Wikipedia:Reference desk/Archives/Science/2011 July 27

= July 27 =

Motor type and most likely wiring scheme
I was given the motor to the right. It was taken from an old window AC unit in the US. I think it's a 3-Phase motor but all the 3-phase_AC color codes both inside the US and outside that I've seen have other than what this motor has: black, brown, red, blue, and gray. Peter Michner (talk) 01:26, 27 July 2011 (UTC)
 * There is nothing recognisable in the photograph to help gauge the size of the motor. (Also the photograph appears to be upside down, or is it attached to the ceiling?)  I doubt a smallish motor for a window air conditioner would be 3-phase.  Perhaps it is a single-phase motor and the extra cables are to facilitate some operating variation such as two-speed or forward-reverse.  Dolphin  ( t ) 03:37, 27 July

2011 (UTC)
 * Sorry about that. It's about 10cm in diameter, (and sitting on the counter in that photo) so about the size of a regular person's fist. The two other pieces of information it gives are a GE sticker on one side and another sticker that says "HAM-3500(W) 120V 60Hz." Peter Michner (talk) 15:03, 27 July 2011 (UTC)


 * If you Google Images "air conditioning stepper motor" you get pictures of similar motors with the same number of wires (5). Therefore I think it's a stepper motor, probably used to control the vent direction. This means you need to connect it to a stepper motor driver, not direct to the mains. --Heron (talk) 08:30, 27 July 2011 (UTC)


 * Interesting. I'd like to see the exact pictures you were looking at, because all the stepper motor wiring diagrams I could find had even numbers of wires, like four or six. Peter Michner (talk) 15:03, 27 July 2011 (UTC)


 * Here is picture #1 in my search results. It has 5 wires. However, from the other information given in this thread after I replied, it seems that the motor in question is not a stepper. --Heron (talk) 17:12, 27 July 2011 (UTC)


 * If its a stepper motor, you may be able to feel 'cogging' as you rotate the shaft by hand.--GearCutter (talk) 12:55, 27 July 2011 (UTC)


 * Actually, it's perfectly smooth. Peter Michner (talk) 15:03, 27 July 2011 (UTC)


 * I just took an ohmmeter to the wires and came up with this table:

This would indicate gray was ground, right? Peter Michner (talk) 22:43, 30 July 2011 (UTC)
 * }
 * That would be a very odd color for a ground lead. What is Ω for Gray to frame? If the roation is perfectly smooth you probably have some type of AC induction motor and the "extra" leads are for speed control or cap start or the like. I'd suggest walking into a local repair shop, preferably one that re-winds on site, and asking. - ArtifexMayhem (talk) 03:06, 31 July 2011 (UTC)


 * Infinity there, too. It's as though the gray wire isn't connected to anything. I opened the motor to see a solid squirrel cage inside, so it's definitely an induction motor. I'll try to find a motor repair shop in my area, probably. Peter Michner (talk) 23:31, 31 July 2011 (UTC)

Identify butterfly or moth species
What species of butterfly or moth (I assume it's one of the two) is this? The photos were taken in Hot Springs National Park near Hot Springs, Arkansas in the United States. Thanks in advance, Ks0stm (T•C•G) 02:26, 27 July 2011 (UTC)
 * It's definitely a butterfly. Butterflies hold their wings vertically at rest, moths fold theirs flat. I think it's a type of swallowtail butterfly. SemanticMantis (talk) 03:54, 27 July 2011 (UTC)
 * Your image agrees closely with this one, which says it is a spicebush swallowtail. Our article spicebush swallowtail has a similar but different picture. The differences could be due sexual dimorphism, or perhaps more than one species goes by that common name. SemanticMantis (talk) 04:03, 27 July 2011 (UTC)
 * I'm doubtful of this assignment - a spicebush swallowtail is a swallowtail, after all, but I can't see the slightest trace of the tail on the wing after which it is named. And mimicry is common among butterflies... Wnt (talk) 06:17, 27 July 2011 (UTC)
 * To begin with, I see only two legs in the side view photo, so I'm thinking Nymphalidae, not Papilionidae. Wnt (talk) 06:24, 27 July 2011 (UTC)
 * This looks like Limenitis, maybe Limenitis arthemis astyanax, which is native to that region. Wnt (talk) 06:32, 27 July 2011 (UTC)
 * Yep, I think you've got it with astyanax. (`Four-footed' does rule out Papilionidae, but many swallowtails have no visible swallowtail, no?). SemanticMantis (talk) 13:35, 27 July 2011 (UTC)
 * Sorry for the confusion - you're right, it's just that the spicebush swallowtail does have one. Wnt (talk) 18:05, 27 July 2011 (UTC)

As seen in Knowing (film), could a solar-megaflare kill literally everyone on Earth?
When I saw the spoilers of the end-scenes on YouTube, my first thoughts were:


 * 1) What about anyone in bunkers deep underground? Could they survive there?
 * 2) How about in submarines deep under the oceans? How far down could the solar flares hit there?

I would have confidence that being deep enough underground or underwater would ensure survival. What do you make of this? --70.179.165.67 (talk) 05:55, 27 July 2011 (UTC)
 * There's no definition of how big a flare has to be before you call it a 'megaflare'. It could just mean 'bigger than the last biggest one'. Presumably if the sun decided to throw half of its mass in our direction then we would be fried. However, in the real world, even the most pessimistic scientists say that a huge solar flare would do nothing more than blow up our power grids. That would be bad enough--millions in the developed world would die--but we would eventually repair all the damage and carry on. I've never heard a serious prediction of a solar flare that could set directly fire to things on the Earth's surface, or even give you sunburn. --Heron (talk) 08:24, 27 July 2011 (UTC)
 * I just (literally minutes ago) finished reading Sunstorm (novel), which is all about the possibility solar burst wiping out the planet, going kilometres deep and boiling off the ocean. (I recommend it by the way)-- Jac 16888 Talk 12:20, 27 July 2011 (UTC)
 * "Millions in the developed world would die." Wrong.  People dependent on life support in hospitals would die, yes, as would (possibly) some people who were using technology to survive a massive heat wave or a terrible storm, but as the flare would not knock out the combustibility of objects, people would be able to create fires and stuff to survive the winter, and sprinkle water on themselves to survive the summer heat, at least until they got the power grids back on-line. Whoop whoop pull up Bitching Betty 23:22, 27 July 2011 (UTC)
 * I think that A sudden destruction of our electrical and telecommunications infrastructure would be a lot more devastating than you believe it would. For example, the sudden shortage of refrigeration would cause food shortages. Fuel shortages would be a serious problem. Partially because people would be burning gas in generators, partially because almost every step of the process of getting oil from the ground into our cars relies on electric pumps. The economy would suffer greatly, that alone could cause huge number of deaths.
 * After a week or so, safe fresh water would be difficult to come by in many areas. Even in areas with plenty of water electricity is often required to pump it into water towers.
 * Virtually our entire economy is dependent on "Just in time" deliveries and manufacturing. Without telecommunications and unlimited gasoline that wouldn't work properly, so even if there was enough food, it wouldn't be in the stores that need it. If those trucks stop rolling and those ships stop sailing people will starve.
 * Even easy things like staying warm in the winter. You talk about building fires, but where are you going to get enough wood to warm up all ten million inhabitants of New York City alone? And then how are you going to get it to where it needs to be? I'm not sure we could harvest and move that much wood now, let alone in the middle of a global crisis.
 * After the power was turned back on there would be long term effects. If this happened during the growing or harvesting season, vast amount of crops might be lost. Which could lead to serious starvation. (Remember, we won't be able to just buy food from other countries if they all had the same problem!)
 * And this all assumes that electronics aren't also damaged in the flare. If microchips are knocked out as well, the vast majority of cars and trucks won't start even if they do have gas! That will make it even harder to transport supplies. (Including gasoline, and the parts we'd need to fix things! Which just compounds the problems!)
 * It wouldn't be the end of the world, it could all be fixed in time. But it would be far worse than you're imagining, because you're only thinking of consumer uses of electricity. You don't realize that everything else you need to stay alive also depends on electricity.  We simply can't go back to an agrarian non-technological life-style with this many people, we need our technology.
 * APL (talk) 00:09, 28 July 2011 (UTC)


 * You grossly underestimate the importance of electricity and the cascading failures such as meltdowns and dam failures that would occur, not to mention huge crop losses, deterioration of frozen foods and medicines, and fires in cities, if there were a loss of generators and transformers. Just as a complete continent wide EMP failure would likely kill millions.  A world-wide event would kill hundreds of millions easily.


 * See the FEMA report. μηδείς (talk) 00:21, 28 July 2011 (UTC)


 * A dam is not held up by electricity. Whoop whoop pull up Bitching Betty 02:03, 31 July 2011 (UTC)
 * Don't be juvenile. Of course they're not held up by electricity, but they're not just simple walls in the water either. (Unless we're talking about the ones made by beavers.) Many of them have moving parts to regulate how much water is allowed through the dam. It's not difficult to imagine that if those were damaged in the flare, or could not be powered, there could be some serious results.  (Letting too much or too little water through could lead to flooding on one side and water shortages on the other.  And letting too little water through until the built up water destroys the dam would be a catastrophe.) APL (talk) 04:00, 31 July 2011 (UTC)
 * Don't they have backup power? I've been to the Hoover Dam, and sure enough it has two Pelton wheels for backup power, in addition to the main turbines.  Maybe the ones in Europe don't, but American ones sure do...  --  An American ultranationalist 67.169.177.176 (talk) 04:35, 31 July 2011 (UTC)


 * Not related to the original question, but does Knowing remind anyone else of Heinlen's The Year of the Jackpot? --Trovatore (talk) 00:24, 28 July 2011 (UTC)


 * A "mega-flare" of this type could only conceivably occur when the Sun begins to shed its outer layers.
 * Or when its luminosity begins to exceed the Eddington limit, whichever comes first. Whoop whoop pull up Bitching Betty 02:03, 31 July 2011 (UTC)

DNA question
What is the difference between:
 * 1) my DNA and my brother's DNA
 * 2) my (ans my brother's) DNA and a chimp's DNA

I just don't know what kind of differences they are. What is in common in the DNA of all members of a species, and what is different in every member? when they say that 99 percent of human and chimp DNA is the same,what are they exactly talking about?Do I have to study genetics in university in order to fully understand it?--Irrational number (talk) 07:31, 27 July 2011 (UTC)
 * This definitely won't be the full answer you're looking for, but consider the vast number of boring mundane operations that need regulating in the body and the make up of tissue and cells. Most of the differences between humans and chimps are superficial, and between humans and cabbages for that matter. Hope this helps. Pascal (talk) 07:58, 27 July 2011 (UTC)
 * If you're looking for raw numbers, humans and chimpanzees share 96% of their DNA, while the average humans differ by only 0.1% (meaning they share 99.9% of their DNA). You can find more information at Human genetic variation. - Running On Brains (talk) 09:57, 27 July 2011 (UTC)
 * That 0.1% turns out to be 4 megabytes worth of individual human genetic variation, per Human genome. 99.17.204.52 (talk) 10:20, 28 July 2011 (UTC)
 * DNA is basically just a (really, really, really) long code of molecules. These codes govern basically everything about your body: making sure your legs grow in the right way, making sure you can digest food properly, etc. A lot of the basic structure in life is similar, throughout ALL life, so a good percentage of these codes are the same in many different species of animals (and even plants!). The more similar the lifeforms, the higher percentage DNA will be the same, which is why chimps, which are primates like us, have 96% similar DNA. But even in other mammals, like squirrels or yaks or beavers, you will find a good chunk of their DNA is similar to ours (don't have the exact numbers, but yeah). Lizards would have a smaller (but still high) percentage, fish probably lower. But yeah, two humans are pretty much the same, DNA-wise. It's tiny, tiny differences in the DNA code that make every person unique (except for identical twins, which have 100% similiar DNA).--66.207.206.210 (talk) 14:21, 27 July 2011 (UTC)
 * For more perspective, we share 70% of our DNA with sea sponges. - Running On Brains (talk) 14:58, 27 July 2011 (UTC)


 * Is it known what percentage of human DNA would also be found in an amoeba? Or in E coli?   Has someone drawn up an extended family tree?  Wanderer57 (talk) 15:27, 27 July 2011 (UTC)
 * That question raises a difficulty that is important to understand. Most of the exons (the parts of the DNA that encode protein structures) in human DNA correspond to exons in the DNA of amoeba and bacteria, and it is possible to compare them -- that's how the numbers that you see are derived.  However, less than 1% of the total DNA belongs to exons.  For the remaining DNA (99% of the total), there is no well-established method of doing cross-species comparisons.  For a long time most biologists thought that the "non-coding" DNA is mainly junk, but over the last decade it has become clear that there is a lot of important stuff there. Looie496 (talk) 16:07, 27 July 2011 (UTC)


 * Here is the basic thing you have to understand. A DNA molecule is a string of "nucleotides".  There are four possible nucleotides, usually labeled A, G, C, and T.  So a DNA molecule can be thought of as a string like "AGGACTTACCTAGGACATTTG...".  The string for each DNA molecule is around a hundred million letters long, though.  If you compare the DNA molecules in your cells with those in your brother's cells, they can be matched up letter for letter, but there will be a few differences -- something less than 1% of the letters for your DNA will differ for your brother.  For somebody less related to you, the number of differences will be larger, and for a different species, larger yet. Looie496 (talk) 15:59, 27 July 2011 (UTC)


 * Thanks very much. So of the 1% or so of human DNA that encodes protein structures, is it known how much would also be in an amoeba, a bacterium, a nematode, an aphid, a tobacco mosaic virus,...?   Is there a lookup table? Wanderer57 (talk) 16:59, 27 July 2011 (UTC)

So is there a accurate boundary between species with regard to DNA difference(or at all)? for example, is it right to say "if the difference is more than X%, then the living things are not of the same species"?--Irrational number (talk) 18:58, 27 July 2011 (UTC)


 * No, there are no official boundaries. In large part, this reflects the fact that much taxonomic nomenclature predates the discovery of DNA.  For modern practice though, there are some rules of thumb.  With bacteria (where reproductive definitions of species are moot), typically one requires a new strain differ by at least 1% from existing species before a new species name is assigned.  Further, one generally expects at least a 4% difference from all existing genera type specimens before proposing a new genera name.  Dragons flight (talk) 20:14, 27 July 2011 (UTC)

Provided you have the same mother, you probably share the same mtDNA.Smallman12q (talk) 02:52, 28 July 2011 (UTC)


 * I was going to look this up but never got around to it, and won't for a while now - but in general, viruses are extremely efficient in using DNA to code proteins - actually going over 100% sometimes, because more than one gene is coded in the same space due to frameshifts. Bacteria spend a short stretch here and there on regulation rather than protein coding, but do so on a tight budget.  The others get increasingly inefficient as their replication rate decreases, and I'd really have to look them up, because it can vary WIDELY among closely related organisms.  For example there is a fish Fugu rubripes which has a very compact genome, even though other fishes have all kinds of spam shoehorned in between the genes.  And of course humans spend DNA without a thought, it's like some kind of Usenet feed full of Make.Money.Fast and Nigerian bank scams. Wnt (talk) 15:09, 28 July 2011 (UTC)

Starting up a nuclear reactor
Where does the neutron used to start a nuclear reactor come from? Whoop whoop pull up Bitching Betty 15:07, 27 July 2011 (UTC)


 * Spontaneous fissions. Nuclear bombs, on the other hand, don't work properly with such a slow-cooking method of starting up (they "energetically dismantle" themselves before they've really gotten going); so they use a neutron source like a modulated neutron initiator. -- Finlay McWalter ☻ Talk 15:12, 27 July 2011 (UTC)


 * The joy of a critical mass is that you don't really need to start it with anything special — once you have the material into a critical configuration, any stray neutrons will start the process. There are lots of neutrons out and about in the world, just zipping along, and as Findlay points out, your fissile material (much less impurities hanging out in the fissile material, like Pu-240) already have background neutron rates due to spontaneous fission. With a reactor you have time to just wait for the thing to start up and grow slowly; as Findlay points out, you can't do that with a bomb, because you need all of those reactions to take place in less than a millisecond. --Mr.98 (talk) 15:25, 27 July 2011 (UTC)


 * To show how easy it is to start a nuclear reactor up, look at Chicago Pile 1, the first nuclear reactor, and see how primitive it was. Most of the complexity in modern nuclear reactors isn't in getting them started, it is in slowing them down and stopping them.  -- Jayron  32  16:22, 27 July 2011 (UTC)


 * Speaking of which, the RBMK style of reactor uses natural uranium, light water, and graphite. I wonder whether - in theory - it would have been possible (survival optional) for people in Neolithic times to create a nuclear reactor using only a natural uranium ore mixed in with soot at the right concentration... Wnt (talk) 18:02, 27 July 2011 (UTC)
 * In theory, probably yes, after all, it has happened naturally without any human intervention at all. In practice, of course, Neolithic peoples would have lacked the very detailed knowledge necessary. Still - intriguing plot idea. {The poster formerly known as 87.81.230.195} 90.197.66.97 (talk) 19:19, 27 July 2011 (UTC)
 * That happened about 2 billion years ago when the natural enrichment of uranium was about 4% of U-235. Nowadays that enrichment is only about 0.7% U-235 which wouldn't be enough for a natural reactor to occur. That's why the difficult step of enriching the natural uranium must be taken before it can be used as fuel for a nuclear reactor. Dauto (talk) 20:27, 27 July 2011 (UTC)
 * If that were true it would be impossible to operate a RBMK reactor with light water and natural uranium. However, it is possible, so it's possible, in theory, that Neolithic peoples could have created an (albeit very simple) nuclear reactor.  However, as it would have gotten hot enough to boil away the water used to cool it, it would probably go supercritical, melt, or both, meaning that it would probably be useless for anything other than starting fires.  OTOH, though, it would have been darn near impossible to shut it down, so it could have been very useful as an area denial weapon or to destroy the land of an opposing tribe or, if dropped into water, as a sort of artificial hot spring which could have been used for military (to gather buckets of scalding hot water to use as weapons, and to wash weapons more efficiently,) civilian (to wash clothing and stuff more efficiently,) punishment (to scald people to death as a form of capital punishment,) or culinary (to boil fish,) purposes. Whoop whoop pull up Bitching Betty 23:33, 27 July 2011 (UTC)


 * That's true. But that would be a very tall order for neolithic people. My point was that the naturally occurring reactors happened during a time when it would have been much easier to produce a sustained nuclear reaction even without graphite as a moderator. Dauto (talk) 00:01, 28 July 2011 (UTC)


 * To be clear, I really don't know if any uranium ore is free enough from the wrong kinds of impurities to be able to start a chain reaction, nor whether enough would occur in one place that it is plausible for someone at a low tech level to collect enough of it. But it seems an amusing scenario for fiction. Wnt (talk) 15:01, 28 July 2011 (UTC)


 * No, a Neolithic tribe couldn't have made a nuclear reactor. Light water is trivial to come by, and smelting uranium might be possible, but there's no way to get the hyper-pure graphite needed -- a minor, unrecognized contamination of their graphite is one of the reasons the German atom bomb project failed. --Carnildo (talk) 01:46, 29 July 2011 (UTC)


 * Smelting is how sulfides are reduced to the bare metal. With uranium, you need to reduce the oxide to the bare metal—you would need something more along the lines of a blast furnace. Whoop whoop pull up Bitching Betty 02:14, 31 July 2011 (UTC)


 * Didn't they have something of the sort in ancient Rome? 67.169.177.176 (talk) 04:49, 31 July 2011 (UTC)


 * Hmmm, nuclear graphite didn't explain this much, though I'd wondered... still, I'm surprised there's enough boron to foul up the reaction (I assume) everywhere soot can be manufactured. Wnt (talk) 04:05, 29 July 2011 (UTC)


 * See Nuclear reactor physics and Startup neutron source. Note that besides providing a reliable source for startup neutrons, they also provide an operational check of the low level power meters before startup. -- 203.82.81.81 (talk) 23:49, 27 July 2011 (UTC)


 * See also neutronium. ~ AH1 (discuss!) 23:35, 28 July 2011 (UTC)


 * Um, why? It looks pretty irrelevant to me. --Mr.98 (talk) 02:03, 29 July 2011 (UTC)


 * The reason the Germans failed is because they didn't have the Borrowdale graphite. Conceivably they (a Neolithic tribe) could have accidentally placed a lump of uranium (wow, awesome dense armor metal) next to a (couple of) lump(s) of Borrowdale graphite (wow, awesome fuel and marking material) and hey presto, the first nuclear reactor. Whoop whoop pull up Bitching Betty 02:14, 31 July 2011 (UTC)
 * Except that you need a lot more uranium than that to have a reactor. CP-1 is probably about as crude a uranium-graphite reactor that you can make (almost by definition, given that it's basically one critical mass, I think), and it required several tons of uranium in a lattice. It isn't the sort of thing you are going to create accidentally. A more plausible (but still silly) idea is slightly less neolithic (but still quite early) people saying, "hey, this graphite would make a great brick! but I bet it'd be better if it had a lump of this dense metal in it! we can make great houses from this! but first let's just pile them all up over here in a big heap..." But it's still a very silly scenario (it would require smelting the uranium and making it into metal, which was not the most straightforward process even for 20th century metallurgists; I don't think uranium is ever found as a metal in the wild). --Mr.98 (talk) 02:49, 31 July 2011 (UTC)
 * Not—smelting! Blast—furnace—ing! Whoop whoop pull up Bitching Betty 03:02, 31 July 2011 (UTC)
 * Hmm... does tungsten carbide (excellent neutron reflector and critical—mass—reducer) exist in the wild? Whoop whoop pull up Bitching Betty 03:05, 31 July 2011 (UTC)
 * And are there any natural processes which can enrich uranium? Whoop whoop pull up Bitching Betty 03:07, 31 July 2011 (UTC)
 * At Oklo, the uranium was (supposedly) enriched by groundwater leaching. FWIW  --  An American ultranationalist 67.169.177.176 (talk) 04:46, 31 July 2011 (UTC)
 * So why couldn't the Neolithes have come across such naturally-enriched uranium (wow! great armor metal!) and just happened to place it within blocks of good Borrowdale graphite and thereby create the first (primitive) nuclear reactor? Whoop whoop pull up Bitching Betty 16:03, 31 July 2011 (UTC)
 * What? At Oklo the uranium was enriched because uranium was more highly enriched 2 billion years ago than it is today. Not because it was naturally enriched in some way. The only thing "enriched" by groundwater leaching at Oklo, I am fairly sure, was the concentration of uranium ore as a whole (not the concentration of U-235 relative to U-238) into an amount that could be of sufficient size for a critical mass. --Mr.98 (talk) 20:37, 31 July 2011 (UTC)
 * Go eat uranium-flavored Sagittaria! Whoop whoop pull up Bitching Betty 21:13, 31 July 2011 (UTC)
 * Why would tons of natural uranium be needed? Critical mass is reportedly much less, and RBMK says a big reactor contains 114 kilograms. Wnt (talk) 22:58, 31 July 2011 (UTC)

Only one higgs?
On the page List of unsolved problems in physics, the section on the Higgs mechanism says: "Does the Higgs particle exist? What are the implications if it does not? Is there only one of them?" Only one? What? The Higgs boson article says nothing about there possibly being only one. Can someone go into this a bit for me, why we think there might be only one, and what the implications are if that is the case. Thanks. --66.207.206.210 (talk) 15:44, 27 July 2011 (UTC)
 * Just to be sure we're on the same page, I read the statement as saying that there is only one type of Higgs particle. Do you read it as saying there is only one particle? Looie496 (talk) 15:49, 27 July 2011 (UTC)


 * (ec) The standard model has only one higgs particle. That's the simplest possible assumption, but nature could be more complex than that and there could be in principle many different higgs particles. Supersymmetric models usually require at least four different higgses one of which is a charged particle. Dauto (talk) 15:51, 27 July 2011 (UTC)


 * This report quotes Fermilab theorists speculating that there might be up to five kinds of "Higgs" bosons. -- Finlay McWalter ☻ Talk 15:55, 27 July 2011 (UTC)


 * That's what I was talking about except that they are counting particles differently than what I did. There is a pair of charged Higgses which are anti-particles of each other. If you count those separately, you have a total of five. If, on the other hand, you chose, as i did, to count them only once, then you get a total of four. Dauto (talk) 19:36, 27 July 2011 (UTC)


 * Well there was this idea once that there was only one electron and it bouncing back and forth in time made all the electrons and positrons in the world and that's why they all had the same charge. Perhaps that has made a comeback? ;-) Dmcq (talk) 17:42, 28 July 2011 (UTC)


 * One-electron universe -- Finlay McWalter ☻ Talk 17:49, 28 July 2011 (UTC)