Wikipedia:Reference desk/Archives/Science/2014 May 30

= May 30 =

Hair follicles
Is it possible that a grey hair can be produced as a result of a damaged hair follicle from over plucking? Has there been any research on this? And also, does the human body attempt to repair damaged hair follicles?
 * Not according to the article. 24.5.122.13 (talk) 02:06, 30 May 2014 (UTC)
 * It doesn't mention overplucking, but it does mention stress. I went from having a few grey streaks when I was 33 to being about half grey when I was 34 after being hospitalized for several months and having several major surgeries.  None of them involved plucking, however. μηδείς (talk) 04:23, 30 May 2014 (UTC)
 * The classic example of how stress causes grey hair is US presidents...just look at photos of them through their terms in office and compare them to other people of similar age. The result is fairly clear. SteveBaker (talk) 15:20, 30 May 2014 (UTC)
 * It's a popular and oft-cited example, but I doubt that it's a particularly good one. The average age of a U.S. President at accession is 54 years, 11 months.  (Only two Presidents came in under the 45-year-old mark, Teddy Roosevelt – who assumed the presidency after McKinley's assassination – and JFK.)  If you take a 55-ish-year-old man – particularly one who started out with a bit of that distinguished-elder-statesman grey at the temples – and add two terms, you get a 63-ish-year-old man.  (George W. Bush, incidentally, hits those averages almost exactly spot-on.)
 * Additional grey should not be surprising or remarkable during the transition from late middle age into one's retirement years. I would also point out, rather cynically, that there may be less use of makeup, concealer, and dye if one's image consultants aren't prepping for another election campaign.  "Compare them to other people of similar age" is a hell of a red herring.  It's easy to find well-preserved and poorly-preserved individuals of any age.  (The years have been much kinder to Sean Connery than they have to Keith Richards.) Ideally, we'd do some sort of twin study, but unfortunately no identical twins have (yet) been elected President.  TenOfAllTrades(talk) 17:53, 30 May 2014 (UTC)


 * Hear, hear. Richard Avery (talk) 08:57, 31 May 2014 (UTC)

Then why do some young people, including some children, have a single strand of grey hair, when they are otherwise perfectly healthy? It can't be related to ageing. 2.221.69.177 (talk) 10:00, 30 May 2014 (UTC)
 * The article says "The age at which graying begins seems almost entirely due to genetics," and earlier "For some people this can happen at a very young age (for example, at the age of 10)." -- BenRG (talk) 18:12, 30 May 2014 (UTC)

Insect identification
Does anyone know what this flying insect is, please?&mdash;msh210 ℠ 06:18, 30 May 2014 (UTC)
 * I wouldn't be able to anyway, but from reading many similar queries on the Ask a Biologist website (have you tried there?), I can say that you'll need to state where in the World this was before anyone can have a realistic chance. The approximate date would probably also help. {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 13:18, 30 May 2014 (UTC)
 * I hadn't and haven't tried there: it's for school use only AFAICT.&mdash;msh210 &#x2120; 21:35, 30 May 2014 (UTC)
 * No, it certainly isn't only for school use. I started to read it regularly as I'm acquainted with someone involved in it, and though I haven't done so for several months, when I did I'd say the questioners were about 35/65 schoolkids/others. (The poster formerly known as 87.81.230.195} 2.123.27.154 (talk) 20:52, 1 June 2014 (UTC)
 * Yes, more info will probably be necessary to get to family_(biology) level or more specific. At the order_(biology) level, I think it's a Hemipteran, a.k.a. a "true bug." The best way to confirm this would be to catch one, and check for sucking mouthparts and 5-segments on the antennae.  SemanticMantis (talk) 15:16, 30 May 2014 (UTC)

Okay, more info: I found it in my home in St. Louis County, Missouri, the other day. There was only one of them (that I saw).&mdash;msh210 ℠ 21:35, 30 May 2014 (UTC)

Flouride
Is there any evidence which suggests that over use of flouride toothpastes are bad for gums?


 * Fluoride seems to say that concentrated fluoride itself is caustic, but of course toothpaste won't contain those concentrations. However, this isn't unique to fluoride, we also ingest many acids and bases every day, but normally not in concentrations that would harm our gums (or anything else).


 * Toothpaste is also abrasive, and a stiff brush can also irritate the gums with overly rigorous brushing. StuRat (talk) 13:28, 30 May 2014 (UTC)


 * Surely "over-use" is by definition bad.--Shantavira|feed me 15:04, 30 May 2014 (UTC)


 * Yes, but not necessarally bad for the gums. StuRat (talk) 16:15, 30 May 2014 (UTC)


 * Flour (note sp.) can be even more hazardous for the general health than fluoride (note sp.). --  Jack of Oz   [pleasantries]  21:29, 30 May 2014 (UTC)
 * Well, not in comparable quantities. --Trovatore (talk) 21:35, 30 May 2014 (UTC)

Optimum speed for an automotive alternator
I have searched for, but not found, speed/current curves for car alternators. Basically I'm looking for the lowest speed at which an alternator will deliver its rated current. I'm working on an alternate energy project where using widely available car alternators (70-100A range) makes the most sense, for a variety of reasons. The Alternator (automotive) article says alternators run at 2 to 3 times crankshaft speed, but says nothing about the optimal speed range. Another issue is the torque needed for starting and at rated output. I'm guestimating that a 100A alternator would need around 2kW of drive power, is that a reasonable estimate? Roger (Dodger67) (talk) 17:45, 30 May 2014 (UTC)
 * The voltage coming out of an alternator depends on two variables: the speed at which the alternator’s field is rotating and the amount of current flowing through the field coil (i.e. the strength of the magnetic field); a regulator varies the latter to keep the output at 14.4V to charge a 12V car battery. This article describes difficulties encountered if trying to run an alternator below the speed range for which it is self sufficient. From Bosch there is a technical specification available to credit card verification. 84.209.89.214 (talk) 19:07, 30 May 2014 (UTC)
 * I'm not sure I would trust that ebook site. If Bosch provides the spec for free then it should be available through them. I doubt that freebookez.com has distribution rights to that, and free things shouldn't need credit card information. K ati e R  (talk) 19:47, 30 May 2014 (UTC)


 * This has output curves for a generic alternator series.  K ati e R  (talk) 19:50, 30 May 2014 (UTC)


 * Alternators in cars and trucks are designed so that there is significant output at engine curb idle speed. Curb idle is usually around 600 to 900 RPM, at the low end for larger V8's and at teh high end for tiny bubble car engines.  Large high speed diesel engines for industrial, marine, and heavy truck use all curb idle at 750 RPM.  You can obtain the alternator speed by measuring the pulley diameters - alternator RPM = curb idle x crank pully / alternator pulley.  Automotive alternators should be around 85 to 90% efficient at crusing RPM (1000 engine RPM typical), so your estimate of mechanical input power is not unreasonable. Floda 121.221.223.1 (talk) 02:20, 31 May 2014 (UTC)


 * Thanks for the good sources - my Google-fu must have been on the blink! Roger (Dodger67) (talk) 14:00, 2 June 2014 (UTC)

How was it possible to destroy treasure in a bonfire?
I've read multiple accounts of defenders in sieges, before a last stand, to make a bonfire and burn their treasure to prevent it from falling into enemy hands. However, as most treasure in pre-industrial times was made out of gold or silver, how can they be damaged or destroyed in a bonfire? If part of the treasure was velvet or similar luxury clothing, then fire can indeed destroy it, but what about gold, silver, gemstones, etc.? Is the heat of a bonfire enough to at least partially melt golden chalices and jewelry? This might decrease their value, but the material can still be salvaged. --5.15.0.179 (talk) 18:02, 30 May 2014 (UTC)


 * It might be helpful if you could link to some specific accounts so we could give a better answer. In some instances, 'treasure' might be rather broadly defined to include all kinds of valuable (including functional) items that could have worth not linked to their intrinsic metal content&mdash;tools and weapons, for instance.  Going from an ingot of steel to a fine sword is a costly bit of labor. (And even when metal can be salvaged, it may require refinement or resmelting to remove impurities introduced during the uncontrolled melt.)  Some gemstones will survive fire better than others; diamond will actually burn in a hot fire.  (This PDF offers some guidance to artists who want to know if precious and semi-precious stones will survive in a kiln.)  TenOfAllTrades(talk) 18:19, 30 May 2014 (UTC)


 * FWIW, some gemstones are heat treated for improvement of colour - lots of interesting material out there. Collect (talk) 18:23, 30 May 2014 (UTC)


 * Diamonds burn...but their ignition point is 850 to 1000 degC. Gold also melts at around 1000 degC, silver at 950.  So doing anything much to these materials requires temperatures around 1000 degC...but a decent log bonfire can reach that kind of temperature in the center - so it's certainly possible.  Gold is really unreactive though - you can't get rid of it by burning it.
 * I've also read about people in these dire circumstances either burying their gold - or tossing it into deep wells.  That seems like a fairly reasonable strategy.
 * SteveBaker (talk) 20:23, 30 May 2014 (UTC)


 * It's irrelevant to the question, but Steve's last paragraph reminds me of the unusual way that two Nobel Prize gold medals were hidden from the Nazis when they occupied Denmark. On the other hand, around the same time Alan Turing buried some silver bars in case England was also invaded, and then never managed to find them again. --69.158.92.137 (talk) 21:18, 30 May 2014 (UTC)


 * It would be interesting to read the accounts. I imagine that sometimes this tactic would pay off handsomely.  For example, if you throw some gold bars in a cottage and set it on fire, a group of raiders isn't going to want to hang around picking through the burning embers thinking there's gold in there somewhere.  Then you come back, spend half a day searching, and your wealth is intact (except for the cottage). Wnt (talk) 22:48, 30 May 2014 (UTC)


 * Some other methods to hide treasure:


 * 1) Break it into small pieces. Gold dust, for example, could be mixed in with grain and hidden that way.


 * 2) Swallow it. Jewels were sometimes swallowed.  They can then be "retrieved" later.  The Crusaders, however, just hacked apart anyone they suspected had swallowed treasure.


 * 3) Put it someplace disgusting, like in a cesspool. They aren't likely to search there. StuRat (talk) 05:30, 31 May 2014 (UTC)

My question was not about "how would you prevent treasure from falling into enemy hands", but how would a bonfire really destroy/damage treasure. An account which comes to my mind is the siege of Dregely where the defenders, near the end of the siege, made a last stand knowing they will all die, but before it, they allegedly killed all their horses and made a bonfire in the middle of the castle and threw all their valuables into it. This event is not present in the Wikipedia article, but I found references to it in ballads and similar works (one even mentions "all their silver, gold and valuables"), so the question is not even about historicity, but about what would really happen in such a situation. I faintly remember other similar stories. --5.15.32.92 (talk) 07:27, 31 May 2014 (UTC)


 * There are many possible answers here:


 * Some gemstones do burn at the temperatures found in a good sized bonfire (eg diamonds) - so these could be totally destroyed.
 * Other gemstones are chemically changed - and may (for example) permanently change color when heated - which might reduce their value.
 * Although gold and silver would not be destroyed or transmuted into some other chemical compound by burning, it might be hard to recover the resulting metal when mixed with ashes and charred wood and such. People who raid towns for their wealth are not necessarily very interested in spending the time to get the crud out of a puddle of molten metal.  It takes some degree of sophistication to separate out these two metals once they were melted together.  Pure gold would be worth more than a low carat gold with a lot of silver mixed into it.
 * The intrinsic value of an item is often in large part derived from the history, utility, beauty and craftmanship of the thing, and only in small part from the value of the raw metals and stones it contains. That first part is effectively destroyed by melting it all into a big, dirty glob.
 * Some items might have a specific function (imagine the King's crown and a ring used to sign documents with an impressed wax seal) - and destroying those might prevent the conquerors from claiming some right (so maybe they won't be accepted as the new King without his crown - and they can't forge documents without the seal).
 * Coins may also have a face value that's more than the metal they contain.
 * Attackers might not even think of digging around in the ashes of a bonfire in the hope of finding a puddle of gold and silver. At the very least, they might waste a lot of time trying to find out where the jewels were hidden before figuring out that the grungy puddle of metal at the center of this large pile of ashes is what their prize should be.
 * If the people within the town knew they were going to die anyway - this might just be a desperation measure - perhaps they didn't even think through the effectiveness of it all.
 * People of the 1500's didn't understand much about chemistry - alchemy was all they knew. Perhaps flawed alchemical reasoning lead them to believe this would work.  It's not like they had a ton of time to think this through.
 * The attackers were not especially technologically advanced either - could they actually recover useful amounts of gold and silver from the resulting mess? Would they even bother to waste time on it when there were more cities to attack.
 * It may simply be a matter of "Find everything of value and toss it onto the bonfire!" - which would certainly have destroyed many of the valuables.
 * In this case, there initially were only 140 or so people defending the city against an army of 10,000. By the time they decided to do this, there may have been no more than a few handfuls of people left - and they'd have been fairly busy trying to stay alive for another day - they might be starving, wounded and in truly terrible shape by this time.  They simply may not have had the luxury of time and energy to think up a cleverer scheme for hiding their gold and silver.
 * Gold, in particular, is a fairly un-reactive element. It's exceedingly hard to convert it into anything other than a chunk of shiney metal.  If not this, then their only choice would be hiding it, or putting it somewhere hard-to-reach.  I think this was a simple and effective way to hide it.
 * In the end, any small gesture of defiance would be of some consolation to the people in their last hours - so the ruler of the town who called upon the people to do this may have been thinking more about their morale for the coming battle than about the actual utility of doing this.
 * SteveBaker (talk) 12:50, 31 May 2014 (UTC)
 * I found the event at Dr%C3%A9gely_Castle and Gy%C3%B6rgy_Szondy; the "treasure-pyre" was described in a modern song.  No idea if there's any truth to it.  It could be a small garble - for example, there were banks in medieval times, and you could certainly burn the letters they used.  But it's easy for me to believe it's just a story; convenient to say gold "was just burned up" when you've taken it for yourself. Wnt (talk) 21:26, 31 May 2014 (UTC)
 * Wow, SteveBaker, a very interesting and very thorough explanation, many thanks!
 * Wnt: that modern song is actually based on a much older ballad where the burning of treasure is also mentioned. And I remember reading about similar events in other cases of last stands, where the defenders burned everything to prevent the enemy from getting it. Anyway, the point of the question was not in which sieges they did it and in which sieges they didn't, but what effects it would have on the treasure, and whether a pyre would be strong enough to damage treasure made of precious metal, which was answered in an excellent way by SteveBaker. --5.15.32.92 (talk) 23:42, 31 May 2014 (UTC)


 * Some treasure was mostly wood, adorned with the metals and gems (or not). Crucifixes, paintings, furniture. Some treasure chests themselves are/were more valuable than the trinkets they held. In the days before radio, carving and painting was the treasured escapism. I think we equate metal more with old treasure simply because it remains. In gold's case, remains shiny. But the non-metal plunder burns easily. Maybe that's what they meant. InedibleHulk (talk) 00:01, 1 June 2014 (UTC)


 * The puffed and slashed clothing of the landsknechte allegedly was designed to show off the costly cloth that was part of their loot. —Tamfang (talk) 06:30, 1 June 2014 (UTC)

Why do animal babies scream?
Why do wild animal babies cry out when you grab them?

What evolunentary purpose does it serve for example for a wild gosling to scream when you pick it up, and the parents don't even run towards you they just hiss a bit and then waddle off with the other babies leaving the captured one to die?

The hypercritical person released the gosling


 * This may be too simplistic of a view, and granted, it's from my own observations, but: It's a natural response for the young of many species, including humans. It attracts the parents' attention and lets the would-be predator know that help may be on the way, similar to a car alarm. Justin15w (talk) 21:52, 30 May 2014 (UTC)


 * If you'd been somewhat closer in size to the goose, then you might've found yourself being attacked by the parents in response to their offspring's alarm call. I have heard of angry parent geese absolutely wrecking dogs and cats, for example. A somewhat larger bird, the swan would likely seriously consider taking you on (yes, never mess with cygnets). --Kurt Shaped Box (talk) 22:56, 30 May 2014 (UTC)


 * I'm suspicious that there is a lot more game theory involved here than people give the animals credit for. For example, I wonder if birds that call an alarm as we walk through their territory really see us as a threat to them so far up in the trees - or rather as a threat to their potential future prey, who for the moment are thus their allies and bestowed with intelligence reports.  But there are so many ways that an alarm can affect the ecology.  To call in predators of the predators, or create a threat that stakes a territorial claim, etc.  How can an ecologist measure the frequency of all of the effects in a wide range of natural environments of a species with such accuracy as to quantify the major effects on fitness, if indeed it even is a matter of natural selection rather than animal culture? Wnt (talk) 04:24, 31 May 2014 (UTC)


 * Besides these excellent points, if the prey didn't scream, the predator might easily grab another one, and yet another one, because they didn't knew there was any danger. --5.15.32.92 (talk) 07:46, 31 May 2014 (UTC)


 * By screaming it warns the other goslings and the parents, i.e. its closest relatives. If a gosling has a genetic variation that makes it scream, then in most cases some of its siblings will also have the same genetic variation (kin selection). Icek (talk) 14:01, 31 May 2014 (UTC)

bottled water
Why does bottled water have an expiry date? Does water "go off"? Think glass bottles because I know plastic bottles grow leeches into the water after a while
 * One would hope there are no leeches growing in the water! There should be an article on shelf life which could answer some questions. One thing about bottled water is that it seems typically to be dated to "expire" some number of full years after the bottling date. ←Baseball Bugs What's up, Doc? carrots→ 22:45, 30 May 2014 (UTC)
 * As Bugs says, there will not normally be leeches growing in the water. I presume you mean to talk about substances leaching from the bottle into the water. (Or was that intended as a joke?) --ColinFine (talk) 17:45, 1 June 2014 (UTC)


 * Glass bottles can still have plastic gaskets or seals in the screw top that can leach phthalates. --Aspro (talk) 23:07, 30 May 2014 (UTC)


 * The laws that apply to expiry dates usually apply to all foodstuffs. There are many foodstuffs that have unnecessary expiry dates. One can choose to ignore them.


 * Does water actually have an expiry date or is it more likely to be a best before date to indicate shelf life? Also this and this both have similar info as to why the date is on there. I found several more with the same story. CBWeather, Talk, Seal meat for supper? 13:22, 31 May 2014 (UTC)


 * It is not in the self interest of a "manufacturer" of bottled water to deliver a product that looks like it can be stockpiled forever, even if it can be. 84.209.89.214 (talk) 19:01, 31 May 2014 (UTC)


 * In terms of food safety, bottled water has a "best before" date -- even if it expires, you can still drink it without ill effect if you have to (but it's better not to, because by that point it starts tasting like plastic). 24.5.122.13 (talk) 00:24, 1 June 2014 (UTC)

dream recall
What substances are scientifically proven to dramatically improve dream recall / memory? Like eating a slice a cheese and remembering every dream you had during the night, but I want references and verifiable facts not hearsay about cheese. Thanks InceptionFan (talk) 22:54, 30 May 2014 (UTC)
 * Here is an article that has some good references. Start there and see where it leads you.  -- Jayron  32  23:02, 30 May 2014 (UTC)
 * A procedure of dream researchers that is also followed by writers intent on capturing plot ideas in dreams is to keep a notebook and pencil ready at their bedside. Dreams can be most vividly recalled immediately after gentle waking from the REM phase of sleep. 84.209.89.214 (talk) 00:22, 31 May 2014 (UTC)

See; Psychopharmacology of REM Sleep and Dreams Richerman    (talk) 10:10, 31 May 2014 (UTC)