Wikipedia:Reference desk/Archives/Science/2014 December 17

= December 17 =

Mystery fruit (?) in hay bale
Here's a good, old-fashioned species ID question for everyone. I am a farm dweller (southeastern United States), and I have been coming across these things in bales of hay from time to time. They are what appear to be very tiny fruit, the largest being maybe 7 or 8 mm in diameter. They don't look ripe to me, but not knowing what they are, I guess that would be a hard call to make. They are yellow (obviously) and full of seeds (hence, fruit). I was brave enough to taste one, and decided I didn't like the taste; decidedly pepper-like, but quite bitter. The skin, though, has a slightly irregular, almost citrus-like texture. Any ideas? Evan (talk&#124;contribs) 05:08, 17 December 2014 (UTC)


 * Horsenettle, Solanum carolinense --Digrpat (talk) 06:41, 17 December 2014 (UTC)


 * Yes indeed. I won't be giving it another taste then, in that case! Glad I spit. Thanks for the reply. Evan (talk&#124;contribs) 06:52, 17 December 2014 (UTC)


 * Is that hay for horses ? If so, I'd be a bit concerned that they may get sick if they eat too many of those. StuRat (talk) 06:57, 17 December 2014 (UTC)


 * Yeah, I've been picking the fruit out before feeding the horses on the off-chance it was bad. I'll start being even more careful, and maybe have a chat with my new hay provider; never seen these in hay from anyone else. Evan (talk&#124;contribs) 07:00, 17 December 2014 (UTC)


 * OK, but don't be too hard on him, it's apparently a bitch to get rid of that weed. I'll mark this Q resolved. StuRat (talk) 07:09, 17 December 2014 (UTC)

Gap in teeth
Some people have a very prominent gap between their front teeth. Here is a photo of an example: Michael Strahan: Why I Never Closed the Gap in My Teeth. Is there a name for that (other than simply "gap")? Also, what causes this? Thanks. Joseph A. Spadaro (talk) 05:17, 17 December 2014 (UTC)
 * Diastema. Evan (talk&#124;contribs) 05:19, 17 December 2014 (UTC)


 * Thanks! Never heard that term before.  Thank you.  Joseph A. Spadaro (talk) 18:12, 17 December 2014 (UTC)


 * Regarding what causes a it, there are physiologically important diestemata (plural) in animal dentition that serve to both prevent food impaction and to aid in occlusion. Animal dentitions are super strange from a human-focused perspective because there are gaps and missing teeth and all sorts of wacky things that exist quite normally that, if found in the human dentition, would appear quite odd.


 * But back to human diastemata -- a midline diastema, as exemplified by Michael Strahan, is sometimes caused by an overly large incisive papilla (I'd steer you toward Google images for this, rather than the Wiki article because the latter is very misleading: the photo is from a terrible angle, exhibits terrible shadowing and the palate manifests a torus palatinus which can easily be mistaken for the focus of the photo as used by the article). Also, if the incisive papilla happens to be positioned a little more anteriorly than normal, the central incisors (which are the two large front teeth) may not be able to erupt into proper position, thus forming a midline diastema.


 * Back to animals, for a second -- I did come across something very interesting recently while reading about the rhinarium, or mammal wet nose. Apparently the groove on the rhinarium, the philtrum, is embryologically similar to the groove primates (and humans) have under their nose, even if they do not possess a wet nose (i.e. haplorhines).  There's much debate about how to classify the various prosimians based on some of the variations that exist with these structures (see here) and, apparently, the presence of the rhinarium and its philtrum creates a gap between the roots of the maxillary central incisors (see second paragraph here).  As a dentist for humans, I can confirm that there is a gap between the roots of maxillary central incisors for humans, even when there is no gap between the crowns (and so, no diasthema) because the two maxillary bones fuse at the midline suture.  I have not seen clinical or radiographic information related to what is meant when the aforementioned citation refers to a gap between the central incisor roots in strepsirrhini, so I can't know for sure the comparative anatomy.  But in humans, the incisive papilla is the exit of the nasopalatine nerve from the nasopalatine canal and if the nerve would exit more anteriorly, I can see it being very much in the way of the two central incisors being close together.  DRosenbach  ( Talk 01:55, 18 December 2014 (UTC)

Thanks, all. Joseph A. Spadaro (talk) 17:00, 19 December 2014 (UTC)

Missing teeth (technical terms)
Inspired by the previous question: Is there a technical name for adult teeth that are missing because they never developed? For example, suppose a person simply doesn't have cuspids and never did, is there a technical name for such missing teeth (or perhaps a name for a medical condition associated with having fewer teeth than normal)? Dragons flight (talk) 05:33, 17 December 2014 (UTC)
 * Hypodontia gives several terms to related this condition. Also "aplastic" can be used to describe any missing organ.--Digrpat (talk) 06:02, 17 December 2014 (UTC)
 * This is anecdote, but the lack of cuspids is rare. The lack of wisdom teeth is most common, and the human jaw is one of our rapidly evolving body parts.  I mention this from my having had impacted molars extracted. μηδείς (talk) 06:54, 17 December 2014 (UTC)


 * Thanks. That's exactly what I was looking for.  Dragons flight (talk) 02:54, 18 December 2014 (UTC)

Heat engine problem
Hi, I'm working on a homework question and basically I feel like I've gotten the whole thing but I'd really appreciate someone else to helping me check because I'm not sure if I did it right.

It's a heat engine problem, going from A to B to C Volumes and pressures are as follows A = 7x10^4 Pa, 2.5*10^-2 m^3 B = 3x10^5 Pa, 2.5*10^-2 m^3 C = 3x10^5 Pa, 7.5*10^-2 m^3

I got that the engine has a power output of 57.5 J by finding the area inside the points (just using 1/2 b*h) and an efficiency of 12% by finding the total heat added by Q=dU+Work from A=>B and B=>, but I'm just not sure if I'm doing it right. Can anyone please help me confirm with their steps?

166.137.252.91 (talk) 05:41, 17 December 2014 (UTC)

I think we're missing some information here. From A to B the pressure goes up and then from B to C the volume goes up. In both steps energy is being added to the gas. But we don't know what kind of gas it is, its mass or its specific heat.50.43.56.168 (talk) 08:28, 17 December 2014 (UTC)

I think I'm supposed to assume it's an ideal gas, and the temperature at A is 290K. 67.247.2.127 (talk) 02:45, 18 December 2014 (UTC)

Your first statement is incorrect. Joules is not a power output. J/s is power and is expressed in Watts (alternatively as horespower). --DHeyward (talk) 06:55, 18 December 2014 (UTC)

What's the centre of mass of the Local Group of galaxies?
What do the galaxies in the Local Group orbit around?Whereismylunch (talk) 07:51, 17 December 2014 (UTC)


 * According to our Local Group article: "Its gravitational center is located somewhere between the Milky Way and the Andromeda galaxies" (although the center of mass and gravity aren't technically the same, they may be close enough for you purposes). However, I don't think it's correct to say that everything in the Local Group orbits about that point, since the way that distance is critical in determining gravitational attraction ensures that each galaxy is far more affected by those galaxies near it than by those far away.  So, in effect, each galaxy will orbit about a different center of gravity, as viewed from it's perspective.


 * To compare with magnetism, we might say that all compasses on Earth should point toward magnetic north, but local variations in the magnetic field, or nearby magnets, can easily change the direction the compass points. It's not that those things are more powerful than the Earth's magnetic north pole, they are just closer. StuRat (talk) 07:58, 17 December 2014 (UTC)

But what's at the gravitational centre? — Preceding unsigned comment added by 199.119.235.178 (talk) 08:58, 17 December 2014 (UTC)
 * Nothing. -- Jayron 32 11:21, 17 December 2014 (UTC)
 * Or, more accurately, the gravitational center is never going to be made of anything, since it's a point, an abstract construct rather than a physical body. To be clear, something might be occupying the space that roughly corresponds to that point, but it needn't be a significant body contributing any particular amount of gravitational force.   S n o w  talk 12:54, 17 December 2014 (UTC)
 * Wikipedia also has an article Centers of gravity in non-uniform fields which may be a bit technical, but does provide some explanation of the concept. -- Jayron 32 13:51, 17 December 2014 (UTC)
 * I was about to link to the same article which explains that the concept is not really clearly defined for clusters of galaxies, but I think our "Local Group" article probably refers to roughly where the CofG would be if (suddenly and inexplicably) a uniform gravitational force suddenly appeared (from the edge of the universe? or the Great Attractor, or Dark flow?) and acted on the whole cluster. It is more usual to call this "point" the centre of mass.  The theoretical point about which the galaxies seem to be revolving (on average, see StuRat's comment above) is not necessarily the same point, but might be somewhere near the centre of mass.   D b f i r s   13:11, 18 December 2014 (UTC)

How accurate is reentry?
The recent test flight of the Orion spacecraft ended with a splashdown in the Pacific Ocean where is was picked up by the USS Anchorage. How far was the ship from the point where the spacecraft touched down? What was the predicted impact point and/or area? Once the retro rockets have been fired, does the spacecraft have any further control of where it lands? — Preceding unsigned comment added by 50.43.56.168 (talk) 08:13, 17 December 2014 (UTC)


 * Well, to give you some idea. The Mars Science Laboratory only went to our nearest planet and yet it missed point zero by 5½ miles. Better luck next time eh.--Aspro (talk) 09:00, 17 December 2014 (UTC)


 * The distances involved in a re-entry procedure are significantly shorter than those of an interplanetary trajectory, such that, under many conditions, a given error in trajectory at the outset results in a larger divergence (in terms of absolute distance between resulting arrival points) for the latter, relative to the former.  S n o w  talk 12:34, 17 December 2014 (UTC)


 * It was 1.5 miles, not 5.5 miles. --Bowlhover (talk) 18:56, 17 December 2014 (UTC)


 * Which, considering a trip of 675 million kilometers and the necessity for incredibly accurate timing (in that each planet is in motion in its own orbit) is pretty impressive in it's own right. Sure, close is often not good enough in astronautics, which is why most missions now include a handful of opportunities for course corrections. Still, if I launched something 675 kilometers via mechanical means and managed to land it within 1.5 millimeters of my (swiftly moving) target, I dare say it would be regarded as the single most impressive thing I'd ever do.  S n o w  talk 20:23, 17 December 2014 (UTC)


 * One of the points about splashing down in the ocean is one can ensure there aren't people anywhere near! So hopefully they were some distance away, especially as it was a test flight. Dmcq (talk) 11:33, 17 December 2014 (UTC)

• I can't find out "How far was the ship from the point where the spacecraft touched down?" however "The target landing accuracy of an Orion capsule using automatic bank angle control of downrange and crossrange, when subject to the full range of atmospheric, aerodynamic, navigation, control, and mass properties dispersions, is within 10 km (5.4 nmi)". a google cache of http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110013203.pdf, which appears to be unavailable at that URL
 * To the question in the OP's heading, the answer would seem to be "not necessarily very accurate". The charts at Splashdown include "miss distances", which indicate rather variable results (though the entry for the Orion test does not include a miss distance). Deor (talk) 12:46, 17 December 2014 (UTC)
 * But they can be. The closest to calculated landing point appears to be "Apollo 16 on April 27, 1972 at 0°43′S 156°13′W by USS Ticonderoga (CVS-14)" only missed by 0.55 km (≈0.34 mile)! Though Aurora 7 on May 24, 1962 missed by 400 km (≈250 miles). As for control of landing point after the retros fire? Yes I believe they can control it,(see cached NASA source below) but the main concern would be to maintain the correct re-entry 'attitude', or the craft may either skip out of the atmosphere or burn up and 'land' as cinders. Where it lands would be a pretty low priority, so long as it's in one piece on water.
 * • Specifically the landing point from Splashdown was 23.6°N 116.4°W, 275 miles west of Baja California. However the Exploration Flight Test 1 page says "23.61°N 114.46°W" 640 miles (1,030 km) SSE of San Diego. 'Miss' distance unspecified as noted.
 * Those 'miss distances' may not be correct! Use with care. The actual HTML version, here, of the source for the Apollo 16 says "3.0 n mi from the target point" (5.56 km; 3.45 miles) not 0.55 km/0.34 miles! That may be a slip of the decimal point. The big 400 km Aurora 7 miss however is supported by the reference on page 225, (PDF 8.162 MB), though the URL has changed.--220  of  Borg 08:16, 20 December 2014 (UTC)

Lioness hunting tactics
I read yesterday in a Simon & Schuster mammal field guide from about 1985 that lionesses tend to kill their prey with a single blow to the back, breaking the spinal cord. I'm not naive enough to simply ask how could it be that striking with a paw leaves the prey with fatal damage but no damage to the lioness' paw, but I was just intrigued at everything that needs to go into such a technique. It seems obvious to me that lionesses do not consider their options like a person would, but of all the possibilities and all the alternatives, I find it fascinating that the lioness would consider this means of execution over, say, chomping on the trachea. I see Youtube videos on lionesses attacking buffalo and they seem to try to bit into the ventral neck, but the buffalo resists. What sort of force is required to tear out a trachea, and why would a lioness find that difficult? Is it really more efficient to snap a spinal cord? Thoughts and insights are welcome. Thanks!  DRosenbach  ( Talk 17:18, 17 December 2014 (UTC)


 * The way the lioness kills her prey is directly related to how she approaches it. The typical approach would be to stalk and then attack from behind - this makes the back of the neck the clearest and easiest target for a killing blow. Going for the throat would require a frontal approach which could lose the element of surprise, as well as leaving the lioness open for a counter-attack from the prey's hooves, horns, etc.


 * There is a lioness-eye-view video of a hunt and kill available here:This is what hunting looks like from a lioness' point of view. (Don't watch it if you may be disturbed by seeing an animal get killed.) The narrator notes that a lioness "will generally sneak up to the prey, as close as possible, and then make a sprint for it." That sneak attack pretty much demands going for the back of the neck rather than the throat. - EronTalk 18:13, 17 December 2014 (UTC)
 * Yep, also going for the throat puts a lion in easy kicking/stomping range of a quadruped. But all of this is massive simplification. Does the field manual mention the technique is to jump on a zebra, overshoot, flip over, almost get trampled then run away? Because that happens a lot too :) Finally a serious spinal injury at the neck makes a mammal stop, nearly instantly - even if it's not dead it's not moving. But I wouldn't want to be around a wildebeest with its trachea recently ripped out. It will still be deadly for an important minute or so, and you lose all that tasty and nutritious blood. SemanticMantis (talk) 18:20, 17 December 2014 (UTC)


 * Here's a few refs - an old paper, and a newer ref . The first (paywalled) link has a table with data on kill rates - males killed a bit more than females, immature and old prey made up the majority of kills, but "prime" healthy prey made up the plurality. Humorously, the latter is on a Lion King fan site, but it does have additional citations, and mentions the importance of cooperative hunting and scavenging. It reports (and you can also see in videos) that often several lions will jump on a prey at once, attacking various parts simultaneously. The point being that kills made by a solitary female are probably a rather small part of a lion's average weekly diet. SemanticMantis (talk) 18:33, 17 December 2014 (UTC)


 * Lions often hunt together, but as for pouncing on the prey together, that's only needed for large prey. StuRat (talk) 18:44, 17 December 2014 (UTC)
 * Buffalo made up over 60% of lion kills in this study - though they do mention that smaller prey are probably underrepresented in their study, because the lions might finish eating before the observers could find the body. SemanticMantis (talk) 18:51, 17 December 2014 (UTC)


 * And for more throat-based killing, check out Cheetahs, they seem to be generally less effective at killing - this paper ] says Cheetah spend several minutes killing prey. Five minutes is common, but 15-25 minutes was not rare, even with small impala fawns.

Some prey revive from strangulation killing attempts and have to be “strangled” two to three more times before death occured.
 * SemanticMantis (talk) 18:51, 17 December 2014 (UTC)
 * Many years ago I read a research paper on Lions' killing methods.(Sorry, can't find it now) They found that most prey were killed by a bite that forced the canines between the vertebrae, rather than crushing the vertebrae. Using high-speed photography and post mortem dissections, they found that lions have some rapid response muscle fibres in their jaw muscles, that can very quickly do a series of test bites until the canine teeth find the softer area between the vertebrae. An amazing bit of evolution!! 122.108.177.30 (talk) 03:44, 18 December 2014 (UTC)

Bugging the outdoors with spiderweb-like antennas
I ran across an interesting story at, in which three planes flew close overhead and fine spiderweb-like fibers were then seen sticking to the landscape. I am for now discounting the site's explanation of "geoengineering" entirely, but assuming the truth of their published lab analysis that indicates the presence of aluminum (1020 mg/kg), barium (34.1 mg/kg), and strontium (70.8 mg/kg). These are small but perhaps not negligible amounts, up to 0.1% aluminum in the sample as collected.

To be clear, I have found a fairly persuasive "debunk" of the story at. If we assume that the witnesses were wrong about the association with the planes and the fall of the webs immediately afterward, or if it's just a remarkable coincidence, the webs are explained; if they were contaminated with soil the aluminum is explained; I'm not so sure about the rarer barium and strontium. The test was consistent with spider silk, which would be more impressive if they hadn't first identified it as wheat flour and bacitracin; suffice it to say that some non-metallic matrix containing peptide has to be the major constituent of whatever these fibers are.

But to be contrary, just because the fibers look natural doesn't rule out another explanation, since they might intentionally be camouflaged. My question is whether this data could be explained with some known form of antenna that could be sprayed through a nozzle as a plane flies overhead, land as an intact radio-reflective surface, and then have a signal bounced off it to measure changes to it, i.e. vibrations caused by the speech of nearby persons? (as a wild guess, probably wrong because it also contains titanium, see ). Alas, I'm not familiar with this literature. How thick would such a metal fiber actually have to be to be used this way? And is this metal composition actually practical to include in some sort of polymer "spider silk" that can be sprayed from a plane?

I'd also welcome any other possible explanations. Wnt (talk) 21:51, 17 December 2014 (UTC)
 * So much of this is such utter nonsense I'm not sure where to start. I don't even believe that a plane flying at 5000-8000 feet could distribute "spider web like fibers" to the ground in anything like a reliable fashion. This is also one of the major problems with chem trails, there is an absolutely immense volume of air to travel through from a mile up and there are all sorts of wind currents and turbulence to get through, to suggest that a spider silk would just gently fall all the way to the ground from where it was dropped by a plane a mile up is ridiculous. Also, known form of antenna and radio reflective surface are mutually exclusive concepts. I suppose you are talking about something like a Laser microphone but that already exists and would be a far simpler way to "bug" someone without the need to spread square miles of high tech spider silk antennas randomly around the country side. Vespine (talk) 23:58, 17 December 2014 (UTC)
 * Well, the non conspiratorial explanation is ballooning (spider) - which can reach the jet stream and return safely to the ground. Therefore, it should not be impossible to drop it from the height of a plane, though getting around the difference in velocity would indeed be an interesting technical problem.  (for example, you can picture a flexible boom that wiggles back and forth, regularly reaching near zero airspeed)  As for chem trails, so far as I know this is simply jet fuel that contains up to 0.3% sulfur; it is said to delay global warming by 6 months, kills 1000-4000 people every year, but hey, it makes the jet fuel 1.6 to 7 cents cheaper a gallon.  Officially not a conspiracy, just business as usual, with a side spin of "good for the environment".   (And where else did people think the chemtrails would be coming from, if not the fuel tank?)  The presumed purpose of the scheme would not be to place a specific bug in a known location, but to place many bugs in multiple locations that are hard to identify as such, so that the conversations of a large number of people are simultaneously screened for bits of interest while being as easy to deny as possible. Wnt (talk) 00:36, 18 December 2014 (UTC)

I came across something that sounds vaguely similar. Google "Huntsville weather anomaly". Here's one site: http://valleywx.com/2013/06/04/mystery-blob-over-west-huntsville/ — Preceding unsigned comment added by 50.43.56.168 (talk) 01:35, 18 December 2014 (UTC)
 * Well for one, I wasn't saying that spider webs 'couldn't be dropped from a plane and land somewhere, my point was that it would not land anywhere near where it was dropped, to the point where it would be practically futile. Notice how low a crop duster flies to spray a field, that's not done from a mile up for precisely the same reason, the amount of spray that would actually reach the ground at the target location would be negligible. Similarly if you dropped cobwebs from a mile up, I propose it would be very difficult if not impossible to say with any level of confidence where those cobwebs would land. If it's purely a 'non targeted' attack and they don't care where it lands, and I'm assuming it's supposed to be covert since no one knows about it, then why wouldn't they just fly the mission at night when no one would notice? I suppose the conspirators were just too stupid to think of that? Or is it because they control all the media and so they don't care if a few people notice? I'm guessing this thread has already been tagged and will be deleted soon and me and you will disappear without a trace? Also, pollution from ships kills about 60,000 people a year, compared to 4000 a year from planes, so I guess the conspiracy should really be "chem wakes" not "chem trails"? And lastly, coal fired power plants kill hundreds of thousands globally with their pollution, what conspiracy is that? chem power plant? Vespine (talk) 02:40, 18 December 2014 (UTC)


 * This is an interesting argument. How well can the path of the dropped material be predicted, given extensive modelling of local weather? Wnt (talk) 13:39, 18 December 2014 (UTC)
 * What kind of answer do you expect? "Well enough"? The question is too vague. IF there was actually some practical requirement for the military to drop spider web like material from a plane flying a mile high, I doubt there is any challenge there that could not be overcome, given enough research and resources. I just don't think the practical need exists and there would be far easier and more efficient ways of achieving a similar result for less cost and effort. Vespine (talk) 23:02, 18 December 2014 (UTC)


 * The aerodynamic coefficient (I just made that up) will make a huge difference. Iron cannon balls will have a fairly predictable trajectory. Threads of spider silk, not so much.


 * Another point is that antennae must have some precisely controlled placement of the antenna elements, not the random distribution you'd get from a spider web tossed from a mile up. A fractal antenna could potentially be disguised as a natural object though, since fractals are common in nature. StuRat (talk) 18:20, 20 December 2014 (UTC)