::See also [[Wikipedia:Reference_desk/Archives/Science/2018_February_25#Why_do_humans_have_body_hair?|this recent RefDesk discussion]]. One reference from that is [https://www.scientificamerican.com/article/latest-theory-human-body-hair/ ''What is the latest theory of why humans lost their body hair? Why are we the only hairless primate?''] from ''[[Scientific American]]''. [[User:Alansplodge|Alansplodge]] ([[User talk:Alansplodge|talk]]) 19:14, 30 April 2018 (UTC)
::See also [[Wikipedia:Reference_desk/Archives/Science/2018_February_25#Why_do_humans_have_body_hair?|this recent RefDesk discussion]]. One reference from that is [https://www.scientificamerican.com/article/latest-theory-human-body-hair/ ''What is the latest theory of why humans lost their body hair? Why are we the only hairless primate?''] from ''[[Scientific American]]''. [[User:Alansplodge|Alansplodge]] ([[User talk:Alansplodge|talk]]) 19:14, 30 April 2018 (UTC)
::: I stick by my "mud ape" idea from last time. [https://phys.org/news/2018-04-giant-slothaccording-ancient-humanfootprints.html This] example illustrates how humans could rely on their ability to retreat safely to muddy, watery terrain (together with teamwork and spears, that is!) to get the upper hand over far more fearsome animals. I might notice that humans wading in muddy waters wouldn't have to worry much about getting their head hair immersed, since they have to breathe... [[User:Wnt|Wnt]] ([[User talk:Wnt|talk]]) 22:06, 4 May 2018 (UTC)
::: I stick by my "mud ape" idea from last time. [https://phys.org/news/2018-04-giant-slothaccording-ancient-humanfootprints.html This] example illustrates how humans could rely on their ability to retreat safely to muddy, watery terrain (together with teamwork and spears, that is!) to get the upper hand over far more fearsome animals. I might notice that humans wading in muddy waters wouldn't have to worry much about getting their head hair immersed, since they have to breathe... [[User:Wnt|Wnt]] ([[User talk:Wnt|talk]]) 22:06, 4 May 2018 (UTC)
::::Another theory is that body hair got almost completely lost after the beginning of upright walking with the necessity of massive perspiration. Hairs on the head were retained as an isolation for the brain, hairy armpits and groin to minimize abrasion of damp skin. Beard and chest hairs were subsequently reintroduced to protect the lungs when man moved to cold regions.
::::By the way, buttocks didn't change shape because of long sitting (apes sit the same way as we do the whole day) but because the huge (in comparison to apes') butt cheeks are possibly necessary for us bipeds to keep the torso upright when standing and to pull the legs backwards when running. Some of this to be found by Desmond Morris. [[Special:Contributions/194.174.76.21|194.174.76.21]] ([[User talk:194.174.76.21|talk]]) 14:35, 7 May 2018 (UTC) Marco Pagliero Berlin
==how human lost his tail?==
==how human lost his tail?==
Revision as of 14:35, 7 May 2018
Welcome to the science section of the Wikipedia reference desk.
The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.
چه عامل ژنتیکی و انتخاب طبیعی باعث شده برخلاف همرده های انسان ، موی سر تا این حد رشد کند؟
the man differed from his ancient grand parents when he went cave and started to hunting.
in such condition :
our tail have been fallen.
our foot changed shape , because of no need to go up from trees .(from Y shape)
our buttocks changed shape , for long duration sitting
our body hair had been lost
our head hair start to grow long--for which reason?
males face start to have long hair (beard)--for which reason?
our face deformed;
normally we became meet eating animals; too we are still eating fruits.
what is the basement reason of our hair length .too our eyebrow hair growth --Akbarmohammadzade (talk) 07:21, 30 April 2018 (UTC)[reply]
I stick by my "mud ape" idea from last time. This example illustrates how humans could rely on their ability to retreat safely to muddy, watery terrain (together with teamwork and spears, that is!) to get the upper hand over far more fearsome animals. I might notice that humans wading in muddy waters wouldn't have to worry much about getting their head hair immersed, since they have to breathe... Wnt (talk) 22:06, 4 May 2018 (UTC)[reply]
Another theory is that body hair got almost completely lost after the beginning of upright walking with the necessity of massive perspiration. Hairs on the head were retained as an isolation for the brain, hairy armpits and groin to minimize abrasion of damp skin. Beard and chest hairs were subsequently reintroduced to protect the lungs when man moved to cold regions.
By the way, buttocks didn't change shape because of long sitting (apes sit the same way as we do the whole day) but because the huge (in comparison to apes') butt cheeks are possibly necessary for us bipeds to keep the torso upright when standing and to pull the legs backwards when running. Some of this to be found by Desmond Morris. 194.174.76.21 (talk) 14:35, 7 May 2018 (UTC) Marco Pagliero Berlin[reply]
How often are all 8 planets on the same side of the sun?
How often are all 8 planets on the same side of the sun (i.e. in a 180 degree arc), when was the last time/will be the next time and are there any resonances among the planets that make it more/less likely than if there were no resonances. If things were completely independent, I believe that the answer would be 1/128th of the time (without loss of generality, assume that Mercury is the most counterclockwise in the arc, and then each of the other 7 have a 50/50 chance of being within 180 degrees clockwise of Mercury, so 1/(2^7).Naraht (talk) 14:17, 30 April 2018 (UTC)[reply]
Long-term predictions of the positions of the planets are not all that simple to work out; given the intricacies of an n-body problem with that many interacting bodies. As noted at the Stability of the Solar System, the movement of the planets is chaotic in the long term, as noted at Lyapunov time, the Solar System loses its useful predictability after 5 million years. --Jayron3215:10, 30 April 2018 (UTC)[reply]
Okay, but I think Naraht is asking for a simple and approximate answer, for which the effects you note are of secondary concern. Attic Salt (talk) 15:18, 30 April 2018 (UTC)[reply]
Not really. Let's say (I don't have the numbers at hand, but let's make some up), that the type of orientation Naraht is talking about only happens once every 10,000,000 years by some overly simplistic calculation. If that were the case, then such a calculation would beyond meaningless since the Solar System is chaotic on any scale larger than 5,000,000 years. It may not be on that scale; if it's every 1000 years or so, then we could work that out. I'm just noting the complexities of the problem. --Jayron3215:23, 30 April 2018 (UTC)[reply]
Regardless, it's a pointless academic discussion anyways, and I seem to have lead you all astray; it seems to happen on order of once every millenium or so; according to this the next time will be in CE 2492. --Jayron3215:53, 30 April 2018 (UTC)[reply]
I don't see anything in that linked article that mentions "millenium or so". Perhaps we might be confused by what is meant by "how often". I suppose the calculation by Naraht is about answering what "fraction of the time" are the planets all on the same side of the Sun. That the next time this happens is what I would call a "deterministic question". Assuming the source you cit is right, and the next time it happens is in year 2492, that would, indeed, be about millennium away from now, but the alignment would then persist for a duration of time. In other words, I don't think that having to wait a while is inconsistent with the possibility that the "fraction of the time" the planets are aligned is 1/128th of the time. Attic Salt (talk) 16:28, 30 April 2018 (UTC)[reply]
Presumably, the longest period of time at once that could be true would be 1/2 of a Mercurial year of 87 days, which would be 43ish days. Hypothetically, if both Mercury and Venus were aligned when the entered the same side of the sun as the other 6 planets, they would be able to squeeze in such 43 day windows 2 more times before Venus passed out of alignment. --Jayron3216:37, 30 April 2018 (UTC)[reply]
Okay, but I don't see anything wrong with Naraht's calculation regarding what fraction of the time the planets are on the same side of the Sun. Do you? Attic Salt (talk) 17:11, 30 April 2018 (UTC)[reply]
1/128th of what time period, though? It would be 1/128th of the time it takes for all 8 plants to "reset" to the same position; we'd have to do that calculation to figure out the amount of time we're talking about. I mean, if we mean 1/128th of a year, that's every 4 months. It doesn't happen that often. --Jayron3217:22, 30 April 2018 (UTC)[reply]
Well, clearly, over timescales much longer than the longest orbital period (Neptune), but shorter than the timescales over which the orbital parameters change. Attic Salt (talk) 18:33, 30 April 2018 (UTC)[reply]
I thought the OP's analysis was rather clever, if not entirely helpful. The duration of any one event is 44 days (half the orbital period of Mercury). I started to write a very boring orrery program to work out an approximate answer. But it was so tedious I gave up. Greglocock (talk) 10:30, 1 May 2018 (UTC)[reply]
Fun fact: this is called syzygy. There's a good Scrabble word. Note as stated in the article, sometimes this is used to mean an exact straight-line alignment of bodies (such as occurs in an eclipse), but it can also be used more generally to mean when all the planets in the Solar System are on the same side of the Sun. --47.146.63.87 (talk) 22:34, 30 April 2018 (UTC)[reply]
I like Naraht's idea of estimating the proportion of time that this condition holds, but I think that that's an underestimate because having Mercury most counter-clockwise doesn't include all possible combinations. Imagine an arc defined by ±90o around bisector of the (smaller) angle Mecury-Sun-Venus. This 180oC arc always includes both Mercury and Venus, then has a 1/(2^6)=1/64 chance of also including the other 6 planets. I think that even this is an underestimate of the proportion of time the 180o condition holds. As others have noted this doesn't help to determine the next time it will happen, but it's an interesting question by itself. Klbrain (talk) 23:27, 1 May 2018 (UTC)[reply]
Your probability is missing a factor 8. For each planet x, the chance that all the other 7 planets are within 180 degrees clockwise of x is 1/27 = 1/128. The 8 cases are mutually exclusive so the chance that at least one of them is happening at a given time is 8 × 1/128 = 1/16. A Monte Carlo simulation with 108 random constellations gave me 1/16.002. The longest possible duration of such an event is slightly longer than a Mercury orbit of 87.97 days. The planets rotate in the same direction. If all 8 planets are lined up exactly at some time then they are within 180 degrees from around 44 days earlier to around 44 days later. PrimeHunter (talk) 23:29, 1 May 2018 (UTC)[reply]
Last time was 07/14/10 to 09/09/10 (57 days). Last time before that was pre-2003 since the configuration of the gas planets made "everything on the same side" impossible from 12/31/2002 to 09/02/2009 (also 2/22/11 to 7/11/17). Next time is July 3 to August 30 this year (Counting Pluto doesn't change anything for as far as I checked (20/02/2002 20:02:20.02200220022002 to 2020)). Considering only Uranus and Neptune, 1993.3 is when they lapped each other essentially removing 1 planet from the odds, 87 years later in 2080.1x is the next time they're on opposite sides of the Sun making it 1/64tb of the time instead of 7/64th of the time. From 7/11/17 to 9/24/28 the gas planets allow, if it's not all on same side for 4,093 uninterrupted days it's the rock planets' fault. Also all gas planets will fit within 72.2 degrees in 2024 — the smallest in 164 years (1997 to 2161). These things will probably make the next decade a fairly good time for "all planets on the same side of the Sun." Sagittarian Milky Way (talk) 08:17, 2 May 2018 (UTC)[reply]
Astrology software. Their positions are extremely good the times I've compared them with the official Jet Propulsion Laboratory (U.S. spaceprobes) ones so I think they're accurate. The version that makes it so easy to find these costs money, I don't know if I want to give free advertising. Sagittarian Milky Way (talk) 16:19, 2 May 2018 (UTC)[reply]
What makes it so difficult to circulate blood with pumps (even external to the patient) and without a heart at all? Blood pump is about something else, but recently a man in Prague survived 6 months with mechanical blood pumps. Wouldn't that be useful for some extremely ill patients? --Doroletho (talk) 15:45, 30 April 2018 (UTC)[reply]
The article could benefit from some expansion around the difficulties of it. It recognizes that "A synthetic replacement for the heart remains a long-sought "holy grail" of modern medicine. " but "embodies subtleties that defy straightforward emulation" is rather a short explanation. I imagine this "subtleties" are maybe reaction to hormones and a two-way neuronal connection to the brain. --Doroletho (talk) 16:03, 30 April 2018 (UTC)[reply]
For any given definition of "success" there have been some successful such transplants, the AbioCor never made it out of clinical trials, but a few patients lived over a year with it. Others mentioned in the article are in various states of development and trials. --Jayron3216:26, 30 April 2018 (UTC)[reply]
I don't think that the autonomic issues is a real problem (feedback systems are fairly straighforward to implement with a pressure sensor). Rather, its damage to the blood cells as they pass through an un-natural pump undergoing un-natural motion, leading to ""pump thrombosis, and hemolysis".[1] To reduce the thombosis, anticoagulants can be given, but they increase the risk of bleeding. Klbrain (talk) 23:42, 1 May 2018 (UTC)[reply]
References
^Rosenthal, JL; Starling, RC (December 2015). "Coagulopathy in Mechanical Circulatory Support: A Fine Balance". Current cardiology reports. 17 (12): 114. doi:10.1007/s11886-015-0670-0. PMID26482757.
Some things that come to mind, though I won't say for sure they apply, are: a) the intrinsic clotting pathway - essentially, blood expects to circulate in a system coated in living endothelium, and when it touches almost anything else there is a chance it will decide there is damage and a reason to clot. b) the atrium, a flexible chamber, with no valve at the rear and with just a little bit of muscle to pump, which accommodates inflowing blood while the atrioventricular valve is shut, in order to give it a way to smoothly keep moving forward and circulating so there is no water hammer effect during that time. Note that even atrial fibrillation causes clotting and can lead to death, so a pump would have to really get that down right. I don't know what they actually do for atria. Also c) I wonder if the muscular contractions and fleshy valves of the heart might have an effect to minimize shear force within the blood compared to an artificial system. Wnt (talk) 13:38, 3 May 2018 (UTC)[reply]
Note that wikt:Lycaon traces back to wikt:λύκος, which claims a Proto-Indo-European heritage. While perhaps the legend might have influenced the precise form of the scientific name, it is basically a grab bag of post hoc efforts to explain the deeds of "Wolf" as an anthropomorphic figure. Wnt (talk) 21:14, 2 May 2018 (UTC)[reply]
May 1
Abortion pill, surgical abortion, and natural abortifacients
While there is an ongoing debate about the abortion pill and surgical abortion, I wonder whether people have considered natural abortifacients to be just as dangerous. "Brewer's yeast, vitamin C, bitter melon, wild carrot, blue cohosh, pennyroyal, nutmeg, mugwort, papaya, vervain, common rue, ergot, saffron and tansy. Animal studies have shown that pomegranate may be an effective abortifacient." Some of them seem to be common household ingredients that can be purchased at the grocery store, and there aren't bans on those things. Anyone can go out and buy yeast, vitamin C tablets, bitter melon, nutmeg, papaya, and pomegranate at a supermarket. Does this mean that a pregnant woman who want a pregnancy have to watch out for those ingredients to make sure that they don't accidentally abort a fetus? SSS (talk) 03:51, 1 May 2018 (UTC)[reply]
No. Basically, once you cut out anecdotal evidence (both modern and ancient), "natural health" websites that are only pretending to present science, and studies of feeding rodents simply infeasible amounts of concentrated food extracts, there is no evidence that any of that crap works. Someguy1221 (talk) 04:31, 1 May 2018 (UTC)[reply]
There certainly are effective plant-based abortifacients. There is any active disinformation campaign by religious loons to sow doubt and confusion about them. It seems that you are either one of them, or have been fooled by them. Abductive (reasoning)07:17, 1 May 2018 (UTC)[reply]
I have never heard of this "disinformation campaign"; perhaps you have a source to share? I think not just people religiously opposed to abortion, but also mainstream physicians, will advise against self-administering "plant-based" abortifacients. A number of deaths have been attributed in particular to pennyroyal (Mentha pulegium), which may well "work", but only in doses that are dangerous to the woman as well. --Trovatore (talk) 07:40, 1 May 2018 (UTC)[reply]
A lot of things can likely cause abortion if ingested in sufficient quantities. Unfortunately they tend to kill or sicken the mother as well. --47.146.63.87 (talk) 04:58, 1 May 2018 (UTC)[reply]
A little, maybe, but many of those things only have an abortifacient effect in very high amounts, more than anyone would likely ingest normally. It's probably a good idea to stay away from loosely regulated things like herbal supplements, especially those with ingredients that lack much quality research. Approved abortifacient drugs are reasonably safe, and certainly much safer than attempting an abortion with untested and dangerous methods. (Of course, I recognize many women are driven to the latter by desperation if they can't access medical abortion.) Let's not forget that pregnancy is fairly risky in itself. A lot of overblown claims about these drugs' dangers come from anti-abortion activists who want to scare women away from considering an abortion. --47.146.63.87 (talk) 04:58, 1 May 2018 (UTC)[reply]
Its effectiveness as an abortifacient is rather questionable, but nutmeg may cause poisoning and has psychoactive effects:
"In the 19th century, nutmeg was thought to be an abortifacient, which led to numerous recorded cases of nutmeg poisoning.[1] Although used as a folk treatment for other ailments, nutmeg has no proven medicinal value.[1]"
"Nutmeg poisonings occur by accidental consumption in children and by intentional abuse with other drugs in teenagers.[3] Fatal myristicin poisonings in humans are rare, but three have been reported, including one in an 8-year-old child and another in a 55-year-old adult, with the latter case attributed to a combination with flunitrazepam.[7]"
"Nutmeg intoxication can vary greatly from person to person, but is often associated with side effects such as excitedness, anxiety, confusion, headaches, nausea, dizziness, dry mouth, redness in eyes, and amnesia.[1][3] Nutmeg poisoning is also reported to induce hallucinogenic effects, such as visual distortions and paranoia.[3] Although rarely reported, nutmeg overdose can result in death, especially if combined with other drugs.[3] Intoxication takes several hours before maximum effect is experienced.[1] The effects of nutmeg intoxication may last for several days.[2][3]"
"Nutmeg was once considered an abortifacient, but may be safe for culinary use during pregnancy. However, it inhibits prostaglandin production and contains hallucinogens that may affect the fetus if consumed in large quantities.[8]"*
"While the spicy scent of nutmeg may be attractive to pets, there is potential for toxicity if large amounts are consumed.[9][10]"
^Stein, U.; Greyer, H.; Hentschel, H. (2001). "Nutmeg (myristicin) poisoning--report on a fatal case and a series of cases recorded by a poison information centre". Forensic Science International. 118 (1): 87–90. doi:10.1016/S0379-0738(00)00369-8. PMID11343860.
Information about abortifacient herbs in the U.S. has been corrupted by the effects of the blatantly unconstitutional but highly successful Comstock Law, and likely others abroad. (This was resisted by revered American anarchist Lysander Spooner, whose delivery service was put down for political reasons but made it possible for a more primly Mormon outfit like UPS to fight its way to legality) Attempts to recover lost witchcraft and folk traditions are ongoing, but it appears that abortion by herbs was probably not very safe or very sure ([2][3][4], from a PubMed search for pennyroyal abortion). But competence is the first casualty of censorship, which often stops the best aspects but never the worst of what it complains about. Wnt (talk) 12:18, 1 May 2018 (UTC)[reply]
Remember folks, laws only stop beneficial things, and if its been regulated by the government, that's because its the best thing ever, and if the government only didn't regulate it, the entire world would be healthier, happier, and would never get sick or hurt ever again! --Jayron3216:21, 1 May 2018 (UTC)[reply]
@Jayron32: Anyone interested can read Comstock Law and decide for himself. Although the stock value of freedom is plummeting fast, and would be given a Sell rating by any competent broker, I don't think the world has fallen quite so far so fast that many others would stick up for this yet. Wnt (talk) 01:39, 2 May 2018 (UTC)[reply]
If the lens is convex, it will focus light toward the centre, but the eye or face will be too close for the focus to a small area. Looking at the Sun is not a good idea in any case. For concave lenses the light is spread out, but then the skin just outside the shadow of the glasses will then get a double done, direct sunlight and light spread by the lens, and then get more solar damage. Graeme Bartlett (talk) 10:42, 1 May 2018 (UTC)[reply]
They don't "amplify" it, as that would need some additional source of energy to be added (see laser).
They can concentrate or focus it though. This is a recognised source of potential fire risk, often when people leave their reading glasses on a sunlit desk, or on a car dashboard. Corrective glasses are of broadly two types: to correct short sight (myopia) or for long sight (hyperopia). These require a change in the focussing power of the lens, so can have this focussing effect. Glasses for short sight are concave and so have a divergent effect - they will not focus light and act as a burning glass. It's glasses for long sight (or reading glasses) which are convex and so can act as a burning glass.
As far as staring at the Sun goes, they make it no worse than it would be for a perfect non shortsighted eye would be. Yet that's not itself a good thing, as the eye naturally focusses on the retina.
There's a famous blooper in the novel Lord of the Flies wherein a group of shipwrecked schoolboys includes "Piggy", a stereotypical fat, nerdy kid, who wears glasses. These glasses are part of a power struggle on the island, as their means of starting a fire. Yet Piggy is short-sighted, so his glasses would have been no use for this. Andy Dingley (talk) 10:52, 1 May 2018 (UTC)[reply]
I remember trying to convince my English teacher of that error, being a shortsighted thin nerdy kid, but had to wait for a sunny day to prove my point. Alansplodge (talk) 12:07, 1 May 2018 (UTC)[reply]
The same error occurs in an early episode of Doctor Who: the Doctor's spectacles ignite some papers, and it is implied that this was the beginning of Nero's fire. —Tamfang (talk) 05:16, 3 May 2018 (UTC)[reply]
Corrective lenses merely cause the incoming light to be focused on the retina as accurately as the natural lens of the eye focuses light for a person that has perfect vision. Thus, the corrective lenses may increase damage, not not beyond the damage a person who does not need them would get. The glasses will in fact also filter out some of the UV, reducing total damage. -Arch dude (talk) 19:17, 1 May 2018 (UTC)[reply]
Dinosaur skeletons
On many dinosaur reference pages, photographs of the "dinosaur skeleton" are labeled as "reconstructed skeleton." This is inaccurate! A real "reconstructed skeleton" would contain all real, fossilized parts. Most skeletons in dinosaur displays around the world (and pictured in Wikipedia) are man-made materials with very few original fossilized bones included (maybe a leg bone or two, and a vertebra or so). In fact, many of them are only scientific guesses at what these creatures looked like! I believe it would be more appropriate to refer to these as "Concept skeleton including fossilized components." Does anyone else agree?Palw49 (talk) 16:08, 1 May 2018 (UTC)[reply]
I'm afraid this isn't the right venue to seek help with this issue. The correct place to ask would be at Wikipedia talk:WikiProject Dinosaurs, which is where you will find editors interested in Dinosaurs who can respond to your question. I would just ask the question there rather than here. --Jayron3216:19, 1 May 2018 (UTC)[reply]
[Edit conflict] You are incorrectly restricting the word "reconstructed" to only one of its accepted meanings. For example, it is common to refer to crime reconstruction, which does not require either every single fact about the crime (which if available would make the exercise unnecessary), or recommitting the crime in question! {The poster formerly known as 87.81.230.195} 2.218.14.51 (talk) 22:10, 1 May 2018 (UTC)[reply]
Yep. Palw49's complaint would go likely nowhere, since a quick perusal of the paleontological literature shows that "reconstruction" is used in a much broader way than Palw49 would like it to be. Wikipedia matches the vocabulary used by subject-matter experts, even it it offend's one reader/writer's preferred definitions. Someguy1221 (talk) 22:08, 1 May 2018 (UTC)[reply]
There was a news story yesterday about someone finding a fossilized horse on their property, intact except for the head. It's reasonable to suppose that when or if the fossil is displayed in a museum, they would include a plastic model of its skull in order to make an attractive exhibit. ←Baseball BugsWhat's up, Doc?carrots→ 11:51, 3 May 2018 (UTC)[reply]
Anti-anthropogenic return to our natural greenhouse
If earth's human society catastrophically (or miraculously) instantly stopped emmitting greenhouse gasses into the atmosphere, how long would the earth take to resume normal (pre-human intervention) atmospheric insolation (Is that the right word? It might not be.) conditions? I'm not asking about a return to normal climate because things like ice caps, which effect climate would take ages to recover. (I imagine the recovery would take as long as the damage took - perhaps centuries?)
Posed differently, what if a social or biological or economic upheaval relatively instantly interrupted all or, let's say, all significant anthropogenic greenhouse gass emmisions, what would happen to the atmosphere then and how quickly?
I think I remember a geography professor once telling me that the correct answer could be measured in weeks.
I nearly wish I hadn't: "If we stop our emissions today, we won’t go back to the past. The Earth will warm. And since the response to warming is more warming through feedbacks associated with melting ice and increased atmospheric water vapor, our job becomes one of limiting the warming. If greenhouse gas emissions are eliminated quickly enough, within a small number of decades, it will keep the warming manageable and the Paris Agreement goals could be met. It will slow the change – and allow us to adapt. Rather than trying to recover the past, we need to be thinking about best possible futures.". Ack! Hayttom (talk) 17:59, 1 May 2018 (UTC)[reply]
Some of the CO2 will last forever on the scale of human history, but it's a relative blink of an eye in terms of Earth's history. Half the excess CO2 will be removed in 30 years, and another 30% within a few centuries. The rest will linger for thousands of years[5]. Someguy1221 (talk) 19:18, 1 May 2018 (UTC)[reply]
Because CO2 stays in the atmosphere a long time, warming will continue but stay in the arbitrarily-defined "acceptable" range if we stop emitting it now. To get back to pre-human levels of CO2, we would need to actively remove it from the atmosphere, via Carbon sequestration of some sort. Note that "pre-human" is lower that "pre-industrial", since humans have been adding CO2 via deforestation for a long time. -Arch dude (talk) 19:10, 1 May 2018 (UTC)[reply]
It's not really "arbitrary"; it's based on what is likely to keep warming to a relatively manageable amount. Beyond that, the effects of warming get worse, and there's increased fear of triggering feedback loops that would push the temperature even higher. I mean, okay, yes, 2 degrees versus 2.1 is kind of arbitrary, but you have to pick somewhere. --47.146.63.87 (talk) 00:29, 3 May 2018 (UTC)[reply]
It seem arbitrary to me. I Have no confidence that a 2-degree warming will be manageable. we have no way of knowing that it will not kick off an feedback loop. The only way to find out is to try it which is a lot testing your food for poison by eating it. -Arch dude (talk) 04:09, 3 May 2018 (UTC)[reply]
In what stage the muscle cell should get the stimulus?
I came across this presentation in which they write that there are 4 steps in muscle contraction: "1. Excitation = nerve impulse, neurotransmitter & excitation of myofiber 2. Coupling = ATP & calcium ions 3. Contraction = muscle cells shorten 4. Relaxation = muscle cell resume normal resting length (ATP)". My question is why the 1st steps isn't considered as relaxation? (I understand that the impulse should not come in the period of relaxation). Based on the reading here on Wikipedia it seems here that the time that the muscle should normally get the stimulus is the latent period. Isn't it? 93.126.116.89 (talk) 00:28, 2 May 2018 (UTC)[reply]
The relaxation period is the time during which the muscle fibers are changing from a contracted state to a resting state. Once the fibers stop changing, the relaxation period is over. Stimuli that arrive during the relaxation period will usually not be fully effective. Is that clear enough? Looie496 (talk) 13:44, 2 May 2018 (UTC)[reply]
Is the Lepton Number of the Universe a large negative value?
Assuming the Universe's Lepton number started at zero, the electron surplus was balanced by anti-neutrinos and Lepton number was conserved (or at least randomly even) thereafter, then shouldn't the Lepton number of the Universe today be a large negative value?
The problem is the No-hair theorem. Every black hole has a lepton number of zero, no matter how many electrons it eats. Since electrons tend to cluster in galaxies where black holes lurk while neutrinos are spread more evenly the overall balance favors anti-leptons over leptons.
If so, what's the current deficit? Around 1% of the total number of electrons, more or less?
Unless I'm missing something, the no-hair theorem the no-hair theorem doesn't say that the black hole can't have a lepton number, just that the lepton number of the black hole can't affect the externally observed parameters (i.e. gravitational and EM properties). Given that there's no way any of the decays which the lepton number is used to explain could occur within a black hole and have an effect outside it, and no limit on the total lepton number for the black hole, I can't see how a contradiction would arise. (of course, whether it's more meaningful to consider a universe with 0 total lepton number but a load of high lepton number black holes, or a universe with a steadily decreasing total lepton number is likely a pretty arbitrary distinction). MChesterMC (talk) 10:58, 2 May 2018 (UTC)[reply]
This paper makes an argument, which I have skimmed in roughly 45 seconds, that seems to be that any other quantum number should have some GUT to explain it that implies that the number isn't really conserved, so black holes with tremendously long lifetimes (or high evaporation energy?) won't. I'll leave it to a better physicist to give a genuine read on this. Wnt (talk) 21:19, 2 May 2018 (UTC)[reply]
Air changes per hour
What is the air changes per hour of a house that is insulated well and has energy efficient double pane windows? I know someone who says that if I cook something with onions and can smell onions the next day that means that the same air from the day before is still there and has not exchanged with outside air. Is that true or false?--User777123 (talk) 04:32, 2 May 2018 (UTC)[reply]
Anecdote is not data, but I agree with /someone/. In our modern energy efficient house I can smell the curry that was cooked the previous day. In my non energy efficient house it clears within a couple of hours. Funnily enough when I asked the builder for the first house to vent the extractor fans to the air rather than the attic he said no. Greglocock (talk) 07:33, 2 May 2018 (UTC)[reply]
Does air changes per hour point you in the right direction? As to the second query, this can be trivially falsified: chemicals from cooking can settle on surfaces. Also, some, but not all of the air may linger. --47.146.63.87 (talk) 07:36, 2 May 2018 (UTC)[reply]
Yes, agreed; this sounds like a "technically true, but practically not so much" kind of thing. Okay, so you fried up some onions yesterday. Assuming the food was eaten, was the pan washed thoroughly? Was the splatter from the oil all wiped up, including the tiny amounts that travel all over, such as the floor? Has the cook themselves washed? Odoriferous compounds could be lurking in many, many places around the kitchen, re-odorizing even perfectly fresh clean air. Matt Deres (talk) 14:27, 2 May 2018 (UTC)[reply]
Onion is particularly hard to clean up odors from; the odiferous compounds are a class of sulfur-containing compounds called thioketones which cling to just about any non-polar hydrocarbon out there, which includes oils (such as are found in skin) and plastics, and such compounds are fantastically resistant to soap as well. There's some reports out there that the smell can be removed by rubbing with a metal object, but this feels (speaking as a chemist) likely hokum; in my experience the only things that work are vinegar or bleach. --Jayron3215:53, 2 May 2018 (UTC)[reply]
Yeah, a cool trick is to boil a pot of vinegar on the stove for about 30 minutes. That will knock down all kinds of cooking odors clinging to curtains, wallpaper, etc. Heaviside glow (talk) 20:18, 2 May 2018 (UTC)[reply]
Can those very big square batteries for flashlights leak if stored for years?
All batteries can corrode and leak if improperly stored. I assume you mean a Lantern battery, and there are dozens of different chemical compositions of such a battery, including wet lead acid versions and dry cell versions, so knowing what it is made of will help you decide how to properly store it. Here is some general advice on how to properly store batteries. --Jayron3217:17, 2 May 2018 (UTC)[reply]
Some lantern batteries (especially ones sold as "heavy duty"[6]) are still zinc/carbon chemistry. Those will absolutely leak all over the place. Other lantern batteries are alkaline batteries[7], just like most normal AAs and will have a similar shelf-life.
Either way, don't count on the battery holding together forever. If you're storing them long-term, there's no harm in assuming they'll leak and taking appropriate precautions. (Like taking them out of devices, and not putting them near anything precious.) ApLundell (talk) 19:17, 2 May 2018 (UTC)[reply]
Batteries have an expiration date/shelf-life. Sometimes it's printed on the package, and not on the battery though. Anyway, I'd say that when properly stored, they won't leak. By properly stored I mean the temperature, humidity they are exposed to. And also whether they are kept mixed with metal objects that could cause a short circuit.--Doroletho (talk) 17:37, 2 May 2018 (UTC)[reply]
Yes. My experience is that it's batteries left in inert devices that are most likely to leak. Inert devices also tend to be left in places that exacerbate the problem: garages and work sheds with little or no temperature and humidity control. Add a little Murphy's law in there and there you go. Matt Deres (talk) 19:38, 2 May 2018 (UTC)[reply]
May 3
program or website to identify stars/constellations?
Sky photoSky map of HST pathHST path MAy 4, 2018HST trail #1HST trail #2
The reason I'm asking is this. I've tried several times in the last few weeks to get a time exposure photo of the Hubble Space Telescope in orbit. I haven't been able to get it. Here is some of my attempt from last night. From the sky map, it rises in the west, goes through the belt of Orion and proceeds until it goes into the shadow of the Earth. It is magnitude 1.5-1.6 just before it goes into the shadow. I took a series of 30 6-second exposures and this is the one that was at 21:58 - the point circled. (The clock in my camera is 16 second fast, but I used a different clock.) I think it should show a short streak. (In other attempts I've tried 20- and 30-second exposures.) Anyhow, I can't see a streak for the HST (there are two airplane streaks lower down.)
The problem is that I can't match the stars in the photo with the ones in the star map, so I'm not positive that I got the right area. The photo shows a lot more stars than are normally visible. You might need to take it into software and reduce the exposure to make it look more like what you actually see. The HST path is from Heaven's Above and I double-checked it with Stellarium.
Thanks, that looks pretty much like the photo - the belt of Orion is near the bottom, about 1/3 of the width from the right and Sirius is about 1/4 of the way from the left, near the streak of an airplane. Then the HST is outside the frame of that photo. I don't see it in any of the photos, and they start about the time it is near Orion's belt. However, there it is much dimmer - 4th to 5th magnitude. And with it moving, maybe it isn't bright enough to show up over the background. It only gets bright just before it goes into the Earth's shadow. I can't see stars through the camera unless they are about as bright as Sirius so I take a wide-angle lens and point in the general direction. That usually works - I've gotten the ISS and Iridium flares that way. But the Hubble is not as bright. Bubba73You talkin' to me?17:06, 3 May 2018 (UTC)[reply]
That match of the image to the star map doesn't look very good. In Gemini (upper right), the green lines end nicely at the stars, but in the lower left they are way off. The green lines near the r in Canis Major should end at Sirius, which is further up and right. The scale of the map is larger than the scale of the image. Maybe the matching software assumed the wrong scale for the image, or the wrong distortion? As I read the prediction and the image, the path of HST would be expected in the upper left of the image.
When carefully examining the image, I can see three aircraft tracks: one close to Orion's belt, one down-right from Sirius and one at the same level near the left edge of the image. I also see one satellite track, in the upper right of the image, passing near ε Geminorum. It's quite bright, so it must be a big satellite. It runs in the right direction for HST, but in the wrong position. So either that is HST, and the position is off because the prediction used the wrong location for your camera or the wrong true anomaly for HST, or it was a big, unknown satellite that happend to be passing over the same part of earth, in the same direction at the same time. That's possible, of course.
As HST has no propulsion, I expect the published orbital elements to be quite accurate at all times. I've always found predictions from stellarium or gpredict of ISS passes highly accurate. But I've never seen HST myself to check, as I live too far north. PiusImpavidus (talk) 10:40, 4 May 2018 (UTC)[reply]
Indeed, the green lines are quite a bit off. The extraction image looks better and indicates that the software identified the stars correctly. I can imagine that there might be problems with capturing the huge field and the strong distortions in the world coordinate system, i.e. fitting a model to describe the mapping between pixel coordinates and sky coordinates. The green lines have to be shifted up a little bit, which makes it even more likely that HST was outside the frame. --Wrongfilter (talk) 11:03, 4 May 2018 (UTC)[reply]
I noticed the airplane trails but not the satellite trail. I've tried about six times to capture the HST in a time exposure the last few weeks but always failed (I've been able to get the brighter ISS and Iridium flares). (And I've triple checked my clock and my location.) I wrote to the Heavens Above guy about it and he says that he checked the HST orbital elements. For a couple of passes I've double checked with Stellerium and it seems to agree with Heavens Above. I'm trying again for the HST in less than 2 hours (using a somewhat wider-angle lens)... Bubba73You talkin' to me?23:49, 4 May 2018 (UTC)[reply]
I finally got it
First, thanks everyone! I finally got the HST but the results are not too impressive (see above). Here is a link to astrometry for tonight's photos. The map shows it just above Antila when it is its brightest (magnitude 1.9). You can see it near the left edge, about half way up. (One of the photos shows two fireflies - probably one blinking twice.) For some reason, I have my camera set to make a RAW file and a JPEG file, but tonight it made two JPEGs instead of a RAW, which gives me less to work with. The overall problem is that at magnitude 1.9 and moving (rather than staying in one place to gather a brighter spot), it is almost lost in the light pollution. These are 10-second exposures. Bubba73You talkin' to me?03:04, 5 May 2018 (UTC)[reply]
I was watching Lost in Space where I often see that some of mountain peaks are leaned over on a fictional planet. What are those geological features and how they form?; though I never seen pictures of such a feature taken from Earth. To understand what I'm talk about, go to [8] and look in the background. PlanetStar07:07, 3 May 2018 (UTC)[reply]
This reminds me of Rodney Matthews, who has done it often; also Crematoria in Chronicles of Riddick. As we don't much see such formations on Earth they seem fantastical and otherworldly, but they are also unlikely. That said, an alien planet that is tidally locked or has other strange factors affecting its winds, or unusual materials, cannot necessarily be predicted from our experience. The most fantastic formation I can think of at the moment here (apart from small stone arches and such) is the Dragon Tooth Mountains, but those go straight up. (I'm not sure what I did wrong with the link but there are lots of search results, see [9] for example)Wnt (talk) 11:32, 3 May 2018 (UTC)[reply]
Rock overhangs exist, but are very limited in size. However, this depends on the strength of the rock and its weight. A material like ice would do better, and low gravity would help. A bigger wildcard is the effect of living organisms - if a planet's microbes evolve carbon nanotubes they might maintain a far larger overhang in order to obtain some nutrient or respiratory need from the winds. (Which should bring us to note that, in alien contexts, there could be a smooth gradation in meaning between a "mountain" and a "tree") Wnt (talk) 13:29, 3 May 2018 (UTC)[reply]
I believe that a group of rock overhangs that stretch for thousands of feet appearing like a mountain tipped over exist on some planets and moons. Maybe fiction-style overhangs exist on Mercury and planets around TRAPPIST-1. PlanetStar07:32, 6 May 2018 (UTC)[reply]
Free fall mechanics
Terminal velocity says in particular: "You can drop a mouse down a thousand-yard mine shaft; and, on arriving at the bottom, it gets a slight shock and walks away. A rat is killed, a man is broken, a horse splashes. For the resistance presented to movement by the air is proportional to the surface of the moving object". I don't much doubt it, but in theory this is paradoxical due to two factors: The larger the surface area, the more aerodynamic drag the falling object experiences and as such a falling horse (or any other larger animal or object) should fall somewhat slower than mouse. Also, due to larger surface area a horse should have less damage upon landing, because of more even pressure distribution upon impact (similar to ski's pressure on snow). Is it because upon impact there's a greater net force due to larger surface area which offsets those factors? 212.180.235.46 (talk) 20:02, 3 May 2018 (UTC)[reply]
Most of these issues are to do with a ^3⁄2 power scaling law with size, from the ratio of volume (length^3, controls mass and weight) and area (length^2, controls strength and air resistance). Pennycuick's Newton Rules Biology (1992) ISBN0198540213 is one of my favourite books on this. A horse will be stronger (bone cross-section) and draggier for air resistance, but it's also heavier (more downward force to accelerate it, more momentum to damage it) and as this ratio between the two factors increases at the ^3⁄2 power, larger animals become more susceptible. Andy Dingley (talk) 20:23, 3 May 2018 (UTC)[reply]
The mouse thing seems not implausible, I once threw a mouse as hard as I could against hard bathroom stuff and it squealed horribly 4 times then limped away (I accidentally glued it to my fingers while making sure it didn't escape during its humane removal. Okay no problem, just softly flick it into the container, stronger flick, still glued, even stronger, then I got scared that that might've triggered its self-preservation fear enough to contort its head enough to bite me (which would hurt like hell since I have very high pain sensitivity) and possibly give me rabies or something so I flicked it as hard as I could and it didn't become unglued till it was near top speed) A baseball is much heavier, roughly similar density and a terminal velocity of ~95mph so maybe. Sagittarian Milky Way (talk) 21:07, 3 May 2018 (UTC)[reply]
...
This does not sound like an appropriate way to remove a mouse. If you aren't able to humanely remove or kill the pest, call a pest removal specialist, so that you aren't causing unnecessary suffering for either the humans or the animals in the area; nor creating a mess.
I was planning to use oil to take as much glue trap glue off as I could in several minutes (without air deprivation or touching his eyes) and depoil it with soap and gently put it in a container to release in the middle of a block wide buildingless area. (it was summer) But the oil must've only dissolved glue in the outer fur layer or something. I left it sustenance the rest of the time I was there (weeks or months) but it never stopped limping so obviously I agree glue trap and release is a not a good method. Of course letting them thirst to death on the glue trap like many people do isn't humane either. The ones stores sell that seem less likely to snap on his torso seem more humane. Sagittarian Milky Way (talk) 22:46, 3 May 2018 (UTC)[reply]
LOL, whole *point* of a glue trap is to torment the mouse... but admittedly, hiring the illegal immigrants you let in the country to kill the mouse you don't want to hurt is a way to take care of multiple problems. :) Wnt (talk) 23:58, 3 May 2018 (UTC)[reply]
This article by Cecil Adams is at least somewhat relevant. It discusses the fact that for cats, for falls above a certain height, the survival rate stabilizes at more than zero. Apparently some studies suggest that the worst height for a cat to fall is about seven stories, above that it switches its strategy from "always land on feet" to "spread out to slow fall", and that strategy sometimes works.(For cats, that is.) ApLundell (talk) 03:10, 4 May 2018 (UTC)[reply]
Yeah, cats land on piles of other cats. Or possibly I meant a "survival rate of more than zero", and have now fixed it. ApLundell (talk) 18:48, 4 May 2018 (UTC)[reply]
AD adequately explained above why the horse's terminal velocity is higher (weight goes as volume, drag as surface (roughly), hence the speed at which drag compensates weight is higher for large animals). The second question (more even pressure distribution upon impact for larger bodies) is correct in assuming that there is a higher "force" at impact for a larger body (modelling of collisions is a complex topic, but as a very first approximation you can consider that what matters is how much kinetic energy has to be dissipated in which amount of time and surface; for the same speed, the kinetic energy goes as mass hence volume, and the collision surface goes as cross-section).
As for the ski remark, I assume this is related to the fact that ski jumping exists (and is not a suicide method when practiced with care) whereas falling from an equivalent height would often be fatal. However this is not due to skis dissipating the impact over a larger surface (if anything, ski area is smaller that a cross-section of human falling flat in the snow). The key point is that as the skier falls over a downward slope while still advancing in the slope direction, the relative velocity of impact is smaller (or equivalently the kinetic energy is not completely dissipated at impact, the skier continues to move). Also, the elasticity ("wobbling") of the skis may allow to release the energy over a longer period of time, but I have no idea whether that effect is significant. TigraanClick here to contact me16:44, 4 May 2018 (UTC)[reply]
I have used weak analgesics to deal with minor pains with significant success, but not to the level of completely eradicating the pain. My question: would a strong analgesic, e.g. morphine, in a high dose, completely eradicate the pain of say, a sharp pinch, in most people?--Leon (talk) 07:44, 4 May 2018 (UTC)[reply]
Per the lead of our article analgesic: Analgesic drugs act in various ways on the peripheral and central nervous systems. They are distinct from anesthetics, which temporarily affect, and in some instances completely eliminate, sensation.. While this does not answer your question as stated, if the real question is whether complete pain suppression is feasible, the answer is yes. TigraanClick here to contact me16:48, 4 May 2018 (UTC)[reply]
There must a limit to how long complete surgical anaesthesia is feasible for. A highly specialized very well paid physician (anesthesiologist) has to watch the pulse, breathing and stuff all the time to make sure level of consciousness stays between subconscious and cardiac arrest, I think there's long-term toxicity or something (I am not a doctor), at the very least the muscles would waste away like the NASA Bedrest Study, it'd be ludicrously expensive, and even if those weren't the case waiting for complete anesthesia without bad side effects like unconsciousness, small therapeutic range or addictability to be invented might require decades or centuries passing for the person in an instant like time travel and not everyone would want to do that. Sagittarian Milky Way (talk) 20:25, 4 May 2018 (UTC)[reply]
The difficulty in answering questions like this is that there is no objective way of measuring pain. The standard way that doctors measure pain is by using what is called a numeric rating scale: "On a scale of 0 to 10, where 0 represents no pain and 10 represents the worst imaginable pain, how would you describe your pain?" (See our pain scale article for further information.) The fact is, when people are given large amounts of morphine, most of them answer with 0. Looie496 (talk) 21:16, 4 May 2018 (UTC)[reply]
Morphine is only a little better than a sugar pill where bone metastases are concerned, and then there's nausea, and pain from tremendous constipation (despite everything). If you think 20 years is long enough for an ex-smoker to breathe a sigh of relief, I know someone who can prove you wrong... Wnt (talk) 21:59, 4 May 2018 (UTC)[reply]
Since morphine and other strong pure mu-opioids (fentanyl, etc) only block respiratory drive, a patient who is intubated and watched by an anesthesiologist can be given enough morphine ALONE for general anesthesia. That means coma and no pain, so that is your answer (unless you demand preservation of consciousness, and then the answer is "no"). This has been tried: back in the days when available gas anesthetics were either flammable or depressant on the heart, morphine-alone was actually sometimes used for anesthesia in open-heart surgery (we have better gas anesthetics now). I'd hate to have to do that on a heroin addict, but it works with the non-opioid dependent. For all I know it works with everybody, if you can get enough opioid in. As a practical matter, you might deplete your pharamacy stock first. SBHarris22:34, 4 May 2018 (UTC)[reply]
some birds photographed near the Port of Anchorage
This is a photograph I took near Port of Anchorage late in the afternoon yesterday. Heavy cloud cover, 40x zoom, camera not designed for low light, so it turned out a little bit grainy. justinacolmena (talk) 17:19, 4 May 2018 (UTC)[reply]
Yes, thank you. It was a little bit dark and hard to see under those clouds. One of them was catching fish in that stream, but I was not able to catch a photo with the fish in its beak. justinacolmena (talk) 18:20, 4 May 2018 (UTC)[reply]
Is the finger in dam short story scientifically possible?
1470 pounds per square inch through a 20mm pipe is only 100 cubic meters per hour, not enough to flood quickly. If the property damage of 100 cubic meters per hour was worth shivering all night to prevent it probably wouldn't have been deserted enough that he wasn't discovered for so long. If it'd erode away to unstoppable breach size in the short time it'd take to get help then that's certainly not a very gracefully failing dam design at the least. Yet his finger could keep the breach the same size all night. Sagittarian Milky Way (talk) 20:08, 4 May 2018 (UTC)[reply]
No, it is not plausible; in an earthen dam, most of the water loss is caused by flow directly through the dam, not through any leaks or holes. Here's a free set of lecture notes from Waterloo's civil engineering department: Seepage in Earth Dams..., pretty standard textbook stuff.
While the main point of a moral story is not its physical plausibility, I don't think you've properly analysed it. You're contrasting the flow through an unobstructed but fixed-diameter pipe with that through an unobstructed and erodable (hence ever-enlarging) hole. However, in the scenario of the story the child's finger blocks the hole so that there is no flow, and hence no erosion. {The poster formerly known as 87.81.230.195} 2.217.209.143 (talk) 23:19, 4 May 2018 (UTC)[reply]
May 5
Is there a way to connect a headset (heaphones and microphone) to a fax machine?
What do I need to connect a modern headset to an old corded Sharp fax machine (UX-P710)? The device has no dedicated headset port. I have read that I need a rather expensive amplifier and dedicated headset (≈ €200/US$220). Is there a more economical solution? The fax machine has a RJ9 4P4C plug on the handset.--Carnby (talk) 11:44, 5 May 2018 (UTC)[reply]
There are 1/8" jack to 4-wire phone adapters. It isn't much of an adapter. It is hard-wired. They go from $5 to $20 on Amazon. You need to keep the handset to hang up the phone easily. But, you don't plug the headset in. You plug in the adapter and plug your standard headset into that. It is not amplified. A handset speaker requires less power than a normal headphone. That is why the amplified version is suggested. Also, the amplified version lets you daisy chain the handset in, giving the option to use one or the other. 209.149.113.5 (talk) 13:53, 5 May 2018 (UTC)[reply]
The question is, why? Couldn't you just attach a splitter to the phone line, and plug both the fax machine and phone into that? I have one for my DSL and landline phone, works perfectly. --47.146.63.87 (talk) 21:01, 5 May 2018 (UTC)[reply]
The fax machine is also a telephone and I want to use a headset instead of the normal handset. I ordered a headset on Amazon, I hope it works.--Carnby (talk) 22:07, 5 May 2018 (UTC)[reply]
May 6
Unknown pet
Yesterday I saw some odd pet walking on a leash in central Warsaw. Neither dog, nor cat, medium-sized, had an elongated snout, orange fur with dark stripes on the spine and tail. Don't have a photo, but if someone suggests an image, I'll probably guess which one. I don't think it's some exotic dog/cat breed. Brandmeistertalk06:53, 6 May 2018 (UTC)[reply]
Could a DC device be 'agnostic' regarding the polarity of the current it receives?
A DC device (like a laptop) forces us to plug it with the right polarity. This wouldn't be too useful, but could a DC plug be indifferent to polarity, since it checks it and adapts to the right one? That is, without a fuse blowing or circuit breaker tripping, in the same way it doesn't matter the way you plug your hair-dryer.--Doroletho (talk) 16:33, 6 May 2018 (UTC)[reply]
First of all, wall sockets are AC, so devices are insensitive to which way they are plugged in. However, the wiring might only switch one side (the live/hot), so maintaining polarity is normally a good idea. Back to your question, the easiest way is to use a bridge rectifier to fix the polarity (they also convert AC to DC), at the expense of a 3Volt drop across the rectifier. LongHairedFop (talk) 16:56, 6 May 2018 (UTC)[reply]
Many older electrical devices don't care - a light bulb, for instance. As far as A/C, polarized plugs came in my lifetime. Before that, things could go either way - things like toasters, etc. Bubba73You talkin' to me?17:29, 6 May 2018 (UTC)[reply]
While some motors that run on DC will reverse direction if the polarity is reversed, other types won't (see universal motor for one such). Subway trains in many cities, including the London Underground run on DC, and there have been some lines where the polarity has been changed at some time. And on the old City and South London Railway from about 1900 to 1915, the third rail was generally positive on one track and negative on the other, but as the trains approached the terminal stations the polarity reversed![10] This didn't mean the train would no longer be able to drive forward. --69.159.62.113 (talk) 06:49, 7 May 2018 (UTC)[reply]
It's not cost-effective. It's trivially easy to create a plug that cannot be plugged in backwards. It's a lot harder and more expensive to add circuitry to accept either polarity. -Arch dude (talk) 18:46, 6 May 2018 (UTC)[reply]
Abies canadensis?
I found this image, which is labelled as Abies canadensis
What is Abies canadensis? A search for this name online found only homeopathy sites. The image is categorized as Picea glauca. If that's what it is, and Abies canadensis is just a defunct alternate name, can we find a reliable source and document that on Wikipedia and Wikispecies? HLHJ (talk) 20:05, 6 May 2018 (UTC)[reply]
I was observing Harbor Seals today and wondering, why are they so varied in color? They range from white with black spots to blackish gray with white spots, and occasionally a sandy-brown tone, with varying spots. Also, do they prefer to mate with seals of the same color, and if not, how is the color of their young genetically determined? 169.228.164.251 (talk) 01:15, 7 May 2018 (UTC)[reply]
Asking "why" in evolution is fraught, since it tends to invite a just-so story by way of response. I'll admit, I have no idea -- many species e.g. dogs and horses have a vast repertoire of colors when bred in captivity, but use much less of it in a truly wild population. Some of the same genes are likely to be involved, but that wouldn't touch on why. Does it help them to be recognized as individuals at a distance in water? Is it balancing selection between different color options that might find safe refuge against predators in different environments? I have no idea, but my gut feeling is that if you see a wide variety of stuff, there ought to be balancing selection acting on something (not necessarily that). Wnt (talk) 02:11, 7 May 2018 (UTC)[reply]
Color morphs, as they are known, are very common in natural populations. In addition to the apostatic selection selection for not looking like what the predator expects as User:Wnt mentioned, there's sexual selection and various types of frequency-dependent selection. For an example, picture a scenario in which black panthers are locally common. Perhaps females will mate with the rarer spotted males until they are more common, then switch back to the black ones. Similarly, females may be reluctant to mate with a male who has the same blotches of color as she can see on her own body, as a method of incest avoidance. Abductive (reasoning)03:30, 7 May 2018 (UTC)[reply]
How many millimeters are the prostate and pancreas from each other in the human body? Do they ever come into contact and push each other? Thanks107.77.230.130 (talk) 07:53, 7 May 2018 (UTC)[reply]
Exact distance will depend on your size, but the pancreas is just under the liver, so will never come into contact with the prostate unless something is very wrong. Fgf10 (talk) 07:59, 7 May 2018 (UTC)[reply]
Resolved
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