Wikipedia:Reference desk/Archives/Science/2010 August 25

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August 25

Growing Tree

A tree is growing. I am 3 feet tall. I stand near the tree and just at near where my head-top corresponds to the tree, i.e. at 3 feet from the ground level, I make a mark of adequate depth that (let's suppose ) will last forever. The tree will grow. What will happen to the mark ? Will it's distance from the ground increase as it will grow  Jon Ascton  (talk) 01:02, 25 August 2010 (UTC)

No. Trees (and almost all plants) grow from the top. Grass grows from the bottom though. Ariel. (talk) 02:13, 25 August 2010 (UTC)

I don't think this is completely right. There is a Birch tree which I used to easily climb when I was a kid at my dad's house. 40 years ago I could reach my leg up and step into the first fork, despite being 10 years old and shorter than I am now. The tree seems to have grown in all proportions, it is now much thicker, much taller and the fork is just above shoulder height. -- ~~

Trees grow both upwards and in diameter. The layer of wood immediately under the bark is the sapwood or living wood. This reference describes the growth process and concludes that the height of a bird-house fixed to the trunk will not increase as the tree grows. Cuddlyable3 (talk) 12:33, 25 August 2010 (UTC)

I will try to get some photos, the fork is definitely much higher from the ground than it was years ago. -- Q Chris (talk) 13:49, 25 August 2010 (UTC)

I think it depends on the age of the tree, if you did it to a sapling then it might move up, I doubt it would happen on a mature tree though. Part of the reason is that botanists measure trees at 1.3m above the ground (diameter at breast height) and if they are studying how fast they are growing will add a line of paint to the tree to speed things up next time round. Q Chris - is it possible that the fork you remember climbing has died/been cut off and isn't the same one you see now? Smartse (talk) 14:10, 25 August 2010 (UTC)

There might be a simple explanation: What you call fork is probably the meeting point of the bark of two upleading branches. That means your original forkpoint is now deeply embedded into the stem, the current fork point is the meeting point of new layers of material. Try to imagine what happens when you surround all existing bark with further layers. And try to follow in mind the middle line of the branches to the point where they meet. -- Tomdo08 (talk) 14:19, 29 August 2010 (UTC)

Well, I just consulted my mom who belongs to countryside and spent her childhood among trees. She says she once marked a tree for it's fruit and though the tree grew high with time, but the marking she made did remain at same level  Jon Ascton  (talk) 06:21, 26 August 2010 (UTC)

Getting an old scientific article - how?

Hi, I would like to read the article "Thinking about the brain" from Francis Crick, which was published in 1979 in the Scientific American of September (241 (3), p.181-188). Is it possible to get that article easy and for free? The licence of my library seems only to reach back till 1984. -- 89.196.35.247 (talk) 02:38, 25 August 2010 (UTC)

Usually Google Scholar is the best bet for things like this, but it shows no online versions, not even non-free. Have you tried looking for hard copies of Scientific American from that era in your library? Looie496 (talk) 02:59, 25 August 2010 (UTC)

Copies from 1979 should be readily available. I suggest you go to your library and ask about inter-library loans. Most libraries are happy to arrange inter-library loans. It is part of their function. Dolphin (t) 03:01, 25 August 2010 (UTC)

Ok, I'll try. Thx for the answers. -- 89.196.35.247 (talk) 09:05, 25 August 2010 (UTC)

Or ask at Wikipedia:WikiProject_Resource_Exchange/Resource_Request and some kind person will make a copy available to you. Smartse (talk) 14:12, 25 August 2010 (UTC)

I got the great idea, to just look at the german version. This one is available at my library and also online. I also asked about inter-library loans, but that was complicated and costs some money. Thx for the help anyway. Won't be the last time I need such articles, Resource Request is also a great hint! -- 141.30.81.231 (talk) 01:15, 27 August 2010 (UTC)

Double check my work?

The question reads as "If a current of 40mA exists for 0.8min, how many coulombs of charge have passed through the wire?" Given that, I used

$.04=(x/48)$

I got an answer of 1.92 coulombs but the book says 192. Who's right? And if it's the book, why? Dismas|^(talk) 05:46, 25 August 2010 (UTC)

I also get 1.92 Coulomb. Typing error? Dolphin (t) 07:15, 25 August 2010 (UTC)

Thanks! Dismas|^(talk) 07:55, 25 August 2010 (UTC)

192 cC or centicoulombs. Cuddlyable3 (talk) 11:17, 25 August 2010 (UTC)

This thread is a bit old, but generally dimensional analysis can increase your confidence in solutions to these sorts of problems. In particular, 1 ampere = 1 columb / second. 67.119.3.248 (talk) 19:16, 30 August 2010 (UTC)

Anesthesia causing nerve damage?

Bear with me here, I have a Chinese co-worker whose wife just had all four of her wisdom teeth out. Apparently this was done with only a little bit of local anesthetic and with the patient fully aware, and in fact sobbing in agony, throughout the procedure. I was horrified. My Chinese friend laughed it off and said that "Chinese people don't use anesthetic because it can cause nerve damage." He seems quite confident in this position, seeing as how his mother is the managing director of a local hospital. I, on the other hand, call bullshit. Thinking critically, I think the likely absence of anesthetic in many parts of post-WW2 China had to be justified somehow, and once cultural acceptance set in the authorities have seen no real motivation to change, despite the modern widespread availability of anesthetics.

I've experienced this reticence to prescribe pain-relievers personally, by the way, when I broke my arm here last year and they were quite shocked by my request for pain-killers after having had my arm set and casted. "You want what? Haha! Silly foreigners aren't as tough as Chinese!" Anyway, back to the original question - has China picked nerve damage as the one aspect of human quality of life out of thousands that they actually care about (ignoring things like air quality, noise pollution, smoking, etc) ? or is this just BS? 218.25.32.210 (talk) 07:46, 25 August 2010 (UTC)

The article Traditional Chinese medicine will be of interest because it is still practiced alongside western medicine. Acupuncture is used for pain relief in TCM which may explain a slowness to accept Western pharmaceuticals such as pain-killers. Cuddlyable3 (talk) 11:14, 25 August 2010 (UTC)

It's not complete bullshit, but it's pretty rare. See Local anesthetic#Undesired effects for more information. Regards, --—Cyclonenim | Chat  12:35, 25 August 2010 (UTC)

In my experience, Chinese people can have some weird ideas on what is and is not safe. I knew a Chinese guy who would not stand within 20 feet of a running microwave because he thought he would get cancer, but he was perfectly fine with smoking. Googlemeister (talk) 13:17, 25 August 2010 (UTC)

Lignocaine#Adverse_drug_reactions has some specifics on a dental anaesthetic which can cause nerve damage. Making assertions from your friend and one doctor to the 1.2 1.4 billion people in the PRC might be a mistake though. Smartse (talk) 14:05, 25 August 2010 (UTC)

(ec)In my experience, Wikipedians can have some pretty offensive ideas about when it is appropriate to draw conclusions about an entire country or ethnic group based on anecdotal information. I knew a Caucasian Canadian woman who wouldn't let grocery store clerks use a bar code scanner on her food because it was "radiation". On the other hand, I haven't met any Chinese people who hold that particular damn-fool belief; I therefore conclude that it's Caucasians – or maybe it's Canadians? – who have 'weird ideas on what is and is not safe'.

Seriously, the Reference Desk is not the place to parade your own personal stereotypes. If you want to talk about what this or that people believe, then use real numbers, from properly-vetted studies. And I note that in the United States, recent studies have found that between half and two-thirds of all Americans believe in angels; a significantly larger fraction than believe the scientific consensus on global warming (about one third). Who's got the 'weird ideas', again? TenOfAllTrades(talk) 14:08, 25 August 2010 (UTC)

I have no direct knowledge of the Chinese culture, but bear in mind that the country faced a long and extraordinary enslavement to opium as the result of more than two centuries of drug prohibition, which according to some was only fully extirpated in Maoist times under the severest coercion. I would not be so surprised if a cultural imprint remains. Speaking as someone who has rejected several overtures by dentists to remove healthy third molars, I think her ordeal may well have been doubly unnecessary. Wnt (talk) 14:09, 25 August 2010 (UTC)

It is possible for there to be temporary (or, very seldom, lasting) damage to nerves simply due to the injection of local anesthetic — the needle may touch or pass directly through the nerve when administering the nerve block, though usually even this does little or no harm. More common is damage to the nerve caused by the extraction itself; damage to the lingual nerve may result when the roots of the wisdom teeth are particularly close to the nerve. This summary is brief, and quite accessible. See also Dental extraction#Complications. TenOfAllTrades(talk) 14:27, 25 August 2010 (UTC)

Damage to the lingual nerve is rare as a result of wisdom tooth root proximity -- this is because the lingual nerve does not enter the mandible (as does the inferior alveolar nerve) but rather courses medially to the body of the mandible. The lingual nerve does exist in superficial soft tissue, but danger to it is likely to occur as a result of an ill-placed incision during surgical extraction of the lower wisdom teeth, regardless of root position. There is a very little bit of supportive literature for danger to the mandibular segment of the trigeminal nerve following the administration of articaine, but this was in a pediatric patient and the reported incidence (depending on whether or not you include one of the instances based on extenuating circumstance) was either 1:100,000 cases or 2:100,000 (1:50,000). So the rate of irreversible damage to the mandibular branch of the nerve due to nerve blocks using articaine is taught as 1 in 50K to 1 in 100K. Still, since articaine is no more efficacious than lidocaine or mepivacaine in respect to mandibular nerve blocks, many dentists opt to not use articaine for blocks. DRosenbach ^{(Talk | Contribs)} 19:25, 25 August 2010 (UTC)

As an additional anecdote, I got 4 baby teeth pulled in two separate operations in a PRC hospital when I was 7, and a fifth tooth pulled by a Chinese Canadian when I was 15. All operations were done with only a bit of local anesthetic and with me fully awake, but I didn't feel any pain; the actual injection of the anesthetic was by far more painful than the actual tooth-pulling. The OP seems to imply that Western dentists use general anesthesia for pulling teeth, which is definitely not the case except in unlikely circumstances (i.e. phobic patients).

As for Chinese people having weird medical concerns, that's definitely true. Most Chinese still subscribe to long-disproven theories from traditional Chinese medicine, and often prefer traditional medicine over scientifically-proven drugs. However, I don't think this is any different from Western people believing in homeopathy, faith healing, EM hypersensitivity, "natural" products (as opposed to chemically synthesized ones), etc. To put it bluntly, the general public is simply stupid, a statement that holds true across all cultures and across all time. --121.29.117.97 (talk) 16:23, 25 August 2010 (UTC)

(In response to one of the above comments) My mom also tries not to stand in front of the microwave for fear of radiation, but unless you have a fair bit of scientific knowledge, it's not obvious why microwave radiation is not dangerous. Consider this explanation that I offered my mom: "That metal surrounding the microwave chamber acts as a Faraday cage, greatly attenuating the intensity of the microwaves. The mesh on the door has very small holes, which don't matter because microwaves have a wavelength on the order of centimeters while the holes are 1 mm in diameter. Furthermore, microwave radiation is not ionization radiation like UV, and the individual photons which comprise it are not energetic enough to cause significant genetic damage, so normal cells are therefore not more likely to become cancerous." I'd be very surprised if a significant proportion of any country's population can even understand that explanation, let alone think up of it. --121.29.117.97 (talk) 16:41, 25 August 2010 (UTC)

In fact, the radiation that the microwave produces is harmful. It's the most harmful microwave radiation because it is at the exact wavelength to heat water, which makes up a fairly substantial part of our bodies ;) The good thing is that it's well contained in the microwave, at least to the extent that it's made it very difficult to determine any negative effect. Another point is that microwaves are used for such short periods (and often without human proximity) that it's unlikely to have a substantially damaging effect. Regards, --—Cyclonenim | Chat  19:16, 25 August 2010 (UTC)

Chinese anaesthetics used during tooth removal is usually just a small amount inejcted via a needle, while Western anaesthetic commonly involves gassing the patient to put them out of consciousness, though I'm sure it's also used vice versa. There have been incidents in Chinese history when painful procedures were done without anaesthetic, but this was usually during the Japanese occupation. See Unit 731. ~AH1^(TCU) 19:06, 26 August 2010 (UTC)

Human Appearance and Incest

If generation after generation of a family line were to have one daughter and one son who would then have children together would the children eventually be genetic clones of their parents? TheFutureAwaits (talk) 09:18, 25 August 2010 (UTC)

No. Each child would inherit a mix of genetic material from both of its parents. To be a clone a child would need to inherit all of its genes from only one parent, which is not possible within the natural human sexual reproductive process. Gandalf61 (talk) 09:25, 25 August 2010 (UTC)

But there are only two sets of genes to mix from and given that each generation would come from siblings most of the genes would be the same with the similarity increasing each generation. So at some point the genotype of the children would be the exact same as their parents, no? TheFutureAwaits (talk) 09:36, 25 August 2010 (UTC)

Oh, I see. You mean that the genetic diversity of this "population" will decrease over time, and so eventually there will be a generation in which the two siblings happen to be genetically identical, and from that generation onwards all of their offspring will also be genetically identical. I suppose that might happen in theory, if you assume are absolutely no mutations. Gandalf61 (talk) 11:13, 25 August 2010 (UTC)

Another question: how long would they be able to do that before their descendants become unfertile/impotent/too deformed to survive until sexual maturity? The Spy Who Came in from the Cold (talk) 09:41, 25 August 2010 (UTC)

Very, very soon I think. In the second generation awful recessive genes will already come to the fore. Recessive genes are important for past battles Humanity successfully fought but where the environment doesn't show them anymore. When that battle comes back again, the few "freaks" will survive and the previous "dominant" gene might not survive in Humanity at all. Until then, we don't need that phenotype. So, if you had such major incest, any recessive genes would come out, and in fact after a few generations you simply would have awfully maladaptive ones, I think it would not be many before the chidlren had an IQ of a squash. (summer squash) 84.153.253.222 (talk) 09:54, 25 August 2010 (UTC)

(edit conflict)What I think the OP is asking is this

At first the father has for chromosome 1, the combination Pp and the mother has Mm. The girl has a 50/50% chance of inheriting the same chromosome as her brother, for MP, Mp, mP or mp. Each chromosome has a separate 50%/50% of being the same in both children.

If the children both have the same two copies chromosome 1, say Mp, and were to have their own children, then each grandchildren would separately inherit Mp (50%), MM (25%) or pp (25%).

(The statistics start getting interesting at this point)

Ignoring cross-over and de-novo mutations, once the two children are homogeneous for a chromosome then all their children will remain that way. Eventually the children will be homogeneous in all their chromosomes. Except for the sex-selection chromosome XX and XY, for which the girl will end up being homogeneous for both her X chromosomes, either from the ancestral father or mother. The boy will have the same X chromosome.

How long does it take for the descendants to become homogeneous in all their chromosomes?

My apologies if I'm not correct in my re-phrasing of the original question. CS Miller (talk) 10:08, 25 August 2010 (UTC)

Yes that's exactly it, thanks for restating it so clearly. I have a feeling they would have homogeneous chromosomes very quickly considering how little difference there is in the DNA between siblings. And once homogeneous then if they had two sons they would both be twins even if they were born years apart. TheFutureAwaits (talk) 11:57, 25 August 2010 (UTC)

The Wikipedia article Incest is about social/legal/religious consequences. The article Inbreeding is informative about biological consequences in humans. Cuddlyable3 (talk) 11:03, 25 August 2010 (UTC)

There are many inbred strains of mice and other animals, so it is not impossible for humans to survive repeated inbreeding, particularly if the number of children with each generation is large. However, inbred mice seem to lack the vitality, fecundity, and intelligence of wild mice. Also consider that as with Tasmanian devils, inbred humans would suffer such odd plagues as contagious cancer. Wnt (talk) 15:18, 25 August 2010 (UTC)

The deal is this - because you get one of each chromosome (except the X & Y 'sex' chromosomes) from each parent (and each parent had a random chance of which of two they had would be passed on), there are 4²² ways of mixing them. So for any two completely unrelated parents, there are 17.6 trillion genetically different boys and 17.6 trillion genetically different girls that they could have as children. However, when a boy and girl sibling mate, then for each chromosome, there are only a few possibilities:

• That the chromosome pair contains one from the grandfather and one from the grandmother (4 possibilities).
• That the chromosome pair contains two identical copies from the grandfather (2 possibilities).
• That the chromosome pair contains two identical copies from the grandmother (2 possibilities).

In the first case, the child would be OK - but either of the other two cases, the child is at great risk.

Normally, we have two different versions of each chromosome - so if one of them is faulty, and cannot produce some critical enzyme or something - then the other will make up for it. But if they are identical (which is a 1/6 chance in that third generation) - then any small flaw is going to manifest itself and you're in big trouble. With 22 (non-sex) chromosomes - the odds are good that several of them will turn out to be like that.

When you push your luck into yet another generation, you might get lucky and fix the problem by the child inheriting one of the duplicated ones and a diffent one from the other parent...but the odds are getting much thinner if there is already a 1/6 chance of the other person having the exact same problem. Once one any one of the four original copies of that chromosome fails to make it into the next generation (the odds of which are pretty high) then it's gone forever and now there are only three versions left...then only two..and finally, only one.

...and that's where things get really nasty. Once both boy and girl child have the same duplicated chromosome pair from the same ancestor - then there is no way (other than mutation) for that to ever get fixed in subsequent generations.

Keep that up long enough and (assuming they don't become sterile or die before having the requisite one boy and one girl) then more and more of the chromosome pairs will be duplicated like that. Only the Y chromosome will be unaffected by the problem since there is only ever one of them in males and any serious defect would have prevented the original male parent from functioning.

Eventually (although it might take a large number of generations to happen by chance) all 22 chromosomes would indeed become duplicated pairs - and the only genetic variation in subsequent generations would be between the boys and the girls.

However, the odds of that happening without the inbreeding killing off the blood line is almost zero. It couldn't happen in reality.

SteveBaker (talk) 15:31, 25 August 2010 (UTC)

Please see e.g. [1] - mice can undergo 55 generations of brother-sister mating (the OUW strain) without any particularly noticeable effects, though sometimes mutants shake out much sooner. I wouldn't doubt that however unremarkable they seem to us, these inbred creatures are C'thulhean horrors from the perspective of a wild mouse, but they are certainly viable. Wnt (talk) 15:45, 25 August 2010 (UTC)

See Charles II of Spain --Dr Dima (talk) 16:21, 25 August 2010 (UTC)

The Golden hamster is a perfect inbreed and there are no obvious problems with it. --Stone (talk) 17:25, 25 August 2010 (UTC)

But it only has a lifespan of 2-3 years max. Not a lot of time to develop cancers. Googlemeister (talk) 18:32, 25 August 2010 (UTC)

This chapter seems to be messed up with additional questions and answers about possible damages. Therefore I would like to summarize and add a little bit:

The question is, if in a row of inbreeding sibling pairs the genome at last will become identical. The answer is, it approximates identity. On average 50% of the genes of two siblings will come from the same source. Also part of the remaining 50% will be identical, too, because the sources are already identical. That means that the portion which is different is around 1/2^(n+1) with n = number of inbreeding generations. With ca 23000 genes you will have less than one gene difference after approximately 14 generations. This of course is a very rough approximation because of multiplication of uncertainty, connectedness of genes, fragility of genes and mutations. Please note for example that you have less than one chromosome difference after approximately 4 generations. Without crossings you would have roughly 15% chance of identity after only 2 generations. There is also the aspect that part of the genome is always maternal and with normal sex there has to be the difference between X and Y. -- Tomdo08 (talk) 16:09, 29 August 2010 (UTC)

do more socially adept people mind less being lied to?

So, this is just my personal experience but I was kind of a recluse and not well-integrated socially, but then later improved substantially. For me personally, it seems I don't really mind being lied to. In fact, I don't consider it any worse than a web server sending other than perfectly formed standards-compliant HTML: in the end, the server sends your browser something because it wants the browser to behave a certain way (and its author knows it will behave that way) and the end result, the experience in browsing that page, is what matters. So with lies, I don't care if it doesn't conform to the truth, I care more about what the end result is of my being lied to. Often it can be obviously beneficial to me, and I don't care. This extends to companies too: a company one of whose products I own was sued for deceptive advertising, as their advertizing made it seem as though their products were hand-made (the ads showed an artizan making them), even though they were anything but: they were mass-produced in factories. I just didn't care. I'm sure a few years ago, I really would have, as you can't show an ad and have ad text all talking about hand-making something, when that's not even how you make it... And now, I think it just adds to my enjoyment of my product.

So, my uestion is whether my "arc" is a usual one: do people, as they become better and better integrated socially and have more and more friends, just mind less and less being lied to? 84.153.253.222 (talk) 09:51, 25 August 2010 (UTC)

I have not found a study of such a subjective issue as minding being lied to. You seem to have developed a tolerance for it, but see Lie#Consequences of lying. Protection against misleading advertising is regarded as important to protect consumers and ensure fair competition, as evidenced by the many national organisations for regulating advertising. Cuddlyable3 (talk) 10:56, 25 August 2010 (UTC)

What you seem to be discussing is a form of instrumental rationality, but you seem to be asking for a value judgment on the issue. That varies across different perspectives. Economic theory has tended to idealize instrumental rationality as the primary motivator in human activities; social theory and psychology have tended to decry instrumental rationality as a relatively low level of cognition and social interaction. The problem boils down to a question of social 'good' vs. personal 'good': e.g. it's one thing if your football coach lies and tells you that you are the greatest team he's ever seen (because that lie can build social cohesion and produce better performance overall), but it's another thing if I lie to your wife/girlfriend that you've been cheating so that I can sleep with her (because that lie could destroy your relationship for my benefit). It's not a simple issue. as a rule of thumb, the more that a lie is seen as a collective social fiction (the way that Santa Claus is broadly treated as real in certain contexts through Western culture) the less objectionable it is; the more a lie is seen as creating an advantage for some at the expense of others, the more objectionable it is. --Ludwigs2 15:29, 25 August 2010 (UTC)

Conscientiousness may be what you are describing - people high in that trait prefer working to having parties, and dislike lying. 92.15.17.245 (talk) 21:02, 25 August 2010 (UTC)

Skin effect and AC resistance

I wounder why it is called AC resistance rather than Skin inductance for instance. I assume, it can't be added algebraically (without vectors or phasors! can it?), to the DC resistance, although I don't know how to get its precise derivation. I'd be obligated to know how to consider both DC and AC resistances at some low and intermediate frequencies. --Email4mobile (talk) 12:26, 25 August 2010 (UTC)

I assume it's called "AC resistance" because it's simply resistance measured using an alternating current.

While we're at it... I wonder whether a bundle of carbon nanotubes used as a power line would be immune to the skin effect, like the ultimate litz wire? Wnt (talk) 14:17, 25 August 2010 (UTC)

biology(human heart rate)

why woman have higer heart rate about 72 to 80 bpm compare with man which is only 64 to 72bpm only? —Preceding unsigned comment added by Syafy (talk • contribs) 13:47, 25 August 2010 (UTC)

I'm not sure it does vary, nor is elevated heart rate (>90 bpm) safe for either sex. See PMID 7963118, PMID 20719745. Bear in mind that exposure even to low levels of nitrogen or sulfur dioxide pollutants leads to measurable alterations of resting heart rate, [2] though this study also finds a measurable sex difference. I do not mean to suggest that the sexes are precisely alike - there are too many papers for me to read that find otherwise on one technical point or another - but I suspect it's more productive to look for other environmental and lifestyle factors. Wnt (talk) 14:41, 25 August 2010 (UTC)

Size. In general smaller hearts beat faster, and women are usually smaller than men. Ariel. (talk) 21:54, 25 August 2010 (UTC)

As for the dangers of an abnormally high resting heart rate, see tachycardia. ~AH1^(TCU) 18:59, 26 August 2010 (UTC)

What kind of bug is this?

I've been searching for quite some time an I am unable to identify this bug. If anyone can help I would appreciate it.

photo 1 photo 2 photo 3

Keegstr (talk) 14:28, 25 August 2010 (UTC)

Please, please PLEASE - when you are asking for identification of animals and plants (and especially insects) it helps us immensely if you tell us where in the world you saw this creature. There are about 2 million species of insects and every scrap of information helps! SteveBaker (talk) 14:41, 25 August 2010 (UTC)

Sorry! It was seen in Chesapeake, Virginia (USA) at the Chesapeake Arboretum. It was on a plant in their herb garden, but I did not get the name of it. Keegstr (talk) 14:48, 25 August 2010 (UTC)

I would think it was some sort of aphid by look, but it seems a bit larger (aphids rarely get over a centimeter in length). --Ludwigs2 15:10, 25 August 2010 (UTC)

Looks like a true bug, suborder Heteroptera, to me. --Dr Dima (talk) 16:35, 25 August 2010 (UTC)

That is a definitely a hemiptera nymph of some sort. Almost certainly heteroptera. Note the lack of wings, which only show up in later (the final?) instars. If you'd like a more precise ID, post it to bugguide.net; the people there are very helpful and knowledgeable. Or you could try browsing through the taxa there and see if you can spy it. -Craig Pemberton

Redshifted starlight

Now we know the universe is expanding because distant stars are moving away from us correct? And we know they are moving away from us because their light is redshifted. So is it fair to say that pretty much all the stars we observe from Earth have their light redshifted? 148.168.127.10 (talk) 15:11, 25 August 2010 (UTC)

See Blue shift. -- ToE^T 15:15, 25 August 2010 (UTC)

Not all stars (and in particular, galaxies) have a positive redshift. But, as Hubble pointed out in 1929, and has been repeatedly re-confirmed with more recent equipment, the overwhelming majority are moving away from us. Nimur (talk) 15:35, 25 August 2010 (UTC)

But if space is expanding at a rate fast that light, how can any stars be moving towards us? 148.168.127.10 (talk) 15:58, 25 August 2010 (UTC)

The expansion of space depends on distance from the observer; it is not faster than the speed of light for most of the observable universe. And, nearby objects may have proper motion in any direction, independent of the expansion of space. The important thing to realize is that the expansion of space is most relevant at very great distances. For nearby objects (like Earth's Moon or Proxima Centauri), the rate of expansion is so small as to be negligible for most purposes. In these cases, the (Newtonian) gravitational and inertial motions of the object are sufficient to explain their apparent velocity toward or away from us. Nimur (talk) 16:09, 25 August 2010 (UTC)

Stars that have a negative radial velocity are approaching the Sun. Sirius, for example is expected to arrive closer than it is now in a few thousand years. ~AH1^(TCU) 18:58, 26 August 2010 (UTC)

The rate of expansion within the Milky Way, and for that matter the Local Supercluster, is zero. Hubble's Law only applies to relative velocities of superclusters. -- BenRG (talk) 23:49, 26 August 2010 (UTC)

Now I'm confused. Do you mean the local supercluster is not expanding at all, or expanding so slowly as to be negligible? Nimur (talk) 15:37, 27 August 2010 (UTC)

I think I meant the local group rather than the local supercluster. I'm a little unclear on whether superclusters are gravitationally bound. In any case, gravitationally bound systems don't expand with the Hubble flow. Earth doesn't expand, the solar system doesn't expand, the galaxy doesn't expand, etc. (Although gravitationally bound systems can oscillate between a minimum and a maximum size, in which case they are expanding half of the time.) -- BenRG (talk) 04:24, 28 August 2010 (UTC)

All of the stars visible to the naked eye belong to the Milky Way galaxy, which is not expanding, so they're as likely to be blueshifted as redshifted. Even the few naked-eye visible galaxies belong to the Local Group, which is also not expanding. -- BenRG (talk) 23:49, 26 August 2010 (UTC)

Stars that have passed near the Sun

I was just reading Barnard's Star for some reason, and was astounded to read that in merely 10,000 years, the star is expected to come from 6 light-years to 3.8 light-years in distance - but will still not be the closest star because Proxima Centauri will have come even closer. I hadn't really understood that stellar proper motions were so large.

Has anyone traced the current motions backward and constructed a table/diagram/video of all the stars passing by the Sun in the past few hundred thousand years? (it would be nice to cover all the recent ice ages, but I don't know how precisely the motions are known...) Wnt (talk) 15:31, 25 August 2010 (UTC)

See List of nearest stars#Future and past. --Dr Dima (talk) 16:49, 25 August 2010 (UTC)

If the Nemesis star exists it's always closer than 3.8 light years and it can come a lot closer. I don't think it's the greatest problem for mankind however. Smartse (talk) 00:53, 26 August 2010 (UTC)

Gliese 710 is expected co come fairly close to the Sun in the future, while Algol had been pretty close at one point. ~AH1^(TCU) 18:56, 26 August 2010 (UTC)

how to tackle Deliquescence property

could you please tell me about some chemicals that will destroy deliquescence property of salts. or any other way to stop the salts from absorbing water from atmosphere EXCEPT using airtight containers...thanx--Myownid420 (talk) 16:33, 25 August 2010 (UTC)ei

You can't destroy the property, you could either store it with a different substance that absorbs water more strongly, silica gel would be the most obvious, but you can also use rice as it too absorbs water pretty effectively. Smartse (talk) 18:52, 25 August 2010 (UTC)

Put a stronger deliquescent in with the salt. --Chemicalinterest (talk) 22:50, 25 August 2010 (UTC)

You need to store the deliquescent salt in a sealed container with a desiccant. Silica gel is a common one, but a lot chemistry labs use calcium chloride in their desiccators. They even sell it doped with Cobalt(II) chloride to know when it is "spent". --Jayron32 04:02, 26 August 2010 (UTC)

Water on skin

If I put water on my skin, will it hydrate it? Is that a secret that skin cream multinationals don`t want us to know? --Quest09 (talk) 16:34, 25 August 2010 (UTC)

Yes, at least to some extent. Have you ever had wrinkled finger tips after swimming? This is due to the skin absorbing water. However, this is not to say that applying water will cure dry skin. Indeed, topical application of water could have a net drying effect in some circumstances. SemanticMantis (talk) —Preceding undated comment added 18:37, 25 August 2010 (UTC).

Wrinkle_(skin)#Pruney_fingers

When advertisements for cosmetics and other "beauty" products tell us that what they are trying to sell us will (re-)hydrate the skin, it often has nothing to do with water. (Or truth.) HiLo48 (talk) 21:00, 25 August 2010 (UTC)

Our moisturizer article, which needs to be way longer, states that the point of a moisturizer is to hydrate the skin while decreasing evaporation. Comet Tuttle (talk) 21:04, 25 August 2010 (UTC)

Despite the name, skin is 'hydrated' with oil, not water. You can not add water to skin since the hydrostatic equilibrium needs to be kept at a specific level. What you commonly experience as 'dry' skin, is actually a lack of oil, not water. Ariel. (talk) 21:58, 25 August 2010 (UTC)

The oil in human skin is sebum. Though that article claims that low levels of sebum do not cause low skin moisture, sebum probably is involved in decreasing evaporation. SemanticMantis (talk) —Preceding undated comment added 22:00, 25 August 2010 (UTC).

Besides oils, humectants also play a role, e.g. glycerine, urea, alpha hydroxy acids such as lactic acid or glycolic acid. Wnt (talk) 14:43, 26 August 2010 (UTC)

I searched "skin hydration", and the first five results were Dead Sea salt, hyaluronan, taurine, stratum corneum and moisturizer. ~AH1^(TCU) 18:54, 26 August 2010 (UTC)

Why does hair grow so long on the human head?

The article on Human hair growth doesn't seem to answer this question. Although, as humans, we're used to the idea that head hair can grow to extreme length compared with that elsewhere on the body, to another species this must surely seem to be as defining a feature for the human species as, say, a peacock's tail is for that species. It doesn't seem to serve any function, other than display. Is that correct? How and why did human hair growth patterns evolve in this way? Has work been done on this? Shouldn't it be referenced somewhere? Ghmyrtle (talk) 20:02, 25 August 2010 (UTC)

This might not be the correct answer, it's just what I've always assumed. The head is very vascular in nature so it transfers heat very quickly. In that sense it's similar to your extremities, except its supply is not cut off when we get hypothermic because our brain always needs oxygen to ensure our survival. The more hair you have on your head, the more air that is present to insulate it, so having hair that grows on your head is pretty useful. What I don't understand is why our hands and feet aren't the same? I mean, in modern times it's possible to cope without hands with the help of modern society, but I doubt our ancestors millions of years ago had it quite as easy. Regards, --—Cyclonenim | Chat  20:10, 25 August 2010 (UTC)

I'm not sure either, but it might also be a consequence of sexual selection - it's for this reason that men have facial hair. — Yerpo ^Eh? 20:16, 25 August 2010 (UTC)

Have a look at a discussion on the same question a few weeks ago[3]. Alansplodge (talk) 20:27, 25 August 2010 (UTC)

Oops, sorry, missed that one.... :( Ghmyrtle (talk) 21:29, 25 August 2010 (UTC)

I assumed it was the other way around - women usually have very little facial hair because of sexual selection. thx1138 (talk) 00:30, 26 August 2010 (UTC)

Well, yes, but long hair has been a sign of "femininity" for a veeery long time. It's the pattern of growth, not just overall length. Of course insulating the brain or some other physiological function might also have something to do with it. — Yerpo ^Eh? 07:51, 28 August 2010 (UTC)

Tree with leaves on bottom but not top

I am curious what could have caused this. Mathew5000 (talk) 20:26, 25 August 2010 (UTC)

Several possibilities: 1) with a lack of water, plants tend to first lose leaves at points furthest from the roots 2) a disease could have taken hold near the top and has started spreading downward from there 3) some insects pests prefer the tops or outermost leaves of trees/plants. It's too hard to tell without being able to look close whether any of these possibilities may be the right one. —Preceding unsigned comment added by 148.177.1.210 (talk) 21:06, 25 August 2010 (UTC)

148 has it. Is it a birch? If so, I'd go with lack of water, because birches tend to like moist conditions. Also could be due to physical damage, such as lightning strike. SemanticMantis (talk) —Preceding undated comment added 22:05, 25 August 2010 (UTC).

I have experienced this problem recently with a Dogwood. It was definitely due to lack of water associated with several years of significantly-below-average rainfall. Dolphin (t) 22:58, 25 August 2010 (UTC)

I have a tree in my neighbourhood that has its very highest branches missing leaves. Not sure what caused this or if it formerly had leaves there. ~AH1^(TCU) 18:46, 26 August 2010 (UTC)

If the plant has anything to say about it, during times of stress, plants try to lose their oldest leaves first, i.e. the less useful ones closer to the ground. John Riemann Soong (talk) 04:52, 27 August 2010 (UTC)

Breeding

Besides dogs, cats, rats, and fish, are there any other animals that have been subject to human breeding programs primarily intended for changes in appearance as opposed to, say, taste, growth rate, song, speed/agility or type and quality of hair/wool produced? Exploding Boy (talk) 22:46, 25 August 2010 (UTC)

We actually have a list: List of domesticated animals Wikiscient (talk) 22:55, 25 August 2010 (UTC)

Oh, didn't read the specific part of your question; not sure, but the list would be a good place to start. Wikiscient (talk) 22:59, 25 August 2010 (UTC)

Hmm, I guess I forgot to add hamsters and maybe rabbits to the above, but the list mostly deals with animals used for work, food, and clothing. Exploding Boy (talk) 23:01, 25 August 2010 (UTC)

(EC) Sorting the list by "purpose," the only item on the list with only "show" for a "purpose" is the Barbary Dove (Streptopelia risoria). Wikiscient (talk) 23:05, 25 August 2010 (UTC)

What got me thinking about it was reading the article Dodo. Since it has a close living relative, and since people have been known to attempt to resurrect extinct dog breeds, I began to wonder whether it would be possible to "recreate" the Dodo, and from there began wondering whether the type of breeding programs that have given us dogs as diverse as Chihuahuas and Irish Wolfhounds have been used on other animals for similar reasons. Exploding Boy (talk) 23:38, 25 August 2010 (UTC)

What would be the point? You wouldn't have a dodo- you would have a bird that looked like a dodo. Anything you would want to study about it (behavior, genetics, etc) would be completely different. 149.169.164.52 (talk) 23:57, 25 August 2010 (UTC)

I know that; that wasn't really the point of my question. Exploding Boy (talk) 23:58, 25 August 2010 (UTC)

All dogs are the same species, so resurrecting an extinct dog breed isn't quite the same thing as recreating a distinct species. Just consider the amount of evolutionary time you are trying to "undo" or recreate, however you want to put it. ALL dogs have a common ancestor 50,000 years ago, the majority of dog breeds today probably have common ancestors only a few hundred years ago. From a cursory look at the dodo article, it appears the dodo's most recent common ancestor is about 20 million years ago. That should put some perspective on it. Vespine (talk) 00:17, 26 August 2010 (UTC)

Again, I know that. It was more about recreating the appearance of the Dodo than the actual bird. Exploding Boy (talk) 00:26, 26 August 2010 (UTC)

Yeah sure, what I said equally apples to appearance. Recreating the appearance of a few hundred year old dog breed is going to be orders of magnitude easier then recreating the appearance of a 20 million year old distinct species. Vespine (talk) 00:33, 26 August 2010 (UTC)

Well, off the top of my head you can add mice and pigeons, although I'm sure there are other domesticated pet species which have been bred for appearance. Equisetum (talk | email | contributions) 00:04, 26 August 2010 (UTC)

Check out the domesticated silver fox. Also budgies are bred for color. Ariel. (talk) 00:06, 26 August 2010 (UTC)

Oh yes, I forgot about silver foxes. Of course, that was about taming rather than breeding specifically for appearance, wasn't it. Exploding Boy (talk) 00:26, 26 August 2010 (UTC)

Horses are bred for looks in addition to other qualities. thx1138 (talk) 00:32, 26 August 2010 (UTC)

Very hard to define 'primary' motivations for selection. In choosing fatter cattle, for example...is a fat sheep 'better'? Natural human tendencies for selecting the 'best-looking' breeding pairs comes into play, so there is a degree of change in appearance in any and all domestication, whether deliberate or otherwise. And over the long timescales, it is impossible to decide whether the many people making the selections were primarily motivated to select for appearance. I think you could find quite strong evidence of it in most pet species. Some that come to mind as, perhaps, more clear-cut primary choices over appearance (and have not been noted here) include Domestic Pigeon / Fancy pigeon, Guinea pig / Hamster / Gerbil / Chinchilla / Fancy rat, Pet skunk, Domestic Canary (and other caged birds, and certainly parrots and parakeets etc), Ducks, and I imagine lots more. Check Piebald too, because there are very very few piebald species in the wild.

With regards to the poor Dodo, a related short poem that I learned in New Zealand springs to mind — try to read it with a Kiwi accent, where 'moa' sounds the same as 'more', and it rhymes; No Moa, no more, in old Aotearoa, Can't get 'em they've et them, They're gone and there ain't no Moa.

For those interested in such topics, I highly recommend the book The Ancestor's Tale.  Chzz  ►  01:09, 26 August 2010 (UTC)

Responding to the question about breeding a bird to resemble the Dodo, that process is called "back-breeding". And there is a Wikipedia article on it, "breeding back". Also see Quagga Project. Mathew5000 (talk) 06:08, 26 August 2010 (UTC)

Budgerigars have definitely been bred for looks, all in the past 200 years. HiLo48 (talk) 06:28, 26 August 2010 (UTC)

Heck Cattle Googlemeister (talk) 14:41, 26 August 2010 (UTC)

Chickens are another example (there has been breeding for other purposes, too, but there's a long established tradition of ornamental chickens). Arguably, humans. Warofdreams talk 14:47, 26 August 2010 (UTC)