presumably have a short-range RF capability, so the clipboard-weilding parking man can interrogate them individually with some kind of handheld wand. If this is correct, I'm impressed that they can run a small computer, a magnetic sensor, and a two-way RF connection all off a battery, presumably for weeks or months on a charge. I doubt that having several hundred of such fancy devices would be cost effective in a carpark that is free.

I've asked several employees, but they didn't know (or have been sworn to secrecy by the carpark bump conspiracy). Does anyone have any idea what these might be, and who makes them? -- Finlay McWalter Talk 19:55, 25 July 2009 (UTC)

Perhaps parking related as you suggest? If not to time the car in and out then at least to tell when the car park is full. SGGH ^ping! 20:00, 25 July 2009 (UTC)

I should point out that there is no "car park full" sign, and no "spaces free" counter sign either, so I don't know what Tesco would do, in practice, with information about how full the lot was (other than internal statistics, which I'd doubt would justify the cost of sensors. And there is no barrier or ticket-machine at the carpark's entrance. -- Finlay McWalter Talk 20:05, 25 July 2009 (UTC)

There's plenty of material on parking space sensors from google, including a paper which shows the internals of one - much the same size as yours. However, per your narrative, it remains a mystery what tesco is doing with the information collected, if anything. Nice shoe, btw ;). --Tagishsimon (talk) 20:06, 25 July 2009 (UTC)

It seems apparent that Tesco has too much money for their own good. Vranak (talk) 20:08, 25 July 2009 (UTC)

I did also consider the possibility that they were passive reflectors, which could be used by a remote-camera system to count and time cars (if the reflector is obscured then there must be a car in the bay) - given the few cctv cameras around, this would have to be done by sensors atop lampstandards - but I don't think there are enough lampstandards for this, and these dull opaque bumps are the very opposite of reflective (I guess they're less reflective than cars, so maybe that's it). -- Finlay McWalter Talk 20:10, 25 July 2009 (UTC)

Meanwhile in SF, "The device, called a “bump,” is battery operated and intended to last for five and 10 years without service." - [18]. --Tagishsimon (talk) 20:22, 25 July 2009 (UTC)

If a camera/reflector system were being used, they would have to install quite a number of cameras or have them very high up since the car in the next space over could block more than a single bump. Dismas|^(talk) 20:27, 25 July 2009 (UTC)

The SF bumps are associated with revenue (I'd guess they'll cost at least $100 each, so they'd have to pay for themselves) whereas my Tesco bumps are in a free lot (and Tescos got to be as wealthy as Vranak says by not wasting money). And the SF bumps look pretty well grouted in - they'd have to be, to stop someone prising them up and making off with them (Berkeley had a vigilante problem a while ago, with someone cutting down dozens of meters to protest parking fees); Tesco's bumps don't seem that secure. Maybe I've misled everyone by suggesting the parking-management idea (which really doesn't seem cost-effective), and they're something much more passive and mundane. -- Finlay McWalter Talk 20:36, 25 July 2009 (UTC)

In the US at least, many shopping centers have free parking lots that are intended for the use of the shoppers, but are not supposed to be use by daily commuters. If a car is parked inthe early morning and is still there five hours later. The owne ofth lot can have it towed away. The bumps could monitor this.-Arch dude (talk) 21:12, 25 July 2009 (UTC)

They have a 2 hour maximum, and they can impose a civil fee (recoverable by court action) in England. But in general shops and shopping centres are rather reluctant to impose these fines (I think they do it for all-dayers, but not for people who stay just an hour longer) as it's a great way to annoy someone and lose their business forever. -- Finlay McWalter Talk 21:18, 25 July 2009 (UTC)

Google rulez! Looie496 (talk) 23:51, 25 July 2009 (UTC)

Awesome google-fu, Looie --Tagishsimon (talk) 23:55, 25 July 2009 (UTC)

Were you referring to Kidderminster, Finlay McWalter? --Rixxin (talk) 15:04, 26 July 2009 (UTC)

Good job on the Google-fu. As an aside in response to concerns about cost, I'll note that the scheme would work very nearly as well if only (say) 1 in 3 'bumps' were genuine and the rest indistinguishable dummies. The purpose is to discourage long-term or full-day parking that isn't related to visits to Tesco. If word got around that a) the bumps are tracking parking, and b) Tesco is issuing tickets or towing vehicles, then the fact that only a fraction of the bumps actually work is irrelevant. (Indeed, from Tesco's perspective the fractional coverage might actually be better — it would convey the message that tickets were being issued and parking rules enforced, while reducing somewhat the number of people who actually get mad about receiving a ticket personally. A similar effect could be achieved by issuing warning notices on first offences and by capping the number of tickets issued per day.) TenOfAllTrades(talk) 16:05, 26 July 2009 (UTC)

What happened to the US space VLBI program?

Looks like the Japanese did Space VLBI back in 1997: http://www.vsop.isas.jaxa.jp. If Moore's law was being followed, which in signal processing (as opposed to consumer goods) I believe it generally has been, we might have had a way to see the ozone spectrum characteristics of Earth-sized habitable exoplanets at 34 THz and below (9-10 micrometers) by now.[19]

However: http://web.archive.org/*/us-space-vlbi.jpl.nasa.gov/

Where did the US lose track and how can we get back on track? I don't want to know who was responsible (although I believe they should be held responsible if they can be identified) nearly as much as I want to know who can bring the thing out of mothballs.

Related research:

• Schneider, J. (2009) "Pathway Toward a Mid-Infrared Interferometer for the Direct Characterization of Exoplanets"
• Schneider et al (2009) "Search for Life on Exoplanets: Toward an International Institutional Coordination"
• Mugnier et al (2009) "Optimal method for exoplanet detection by angular differential imaging"

99.60.2.113 (talk) 19:59, 25 July 2009 (UTC)

I know a girl who's doing work with Cluster that one might call "VLBI"-like. That is an ESA satellite constellation, but the research is funded by the NSF (I think). I think there is also a new replacement small-satellite system (either IMAGE or THEMIS, both NASA missions; these have sensors which can also be used for VLBI-like work. The work that I am aware of is mostly using synthetic-aperture for terrestrial observation, though. I don't know if these satellites have useful science data for studying exoplanets. As far as the US "losing track", I agree that we're underfunding our space research; but you might want to look at this article. Space research is always lower-priority for government spending; and these days it is even lower priority than usual. Nimur (talk) 02:48, 26 July 2009 (UTC)

Also, I don't think any reliable economist or researcher has ever suggested that Moore's law even remotely applies to space research. An engineering professor explained Moore's law best during an ASIC class a while back. The "law" is only preserved because of an economic feedback loop, where profit is fed back into the engineering investment to double the performance. This produces more profitable products, so more profit can be fed back into the research. And as all engineers know, positive-feedback leads to exponential growth. Space research has no such profit-return path (or at least, not on the 18-month time-scales). Moore's law does not hold. Nimur (talk) 03:28, 26 July 2009 (UTC)

The necessary profit motive exists in, e.g., fiber optic communications bandwidth markets, which have been improving along with the continuing miniaturization of integrated circuit photolithography.

Why can't we use any two existing infrared space telescopes for VLBI? HowDoIUseUnifiedLogin? (talk) 06:58, 26 July 2009 (UTC)

We can, provided their data is sufficiently synchronous; but remember, our best timing accuracy is usually GPS time (depending on your circuitry, this can be anywhere from millisecond-accuracy to maybe nanoseconds with some phase locked loop filling in the subsampled time intervals. For interferometry, you need timing accuracy on the order of the wave period for the frequencies you are looking at; that makes VLBI very hard unless the equipment has been specifically designed to measure coherently. At lower frequencies, such as those EM waves suitable for electromagnetic surveys of the terrestrial and near-earth environment, VLBI is much easier. Optical surveying of exoplanets, though, is a whole different animal. Nimur (talk) 16:15, 26 July 2009 (UTC)

In fact, after searching yesterday and today, I could not find any real VLBI observations of exoplanets at optical wavelengths. Simulations abound - but this is because in MATLAB, any arbitrary timing coherence is possible. An actual satellite cluster must have synchronized clocks (or other wave coherency system) that is as accurate as the frequency of observation. This is not a "small detail", it is a major engineering obstacle that (at infrared wavelengths) pushes several orders of magnitude beyond the state of the art in clock coherency and accuracy. Nimur (talk) 16:18, 26 July 2009 (UTC)

Assuming that the timing and therefore the position information is poor, which I am not sure is a reasonable assumption given modern chip-scale atomic clocks, is there any reason that a brute force search for the matching phases isn't possible? It would seem that the features of the image including the spherical Bracewell-nulled star, possibly the elliptical interplanetary dust cloud emitting blackbody IR, and certainly the planets in question would all provide sufficiently discernible features for pattern recognition which would be distorted in a way that should be obvious to an algorithm when the phases aren't correctly matched. If brute force phase matching is possible, how about a binary search? 99.35.130.129 (talk) 17:26, 26 July 2009 (UTC)

It's not a matter of precision, it's a matter of accuracy. As you point out, we can make clocks that are precise to amazingly small time-intervals - but those clocks need to by synchronous across satellites which are tens of thousands of kilometers apart. That part has not made recent advances - as I said, GPS is our best bet, and it's about 1 ms accurate. It works great if you are doing low-frequency research. To be honest, I have no idea what "Bracewell nulling" is, this paper seems to mention it.

Bracewell, R.N, and MacPhie, R.H.. Icarus, vol 38, 1979: available here Nimur (talk) 18:05, 26 July 2009 (UTC)

Bracewell wrote in 1979, "... it is not clear whether technology or astrophysics will be limiting. It is conceivable that bulk motions of the stellar envelope ... could foil attempts to exhibit ...periodicity." This is the crux of the issue. Even in 2009 (thirty years later), we still have neither the technology nor the astrophysical understanding to be sure we are isolating the exoplanet via angular resolution; the interferometric approach suffers similar problems. Clearly this is an area that can benefit from further basic science research as well as technology improvement; the 1979 paper gives a great overview of the challenges and also has provides some formulae and some example numbers you can crunch for yourself, to determine the necessary engineering constraints for a given exoplanet size. In summary, "we aren't there yet."

Also, you seem to think that phase error "should be obvious to an algorithm when the phases aren't correctly matched" - but that is unfortunately not the case - phase noise. If you can think of such an algorithm which eliminates phase noise, and it actually works, then you'll have made a really solid contribution to interferometry, and signal processing in general! Nimur (talk) 18:29, 26 July 2009 (UTC)

The solution is independent of the time scale limiting initial phase matching accuracy. The interferometric image combination does not discard information, therefore it is a convolution. Expected star, background, and planetary images can be similarly convoluted to derive patterns, comparisons against which a search through the possible timing differences can be guided by to finish in O(log(N)) time. These convolved but information-rich patterns can be combined for comparison templates allowing an even faster phase match search.

There may be an even simpler algorithm. Please consider the phase vocoder used for pitch ("autotune") and time shifting. The total magnitude (or energy?) of changes it needs to make to match phases for resynthesis is proportional to how well the waveforms are matched. A calibration system at that level of sophistication could be tuned on a variety of wavelengths even if starting at 34 THz would be much harder. 99.35.130.129 (talk) 20:58, 26 July 2009 (UTC)

More related research:

• Pallé et al (11 June 2009) "Earth's transmission spectrum from lunar eclipse observations" Nature 459: 814-16
• Le Coroller et al (2004) "Tests with a Carlina-type hypertelescope prototype" Astronomy and Astrophysics 426: 721-8
• http://collab.digitaluniverse.net/wiki/Interferometry_from_Space - currently omits heteroscopic space VLBI
• Closure phase - a method of calibrating two VLBI telescopes with a third

99.35.130.129 (talk) 21:44, 26 July 2009 (UTC)

Why do buildings have foundations?

What is the reason for having foundations for buildings? Surely it does not make any difference if the weight of a building such as a house is supported on the surface of the ground or a few feet below? 89.243.185.143 (talk) 20:35, 25 July 2009 (UTC)

There are a number of reasons for considering sunken foundations, such as development of lateral capacity (i.e. preventing movement), penetration of soft near-surface layers, and penetration through near-surface layers likely to change volume due to frost heave or shrink-swell - see Shallow foundation. But there are above-ground foundation systems, such as concrete on grade, which are suitable for more temperate climates. See also Foundation (engineering) and Deep foundation. --Tagishsimon (talk) 20:53, 25 July 2009 (UTC)

Look at Foundation (engineering), Shallow foundation, Consolidation (soil) and Bearing capacity. Oh and read the Parable(?) of the man that built his house on sand, http://www.thisischurch.com/sermon/wiseman.htm ny156uk (talk)

Around here, the Frost line can be as much as 4 feet deep. So when the ground heaves (see frost heave), anything above it will move up. You don't want this happening under just part of your structure. Dismas|^(talk) 21:05, 25 July 2009 (UTC)

The simple answer is: buildings are expensive. While a house could be built for tens of thousands of dollars, many academic buildings are vastly more complex, and expensive the same way. At the same time, these buildings LAST. Many famous University buildings have been built more than a hundred years ago. So, when a foundation pays for a building, it is one of the longest-lasting charitable actions they can do, while at the same time there is a big financial need for support in building the buildings, which explains both the foundations' and the universities' / other bodies' eagerness to take on these kinds of projects. It's just basic economics, really. 82.234.207.120 (talk) 21:43, 25 July 2009 (UTC)

↑ cute.--70.107.76.121 (talk) 22:39, 25 July 2009 (UTC)

Does it help if the foundation rests on a solid rock..efeller? Nimur (talk) 18:50, 26 July 2009 (UTC)

The surface of the ground has several problems. In most places it consists of topsoil, full of organic matter that can decay or change. In areas prone to freezing the ground can expand and contract as it freezes, moving up and down. Even in areas where that isn't an issue, the ground will expand and contract according to its moisture content. You always want the material under a building to be essentially unchanging. Furthermore, the soil near the surface has almost always been disturbed by human activity, either building or agriculture and may not be consistent in nature, or may be insufficiently compacted. It is actually worse to have inconsistent bearing under a building than to have poor, but consistently poor bearing, as then different parts of the building will move in different directions, always a bad thing. With rain, freezing, topsoil and disturbance, even light foundations should be at least 18"/1/2 meter below grade, or have the soil cut out to that depth and replaced with a material of predictable characteristics. The better the bearing capacity of the material, the smaller the foundation may be.

It's worth noting that the skyline of Manhattan roughly parallels the availability of Manhattan schist at a depth convenient for the placement of skyscraper foundations. Where it's deeper, like in Greenwich Village, buildings are shorter in stature, as it's hard to spread the load of a tall building over a wide enough area in soil without resorting to pilings. Also, for a tall building, the foundation must resist the wind load or overturning moment, and even in a small building you don't want it tossed by the wind (think about trailers vs. tornadoes). Acroterion _(talk) 00:04, 26 July 2009 (UTC)

If a church is built on the rock it will stand, even when steeples are falling [20]. Edison (talk) 03:14, 26 July 2009 (UTC)

Surely it does not make any difference if the weight of a building such as a house is supported on the surface of the ground or a few feet below – actually, it makes a big difference. Try building something with sticks. You'll find that when they're stuck in the ground you can actually build a stable structure. Otherwise, things tend to fall over. Vranak (talk) 17:17, 26 July 2009 (UTC)

That's mostly an unrelated phenomenon. Sticks shoved in the dirt are stable due to the soil surrounding them holding them in place, that is mostly not the case for buildings. While having dirt around it sure doesn't hurt, the purpose of digging is simply to reach a stable level. Matt Deres (talk) 16:08, 28 July 2009 (UTC)

example of easy irrational problem?

I am looking for an example of an easy irrational problem or task, that is impossible for the deductive, rational left-brain (or a rigorous computer program etc) to solve or answer, but is so easy that EVERYONE who has both brain hemispheres can solve it, even the most rational, Asperger's-suffering mathematician on Earth. But where the solution MUST be done by their right brain.

Any ideas for what such a problem or task might be? (It's actually okay for me if a percentage of the rational people above mentioned fail at the task -- I am really looking for something almost all of them can do [but which is irrational, can't be done by the left brain].) Thanks! —Preceding unsigned comment added by 82.234.207.120 (talk) 21:49, 25 July 2009 (UTC)

Well, assuming the Church-Turing Thesis is true, and the brain is just a meat computer, there is no such problem. There are many problems that are very hard for computers using our current techniques, but which humans are very good at. Recognizing faces from minimal cues is one. Noisy image recognition is a related one. I would suspect music appreciation is similar - if a computer can recognize the Eroica as truly great music, I'd be surprised. --Stephan Schulz (talk) 22:24, 25 July 2009 (UTC)

Some experienced mathematicians are unable to complete the following series which is often solved easily by children:

3, 3, 5, 4, 4, 3, 5, 5, 4, 3, 6, ?

Cuddlyable3 (talk) 23:18, 25 July 2009 (UTC)

However, a computer with access to Google or the OEIS can also solve that easily, so it doesn't seem to be what the OP is after. Algebraist 23:22, 25 July 2009 (UTC)

Your conditions are so stringent that they probably make the problem impossible. For one thing, the standard left brain/right brain distinctions don't apply to everybody -- many left-handers have different lateralization. If you restrict yourself to people with the standard lateralization (i.e., ordinary right-handers), probably the most basic function that is highly right-hemisphere-dependent and not solvable by logic is recognizing people's faces. However, people with autism or Aspergers, and some other hyper-rational people (Isaac Asimov for example), are often impaired at this. Looie496 (talk) 23:36, 25 July 2009 (UTC)

Ho ho ho it looks like the problem I posed separated the left-brainers from the right-brainers. (Once you see it, it is a no-brainer.) To Algebraist I think we must distinguish between solving a problem and looking for someone else's solution. The GIGO principle suggests there is no irrational act that a computer might not do. Cuddlyable3 (talk) 23:42, 26 July 2009 (UTC)

For those of us really bad at spelling it does not become a "no-brainer" even after it's explained. It's not so much a puzzle as much as an exercise. It tests whether or not you've ever seen a puzzle of this sort before, and whether you have the patience to grind through common series until you find it. For me, I can't do these without writing down the words and counting the letters (Even so, how do you spell "eight"? I can never remember.), so I stopped after checking only two series.

It may have successfully identified me as a math centric person, but I'm not confident it worked the way you expected. I did at least correctly identify it as potentially being a count-the-letters puzzle.

(Incidentally, I was going to guess '6' because of the pairs of repeats in the series, So at the very least you're going to want to end the series on a different element.) APL (talk) 15:10, 27 July 2009 (UTC)

So ... what's the solution to the series? APL (talk) 19:32, 26 July 2009 (UTC)

Well, I have pretty serious Asperger's and I got it in about 10 seconds. The clue that made it easy was that the questioner didn't think I'd be able to solve it - which told me I shouldn't be looking at a numerical solution. However, smart people can think laterally too - so let me give you a clue: ONE,TWO,THREE,FOUR,FIVE,SIX,SEVEN,EIGHT,NINE,TEN,ELEVEN,...got it now? How about A,B,C,D,E,H,I,K,M,O...what's next? If you need to give me a problem I can't solve, have me talk about small British cars from the 1960's to an average person at a party. Challenge me to stop talking when the other person gets bored. I have no clue how to do that. Fortunately, people who know me well know that I'm also not in the slightest bit offended when I'm told that I've explained that enough already! SteveBaker (talk) 22:32, 26 July 2009 (UTC)

You probably wouldn't be far off if you just didn't start! --Tango (talk) 00:43, 27 July 2009 (UTC)

Ah. One of those. I tried the days of the week and the months of the year, couldn't make it fit so I tried a different tack. Are non-logical people (Esp, children) really so good at these? If so I must be pretty non-typical. Forget common series; I can't remember how many characters are in my name without seeing it written or counting on my fingers.

Not to make light of Asperger's at all, but I have to ask, for your party question, from the point of view of designing an algorithm, couldn't you get a rather close approximation by judging the interval between intelligent questions? APL (talk) 04:44, 27 July 2009 (UTC)

This series depends heavily on how you choose to visualize numbers. If you see the word "three" in your head upon seeing "3", the solution is easy to get. If you see 3 apples, 3 spheres, or the Arabic numeral "3" and have never visualized numbers any other way, it might take a while. --Bowlhover (talk) 06:16, 27 July 2009 (UTC)

no, the recognizing faces thing is totally a great example! It's "irrational". A mathematician would have nothing to say about what he's calculating or reasoning while he's doing that: literally nothing. You put them in front of a computer and tell them to write down their algorithm in pseudocode, they would say they're not following an algorithm, it's a nonsensical request. But you ask them to code approximately how they do their grocery shopping, they can lay down pseudocode before you've finished your sentence!!! So I like the example a lot. It's something "irrational" and yet all mathematicians can recognize SOMEONE. Can you give me more examples of this, of something "irrational" that all people, even mathematicians do? Also, the brain laterization thing isn't the crux of the request, but the "irrational" problem solving is!! Thanks. 82.234.207.120 (talk) 00:20, 26 July 2009 (UTC)

One simple problem of this type is to decide whether or not a sentence is funny. -Arch dude (talk) 02:12, 26 July 2009 (UTC)

Facial recognition can be performed algorithmically. See Facial recognition system. Maybe some mathematicians do not think about it in an algorithmic way, but clearly the problem can be set up, defined, and solved algorithmically. The accuracy is becoming very high, and in some professional-grade systems, beats human face-recognition error according to some metrics: "Computers outperform humans at recognizing faces in recent tests". Nimur (talk) 03:10, 26 July 2009 (UTC)

I'm not sure that a human being could consciously eyeball the measurements needed for a facial recognition algorithm. APL (talk) 04:44, 27 July 2009 (UTC)

How about just having a normal conversation? AI's still don't pass the Turing test. Robots with AI are also apparently very bad at soccer. Then of course there are those images of a word that you're supposed to type. Some of them have been broken, but in general it's a very hard problem. Check out the Artificial Intelligence page for for a more thorough description of the types of problems computers are comparatively very bad at. The original question wasn't really about computers per se, but I'm not sure how to tell if a problem is impossible with only the "left brain." Rckrone (talk) 06:06, 26 July 2009 (UTC)

Rckrone may be referring to CAPCHA . Cuddlyable3 (talk) 23:54, 26 July 2009 (UTC)

Oh yeah, I forgot that had a name. Also I did a really horrendous job of describing it. Rckrone (talk) 02:40, 27 July 2009 (UTC)

Certainly there are problems you can set up that a computer can't solve - but you'd be hard-pressed to find a human-solvable problem that a computer will never be able to solve (presuming it's given the same data and life-long learning that the human gets). Remember - people said that a computer would never be able to beat a grand master at chess - or that it would never be able to drive a car. It's dangerous to make these claims. But that's not what the questioner is asking. We're supposed to be finding problems that a highly logical brain can't solve - that more 'normal' people don't find difficult. SteveBaker (talk) 22:32, 26 July 2009 (UTC)

Well in that case I think Stephan Schulz has it right. There's no reason a sophisticated enough computer couldn't perfectly emulate a human brain. Rckrone (talk) 02:40, 27 July 2009 (UTC)

Hey! I may not always have it (I'm not Steve Baker), but if I have it, I always¹ have it right! --Stephan Schulz (talk) 11:29, 27 July 2009 (UTC)

¹ ...for sufficiently small values of always!

That isn't quite correctly stated. There is no conceivable computer that could perfectly emulate a grain of sand. A better way to put it is that there is no valid reason to think that the brain performs any useful function that couldn't be emulated by a computer. Looie496 (talk) 02:52, 27 July 2009 (UTC)

CAPTCHAs are designed to exploit the current gap between what humans can solve and what computers can solve. Ironically, they've been quite effective at driving research in these areas, research that continually proves each new CAPTCHA vulnerable to sophisticated machine learning methods. There will probably for a long time to come be tasks that humans perform better at than computers, but the gap continues to close. Dcoetzee 21:37, 27 July 2009 (UTC)

Which cow breed is this Swiss cow?

A swiss cow seen near Oeschinen Lake.

Hi, I took this photo of a cow in Switzerland a short while ago. I would like to know which breed it is such that I can update the file page description and categorize it properly. I guess it must be some breed of Bos taurus, but I am at a loss which one. Thanks in advance. --Slaunger (talk) 22:12, 25 July 2009 (UTC)

Montbeliarde Cattle? I'm not sure, I'm not an expert in that field :) . And it is Swiss, not Swizz. Actually, more like French ;). --Dr Dima (talk) 22:38, 25 July 2009 (UTC)

Sorry about the terrible spelling (which I've corrected now). I am not a native speaker nor speller... OK. I do not feel too sure when seeing the photos of that breed, and I think I would like a second opinion, but thanks of for your time. --Slaunger (talk) 22:52, 25 July 2009 (UTC)

I asked my wife, who works in the dairy industry, what breed it is and she doesn't know. She was able to definitively say that it's a beef breed though, as opposed to a dairy breed. Dismas|^(talk) 01:38, 26 July 2009 (UTC)

The English Wikipedia distinguishes between Simmental Cattle and Fleckvieh cattle which are treated as the synonyms by the German Wikipedia de:Fleckvieh. The Swiss are trying to establish "Swiss Fleckvieh" as a separate breed and are limiting the Red Holstein influence for that purpose. It's a dual purpose breed (beef and milk) like lots of the "older" breeds. Here's a picture for comparison,[21] looks pretty much like yours. 71.236.26.74 (talk) 03:34, 26 July 2009 (UTC)

Thanks for that thorough answer. I did have a look at the Simmentaler before asking but the photos does did not look quite right to me. --Slaunger (talk) 10:14, 26 July 2009 (UTC)

I don't think there is enough information in one photograph of a semi-recumbent animal to accurately identify the breed. Richard Avery (talk) 19:46, 26 July 2009 (UTC)

I understand your concern. I think I will conclude from this that "It is most likely a Swiss Flechvieh, could also be a Flechvieh, a Simmentaler or another dual purpose breed (beef and milk)." Finally, one of the Wikipedia articles points to a dedicated German Flechvieh site, which i have seen has a forum, where one can ask questions. I think I will also ask the question there, as they should know if any if it is a Flechvieh or not. Last, but not least, thanks for the help and feedback here. It is very much appreciated. --Slaunger (talk) 21:04, 26 July 2009 (UTC)

July 26

Cat bird owl?

There are so many hoaxes on the internet and on youtube, that I assume this is just pixel animation, but I was curious if it possibly wasn't what the hell is going on in this video where a startled owl stretches out into a cat-like resemblance? Like I said, I'm assuming it's fake until told otherwise, but it's pretty cool looking and there's something about that looked real enough that I thought I'd ask.--70.107.76.121 (talk) 00:24, 26 July 2009 (UTC)

Okay, now I really want to know just what's being said in these videos. Here's another; same owl type, totally bizarre stuff. Anyone speak Japanese?--70.107.76.121 (talk) 00:30, 26 July 2009 (UTC)

Some owls have large ears reminiscent of cats. There's no trickery in the first video; I couldn't spare 3:20 to view the second, but both appear to be about owl training. --Tagishsimon (talk) 02:10, 26 July 2009 (UTC)

I speak Japanese, and all it is saying in the second video is that the owls change shape according to what other owls appear in their vicinity. One changes shape to make it look bigger, signifying 'I am bigger than you' and the other changes shape to make itself look smaller, though the reason is not given. Also, the trainers are using both male and female owls for this experiment/show. --KageTora - (영호 (影虎)) (talk) 02:39, 26 July 2009 (UTC)

I definitely agree that the video is legit. It's a defensive response. The purpose might be to disrupt a potential predator's search image. Sifaka ^talk 05:15, 26 July 2009 (UTC)

Searching Japanese Wikipedia for アフリカオオコノハズク leads to Northern_White-faced_Owl although the English article doesn't mention its ability to change its shape like that. The Japanese article seems to have a bit more information but I don't know what it says. Rckrone (talk) 05:39, 26 July 2009 (UTC)

Am I the only person here who finds that transformation to be fairly unsettling - on a visceral level? --Kurt Shaped Box (talk) 07:14, 26 July 2009 (UTC)

If it's to deter predators, as suggested above, then that's probably the intention - ie to look like a bag of bones and sinew and not a very good meal.83.100.250.79 (talk) 08:51, 26 July 2009 (UTC)

Specifically, it's something about the way that the owl's face and eyes appear to change shape that trips off a feeling of 'wrongness' somewhere within me. --Kurt Shaped Box (talk) 09:10, 26 July 2009 (UTC)

It's all very simple. The owl has a face just like we do. It has muscles that change shape. The owl got scared (but not enough to fly away), so he shrunk away from the jack-in-the-box. The difference is, the owl is covered with feathers. Muscles retract, feathers go with it, and it's face changes shape significantly. If your face was covered in feathers it would be quite a sight when you got shocked, too. Vranak (talk) 17:15, 26 July 2009 (UTC)

Aye, birds' faces can be very expressive at times, despite being covered in feathers. I don't know if we could pull off 'curiosity' or 'anticipation' when similarly covered. A Budgerigar (for example) can. --Kurt Shaped Box (talk) 20:16, 26 July 2009 (UTC)

In the second video, the narrator said that it elongates its body to appear as a tree or branch. It squints its eyes so they are less visible. -- penubag  (talk) 09:08, 28 July 2009 (UTC)

Light energy

Light is frequencies of energy that the eye can see.Frequencies in the blue light field will create a magnetic field. Other levels will create cold temperatures. Who can help me prove this?

Light is not "frequencies of energy" - it is "frequencies of electromagnetic waves", usually referring to those frequencies we can see with the human eye. All light has both an electric field and a magnetic field because light is an electromagnetic wave. Light does not "create" a magnetic field. It is a wave phenomenon which includes a time-varying magnetic field. This has been proven many times by many different methods. See wave-particle duality for more on this topic. I am not sure what you mean by creating cold temperatures; do you mean laser cooling? Nimur (talk) 04:14, 26 July 2009 (UTC)

Your first phrase reminded me of St. Elmo's fire, but that works the other way round. The light is due to the electric field.71.236.26.74 (talk) 04:23, 26 July 2009 (UTC)

Is it common to imagine that puffins are bigger than they are?

I saw a puffin in real life not so long ago. I was surprised at how small it was. When you see them on wildlife shows on TV, they look much bigger. I was expecting something about the size of a medium sized penguin. --84.69.249.254 (talk) 07:29, 26 July 2009 (UTC)

On TV they are trying to show as much detail as possible, so they'll do close-ups. It's not uncommon to imagine stuff you haven't seen in real life as larger than it is. I still run into rivers that I only used to know from maps and am frequently underimpressed with the width of them. Very few held up to my idea of what a well known river should look like. As for animals, there's an anecdote about Malaria researchers showing a film about mosquitoes to some villagers in Africa and being told that there was no danger because the local mosquitoes never got as big as the one in the film. So apparently the effect isn't unheard of nor limited to puffins. 71.236.26.74 (talk) 08:07, 26 July 2009 (UTC)

Antarctic penguins suffer similar size-inflation. Television documentaries film the penguins via telephoto lenses, because they are not allowed to approach the birds (environmental and wildlife protection mandates are very strict in Antarctica - though how they are enforced is always a mystery to me). The result is a shot of birds against a barren, treeless ice landscape. With no measure of perspective, these birds appear huge - I always thought the Emperor Penguin would tower above an upright 6-foot human; but in fact the largest of them are only about four feet tall. But from these sorts of photos, how can you possibly tell? The only objects available for visual height reference are... other penguins. For all you know, those penguins could be twenty feet tall. Similar issues plagued the Apollo moon landers - without visual cues about height, it was very hard to tell pebbles from boulders; small holes from large holes; bumps from mountains; depressions from canyons. Human visual perception relies very heavily on the subtle peripheral clues to help judge perspective, distance, and size. Nimur (talk) 18:56, 26 July 2009 (UTC)

FWIW, when I was a kid, I used to think that the Emperor Penguin was about the same size as a human - a similar height to the extinct Anthropornis (I was just reading about that), I guess. I also imagined the Wandering Albatross as being man-sized, when stood up straight. --Kurt Shaped Box (talk) 12:55, 27 July 2009 (UTC)

The angle the photo is taken from gives a slight clue about size - a twenty foot tall penguin is likely to be photographed from below, any other angle implies it is smaller. (The horizon usually marks where human eye level is, on all objects in the photo, in flat terrain.) And I share the puffin experience - when I first saw one next to a person I was disillusioned and disappointed by its dinkiness. This anecdotal evidence doesn't really answer the question, though. 213.122.53.30 (talk) 18:13, 27 July 2009 (UTC)

Come to think of it, the lack of a horizon in puffin photos might be part of the problem. An image search produces lots of photos with blurry backgrounds, and any hint of a horizon is irregular and bumpy because that's the sort of place where puffins live. 213.122.53.30 (talk) 18:24, 27 July 2009 (UTC)

Name of tree?

What is the name of this tree? [22] I found lots of these [23] on the ground near it, what part of the tree was it? This tree is found in Auckland, New Zealand. thanks F (talk) 09:18, 26 July 2009 (UTC)

Liquidambar orientalis or Liquidambar styraciflua--Digrpat (talk) 13:21, 26 July 2009 (UTC)

thats a plane tree or plain tree (i dont know the spelling) but theres heaps of them in cambridge (new zealand)

Black Box

What are the components of a black box in the aeroplane??How is that it suffers very little damage and hence recovered fair enough???Also any idea of what kind of metal it is made up of??? —Preceding unsigned comment added by Gd iitm (talk • contribs) 14:46, 26 July 2009 (UTC)

Flight data recorders are located in the tail, so that the entire front of the aircraft will act as a “crush zone” that will reduce the shock that reaches the FDR. Modern FDRs are typically double wrapped in strong corrosion-resistant stainless steel or titanium. Red Act (talk) 14:59, 26 July 2009 (UTC)

IMHO, I don't think anyone other than Amelia Earhart ever referred to a Flight data recorder as an "FDR". (She was a big supporter of his, so that would explain it.)  ;-) 98.234.126.251 (talk) 23:28, 26 July 2009 (UTC)

They are also (typically) bright orange spheres - the name "black box" is singularly inappropriate! The sphere is a stronger shape than a box - and orange is a more visible color than black in a burned out wreckage! Actually, these devices are quite often damaged in a crash - but they are designed in such a way that the recording can still be recovered even when the damage is pretty serious. SteveBaker (talk) 22:08, 26 July 2009 (UTC)

Commercial airliners normally carry a flight data recorder in the tail and a cockpit voice recorder near the front. These units are orange painted rectangular boxes, similar in format to other modular equipment that is made for easy replacement. SteveBaker's notion of spherical units seems far fetched, but no more so than this movie dialogue:

King Marchand: Stick around, I might want to play some golf.

'Squash' Bernstein: Boss, it's snowing outside!

King Marchand: We'll use red balls. Victor Victoria (1982) Cuddlyable3 (talk) 22:43, 26 July 2009 (UTC)

You can find a picture of a data recorder and a voice recorder here: NTSB.gov. — QuantumEleven 08:57, 27 July 2009 (UTC)

They are called "black boxes" because they are sealed off from the outside world, so are a Black box in a computing/electronics sense, not by colour. The article includes several photos of aircraft ones of various ages. -KoolerStill (talk) 16:22, 27 July 2009 (UTC)

Black boxes was a generic name for all aircraft Line-replaceable units which were all painted black. It is just that the voice recorder and data recorder became better known to the general public as (one of the) black boxes although they were not painted black like the rest. MilborneOne (talk) 16:41, 27 July 2009 (UTC)

Relative velocity

Suppose imagine that you are driving the car down a beautiful country side.The trees nearby i.e.on the the either side of the road appear to go pretty fast while the mountains atleast a mile away from the road appear to pass by pretty slow.It is a common observation.But relative velocity doesnt talk about distance anywhere.In common high school problems of calculating the relative velocity, it just says "put the negative of your velocity on the object of observation and you get the velocity at which the object(can be tree or mountain) APPEARS to pass." But the following technique doesnt work in my case why?? —Preceding unsigned comment added by 117.193.128.83 (talk) 16:39, 26 July 2009 (UTC)

You are describing parallax. What you observe isn't actually the trees or mountains moving, it's the angle to them changing. The angle is a function of both speed and distance. --Tango (talk) 16:44, 26 July 2009 (UTC)

Think in terms of angular speed, which is what the eye perceives. --Bowlhover (talk) 18:11, 26 July 2009 (UTC)

See also visual perspective. As you well know, this pencil has a constant diameter; but looking at it, it appears to get smaller in the distance. This is the same effect which makes the apparent motion speed seem slower for the distant mountains. Nimur (talk) 19:00, 26 July 2009 (UTC)

More specifically - the effect of perspective is that the apparent size of an object is proportional to one over the distance. What this means is that when you halve the distance between you and some distant object, the size doubles. When a tree is (say) 100 meters away, you only have to drive 50 meters to make it appear to double in size. When it's 50 meters away, you only have to drive 25 meters for it to double in size - so that nearby tree seems to grow FAST! However, if you're looking at a house that's 10km away - you have to drive 5km for it to double in size - which means that it takes a couple of minutes to double in size. For a mountain that's 50km away - it could take you 15 minutes to drive the 25km it takes to make it double in size. SteveBaker (talk) 22:03, 26 July 2009 (UTC)

I think I havent worded my question properly.I didnt mean to ask about the size of the object growing.I am sticking to the concept of relative velocity alone.I meant you are driving and to the left or right of the car ,the trees etc APPEAR( this has a unique meaning) to pass by and I DIDNT ask about approaching a tree and hence its size growing. (APPEARS in caps because...consider this---u are in space and u observe some stone approaching you.But there u dont really know whether you are approacing the stone or the stone is approaching you or both approaching each other.This is because you have no references at all in space unlike earth where you have the sky,winds etc as references) so just by going by relative velocity,I still havent got a satisfactory answer.I seriously doubt if it is connected to angular velocity.Nimur your answer does give me a vague idea but I am not very clear about your answer. 203.199.213.67 (talk) 04:30, 27 July 2009 (UTC)

Also the visual perspective website tells only about the smaller size of the distant objective but nothing about the relative velocity as asked by the person above.203.199.213.67 (talk) 04:33, 27 July 2009 (UTC)

Lets get one concept straight. Say you look sideways at a far off mountain while driving a car forward at 40Km/hr, the mountain does indeed go backwards at 40Km/hr, with respect to us. There's no doubt about that. But it appears to go much slower than that because of its distance. Your car window has a certain size, lets call it say one meter. Lets say your eye can see through the window, but only within certain angles - you can't look at something right behind you or right in front of you using this window, as you're not turning your head around. Lets say you can see only around 30° to either side of the center of your window. Now, the whole thing becomes much simpler and easier to understand. Say you spot a tree some 10m away. Now, complete the triangle of your line of sights on either side using the 10m as the altitude of your triangle. Using trigonometry, you can figure out the length of the base of the triangle, which is the distance for which the tree will be visible. This turns out to be 5sqrt(3) meters. So if you're going forward at 40Km/hr, the tree whizzes past in 0.78 seconds. But if the tree is replaced by a mountain 10Km away, the same base of the triangle, which is nothing but the distance for which you see the mountain, turns out to be a thousand times greater, which means it will take 778 seconds, or over 10 minutes to go past. So you see, as the others explained, its nothing but perspective, it looks as if it is going much slower, as we realize the change only in angle, not in distance. I hope I was clear enough to understand. Rkr1991 ^{(Wanna chat?)} 05:47, 27 July 2009 (UTC)

Suppose that while you're in your car, a nearby house and a distant mountain both take up 20 degrees of your field of view. Your car moves 20 m and you completely passes the house, but 20 m is nothing compared to the mountain, so the mountain seems to have barely moved.

The phenomenon you describe has everything to do with angular velocity. After all, the eye has no way of measuring actual velocity, so perceived speed corresponds to how quickly an object crosses your field of view (measured in degrees). If it zips by like nearby objects do, you think it's fast; if it takes ages to cross your field like a faraway house, you'd think it's slow. You might ask why evolution didn't wire the brain so that it can calculate actual speed from angular speed, but that's a question I'll have to leave for another ref desker. --Bowlhover (talk) 06:04, 27 July 2009 (UTC)

Because it can't be wired in! There's a shortage of input information, if the target is very far away. Even with stereo vision (two eyes), our depth estimation is still pretty poor (especially at far distances where the parallax of our eyes is negligible). To convert apparent angular motion into actual velocity, you also need a depth estimate. At close range (2 or 5 meters), we're pretty good at doing that. At long ranges (hundreds of meters and beyond), we're not getting actual depth information from our stereo vision (the parallax is beyond the range of our perception); we have to use other contextual clues to estimate depth, but these are unsuitably inaccurate. Nimur (talk) 15:37, 27 July 2009 (UTC)

My previous answer is still correct - but perhaps some more explanation is required. Our ability to perceive distance directly is by one of two mechanisms:

• by using the amount of distortion in the lens of the eye required to get a sharp focus.
• by using the amount by which our two eyes have to point inwards in order to form a single image. :The problem is that neither of those two techniques are sensitive enough to work beyond maybe 20 to 40 feet. Beyond that, we have to rely on the rate at which things change size as we move towards them (or they towards us). For very distant objects, (as I explained before) the size doesn't change rapidly enough for us to really notice that gradual increase - so it looks like far distant objects aren't moving at all...and we really can't tell how far away they are. For closer objects, the rate of size growth increases dramatically and it gets easier and easier to figure out how far away they are and how fast they are moving towards us (or us towards them). It really is all a matter of how the laws of perspective work. SteveBaker (talk) 18:24, 27 July 2009 (UTC)

If the nearby trees and the mountains a mile a way were really passing by, and you were standing still, the mountains would appear to move more slowly than the trees, because they are a mile away. Therefore they do indeed appear to pass at a speed equivalent to the negative of your velocity, when you are moving. That's what it would look like. 213.122.53.30 (talk) 19:02, 27 July 2009 (UTC)

Heh, I seem to have said that the mountains would appear to be moving more slowly than the trees, and also that they would both appear to be moving at the same speed. Oops. Both those things are true, though! Evidently "appear" has a flexible meaning. 213.122.53.30 (talk) 19:06, 27 July 2009 (UTC)

They do move at the same speed, but they don't appear to do so. That was the question. Rkr1991 ^{(Wanna chat?)} 10:06, 28 July 2009 (UTC)

Heart transplant: nerve connections

How does a transplanted heart connects to the brain?--Quest09 (talk) 19:49, 26 July 2009 (UTC)

Nerves severed in the tranplantation do grow back after a few years. However the patient does suffer from having no autonomic control prior to nerve regrowth, one of this is the increase firing rate of the SA node, with hemodynamic problems, hypertension, and arrhythmia also prevalent in postop patients. Sjschen (talk) 20:08, 26 July 2009 (UTC)

That means that the person won't need an artificial pacemaker? Can the new heart start firing by itself, perhaps after a small electrical shock?--Quest09 (talk) 15:53, 27 July 2009 (UTC)

Assuming nerve and muscle connections within the heart are all intact, the heart will beat spontaneously without external nerve connections. See Cardiac cycle#Regulation of the cardiac cycle. We don't have an article about suspended heart (or at least not a redirect to a related article), but one can remove a heart (I think it's most commonly done with frogs?), place it in an appropriate medium, plumb some vessels to it, and study the beating (and chemical effects on it) in vitro. DMacks (talk) 22:19, 27 July 2009 (UTC)

Elevator logic control

This question has been dual-posted at the Computer Desk, here. I am consolidating the answers from Science Desk to the post over there to avoid confusion and redundancy... Nimur (talk) 23:20, 26 July 2009 (UTC)

July 27

Chesty Coughs

When you have a chesty cought does it make any difference whether you cough up or swallow phlegm? Sometimes i'm too lazy to cough it up and just swallow it, assuming it will go into my stomach anyway, but i just wondered whether this was true or not? perhaps somebody could tell me. thanks! 140.247.249.83 (talk) 05:41, 27 July 2009 (UTC)

First let me tell you what phlegm is made up of.Then it is up to you to decide whether to swallow it or not.The respiratory and nasal passages are lined by mucous membranes.These are bronchial mucosa and nasal mucosa.They have epithelial tissue that secrete mucous.The main function of mucous is to trap the germs and bacteria that enter the respiratory passages.(another function is to keep the passages moist).So during fever there is surge in number of germs and hence the mucous production in the respiratory passages increase...the result of which you get chesty coughs.The components of phlegm are mucous,dead germs,proteins,lipids,immunoglobulins and many other inorganic ions that form the minor part of it.So best not to swallow it..because it may contain some live germs.Also the idea of swallowing dead germs may make you feel disgusted.So best eliminate it out of the body.Gd iitm (talk) 06:16, 27 July 2009 (UTC)

If you do, make sure you do it in a fashion that is not likely to infect other people, i.e. spit it into a tissue and dispose properly of the tissue. Don't just gob it on to the floor. This was illegal in some places!--TammyMoet (talk) 09:37, 27 July 2009 (UTC)

Whatever live germs you cough up will very likely be killed by your stomach acid. It's almost certainly harmless to swallow the phlegm. --Stephan Schulz (talk) 12:34, 27 July 2009 (UTC)

Gd iitm, that's a joke, right? Whatever live bacteria happen to be in your phlegm are going to be digested when you swallow them. Tempshill (talk) 15:53, 27 July 2009 (UTC)

99 % of bacteria get digested by HCl in the stomach.But doesnt the thought of swallowing 99% dead bacteria and 1% alive make u feel disgusted?? —Preceding unsigned comment added by 117.193.140.74 (talk) 05:48, 28 July 2009 (UTC)

I remember George Carlin once using a factoid in his routine that swallowing saliva is linked to cancer. I have to assume he didn't just invent this factoid, and that there was a real research paper on the subject. Also, traditional Chinese wisdom advises a person to spit rather than swallow. If you're too lethargic to get up and spit, perhaps improvise a spittoon. I used to do this. Expect people to complain. It's your life and your body though so don't worry too much, just be as discreet as humanely possible. Vranak (talk) 16:01, 27 July 2009 (UTC)

That's totally ridiculous! Saliva is crucial part of the digestive system - aside from lubricating the food, it contains an important enzyme that breaks down starch into sugars. (Try chewing a piece of dry, non-sweetened bread for longer than you really need to - and you can taste how it gradually becomes sweeter as the saliva turns the starches into sugar). Not swallowing the saliva is therefore impossible! SteveBaker (talk) 18:12, 27 July 2009 (UTC)

George Carlin was a comedian. He said a lot of very true things in his routine and, in a way, he's correct here too (or at least making the point) that living causes cancer. Vranak should have explicitly specified he was quoting a comedian, who was using the concept for rhetorical effect anyway. Matt Deres (talk) 19:04, 27 July 2009 (UTC)

Well regardless, I spit hundreds of times a day and I have never gotten sick since starting. Vranak (talk) 22:44, 27 July 2009 (UTC)

Now consider where the phlegm is going - into a handy bag full of hydrochloric acid. Best place for it. 213.122.53.30 (talk) 18:40, 27 July 2009 (UTC)

Indeed - put those (maybe) live bacteria outside your body and there is every chance that they'll get back in again through your nose and you'll have to fight them off all over again - or maybe they'll go on to infect someone else near and dear to you. Dumping the little buggers in vat of hot hydrochloric acid is a great solution to the problem! Heck, you'll even get some vitamins, protein and carbohydrates back from them - phlegm is practically a health food! (OK - I think I went too far!) SteveBaker (talk) 13:20, 28 July 2009 (UTC)

Yeah, I'd imagine most organisms don't end up possessing the ability to live in your stomach by accident. Germs tend to specialize—a cold virus won't find itself in your stomach and then just decide a vat of acid would be a good place to stay. So unless you happen to have cholera or something like that in your mucus for some reason, recycling might not be a bad idea. Alfonse Stompanato (talk) 21:17, 28 July 2009 (UTC)

Common mistake

People make the common mistake of saying that their "weight" is xkg, rather it is the mass. I was reading the T-90 tank page and found that the weight is stated as 46.5 tonnes. Shouldn't it be mass? Thank you.--116.71.54.57 (talk) 07:17, 27 July 2009 (UTC)

Call me a descriptive linguist, but it seems unfair to call it a mistake when, in common usage, weight means mass. In engineering usage though, you're probably correct. AlmostReadytoFly (talk) 08:09, 27 July 2009 (UTC)

No it shouldn't be 'mass'. As AlmostReadyToFly notes - the term Weight (like a shockingly large number of terms in English) has more than one appropriate meaning (http://www.answers.com/weight) - it even referencs this in the opening section of the article. 194.221.133.226 (talk) 10:01, 27 July 2009 (UTC)

Weight means lots of things as the list on answers.com demonstrates but none of them is mass, which is the correct category for an object without a specified location. The weight of an object varies by several percent moving from pole to equator and the fact that it is locally equivalent to mass does not in my view suddenly make the error correct. --BozMo talk 10:59, 27 July 2009 (UTC)

Citation for the several percent? Aaadddaaammm (talk) 11:09, 27 July 2009 (UTC)

It's actually about half a percent. See Earth's gravity. Algebraist 11:25, 27 July 2009 (UTC)

Ok, half a percent at sea level and a bit more to the top of Kilimanjaro (the article isn't quite right but pretty close AFAICT). That's why the earth is oblate. --BozMo talk 12:43, 27 July 2009 (UTC)

Other way around: the strength of the gravitational field varies because the Earth is oblate. The Earth is oblate (primarily) because of its rotation. — Lomn 13:16, 27 July 2009 (UTC)

Nah. It is the rotation which makes the net weight less on the equator which makes things bulge. --BozMo talk 13:30, 27 July 2009 (UTC)

You are both kind of right. The rotation causes the bulge in the manner you describe, but gravity on the bulge is less because you are further away from the centre of the Earth (there is also a contribution from the rotation itself). --Tango (talk) 13:49, 27 July 2009 (UTC)

Weight isn't an 'incorrect' term - it has a perfectly simple, clear, valid meaning in physics and elsewhere - the only important things to understand is that (a) weight and mass are not the same thing - and (b) an object's weight will change depending on where you put it. Talking about the weight of a tank - which is pretty much only going to be trundling around on the surface of the earth - and highly unlikely to ever be driving around on the moon - is not at all unreasonable. Certainly there are small variations in the weights of objects depending on whether they are at the poles or the equator - parked on top of a mountain or near a magnetic anomaly caused by some particular flook of geology...but those differences are likely to be negligable compared to things like the amount of fuel and ammo the thing is carrying. So we should not be overly anal about our descriptions of things like that. Worse still, from an encyclopedic point of view, we are unlikely to be told either the mass of the tank or it's weight in Newtons. Since we're required to have references to back up what we write - it may actually be necessary to state the weight - and to give it in kilogrammes (with the implication that it's kilogrammes-force that we're really talking about). Most of our readers would have no clue what a Newton is anyway! There is utility in being useful, clear and understandable - and talking about the weight of a tank in kilo's is just fine. SteveBaker (talk) 18:06, 27 July 2009 (UTC)

Not to mention that almost no one knows their "mass". Scales, by definition of the way they work, measure weight, not mass. Besides, us stupid Americans still use pounds (scientists aside), which can describe both weight and mass.-RunningOnBrains^(talk) 18:31, 27 July 2009 (UTC)

The problem with allowing definition to become common usage and be divided by the lowest common denominator (warning: mathmo alert: things do not fall to their lowest common denominator in maths as the LCD of a list of numbers is larger than any of the numbers, they fall to their highest common factor or become divided by their lowest common denominator) is that education becomes nigh impossible. We make a lot of effort with kids when they are aged about 12 to understand the different between mass and force, speed and velocity etc just as we are careful in teaching kinds the difference between strength toughness etc. So commonplace poor usage should not be "just fine". --BozMo talk 18:38, 27 July 2009 (UTC)

If you consider "weight" to be short for "weight on earth", can you accept it as an accurate description of a quality of a tank? Words in context carry all kinds of subtextual meanings. Between the lines of the blankly-stated statistics of the tank we can read the assumption that people only very rarely care what it weighs on other planets. This may be a good thing. 81.131.54.159 (talk) 19:24, 27 July 2009 (UTC)

Accurate, just about. Optimal in terms of opportunity to be more educational, no. --BozMo talk 20:18, 27 July 2009 (UTC)

Like I say, missing an opportunity to educate readers into being engineers and physicists may be a good thing. The world also needs other kinds of people. 81.131.54.159 (talk) 20:25, 27 July 2009 (UTC)

That statement is so absurd, I don't know where to start. You're saying that we should take people who otherwise would be scientists and engineers and...not educate them? What "other kinds of people" did you have in mind? -RunningOnBrains^(talk) 20:34, 27 July 2009 (UTC)

Golfers, taxidermists, and so on, you know. People who quite rightly don't want to distinguish mass from weight. Maybe even some scientists, like botanists. It's desirable that they don't waste their attention on such matters, unless interested. I'm not sure why those people would be looking at the T-90 tank article, but it takes all kinds, is what I'm saying. 81.131.54.159 (talk) 20:52, 27 July 2009 (UTC)

It's also desirable that they don't get frustrated or irritated and go read Britannica. APL (talk) 00:50, 28 July 2009 (UTC)

Not everything has to be an opportunity for education. Stating the weight of a tank in Newtons will have precisely one consequence: Not one single person who actually wants to know the answer will actually understand it - and not one of them would bother to look up "Newton" to find out. Nobody wants to know the mass of the tank either...for any concievable practical purpose, the weight is the thing you need to know.

Just as scientists have to know not to use more precision in stating a result than is actually appropriate - just as we know that it's pointless to talk about having to go out and cut the Chloridoideae (when we are really going to mow the lawn) - we have to understand that there are times when a more approximate take on things like this is actually more appropriate than strictly adhering to the underlying physics. Nobody (and I mean NOBODY) gives a damn what the tank would hypothetically weigh on the moon. Nobody cares that the weight might be 'off' by a few percent because we weighed it at the equator rather than in the tropics. Our bathroom scales measure in pounds and kilos - every measurement of weight throughout all of society EXCEPT a very few physicists and other science nerds is in pounds or kilos. So what? So long as the people who need to know are aware that this "mistake" is made everywhere - we're OK. How many members of the public would understand if you said that you accelerate your car by putting your foot on the brake pedal? How many could tell you why 'velocity' is not the same thing as 'speed'? There is a place for rigor and a place for getting the message across in a comprehensible manner...and this falls firmly into the latter category.

Sure, we have a responsibility to educate people - but pissing them off by making these tiny pedantic statements does precisely the opposite - it completely alienates them. We need to teach them the scientific method - that homeopathic medicines are just water - that evolution is real - that the greenhouse effect is killing our planet - that you can't buy a herbal capsule that'll make "certain parts of your body" larger. Pick your battles - mass versus weight isn't one of them! SteveBaker (talk) 01:00, 28 July 2009 (UTC)

<deindent>
I'll second Steve's point that we should aim to teach the scientific method instead of fixating on scientific terminology. In fact, I would go further and say that a skill even more basic and indispensable that the scientific method is to learn to read and interpret statements in context, rather than try to parse them like automata. Fortunately, we humans are quite good at that! For engineers collaborating on a project, it is critical to get their units right; however, if a lay reader is actually confused by the statement that "tank x weighs y kgs", they have missed out on a basic cognitive and linguistic skill.
If one is talking to an elementary school kid about the T-90 talk, it is much better to tell her that the tank weighs as much as 700 grown men, than to talk about 46.5 tonnes or (worse) 460kN. On the other hand, if I am driving the tank across a bridge, I better know its weight (including that of the men, fuel and arms onboard) and the bridge's load-bearing capacity (along with the applicable margins). In short: context matters, and understanding that is more important that false precision and pedantry. Abecedare (talk) 01:48, 28 July 2009 (UTC)

I agree with the point of view expressed above by Steve and Abecedare. Context does matter. I am a physics teacher but I have no problem with the statement that a tank weighs 46.5 tonnes. I also have no problem with telling my kids to close the fridge to keep the cold from coming out. Some of my colleges pedantically state that the cold does not come out, and that we I should say that the heat is going in. I also have no problem with stating that the station is stationary while the train is moving, eventhough I know that movement is relative. Dauto (talk) 04:44, 28 July 2009 (UTC)

We obviously don't share a common perception of the kind of person who comes to Wikipedia for info on how much a tank weighs or what its mass is. If someone is relying on that to build a bridge they haven't read the disclaimer. The fact your scales aren't in Stone though is a give-away that you live in the land of loose language usage so the consistency I see. --BozMo talk 13:22, 28 July 2009 (UTC)

Is there some honest confusion that you are legitimately worried might occur? I am having a hard time imagining a scenario where a person, curious about the weight and/or mass of a tank would be confused by the articles as they stand.

I can see how this current system might confuse martians, but that works in our favor. It will lead them to believe that our Earth militaries are three times more powerful than they really are. p.s. This is the Reference Desk, changes to wikipedia policy go in the wp:Village Pump. APL (talk) 18:35, 28 July 2009 (UTC)

But the tank page says Weight: xkg. Any guy with a little knowledge of physics will tell you the problem is that weight and Kg are not same. It should be either Newtons, which would not help the average reader, or mass. I dont see where the problem is.--116.71.34.182 (talk) 16:47, 28 July 2009 (UTC)

The real issue here is that reliable sources and tank experts conventionally describe tanks in terms of their weight, not their mass. There appears to be no standardization to account for variation in weight in different locations, and consequently we have no access to the actual mass data for these tanks. Hence the question of which to describe is moot, because only the weight is known. Dcoetzee 19:48, 28 July 2009 (UTC)

There is no problem. We are only pointing out that the word weight can be used as a synonim for mass in coloquial language just as the words 'work' and 'field' have different coloquial meanings than the ones used by physicists. That's why context matters. There is no possibility of confusion since the units make clear wheather one is talking about mass or force. Dauto (talk) 20:08, 28 July 2009 (UTC)

But wouldnt a kid, assuming he is reading the page, be misguided and hence confused between what he learned in class and read here on wikipedia. I was just saying that here on wikipedia, with genius guys like Steve Baker, Runningonbrains (list goes on forever), such a mistake would be like 2+2=5.--116.71.34.182 (talk) 20:07, 28 July 2009 (UTC)

Kids also can learn that words have different meaning depending on the context. Dauto (talk) 20:11, 28 July 2009 (UTC)

Exactly. Training kids to be deliberately confused when someone tells them a weight in kilos is POINTLESS. By all means tell them that in formal scientific writing you have to be really careful not to make this faux pas - but that in normal usage, telling someone the mass or specifying the weight in Newtons is just as bad. If that's the hardest lesson a kid ever has to learn in science class, (s)he's doing pretty good! Words are just words - we can make them do whatever is convenient. Having that underlying understanding is important - but having a tolerance for the daily screwups of well meaning non-scientists is just as vital. SteveBaker (talk) 21:55, 28 July 2009 (UTC)

Knee surgery procedure

Hi,

I'm looking for the name of a operation. In it, the part of the femur where the patella ligament attaches is cut off, and moved to the side or down. I think it starts with an L, and I'm thinking something like "Lithuan". Any ideas? Aaadddaaammm (talk) 11:08, 27 July 2009 (UTC)

Lateral Release [24] Livewireo (talk) 15:29, 27 July 2009 (UTC)

Thanks for the reply, but that's not it. The ligament going down from the patella attaches to the tibia/femur (not sure which) at a certain point. In this operation, the bone is cut, and moved with the ligament still attached. —Preceding unsigned comment added by Aaadddaaammm (talk • contribs) 16:03, 27 July 2009 (UTC)

The only other thing I can think of would be patellar luxation which is pretty common in dogs (and people with ACL damage). It doesnt describe the procedure, but rather the diagnosis. Most knee surgeries can be performed with an arthroscopy without having to perform an open surgery. Livewireo (talk) 20:57, 27 July 2009 (UTC)

Not with an L but it sounds as though you're looking for Osteotomy or more precisely one subform of that. 71.236.26.74 (talk) 01:53, 28 July 2009 (UTC)

Automotive suspension

What are the necessary equations or formulas used for designing the automotive suspension and also to know its load carrying capacity? —Preceding unsigned comment added by 41.220.75.15 (talk) 13:37, 27 July 2009 (UTC)

Wikipedia has many articles about automobile suspension. An independent suspension for one wheel is a Dashpot that comprises a compression spring that can be treated by Hooke's law and a Shock absorber. Cuddlyable3 (talk) 15:16, 27 July 2009 (UTC)

Carrying capacity is generally estimated from materials strength. Because a suspension often has a complex geometry, simple equations are not very helpful, so Computer Aided Design and finite element analysis are used to compute the stresses. Nimur (talk) 15:28, 27 July 2009 (UTC)

The problem with Hooke's law is that it's only an approximation - and also there are many other constraints - the ability to set toe-in and camber angles for example. If there are formulae out there - they aren't simple! It would help us to know what exactly you're trying to do. Calculating the load carrying capacity for a particular vehicle is tricky - it's rarely possible to find out the spring stiffnesses and shock absorber parameters for any particular car. If you're trying to design a suspension to carry a particular load, then that's another matter - but you have lots of other constraints to consider. We need more information about what you're attempting to do. SteveBaker (talk) 17:51, 27 July 2009 (UTC)

Powering a guitar amplifier outside (in DRY conditions, of course)

Hey guys, little bit of a dillema for those good with technology to help me sort out.

Me and my friend are keen musicians, and when we're writing we often head out to a field somewhere (in bright, sunny weather, might I add, so the following need not be waterproof) to play. Usually this just consists of us heading out with our acoustic guitars and a pen and paper, so there's not much need for anything to power us. However, I'm now starting to considering taking a really small amplifier out with us so I can play a bit of electric guitar along with his acoustic. Something like this should do the trick nicely. It's advertised as a 15-watt amplifier, but the speaker is at least 20W so I presume I need something that can power 20W for a few hours.

Now here's the catch. I know I can just buy a simple petrol or diesel generator to power this and anything else I might need with it, but I don't fancy having to keep topping up with petrol everytime I want to out, even though it is only a semi-regular occurance. I was thinking that a solution might be using a solar power supply/generator. My problem is I'm having issues finding anything that would sufficiently power this amp for at least 2-3 hours. Does anyone have any ideas, or alternate solutions, to this issue?

Thanks in advance!

Regards, --—Cyclonenim | Chat  16:37, 27 July 2009 (UTC)

Your best bet is to get a battery-powered travel amplifier. Some of these operate on reasonable batteries (I think my Vox practice amp (one of these) can be powered off 8 D cells six C batteries, though I don't ever really bother). Solar power is going to be a lot of trouble (panels are fragile, heavy, and unreliable). The Vox DAs are not tubes, but I challenge you to tell the difference on a double-blind test! Nimur (talk) 16:45, 27 July 2009 (UTC)

Also, a note about power ratings - there is "power rating" and there is "actual power consumption." These two numbers are not necessarily at all correlated, thanks to the magic of marketing B.S. - and electrical power may have absolutely no meaningful bearing on acoustic power out. Your 15 watt amp has a 20-watt rated speaker, but that means that drawing more than 20 watts will damage it. The actual power consumption depends on a lot of things - steady-state current flow, and also the dynamic power (which will depend on how loudly you play). On some amps, static power draw is so high that there's no penalty to "battery life" if you crank the volume. On other amps, keeping the volume low will dramatically increase your play-time. The Voxes have a power level switch to hard-limit power to various wattages (at very slight expense to tone quality). Nimur (talk) 16:50, 27 July 2009 (UTC)

Heh, I can't believe I'd completely forgot about the possibility of using batteries. This should more than meet my needs. Thanks :) Regards, --—Cyclonenim | Chat  17:05, 27 July 2009 (UTC)

If you seriously want to use a proper power amp - get a car battery and a 12 volt 'inverter' (you can pick them up in most car accessory places). That will give you a regular 110volt power outlet that you can just plug your amp into. How long the battery will last depends on how much power the amp draws - but I think you should be OK for at least a couple of hours. Then you can recharge the battery with a regular car charger. SteveBaker (talk) 17:31, 27 July 2009 (UTC)

I am curious to hear how acoustic plus electric guitars plus a petrol or diesel generator would harmonise. The advertised 15W amplifier appears to be a single-tube Class A design that must consume continuously over 30W plus tube heater. The claim that the speaker can handle 20W says nothing about the amplifier power consumption, but is nice to know. As the OP realizes, a transistor amplifier/speaker combo running from batteries is a better choice for outdoor use. Most economical transister audio amplifiers are Class B designs that consume much less power that Class A. There are a couple of cautions:

• If you like to crank up the volume then valve amplifiers are almost indestructable while transistor amplifiers may be unforgivingly vulnerable and die expensively in a millisecond.
• SteveBaker dazzles us with the wonders of automotive technology but if you plan to run a 12VDC-->110VAC inverter from your own car battery then at the 110VAC output you can draw less than 0.9x 9% of the amp-hour capacity of the battery (and the real amp-hour capacity decreases from the day the battery was put in the car) and then your car won't start. Cuddlyable3 (talk) 22:42, 27 July 2009 (UTC)

According to (for example) [25], a typical car battery will produce 45 amp/hours...which means you can pull maybe 40 amps out of it safely - and if you do, it'll run down in an hour or so...but there is no way your guitar amplifier pulls 40 amps! Picking a guitar amp more or less at random: [26] says that a 2x30Watt Roland amplifier pulls 68 Watts at 110v (yes, I know - it's easy to get confused between audio watts and electrical watts - but these are honest-to-goodness 110volt electrical watts)...that's like one lightbulb... Watts=Volts x Amps - so you'll need about a half an amp of electricity if you have the amplifier turned up full. The inverter isn't anything like 100% efficient - so let's assume you need an entire amp to run your amp! That means you'll be able to play for several days before you have to recharge the car battery...and perhaps we'll quietly ignore Cuddlyable and you could forgo lugging a car battery around and just plugging the inverter into the aux outlet on your car. The aux outlet on my car has a fuse on it that'll blow if you try to pull more than about 2 amps - so if the fuse doesn't blow - the theory says that you're good for maybe 10 hours of hard outdoor rocking before the car won't start! However, your battery might be a crappy one that's about to fail anyway - so I'd want to start the car and run the engine for 10 minutes every few hours just to keep the battery topped up. SteveBaker (talk) 00:36, 28 July 2009 (UTC)

I've got a car, but I'll be honest I'm no good with them mechanically. Does running the engine actually recharge the battery, or does it just kind of keep it level? If it recharges it, I'm more than happy to use this idea of just using my car's battery to power the amp. Do inverters plug straight into the cigarette lighter? If so, I already have one which I can plug mains stuff into. Regards, --—Cyclonenim | Chat  13:19, 28 July 2009 (UTC)

A decent car alternator puts out 200 amps when the car engine is running at between 2000 and 3000 rpm. The battery holds around 45 amp-hours - so expect an utterly dead battery to recharge in about 15 minutes if the engine is revving. However, you're not going to get the battery that dead are you? (If you did, the car wouldn't start). So after a few hours of guitar playing, it's probably going to recharge in 10 minutes at idle - maybe 5 minutes at 2000 to 3000 RPM. The wheels don't have to be moving to recharge the battery - you can leave the car in neutral or park with the engine running and a brick on the gas pedal and that'll work just great. Don't rev the car much above ~3000 rpm because it'll probably overheat if it's not moving (if you do - keep an eye on the temperature gauge!). Some inverters plug into the 12v cigarette lighter socket - but those are somewhat limited on the amount of 110volt current they can produce because it'll blow the fuse in the car. The wires running to the cigarette lighter are usually rather flimsey and not meant to carry a lot of current. Not knowing what capacity of fuse your car has - I can't say whether that'll happen with the guitar amp or not...but my guess is not. The inverter I have can connect via the cigarette lighter outlet and produce 50 watts - which is a bit marginal for a large guitar amp - but more than enough for a practice amp. But my inverter also has another cable you can plug into the back that has heavy-duty cables and two big crocodile clips (just like the ones you find on jumper/booster cables). You can clip those directly onto the car battery (Red to '+', Black to '-'!) - thereby bypassing the fuses in the car and using the nice chunky wires. In that mode, it'll easily produce enough power to run a TV, my laptop and a table lamp for an hour or two when the power drops out during a storm. I have a couple of old truck batteries lying around at home that I keep charged for just that eventuality - truck batteries hold more amp-hours than car batteries. If you can find a cheap marine battery - you could do even better - but your needs are SMALL. SteveBaker (talk) 21:47, 28 July 2009 (UTC)

Just to clarify, if your amp actually draws 68 watts, then assuming a 12-volt battery your inverter-amp combo is going to draw almost 6 amps per hour (assuming the inverter is 100% efficienct), so you'll pull 40 amp-hours out of the battery in about 7 hours. (If I read Steve right, he seems to be assuming a 110-volt car battery.) 4.255.43.12 (talk) 02:01, 29 July 2009 (UTC)

What percentage of its charge does a battery recover during 10 minutes running time in a German retro copy of an undersized British box on wheels ? Cuddlyable3 (talk) 13:30, 28 July 2009 (UTC)

My experience is that you need to either rev the engine or actually drive the car at speed to get actual recharging. A ten minute tour will charge up the battery. Ten minutes idle won't do much. But I haven't done the car party thing much since the later engine management systems have come around. Cuddlyable, are you being mean? Didn't SB get his Mini miniaturized on the highway a few months ago? Or has he got a new one? Franamax (talk) 14:28, 28 July 2009 (UTC)

My wife and I now have two shiney red MINIs ("Captain Scarlet" and "Poppy" - one paid for by the insurance company in exchange for the cold, dead corpse of poor "Chubb-Chubb") - both 2009 models - and I have a rather fetching British Racing Green 1963 Mini called "Toad" (or, more often, "Towed").

But back to the question. Yes, the battery will recharge at idle - although it'll take longer than if the engine is revving a bit higher. However, it's totally unrelated to the wheels rotating - so you can put the car in neutral and place a brick onto the gas pedal and it'll charge the battery faster than idling it...the higher the revs, the faster the battery will recharge. The precise amount of time it takes to recharge the battery depends on the car - some have bigger alternators than others - some have bigger batteries than others - some use more current because they have computers and electronic dashboards and such. On my car, the battery would recharge faster by revving the engine when in neutral than if you drove it round the block a few times because the car has an electric power steering pump that consumes power whenever you turn the steering wheel. However, the battery will recharge pretty quickly in any eventuality...I would certainly just let it idle for 10 minutes every couple of hours. SteveBaker (talk) 21:12, 28 July 2009 (UTC)

How come it's supposed to be slightly difficult and time consuming to do then? Or is that only if the battery runs out entirely? Regards, --—Cyclonenim | Chat  22:46, 28 July 2009 (UTC)

I offer condolences on the loss of poor Chubb-Chubb, taken from you when his odometer was yet in its prime, in the certainty that he abides in the Great Wrecking Yard from which at the last toot-toot all good Minis shall be recycled. Amen. The OP wants to play music and not have to mess with fuel. If SteveBaker gets his way the OP will have to stop playing every few hours and rev up his car for a very uncertain time. I don't see any calculation of how long and how often that has to be. No one has mentioned the limitation of having to be joined by a cable to a car when one wants to play in a field somewhere. I think I last saw the brick-on-accelerator trick in a B-movie about a faked suicide. When the music stops and the OP's car won't start, Steve should offer to send the 46-year old Toad a-fetching home from that field two musicians, an inverter and a 110V mains powered amplifier (none operational). I don't wish to sound mean but a lead-acid car battery has a bad power-to-weight ratio for this application. It is optimised to deliver a brief huge starting current, which is no use here. I understand the enthusiasm to exploit someone else's car as a generating station but it is no improvement on Nimur's fitting recommendation. That was to use a battery-powered amplifier. With the money saved by not repeatedly driving a car to go nowhere and not buying an inverter, cable, connectors etc., buy instead NiCd cells that are lightweight and chargeable anywhere. It's not difficult to work out how long playing time they give, and the OP can play that time to the full and still get home before it rains.Cuddlyable3 (talk) 13:39, 29 July 2009 (UTC)

XTraordinary stuff !!!

Can things which are against the laws of science such as levitation, mind reading, controlling ones mind exist ??? Also does the much hyped spoon bending due to pshycic powers exist???There are just claims but has anyone really witnessed it???gdsrinivas 17:02, 27 July 2009 (UTC) —Preceding unsigned comment added by Gd iitm (talk • contribs)

Everything you've mentioned there can be classified under pseudoscience in the sense that some people proclaim it's all real and true, when really there's absolutely no evidence in favour, and often evidence against, their plausibility. There's nothing about science which says these things won't be possible in the future with the advancement of civilization, but I suspect it's quite a way off and by no means available at the moment. Regards, --—Cyclonenim | Chat  17:07, 27 July 2009 (UTC)

There’s a $1,000,000 prize available to the first person who can show that any paranormal phenomenon like that is real. Although the prize has been available for 13 years now, it has yet to be collected. So either not a single person who can do paranormal stuff like that is bothering to take the time to collect their $1,000,000 for some inexplicable reason, or paranormal stuff like that doesn’t really exist. Red Act (talk) 17:15, 27 July 2009 (UTC)

If they could be shown conclusively to exist - they wouldn't be outside the laws of science because scientists would be revising the laws to include them. The reason they lie outside of those laws is because they don't exist - and have been shown to be fraudulant. Uri Geller (of spoon-bending fame) was conclusively (and very publically) shown to be a total fraud by James Randi in that famous 1973 episode of the Tonight show...and on at least two subsequent occasions. These days, it is REALLY safe to say that all of this paranormal stuff is junk. Treat paranormalists as you would a stage magician - by all means be amused by their capers - but keep a careful and skeptical eye out for the trickery that you KNOW is going on somehow, someway. SteveBaker (talk) 17:27, 27 July 2009 (UTC)

Steve "If they could be shown conclusively to exist - they wouldn't be outside the laws of science because scientists would be revising the laws to include them" is semi profound. We cannot really talk about "against science", just consistency of the scientific world. Of course Science is incredibly consistent (statistically at least) whenever we measure it and even many (?most) religious people regard "miracles=signs" as demonstrations of a wider narrative theme but not to be scientific inconsistencies. There is a little wrinkle there somewhere though. Extremely deep in the scientific assumptions are some dogmas about observation/decision/understanding (one step up from cognito ergo sum) and these include assumptions about the existence of an observer not interfering with whether laws apply. These kinds of dogmas like the assumption we are not a brain in a vat are things scientists to a degree take on trust; although we are completely right to do so they cannot really be completely ironed out. --BozMo talk 17:54, 27 July 2009 (UTC)

While we're taking all the wind out of your sales, it's worth noting that the scientific world has presented bountiful alternatives if you want to know about bizarre, freakish, yet totally true phenomena. I think that mind-altering parasites are, for example, waaaay more "xtraordinary" than some guy who claims he can bend a spoon (even if he could do it with his mind, it's still just a spoon, whoop-dee-doo). --98.217.14.211 (talk) 17:51, 27 July 2009 (UTC)

Scientists have not had a great track record of gracefully accepting as "science" things running contrary to their beliefs. From the early 19th century to the present, establishment science has denied many things that had good evidence: that stones can fall from the sky, evolution, germs as a cause of disease, relativity, and various forms of speech by animals (Washoe the chimpanzee, Alex the parrot) The deniers often go to their graves not accepting scientific revolutions, as described in "The structure of scientific revolutions" by Kuhn. "Science" eventually accepts the new paradigm, even if many working scientists do not. The pseudoscience phenomena mentioned above lack the robustness of the earlier things rejected as pseudoscience, in that they are not reproducible in the labs of skeptics., and a simpler and adequate explanation of a bent spoon is that it was bent by human hands and conjurer's skills, rather than by mysterious psychic abilities. Edison (talk) 19:42, 27 July 2009 (UTC)

In other words: none of the paranormal things the OP refers to have been shown to actually happen beyond reasonable doubt, but this don't mean that they fundamentally cannot happen, or cannot conceivably be scientifically proven and explained at some point in the future. The search for the truth is an ongoing process. 98.234.126.251 (talk) 23:29, 27 July 2009 (UTC)

No - it's more than that - the things our OP refers to have never, not even once, been successfully demonstrated in any kind of rigorous experiment. That's emphatically NOT because scientists don't want to do that. The very existence of the James Randi $1,000,000 prize proves that. If you can do one of these miraculous things - go and show James Randi and he'll give you A MILLION DOLLARS! Why is it that not one single person has done that? The pseudo-science nut-jobs claim that science is denying their abilities - and that's true, and it'll continue to be true unless someone with real, honest-to-goodness magical abilities comes forward, is tested and ISN'T shown to be a charlatan. So far, of the hundreds of people who've tried, every single one of them has proven to be a charlatan when the bright light of scientific testing is shone on them. There is a deep misunderstanding of what scientists are like...we love nothing more than to have some important law or theory overturned - that's the most exciting thing we can imagine - that's the thing that would open up more fruitful areas of study than anything else. But we've tried all of this stuff - we had people with decks of playing cards with circles, squares, triangles and waves on them, we did statistical studies on telepathy and god knows what else right through the 1960's and 70's...and it's all bullshit. Worse even than that is that most laypersons are happy to say "Wow! This guy can bend spoons with his mind!"...and kinda leave it at that. The bigger question is "Where does the energy come from to bend the spoon?" - if it comes from the guy's mind - then how come we can't detect any magnetic field, gravitational or radio waves, no light, no cosmic rays...what could possibly be transmitting that energy? The only answer could be some entirely new force that we have no inkling of whatever. But what are the odds that just one person can produce these forces - that we can't measure in ANY other way than by large chunks of metal being bent? How come nobody through all of history has ever come across any effect that's even remotely like this? How did the guy who bends the spoons learn to do it? If this one, single paranormal thing were true - pretty much all of science would have to be rewritten. What are the odds that all of the things we've successfully designed and built actually works - despite this massive hole in our understanding? It really does seem impossible for anything that major to have escaped our careful searching for a couple of hundred years. So that's what's on one side of the 'scales of truth'. What's on the other side? Well, we have the word of one person who claims to be able to do this - minus all of the professional magicians who claim to be able to reproduce the exact same demonstration using techniques which they openly admit are pure trickery. It hardly balances does it?

By comparison, the other examples you gave were pretty minor.

• Not believing that rocks can fall out of the sky was an error - but when we finally figured out what it was, it hardly required us to change our ideas of how the universe worked at all. We already knew about comets - the idea that something like that could fall out of the sky wasn't really very profound. Not one existing law of nature had to be rewritten. Gravity, light, matter, energy, magnetism, mechanics, chemistry...all of those things were still 100% as they'd been described.
• Evolution filled a hole in our understanding - it didn't overturn ANY well respected existing scientific theory. It pissed off a whole load of religious people - but science simply didn't know how speciation came about - and this explanation filled a hole.
• Germs as a cause of disease - pretty much the same deal. We didn't really know how that stuff worked - this was a great explanation.
• Relativity - is actually the only one of your examples that is a REAL case where our current understanding was actually completely overturned...but it didn't come about because of an EFFECT that science was denying. We knew there was something odd about the nature of the speed of light and we'd been doing experiments for decades to try to understand why we couldn't detect a universal Luminiferous aether. When Einstein's explanation appeared, there was reasonable skepticism...but within months of the experiments that measured the displacement of stars during a solar eclipse, pretty much the entire scientific community changed direction and lined up behind the new theory.

SteveBaker (talk) 00:06, 28 July 2009 (UTC)

There are many cases where the leading lights of the scientific establishment (Lord Kelvin) proclaimed something was impossible a couple of years before someone demonstrated it, such as the "subdivision of the electric light," i.e. the invention of electric lights which culd furnish 16 candlepower or so to illuminate one room efficiently. There were doctors in the late 19th century who still practiced medicine, denying the "germ theory" of disease. Which scientists before evolution was written about acknowledged the "hole" that you say it filled? Wasn't heavier than air flight said to be impossible (Lord Kelvin)? The "leading scientists" denied radio waves and said it was "merely induction" when Preece and Thomas Edison ("etheric force") demonstrated wireless transmission of radio signals[27], until Hertz demonstrated the same phenomena with a mathematical basis in Maxwell's work. See [28] for some examples of the scientific establishment making asses of themselves. Edison (talk) 05:43, 28 July 2009 (UTC)

But almost all of your examples are not holes in fundamental scientific laws and theories - they are engineering matters. Sure, Kelvin believed that it was an impossible engineering problem to produce a 16 cd electric light - but I very much doubt he had basic theory proving that it was impossible. I very much doubt that we'll ever be able to send a living human to Alpha Centauri...but that doesn't mean that it's impossible. The laws of physics permit it - it's just an engineering problem that I don't believe we can overcome. Now, if I'm proven wrong, that's not great for my reputation - but it wouldn't in any way undermine the laws of physics. However, when I say that we'll never travel faster than the speed of light - that's a much more solid claim. We have laws of physics that guarantee that's true. In order to refute THAT claim, we'd have to rewrite huge swaths of solid physical laws and theories...it would be a major thing indeed if that were somehow to be found to be possible. Almost all major advances in science and technology are either exploiting well-known physical principles in a more extreme manner than previously expected (electric lights, heavier-than-air flight) - or they are filling in gaps in our scientific theories (evolution, radio waves, germ theory). Not one of the things you describe changed any pre-existing law or theory of nature...the number of times THAT has happened over the 150 to 200 years since we started following "the scientific method" you can count on the fingers of one hand...relativity is the only one I can think of right now...and that isn't something that affects 'normal' day to day life - it found an error in an existing law that only affects the most extreme condititions - it doesn't make any difference to how most simple day-to-day events are interpreted. To demonstrate relativity actually doing something requires some pretty extreme experimentation. In Einsteins' day - the only way to prove it was to measure the position of a star during a total solar eclipse! Levitation, mind reading, spoon-bending-with-the-force-of-thought are all things that would require us to rewrite fundamental laws/theories - in regions where they have been exceedingly well tested over 150 years. So the likelyhood that they are true is essentially zero. SteveBaker (talk) 13:11, 28 July 2009 (UTC)

When a scientist makes extraordinary claims, others often treat them with skepticism until irrefutable proof is presented. That attitude is perfectly fine, and doesn't mean every single theory that the scientific community doesn't believe in must be true. --Bowlhover (talk) 08:45, 28 July 2009 (UTC)

Agreed. "They said that about Einstein/Newton/Galileo too!" is a ridiculously common (perhaps *the* most common) pseudoscientist/crank rebuttal to sceptics. Doesn't make any sense whatsoever, if you think about it for a couple of minutes. Bonus points if they come out with something really fuckwitted, like "IT WAS BECAUSE OF PEOPLE LIKE THAT COPERNICUS WAS BURNED AT THE STAKE!" (and mean it). --Kurt Shaped Box (talk) 09:18, 28 July 2009 (UTC)

"...but they also laughed at Bozo the clown" is the standard retort. --Stephan Schulz (talk) 13:26, 28 July 2009 (UTC)

Edison, as a scientist my self I don't really give a crap what scientists "say". That is appealing to authority, as opposed to rational, free thinking which a scientist should be doing. Every scientist on the planet has an opinion on something, and that is fine as bias is hard-wired into us. As long as they don't show bias in their scientific method when conducting research, then I will respect their results. --Mark PEA (talk) 09:51, 28 July 2009 (UTC)

One way in which the scientific establishment mistakenly rejects new discoveries is by saying "Oh, this is just a rediscovery of such and such. Nothing new here." Pre-Hertz demonstrations of radio wave transmission and reception by Preece and Edison were dismissed as "mere induction." Radio might have been in general use several years earlier if the demonstrations had been accepted as a new phenomenon. Technicians and inventors often work years ahead of "scientists." If someone next month demonstrated some type of cold fusion, many would dismiss it without close analysis as a mere replication of the Pons-Fleischman experiment. Demonstrations of animal communication by Washoe (chimpanzee) and other chimps, or by Alex (parrot) are false dismissed as being a recreation of Clever Hans, the horse who just watched his master for cues, or as mere Operant conditioning. In the face of "irrefutable proof" scientists may redefine the terms. If science said that only humans use tools, and chimps are observed carrying around rocks to break open nuts, then rock use is defined out of being tool use, and it must be "make and use tools." If chimps are then seen fashioning sharpened sticks to spear bush babies in their hideyholes, the definition of tool use must be redefined again. Granted the "not invented here" attitude commonly applies to engineering devlopments or inventions. When Morse demonstrated he could instantly send telegraph messages between remote parts of the U.S. capitol building, politicians thought he was a madman, and said why not just send a messenger, instead of all that cumbersome apparatus, even though Morse had explained it was just as fast for extreme distances. When Chester Carlson demonstrated the Xerox it took many years to convince the business world that instant copying was useful to businesses. This was in 1948 ("They all laughed," by Ira Flatow, Harper Collins, 1992, chapter 11): "An interesting gadget, but no future." Tesla in 1898 demonstrated a radio steered torpedo, but no one could see the point of it, since they never had used one in a war. Another way in which mainstream science fails is by assuming something is impossible by analyzing it with the wrong model. The claims that electric lighting could not be "subdivided" were mathematically supported by leading physicists, but they assumed the light of 16 candlepower would be a grossly inefficient and impractical little bitty arc light, and did not allow for it being an incandescent light. We cannot send people to other star systems with rockets, so it is impossible. Physics says it would be easy if you could maintain a 1 G thrust the whole way, but we know of no present means of achieving that. A lab can also do an intentional nonreplication of some new phenomenon, to discredit the discoverer, and attribute the phenomenon to uncontrolled experimental confounds, thus delaying its general acceptance. Going way back to Newton writing that a prism could split sunlight into its spectral components, one of his competitors wrote that he could not replicate it, and that Newton probably just reflected the light off one face of the prism and the color was likely stained by dirt on the surface. The Edison effect, or one way flow of electricity from a filament to a charged plate, was denounced as just a stream of carbon particle breaking off the filament and carrying charge, delaying by years the "invention" of the vacuum tube diode and the advent of electronics. In the case of pooh-pooing by trivializing alternative explanations of a new discovery, the normal process of science should make things right over time, as others are able to replicate it or "reinvent" it, while carefully controlling the claimed confound. The cycle of "Discovery-alternative explanations-elimination of alternative explanations by experiments with new controls" is a healthy one for science, except when the initial poo-pooing by authority figures shuts down a promising field for many years ("Sorry, we will not fund your harebrained research, because Professor Authorityfigure has poo-pooed it. Therefore we will not waste our time reading your proposal.")- Let it be said, I never filed a research proposal for a grant that was not approved, so I do not speak from hard feelings. Edison (talk) 15:58, 28 July 2009 (UTC)

Your examples are not scientific errors - they are errors of belief at the engineering level. Producing more and more of those example is very easy indeed - I could quote the guy who tried to solve the problems of determining one's latitude precisely in a sailing ship by killing a dog at exactly noon at the naval base and seeing when it's identical twin (which had been placed aboard ship) woke up and whined! But it doesn't help answer the OP's question in the slightest. Sure Tesla demonstrated a radio steered torpedo - but nobody previously said that science precluded that due to some fundamental law of nature. That the torpedo actually worked was a demonstration that Tesla had a better command of TECHNOLOGY than his detractors. But it didn't cause a single scientific law or theory to require modification in the slightest bit. If he'd found a way to power it with a perpetual motion machine - or control it via "thought waves" instead of radio - or make it travel faster than light...THEN he'd have produced a scientific breakthrough rather than a mere engineering marvel. That's not to detract from the cleverness Tesla provided - it's just that you're answering an entirely different question...one that I doubt anyone here is denying. Our OP is postulating things that - if true - would require a profound revisiting of most of what we think we know about how the universe works. A radio controlled torpedo is no more remarkable (in principle) than the next generation of iPhone...clever technology - but no new science whatever. SteveBaker (talk) 21:01, 28 July 2009 (UTC)

Mind reading, then is also just an engineering problem. Scientists already can determine an amazing variety of things about what someone is thinking by functional MRI. The denial of the possibility of subdivision of the electric light was not presented as an engineering statement but as a scientific one. I think you are making a false distinction between "science" and "engineering" (or technology). It would It should be a clearly disprovable assertion, or it is not science. The source should be a refereed scientific journal, a college level science textbook, or a distinguished scientist of the stature of Lord Kelvin, such as a Nobel laureate. I suspect that such listings are rare, because the writer would know he might be held up to ridicule if the stement were refuted. Examples might be like "Cold fusion is impossible," "Visits from or radio transmission from extraterrestrials are impossible." Would those be engineering or science statements? Edison (talk) 22:05, 28 July 2009 (UTC)

How did we get this far without a link to the relevant xkcd comic? — DanielLC 05:50, 29 July 2009 (UTC)

Resources for cultivated plant identification?

Hi all - I'm a Seattle resident looking to learn more about identifying plants, particularly flowering plants. I already found the National Audubon Society Field Guide to North American Wildflowers: Western Region and the Peterson Field Guide to Pacific States Wildflowers, but neither of these tells me anything about cultivated flowers. Most of the books I can find on cultivated plants are written for gardeners, which I am not. Any tips? Dcoetzee 18:29, 27 July 2009 (UTC)

Are you trying to source a plant for a situation or identify a plant you have found? --BozMo talk 18:45, 27 July 2009 (UTC)

I photograph plants in gardens and botanical gardens and I'd like to identify them (either at the time of photographing, or later based on the photograph). Sometimes they are labelled, but often they are not. I also have a personal interest in plant identification. Dcoetzee 20:17, 27 July 2009 (UTC)

Hi Derrick, I use a combination of two sites for identification of plants; one is the Wild About Britain identification forum and the other is the UBC (University of British Columbia) Botanical Garden forum. Between the two of them, I usually manage to get a definite genus and often a species match. Obviously, unless you plan to be travelling across the pond, the first link is no good to you, but the UBC forums are international and should hopefully be able to satisfy most of your needs. There is a good level of activity there, so it usually doesn't take too long to have queries answered. Hope that helps. Maedin\^talk 20:36, 27 July 2009 (UTC)

I realise I wouldn't have much trouble getting a hold of people who can help me identify things, but I really want to learn to identify things myself, so that I can make quick identifications in the field and help others identify things. These people must have learned somewhere, right? Dcoetzee 20:49, 27 July 2009 (UTC)

If you aren't going to undertake formal education or training, then I presume that most people learn by experience. Just by using the forums I have learned more about plants, hopefully in a manner that will stick with me. Other than that, I don't know what to suggest, apart from approaching a gardener or a botanist and requesting introductory lessons or guidance. You could also try to approach the families of plants in a logical manner and begin by studying overall characteristics, before narrowing down to genus or species. That would allow you to use your identification books more effectively. Maedin\^talk 20:57, 27 July 2009 (UTC)

I wouldn't mind formal education or training, I just don't know what background is pertinent. I'm pretty sure I need some basic anatomy and taxonomy, not so sure about genetics and genomics or cell biology or microbial plants. I'll be attending UC Berkeley but they don't appear to have specific classes in plant anatomy or identification (see plant biology classes). In any case I've mailed the department's advisor and I'll see if they can help with this. Dcoetzee 21:21, 27 July 2009 (UTC)

I think you are looking more for something like Botany and Horticulture. This link says Berkeley lumps that in with plant biology [29]. Maybe you could do something in the extracurricular area. This looks promising [30]. From your catalog the plant morphology classes have a different focus, but may still get you the information you seek C107 + C107L. This book is quite old, but may still be a good place to start. [31] There seem to be various versions about. [32] I'm not sure whether the online download is the same as the full 6 volume book. This seems to indicate only 3 of the 6 volumes can be downloaded if I'm reading it right [33]. See if your library has a copy for comparison. This site may also be a useful resource [34]. This is a lot to check, but may help [35] Hope this helps. 71.236.26.74 (talk) 01:21, 28 July 2009 (UTC)

Thank you for your help! Dcoetzee 19:57, 28 July 2009 (UTC)

A good first step is to learn the characteristics of at least the common plant families. You could start with a website like [36]. It is very satisfying to look at a plant and be able to tell, without looking anything up, what family it belongs to. The links at the bottom of that site are also useful - especially the bottom one on botanical Latin, try looking up some names that you see in plant labels in botanic gardens - they are a lot easier to remember if you know what they mean. Finally, if you get into some of the more technical literature some sort of glossary would be very useful, as the description of plants - phytography - is a whole new language. I'm sure good online ones exist but a quick and dirty google search only brought up books such as this one [37]. 84.12.138.49 (talk) 21:45, 29 July 2009 (UTC)

P.S. One book I just found seems just about perfect for what you want. It covers North temperate regions (I assume this includes Seattle), concentrates on flowering plants, and includes cultivated plants. —Preceding unsigned comment added by 84.12.138.49 (talk) 21:51, 29 July 2009 (UTC)

which vein is involved in echymosis over mastoid process in battles sign

which vein is involved in echymosis over mastoid process in battles sign —Preceding unsigned comment added by Ashupg (talk • contribs) 19:01, 27 July 2009 (UTC)

Is "echymosis" a typo of ecchymosis? Dogposter (talk) 20:55, 27 July 2009 (UTC)

We do have an article on Battle's sign, but it unfortunately doesn't say which vein is involved. Red Act (talk) 21:00, 27 July 2009 (UTC)

According to this, Battle’s sign results from the extravasation of blood along the path of the posterior auricular artery. Red Act (talk) 21:22, 27 July 2009 (UTC)

I have updated the Battle's sign article to include this information. Red Act (talk) 21:53, 27 July 2009 (UTC)

Butterfly effect - Changing the evolution of species with time travel

There have been lots of instances of the Butterfly effect in films and TV programmes (including the Simpsons) where somebody has travelled back in time, has killed some plant or animal, and has significantly changed the evolution of species. I wonder if there has been any serious scientific work done on the issue of how much impact the killing of a single individual can realistically have on the evolution of the species, and of other species. I would imagine that if all of the evironmental pressures remained the same, then the killing of an individual would actually have a minimal effect on the evolution of a species, because any mutation that individual had would no doubt be acquired my another individual soon enough - but soon, enough every individual would be slightly different. Perhaps treading on a rodent 100 million years ago might mean that Barack Obama would be Susan Stout instead, but would not make him a 20 foot lizard. But, has there been any serious research or publications that are relevant to this. Would really appreciate any help. Thanks Squashed Star (talk) 19:55, 27 July 2009 (UTC)

There are too many variables and hypotheticals to take into account. It might have no effect, it might have a large effect. Individuals sometimes don't matter, individuals sometimes do matter. I'm not sure there is any very scientific way to approach the question, given the magnitude of the uncertainties involved. --98.217.14.211 (talk) 20:14, 27 July 2009 (UTC)

It's not hard to imagine a situation in which killing an individual could have a significant impact. If the population in a region has been temporarily reduced to a level at which it can barely sustain itself, the death of an individual could have a dramatic effect. And just as an individual human touches many people in their lives, an animal modifies the behaviour of virtually every other animal it comes into contact with, and it's difficult to predict the long term effect of this. Dcoetzee 20:20, 27 July 2009 (UTC)

But if a population is big enough, and "real, text book evolution" is taking place, killing one individual should have no effect. That one that you kill can't be a special one, because evolution does not work by macro-mutants. The pressures are still the same so at least a similar solution should be found. Aaadddaaammm (talk) 20:48, 27 July 2009 (UTC)

Yeah, but consider this hypothetical scenario: you kill a prey animal which, if it had lived, would have distracted a group of predators from pursuing a harder-to-catch prey, who would have led the predator to its nest and caused its entire colony to be eradicated, which happens to be the only one remaining in the region. The point of the butterfly effect is that small things can lead to larger effects in a chain reaction. Dcoetzee 20:57, 27 July 2009 (UTC)

"If a population is big enough" is certainly a subset of the original question. However, there have been times in researchable history where populations dwindled to a few survivors only to roar back into prominence some time later. The most recent article was about wild cats in Africa, if I recall. In such a case, going back and "selecting against" one of the few surviving members could have a dramatic effect on the future size (or extinction) of the population. --66.195.232.121 (talk) 21:05, 27 July 2009 (UTC)

The main problem with research in this field is that, absent time travel devices, and absent access to parallel, almost-identical universes in which alternate events occur, there is no control available so we can compare what would have happened otherwise. Because of this, it's all speculation, so it's OK to stick with Homer Simpson. Tempshill (talk) 21:16, 27 July 2009 (UTC)

Jacques Hadamard just thinking aloud about the butterfly effect has had repercussions in literature, chaos theory and ripples of the event persist over a century later here in Wikipedia. The consequences of a hypothesis that travelling back in time is possible (if true) would be at least as great a perturbation to the way things are, and to actually do anything when one arrives in the past would cause an even greater upset. The OP's question, which I cannot answer, boils down to whether the upset would decay over time and whether the residual effect today would bother us. I think we could tolerate a US president named Susan. Cuddlyable3 (talk) 21:54, 27 July 2009 (UTC)

The very idea of 'time travel' is patently preposterous and denotes a serious misunderstanding of the nature of things. So anything predicated on 'travelling back through time' cannot be spoken of sensibly. Napoleon Dynamite got it right when the uncle tried to return to his high school days and just ended up electrocuting his testicles. Vranak (talk) 22:21, 27 July 2009 (UTC)

That's a rather rigid response. It's true that at our current level of scientific understanding and technology level we cannot conceive a realistic method of time travel, however that's not to say we couldn't at some point in the future do so. Exxolon (talk) 22:44, 27 July 2009 (UTC)

The trouble with that kind of thinking is that it prevents you from ruling out anything whatever - this makes doing science impossible. You'd be unable to do even the most mundane activities or come to the most basic conclusions without having to worry that some future development would utterly overturn it. We have to say that occam's razor says "NO!" to time travel until/unless some spectacular new science comes along. Meanwhile - the only rational and sane way to proceed is to make the strong assumption that it cannot exist. SteveBaker (talk) 23:29, 27 July 2009 (UTC)

Well, there are different levels of "ruling out". If someone walks up to you on the street and says he's from the future, doesn't have any 2009 money to make stock picks with, but if you'll give him yours he'll make you rich — yes, we can rule that out. On the other hand, if a respectable physicist wants to study a theory that might imply time travel in principle — if it looks vaguely plausible to other experts, fund it. You never know. --Trovatore (talk) 01:55, 29 July 2009 (UTC)

Certainly the butterfly effect exists. Changing any small thing today could potentially have a deep and profound effect on what happens in the future. That has nothing to do with time travel - it's more a function of Chaos theory. Chaotic systems (which many systems here on Earth are) can amplify small changes into big changes. Of course, there is no way to plan for that - and equally, no way to know whether some other small change wouldn't cancel out some of the effects of the first one. But there are plenty of cases in history where a very small change would have made a lot of difference. On 28 June 1914, three police officers got into the wrong car by mistake. Had they gotten into the right car - neither you nor I nor anyone else here would exist! Because...as a result of them getting into the wrong car, Archduke Franz Ferdinand didn't have sufficient protection in some parade or other - so he got assassinated - which started the first World War. Most of us are either 'baby-boomers' or descendants of baby boomers - the baby boom only happened because of soldiers returning from the second world war - which would undoubtedly have played out very differently if the first world war hadn't happened - our parents would have met different spouses - our genetic makeup would be different - and so would be that of Jimmy Wales - so no Wikipedia. It's pretty safe to say that everyone reading this thread would not exist...or at least not precisely as we are now. So three cops get into the RIGHT car - and all of us pop out of existance! But if three cops in a sleepy little village in (say) Argentina had gotten into a different car than they actually did - would the effect have been so profound? It's hard to say. Chaos theory says that the consequences could easily be just as severe - but it's really impossible to know specifically. I suspect that ANY change 100 years ago would produce effects that would be just as dramatic. SteveBaker (talk) 23:29, 27 July 2009 (UTC)

Sure, that's one extreme view of the butterfly effect. The other is that events take place more like a river flowing downstream. If you throw a rock into the water at 8:00AM rather than 9:00AM, the individual water molecules disrupted by your rock throwing will all be different; but the ripples look about the same, and from the viewpoint of a bystander along the river, it doesn't make a shade of difference. Anyway, to go back to the OP's question, you will notice that beyond this kind of speculation, nobody has cited any "serious scientific work" on the butterfly effect, let alone your related evolution question, which is what you had asked about. Tempshill (talk) 00:09, 28 July 2009 (UTC)

But who's a bystander in the History of Planet Earth? If cats instead of primates occupied our spot on the food-chain, I suppose the rest of the solar system would be pretty much the same. But it would make a big difference to the hypothetical time traveler returning from the Cretaceous to modern day after stepping on a butterfly. APL (talk) 00:45, 28 July 2009 (UTC)

@Tempshill: This is the RD - we don't have to cite serious scientific work - we have merely to link to appropriate articles - which in turn cite the serious scientific work. Hence, I linked to Chaos theory - which has 50+ references, 50 more citations in the scientific literature and about a dozen other useful web links for our OP to follow. Chaos theory is a solid mathematical field - it shows that the kinds of systems that have a sensitive dependence on initial conditions do not settle down after a small disturbance - instead, they magnify it. The mathematics also shows how to identify such chaotic systems - and indeed the entire field was discovered as a result of weather prediction studies in which it was discovered that the earth's weather conditions are indeed 'Chaotic' in the mathematical sense of the word.

If the weather were the only chaotic system on earth, we'd still have a situation where a tiny change sufficiently long ago would cause huge changes down the line...but it's not. Chaotic systems are everywhere. Our entire society is one gigantic chaos engine. One kid films himself playing with a toy light sabre in his garage - and a few weeks later, half the people on the planet have seen the video. Monty Python do one sketch that makes 'Watney's Red Barrel' beer seem un-cool, the company that makes it goes bust within a year - the entire British brewing industry flips over to "Real Ale" - pubs become more family friendly and the whole dynamic of how "guys" go off down to the pub leaving their wives behind is erased in just a few years. One guy comes up with the concept of a "wiki-wiki-web" and six years later almost all of human knowledge is encapsulated in one - millions of people rely on it.

Animal populations undergo boom/bust cycles for reasons that are far too obscure to ever decypher - because they are chaotic. Financial markets...chaos. Traffic speeds down a freeway...chaos. It's everywhere. If you look at the underlying mathematics - it's plain to see that the big picture is NOT one where these kinds of ripples 'die down' over time - they magnify enormously from small beginnings.

The problem is that we never really know what would have happened if any particular ripple hadn't started - all we know is that there are a tens of thousands of examples where the tiniest of nudges changed everything that followed.

SteveBaker (talk) 01:21, 28 July 2009 (UTC)

It seems unlikely that Barack Obama could become a murdered female caucasian graduate student in psychology, born long before he was, for whom a library was named: [38]. Edison (talk) 05:26, 28 July 2009 (UTC)

It's difficult to frame this question in a way that even makes sense. In order to say that some event had an effect you have to suppose that there was an alternative (if it had not happened then the future would have been different). But in order to attribute the whole future course of history to that fateful moment, you have to suppose that everything after that was a necessary consequence of what came before. That rarely makes sense. In the case of the "butterfly effect" you could argue that the butterfly had the choice to not flap its wings but the air didn't have any choice in how to respond (though I'm not sure I believe that—they're both quantum systems of similar complexity), but there are other butterflies, and other animals, and people, and how do you distribute the blame? It's not a linear system. And there's no way you can do that kind of thing in the case of an assassination. If the assassin could have not pulled the trigger then everyone else could have chosen to not react in the way that they did.

Also, though you can formalize what it means for a system to be chaotic, I don't think there was ever any mathematics or physics behind the butterfly effect specifically, i.e. the claimed influence of butterfly flight on weather patterns. The fact that the weather is hard to predict doesn't imply that it's unstable under perturbations of that particular form, and I'm not sure it actually is. -- BenRG (talk) 16:19, 28 July 2009 (UTC)

What are these creatures/objects?

Hi, everyone, as I was uploading images of South Korea, especially Andong areas in the east southern part of Korean peninsula, I found them, but don't know what they are. Thus, the photo names are incorrectly named because of my ignorance, but I want to fix them. The photographer is a foreigner and inactive for a while, so I stumble here to seek a help from those who are knowledge of biology...If you could answer my questions, I would appreciate your input. Thanks.--Caspian blue 21:18, 27 July 2009 (UTC)

• 
  1. What is the name of the bug?
• 
  2. What function do these rocks have?
• 
  3. Mushroom?
• 
  4. Mushroom?
• 
  5. What mushroom species?
• 
  6. Bird nest?
• 
  7. What berry?
• 
  8. Pumpkin or gourd?

1. Probably a swallowtail butterfly larva. Check Old World Swallowtail which is found in Korea. Here is a taxonomy sheet with pictures which may be helpful [39] Sifaka ^talk 21:39, 27 July 2009 (UTC)

2. This is a kind of ancient burial called Dolmen. In Korea, they call it 고인돌. Elkellogg54 (talk) 21:46, 27 July 2009 (UTC)

also see Megalith#Asian_megaliths83.100.250.79 (talk) 23:54, 27 July 2009 (UTC)

3 Likely a mushroom (pretty sure it's not a lichen), probably the same species as #4. Sifaka ^talk 21:50, 27 July 2009 (UTC)

4 Definitely a mushroom of the bracket variety. These are going to be hard to identify by look and geographic location alone, but the family is probably Polyporaceae. Sifaka ^talk 21:50, 27 July 2009 (UTC)

Maybe Genus trametes [40]? Sjschen (talk) 18:52, 28 July 2009 (UTC)

5 I'm not sure it can be definitely IDed without a shot of the underside and a spore print. Those flecks on the cap make me think genus Amanita, but that's a real tenuous guess. Sifaka ^talk 22:05, 27 July 2009 (UTC)

6 Almost certainly a bird nest. No guesses yet as to what kind of bird. Sifaka ^talk 22:12, 27 July 2009 (UTC)

7 Maybe a cherry? Sifaka ^talk 22:12, 27 July 2009 (UTC)

I'm almost certain it's some kind of crabapple, if you look at the base of the fruit you'll see where the flower used to be. Sjschen (talk) 18:52, 28 July 2009 (UTC)

8 (Almost) definitely a pumpkin. FWiW 98.234.126.251 (talk) 23:09, 27 July 2009 (UTC)

But it really really looks like a gourd[41][42]. I'm also not sure pumpkins are grown on trellises? Sjschen (talk) 19:28, 28 July 2009 (UTC)

Thank you for the answers everyone. I really appreciate your help. --Caspian blue 03:31, 29 July 2009 (UTC)

day and night on gas giants

Do Saturn, Uranus, and Neptune have daytime or it is always nighttime? The differ between gas ginats and rocky planets is thye rotate faster on axis and the day/night is less than 18 hours. And they have so little sunlight penetrating through if they have a solid surface, then they would be always nighttime. —Preceding unsigned comment added by 69.228.145.50 (talk) 22:16, 27 July 2009 (UTC)

Daytime and nighttime isn't caused by penetration of light through the planet, as I guess you've noticed by observing our own planet. The speed of rotation doesn't effect the existence of daytime and nighttime, it only shortens or extends the respective durations of each. So yes, they would have a daytime (the side facing the sun) and a nighttime (the side being blocked by the other). I struggled reading your question, so if I misunderstood please do clarify. Regards, --—Cyclonenim | Chat  22:46, 27 July 2009 (UTC)

Well, there wouldn't be much light coming from the sun right down at the "surface" (to the extent that gas giants have something like a "surface" under all that metallic hydrogen and stuff)...but there would be some teeny-tiny number of photons making it down that deep - and there would be more of those on the side of the planet facing the sun than on the side pointing away from it - so technically, even down on the surface of the rocky core, there would be "day" and "night". But to human eyes, it would pretty much look black all the time. But higher up in the atmosphere day/night cycles are just like on earth. The question of how long day and night lasts is a little tricky since different parts of the atmosphere are rotating at different rates. SteveBaker (talk) 23:04, 27 July 2009 (UTC)

OKay, I got the point.--69.228.145.50 (talk) 23:42, 27 July 2009 (UTC)

Shotgun backfiring

What is the sequence of events involved in a semi-auto (not pump-action or double-barrel) shotgun backfiring? I know that the breech gets forced open somehow or other, but how exactly does it happen? Also, if a shotgun backfires, what kinds of eye/face injuries can you expect? Would those injuries be readily reparable by surgical means? (No, I'm not looking for medical advice, I need to know these things for a short story that I'm writing.) Thanks in advance! 98.234.126.251 (talk) 23:18, 27 July 2009 (UTC)

As far as the second part of your question goes, it's hard to say -- much depends on how close to your face the weapon is when it backfires, and how the backfire actually takes place. In a worst case scenario, you could undoubtedly be killed; people have ended up death from firing blanks, for example. You could definitely lose an eye or get badly scarred. Cosmetic surgery is pretty good, these days, so it's possible that the damage could be repaired, but it's impossible to generalize. It all depends on how the force from the backfire is directed, how close the shooter's face is to the backfire, what kind of a shell the shooter is firing, the model of the weapon, etc.

Suffice to say that you can get hurt really badly, but if you don't get hurt too badly, they can patch you up well enough to keep you from being horribly disfigured, even if there's a bit of scarring. -- Captain Disdain (talk) 09:08, 29 July 2009 (UTC)

July 28

gaps

Is there a list of gaps in knowledge such as the first seconds of the big bang or in the trail of evolution, etc. -- Taxa (talk) 00:37, 28 July 2009 (UTC)

Yes. List of unsolved problems. --Tango (talk) 00:58, 28 July 2009 (UTC)

What pH ranges denature melanin?

It's probably an equilibrium reaction so pHs that would cause dynamic equilibriums of a few power of 10 percentages like 99/90/10/1/0.1% denatured etc. or a formula to find some values myself would be sufficient. Sagittarian Milky Way (talk) 00:46, 28 July 2009 (UTC)

By definition, denature reactions are not reversable, so it would not be an equilibrium situation. Denaturing destroys the Tertiary structure of the protein in such a way that it would be impossible to get it back by simply returning to prior conditions. You don't get a liquid egg back just by cooling it down! Otherwise, I don't have the answer to your main question, but I wanted to make sure you get the terminology right. --Jayron32 04:06, 28 July 2009 (UTC)

Our denaturation (biochemistry) article disagrees, noting (with examples) that the process may be reversible. However, still, I don't know the answer to the original question, except that it also may depend on how severely and reversibly you want to do it. DMacks (talk) 04:33, 28 July 2009 (UTC)

As DMacks notes, there are quite a few proteins which will spontaneously refold under appropriate conditions. (They're almost entirely all small, single-domain proteins, and even among that class they're not a majority — but there are definitely a few.) Perhaps a bit more important to this question, however, is that melanins are not proteins. They're small molecules derived from tyrosine, so the refolding issues associated with protein re/denaturation don't really apply here.

Unfortunately, I don't have a good answer for the original question; it's out of my field. From a bit of Googling, it appears that the extended structure of melanin is still something of an open question — apparently individual melanin molecules combine into larger complexes in vivo, but it is undecided whether these are small oligomers (tetramers), large networks, or some combination thereof. Moreover, it also appears that 'melanin' is actually a mixture of a number of chemically-related compounds, so any measurements of physico-chemical properties ought to be taken with a grain of salt. TenOfAllTrades(talk) 13:01, 28 July 2009 (UTC)

Super fast raster scan

An experiment I am conducting requires a display which updates at least fifty times the frame rate of a normal monitor, could I modify a CRT television to do this, or could LED's or lasers achieve this speed? If made a CRT with multiple beams could this do the trick? Also is their any way to electronically create a scanning transparent "hole" area that lets light through from ALL angles, equivalent to the mechanical Nipcow disc-could an LCD do this or is it more complicated? Trevor Loughlin (talk) 02:47, 28 July 2009 (UTC)

What possible purpose could there be? "Displays" are there for someone or something to see. No human or other earthly animal could derive more info from a display that refreshed that rapidly than from a more normal one. No, you could not "modify a CRT television to do this." You could spend a huge amount of money to have such a pointless device engineered from scratch. Edison (talk) 05:20, 28 July 2009 (UTC)

Come, now, his experiment might have some angle you haven't thought of. Maybe he wants to film a scene of himself singing a song, with a high-speed camera capturing this at 2000 fps, while this experimental monitor is in the background playing back a scene from Apocalypse Now at 2000 fps, so when it's played back as a 60 fps video, you're watching him react in really slow motion to Captain Willard dancing in front of the mirror. Or he's making a monitor for the benefit of houseflies. Tempshill (talk) 05:56, 28 July 2009 (UTC)

One could modify just the vertical timebase (and its synchronising) of a CRT TV monitor to run faster and deflect less. The flyback speed cannot easily be increased so one might get about 8 to 10 usable lines updated at, say, 1500 Hz. That is a very shallow "widescreen" raster. Phosphor decay time would limit the speed of updating a picture element from white to black. I don't see any use for an LCD on a Nipkow disk. There are shine-through LCD frame display panels for use on overhead projectors but their rasters are for standard data formats. Cuddlyable3 (talk) 10:17, 28 July 2009 (UTC)

This is one of those areas that I've personally researched. In a project I was working on, we needed a 180Hz refresh rate display system...just three times the speed of a typical computer display.

You really can't do that to a CRT. What you are attempting is a research project in it's own right. The project that tried to drive a CRT at 180Hz failed for all sorts of complicated reasons - we never got much more than 120Hz. Getting sufficiently powerful coils with the right inductance to run at three times the usual rate was "non-trivial". Your idea of putting 50 beams into one CRT in order to get around that problem (aside from being an exceedingly tricky problem for making the device and aligning all of those beams to the shadow-mask) wouldn't work because the persistance of the phosphors. When you hit the phosphor with an electron beam to make it glow, it takes around 1/150th second for the light from the phosphor to drop back to somewhere near zero - which really limits you to around 150 frames per second - nowhere near the 3,000 frames per second you're looking for!

LCD and plasma and LED and OLED displays all have the same problem. I don't think the tiny mirrors in a DLP projector could move that fast either...and that means that NONE of the 'conventional' display approaches used in consumer or even professional display products are going to come within a factor of 10 of what you claim to need.

I think you're going to need a laser display - but even then, it's an insanely difficult problem.

Scanning a laser display is typically done with mirrors that are moved around using piezo-electric crystals...but the momentum of the mirror and the force needed to accelerate it would be spectacular. That drives you to using a smaller, lighter mirror - but then the actuators that drive it have to be small - and you end up in a spiral of smaller mirror needing smaller actuators that have less power so you need an even smaller, lighter mirror...So I don't think you can move even a tiny mirror fast enough to do that.

Another approach is to aim the laser at a spinning cylinder with mirrors mounted onto it...let's say you make a 10 sided cylinder with mirrored facets...you'd have to machine it out of some very strong metal and polish it to make the mirrors. Point the laser at it and spin the cylinder and the laser will be reflected from one rotating facet after another. This will cause the laser to scan sideways 10 times for each revolution of the cylinder - just like the line-scan on a TV set. Use one cylinder for the horizontal line-scan and another spinning much more slowly for the vertical scan. The problem is that to get a 3000Hz refresh rate with 10 sided mirror cylinders, the vertical scan cylinder has to rotate at 300 revolutions per second and the horizonal one by 300 multiplied by the number of scanlines you need. If you have 500 scanlines - you need your line-scan cylinder to spin at 150,000 revolutions per second!! There isn't anything I could imagine that wouldn't disintegrate if you did that - and machining that cylinder to the precision needed to avoid vibrations would be a major engineering feat!

In the distant past, people scanned images using a tank of mercury and an acoustic stimulator that produced ripples in the liquid that travelled outwards. Aiming the laser at the liquid surface produced a scanning effect as the laser reflected off of each wave in turn. This works pretty well - although the scanning is very non-linear and you have to electronically pre-process your video stream to counteract that. In order to get 150,000 scanlines per second, you'd need to use a 150kHz audio source to make the ripples. I don't know what kind of quality of ripple you'd get if you did that (what's the speed of sound in mercury? That would determine the wavelength of the ripples.) That's maybe do-able. Then either some more complicated mirrors to get to a second mercury tank with 3kHz ripples - or (more conveniently) a 3000 revolutions per second spinning 10-sided mirror (which would still have to be insanely carefully machined and mounted to avoid it destroying itself...but not impossibly so. 3000 revs per second is 180,000 rpm - which is only 20 times faster than (say) a car engine spins...it's tough but just barely possible. You might even get a small piezo-electric actuator to vibrate a mirror at those kinds of speeds.

In order for the image to be bright enough - the laser would have to be a pretty powerful one - and of course if you want a color image, you need three of them.

The result is:

• Three dangerously bright lasers.
• A tank of poisonous mercury.
• A spinning death-trap.

Definitely a recipe for killing yourself if you don't know what you're doing!

From the relative naivity of your question - I doubt very much that you have the skills to come even within a factor of 10 of your goal. This is a multi-million dollar display research activity...and people who are about to launch into multi-million dollar display research activities don't usually start off by wondering if they can just adjust a TV!

I'm also puzzled by what you think you're going to drive this monster with? I can't think of any signal sources (like computer graphics cards, DVD players or anything else like that) which could provide a fast enough signal to drive this thing.

Perhaps you should tell us more about why you need it. I bet there is something else you could do that would work better.

SteveBaker (talk) 12:45, 28 July 2009 (UTC)

Just a small comment, but it is certainly possible to replace CRT phosphors with other materials that can reset much faster. I routinely work with fluorescent organic compounds with an excitation lifetime of a 100 ns or so. I suspect something similar is also achievable for LEDs. It would be an expensive custom job to create such a thing, but the engineering to create the screen strikes me as straightforward (provided money is no object). So, if you can get the rest of the control electronics to run at that speed I don't think designing an appropriate screen is really a limiting factor. Dragons flight (talk) 20:44, 28 July 2009 (UTC)

Quite a number of computer CRTs claim to support a refresh of 160Hz. You can get the comp to use this refresh as well. This is usually at rather low resolutions obviously (e.g. 640x480). Are these not really refreshing that fast? Nil Einne (talk) 01:48, 29 July 2009 (UTC)

Yeah - but they get pretty smeary at those rates. Looking at the screen with the naked eye - you really can't tell but for applications such as our OP evidently has in mind (see below), this smearing would result in a blurry image in the 3rd dimension. SteveBaker (talk) 02:50, 29 July 2009 (UTC)

If I recall correctly a half-silvered mirror will block (one polarisation of) light when charged (or carrying an electric current) - this could form the basis of a high speed light switch - since there are no moving parts. However it sounds like you'd need an array of these things - which as far as I know doesn't exist - eg you'd have to make it yourself - each array element would require an independent electrical supply - I'd guess you'd photlithography equipment at the least. 83.100.250.79 (talk) 14:00, 28 July 2009 (UTC)

If that was workable - we probably wouldn't be using DLP's to do that job...so probably those things don't switch as fast as you think they do. But DLP's are nowhere near fast enough...and really, neither is anything else that I can think of. Worse still - if you have a million pixels per frame and a 3,000 frames per second display - you need to feed it with with something like 75 Gigabits per second of data. That's extremely non-trivial...even if you manage to figure out a way to display it. SteveBaker (talk) 20:37, 28 July 2009 (UTC)

It's not the speed it's the heat that is a problem - a mirror reflects - these absorb the light. Why not check you understand first?83.100.250.79 (talk) 12:24, 29 July 2009 (UTC)

I am not giving much away, because it will result in a piece of consumer elecronics that no-one has a perfect version of even for use by large organisations. What if i had ONE spinning mirror for the horizontal scan and hundreds of individual lasers each with a light valve for the vertical "scan?" —Preceding unsigned comment added by Trevor Loughlin (talk • contribs) 15:00, 28 July 2009 (UTC)

As a point of interest, this user has invented a "retrocausal information transfer" device. He may actually be posting from the future. APL (talk) 15:26, 28 July 2009 (UTC)

As a second point of interest, are you trying to build a "swept volume" volumetric display? It sounds like it, but I don't see how those could ever become "consumer electronics". Hidden surface removal alone sinks it for most applications. APL (talk) 20:19, 28 July 2009 (UTC)

(ec) No - I bet I know exactly what he's planning to do. He wants to create a viewer-independent 3D display - probably by reflecting the 3000Hz image off of a moving screen or spinning the monitor or some such trick. However, there's no such thing as a free lunch - and the amount of information density required to do 3D in such a brute-force manner is HUGE. Getting this down to a price where a consumer could afford it is a major undertaking. If our OP had a hope in hell of doing that - he wouldn't be asking WP:RD/S whether it's possible to modify a TV set to do it! He'd be employing a bunch of professionals who already know the problems and have ideas for the answers. The trick for doing viewer-independent 3D is to take advantage of some of the natural constraints of the scenes you'll want to render. But we're not being told what it needs to do in enough detail to answer the question to speculate on that - and I'm not providing free consultancy in order that someone else can make a fortune! I charge $200 an hour for that (my email address is on my User: page)! Suffice to say that getting enough information into this thing will be a nightmare - and the cost of doing 3D in this way is pretty extreme. SteveBaker (talk) 20:30, 28 July 2009 (UTC)

Oh, I get it now. Not volumetric, but showing a different image to each degree of the circle around the volume. Even if you could work out the optics you'd need a monster of a computer to drive it. APL (talk) 04:30, 29 July 2009 (UTC)

Oh - this old thing again! [43] SteveBaker (talk) 20:43, 28 July 2009 (UTC)

Yes APL you have got it. You guys are not just nerds, you are smart. The high speed CRT or laser television image would create a circle with all the 3D pixels for each point of the image.For the hole,LCDs or alternatively a mechanical method capable of creating a scanning hole I have thought of(thousands of times better than the nipcow disk in terms of space to image size and definition) would provide the "hole" which would only have to scan at NORMAL television refresh rates. The speed requirements of the CRT/Laser screen behind it could be reduced by using multiple image circles with very little reduction in the viewing angle be for they interfered with each other.I admit the electronics for such a high data rate could be a slight problem. What about a programmable custom chip? Trevor Loughlin (talk) 14:26, 29 July 2009 (UTC)

That will be expensive and require an advanced engineering training. As much as I would like to encourage amateur hobbyists to engage in electronics design, let's be serious. A beginner will take one look at the HDL hierarchy or the ASIC netlist, and run away screaming in horror. But, don't let my dismal view on things dissuade you. Go ahead and download some free, free, opensource HDL and ASIC schematics from OpenCores Project Repository. You can buy starter kits for around two or three hundred dollars; but for the data rates I'm guessing you need, you may want to go for a high-end system. Funding should be no problem with all the casino earnings from the retrocausal information transfer device. Nimur (talk) 17:06, 29 July 2009 (UTC)

Chlorine

Chlorine used in swimming pools is harmless but chlorine gas used in the world wars was lethal. Why? Is the chlorine in swimming pools used in very low concentrations so that it is not harmful? Many thanks for any help. Chevymontecarlo (talk) 06:23, 28 July 2009 (UTC)

see Chlorination 71.236.26.74 (talk) 07:04, 28 July 2009 (UTC)

It's also very important to note that ions can be very different from their neutral atom counterparts. Sodium is a metal that likes to pretty much blow up when you throw it in water, and as you said, chlorine is a lethal gas; yet sodium chloride (Na⁺ Cl^-) is something we all need to live. -- Aeluwas (talk) 07:27, 28 July 2009 (UTC)

True but irrelevant, since chloride is not used in swimming pools while chlorine is. Algebraist 13:47, 28 July 2009 (UTC)

Hmm, I thought the chloride in swimming pools was mostly in the form of hypochlorite ions... but I've never owned a pool. ;) -- Aeluwas (talk) 14:10, 28 July 2009 (UTC)

Yes chlorine is in small concentrations, also it's dissovled (mostly) in the water, rather than as a breathable gas.83.100.250.79 (talk) 11:05, 28 July 2009 (UTC)

To rephrase the question for the OP; water in small volumes is required for life, but if I immerse you in a large volume of water, you would die! See the deal? Very few things are harmful at all amounts or healthy at all amounts. Some harmless things become harmful depending on the amount/concentration. Chlorine is no different in this regard. In small amounts, it kills bacteria, but not you. In larger amounts, it'll kill you too. Most disinfectants/antiseptics have the same basic properties. --Jayron32 13:11, 28 July 2009 (UTC)

But harmless the stuff in swimming pools is not. Just opening the packet before I add it to the dispenser is enough to bring tears to my eyes and make me cough. I have lots of bleach holes in my gardening trousers from premixing it. --BozMo talk 14:23, 28 July 2009 (UTC)

It's still a concentration issue...think about how small an amount from the packet has an effect, but then how much it gets diluted before you swim in it. The relative amounts in "Large amount, immediate and serious effects vs small amount, mild and weaker effects" depend on the intrinsic nature of the chemical you're using. Some are extremely potent or reactive, so even only a few grams is a "large amount" of that chemical and a "small amount" is measured in parts per million dilution. DMacks (talk) 15:26, 28 July 2009 (UTC)

Large pools often use bottled chlorine gas. Google "chlorine gas pool accident" to see some examples of what can go wrong. Rmhermen (talk) 16:55, 28 July 2009 (UTC)

I have heard the new trend is towards salt-water pool sterilization. Vranak (talk) 17:46, 28 July 2009 (UTC)

Virtually everything has several levels...

1. A no effect level (NOEL) - any dose below this has no effect
2. (for drugs)A therapeutic level - the amount of drug necessary to give the desired result
3. A toxic level - the amount to start causing unwanted effects
4. A fatal level - speaks for itself.

So for tiny amount of chlorine in water, then no effect. *Carefully* sniff some gas, and it will make your nose smart - or as one student did when I was at school, sniff too much and you fall over and go to A&E (don't have chemistry lessons like that any more...)  Ronhjones  ^(Talk) 20:02, 28 July 2009 (UTC)

Unsolved problems in astronomy

What is the significance of the asterisks in the Unsolved problems in astronomy article?--Shantavira|^{feed me} 07:41, 28 July 2009 (UTC)

Probably the same as in the Unsolved problems in physics article http://en.wikipedia.org/wiki/Unsolved_problems_in_physics .

** Problems marked with two stars are considered by a significant number of physicists to be resolved, though there is still significant debate about them.

*** Problems marked with three stars are considered by some physicists to be outside the purview of physics, more properly philosophical in nature.

**** The existence of problems marked with four stars is disputed.

You're probably right since User:Allen 124 who created this page [44] later removed some of the same problems from the physics page [45] (although they were restored, as they should have been) Nil Einne (talk) 00:04, 29 July 2009 (UTC)

code for jpg please..

I am using some matlab image processing codes in my experiment.unfortunately .. i found the standard code for bmp files only..can any one help me with ..the jpg version of this code..

err... on trying with the jpg version .. i got some .. problems .. with matrix dimensions.. kindly if someone could fix .it.

CODE: %This code would attempt to analyse the flame area and do the following %1. Frequency analysis of flame area %2. Frequency Analysis of fractal dimension of each static image %3. Correlation Dimension or Embedding dimension of area %-------------------------------------------------------------------------- image_thresh = 70; n_img = 1000;%Number of images in present sequence sampling_freq = 315;%Hz %-------------------------------------------------------------------------- %The starting string of the file name

string_start = 'vc';

%The file extension extension = '.bmp';

%3-D array for image import %pile = ones(256,256,n_img); intensity = zeros(n_img,1); for image_num = 1:n_img %loop counter variable image_num

   img = zeros(256,256);
   %IMAGE LOADING
   image_num_name = image_num - 1;
   image_processed = zeros(256,256);

aniket .. 59.93.135.1 (talk) —Preceding undated comment added 08:38, 28 July 2009 (UTC).

Well, that code is extremely incomplete, and doesn't really do anything that matters. But in any case this is the wrong place for your question, you'll have better luck at Wikipedia:Reference desk/Computing. Looie496 (talk) 15:56, 28 July 2009 (UTC)

When maths go horribly wrong

Okay, so I'm trying to calculate the relative abundance of the two nitrogen isotopes, knowing the mass of both isotopes and of nitrogen as a whole. Nevertheless, somewhere down the road the equation goes horribly wrong:

Step 1: X * 14,0035 + (1-X) * 15,0001 = 14,0067

Step 2: X + (1-X) * 15,0001 = 14,0067
                              -------
                              14,0035

Step 3: X + (1-X) * 15,001 = 1,000229

Step 4: X + (1-X) = 1,000229
                    --------
                     15,001

Step 5: X + 1 - X = 0,066681

Step 6: 1 = 0,066681

Can anyone please point out in which step I made the mistake? Thanks a lot! --Leptictidium (mt) 11:08, 28 July 2009 (UTC)

• Step two and step four both appear to be erroneous. Correct solution should be:

$140035X+(1-X)150001=140067\implies -9966X+150001=140067\implies X={\frac {4967}{4983}}$ Noodle snacks (talk) 11:17, 28 July 2009 (UTC)

Through which mathematical operation does $140035X+(1-X)150001=140067$ become $-9966X+150001=140067$? --Leptictidium (mt) 11:38, 28 July 2009 (UTC)

Take $140035X+(1-X)150001$

multiply out $(1-X)150001$ to become $150001-150001X$

which makes $140035X+150001-150001X$

which is $-9966X+150001$ -- Finlay McWalter Talk 11:46, 28 July 2009 (UTC)

You messed up between step 1 and step 2. Let's replace those constants with nice simple names so I don't have to type those L-O-N-G numbers all the time!

Step 1 is essentially:

  A = 14,0035
  B = 15,0001
  C = 14,0067
  X * A + (1-X)* B = C

In getting to step 2 you tried to divide though by A but screwed up. When you divide both sides of the equation by something - you have to divide EVERYTHING in the equation by that something:

  X*A   + (1-X)*B   = C
  X*A/A + (1-X)*B/A = C/A     -- Divide through by A
  X     + (1-X)*B/A = C/A     -- Cancel A/A

You missed out the A to the right of (1-X)*B! But that approach is ugly.

A better way to simplify would be to collect up the 'X' terms:

  X*A + (1-X)*B = C
  X*A + B - X*B = C    -- Multiplied out (1-X)*B
  X(A-B) + B    = C    -- Collected & factored out the X terms
  X(A-B)        = C-B  -- Subtract B from both sides
  X = (C-B)/(A-B)      -- Divide through by (A-B)
  X = (14,0067 - 15,0001) / (14,0035 - 15,0001)  -- Substitute A,B,C back into the equation
  X = 0,9967890828     -- Do the arithmetic.
  X = 0,99679          -- Round off to 5 decimal places.

QED SteveBaker (talk) 12:07, 28 July 2009 (UTC)

Vibrating parts of the body

Sometimes a few parts of the body vibrate involuntarily for a while and then get back to normal.Like say the right eyelid vibrating,left forearm parts vibrating etc.The nature of vibraion is only short lived. So what is the cause of such vibrations?? What do they indicate??117.193.146.232 (talk) 14:29, 28 July 2009 (UTC)

Some sort of spasm or tremor? DMacks (talk) 15:20, 28 July 2009 (UTC)

Ya kinda tremor ...short lived tremors. —Preceding unsigned comment added by 117.193.131.226 (talk) 17:36, 28 July 2009 (UTC)

These are commonly known as tics or "nervous twitches". The cause isn't really very well understood (many people show them when anxious) -- however there is a neurological disorder called Tourette's syndrome in which tics occur very frequently. Looie496 (talk) 15:49, 28 July 2009 (UTC)

Do not confuse tics which have neurological origin with twiches which are small muscles spasms. 71.203.58.148 (talk) 19:41, 28 July 2009 (UTC)

Looie i dont think tics as you mentioned above answers the question.As a further add on..I myself have experienced some vibrations or tremors you may say ,on my eyelids.It is something which you can feel. —Preceding unsigned comment added by 117.193.131.226 (talk) 17:49, 28 July 2009 (UTC)

I do want to note that Wikipedia can't give any medical advice which includes guessing why your eyelid might be vibrating. You can ask if there is anything else besides tics that might cause that sensation. Sifaka ^talk 17:53, 28 July 2009 (UTC)

Better yet, just go see your physician. Any number of things can cause twitches, including nervous disorders at the extreme end. On the other hand, it may be nothing, so get it checked out. Regards, --—Cyclonenim | Chat  18:31, 28 July 2009 (UTC)

The article you are looking for is Fasciculation. Small, rythmic contractions of an eyelid is a very common phenomenon - so common, in fact, that it has a name in Norwegian (leamus). This term is usually used about fasciculations of an eyelid, but can also be used about fasciculations of other muscles. This was one of the first hits on google.no (the site is well-reputed), and I'll translate the relevant part:

By definition, fasciculations are involuntary muscle contractions, that are sufficiently strong to be visible (or palpable) on your skin, but not strong enough to cause movement of the joint that the muscle controls. Fasciculation is a completely normal phenomenon, and only in exceptional cases a sign of disease. Most people experience fasciculations to a lesser or greater extent in periods of their life. When fasciculations are a sign of disease, they are always accompanied by other, more serious symptoms.

--NorwegianBlue ^talk 18:54, 28 July 2009 (UTC)

In my opinion, the last sentence is the one you need to pay most attention to. See your physician. Regards, --—Cyclonenim | Chat  18:55, 28 July 2009 (UTC)

killed while having sex

has anyone ever been killed while having sex? have they been killed bya third party? or by an accident? and is it more likely to happen in gay or straight sex? Questionabout"theman" adolf (talk) 14:40, 28 July 2009 (UTC)

I doubt there are statistics re: gay or straight in terms of death-while-sex, but certainly people have been killed while having sex both by third parties and by accidents. Why would you presume that it hadn't happened? That people were somehow immune from death by accident or murder while having sex? --98.217.14.211 (talk) 15:14, 28 July 2009 (UTC)

Do automobile, motorcycle and airplane crashes count? How about shootings by jealous spouses? Edison (talk) 15:21, 28 July 2009 (UTC)

There have probably been heart attacks. Or does auto-erotic asphyxiation count (see also Michael Hutchence)? AlmostReadytoFly (talk) 16:00, 28 July 2009 (UTC)

A few years ago, various magazines, including I think the UK's Bizzare, ran photos of a man killed by a falling rock while having sex with a chicken. (He was indulging his avian lust in a cranny in a cliff, and a piece of the cliff face immediately above him became loose.) 87.81.230.195 (talk) 16:04, 28 July 2009 (UTC)

Mostly all spermatozoids are killed when males have sex.--Quest09 (talk) 17:53, 28 July 2009 (UTC)

Millions of males a day die while having sex, see this. -- penubag  (talk) 20:09, 28 July 2009 (UTC)

Clearly the OP is asking about humans. Same goes for Quest09's response. --Sean 21:38, 28 July 2009 (UTC)

See Nelson_Rockefeller#Death if that counts. 70.90.174.101 (talk) 03:11, 29 July 2009 (UTC)

Heart attacks are fairly common during sex, but does dying of a heart attack count as "being killed?" Edison (talk) 18:43, 29 July 2009 (UTC)

How much does a ton of carbon cost at the Chicago Exchange?

I was planning on buying some carbon offsets, and was looking at the website liveneutral.org. Liveneutral buys carbon credits from the Chicago Climate Exchange, and doesn't do anything else, like reforestation. Liveneutral's price is a set $12/ton. How can I find out what those credits actually cost at the Chicago Climate Exchange? Their website is a little confusing...

Thanks! — Sam 63.138.152.238 (talk) 17:41, 28 July 2009 (UTC)

If I'm reading the chart right, it looks like it's trading at about $0.50 per metric ton. It looks like it peaked about a year ago at over $7 per metric ton. APL (talk) 18:23, 28 July 2009 (UTC)

That's what I figured as well. I'll have to write to them to see how they can explain charging $12/ton when all they appear to do is buy carbon credits. — Sam 63.138.152.155 (talk) 20:11, 28 July 2009 (UTC)

Gears

How does the gear system in clocks work??? —Preceding unsigned comment added by 117.193.131.226 (talk) 17:51, 28 July 2009 (UTC)

Well.. from minutes to hours there is a 60:1 step down gear, hopefully that doesn't need more explanation. If you are wondering about old wind up watches then the second counter mechanism is controlled by an Escapement.

There's more info at Wheel train (horology) which should give you all the answers you need.83.100.250.79 (talk) 18:05, 28 July 2009 (UTC)

I think the article you are looking for is Movement (clockwork) (which is oddly not linked from the clock article). — Sam 63.138.152.238 (talk) 18:06, 28 July 2009 (UTC)

It is now. Livewireo (talk) 20:11, 28 July 2009 (UTC)

What is it called when a swallowing attempts to pull down your own throat?

Caused by trying to swallow with too little "lube". Sagittarian Milky Way (talk) 18:23, 28 July 2009 (UTC)

"Getting something stuck in your throat". Couldn't find any specific medical term on wikipedia. 71.236.26.74 (talk) 06:00, 29 July 2009 (UTC)

Hot air

What's the effect called where hot air, or heated air, distorts light so it all seems blurry/wriggly? You can see it on hot days over long distances, or above a toaster (where I saw it this morning) for example. Regards, --—Cyclonenim | Chat  18:27, 28 July 2009 (UTC)

Heat shimmering/heat shimmer. [46]. - Nunh-huh 18:34, 28 July 2009 (UTC)

Caused by refraction of light in different densities of air at different temperatures. Sjschen (talk) 18:36, 28 July 2009 (UTC)

See also Schlieren photography. DMacks (talk) 18:41, 28 July 2009 (UTC)

The effect is refraction. See also mirage. Red Act (talk) 18:55, 28 July 2009 (UTC)

"Heat wave distortion" gets a few ghits too. Aaadddaaammm (talk) 19:22, 28 July 2009 (UTC)

The answer to your question is refraction of light.To get into more detail consider this.You have lit a bonfire.The air vertically above the bonfire is much hotter than the air surrounding the fire.Hotter the air, the lesser is its density.The air surrounding it is comparitively denser.Obviously the air nearer to you is very dense.Now the light has to travel through this range of varying densities of air and hence suffers a series of refractions which make the air to give it a quivering appearance.The densities of air also keep varying constantly which further add to the quivering effect.gdsrinivas 19:29, 28 July 2009 (UTC) —Preceding unsigned comment added by Gd iitm (talk • contribs)

The reason for the ripples is just turbulance in the air - much as smoke tends to curl and bend, so does the clear air that causes this shimmering. The difference between the refractive index of warm and cold air explains why the light coming through is distorted differently - and as the hot and cold air mix, you get this effect. SteveBaker (talk) 20:14, 28 July 2009 (UTC)

Turbulance? Hmm, I would say above your toaster it is very unlikely to be "turbulence" which I think is generally characterized by multiple length-scales of eddies? The formation of simple laminar and eddy flow as the buoyant laminar flow breaks up seems much more likely. But I couldn't be bothered to calculate a Reynolds number to check so I'll have to give SB the benefit of the doubt. And as Steve has said using the right technical term isn't the most important thing.... --BozMo talk 22:25, 28 July 2009 (UTC)

A quick look through my Fluid Dynamics library seems to indicate that twenty years ago (when all the books were written) the correct term for the flow above your toaster was laminal flow transitioning to an irregular "vortex street". Emphatically not turbulence. There you go then, that should change your whole perception of things. Unless I am out of date which is possible. --BozMo talk 22:40, 28 July 2009 (UTC)

Yeah - that's all true - but I don't see that same kind of shimmering over my toaster (at least, I just tried it with my toaster and it doesn't seem to generate anything like that). We're talking about much larger differences in temperature and much larger sources...I doubt that the airflow stays laminar under those kinds of situtaion. SteveBaker (talk) 02:33, 29 July 2009 (UTC)

My guess is actually that the "shimmer" is a coherent higher frequency eddy structure and that the distortion from the pure turbulence would be whiter in frequency terms. However both could exist in the same flow and I didn't do any serious stuff on flow since the early nineties. --BozMo talk 06:03, 29 July 2009 (UTC)

By the way are you a chemical engineer? In pipeflows people tend to talk about laminar or turbulent as though these were the only flow types but when talking of ddc buoyancy wakes jets etc they use a fuller range of flow regimes. --BozMo talk 06:14, 29 July 2009 (UTC)

Chains and Pulleys

Recently I paid a visit to a big construction site.There heavy objects were lifted,adjusted,shifted etc using a multiple groved hand operated pulley.This pulley had many grooves and had lengthy chains running through it.It wasn't a usual one.Also the chain was pulled effortlessly and had to be pulled long for a small movement.How does this work??? —Preceding unsigned comment added by 117.193.129.196 (talk) 19:47, 28 July 2009 (UTC)

To start - it sounds like a Block and tackle - this explains the easy of use and long pull.

They can also be used with chains -see http://www.h-lift.com/chainblock.htm

Potentially it may have been more complicated than block and tackle - some have ratchets to stop the thing falling.83.100.250.79 (talk) 19:55, 28 July 2009 (UTC)

Also there are chain lifting gears with continuous (looped) pulling chain with gears to give mechanical advantage plus ratchets.

—Preceding unsigned comment added by 83.100.250.79 (talk) 19:56, 28 July 2009 (UTC)

It's a simple matter of mechanical advantage. If you wrap a rope or chain around a pair of pulleys so that the rope goes up and down between them several times...let's say 6 times...then for every foot you pull on the rope, you've only moved the bottom pulley one sixth of that...two inches...that's because you had to shorten all six lengths of rope equally - and one foot of rope shared out six ways is two inches off of all of them. However, when you pull on that rope with a certain amount of tension - you are effectively pulling on all six lengths of rope at once - so the pulley at the bottom moves up with the force of six times the amount of tension. You are exchanging a big, gentle movement for a small powerful one...that's called "Mechanical advantage" - and it's the same principle as using a long lever - where you move one end of the lever gently through a large distance - and the other end moves through a much smaller distance - but is able to apply proportionately more power. Similar ideas explain how the hydraulics in your car brakes allow you to apply all of that force to slow the car down using a large (but fairly gentle) push on the brake pedal.

The grooves you see in the pulleys are there to stop the rope or chain from getting tangled up as it goes around and around them - pulleys that are designed for chains also have dimples in the pulley to allow the chain links to settle into them and reduce the tendancy to slip. SteveBaker (talk) 20:11, 28 July 2009 (UTC)

Birds vs. Insects

Why have insects (specifically ones possessing flight) failed to inhabit the ecological niche of birds (and vice versa)? What limits an insect's size that doesn't constrain a bird's?

Alfonse Stompanato (talk) 21:03, 28 July 2009 (UTC)

Having an exoskeleton and inefficient lungs limits the size of insects. - Nunh-huh 21:10, 28 July 2009 (UTC)

Our Meganeura (giant prehistoric "dragonflies") article says (with references):

Controversy has prevailed as to how insects of the Carboniferous period were able to grow so large. The way oxygen is diffused through the insect's body via its tracheal breathing system puts an upper limit on body size, which prehistoric insects seem to have well exceeded. It was originally proposed (Harlé & Harlé, 1911) that Meganeura was only able to fly because the atmosphere at that time contained more oxygen than the present 20%. This theory was dismissed by fellow scientists, but has found approval more recently through further study into the relationship between gigantism and oxygen availability. If this theory is correct, these insect giants would have been perilously susceptible to falling oxygen levels and certainly could not survive in our modern atmosphere.

However, more recent research indicates that insects really do breathe, with "rapid cycles of tracheal compression and expansion". If correct, then there is no need to postulate an atmosphere with higher oxygen partial pressure.

So I think the answer is "nobody knows". Insects don't have lungs, so that certainly places some limit, but not necessarily the limit that they're at now. --Sean 21:34, 28 July 2009 (UTC)

Well in a way they have - or rather one specific species has. The Humming-bird Hawk-moth seems to occupy the same niche in England and Europe that Humming birds do in the tropics. (I can't believe we don't have an article on Humming bird hawk moths - have I given the wrong name?) --TammyMoet (talk) 08:24, 29 July 2009 (UTC)

Macroglossum stellatarum. --Cookatoo.ergo.ZooM (talk) 10:09, 29 July 2009 (UTC)

Also fixed the link to the redirect above. --Stephan Schulz (talk) 11:24, 29 July 2009 (UTC)

Thank you! --TammyMoet (talk) 12:02, 29 July 2009 (UTC)

apparent size of celestial body?

How do astronomers measure the apparent size of a celestial body from Earth? Would it be in degrees of how much of the sky it covers? Or how many millimetres the object covers if a ruler is held out at a certain distance from the observer, or etc? Is there a term for this? Is it called "apparent size" or ? --69.165.137.164 (talk) 21:43, 28 July 2009 (UTC)

Our apparent size article would be a good place to start:) DMacks (talk) 21:48, 28 July 2009 (UTC)

"Angular subtense" or "angular diameter" is a term used to describe that which you ask about. Degrees, minutes, and seconds (or decimal fractions of a degree) could describe the apparent size. Edison (talk) 18:41, 29 July 2009 (UTC)

July 29

Is this true or made-up? Thanks.

"The concept that light appears to travel faster than the speed of light to an outside observer is known as super-luminous motion....If you have a charged particle moving close to the speed of light at angle 1/gamma (where gamma is the Lorentz factor) with respect the the observer. the particle can appear to be moving faster than the speed of light in the reference frame of the observer. However, the particle isn't actually moving faster than the speed of light. The speed of light is an Absolute. This effect is also known as relativistic beaming and is common in many Active Galactic Nuclei galaxies." [47] Imagine Reason (talk) 01:37, 29 July 2009 (UTC)

Well Relativistic beaming is real - our article is pretty clear and although it only has one reference, it's a good one. However, neither our article, nor it's reference talks about things appearing to move faster than the speed of light. Weird. SteveBaker (talk) 02:29, 29 July 2009 (UTC)

The speed of light may or may not be an absolute. There is a hypothetical particle knows as the tachyon which travels at superluminal speeds.CalamusFortis 03:08, 29 July 2009 (UTC)

That comment is super misleading. There is no reason to believe that the speed of light is not absolute, and every reason to believe it is. Sure it is always a possibility that our physics is wrong, but this question is asking a specific question about our current understanding of physics. It is not asking for wild ass speculation and ungrounded bullshitting. The question also has nothing to do with tachyons. APL (talk) 04:13, 29 July 2009 (UTC)

Indeed - there is a hypothetical space craft called "the starship enterprise" which travels at superluminal speeds too...and it's just about as real as tachyons. Just because we give something like that a name - doesn't bestow any additional legitimacy upon the hypothesis! SteveBaker (talk) 22:25, 29 July 2009 (UTC)

No, no particle can "appear" to travel faster than light. It's a cornerstone in relativity that all observers can agree on the laws of nature independent of how fast they'r travelling relative to each other. No observer should therefore observe a violation of the speed limit. Here's how I think it's meant to be interpreted:

Imagine that you'r shining a flashlight on a faraway wall. You move your flashlight a little and the point of light on the wall zips sideways. If the wall was further away, the point of light would move faster along the wall. Eventually, if the wall was far enough away, the point of light would move faster than the speed of light. However, no photons in the ray of light exceed the speed limit and it's impossible to transfer information at superluminal speed using the blob of light on the wall, as noone at the wall can affect its path or any other property. EverGreg (talk) 11:05, 29 July 2009 (UTC)

yes. I'm mentioning the light-ray because I'm guessing that's the effect in the relativistic beaming, though from what BenRG is saying, I'm not so sure anymore. :-) EverGreg (talk) 17:01, 29 July 2009 (UTC)

See also Faster-than-light#FTL phenomena. There are all sorts of cases where something can be made to exceed the speed of light relative to something else. The deal is, no information can travel at greater than the speed of light, so such actions are not useful. --Jayron32 11:15, 29 July 2009 (UTC)

I think that quote is referring to the following fact: suppose you're at (0,0) and an object at (D,0) is moving with velocity v = (v_x, v_y), so after a time dt it's at (D + v_x dt, v_y dt). The light from (D,0) will reach you after a time of D/c and the light from (D + v_x dt, v_y dt) will reach you after a time of, to first order, dt + (D + v_x dt) / c = D/c + (1 + v_x/c) dt. The object's angular displacement over that time, meanwhile, is Δθ ≈ (v_y/D) dt. If you (wrongly!) approximate the object's tangential velocity as distance times angular displacement divided by time then you get D [(v_y/D) dt] / [(1 + v_x/c) dt] = v_y / (1 + v_x/c), which is off by a factor of 1 / (1 + v_x/c) and can exceed c. That's not surprising since the calculation is wrong (and would be wrong even in a Newtonian universe), but for some reason astronomers think it's interesting and call it "apparent transverse velocity" or some such. This doesn't agree with the paragraph's claim that the critical angle is 1/gamma, so it may be referring to a more sophisticated wrong calculation that gets a more sophisticated wrong answer. This "effect" is discussed briefly at Faster-than-light#Astronomical observations, which cites a paper that unfortunately doesn't seem to be available online. -- BenRG (talk) 16:08, 29 July 2009 (UTC)

Hypothetical math! ~~ Volume of water required for "the Great Flood" in Genesis?

Genesis 7:19 ~ 21 says that even the tallest mountains in the world were underwater. So, assuming that we need enough water to submerge Mt. Everest, just how much water do we need?

Bonus points for calculating the proportion of needed water against the world's current water volume! 95.172.239.38 (talk) 04:45, 29 July 2009 (UTC)

You only need enough water to submerge the "known world" to the writers at the time. That may have been as little as submerging Mount Sinai. 71.236.26.74 (talk) 05:46, 29 July 2009 (UTC)

Mean radius of the Earth is 6371.0 km and elevation of Mount Everest is 8.848 Km.

Approximate volume of water required to submerge the Mount Everest is = volume of sphere of elevation - volume of mean radius = 4/3*(6371+8.848)^3 - 4/3*PI(6371)^3 = 4521140066 km3

From this value, subtract volume of all mountains and land above mean radius. I guess 5 % of it. That gives us 4,295,083,063 km3

There is approximately 1,360,000,000 km3 water on earth.

Three times more water is required, approximately :) - manya (talk) 06:01, 29 July 2009 (UTC)

Apparently there is an entertaining book by someone called Bernard Ramm who tried to do all the flood maths and stuff on Polar bears getting back to the North Pole. James Barr reviews it in his book "Fundamentalism" but the review is short: "much good fun can be had reading Bernard Ramm". --BozMo talk 08:48, 29 July 2009 (UTC)

We don't know how tall the moutnains were at that time, that's the problem. Mount Sinai, as noted by 76., may have been as tall as any mountain was anywhere in the world. there could have been violent movements of the earth as well during that time. (And, I thought I read somewhere where Mt. Everest was getting higher., as the one continental shelf was pushing against another.) Some Christians believe that Pangea existed before the Flood.Somebody or his brother (talk) 13:52, 29 July 2009 (UTC)

Come on folks, Mount Ararat, which is mentioned in the flood story as the first land to emerge, is way higher than Mount Sinai. (Ararat is over 5000 meters, Sinai less than 2300.) Looie496 (talk) 16:19, 29 July 2009 (UTC)

If we introduce the extreme beliefs of some Christians that the continents have moved around dramatically around in the time humans have been on Earth, and that the heights of mountains changed dramatically in that span, then the volume calculation might as well set pi equal to three, since that is the value given by Kings 7:23, where a round font was said to be ten cubits across and thirty cubits around. Edison (talk) 18:31, 29 July 2009 (UTC)

You've touched on a small hobby-horse (hobby-pony?) of mine, Edison. If the figures of ten and thirty are considered to be not precise, but rounded to the nearest whole number, they're not incompatible with the correct value of pi. 87.81.230.195 (talk) 03:01, 30 July 2009 (UTC)

Clearly God manipulated the geological record to test our faith in the Bible and decide who should be saved! (More faith=more gullible=less worthy of immortality.) --99.237.234.104 (talk) 02:37, 30 July 2009 (UTC)

Oblation

While re-reading Kim Stanley Robinson's Red Mars, I encountered the unfamiliar term "oblation:" The sun was...small and round even though it was near setting; there wasn't enough atmosphere for oblation to enlarge and flatten it. I know what he means, but in trying to read about the actual science behind it, I can only find a religious meaning with Google, including our own oblation article. Does this phenomenon have another name, and how do I read more? - Draeco (talk) 04:59, 29 July 2009 (UTC)

From the context I would guess that what he meant is that the atmospheric refraction was insufficient to make the Sun look oblate (meaning here - looking like an ellipse rather than a circle) close to the horizon because the atmosphere was too thin to perceptibly refract the sunlight. --Dr Dima (talk) 05:39, 29 July 2009 (UTC)

We have nice examples of the atmospheric refraction distorting the apparent shape of the sun disk near the horizon in the green flash article. At any rate, the proper name of the phenomenon is "atmospheric refraction" :) . By the way, I wonder if KSR was really right about Mars atmosphere being too thin to do that. It's not just density, it's the density gradient that counts. And, Mars atmosphere being colder than ours, the gradient may be not too low... --Dr Dima (talk) 05:49, 29 July 2009 (UTC)

The speaker was very near the Martian north pole at that time, if that helps justify him. - Draeco (talk) 15:45, 29 July 2009 (UTC)

this is an image of Martian sunset taken by Mars Pathfinder. The colors are real. The color variation is due both to the light scattering on the dust and to the atmospheric refraction. Note that the Sun disk looks distorted (elongated vertically). So yes, Martian atmosphere can distort the apparent shape of the Sun near the horizon. --Dr Dima (talk) 16:18, 29 July 2009 (UTC)

On the other hand, the first part of the circumstance ("enough atmosphere for oblation to enlarge... it") smacks of the moon illusion. Additionally, our article there notes that flattening occurs in the vertical, not the horizontal. As such, I expect the vertical elongation in Dr Dima's image is a lens artifact or a squashed image, not a true representation. — Lomn 18:18, 29 July 2009 (UTC)

Note: the vertical distortion of the image may also be a function of the three exposures used to create the color image. Any motion of the sun between exposures would cause apparent vertical elongation when combined. — Lomn 18:29, 29 July 2009 (UTC)

Yes, Lomn, you may certainly be right about the vertical elongation being the artifact of the several exposures used to acquire the color image. Indeed, according to jpl.nasa.gov, the imager on Mars Pathfinder used a set of filters on both of its optical channels. That means that it required several consecutive exposures to take real-color images, pausing between exposures to rotate the filter wheels. However, I do not think that the atmospheric refraction always causes a vertical flattening; not even on Earth. Indeed, there is a well known "Etruscan vase" atmospheric effect where the apparent Moon disk is dramatically distorted and elongated vertically. So, lest we -God forbid!- dare bring the Original Research into this Temple of Wiki, we should probably leave the verdict on the question of whether the Martian atmospheric refraction is strong enough as "inconclusive". --Dr Dima (talk) 19:49, 29 July 2009 (UTC)

Conservation of energy

Let's say we have a collision between two atoms, where energy cannot dissapear in the form of internal kinetic energy or whatnot(let's pretend that, in this particular case, a photon isn't released). What theoretical argument justifies kinetic energy being conserved(in other words, how do we know that the work done on one atom = the negative work done on the other)?

If no energy is dissipated, the collision of fully elastic, i.e. in a frame of reference moving with the barycenter, both will have the same speed after the collision (but different directions). "Negative work" does not make sense here - "work" and energy are undirected scalars. Hence the kinetic energy before and after the collision will also be the same. --Stephan Schulz (talk) 08:25, 29 July 2009 (UTC)

Stephan, the question did not specify that you had to work on the reference frame of the center of mass. Negative work makes perfect sense on a different reference frame. Dauto (talk) 12:18, 29 July 2009 (UTC)

Conservation of energy is shown to hold empirically. Any physical theory is based on a set of axioms, which have to be accepted as true (hopefully because they match experimental evidence), and the rest of the theory is derived from there. Energy conservation I think is usually taken to be an axiom, but there are equivalent ones. Conservation_of_energy#Noether.27s_theorem mentions that time translational invariance of physics implies conservation of energy. Rckrone (talk) 15:45, 29 July 2009 (UTC)

To say that the reason the total kinetic energy remains constant is because energy is conserved, followed by saying that energy is conserved because it's an elastic collision, is circular logic. My question is, why is energy conserved in such a situation? And I would like to hear an explanation other than Noether's theorem, because conservation of energy was well understood before her time. I doubt a derivation using Newton's laws would be hard, and I have a rough sketch of what it would look like in my head (the atoms slow down because of the electric force bewteen them, hence energy is stored as potential energy, which should the push the atoms away with the same work), but the details are lacking.

And I wouldn't consider conservation of energy to be an axiom (at least not in classical theory), but rather Newton's laws to be the 'axioms', because from them, conservation of momentum and the like are able to be explained.

Let me turn your question around (and maybe let you clarify what you're really asking): where do you propose happens if energy is not conserved via work/change-in-velocity during the collision? Either the energy goes "somewhere else" (not into kinetic energy in the particles--conserved, but in some other variable in the system) or it disappears entirely (not conserved at all in the whole closed system). DMacks (talk) 19:30, 29 July 2009 (UTC)

Conservation of energy is not a consequence of Newton's laws. Rckrone (talk) 20:47, 29 July 2009 (UTC)

Are you sure? The interaction bewteen two bodies is mediated by the Coloumb force, and apparently (I remember reading this somewhere) because the Coloumb force can be represented as a gradient of a potential, energy is conserved.

Newton's laws alone only give you conservation of momentum. Coulomb's law together with Newton's laws does imply that energy is conserved when the only force is the electrostatic force. In other words, the electrostatic force as defined by Coulomb's law is a conservative force. (That article also goes into how you would go about proving whether a given force is conservative.) If you had a full description of all the fundamental forces, you could prove from that the conservation of energy generally. However, I don't think there's an accurate self-consistent theory like that right now, since quantum gravity is still a problem. Rckrone (talk) 03:40, 30 July 2009 (UTC)

Trees showing the undersides of their leaves before a summer storm

When I was a lil guy, I always heard that you could tell a summer storm was coming if the trees (especially silver maples and tuliptrees) showed the undersides of their leaves. I was thinking about this yesterday when driving home from a job:

1. at one point on the highway, I noted that many of the trees had upturned leaves
2. a few miles up the road, I went through part of a storm
3. past the storm, the leaves were turned up again, then after a few more miles they weren't

...so there's at least some anectdotal evidence from yesterday's commute :-).

I'm wondering though if this really does work, and if so, why? Is it something to do with an updraft? Buildup of electrical charge before a storm? --SB_Johnny | ^talk 09:32, 29 July 2009 (UTC)

We have an article on the weather stick. The web page that article uses as a reference says that the branch is responding to relative humidity.[48] Other web pages claim that it’s barometric pressure.[49] So far, I haven’t found a really reliable source that would give a definitive answer. Red Act (talk) 12:29, 29 July 2009 (UTC)

this link (can only access Google cached version for some reason) goes to a discussion among some university professors who conjecture that it has to do with a shift in winds. this link (warning .pdf!) concurs, saying that the leaves grow according to prevailing winds, and the approach of a storm, being a non-prevailing wind, will turn them over. Some jerk on the Internet (talk) 12:45, 29 July 2009 (UTC)

The experiment reported by this web site referenced by the weather stick article does make it look like it’s the relative humidity that’s affecting the stick. However, the experiment doesn’t control for other possible changes, such as barometric pressure, so it’s not quite conclusive. Red Act (talk) 12:54, 29 July 2009 (UTC)

Chlorhexidine

Chlorhexidine is widely used in medicine and dentistry as several % solution. What is chlorhexidine itself, is it solid or liquid? What is its appearance? Renaldas Kanarskas (talk) 10:50, 29 July 2009 (UTC)

Our article on Chlorhexidine has many external links to pages at other sites, such as in the infobox. According to this one: [50] from Chemspider, the melting point is 134 Celsius, which would make this a fairly low-melting solid in native state. --Jayron32 11:08, 29 July 2009 (UTC)

It's solid at room temperature. It's "white to pale yellow" in color.[51] Red Act (talk) 11:19, 29 July 2009 (UTC)

Thank you both! Renaldas Kanarskas (talk) 19:59, 29 July 2009 (UTC)

Charging an 18V battery for a drill

Hi all, I have two questions about charging up my cordless drill:

• I have an 18V battery for my Black&Decker drill. The drill came with a plug (wall wort and 5-6 mm jack) which, if you you have the battery inserted in the drill and the plug connected to the drill, you can charge the battery. The question is: I may or may not have lost the plug. I have one that has an output of 5.0V and 2.6 A with the right size jack, but am I right in thinking that this can't be the plug, because the transformer would need to supply at least 18V to charge the battery?
• Apart from this one plug (which has to go through the drill, making it annoying), why do all my power tool batteries need to be charged with some stupid expensive shoe like this or this? Why can't they just have a jack that lets them plug into the wall? Are they just trying to make me spend more money?

Thanks! — Sam 76.24.222.22 (talk) 12:25, 29 July 2009 (UTC)

I am not an electronics expert but I would have expected a much more powerful charger, I think that charger would take a long time to charge a battery of even only a few AH. As for the charging stations, the intention is to have 2 batteries, one on charge with the other in the tool for constant usage. 81.144.241.243 (talk) 13:01, 29 July 2009 (UTC)

See if it's not on this page [52]. If not you'll probably have to do a 2 step process here [53] First enter the model number of your cordless drill in the "need a manual" window (unless you are more organized than most and actually still have that) That will tell you what they call the wall wart/battery charger/power adapter /etc. and if you are lucky also a part no. Enter either the part no. or the description in the search window on top of the page (underneath the DeWalt logo). If that doesn't get you anywhere call their customer service [54] (USA 1-888-678-7278). Good luck. 71.236.26.74 (talk) 14:03, 29 July 2009 (UTC)

There does not appear to be standardization of voltage and plugs. The wall wart you have with a 5 volt output would not be able to recharge your 18 volt battery. It is a good practice to get a white paint marker, and write on each adapter what device it works with, because eventually they are bound to get separated. The adapters often just have the name of a factory in China on them and not the brand or model of device they are supposed to power or charge. Edison (talk)

High performance batteries and their chargers have specific voltage/current characteristic and charging time. They are designed together as a system and the manufacturer has to accept liability of overheating, explosion, chemical leakage or damage. This means it is to your advantage to have the charger and battery that the supplier guarantees for use together. It is inconceivable that any honourable company could dream of making a profit from your purchase. Cuddlyable3 (talk) 16:13, 29 July 2009 (UTC)

Calcium Chloride in Damprid?

Is the calcium chloride in Damprid really just regular ole table salt that I can buy in the grocery store? If so, wouldn't it be cheaper for me to buy a bag of salt instead spending a lot of money buying the refills? --Reticuli88 (talk) 13:18, 29 July 2009 (UTC)

Sodium Chloride is "just regular ole table salt", more or less, but no that's not Calcium Chloride (which is nastier). On damp removers the reusable ones are Silica based but have lower capacity. There may be cheaper places to buy Calcium Chloride--BozMo talk 13:26, 29 July 2009 (UTC)

I think you can buy CaCl2 at a hardware store in large bags for use as ice melter. Coolotter88 (talk) 13:36, 29 July 2009 (UTC)

Bunsen Burners and Gas stoves

This has been puzzling me for long.Consider that you are lighting a gas stove or bunsen burner.When you light it,the gas gets ignited and undergoes combustion and hence it burns.The burning process takes place only outside the outlet.What is the mechanism that prevents the fire from spreading inside along the tube and into the gas cylinder and the final KABOOOOOM ???gdsrinivas 13:35, 29 July 2009 (UTC) —Preceding unsigned comment added by Gd iitm (talk • contribs)

probably because the gas pressure inside the pipe is higher than outside so the flames are blown outwards. also, there is no oxygen in the pipe to support combustion so the gas will extinguish any flame that manages to make it inside. Coolotter88 (talk) 13:38, 29 July 2009 (UTC)

In a bunsen burner,there is a hole at the bottom for mixing of air and gas.So it is a mixture of air and gas along the entire length of the bunsen burner.Now how do you explain it??gdsrinivas 13:43, 29 July 2009 (UTC) —Preceding unsigned comment added by Gd iitm (talk • contribs)

"Back burning" can occur in a bunsen burner. No flame shows and it smells bad. I think it can be provoked by throttling back the gas supply. It can be corrected by thumping the rubber supply pipe. Cuddlyable3 (talk) 13:48, 29 July 2009 (UTC)

yeah, probably the gas pressure pushes the flame outwards. When you light the bunsen burner, it's like a jet. Coolotter88 (talk) 13:52, 29 July 2009 (UTC)

There are two features here. Even in a tube of perfectly mixed methane and air, the speed at which a flame propagates into the mixture (the Flame speed) is limited (by memory about 5 cm a second I think) so if the flow speed exceeds this the flame will be being blown away not traveling down the tube. The flame only stays put on a bunsen burner because the double burner edge creates a recirculating eddy: try to light a straight tube of premixed air and you will fail. Gas stoves have similar design features. The second feature to stop this inadvertently happening at low nozzle speed is a Flame trap which is made of wound up nit-mesh: the flame cannot penetrate it because the heat loss to the metal fibres quenches the flame. However do not be fooled into thinking the gas emerges completely premixed; close inspection reveals a rich premixed inner flame (blue, the characteristic colour of Carbon Monoxide flames) and a CO rich diffusion flame outside it. Clever chap Bunsen. --BozMo talk 13:57, 29 July 2009 (UTC)

Your description of Back burning would indicate a cheap version of a Bunsen with no flame trap I guess. --BozMo talk 14:00, 29 July 2009 (UTC)

Thats a nice question.But when I asked one of my friends he said it was one of the important concepts in fluid dynamics.Any info based on this???thanks117.193.144.206 (talk) 16:29, 29 July 2009 (UTC)

As an add on to the question why does the flame occur only exactly at the top of the bunsen burner opening???Why not it occur a few centimetres above the bunsen tube or a few centimetres inside the tube???117.193.144.206 (talk) 16:36, 29 July 2009 (UTC)

BozMo please explain this :The flame only stays put on a bunsen burner because the double burner edge creates a recirculating eddy.117.193.144.206 (talk) 16:38, 29 July 2009 (UTC)

I am not very good at explaining things. Flames are just reaction fronts which eat into flammable gas mixtures. To ignite the gas coming rapidly out of a pipe end you need an ignition source where the gas comes out (or with very fast turbulent flow ignition further downstream). Otherwise the flame will blow itself out. For a burner this could be a pilot light by the pipe end but if you can induce an eddy by the pipe end (a recirculating piece of flow) then the gas which is already burning keeps the flame going by reintroducing a piece of flame into the flow. This is the purpose of the double skin on a Bunsen. Unfortunately the Wikipedia article on Bunsen burners is not very good apparently because there isn't a very good reliable source on Bunsen's. However I have written a few peer reviewed papers on gas combustion [55] [56] and I do have some idea what I am talking about. --BozMo talk 19:42, 29 July 2009 (UTC)

If you understand flow dynamics I should add that a stagnation point is sometimes sufficient but not as stable and that just having a thick tube wall works at some flow rates. However if you get a pair of pliers and squeeze the two walls of a Bunsen together (so that you just have a circular pipe end) the flame will blow itself out. --BozMo talk 19:50, 29 July 2009 (UTC)

Volume to pressure ratio?

How can I know the volume of a gas, knowing the capacity of its container (50 L), the amount of moles (64,48) and the pressure (1,621,200 Pa), but not knowing the temperature? Thank you. --83.56.187.237 (talk) 19:58, 29 July 2009 (UTC)

You just defined the volume as 50 L. Temperature is the unknown, as you surmised, and can be calculated easily (assuming an ideal gas). — Lomn 20:02, 29 July 2009 (UTC)

Thank you, what a blunder! Therefore, what should I substitute for $R$ in the following state equation in order to determine the temperature?

$1,621,200\cdot 50=64,48\cdot R\cdot T\,\!$

--83.56.187.237 (talk) 20:20, 29 July 2009 (UTC)

R is the gas constant. Just make sure you use the right value for the units you're using. Rckrone (talk) 20:26, 29 July 2009 (UTC)

Precisely. I'm probably stupid, but I don't know which is the right value I should use. --83.56.187.237 (talk) 21:04, 29 July 2009 (UTC)

Well I'm not going to do your homework but you need to select the gas constant from the list that uses the same units as your problem. The closest one is in m3 Pa K−1 mol−1. Since you have your volume in L instead of cubic meters, you need to convert that 50L into cubic meters. Then you can use the R constant from the list at the article and it will work (because it's all in consistent units). TastyCakes (talk) 21:16, 29 July 2009 (UTC)

First I would recommend leaving the units in your equation. That makes everything much easier. It's not important that you choose R so that all the units cancel out right away. You can use unit conversion where necessary to get things into the form you need. So for example if you choose R = 8.314 472 m³ Pa K⁻¹ mol^-1, you'll be left with L on one side of the equation and m³ on the other, but we know that m³ = 1000 L. Any of the values for R on that page will work, but some will just require more unit conversions than others. Rckrone (talk) 21:44, 29 July 2009 (UTC)

Damps in coal mines

Reading Firedamp, I'm curious — using current technology, would it be possible/likely for coal mining companies to collect these gasses in mines and sell them for fuel? Nyttend (talk) 20:10, 29 July 2009 (UTC)

See Coalbed methane. That seems to be the general idea there. Rckrone (talk) 20:38, 29 July 2009 (UTC)

(EC)The concentration of methane in a coal mine might vary significantly over time and might be too low to run an internal combustion engine, but methane recovered from landfills also varies. Firedamp does not say what the methane concentration is as commonly found. It might be higher in rooms of abandoned mines than in working mines, so some mines might work better than others as possible sources. See Biogas. The solution with gas from landfills is to mix it with sufficient natural gas to properly run an engine such as a modified diesel to generate electricity, if the concentration is too low. The mix can be automatically adjusted as the concentration varies. Edison (talk) 20:40, 29 July 2009 (UTC)

Flufenamic acid

Our article on flufenamic acid, or fenamic acids in general, lists them as NSAIDs. However, I am not at all sure they inhibit COX. Do they? What flufenamic acid actually does is to block the Calcium-sensitive nonselective cationic current in neurons. What does that have to do with the anti-inflammatory action?! Any input is welcome. Thanks in advance, --Dr Dima (talk) 20:31, 29 July 2009 (UTC)

A Google Scholar for "flufenamic acid NSAIDs" gets a bunch of hits, including PMID 10866999 which seems to be relevant. Looie496 (talk) 23:06, 29 July 2009 (UTC)

Thanks Looie. So it does affect both COX expression and COX activity (as well as cation currents, Ca ion balance, and who knows what else...). It figures. Thanks. --Dr Dima (talk) 23:37, 29 July 2009 (UTC)

Dragons of Eden updates

Has Carl Sagan's The Dragons of Eden ever been updated since it was first published in 1977? NeonMerlin 21:02, 29 July 2009 (UTC)

It doesn't look like it. There was a paperback edition published in April of 1978 and a 'mass market' paperback in 1986 - but from what I can see of them in Google books and Amazon - they contain the same text as the 1977 version. Neither of them say anything about being revised - and there is only one author's copyright date. SteveBaker (talk) 21:31, 29 July 2009 (UTC)

Eurasian plate

is Eurasian plate (western part) moving north or it is moving south in altitude. Eurasian is a large plate. The east plate is China, Japan, Phillipines, surrounding by Yellow Sea. Part of east half of Eurasian plate is moving southeast. Africa is suppose to collide with Europe, closing all the oceans nearby.--69.228.145.50 (talk) 21:19, 29 July 2009 (UTC)

Help idenfying the following yard plants

The first is some kind of berry bush that has some kind of little (Chinese) red jack-o-lantern type fruit.

The second is uncut and thinned out (crab?) grass that when watered every day and cut every week grows very dense to make a lawn.

The third has fronds with very thin and tough stems.

All three are located in coastal mid Florida but no one here can identify the first two without the berries and the watered and cut grass roots.

No one here has a guess what the third one is either except that it might also be native to China. -- Taxa (talk) 23:21, 29 July 2009 (UTC)

Drugs to make me smart

Can I get drugs to make me more intelligent to pass my exams? —Preceding unsigned comment added by 79.75.104.10 (talk) 23:31, 29 July 2009 (UTC)

Not really, no. There are many nootropic drugs, of various legal status, but none of them will really make a difference if you haven't studied for the exams. --Dr Dima (talk) 23:47, 29 July 2009 (UTC)

Sure they can. Try caffeine, preferably as coffee, which will also prevent dehydration. —Preceding unsigned comment added by 84.187.91.197 (talk • contribs) 00:12, 30 July 2009

I'm not sure if the OP is expecting to become somehow become more knowledgeable after eating the drug, as in the case where he/she doesn't study. Rather, I think the question is whether there are any drugs which will make your brain more active and sharper for a limited period of time, much like a steroid does to the body. Such a drug would be highly useful in a competitive exam, where speed and accuracy are essentially more important than knowledge. So I'm interested in knowing some answers, too. Rkr1991 ^{(Wanna chat?)} 00:59, 30 July 2009 (UTC)

There definitely are such drugs, amphetamine is the most widely used. Unfortunately it is illegal and highly addictive. Looie496 (talk) 01:21, 30 July 2009 (UTC)

In my experience, smart drugs seem to make me just smart enough to realise they're not having any effect. Adambrowne666 (talk) 01:38, 30 July 2009 (UTC)

If such drugs existed, were legal, and could be sold without a prescription - you can be 100% sure that you'd know it because you'd be bombarded with adverts for them every time you turned on the TV. Instead, the best we get are exceedingly dubious "food supplements" that can claim just about anything without any proof whatsoever because they fall through a convenient loophole in the law. I agree that caffeine is really the only one with any kind of a legitimate track record. It doesn't make you more intelligent though - it just ensures that you're awake. But even then, you have to be quite careful because if you take too much of the stuff, you'll become super-nervous and jittery - and that's just as bad as being half asleep! IN terms of not-legal-without-a-prescription, I've heard that some people take beta blockers because (as our article says) "Beta blockers protect against social anxiety: Improvement of physical symptoms has been demonstrated with beta-blockers such as propranolol; however, these effects are limited to the social anxiety experienced in performance situations. (example: an inexperienced symphony soloist)" - which can leave a person with exam anxiety feeling calm and relaxed. Not more intelligent - but perhaps calm enough to be able to better use the intelligence you already have. But these things can be dangerous - and taking them without a doctor's advice would be pretty amazingly stupid. SteveBaker (talk) 03:57, 30 July 2009 (UTC)

During the past 5 years or so there has been a large upsurge in the number of "smart drugs" that are sold in schools. The studies I have seen on these drugs say they range from ineffective to ineffective and dangerous. Even caffeine has debated impact on grades. While it would help you stay up the night before to study and help you stay aware during the exam itself, it lacks the ability to give you the mental agility provided by a good nights sleep. Using caffeine to stay up will not help with any exam that takes abstract thought, though could help with other types of exams. Anythingapplied (talk) 04:11, 30 July 2009 (UTC)

New word phenomenon?

A few months back, I stumbled upon a wikipedia article that explained a phenomenon about when people learn new words (i.e. 'perfunctory') and over the course of the next few days, they see that word more often (i.e. in a book, a newspaper article, billboard on the highway.) What is this effect or phenomenon called? 24.148.59.37 (talk) 02:32, 30 July 2009 (UTC)

It sounds like a form of confirmation bias. Or at least related to it. --Jayron32 04:33, 30 July 2009 (UTC)

It's not just with new words, either. I remember when I was a kid, when my dad got a new car, suddenly the streets seemed to be full of the same model. It might not even be a cognitive bias, it could just be that since the word is new, it is forefront in your consciousness and seeing it easily reminds you that you just learned it. Over time it falls back to the "just another word" status of everything else in your vocabulary, and seeing it does not trigger the "hey that's that new word" thought. Maelin (Talk | Contribs) 04:39, 30 July 2009 (UTC)

Spider identification

Is this spider found in mid-Missouri an orb spider? Just wondering if I should shoo it off the porch or invite it to stay a while. -- kainaw™ 02:37, 30 July 2009 (UTC)