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June 25

A refrigerator that powers itself.

Is it possible to make a refrigerator that powers itself? Imagine a Carnot engine that uses the temperature gradient to power a refrigerator, maintaining the temperature gradient. 203.45.159.248 (talk) 09:58, 25 June 2014 (UTC)[reply]

What you have described is a perpetual motion device; it assumes greater than 100% efficiency, since the cold box itself could never be perfectly insulated. AlexTiefling (talk) 10:07, 25 June 2014 (UTC)[reply]

I just saw a promotional video the other day about a refrigerator that Coke has developed that uses sunlight and plants to keep things cool. It requires no electricity. Dismas|^(talk) 10:16, 25 June 2014 (UTC)[reply]

It would be using an external energy source, however unconventional. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:19, 25 June 2014 (UTC)[reply]

Lol, sunlight definitely counts as a source of energy! Zzubnik (talk) 12:18, 25 June 2014 (UTC)[reply]

Precisely. Purists may not regard the sun as a perpetual motion "machine", but for all practical purposes it's a perpetual energy source. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:22, 25 June 2014 (UTC)[reply]

The pot-in-pot refrigerator works without electricity, but of course someone has to expend energy by regularly adding water to it and the Sun's energy is required to evaporate the water. Richerman (talk) 12:37, 25 June 2014 (UTC)[reply]

You could (probably) build a solar-powered Einstein refrigerator (gas is the normal heat source for them). CS Miller (talk) 12:47, 25 June 2014 (UTC)[reply]

Or a Thermoelectric_cooling refrigerator (better known as a "Peltier cooler") which runs from a 12-volt power source could be powered by a solar array charging a 12-volt car battery or a stack of such batteries. Peltier coolers are cheap (<US$100) and plentiful under the "Koolatron" and other brand names; the Coleman sporting goods company has sold them for years. I own several. Harbor Freight Tools sells a portable solar array with charging circuitry for one or more 12-volt car batteries for US$150 or so. The batteries themselves cost less than US$80 each at auto parts stores new, or much less used from junkyards.

The mechanism here is using a bimetallic junction (a Peltier device) to transfer heat outside an insulated box by running electricity through the junction in the proper direction. Interestingly, these coolers can be made into warmers (for food, etc) simply by reversing the direction of electricity through the Peltier device, a simple matter of removing the power plug from the cooler and flipping it as you re-insert it, so the power wires are connected in reverse order than before. loupgarous (talk) 07:01, 26 June 2014 (UTC)[reply]

Thinking about it, though, it depends on what you mean by "refrigeration." Very hot food could be placed inside a Peltier junction "refrigerator," so that its heat was transferred through the junction by an electric fan... and NOT applying power to the junction, electricity could be tapped from that junction (by the Seebeck effect) to charge a very efficient battery... which would store power then used later to drive the Peltier junction and fan to cool the food further than it was cooled by losing heat initially by simple radiation into the insulated box to then drive the Peltier device as a passive heat-driven generator.

The food wouldn't get as cool as it would have just sitting on a table top, because convective transfer of heat to the open air is a much more efficient way of cooling food - it couples the hot food to a heatsink the size of the Earth's atmosphere. The food just never gets cool enough to be safely stored that way outside a REAL refrigerator or the outside of a home on a winter day. But technically, power could be generated by Seebeck effect from some very hot food radiating its heat to a Peltier device, then stored to cool the food further. It would just be a ruinously inefficient process. Joule heating would rob you of energy at every step in the process, to say nothing of the power consumed by the fan pushing the warm air past the Peltier device, which would have to be re-configured from its commercial state to be a more efficient Seebeck effect generator. Not a practical or even a reasonably effective refrigerator at all.

This takes what I assume is the original poster's point that the food has heat that could, theoretically, drive a Carnot cycle or other heat transfer device - but inefficiencies in operating such devices make that scheme much less efficient than letting the food cool in the open air, also a heat transfer device with the advantage of coupling ultimately to comparatively huge heatsinks like the air inside a building or the Earth's atmosphere without the use of outside power to effect the heat transfer. loupgarous (talk) 07:20, 26 June 2014 (UTC)[reply]

As a practical example, look at a microprocessor. A passive Peltier device is easy with one side at ambient and the other junction at the CPU temperature. The ambient side forces a cooling. But a heat pipe is much more efficient. The last time I looked the thermal conductivity of the wires contributed more than the passive Peltier junction. Active Peltier can force a temperature at the CPU but the heat generated is pretty large. It's not particularly effective at heat transfer. If it were, the CPU heatsink would be far way and submerged in liquid, connected only by wires. But in reality, most efficient CPU cooling brings the liquid to the CPU without any Peltier effects. Thermocouples use elements like platinum/rhodium junction at near 0 currents for temperature measurement. Forcing a temperature at the juncion incurs IR drup that is usually unacceptable. Not sure what the commercial cooler use or what their range is. I believe they need a fan at the cold end for IR drop waste heat. --DHeyward (talk) 09:36, 27 June 2014 (UTC)[reply]

You have a missconception of the Carnot engine and thermodynamics. It "feeds" on a thermic difference and you want to use it to poduce its own food. Its efficiency factor would have to be higher than 1 because it had to compensate the thermic loss by leakage of the refrigerator on top of being a perpetuum mobile, which in theory has an efficiency factor of exactly 1. Thus this is impossible². --Kharon (talk) 17:45, 27 June 2014 (UTC)[reply]

Electric Power vs Horse Powet

Is it true that an electric eel(by its elecyric shock) can paralysie a horse or it is just a misconception? — Preceding unsigned comment added by 106.212.123.52 (talk) 23:49, 25 June 2014 (UTC)[reply]

According to the National Geographic article here they have been known to knock a horse off its feet. Also see an alligator getting more than he bargained for. Richerman (talk) 00:44, 26 June 2014 (UTC)[reply]

The Electric eel has electric organs capable of producing potentially-lethal shocks that allow them to stun prey. However horses are not the eel's natural prey and the linked article notes that the shock's short duration (<2 ms) make it extremely unlikely to be deadly to an adult human. In 2011 two racehorses were fatally electrocuted in a freak accident where they may have contacted underground cables. Humans who generally wear insulating footwear, in contrast to conductive metal Horseshoes, noticed only slight tingles when walking with the affected horses. The newspaper article claims that "Horses are far more sensitive to electricity than humans...Their heavy muscles, thick tendons and large bony skeletons keep electrical currents in their body longer, causing more damage". Exposure of a horse to electric eel shock is very unlikely, though horses are routinely restrained by electric fences. 84.209.89.214 (talk) 01:07, 26 June 2014 (UTC)[reply]

A horse walking in a river could easily get a shock from an electric eel Richerman (talk) 01:53, 26 June 2014 (UTC)[reply]

Sounds like complete misconception. The energy from the eel is very small. The voltage and current are impressive but unlike utilities, the duration is finite. The most it could do would be to contract muscles in the leg but only for a very short duration. The duration of shock is much too short to affect heart muscle (I believe 25mS or longer is required where the eel is at about 2 mS). Longer muscle groups like legs and back are affected by shorter pulses (one of the reasons a Taser causes legs and back muscles to spasm without affecting heart muscle). At 2 mS, a 600V, 1A shock is 1.2 Joules of energy. A cell phone battery, I believe, has about 15,000 Joules. Can you stop a horse with a cell phone? --DHeyward (talk) 10:13, 27 June 2014 (UTC)[reply]

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

No jokes/trolling on Ref Desk please; try Yahoo!Cancers instead

The following discussion has been closed. Please do not modify it.

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]

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]

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]

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 + 12H₂O--> 4PO₄^-3

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

Step 4

Balance H using hydrogen ions

Oxidation half reaction: P₄ + 12H₂O--> 4PO₄^-3 + 8H⁺

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]

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]

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]

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]

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]

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

[1]

Revision as of 22:57, 29 June 2014 edit 84.209.89.214 (talk) →‎RGB colour model: Attempted image of CIE 1931 color space ← Previous edit		Revision as of 22:59, 29 June 2014 edit undo 86.179.117.18 (talk) →‎RGB colour model Next edit →
Line 367:		Line 367:

	:No, that diagram [[MacAdam ellipse\|isn't perceptually uniform]]. [http://asada.tukusi.ne.jp/chromaticglass/my_images/sRGBuv400x400.png This diagram], which uses [[CIELUV]] instead of [[CIE 1931 color space\|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. -- [[User:BenRG\|BenRG]] ([[User talk:BenRG\|talk]]) 22:20, 29 June 2014 (UTC)		:No, that diagram [[MacAdam ellipse\|isn't perceptually uniform]]. [http://asada.tukusi.ne.jp/chromaticglass/my_images/sRGBuv400x400.png This diagram], which uses [[CIELUV]] instead of [[CIE 1931 color space\|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. -- [[User:BenRG\|BenRG]] ([[User talk:BenRG\|talk]]) 22:20, 29 June 2014 (UTC)
			::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). [[Special:Contributions/86.179.117.18\|86.179.117.18]] ([[User talk:86.179.117.18\|talk]]) 22:59, 29 June 2014 (UTC)