Wikipedia:Reference desk/Archives/Science/2009 January 4

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January 4

Engineering indexes

I'm trying to get a handle on the publication history and relative importance of an engineer in the area of civil and mechanical engineering. He does work in earthquake resistance of structures and (more recently) mitigation of explosion damage to buildings.

I'd rather not name the individual in question, since I don't think the poor guy wants to see a Ref Desk discussion about him pop up the next time he does a vanity search on Google. For testing purposes, some of the (recently-deceased) 'grand old men' of the field include George W. Housner and John Blume.

Can anyone who has some experience with civil engineering research point me to the typical indexes and sources one might use to check out an engineering researcher's background and academic credentials? (I know that in the biomedical sciences I'd hit PubMed/Medline, and that for pure math and physics I'd go straight to arXiv — is there an engineering equivalent?) TenOfAllTrades(talk) 01:32, 4 January 2009 (UTC)

Try Engineering Village (also known as Inspec, Compendex), Web of science (also known as Institute for Scientific Information (ISI) database), , Scopus, or simply Google Scholar. These all are general engineering databases; I am not aware of any specialized to Civil Engineering alone. Abecedare (talk) 01:45, 4 January 2009 (UTC)

Frequency of mass

Since all mass has an associated energy according to Einsteins E=mc^2, and E=hf (according to Planck?); then can it be said that every mass has associated frequency and is traveling at the speed of light through something? If not, why not?--GreenSpigot (talk) 02:25, 4 January 2009 (UTC)

De Broglie hypothesis. Algebraist 02:29, 4 January 2009 (UTC)

Aha! But is everything traveling at c?--GreenSpigot (talk) 02:44, 4 January 2009 (UTC)

No. Algebraist 02:50, 4 January 2009 (UTC)

All matter has an associated wave. For 'macroscopic' objects (like Aardvarks...I'm trying to work Aardvarks into as many answers as possible today!) - the frequency is insanely high. De Broglie says that the wavelength is planks constant divided by momentum (which is mass times velocity). Since plank's constant is an insanely tiny number and we're dividing it by a macroscopic mass - the wavelength is tiny and therefore the frequency is crazily high. 6.6×10⁻³⁴ divided by the momentum of a typical Aardvark (we'll go with 66kg because it's a BIG aardvark and it's just fallen off a cliff so it's moving at 1ms^-1 relative to us) gives it a wavelength of 10^-33 meters - and an Aardvark frequency of about 3x10⁴⁰Hz (why is this not mentioned in Aardvark?). Considering that the highest frequency we 'naturally' consider dealing with is cosmic rays at about 10¹⁹Hz - this is an outrageously high frequency! SteveBaker (talk) 02:54, 4 January 2009 (UTC)

Spuriose Planck derivation, SteveBaker

The calculation never made sense. A macroscopic object is not a mote; it's a bunch of motes. Usually when we count quanta we put a n as the integral coefficiend, as in E=nh/t. So unless every atom in something is entangled or otherwise in a Fermi condensvum, the h/mv is bogus. -lysdexia 01:25, 9 January 2009 (UTC)

Yes but the aardvark universe is outrageous. Does, therefore, all matter travel at 'c' in the space time continuum?--GreenSpigot (talk) 02:59, 4 January 2009 (UTC)

A wave packet...possibly a falling aardvark

Not exactly. You have to distinguish the concept of a 'wave packet' which has a group velocity that isn't tied to the wave's speed (which is indeed 'c'). The graphic (at right) gives some kind of a visualisation of what's going on. The big bunched-up blob is the particle and it is moving across the screen at whatever (sub-light) speed it needs to...but the high frequency squiggles inside are moving along at the speed of light. Technically - the particle is spread out over space - it's not a point as you might expect - and that's something that comes out in Schrodinger's equation as a 'probability density function'. The blob is showing us the probability that the particle is at such-and-such position. In the case of an electron (for example) this is a rather diffuse thing - it's mass is tiny so it's wavelength is rather long - so we have the whole Heisenberg uncertainty principle business going on - where we don't know where the particle is if we measure it's momentum accurately (which you'll recall figures into that wavelength calculation from De Broglie) - or if we pin down it's position accurately - we can't know it's momentum. Our Aardvark however has a VERY small wavelength - so (fortunately for anthills everywhere) we know pretty much exactly where they actually are. SteveBaker (talk) 03:20, 4 January 2009 (UTC)

Just want to check, is it appropriate to say that a macroscopic object is associated with a well-defined wavelength, as per de Broglie? Not that I know much about this at all, but I felt it strange to describe an object by a wave with a wavelength much smaller than the object itself and therefore thought it applied only to particles. —Bromskloss (talk) 16:37, 5 January 2009 (UTC)

Advantage of large population

What are the advantages of the world population being as large as it is, and what would the potential advantages be of it being even larger? NeonMerlin 04:25, 4 January 2009 (UTC)

Well, "large labor pool" comes to mind, but since we're no longer engaged in massive slave labor-driven projects, that may not be such a huge advantage. Overpopulation is increasingly becoming a problem as it is; I'd be inclined to think that the advantages are far outweighed by the disadvantages. I'd be very interested in hearing arguments and facts to the contrary, though. -- Captain Disdain (talk) 04:42, 4 January 2009 (UTC)

I've been thinking a lot recently about the opposite case - the downsides of a falling population. But if I reverse my 'time arrow' - I can come up with some relevent thoughts on this topic:

Any possible benefits of population growth can't be in the form of production or consumption - because at best they cancel out - and at worst, consumption outstrips production because of limited resource availability. (Food, water, land, minerals, fuel, plants, animals - you name it!)

So the benefits of more population could only be in the areas of things like ideas or software - where one idea can serve any number of people and a piece of software can be copied as many times as you like - hence more people means more ideas and therefore more benefits.

Let's imagine a world where the population doubled:

Consider (say) the business of making cars. If you have twice the number of people - you need twice the number of cars but you have twice the number of people to work in car factories to make them - so no benefits.

But consider the business of making computer games. If you have twice the number of people writing them - then there are twice as many different titles on the store shelves - but the cost of physically manufacturing twice the number of disks is very tiny. So we'd have twice as much variety - twice as much choice. Since the total number of games sold would double - and the total number of people working on them would also double - the profit (and cost) per game wouldn't change. You'd expect to see twice the number of new movies made each year - twice the number of new opera's written.

So if more choice is a good thing - then so is more population.

Sadly - doubling the population also doubles the amount of CO2 pumped into the atmosphere - doubles the rate at which we pull fish out of the oceans (which dramatically reduces the fish population - resulting in immediate disaster) - doubles the amount of fossil fuels we need - and therefore halves the amount of time until we run out. This would be a truly monumental disaster.

So I see almost 100% downside - but in areas where ideas matter - it's possible there would be some upside. Of course in some fields there is already too much in the way of new ideas. Scientists find it increasingly impossible to keep up with the latest news in their chosen fields because the journals where such things are reporting are proliferating too greatly. Every year there are movies that I'd be interested to go and see - but there are more of them than I have time for. So ultimately - even this small upside loses it's value. I suppose our notional car factory has twice the number of clever guys figuring out fuel saving strategies - so there might be some claw-back there - but I think it's small.

Interestingly, the small upside of a growth in ideas is a major problem with shrinking population size...if we could somehow halve the world's population (which would solve an AWFUL LOT of problems!) - the number of new movies, new computer games, clever new products from Apple corp - all of those things would slow down dramatically. With half the number of people making new TV shows - but the exact same number of hours to fill each week - the number of reruns on TV would skyrocket. That would be necessary too because with only half the number of people to advertise to - the advertisers can't afford to spend as much.

I think mankind could take care of that though - and in a sense things like Wikipedia are already doing that. By getting a better quality of life for this smaller population (because we have less to struggle with in terms of pollution and dwindling natural resources) - people could have more leisure time. We could improve things like the Internet (half the number of people means more bandwidth per person) - and have better penetration of arts and sciences from other cultures - and have a larger PERCENTAGE of the population generating interesting new content. Within limits - it's probably manageable.

SteveBaker (talk) 05:45, 4 January 2009 (UTC)

I suppose one could come up with a scenario where a large population is necessary to save the Earth, like a meteor heading towards Earth and everyone working to create the rockets and equipment needed to save the Earth. It's an extremely unlikely scenario, though.

There is a huge benefit to an ever-increasing population, however, in that more workers are then available to support the retired population. China is headed into a period where this law will work against them, as their One Child Policy has produced workers who now must support two retired parents, and, in some cases, four retired grandparents, in addition to their own children. That's a lot to ask of a single worker. While an ever increasing population isn't the same as a large population, it inevitably leads us there. StuRat (talk) 14:46, 4 January 2009 (UTC)

A large population may be nessecary when people decide not to reproduce. This is happening in some European countries and the population is falling. Developing countries are still reproducing quickly but even their population increase will soon decelerate. ~AH1^(TCU) 14:54, 4 January 2009 (UTC)

Except that people stop reproducing precisely because of the large population. This can be due to wanting to prevent the global problems caused by overpopulation, or due to more immediate concerns. For example, a lack of housing can make people reluctant to have children, if they know they will all be crowded into the same small apartment. StuRat (talk) 15:04, 4 January 2009 (UTC)

This is not a professional answer, rather some thoughts and additional questions. An ever-increasing population in which more workers are necessary to support the retired sounds a lot like a pyramid scheme. Given finite resources, wouldn't this eventually lead to collapse? Also, the idea that people stop reproducing precisely because of a large population seems like a good model given the assumption of very short lifetimes - won't our huge rate of resource consumption, combined with our long lifetimes lead to an overshoot above the equilibrium, followed by a shortage of resources? 41.243.38.111 (talk) 19:22, 4 January 2009 (UTC) Eon

I think it's more likely that people reproduce less because they often have guaranteed pension now and don't need to rely on their children to support them when they are old. Another important reason may be "the pill". Icek (talk) 14:15, 5 January 2009 (UTC)

SteveBaker said that increasing production and increasing consumption would cancel out. This is false. Cost does not increase linearly with production. Some times, the cost per unit decreases, hence Mass production. Software is the extreme form. Other times, the cost per unit increases, such as energy. The question is which happens more. Also, StuRat said that people stop reproducing because of large population. IIRC, it's mostly based on how well off they are. People who are better off have fewer kids. — DanielLC 22:36, 4 January 2009 (UTC)

For your argument it is sufficient that the cost is not proportional to production; e. g. there is some fixed capital cost and linear operating cost. Icek (talk) 14:09, 5 January 2009 (UTC)

Well - yes - but that effect decreases with volume. Sure, a big car factory that only makes one car a day is going to be way less efficient than one that's utterly maxed out on production. However, at some point that factory can't make anymore and you have to build a second factory - and then your fixed costs just doubled. So the idealised view isn't really right. Cars made by (to take an example I actually know about) the MINI company (a subsidiary of BMW) in just one heavily loaded factory in Oxford cost a comparable amount to similar cars made by Honda, Ford and others - yet their production is about a quarter what each of their rivals makes each year. So in that case, there was little if any savings through volume because the other companies have to have multiple factories running. Also, as volume increases, the fraction of the cost of the item in terms of labor and raw materials starts to dominate the selling price. Sure, you save on the initial design costs - but those will become increasingly negligable as more cars are sold. I think the benefits of a larger population in terms of reduced cost per item are going to asymptote to almost nothing in most industries. (Although - as I said - there are exceptions such as the software, movie and TV businesses).

You don't have to build a second factory, you can just expand the bottlenecks. You don't have to design a new car. You can just build the old one. You don't even have to design a new factory. Your resources and advertising may be cheaper in bulk. There's a reason markets tend to get dominated by a few large corporations. On the other hand, as production in general increases, you have to mine less easily accessible ores. You can no longer get cheap power from things like geothermal energy. That sort of thing also happens on a smaller scale with individual businesses, I just can't think of any good examples at the moment. — DanielLC 18:59, 5 January 2009 (UTC)

Look at our diseconomy of scale article for more examples. I wish I'd written it myself. :-) StuRat (talk) 03:04, 6 January 2009 (UTC)

A related question: What is the lower limit for the population at which we still could have as high a standard of living as we have it now in industrialized nations? We would need a sufficient number of experts from every profession (well, in an ideal world, maybe some professions wouldn't need to exist, like lawyers), but I have little idea about what's the number of people that could be considered "sufficient". Icek (talk) 16:46, 5 January 2009 (UTC)

The tricky part is in areas of entertainment and such. You could probably reduce the world population to a few millions and still keep agriculture and technology running. But we would be unlikely to be able to afford (for example) the Hollywood movie business. The latest James Bond movie cost $230,000,000. If we only had 2 million people - the cost of making that movie would be pretty similar to what it is today. But then everyone would have to pay $120 to go see the movie in order for it to break even...and that assumes that every single person wants to see it! That means that movies at that production price simply won't exist. However, with more or less unlimited natural resources - it's likely that overall prosperity would be vastly bigger - and perhaps then $120 to see a movie isn't so unreasonable. But then consider that with around 3,000 times less people around than there are now - there would only be a handful of talented actors - maybe only one or two movie directors - it would be REALLY tough to keep that kind of activity afloat.

The problem with answering this clearly is that there are just to many variables. If we reduced the population by the same factor throughout the world - the consequences would be different than if all but a few countries were simply eliminated. Having just a couple of million people spread throughout the world would cause transportation nightmares - pushing everyone together into just one region the size of (say) a single US state would have different consequences because we'd be unable to take advantage of natural resources throughout the world.

SteveBaker (talk) 18:04, 5 January 2009 (UTC)

If we're going to assume a good infrastructure everywhere or something else that doesn't exist in reality, increasing the standard of living elsewhere to make up for it would be trivial. If not, I doubt this is possible with a population of any size. — DanielLC 18:59, 5 January 2009 (UTC)

If the population increase is mostly among low IQ religious fundamentalists, it will be a disadvantage.

Small populations, by our current standards, can support fantastic intellectual ferment and artistic genius, by any standards. London in the time of Shakespeare and Renaissance Italy are two examples that spring to mind. With a smaller population, your chances of meeting the great ones of your generation increase. Would you rather see a James Bond movie, or an original production at the Globe? Hang out at Starbucks with some coders who did CGI for Harry Potter, or in a tavern where Michaelangelo's apprentices drink? OK, leave out the smallpox and forced marriages. My point is that what nowadays would be the population of a small town can, with the right leadership and cultural infrastructure, support enormous human creativity and the productivity of intellectual capital that withstands time. BrainyBabe (talk) 11:26, 10 January 2009 (UTC)

Acceleration?

In this video, the parameter "acceleration" is specified in a couple of places. For example, "Acceleration ramp from 0 to 30g." What does this mean? I can't think of anything else to control on a wave generator besides frequency and, perhaps, amplitude. Besides, in a simple harmonic oscillator, acceleration is not constant anyway. --VectorField (talk) 04:49, 4 January 2009 (UTC)

Well, it didn't actually say it was a simple harmonic oscillator - so I suppose an initial accelleration at the start of each cycle is possible. But I agree - it's a strange way to state the amplitude and/or wave-shape. I presume that this number comes about because of the mechanism they are using to shake the liquid...but it's hard to know. SteveBaker (talk) 05:14, 4 January 2009 (UTC)

It's common practice with shaker tables, like the one in the video, to specify the output in units of acceleration. This is because standards for vibration and shock tolerance, such as those in MIL-STD-810, are specified in units of acceleration. For a sinusoidal waveform, the stated acceleration is usually the RMS value, but for other waveforms it could be the peak. You can convert from acceleration to displacement by integrating twice:

a = A sin ωt ==> v = -(A/ω) cos ωt ==> d = -(A/ω²) sin ωt

where a is instantaneous acceleration, A is peak acceleration, ω is angular frequency, v is speed, and d is displacement. The last expression shows that peak displacement (what you called amplitude) is A/ω². Don't forget to convert your 30g figure into m/s².--Heron (talk) 12:31, 4 January 2009 (UTC)

RMS acceleration makes sense, but strikes me as a queer way of specifying amplitude. Perhaps acceleration is more relevant to durability than amplitude? So,

rms acceleration = 30g = 300m/s² -> max acceleration = 600m/s² -> displacement = A/ω² = 600m/s² /(2π 120hz)² = 1.06mm.

That sounds about right for a displacement, eh? --VectorField (talk) 00:42, 5 January 2009 (UTC)

Almost right. I think you want to multiply RMS by root 2, not 2, to get peak. As you say, acceleration, not amplitude, is what breaks things. In vibration testing, nobody cares what the amplitude is, as long as it's small enough to fit inside the test chamber. :) --Heron (talk) 21:47, 5 January 2009 (UTC)

It means that the acceleration starts at 0g and increases in a linear manner up to 30g. Whats the problem with that?--GreenSpigot (talk) 01:24, 5 January 2009 (UTC)

Why is Jelly easier to swallow than water?

During the last week or two I've been suffering from the acute phase of Infectious mononucleosis/Glandular Fever. During this time many of the symptoms are quite like tonsillitis and swallowing is painful. Can anyone suggest a good scientific reason as to why Jelly is less painful to consume than water is? Noodle snacks (talk) 06:47, 4 January 2009 (UTC)

Well if you're a UK resident, and jelly is what kids eat with ice cream (as opposed to the US meaning of "jelly" which is "sweetened fruit preserve"), there are two effects: one is that jelly is almost always served cold, which numbs the throat. The other effect is the gelatine (or gelatine substitute) used to set the jelly, which will coat the throat and soothe the inflammation. --TammyMoet (talk) 10:52, 4 January 2009 (UTC)

Water can also contain some irritants, like chlorine products, used to kill off the little nasties. This is true of tap water and bottled water that the makers fill from tap water. In addition, bottled water may contain some irritating chemicals which have leeched out of the plastic bottle into the water. StuRat (talk) 14:33, 4 January 2009 (UTC)

Such as Bisphenol A. However, what if it's previously boiled water? ~AH1^(TCU) 14:51, 4 January 2009 (UTC)

That would kill bacteria in the water, and maybe reduce the amount of chlorine products, but I doubt if it would remove chemicals leeched in from the plastic much. Just letting water sit for a while (in a glass container) also seems to allow chlorine products to vent off. StuRat (talk) 14:58, 4 January 2009 (UTC)

I'm not convinced the amount of Bisphenol A is enough to be much of an irritant. Indeed even chlorine. Note also any jelly made from said water is likely to contain the same chemicals. However the surface area your exposed to may be lower. IMHO the primary advantage other then the ones Tammy mentioned is that jelly is a softer product then water. Okay it's difficult to compare since jelly is a solid and water a liquid but IMHO it's true. Nil Einne (talk) 15:23, 4 January 2009 (UTC)

If by jelly we mean the fruit spread, then the plant which produces the fruit has filtered out many of the irritants, like chlorine, from the water. If by jelly we mean some concoction made with water and gelatin, then it has probably been let to sit long enough for most of the chlorine to outgas. StuRat (talk) 16:41, 4 January 2009 (UTC)

I'm still not convinced. According to [1] [2] (not the greatest sources but the best I could find) the halflife of chlorine in water is 1-5 hours. If your talking about a hospital setting I doubt the jelly would have been made more then 6 hours beforehand. Even in a home it seems resonable the jelly woulkd often be consumed within 3-6 hours of it being made. Perhaps not entirely consumed but the OP didn't say the jelly is fine if it's 2 days old but if it's just recently made its not. More importantly, whether at home or in a hospital there's a very good chance the jelly would have been covered for most of the time. Furthermore, it seems entirely plausible the half-life of chlorine in set jelly which is therefore solid/semi-solid would be significantly higher. All in all, particularly given it's not uncommon people will have an uncovered glass of water besides them for several hours it seems entirely plausible to me the water will actually have less chlorine then the jelly. BTW the production of jam does require water although that wasn't what were talking about. P.S. If you're in the US apparently a lot of water is now chlorinaminated and although I'm guessing the OP isn't from the US, in that case even leaving the jelly to set in the open air is not going to help you much. Nil Einne (talk) 10:20, 5 January 2009 (UTC)

I wasn't thinking of a homemade gelatin dessert, but one bought at a store (such as the two shown at the top of that article). Perhaps the original poster can tell us which one they meant ? StuRat (talk) 18:15, 5 January 2009 (UTC)

Another possible downside to drinking water is that hard water (such as well water), may contain high mineral levels, some of which can act as irritants. If the water is treated with a water softener, then it will have a high sodium level, instead, which can also be an irritant. StuRat (talk) 14:58, 4 January 2009 (UTC)

Alternatively, it may be the lack of stuff in the water. Pure water is bad for exposed (rough, raw) tissue. Try a lightly-salted water. Not good for hydration, though. Saintrain (talk) 19:52, 4 January 2009 (UTC)

Nothing at all to do with "stuff" or irritants, and everything to do with viscosity. Swallowing is a reasonably well-studied phenomenon, as it's necessary to evaluate stroke victims who have swallowing difficulties before permitting them to try to eat. In brief, the ease of swallowing varies with the amount you're trying to swallow at once (bolus volume), and by the consistency of what you're trying to swallow (liquid, semi-solid, and solid). Studies have shown that it's easier to swallow low bolus volumes, and it's easier to swallow semi-solid than liquid. [3]. - Nunh-huh 02:29, 5 January 2009 (UTC) (P.S. is British "jelly" the same as American "Jell-o"?

) <- Here's a closing parenthesis for you. Yes, I think you're right on the Jell-O theory, with the general name being gelatin dessert. StuRat (talk) 03:10, 5 January 2009 (UTC)

Many thanks for the ")". I have a chronic shortage. And for solving the "jelly" mystery for me...though in America it's traditionally accompanied by whipped cream, not ice cream! - Nunh-huh 03:30, 5 January 2009 (UTC)

Placebo

I was reading the wiki article on placebos and the placebo effect. I'm a major non-subscriber to non-western medicine. (Obviously the corollary is that I'm a major subscriber to western medicine.) I don't buy astrology, and I don't like religion or god, I don't believe in 'mystical energies' or in the healing power of faith.

My question therefore is--after reading about the placebo effect, people can actually get (somewhat) better just by thinking that they are? I don't really understand how that's possible, what's relieving the pain, or helping the suffering?207.172.70.176 (talk) 07:28, 4 January 2009 (UTC)

When given a placebo, there is no external, bioactive treatment relieving the pain, or helping the suffering. However because your body thinks it has been given something that has that effect, it is "tricked" into thinking it is feeling better. While there are obviously limits to the placebo effect, its remarkable how powerful, or influential, expectation is how our body reacts to injury or treatment. Have you ever noticed that you can cut yourself without even noticing (suggesting, therefore, there is no pain), but the moment you become aware of the cut it begins to throb? You see this in children (and association footballers) all the time, when they take a few moments for their brain to realise what just happened to them after they fall over, then they begin to cry. This is essentially the placebo effect in reverse: when you expect something to be painful, you begin to feel pain. Likewise, when you expect something to remove pain, the pain is attenuated. It works because pain and suffering are essentially mental states (in comparison to nociception). You can train the brain (through meditation, for example) or trick it (by placebo) to bypass or escape these states completely. See also Health applications and clinical studies of meditation.

While its relatively easy to appreciate how the interpretation of pain in the brain can be modulated by expectation of relief, its harder to explain how physiological effects are mediated by placebo, but they are. For example, a notable study showed that men with an enlarged prostate who were given a placebo reported improvements such as faster urine flow, and many even suffered from side effects (including impotence, diarrhea and constipation) - the so-called "nocebo" effect. The mechanism of these physiologic responses to a placebo are unknown, but the researchers suggest the the expectation of relief could have resulted in smooth muscle relaxation around the bladder, colon, prostate and urethra, which resulted in the effects reported.

So while relief of symptoms are now well established, what isn't clear, is whether anything can really be "cured" by placebo. People might feel better, but they aren't really "getting better" (in the example above, the paitients' prostates were still enlarged, even though some of the adverse effects of the enlargement was nullified by the placebo). There are occasional claims that people have been cured of cancer by placebo, but preciously little data to back it up. Rockpocket 08:18, 4 January 2009 (UTC)

I would note two distinct effects:

1) Placebos sometimes make people report that they are better, when they really aren't, as measured in any objective way. For example, somebody reports their flu is improved, but an analysis of their spittle finds the same count as before.

2) Placebos sometimes actually make people better, as measured in some objective way. There could be several mechanisms to explain this. Here are two:

a) It causes different behavior which helps reduce the disease. For example, if you have a rash, scratching it can make it worse. If the placebo convinces you that it doesn't itch any more, you stop scratching and the rash heals faster.

b) It reduces stress, which is known to trigger or worsen symptoms. The exact mechanism may be related to stress hormones in the blood, like adrenalin, which cause physical problems when they remain for extended periods.

I would expect that auto-immune diseases would benefit more from placebos, as they are more likely to be triggered by stress and behavior. StuRat (talk) 14:23, 4 January 2009 (UTC)

Also, a study shows that half of all American doctors have no ethical issues with prescribing placebos. ~AH1^(TCU) 14:49, 4 January 2009 (UTC)

Another reality is that many symptoms simply resolve if one is patient. A placebo, like any other medicine, is given a little time to work by the taker. If the symptoms are self-limited, the placebo gets the credit. --Scray (talk) 15:47, 4 January 2009 (UTC)

I haven't done much reading on the subject, it's generally believed that the opioid system is involved in the placebo effect, as an opioid receptor antagonist such as naloxone can block many of the effects of a placebo. Here's a ref: http://www.ncbi.nlm.nih.gov/pubmed/15820838 --Mark PEA (talk) 16:45, 4 January 2009 (UTC)

Animal cooperation and co-learning

it just struck me, can you teach animals to teach others explicitly or not.

Train a rat that when an LED in a box turns on, if you don't do something in 15 seconds it will shock you. Then can you put another rat in the cage and have him watch the other doing that?

Similarly, If you have two cages and two rats, but both levers have to be flipped for it to do anything.

I'm not asking for theories, I just want to know if anyone did this in the past, any reports on it... 68.37.71.40 (talk) 08:04, 4 January 2009 (UTC)

Animals rarely teach one another, but they often learn from each other. There is a subtle, but important difference: Teaching is a form of altruism, it requires the teacher modifies their behaviour to explicitly assist the student. Learning simply means the student watches and copies, at no cost to the teacher. While there are loads of examples of animal learning, there are only rare examples of animals teaching one another: See PMID 16407943 for one such example. Another possible example is Bonnie, a 30-year-old female orangutan at the Smithsonian National Zoo. She made headlines when she worked out how to whistle (the first primate to ever do so [4]) then soon after another orangutan, Indah, a friend of Bonnie's, aquired the skill also. Its not entirely clear, though, whether Indah simply copied Bonnie, or there was genuine teaching involved. But the fact that no other primate has copied human whistling, despite significant efforts to teach them, suggests there could have been some teacher/student interaction between Bonnie and Indah. Interestingly, this was done spontaneously and without human influence. Whether animals can be taught by humans to teach each other is an intriguing question. Rockpocket 09:06, 4 January 2009 (UTC)

What about birds giving flying lesson to their young? That's surely teaching. --86.125.163.133 (talk) 12:15, 4 January 2009 (UTC)

You you have any reliable examples of birds giving flying lessons to their young? Rockpocket 19:57, 4 January 2009 (UTC)

How about a mother predator who will catch prey, bring it back to her offspring, still alive, then let them practice catching it ? StuRat (talk) 14:12, 4 January 2009 (UTC)

That's learning, not teaching. The mother doesn't give feedback to the kids about how to improve, but rather demonstrates how to catch the prey and the children copy her. —Cyclonenim (talk · contribs · email) 14:38, 4 January 2009 (UTC)

I disagree. The mother will show them the proper technique (without the final kill), then encourage the young to do the same. If they don't she will show them again and again, until they get it right. This "showing them" phase has no benefit to herself, but is solely designed as a demonstration for her offspring. StuRat (talk) 14:52, 4 January 2009 (UTC)

Ah, very true. Good point. —Cyclonenim (talk · contribs · email) 17:22, 4 January 2009 (UTC)

Yes. Prey-handling skills have been demonstrated to be taught in meerkats (see PMID 16840701). But as Maelin points out, below, it all depends on how you wish to define teaching. A strict definition would require awareness of the ignorance of students and a deliberate attempt to correct that ignorance by the teacher. That is very difficult to demonstrate in animals. It unlikely the adult meerkats are actually thinking about teaching (our impression that they are, is just anthropomorphising on our part). Rather they are responding innately. The outcome may appear similar, but there are key mechanistic, behavioural differences. Rockpocket 19:53, 4 January 2009 (UTC)

One difficulty in the question is that it's not clear, even in situations where teaching appears to be going on such as predators bringing wounded prey for their offspring, whether the teacher is actively aware that the goal of the exercise is learning. Real teaching is a remarkably complex cognitive process, when you think about it. It requires the teacher to be able to model, in her head, the mind of her student - to create a mental representation of another mind with different knowledge to her own. The teacher then needs to work out how her own actions could increase the knowledge in that modelled mind of her student. This is an incredible bit of cognitive work going on here and it's not at all obvious whether any other species at all are capable of it. A leopard dragging wounded prey back to her young may not, at any stage, be aware that her goal is to educate her cubs. It may (indeed, probably is) simply be a purely instinctive behaviour, with the mother never realising (nor, perhaps, even being capable of understanding) that she is helping her cubs to learn. We humans are truly amazing creatures. Maelin (Talk | Contribs) 15:32, 4 January 2009 (UTC)

Wow, some of the best theroies on those type of experiments appear in the Saw movies but they involve only human behavior. The easiest to understand is probably in the wild, some chimpanzees eat termites by licking a stick and poking it into the termites hole so that little termites will stick to it and they learn that by watching each other. Also some types of monkey eat walnuts and they learn from each other to break them open using a rock (sorry can't rembember the exact monkey but they are strong little guys). All creatures possessing them have the capability to learn stuff but even your lovable Boxer dog will forget he has a neck and choke himself to death on his leash just because he is happy to be alive (ie, yes they are all capable but some would rather die or feel pain forever than participate in a pointless electrocution box) ~ R.T.G 18:02, 4 January 2009 (UTC)

I once had students try putting a naive rat in a Skinner box to see if the naive rat would learn from the highly trained rat that pressing the lever repeatedly brought water as reinforcement. Sadly, the naive rat just took the reward when it arrived and never pressed the lever, then the rats would fight. This is unpublished and thus anecdotal. Humans or apes might be quicker to learn by observation. Edison (talk) 22:42, 4 January 2009 (UTC)

Washoe is said to have taught some of the sign language she knew to another chimpanzee. Whether that was a deliberate attempt on her part, or perceptiveness and copying behavior on the part of the other is unclear. This article discusses orangutans playing charades in order to get specific desired food items. The article points out that "charades relies upon an awareness of what others do and do not understand". Recent research suggests that dolphins may possess a concept of mind. Finally, this article gives a good overview of animals teaching their young, but it is pretty loose on the definition of what constitutes "teaching." 152.16.16.75 (talk) 02:09, 5 January 2009 (UTC)

Where/when was c first used as the symbol for the speed of light?

Can anyone tell me where/when c was first used as the symbol for the speed of light (or for an equivalent like Maxwell's ratio of the electrostatic to electromagnetic unit, which has the dimension of length/time)? I know modern notations of Maxwell's equations contain c, but I don't have access to Maxwell's Treatise to find out whether it was Maxwell, Fizeau or someone else who may have first used the symbol c.Yetanothername (talk) 08:16, 4 January 2009 (UTC)

Although I'm not usually one for short answers, I'll just have to say click here. So much more information than I could even paraphrase with any justice. It's dry, I know, but what better scientific material is there right? Good day to you and I hope that helps. Operator873 (talk) 12:41, 4 January 2009 (UTC)

Great link! --Scray (talk) 15:52, 4 January 2009 (UTC)

The link is superb, and exactly what I was looking for! (I had always doubted the validity of Azimov's remark, but I see there is also more basis for it than I suspected.)Yetanothername (talk) 19:10, 4 January 2009 (UTC)

Time dilation

In the time dilation article it says that:

"In special relativity, the time dilation effect is reciprocal: as observed from the point of view of any two clocks which are in motion with respect to each other, it will be the other party's clock that is time dilated. (This presumes that the relative motion of both parties is uniform; that is, they do not accelerate with respect to one another during the course of the observations.)"

But if it were so, then wouldn't the two effects cancel each other out, and leave us with no time dilation whatsoever under special relativity? Then why do physics textbooks say that we can travel into the future by traveling close to speed of light, when we see that Earth's clocks ticks slowly at us too due to the reciprocal time dilation effect?

Thanks.

76.68.9.253 (talk) 15:31, 4 January 2009 (UTC)

In a word, no. Take two observers which are not accelerating; say, a man on a space walk in the middle of nowhere, and a man in a spaceship. The man on the spacewalk sees the spaceship traveling at 0.4c past him, and (if he could somehow see a clock on the spaceship) he would see the spaceship's clock running more slowly than his wristwatch. However, remember that neither man is accelerating: this the key point of special relativity! Because neither man is accelerating, there is no physical difference between the spaceship moving toward the spacewalk man at 0.4c, or the man moving towards the spaceship. Because of this "relativity" of non-accelerating frames (or lack thereof), the time dilation effect works both ways. If the man in the spaceship were able to see the spacewalk man's wristwatch, he would see that the wristwatch is running slower than his own clock.

In the case where you would use near-light-speed travel to travel into the future, you would only notice this change if you returned to the place where you started at rest (say, Earth). This would require a great force accelerating you away from Earth to a high speed, then an even greater force to accelerate you back. It is these great accelerations which lead to a different time effect, which is covered by general relativity, not special relativity. -RunningOnBrains 16:59, 4 January 2009 (UTC)

Thanks for the detailed response. It cleared up a long-standing confusion I've had with the twin paradox (I guess I should have consulted that article in the first place). Actually I was going with a different vein in my last question, allow me to rephrase it more clearly using the following scenario:

Let's say that about six months after a spaceship left earth, one of the astronauts traveling on the spaceship gives birth to baby A. By now the spaceship's engines are shut off and so the spaceship is coasting at a constant velocity 0.9c relative to earth ("for all eternity" -- as deemed by mission control), so that both earth and spaceship are now inertial frame with relative velocity 0.9c between them. Now, AT THE SAME TIME as baby A's birth on the spaceship, one of the mission directors gave birth to baby B on Earth. So that baby A and B are born at the same time, and are traveling in their respective inertial frames of reference that are 0.9c relative to each other at their birth and until their death. If both babies live to be 75 years old in their proper times, will B appear to die earlier than A to A's frame of reference, or will A appear to die earlier than B to B's frame of reference?

Thanks.

76.68.9.253 (talk) 18:24, 4 January 2009 (UTC)

That 'AT THE SAME TIME' is frame-dependent. Is it at the same time in earth's frame, or in the spaceship's frame? It can't be both. Algebraist 18:26, 4 January 2009 (UTC)

Let's say at the same time in earth's frame. And I also realized that I have phrased the final question incorrectly, allow me to rephrase it as follows:

If both babies live to be 75 years old in their proper times, will B see herself die ahead of A, since B sees A's clock dilated; or will A see herself die ahead of B, since A also sees B's clock dilated?

Thanks.

76.68.9.253 (talk) 20:07, 4 January 2009 (UTC)

after reading the Relativity of simultaneity article suggested by the Algebraist, I've reached a disturbing conclusion: B will see herself die ahead of A in B's frame of reference, and A will see herself die ahead of B in A's frame of reference, and BOTH ARE CORRECT!!! In fact, since A and B are separated in space, there will always exist frames of reference in which A died earlier than B, and frames of reference in which B died earlier than A, both observations are correct. Am I right?

Thanks,

76.68.9.253 (talk) 20:16, 4 January 2009 (UTC)

Yes - the disturbing thing about relativity is the end of the concept of 'simultaneous'. Observers moving at different speeds will come to different conclusions about the order that events happen...and the death of the twins is no exception to that. There are yet weirder things to consider because it's not just time that gets distorted - mass and distance also get changed. The Ladder paradox (and the related man-falling-into-hole paradox) really hurt my brain. SteveBaker (talk) 21:52, 4 January 2009 (UTC)

Thanks for the article, SteveBaker. My brain is already popping. 70.52.150.155 (talk) 20:58, 5 January 2009 (UTC)

Asteroid orbital elements

Hi. I'm looking for orbital elements for the asteroid 99942 Apophis. I need an online source from which I can copy-and-paste in a manner similar to this. I can easily find comet data such as from here, but I cannot find the asteroid data, can someone help search for such a site? Thanks. ~AH1^(TCU) 15:45, 4 January 2009 (UTC)

There is the JPL Small-Body Database browser. (Which I notice has fixed the problem with their precision field, since the last time it was mentioned here.) I think that gives you most of what you're looking for, but I'm no astronomer, so don't take my word for it. APL (talk) 16:30, 4 January 2009 (UTC)

The JPL site linked above gives the orbital elements, but not in a convenient format for cut and paste. Try going to the Minor Planet & Comet Ephemeris Service. Enter 99942 Apophis in the box below "Enter a list of designations..." and then scroll down and select the check box next to MPC 8-line for the format. You can leave the rest of the form set to the defaults. Click on the Get Ephemerides... button. The formatted orbital elements are at the top of the page. Here is a sample of the data that can be entered in the sky mapping website:

(99942) Apophis
Epoch 2008 Nov. 30.0 TT = JDT 2454800.5                 MPC
M 254.96401              (2000.0)            P               Q
n   1.11252452     Peri.  126.40626     +0.87279766     +0.48748942             T = 2454894.91229 JDT
a   0.9224220      Node   204.44527     -0.46434998     +0.81417405             q =     0.7460436
e   0.1912123      Incl.    3.33142     -0.15034405     +0.31539607    Earth MOID = 0.00052 AU
P   0.89           H   19.2           G   0.15           U   1
From 989 observations at 2 oppositions, 2004-2006, mean residual 0".47.

Thanks! ~AH1^(TCU) 23:26, 7 January 2009 (UTC)

Note that I added the name (99942) Apophis on the first line. --mikeu ^talk 16:26, 7 January 2009 (UTC)

Please identify this flower

Please identify the species of this flower, so that I can (or you can) include that in the image description page. --Kprateek88(Talk | Contribs) 16:37, 4 January 2009 (UTC)

It will dramatically assist identification if you specify the time and location that you took this photo. Nimur (talk) 17:49, 4 January 2009 (UTC)

Metadata on the description page says 28 December 2008 in Indore, India — Matt Eason ^{(Talk &#149; Contribs)} 18:10, 4 January 2009 (UTC)

That's right. This was in some sort of a garden, so it's likely that this flower was planted there (as opposed to occurring naturally). --Kprateek88 (talk) 11:14, 5 January 2009 (UTC)

It looks like some kind of Coreopsis. There are several different species and cultivars that are commonly grown in gardens throughout the world.--Eriastrum (talk) 21:14, 4 January 2009 (UTC)

According to Wikicommons, where this photo can be seen, it is a species of cosmos. [5] . Richard Avery (talk) 08:47, 5 January 2009 (UTC)

Special relativity, time dilation, practice?

(In responese to the Time dilation question above) So, equipment available today could use a laser to broadcast pulses and a receiver to time them at enormous speeds. My wireless receiver at home goes at 384,000,000 binary digits per second (its pretty advanced but its a non-expensive Motorola bluetooth type thing). Is it not possible to set up a supersonic craft with a transmitter/reciever and one on the ground which stay in line with each other and measure timing variations relative to speed? Surely if the speed of light would cause 8 x reduction in time-speed (is it 8 in Einsteins theories?) the fluctuations at double the speed of sound (which planes are capable of) could be measured by todays extremely capable hardware? Any notable time-speed theory experiments? ~ R.T.G 17:42, 4 January 2009 (UTC)

We can doa lot better than that. Please see the GPS article. the GPS system works by placing extremely accurate clocks in extremely well-known orbits. Orbital speed is a lot faster than aircraft speed. The GPS system must account for both the slowing predicted by special relativity and for the speed-up caused by general relativity. The fact that the system's accuracy requires these corrections is a proof that the effects exist. -Arch dude (talk) 18:14, 4 January 2009 (UTC)

It does say that at GPS#Relativity thanks Arch dude ~ R.T.G 19:00, 4 January 2009 (UTC)

The specific experiment you describe has also been done several times - flying an atomic clock around the world on airliners is sufficient to produce measurable time differences with one sitting on the ground. According to [6]:

"Two scientists, Hafele and Keating, did the most direct test of relativity possible, in 1971 they flew one set of atomic clocks around the world on a commercial jet liner and then compared them to a reference set left behind on the ground. The scientists flew the clocks around the world twice, once east to west and then west to east."

"The atomic clocks on the planes flying east lost 184 nanoseconds ... They gained 125 nanoseconds due to the gravitational red shift. The planes flying west gained 96 nanoseconds due to their motion and gained 177 nanoseconds due to gravity. The measured effects were within 10% of the predicted effects which was within the 20% error in the experimental technique. (The effect of gravitational redshift has now been confirmed to better than 1%)"

SteveBaker (talk) 21:43, 4 January 2009 (UTC)

It always seemed to me to be discussed as an unproven theory. Doesn't the fact that the direction of the plane affected the amount of difference show some proof that gravity and friction were not the only forces at work? Maybe not proof of a time-material but at least shows a strength in cosmic (or other) influences in motion. Wow. That will be their warp drive. ~ R.T.G 01:05, 6 January 2009 (UTC)

Oh - no - far from it! It's an exceedingly well proven theory - there have been hundreds (at least) of completely different tests of relativity - and they all come out right on the money. The reason the direction matters in the airplane experiment is because the earth is rotating with one plane and against the other - so their relative velocities are not the same. As the article says - the results were within 10% of the predicted value - within error estimates of 20% - which means "it worked!". There are plenty of scientific theories to be skeptical about - but relativity shouldn't be high on your doubt-list! SteveBaker (talk) 02:11, 6 January 2009 (UTC)

What is the difference between neuronal circuitry and neural circuitry?

Hi: I'm working on the Wiki article about the essay "Is Google Making Us Stupid?" and I have been unable to determine the difference between the adjectives neural and neuronal. The question has also been posed at WikiAnswers by someone other than me. If you could enlighten me about the differences I would appreciate it. Nicholas Carr, in his essay "Is Google Making Us Stupid?", says "Over the past few years I’ve had an uncomfortable sense that someone, or something, has been tinkering with my brain, remapping the neural circuitry, reprogramming the memory." However, in an email, he told me that "Given what we know now about neuroplasticity, it seems certain that internet use is changing our neuronal circuitry." So he even seems to use the terms "neural circuitry" and "neuronal circuitry" interchangeably. The same goes for "neural network" and "neuronal network", as well as "neural level" and "neuronal level"—terms which are used on page 117 of Norman Doidge's book The Brain That Changes Itself without any apparent differences. I can't see any at least. Sincerely, Manhattan Samurai (talk) 19:18, 4 January 2009 (UTC)

"Neural" means "of, relating to, or affecting a nerve or the nervous system" (Merriam Webster), whereas "neuronal" means "of, or relating to a neuron" (Wictionary - MW just redirects to "neuron"). That is, "neural" involves the large scale nervous system, whereas "neuronal" involves the small scale nerve cells (neurons). However, since the nervous system is made up of neurons, something that relates to or affects the neurons will relate to or affect the nervous system as well, so the to can be taken as synonyms in most cases. I'd use "neural" in most cases (being the older and more widely used word), only using "neuronal" when I wanted to stress the "on the cellular level" connotation. -- 128.104.112.113 (talk) 20:05, 4 January 2009 (UTC)

I agree. In my personal experience as a jobbing neuroscientist, they are often used interchangably. I get the impression neuronal tends to be used more often when referring to specific, defined circuits (because it pertains to specific neurons), whereas neural is more often used when referring to more complex, undefined circuits (because it pertains to the nervous system). That said, there are plenty of examples of the opposite [7]. I'd just choose one, and stick with it. Rockpocket 20:17, 4 January 2009 (UTC)

Thanks. I too came to a feeling that neuronal was low-level and neural was high-level. However, sticking to one or the other is out of the question considering everyone I have come across uses both terms.Manhattan Samurai (talk) 21:25, 4 January 2009 (UTC)

I meant stick with one type of usage in the article (unless in a quote), per WP:MOS. Since there is significant ambiguity, it probably doesn't matter which is used in the article, but consistency would certainly make it easier for the reader. Rockpocket 22:05, 4 January 2009 (UTC)

I actually would like to give brief definitions within emdashes for when I use either "neuronal circuit" or "neural circuit". I really think there is a very specific definition for both terms and they just haven't been sufficiently made explicit yet. I'm coming to my own intuitive definitions. I mean neuronal circuits would probably be very much within the synapses of a neuronal grouping, right? While neural circuits would be higher level functions that are using several different components of different brain areas to produce higher level functions like reading and writing, or interpreting symbols, or something like that.Manhattan Samurai (talk) 13:33, 6 January 2009 (UTC)

It's very puzzling. I mean at a neuronal level you would have neuronal links, which could form neuronal circuits within neuronal networks, right? And at a neural level you would have neural links, which could form neural circuits within neural networks. You would think those would be entirely different things but maybe not. What is a neuronal link? A link between two neurons? What is a neural link? A link between two nerves? Mysterious.Manhattan Samurai (talk) 18:43, 6 January 2009 (UTC)

On page 249 of The Brain That Changes Itself Doidge, in writing about old-think on the brain's inability to rejuvenate itself, "Besides, scientists asked, how could a new neuron enter a complex, existing neuronal network and create a thousand synaptic connections without causing chaos in that network? The human brain was assumed to be a closed system." Does the context suggest whether or not you should use neural or neuronal?Manhattan Samurai (talk) 22:37, 6 January 2009 (UTC)

Yes, intuitively I would say the its context specific and that particular uses makes sense to me. This example is pretty specific, right? A single neuron is being discussed and, with its interaction with other, local neurons, hence together they form a neuronal network. If I was talking in more abstract, generalist terms ("the brain largely remains mystery. Simple molecular inputs are integrated into circuits that talk to each other in an unfeasibly complex neural network, the result being a coherent output"), then neural network would sound better. But I think its a mistake trying to pin down a precise and different definition for each. Its more of a semantic issue, I feel. Rockpocket 08:13, 7 January 2009 (UTC)

Okay, and this follows somewhat from what Looie496 said at WikiProject Neuroscience: "since most neuroscientists believe that memory is stored in the brain by altering connections between neurons, it follows that anything whatsoever that you remember produces a change in neural circuitry." Thanks again, Manhattan Samurai (talk) 09:34, 7 January 2009 (UTC)

Looie496 had said, right before the above paraphrase, that neural is the more common usage of the two terms. But I get it, and I have a method that I can apply. Anything high-level will need the word neural, but anything low-level can use the word neuronal. Should this nuance be written up somewhere? It seems to need to be addressed definitively.Manhattan Samurai (talk) 12:45, 7 January 2009 (UTC)

How often do transposons jump?

Depending on the type, transposons can either jump around in the genome or they can proliferate by copy-and-pasting. I wonder how often this happens. Will a typical active transposon in a cell of my body jump once an hour, or once a month, or is it a rare event happening only a few times in my body in my life, or even rarer than that? I suppose the rate depends on the type of cell? Thanks, AxelBoldt (talk) 22:12, 4 January 2009 (UTC)

That is a really difficult question to answer, because actually observing transposition as it happens is like looking for a needle jumping around a haystack. Moreover different transposons will have very different rates of transposition, so generalizing is probably not helpful.

Nevertheless, some studies in Saccharomyces cerevisiae Ty retrotransposons have been carried out (we only have an article on Ty5, but the one they used was Ty1). The experiments were quite complicated, and contain a few assumptions that may or may not be accurate, but the bottom line was that a Ty1 transposition would occur in 1% of cell divisions observed. Given the number of transposons in the genome (and assuming each could function equally well in their assay), they calculated that the mean rate of transposition per Ty1 element was between 10^-4 and 10^-3 per generation. Therefore, calculating in a few more assumptions, on average Ty1's transpose once every 2000 to 20,000 hours. Thats between once every 2.5 months, and once every 3 years.

The authors predict that this rate estimate is probably erring towards the high side, and it could be more than 10-fold slower but not likely to be faster. Its also worth noting that Ty1 appears to have a higher transposition rate than Ty2 in their assays system (by as much as 25:1), and so could be an unusually active transposon and therefore not typical. Then you have to ask yourself, how applicable is this to human transposons? Rockpocket 00:07, 5 January 2009 (UTC)

Thanks a lot, that was a very thorough answer. If we take the rate "once every couple of years" as a rough estimate, another important piece of information would be the total number of active transposons in the human genome. Would you like to add some of this to the transposon article? I could also do it if you give me the reference for the paper you mentioned. Cheers, AxelBoldt (talk) 02:01, 6 January 2009 (UTC)

Sure, the primary reference is PMID 17815421 (though PMID 1662752 also discusses the data). Rockpocket 06:52, 6 January 2009 (UTC)

Rock, do you have any information on what actually causes a transposition event? It's always seemed to me that the jumpable transposon should be created either once per gene transcription (or once per DNA replication, depending on the type) - or never at all, if there's no promoter sequence for it. Is it just an accidental transcription, is there an active system to repress transposons, what? I may have just spotted an interesting paper at PMID 2851719, but if you have any general information, it's appreciated! Franamax (talk) 07:20, 6 January 2009 (UTC)

And to follow up on a brief look at the paper I just mentioned, "regulation of Ty transposition occurs at a posttranscriptional level" seems to imply an active system for repression - so do you know what that system is? and that paper involves dropping in GAL1 promoters to fire up the Ty elements - so again, what activates them in the wild? Franamax (talk) 07:27, 6 January 2009 (UTC)

I think the mechanism of transposition induction is likely to vary between Class I and Class II transposons. I'm far from an expert on the subject (though I do find them fascinating), but I know there are some examples of inducing agents. Copia has been shown to be responsive to a "variety of environmental stresses" [8] (possibly because it contains heat shock promotor-like sequences.) Both the Tys in cerevisiae and IS₁₀ (in E. coli) are induced by DNA damage via UV light or 4-nitroquinoline-1-oxide treatment. [9] I'm not sure the mechanism for this has been elucidated, but it appears to be under the control of the SOS response in bacteria. [10] So it appears that at least one endogenous mechanism is stress related, which kind of makes sense, I suppose.

There are both epigenetic, and genetic mechanisms are involved in repression of transposition. An example of the former: biotinylation of histones appear to repress transposition in some systems [11] In the case of the P element, the presence of a genes that inhibit transposase is sufficient to inhibit transposition (and, it follows, genes that promote transposase expression will induce transposition). I don't know whether there is a co-ordinated "active repression system" per se, or its simply the case that the transposons are by default quite stable, or that their RNA usually gets degraded by nonsense mediated decay, and there has to be specific (and quite rare) circumstances for them to escape that and fully retrotranspose. Rockpocket 08:25, 6 January 2009 (UTC)

Thanks. Fascinating? Yes, maximally so. I like the idea that HSP's would induce transposons, along the lines of "we've got a problem here, time to shake things up to see if we can find a new solution". I recall a paper about induction of HSP90 in A. thaliana which produced generationally stable phenotype changes - you've provided a clue to a possible mechanism. I recall also that I've seen some evidence that the homeobox genes seem particularly resistant to transposon insertions (which probably is the only thing keeping us from getting angel wings :). A vastly interesting topic - we seem to be getting closer and closer to adding a {{historical}} tag to the Junk DNA article. :) Franamax (talk) 09:02, 6 January 2009 (UTC)

I agree, a HSP-mediated mechanism makes intuitive sense to me. It hints at how transposons could play a role in generating genomic diversity at times of changing selective pressures. Rockpocket 07:55, 7 January 2009 (UTC)

This article describes piRNA and siRNA as active defense mechanisms against transposable elements. AxelBoldt (talk) 23:11, 9 January 2009 (UTC)

Hard-boiled eggs

When peeling a hard-boiled egg, sometimes the membrane is very hard to detach from the flesh, yet other times it comes away readily. What causes this difference, and is there any way to ensure that it peels away easily more often? (I am referring to hens' eggs in particular). DuncanHill (talk) 23:15, 4 January 2009 (UTC)

For hens' eggs, I was shown when I was a child that after boiling, you must quickly dunk the eggs in cold water specifically to make them easier to peel. I don't know if that works for roosters' eggs, so it is good you are only interested in hens' eggs. -- kainaw™ 01:23, 5 January 2009 (UTC)

Yes very good.... I of course intended the eggs of Gallus gallus, rather than those of any other fowl. DuncanHill (talk) 01:43, 5 January 2009 (UTC)

Yeah, that'll do the trick. The idea is that the soft insides of the egg contract in the cold water, while the hard shell doesn't. This makes it easier to peel the shell off. -- Captain Disdain (talk) 01:38, 5 January 2009 (UTC)

It's not the hard shell I'm worried about, but rather the soft and flexible membrane. DuncanHill (talk) 01:44, 5 January 2009 (UTC)

Are not roosters male birds that don't lay eggs?--GreenSpigot (talk) 01:45, 5 January 2009 (UTC)

Indeed, Kainaw was pointing out the redundancy of my specifying hens' eggs. DuncanHill (talk) 01:47, 5 January 2009 (UTC)

Sometimes a little redundancy doesn't hurt. At least you won't get hard-boiled snake's eggs. The dunking treatment is supposed to make the inside of the egg contract, while leaving the membrane adhering to the shell, so it is indeed designed to deal with the membrane. The trick is to dunk and then peel rather rapidly, as if you leave the egg sitting around for a while you loose the advantage of the contraction of its insides and the membranes re-adhere. - Nunh-huh 02:32, 5 January 2009 (UTC)

I just figured that he specified hen's eggs in case someone might have thought to ask for him to specify between chicken eggs and, for example, quail eggs. Dismas|^(talk) 03:07, 5 January 2009 (UTC)

Well, yes, but the quail that lays the eggs is the hen... - Nunh-huh 03:55, 5 January 2009 (UTC)

Dismas is right, I meant chicken eggs, as opposed to those of other fowl. I was using the word hen in its common usage to mean a female Gallus gallus. By the way, we have cocks here, not roosters. DuncanHill (talk) 11:56, 5 January 2009 (UTC)

Ah, nothing like Ref Desk pedantry ("I am soooo clever!") to completely derail something. And if you hadn't specified chicken eggs, you'd probably get some response about how duck eggs might be totally different, and thus there's no way to answer the question without more information. (Can you tell I have grown quite tired of this sort of "wit"?) --98.217.8.46 (talk) 15:47, 5 January 2009 (UTC)

Your complaint would have some weight if the comment you are complaining about didn't supply an answer. However, as can be seen, the main substance of the comment contained an answer that has been verified by others as being correct. -- kainaw™ 02:52, 6 January 2009 (UTC)

Don't hard-boil chicken eggs. Eggs plus cold water, bring to a boil, remove from heat, wait for 17 (seventeen) minutes, remove eggs from hot water and put into cool water. Fresh eggs will always be more difficult to peel than 2 to 3 week old eggs - its the law! hydnjo talk 02:38, 5 January 2009 (UTC)

I'd like to speak in favor of the 70° egg (see [12]). Some prefer 65° or 67° eggs, but for any of these you really need a water-bath with a thermostat. - Nunh-huh 02:46, 5 January 2009 (UTC)

The biggest factor I've found is using the aged eggs like Hydnjo suggestion: 2 to 3 weeks old. Anythingapplied (talk) 19:20, 5 January 2009 (UTC)

The only thing tasiter than a hard boiled Gallus gallus hen egg with a little salt on it is a devilled one of same. I've never had me fill of 'em. Yum!. Edison (talk) 04:12, 6 January 2009 (UTC)

ZMF in special relativity

If the centre of mass of a two body system has non-zero momentum what is the simplest way to calculate the energy available for particle creation (the total energy of the particles in the ZMF less their rest energy) from data of the particles energy in the lab frame.

The only method I can see that I am sure that works is to calculate the particles velocitys from their energys, then using the rule for velocity addition, caluclate their velocities in the lab frame, and then from this calculate their energies in the ZMF. However due to the need to calculate the velocity of the ZMF. And the equations get extremely complex and messy and I am sure there must be a simpler way. Is their a quick way to calculate the energy stored in the system as moving the centre of mass? —Preceding unsigned comment added by 84.92.32.38 (talk) 23:31, 4 January 2009 (UTC)

Unfortunately I don't know an easy way, as their always seem to occur quartic equations. But at least they can be solved in radicals. Icek (talk) 18:09, 5 January 2009 (UTC)

There is a way to do this using four-vectors, in particular, the four-momentum. The four-momentum is special because a Minkowski norm of a four-momentum vector is invariant under translation into different frames of reference. I'll state (without proof) that the total energy available for particle creation is ${\sqrt {-(p_{1}+p_{2})\cdot (p_{1}+p_{2})}}$, where $p_{1}$ is particle 1's four-momentum and $p_{2}$ is particle 1's four-momentum.

Expanding this out using the distributive law (which holds for the Minkowski inner product), this because ${\sqrt {(-p_{1}^{2}-p_{2}^{2}-2p_{1}\cdot p_{2})}}$. Evaluating the Minkowski inner products results in: ${\sqrt {(m_{1}^{2}+m_{2}^{2}+2(E_{1}E_{2}-{\vec {p_{1}}}\cdot {\vec {p_{2}}}))}}$. For reference, $p_{1}^{2}$ was evaluated in particle 1's rest frame, $p_{2}^{2}$ was evaluated in particle 2's rest frame and $p_{1}\cdot p_{2}$ was evaluated in the lab frame. Also, note that ${\vec {p_{1}}}$ and ${\vec {p_{2}}}$ are ordinary three-vectors (ie. normal momenta). If $\theta$ is the angle between the two particles then the total energy available for particle creation is ${\sqrt {(m_{1}^{2}+m_{2}^{2}+2(E_{1}E_{2}-\left\vert {\vec {p_{1}}}\right\vert \left\vert {\vec {p_{2}}}\right\vert \cos \theta ))}}$. Knowing the particles' rest mass and energies in the lab frame, you can calculate the magnitude of their three-momenta in the lab frame and just substitute into the most recent equation.

To prove my previous statement (that the total energy available is just the square root of the sum of four-momenta dotted with itself), let the lab frame be the ZMF so that the 3-momenta are equal in magnitude but opposite in direction. Then you should get ${\sqrt {-(p_{1}+p_{2})\cdot (p_{1}+p_{2})}}={\sqrt {E_{1}^{2}+E_{2}^{2}}}$ (in the ZMF). Someone42 (talk) 11:24, 6 January 2009 (UTC)

I see there is a more elegant way than what I suggested ... just a small correction: The right hand side of the last equation should be ${\sqrt {(E_{1}+E_{2})^{2}}}$