Wikipedia:Reference desk/Archives/Science/2012 September 26

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September 26

Space and radiative cooling

Assuming a distance of 1 AU, how fast (in terms of Kelvin per second) would a human cool when they are exposed to the vacuum of space, both in sunlight, and in shadow? This is not a homework question, just curiosity. Plasmic Physics (talk) 02:47, 26 September 2012 (UTC)

I assume you mean 1 AU from the Sun. The sunlight case is complicated. If they aren't rotating relative to the Sun, the side facing the Sun may actually get hotter, while the side away from the Sun freezes. Human bodies are fairly good insulators, especially after they die and their circulatory system stops. StuRat (talk) 02:57, 26 September 2012 (UTC)

I should then specify that heating/cooling takes place in an unpolarised fashion, and that the person remains alive. Plasmic Physics (talk) 03:06, 26 September 2012 (UTC)

Any object subject to purely radiative cooling can be approximated as a "black body", and thus obeys the various laws regarding black body radiation. I think you can derive cooling rates from the Stefan–Boltzmann law, which relates the "emissive power" (power is rate of work, so should be related to how quickly energy is emitted) of a black body to the fourth power of its absolute temperature. This may not be the exact right law, but one of those, or a related one, should have the right answer. That should cover the "cooling in shadow" event. As with every physics article at Wikipedia, there's very little here in terms of making it accessable to the non-expert. --Jayron32 03:12, 26 September 2012 (UTC)

See also Black-body_radiation#Temperature_relation_between_a_planet_and_its_star, since a human floating in space around the sun is just a really small planet, that should give good info. So, betweem the Stefan-Boltzmann law and the information on the planet-sun temperature relationship, one should be able to derive both scenarios (shadow and in sunlight) --Jayron32 03:16, 26 September 2012 (UTC)

Using the approximation Jayron suggested, calculating the radiative power of a human body for a given skin temperature is relatively easy, but it would be harder to calculate the time-evolution of energy loss from the body as a whole, because of the insulating effects Stu mentions. That is, the skin might get cool very quickly, greatly slowing radiative heat transfer, while leaving the inside of the body quite warm. There is substantial research in the forensic sciences on how the core body temperature evolves after death (useful in estimating how long a person has been dead), but I don't how easy it would be to apply that knowledge to this situation (perhaps there will be substantial research on it in the future, when dumping bodies into space becomes a common way to dispose of, or create, murder victims). Someguy1221 (talk) 03:28, 26 September 2012 (UTC)

Couldn't internal heat-transfer relationships within the body be approximated via Newton's law of cooling? --Jayron32 03:56, 26 September 2012 (UTC)

Live humans are quite good at internally conducting heat, due to blood circulation. If Stu or anyone else doubts this, try the following: Go into a reasonably large cold room, say about 12 to 16 C, without any clothes on. Place a 1200W electric bar heater about 500 mm from your feet, while you sit on something, so that almost all the radiated heat that falls on you falls on your legs. If you are like me, the skin on you legs will get quite noticebly hot, but not such that your skin will be harmed or even uncomfortable. What is important, is after 15 to 20 minutes or so, you'll be hot and sweaty all over, even though most of your skin is exposed to 12 to 16 C, normally low enough to produce shivering. (I'm accustomed to a mediteranian climate).

But what complicates the calculation the OP wants is that the body has the ability to reduce blood flow to the skin to very high and very low levels as required for core temperature regulation, and sweating will be turned on if core temperature cannot be controlled by only adjusting blood flow - same with shivering if you are too cold. It does appear that the body does not have the ability to adjust blood flow and sweating to selective areas if part of you is exposed to cold and part of you to hot. However, if skin does get very hot, an inflamation reaction will result, increasing blood flow locally.

Ratbone58.169.235.242 (talk) 04:53, 26 September 2012 (UTC)

Assuming black-body radiation, no sunlight, surface area of 1.9 m² for a man, dQ/dt=1.9*5.67 10^-8* T⁴ (ignoring background radiation; starting off at 37°C, heat loss would be at 995 Watt. But actual skin temperature and such would give different results. At 0°C skin temperature, loss would be 600W. For a 70kg body, equivalent heat capacity of 70% water, that would take 340 seconds to drop the mean body temp with 1°, assuming he's dead. More accurate calculations that include metabolism, insulation .. would be much work (would still be not very realistic anyway, without oxygen supply, embolism due to air bubbles killing him...) Ssscienccce (talk) 07:15, 26 September 2012 (UTC)

In sunlight, it would depend on the total surface area as seen from the sun (the area of the shadow he would cast if there was a plane perpendicular to the rays right behind him), logically that must be less than half of the total surface area (and I just realize that in the calculation above, 1.9 surface area would imply arms, legs, fingers, toes and even but cheeks outstretched, wide apart so they don't block/reabsorb the heat... so these numbers should be lowered a bit. Anyway, the solar constant is about 1.360 kW/m², so multiply with the surface area perpendicular to the rays and subtract from the heat loss to get net loss. Cooling would stop once equilibrium was reached. the figures of -18.8° to 1.3°C depending on albedo from the section Jayron32 linked to would be reasonable for our man in space i guess. Ssscienccce (talk) 18:52, 27 September 2012 (UTC)

Curious: a person would suffocate before they would freeze, unless they are wearing a skin-tight suit with resperatory gear. Plasmic Physics (talk) 05:59, 29 September 2012 (UTC)

Tuition returns on net present value of tax revenue

On the two graphs in Figure 2 on page 43 of this report we see the relative lifetime earnings of women and men who have attained five different categories representing various levels of education. I would like to use this data, along with college tuition costs, attrition rates and the like, to derive the net present value of government tuition subsidies on changes in future taxpayer revenue. I.e., I would like to know, for every $1 spent subsidizing college tuition, how many dollars in present value terms a government can expect to collect in additional tax revenue over the life of the taxpayer on whom the tuition subsidy is spent. What other information would I need to calculate this? What formulas do I need to use as a function of the variables involved? I haven't really ever done something this ambitious in math before, but I'm determined to stick with it until I get a valid answer. —Cupco 13:39, 26 September 2012 (UTC)

Calculating NPV can be as simple or as complex as you like and depending on circumstances. But as the graph plots earnings as a ratio to "ecomomy wide average", a lot of the work is already done for you. You can get a meaningfull NPV figure in your case by just suming the earnings ratios for each year. The basic priciple of NPV is that a dollar in the hand now is worth more than a dollar in the hand later, if the earning capacity of money exceeds the inflation rate. Normally, in calculating NPV, you scale the cash flow in each year upward for each year you need to come back to the present year. For example, if inflation is 3% per year, a dollar one year from now is the same as $0.97 now; a dollar 10 years from now is the same as 0.97^(10-1) = $0.76 now. Inflation is automatically accounted for in your case as it is built into the "ecomony wide average". In business, you would factor in a "cost of money" - this can be a borrowing/lending interest rate (as if you have a dollar now, you could lend it out and get interest, hopefully above inflation), or an opportunity cost - if you spend a dollar on x, then you can't spend it on y, z, etc, each of which will have some rate of return. Eg if we assume interest rate is 3%, a dollar 10 years from now is equivalent to 1.03^(10-1) = $1.31 now. Inflation brings NPV down, interest rates and opportunity cost increase it.

To sum up, to calculate NPV, you need to assume a value (different for each year if deemed appropriate) of inflation, and a value for the "cost of money" (interest or opportunity), again different for each year. You should see from this that in the conext of your specific question, there may be no one right answer, so just go with the simple solution above.

I usually, rather than use smart looking math formulae, just set up a simple spreadsheet with one column for each year for cash flow, and another set of colums ofr the NPV of each year. In most business planning, you don't know exact future inflation rates and costs of money, likewise you can only estimate cash flows as between a low and high value, with a typical or design centre value, and they all vary form year to year. So what you do is set up Lo, Med, and Hi cash flow columns. This is a very powerfull technique that can do what "smart" formulae cannot do.

Wickwack58.169.235.242 (talk) 15:02, 26 September 2012 (UTC)

• There are many (im?)ponderables here. What will the country's emigration rate be? Will you train all these people and then they just leave when they're hired up for huge sums by the Eurekavilles that spring up after the Syrian Renaissance? But the first problem is that you're starting with a personal statistic and trying to get a national statistic. When that college graduate gets the good job and makes $1 million more, is there some lesser college graduate or dropout who is losing it and losing the equivalent amount? Wnt (talk) 15:36, 26 September 2012 (UTC)

Good points. I've got to assume no emigration which may or may not be unrealistic. The extent to which people taking advantage of subsidized education stay where they went to college seems to change over time, but it's not too unreasonable to assume that it will even out in the long run. I'm not trying to get any national statistics, just the change in taxable earnings for each individual. I need to think more about the displacement issue you raise; there is evidence that economic achievement isn't zero sum, but I'm not sure how convincing those arguments are. —Cupco 15:42, 27 September 2012 (UTC)

I also think that this is one of many topics where data aggregation obscures what is happening, rather than providing noise suppression via statistical averaging. Consider my territory - Western Australia: Due to having an ecomomy largely based on mining, coupled with a stupid government policy (govt since voted out) of encouraging university courses that have high female enrolment and discouraging courses with high male enrolment, graduating in engineering leads to high salaries thru supply and demand. However, sofware engineers don't do so well. Graduating as a nurse or schoolteacher affords you a low salary, lower than many tradesmen. However, in England, which historically has had an industrial focus and good universities, but now has little mining or industry, engineers don't get paid much at all. Also, consider medicine: The personal income of doctors is good but not that good (they have large overheads for receptionistes, nurses, offices, and equipment), but (in my country anyway) they spend up to 13 years at Uni and the courses are expensive to run. So the return on investment on a personal basis may be quite low. I've never met a specialist/consultant that didn't enjoy what they do though. I have a cousin who has a Masters level qualification in music and she's very talented. Her CD's have sold well, and she gets played on radio stations. But, she'd probably be just as well off without any qualifications at all. Talent is talent. On an NPV basis, her Uni course is probably very negative. Now, how much is job satisfaction worth? Wickwack121.221.26.222 (talk) 23:44, 27 September 2012 (UTC)

It's true that there is a large variation among professions, but I also want to assume that those average out to the population means over the long run. In the 1980s there was a huge glut of M.D.s in the U.S., but now there's a terrible shortage. At least it is equalizing general practitioner salaries with those of specialists, somewhat. But the data in the report linked above doesn't even consider the postgraduate professions. There's a 40% salary premium from high school dropout to college grad, and that has to mean a lot in present value for taxpayers to subsidize it. I took your advice about doing a spreadsheet, by the way. An analytic solution isn't possible because the curves are arbitrary. —Cupco 01:54, 28 September 2012 (UTC)

delayed capsaicinoid pungency

Some chilli peppers produce an immediate burning sensation when eaten, others produce a delayed and slowly increasing burn which continues to increase after consumption stops. Has any work been done to link the type of pungency with specific capsaicinoids? — Preceding unsigned comment added by 86.178.131.43 (talk) 14:39, 26 September 2012 (UTC)

That's going to be determined by three factors: (a) the concentration of the chemical; (b) the binding affinity of the chemical to capsaicin receptors; (c) the rate of clearance of the chemical from the area. If you have a high concentration, low binding affinity, and high rate of clearance, you get an effect that hits fast and doesn't last long. If you have a low concentration, high binding affinity, and low rate of clearance, you get an effect that builds gradually and lasts a long time. Our receptor (biochemistry) article contains additional information. Looie496 (talk) 15:51, 26 September 2012 (UTC)

Thank you, that clarifies the mechanism. But I believe that some capsaicinoids with a low degree of pungency are hydrolysed by the enzymes in saliva into a more active form, thus giving a delayed effect. I can, however, find no verification for this hypothesis.86.178.131.43 (talk) 21:09, 26 September 2012 (UTC)

You might also look into how the chilies are dried/cooked/prepared, as th eir preparation in oil or water and so forth will affect how they are presented to the taste buds. μηδείς (talk) 20:30, 26 September 2012 (UTC)

True, but some chillies seem to exhibit a delayed pungency regardless. 86.178.131.43 (talk) 21:14, 26 September 2012 (UTC)

Let me acknowledge that as you quite rightly point out, my answer only gave a set of basic factors that apply in all situations -- there are other factors such as chemical transformations, buffering, penetration through barriers, etc., that can affect the timing in particular situations. Looie496 (talk) 23:12, 26 September 2012 (UTC)

Thank you, your answers have been very helpful. I now have a much clearer understanding of the factors involved.86.178.131.43 (talk) 17:47, 27 September 2012 (UTC)

I don't feel like we gave a decent answer here, but it's a hard one to research. It would be easier if you could name one or more specific varieties of chili peppers that have this effect; then you or I could go to www.ncbi.nlm.nih.gov and see what we could come up with about their chemical constituents, then see what is known about the metabolism and receptor activity of each of those constituents. Wnt (talk) 21:46, 28 September 2012 (UTC)

Male pattern baldness

Hello. What type of doctor would be the best specialist to see concerning male pattern baldness? In other words, what type of doctor specializes in that field? Thanks! 64.252.1.35 (talk) 16:03, 26 September 2012 (UTC)

The branch of medicine that deals with the scientific study of the health of hair and scalp is called trichology. Gandalf61 (talk) 16:06, 26 September 2012 (UTC)

Thanks. I will read that page more thoroughly, as I only scanned it quickly just now. But, I am asking what specialization of medical doctors would one visit for this matter? A dermatologist? A urologist? Something else? I never heard of a doctor that goes by the title of "trichologist". Or are there such, out there? Thanks! 64.252.1.35 (talk) 16:15, 26 September 2012 (UTC)

Here is one such in the UK. You certainly wouldn't visit a urologist for male pattern baldness! --TammyMoet (talk) 16:32, 26 September 2012 (UTC)

Thanks. But Kingsley is not a medical doctor (from my reading of his website biography). A urologist specializes in the male reproductive system (e.g., hormones, testosterone levels, etc.) ... it's not such a stretch that he would/could deal with related hormonal issues (baldness, etc.). Thanks. 64.252.1.35 (talk) 16:50, 26 September 2012 (UTC)

Just a correction - a urologist specializes only in the urinary system (of males and females), so is concerned with the testes only to the extent that they are a peripheral part of the urinary system. One who deals with hormone levels (including the reproductive system, again of both males and females) is an endocrinologist. 24.92.74.238 (talk) 00:27, 27 September 2012 (UTC)

Yet when a man is forced through micturitic urgency to take a leak down an alley or beside a parked car, thinking and hoping nobody will see him, but he gets sprung by a passing police officer, he'll be accused of exposing not his urinary machinery but his sexual organs, when sex was absolutely thelast thing on his mind at that moment and all he cared about was relieving his bursting bladder. -- Jack of Oz (Talk) 09:26, 27 September 2012 (UTC)

This is often cited as evidence that "the creator" is actually a municipal planning committee. Nobody else else would deliberately co-locate a sewerage works and entertainment area. Roger (talk) 10:34, 29 September 2012 (UTC)

Actually, shouldn't you just see your primary care physician for that? If you need a specialist, I would try a dermatologist. Their specialty does include care of the scalp and hair growth.--Srleffler (talk) 16:55, 26 September 2012 (UTC)

Since baldness is not a life-threatening condition, many nations allow non-doctors to treat it. The non-doctors would typically be cheaper, and insurance may not cover hair replacement, making a doctor too expensive for most people. Therefore, you may find very few actual doctors practicing in that field. StuRat (talk) 20:59, 26 September 2012 (UTC)

I don't believe there is an effective non-medical treatment for male pattern baldness. Going the route primary care physician > dermatologist OR plastic surgeon (for hair transplant) is probably the standard procedure. OsmanRF34 (talk) 15:00, 27 September 2012 (UTC)

I wouldn't call them "non-medical", but non-surgical options like finasteride and minoxidil are effective for some. StuRat (talk) 02:46, 28 September 2012 (UTC)

What causes these lines on paper birch leaves?

See:

• https://www.dropbox.com/s/jemhyv8kv9p8rjc/IMG_7708.JPG
• https://www.dropbox.com/s/1sdtqihuv17t0u7/IMG_7710.JPG

Is this a worm? A larva? Something else?

What causes these lines on the paper birch leaves? These were in the South Chilcotin Mountains Park, in British Columbia, Canada.

Edit: This was probably trembling aspen, not paper birch.

66.183.102.159 (talk) 18:55, 26 September 2012 (UTC)

It's a larva, of the Birch Leafminer. See this pic: [[1]]. Dominus Vobisdu (talk) 19:10, 26 September 2012 (UTC)

I thought this, too, but why do all the leaves seem to only have a single trail? From Birch leafminer: "A single leaf can contain as many as 40 larvae whose mines may merge to destroy the total photosynthetic area of the leaf." Also, images from Google image search for birch leafminer damage look different. The second picture on the page you link to matches what I saw, though. 66.183.102.159 (talk) 19:12, 26 September 2012 (UTC)

And I'm seeing talk of kidney-shaped mine damage from leafminers & am as confused. --Tagishsimon (talk) 19:16, 26 September 2012 (UTC)

After a bit more searching, it looks more like the common aspen leaf miner. Perhaps I had the tree species wrong. 66.183.102.159 (talk) 19:18, 26 September 2012 (UTC)

Leafminers are not a single taxonomic group. That name refers to any insect whose larvae, well, mine leaves. They could be flies, beetles, butterfilies or wasps.

Common names don't really have any scienctific significance, and there are probably several different unrelated insect species that go under the name "Birch Leafminer". Each species has its own characteristic burrowing pattern, some, such as the one in question here, has what is called a "serpentine" pattern. Others have spindle-shaped or kidney-shaped patterns, etc.

My guess is that the culprit in question here is a species of Liriomyza. Your guess about Phyllocnistis is another possibility, and ther are undoubtedly other possibilities as well. Without examining the insect in question, though, it's impossible to tell. Dominus Vobisdu (talk) 19:41, 26 September 2012 (UTC)

Also, some leafmining insects are fastidious, meaning that they strongly prefer only one species or taxon of plant as their host. Others are more catholic in their choice of host. Dominus Vobisdu (talk) 20:31, 26 September 2012 (UTC)

At a molecular level

I've been informed in an advert that Esso fuel works at a molecular level. Wouldn't that be true of all fuels? Do they think the public are really stupid? Or am I stupid and missing something obvious? Itsmejudith (talk) 19:49, 26 September 2012 (UTC)

HAHAHAHAHAHAHaHaHaHaHaHahahahaha! Yes. See combustion and combustion engine. μηδείς (talk) 20:26, 26 September 2012 (UTC)

Slight correction - they know the public are really stupid. Adverts like that really depress me because marketing people for big firms like Esso tend to be very good at their jobs, so they wouldn't create adverts like that if they didn't work. --Tango (talk) 21:17, 26 September 2012 (UTC)

Public ignorance is one of the major pillars on which advertising is based. For me the best (or worst) example of using public ignorance is anti-ageing and anti-wrinkle creams, pure bull**it - the information, not the cream! Richard Avery (talk) 21:48, 26 September 2012 (UTC)

On the bright side, let's remember that only the stupidest part of the public seems likely to be affected by this kind of advertising in the first place, so I'd expect them to be pitched to an audience of well below average intelligence and/or educational level. Wnt (talk) 12:38, 27 September 2012 (UTC)

Another factor is that those who work at advertising agencies may not have any background in science, so they really don't know when they are spouting pure BS. A similar problem exists in the courts. StuRat (talk) 21:52, 26 September 2012 (UTC)

• Well, that isn't exactly what they say, in the ads that show up when you Google. They say they have developed a fuel "that works at the molecular level to help remove engine deposits", or minor variations of that phrasing. That isn't really how I would say something, but it isn't quite as inane as the question suggests. (And it isn't true of all fuels, either.) Looie496 (talk) 23:05, 26 September 2012 (UTC)

• What's the alternative to working at the molecular level ? Tossing sand into the engine to grind down the deposits ? I can't see any down-side there... :-) StuRat (talk) 23:10, 26 September 2012 (UTC)

"working at molecular level" is just an adman's perky way of saying "the chemistry of the additives does this...". Refineries have been adding deposit eliminating and removing substances to fuels for decades. If you include reducing/eliminating lead & lead oxide deposits, they've all been adding stuff to get rid of that almost since adding lead to increase the octane rating, and that began in the 1920's. Adding substances to reduce gums from rings etc has been routine for at least 30 years. See Internal Combustion Engines, 2d Ed, Richard Stone 1992, pub:SAE.

The most hilarious fuel marketing campaigns occured in Western Australia in the 1960's and 70's. The prominent fuel companies, as measured by the number of branded service stations, back then were BP, Caltex, Shell, Esso, and Ampol. They all had marketing that claimed/suggested that each had their own special additives in the fuel. In fact, there was only one refinery and distribution system (owned by BP) - all service stations, regardles of branding, sold gasoline made by BP. Ratbone120.145.8.132 (talk) 00:19, 27 September 2012 (UTC)

That of itself does not invalidate the vendors claims. It is possible for a single manufacturer to blend petrol to different recipies for each customer. --Tagishsimon (talk) 12:59, 27 September 2012 (UTC)

Ain't they effective at removing oil deposits rather than engine deposits? ;) — Preceding unsigned comment added by One.Ouch.Zero (talk • contribs) 07:04, 27 September 2012 (UTC)

Was that deposits of oil, or something deposited by the oil? Actually, engine deposits come from all these sources: deterioration of oil, substances in the fuel, chemical reactions between fuel and oil and engine metal parts, and dust and other substances in the air (the air filter does not filter out everything). Ratbone58.164.231.128 (talk) 12:16, 27 September 2012 (UTC).

Deposits of oil. Many have been exhausted since the development of additives. So many that it cannot be coincedential. ;) - ¡Ouch! (^{hurt me} / _{more pain}) 15:17, 27 September 2012 (UTC)

Chimpanzee-Human percentage of relatedness

Old estimates were around 99%, but a paper in 2007 supposedly lowered it to 94%. Yet, the recently published data on the Bonobo genome says that they share 98.7% (again around 99%) with humans and 99.6% with chimps. Bonobos split from chimps, so there is no way they are closer to humans than chimps are to us. What is the most up-to-date analysis of chimpanzee-human relatedness? --Ghostexorcist (talk) 21:39, 26 September 2012 (UTC)

You get different answers depending on how you measure it. See the discussion near the bottom of this Q: Wikipedia:Reference_desk/Archives/Science/2009_November_5#Drosophila_melanogaster_and_human_genome_homology. StuRat (talk) 21:46, 26 September 2012 (UTC)

Is it so that DNA similarity is necessarily equivalent to relatedness? Perhaps in the technical use of the term, it might even be the definition of relatedness, but DNA is a very funny thing, and speaking of relatedness tends to take a journey into colloquial terms. I mean, turkeys have 80 chromosomes, while tigers have 38 and earthrworms have 36. I know it's not even remotely analogous to the point your making, but we don't take this to mean that earthworms are more closely related to tigers than either tigers and earthworms are to turkeys? I don't know...something just irks me about strictly defining relatedness by DNA. DRosenbach ^{(Talk | Contribs)} 15:04, 27 September 2012 (UTC)

But we know the reason why we have 46 chromosomes and chimps have 48 is because our chromosome #2 is simply a fused version of the corresponding primate chromosome. I've never heard anyone claim that animals with similar chromosome numbers were related. Tigers and worms are obviously not related because they are not even close to being apart of the same family. Animals can have different chromosome numbers and still be closely related. For instance, a horse has 64 chromosomes, while a donkey has 62. Relatedness is based on the similarity between DNA sequences, as well as other factors like anatomy. Horses and donkeys are obviously extremely similar in body form. The same goes for humans and primates. Creatures separated by large amounts of DNA differences tend not to be physically similar. For example, a cat is similar to humans because its a mammal, but a sea sponge isn't. --Ghostexorcist (talk) 16:43, 27 September 2012 (UTC)

A lot of DNA is junk, so it would be theoretically possible for two very closely related species to have all the important DNA in common and all the junk DNA be different, so that, by just comparing the amount of DNA in common, they would appear to be very distantly related. However, evolution just won't lead to such a result. So, measuring the amount of DNA in common is a rough way to measure how related two species (or individuals within a species) are. StuRat (talk) 02:40, 28 September 2012 (UTC)

The notion of "junk DNA" is on the decline, perhaps. -- Scray (talk) 04:31, 29 September 2012 (UTC)