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June 26

laying of unfertilized eggs

For animals which lay eggs with shells, do most of them have the capability of laying unfertilized eggs? If so, do they follow some cycle like the menstrual cycle? If not, what determines whether they lay unfertilized eggs? Thieh (talk) 00:42, 26 June 2014 (UTC)[reply]

That would seem to waste a lot of resources. Even in chickens, I bet that trait was rare, until people bred them specifically for that trait. StuRat (talk) 01:18, 26 June 2014 (UTC)[reply]

There is the exception of certain reptilian species which sometimes reproduce by parthenogenesis, in which case laying unfertilized aggs is not a waste of resources, but an alternative reproductive strategy. I am not aware of any birds that reproduce by parthenogenesis, but, if there are, all of those offspring would be males due to ZW sex-determination. Robert McClenon (talk) 01:28, 26 June 2014 (UTC)[reply]

Turkey parthenogenesis is a fascinating example of a higher vertebrate that can regularly reproduce asexually. Here's a photo of a poult. Most resources agree: they're always born male! Nimur (talk) 04:21, 26 June 2014 (UTC)[reply]

They would always be male, because of ZW sex determination. If the unfertilized egg has a Z chromosome, and becomes diploid parthenogetically, it becomes ZZ, male. If the unfertilized egg has a W chromosome, and becomes diploid parthenogetically, it becomes WW, which is not viable. This is a disadvantage to parthenogenesis in birds, because only half of the eggs will survive. I don't know of any mammals that reproduce by parthenogenesis, but, if they did, they would have a better survival rate, because they would all go from X to XX, and so would all be females. Robert McClenon (talk) 22:28, 26 June 2014 (UTC)[reply]

I suppose there could be one advantage to laying unfertilized eggs, if they are mixed in with a clutch of fertilized eggs, they might act as decoys to keep predators away from the fertilized eggs. And, if the chicks which hatch then eat the unfertilized eggs, the resources wouldn't be wasted. Of course, fertilizing all the eggs seems an even better strategy. StuRat (talk) 01:33, 26 June 2014 (UTC)[reply]

All egg-laying animals initially produce unfertilized eggs in the hope that they will be fertilized. In the wild most of them get fertilized, but with birds such as chickens we artificially separate the males and females so that can't happen. I have read that chickens only keep laying if you keep removing the eggs so that they can't sit on a full clutch but I can't confirm that with a reliable source. It does say in our chicken article "Under natural conditions, most birds lay only until a clutch is complete, and they will then incubate all the eggs. Many domestic hens will also do this–and are then said to "go broody". The broody hen will stop laying and instead will focus on the incubation of the eggs (a full clutch is usually about 12 eggs)". There is an interesting discussion about laying unfertilized eggs here Richerman (talk) 09:48, 26 June 2014 (UTC)[reply]

Domestic chickens kept as layers have been selectively bred to produce lots of eggs. Also, they can only do so because the food we give them is designed to give them all the nutrients necessary for egg production - chickens kept for meat are given a different diet that is designed to produce muscle mass. Chickens tend to produce eggs during the summer months and stop laying as the days get shorter. To maximise production, commercially kept caged chickens are kept inside under artificial light with a fixed day length. If you think about other species such as fish or frogs they produce lots of eggs which are fertilized outside the body as they are laid - the chances are that some of these will not get fertilized. Queen Honey bees produce some unfertilized eggs and these develop into male drones. Richerman (talk) 16:00, 26 June 2014 (UTC)[reply]

Bees and other eusocial Hymenoptera have a different sex determination system than mammals or birds, in which males are haploid and females (including workers, who are technically sterile females) are diploid. Robert McClenon (talk) 22:28, 26 June 2014 (UTC)[reply]

Detached aircon units

I know this is slightly similar to the question about fridges above, but: In a hot room, not long ago, we had an air cooling machine, only it was located entirely inside the room, so no air could be transferred between it and the outside. The relevant articles are air conditioning#evaporative coolers, air conditioning#portable units and evaporative cooler, but there seems to be some confusion over terminology, since the first two sections I linked will both link to the article evaporative cooler. The first of those refers to models that exchange air with the outside; the second does not. I'm thinking about the second type. Am I right that it can only work for a brief period, because in a room full of people, the body heat will bring the temperature back to exactly the same equilibrium point, with a higher humidity? In other words, after the brief time for which the cooler works, the air should be just as hot, but more humid. Am I right? IBE (talk) 05:18, 26 June 2014 (UTC)[reply]

That's right. If the system is closed then the neat heating effect of the aircon is positive, and the absolute humidity will have increased. In my opinion the equilibrium temp will be higher than before because of the additional heat load of the aircon's motor. RH could go either way. Greglocock (talk) 06:21, 26 June 2014 (UTC)[reply]

Could it have been a ductless conditioner? That is, rather than the AC unit supplying chilled air directly to the room (sometimes via a duct), it cools water which is circulated around the building. This means all there is in each room is a box with the heat exchanger and usually a fan to draw the warm room air over the exchanger. The equipment in the room is much smaller and quieter, and in some buildings it can be easier to route the small diameter water pipes rather than larger air ducts; and its easier for maintenance personnel to work in a single plant room than to have to disturb people in their offices. The box in the room (usually attached to the ceiling or wall, or in a panel in a suspended ceiling) is often called the chiller; several chillers may be connected to a single larger AC unit on the roof or wall of the building. All of this is still a "real" air conditioner, not just a swamp cooler - it's as effective as a ducted system (although more complicated, and a bit less efficient, because of the water circulation system). -- Finlay McWalterᚠTalk 13:35, 26 June 2014 (UTC)[reply]

In a closed, evaporative system, the dew point will rise in the room as the air saturates with water vapor and the air cools with the removal of latent heat. The higher the dew point, the lower the efficiency. Evaporative systems are usually open systems because the ambient air dew point is very low and doesn't rise. The difference between dew point and ambient temperature is similar to the temperature difference in a compressor-style air conditioner (the A/C temperature difference is constant and is affected by ambient temperature.) If you close off an evaporative cooler, the latent heat in the air that can be removed becomes less as the humidity/dew point rises. At the point where the dew point and air temperature are the same, the air is saturated and there is no more evaporative cooling. This temperature will be less than the the starting temperature and will happen as long as it's closed. Adding the heat of the motor/pump becomes a rate equation as to whether the system can add water as fast as the air can absorb it. --DHeyward (talk) 10:59, 27 June 2014 (UTC)[reply]

what is

semicolon cancer? — Preceding unsigned comment added by 121.7.234.202 (talk) 06:55, 26 June 2014 (UTC)[reply]

If you want to make bad jokes here, please ask or answer a legitimate question first. 24.5.122.13 (talk) 07:37, 26 June 2014 (UTC)[reply]

if it's from here, then it's a play on words (see colon cancer and semicolons). Perlis's quote itself is an observation on programming language syntax presented as nutritional advice. Asmrulz (talk) 07:46, 26 June 2014 (UTC)[reply]

That kind of joke was going around in 1985, that President Reagan had a semicolon. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:24, 26 June 2014 (UTC)[reply]

oh.... Asmrulz (talk) 07:04, 27 June 2014 (UTC)[reply]

One can safely say that "semicolon cancer" (a half-life-threatening condition BTW) is a multi-word portmanteau, just like the saying, "It's pissing racehorses."

Contrast period pain.

On a slightly more serious note, see San Serriffe, a fictional island shaped like a semicolon. - ¡Ouch! (^{hurt me} / _{more pain}) 09:47, 27 June 2014 (UTC)[reply]

Hippo's mouth

The excellent photo at the top of this BBC News page shows the inside of a Hippo's mouth very well. What are the interesting frilled structures to the left and right of the throat (just below the upper teeth) and what is their function? --Dweller (talk) 09:25, 26 June 2014 (UTC)[reply]

Tonsils? Richerman (talk) 13:04, 26 June 2014 (UTC)[reply]

Salivary glands. If you look in a mirror under your tongue, ours look rather similar. StuRat (talk) 13:20, 26 June 2014 (UTC)[reply]

I googled "hippopotamus mouth parts" and came up with nothing except pictures of hippos with their mouths open. StuRat might have it. To me the interesting thing is, what if they don't do something to curb this burgeoning wild hippo problem. Imagine biologists a few millennia from now being completely baffled as to how the hippo came to exist in South America. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:23, 26 June 2014 (UTC)[reply]

But those frilled structures aren't under the tongue, they seemed to be attached to the inside of the cheeks. In humans that is close to where the parotid glands are, but whether hippos have parotids is a subsidiary question. I don't have anything similar under my tongue (should I worry?). Richard Avery (talk) 07:36, 27 June 2014 (UTC)[reply]

Wharton's ducts are the relevant human structure - a Google image search (perhaps not immediately after breakfast) gives us lots of photographs of them in various states of blockage and infection. You should, of course, contact your doctor or dentist if you are worried about them. Tevildo (talk) 07:55, 27 June 2014 (UTC)[reply]

Salivary glands are usually "lumpy" or "frilly" to increase surface area. The area under a human tongue is usually more in the "lumpy" category. The placement of the salivary glands can move around the mouth a bit in different species, too, much as, say, hair patterns vary by species. StuRat (talk) 01:51, 28 June 2014 (UTC)[reply]

aeolinite definition

Geotechnical term. I believe it is limestone. However, I would feel more comfortable if this can be confirmed. Thank you24.226.73.86 (talk) 21:56, 26 June 2014 (UTC)[reply]

See BITUMEN STABILISATION OF A LIMESTONE (CALCAREOUS AEOLINITE) used as a pavement material in Australia. 84.209.89.214 (talk) 22:13, 26 June 2014 (UTC)[reply]

I'm not an rock expert, but from the Eolianite and Limestone articles, it sounds like the most common form of eolianite is a kind of limestone, but some eolianite isn't limestone, and some limestone isn't eolianite. The defining characteristic of eolianite is that it is formed by the lithification of sediment deposited by the wind. Red Act (talk) 22:23, 26 June 2014 (UTC)[reply]

June 27

Expensive fish ...

Clown featherback is in German "Tausenddollarfisch", in English Thousand Dollar Knife Fish.

1. Question: Why is the name "Thousand Dollar Knife Fish" not mentioned in the article?

2. Question: What is the ethymology of "Thousand Dollar Knife Fish"? (Who, when and why?). Thx for answers! GEEZER^{nil nisi bene} 12:00, 27 June 2014 (UTC)[reply]

It's a knifefish with a row of circular markings on its side resembling coins. But only 5-10 or so, not a thousand. -- Finlay McWalterᚠTalk 12:13, 27 June 2014 (UTC)[reply]

A translation of its german name is just a Cross-reference. Wikipedia is not a dictionary and thus does not want to collect names and terms but information. --Kharon (talk) 17:23, 27 June 2014 (UTC)[reply]

OK, you're off the hook (...) on both accounts. I found the first mentioning in "Die Aquarien- und Terrarien Zeitschrift, Band 30–31, Alfred Kernen Verlag, 1977".

Case closed. GEEZER^{nil nisi bene} 10:19, 28 June 2014 (UTC)[reply]

MH 370

What is the explanation of the pings detected during the search operation for MH 370.I cannot find any satisfactory explanation for this anomaly .18:06, 27 June 2014 (UTC)~

MH370: possible black box 'pings' spur on search for missing airliner (The Guardian 6 April 2014) See the article Flight recorder. 84.209.89.214 (talk) 19:53, 27 June 2014 (UTC)[reply]

(ec) If you read transcripts of the press conferences from the Joint Agency Coordination Centre (the Australian and international intergovernment agency that is coordinating the search), they distinguish between two categories of ping: satellite radio "pings", and SONAR "pings". Particularly, the early April acoustic signals that were detected by Ocean Shield were publicized and described. The explanation provided by Angus Houston pretty clearly outlines the technical challenges and uncertainties involved in detecting and interpreting such signals. What exactly do you find anomalous? Nimur (talk) 19:54, 27 June 2014 (UTC)[reply]

Voltage divider

Do I need high power resistor in a voltage divider circuit to measure DC voltage upto 100V electronically ? — Preceding unsigned comment added by 39.42.126.189 (talk) 20:25, 27 June 2014‎

Not as long as you're careful to choose resistance values that are high enough. The power a resistor dissipates due to Joule heating is given by P=V²/R. So calculate the maximum V across each resistor, and then pick values for the R's to be at least big enough that the P's don't exceed the power rating of your available resistors. Red Act (talk) 21:19, 27 June 2014 (UTC)[reply]

The article Potentiometer (measuring instrument) is of interest. However exercise caution because you are dealing with a possibly lethal high voltage. Modern Voltmeter instruments have conducting metal parts insulated for safety. 84.209.89.214 (talk) 01:39, 28 June 2014 (UTC)[reply]

If I choose values in Kilo Ohm, will it be safe ? 39.42.126.189 (talk)

No, that would quite likely not be safe. If you apply 100V across a pair of resistors that total, say, 10kΩ, the resistors would need to dissipate a total of 1W, which is a problem because most resistors are only rated for a fraction of a Watt. If you don't know the power rating of your resistors, it'd be safest to assume that they're only rated for 1/8W, which is the smallest power rating that they're likely to be. (At least, 1/8W is the smallest power rating of the resistors Radio Shack sells.) Assuming most of the power is dissipated from just the larger of the two resistors, at a 1/8W rating and applying a little bit of a safety margin, you'd want the two resistances in the voltage divider to total 100kΩ at the very least, to make sure you don't smoke the larger of the two resistors in the voltage divider. Red Act (talk) 05:50, 28 June 2014 (UTC)[reply]

I should resistor with a power rating of at least 2W or is 1W resistor good enough ? 39.55.175.44 (talk) 12:29, 28 June 2014 (UTC)[reply]

Again, it depends on the resistance. Rearranging the equation I gave above, a resistor with a power rating of P watts that needs to be able to handle up to V volts across it needs to have a resistance of at least R=V²/P ohms. So for example with V=100V and P=1W, the resistance R has to be at least (100V)²/(1W) = 10kΩ. Or as an alternative but compatible example, using the equation in the form I gave originally, if you need a resistor that you've already chosen to be 10kΩ to handle 100V across it, then the power rating of the resistor needs to have a power rating of at least (100V)²/(10kΩ) = 1W. Red Act (talk) 15:25, 28 June 2014 (UTC)[reply]

What will be disadvantage of using a resistor with high power rating, this voltage divider circuit will be permanently left in. Do resistor with higher power rating will draw more power and waste it as heat ?

Every resistor carrying a current I dissipates a power P as waste heat. You need to know Ohm's Law to appreciate that P (in watts W) can be calculated in any of these ways:

P=IV=I^{2}R=V^{2}/R

The power rating of a particular resistor is just the maximum power that it can tolerate; the above equation decides the actual power. Choosing a higher power resistor than a circuit really needs is typically a good decision because a big component that only heats up slightly is more reliable in the long term than a small component that heats up a lot. Obviously that strategy should not be taken to extremes, for example a mobile phone that used 20 Watt rated resistors throughout would need a wheelbarrow to carry it around. But it could still work and the actual power of, say, a resistor of 10 kΩ carrying 1 mA would still be only 0.0000000001 W (= 0.0001 μW) by the above equation. 84.209.89.214 (talk) 19:20, 28 June 2014 (UTC)[reply]

Let say, the maximum current which will be following through that circuit is 8A at 100V. what values of resistors should be used ?

Shouldn't the current flowing through a Voltage divider circuit should be kept minimum ? Afterall, maximum current should be following through load circuit ? 39.42.120.65 (talk) 19:44, 28 June 2014 (UTC)[reply]

No let's not say that you will waste 800 watts (enough energy to heat a room, illuminate a village or blow-dry someone's hair) in a circuit just to measure a voltage. Please pay attention to the references and examples already given. 84.209.89.214 (talk) 02:02, 29 June 2014 (UTC)[reply]

Thanks Got it. 39.42.120.65 (talk) 05:18, 29 June 2014 (UTC)[reply]

Eating clay as detox

It is apparently Calcium bentonite. I don't have detox cures in high regard, nor I believe that we are full of toxins. But could this have some benefit in getting rid of metals or fat in the body? It is even used inFuller's earth that has medical uses. OsmanRF34 (talk) 21:39, 27 June 2014 (UTC)[reply]

Only before the fats or the heavy metals are actually absorbed into the body -- once in the bloodstream, fat can only be burned off through physical activity, and heavy metals require chelation therapy (which has all sorts of nasty side effects) to remove from the body. 24.5.122.13 (talk) 01:00, 28 June 2014 (UTC)[reply]

Note that some animals eat clay after they get indigestion (or ahead of eating problematic foods, to prevent it). Some parrots and primates, as I recall. StuRat (talk) 01:44, 28 June 2014 (UTC)[reply]

Geophagy. Wnt (talk) 03:57, 28 June 2014 (UTC)[reply]

Well, how do you know that they're not eating dirt just because they're very hungry and can't find anything else to eat (as was the case, for example, with some Gulag inmates who were forced to do hard labor on a starvation diet^[1]?) 24.5.122.13 (talk) 08:14, 28 June 2014 (UTC)[reply]

Maybe sometimes they do, but the article has all kinds of references to support it being a deliberate, non-starvation situation. Matt Deres (talk) 11:43, 28 June 2014 (UTC)[reply]

"Well, how do you know that they're not eating dirt just because they're very hungry and can't find anything else to eat (as was the case, for example, with some Gulag inmates who were forced to do hard labor on a starvation diet" The Parrot Gulag, by Budginitsyn? Priceless μηδείς (talk) 22:40, 28 June 2014 (UTC)[reply]

The official advice of the English NHS, which is hardly a hotbed of quackery, is "Kaolin is an adsorbent that helps to absorb toxins from the gut". At least in Britain, this is a common treatment which can be bought (almost invariably mixed with morphine) over the counter. 84.13.54.182 (talk) 22:48, 28 June 2014 (UTC)[reply]

I think it's even more familiar as Kaopectate, though apparently the U.S. pulled their license to sell clay. Wnt (talk) 03:34, 29 June 2014 (UTC)[reply]

The key word here, though, is from the gut (as opposed to from the bloodstream). 24.5.122.13 (talk) 04:18, 30 June 2014 (UTC)[reply]

References

^ Solzhenitsyn, Alexander (1980). The Gulag Archipelago, vol. 2. Paris, VT: YMCA-PRESS. pp. 129–130. ISBN 5-265-01557-4.

Is a true one-way mirror really impossible?

A Google search finds sources that say that such a mirror would violate the laws of thermodynamics. But I question that argument since any resulting heat transfer can be offset by conduction, or possibly convection around the mirror as well, so the heat transfer always follows the temperature gradient.

Even if a one-way mirror for the entire electromagnetic spectrum cannot exist, could it still be possible to make a one-way mirror for e.g. the visible spectrum only?--Jasper Deng (talk) 22:46, 27 June 2014 (UTC)[reply]

Sure - you just need a really thick wall to block the photons, and somebody to open a doorway whenever they see a photon coming from the correct direction! Nimur (talk) 22:58, 27 June 2014 (UTC)[reply]

In particular, it would violate Clausius's statement of the Second Law - "Heat can never pass from a colder to a warmer body without some other change, connected therewith, occurring at the same time." Allowing the heat to flow back to the colder body after it's gone in the illegal direction doesn't fix things - the "at the same time" is an equally important part of the statement. Tevildo (talk) 23:13, 27 June 2014 (UTC)[reply]

There is no theoretical obstacle from a thermodynamic perspective, if you consider a circulator or even an optical circulator system. It requires an extra "face" to the mirror, so that a black body can be coupled into the system. Light goes from A to to the black body; thermal radiation only goes from the black body to B, and light goes from B to A. So A can observe B, but B can only see the heating effect of A on what is hopefully a perfect black body. We don't need Maxwell's demon to solve this one. —Quondum 23:35, 27 June 2014 (UTC)[reply]

See also Optical isolator, where the thermodynamic topic is also mentioned. —Quondum 23:43, 27 June 2014 (UTC)[reply]

Isn't a camera on one side of a wall and a monitor on the other side logically a one-way mirror ? StuRat (talk) 01:45, 28 June 2014 (UTC)[reply]

Well, it's not a mirror, but other than that, sure.

It does deserve the term one-way mirror more than the topic of our one-way mirror article does, though. The proper name for that is two-way mirror. Unfortunately the wrong side won that argument. --Trovatore (talk) 01:47, 28 June 2014 (UTC)[reply]

You can also put a duplicate monitor image on the side with the camera, to make it into a "mirror". And, since one camera wouldn't quite mimic a mirror, you could have many tiny cameras each displaying just a few pixels. It should be possible to make it pretty much indistinguishable from a real mirror. If you can make the camera the size of a pixel, you could have each camera surrounded by 6 pixels, where those 6 would display the color detected by the camera (possibly blending the color with colors detected by nearby cameras). StuRat (talk) 01:53, 28 June 2014 (UTC)[reply]

Any thermodynamic argument against such a mirror is going to rely on it being a mirror — that is, a passive device that doesn't need to be powered. Of course, if you supply energy and negentropy to the system, you can (approximately) reconstruct any wavefront you want. --Trovatore (talk) 02:03, 28 June 2014 (UTC)[reply]

I think a passive "mirror" that radiates all the energy that it receives from the other side as pure black body radiation, while transmitting images faithfully in the other direction, qualifies under the intent of the concept "one way mirror" even though it reflects nothing, and satisfies the thermodynamic constraints. Of course, if one wanted it to look like a mirror rather than like a room-temperature black surface, one could just put a partial mirror on the one side. —Quondum 02:37, 28 June 2014 (UTC)[reply]

Doesn't even a conventional mirror absorb and/or scatter some percentage of the light that hits it? ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:41, 28 June 2014 (UTC)[reply]

A one-way mirror is similar to an irreversible reaction - light flows from an area of high concentration to an area of low concentration. In the case of the chemical reaction, people may omit the back arrow once it becomes a sufficiently complicated exercise in entropy on one side (for example, when you use pyrophosphatase to enhance an ATP-dependent reaction in biology). So an interesting question would be if you can spice up a one-way mirror in some similar way, i.e. by splitting the photon somehow into two or even three weaker photons in a coating on the protected side, and then putting some kind of band pass filter in the mirror so that the weaker photons can't make it back through unless they somehow manage to meet up and recombine. That way even if your perp suddenly whips out a super-mag flashlight to shine through the glass, your protected witness should remain unknown to him. Wnt (talk) 03:55, 28 June 2014 (UTC)[reply]

I already linked to optical isolator above – it already exists, only it is not similar to a one-way reaction. Light goes one way, not the other. No matter that one shines a bright light from the one side. Simply sandwich a 45-degree Faraday rotator between two polarizing filters oriented at 45 degrees. —Quondum 05:24, 28 June 2014 (UTC)[reply]

An isolator is quite different to a (hypothetical) one-way mirror. Both transmit electromagnetic radiation in one direction only (say from side 1 to side 2). However, an isolator absorbs radiation travelling the other way (impinging on side 2), whereas a mirror would reflect it (or it wouldn't really deserve to be called a mirror).

The mirror would violate conservation of energy (unless it had a power supply), the first law of thermodynamics. Suppose the mirror was illuminated from both sides with radiation of equal wavelength and equal amplitude, then on side 2 of the mirror, the reflected wave would interfere with that transmitted from side 1. If the relative phase of the incoming waves was adjusted so that the interference was constructive, then the combined wave leaving the mirror would have twice the amplitude and carry four times the power of each of the two incident waves. Overall the mirror would be sending out twice as much power as it was receiving. --catslash (talk) 00:07, 1 July 2014 (UTC)[reply]

June 28

Rescue dogs

What are some of the mission-specific commands given to SAR dogs (e.g. to commence a specific type of search, to return to handler, to leave a dangerous area, etc.)? Thanks in advance! 24.5.122.13 (talk) 01:04, 28 June 2014 (UTC)[reply]

Have you read SAR dog#Training ? 84.209.89.214 (talk) 01:18, 28 June 2014 (UTC)[reply]

Yes, but the only actual commands it mentions is "Go find!" and "Show me!" -- what other commands (if any) are there? (I don't mean generic commands like "Heel!", "Sit-stay!", etc. -- I mean commands specific to the search-rescue mission.) 24.5.122.13 (talk) 01:48, 28 June 2014 (UTC)[reply]

How certain are you that the dogs get more commands than that? Dogs are marvelously intelligent creatures, especially next to things like trees and congressmen, but I doubt search and rescue dogs are doing anything more complex than playing the "find the smell and get a treat" game. "Go find" and "show me" are sufficient commands for what they need to do. As with any tool, it's up to the humans to do the real work and use the dogs properly. --Jayron32 03:46, 28 June 2014 (UTC)[reply]

[1] [2] [3] [4] [5] Snow talk 04:28, 28 June 2014 (UTC)[reply]

Thank you for all this info, SnowRise! This is lots of great research info, with the Koven link being particularly helpful. (Now I know how TJ, the ski patrol leader, will communicate with his rescue dog Detrick while they're digging up victims from that super-avalanche.) 24.5.122.13 (talk) 08:01, 28 June 2014 (UTC)[reply]

De rien. Stay safe. Snow talk 11:39, 28 June 2014 (UTC)[reply]

What's going on in Darwin?

Checking up on something at WP:ANI led me to http://www.ntnews.com.au, where to my surprise I saw that today's temperatures for Darwin are 18°C and -31°C. What's going on? How do they have such a horribly cold day, so far north in the tropics? Nyttend (talk) 03:53, 28 June 2014 (UTC)[reply]

Sounds like a mistake. I would guess that's supposed to be a low of +18°C and high of +31°C. StuRat (talk) 04:06, 28 June 2014 (UTC)[reply]

Yes, it looks like a typo. weather.com says that the observed low and high in Darwin, AU on June 27 were +19°C and +29°C, respectively.[6] Red Act (talk) 04:17, 28 June 2014 (UTC)[reply]

The lowest temperature ever recorded in Australia was nowhere near that low. Something like -17°C, in the Snowy Mountains (a long way from Darwin), in the 1990s. -- Jack of Oz ^{[pleasantries]} 06:44, 28 June 2014 (UTC)[reply]

Okay, all of this makes a lot more sense than I was imagining; thanks for the confirmation that I'm not going crazy and that the world isn't about to go into deep freeze. Nyttend (talk) 11:27, 28 June 2014 (UTC)[reply]

why so few craters?

Why does this video] from LRO show so few craters? Were the pictures taken when there were no shadows? Bubba73 ^{You talkin' to me?} 05:58, 28 June 2014 (UTC)[reply]

Are we watching the same video? I see about as many craters as I would expect given the resolution of the video and the size of the moon in that video. Which crater do you find that is missing? --Jayron32 06:03, 28 June 2014 (UTC)[reply]

Few? There seem to be plenty of craters to me - but yes, clearly the image is a composite made of images with the orbiter directly over the sunlit side of the Moon, meaning that shadows are minimised. AndyTheGrump (talk) 06:07, 28 June 2014 (UTC)[reply]

Compare that to the photo I just added. Bubba73 ^{You talkin' to me?} 07:01, 28 June 2014 (UTC)[reply]

The near side of the moon has many lunar maria ("seas"), very large craters that have been filled with relatively dark, smooth lava. The far side of the moon has only a few small maria. There are craters everywhere, but most of them are smaller and much lighter in color than the maria. From Earth, we only see the near side, so we see a lot of the surface covered in dark maria. Perhaps you're just noticing that the rest of the moon looks very lighter and much different. --Amble (talk) 07:17, 28 June 2014 (UTC)[reply]

No, what I'm actually asking about is that plenty of craters are visible in that photo, but I don't see many in the video. It must be because the shadows make them visible. Bubba73 ^{You talkin' to me?} 11:39, 28 June 2014 (UTC)[reply]

Indeed. Our fake libration animation gives the same erroneous impression. To the beginner, it might seem that the full moon is the best time to check out our nearest neighbour, but in fact that's a pretty poor time to look at it because many of the interesting features are wiped out by brightness and lack of contrasting shadows; you see a lot more when the sun's rays strike the moon from an angle rather than directly overhead. Matt Deres (talk) 12:11, 28 June 2014 (UTC)[reply]

It must be more deliberate than that. The Lunar Reconnaissance Orbiter doesn't just sit somewhere near the sun taking pictures; it's in orbit around the Moon and would tend to pick up many shadows. It generated highly detailed topographic maps. And of course the poles of the Moon aren't without shadow. So this particular video must have intentionally extracted just the albedo from its data by some means. Wnt (talk) 13:12, 28 June 2014 (UTC)[reply]

Bubba: OK, I thought you might have been looking at the Maria since they are the most familiar kinds of lunar crater visible from Earth. This page [7] from Arizona State University has some information about how the image was made. Essentially, they made images in strips when the sun was overhead, corrected the off-center parts of each strip, and stitched them together to make a single image with no shadows. As you say, that shows you just the albedo with none of the lighting cues that usually make craters more visible to the eye. --Amble (talk) 01:03, 29 June 2014 (UTC)[reply]

It looks as though the craters have all slumped, or been weathered, flat. Reminds me of Callisto. —Tamfang (talk) 03:31, 29 June 2014 (UTC)[reply]

Tesseract house

Would it be possible to build a house like this at all, even if it was with sufficiently advanced technology? Feitlebaum (talk) 23:38, 28 June 2014 (UTC)[reply]

There's absolutely zero evidence of a macroscopic fourth dimension of space, so unless your sufficiently advanced technology involves relocating to a radically different universe, no. AlexTiefling (talk) 23:50, 28 June 2014 (UTC)[reply]

Heinlein's story tells of the building of a house in the shape of the 3-D projection of an unrealizable 4-D tesseract, and this is possible. However after an earthquake it would not behave in the impossible way described in the story. Linking to Clarke's three "laws of prediction" (scarequotes deliberate) suggests a love of science fiction but does not affect the answer given. 84.209.89.214 (talk) 01:44, 29 June 2014 (UTC)[reply]

There was a study published about 2000 that with a few weeks intensive use of 4D virtual reality goggle you could learn to navigate and comprehend $D shapes and spaces as intuitively as 3D. μηδείς (talk) 18:10, 29 June 2014 (UTC)[reply]

June 29

Glasses

Why do so many people wear glasses the older people get. In school at early ages, only a few people wear glasses but every year in school this increases and by the time people are in college or start working, so many people wear glasses. Sometimes it seems like over half the population does. Why?
— Preceding unsigned comment added by 90.194.55.177 (talk • contribs) 00:38, 29 June 2014 (UTC)[reply]

First, some forms of nearsightedness (myopia) develop gradually over one to three decades. Also, there have been suggestions that frequent use of near vision can activate a genetic tendency to nearsightedness, and frequent use of near vision is a feature associated with reading in school. Second, after approximately 40 or 45, presbyopia sets in, requiring reading glasses for reading. Robert McClenon (talk) 02:15, 29 June 2014 (UTC)[reply]

One more point: unless eye tests are arranged by the school or the child's parents, myopia might go unrecognized for a while, because the child simply thinks everybody sees that way. I did. How long it takes for someone to realize might depend on how things are done in the particular school, i.e. how often a child has to read written text from a distance. --70.49.171.225 (talk) 05:45, 29 June 2014 (UTC)[reply]

By the way, in a complex human society with division of labor but without glasses, nearsightedness is not actually a disadvantage. Nearsightedness in adolescence would steer a person into a trade or craft involving near vision, such as weaving or woodworking, and a naturally nearsighted person continues to have good near vision after the onset of presbyopia. In a complex human literate society without glasses, nearsightedness may have actually been beneficial, because one could become a scribe, a high-status occupation. So evolution in humans never selected against nearsightedness. Robert McClenon (talk) 02:15, 29 June 2014 (UTC)[reply]

This presupposes that the nearsighted actually see better up close than those with normal vision. Is this true ? StuRat (talk) 15:55, 29 June 2014 (UTC)[reply]

What it presumes is that the nearsighted can see better up close after age 40 than those with normal vision. Robert McClenon (talk) 19:54, 29 June 2014 (UTC)[reply]

Of course, a lot of scribes were nominally celibate. —Tamfang (talk) 03:27, 29 June 2014 (UTC)[reply]

See Human eye#Effects of aging and Presbyopia. Red Act (talk) 02:21, 29 June 2014 (UTC)[reply]

I've read speculation that nearsightedness was more prevalent among long-settled agricultural societies like China and much of Europe than areas where hunting or pastoralism required one to see animals is the distance rather than the crops at your hands and feet. Probably read this in Discover, it's not something I'd have seen in a technical source. My nephew, BTW, was fitted for glasses before he was three, his squinting and refusing to sit as far away as the couch to watch TV was a dead giveaway. μηδείς (talk) 18:06, 29 June 2014 (UTC)[reply]

NML Cygni

Move from Portal talk:Astronomy by -- Moxy (talk) 08:17, 29 June 2014 (UTC) ...user notified[reply]

i've got a question concerning the radius of NML Cygni: this article http://arxiv.org/abs/1207.1850 has been quoted as the source of the radius of 1650 R_☉. however, i could not find 1650 R_☉ in the article. all i could find was the following sentence on page 10: NML Cyg’s stellar size of 16.2 mas from Blöcker et al.(2001) was derived using the Stepan-Boltzmann law, adopting Teff=2500 K and a distance of 1.74 kpc. Rescaling this stellar diameter with our distance of 1.61 kpc gives 15.0 mas. well, mas are milli arc seconds, i suppose.

using http://www.wolframalpha.com/input/?i=1.61+kpc*sin%2815+milliarcseconds%29 i get a diameter of 3.613 billion km. this is far from the 2.29 billion km quoted for NML Cygni. can anyone explain, how the 1650 R_☉ were calculated? many thanks --Agentjoerg (talk) 08:01, 29 June 2014 (UTC)[reply]

Note to readers who don't recognize the symbol next to R (or whose browser doesn't render it): it`s the Sun; R_☉ is its radius, about 700,000km on a sunny day.

The Stepan[sic]-Boltzmann law (yahoo only found it in that source) is the Stefan–Boltzmann law.

The 2001 figures return 4.2 billion km, or about 6000R_☉; a factor of 1.8 compared to 2*1650R_☉. - ¡Ouch! (^{hurt me} / _{more pain}) 09:23, 30 June 2014 (UTC)[reply]

Shortcut to balance redox equations

I am trying to find a shortcut method to balance redox equations.

(There is one such method for the simple (non-redox) chemical equations. source: http://www.nyu.edu/classes/tuckerman/adv.chem/lectures/lecture_2/node3.html) (I know the original method to balance an equation by oxidation numbers, but just trying to find if there exists an shortcut method for this. This is not my homework. I can balance these equations, but the original method is too long and boring.)

The problem with this type of equation is - we are not always given H₂O and H⁺ on any of the sides. If we were given all of the resultants and the products, we could solve the equation simply by the algebraic method. (see the link above)

I think that the main thing I have to figure out is - how to determine the side, on which H₂O or H⁺ is, at first sight.

e.g. 1) S + HNO₃ ---> H₂SO₄ + NO
   2) P₄ + NO^3-  ---> PO₄^-3 + NO₂
   3) FeS + H₂O₂ ---> FeO + SO₂

The answers to the above equations is respectively -- 1) S + 2HNO₃ ---> H₂SO₄ + 2NO 2) P₄ + 20NO^3- 8H⁺ ---> 4PO₄^-3 + 20NO₂ + 4H₂O 3) FeS + 3H₂O₂ + 5Fe⁺² + 2H₂O ---> 6FeO + SO₂ + 10 H⁺

Ravishankar Joshi

The algebraic method expresses the problem as a set of simultaneous equations. Your boring job of solving them can be delegated to a computer programmed to perform Gaussian elimination which is a well known routine. Balancing any given chemical equation makes a nice exercise in any programming language; simple BASIC will do because calculating speed will be insignificant. 84.209.89.214 (talk) 11:27, 29 June 2014 (UTC)[reply]

If you're allowed to use both H⁺ and H₂O, then because the hydrogen ions are an oxidizing agent, you can use them to balance the equation. What I remember about them is that on the left side, you use them if the solution the reaction is in is acidic (it's been a while since I've done this).--Jasper Deng (talk) 18:34, 29 June 2014 (UTC)[reply]

The steps for balancing these are as follows:

Step 1) Split the reaction into 2 half reactions (an oxidation and a reduction)

Steps 2-5 apply for each half reaction separately

Step 2) Balance all NON-H and NON-O atoms with coefficients for each half reaction
Step 3) Balance the O with extra water molecules. Simply find the side of the reaction that has too few O atoms, and add that number of water molecules (H₂O) to that side.
Step 4) Balance the H with extra hydrogen ions (H⁺). Simply find the side of the reaction that has too few H atoms, and add that number of H⁺ ions to that side.
Step 5) Balance for charge by adding extra electrons to the side whose charge is too positive.
Step 6) Multiply the half-reactions by some whole number ratio to get an equal number of electrons in the two reactions
Step 7) Recombine the two half reactions, and eliminate any common items on either side of the reaction arrow.

Easy peasy, lemon squeezy. Here's how to do it for #2 above, just for example:

Step 1

split to half reactions

Oxidation half reaction: P₄ --> PO₄^-3

Reduction half reaction: NO₃^- --> NO₂

Step 2

balance for non-O and non-H atoms:

Oxidation half reaction: P₄ --> 4PO₄^-3

Reduction half reaction: NO₃^- --> NO₂

Step 3

Balance O using water

Oxidation half reaction: P₄ + 16H₂O--> 4PO₄^-3

Reduction half reaction: NO₃^- --> NO₂ + H₂O

Step 4

Balance H using hydrogen ions

Oxidation half reaction: P₄ + 16H₂O--> 4PO₄^-3 + 32H⁺

Reduction half reaction: NO₃^- + 2H⁺--> NO₂ + H₂O

Step 5

Balance for charge using electrons

Oxidation half reaction: P₄ + 16H₂O--> 4PO₄^-3 + 32H⁺ + 20e^-

Reduction half reaction: NO₃^- + 2H⁺ + e^- --> NO₂ + H₂O

Step 6

Equalize electrons by multiplying

Oxidation half reaction: P₄ + 16H₂O--> 4PO₄^-3 + 32H⁺ + 20e^-

Reduction half reaction: 20NO₃^- + 40H⁺ + 20e^- --> 20NO₂ + 20H₂O

Step 7

Recombine and eliminate common terms

P₄ + ~~16H₂O~~ + 20NO₃^- + 40 8H⁺ + ~~20e^-~~ --> 4PO₄^-3 + ~~32H⁺~~ + ~~20e^-~~ + 20NO₂ + 20 4H₂O

What you are left with is:

P₄ + 20NO₃^- + 8H⁺ --> 4PO₄^-3 + 20NO₂ + 4H₂O

There ya go. --Jayron32 19:04, 29 June 2014 (UTC)[reply]

Should "12" be "16" at steps 3 and 4? Tevildo (talk) 20:22, 29 June 2014 (UTC)[reply]

So fixed. Wikimarkup makes debugging rather difficult on the fly. --Jayron32 23:15, 29 June 2014 (UTC)[reply]

Organs alive outside the body.

I'm curious to know if organs are able to be supported outside the body on a long term basis? We know that organs require a healthy blood supply and circulation in order to survive. With modern medicine and science could this not be achieved? Perhaps technology could go a step further in the form of a machine that actually simulates the environment of the body.

Building on this, could we then support a fully functioning female reproduction system? Infants could be spawned without the need for a human host. How feasible would all all this be?

And whilst we're at it, I know during brain surgery the brain is actually exposed with the patient conscious. So what would happen in a scenario with a large portion of the skull missing, exposing the brain. Would the said individual be able to function normally for a period of time (beside the distress of having your brain exposed of course) If not, what would be the cause of death?

Liver dialysis, artificial hearts, and even hemodialysis remain crude stopgaps that range from inadequate to laughable as substitutes for the actual organs. Parenteral nutrition is not so good either. Wnt (talk) 12:50, 29 June 2014 (UTC)[reply]

This chap (the Daily Mail, I'm afraid, but it's reliable enough in this sort of situation) has survived for a year without half his skull, and isn't at imminent risk of death. He's by no means alone in his predicament, as a Google image search for "missing skull" will confirm. See also human skull, trepanation and craniectomy. Tevildo (talk) 13:16, 29 June 2014 (UTC)[reply]

Note that scientists are working on ways to grow replacement organs for implantation, and this, of course, requires that those organs survive outside the body for an extended time. There was the famous pic of a human ear being grown on a mouse's back, for example. StuRat (talk) 17:09, 29 June 2014 (UTC)[reply]

Don't know if it counts as an example to your satisfaction, but a hernia in the abdominal wall can allow theintestines to escape the inside of the wall and roll around just under the skin of the belly like sausage links on the run. That's a very dangerous condition, but yo can live that way indefinitely. Advertisements for Truss (medicine) were common when surgery was less available. μηδείς (talk) 17:57, 29 June 2014 (UTC)[reply]

You might want to read this. A lot of scientific detail on organ preservation, but not too incomprehensible to regular people. InedibleHulk (talk) 18:18, June 29, 2014 (UTC)

Okay, back to my second question regarding brain exposure, I mean literally an exposed brain, no tissue or flesh covering it. Is it possible to function normally in this condition? Obviously, aside from the somewhat obvious mental distress. If not, what would be the cause of death?~~

Infection - specifically, encephalitis - would be the big risk in that situation. However, unless Jeffrey Dahmer was responsible for your treatment, some sort of scar tissue would form over the exposed brain (probably from the dura mater, if that was damaged - see this fascinating article about an experiment with rats) to provide an adequate barrier to bacteria. Tevildo (talk) 21:03, 29 June 2014 (UTC)[reply]

Maybe goes without saying, but you'd want to keep large objects off of it, too. And the sun, rain and snow (at least until your scar grows in). Not sure of the physiology, but it seems like a recipe for strokes and seizures, especially in autumn. Unless your hypothetical guy can wear a helmet. Then it's mainly the dirt and swelling. InedibleHulk (talk) 21:22, June 29, 2014 (UTC)

This equally-fascinating article would appear to indicate that keeping the sun off isn't a major consideration. Incidentally (and perhaps one for the language desk), I note that vivisectionists were using "sacrificed" as a - euphemism? - in 1949. When did this usage first come in? Tevildo (talk) 22:34, 29 June 2014 (UTC)[reply]

Hey, if a priest can get the genetics ball rolling, it's only fair that scientists can appease the Lord of Light every 28 days, if that's their hobby. But yeah...a bit weird. Maybe we can still trust them with our exposed brains, though. Good find! InedibleHulk (talk) 00:49, June 30, 2014 (UTC)

What would happen if you were sweating in the sun, and it leaked in? Saltwater's no good for metal electronics. Same deal? InedibleHulk (talk) 00:58, June 30, 2014 (UTC)

Aside from irrelevant aquarium stuff, a quick Google finds this charming brain-eating amoeba. Seems freshwater isn't great, either. InedibleHulk (talk) 01:01, June 30, 2014 (UTC)

(see primary amoebic meningoencephalitis for that --catslash (talk) 00:17, 1 July 2014 (UTC))[reply]

How to remove rust from stainless steel

I have a pair of spoons that, well, "spooned" in the dishwasher. One apparently has a flaw in the surface that allowed iron to escape, and the area between the spoons stayed wet and formed a rust ring on both spoons. I tossed out the one with the flaw, but can the other be saved ? So far I tried using steel wool on it, which removed some, but not all, of the rust stain. Obviously I want to avoid damaging the surface. StuRat (talk) 17:01, 29 June 2014 (UTC)[reply]

Try this. --Jayron32 17:06, 29 June 2014 (UTC)[reply]

(ec) You could try citric acid. - Lindert (talk) 17:09, 29 June 2014 (UTC)[reply]

Toothpaste is a very fine abrasive. You could polish out the corrosion pits on top with it if these spoons are worth the work. --Kharon (talk) 20:57, 29 June 2014 (UTC)[reply]

No, the spoon with the corrosion pit is in the trash. It's the other one I'd like to save, so my set of flatware isn't so short of spoons that I have to buy another set (you can never find an exact match to replace the missing ones). StuRat (talk) 14:58, 30 June 2014 (UTC)[reply]

I dread to think how long they were left like that for a rust ring to form, weeks at a guess. Anyway the sad thing you have learned is that cheap stainless steel isn't stainless. Greglocock (talk) 22:23, 29 June 2014 (UTC)[reply]

As with cheap copper-based utensils with a coating to make them look like silverware. Used by low-income Irish, when the veneer wore off and the underlying metal became corroded, the folks would discuss "The greening of the ware". ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:26, 29 June 2014 (UTC)[reply]

^{[clarification needed]} Bugs, you're going to have to explain; I don't get it. Nyttend (talk) 02:58, 30 June 2014 (UTC)[reply]

The color copper turns when it oxidizes + "The Wearing of the Green". (Blame Johnny Carson for this one.) ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:20, 30 June 2014 (UTC)[reply]

I thought maybe you were getting at the oxidising, but I'd never heard of "The Wearing of the Green". I thought maybe it was "wear" in the sense of "wow, that's worn; it needs replacement". Nyttend (talk) 03:32, 30 June 2014 (UTC)[reply]

I was told that, at least with acetic acid (vinegar), you have to heat the reactants to start the acid-base reaction. I'm not sure of it, but it may also be possible to use electrolysis to reduce the iron back to the free element (the main problem I can think of is that water might be too easily reduced instead); my book mentions the untarnishing of antique silverware this way.--Jasper Deng (talk) 03:13, 30 June 2014 (UTC)[reply]

How to identify quality stainless steel ?

This brings up the obvious Q, how do I find stainless steel flatware that won't have flaws in the surface ? Or do I just buy a really expensive brand and hope they are good ?

1) Is there no way to tell before I make the purchase ?

2) Is there a test I could do immediately when I get them home, so I could return them if defective ? (I'm thinking submerge them in bleach so any corrosion will happen far sooner.) StuRat (talk) 14:58, 30 June 2014 (UTC)[reply]

No, there is no easy way to tell. I'd use either salt water or whatever it you usually use to rot your utensils. Even with engineering grade stainless steels, such as 304, their life in seawater is supplier dependent. 316 is generally pretty good wherever it comes from. Greglocock (talk) 22:16, 30 June 2014 (UTC)[reply]

RGB colour model

In the diagram here, is "Area of triangle / Area of grey shape" a sensible estimate of the proportion of the colour space of human vision that can be represented by the RGB colour model? 86.179.117.18 (talk) 20:23, 29 June 2014 (UTC)[reply]

No, that diagram isn't perceptually uniform. This diagram, which uses CIELUV instead of CIE xy, is better. Surprisingly, I couldn't find an appropriate image on Commons. Note that there are many color spaces called RGB. The diagrams above show sRGB, which is the de facto standard. Adobe RGB and CIE RGB cover more colors than sRGB. -- BenRG (talk) 22:20, 29 June 2014 (UTC)[reply]

Thanks, by the way, in the theory of RGB colour models, is it assumed that the intensity of a colour can vary continuously from zero to any desired brightness? (I understand, of course, that in any practical implementation the intensity of light is limited to what the device can physically pump out). 86.179.117.18 (talk) 22:59, 29 June 2014 (UTC)[reply]

The RGB color model is typically applied to a set of 3 primary color lights whose intensities are each separately controllable in 256 steps from zero to a maximum whose absolute intensity need not be specified. However the relative peak intensities represented by [RGB] = [255 255 255] are in proportions that give a reference White point. 84.209.89.214 (talk) 00:52, 30 June 2014 (UTC)[reply]

sRGB has a nonlinear intensity curve which is only defined for values from 0.0 to 1.0 (or 0 to 255). If you use a linear (energy) scale then the values can be arbitrarily large or even negative. If they are allowed to be negative then any set of three primaries is equivalent to any other, since they are just different bases for the same space of colors. -- BenRG (talk) 02:26, 30 June 2014 (UTC)[reply]

June 30

Live and Neutral

Why does the resistance becomes almost zero when a live wire touches a neutral wire? — Preceding unsigned comment added by 182.66.60.246 (talk) 03:14, 30 June 2014 (UTC)[reply]

Resistance between what two points? But assuming a wire has little resistance in general, obviously connected wires still have little resistance. Do you mean potential (voltage)? That's a more surprising case. Again assuming low-resistance conductors, the voltage of a "high voltage" line drops when it touches a ground/neutral line. But then remember that voltage is a difference not an absolute value, and the ground/neutral is the usual reference point. And it's not surprising that connecting two wires causes them to have the same voltage as each other. Attaching a live wire to ground causes (almost) all the current to flow that way, so it doesn't seem that unusual that connecting a wire to neutral causes it to have little or no measurable voltage with respect to neutral. DMacks (talk) 03:21, 30 June 2014 (UTC)[reply]

See Short circuit. 24.5.122.13 (talk) 04:16, 30 June 2014 (UTC)[reply]

Current Induction

What happens at atomic level in a coiled wire when a bar magnet in moved in and out of coil which induces curret in the wire? — Preceding unsigned comment added by 182.66.60.246 (talk) 03:22, 30 June 2014 (UTC)[reply]

In the frame of the wire, the magnetic field strength changes as the magnet moves around; an electric field is produced according to Faraday's law of induction. In the frame of the magnet, it's just the Lorentz force on the charges moving along with the wire. --Tardis (talk) 03:52, 30 June 2014 (UTC)[reply]

Although your question specifically requests an explanation at the atomic level, a conduction electron in a piece of metal isn't actually closely associated with any particular atom at any given time. So it works reasonably well to think of the conduction electrons as forming an "electron gas" that's confined to the wire, independent of any atoms. For details, see Free electron model and Nearly free electron model, or if you're super interested study a beginning book on solid-state physics, which will require an understanding of quantum mechanics as a prerequisite. Red Act (talk) 05:50, 30 June 2014 (UTC)[reply]

Passenger Aeroplane

What happens to those carbon dioxide which are exhaled by passengers of a passenger aeroplane and there is no accomodation of it although the plane is totally airtight? — Preceding unsigned comment added by 182.66.60.246 (talk) 03:39, 30 June 2014 (UTC)[reply]

Passenger aircraft aren't totally sealed. As our article cabin pressurization explains, in most passenger jet aircraft bleed air extracted from the engine compression stages is fed to the cabin, and subsequently exits via an outflow valve. Boeing have recently gone over to using electrical pumps to provide inlet air instead - reducing the risk of introducing contaminated air into the cabin. AndyTheGrump (talk) 03:51, 30 June 2014 (UTC)[reply]

That's true - but even if it were not, a person can live on about 16 cubic feet of air per hour (see calculations here, for example) - limited by the amount of exhaled CO2 rather than the amount of oxygen used. According to Boeing, the 747-8 has a cabin volume of about 30,000 cubic feet for around 450 passengers...which is 66 cubic feet each. So without the air being replaced at all, the passengers could survive for around 4 hours on just the air in the cabin.

Put another way, you only need to replace 16*450=7200 cubic feet of air per hour...which is 120 cfm. The extractor fan in my bathroom is rated at 110 cfm - so if the passengers are mostly just sitting quietly or sleeping, it could probably exchange enough air to keep the entire 747 ventilated.

SteveBaker (talk) 04:17, 30 June 2014 (UTC)[reply]

For reference, a cubic feet is 28 litre in proper units. 131.251.254.110 (talk) 07:45, 30 June 2014 (UTC)[reply]

The 16 cubic feet Steve cited would be at sea level. In a pressurized aircraft the internal air pressure is only around 3/4 to 4/5 of sea-level pressure, which suggests that a somewhat larger volume of air per hour would be needed. (Not necessarily 4/3 to 5/4 as much, because it depends on human response to oxygen and CO2 at those pressures. But probably something like that.) Of course this is just a detail and does not invalidate Steve's comment, or for that matter, Andy's. --70.49.171.225 (talk) 08:05, 30 June 2014 (UTC)[reply]

I don't trust first-principles calculations on matters like this because biology has a way of surprising us. But my guess (and anything other than literally looking at data from a submarine accident or something is just a guess) is that the partial pressure of CO2 ought to be the more limiting factor, and would not depend on atmospheric pressure. Wnt (talk) 11:26, 30 June 2014 (UTC)[reply]

"Totally airtight?" Passenger airplanes with pressurized cabins cannot be accurately described as totally airtight. For much of a flight, the air in the passenger cabin is at constant pressure but not because the cabin is airtight. The pressure is constant because air is allowed to escape from the cabin at the same rate as fresh air is introduced by the cabin pressurization system. There is a significant amount of fresh air being introduced to the cabin every hour, and the same amount escaping. The escaping air contains a slightly higher-than-normal amount of CO2 and water vapour, and a slightly lower-than-normal amount of oxygen; and the introduced air contains normal CO2, water vapour and oxygen. Dolphin (t) 12:43, 30 June 2014 (UTC)[reply]

Some comments:

1) People with breathing problems, like asthma, might die far sooner from excess carbon dioxide.

2) Everyone would be made uncomfortable far earlier.

3) Ironically, "bad air" is more of a problem for planes stuck on the tarmac, as the air exchange system depends on running the engines, and they don't want to do that on the ground for an extended period, or they need to return to refuel before take-off. StuRat (talk) 14:51, 30 June 2014 (UTC)[reply]

Interstitial tear of the Posterior cruciate ligament

What is a Interstitial tear of the Posterior cruciate ligament in the knee? Is is classified as a grade 1, 2, or 3 tear? Just to clarify I do not have a knee injury and I am not asking for medical advise, I just like learning about the anatomy of the knee. --Sara202020 (talk) 07:13, 30 June 2014 (UTC)[reply]

See Posterior cruciate ligament. An interstitial tear is one which occurs in the body of the ligament, rather than a tear where one of its ends detaches from the bone. (See this article about the rotator cuff for an explanation of the terminology). The grade of a tear depends on its severity, rather than its location, so an interstitial tear can be any of the three grades. Tevildo (talk) 11:45, 30 June 2014 (UTC)[reply]

Trimix (injection)

Trimix (injection) talks about Trimix injections, but http://finance.yahoo.com/news/ed-patients-now-60-days-123000584.html talks about Trimix gel. Is Trimix gel even a thing, or is it a scam like like "herbal Viagra". Either way, the Wikipedia page should mention it. 76.194.214.123 (talk) 09:07, 30 June 2014 (UTC)[reply]

Colour space and spectrum colours

What proportion of the colour space of human vision is covered by the spectrum colours (rainbow colours)? Since human-perceived colours are described by three numbers, and spectrum colours by two (wavelength and intensity), it seems to me that the mathematical answer to this question should be zero, but can that actually be correct? 86.179.117.18 (talk) 13:12, 30 June 2014 (UTC)[reply]

It's more-or-less true that the spectral colors, distinguishing different intensities, form a 2-D surface within the 3-D color space that humans perceive, and it's true that a 2-D surface has zero volume. However, in reality humans have a non-zero just-noticeable difference in color perception, such that there's a small but non-zero volume within the 3-D color space that's perceptually indistinguishable from the spectral colors. Red Act (talk) 14:47, 30 June 2014 (UTC)[reply]

One useful way of characterizing a color is in terms of hue, saturation, and intensity. In that scheme, the "spectrum colors" are the colors that have maximum saturation. Looie496 (talk) 15:20, 30 June 2014 (UTC)[reply]

An actual numeric answer to your question may be hard to come by, but I'd think that 1% would be a good order-of-magnitude estimate, given that the number of distinguishable colors increases by roughly a factor of 100 for each additional dimension in an animal's color space, according to Color vision#In other animal species. The Color difference article talks about some of the complexities involved in trying to come up with color space models such that just noticeable differences between two colors are equivalent to the same Euclidean difference between points in the color space model, anywhere within the color space. A big part of the difficulty with perceptual non-uniformities in the models is due to the human eye being more sensitive to some colors than others; see Color vision#Physiology of color perception. Red Act (talk) 16:11, 30 June 2014 (UTC)[reply]

Thanks for the replies. 86.179.117.18 (talk) 16:33, 30 June 2014 (UTC)[reply]

regarding species

I always wondered: if a biological variety A of a species X can have offspring with variety B (of X), and B with C (of X), A need not be able to with C. So, if A and C don't produce offspring, is A a species with respect to C? - SCIdude (talk) 14:26, 30 June 2014 (UTC)[reply]

Our article ring species addresses this. -- ToE 14:51, 30 June 2014 (UTC)[reply]

Yes. As the article says, A and C would be considered the same species if they can have fertile common descendants, even if not directly. However in practice things can sometimes get a bit tricky. I read an article a couple of years ago (can't remember how to find it) about a case involving two varieties of fish that were classified as distinct species because they did not interbreed. However, when a third variety of fish was introduced into the environment, it was capable of breeding with both of them. What this sort of thing really points out is the arbitrariness of the "species" concept. Many modern biologists no longer take it very seriously. Looie496 (talk) 15:11, 30 June 2014 (UTC)[reply]

Well, we can take the concept of "species" seriously, even if we acknowledge the species problem. Systematics and cladistics seem to be replacing taxonomy, and there are ontological problems with the notion of defining species by ability to produce fertile offspring -- but for most purposes it's just fine to talk about Apis mellifera or Carduus nutans or other common species. Yes, there are ring species and cases where species don't make a lot of sense (e.g. archaea). But just because there are corner cases and tough calls doesn't mean species designations are completely arbitrary. Unless your goal is to resolve evolutionary relationships, species work just fine for most biological applications. SemanticMantis (talk) 15:51, 30 June 2014 (UTC) (p.s. Dialect continuum is a nice analogy for ring species.)[reply]

Micro SD type of and how many GBs

How many types of micro SD cards there are and how many gigabytes can they carry? — Preceding unsigned comment added by 162.219.184.233 (talk) 15:04, 30 June 2014 (UTC)[reply]

This question belongs on Wikipedia:Reference desk/Computing. Looie496 (talk) 15:13, 30 June 2014 (UTC)[reply]

Yes, and the questioner should ask a more specific question there if they don't find what they want in our Secure Digital article. -- ToE 21:08, 30 June 2014 (UTC)[reply]

Water plant in Dutch nature reserve

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Hello, would anybody be able to identify the water plant shown on this picture? Someone found it in a wetland reserve in the North of the Netherlands. A quite long discussion in the nl.wiki Biology café gave no satisfying result, though Ludwigia and Salix were mentioned. Regards, Apdency (talk) 15:42, 30 June 2014 (UTC)[reply]

Are you sure it's a water plant at all ? Those usually don't grow up beyond the waterline much, but just float on the water and spread out, as that's a more effective way to increase the amount of sunlight that hits the leaves. See water lily or lotus flower for examples. I'm wondering if this isn't a terrestrial plant which is in an area that's been flooded. StuRat (talk) 16:08, 30 June 2014 (UTC)[reply]

Uhm, having read that, I was planning to propose Vaccinium corymbosum, but now I see that on Commons, EB Doulton already did the work. Apdency (talk) 16:55, 30 June 2014 (UTC)[reply]

But that's a North American plant, so it would have to be an invasive species, if present in the Netherlands. StuRat (talk) 17:08, 30 June 2014 (UTC)[reply]

I learned that it has been imported there from North-America in the 1940s. This Dutch language page is one of the sources; it also shows other pics of Vaccinium corymbosum in that particular reserve ('Fochteloërveen'). Apdency (talk) 19:07, 30 June 2014 (UTC)[reply]

RGB colour triangle

In an RGB colour triangle, such as the one here, I understand, of course, that the corner points are R, G and B, and that the RGB values of the interior points are somehow related to the distances to the corners. However, this "somehow related" calculation can be done in numerous different ways, and the resulting triangles will contain different subsets of all the possible RGB colours. Even if it is desired to have (255, 255, 255) at the centre of the triangle, there will still be many ways to do it. What is the reason (if any) for choosing one method over any other? Is there one particular method that makes special sense? 86.179.117.18 (talk) 17:00, 30 June 2014 (UTC)[reply]

File:GammaFunctionGraph.svg

Example of CRT gamma correction. The dotted line indicates a linear transfer function (γ=1); the solid line shows how a typical CRT behaves; the dashed line represents the inverse function.

Points in the RGB color space corresponding to linear steps in each coordinate i.e. 0% 25% 50% 75% 100%. The actual intensity steps depend on the gamma of your display.

The corner points have [RGB] coordinates [255 0 0] [0 255 0] and [0 0 255]. The sides are the locii of coordinates [0 n n] [n 0 n] [n n 0]. Ideally the intensity of each primary light is proportional to its coefficient 0...255 and the white point is at the Centroid of the triangle. However a typical CRT has a power-law luminance response, typically gamma=2.2, so will not respond proportionally to [RGB] coordinates. The solution is to apply Gamma correction. This color list attempts to show the difference gamma correction makes but will be constrained by the display you actually use. 84.209.89.214 (talk) 18:05, 30 June 2014 (UTC)[reply]

Ultimately, the choice of color-coordinates (and the various ways that you can plot them) are heuristics guided by data collected during several landmark perceptual psychology experiments. For example, CIE 1931 uses data that was collected by the world's preeminent psychologists in 1931; CIE 1976 uses essentially the same methodology and new data collected in 1976... Now, if I understand correctly, humans didn't evolve very much during those decades, so if the data was actually representative of the human population using sound scientific methodology, these color spaces should be exactly the same.

To be perfectly honest, the whole concept of projection into "perceptual" colorspace is, in my opinion, a lot of false precision puffed up by people who call themselves color scientists. (I have yet to meet a "color scientist" who is an optical physicist but I've met plenty who studied art or film or photography - they're really interested in the artistic side of science). Since I started off my career as a pedigreed optical physicist, I am incredibly frustrated by these silly color spaces: all I want is an imaging spectrometer and an intensity-versus-wavelength or frequency spectrum plot across the visible spectrum. That is a precise methodology: we can build machines (spectrum analyzers and photon counters) that exactly tell us everything that matters with respect to the color. We can build other machines (monochromators and tunable lasers, for example - or even just regular illuminants and calibrated color filters) to precisely reconstruct any combination of colored light, with arbitrary precision. Any sufficiently-well-sampled reconstruction of a scene that produces the same spectrum is guaranteed (as a side-effect) to also have the same coordinates when projected into a 3-element perceptual colorspace - which is, at the core, nothing but an obscenely under-sampled coordinate-transform of the frequency spectrum. With a bit of linear algebra, you can construct any color space you like, subject to any constraint you wish to impose, and produce a brand new n-element colorspace; and if your linear algebra exactly matches that used by the CIE or the ITU or any of the other prestigious consortiums, then you get one of their numerous "standard colorspaces." Nimur (talk) 18:21, 30 June 2014 (UTC)[reply]

Correct, but encoding an movie with a seperate spectrum stored for each pixel will take a lot more storage/bandwidth, and making a display that reconstructs that spectrum at at each pixel doesn't sound cheap. The reason three dimensional color spaces work pretty well are because in the end that spectrum gets broken down to responses from three (technically four) types of receptors in the eyes so, like you say, it's all linear algebra from there. Katie R (talk) 19:18, 30 June 2014 (UTC)[reply]

....linear algebra based on an approximate, implementation-dependent, somewhat-standards-compliant heuristic. I don't mind the imprecision; I don't mind the psychology-based perceptual heuristics... what irks me is the phony pretense of numerical accuracy - which is, I think, the same thing that the OP's question is getting at. Nimur (talk) 19:25, 30 June 2014 (UTC)[reply]

For tasks such as paint mixing and textile production, a precision no less than the ability of a critical eye to distinguish a difference between colours is justified and, in practice, is paid for in a commercial system such as Pantone's which samples thousand(s) of colours. According to Pantone, the colour of 2014 shall be Radiant Orchid! One sympathises with Nimur's disdain for the arty fashion designers and other consumer-oriented companies that don't care much about electromagnetic spectral analysis of that shade. 84.209.89.214 (talk) 00:19, 1 July 2014 (UTC)[reply]

Thanks for all the replies. Let me put it another way. Is there anything special or significant, either physically or perceptually, about the subset of RGB colours that are displayed in the colour triangle? I apologise if this question has actually been answered above, but if it has, I'm sorry, I can't pick it out. 86.179.117.18 (talk) 19:33, 30 June 2014 (UTC)[reply]

The color triangle has no utility until 3 practical phosphors (for a CRT) or dyes (for a positive film) are formulated that can reproduce a generous Gamut of colours. The article Phosphor shows the plethora of chemical formulations that have been investigated. Development of color TVs took a long time due to the long search for a red phosphor; for this purpose a rare earth phosphor YVO4,Eu3 was introduced in 1964. The RGB triangle is thus dictated by the state-of-the-art of additive colour reproduction, just like the subtractive CMY (Cyan, Magenta, Yellow) triangle for printing is limited by practical ink formulations. In this case, 3-ink colour printing is incapable of showing a deep black and in practice a fourth ink is needed for good quality images, see CMYK color model. 84.209.89.214 (talk) 23:49, 30 June 2014 (UTC)[reply]

Phrased another way: we know how to build tri-color-filter-arrays - "red/green/blue" combinations - for things like television displays and camera sensors and printer inks, such that the "greenish" color matches the average human eye's perception of green; and the "reddish" color filter matches the average human eye's perception of "red"... or can be emulated by some combination of those inks/phosphors/dyes. This lets us use only three numbers - we can call them "R,G,B" or "X,Y,Z" or "n1,n2,n3", or {z[0],z[1],z[2]} to approximate a full color spectrum. This is possible because researchers and industrialists have spent years experimenting with various printable inks, chemical dyes for phosphors and LCD panels, and so on. The color triangle is just a plot that idealizes the possible combinations.

The subset of RGB values inside the color triangle therefore correspond to all the possible combinations of (printer ink, or LCD pixel brightnesses on your computer screen, and so on). The "size" of the triangle, loosely speaking, shows the extent to which such inks/dyes/phosphors can reproduce all possible colors that humans can normally see. A standard colorspace can be compared, in triangle-form, to the calibrated colorspace of any machine, enabling designers to determine how one set of chemical dyes compares to another; or how one brand of television hardware corresponds to another, and so forth. Nimur (talk) 00:13, 1 July 2014 (UTC)[reply]

Inks for Color printing are normally the subtractive primaries cyan, magenta and yellow, not RGB. 84.209.89.214 (talk) 00:39, 1 July 2014 (UTC)[reply]

Different coordinates, different color limitations, exact same methodology. Let me emphatically reiterate: when you represent the complete spectrum, everything is incredibly simple. There's no such thing as "additive" or "subtractive" color. All that matters is the intensity at each wavelength. Nimur (talk) 01:37, 1 July 2014 (UTC)[reply]

The subset of RGB values inside the color triangle therefore correspond to all the possible combinations of (printer ink, or LCD pixel brightnesses on your computer screen, and so on). -- Now I am totally confused. How can this be true? Surely numerous RGB combinations -- in fact most combinations -- are not present in the colour triangle??? This is the whole basis of my question: Is there anything fundamentally significant about the subset of combinations that are present? 86.179.117.18 (talk) 02:13, 1 July 2014 (UTC)[reply]

[1] Solzhenitsyn, Alexander (1980). The Gulag Archipelago, vol. 2. Paris, VT: YMCA-PRESS. pp. 129–130. ISBN 5-265-01557-4.

[1]