Wikipedia:Reference desk/Archives/Science/2011 February 17

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February 17

Organic chemistry nomenclature

How are organic compounds named if one of the side chains is branched? For example, what would the name be of the chemical that results when a methyl group is attached to the second carbon of the propyl group in 5-propylnonane? --75.15.161.185 (talk) 01:19, 17 February 2011 (UTC)

It's all part of IUPAC nomenclature of organic chemistry. You treat the main attachment as itself a parent to which are attached more groups: "(A attached to B) attached to C". When identifying the A on B, with the same rules of group-names, precedence, etc as usual are used, with the additional detail that the carbon in B that attaches to C is considered position #1 in the B sidechain. So instead of propyl, you have 2-methylpropyl, and that whole thing is at position 5 on nonane: 5-{2-methylpropyl)nonane. IUPAC nomenclature. You may also see it named as some relationship to "a four-carbon unit" attached, with some name related to Butyl used to indicate that it's not a literally a -CH2-CH2-CH2-CH3 attached. DMacks (talk) 01:37, 17 February 2011 (UTC)

mDNA

Hi all, I have a question about mDNA populations. If a small group (20) of individuals descended from the same woman (let's call her April), were to assimilate with a large population (20000) that were descended from a different woman (May), am I correct in assuming that the record of April's mDNA would most likely quickly end, and all of the descendents of both groups would eventually only show mDNA for May? Sorry if that's confusing. Let me know, and I'll clarify. One note: I am not even remotely a geneticist. Falconus^{p t c} 04:09, 17 February 2011 (UTC)

Edit: I'm assuming that neither group is more prolific reproduced at a higher rate than the other (i.e. each woman has the same number of average kids). Falconus^{p t c} 04:10, 17 February 2011 (UTC)

It might disappear but it doesn't have to. If all else is equal, the proportion of mDNA coming from each woman will remain on average constant. There will, however, be random fluctuations, and the proportion coming from April is so small that those random fluctuations may at some point bring it down to zero. This is more likely if the population size decreases, less likely if it increases. Looie496 (talk) 06:33, 17 February 2011 (UTC)

Gambler's ruin is relevant here. Dauto (talk) 06:55, 17 February 2011 (UTC)

You've probably already read the article Mitochondrial Eve, but if not it touches on this topic and has further links of possible interest, in particular that on Genetic drift. --87.81.230.195 (talk) 12:06, 17 February 2011 (UTC)

Okay, thank you. Falconus^{p t c} 17:02, 17 February 2011 (UTC)

Some comments:

1) You said 20 individuals, but only the number of females in the small group would matter, as the men don't pass on their mitochondrial DNA.

2) Note that it doesn't matter whether the women in the smaller group (or the larger group, for that matter), continue to mate within the group or with the other group, it's only the number of female offspring each have that matters for this calculation.

3) The chances of the small group of females not having any descendants after a given period of time should be the same if they are in the small group versus the large group, unless being in the larger group either helps or inhibits them from reproducing. It could help if the larger group provides advantages in protection from nature that keeps them alive longer, or it could hurt if the larger group either kills them or prevents them from breeding, as a form of eugenics. StuRat (talk) 17:48, 17 February 2011 (UTC)

StuRat, what you said above is not exactly correct. Read the (introduction of the) article I linked above and see if you understand why being absorbed by the larger group may over time spell doom for the smaller group's genes. Dauto (talk) 01:00, 20 February 2011 (UTC)

Assuming that you mean the risk of all carriers of a specific mDNA strand dying out, over time, I don't see how this risk is either necessarily higher or lower, given their inclusion in a larger group. I did mention possible reasons why it might, in my third point. What part of my statement do you think is incorrect, and why ? StuRat (talk) 21:57, 20 February 2011 (UTC)

Spinning knob, BMW iDrive question

Can spinning the knob on a BMW iDrive (http://www.bmw.com/com/en/newvehicles/3series/sedan/2005/allfacts/_shared/img/ergonomics_idrive.jpg) too fast cause any damage to it? I don't mean spinning it at a ridiculously fast rate, but spinning it very quickly to lets say go through 50 songs at a somewhat fast rate rather than doing it slowly or at a normal rate and doing it for a long period of time (for several months lets say).

Are you planning to connect it to the drive shaft or something? Turing the knob continuously for several months is very likely to damage it. It probably was only designed to be turned a few dozen times per day and the "bearings" will likely fail, the paint will wear off and particles will get into the sensors. Graeme Bartlett (talk) 13:11, 17 February 2011 (UTC)

... but, apart from physical wear, it is extremely unlikely that you will damage the electronics by sending fast signals to the processor. Dbfirs 13:22, 17 February 2011 (UTC)

It's unlikely to damage the processor. It might crash the software or cause other unexpected effects, but it should be possible to reset the software. Since the iDrive can control electromechanical systems such as CD, it may cause damage to those systems if you repeatedly change the settings (through wear and tear, possibly heat damage, or other methods). It may also void your warranty. --Colapeninsula (talk) 16:13, 17 February 2011 (UTC)

I was just wondering about physical wear. My friend spins it very fast and I got upset with her because I'm pretty sure it will damage the bearing overtime. We had an argument over it and she was upset because she thinks it won't damage it and I think it will.

As long as she is using a fairly gentle touch, I would value friendship more highly than the very slight possibility of damage. This control is new, so there is probably not much evidence of durability in use, but I expect that BMW have thoroughly tested the control on their test benches and designed it to last at least the lifetime of the car, even with heavy use. You don't say whether you are skipping through songs on a CD or on a flash drive, but I expect that the circuitry does not issue a read command until the control indicates a particular track, so there might be lower total wear from skipping quickly through the list. Dbfirs 23:42, 18 February 2011 (UTC)

What is this?

Is it a fish, or amphibian, or what? Its geocoded. Taken in Laem Phak Bia, Ban Laem, Phetchaburi, Thailand at the edge of a river. JJ Harrison (talk) 12:33, 17 February 2011 (UTC)

That's a mudskipper. It is indeed a fish, amphibian, or what. 81.131.41.98 (talk) 12:40, 17 February 2011 (UTC)

(EC) It's certainly a fish, more precisely a Mudskipper, but there are very many species of mudskipper and at least two that both live in this general area and have blue spots. The closest visual match I can find after a short google search on Mudskipper Thailand blue spots is Boleophthalmus pectinirostris, but Boleophthalmus boddarti is also a possibility and from the links' text seems more likely to be found in Thailand. --87.81.230.195 (talk) 12:55, 17 February 2011 (UTC)

Thanks for the information. I'll have a look at the species tomorrow. If it helps it'd be in a Brackish intertidal zone with Mangroves abound. JJ Harrison (talk) 13:17, 17 February 2011 (UTC)

Oh, from the photos, it looks to be Boleophthalmus boddarti - it has dark brown stripes rather than spots. 58.6.128.181 (talk) 13:19, 17 February 2011 (UTC)

You should add this photo to the appropriate article; it shows off the colors and anatomy well (at least for the front half of it which is in sharp focus), and it's a pretty specimen. Comet Tuttle (talk) 20:54, 17 February 2011 (UTC)

Thanks, I intend to. JJ Harrison (talk) 02:40, 18 February 2011 (UTC)

I concur that Boleophthalmus boddarti is, on reflection, a better visual match of the two species so far suggested, considering that the ones in that link are males displaying, and therefore probably at their showiest, but it would be useful if an ichthyologist could confirm whether your less gaudy specimen is a non-displaying male, a female, or yet a third species. 87.81.230.195 (talk) 08:19, 18 February 2011 (UTC)

Great picture! It makes me think of a prehistoric ancestor of some sort.--Brianann MacAmhlaidh (talk) 12:05, 20 February 2011 (UTC)

Spin Integer

Reading Spin section and basic concept of elementary particles I have some doubts: Since spin of electrons is identified with angular momentum and in consequence causes a magnetic effects, what is concept of spin in photons ? Why we call spin +- n.(1/2) for leptons/quarks and integer spin +- n.1 for bósons ?

Per the photon article, photons do carry spin angular momentum, and the spin state of a photon corresponds to its circular polarization state. I'm not sure what you're asking with the second question. The unit is h-bar, the reduced Planck constant, and those particles have spin in integer or half-integer multiples of it. Plus and minus are whether the component of spin is parallel or anti-parallel to the direction it's measured in. --Dan Wylie-Sears 2 (talk) 17:39, 17 February 2011 (UTC)

The precise relationship between the spin $s\,$ and the spin angular momentum $L_{s}\,$ is given by $L_{s}=\hbar {\sqrt {s(s+1)}}$. So the spin angular momentum of an electron is $L_{s}=\hbar {\sqrt {\frac {3}{4}}}$, and the one for the photon is $L_{s}=\hbar {\sqrt {2}}$. Dauto (talk) 20:06, 17 February 2011 (UTC)

The OP may be asking a much more in-depth question about the difference between the mathematical formalism of bosons and fermions that is apparent in the integer vs half-integer spins. As I recall, the formalism can be explained in some sense by noting that bosons can be swapped freely with each other, up down in out, having a wavefunction with this symmetry. By contrast, fermions are antisymmetric, flipping their wavefunctions around when swapping places and preventing each other from entering the same quantum state.

Now here's a really simple illustration of how this makes the spin rule (and this is totally not going to be very accurate in reality): in the symmetric case, wave A adds with wave B to make wave C, but we must make sure we normalize (because wave^2 = 1, since it's a probability), so we get C=(A+B)/sqrt(2), and this seems perfectly natural. If they are fermions, however, the sign flips when the two combine, giving two possibilities for C: (A-B)/sqrt(2) and (B-A)/sqrt(2). But this must again be normalized, so each state only has a contribution of 1/2, so when we extract the angular momentum from the particle linearly and get an integer, a given fermion state gives us a half-integer result. Again, this is totally not accurate, but just an illustration because I'm tired. SamuelRiv (talk) 05:34, 18 February 2011 (UTC)

I was under the impression that the spins simply add as vectors in three dimensions. The formula for the electron makes sense because it is simply the square root of 1/4 + 1/4 + 1/4 - the result of having a spin of ±1/2 hbar in three different dimensions. What confuses me a bit is that the photon by this logic has a spin of ±1 hbar in two dimensions, and 0 in the third. Looking over circular polarization, elliptical polarization, sinusoidal plane-wave solutions of the electromagnetic wave equation etc., there's always a sense that two independent parameters of the photon's polarization can vary while a third is zero, but I don't really understand it. Looking at various types of photons, which axis has zero angular momentum for each one, and which axes are ±1? Wnt (talk) 02:20, 19 February 2011 (UTC)

I think you might be trying to extend Fermi spin statistics to spin-1 particles, or perhaps trying to associate each spin state with a given vector, but I'm not sure. A good place to start would be looking at Pauli matrices, where you have σx, σy, σz for the three dimensions. Not that an actual spin state is defined by some combination of all three matrices, and those states are given relative to some reference axis. The associated particles (for spin-1/2) can be in any spin state they want as long as they are all linearly-independent, and as such with the 2x2 matrices there can only ever be two linearly-independent representations, thus spin-up and spin-down, regardless of the actual axes chosen. The 3x3 matrices describe spin-1, which does not make restrict multiple particles from being in the same spin state, but they can be used if you need to define the contributions of spin to each axis of a photon's propagation. Note, however, that the spin is distributed proportionally - there is no single vector of a photon that necessarily gets "more or less" spin. Also note that every spin contribution is 1 - the matrices are unitary. SamuelRiv (talk) 21:12, 19 February 2011 (UTC)

Wnt, that's not how it works. What you actually have is a spin of ±1/2 hbar in one direction (often taken by convention to be the z axis) and unknown (and unknowable because of the uncertainty principle) components along the other two directions. Dauto (talk) 16:12, 20 February 2011 (UTC)

yogurt

Approximately how long would it take for yogurt to go off in a 60 degF environment instead of the 35-40 degF environment of a refrigerator? Googlemeister (talk) 17:13, 17 February 2011 (UTC)

That would be highly dependent on the amount (and type) of bacteria present initially. If it was completely sterile, it might stay edible for years. Those yogurts with "active yogurt cultures" are not sterile, but there might be others which are. StuRat (talk) 17:35, 17 February 2011 (UTC)

Nonvolatile, Nonflammable oil ?

I want a material which doesn't evaporate and isn't flammable. The application is to mix it with asphalt concrete to keep it from drying out and cracking. I believe shredded tires were used for this in one test case, but then the road caught fire. Of course, I doubt if any oil doesn't evaporate at all or is completely inflammable, so I will settle for an oil or other liquid which can be mixed with asphalt and will evaporate very slowly (over decades) and be only slightly flammable. StuRat (talk) 17:32, 17 February 2011 (UTC)

Nonflammable lubricants like Krytox might work - but they're pretty expensive if you're planning to mix it in bulk quantities. You should really specify how non-flammable you need: Krytox won't combust even in a pure 100% oxygen environment with a spark present; but that's a little overkill for most purposes. On the other extreme, vegetable oil is cheap and pretty "nonflammable" but can definitely ignite in certain conditions. Nimur (talk) 17:45, 17 February 2011 (UTC)

Well, I just don't want the road to catch fire. I suppose the worst case scenario is when a gasoline tanker truck has an accident, leaks gasoline all over the road, and it burns off on it's own. That would give us a very high temperature, but just the normal level of oxygen in air and the normal amount of surface area for a road. Also, we must consider that the asphalt concrete won't be 100% this material, but will contain other nonflammable materials, as well. Perhaps a coating of sand on top might both increase friction and decrease flammability, although it would tend to increase tire wear. In this scenario, I'd expect the road under the gasoline to be destroyed, but want to avoid a chain reaction where the whole length of the road burns. So, given these constraints, what material would work ? (If the answer is "none", perhaps "fire breaks" would be needed, in the form of periodic stretches of nonflammable road, like cement.) StuRat (talk) 17:59, 17 February 2011 (UTC)

The vegetable oil suggestion brings up another constraint, it can't be readily biodegradable. Presumably vegetable or animal oils would be broken down by bacteria in short order. StuRat (talk) 18:21, 17 February 2011 (UTC)

Asphalt concrete wont really sustain combustion without an external source of heat. It goes out very quickly.--Aspro (talk) 18:06, 17 February 2011 (UTC)

Right, and I want to keep it that way, with this new nonvolatile oil. So I suppose any material that isn't more flammable than the asphalt component of petroleum would work, but we might also be able to use something slightly more flammable. StuRat (talk) 18:09, 17 February 2011 (UTC)

What is the exact application?

Part of degradation of asphalt cement is due to oxidation. Polychlorinated biphenyl would resist oxidization but people like Ralph Nader would get very upset with you. If the surface area is small then you would be better off using an “ Aggregate Bonding Resin” which is usually a polyurethane formula. Epoxy would be best from the non flammability point of view.--Aspro (talk) 17:55, 17 February 2011 (UTC)

The exact application is a driveway 50 feet long and 8 feet wide. I'm tired of having to do maintenance ever year and rebuild it every few years. The asphalt cement starts out soft, but becomes hard as rock in a few years, so it seems the volatile liquids have all evaporated by then. It is subject to salt exposure and the frost/freeze cycle, as well as direct sunlight and a 2 ton car or truck driving over it about 5 times a day and parking on it 2/3 the time, in roughly the same spot. StuRat (talk) 18:09, 17 February 2011 (UTC)

Assuming the foundation bed is solid, it might be that your not sealing it with a coat of tar before the asphalt gets laid. There are other stuff on the market sold as "Asphalt Driveway Sealer" which might also mitigate the problem. There are also emulsified tars that one can just sprinkle on from a watering can but I don't know how well they perform. Also, it might not be thick enough, with an aggregate large enough, for the amount of use your subjecting it to. Ask a civil engineer for the right spec. One last thing: Make sure nobody cleans their engine with an 'Engine Degreaser' as they contain oil emulsifiers that ruin asphalt surfaces.--Aspro (talk) 18:30, 17 February 2011 (UTC)

Yes, the annual maintenance involves applying the sealer in the fall. Quite the hassle, though, as it requires several dry days, is a lot of work to apply, and means I can't use the driveway for several days, forcing me to park on the street. And, even worse, the sealer seems to contain water, and, therefore, as it evaporates, the sealer shrinks and cracks, providing new locations for ice to form in winter. There has to be a better way. StuRat (talk) 19:05, 17 February 2011 (UTC)

Asphalt Institute has a FAQs page that might hold some answers. Asphalt Pavement Thickness and Mix Design--Aspro (talk) 19:00, 17 February 2011 (UTC)

At the risk of spamming, products such as this or this might suit your needs. I doubt you're local to that business, but it's apparently part of a much larger chain of businesses that operate under a variety of names in the US and elsewhere. In addition, you could try searching for those product brand names in a more restricted Google search to see if there's a seller near you. (full disclosure: I happen to know the owner) Matt Deres (talk) 19:09, 17 February 2011 (UTC)

Silicone oil is a nonvolatile, nonflammable oil - but I don't know how it would affect the properties of asphalt. 148.177.1.210 (talk) 19:10, 17 February 2011 (UTC)

In general, this topic sounds like one of these ideas that can go unbelievably wrong. If you experiment on your driveway with some new chemical, at best it will probably fall apart in some unexpected way, and at worst... well, picture your neighborhood as a Superfund site (after your assets are exhausted). I know that they use silicone oil in McDonald's french fries, but if your neighbor finds it in a test of his drinking water I doubt you're going to convince the court of that without paying a whole lot for lawyers and expert witnesses. Wnt (talk) 19:29, 17 February 2011 (UTC)

We have city water here, not well water. StuRat (talk) 19:41, 17 February 2011 (UTC)

1) The silicone oil idea sounds like it might work. How cheaply can you buy it in bulk ?

2) Another thought is an epoxy, such as this one: [1], mixed with sand or some other filler. How cheaply can this be bought in bulk (and do they have a system for dispensing it in bulk, rather than 8 ounces at a time ?). ? StuRat (talk) 19:38, 17 February 2011 (UTC)

Epoxy is expensive. Sounds like you need a proper civil engineer to advise you. Such a surface properly applied should last a generation. The tech is tried and tested. Look at the pounding a road undergoes, and they last for a couple of decades before they need resurfacing. --Aspro (talk) 21:45, 17 February 2011 (UTC)

I largely agree (in fact I was thinking myself it seems strange this is a problem since AFAIK it's not such a big deal for roads etc or even many other driveways which don't need resurfacing every year.) Although it sounds like StuRat has a very unusual driveway. At least I'm not aware of many home driveways where a petrol tanker having an accident and leaking over the road is a concern in any way. For most of us, we'd probably be more worried about the tanker hitting the house anyway in the unlikely event one does have an accident. Nil Einne (talk) 23:12, 17 February 2011 (UTC)

Roads around here don't last that long, and need constant patching until they are resurfaced. And don't we have any civil engineers here ? StuRat (talk) 00:12, 18 February 2011 (UTC)

Just curious but is there a reason you need your driveway to be able to withstand a fuel truck fire? It sounds like overengineering the problem. Googlemeister (talk) 14:27, 18 February 2011 (UTC)

That's a worst-case scenario. And I said I expected the driveway under the gasoline to be destroyed, but didn't want the whole length to burn, and thus catch the house and neighbor's house on fire. A fuel truck fire may be unlikely, but a car leaking gasoline and starting a fire seems conceivable. I've had a car with a fuel leak before. StuRat (talk) 19:21, 18 February 2011 (UTC)

Can a road made with recycled tires really sustain an expanding fire? It is true that many of the components of ordinary asphalt are petrochemical, yet it seems to endure many accidents and house fires without trouble. There is very little present to act as a wick. Wnt (talk) 01:29, 19 February 2011 (UTC)

...whereas tires, also made from petrochemicals, will sustain a fire, once started. So, the percentage of shredded tire in the road should control whether the road is flammable, or not. StuRat (talk) 21:50, 20 February 2011 (UTC)

The entirety of my answer can be expressed in three letters: EPA. Wilford Nusser (talk) 09:15, 21 February 2011 (UTC)

Not really. I have no idea what you mean. StuRat (talk) 19:47, 21 February 2011 (UTC)

Chemistry and Lifetime

Hi, I want to study chemistry so it is so important for me to know wether spending much time in labs has a bad effect on health or not.My chemistry teacher says that (on average) chemists live 10 years less than other people because of their contact with chemicals.Is that true?--95.82.49.189 (talk) 18:01, 17 February 2011 (UTC)

That would depend on what chemicals you're working with. If you're working for the army, developing nerve agents, I would find this believing. For someone working with glue or something harmless, I wouldn't see why they would live any shorter. --T H F S W (T · C · E) 18:06, 17 February 2011 (UTC)

(ec) It would also depend on if you do chemistry "old school", including smelling and tasting chemicals to identify them, which can shorten your lifespan by a significant amount, or keep them all properly sealed. StuRat (talk) 18:15, 17 February 2011 (UTC)

You might become more aware of all the opportunities for harmful chemical exposure outside the lab and so avoid them.--Aspro (talk) 18:12, 17 February 2011 (UTC)

If your chemistry teacher says that chemists live 10 years less than other people because of their contact with chemicals, then he doesn't know what he is talking about. There is no such evidence. At least in industrialized nations, chemists work in environments where their exposure to chemicals in negligible. And even if your job included smelling and tasting chemicals to identify them, I strongly doubt that would have any significant effect on life expectancy unless one routinely worked with extremely toxic/carcinogenic substances. 148.177.1.210 (talk) 19:07, 17 February 2011 (UTC)

As a trained scientist, you may often be the best-qualified person to evaluate the risks of a particular hazard, be it biological, chemical, radiological, or so on. At the same time, you should always consult Material Safety Data Sheets, EH&S guidelines, and comply with all relevant legal and institutional rules. Working for a university, government lab, or corporate research and development, you will almost always have an on-site Environmental Health and Safety team who are aware of known risks and take steps to mitigate them. Let me also make this abundantly clear: as a scientist, you are never required to deal with hazardous materials; your particular career and research directions may take you where-ever you want, including forays toward the hazardous; but there are plenty of ways to pursue a career in the hard sciences, including chemistry, without ever exposing yourself to anything seriously hazardous. I think it's patently false to suggest that chemists have shorter life-expectancies, on the whole, than other professionals. Unless anyone can show some data to the contrary, I'd say your teacher is incorrect. Nimur (talk) 19:28, 17 February 2011 (UTC)

Ask for the evidence, as you should in almost everything. It seems rather irresponsible for a teacher to potentially snuff out student interest like that. 66.108.223.179 (talk) 19:55, 17 February 2011 (UTC)

Answerers, note that the OP is from Iran, where I'm guessing funding for things like fume hoods and dedicated Environmental Health and Safety teams might be tighter than it is in richer countries. At least, their science budget as a whole is quite tight there (see Science and technology in Iran#Budget), which seems like it might make it more tempting there to skimp on safety equipment and procedures. I don't at all know that that's actually the case; my point is just that it's questionable to assume that the job of a chemist is equally safe in all countries. Red Act (talk) 21:01, 17 February 2011 (UTC)

One thing is that you have to do the statistics with the people already dead, to do the statistics with the students in the 1990s will not give you anything. So lets look at the chemists now 100 years old, they studied in the 1930s and worked in a time when most of the dangers of chemicals where underestimated and some very dangerous chemicals like tetrachloromethane were used as standard solvents. Fume hoods, gloves and other worker safety things were not established in a necessary way. So that these chemists have a shorter live than others should be possible. Now the things a re much better and during my studies I was not allowed to handle for example thallium, cadmium, beryllium and uranium due to safety restrictions.--Stone (talk) 21:48, 17 February 2011 (UTC)

If anything, a study of chemistry, makes one aware of the true and proportional dangers of chemicals. Reflecting upon what your teacher said, I am reminded of he idiom [2]. A psychologist will also point out, that teachers tend to score high on the neurotic scale. Questioning what you have been told, shows the promising trait of a scientist (or of a preconscious child that should have been strangled at birth). --Aspro (talk) 22:29, 17 February 2011 (UTC)

This is a Reference Desk, no? Look at Average Age at Death of Scientists in Various Specialties. Male chemists do indeed have an average age at death four years younger than male non-scientists. Male's in radiation sciences do the worst. Notice, however, the small sample sizes and large standard deviations, though it is still possible to draw statistically significant conclusions. The authors point out that those in fields requiring them to be active: archeology and agricultural sciences, for example, tend to do better, probably as a result of getting plenty of exercise. Buddy431 (talk) 23:10, 17 February 2011 (UTC)

Disclaimer: Buddy431's article is from the year 1969. (Though I salute him for actually supplying a reference.) Comet Tuttle (talk) 23:22, 17 February 2011 (UTC)

I agree with the lack of exercise comment. Also note that, tied for the worst, is those who work in administration. I suspect that the lack of exercise, combined with stress from fighting over budgets, leads to their early demise. StuRat (talk) 00:08, 18 February 2011 (UTC)

There may be confounding factors in the study (though I concur with Comet Tuttle, and strongly endorse his salute for the use of a proper source). The data are based on deaths reported in Science (the journal) obituaries between 1958 and 1968, which is going to automatically skew the death stats for radiation workers towards a younger age. (The number of radiation researchers would have grown remarkably during the late thirties and onward; few scientists starting their careers during this period would have even reached retirement age by the end of the study, meaning that any death in this group would be 'premature' because the 'natural causes' deaths wouldn't have had time to occur. This effect is even more pronounced among female radiation scientists, where only one woman – 42 years old at time of death – was tabulated.) Interestingly, the average age at death of male radiation workers (Table 1) was tied with administrative workers for the shortest lifetimes—unless filing cabinets are extraordinarily dangerous, it suggests further subtle biases in the dataset. TenOfAllTrades(talk) 02:56, 18 February 2011 (UTC)

I provided a possible reason for that, right above your response. StuRat (talk) 19:17, 18 February 2011 (UTC)

As an electrical worker, I was exposed to several severe electric shocks, high levels of electromagnetic fields, mercury, lead, and solvents such as 1-1-1 trichloroethane, as well as PCB and asbestos. Each of these factors is more likely to shorten lifespan than to lengthen it. I have no doubt that industrial chemists in a lab or factory get exposed to various carcinogins, dangerous chemicals and hazardous conditions at higher levels or frequencies than the general population. Edison (talk) 03:02, 18 February 2011 (UTC)

This posting contains a list of references that specifically address the question of longevity among chemists. My very brief assessment of the listed studies suggests that the overall mortality rate is lower among chemists than among their peers, but chemists' overall risk of cancers is somewhat higher. An unavoidable challenge in any study of this type is that the data will always be most relevant to the industrial hygiene and health and safety practices of a few decades past. TenOfAllTrades(talk) 03:14, 18 February 2011 (UTC)

The usual story is that organic chemists in particular once were reduced in lifespan by ten years, but that invention of the fume hood and other precautions put an end to the problem. Though it is widely told, I've never seen a reference to the data - for all I know it's a ruse to sell more fume hoods... Wnt (talk) 14:57, 18 February 2011 (UTC)

The usual story I heard in school is that it's bimodal...those that don't blow themselves up or poison themselves early in their careers often progress into management or professorships and mostly supervise others from afar rather than continuing to be exposed. But more seriously, modern safety standards definitely have an overall impact (and not just in the MSDS-level paranoia)..."no smoking in lab" (cf. [3]) and the more recent move towards non-heated non-alkali-metal solvent purifications definitely cuts down on ether-still explosions. There might be actual data available for the latter's effect, since lab safety groups are starting to prohibit distillation except in cases where there is no other viable method and companies are charging outrageous prices for Grubbs column setups. DMacks (talk) 17:12, 18 February 2011 (UTC)

Time in a shuttle launch video

Hi all. In the following video: [4] of a compilation of shuttle launches, there is a time counter visible at 0:52 to 1:04. I noticed that it had a weird way of incrementing the seconds. For example, it seems to get to something like 18:31:29 and then goes to 18:32:00. Any idea what this timing scheme is called and why it's used? Thanks. - Akamad (talk) 18:35, 17 February 2011 (UTC)

See Time code it's counting video frames in NTSC, i.e. 30 frames per second. Ariel. (talk) 18:47, 17 February 2011 (UTC)

And, because the video has been re-processed (transcoded) by Youtube (and possibly by others), some frames may be missing from the raw original 30-frame-per-second stream (roughly speaking, for the purposes of reducing file size).

Totally unrelated to the video frame counter, NASA's shuttle launch sequences use a non-intuitive timer for countdowns: see "NASA Countdowns" for an explanation of why those clocks don't run exactly "in-order". On most spaceflight missions, there is a Mission Clock, which times "important mission events", (so it stop, restart, and can even run "out of order" in certain cases, particularly during the countdown) and there is also a regular time-clock in UTC that runs perfectly sequentially. Nimur (talk) 19:35, 17 February 2011 (UTC)

Thanks all. That makes sense. - Akamad (talk) 21:08, 17 February 2011 (UTC)

Gazelle

I remember reading a while back that there was a species of gazelle (or something similar) which slept in 20-30 minute increments. Does someone know the name of the species? 74.15.137.130 (talk) 18:54, 17 February 2011 (UTC)

That is quite plausibly true of all gazelle species. Roger (talk) 19:12, 17 February 2011 (UTC)

There is this:[5] which claims that the Thompson Gazelle only sleep for 1 -5 minutes at a time. However it cites an encyclopaedia called Wikipedia and we all know how reliable that is -don't we!.--Aspro (talk) 22:35, 17 February 2011 (UTC)

Thanks! 74.15.137.130 (talk) 16:34, 18 February 2011 (UTC)

Undulatus asperatus

Our article isn't really clear on how they form. Is it vertical wind sheer that causes the strange folds? And what conditions do they develop from and what type of cloud, if any? --T H F S W (T · C · E) 23:46, 17 February 2011 (UTC)

I believe they are rare enough that the cause is not yet known. Getting them classified as a cloud formation is likely the first step in getting the funds to study them. The last footnote provides this quote: "The Royal Meteorological Society is now gathering detailed weather data for the days and locations where the asperatus clouds have been seen in an attempt to understand exactly what is causing them". If you want speculation, it looks like something is causing them to stay in distinct layers, such as temperature or air-density differences, so that when perturbed by winds, they form ripples instead of mixing evenly. StuRat (talk) 00:01, 18 February 2011 (UTC)

Per above, it isn't certain the conditions that lead to their formation, but basically, they take the form of the normal eddies and circulations in the atmosphere that we usually don't see in the absence of a visible median. Juliancolton (talk) 01:18, 20 February 2011 (UTC)

Yes, I'm reminded of smoke from a cigarette, which similarly seems to stay intact for some time, and thus shows the normally hidden air currents in a room. I wonder if there is another similarity here, such as a temperature difference which prevents mixing. StuRat (talk) 22:07, 20 February 2011 (UTC)