Wikipedia:Reference desk/Archives/Science/2014 July 31

= July 31 =

Lobster behavior
I've noticed that lobsters in tanks mostly seem to climb on top of each other in one corner, with the exception of maybe one or two loners. I don't think of lobsters as social animals, so just what are they doing ? Trying to escape ? StuRat (talk) 04:09, 31 July 2014 (UTC)


 * This would probably be the best source of info I found, these:, , , ,  also provide some info, mostly of the same sort. It appears that lobsters are solitary, except for mating periods, when in nature, but do establish a social hierarchy when confined together. As for what exactly the ones in tanks are doing, I didn't locate a direct answer. --These , and , may also be of interest, though more tangential - sadly, they also fail to answer your specific question. If I can find anything more directly relevant, I'll share it.Phoenixia1177 (talk) 05:14, 31 July 2014 (UTC)


 * Personal Speculation Alert: As a former freelance whelk-gatherer (no, really!) I used to visit a local seafood wholesaler to sell my harvest, where freshly caught lobsters were kept in large though shallow concrete pens of constantly renewed fresh seawater. In these, presumably fairly benign, conditions they appeared to space themselves out to the extent possible. I suggest that in the smaller tanks (in restaurants?) you've seen, the conditions (temperature, salinity, light levels) may be much less pleasant and may vary greatly in different locations in the tank, so the lobsters are seeking the least uncomfortable spot, overriding any aversion to proximity. Maybe there's a PhD research opportunity here for someone. {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 14:18, 31 July 2014 (UTC)


 * Or an IgNobel Prize. Dismas |(talk) 18:29, 31 July 2014 (UTC)

Aircraft
Is there a range of airplane classes which rarely fly outside of airways or the "special airspace" around airports?

By class I mean something like jetliner > commuter jet/small jet service to podunk airport > small bizjet > multi-engine propeller > single-engine propeller

The article says airways are 9.2 regular miles wide. With GPS available today, do they fly much closer in reality? (at least if they have a sufficiently bureaucratic employer?) Actually, with today's safety, even the jetliners might stray far with planes being at the same mile marker due to merging, all the slow biz-jet/commuter jet passing, climbing, descending and sharing of airways by numerous airport pairs lying near a straight line. (I've heard they seperate opposite directions by altitude) Do they at least go out of their way to stay in the zone, going to the outer edge of an airway if need be to avoid clipping the inner angle of an intersection?

When do aircraft use great circle routes (possibly wind modified) instead of airways? In uncongested enough airspace I assume? Victor airways says they're not mandatory. Airlines even nix the magazine to save fuel. So is it possible that airlines use great circles to save even a mile of distance? Sagittarian Milky Way (talk) 18:02, 31 July 2014 (UTC)
 * See Airway (aviation). Airways can be deviated from.  Airways can't.  Rojomoke (talk) 20:16, 31 July 2014 (UTC)
 * Based on your link, I think you mean Air corridors can't be deviated from. SemanticMantis (talk) 20:56, 31 July 2014 (UTC)
 * No, I think the joke is in reference to airway, which is our article on the topic as it pertains to breathing / respiratory systems. Nimur (talk) 21:04, 31 July 2014 (UTC)
 * No, just me editing while tired. Rojomoke (talk) 03:28, 1 August 2014 (UTC)
 * You probably should start with National Airspace System (which applies to the United States). If you're interested in international air traffic, still start by learning about the US airspace systems, and then be prepared to learn about many extra complexities, bureaucracies, and special-cases.
 * By using "class" in this way, you are misusing technical terminology. Aircraft are categorized and subclassed; pilot ratings are also classed.  In addition (just to make sure you study for your written tests!), airmen are also categorized and classed.  For example, you can be an "Airplane / Single Engine Land" category/class airman.  The aircraft itself will be a "normal" class.  Don't get confused!  Not only will this question be on the test - if you get the answer wrong, you might be taking the wrong test!  These terms are defined in 14 CFR Part 23, which you can browse online.  Speaking from experience: there are no good references for this topic.  There are plenty of bad references!
 * Congestion isn't something the pilot can control: in most cases, the pilot is only responsible for separation. Air traffic control exists to help pilots maintain separation, even in conditions that preclude visual contact with other aircraft.
 * Aircraft do not need to fly in the airways: they need to comply with regulations, and be familiar with the many many rules that apply to different airspaces. Pilots are trained to plan a flight, taking into consideration "all available information" - which means basic geography, regulatory rules, temporary restrictions, airspace types, air traffic, weather, pre-flight briefings, forecasts, posted signs, placards, PIREPs, NOTAMs, ... ... and all available information.  The airways exist because they are commonly-useful in flight planning.  There is no requirement to operate only on those routes.
 * Nimur (talk) 21:04, 31 July 2014 (UTC)

Do nocturnal humans exist?
Some people are night owls, but I think most of them are not really nocturnal as exposure to daylight early in the morning (when they normally would still be sleeping) would shift their biorithms to become less night owl-like. So, are there people who naturally become sleepy at, say, 10 am in the morning when exposed to daylight from 6 am onwards? Count Iblis (talk) 22:07, 31 July 2014 (UTC)


 * See Circadian rhythm. We have mechanisms which continuously recalibrate our rhythm. So, unless you are completely isolated from all zeitgebern, I don't think that it is possible. Especially in your case, since you explicitly state that the subject is exposed to daylight. Plasmic Physics (talk) 22:27, 31 July 2014 (UTC)


 * I have no sources, just speaking from personal experience, but I've worked nights for many years (8+), and I am tired everyday around 9-10am, and I feel extremely out of sorts taking a week off and moving back to a normal schedule (it's hard not to since the rest of the world does). I am routinely exposed to sunlight and I sleep in a room that is not pitch black, but has windows through which sunlight comes. Moreover, for most of my life, I've been inclined to sleep during the day and wake at night, even as a child, I had difficulty sleeping at night and was prone to naps in the day. I'm not saying that I am nocturnal, but I do find that early morning conditions make me tired and regularly notice that around dawn, when going out for a cigarette at work, I am prone to yawning and feeling that it is "late" - around noon, if I stay up, I feel quite very much how most people describe staying up till after midnight to feel. Again, I am just one anecdote, but it seemed relevant.Phoenixia1177 (talk) 00:17, 1 August 2014 (UTC)


 * Yes, people with delayed sleep phase disorder exist. Red Act (talk) 00:40, 1 August 2014 (UTC)


 * Yup. And non-24-hour sleep–wake disorder, apparently common among blind people, has been the topic of some drug marketing campaign or other in the United States (where we have such things) for the past six months or so. Evan (talk&#124;contribs) 01:55, 1 August 2014 (UTC)


 * On a related anecdotal note, I have a friend who swears that exposure to bright light makes him sleepy rather than wakeful. I'm not sure if there's a clinical term for that kind of paradoxical reaction, but I'm inclined to believe him based on personal observation. Evan (talk&#124;contribs) 01:59, 1 August 2014 (UTC)


 * Exposure to bright red light in the afternoon can mimic the effect of sunset. μηδείς (talk) 15:50, 1 August 2014 (UTC)


 * Interesting, I guess you would expect that there would have to be a small fraction of the populaton who are nocturnal. From an evolutionary point of view, this makes sense as an insurance policy to make a rapid evolution toward nocturnal humans possible. The longer this would take if it were necessary, the greater the chances are that we would go exinct. Count Iblis (talk) 02:11, 2 August 2014 (UTC)


 * Evolution doesn't take out 'insurance policies'. 03:45, 2 August 2014 (UTC)


 * But it does make sense in terms of group evolution for a small fraction of the group to be nocturnal, so that they could stand watch for nocturnal predators, or for a night raid by an enemy tribe... 24.5.122.13 (talk) 04:05, 2 August 2014 (UTC)


 * Group selection is a controversial topic, and by no means the established consensus amongst evolutionary biologists. AndyTheGrump (talk) 04:24, 2 August 2014 (UTC)

Propellantless thrusters
Please share your opinions on whether this is likely to achieve additional independent confirmation:

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140006052.pdf

http://www.wired.co.uk/news/archive/2014-07/31/nasa-validates-impossible-space-drive

98.147.125.124 (talk) 23:59, 31 July 2014 (UTC)


 * "We don't answer requests for opinions, predictions or debate". AndyTheGrump (talk) 00:37, 1 August 2014 (UTC)
 * Perhaps the poster used a poor choice of words. Nevertheless, we have a related articles already: Magnetoplasmadynamic thruster & Quantum vacuum plasma thruster; so, in the Wikipedia-sense, the answer is "yes".   —71.20.250.51 (talk) 00:58, 1 August 2014 (UTC)
 * These forces are known for long time but they are near useless because you can not produce enough thrust with such devices in reasonable dimensions. They are highout thinkable as maneuvering thrusters for small satellites but not suited to propulse interplanetary journeys. Space technology is already very highly sophisticated and in addition always open to new concepts, like for example Laser propulsion. So if NASA is checking it out it usually just means its "interresting", not that it is likely usable. --Kharon (talk) 02:29, 1 August 2014 (UTC)


 * The magnetoplasmadynamic thruster is very real but requires a propellant so it is not relevant to this discussion. The quantum vacuum plasma thruster is the relevant article and since it exist the subject is by wikipedia considered notable, not necessarily possible. To me it seems like the principle should work in theory, but I don't know what forces to expect and the measurements done so far doesn't seem that reliable. Ulflund (talk) 02:45, 1 August 2014 (UTC)
 * It is related, if not relevant in regards to the linked articles, e.g.: "...using classical magnetoplasmadynamics to obtain a propulsive momentum transfer via the quantum vacuum virtual plasma..."  71.20.250.51 (talk) 04:06, 1 August 2014 (UTC)

Do these have specific impulse measured in time (seconds) which we can compare to other thrusters? How about something less esoteric like Newtons per Watt? 104.128.96.117 (talk) 20:05, 1 August 2014 (UTC)
 * Solid technical information about the performance of the device as a thruster might be a bit much to hope for, given that the experimental results barely count as a positive result, if indeed they count as a positive result at all.


 * NASA devoted all of 40 person-days to performing the experiment. The test device involved was recycled from a little experiment performed in 2006, and almost looks like you could build it from $100 worth of parts from Radio Shack.  One of the parts identified in the photo is an "8oz can lid"!  The measured "approximately 30-50 micronewtons" of force (quite a large relative range) was only a few times larger than the minimum the measurement device was designed to be able to measure.  And the same measurement device also measured a non-zero force on a "null" test object, that was similar to the "real" test object but was modified to be non-functional.  Under the circumstances, the measured force sounds like it was well within the range of experimental error.  The Wired article makes the outcome of the experiment sound much more exiting than it really is, but then, Wired is far from being a peer-reviewed journal.  Red Act (talk) 21:26, 1 August 2014 (UTC)


 * I will note in passing that David Hambling appears to be Wired's designated bad-physics cheerleader: . He's been on about the EmDrive and related reactionless drive pseudo-technologies for years, and he's been a credulous mouthpiece for Andrea Rossi's cold fusion device almost as long.  He's good at gee-whiz wishful-thinking wonder, but short on critical evaluation of the technologies he writes about. TenOfAllTrades(talk) 21:46, 1 August 2014 (UTC)


 * Yeah - I agree. This is most definitely a case of "Extraordinary claims demand extraordinary evidence".  A claim to have successfully violated fundamental conservation laws is without doubt "extraordinary" - and an experiment where the results lie so close to the error bars has to be treated with skepticism.  Right now, there may be enough evidence to spend some money to do the experiment with better equipment - but there certainly isn't enough to say that anything whatever of value has been discovered. SteveBaker (talk) 05:23, 2 August 2014 (UTC)