Wikipedia:Reference desk/Archives/Science/2016 December 15

= December 15 =

What street legal road vehicle has the biggest weight to ground contact area ratio?
Things like 18-wheelers, cement trucks, bulldozers, tractors that can be driven on roads and so on. Sagittarian Milky Way (talk) 05:26, 15 December 2016 (UTC)

2. What tank has the most weight to ground contact area on paved roads?

(with a tread that could conceivably go on paved roads. I don't know how long this tread-style or the road would last on an Interstate or Autobahn but maybe it's long enough that it might happen in war? (no time to switch tread/tank will go off-road at its destination, that kind of thing) Sagittarian Milky Way (talk) 23:49, 14 December 2016 (UTC)
 * Do you have reason to believe it isn't the Crawler-transporter? -- Jayron 32 23:56, 14 December 2016 (UTC)
 * Question amended. Sagittarian Milky Way (talk) 02:28, 15 December 2016 (UTC)
 * I'm not sure that clarifies your question at all, I don't believe any of those tanks or bulldozers are "street legal" in any country. What are you actually interested in? what tank will damage a road the least? Are you interested in Continuous track?  There ARE tracks designed specifically for paved roads used on tanks and construction vehicles, that are made of rubber or have rubber "pads". The article even has a picture of such pads used on an M1 Abrams.. Vespine (talk) 04:05, 15 December 2016 (UTC)
 * I thought they just drove the bulldozer on public roads when delivering it. Maybe not. And the Interstates and Autobahn were intended to help national defense. Wouldn't tanks be part of the anti-invasion road users? Sagittarian Milky Way (talk) 05:26, 15 December 2016 (UTC)
 * See Longer Heavier Vehicle. 92.8.63.48 (talk) 10:11, 15 December 2016 (UTC)
 * I suggest those things they move power station transformers on, for example http://www.dailymail.co.uk/news/article-2508878/Biggest-load-transported-Britains-roads-weighing-SPACE-SHUTTLE-crawls-destination-4mph.html and http://www.livetrucking.com/this-may-be-the-heaviest-oversized-load-ever-hauled-in-america/ As to tanks, you can drive them on road in the UK, provided they are registered and have a valid MOT. You need a civilian H category licence, and if you have a standard car licence (category C) you automatically have a provisional licence for a fully tracked vehicle. --TrogWoolley (talk) 11:58, 15 December 2016 (UTC)
 * It may also depend on whether you count things like this as one vehicle Nil Einne (talk) 22:07, 15 December 2016 (UTC)


 * The whole idea of using a track is to reduce the mass/area ratio. A bicycle, (or God forbid a petite lady wearing spike heels) has a larger mass/area ratio than a tank, I think. Just looking at my car, I think it supports >1 ton on < 1/ft2, while the 54-ton M1 Abrams appears to have > 60 ft2 of track. -Arch dude (talk) 04:00, 16 December 2016 (UTC)

What species is this?
What species is ? Some. I found it on a trip to Florida a couple years ago. ThePlatypusofDoom (talk) 01:59, 15 December 2016 (UTC)
 * It is a true iguana, one of the largest true lizards found in Florida (or the entire United States, for that matter). You may also find alligators and crocodiles of various species in Florida; they look totally different.
 * Here is a great brochure from the University of Florida: Dealing with Iguanas in the South Florida Landscape. There is some debate about whether iguanas are actually native or are escaped pets.  (Most sources, including the National Park Service, consider them nuisance pests and an invasive species; state and federal agencies generally agree that iguanas do not belong in Florida). It is generally legal to hunt and destroy (or eat) iguana in most parts of the state of Florida (excluding the Everglades!) without a permit, but reliable sources recommend that you call a wildlife removal expert - or just leave them alone.  Personally, I think iguanas are great, and like many introduced reptiles, should be allowed to integrate into the Florida ecosystem.
 * American alligators are very common; American crocodiles are rare but present in South Florida; and even Nile crocodile has been confirmed by several reptile scientists in Florida. Be careful if you sleep in the swamps... and don't forget your permit!
 * Nimur (talk) 02:43, 15 December 2016 (UTC)


 * "... should be allowed to integrate into the Florida ecosystem." You're entitled to your opinion, but I want to clarify that it is not an opinion shared by most mainstream professional ecologists and conservationists. Generally speaking, invasive species tend to decrease ecosystem function and biodiversity (see e.g. ). Note that not all introduced species are considered invasive species, and sometimes introduction of species results in neutral or lateral changes, i.e. community assembly (see e.g. ).  Most conservationists do not advocate a laissez-faire approach to invasive species, due to their ability to degrade ecosystem services.


 * That's just general principles, so I had a quick look: Here  are a few articles specifically addressing the problems caused by invasive snakes in FL, here  is one specifically about iguanas in FL. Among other effects seen as deleterious, they can increase erosion and pass salmonella to humans.
 * Control and management of invasive species is very expensive, but so are the potential costs of letting species run amok and messing up the ecosystems that our society depends upon. If you have any reliable scholarly sources advocating *against* removal and control of of exotic reptiles in FL, I'd be curious to see them :)  SemanticMantis (talk) 18:13, 15 December 2016 (UTC)
 * Sure - to stymie and defuse the defamatory accusations that my opinion is exclusively derived from original research, I can point to is 36 C.F.R. §2.2, Wildlife Protection, and the observation that within the boundaries of the Everglades, you can not hunt the iguana, or any other invasive species, without special permission. The National Park Service lists the iguana as "invasive" and/or "Status Unknown" in the Everglades, but federal law forbids you from disturbing them if you find them.  To my knowledge, there is no Invasive Species plan for iguana removal or control inside the Everglades.  So - within the boundaries of the National Park, where the ecosystem is ostensibly better-protected than in the rest of the state, you can be arrested and charged with a federal offense for eating any iguana that you find; everywhere else in the state, you're free to chomp away (and you may wear roller skis while doing so - something else that is explicitly forbidden inside the Everglades, §2.20).  Whenever you visit a national park in a state where you can eat any animals you find without permit, be sure to check in with the Rangers: federal wildlife protection laws always supersede local or state rules.  If no special permit was issued, always err on the legally conservative side - allow the invasive species to eat you, rather than for you to eat it.  WP:OR: this requires great discipline when you encounter a possibly-non-native crocodile, and can certainly test the depth of your conservationist persuasion.
 * In total seriousness, invasive reptile species are a problem in South Florida, but I do not believe mass-extermination is a great path forward. Don't eat the invasive species that you find in Florida swamps; and the animals will frequently reciprocate.
 * Nimur (talk) 18:48, 15 December 2016 (UTC)
 * Thanks! My understanding is not so much that they are protecting iguanas in the everglades but that they are protecting the everglades. That is, they think that allowing open hunting would disrupt more of that sensitive system than would be ameliorated by removal of the iguanas. It's not so much that the want to keep iguanas there, or think the iguanas are not causing problems, but that the iguana problem is less bad than the effects of hunters. I can't find any official state documents to the effect, but my claim is based on discussions with FL ecologists.
 * You are right, mass extermination is not really viable for most invasive species, and almost certainly not for FL iguanas and snakes, that's why we tend to focus on control and management, rather than eradication. There good reasons the state of FL provides incentives  for killing big snakes. My WP:OR is that eating invasive species can be a fun and tasty way to protect native species and ecosystem services, where allowable by law: win-win ;) SemanticMantis (talk)
 * Nimur, iguanas are NOT named in 36 C.F.R. §2.2. That is a blanket statement against hunting, except as authorized pursuant to federal law. Just reading the statute, I don't know that hunting iguanas is illegal in the Everglades. I only know that all hunting must first be authorized by federal law, which shall be determined as "activity is consistent with public safety and enjoyment, and sound resource management principles." There may be a blanket ban on all hunting in the Everglades, and there may even be a reason why they don't want to authorize it just for iguanas (hunter impact on land, other species being accidentally or intentionally targeted, etc). 36 C.F.R. §2.2 doesn't prove that iguanas are a good or acceptable invader. --OuroborosCobra (talk) 22:02, 15 December 2016 (UTC)

Crosses with more than 2 traits
There are monohybrid (with 1 trait and 4 squares in a Punnett square) and dihybrid (with 2 traits and 16 squares in a Punnett square) crosses. Are there also "trihybrid" (with 3 traits and 64 squares in a Punnett square) and "polyhybrid" (with n traits and 4n squares in a Punnett square) crosses? GeoffreyT2000 ( talk,  contribs ) 02:17, 15 December 2016 (UTC)
 * I've seen it done with three genes in a serious research article. I think past that point, it's just not an efficient way to present data, so I doubt you'll find many people using them except as an exercise in ridiculousness. Someguy1221 (talk) 07:16, 15 December 2016 (UTC)
 * Such things certainly exist in principle. Here someone has written out a full 256-cell Punnett square for a tetrahybrid cross (4 traits). Here is a method for solving a trihybrid cross without using a Punnett square that is generalisable to any number of traits. Whether such things exist in practice, outside of academic examples to illustrate genetics concepts, I'm not so sure.  PubMed and Web of Science, two databases of academic literature, both return zero results for "trihybrid cross" (in the sense meant here) or "tetrahybrid cross", so they don't seem to be common.  I guess one might carry out a trihybrid or higher order test cross for the purpose of genetic mapping. Adrian J. Hunter(talk•contribs) 07:34, 15 December 2016 (UTC)
 * The Punnett square article describes a "forked-line method" which is indeed more convenient. Ultimately though, what you need to make a four-gene Punnett square relevant is some kind of combinatorial phenotype where you can say that having this and this and this and not that puts you in one category or another.  But while there are many polygenic traits I don't know of any that are really that... binary.  (Indeed, I just noticed the link I cited turns out to be a redirect to quantitative genetics!)  I mean, if four genes affect something you're realistically going to be looking for how much quantitatively each allele affects the outcome and add them up. Wnt (talk) 02:30, 16 December 2016 (UTC)

narrow width of solar system
when it is winter in north part of earth ,the planet is closer to the sun, so when it be so for all the planets(little diameter of ellipse ) ,this says us that we have narrow width for solar system(at same side). the question is this : is it so (such as elliptic galaxies )or varies for some parts of system?--Akbarmohammadzade (talk) 05:10, 15 December 2016 (UTC)
 * The point in its orbit where a planet approaches the sun most closely is the "perihelion".  Every planet's perihelion moves (at a different glacial pace) eastwards among the stars (as viewed from earth).   Here are their current heliocentric longitudes:


 * Mercury 77 degrees
 * Venus 132 degrees
 * Earth 103 degrees
 * Mars 336 degrees
 * Jupiter 15 degrees
 * Saturn 92 degrees
 * Uranus 171 degrees
 * Neptune 45 degrees.

Of course everything that circles the sun in an elliptical orbit has a perihelion (that includes Pluto and the minor planets (asteroids)). 92.8.63.48 (talk) 10:21, 15 December 2016 (UTC)
 * I notice there's a 165-degree sector that none of these perihelia currently fall into, or in other words a weak clustering to (almost) one side of the Sun. This could of course be due to random chance, but I wonder if any gravitational effects of, say, "Planet Nine" could be influencing this. {The poster formerly known as 87.81.230.195} 90.200.136.117 (talk) 18:15, 15 December 2016 (UTC)
 * [Banned user's contribution deleted]

is it so that comets have half life?
--Akbarmohammadzade (talk) 06:38, 15 December 2016 (UTC)


 * No. Half-life is not a term used to describe comets. They do get smaller over time (if that's what you mean) due to outgassing and other factors. 196.213.35.146 (talk) 10:28, 15 December 2016 (UTC)


 * The term can be used in terms of certain fixed risks, such as ejection by close approach to a planet.  However, it seems true that the composition of a comet will change as it evaporates, and so its rate of evaporation will change, making a "half-life" for mass problematic. Wnt (talk) 12:21, 15 December 2016 (UTC)


 * As a comet deteriorates, would its surface-area-to-volume ratio increase, and thus accelerate the deterioration? ←Baseball Bugs What's up, Doc? carrots→ 15:13, 15 December 2016 (UTC)


 * Yes, but at the same time the volatile parts are likely to outgas, leaving less volatile rocky parts. Think of how a pile of mostly snow becomes a smaller, dirty pile of mostly rock in spring. StuRat (talk) 16:04, 15 December 2016 (UTC)
 * Don't I know it. I can think of some in the upper Midwest that lasted well into May. ←Baseball Bugs What's up, Doc? carrots→ 20:17, 15 December 2016 (UTC)


 * This may be the first time I've seen in terms of used to mean to describe, almost a reciprocal of the sense most familiar to me. —Tamfang (talk) 18:38, 17 December 2016 (UTC)


 * The term "half life" is usually reserved for things that decay exponentially, because if something decays exponentially the time from when it is size X until it is size X/2 is constant, regardless of the value of X. Comets decay, but not exponentially, so they don't have a well-defined half life. Looie496 (talk) 15:19, 15 December 2016 (UTC)
 * Does anyone have a ref for the decay rate of comets, or even for any individual comet? SemanticMantis (talk) 17:58, 15 December 2016 (UTC)
 * Factors mitigating against calculating regular decay rates for comets in general would be their probable widely differing composions, and for particular comets their unpredictably variable orbital period and closeness of perihelion passages due to perturbations by the larger planets (Comet Shoemaker–Levy 9 being an extreme example). I'm sure some rough estimations have been made for short-period comets like Halley's. Of course, short-period comets have already been perturbed from much longer original orbits, and some have been observed to disintegrate entirely on their most recent/last perehelion, while others have become extinct, so are not really detriorating further, and may be indistinguishable from asteroids – see Fate of comets. {The poster formerly known as 87.81.230.195} 90.200.136.117 (talk) 18:37, 15 December 2016 (UTC)

how can explode a bomb in vacuum space?
--Akbarmohammadzade (talk) 06:58, 15 December 2016 (UTC)


 * Easy. Just detonate it. Remember - an explosion does not have to produce a "fireball". See here for a discussion. 196.213.35.146 (talk) 10:47, 15 December 2016 (UTC)


 * Bombs combine fuel with an oxidizer, or otherwise involve a self-contained reaction. If you rely on external air for combustion, that is merely a fire - it might be a big one, but it cannot draw in air fast enough to count as a detonation. Wnt (talk) 12:23, 15 December 2016 (UTC)


 * Among the many experiments conducted during Project Apollo, the Apollo 17 Lunar Seismic Profiling Experiment (NSSDC 1972-096C-06) was conducted by astronauts on the surface of the moon during Apollo 17. Here is a narrative description from NASA's Lunar Surface Journal: The Beginning of The End The End of the Beginning, including a link to Technical Note TN D-7141 Spacecraft Pyrotechnic Systems (March 1973).  NASA has published extensive documentation on the difficulties of safely transporting and using explosive charges on the Moon.
 * A set of eight explosive charges were emplaced on the moon by Apollo 17 astronauts, and the charges were detonated after they returned to orbit. The purpose was to collect information about the geology - selenology - of the rock underneath the surface of the moon.  This scientific technique is a standard method used by geologists on Earth: the explosive detonation transmits acoustic energy into the rock, and scientists study the echo recorded by sensitive microphones - geophones, or seleno-phones, as it were - Apollo scientists called them "geophones."  By studying the echo, scientists can interpret all the different layers of rock that the sound energy is bouncing or reflecting or refracting through.  Because there is effectively zero air at the lunar surface, the only acoustic signal recorded by the microphones is the sound-signal that propagates through the solid rock - otherwise, the explosions are completely silent!
 * Here is a photograph: (this is probably a crop from photograph AS17-143-21838, with Gene Cernan and explosive charge #5).  You can see the explosive charge and its radio-antenna in the foreground.
 * This profiling experiment was probably the most prolific use of an explosive charge in the vacuum of space. But, every time we launch a spacecraft that uses a rocket motor, or with an explosive bolt to separate stages, a small controlled explosion is happening in the vacuum of space.  This isn't new: we've used explosive bolts since our very first spacecrafts.
 * The physics is actually really easy to describe: the explosive must be completely chemically self-contained; the stoichiometry must not depend on any outside air; and once the charge sets off, the explosive chemical reaction must use up all of its fuel and oxidizer before the constituent pieces are mechanically separated. That makes for a great chemistry challenge - you need stuff that detonates really fast (but not too fast)!  And once the pieces start flying, there is no air pressure to retard the outward expansion - so the explosions look really boring, as the gas expands in a nearly-perfectly-spherical, isotropic, laminar-flowing sphere-wave "shock front" with no external matter to shock.
 * Like everything else in space-engineering, you start to understand how things work in space by learning really simple basic science - chemistry and physics. Then, you spend years and years and years studying non-idealities and confounding factors that affect real systems, building your knowledge and perturbing the perfect simplicity of the simple basic science; in the case of explosives, that would be complicated stoichiometry and supersonic fluid dynamics and so on.  Then, when you finally get to work on a space engineering application, there's no air, no net force due to gravity, and so on, all the really simple basic science applies without any of the terrestrial complications.  The only hard part is getting high enough for any of this to matter.  We are stuck here until somebody solves the energy problem!
 * Nimur (talk) 17:11, 15 December 2016 (UTC)


 * Perhaps the OP was picturing a scenario where the is no air - not a vacuum per se. Think of a torpedo on the other end of the scale. The "bomb" is still a self-contained unit with no real need of air to explode. 41.13.204.236 (talk) 19:20, 15 December 2016 (UTC)
 * Even a regular bullet does not rely on any "outside air" to fire, you can shoot a bullet in the vacuum of space, or even underwater. The explosion inside the bullet casing will take place without any additional air. Underwater the resistance of the water will stop the bullet very quickly, but it will still fire. Vespine (talk) 23:09, 15 December 2016 (UTC)

Identify an office machine (checkwriter)?
Can anyone help narrow down the make and model of the office machine shown in this joke image? It appears to be a fancy checkwriter (as some of its keys are arranged much like those on this Protectograph). The maker's mark is "National" - there was at one point a National Typewriter Company, but their mark doesn't ever seem to have resembled that. This one looks to be electric, and from its styling and that of the woman's clothing suggests it's from the 1950s or maybe 1960s. -- Finlay McWalter··–·Talk 23:48, 15 December 2016 (UTC)
 * The mark belongs to the National Cash Register Company, before they became known as NCR Corporation. I haven't been able to identify the specific machine, but I'm going to guess that it was actually designed for use by banks, not for check writing specifically, and this may explain why its identity is so obscure (since there would have been far fewer of these made).  General Ization   Talk   00:01, 16 December 2016 (UTC)


 * Ah, of course, NCR! Armed with that, I found this page which has a bunch of pictures, including the specific ad from which the joke image was derived. Thanks for your help. -- Finlay McWalter··–·Talk 00:16, 16 December 2016 (UTC)


 * I can actually remember a time when account balances at banks and also early merchant charge accounts (pre-plastic credit cards) were kept on printed cards like those depicted in the platen of the machine. But I date myself.  General Ization  Talk   00:06, 16 December 2016 (UTC)


 * I think this is an ad for the same or a similar NCR machine.  General Ization  Talk   00:18, 16 December 2016 (UTC)
 * The same ad you mention.  General Ization  Talk   00:19, 16 December 2016 (UTC)


 * Here is a March 1955 advert of the National Accounting Machine. -Modocc (talk) 00:35, 16 December 2016 (UTC)