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October 22

Does alcohol take 30 minutes to kill bacteria?

Per the question, does alcohol kill "bacteria" quickly, or does it take 30 minutes as this website which is affiliated with the Washington State University College of Veterinary Medicine states: "Alcohol takes about 30 minutes before bacteria are killed, so just swiping the hair with alcohol is not effective in killing bacteria." A CDC website says many named things are killed in 10 to 15 seconds by certain typical alcohol mixtures, but mention that a "culture phase" of some named things takes 20 minutes to die. Are the 20 minute holdouts the "bacteria" that WSU is worried about, and are they correct to dismiss the ability of alcohol to quickly kill the named species? Is it just reassurance and theatre when nurses clean an arm or the top of a vial with alcohol before doing an injection, when they don't wait 30 minutes before doing an injection? Edison (talk) 03:12, 22 October 2015 (UTC)

It's a vague question. The diversity of bacterial life is possibly greater than the other kingdoms of the tree of life, so asking a general question like "does X kill bacteria" is basically meaningless. Which bacteria? There are different species of bacteria more different from each other than you are from a jellyfish.--Jayron32 03:22, 22 October 2015 (UTC)

I think it's clear from the context of the linked page that the bacteria in question are those which might be found on a cat's skin and potentially pathogenic in an immunocompromised cat. - Nunh-huh 04:09, 22 October 2015 (UTC)

Hand sanitizer has some relevant info. I think the answer is both. A lot of bacteria is killed quickly, some bacteria is more resistant. That seems to be precisely what the article you linked says. Vespine (talk) 04:01, 22 October 2015 (UTC)

I agree, and suggest that the linked page is simply saying, "if you have an immunocompromised cat, don't rely on alcohol to sterilize injection sites, we have other things that work faster." Also, generally, when discussing antiseptic solutions, you need to specify the concentration of the solution for the discussion to have much meaning. - Nunh-huh 04:09, 22 October 2015 (UTC)

Too "ridiculously vague?" Apologies. Sorry to have provoked the bitey response. Should have specified Becton Dickinson Alcohol Swabs, no. 326895, 70% isopropyl Alcohol, inactive ingredient water, intended for use as an "antiseptic skin cleanser." Do they kill all important pathogens in a few seconds, or does it take "30 minutes" to kill "bacteria" as the Washington State University site states. WSU suggests that they are a waste of time unless you wait 30 minute , a practice which I doubt is ever done. Would they kill "all bacteria" even in the absurd 30 minutes wait scenario? Clearly they don't kill all dangerous pathogens since in recent well publicized cases similar non-sterilized swabs carried bacillus cereus and actually caused serious or fatal infections. Why aren't such swabs sterilized as well as being saturated with 70% isopropyl alcohol? Edison (talk) 04:30, 22 October 2015 (UTC)

Unfortunately, Jayron has taken it upon himself to ridicule others on the Ref Desk, and any excuse will do. Your Q was fine. If he needed clarification, then he should have asked for it, without the ridicule. StuRat (talk) 14:24, 22 October 2015 (UTC)

The Bacillus cereus contamination is undoubtedly a result of survival of the spore form of the organism, which can survive 90% solutions of ethanol for months . Another point to consider is that these days diabetics are generally told that swabbing the skin before testing glucose/injecting insulin is a useless exercise. Though diabetics are immunocompromised by definition, they are presumably less so, or compromised in a rather different way, than the cats in the original page. ("Several studies have reported that there is no increased risk of infection from single-use syringes, pen needles, or lancets when alcohol swabs are not used. Most current practice guidelines, including those from the American Association of Diabetes Educators, no longer recommend the use of alcohol swabs, which can lead to dry skin.") - Nunh-huh 06:31, 22 October 2015 (UTC)

Re: "diabetics are immunocompromised by definition". In what way ? Poor circulation to the extremities is common, and that might lead to increased risk of infection there, since the immune response depends on the circulatory system. Is this what you refer to ? In that case, since diabetics inject insulin into fatty areas on the abdomen, not the extremities, that shouldn't be a concern there. StuRat (talk) 14:19, 22 October 2015 (UTC)

Diabetics are classified as immunocompromised on the basis of empirical evidence showing increased susceptibility to frequent and protracted infections. There are also differences in which organisms are likely to cause a specific syndrome in diabetics vs. euglycemic individuals. The observation was made first, and the explanations later. There are several immunological abnormalities that have been described in diabetes. I think the most prominent are defects in complement-mediated opsonization and phagocytosis. T lymphocytes may also be implicated. Lowered secretion of inflammatory cytokines and disorders of humoral immunity and neutrophil function have also been noted. All of these are worse when the hyperglycemia/diabetes is poorly controlled. The circulatory difficulties are as you note, and can cause difficulties in treating skin ulcers/osteomyelitis or other infections, but aren't considered "immune" problems. While diabetics typically inject insulin into the abdomen or upper thigh, they still do glucose testing on fingertips (though that hurts a great deal more than testing on, say, a forearm; the fingertip testing is more reliable during episodes of hypoglycemia). - Nunh-huh 22:27, 22 October 2015 (UTC)

Based on personal experience, I think we are talking about hyperglycemia encouraging persistent sores, not diabetes causing actual leukocytic immunosuppression. Having lost over 60 lbs and finding I actually have to work hard at raising my blood sugar over 120, as a controlled type II diabetic, I doubt it is the condition, rather than the symptom, which is the problem here. μηδείς (talk) 04:23, 24 October 2015 (UTC)

The alcohol would all have evaporated after a few minutes so a 30 minutes wait would be pointless. There is some useful information about alcohol as an antiseptic here under Mechanisms of action:Alcohol. Richerman (talk) 15:30, 22 October 2015 (UTC)

But just as comparative statistics on infection rates were used to promote the sterile method for surgical practice in the 1870's,greatly reducing strep and staph infections at incision sites, someone must have done a study of post-injection infection rates with and without an alcohol wipe of the site before it became common practice. An 1882 manual on hypodermic injections made no mention of sterilizing the needle or of using sterile liquid for making solutions to inject, let alone wiping the site with alcohol.The author did caution against using a needle on someone again after it had been used on "an infected person." So when did the swipe before the jab become common practice? By 1915a nursing manual called for wiping the skin with alcohol or another antiseptic before doing an injection. beforeSwipe before jab has been the only practice I have seen used in a doctor's office, neglecting the recommendations listed above against alcohol wipes for diabetics who are doing pricks for blood testing or who are injecting insulin or diabetic meds under the skin. What do peer-reviewed studies and recent medical textbooks say about complication/infection rates with and without alcohol wipes before subcutaneous or intramuscular jabs or placement of IVs? This is a general scientific question going beyond diabetics or immunocompromised cats. If some doctor says "I did 5000 injections without cleaning the skin and there were no infections," I wonder how many of the patients were examined to determine if there was in fact an infection, or if the doctor was merely unaware of any infections, though some might have occurred without the patient making his way back to the office for followup. Patients might think that some soreness, redness or a bump under the skin were to be expected after an injection. WHO (2010) ,"Best practices" calls for alcohol wipe before injections.A 2003 WHO publication says it is unnecessary, as do many websites. How can these divergent recommendations all be correct and evidence based? Edison (talk) 23:27, 23 October 2015 (UTC)

The "Best practices" paper you link relates to injections in health-care and related facilities, while the 2nd WHO paper seemingly relates to all injections, but with an eye to "transitional and developing countries". The setting of the injections may bear upon the recommendations; organisms found in health care facilities are often more virulent than those found on one's own skin at home. Different areas also have different standards of personal cleanliness. Note that the (2nd) best practice recommendation states it is based on "expert consensus and theoretical rationale" rather than "well-designed studies", and the (1st) best practice recommendation fails to identify its basis. - Nunh-huh 00:23, 24 October 2015 (UTC)

I wonder if anyone has considered the possibility that alcohol may kill benign bacteria, allowing more dangerous microorganisms to grow on the skin. StuRat (talk) 04:32, 24 October 2015 (UTC)

ADP engine

Any idea what this "ADP engine" is referring to? It's from a free MIT source material site, but I can't figure out which chapter it came from. I came across the picture from here, with no link to the actual webpage containing it. 731Butai (talk) 08:23, 22 October 2015 (UTC)

Advanced Ducted Propfan according to goooooooogle. DMacks (talk) 08:34, 22 October 2015 (UTC)

Correct, or "Advanced Ducted Propulsor". Wikimedia has a picture of it: File:Pratt & Whitney Advanced Ducted Propulsor engine test.jpg, and it's briefly described in the Popular Mechanics magazine of Oct. 1993, p. 28 - Lindert (talk) 08:38, 22 October 2015 (UTC)

Trans-species?

So there's being transgender, which is a gender identity issue. But is there a condition in which people feel they are the wrong species. Born a human but with the brain or mind of a sheep, dog, cat whatever. It seems like people naturally have a very strong connection with animals and maybe that's part of it. Any name for this or exampleS? — Preceding unsigned comment added by 80.195.27.47 (talk) 11:40, 22 October 2015 (UTC)

Zoanthropy is the term for the psychological condition, this is sometimes informally known as Species dysphoria. Otherkin is the popculture concept.--Jayron32 11:54, 22 October 2015 (UTC)

Note that it's possible to have the brain of the opposite gender, and this can happen due to hormone levels during development, etc. However, having the brain of another species isn't actually possible, AFAIK. If this is possible, then it would only be between closely linked species, like dogs and wolves. StuRat (talk) 14:28, 22 October 2015 (UTC)

Note, however, that mind =/= brain. --Jayron32 14:42, 22 October 2015 (UTC)

<flame bait>I'm tempted to ask whether physicians offer species reassignment surgery to deal with the problem, and whether government entities are enlightened enough to recognize this in legal documents, dog licenses &c. Wnt (talk) 15:55, 22 October 2015 (UTC)</flame bait>

See Dennis Avner. Note that his appearance is rather - striking. Tevildo (talk) 21:29, 22 October 2015 (UTC)

If you knew if was flame bait, why the fuck'd you post it? AlexTiefling (talk) 21:48, 22 October 2015 (UTC)

Because it's interesting. Wnt (talk) 22:05, 22 October 2015 (UTC)

Understanding time

what is name of light-flashlike "things" seeing during closed eyes in dark

floating light-dark thing, not describable, seeing stars?Mahfuzur rahman shourov (talk) 15:41, 22 October 2015 (UTC)

I'm tempted to say "orgones" -- but no. Honestly, I think it's a phosphene/"Prisoner's cinema.

Two common visual elements that meet the above definition could be Floaters (small specks of impurities in the vitreous humor of the eye) and Phosphenes, which are flashes of light caused by sources other than light itself (for example, by variations in pressure due to rubbing they eye, irritations to the optic nerve or retina, blows to the head, etc.) Both floaters and phosphenes could be benign, or COULD be a sign of underlying problems, if you have concerns, consult a medical professional such as an optometrist or an ophthalmologist. --Jayron32 16:06, 22 October 2015 (UTC)

Some information in our (rather sparse) flash blindness article. Alansplodge (talk) 16:08, 22 October 2015 (UTC)

See here. Richerman (talk) 16:33, 22 October 2015 (UTC)

Phosphenes appear gradually, they are more light phenomena than flashes. Photopsia on the other hand do flash and should be checked by a medical professional. Ssscienccce (talk) 21:10, 22 October 2015 (UTC)

@Wnt:OP has memory found article rationalwiki surfing 2011, 4 year past, less chaotic timeMahfuzur rahman shourov (talk) 17:00, 22 October 2015 (UTC)

• there's also the ability to see infrared when two photons hit the same pigment simultaneously: http://www.nature.com/news/photons-double-up-to-make-the-invisible-visible-1.16459. Interesting, although I doubt that fits the OP's criteria. μηδείς (talk) 19:25, 23 October 2015 (UTC)

Not directly responsive, but you may also be interested in Eigengrau. --Trovatore (talk) 01:05, 23 October 2015 (UTC)

As Ssscinccce mentioned, unexplained flashes can be a symptom of a serious condition such as retinal detachment or posterior vitreous detachment. We can't give medical advice, but anyone who has such flashes might seriously consider asking a professional about it. --Trovatore (talk) 03:53, 23 October 2015 (UTC)

Carbon nanotubes in clothing (NOW?)

This story claims that carbon nanotubes are showing up in asthma patients, and says "Carbon nanotubes are often used in the production of computers, clothing and technologies for healthcare because of the material's highly durable and conductive properties." Our article on carbon nanotube mentions using it in bulletproof clothing (hypothetically) and web searching comes up with some story about using it against chemical weapons somehow ... but it seems like more of the same old same old. "You could do anything with carbon nanotubes, if you could do anything with carbon nanotubes." But what's the truth? Can people recommend a current source for where they are being used and what the environmental exposures really are? Wnt (talk) 16:36, 22 October 2015 (UTC)

The full journal article is freely accessible here . At a skim, they claim that "Anthropogenic carbon nanotubes were found in all samples", but later acknowledge that "natural and anthropogenic sources might be an important component of ." This looks like sloppy writing at best. I don't think there's any way to distinguish a man-made nanotube from a naturally occurring one. Actually it's a bit of a fuzzy line, e.g. "These nanostructures are similar to those present in dusts and vehicle exhausts collected in Paris" - now technically those are man-made, but it's a side effect of combustion, not an intentional manufacture for use in a specific industry. It is conceivable to distinguish CNTs of intentional manufacture from CNTs that form from routine combustion by comparing statistical distributions of various features, but the authors of the Ebiomedicine article did not do that. I think the tech times' claim that "Carbon nanotubes are often used in the production of computers" is just false. Carbon_nanotube#Natural.2C_incidental.2C_and_controlled_flame_environments specifically discusses how they can be made accidentally by humans and even naturally by e.g. wildfire. SemanticMantis (talk) 16:58, 22 October 2015 (UTC)

Here's a recent review of environmental exposure to CNT, human health effects, and some further refs. SemanticMantis (talk) 17:35, 22 October 2015 (UTC)

At a New Year party about a decade ago, someone asked whether Eric Drexler's new shirt was silk; no, he said, some kind of synthetic. "Buckytubes!" said I, and he laughed politely. —Tamfang (talk) 05:25, 23 October 2015 (UTC)

This looks like typical media spin on a normal journal article to me, tbh. Long on speculation about "what we don't know could be killing us" and short on facts. shoy (reactions) 13:43, 23 October 2015 (UTC)

October 23

How can In-situ Fabricator grab bricks?

How can In-situ Fabricator grab bricks? See . I thought at first that it had claws, but it does not grab them by the sides. It has a plate that pull the bricks up. (Close-up at the bottom of the linked article). --Scicurious (talk) 02:01, 23 October 2015 (UTC)

Around 1:55 in the video: https://www.youtube.com/watch?v=jjcXJ8EU48o It's suction, or a "vacuum gripping system with flexible sealing foam". See here for example, second picture and the "Modular Vacuum Grippers" section. Ssscienccce (talk) 02:48, 23 October 2015 (UTC)

Speed of Gravity

Before I decided to post this, I looked it up. The Misplaced Pages article on this subject is long, drawn out, confusing, and as near as I can tell, inconclusive. I looked at the talk page as well and it's even worse. So, my question: All the objects in our solar system are all pulling on each other all the time. They are also in motion all the time. So when the moon pulls on the Earth, is the pull coming from where it was a second and a half ago, or is it coming from where it is now? The moon is moving pretty quick, but in a second and half it's only going to a go about a mile. We can we tell the difference in the direction of the moon's pull, but can we determine it that accurately? 50.43.33.62 (talk) 04:44, 23 October 2015 (UTC)

I don't know how accurately it's been measured, but in theory it comes from a "current location" that's extrapolated from its location 1.5 seconds ago, which is very close to its actual current location unless something extraordinary happened in those 1.5 seconds. "Where it was 1.5 seconds ago" depends on your choice of reference frame, so the force can't come from there in a relativistic theory. It can't come from the actual current location because that location won't be available for another 1.5 seconds. -- BenRG (talk) 05:04, 23 October 2015 (UTC)

I think that explanation is too facile, since "where it is now" is also frame-dependent. Here's another attempt. Imagine a sphere with very long straight spines sticking out in all directions. If the sphere moves inertially, the spines always point toward where the sphere is "now" in any inertial reference frame. They don't lag behind the sphere because there's no relativistically invariant notion of "behind". That's how the fundamental forces work. On the other hand, if the sphere shoots bullets in all directions (in vacuum), the path of each bullet points back in spacetime (and hence in any spatial projection) to where the sphere was when it fired that bullet, not where it is now. That's how light works. -- BenRG (talk) 05:31, 23 October 2015 (UTC)

Here's an easy way to understand it: The moon moves in a certain direction, and it "releases" gravity. That gravity also moves! And it moves in the same direction the moon was moving when it released the gravity. So the pull of gravity is toward where you would expect the moon to be. Unless something changes the path of the moon. If that happens then the real location of the gravitation force, doesn't match where the force is felt. But only relativity noticed the mismatch, Newtonian physics assumes gravity moves at infinite speed. Ariel. (talk) 06:06, 23 October 2015 (UTC)

I have sometimes seen gravity of massive objects represented as a flat sheet with divots where those massive objects are. Those divots are circular and spread out evenly in all directions - like when you drop a round object into calm water. So presumably the idea would be that if one massive object is close to another, it's always somewhere within that divot. It doesn't suggest there is any "catching up" to do. ←Baseball Bugs carrots→ 06:32, 23 October 2015 (UTC)

The gravity field in the solar system (and I suspect throughout the universe) is static. Therefore gravity forces dont have to travel: they are already there. We are still trying to detect gravitational waves with the LIGO experiment. To date none have been found. I think this is what the Wabbit was trying to say, I think, in its own innocent way.--213.205.252.46 (talk) 14:45, 23 October 2015 (UTC)

It? Ahem.

If gravity affects space itself, then looking for gravity waves might not work. ←Baseball Bugs carrots→ 14:54, 23 October 2015 (UTC)

This is one of those things that is a semantic distinction which is hard to get at, and sometimes people are answering two different implied questions, which is why we have some confusion. There's two questions really we need to get at:

• At what speed does gravity itself travel?
• At what speed will objects respond to gravitational forces?

The answer to the questions then ALSO depends on which theory of gravity you're working from. For example, if you're working with the as yet unsupported graviton theory, then gravity is modulated by force carrier particles, and the answer to both questions is "the speed of light". If you're working under general relativity, then gravity isn't really a force, it's a property of space-time, and as an existing property, it does not properly "travel", and the first question is meaningless. The second question would still be the speed of light, however. --Jayron32 15:02, 23 October 2015 (UTC)

Gravitons don't really change anything. If you quantize a classical field theory, you get particles as a side effect. The particles don't replace the field, and shouldn't be confused with classical particulate matter. The best answers to your questions could be debated, but shouldn't be different in classical vs quantum field theory. -- BenRG (talk) 21:42, 23 October 2015 (UTC)

• I always thought the Tests_of_general_relativity#Perihelion_precession_of_Mercury was due to the propagation of gravity being at the speed of light, and not instantaneous. I may be totally off there, and our article doesn't make that claim. But if the difference is not due to the speed of propagation of gravitic changes, what is it caused by? μηδείς (talk) 19:24, 23 October 2015 (UTC)

(Disclaimer: I'm not a physicist) In a sense your statement is true, because gravity having a finite speed of propagation is one of the things underpinning general relativity. By contrast, Newtonian mechanics predicts that gravitational effects propagate at infinite speed. But the explanation I've heard for the precession of Mercury is that when you get sufficiently close to a very massive body like a star, spacetime is warped enough that you start seeing effects that differ from Newtonian predictions. Mercury is close enough to the Sun that these effects become apparent. As you might know, Newtonian mechanics is still a good approximation for how gravity behaves, in most cases. Relativistic effects only become significant once you get close to a large enough mass, or get up to significant fractions of c. The ultimate demonstration of this is, famously, a black hole; as just one example, close enough to a black hole (but still outside the event horizon), it's impossible to stay in an orbit around the black hole, because spacetime is so distorted. But, you can still maintain your position if you can apply enough force to avoid being pulled towards the black hole, say by pointing a sufficiently powerful rocket engine towards it. --71.119.131.184 (talk) 20:23, 23 October 2015 (UTC)

Mercury's anomalous precession is due to the non-flat spatial geometry around the sun. specifically the fact that the circumference of a circle is less than 2π times the radius. It may disappear in an appropriate c→∞ limit (I'm not sure), but it's not caused by the gravitational force "lagging behind" in the sense of aberration. If there were aberration (if the force was toward the optical position of the sun), orbits would gain angular momentum and spiral outward. This was historically used as an argument against gravity having a finite speed (at least a speed comparable to the speed of light). See Speed of gravity#Laplace. -- BenRG (talk) 21:32, 23 October 2015 (UTC)

Thanks, @BenRG:, I was afraid someone might say that. I am only just educated enough in physics to comprehend your very helpful answer. μηδείς (talk) 04:02, 24 October 2015 (UTC)

General relativity is the gateway ref here, but from context above I think it's worth pointing out gravitomagnetism, gravity waves etc. In electrostatics things get complicated when the charges move; the same is true for gravity. How complicated can be illustrated by weirdness ranging from the Tipler cylinder to less apocalyptic frame dragging around compressed stars, even to Mercury. But nobody wants to work out tensors with a pen and paper on a homework problem, so our awareness tends to shy away from this part of the theory. Wnt (talk) 21:25, 23 October 2015 (UTC)

When I was in college, I asked this of a professor who had done work in General Relativity. He said the speed of light. Bubba73 04:06, 24 October 2015 (UTC)

How old is the Suidae family?

--Romanophile (talk) 08:18, 23 October 2015 (UTC)

Possibly Eocene, definitely Oligocene, but to quote this paper on the phylogeny, "The Paleogene history of Suidae is still almost unknown and the early evolutionary history of the family is therefore poorly documented". Mikenorton (talk) 08:38, 23 October 2015 (UTC)

Yes, our article on the peccaries agrees that they were differentiated in the late Eocence or early Oligocene.

This is a rather technical question; is it just a matter of curiosity, or are you looking for a source for scholarly purposes? μηδείς (talk) 03:57, 24 October 2015 (UTC)

I would tell you, but I dislike you. --Romanophile (talk) 06:46, 25 October 2015 (UTC)

Why does hair growth in the ear increase among elderly humans?

What biologically clicks at that later stage in life to stimulate follicles in the ear? 20.137.7.64 (talk) 14:35, 23 October 2015 (UTC)

Who says it does? ←Baseball Bugs carrots→ 14:52, 23 October 2015 (UTC)

Misplaced Pages. "Hair growth within the ear canal is often observed to increase in older men" Me: why? I see a mention of the Y chromosome in that link #2, but nothing relating the age factor.20.137.7.64 (talk) 15:04, 23 October 2015 (UTC)

Lots and lots of people claim this, surely you've heard of the notion? It may even be true. Here's some coverage from Popular Science , and here's some coverage at Straight Dope. SemanticMantis (talk) 15:02, 23 October 2015 (UTC)

This is a pretty comprehensive answer from a Newspaper health column, noting that, during the aging process, the cycle of growth and shedding of hair changes, so that hairs that would have normally been shed after only a short time may remain and continue to grow for longer times. The reason why this happens in old age among men is not entirely known, but it is suspected that it may be due to the cumulative effects of testosterone on the hair cells in those body areas. That is, it isn't the momentary level of testosterone in the body, but rather the fact that an older man has had many decades of a certain level of testosterone in the body, and the cumulative effects of testosterone changes the way hair grows, which is why older men have hair growing out of various body parts that they didn't notice in their youth. That makes some sense (though as noted, it's a speculative reason, and not entirely well understood), since one of the effects of testosterone is increased hair growth. --Jayron32 15:55, 23 October 2015 (UTC)

It is not well documented that there is an increase in the quantity of hairs. Pretty much everyone has some hair inside their ears - they are just small and thin. They go from the anagen (growing) phase to the catagen (stop growing) phase very quickly. As people age, many areas of the body tend to have hairs that stay in the anagen phase longer and longer. So, the hairs grow for a longer period of time - getting longer than thicker. Therefore, if it is true that the quantity of hair remains constant, the length and thickness of hair will increase. Unfortunately, it is not known what causes the change in anagen duration. Testosterone is a prime suspect, but the actual mechanism has not been published in any of the AMA journals (I did a very wide search, but it is possible I missed one). 199.15.144.250 (talk) 16:38, 23 October 2015 (UTC)

From an evolutionary POV, we should also ask what the evolutionary advantage was, of prolonged exposure to testosterone causing changes in hair growth patterns. Knowing people's ages is important for survival of a group, and this is just one of many age markers. For a practical example, a tribe might put more weight on the advice of elders, who presumably have more experience, and more hair in the ears might be one way to identify such elders. StuRat (talk) 20:46, 23 October 2015 (UTC)

I have the feeling that any effect from testosterone on ear hair is probably not driven by evolution. Testosterone does have well-documented effects on hair follicles, specifically the androgenic hair, but those effects are along the lines of signaling sexual maturity. Not every characteristic of an organism is the direct result of natural selection; some things are just random. Evolution is a messy and chaotic process, and we need to be careful not to assume every trait is the result of a "just-so story". --71.119.131.184 (talk) 21:34, 23 October 2015 (UTC)

Yes, what you are mentioning is spandrel (biology). I suspect ear hairs must be developmentally more closely related to beard hairs, given the latter don't seem to suffer the ravages of old age, but that's just my guess. μηδείς (talk) 22:22, 23 October 2015 (UTC)

Just for the fun of it I will mention the wonderful product at cat-ears.com, which is intended to reduce wind noise when cycling. Ear hair has a potential benefit of providing noise cancelling function. See also "dead cat" windscreens for microphones. Or it could be a spandrel, hard to say :) SemanticMantis (talk) 22:52, 23 October 2015 (UTC)

I am jealous. Back when I rode bikes they didn't have helmets. I do still have the scars.... μηδείς (talk) 03:47, 24 October 2015 (UTC)

Deriving energy from air pressure changes

If you have a large air reservoir, such as a cave system, with a small opening (perhaps one you sealed up), I would expect that air would blow in and out of that opening at high speeds, and thus could power a windmill, whenever the air pressure changes. Has this method ever been used to produce energy ? StuRat (talk) 21:06, 23 October 2015 (UTC)

To store and then release energy, something along those lines can be done: Compressed air energy storage. As to producing energy, if air is blowing in and out of somewhere, that's wind. You don't need to force the air through a confined space to make it turn a windmill. If you do, you lose some of the energy available to turn the windmill. Compressing a gas heats it up, and some of the heat will be transferred to whatever it's in contact with. --71.119.131.184 (talk) 21:23, 23 October 2015 (UTC)

I don't think you got the gist of the Q. The air pressure differential between the air inside and outside the cave will cause wind to blow, and that differential will occur whenever the air pressure rises or falls due to changing weather. Sure, you can put windmills in other places, but this one would provide energy at different times than those, and perhaps fill in the gaps. StuRat (talk) 04:42, 24 October 2015 (UTC)

You would need an enormous cave to get the benefit of slight changes in atmospheric pressure, and the cave would need to be well-sealed without openings elsewhere. You could generate electricity only during changes in pressure, so the system would not be cost-efficient. I don't think it has ever been tried. Dbfirs 09:10, 24 October 2015 (UTC)

My great-grandparents owned a good-sized cave that we used to visit when I was a kid. I don't recall any significant wind blowing in or out. From the standpoint of atmospheric dynamics there's no reason there should be (assuming the cave system is effectively closed). Shock Brigade Harvester Boris (talk) 18:31, 24 October 2015 (UTC)

I don't understand your comment. Air pressure outside changes with the weather. Air then needs to move into or out of the cave to equalize the pressure. If there is a large opening, or many small openings, that wind going in or out may not be noticeable. But, a huge cave with a small opening should provide a strong wind for an extended period, until the pressure equalizes. It might be particularly useful to charge batteries to light the cave, say if the cave is nowhere near the power grid and not in a location that gets much sunlight or regular wind (perhaps because it's in a jungle). Of course, getting in and out of the cave, past the windmill, could be problematic. A separate, sealable door would solve that. StuRat (talk) 20:55, 24 October 2015 (UTC)

Sure, there would be a flow of mass in an out of the cave. But would the mass exchange produce a "strong wind"? Instead of arguing generalities try putting numbers on "huge cave", "small opening", and working it out. The math is not hard. Assume dp/dt of 100 Pa/hr, which is a reasonable value for pressure change following a frontal passage. For simplicity you can neglect the effect of adiabatic expansion on temperature of the air in the cave. Shock Brigade Harvester Boris (talk) 21:30, 24 October 2015 (UTC)

No need to speculate - there is a device called the "Atmos clock" which is powered in exactly the way you describe. The problem is that you're going to need a very large, well-sealed cave in order to generate much energy. It doesn't take much to power a clock. SteveBaker (talk) 02:18, 25 October 2015 (UTC)

That's interesting, but it uses a very small pressure chamber, while mine would be massive. Surely enough to power some LED lights to illuminate the cave. StuRat (talk) 03:46, 25 October 2015 (UTC)

I suppose you could use it to signal the approach of an anticyclone or depression, but a barometer would be simpler. The cave system might keep a battery charged to power a few LEDs when a series of fronts are passing, but a small windmill on top of the cave would be more reliable as a regular source of electricity, and much less expensive to install. If you have a particular cave in mind, try burning a candle in the entrance to see what the airflow is like. Dbfirs 07:07, 25 October 2015 (UTC)

Just for some back of the envelope calcs, if that clock uses an air reservoir 1 meter cubed, and my cave is 1 cubic km, that's a billion times more air, so should produce a billion times as much electricity. That should be a significant amount of power. StuRat (talk) 01:43, 26 October 2015 (UTC)

Those clocks use expansion of a liquid from temperature changes. I know of no clock that uses airflow, and the diurnal temperature change outside the cave would have little effect inside. Dbfirs 12:15, 26 October 2015 (UTC)

Color perception

Hey baseball bugs, I've always wondered if different people see and experience color in totally different ways. I'm also at a loss on how to either prove, or disprove this notion. Here's what I mean. Is it possible that when I see the color red for instance, that it's actually someone elses green? How can we be sure that we all perceive the correct colors? I'm confused. — Preceding unsigned comment added by 80.195.27.47 (talk) 22:47, 23 October 2015 (UTC)

Yes, humans have been discussing this for a long time, see qualia and refs therein. SemanticMantis (talk) 23:31, 23 October 2015 (UTC)

Do you not remember being taught colours when you were very young? We learn to associate the standard names with whatever variation we perceive. Some societies use very different names, so learn to "see" a slightly different spectrum. Dbfirs 00:38, 24 October 2015 (UTC)

There is actually a recently discovered objective answer to this question, referenceable to a very reliable source. Since my name is Bugs I won't post it. μηδείς (talk) 03:44, 24 October 2015 (UTC)

@Medeis: Would you kindly clarify the second part of that post. Are you saying that you also post under the name Baseball Bugs? Akld guy (talk) 05:14, 24 October 2015 (UTC)

Oops. added the missing "not". μηδείς (talk) 16:38, 24 October 2015 (UTC)

Thank you. It simply didn't occur to me that there might be a skipped word there. Akld guy (talk) 18:14, 24 October 2015 (UTC)

I think it's rather obvious that Medeis meant to say that his name isn't bugs and that he was making a snarky critique of the fact that the OP addressed their question to Bugs specifically for some reason. I've no idea why the IP would directly inquire of Bugs for an answer to that question in particular, but I'm even more confused (as I have found myself on a not small number of occasions...) as to why Medeis feels a passive-aggresive response improves a situation like this.

Anyway, turning to the actual question at hand, SemanticMantis was quite right to point the OP to qualia. I'd add for the OP only that, while there are deep questions of subjectivity implied here that have largely thwarted ancient philosophers and modern cognitive scientists alike in trying to nail down, as someone who comes from a deep background in visual cognition, I take the pure subjectivity/"we can never really know if what we experience is close to what others experience" notion with a grain of salt. While consciousness and experiential sensation are as-yet poorly-defined and -understood phenomena, we do know a decent bit about the mechanics of the systems implied in their creation. That is to say, we may not know all the ins-and-outs of how conscious experience arises from the sensory organs and the brain, we do know how a great deal about the mechanics of said sensory organs and we know which areas of the brain are involved with the creation of specific types of sensory phenomena, and a fair bit about their general structure. And one of the things we know is that, much like other neural modules, they tend to be pretty similar across members of a given species. So, while there's really no way any of us will ever know for certain, I suspect that (assuming you have generally typical vision in the empirically testable sense - no colour-blindness, no impairment of vision arising from defects in the eyes or visual centers of the brain) you and I see "red" in very much a similar fashion. Certainly, it's highly unlikely that what I experience as red, you experience as green and vice-versa. While the philosopher in me must concede that there is no way to know for certain, or even to conceptualize what it might be like to experience another's senses, as a scientist with experience in this area, every materialist clue I know of leads me to believe that we're mostly experiencing the same colors from a given source of stimulation.

For me, the much more interesting question is, what is like to experience reality from the perspective of a creature that has an entirely different kind of sensorium or even a different type of modality to a sense we are roughly familiar with? What's it like to see colours we don't have names for because of different types of ocular photoreceptive cell sensitive to different wavelengths of light, or because the mechanics of the eye cause it to focus in a different way, or because the visual array processes that data drastically differently because of the ecological niche in which the organism evolved? I've spent a great deal of my life wondering about and studying those questions and it's a funny thing to pre-occupy oneself with, because at the end of the day, I'm forced to admit that I'm no closer to an answer for the subjective questions that then arise than literally any other human who has ever existed! To say nothing of speculating on what it might be like to "see" in ways that don't involve photoreception but may use similar areas of the mammalian brain to construct a 3D environment from other sensory modalities. Here's an old chestnut for you: do bats dream in sonar? Snow 09:23, 24 October 2015 (UTC)

And do androids dream of electric sheep? Richerman (talk) 09:33, 24 October 2015 (UTC)

The OP had asked a question on the language desk that mentioned colors, and I was one of the responders. As to why he singled me out here, I expect he was drawn by the charismatic nature of my user ID. ←Baseball Bugs carrots→ 18:14, 24 October 2015 (UTC)

• To add some pointers, this question was first posed by John Locke in the 17th century, and has been discussed by philosophers ever since. It is generally known as the inverted spectrum problem, and remains very controversial. Looie496 (talk) 12:20, 24 October 2015 (UTC)

@Looie496, SemanticMantis, Dbfirs, Medeis, and Snow Rise:commenter think answers in philosophy category, not science desk, humanity deskMahfuzur rahman shourov (talk) 15:16, 24 October 2015 (UTC)

This is a very interesting question with regards to animal behaviour. Some animals (e.g. some birds, rodents, fish) are visually receptive to UV (most humans are not because it is blocked by the cornea). My understanding that the signals from the cones are not kept separate, but are summed, so animals with UV reception do not see just additional colours in the UV part of the electromagnetic spectrum, but all their perceived colours are changed. Some vipers and invertebrates "see" in infra red!DrChrissy 18:41, 24 October 2015 (UTC)

Quite right on the first point, although I'd used a different term than "summed". Suppose we had a tetrachromat (an organism whose eyes has photoreceptors keyed to four different spans of wavelength of light), as opposed to the three humans have. Let's further suppose that three of those cell types are identical to the three humans have. That creature's eyes would not be able to just perceive an extra 25% of colours. Rather they would be capable of discerning a 100 times as many hues. And virtually everything they saw would have a different colour from how we perceive it, because it would be "tinged" in ways we can't perceive.

On the other hand, just because you have an eye capable of absorbing a photon of a particular wavelength and translating that to the firing of a neuron does not mean you automatically get all of the benefits of "perception" of all of the "colours" that can come from combining all such stimuli into a hundred million hues, because this perception arises as much out of how the nervous system of the organism utilizes that information as it does the raw data itself. So even though there are creatures who do in fact have four or more types of photoreceptor in their ocular organs, all evidence suggests that they actually "see" colour in a much more limited fashion, as the visual cognition portion of their brains are generally vastly more simplistic than our own. They are probably just perceiving a very small number of colours from within the span that their eyes can detect, because those wavelengths happen to correspond to environmental ques that are important to them in their ecological niche.

I think it's also important to distinguish in your pit viper/invertebrate example that these are actually two vastly different modes of sensation. Those snakes that are sensitive to distal/non-tactile heat perception accomplish this feat through a specialized organ that actually perceives the heat itself. This is very different from those organisms who see into the infrared (or, as is often more accurately the case the "near infrared") spectrum through photoreception. The radiative source may be the same for both, but the mechanism for perception of it is worlds apart. Snow 21:34, 24 October 2015 (UTC)

The question is easily answered. Many, many people are colorblind (I'm not considering the kind where they can't see any colors - but rather the various kinds where color perception is somehow reduced or limited). Those people quite clearly see color differently than those of us who have full color vision - yet they assign the same names and associations to those colors - and very commonly don't realize that they are colorblind until some specific incident makes it obvious. John Dalton was the first person to comment on the subject - even though there must have been millions of color blind people before his time. His remarks are quite telling: "...that part of the image which others call red appears to me little more than a shade or defect of light. After that the orange, yellow and green seem one colour which descends pretty uniformly from an intense to a rare yellow, making what I should call different shades of yellow".

But an enormous number of people before Dalton must have gone through their entire lives not realising that what they were seeing as "green" was really "yellow" (or whatever).

SteveBaker (talk) 02:15, 25 October 2015 (UTC)

For colorblindness, see the third section of Misplaced Pages:Reference desk/Archives/Science/2015 October 17, where we discuss the "EnChroma" company's new glasses that help alleviate some of the problems caused by colorblindness. Nyttend (talk) 02:25, 25 October 2015 (UTC)

Notice though that there is a subtle difference between what you are discussing and what the OP was inquiring about (as I read the question anyway). Those with colourblindness simply have a lower number hues that they can see. But they don't perceive red as green and vice versa, as the OP was inquiring about. The colours they are physically able to precept, they presumably see the same as anyone else capable of perceiving that colour. Or perhaps not, but that's the philosophical question the OP is raising, anyway. There's a difference between the question of what a person perceives based on the adequacy of the mechanisms that receive the sensory stimuli and the question what a person perceives based on how their minds process that information and the confusing issues of subjectivity raised thereby. Today we can easily test and account for the former (not withstanding the fact that, as you say, many people throughout the ages probably had no idea they were colourblind) but we have absolutely no way to validate the latter. Snow 02:49, 25 October 2015 (UTC)

You'll have to forgive me, @Snow Rise: some patience for having no desire to directly answer an OP whose very question is worded as a challenge to a rather well-esteemed good-faith regular here. Especially when that regular has been the subject of direct attacks against his user name for the recent passing season.

There is indeed a peer reviewed university professor whose work does show that one can in reality prove that certain people with a rather unusual genome do have a reversed color spectrum compared to that of the conventional population, and Locke's hypothesis is both answered in full and disproven.

I have both that post-grads' paper proving that Locke's notion can be shown to be false, and his college textbook which disproves the supposition. But for some strange reason, I don't feal like bothering to answer, given the way the question has been posed. TANSTAAFL. μηδείς (talk) 04:50, 25 October 2015 (UTC)

Was referencing Bugs by name meant as a challenge to him? Even if the OP had a difference of opinion with Bugs in another thread elsewhere, the wording here didn't seem terribly confrontational ("Hey Bugs, I've always wondered..."). Anyway, even if you are correct and you didn't feel compelled to provide a substantive answer to the question, surely the best option is to provide no answer at all, rather than a passive-aggressive "I could tell you but I'm not gonna, nyah."

Anyway, getting back to the issue at hand, I'm confused as to what you mean by "a reversed colour spectrum"; perhaps direction to the relevant research or some sort of contextualization would help to make sense of that statement, but as it stands, it's word soup. No one has a personal colour spectrum; the colour spectrum is simply a representation we use contextualize the qualia associated with the sensations which result from perceiving certain wavelengths of light. Saying you can reverse that is like saying you can reverse the smell of something; it just doesn't make any kind of sense.

Furthermore, I think you've either misunderstood the question or your source if you feel that there is any way to empirically validate that the subjective experience of identical stimuli represents an identical experience between individuals. This is one of the oldest and most unapproachable questions in the history of philosophy, science, and indeed human experience broadly and I'm pretty sure we'd have all heard about it if someone had found a way to prove this and frame it in a manner that made any kind of sense in natural language.

All of that said, I'd love to see the paper to which you allude; this area used to be my bread and butter and I'm always happy to hear of perspectives within it. Snow 09:24, 25 October 2015 (UTC)

TheDress is probably as good empirical evidence as any that people with apparently normal vision _don't_ perceive colours similarly. Tevildo (talk) 16:15, 25 October 2015 (UTC)

I beg to differ; I think that example is great empirical evidence that even in this era of science and technology, most people aren't scientific. They don't understand that even when we address a difficult problem we must do so methodically. Most commentaries that I have read on this "phenomenon" imply that the authors don't understand the very essential basics of how digital imagery works on modern computer hardware, ... but it's worse than that! They don't even understand the scientific method. If everybody was tested in controlled conditions with a calibrated display on one computer, with one well-understood color image pipeline, we could draw conclusions about cognitive perception of colors. But, in the case of millions of independent internet commentators who all have "opinions about color," we had no methodology! The ensemble of subjects was a massive distribution of "independent observers" who all reported subjective opinions based on viewing unknown and widely diverse source images (not every copy of the image file distributed on the many different websites and sources across internet was anywhere close to bit-identical!) Thousands, if not millions, of diverse source image data were applied through each individual observer's personal computer or mobile device, all using different software and hardware processing stacks to convert from a compressed image file, rendered to a colorspace in software or hardware, and then output to millions of individually-owned displays, whose software, firmware, and hardware calibration, quality, and default settings are all unknown. The human test subject viewed the result in an unknown room, in unknown conditions, at unknown time of day, with unknown physiological and psychological conditions.

The failure to control the easy parts of the problem demonstrates the main issue with pop-science discussion about "qualia" and "psychoperception." We have a lot of very difficult unsolved problems related to cognition; but we also have a lot of very difficult, already-solved problems related to optical physics, computer image processing software, human eye anatomy, and so on. You can't expect to make forward progress in understanding of cognition and perception if you dive right into the "unsolved" parts without thoroughly understanding the already-solved parts!

We already know, from controlled experiment, that room lighting changes perception of color. Blood pressure, blood oxygenation, sleep deprivation, age, general health, eye health... all affect human vision. If we wish to test color perception on an audience, we must control for these known effects!

About the only thing we can learn from this "experiment" is that even many educated people do not really know the nitty-gritty details about how bits in a computer system actually get converted back into real actual colored photons. However, lots of people are ready to draw profound conclusions about mass psychology and color perception of those unknown photons!

Nimur (talk) 22:57, 25 October 2015 (UTC)

The matter is even more complicated than all that. Point in fact, this phenomena has been studied in a controlled manner with regard to some of the psychophysical phenomena you reference, but, even so, far from this phenomena providing "empirical evidence that people with apparently normal vision _don't_ perceive colours similarly", it actually just further highlights how difficult the question raised by the OP is. Even if we somehow found a way to control for all of the above criteria (a tall order indeed), and the many other possible conflating factors in the stimulus, the environment and the individual, we still would be no closer to answering this question empirically. Because we have no way to dependably measure the element which is actually being tested for. You could have identical displays, under identical conditions, and you could even (brain in a jar style) hypothetically plug those people's optic nerves into identical artificial eyes to look at the dress, but at the end of the day, what is being reported is still a subjective experience. And we have no way to share that experience than with human language. So one person says he bands are gold and another says they are brown. How do you know that they aren't actually seeing the same thing but just associate a different word with it?

I absolutely agree with you that there are a lot of factors here that need to be controlled for that people just don't intuitively appreciate as a general rule. But ultimately that's just a side issue. Even though we don't remotely have the technical ability to control for all of those factors, those still represent the "easy" part of the problem faced here. The real difficult part is not just something that is beyond our current level of technical expertise, but which we can kind of see how we might approach it if we only had vastly more sophisticated technique (as with the examples you listed above) it is something so confusing and beyond our ability to conceptualize that we just don't even yet have the first idea of how to tackle it, or even how to properly describe what it is we are really trying to measure. It just goes too far beyond the sort of phenomena our minds are intuitively designed to understand, and there's even a certain concession amongst cognitive scientists that it may be something we can never understand. Snow 23:32, 25 October 2015 (UTC)

October 24

Science is a scam?

any additional references or input to clarify the validity of this article I really like science and this made me upset. 199.19.248.27 (talk) 03:00, 24 October 2015 (UTC)

Most of that article is correct, but I will add a few comments:

1) Not all scientific publishers are scammers. That is, they don't all require payment and publish ANYTHING as long as the check clears. The most prominent scientific journals don't do this. So, the trick is to know which ones are reputable and which are not. I'm not sure if they have an accreditation system like universities, but, if not, it is sorely needed, since, just like a degree from a diploma mill, anything in one of those journals should be ignored.

2) You need to look at the funding of a study. If it was funded by anyone with an agenda, like the company trying to convince you to buy their product, then you should assume the study will be biased.

3) We need more government funding of university studies. This will provide unbiased studies and also help to support higher education.

4) I agree that the process for approval of new meds is fundamentally flawed, in the US. I personally avoid any new meds, and only trust them after they've been used for years. For pain relief, for example, I use aspirin, since I figure all the side effects are known by now. I'm particularly wary when a doctor recommends a new med for a condition for which the current med seems to be doing a good job. That doesn't appear to pass a risk-benefit analysis. That is, there's lots of risk in a new med, and very little benefit if the old med is getting the job done. And if diet and exercise can make the use of meds unnecessary, all the better. StuRat (talk) 05:01, 24 October 2015 (UTC)

It's not really the science that's the scam. Wherever it is you have to go, there's always somebody to rob you of your lunch money on the way. You need a medicine? They can make it for a dollar but they'll charge you every penny you have. You want a genetic test? They could run them all for a few hundred, but the doctors will only ladle them out one at a time for you not much less than that, companies and regulators getting their cut. The muggers on the street and the kidnappers at ISIS aren't really much different from doctors or anybody else. And if you want science recognized, yeah, sure 'nuff, there's some company demanding it own the presentation of your results, which will puff them up if they're nothing or keep others from learning about them if they're good.

There's a different model, with strong support in the scientific community, of open publishing, but that involves companies trying to get paid in advance, and so they have zero standards. Which is pretty much what they should have, logically, but the culture still is expecting the person who publishes the paper to be the one to evaluate it, even though that isn't going to work with open source, and never was all that great a system otherwise. Wnt (talk) 10:12, 24 October 2015 (UTC)

Publication bias is real, but people know it exists, and take it into account. Over time the truth will come out, wrong results won't stand forever. That also applies to the second item, scientists not having to show their work. The other four items mentioned in the article only confirm that we live in a capitalistic world. There are more fundamental problems the OP can worry about, problems that won't fix themselves, especially related to medical care: Studies show that medical errors in hospitals generate more income and increase profits. It means that bad practices are rewarded, good practices punished; that good hospitals may have to close while the bad ones can expand. It could perhaps explain these two reports:

Survival rates for patients with acute heart conditions go up when they are admitted to hospital during cardiology meetings, in other words: If you have a heart condition, you're more likely to survive when the people specialized in that condition are absent...

The "economic cost" of avoidable medical errors in the US has been estimated at 1 trillion per year. (although I'm not a fan of such inflated "economic cost" calculations) Ssscienccce (talk) 11:36, 25 October 2015 (UTC)

The Scientific method, as purely and virtuously applied, is one of the best systems of thought we've got. You have only to compare the post-Renaissance world to the Middle ages, or look at advances such as the germ theory of disease, or genetics, or the moon landings, or the Global Positioning System, to convince yourself of this.

But science is carried out by human beings, and human beings are, alas, endlessly fallible, and not all of them are equally virtuous, and some of them are careless or downright evil. So some science will inevitably be flawed.

The good news is that one of the bedrock principles of the scientific method is its explicit protections against human fallibility. The bad news is that, as in any tussle between cheaters and cheater-detectors, at any given time the sophistication of the cheaters may be sneaking out in front of the mechanisms designed to detect them. So we've got to remain eternally vigilant, but by no means do I think we should write the scientific effort off as a failure. —Steve Summit (talk) 12:26, 25 October 2015 (UTC)

@Scs, StuRat, Wnt, and Ssscience:good evil bad moral human make, not objective, science independent of moral, not good badMahfuzur rahman shourov (talk) 15:21, 25 October 2015 (UTC)

Science should be independent of human morality, but as long as people remain determined to falsify "scientific" results to support their own agenda, and suppress results which don't, the two are intertwined. StuRat (talk) 18:34, 25 October 2015 (UTC)

One bit of good news about science is that bad science can only reign for so long, before it is dethroned. For example, if you claim you have a car that runs on water, with no other energy source, then you will be expected to prove it with actual demonstrations. If you do so with a faked experiment with a hidden energy source, to get investors, they will expect to see production models soon. At that point the scam is up and you go to jail. StuRat (talk) 18:43, 25 October 2015 (UTC)

terms of genetics, memetics and related subjects which describe "carrier" of "malevolent" gene, meme(thought) etc is "reverse-aware" about the malevolence e.g carrier was convinced, thinks that carrying and spreading is beneficial

OP curious while looking into cultist incident sample, thought spread activitiesMahfuzur rahman shourov (talk) 14:40, 24 October 2015 (UTC)

Behavior-altering parasites and parasitoids? Wnt (talk) 15:43, 24 October 2015 (UTC)

Are voles slower than mice and hamsters ?

On the PBS TV show Nature, about 45 minutes into the "Pets: Wild at Heart" episode, there is a scene with a house cat chasing a vole. The cat has no trouble catching it. This contrasts with cats I've seen chasing mice and hamsters, where they have a very difficult time keeping up (although the prey constantly changing direction helps it flee). So, are voles somehow less able to flee ? Or maybe this one was injured or drugged for the show ? StuRat (talk) 17:57, 24 October 2015 (UTC)

According to http://www.speedofanimals.com, the top speed of a domestic cat is 29.8mph, the top speed of a house mouse is 8.1 mph. According to http://purelyfacts.com/question/12/which-is-faster-a-squirrel-or-a-hamster?DDA=111&DDB=50, the top speed of a hamster is 4mph. So your premise is decidedly flawed. According to http://www.softschools.com/facts/animals/vole_facts/334/, the top speed of a vole is 6mph.

SteveBaker (talk) 02:03, 25 October 2015 (UTC)

Maybe it's a question of manueverabilty then. The vole seemed to run straight, while the mice and hamsters I've seen constantly changed direction to keep the cat from catching them. StuRat (talk) 03:40, 25 October 2015 (UTC)

I rather suspect whatever cats you have watched stalk mice and hamsters are either poor or apathetic hunters for whatever reason. In general, domestic cats are highly adapted to hunting mice and usually if a cat and a mouse are in the same space, and the mouse does not have direct access to an escape route from which the cat is obstructed, that mouse's time is up. Indeed, if the mouse has more than a minute to live it is generally the result of the cat's willingness to draw the experience out. Your average outdoor domestic cat kills between 2-6 animals per day, 1-2 of which are likely to be a rodent. Some cats are more aggressive than others in this respect though: https://www.youtube.com/watch?v=UmKS07QYFD. Snow 03:44, 25 October 2015 (UTC)

• Having captured cottontail rabbits, domestic mice, mice, opossums, muskrats, shrews, moles and voles by hand; but never cats; I can assure you voles are at the slower end of that spectrum. The issue is always the habitat, never the inherent speed. Voles tend to hide, and when they can't, as in your dad's garage, they are eminently catchable. (I will add that I have also "chased" and caught dogs, but never caught or expected to catch woodchucks, grey squirrels, or chipmunks( μηδείς (talk) 04:13, 25 October 2015 (UTC)

• They could hide pretty well in a garage too, whether under a car, between gas cans, behind a tool cabinet, etc. StuRat (talk) 04:33, 25 October 2015 (UTC)

• Ah, yes. But given that my dada's prefered method of grain storage is hanging it in plastic bags from the rafters. . . . 05:26, 25 October 2015 (UTC)

Shrews are probably as fast as mice I think but cats don't seem to find them much trouble. I saw a pair of cats playing a 'tennis' game with one once with a cat on either side of a vegetable row, they'd bat the shrew each time it came their side and then the cat on the other side batted it so it ran back again. After a few minutes they just left it alone and walked away rather than killing it which was a bit surprising. Dmcq (talk) 22:15, 25 October 2015 (UTC)

"If there's a bustle in your hedgerow...there are two paths you can go by...". StuRat (talk) 01:35, 26 October 2015 (UTC)

Why is Missouri river considered a tributary

If the Missouri river is longer than the Mississippi river, then why is it considered a tributary instead of as the trunk? — Preceding unsigned comment added by 24.207.79.50 (talk) 20:43, 24 October 2015 (UTC)

Which river is wider when they join ? Of course, there's no hard-and-fast rule, but I think that's what most people would consider. StuRat (talk) 20:47, 24 October 2015 (UTC)

Tributary has some info, and check out Strahler_number too. SemanticMantis (talk) 21:45, 24 October 2015 (UTC)

The main river is the Missouri, but the Mississippi name came first, even though its northern portion is geographically a tributary. ←Baseball Bugs carrots→ 00:28, 25 October 2015 (UTC)

The name is crucial. StuRat's criterion is that of the main stem, which almost always holds true, but not quite: as you can see from the image to the right, at Cairo, Illinois, the Mississippi River is smaller than the Ohio River, and the combined river keeps going in the direction that the Ohio was going before the confluence, but we still call the Ohio the tributary, not vice versa, because the name "Mississippi River" is applied to everything from Nawlins to Lake Itasca. Nyttend (talk) 01:04, 25 October 2015 (UTC)

As User:Baseball Bugs noted, the Mississippi is named as the main river, even though it is hydrologically a tributary, because the length of the Missouri River was not known until the Lewis and Clark expedition. The Mississippi was explored earlier. That is a historical reason. Robert McClenon (talk) 01:18, 25 October 2015 (UTC)

With the Ohio and the Mississippi, the case was slightly different — Hernando de Soto discovered the Mississippi more than a century before the La Salle Expeditions discovered the Ohio, La Salle started from the upper end and couldn't have identified it as the same river (the Cairo area wasn't explored until long afterward), so the river at Nawlins and the river at Pittsburgh got separate names, leaving the lesser branch near Fort de Chartres to keep the grander name. So while it wasn't as clear-cut as the Mississippi and the Missouri, it was still a matter of exploration history. Nyttend (talk) 01:31, 25 October 2015 (UTC)

Hanging chads! μηδείς (talk) 04:03, 25 October 2015 (UTC)

We have an article called Mississippi River System, which is also called the Missouri-Mississippi-Ohio watershed, among other things. The excellent illustration with that article shows that the Missouri is the main river, and others all run into it eventually. As noted above, it's an accident of history that the river running through New Orleans is called the Mississippi. Had the pioneers had access to this map, they might have named things differently. ←Baseball Bugs carrots→ 14:27, 25 October 2015 (UTC)

October 25

Daylight saving time

Thank you for your article on the above. Could you explain to me why there is such a great discrepancy in the dates of starting and ending DST?

In Ireland 2015, DST started on 29/3/2015 and ended 25/10/2015.

The start date in March is 119 days after the winter solstice (21/12/2014). The end date in October is 57 days before the winter solstice 21/12/2015.

I assume the Earth travels around the sun going to and away from the solstice at roughly the same speed and that daylight length is roughly equal for each corresponding day either side of the solstice. Why then the discrepancy?

Should not the two dates be an equal number of days away from the solstice?

Many thanksUnseenUni (talk) 10:08, 25 October 2015 (UTC)

The short answer is that in many cases, DST decisions are based on politics, not logic or science. —Steve Summit (talk) 11:31, 25 October 2015 (UTC)

There is significant logic to the concept of commencing daylight saving on or after the vernal equinox; and ending on or before the autumnal equinox. However, it is too simplistic to imagine that the weather around the vernal equinox is similar to that around the autumnal. At the time of the vernal equinox the whole hemisphere is still showing the last of the effects of winter so the weather is generally colder than around the time of the autumnal equinox when the hemisphere is still showing the last effects of summer. This consideration is relevant when decisions are made about the start and finish dates of DST. Dolphin (t) 11:40, 25 October 2015 (UTC)

You're making it sound like there's science behind it. Try candy. 99.235.223.170 (talk) 13:18, 25 October 2015 (UTC)

Heck, even the time zones that serve as a starting point for the need for DST are politically motivated. - so no, it's definitely not science. SteveBaker (talk) 14:30, 25 October 2015 (UTC)

• It's certainly not a coincidence that the US'll be moving the clocks back in the wee hours of Nov. 1st, right after trick-or-treating ends. μηδείς (talk) 16:04, 25 October 2015 (UTC)
  • Not too many years ago, it was the Sunday before Halloween. Presumed to be safer for the kids this way. ←Baseball Bugs carrots→ 16:24, 25 October 2015 (UTC)
    • Yes, we never started trick-or-treating until it got dark, but nowadays trick-or-treating is pretty much over by the time it gets dark. μηδείς (talk) 17:05, 25 October 2015 (UTC)
      • Maybe that was in the days before child-haters started putting razor blades in the apples, and such stuff as that. ←Baseball Bugs carrots→ 18:47, 25 October 2015 (UTC)
        • Does it harm a kid less if he bites a razor blade before it's dark? --3dcaddy (talk) 00:33, 26 October 2015 (UTC)

Baseball Bugs. I suggest you read Poisoned candy myths. And if you already knew that it was a myth then you should have said so. CambridgeBayWeather, Uqaqtuq (talk), Sunasuttuq 00:26, 26 October 2015 (UTC)

CambridgeBayWeather I do not believe it's a myth. Do not believe everything you read in wikipedia. Do believe everything you read in snopes, which claims that some tampering of the trick-or-treat loot with razor blades and the like is documented. --3dcaddy (talk) 00:34, 26 October 2015 (UTC)

And note, in the Snopes page, that there were news reports of this sort of tampering as early as the 1960s... decades before DST in the US and Canada was extended past Halloween. --70.49.170.168 (talk) 05:40, 26 October 2015 (UTC)

The DST time change is synchronised throughout the EU, and occurs at 01:00 UTC on the last Sunday in March, and and 01:00 UTC on the last Sunday in October. See Summer_Time_in_Europe for the details. I don't know why those dates were chosen, but Sunday morning is the least disruptive time to change the clocks. — Preceding unsigned comment added by 62.56.61.161 (talk) 19:35, 25 October 2015 (UTC)

To address the OP's –

"I assume the Earth travels around the sun going to and away from the solstice at roughly the same speed and that daylight length is roughly equal for each corresponding day either side of the solstice. Why then the discrepancy?"

– this is not entirely true, because Perihelion occurs in January, so the earth is travelling slightly faster in its orbit between the Autumn and Spring equinoxes than it is between the Spring and Winter Equinoxes. See Equation of time. {The poster formerly known as 87.81.230.195} 185.74.232.130 (talk) 14:45, 26 October 2015 (UTC)

for faster cooling, leave in open air or put object in palm

OP curious, cooling things, only these optionsMahfuzur rahman shourov (talk) 14:33, 25 October 2015 (UTC)

If it's a pot of boiling water, definitely leave it on the stove rather than putting it in your hand. In general, unless the air temperature is 98.6 degrees, leaving it in open air with circulation on all sides of it (such as a cooling rack) should be faster than in your hand. ←Baseball Bugs carrots→ 14:40, 25 October 2015 (UTC)

@Baseball Bugs:air is in 20-35 celsius rangeMahfuzur rahman shourov (talk) 14:51, 25 October 2015 (UTC)

Sure. The point being that if the air is warmer than your hand, leaving it in open air might not be as fast, but it might be safer. If the object is very much warmer than your hand is, it could cause serious damage. ←Baseball Bugs carrots→ 15:00, 25 October 2015 (UTC)

Let's remove some variables. Given an object that is not too hot to hold and small enough to fit in your hand, and given your hands are some temperature around 36c, if the air is at the SAME temperature as your hands, your hands will cool the object down faster. Water is a much better conductor of heat than air. This is why you can stick your arm into a 100c oven, but you couldn't stick your arm into a 100c pot of water. Conversely, you can easily hold your arm in a fridge that is 4c but holding your arm in 4c water would become very uncomfortable very quickly, the water is "cooling down" your arm much faster than the air. The fleshy parts of your hand is 70-80% water and your circulatory system conducts at least part of the heat away from your hand, so hand wins. However if the air is colder than your hand, or if the air is moving quickly, like a fan over a heat sink, this will affect the results considerably. At some point when the air is cold enough or moving enough the air will win, there is no universal answer. Vespine (talk) 01:21, 26 October 2015 (UTC)

Note that there are other factors at work besides the temperature of the "sink" (air or hand):

1) The density of the material also matters. A more dense material is able to hold more heat, and thus draw away more heat. The density of the human hand is roughly that of water, which is far higher than air.

2) Circulation also matters. If there is no wind, circulation in air may still occur due to convection, but this is rather dependent on the shape of the container. As for circulation in the hand, this is driven by the heart and circulatory system. So, which would have faster circulation is hard to say. StuRat (talk) 01:17, 26 October 2015 (UTC)

I see your point. It would also be helpful if the OP would tell us just what kind of object he has in mind, and how hot it is. ←Baseball Bugs carrots→ 01:47, 26 October 2015 (UTC)

Calorie / Energy requirements men vs women

Why is it men always have a higher nutritional requirement than women. Surely, a man and woman of equal statute require the same level of food? — Preceding unsigned comment added by 80.195.27.47 (talk) 17:23, 25 October 2015 (UTC)

testosterone production by testicles, resulting anabolismMahfuzur rahman shourov (talk) 17:40, 25 October 2015 (UTC)

If by "nutritional requirement" you mean calorie intake, men tend to be taller and more massive, due to the anabolic effects of testosterone, so, on average, men will burn more calories. Of course, when comparing individuals, rather than looking at population statistics, there will be a lot of individual variation. Certainly, women require more calories than they otherwise would when pregnant or lactating. --71.119.131.184 (talk) 17:48, 25 October 2015 (UTC)

Re: "men always have a higher nutritional requirement than women", I believe this is an incorrect statement. For example, a male midget presumably needs fewer nutrients than a female giant. As for two of the same mass, I'm not sure this statement is true, then, either, although men tend to have more muscle and women have more fat, and muscle burns more calories than fat. StuRat (talk) 01:21, 26 October 2015 (UTC)

This is just a very rough guideline. It's quite easy to find some articles discussing this very subject. In short, the 1st IP's reply pretty much sums it up. Vespine (talk) 04:29, 26 October 2015 (UTC)

@Vespine:first ip reply same mine,i post beforeMahfuzur rahman shourov (talk) 15:08, 26 October 2015 (UTC)

Power → acceleration at low speeds

Hello all. Trying to calculate vehicle acceleration and top-speed, based on engine power output. Traditional formula: power = mass × acceleration × velocity. But that seems to imply that at v=0, any power gives infinite acceleration?

Turning to the formula for kinetic energy, the kinetic energy = 0.5 × mass × v². So if during a given period of power usage the kinetic energy has changed by δKE, then velocity after that timestep is v2 = sqrt(v1² + (dt × 2 × δKE / mass)). Does this work? What are the units? 146.198.171.0 (talk) 19:36, 25 October 2015 (UTC)

You may find Zeno's paradoxes to be somewhat relevant. ←Baseball Bugs carrots→ 20:11, 25 October 2015 (UTC)

Indeed, or just a formula that allows calculating the "velocity after x seconds from a standing start" without having to use tiny timesteps to get sufficient accuracy... 146.198.171.0 (talk) 20:20, 25 October 2015 (UTC)

You can just use:

${\displaystyle v={\sqrt {{2Pt} \over {m}}}}$

where ${\displaystyle v}$ is the velocity, ${\displaystyle P}$ is the power, ${\displaystyle t}$ is the time, and ${\displaystyle m}$ is the mass. The energy supplied to the body is just Power x Time, and the velocity can be calculated using the formula for kinetic energy. Tevildo (talk) 21:46, 25 October 2015 (UTC)

${\displaystyle v={\sqrt{2Pt \over m}}}$ and ${\displaystyle a={\sqrt{P \over 2mt}}}$ units are m/s, W, s, kg, m/s²

But to know the acceleration at low speeds, you have to know the power at low speeds, and that will be a function of speed...

Usually the torque, not the power is used: an engine can produce torque at v=0, but not power, because as you say, that would result in an infinite acceleration. The torque an engine can produce is limited, and the power equals torque*angular_speed, so at small speeds and with torque limited, you won't be able to use max power. A typical curve is found here With only power given, I guess you can use the formula above, but realize that the resulting acceleration at low speeds is not realistic. Ssscienccce (talk) 21:44, 25 October 2015 (UTC)

I see Tevildo was faster... weird, my time stamps is 2 minutes before his, but when I saved his post appeared... Ssscienccce (talk) 21:50, 25 October 2015 (UTC)

Same here. ;) We must have _just_ missed an edit conflict. Tevildo (talk) 22:03, 25 October 2015 (UTC)

And even power & torque curves for an electric motor, such as this one (for various versions of the Tesla Model S), show zero power at zero speed, though they do have their best torque at low (including zero) speeds. -- ToE 03:19, 26 October 2015 (UTC)

The original question essentially stems from the commission of a division by zero error. The formula, ${\displaystyle P=a\times v\times t}$, contains values (acceleration, velocity, and time) that are related to each other by differentiation. They are not ordinary numbers. When you attempt to solve for power at a velocity of zero, you must account for the fact that instantaneous application of a differential element of acceleration will instantaneously and continuously affect that velocity. Essentially, you are seeing a solution where an infinite amount of power is applied for an infinitely short amount of time, and your intuition is that this is somehow meaningful ... but it's not, because not all infinities are equivalent when you compare their sizes. This is a technique of calculus; you cannot simply treat the values in this equation as regular constant numbers and solve algebraically. The simple formula only works as a steady-state simplification of a more complete treatment of the kinematics. The power applied when velocity is exactly zero is not a meaningful quantity: power is a derivative of total energy.

Using the same division-by-zero error, we can manipulate the equation ${\displaystyle P=a\times v\times t}$ to incorrectly demonstrate that at zero velocity, power is zero, power is "one," (in arbitrary units), power is infinite... the magic of wrong math is that it can rapidly become very wrong!

When we try to teach physics without calculus, some books simplify this by considering average power, which is rate of change of energy per unit of time, averaged over a non-zero amount of time. This lets students solve simplified problems using only the techniques of algebraic equation manipulation. But, if you use this simplified variation, you must not try to take the equation to the limit as the time interval goes to zero: we have an entire branch of math that explains how to construct that problem more effectively. Nimur (talk) 22:19, 25 October 2015 (UTC)

Nimur, are you saying that there exists a differentiable function v(t) with v(t₀)=0 for which p(t₀)≠0 when we define p=d/dt(0.5·m·v) for a fixed value m? -- ToE 02:59, 26 October 2015 (UTC)

The power you're using there is the change of KE of the vehicle over time, not the engine's power. What you've discovered is that the car's efficiency is instantaneously 0 when it is stopped. This should come as no surprise: it's certainly 0 while sitting still, and it's not unreasonable that it should increase continuously therefrom as you accelerate. --Tardis (talk) 16:02, 26 October 2015 (UTC)

Condoms

Who do condoms only cover the shaft of the penis and not the scrotum or areas around it? 2A02:C7D:B8FF:7E00:C1D3:14DB:4194:8D14 (talk) 19:56, 25 October 2015 (UTC)

That's not always true. — Preceding unsigned comment added by Baseball Bugs (talk • contribs) 20:34, 25 October 2015 (UTC)

WP:NOTAFORUM Try to bear in mind that if someone does not (or cannot) follow up your link, they may very well go away with misinformation about an important topic, taking your comment at face value. Regardless, there are plenty of places on the internet where you can reference your favourite comedies to your heart's content; WP really should not be one of them. Snow 21:55, 25 October 2015 (UTC)

On the contrary, wearing a rubber suit should afford great protection. ←Baseball Bugs carrots→ 01:38, 26 October 2015 (UTC)

I don't think you read what I wrote. Snow 02:10, 26 October 2015 (UTC)

I don't think you watched the video. And calling it "misinformation" is silly - as well as being untrue. ←Baseball Bugs carrots→ 15:48, 26 October 2015 (UTC)

The reason that condoms can help prevent infection for many (though by no means all!) STD's without covering the entire surface of the male genitalia is two-fold. First, this typically suffices to capture the fluids produced by the penis during copulation which are often the medium through which infection can be spread; this obviously protects the man's partner. But the condom also protects the person wearing it by covering the glans, meatus, and (in the uncircumcized), the foreskin; the surface tissues of these structures contain specialized cells which are particularly vulnerable to the pathogens responsible for some STDs. It also helps prevent fluids from entering back into the urethra, to similar effect. These protective measures are not, of course, 100% effective, nor do they prevent against all forms of STD, but they do help markedly with regard to some of the most vulnerable tissues and some of the worst diseases. Snow 21:55, 25 October 2015 (UTC)

Note that the scrotum is important for thermal control of the temperature of the testicles, which in turn is important for sperm production. Of course, if he is using a condom you might assume he doesn't care if the current batch of sperm live or die, but nature has also provided men with an aversion to any temperature which causes sperm to die, so having the testicles overheat would completely ruin the experience for most men. StuRat (talk) 01:26, 26 October 2015 (UTC)

I see. Then why do many people not use condoms for oral sex whether cunnilingus or fellatio? Surely that's just as risky as for example saliva or other fluids could come into contact with those vulnerable surface tissues you mentioned. — Preceding unsigned comment added by 176.24.24.18 (talk) 07:36, 26 October 2015 (UTC)

Using a condom during fellatio is definitely recommended, particularly during high risk encounters (with prostitutes for example). Using a cut out condom is one option, but a dental dam is much preferred during cunnilingus. See oral sex and safe sex for more information. As to why some people don't use such recommend protections, people make their own decisions based on a whole host of facts and STI risk is only one thing they may consider, and many people may not even properly understand the risks anyway. After all, some men receive bareback anal sex from a male prostitute, something which would generally be considered a really high risk activity. And the problems married couples, particularly a wife faces trying to negotiate condom usage with her husband, both as a contraceptive and for protection against STIs in some regions with high rates of HIV are commonly discussed . Nil Einne (talk) 12:02, 26 October 2015 (UTC)

October 26

Do great apes have senses of humour?

(Besides modern humans, obviously.) --Romanophile (talk) 05:41, 26 October 2015 (UTC)

Dr Marina Davila-Ross certainly seems to think so. Vespine (talk) 05:54, 26 October 2015 (UTC)

From Koko "Koko has also been reported to use language deceptively, and to use counterfactual statements for humorous effects, suggesting an underlying theory of other minds." with reference. --Jayron32 15:13, 26 October 2015 (UTC)

DHT and activities.

Do testosterone boosting activities like masturbation and anaerobic exercises like intense weight lifting and pushups etc... increase DHT and accelerate hair loss ? Does Minoxidil 5% in such a case block DHT at the follicles or become helpless ? What about Finasteride 1mg ? Does it become helpless if testosterone is too high ? — Preceding unsigned comment added by 175.101.24.136 (talk) 13:02, 26 October 2015 (UTC)

Watertighting wheel wells of amphibious cars

How is there a watertight seal between the wheel wells and the drive shaft while still allowing the axle to spin in most amphibious automobiles? 20.137.7.64 (talk) 13:22, 26 October 2015 (UTC)

Stuffing_box#Gland 196.213.35.146 (talk) 14:00, 26 October 2015 (UTC)

Horse vs Bicycle

Who would win in a 50 mile race; a man on a bicycle or a man on a horse? 202.20.99.196 (talk) 16:21, 26 October 2015 (UTC)

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