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April 10

Overlook, Portland, Oregon aka Swan Island

Can anybody help me find some information about the environment of Overlook, Portland, Oregon aka Swan Island prior to the industrialization of the 20th century and after it to the present day? Like flora and fauna. If not something about island ecosystems in the lower reaches of the Willamette River where it meets the Columbia. Again very specific, so I don't care anything about the ecosystem of Oregon in general only that specific region and if not only region similar to it on the islands of the lower reaches of the Willamette River where it meets the Columbia.--170.140.214.104 (talk) 16:20, 10 April 2013 (UTC)

Good luck. According to this source, in 1841 there was "a dense stand of oak trees" that were cut down to build the Star of Oregon. Sean.hoyland - talk 17:06, 10 April 2013 (UTC)

Searching with the term "Columbia River Estuary" might help a little. The Columbia River Estuary reaches to Bonneville on the Columbia and Willamette Falls on the Willamette, and as a topic of study tends to focus on the ecology (present and historic) of the rivers and their many islands, wetlands, floodplains. I didn't search very hard, but some possible leads: This page, [1], the slides of some presentation, says the Willamette River was much shallower, with broader wetlands along it, and that apparently the main channel went east of Swan Island instead of west as it does today (the east channel is now just an inlet/lagoon). One of the slides shows the Swan Island area's bathymetry in 1888 and 2001, another changes in "off channel habitat". It also mentions (as do many other sources) how dam building on both rivers has radically altered the river flow (flow seasonality and freshet magnitudes are greatly reduced now—that is, water flow and river levels used to change dramatically over the course of the year, but now they don't much). And this page, [2], which among other things describes historical conditions at various sites around the Willamette-Columbia confluence. As with other sources, it mentions the historic abundance of Sagittaria latifolia (wapato) on the river islands around what's now Portland. Another thing you could do is look for sources on other islands in the area that are more likely to the kind of info you want. Sauvie Island comes to mind as one for which there's likely to be a lot of info. We have a few excellent/featured pages about wetlands and small streams in the Portland area, like Columbia Slough, Johnson Creek (Willamette River), and Tryon Creek. While these pages might not answer your questions directly, they might help give a general sense of things, and their reference sections might have useful sources to check. Pfly (talk) 08:05, 11 April 2013 (UTC)

PS, you could also ask over at Wikipedia talk:WikiProject Oregon, where there are many friendly folk who know an amazing amount of stuff about Oregon and the Portland area. Pfly (talk) 05:56, 12 April 2013 (UTC)

Jewellery chain

Is there a page (maybe on the internet?) that shows/teaches how to make singapore chain, or box chain ([3]), and other designs, such as in Jewellery chain?Curb Chain (talk) 17:17, 10 April 2013 (UTC)

Are there materials that turn light into sound?

Clearly it is possible to hook up a solar cell to a loudspeaker. Shine light on the solar cell, the loudspeaker produces a tone.

Are there (artificial?) materials that do this spontaneousely? Materials that absorb light energy and re-radiate it acoustically? 81.11.175.240 (talk) 18:43, 10 April 2013 (UTC)

well this is not very general but it technically does meet the requirements: the laser light–generated using a commercial laser–ionizes a small area of water, which superheats, creating an explosion of steam that generates pulses of sound waves at about 220 decibels. Gzuckier (talk) 20:02, 10 April 2013 (UTC)

The problem which you would need to overcome is that light is electromagnetic while sound is kinetic. I also doubt hooking up a speaker to a solar cell would produce any audible tone, unless you also hooking up a tone generator. Or, maybe you could put a fan in front of the solar cell so that it is covered and exposed at an audible frequency. but then you're still not really getting "light into sound", you're generating a tone using sunlight as the "carrier wave". In a more convoluted way, we turn light into sound when we speak :) Vespine (talk) 00:49, 11 April 2013 (UTC)

A cat placed into a sunbeam will often purr. I know, I know, not right. But what I'm trying to get at here is that the transformation of electromagnetic energy into acoustic energy is probably only accomplished through some sort of complicated intermediary, such a large biological organism. For non-biological approaches, maybe something like the crack of a melting iceberg? Again, not exactly what you're asking for. --Mr.98 (talk) 01:14, 11 April 2013 (UTC)

I wonder if we could somehow involve Piezoelectricity? But that still requires voltage, not light, so not really any different to your speaker idea.... Vespine (talk) 06:01, 11 April 2013 (UTC)

The simplest way I can imagine to go from light to sound would be a material with albedo that changes depending on temperature. As it heats up, it gets more reflective. This causes it to absorb less light energy and cool down. Once it is cooler it is less reflective and able to warm up more again. Then you would have to find a way to make the interaction happen quickly enough that the thermal expansion/contraction creates an audible noise. The overall system would need to be underdamped to be able to sustain the oscillation, and I'm not sure if that is possible. 38.111.64.107 (talk) 13:52, 12 April 2013 (UTC)

Bed bug feeding frequency

Every few days I wake up with a bite and I'm wondering whether I might have bed bugs. At some point I also had a rash around my jaw which I attributed to acne. I don't know when that was though. I'm wondering how long bed bugs could go without nutrition? If I go home (I'm a student), how long should I stay away to ensure bed bugs have all died? I haven't noticed any other signs though. It might be something else biting me. Playful spider perhaps. --2.97.27.107 (talk) 21:12, 10 April 2013 (UTC)

Have a look at Bedbug#Feeding_habits. It explains they prefer to feed every 5-10 days, but in some circumstances can last much longer, up to a year. As far as I know, adaptation to rare feeding is common in blood suckers, with some ticks and fleas reliably going several months without a fresh blood meal. Also note that bedbugs can "share" their meals, by piercing the stomachs of their peers and stealing their meal. If that sounds bad, it's just the start. Bedbugs also procreate though traumatic insemination! SemanticMantis (talk) 22:28, 10 April 2013 (UTC)

Unfortunately, if your bed bugs were mature and have laid eggs, you can't just wait for the adults to die. The eggs could be in the seams of your clothing, or your luggage, or anywhere in your bedroom. Have a look at the Bed bug article for other evidence to look out for before you take drastic measures. I hope the cause is something less persistent. Dbfirs 08:23, 11 April 2013 (UTC)

Although the question isn't strictly a request for medical advice, it would probably be in your best interest to consult a professional - in this case, the Orkin Man, or some equivalent. ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:17, 11 April 2013 (UTC)

synthesising DNA

hi there, I was wondering if there was a technique which would produce the synthesis (rather than the sequencing) of a specific strand of DNA with a known sequence? Presumably using its base nucleotides? Does it work? Would it work?

could you set up a basic but high yield automated process to carry out protein synthesis from the amino acids, even for longer & more sophisticated proteins?

I'm already familiar with PCR, selecting existing sequences or alleiles for amplification or expression invitro - I'm interested in synthesising very long strands or sequences which may not be found in nature.

Thanks! Horatio Snickers (talk) 21:23, 10 April 2013 (UTC)

See Artificial gene synthesis. Dmcq (talk) 21:30, 10 April 2013 (UTC)

Not only can it be done, it is regularly done these days. If you Google "gene synthesis" you can find companies that will do it for you over the internet. Like gene sequencing, the price has dropped dramatically over the past 10 years, though it is still relatively more expensive than sequencing. --Mr.98 (talk) 23:50, 10 April 2013 (UTC)

Rabies-like symptoms in ducks

A friend of mine was pursued by an aggressive duck apparently intent on attacking, in a manner described as being reminiscent of rabies. Only mammals have rabies, though; can any diseases cause rabies-like symptoms in ducks? הסרפד (call me Hasirpad) (formerly R——bo) 22:52, 10 April 2013 (UTC)

Birds can be aggressive, especially when defending their nesting areas. Geese are notorious for attacking people. See Friendly Persuasion. RNealK (talk) 23:14, 10 April 2013 (UTC)

Sorry, I didn't provide all the details of the circumstances, which make the above explanation unlikely:

Would ducks nest in high-traffic public parks? Would a provoked duck pursue the provoker—presumably well past her nesting grounds? הסרפד (call me Hasirpad) (formerly R——bo) 23:45, 10 April 2013 (UTC)

Not only mammals can get rabies, it can infect any warm blooded animal, including birds, however apparently birds have only been infected in experiments and not found in the wild. I saw a video on YouTube of a pelican eating a seagull and the explanation someone gave is that there is a rabies like disease that pelicans can get, so maybe it wasn't rabies, but something rabies like. In Australia, there is no actual rabies virus in the wild, but we are warned about fruit bats in particular because they can carry rabies like diseases. I just did a quick Google and it appears to be this Australian bat lyssavirus: closely related to rabies. Maybe there's something similar in birds. Vespine (talk) 23:51, 10 April 2013 (UTC)

Having said that, I also think you don't need rabies or any rabies like disease to explain an aggressive duck, maybe it was just an aggressive duck? There are plenty of aggressive dogs and most don't have rabies too. Vespine (talk) 23:53, 10 April 2013 (UTC)

Once, when sitting on the ground in a public park, I was mobbed by ducks that wanted my White Castle hamburgers. Deor (talk) 00:29, 11 April 2013 (UTC)

Let me guess: To get even with them for attacking, you gave it to them. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:52, 11 April 2013 (UTC)

More or less. While I was fighting some of them off with my left hand, others managed to snatch a burger from my right hand. At that point, I gave up.Deor (talk) 10:44, 11 April 2013 (UTC)

• Yes, land and waterfowl will nest in public parks. Yes, they can be very aggressive, especially given they nest on the ground. Swans have killed people and there are stories of rapes. Turkey attacks were a big item in NJ last summer in various municipalities. A girlfriend of mine was terrified of ducks, and she would murmur "the ducks... the ducks..." like the ending of Apocalypse Now. My younger sisters went to the Schuykill to feed the ducks popcorn and were attacked and bitten and left in tears. Male ducks gang up on and rape females, sometimes drowning them in the process. Remember, these little monsters are just velociraptors with beaks instead of teeth. μηδείς (talk) 17:45, 11 April 2013 (UTC)

Birds are mean sons of bitches. Like Medeis says, they are the only living dinosaurs. Shadowjams (talk) 20:56, 11 April 2013 (UTC)

Why didn't jurassic park have any giant rabid ducks that would have been cool.165.212.189.187 (talk) 17:30, 12 April 2013 (UTC)

There were duck relatives at the end of the Cretaceous, but not during the Jurassic. See. μηδείς (talk) 03:10, 13 April 2013 (UTC)

April 11

could a black hole exist at the center of a neutron star?

thanks, Rich76.218.104.120 (talk) 03:12, 11 April 2013 (UTC)

Not indefinitely. Plasmic Physics (talk) 03:30, 11 April 2013 (UTC)

What he said. Neutron star matter is expected to be fluid, so it would presumably just flow into the black hole and be consumed over time, and you would not have a neutron star for very long. Someguy1221 (talk) 06:16, 11 April 2013 (UTC)

And by "not very long" we're probably talking milliseconds! SteveBaker (talk) 11:22, 11 April 2013 (UTC)

perhaps you're right, whether it would be milliseconds or microseconds or days or what. I wondered if rapid rotation would play a role. But subatomic particles that decay in microseconds or less are still of interest in physics. i've also heard that very small black holes don't eat much, so i'm not convinced by the mere fact of of a LOT of [fluid or otherwise] mass pressing in on a black hole inside a neutron star would for sure cause it to take in all the neutron star's mass. If the black hole were small enough, i thought the "black hole evaporation" tendency could be roughly cancelled by the ready availability of mass inside the star.{to keep the black hole going, yet have the neutron star containing it exist for a "long" period of time}76.218.104.120 (talk) 12:28, 11 April 2013 (UTC)

Black hole evaporation ius one of those unproven ideas like gravitons, string theory, branes, etc. Much may be written but far less proof exists. Rmhermen (talk) 12:57, 11 April 2013 (UTC)

Thought I would check those intuitive answers with a back of an envelope, non-relativistic, much hand waving calculation. Assume that the rate of growth of the black hole is limited by area of its event horizon, the speed of light and the density of the surrounding material. Then in a "best case" scenario (or worst case from the POV of the neutron star) we have

${\frac {dm}{dt}}=4\pi r^{2}c\rho$

and for a non-rotating black hole r is the Schwarzschild radius

$r={\frac {2Gm}{c^{2}}}$

so

${\frac {dr}{dt}}={\frac {8\pi G\rho }{c}}r^{2}$

Integrating this gives

${\frac {1}{r_{0}}}-{\frac {1}{r_{t}}}={\frac {8\pi G\rho }{c}}t$

where r₀ is the initial radius of the black hole. If r_t is much greater than r₀ then we have

$t\approx {\frac {c}{8\pi G\rho r_{0}}}$

Taking a typical density at the centre of a neutron star to be 10¹⁸ kg/m³, then I make the time taken for the black hole to absorb the whole star to be of the order of 0.2 metre seconds divided by the initial radius of the black hole. For a millimetre sized black hole, this gives a timescale of minutes rather than milliseconds. Gandalf61 (talk) 13:16, 11 April 2013 (UTC)

Your calculation neglects the (very important) fact that the density around the black hole would not remain constant during the collapse. Dauto (talk) 15:59, 11 April 2013 (UTC)

Look for instance [4] where a detailed computer simulation shows that the collapse happens in less than 10 ms. Dauto (talk) 16:16, 11 April 2013 (UTC)

Haven't looked up the paper yet, but I'd just point out a possibly very important consideration: All that mass going into the black hole is going to be accompanied by a truly spectacular release of energy. Maybe enough to blast away part of the neutron star? Don't know; it's not like I can solve the equations (or even formulate them) in my head. Does the paper take that into account? --Trovatore (talk) 16:19, 11 April 2013 (UTC)

shall i take away a "yes" to the original question--that a black hole can exist inside a neutron star, regardless of how long it lasts?76.218.104.120 (talk) 04:24, 12 April 2013 (UTC)

Yes. Plasmic Physics (talk) 04:34, 12 April 2013 (UTC)

I hate when a potentially simple answer is complicated with obtuse mathematics and peripheral theory. It is akin to verbosity. Plasmic Physics (talk) 04:46, 12 April 2013 (UTC)

Well, I hate trivial soundbite answers because they are so facile and uninformative. I didn't know that a black hole could absorb something as massive as a neutron star in milliseconds. Now I know that (a) yes it can and (b) the scenario has been studied in detail. So I have learned something. Gandalf61 (talk) 09:04, 12 April 2013 (UTC)

With respect to the OP, it doesn't matter whether you learned something does it now? Giving a concise answer takes priority over divergent exploration of related notions. Its only fair to first answer the OP's question, before endulging in such a manner of discussion. Plasmic Physics (talk) 09:40, 12 April 2013 (UTC)

Well, I certainly don't think the OP learned anything from your trite "Not indefinitely" response, beyond the fact that you couldn't be bothered to take their question seriously. Thanks to the further discussion, we know how long it takes for the neutron star to collapse, and we have an source for that information. Gandalf61 (talk) 10:34, 12 April 2013 (UTC)

You're missing my point - the OP never inquired for an expanded answer, which is clear from his most recent post. Plasmic Physics (talk) 11:06, 12 April 2013 (UTC)

Actually I learned a lot from all of you and I appreciate both Gandalf's and Plasma's help! I'll admit I did press for a yes or no which in past inquiries I have not always gotten, due to a delightful tendency(No sarcasm here, it's not just delightful, it's also educational)of refdeskers to go off on tangents. -Rich199.33.32.40 (talk) 21:42, 12 April 2013 (UTC)

8th dimensional space

so i was looking at 8th dimensional space page the quantum entanglement and alternate realities i need help to see if i am right

so pretty much 8th dimension is saying there our many universe like ours but different at the same time and if one were to get to one of these many dimensions it would cause a tear in space causing a new reality and if one travels though many tears it cause confusion in the universe meaning the quantum entanglement if my idea of what these are are wrong let me know plases — Preceding unsigned comment added by 99.12.149.156 (talk) 03:36, 11 April 2013 (UTC)

I can't see how you got all that from our article on Eight-dimensional space, so you must have been reading this somewhere else. Sorry to tell you, but it sounds like a bunch of science fiction nonsense. Someguy1221 (talk) 06:18, 11 April 2013 (UTC)

You should be asking the real expert: particle physicist Buckaroo Banzai. Clarityfiend (talk) 07:15, 11 April 2013 (UTC)

There is some confusion here. The word "dimension" has two meanings:

• In the sense of "eight dimensional universe", the meaning is like "three dimensional universe" - we'd be talking about a universe where there are more directions you could move in than just the north-south, east-west and up-down that we are normally aware of.
• In the sense of "travelling between dimensions" - we're talking about "parallel universes".

Generally, scientists only use the first of those two meanings. The two meanings of the word are not connected or related in any way.

When we are considering quantum entanglement and things like certain interpretations of the Schrondinger's Cat thought experiment - then we are talking about parallel universes...not extra spatial dimensions. "Tears" that allow you to move between parallel universes are in the realms of speculation and science fiction. As far as I know, there is no evidence that they might exist from mainstream physics...quite the contrary in fact...there is reason to assume that they'd be fundamentally walled off from each other.

When we're talking about "extra dimensions" in ideas such as string theory - then we're talking about "directions you can move in".

You're basically stuck in this universe - and whether there are others (due to quantum effects, for example) is an undecided question.

SteveBaker (talk) 11:22, 11 April 2013 (UTC)

There is one more scientific usage of the term "dimensionality" - the usage in the sense of degrees of freedom in a generalized coordinate system. For example, if we are describing an n-body simulation, it is common to call this a n dimensional problem, (or even more accurately, a 6-n dimensional problem, for example, accounting for velocity and position of each object in conventional dimensions x, y, and z; by extension, you can add one dimension to each degree of freedom in the problem). When we generalize a coordinate system, we can apply constraints based on physical law, and reduce the complexity of the problem to a lower dimension.

In this usage of the term, it is frequently helpful to understand the distinction between the rank and the size of a problem-space. A problem can be n-dimensional, but modeled with extra dimensions; this is called "degeneracy", and it can be helpful for practical purposes, even if it adds no new information. Nimur (talk) 21:07, 11 April 2013 (UTC)

This is almost surely a reference to http://www.tenthdimension.com/ — whether that pseudo-spatial interpretation is worth anything is beyond the scope of this comment. --Tardis (talk) 03:12, 12 April 2013 (UTC)

cyanoacrylate bond inhibitors

I recently bonded some rubber like swim fin material to itself and a glass fiber and resin material using a high quality cyanoacrylate with the manufacturer's 'filler' powder for plastics and rubber. Initially the bond seemed to hold but failed after several 20-30 minute uses on a swim fin in a chlorinated swimming pool. I am thinking that the bond may have been effected by residual chlorine compounds left on the surface prior to bonding. Other uses of the bonding product yielded exceptional results on similar rubber like materials where chlorine was not involved. Are there known adverse effects to bonding where chlorine compounds are present? What other chemical conditions might adversely affect bonding? Suggestions?

A prompt reply would be appreciated.

Walt Silfies - 50.53.114.100 (talk) 07:11, 11 April 2013 (UTC)

I don't see anything out there about reactions with chlorine - just about the only thing that I see might be that cyanoacrylate doesn't stick well to glass - so perhaps the glass fiber material is the cause here. That sounds like a bit of a stretch to me - but it's all I could find. SteveBaker (talk) 15:43, 11 April 2013 (UTC)

can you examine to see what failed? i.e. did the glue come loose from the rubber, or from the fiber/resin, or did the glue stick to both but deteriorate itself? my experience with cyanoacrylates and rubber is that it works very well (I use it to patch pinprick holes in bike tire tubes) but that hasn't involved immersion. re chlorinated compounds, stuff like chloroform is a good solvent for many plastics but whether that exists in enough concentration in a pool and/or whether it would attack acryclics, I don't know. Gzuckier (talk) 16:49, 12 April 2013 (UTC)

Perception of pain, which part of the brain is the gatekeeper?

I've always wondered how people can exert so much control over their perception of pain. If the stimulus is the same, the same sensory neurons fire and in the end the same regions in the brain get stimulated to an equal degree, then how is it possible to change your perception of pain, between the same stimuli? When I am on an operating table, unconscious, does my " body " still feel pain, even though I don't " know " that it is there? Can the part of my brain that is conscious effectively act as a signal limiter? Who is the gatekeeper? Has any research been done on this? 137.224.239.102 (talk) 08:45, 11 April 2013 (UTC)

Basically, the thalamus, though it isn't a conscious process. See nociception for details. - Nunh-huh 09:40, 11 April 2013 (UTC)

Many aspects of pain are still very mysterious to us, and the answers to the questions really aren't known with any clarity. Part of the difficulty is that what we call pain is actually a mixture of several aspects -- Ronald Melzack identifies three that he calls "sensory-discriminative" (sense of the intensity, location, quality and duration of the pain), "affective-motivational" (unpleasantness and urge to escape the unpleasantness), and "cognitive-evaluative" (cognitions such as appraisal, cultural values, distraction and hypnotic suggestion). (Note: I've copied that from our pain article, which is worth reading.) Each aspect is implemented by a different brain system, and differently affected by brain manipulations. We are only beginning to understand the systems and their interactions. One thing that is clear is that there is a lot of "top-down" circuitry that allows higher brain levels to modulate signals at lower levels, even down to the spinal cord. Looie496 (talk) 15:42, 11 April 2013 (UTC)

Thanks for the answers! :) 137.224.239.102 (talk) 17:42, 12 April 2013 (UTC)

Are there drugs that boosts willpower?

Are there drugs/medicines that boosts willpower? — Preceding unsigned comment added by 50.100.191.39 (talk) 18:41, 11 April 2013 (UTC)

Certain stimulants like Ritalin have this effect. Many students who study boring subjects like law take such drugs. Count Iblis (talk) 18:54, 11 April 2013 (UTC)

Law's only boring for most people. Some of us actually enjoy it. Shadowjams (talk) 15:01, 12 April 2013 (UTC)

Read:Dutch courage. Alcohol can depress some parts of the brain (as can some other drugs) that usually inhibit some forms of action. People that show the quality of having great will-power often have a low level of fear. Amphetamines were taken by the hand-full by American pilots during the second world war, because they did not only keep them alert but made them feel immortal and fearless, yet people may not survive very long with just that attribute. I think therefore, you may be asking about the type of will-power that brings successes. That requires a blend of other attributes. In that respect, I haven't come across any drugs that can have any long term benefit. Before anybody else steps in and pontificates, I'm not including Entheogens because these require the individual to also intellectualize (e. i., WORK) on seeking out whatever understanding they can glean from their experimental voyages. Will-power proper, I think, is a product of clear thought. Trying to think and carry out a plan of action whilst one's brain is under the influence of supposed artificial enhancements -will not achieve this. --Aspro (talk) 20:33, 11 April 2013 (UTC)

The question is ill-formed. There are various reasons besides akrasia that people lack the will power to do things--fear; lethargy; craving; compulsion. There are all sorts of drugs to treat anxiety, hunger, tiredness, OCD. So the broad answer is yes, drugs from caffeine and alcohol, to cigarettes and amphetamines, to xanax and zoloft all effect the mind. μηδείς (talk) 21:51, 11 April 2013 (UTC)

Given that a question is a request to be informed, I think that goes without saying. 202.155.85.18 (talk) 02:02, 12 April 2013 (UTC)

It's a good question, Medeis is being too glib about it. Although we usually think of willpower as a good thing... however it's probably better characterized as drive. In most mammal's evolution pleasure (or avoiding pain) and drive were yolked together, but in some instances, and especially when you start having fun with various plants, those two are distinct. There is a lot of really nuanced research on the subject... and then there's breathless articles comparing a book/movie to real life that center around modafinil. But also testosterone, amphetamines, and all sorts of other psycho active drugs affect motivation. It's quite complicated. Shadowjams (talk) 14:59, 12 April 2013 (UTC)

The basic problem here is that the concept of willpower is essentially dualistic. In terms of the "ghost in the machine" metaphor, willpower is the degree to which the ghost exercises control over the machine. But whenever one tries to understand dualistic concepts in biological terms, one runs into unsolvable boggles. Looie496 (talk) 15:37, 12 April 2013 (UTC)

Exactly, the question is based on the false assumption that there's some one thing called willpower and that a certain drug can turn its knob up higher. There are all sorts of reasons why one might fail to achieve a goal one has in mind. μηδείς (talk) 17:21, 12 April 2013 (UTC)

Launching yourself from lying on the ground to upright position using only your arms muscles

Are there people who can do this? I've seen people do so-called Muay Thai push-ups, so it seems to me that it is possible. It would require more strength than you need to do the Muay Thai push-ups, but then there are people who can do hundreds of these in a row. However, I've never seen or heard about people who can launch themselves up from lying to standing position using a push-up move. Count Iblis (talk) 19:17, 11 April 2013 (UTC)

Lying on your back or chest? I can do "kip-ups" which is lying on back to standing upright. But this involves alot of leg motion.165.212.189.187 (talk) 20:17, 11 April 2013 (UTC)

I found this, but I suspect some trickery. Alansplodge (talk) 21:59, 11 April 2013 (UTC)

I agree it looks suspicious. For example, just before the young man gives a big push to get up to the vertical, the bottom of his T-shirt rides upwards a couple of inches for no apparent reason. Now if the whole thing were actually performed in reverse and then played backwards, I can imagine the bottom of the T-shirt riding upwards as he fell forwards and downwards, and then extending to its proper position after he came to rest. Dolphin (t) 08:16, 12 April 2013 (UTC)

It's beyond "suspicious"...it's an obvious fake, and a very poor one at that. YouTube demonstrations of any kind have to be viewed with deep suspicion - there are *FAR* more fakes than there are real demonstrations. SteveBaker (talk) 16:36, 12 April 2013 (UTC)

Agreed - I was just being charitable. Alansplodge (talk) 18:09, 12 April 2013 (UTC)

I bet you could do it on the moon, although you may have to take off the space suit. Gzuckier (talk) 16:51, 12 April 2013 (UTC)

Oh no you don't - Charlie Duke shows how it's done. Alansplodge (talk) 18:16, 12 April 2013 (UTC)

Ha, so except that fake video, no real evidence! Perhaps the Refdesk volunteers should try this and upload videos of their attempts! Count Iblis (talk) 12:31, 13 April 2013 (UTC)

I don't suppose using a trampoline is allowed? :) Wnt (talk) 22:15, 13 April 2013 (UTC)

It would be an interesting experiment to get some really fit volunteers and a variable slope that can pivot from 0 degrees (flat on the ground) up to 90 degrees (like a wall). By finding the minimum angle from the ground we could make a good guess whether it is impossible; If nobody volunteer could push themselves upright at a slope of less than 45 degrees I would think that doing it from zero degrees would not be humanly possible.

You would need fit volunteers of various builds (heavy muscled to light athletic) and heights. My guess would be that the shortest people with a light athletic build would do best. -- Q Chris (talk) 13:57, 15 April 2013 (UTC)

April 12

Low mass white dwarf actually currently exist

Since the article said white dwarf can be 0.17, do the white dwarf dwarf being 0.17 actually exist currently, or is it just the estimation of the stars did not yet come off the main sequence. Is this true alot of white dwarf are binary stars, can 0.5 solar mass white dwarfs? is it more common for white dwarf to be single star system, or binary star system? Is white dwarf all the exact same size on single star system/non-binary star ssytem? or the Solar mass determined by white dwarf has to determine exactly how big the white dwarf has to be?--69.226.42.134 (talk) 00:36, 12 April 2013 (UTC)

I struggle to see how a very small white dwarf (such of 0.17 solar masses) could form other than from a small red dwarf collapsing. Red dwarf stars live for a very long time, so none of them are dead yet. That would suggest there are no very small white dwarf stars. A lot of stars are in binary systems and they will generally remain in those systems when they die, so yes it is true that a lot of white dwarfs are in binary systems - I don't know if it is more than half, though. The size of a white dwarf is determined by the size of the star that formed it. In a binary system, there might be some transfer of matter between the stars that can change things. In a non-binary system, there obviously won't be. Does that answer most of your questions? I found them a little hard to understand... --Tango (talk) 11:43, 12 April 2013 (UTC)

Stars loose a substantial fraction of their original mass when they go through the late stage of red giant/Asymptotic giant branch and planetary nebula stage, so the white dwarf may end up much lighter than the original star. With that said, I have to say I don't really know what the lightest white dwarfs masses are. Dauto (talk) 19:09, 12 April 2013 (UTC)

See SDSS_J0106-1000. Ruslik_Zero 19:19, 12 April 2013 (UTC)

Fascinating case! I'm trying to picture what it will look like as they get very close together. I suppose Roche lobes can't actually have condensed matter going all the way to the center because it should be under zero pressure there. I suppose if humanity somehow doesn't self-annihilate, the more lunatic descendants of our race will dive through that strait for excitement. When the stars do start to fuse ... I suppose they'll still be rotating too fast to have enough pressure in the center for helium fusion, but it would start somewhere under the combined pole?Wnt (talk) 22:13, 13 April 2013 (UTC)

Bird evolution

Are the falcons, parrots, and sparrows really the closest relatives of one another, as people say? If so, who evolved from whom in this taxonomy? And also, if the falcons and the passerines are so closely related, which of the passerines are the most closely related to the falcons? (I'm guessing it would be the swallows, based on purely morphological info, but I can't be sure). Oh, and are the whippoorwills more closely related to the swifts, or to the owls? 24.23.196.85 (talk) 05:50, 12 April 2013 (UTC)

None of those groups evolved from another of them. Their most recent common ancestor was a member of neoaves but not of any of those groups (according to our articles). All falconiformes are equally closely related to all passerines. Regardless of which falcon and which passerine you pick, you get the same ancestral species as their most recent common ancestor. And according to our articles, whippoorwills are more closely related to swifts than to owls. Looie496 (talk) 06:43, 12 April 2013 (UTC)

(EC) You may be thinking of discussion surrounding some recent studies like [5] [6] [7] [8]. You should be able to read both studies (the former may require free registration) and although they may be a little difficult for someone without a biological background to properly understand, you should get some idea and should also be able to view the various trees shown and seek help here to understand the parts which are confusing. The 2008 study (first 2 links) in particular was and is I believe regarded as fairly significant, you should be able to find a fair amount of discussion of it in blogs and other such sources, although looking for the better ones may be difficult, I think [9] is okay. As mentioned in our article Evolution of birds#Classification of modern species, this is still an area of some flux (as with quite a lot of taxonomy, particularly given the increasing ease of genomic analysis) and the 2008 study is obviously only about 5 years old although I don't know specifically how well the relationship between the species you mention is supported. I would note statements like 'who evolved from whom in this taxonomy' should generally be avoided when talking about extant species as neither extant species is going to be the same as the ancestral species. Similarly for statements like 'which of the passerines are the most closely related to the falcons' as most likely they all have the same most recent ancestral species. Nil Einne (talk) 06:51, 12 April 2013 (UTC)

Thanks! Maybe I should have put the question about "who evolved from whom" another way: which of the three orders (falcons, parrots and passerines) is the closest to their common ancestor, and which is the most distant? 24.23.196.85 (talk) 01:06, 13 April 2013 (UTC)

Most evolutionary biologists would consider them all to be equally distant from the common ancestor. That's because the usual way of measuring distance is time since the split. There are other possible measures, for example disparity between genomes (which can vary because there is some variability in rates of mutation). Even for that you would probably find that they are all at nearly the same distance, and it would be quite difficult to find out which is closest. Looie496 (talk) 02:19, 13 April 2013 (UTC)

Right, I was asking about genetic distance from the common ancestor. But I wouldn't be surprised if the answer comes out to be "Insufficient Data". Thanks for the info! 24.23.196.85 (talk) 03:29, 14 April 2013 (UTC)

Sediba's hands.

Can anyone figure out what's going on with Sediba's hands in the skeleton on the right, here? μηδείς (talk) 10:00, 12 April 2013 (UTC)

Have you mis-read the caption? H sediba is in the middle. The one on the right is a chimp. Rojomoke (talk) 12:13, 12 April 2013 (UTC)

I assumed the caption above was for the picture above--but please look at the hands (and the snout) and tell me if that looks like any great ape you've ever seen. The thing has effing flippers. Or am I missing something? μηδείς (talk) 12:59, 12 April 2013 (UTC)

There seem to be a few fingers missing. Dauto (talk) 14:32, 12 April 2013 (UTC)

It might help to look at http://www.boneclones.com/KO-303.htm. Looie496 (talk) 17:10, 12 April 2013 (UTC)

According to Looie's link the shape looks right, It still seems quite odd that the hand is the length of the femur. μηδείς (talk) 17:15, 12 April 2013 (UTC)

A Google search provides images of chimp skeletons (also orangutans and gibbons). The hands in OP's picture are in the foreground and the phalanges of the left hand are splayed, which makes the hands appear larger, but the relative size does seem to be typical of a chimppanzee. The snout length and nasal opening do appear different than in other images of chimpanzee skeletons, but these are the only images I've seen recently, so I'm far from expert.--Wikimedes (talk) 19:39, 12 April 2013 (UTC)

So in other words the chimp is standing with his hands toward the camera, like this? I suppose that would explain the otherwise apparently freakish proportions. μηδείς (talk) 19:57, 12 April 2013 (UTC)

Motion of electrons

What type of motion of electrons around the nucleus? It is circular, periodic, uniform, non-uniform or other motion? Scientist456 (talk) 12:27, 12 April 2013 (UTC)

No one knows, I asked a similiar question here some time ago. Plasmic Physics (talk) 12:36, 12 April 2013 (UTC)

I suggested two types of motion, which are both wrong (now I know): random teleportation; and they exist everywhere at one in the form of an electronic fog, the mass and charge density profile of which is described by the schrodinger equation. Plasmic Physics (talk) 12:40, 12 April 2013 (UTC)

Electrons don't move in a classical motion. Indeed, they are not classical particles. Their distribution probability is governed by quantum physics. Some simplified models assume discrete circular orbits with additional constraints. See Bohr model, Matter wave and Pauli exclusion principle. --Stephan Schulz (talk) 12:46, 12 April 2013 (UTC)

So, basically they slosh? μηδείς (talk) 13:00, 12 April 2013 (UTC)

... and sometimes they tunnel. See atomic orbital for more information. Gandalf61 (talk) 13:10, 12 April 2013 (UTC)

Periodicity figures strongly in quantum mechanical treatments of particle motion (basically to prevent particles from interfering with themselves), see for example particle in a box. Atomic_orbital#Orbitals_table has drawings of the shapes of probability distributions of single electrons of different energy levels orbiting a nucleus.--Wikimedes (talk) 19:13, 12 April 2013 (UTC)

From my limited knowledge- the electrons are in various shaped shells which are a probability density function. There is something called the measurement problem [[10]] which prevents the particle from behaving in the classical sense. — Preceding unsigned comment added by Ap-uk (talk • contribs) 23:32, 13 April 2013 (UTC)

Invasive species

Humans have invaded the entire planet, each and every continent, oceans, destroying all ecosystems and making other species extinct. They why humans are not considered invasive species? --Yoglti (talk) 16:53, 12 April 2013 (UTC)

Who says that humans are not considered invasive species? Looie496 (talk) 17:12, 12 April 2013 (UTC)

See Gaia hypothesis. --TammyMoet (talk) 18:27, 12 April 2013 (UTC)

the idea of invasive species is a matter of point of view, really. it's not like the biosphere of the earth is defined or has a defined goal. one species piggy backs on another and ends up in a new area and does well. doesn't matter if it's in the bilge of a ship or the large intestine of a dinosaur. but as far as being responsible for extinctions, we are definitely number one, i would guess Gzuckier (talk) 20:01, 12 April 2013 (UTC)

Why Wikipedia article Invasive species does not list humans? --Yoglti (talk) 09:43, 13 April 2013 (UTC)

Because we're too arrogant? It's not really the point of the article, we don't really compete in any ecological niche any more, we're "out of the race" so to speak. Vespine (talk) 23:04, 14 April 2013 (UTC)

Limits of knowledge

If knowledge, memories, thoughts, are just connections made in our brains, does that mean that knowlede has limits? I mean its possible that we might not even comprehend all there is to know about the universe?203.112.82.128 (talk) 17:52, 12 April 2013 (UTC)

Yes, you can only store a finite amount of information in your brain. You can't even know the exact state of your own brain, because that would require at least the full brain capacity while a lot of that is already in use to perform essential functions. Count Iblis (talk) 17:56, 12 April 2013 (UTC)

Haldane's Law (excuse the archaic language): "The universe is not only queerer than we imagine, it is queerer than we can imagine" --TammyMoet (talk) 18:26, 12 April 2013 (UTC)

yeah, after studying a lot of philosophical basics lately (The Great Courses, better than my college humanities requirement) i've come to doubt not only that humanity is capable of understanding the underlying reality of the universe, but that there even is an underlying reality; as well as that humanity is capable of understanding the functions of "mind" as distinct from brain. Gzuckier (talk) 20:07, 12 April 2013 (UTC)

However, with the invention of writing, it became possible to store knowledge outside the brain. And, with the internet, we can now potentially quickly access all knowledge we have accumulated. Wikipedia, of course, plays an important role in all of this.

I like to think of knowledge like a program and data. The data can be stored outside the brain, with the brain just holding the program to use that knowledge. For example, say I want to determine the volume of a sphere. I access the data externally, to get the formula to calculate it. The formula is V = 4πr³/3. Now I use the program in my brain to determine that r means the radius and π means ≈3.14159 (or I look that up, if I don't know it already). I then use the program in my brain to tell me how to multiply, divide, and cube numbers, probably using a calculator. This is a very simple example, but we can potential solve much more complex problems in this manner. StuRat (talk) 20:21, 12 April 2013 (UTC)

I apologize but i think im looking for a different answer and its my fault because i didnt formulate my question well. What im trying to get into is, say a coin, there is only heads and tails, so there is just two outcome if you flip a coin, now go to our brains, there is just limited number of combination of connections in our brain right? Now my question is, given that the method on how we understand things are just one combinations of our connections in our brains, is it possible that there are certain data in our universe that we will never understand simply because its something that needs to be a set of connection that our brain is not capable of doing? for example, back to the coin, is there a data that niether heads nor tails can understand? Im not a native english speaker so please try to understand and thanks in advance. 203.112.82.1 (talk) 22:01, 12 April 2013 (UTC)

but that's the question; how is information stored in the brain? it's definitely not the way it is in computers. to me it seems to be more diffuse; i.e., you can forget what your grandmother looked like, but you won't forget that you had a grandmother, or that your grandfather was married, or that your mother had a mother, or what a grandmother is in general. it's like every concept/meme has a bunch of loose ends that tangle up with the loose ends of other concepts, somehow, in such a way that much of the structure assembles itself from what it connects to. as if you have a grandmother-shaped region in your model of the world, and even if you've forgotten or never had the memory of your senses in reference to your grandmother to fill in the hole, that grandmother-region still must exist and be referred to as grandmother by the rest of your mental world. so, what are the limitation of something like that in terms of finite number of neurons and synapses? well, you certainly can't know everything about the universe in perfect detail, i.e. the state of every subatomic particle, but that might be as much an effect of the finite amount of time you have to investigate than of your storage. Gzuckier (talk) 01:14, 13 April 2013 (UTC)

• Tangentially related to this discussion are concepts like the Bekenstein bound and Bremermann's limit. The math and physics there is pretty dense, but the concept is sound: there has to be an upper limit to the amount of information we can store about anything, and how well we can retrieve it. We can't know the entire universe, because to store information about the entire universe would require an entity at least as large as the universe and separate from it. The entire field which deals with quantifying information, including its storage and retrieval, is known as Information theory, which in part deals with the very question of how much information can be stored in a given medium. For example, the theoretical maximum amount of information stored in your brain is constrained by the number of cells and synapses in your brain. Now, this theoretical limit is probably orders of magnitude more than the functional limit, but it's a starting point, and indeed, is a subject which is well studied and explored, if you have the time to research it and the ability to weed through some fairly arcane mathematics. --Jayron32 05:30, 13 April 2013 (UTC)

• But that's why we have models. A simplified model allows you to store most of the important information about an object in much less space. Take the blueprints for a building. They may not note where every nail is, but you don't normally need to know that, and, if you need that level of info, you can go and look for the nails at that time. StuRat (talk) 17:59, 14 April 2013 (UTC)

It is already clear to me that there is a limit in how much info our brain can store, im more interested in what is the limit of what our brains can understand. In theory, if i study hard enough, i would be able to understand special relativity , but is there any concepts out there that our brains are not wired to understand? I mean of course if the answer is yes, we wont know the things we were not able to know, im just curios if there is any research or concepts that tackles this subject. I dont know if gzuckier already answered this, if so, can you please explain more 203.112.82.128 (talk) 17:53, 13 April 2013 (UTC)

I'm not sure I grok what you mean by "understand". You say "are there any concepts out there that our brains are not wired to understand". Concepts are all human-created things, so theoretically no, there is no concept which cannot be understood by any human. In order to be a concept, it has to have been conceived by somebody, which means that at least one person understands it. Now, colloquially, there are certain famous "concepts" which have been (jokingly or a bit tongue-in-cheek) said to have been incomprehensible. Lord Palmerston famously said of the Schleswig-Holstein Question that "Only three people...have ever really understood the Schleswig-Holstein business—the Prince Consort, who is dead—a German professor, who has gone mad—and I, who have forgotten all about it." and Richard Feynman once famously said of Energy, "It is important to realize that in physics today, we have no knowledge what energy is." Now, that doesn't mean that these problems are entirely incomprehensible (many historians have extensively studied the Schleswig-Holstein question, for example, and some I am sure have a good handle on it, and energy is something which many physicists study extensively, Feynman's quote is merely a negative assertion of the Dunning–Kruger effect, which notes that the deeper physicists get into energy, the harder it is to define it in as simple terms as, say, a high school physics text does). But fundamentally, no, there is no concept which is entirely incomprehensible to any humans insofar as any coherent concept is a human-created thing in the first place. If you really want to get deep into this, do some reading in the branch of philosophy called Epistemology. --Jayron32 03:30, 14 April 2013 (UTC)

When I say "understand" I mean when you are introduced to a data, your brain rearrange its connections so that you would comprehend the data in front of you. and since brain is just a finite thing, I assume there is only finite ways of rearranging those connections, meaning there's a limit of what we can "understand", I dont think im asking about the philosophy of it but simply the physical limits of our brains. 203.112.82.1 (talk) 16:03, 14 April 2013 (UTC)

In this sense, you can understand everything. The brain is capabable of universal computation (the limits only being the amount of data it can process). At various levels, if there is anything to understand about some natural phenomena, you can formulate it in terms of simple equations, which the brain can easily handle. If it's not a matter of something you can formulate using a few bits of information, then you cannot say that there is a clear cut explanation for the observed phenomena, as it would depend on a large number of variables. So, there would then be nothing to explain. Count Iblis (talk) 16:18, 14 April 2013 (UTC)

You seem to have ignored my comment on our ability to store information externally to our brain. To use a computer analogy, the RAM is the where the "programs/intelligence" is normally stored, but the data is largely on the hard drive or other external media. Similarly, humans only need to store the intelligence in their brains, and can access the data from other sources, like Wikipedia. StuRat (talk) 17:54, 14 April 2013 (UTC)

Oh no, I understand your answer that knowledge can be stored outside of our brains, but I just thought that it is not what I'm asking about. To use your computer analogy, what i was asking is if there is a file type that my computer cannot read, for example the brain is capable of reading .jpg or .gif files, but is there a .wiki of .xyz that we will never comprehend? 203.112.82.1 (talk) 20:37, 14 April 2013 (UTC)

Stud finders

Looking at the reviews of stud finders on Amazon, all of them have mixed reactions. Some people say they work as they should and others say they don't. I'd like a stud finder but would like one on which I can rely. Are some people just using them wrongly? Some people say they're inconsistent. --2.97.27.107 (talk) 17:54, 12 April 2013 (UTC)

They are many types of walls and a few types of stud finders. Most work fairly well on modern drywall (plasterboard)-type walls. But on my old over-an-inch thick plaster/gravel/horsehair on metal lath walls, none ever work. Rmhermen (talk) 19:05, 12 April 2013 (UTC)

I've tried out maybe 4 or 5 different types over the years, both the magnetic (looks for nails) kind or the electronic (capacitance I assume) kind, not any of them worked any better than just pounding on the wall and listening for the change in sound. Gzuckier (talk) 20:09, 12 April 2013 (UTC)

Yeah, I think I'm just gonna knock on the wall. Thanks 2.97.27.107 (talk) 21:08, 12 April 2013 (UTC)

Drilling exploratory holes with a really thin drill bit is another strategy, the idea being that the holes are so tiny you can patch or cover them easily and they will never be noticed by most observers. HiLo48 (talk) 23:05, 12 April 2013 (UTC)

Studs are also spaced a standard distance apart, usually, so once you've found one, a ruler is usually helpful. In most houses, electrical outlets and switches are required to be in junction boxes which are bolted to a stud. In the United States, the standard is 16 inches center-to-center between studs. So, if you start at the wall switch, find the stud it is attached to, then measure off 16 inches, you should find another stud. And so on. --Jayron32 03:55, 13 April 2013 (UTC)

Maybe. 16" is a modern standard for exterior walls in many locations. But other walls (especially interior) may be 12", 16", 18", 19.2" or 24". Not to mention doubled studs, ones moved over for pipe runs, bizarre window framing. And it depends on local codes for climate, hurricanes, type of stud, etc. Construction practices have changed greatly even in recent years. Rmhermen (talk) 16:16, 13 April 2013 (UTC)

Most stud finders I think, work well for most people. The problem may be in part that complaints are, as the OP opinions, by some people who don't know how to use them properly and impart because some walls (as found by editor Rmhermen above) defeat the capabilities of cheap stud finders. Borrow a cheap stud finder to see if it suits your walls – if so good – answer obvious. If not borrow a professional stud finder. If you find that better -then buy one. Don't know what part of the world your in but a professional quality SUB-SCANNER M12 is not expensive when you consider how much it would cost you to get a professional trades person in to do the job. These detectors have the necessary discrimination to cope with most walls.Aspro (talk) 19:31, 13 April 2013 (UTC)

biology

Is there possibility of multiple nipples in one brest of a human female ?If so then what is the reason? — Preceding unsigned comment added by Titunsam (talk • contribs) 18:25, 12 April 2013 (UTC)

The article you want is probably supernumerary nipples. Rmhermen (talk) 18:53, 12 April 2013 (UTC)

Um, witchcraft. μηδείς (talk) 19:58, 12 April 2013 (UTC)

Francisco Scaramanga. Though i don't think Christoper Lee is female. --Jayron32 02:32, 13 April 2013 (UTC)

It is not limited to females (or humans for that matter) Roger (Dodger67) (talk) 12:03, 13 April 2013 (UTC)

the real star wars universe in 2014?

I want the real Star Wars universe by next year please. Contact NASA. SmallSoldiers123 (talk) —Preceding undated comment added 21:39, 12 April 2013 (UTC)

Is there a question? But here is NASA's contact page. Cheers. --Wirbelwind(ヴィルヴェルヴィント) 22:06, 12 April 2013 (UTC)

Resolved

April 13

Minimum population required for the survival of a race.

The article on Angam Day currently states:

Upon eclipsing a population of 1,500, a number considered to be the minimum required for the survival of a race, Angam Day was declared.

Does a race really need a minimum population of 1,500 to survive? If true, why? If false, how many people does a race need to avoid extinction? Thank you in advance. --190.19.69.254 (talk) 04:33, 13 April 2013 (UTC)

Hmmmm. That's a pretty ugly part of that article. I would much prefer that the term ethnic group had been used throughout. Race is an unclear word with unfortunate connotations. The article Nauruan people, linked from Angam Day, avoids the term race completely. I note that the claim of 1,500 being the minimum number for a race to survive is unsourced. That's not good, and only makes things worse. I went hunting and couldn't find a source myself. You've got me thinking about what we should do with the article. HiLo48 (talk) 04:54, 13 April 2013 (UTC)

Reads like unmitigated bullshit to me. What makes an ethnic group (or race) a distinct unit is a shared culture. I'm not sure there's any arbitrary lower or upper limit on that, merely that the group has a certain level of cultural cohesion and distinctiveness, and I certainly can't find any literature that indicates that there's some official or "scientific" or whatever reason that would indicate that 1500 is some magic number. --Jayron32 05:00, 13 April 2013 (UTC)

The article clearly states that the number 1500 came from Brigadier General Griffith, the Australian administrator. It does not claim that the number has any deeper validity. It doesn't cite a source for that, but I don't see anything implausible about it. Looie496 (talk) 05:17, 13 April 2013 (UTC)

The article makes that assertion, but that assertion (nor the quote from Griffith) has any sources to support it. The big issue is if Griffith said directly, "if the Nauruans were to survive as a race, the population should be no less than 1,500.", then we would need to put quotes around that, as I have done, and provide a footnote to make it clear where the quote comes from. Without sources, the statement really shouldn't stand, however. --Jayron32 05:22, 13 April 2013 (UTC)

For what it's worth, I've managed to work out that the person referred to here is Thomas Griffiths (general). I'll add a wikilink to our article (and fix the spelling). Looie496 (talk) 16:46, 13 April 2013 (UTC)

The problem is extremely difficult for human populations because "survive" can mean "not all die" or "survive as a distinct culture". But if a group of people were cut off from the rest of humanity for some considerable time (either physically cut off - or culturally unwilling to take mates from outside of their cultural group) - then genetics and inbreeding would be the problem. The considerations in our Minimum viable population article would take effect. For large vertebrates, the accepted number is between 500 and 1000 individuals if the population is carefully managed (ie scientists decide who breeds with who!) - and more like 4,000 if not carefully managed. On that basis, you might think that 1500 people isn't enough - but it's in the right ballpark, and this isn't an exact science. But that kind of complete elimination of mating outside of that cultural group seems unlikely.

A classic example of how this can happen is the Pitcairn Islands - which was uninhabited until six men, eleven women and a baby arrived there after the infamous "Mutiny on the Bounty" incident in 1790. Since the island was hundreds of miles from any other land - and not of much interest to anyone, the hapless mutineers were left alone - and (inevitably) the population steadily grew to around 600 people. This is widely accepted as being the most inbred group of humans in the world. But even with such extreme in-breeding, the occasional outsider has managed to add enough genetic variation to keep the population viable - and according to most studies, they aren't suffering too badly.

So we can conclude that there isn't some magical cutoff at 1500 people...at least not genetically. SteveBaker (talk) 13:16, 13 April 2013 (UTC)

someone wrote a program to find that out. i just can't remember who, or the program name, or when. 70.114.248.114 (talk) 03:48, 14 April 2013 (UTC)

Seasonality of human hair growth

My friend, in her early seventies, is convinced that her hair grows more quickly in the Spring and more slowly in the Winter. Her evidence for this is the much shorter length of time it takes for white roots to appear after she has dyed her hair. (I have no reason to doubt her eyesight.) This sounds like folklore to me but I can find nothing to indicate that anyone has ever studied the matter. Thank you for your help. — Preceding unsigned comment added by 109.12.63.61 (talk) 07:24, 13 April 2013 (UTC)

This is an interesting question, as it is one of the few topics on which I think the written word does not match reality. If you google (google "rate of hair growth") or search in textbooks, you find almost all estimates lie in two categories: Those which say hair grows at a constant rate of 0.5 inch (13 mm) per month no matter what (the Wiki article human hair growth is one example), and those that say it varies depending on age, health, intake of certain vitamins, race, and a few other minor factors and is between 7 mm and 20 mm per month, which seems much more likely. What seems difficult to find is any refrence that says it varies depending on where on the head it grows from, and there's no reference that says it is seasonal, depite the fact that it most definitely IS seasonal for other mammals. Hairdressors are taught that it grows at a constant rate.

However, in my experience, it grows considerably faster on the back of my head and neck, and a lot slower on the top of my head. It also grows quite a bit faster in autum and slowly during winter. This is reflected in when I need to go to the hairdressor. I'm also in my seventies. I'm sure that it grew faster when I was younger, but suspect that the variation in growth rate was hidden when I had a younger thicker hair.

In my experience, cutting hair very short and cutting frequently casues it to react by growing faster. However hairdressors are taught that that is a fallacy. I had a friendly argument about it once with a hairdressor friend, so I experimented over a two year period, keeping records. I was right. However, I live in a hot climate, and cutting hair short probably raises skin temperature. If I lived in a cold climate, it may well be that cutting hair short would lower the skin temperature and therefore the growth rate. This suggests a conflict between two factors: skin able to grow hair faster when it is warm during warm weather, and the evolved capability of mammals to grow a thick winter coat in time for winter.

Wickwack 121.215.67.60 (talk) 08:41, 13 April 2013 (UTC)

You're in your seventies and it still grows on the top of your head? I'm jealous. HiLo48 (talk) 08:45, 13 April 2013 (UTC)

Don't fret too much. It grows so slowly on top, and so thinly, it might as well not bother. But I still need to have it cut from time to time. Wickwack 121.215.67.60 (talk) 08:54, 13 April 2013 (UTC)

Sorry Wickwack, although I defer to your superiority in age, I'm afraid hairdressers are taught that hair grows at different rates according to both position on scalp and time of year. Now if only I could find a reference for it. (I know they're taught it as I sat in on some of the sessions for the hair students when I was a therapy mature student about 5 years ago.) --TammyMoet (talk) 13:45, 13 April 2013 (UTC) I found this study which looks like a pretty neat exemplar of how to do citizen science! --TammyMoet (talk) 13:51, 13 April 2013 (UTC)

Very good Tammy! I only wish that age did bring superiority! Perhaps hairdressers are better taught in your country (the UK if I remember right), or perhaps knowlege has been updated since the hairdressors I've known did their training. I've found them adamant that it grows at a constant rate. The study you found has some limitations though - for instance they assert that temperature has little to do with it, but haven't proved it. One reasonably expects that hair growth rate is dependent on skin temperature, but the skin temperature relationship to climate would be confounded by the human practice of adjusting clothing to suit the season. They tested only one person. Did they check that she had the same diet/nutrition/calorific intake throughout? Wickwack 121.221.31.213 (talk) 14:34, 13 April 2013 (UTC)

You're indeed right to highlight the role played by diet and nutrition in hair growth: the study also failed to take blood samples to check on the endocrine status of the subject as I've found elsewhere that thyroid status affects hair growth as does oestrogen/progesterone status in women. It's not a complete study by any means, but an example of what can be achieved by someone wishing to follow the scientific method and make a difference. --TammyMoet (talk) 15:37, 13 April 2013 (UTC)

ques on tetrahedral and octahedral voids

A compound formed by two element a&b the anion b are located at the corner of the cube and face centres whereas cation a occupy all the tetrahedral void what is the simplest formula of the compound? — Preceding unsigned comment added by 70.39.184.248 (talk) 09:59, 13 April 2013 (UTC)

Please do your own homework.

Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know. Roger (Dodger67) (talk) 11:59, 13 April 2013 (UTC)

What is a microstate?

Entropy is by definition $-k\sum _{i=1}^{\Omega }P_{i}\ln P_{i}$ where k is Boltzmann's Constant and $P_{i}$ is the probability of a particular state given our limited knowledge of the system. But, how is state defined? What fully characterizes a physical state?

150.203.115.98 (talk) 10:26, 13 April 2013 (UTC)

It is the complete information about the system. Suppose you have two systems in different physical states, then that means that there exists an experiment that you can do on the systems which will have a different outcomes, at least statistically. If on the other hand the two systems are in the same physical state, then no experiement can have (statistically) different outcomes.

You can then try to define the state of a system by specifying a list of experiments and what the outcomes of each of these experiments should be. In quantum mechanics, the outcome of a measurement is, in general, not pre-determined. Now, you do one experiment and then immediately repeat that same experiment you will get the same outcome (in the limit that the time between them is zero). If you do experiment A and then experiment B, you can compare that with doing this the other way around. If there is no difference, then measuring B will give you independent information than you get from measuring A. You can then add another such experiment C that doesn't interfere with A and B. If you try to make this list of experiments larger and larger, you will find that some point, you can no longer make this list larger. You will then have what is called a "complete set of observables" for the system. Then the state of a system is completely defined by specifying a list of the outcomes for each of the obsevables contained in such a list. The outcome of any other experiment can be predicted (in the form of a probability ditribution over the possible outcomes) when the state is specified. Count Iblis (talk) 12:27, 13 April 2013 (UTC)

That's really interesting, and I can see the article Complete set of commuting observables now. A state is basically characterized by its measurable properties, which makes sense, especially from a pragmatic point of view. It doesn't really make sense to call two states "different" if there doesn't exist any experiment, even in principle, to distinguish between them.

Now, suppose you have a physical system, and you want to change its state. How would you do this, in general?

150.203.115.98 (talk) 15:09, 13 April 2013 (UTC)

Changing state is already described in "general" terms. In various branches of physics, state change is described mathematically; for example, in quantum mechanics, physicists talk about "applying an operator" to the system. This is about the most precise and generalized way we can describe changing state for one variable, subject to physical constraint. Unfortunately, such generalization tends to be a bit obtuse, and some people find these decriptions difficult to intuitively connect to experimental physical systems. This is because the specific way you change a particular state for a particular system depends on what physical process corresponds to the change of that state variable. In other words, we write a very clean mathematical formalism to describe an operator; but it is not always immediately evident how that operator corresponds to an experimental procedure.

For example, in atomic physics, one state variable models the energy-level of the electron; you can change that energy level by (in general) applying an energy transform operator to the electron. In specific cases, that operation manifests as compton-scattering; or shooting laser photons at the atom; or colliding the atom with other warm atoms (thermal excitation); and so on; in each case, practical details arise; it may be impractical to change one state-variable without affecting thousands of other parameters. Nimur (talk) 16:57, 13 April 2013 (UTC)

An example of a particular state is an associated energy level, such as the ground state of a partice. Plasmic Physics (talk) 12:28, 13 April 2013 (UTC)

In thermodynamics, a microstate describes the position and momentum of every particle. It's the full description of the system. For example, with N particles, "particle 1 is at (3,2,5) and moving at 3/ms north, particle 2 is at (4,5,1) and moving at 9 m/s east, etc" counts as a microstate. A macrostate is something you care to measure on a macroscopic scale. For example, what's the density of the gas? How uniform is the gas? What's the velocity distribution of its particles?

There is an inherent arbitrariness in the definition of a microstate. If particle 1 is moved by 1 nm, does that count as the same microstate, or a different one? How about 0.0001 nm? First, this doesn't actually matter--entropy is defined as the logarithm of the number of microstates, so changing the precision with which you distinguish microstates only changes entropy by a constant. Differences in entropy would stay the same. Second, quantum mechanics sets a fundamental limit on how accurately you can measure phase space. dx*dp cannot be smaller than Planck's constant, because the uncertainty principle says you can't simultaneously measure position and momentum more accurately than that.

Over time, systems tend towards the macrostate with the most microstates. For example, their velocity distributions tend to become the Maxwell distribution. "A uniform gas" accurately describes many more microstates than "a gas in a container where half the container is empty". This isn't surprising--of course if every microstate is equally likely, and the particles randomly choose one, that microstate would most likely correspond to the most likely macrostate. This tendency towards the most likely macrostate is the second law of thermodynamics. --140.180.240.67 (talk) 18:34, 13 April 2013 (UTC)

Does that agree with the definition Count Iblis gave? And, don't you need to know other properties of the particles such as their mass, charge etc.? And

150.203.115.98 (talk) 20:10, 13 April 2013 (UTC)

You do. I was giving a simplified classical view of an ideal monoatomic gas, which I think is helpful for intuition. For such a gas, all the molecules can be considered point sources with no charge and the same mass. Sorry for not stating this explicitly. --140.180.240.67 (talk) 20:20, 13 April 2013 (UTC)

Eyesight

Can a teenagers social development be affected by poor eyesight? — Preceding unsigned comment added by 176.250.139.80 (talk) 11:15, 13 April 2013 (UTC)

Yes. (Strange question.) HiLo48 (talk) 11:21, 13 April 2013 (UTC)

Obviously anything that affects communication affects social development. However, what do you mean by "poor eysight"? Deficiencies that can be corrected with spectacles should not affect it, except to the extent that wearing spectacles may temporarily affect self esteem or may limit playing in team sports. Wickwack 121.221.31.213 (talk) 11:30, 13 April 2013 (UTC)

If you hadn't just admitted to being in your 70's, calling glasses "spectacles" would have told me. :-) StuRat (talk) 04:04, 14 April 2013 (UTC)

One tries to write for an international reader here. "Glasses" has multiple meanings, (e.g., magnifying glass) while "spectacles" has only two, and it's obvious which of the two meanings applies here. Wickwack 121.221.215.92 (talk) 09:49, 14 April 2013 (UTC)

...And of course it's a matter of degree. If the person's eyesight was sufficiently good that glasses were only needed for some specific task like driving or reading - then the effect should be very small indeed. On the other hand, I know an adult who's corrected eyesight is so bad that he can only read things a few inches from his nose - even with thick, heavy glasses. He can't drive, play video games or watch TV at all. Since those are all major teen social activities I'm sure that must cause significant social impairment in teenagers. On the other extreme, my son is mildly red/green color blind and sailed through most of his teenage years without even knowing it - which implies that there was no social impairment whatever. So the answer to our OP is obviously: Yes, it's possible for extremely poor eyesight to cause serious social impairment - but mildly poor eyesight does not cause impairment. It's not a very useful answer without knowing details about a specific case - but in that case we'd be unable to offer advice because it would constitute "giving a medical prognosis" - which we're strictly prohibited from doing. SteveBaker (talk) 12:48, 13 April 2013 (UTC)

While I don't disagree it's a matter of degree and quite variable depending on the imparity, I don't think it's as simple as you suggest particularly since the question was about 'social development be affected' which can be very broad. For example, depending on the person's interaction with peers, teachers and parents, I imagine it's entirely possible they will go through their teenage years with a mild myopia without really realising it, yet it will still affect them (e.g. they will avoid certain activities and be less good at them then they would be if it were corrected). Of course the same could happen for a whole host of other reasons. As Wickwack mentioned, even with perfect correction with glasses it can still have effects since it can affect self esteem, interaction with peers and in some cases the presence of glasses makes it more difficult to participate even without considering those effects. (Again these can also arise for a whole host of other reasons.) Contact lenses can help, but have their own issues. And depending on factors like whether the person is going to need glasses in addition (for times when they don't want to or can't where contacts), the level of the correction required (particularly astigmatism), how frequency the prescription changes and the price in the locale, contact lenses may not be financially possible. Of course for some people and in some places, corrective lenses of any kind may not be possible for financial reasons. Nil Einne (talk) 14:21, 13 April 2013 (UTC)

http://www.youtube.com/watch?v=ls2lC7DQFMI --Digrpat (talk) 23:06, 13 April 2013 (UTC)

In the case of uncorrected poor vision, there can be an interesting split in school. Some will move to the front of the classrooms, in order to see what the teacher is writing on the board, and tend to become "teacher's pets", while others will give up and fall behind in school. Either path could potentially negatively affect their social development. StuRat (talk) 04:12, 14 April 2013 (UTC)

Last spacecraft launch to orbit with *one* astronaut?

When is the last time that a spacecraft launch occurred which made at least one orbit that only had *one* astronaut in the capsule. If this was a private company, when is the last time that a National space agency did so. In either event, was the last launch in the Mercury program the last time the United States did so?Naraht (talk) 11:35, 13 April 2013 (UTC)

The most recent manned space flight with a single crew member seems to have been Shenzhou 5, the first manned space flight of the People's Republic of China, in 2003. Gandalf61 (talk) 12:23, 13 April 2013 (UTC)

The last U.S. single astronaut mission was Mercury-Atlas 9 in 1963. The last Soviet one may have been Soyuz 3 in 1968. No private company has yet done orbital flight. The company SpaceX is trying to do the first private manned orbital spaceflight in mid-2015 but it will carry a crew of three. Rmhermen (talk) 15:30, 13 April 2013 (UTC)

Cost of RNA vs protein

Hi Ref Desk,

I'm wondering what the energy cost to cell is for making an RNA molecule vs the protein for which it codes. Intuitively, I would say that the protein is much more expensive, but a study ([11]) suggests that RNA costs 5x more energy than a protein (49.3 phosphate bonds per nucleotide (x3!) vs 30.3 per amino acid)! I can't find any other estimates to compare this to - any tips?

Cheers,

Aaadddaaammm (talk) 12:16, 13 April 2013 (UTC)

It's not common for someone to come to us with a good reference in hand - thanks! You probably are aware already, but I should say a key thing to bear in mind here is the difference between total synthesis vs. polymerization of precursors. RNA and protein are both going to get degraded sooner or later back to amino acids and XMPs, so the total synthesis doesn't really apply except in growing populations of cells.

So far as I recall, the basic ratio for polymerization should be just one pyrophosphate released per charged amino acid in aminoacyl tRNA synthetase, with that energy being sufficient to power the ribosome, but EF-Tu/eEF-1 contributes another phosphate bond to improve accuracy. (Note that pyrophosphatase makes the PPi effectively count as two bonds split) Other elongation factors exist, for example EF-G at the end of the protein. I can't rightly recall at the moment where the other ~P the author of your reference comes from during elongation. So we're talking about 3 ~P I can count (ignoring the one extra at the end), 4 according to the author, plus parts. By comparison, I would count the "cost of polymerization" in the RNA as being a PPi per bond created (i.e. XTP to XMP). So to me the ratio that would seem to matter in steady-state metabolism would seem more like 2:3 with the amino acid being only a bit cheaper than a codon.

Anyway, what's interesting to me about this is that the selective pressure against having a high level of mRNA and protein per cell seems like it is going to be much less for an organism that remains in a stable state for a long period of time than one which is is exponentially growing. If an organism's whole ecology is geared toward putting on weight and splitting, that seems like it ought to lead to different overall gene expression level than if it is trying to hide for a long time and avoid getting eaten. Hmmm... Wnt (talk) 19:48, 13 April 2013 (UTC)

It's worth bearing in mind that a single mRNA molecule, once transcribed, can be translated multiple times. (Heck, multiple ribosomal complexes can attach to the same mRNA simultaneously, allowing translation of multiple copies of a protein at the same time from a single mRNA: [12].) What this means is that the energy 'overhead' cost of one mRNA molecule can – potentially – be 'amortized' over many, many translated protein molecules. In other words, even if transcription is 'expensive' on a per-base basis, it still accounts for a relatively small part of the entire protein biosynthesis energy budget because mRNA is reusable. TenOfAllTrades(talk) 03:23, 14 April 2013 (UTC)

Spatial Encoding

Since my question has been removed I post it here.

What are the typical computer video compressions algorithms names which use the human retina approach?2A02:8422:1191:6E00:56E6:FCFF:FEDB:2BBA (talk) 21:09, 13 April 2013 (UTC)

(I see where this was removed from Talk:Retina) - unfortunately, it is possible that this still isn't the best place, that Wikipedia:Reference desk/Computing would get you better answers. I'm certainly not aware of any video compression that attempts to follow the retina's approach literally. Figuratively... I can't tell. For example, if I do a Google search for "video compression" "edge finding" I get [13], but I can't really say whether that method of finding dominant edges to align stereo pairs has any relation to the biological scheme at all; certainly it is not a direct copy.

My gut feeling is that the two circumstances aren't comparable because we accept a huge loss of resolution from our retina. We aren't aware of individual rod and cone inputs on their own. So any computer algorithm that worked just like the retina would be seen as a really crummy way to store an image, until such time as the images are sooo high res that we really don't care. I think... Wnt (talk) 22:01, 13 April 2013 (UTC)

Why do you say there's a huge loss of resolution? As far as I know the eye's resolving power is pretty close to the cone spacing. -- BenRG 00:15, 14 April 2013 (UTC)

Our vision isn't nearly as good as it seems. We have lots of blind spots where we looked at something bright and burnt out a few cons and rods, or a blood vessel covers them, etc. Why don't we see black spots all over our field of view ? Out brain does an amazing job at filling in the missing spots. Unfortunately, this also means we aren't always seeing reality, but sometimes just what our brain makes up to fill in the gaps. StuRat (talk) 07:09, 14 April 2013 (UTC)

Perception is reality. 202.158.66.204 (talk) 09:56, 14 April 2013 (UTC)

Thanks for the quick answer I had thought to this. There are projects for getting 60TB per hard drive for the end of the decade. As it did for The GB step,there are reason to full the space. there will exist camera that would produce 25GB images with actuals compression techniques.

I can't imagine diffuser aren't planning the result for video download.I'm sure the algorithms are already written.

By the way I was thinking about the retina side only (no real care about the second eye) and not the decompression methods.

The method of "decompression" is always varying from person to person and time (optical nerves and human brain ). 2A02:8422:1191:6E00:56E6:FCFF:FEDB:2BBA (talk) 22:28, 13 April 2013 (UTC)

My knowledge of the spatial encoding in the optic nerve is based entirely on having read the article section just now, but it looks very similar to the wavelet transform, which is used in JPEG 2000, for example. The most popular video compression formats right now (e.g. h.264 and all versions of MPEG) don't use wavelets, but do use the discrete cosine transform, which is closely related. All image and video compression is based in one way or another on human vision. Even "uncompressed" images represent colors as RGB triples, a representation that's closely tied to human standard color perception. -- BenRG 00:15, 14 April 2013 (UTC)

• I don't really see how the retina can be compared to any image compression algorithm. The huge difference is that the retina has quite a small high-resolution zone, called the fovea -- it is roughly the size of your fist held at arm's length. The most important type of compression the retina uses is to represent only this very small region at high resolution. Nothing like that could work for a computer representation, because there is no way of knowing what part of an image will be the focus of attention. (I'm oversimplifying a bit, but I don't want to flood the board with verbiage.) Looie496 (talk) 03:15, 14 April 2013 (UTC)

Plaster of Paris as a structural material yet it is relatively water soluble, what gives?

Calcium sulfate dihydrate, the main component of plaster of Paris, has a solubility of 2 g/L. Yet this material is used to make all sorts of structural materials. So what I am trying to figure out is why doesnt this stuff dissolve? Perhaps the plaster components are relatively crystalline and have a low surface area, but still I would think that after a few years or decades (see Borujerdis House as one of many antiquities made of P of P) of rainy weather that it would be corroded away. Or, maybe this material is not used for exteriors very much except in dry climates.--Smokefoot (talk) 23:53, 13 April 2013 (UTC)

Paster of Paris is never used as a structural material, not in my country anyway. The term "structural" denotes a material that is load bearing. Plaster of paris is only used in non-load-bearing and decorative applications - someting else underneath (brick, concrete, framework, etc) takes the load - load being either static & dynamic downward forces due to gravity and/or wind loading. Actually, the ability of moisture to wreck plasterwork can be considered a virtue. It lets you know you have rising damp, or a leak in the roof, well before real structural damage is done, and it is easily repaired at mimimal cost. Where used as suspended ceilings where it must sustain its own weight, it is re-inforced with cellulose fibres or other semi-woven material.

I know nothing about the Persian building you cited, but none of the inticate work shown is structural. There's nothing wrong with using plaster work to decorate ceilings and other inside surfaces - this is extremely common in modern western buildings. Despite the labelling on the images, I expect the exterior decoration (which is applied, not structural) is all water-resistant stucco, not plaster. Wickwack 121.215.41.163 (talk) 02:56, 14 April 2013 (UTC)

Oh, good points. I used the wrong wording (structural). My question is simpler - why would anyone decorate the exterior of any building with a material that is fairly water soluble. --Smokefoot (talk) 03:04, 14 April 2013 (UTC)

Read Whitewash. Also note that Persia had (and still has) a rather dry climate, so water solubility wouldn't have been a big problem there. 24.23.196.85 (talk) 03:38, 14 April 2013 (UTC)

I thought so too, but fortunately I checked before writing my first post. It turns out that their annual precipitation (680 to 1700 mm) is somewhat greater than the precipitation where I live (Western Australia), hardly dry, and you certainly would not use plaster on an external surface here. That's why I think that the external decoration is not plaster but stucco. One of the characteristics of whitewash is that is a non-durable paint (once popular in the US) requiring regular re-application. If you used it for the sort of decoration depicted in the OP's link, you'd soon end up with a smooth surface and no decoration. Wickwack 60.230.245.70 (talk) 06:29, 14 April 2013 (UTC)

I think that stucco and plaster of Paris are the same thing (despite what is stated in stucco), calcium sulfate, which is fairly water soluble, so now what? --Smokefoot (talk) 12:32, 14 April 2013 (UTC)

There are various recipes for stucco. Stucco can indeed be made with plaster of paris. It can also be made with portland cement, which makes it completely waterproof, but with a lower quality finish. It also gives an ugly grey colour, but that can be fixed with pigments. There are a number of other water resistant mixes, eg lime-based (as in mortar used to stick bricks together), and you can also use a combination of plaster of paris with cement to give a degree of water resistance. Wickwack 124.182.15.108 (talk) 12:50, 14 April 2013 (UTC)

The answer might just be Relative humidity. Homes which use plaster are usually heated (which lowers the average RH). In older homes that have old fashioned larder rooms, the plaster in them (if they are plastered at all) often become crumbly. Plaster needs to be fairly damp in order to disassociate like this. In the tropics, were relative humidity is high and a artificial heat is not required, then plaster is seldom seen. If it is used, then a lime based wall coating is probably leaning towards hydraulic lime and that is not plaster of paris.Aspro (talk) 20:02, 14 April 2013 (UTC)

April 14

What is this engine part?

What's the part in the red oval?

Shown is a picture of the engine of a 2004 Ford Escape. The silver cylindrical part in the red oval has a cable socket coming in on the left. I just repaired the cable and got the vehicle to work again, the problem being that it would start up fine but die within a second, unless I gave it gas, in which case it would keep running, until I took my foot off the gas, at which point it died. So whatever this part is seems to be related to the idling circuit. Like I said, the car works now. I'm just curious what the part is. Peter Michner (talk) 04:29, 14 April 2013 (UTC)

I'm pretty sure that's the oxygen sensor. But I'm not a mechanic. --Jayron32 04:46, 14 April 2013 (UTC)

Scanning some other stuff, it could also be part of the Exhaust gas recirculation (EGR) system. There's a bit called the "DPFE sensor" or "Differential Pressure Feedback (EGR) sensor" which looks like it is in about this location. I think this diagram is from a 2001 Ford Escape, and the DPFE sensor looks to be in about the location it is in your picture. But I'm just guessing here. --Jayron32 04:56, 14 April 2013 (UTC)

Thanks, looks like it's definitely called the idle air control valve Peter Michner (talk) 06:35, 14 April 2013 (UTC)

4D strorage device

How would one encode information onto a 4D crystal such as the example recently created? Plasmic Physics (talk) 07:20, 14 April 2013 (UTC)

Would there be any advantage over a conventional 2D storage device such as a USB stick? Plasmic Physics (talk) 10:04, 14 April 2013 (UTC)

I think you probably mean 3D, not 4D? If that's the case, see 3D optical data storage and Holographic data storage. Red Act (talk) 12:56, 14 April 2013 (UTC)

I think the question refers to this weird press release. As near as I can make it out they made a simple quantum system that has angular momentum in its ground state and for some reason called it a "4D crystal". Since it's in the ground state, you can't encode any information into it. -- BenRG 15:52, 14 April 2013 (UTC)

If anyone cares, here's the paper and here's the theoretical treatment it cites. The theoretical preprint, which is by Frank Wilczek, starts with a point particle confined to a circle through which there's a magnetic flux. He shows that the ground state has nonzero (orbital) angular momentum and seems to think that's surprising, having apparently forgotten that the ground states of a lot of atoms have that property. He discusses how this counterintuitive result can possibly be true. The answer, of course, is that the particle is uniformly smeared around the circle; it's a "clock" whose hand is in a uniform superposition of all directions at all times. It's rotating, but it doesn't tell time. He then introduces more particles to the loop and a mutually attractive force and shows that they clump together, and seems to argue that this clumping will counteract the smearing out. I don't know how a guy who won a Nobel prize for explaining the structure of hadrons could make that mistake, but as far as I can tell he did. In reality switching from a point particle to a clump changes nothing because the clump is a composite particle (like a hadron) whose position can be characterized by a single angular parameter, and the wave function in terms of that parameter is the same as before. It has to be because a ground state is a state of definite energy, and in a state of definite energy the probability density is time-invariant. He even mentions that fact at the start of the paper, but seems to believe he can circumvent it. Really bizarre. The experimenters have the same misconception about the state they created, but they're experimentalists so it's easier to understand. Wilczek's preprint is apparently unpublished, and maybe PRL accepted the experimental paper because of something interesting on the experimental side. They should have made them drop the crystal-power nonsense, though. -- BenRG 20:03, 14 April 2013 (UTC)

The thought occurs to me that Frank Wilczek may have been making an elaborate joke. He also speculates about iGlasses and iQuasicrystals (the "i" meaning "imaginary", possibly also a play on words). — Quondum 20:56, 14 April 2013 (UTC)

However, 3D storage may make sense to replace 2D. Or, a convoluted surface like in the brain, designed to increase surface area. This would get by the problem of how to access and change data deep inside a 3D object (something like a CAT scan could conceivable read data inside a 3D object, but changing it is a bit more of a challenge). So, maybe 3D storage for read-only memory, with convoluted 2D storage for read/write memory. StuRat (talk) 18:08, 14 April 2013 (UTC)

Compromised title

When searching for "Thin Layer Extraction" one is only redirected to the article "Liquid-Liquid Extraction" that refers to "Thin Layer Extraction" through a dead link. There exists apparently no article by the name "Thin Layer Extraction" to be edited. I have prepared an extended article on "Thin Layer Extraction" and I am unable to create it under this name. How else can one assign a title to a new article? RogerLie (talk) 14:23, 14 April 2013 (UTC)

Questions like this are better asked at the Help desk, but I'll answer anyway. The trick for bypassing a redirect is, after clicking on Thin Layer Extraction and being taken to the Liquid–liquid extraction page, note at the top a line saying Redirected from Thin Layer Extraction. If you click on the link in that sentence, you are taken to the redirect page. You can then edit it to turn the redirect into an article, or you can look at the Page History, which, to save effort, is here.

I note when I look at the page history that you already created a version of that article, back in 2009. It was turned into a redirect a few months ago because an editor felt that the article did not establish that the topic is sufficiently notable. In other words, it is not clear that the term is used in the literature to a significant degree. If you think you can resolve that issue, then you can either edit the redirect page to turn it back into an article, or else revert back to your earlier version and make improvements to it.

If you have further questions about how to edit articles, please ask them at WP:HELPDESK. Regards, Looie496 (talk) 15:09, 14 April 2013 (UTC)

RAST

Is RAST test an example of RAS syndrome?? My textbooks all say that "RAST" stands for "radioallergosorbent" (presumably the T is the final t in that word, which would make it more correctly RASt) and google doesn't show anyone referring to it as a RAS Test. 2.98.248.78 (talk) 15:35, 14 April 2013 (UTC)

The Department of Redundancy Department is definitely interested in this question. Looie496 (talk) 15:56, 14 April 2013 (UTC)

Yes. Affirmative. StuRat (talk) 18:12, 14 April 2013 (UTC)

Power-to-weight ratio: electric and combustion motors

What of both have a better power-to-weight ratio? Even not considering the storage (battery/tank), can an electric motor ever have a better power-to-weight ratio? OsmanRF34 (talk) 19:28, 14 April 2013 (UTC)

See Power-to-weight ratio. The Hi-Pa Drive electric motor has a (theoretical) power/weight ratio of 2.92 hp/lb, better than the Wankel engine at about 1.0 hp/lb, and much better than a conventional Otto engine. The advantage of IC is not so much the weight of the engine, but the weight of the fuel compared to the equivalent battery. Tevildo (talk) 22:10, 14 April 2013 (UTC)

Shouldn't this graph be periodic?

Why is the current/voltage diagram in Franck-Hertz experiment not actually periodic? Why is there an overall upward trend? Wouldn't you expect the function to be truly periodic according to the theory presented in the article?

150.203.115.98 (talk) 22:43, 14 April 2013 (UTC)

No. As voltage increases, electrons are drawn more quickly from the cathode and through the mesh, so current increases. This isn't surprising--if you increase the voltage across a resistor, current increases, and for similar reasons. --140.180.243.134 (talk) 23:27, 14 April 2013 (UTC)

That certainly explains why the current increases between the peaks, but shouldn't the current drop down to zero at each multiple of 4.9 Volts, and start again? 130.56.234.8 (talk) 01:49, 15 April 2013 (UTC)

A resistor isn't really the best comparison in this case, although the basic principle is correct. The null hypothesis for the experiment is that it should behave like a vacuum diode, so the curve would follow Child's law, I ∝ V^(3/2), if there were no interaction between the electrons and the gas. Tevildo (talk) 23:29, 14 April 2013 (UTC)