Wikipedia:Reference desk/Archives/Science/2016 May 28

= May 28 =

Floating ants
Some species of ant create floating ant rafts. Are there any other animals that do this? The Quixotic Potato (talk) 13:38, 28 May 2016 (UTC)
 * Are you asking whether other animals make floating ant rafts? ←Baseball Bugs What's up, Doc? carrots→ 15:12, 28 May 2016 (UTC)
 * No, although I would be interested in other animals that do make floating ant rafts. I am asking if there are other animals that use this (or a similar) strategy. The Quixotic Potato (talk) 15:42, 28 May 2016 (UTC)
 * Does walking on water count? 2600:8806:4800:5100:999C:4F9C:9265:8CEF (talk) 18:50, 28 May 2016 (UTC)
 * Janthina janthina floats on water surface "by means of a bubble raft made by its foot, which scoops up bubbles of air and, after enveloping them in mucus, adds them to its raft". Also, foxes are known to get rid of fleas by making factual rafts for them by taking something into the mouth and submerging themselves into the water. Fleas are forced to "evacuate" into whatever the fox holds in the mouth which is then released adrift. Brandmeistertalk  21:19, 28 May 2016 (UTC)
 * The story about foxes is pretty cool, but unfortunately it doesn't seem to be true. Fleas can live over 12 hours in water . In fact, if a drowned person has fleas, whether or not they are still alive can help determine the time of death. This story goes back to at least the 1890s. The Quixotic Potato (talk) 03:16, 2 June 2016 (UTC)


 * Hey look, we have an article on animal locomotion on the water surface. Also, they're not animals and they don't use "rafts", but coconuts are adapted to float in water, in order to carry the seed long distances. --71.110.8.102 (talk) 21:18, 28 May 2016 (UTC)
 * Have a look at Diving bell spider. It's not really the same as forming a raft, but possibly related.  These spiders spin a web between 2 aquatic plants, then fill the web with air which forms a diving bell that they live in. DrChrissy (talk) 22:08, 28 May 2016 (UTC)
 * No man is an island. Vespine (talk) 00:13, 30 May 2016 (UTC)
 * http://watchmen.wikia.com/wiki/Marooned#Issue_24 The Quixotic Potato (talk) 05:41, 31 May 2016 (UTC)

Thanks all! I learned some new stuff. It seems like the strategy ants are using is rare or unique. The Quixotic Potato (talk) 12:58, 31 May 2016 (UTC)
 * I just found this very interesting scientific paper on the subject. DrChrissy (talk) 14:37, 31 May 2016 (UTC)
 * Awesome, thank you! Maybe tiny robots can use a similar strategy in the future. The Quixotic Potato (talk) 15:21, 31 May 2016 (UTC)
 * They are already on the case here| DrChrissy (talk) 15:29, 31 May 2016 (UTC)


 * Hey QP - I'm a little late to this interesting question. Lots of other ants also raft btw, but I don't think you're interested in cataloging all the ant species that raft, right? Anyway, check out the Antarctic Collembola Cryptopygus antarcticus  - they seem  to use their moults as an "edible raft" - this study does not seem to mention them linking up arms/legs though. These  cormorants raft, but they already float, and seem to be using the raft as a predation strategy.
 * The thing to remember is that eusociality is really uncommon. It's not even that common among the hymenoptera, and most non-ant hymenoptera can fly, so don't need to float. The point is the ant raft only makes sense because of the haplodiploidy, making sisters more related to eachother than their parents. In this manner, it makes evolutionary sense to kill off a high percentage of ants so the rest can survive, but that level of extreme altruism just doesn't apply to most critters. For a related example of suicide to help the group survive harsh conditions, check out the Dictyostelids and their awesome grex - at the end of the sporing cycle, most have died but a few germ cells live on - so in some sense that is highly analogous to the rafting dispersal of S. invicta, but with resource scarcity taking the place of drowning threat. SemanticMantis (talk) 15:00, 1 June 2016 (UTC)
 * Hiya! Thanks for your comment. Ants are fascinating (to me) and they are incredibly successful. To be honest, many topics related to this stuff are very interesting to me, and I always follow all the links and I google every word/concept I do not understand. I do often answer questions on the RefDesk; but I am mainly here to learn. There are only a few things I am not interested in (for example soccer and pop music)! My smartphone has a small screen; when I get back to my desktop PC I can read everything more easily. Thanks again, The Quixotic Potato (talk) 15:22, 1 June 2016 (UTC)
 * Semantic, please could you clarify what you mean by "...it makes evolutionary sense to kill off a high percentage of ants so the rest can survive". I thought the rafting was a survival strategy in response to flooding.  Are you perhaps thinking of it more as a dispersal strategy? DrChrissy (talk) 16:30, 1 June 2016 (UTC)
 * Hey, good question. What I was eliding is the whole "evolution of altruism" thing. In the social hymenoptera, all kinds of sacrificial behaviors have developed that we don't see in other clades. So for instance, any little bug could conceivably link up arms with buddies to better survive floods, but the vast majority don't. One reason why is because it doesn't generally doesn't make sense to help others survive if you might die. With ants, the whole thing is rearranged due to haplodiploidy and sterile workers. In that case, future sisters and the queen are more important than an ant itself is, so they are usually sort of "happy" to die for the sake of the colony. From the superorganism perspective, it doesn't matter if 90% of the ants die as long as the queen survives. But if the queen dies, even 100% non-queen survival might mean death of colony. I think you might already understand all that but I'm not sure.
 * Actually this gets really tricky really fast, because some ants are happy to find and join new homes if their queen dies. The Pharoah ant is famous for that- you can fly some workers around the world and they will happily get to work in their new colony, serving their new queen. But fire ants are super territorial, and will murder conspecific non-nestmates on sight. But there's also a polygyne form, they might be less agressive to non-nestmate conspecifics. I don't know how that works out, but I know the Argentine ants also raft . They are monogynal in their native range, but polygynal in the USA, and that might start to eventually change their rafting behavior. This is thought to be due to a founder effect messing with mechanisms kin recognition. In that case, a non-nestmate conspecific is murdered in Argentina, but accepted as a friend in the USA. So now I've gotten carried away about ants, but all of this does I think have bearing on evolution of rafting. Finally, I think the primary purpose is indeed survival, but there is a secondary role of dispersal, that's at least part of why fire ants have spread so well. When Wilson noted the first colony in the USA, it could have moved miles in one flood, a thing that non-floating ants would likely not be able to do. Here  is an article that discusses a bit about how rafting has shaped ant dispersal across the Bahamanian archipelago - I've only skimmed it but it seems to indicate an important role for raft-based ant dispersal. SemanticMantis (talk) 20:33, 1 June 2016 (UTC)  PS., feel free to ping me on older threads or any time you want a response from me specifically - I only caught this follow up by chance, and sometimes I do fail to check in on WP for days at a time :)
 * Semantic - thanks so much for taking the time to explain this. I am an ethologist in real life so this all makes sense.  I find this so interesting because before this thread, I had always assumed the ant rafts were simply accidental aggregations caused by the ants all trying to avoid flooding and climbing up the nearest dry object, i.e. another ant.  It appears I was very, very wrong.  Once again, thanks for the great explanation and I love the way you talk about evolution happening in the present - something many people forget. DrChrissy (talk) 15:11, 2 June 2016 (UTC)

Is it possible to align the rotation of molecules in a liquid, and does this affect its bulk properties?
Is it possible to use something like polarized far-infrared light to mess with the rotational modes of individual molecules inside a liquid such as water, so that they all rotate only along one axis? If you did that, would it become a liquid crystal or something else? I found myself looking for "liquid crystal phase of water" and came up with an apparent quackjob yet I'm not sure if some of it is real or not. If you're wondering, the application I had in mind was an alien fish that beams a powerful cone of thermal radiation to confine its prey to the "more liquid" water in the middle. Yes, I assume this is not possible, but I don't *know* that, and that's what got me wondering... Wnt (talk) 17:41, 28 May 2016 (UTC)
 * Hopefully a prey will evolve that's fast enough to swim the cone fish to exhaustion. Then a thermal confinement beam fish will evolve with the intelligence to restrict prey in 3 dimensions with a second fish's beam perpendicular to the first 's and unrestrict it only so the third fish can get in to eat it. Then a prey will evolve some exotic physics like orientation randomizing electric fields that'll let it escape the beams. 500 million years later, every surviving fish destroys the surface tension of any water it's touching with cell-sized hydrogen bond-breaking electric fields or a supercavitating stick with a disc at the bow that enables it to swim at over 200 miles per hour. Sagittarian Milky Way (talk) 18:53, 28 May 2016 (UTC)
 * My immediate thought is that the aligned state would be very low entropy, so in effect very very cold.
 * You can have some very low temperature modes in an otherwise not low-temperature system -- for example, I think it's possible to use NMR to cool some of the nuclear modes -- but for to be possible and to have a relaxation time more than a fraction of a fraction of a second the modes in question need to be substantially isolated or non-interacting with the rest of the system. So you would need somehow to stop the molecular rotation mode interacting with other modes of the system, otherwise it would very rapidly get re-thermalised.
 * In particular, a characteristic of liquids is random motion with lots of intermolecular collisions. I imagine these would rapidly excite the rotational modes to a thermal spectrum, even if you started with the rotation modes in a particular state or a ground state.
 * It is possible, I think, to use lasers to remove rotational energy or to put a molecule into a particular rotational state -- eg in an ion trap. But I think only when it is very very cold, and when there are not too many ions or molecules around to bump into it (or they are having their motion controlled).
 * So it seems to me a pre-requisite would be for the molecules have to be a non-liquid state to achieve the alignment, thus defeating the question.
 * But I am interested to see what others have to say -- are there any exotic states of exotic materials which might make this more possible? Jheald (talk) 19:38, 28 May 2016 (UTC)
 * On second thoughts, is this similar to what's happening with the paramagnetism of liquid oxygen ? (except I think that's a coupling of electron spin quantum numbers, rather than orbital angular momentum quantum numbers).  For substances that are gases at ordinary atmospheric temperature and pressure, there are temperatures (not even that low) where rotation modes normally get quenched out (due to large energy level spacings), but the molecules are still in a liquid phase.  Could the molecules of such a system be put into a higher rotation state (perhaps coupled between molecules, if they had a dipole?).  Could the rotation state survive molecular collisions?  I am dubious, I think the energy would rapidly get dumped into translational modes with smaller spacings, and rapidly thermalised away.  But possibly I'm wrong?  Maybe someone can answer this a bit more rigorously?  Jheald (talk) 20:04, 28 May 2016 (UTC)

Filling the tank of a rental during a hot day, checking out, and getting the gasoline level checked at night
You fill the gasoline tank (50 l) of a rental car during a hot day and drive it back to the rental agency (about 100 meters). Some hours later, or even the next day, the temperature drops, 10 C or more, and the rental agency decides to check whether you filled the tank, according to contract, completely. Would they notice a big difference in the volume of gasoline in the tank? Would they just read the car's own indicator or use an independent tool? If they decide to put more gas in the car, how much could it be. --Llaanngg (talk) 17:57, 28 May 2016 (UTC)


 * "the volume of a litre of petrol changes by approximately 1.2ml per 1°C, and diesel changes by approximately 0.8 ml per 1°C." So 50 * 10 * 1.2 = 600ml. --Tagishsimon (talk) 18:23, 28 May 2016 (UTC)


 * Two points as to the computation. (1) You also have to consider how the volume of the tank changes with temperature, which would depend on what it's made of.  (2) When you fill up, the fuel is at the temperature of the underground storage tank it came from, not at air temperature.  If the fuel later warms up on a hot day, the tank may become overfull.


 * As a practical matter, when I've returned a rental car I've sometimes seen them just read the fuel gauge and write down the reading top the nearest multiple of 1/8 of a tank. It hasn't been worth their time to worry about charging for smaller fractions.  But that doesn't mean that all companies would do that, or that they will continue to do so when fuel prices are high. --69.159.60.83 (talk) 18:38, 28 May 2016 (UTC)

Supersonic kick in the cabin
In one documentary I heard that Concorde pilots felt a slight kick when the aircraft went supersonic. Could the same kick be felt by passengers in the cabin and were there any other clues for passengers at the moment when Concorde or Tu-144 went supersonic? Thanx.--93.174.25.12 (talk) 20:48, 28 May 2016 (UTC)


 * There is no particular physical mechanism that would cause a 'kick' at exactly M1, unless the flight engineer kicked the pilot's seat as a joke. But you saw it on TV... Greglocock (talk) 22:15, 28 May 2016 (UTC)


 * I don't think this is correct. I've read about the "kick", and Supersonic speed seems to back this up. See below. --71.110.8.102 (talk) 22:39, 28 May 2016 (UTC)


 * Why do you think the pilots would have felt it, but the passengers wouldn't? I don't see why they wouldn't have. The "kick" is the reduction in wave drag once the craft "breaks" the speed of sound. I've read that it's not as dramatic as some people expect, though. It's not like the Millennium Falcon jumping to hyperspace. The only other sign of a craft designed for supersonic flight going supersonic is vapor cones that sometimes form around points on the craft, but whether these form depends on atmospheric conditions. I specified "designed for supersonic flight" because craft that aren't will experience significant turbulence if they approach the speed of sound, bad enough to tear the craft apart in some cases. That you could certainly feel! This is what gave rise to the idea of a sound barrier, when people were first trying to design supersonic aircraft. --71.110.8.102 (talk) 22:39, 28 May 2016 (UTC)
 * Edcon Au contraire as we say in France. Beyond Mach 1.0, the drag coefficient falls off quite rapidly with increasing velocity. It is therefore possible that,(if the engine thrust remained constant), passengers would expereince an acceleration (and therefore a force) just after going supersonic. Otherwise known in the trade as the 'kick in the pants effect'.--178.106.99.31 (talk) 22:46, 28 May 2016 (UTC)


 * Rapidly? 20% for 0.1 increase in Mach number? That is not kick in the pants territory. The article Supersonic speed does not support any kick assertion. Greglocock (talk) 23:52, 28 May 2016 (UTC)


 * For what it might be worth in reference to this question, I recall reading in The Right Stuff that pilot Chuck Yeager experienced increasing vibrations of the plane until he actually broke the sound barrier, and then things got a lot smoother. So there was at least some kind of change that he experienced. ←Baseball Bugs What's up, Doc? carrots→ 00:32, 29 May 2016 (UTC)


 * Sure, but an increase in vibration, followed by a decrease in vibration, is not what the OP was describing. And there's no reason to think the maximum would necessarily be at M=1.0 either. The whole 'kick' thing sounds like fanboi nonsense. Greglocock (talk) 06:04, 29 May 2016 (UTC)


 * I have read that in modern supersonic aircraft the pilots are totally reliant on the Machmeter to know when the aircraft reaches Mach 1.0 and passes it. I think a perceptible kick in the pants would be the result of a pair of engines having their afterburners ignited. Dolphin  ( t ) 08:05, 29 May 2016 (UTC)


 * I believe that there was a large digital machmeter on display in the passenger cabin, so that people could tell when they were flying faster than sound. Concorde History - Supersonic Proving quotes Robert Hotz, editor of Aviation Week and Space Technology: "The most sensational aspect of flying as a passenger at Mach 2 in a supersonic transport is that there are no sensations whatsoever that differ from those in the current generation of subsonic jets . .". What was it like to fly on the Concorde? says: "The highlights for me: Knowing that you're going Mach 2. You really can't feel it, but you know it thanks to altitude and speed gauges placed prominently in the cabin." Alansplodge (talk) 14:01, 29 May 2016 (UTC)


 * The answers are about smooth supercruise but the question is about transonic transition. Whether the Concorde had a less prolonged interval of shaking at transition than early fighter planes, I don't know.  Jim.henderson (talk) 16:00, 29 May 2016 (UTC)
 * Quite right, but if there had been any detectable transonic effects, surely these writers would have mentioned them. As usual, it's much harder to prove that something didn't happen, than to prove that it did. Alansplodge (talk) 20:02, 29 May 2016 (UTC)

Dehorned Rhinos
I saw a very sad picture of a dehorned and facially injured rhino in the news today. The rhino is still alive and being cared for. But: is it possible for the rhino to regrow its horn in time?--178.106.99.31 (talk) 22:56, 28 May 2016 (UTC)
 * Googling the subject of horn re-growth, consensus is that both rhino horns and elephant tusks will eventually grow back if they're not cut too close to their "roots", though it takes a while. ←Baseball Bugs What's up, Doc? carrots→ 00:29, 29 May 2016 (UTC)
 * But note these are very different biological tissues.  Rhino horn is keratin - dead tissue like our fingernails.  Elephant tusks are modified incisor teeth. Having said this, apparently both can regrow. DrChrissy (talk) 15:00, 29 May 2016 (UTC)
 * Yes, different types of tissue, but both can regenerate. The only reason for killing the beasts is laziness on the part of the poachers. ←Baseball Bugs What's up, Doc? carrots→ 16:04, 29 May 2016 (UTC)
 * I have to admit I had forgotten that elephants grow another tusk. This process is known as polyphyodonty and occurs among mammals in (only?) kangaroos, elephants and manatees. DrChrissy (talk) 16:33, 29 May 2016 (UTC)


 * While I'm in no way defending poachers, taking the horns or tusks off without killing the animal entails additional costs and risks and reduces what you can take. As the earlier linked Quora discussion says. If you want to simplify, it would be better to say "greed" rather than laziness. Nil Einne (talk) 16:39, 29 May 2016 (UTC)


 * I always thought these actions were done by conservation groups to mitigate poaching. Poachers aren't interested in elephants without tusks or rhinos without horns.  --DHeyward (talk) 09:38, 30 May 2016 (UTC)
 * The Quora discussion also explains why actions by conservation groups aren't necessarily effective by themselves. Nil Einne (talk) 04:24, 31 May 2016 (UTC)


 * Elephants grow new cheek teeth (six sets per lifetime) not new tusks. μηδείς (talk) 17:59, 29 May 2016 (UTC)
 * Would it be possible for you to supply an RS for that - I am not challenging your statement, but this should be clearer in the Elephant article. DrChrissy (talk) 18:49, 29 May 2016 (UTC)
 * The article Elephant says "Unlike most mammals, which grow baby teeth and then replace them with a single permanent set of adult teeth, elephants are polyphyodonts that have cycles of tooth rotation throughout their lives. The chewing teeth are replaced six times in a typical elephant's lifetime."--Phil Holmes (talk) 08:47, 30 May 2016 (UTC)
 * Sorry, I simply read the article, whose meaning is plain and which is itself referenced, although I don't own that reference. Not having ever heard of elephants losing their baby tusks, I think the burden would lie on the person who wanted to add the negative claim to the article.  But I see no need to add that claim, for the same reason I see no need to add a claim that says, unlike some lizards, elephants cannot autotomize their tails and regrow them. μηδείς (talk) 21:27, 31 May 2016 (UTC)
 * Just to clarify, my concern is use of the term "cheek teeth". The tusks are incisors and, to the best of my knowledge, are not usually considered as cheek teeth.  It would be ideal to find an RS that states specifically, "tusks can regrow". DrChrissy (talk) 22:32, 31 May 2016 (UTC)