Wikipedia:Reference desk/Archives/Science/2009 November 1

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November 1

Numbering of Magicicada broods

Why are the Magicicada broods numbered the way they are? For Brood I (for 17-year cicadas), the year number of emergence leaves a remainder of 6. Why not 1, or 0? —Preceding unsigned comment added by 75.37.158.42 (talk) 04:16, 1 November 2009 (UTC)

They are probably numbered after the first year someone started numbering them. But the numbers are clearly intended to be fairly arbitary because they numbered the 13 year cicadas with the next available numbers after the 17 year variety. I don't think there is anything particular to read into the choice of numbers. SteveBaker (talk) 21:52, 1 November 2009 (UTC)

They're prime numbers, making it very hard for a predator on a shorter cycle to track to the cycle of the cicadas.[1] Fences&Windows 02:46, 6 November 2009 (UTC)

Oh, whoops, that wasn't the question. The numbering of the broods by Charles Lester Marlatt in 1907 was arbitrary, but it stuck. Fences&Windows 02:56, 6 November 2009 (UTC)

What specific type of foam is this? (Think tool/bike grips)

Can't find a definitive answer on this anywhere. There are two specific materials I can't identify that I see used in handles/grips of all kinds; ex: tools, fishing rods, bike handlebars, etc..

The first one is in tube form, with an 1/4" wall. It feels squishy and soft (firmer and deforms less than visco-elastic foam) and has a somewhat rubbery feel. The inside of the tube is smooth and shiny like neoprene you'd fnd in a wetsuit or gasket, and the outside has a matte, smooth texture that I assume makes this open cell foam. The second material is similar, except the cell size is much larger, and thus the texture is more 'pebbly' as. It is in a sheet 1/4" thick.

Other than that (admittedly) poor description, all I can add is: the material isn't 'plasticky' feeling like extruded polyurethane tubing for pipe insulation, nor is it low-density like polyurethane foam for upholstery. It's also not so dense that it'd hurt you if someone threw a chunk at you.

Looking around, the likely suspects I've found across were EVA and a PVC variant (may be a trade name) called NPVC. Neoprene also, but I rarely see it in the thicknesses used in these products, or with any texture. So, does anyone know exactly what I'm talking about? Please don't say foam rubber. That much is obvious :) Thanks in advance.

KA - 97.82.253.69 (talk) 04:28, 1 November 2009 (UTC)

NPVC stands for Nitrile PVC. It is pretty much the standard for foam grips. There are many variants of it because it is easy to adjust the formula when producing the grips. -- kainaw™ 04:39, 1 November 2009 (UTC)

I couldn't have asked for a better answer. Many thanks. 97.82.253.69 (talk) 09:29, 1 November 2009 (UTC)

Power vs frequency

Why does the power/torque of an Internal Combustion engine depend on its RPM? —Preceding unsigned comment added by 116.90.224.116 (talk) 07:00, 1 November 2009 (UTC)

You can answer that loads of ways but basically RPM gives the rate at which fuel is burned (RPMxnumber of cylindersxamount of fuel per cylinder) or alternatively the number of explosive pushes by the cylinders which the engine harnesses. So at low RPM power is proportional to RPM but at high RPM the efficiency falls away for several reasons. If you give the approx level of the question it is easier to pitch the answer. --BozMo talk 09:55, 1 November 2009 (UTC)

For the same reason that you have to breathe faster to run faster. Cuddlyable3 (talk) 12:34, 1 November 2009 (UTC)

I'm going to do some simplifying here, but broadly what I'm saying is correct. Torque depends on RPM because the engine isn't equally efficient throughout its rev range. At low revs engines typically do not fill and empty the cylinders efficiently. At high revs it's often the case that the valve openings are too small to allow the combustion gases in and out of the cylinder fully. As a result, maximum torque is often somewhere in the middle of the engine's rev range. Power is given by torque multiplied by revs, so, if the torque was constant over the rev range, power would linearly increase with revs. Since torque drops off at high revs, we find that power will eventually do so as well, but because of the rev multiplier, it's always higher up in the rev range. --Phil Holmes (talk) 18:58, 1 November 2009 (UTC)

lightening shock

if electricity is been harnessed from lightening why does the rain water that flows from the same place conduct? what s the mechanism behind that? —Preceding unsigned comment added by Srividhyaathreya (talk • contribs) 08:02, 1 November 2009 (UTC)

Each little drop of water carries a small static charge. Electricity is not being conducted in the normal sense of electrons flowing in a medium, but though the bulk travel of charged drops. The air only conducts when a high voltages starts to cause a breakdown. Graeme Bartlett (talk) 10:59, 1 November 2009 (UTC)

career

i m an electrical engineer from India. i wish to enter into the field of space science. can i pursue an m.e or m.s. in aerospace engineering. if not what is the apt course to become an astronaut or a space scientist? —Preceding unsigned comment added by Srividhyaathreya (talk • contribs) 08:05, 1 November 2009 (UTC)

I would expect that you may be employed as a support person, however to be an astronaut, you should qualify as an aircraft pilot first. As a space scientist, you had better get a PhD in physics. Graeme Bartlett (talk) 10:56, 1 November 2009 (UTC)

You don't need to be a pilot to be an astronaut. Pilots of spacecraft will generally be pilots, but there are scientists and engineers that become astronauts too. I would expect a PhD is required to do scientific research in space. --Tango (talk) 19:43, 1 November 2009 (UTC)

See Astronaut#Training for NASAs requirements. Other space agencies will be similar. --Tango (talk) 19:45, 1 November 2009 (UTC)

Right, there are lots of different researchers in space, not just physicists, and definitely not just pilots... it is not the 1960s anymore. --Mr.98 (talk) 20:45, 1 November 2009 (UTC)

Inflammatory result of depolarization theory regarding migraines

That title could've been better. But! I've been reading up on your excellent migraine article, and it lists, among other things, depolarization and serotonin levels as resulting in pain. It is the first I am interested in, because browsing through depolarization and action potential, I am hard pressed to understand exactly what it is that causes an inflammatory agent to be released when a depression occurs. I am quite the noob on this field, and so I feel I may have missed something. As I have understood this matter, a depolarization essentially inhibits to a great extent the cells' ability to communicate, suffering from reduced or nonexistant permeability. Under any circumstance, your help is much appreciated! 91.149.2.165 (talk) 10:40, 1 November 2009 (UTC)

Studies in psychoneuroimmunology have shown that during depression proinflammatory neuropeptides (SP) and cytokines (e.g., IL 1 and IL 2) are released as a result of over activation of the sympathetic nervous system and the HPA axis->leading to acute phase response and to the release of Acute-phase proteins. This is only part of the phsyiological effects of different negative emotional situations.--Gilisa (talk) 11:46, 1 November 2009 (UTC)

I am terribly sorry for having used the word "depression", when I in fact meant cortical spreading depression! I understand your answer thus has less validity. :) 91.149.2.165 (talk) 12:19, 1 November 2009 (UTC)

Actually it does have connection after all as cortical spreading depression may lead to the release of SP, but I don't familiar with works on this mechanism and neuroimmunology is not my expertise. I addressed your question to Dr Dima, he may know the answer.--Gilisa (talk) 13:03, 1 November 2009 (UTC)

Absolutely marvellous! Thank you for taking your time on this issue, I certainly hope for a good answer =) 91.149.2.165 (talk) 13:54, 1 November 2009 (UTC)

You welcome! I'm hoping for a good answer myself.--Gilisa (talk) 14:24, 1 November 2009 (UTC)

I will start from the end. When membrane of a neuron is depolarized by injecting electric current into the neuron, such depolarization leads to increased spiking probability. However, membrane depolarization in general does not imply increased spiking (and membrane hyperpolarization in general does not imply depression). When membrane is depolarized due to change in ion concentrations in the cell and around it, or due to change in conductances of particular type(s) of ion channels, such depolarization may be associated with either increased or decreased spiking probability. There is no contradiction, therefore, between depolarization and depression in the cortical spreading depression in a migraine. That being said, I do not know what exact changes in channel conductances and in the ion balance occur in the neurons in the areas affected by the spreading depression. I never worked on migraine or anything closely related. What I do know is that the depolarization is thought to be not produced by serotonin directly. According to the theory I am somewhat familiar with, mutations in a certain subunit of the voltage-gated P/Q-type calcium channel, or possibly other "channelopathies" in the brain stem, result in the over-active vascular response to the increased activity in certain areas of the cortex (see e.g. this article). Change in blood supply affects the activity in the cortex, which affects the blood supply even more, closing the positive feedback loop. Serotonin, it seems, mostly acts on the blood vessels and not on the cortex neurons in this case. However, with serotonin you never know, as most of its effects are modulatory rather than direct; and I am certainly not a migraine expert. I hope this helps in any way. --Dr Dima (talk) 17:46, 3 November 2009 (UTC)

Thank you, Dr Dima, for your time and answer. =) I am most thankful. I will study the article, and hopefully learn even more! 77.18.72.142 (talk) 19:51, 4 November 2009 (UTC)

subsequent natural GMO

How likely or what is the probability that a GMO such as corn with a GM to produce an insecticide or a cow designed to give milk with antibodies could undergo subsequent natural GM from a virus or pollutants or electromagnetic radiation resulting in an increase in production of insecticide or antibody which might render the GM product harmful? Biggerbannana (talk) 11:29, 1 November 2009 (UTC)

About the same as ordinary corn or an ordinary cow. We can't predict anything else. Cuddlyable3 (talk) 12:30, 1 November 2009 (UTC)

Perhaps then it depends upon where something grows but I can't find a map anywhere of areas with high numbers of trees that have large cancerous type growths on their trunks although they appear to be in areas near where phosphorus was discovered and is mined in South Florida and in other areas most likely to have phosphorous deposits which has a lot of radioactivity. Biggerbannana (talk) 14:50, 1 November 2009 (UTC)

In "captivity", these products' reproductive cycles are fairly closely tracked - it's unlikely that anything untoward would happen. The issues arise if they escape into the wild. In that case, those transgenic genes would continue to work and to be selected for (or against) and be possible targets for mutation. However, if the genes don't confer any particular benefit to the organism in the wild (for example, a sheep that produces human insulin in her milk) - and since the organism has to expend energy to produce these extra things - the odds are good that they'd be selected out after enough generations. If they DO offer benefits (resistance to certain common insects) - then they might be strongly selected for - and spread out into the wild population. There is evidence that this has happened already with Starlink corn. However, evolution is only going to operate in ways that strictly benefit the organism - which means that there has to be a balance between the cost to the organism to produce whatever this effect is - and the benefits. The fact that wild versions of the organism didn't already evolve this kind of protection suggests that the cost may have been higher than the benefits - but it's really tough to know. Of course it's much less likely that it would be a virus, pollutants or radiation causing the gene to mutate (a relatively rare event) so much as it's likely that mixtures of the transgenic gene with other (relatively rare) genes already out there in the wild population would increase the effectiveness of the transgenic gene in some way (eg by feeding it's chemical pathway with more inputs). So the odds aren't zero that the release of transgenic organisms might cause gradual evolution of novel new features. SteveBaker (talk) 15:25, 1 November 2009 (UTC)

Sounds like what you are saying is that because the two conductor extension cord I found at a local South Korean flea market had blades made of pot metal and 26 gauge copper wires covered by thick insulation attached only by the pressure of the molded plug holding the blades and wires together is okay even though they violate the electrical standard because they will melt quickly and act like a fuse despite the unlikely possibility of not melting quickly and instead heating up slowly resulting in a fire. Biggerbannana (talk) 16:44, 1 November 2009 (UTC)

That is one of the worst rationalizations I've read here - to the point that it is very difficult to assume that you are actually asking a question and not just ranting about GM products based on little (or no) actual knowledge of GM. He stated that evolution works towards the benefit of the organism. If a genetic modification does not benefit the organism, it will not tend to spread. Try - though I know it is very difficult - to relate that to an organism, not an extension cord. -- kainaw™ 20:10, 1 November 2009 (UTC)

The reference being that anyone can produce inferior goods or follow an insufficient regimen to make money without dependence upon repeat buyers. Biggerbannana (talk) 04:37, 2 November 2009 (UTC)

(It's of note, of course, that "benefit of the organism" is not the same thing as "benefit to people." Mutations in viruses that are good for the organism are often quite bad for humans!) --Mr.98 (talk) 22:49, 1 November 2009 (UTC)

I will also add that although what SteveBaker says is correct, it's possible that increased production can be harmful to other creatures (such as humans who eat the cow or corn), although usually indirectly e.g. massively increased production of antibiotics creates promotes resistance in those infectious agents, thereby making the disease harder to cure in humans. ~ Amory (u • t • c) 21:19, 1 November 2009 (UTC)

It may be worth remembering that many plants that we eat already have a number of compounds which are clearly harmful to humans in sufficient quantities. E.g. solanine in potatoes. A far greater concern then any potential (direct) harm to humans is the ecological effects of transgenes. In particular, if the transgene is beneficial to the plant but harmful to something else (e.g. insects or other plants) if the transgene spreads as SB mentioned and spreads widely enough this may have a negative effect on the ecological balance. A key issue is whether and what other wild species the transgene can spread to, as most plants cultivated for food don't survive particularly well in the wild because they're so screwed up, the addition of whatever transgenes is probably not enough to make them into weeds. Note in case it isn't obvious, this doesn't usually doesn't require any mutation. A terminator gene would hopefully nearly eliminate the spread. All this is something that has received plenty of research, so you could easily find many references if you are interested Nil Einne (talk) 22:55, 1 November 2009 (UTC)

Lots of things may have benefited the dinosaurs to our detriment but praise God for the asteroid. Wild or captive anything which might give our molecular adversaries a distinct and overpowering advantage in the long term is still not a good thing even though not present in the short term. Scientists pride themselves on thinking of every possible scenario and that is where the problem lies. Biggerbannana (talk) 04:45, 2 November 2009 (UTC)

I'm not sure "Scientists pride themselves on thinking of every possible scenario" is really the point. I mean, what? Imagine Reason (talk) 19:15, 2 November 2009 (UTC)

The problem comes when scientists fail to live up to their expectations and a few unwelcome scenarios slip passed. In such cases we see reactions from others and unfortunately as a matter of pride a complete effort at dismissal. The Titanic is unsinkable. The seals on the Space Shuttle boosters work great. The American Colonies support Britain. I've probably forgotten a few other better examples. Biggerbannana (talk) 21:06, 2 November 2009 (UTC)

Humans did not coexist with dinosaurs. Please do not use this space to promote a God of some belief system even if you think He willed an asteroid to impact Earth. The Titanic sank because of failed seamanship and inadequate engineering. The seals on the Space Shuttle failed because of failed corporate engineering. The American revolution arose because of failed foreign policy by Britain. No scientists were implicated, least of all any GM biologists who would be relevant to the OP meaning the Original Post not the subsequent debating by the same user. Cuddlyable3 (talk) 22:53, 2 November 2009 (UTC)

I think BiggerBannana is referring to the notion of hubris. That GMO proponents seem to operate on the premise that we understand all the variables and modes of interaction, and that even if we did not, the consequences would be manageable. Further, I believe that BB's reference to God is an allusion to scientism. Unomi (talk) 00:05, 7 November 2009 (UTC)

PCR for diagnosis of genital warts

Hi the wikipedia article on genital warts says that less than 1% of people infected with the HPV virus develop visible warts. I'm doing some research into how genital warts are diagnosed in the UK. The only diagnostic tests mentioned on the NHS website are: warts being examined by a doctor and colposcopy. However, if the wikipedia article is right, then 99% of people with genital warts will not be diagnosed by these methods! I've also read that PCR can be used to diagnose genital warts, this could be used to diagnose the vast majority of people who are asymptomatic. My question is does the NHS provide PCR tests for genital warts? Thanks to anyone who can help! RichYPE (talk) 14:26, 1 November 2009 (UTC)

If you are unable to find this information online, you could try calling the NHS' telephone health information line, NHS Direct. TenOfAllTrades(talk) 15:00, 1 November 2009 (UTC)

This question verges on the strict "no medical questions" rule, so I'll answer carefully. Useful search terms would be "genito urinary". The NHS wesites I've seen say that they diagnose by looking, and that only visible warts can be treated. Here's some websites: WARNING: REVOLTING IMAGES http://www.chestersexualhealth.co.uk/genitalwarts.htm - and another link that talks about visual diagnosis http://www.nhsdirect.wales.nhs.uk/encyclopaedia/g/article/genitalwarts/. Remember Civility (talk) 15:58, 1 November 2009 (UTC)

It's a prohibition again medical advice, not medical questions. The OP is clearly not asking for medical advice. --Mr.98 (talk) 16:24, 1 November 2009 (UTC)

thanks for the clarification. I should have been more precise: "Some may think my answer verges on the strict no medical advice rules, but don't worry, I'm being careful". Is that better? Remember Civility (talk) 19:23, 2 November 2009 (UTC)

Also deleting a warning against a known hazard as if it were medical advice is extremely careless. Maybe even culpable. Biggerbannana (talk) 18:59, 1 November 2009 (UTC)

Again, nobody is talking about personal or at-home treatments. (In any case, the treatment plan you mentioned would only be prescribed by a doctor, and would carry copious instructions and warnings and etc. on it anyway.) --Mr.98 (talk) 00:41, 2 November 2009 (UTC)

My understanding is that acetic acid is not prescribed to the patient by the doctor but is used much as a laboratory stain to reveal altered tissue and therefore no warning is called for between doctor and patient but rather between the pharmaceutical company and the doctor. Common sources of acetic acid (vinegar) do not have warnings in regard to its use as a stain or as a cure for wards by its constant or prolonged application to a wart. Ignoring or thwarting the opportunity to provide such warning here does not accomplish the Wikipedia ban of giving medical advice but rather opens the Wikipedia to a potential charge of culpable negligence. Warnings are not medical advice but the responsibility of anyone with knowledge of the danger to convey that knowledge to others. Biggerbannana (talk) 15:47, 2 November 2009 (UTC)

Nobody is talking about treatments, and I've never heard of anybody trying to use vinegar at home (I don't really think you know what you are talking about, regarding what doctors prescribe). You are being ridiculous regarding "potential charge of culpable negligence", because Wikipedia is not recommending anyone do anything, much less anything negligent. You might as well argue that Wikipedia is negligent because every time somebody asks about electricity we don't warn people about the risk of electric shock. If you really have a problem with the medical policy here, just take it to the talk page. You are creating an issue here out of nothing and being silly. --Mr.98 (talk) 23:27, 2 November 2009 (UTC)

I support Mr.98 here. This section is for responses to the OP's question within Ref. Desk policies, not for inventing pseudo-legal accusations. Cuddlyable3 (talk) 11:30, 3 November 2009 (UTC)

chemical induced orgasam

I've heard that electricity has been used to stimulate the genital region but I do not know if it is to the point of orgasm. Is there chemical which can do this? Biggerbannana (talk) 18:55, 1 November 2009 (UTC)

SSRI usage can sometimes result in spontaneous orgasms.[2] Red Act (talk) 19:22, 1 November 2009 (UTC)

Conversely, SSRIs can also prevent orgasm. Mitch Ames (talk) 23:43, 1 November 2009 (UTC)

Clomipramine, which is a TCA, can also cause spontaneous orgasms. Interestingly, these antidepressant-caused orgasms are sometimes triggered by sneezing.[3] Red Act (talk) 20:12, 1 November 2009 (UTC)

Effect of optimism on health

I've often heard it claimed as folk wisdom that "positive thinking has been proven to have a positive effect on recovering from illness" or something similar. My understanding is this is likely based off a few hastily done studies in the seventies which probably found nothing more than the obvious link of heavy stress and it wearing out the body. Additionally, further studies that were done extensively failed to show a link. Do we have an article on this, or anything to back it up? I read this in a magazine, and I would like to probe more in depth; my scientific mind finds it very unlikely that the new age baloney about just having a positive attitude vs. a resigned attitude will have any effect on your illness; short of, of course, extreme stress. Magog the Ogre (talk) 20:16, 1 November 2009 (UTC)

I don't have a lot of knowledge of this topic but I think there is some pretty solid evidence, see PMID 17709956 for example. For your scientific mind, one basic mechanism is that a variety of negative emotions increase the activity of the HPA axis, which leads to increased cortisol secretion, and cortisol has a variety of effects that tend to impair responses to illness, including direct suppression of immune responses. There are currently several whole journals devoted to studying the interactions between the nervous system and the immune system. Looie496 (talk) 21:04, 1 November 2009 (UTC)

I believe the entire institution of placebos may undermine your pessimistic approach towards optomism. Not to mention psychological disorders, in which the mind is essentially the object of the ailment. :) DRosenbach ^{(Talk | Contribs)} 21:06, 1 November 2009 (UTC)

Actually it was found that people who can find attributions for "why me" or to give meaning for live threatening diseases thay were dealing with are more adaptive and have higher survival rates.--Gilisa (talk) 21:40, 1 November 2009 (UTC)

To DRosenbach: the placebo has less to do with actually getting better than how one reports his/her symptoms? I.e., did you feel noticeably better when taking this/that drug? To Gilisa: do you have any sourcing? It's precisely this type of thinking for which the author of the magazine article I was reading was critical. Magog the Ogre (talk) 00:02, 2 November 2009 (UTC)

Did you read the linked article on placebos? The changes are a lot more complicated then simply different reports of symptoms and the article is resonably detailed and sufficiently referenced Nil Einne (talk) 00:32, 2 November 2009 (UTC)

Look at "The Search for Meaning Following a Storke" by S.Z. Thompson (1991) for a review. It's a bit old one but still invariably cited even in recent articles on similar issues. The effects of negative mood on one's health are obvious and were demonstrated using the most rigorous experimental methods and proven to the molecular level. It's a bit harder to make molecular studies on happiness, but at the least-being happy means not being depressed.--Gilisa (talk) 12:52, 2 November 2009 (UTC)

I speculate that optimism and good health could both be the result of having sufficient levels of Vitamin D in the body. People in northern latitudes are thought to be deficient during the winter (see Scientific American article from November 2008), and personally I always find the darkening nights of autumn a depressing time, for example. I have seen a scientific paper that speculated that the health benefits of fish could be as a result of their Vitamin D content - do not know if there is any triuth in that. Note that excessive consumption of Vitamin D is harmful and dangerous. 78.146.167.26 (talk) 15:06, 2 November 2009 (UTC)

How much land is needed to support people?

Hi,

For one average person, or family, in 'the west', lets say Western Europe, how much land in terms of agricultural area is on average needed to support them in terms of food. I know there is no specific amount and the numbers vary widely depending on the habits of countries, eg fish/carbohydrate based diet, and depending on the quality of land in said place but there must be some sort of figure saying something like 'on average one person consumes 1/4 acre of wheat per year' or something like that. Also any figures for other natural resources eg timber, water etc would be useful. Thanks, --86.136.37.191 (talk) 21:47, 1 November 2009 (UTC)

Someone asked a similar question here. People there gave a wide range of answers, I think it really depends on what kind of crop and how much diversity the people eat. Potatoes are famously compact, while any kind of meat is going to require much more overall. Someone at that link said .5Ha per person for a typical Western diet. I would also think it depends heavily on the quality of the land, specifically whether it gets enough water. Sorry, I guess this turned out to be a pretty waffling response ;) TastyCakes (talk) 21:55, 1 November 2009 (UTC)

Oh, also I would imagine if you're in a year round warm climate that gets lots of rain, like much of the equator, each acre is going to be more productive overall and the land needed per capita is going to get smaller. This list gives an idea of this. In Bangladesh, there are apparently 1,946 people per square km of arable land, which is just over .05 hectares per person, and I doubt they are a big net importer of food (although maybe I'm wrong on that). TastyCakes (talk) 22:27, 1 November 2009 (UTC)

Oh, and this page gives some crop yields in tons per hectare. You have to click on the "Table" icons on the left to see them. TastyCakes (talk) 22:30, 1 November 2009 (UTC)

The Tables are likely in tonnes per hectare (t/ha) and not tons per hectare.

Yes, sorry that is likely correct. TastyCakes (talk) 04:04, 2 November 2009 (UTC)

Does phosphorylation occur only with OH / COOH groups?

In order to be phosphorylated, you kind of need to have slight nucleophilicity to begin with right? You can't phosphorylate something if it doesn't have a nucleophilic -OH group to begin with? (The -OH group can be part of a pi system like a carboxylic acid.) John Riemann Soong (talk) 23:08, 1 November 2009 (UTC)