Wikipedia:Reference desk/Archives/Science/2010 October 5

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October 5

E=mc²

Is there a way to derive E=mc² without integral calculus? 74.15.136.172 (talk) 00:02, 5 October 2010 (UTC)

Well, the original derivation required no calculus (just some clever algebra), I'm fairly sure: [1] --Mr.98 (talk) 00:15, 5 October 2010 (UTC)

By dimensional analysis, any high school student with a basic knowledge of algebra and of physics should be able to determine that the units of measurement require the E=mc² equation, perhaps with some proportionality constant multiplied by side of the equation. What are the units of energy? Kilogram meters squared per second squared. What are the units of mass? Kilograms. What are the units of c²? Meters squared per second squared. Then see if any other power would allow the equation to balance. For instance, if I asserted that "E=mc" you could easily prove me wrong, the same as if I asserted that "E² =mc" or that "E⁷=m⁴c³. Outside the Einstein equation, you would be required to assert that "meters = meters cubed " or some such obvious nonsense. Edison (talk) 01:19, 5 October 2010 (UTC)

Dimensional analysis tells one that a mass multiplied by a velocity squared gives a result that has the same base units as an energy unit, but I would hesitate to call that any sort of 'derivation'. (Consider that atomotive fuel efficiency is often cited in liters per 100 km — volume per length, which is dimensionally equivalent to an area. Nevertheless, it wouldn't make intuitive or physical sense to describe one's mileage in units of square meters.) It's possible to determine that E=mc² contains all the terms to the correct order to give energy, but that's a very thin explanation, and it doesn't tell us why no other physical constants or measurements don't play a role. For example, E = Gm²/l, where l is the length of the object, m is its mass, and G is the gravitational constant also gives the correct units, but is a totally meaningless formula. TenOfAllTrades(talk) 02:51, 5 October 2010 (UTC)

While the rest of your comment is spot on, it is both intuitive and physically meaningful to speak of fuel consumption in terms of area (or fuel efficiency in terms of inverse area). The area is the cross section of fuel needed to travel a given distance, if that volume of fuel is stretched out over that distance. So if my tractor consumes 1 l / km = 1 mm^2, then it could travel indefinitely were it fed by a prepositioned fuel supply of 1 mm^2 cross sectional area along the route traveled. -- ToE^T 10:32, 5 October 2010 (UTC)

In the article the guy above linked to, how did the equation l' = l(1 - (v/c)cosθ)/sqrt(1 - (v/c)²) come about? 74.15.136.172 (talk) 02:57, 5 October 2010 (UTC)

That first equation is just the Lorentz transformation of the photon energy, where the Lorentz boost is at an angle $\phi$ to the photon momentum. You can see a Lorentz boost in a general direction at the bottom of this section. 129.234.53.175 (talk) 14:57, 5 October 2010 (UTC)

I didn't understand half of the above; but I did enjoy Brian Cox's Why Does E=mc²?[2] Bazza (talk) 14:49, 5 October 2010 (UTC)

There is no real rigorous derivation of E = m c^2. You have to ask yourself from what theory you want to derive this from? Obviously, any rigorous derivation has to start from the postulates of special relativity, but then the derivation is trivial. Rather what passes for a derivaton of E = m c^2, is a heuristic arguments for thehttp://en.wikipedia.org/w/index.php?title=Wikipedia:Reference_desk/Science&action=edit&section=26 correct equation. Einstein's argument makes electromagnetism compatible with mechanics, but then electromagnetism is obviously already a relativistic phenomena. A rigorous agument obviously would not be allowed to invoke the properties of electromagnetic radiation!

Einstein later gave a similar argument (I think in 1936), which is far simpler. Suppose you have two objects of mass M floating in space, a distance L apart at rest w.r.t. each other. No external forces act on the masss. Then one object emits a photon of energy E, which is absorbed by the other mass. The photon as a momentum of E/c, so when one object emits it, it gets a velocity of v = E/(M c). The photon reaches the other object in a time of t = L/c. By that time the object that emitted the photon has moved by a dstance

d = v t = E/(M c) L/c = E L/(M c^2).

So, this suggests that in the original center of mass frame, the center of mass of the two object system will move by a distance d/2. But ths can't be true, because there are no external forces acting on the two objects. The exchange of the photon happened within the two object system, so momentum must be conserved. In the original center of mass frame, the momentum must remain zero and the center of mass cannot have moved at all. But the end result is undeniably that just after the photon has been absorbed, one object has moved by a distance d. So, if the center of mass does not move, then the masses must have changed.

If an amount of mass delta m has been exchanged in this process, then that would contribute to a shift in the center of mass of (delta m L)/(2 M) in the opposite direction. This has to compensate for the shift of d/2, so we find that:

delta m = M d/L = E /c^2

Count Iblis (talk) 15:13, 5 October 2010 (UTC)

I don't know whether this counts for your purposes as a derivation, and it's probably what Count Iblis would consider trivial, but from the definition of the four-momentum $(E/c)^{2}-|{\vec {p}}|^{2}$ (where ${\vec {p}}$ is the three-momentum) is an invariant quantity, which turns out to be equal to the square of the rest mass times the speed of light, all squared: $m_{0}^{2}c^{2}$. It's only a few bits of algebra from there to $E^{2}=m_{0}^{2}c^{4}+|{\vec {p}}|^{2}c^{2}$ and $E=mc^{2}$ drops out when ${\vec {p}}$ is small, or 0 as must be in the particle's rest frame, by definition. Couple of fun things that follow from this are a definition of momentum for a massless particle like a photon as $E/c$, and the fact that taking the negative square root possibility (i.e. $E=-mc^{2}$) seriously is what first led Dirac to think about antimatter, though we now tend to think about it rather differently. --81.153.109.200 (talk) 16:08, 5 October 2010 (UTC)

On another tangent...

This question or ones like it come up from time to time, and eventually something in the back of this very old mind fired. I took QM in 1971 -- it's possible that some of the concepts have changed a bit since then :-) .

If I Recall Correctly (not guaranteed!), the most significant part of Einstein's famous equation is not what you see, it's what you don't see. Starting in high school Physics, everybody learns that potential energy of a moving particle is ½Mv². No problem.

As v approaches c, what happens to the ½? That's the insight that Al brought to the table. Isn't it?

DaHorsesMouth (talk) 01:37, 6 October 2010 (UTC)

I do not think that is correct. E=Mc² is not the kinetic (i think you meant kinetic not potential energy) of a mass at the speed of light but the total energy of the mass regardless of speed. The kinetic energy goes towards infinity as the speed goes towards the speed of light in vacuum. --Gr8xoz (talk) 04:00, 6 October 2010 (UTC)

I concur. I always thought it was neat (and maybe instructive) that you can see the two contributions to the energy appear distinctly in the low-speed limit of the relativistic energy expression:

$E=\gamma (v)m_{0}c^{2}={\frac {m_{0}c^{2}}{\sqrt {1-v^{2}/c^{2}}}}\approx m_{0}c^{2}\left(1+{\frac {v^{2}}{2c^{2}}}+...\right)=m_{0}c^{2}+{\frac {1}{2}}m_{0}v^{2}+...$

It's always reassuring to see familiar limits. 129.234.53.175 (talk) 13:24, 6 October 2010 (UTC)

DNA

Is it possible to obtain a DNA sample from a living person, and another sample later on, of a deceased person, and confirm that the sample is from the same person? Also are you able to tell approximately the time/date of death from a DNA sample? Can DNA show medical conditions such as diabeties or cancer? —Preceding unsigned comment added by Aneelr (talk • contribs) 01:11, 5 October 2010 (UTC)

Yes, no, no (but DNA could show a tendency toward diabetes or cancer). (I pronounce myself subject to correction on the third answer). Edison (talk) 01:22, 5 October 2010 (UTC)

DNA can show if you have a Genetic predisposition toward a disease.Smallman12q (talk) 02:01, 5 October 2010 (UTC)

Certain diseases, like Cystic Fibrosis, are completely determined by DNA. It is pretty trivial to tell whether a person has cystic fibrosis (or more importantly, whether they are capable of passing it on to their offspring) by looking at only a small section of their DNA. Such testing is a common way to determine if a baby has Cystic Fibrosis. Tay-Sachs disease is another such disease. With both of these examples if a person has two recessive copies of a particular gene, they have the disease. If they don't, they don't. There are different tests for each disease, including a genetic test for each. While it is typical to only perform such tests on a living person, I see no reason why it could not be performed on the DNA of a deceased person, provided the DNA had not degraded too much. Buddy431 (talk) 02:13, 5 October 2010 (UTC)

You might be able to tell if a person has a viral infection, or even certain types of cancer, through a DNA test, but (as I understand it) there's a risk of false negatives – i.e., that the person has the condition but you don't see it – when you are just running a standard DNA test from a single biological sample. So, if you had a sample of breast tissue, you might be able to tell if the woman concerned had breast cancer from a DNA test, although there would be simpler ways of doing it, the DNA test usually comes after you've confirmed cancer by more traditional means. If you could reliably tell that a woman had breast cancer through a DNA test on a blood sample, you would become very rich indeed. Each cancer is distinct in this respect: leukemias, for example, should be much easier to detect by DNA testing on blood than cerebral cancers. Physchim62 (talk) 02:54, 5 October 2010 (UTC)

In general, we expect a person's DNA to remain exactly the same throughout their life. DNA mutations happen a cell-at-a-time, so if a mutation does occur, there's no reason to believe that any other cell in the body has that same mutation (unless the mutation causes the cell to reproduce out-of-control). DNA is great for identification because of its constancy. Paul (Stansifer) 19:43, 5 October 2010 (UTC)

Robert G. Edwards

After how many year since he first developed the in vitro fertilisation until he got the Nobel prize?174.20.65.111 (talk) 02:21, 5 October 2010 (UTC)

From our article on Robert G. Edwards, the first in vitro fertilization of a human egg was in 1968 (42 years ago), and the first baby born using the technique was in 1978 (32 years ago). Physchim62 (talk) 02:25, 5 October 2010 (UTC)

WOW he finally got the Nobel prize after like 40 years. The Nobel prizes reward are too late! Some people may not live that long to receive what they deserve.174.20.65.111 (talk) 03:16, 5 October 2010 (UTC)

It's particularly impressive in view of the fact that Nobel's will, which set up the prizes, specified that they should be for work done in the past year. But there are good reasons why it was felt that following this rule was inappropriate. See Nobel Prize#Recognition time lag. --Anonymous, 03:25 UTC, October 5, 2010.

Indeed. In this case, Edwards had a coworker called Patrick Steptoe, who was a gynecologist and developed laproscopy to collect the eggs needed for IVF: Steptoe died in 1988, so never received the Nobel Prize that many believe he deserved. Physchim62 (talk) 03:32, 5 October 2010 (UTC)

Note that the Fields Medal, sometimes referred to as the "Nobel Prize of Mathematics", is only awarded to mathematicians under the age of 40, because "... while it was in recognition of work already done, it was at the same time intended to be an encouragement for further achievement on the part of the recipients ...". As a result, Andrew Wiles did not receive one for his proof of Fermat's Last Theorem, however the IMU did presented him with a plaque which has been referred to as a "quantized Fields Medal". -- 124.157.234.91 (talk) 09:00, 5 October 2010 (UTC)

Good-smelling bad smells

Under our kitchen sink we keep a coffee container of old coffee grounds and the juiced parts of fruits and veggies. When I open it u to add to it, I try to breath out of my nose for fear of getting a whiff of foul smelling compost. To my surprise this evening I opened it and got a not so offensive smell up my nose, and, in fact, it smelt good, like a bad-selling flavor of ice cream. What causes this? Thanks Wikipedians! schyler (talk) 02:45, 5 October 2010 (UTC)

Coffee grounds are a cheap deodorizer. They are known to be used, for example, at perfume counters in stores to "clear the palate", so you can properly smell each perfume and not keep smelling the previous perfumes. It is likely that the coffee smell overwhelms your sense of smell in general, which "clears out" the other smells. this Google search turns up lots of stuff on using coffee in this way. --Jayron32 03:12, 5 October 2010 (UTC)

If your house is warm enough, the fruits and veggies may have begun fermenting. While I wouldn't call that smell especially pleasant, there is a sickly sweetness to it that might be reacting well to the coffee. Hobo Irish-Cream ice cream, perhaps? Matt Deres (talk) 04:30, 5 October 2010 (UTC)

Pruno perhaps? --Jayron32 04:33, 5 October 2010 (UTC)

Gravitational constant

why does the gravitational constant decrease when we go towards the centre of the earth? —Preceding unsigned comment added by 120.56.189.145 (talk) 07:35, 5 October 2010 (UTC)

It doesn't. The Gravitational constant is, as its name suggests, a constant (unchanging) value. The actual gravity experienced may however vary, so perhaps you are thinking of that; see Earth's_gravity#Variation_in_gravity_and_apparent_gravity. --jjron (talk) 07:57, 5 October 2010 (UTC)

Yes. Basically the reason is simply that when you are below ground, some of the Earth is above you, so it is pulling you upwards instead of downwards. --Anonymous, 08:00 UTC, October 5, 2010.

See shell theorem. The outer shell of the earth, above you, does not attract you at all. 157.193.175.207 (talk) 08:00, 5 October 2010 (UTC)

Re 157.193.175.207 - that would seem to be assuming a hollow sphere (point 2) so not apply; the Earth is obviously not hollow, so would more closely approximate point 3, i.e., "...the gravitational force varies linearly with distance from the centre, becoming zero at the centre of mass." --jjron (talk) 08:27, 5 October 2010 (UTC)

No, it doesn't assume a hollow sphere. You can write the total force caused by the (full) earth as the force caused by the (full) sphere beneath you (whose mass varies as r^3 and r^3/r^2=r thus linear) + the force caused by the (hollow) shell above you (which is 0). The variation isn't caused by the upper layers attracting you in the opposite direction, it's because the upper layers don't attract you at all, thus only the mass beneath you influences g. 157.193.175.207 (talk) 09:19, 5 October 2010 (UTC)

Obviously each individual part of the shell does exert a gravitational attraction - gravity isn't switched off. But inside the shell, the attraction due to a specific part of the shell is balanced by an equal and opposite gravitational attraction from another part of the shell. So the net gravitational attraction due to a hollow spherically symmetric shell is zero at any point inside the shell. The rest of the analysis above is fine. Gandalf61 (talk) 11:10, 5 October 2010 (UTC)

The shell theorem assumes a uniform shell, which is not the case for a real Earth with a non-homogeneous, constantly-convecting interior. The correct solution is to actually integrate the density for each unit-volume. The shell theorem will still approximately hold, because azimuthal density variations in the density of earth's interior are small relative to the scales involved. Nimur (talk) 17:59, 5 October 2010 (UTC)

At that level of detail, you'll probably want to include the effects of the Sun and the Moon (etc., etc.) as well. -- 140.142.20.229 (talk) 21:55, 5 October 2010 (UTC)

But then we get into discussions of Mach's principle, which if you take it seriously enough means that we have proof that the cosmological assumption of a homogenous and isotropic universe on large scales holds, and we don't have something like a fractal cosmology. --81.153.109.200 (talk) 05:35, 6 October 2010 (UTC)

Dealing with excessive moisture inside an apartment...

As autumn progresses into winter, we are getting more and more condensation on the interior surfaces of our windows. This led to a serious mold problem in one particular corner last year. I'm a bit at a loss as to how to lower the humidity of our apartment's air without resorting to opening the windows and freezing ourselves. Currently, I'm simply wiping down the windows. That prevents pooling along the sills, but only transfers the moisture to the towels -- it's still in the apartment and when the towel dries the moisture has simply returned to the air. Thus the cycle continues. We don't have an electric clothes dryer, and we have under-floor heating. I suppose I could leave the oven door open... Suggestions? The Masked Booby (talk) 09:24, 5 October 2010 (UTC)

Dehumidifier? You could pour the water down the sink. Dismas|^(talk) 09:44, 5 October 2010 (UTC)

Our article on dehumidifiers does not mention the small, cheap, chemical dehumidifiers you can get. These use a sachet of crystals which absorb water from the air. DuncanHill (talk) 09:46, 5 October 2010 (UTC)

Some form of dehumidifier is definitely the only good option here - in some way, you need to reduce the amount of water vapour in the air. By the sound of the original question, the scale of the problem here may be beyond efficient usage of chemical dehumidifiers, and one of the electrically-powered ones would strike me as a good investment. It may be worth leasing one for a week or two from an equipment hire company, just to see to whether it effectively solves the problem or not - you can then consider buying one. ~ mazca ^talk 10:08, 5 October 2010 (UTC)

Why would leaving the oven door open help? Your problem is that warm, wet air is hitting the window, which is cold from the cold outside, and water is condensing out. Solutions are: warm the inside of the window (double glazing helps, if you can get it, or directing warm drier air to blow over the window as in a car) and reduce the moisture in the air (you can achieve some of that by turning the heating down, but I'm guessing that would get unpleasant). A cheap, passive dehumidifier using cheap, replacable crystals that dissolve as they absorb the water, may be your best bet, although you may need several large ones scattered in the worst spots. I've also had luck using anti-mould spray (in a well-ventilated room), which then reduced later mould growth. 109.155.37.180 (talk) 09:58, 5 October 2010 (UTC)

In winter humidity is already pretty low, if you dehumidify on top of that you will have a very unpleasant living experience. Can you read the Dew point article, and estimate what temperature your window is? Look specifically at the section "Calculating the dew point". I think you will find it's impossible to dehumidify your apartment enough. You can lower the temperature of the apartment, or insulate the windows.

My suggestion: Get those plastic window films that cover the entire window (something like this, or just google for "Plastic Window Insulation"). Use that to insulate the window to some degree. Your second option is to give the moisture a place to drain - drill holes in the sill probably. Ariel. (talk) 10:59, 5 October 2010 (UTC)

Approach it systematically. Identify all the things that put moisture into the air. Breathing, house plants, cooking, gas cookers (two molecules of water form every one of methane burnt), portable gas fires, perfume candles, hot showers/baths, boiling kettles etc. Then look at all the reasons the moisture content remains high (water has a very high vapour pressure and it wants to get out into the blue yonder). People with under-floor heating often find it expensive in properties where the floor is not insulated properly to stop the heat being conducted downwards. So they draft-proof the house till is near air tight and unhealthy. Can't remember the numbers of cu ft per hour it thought human needs but you need, but the air itself needs to have been completely changed over the course of two hours in a normal house. Get a good electric hygrometer. Cheap hair tension hygrometers are nigh on impossible to calibrated properly. Check the Relative Humidity reading for each room. If anywhere is equal to, or more than 45% Relative Humidity and if the RH higher than that outside then you definitely do not have enough ventilation. Moist air rises so you only need a high window to be part open in that room. That should not overly cool the room. Try turning the floor heating down and use a fan heater as a supplement, if the floor heating is inefficient and wasteful. Some windows and wall have small ventilation ports which have been blocked up- reopen them as that's what they are their for. If you in an oldish apartment with people living below, the service pipe runs may be a conduit for all their moisture laden air to enter your apartment, so check that. This may be all that needs to be done to mitigate the problem. Dehumidifiers make a noise when running, and although cheap to run in the US they are much more expensive in Europe and else where . So it is worth doing these checks first.--Aspro (talk) 16:21, 5 October 2010 (UTC)

The question is very puzzling.I consulted with the guy from the hardware store. Where is the moisture coming from? In the baseline case, if the inside temperature is higher than the outside temperature due to a furnace, the relative humidity inside will be lower than the outside r.h., with similar dew points, and there should be "dry air" inside leading to static shock from shuffling on the carpet, and nosebleeds due to dry air. That is the case in my home at present, with no humidifier operating and the furnace operating. If there is a humidifier, or if you have water boiling on the stove all the time, or if you run the shower a lot, or if you operate a clothes dryer without venting it outside, then the relative humidity inside might be so high that water condenses on the windows. Dehumidifiers are rarely needed in the winter. The basic process of space heating lowers the humidity so much that static electricity and dry nose rule, and furniture dries out so the wood cracks and the joints come apart. Is there a humidifier on the furnace and is it set too high relative to the outside temperature? Edison (talk) 04:18, 6 October 2010 (UTC)

OP here. I really appreciate you guys trying to help. It seems some regional differences are at the cause of my unusual problem... I live in NE China. We have under-floor heating supplied at will by the local government. We cannot control the temperature, nor can we control when it's on or off. We just get it. Also, we don't have a clothes dryer and hang-dry all the laundry indoors during the winter. (the coal soot and dust air pollution here will ruin anything hung outside) Combined with 2 people showing each morning, our 115 square meter apartment gets pretty humid. Thank you to everyone who has made suggestions so far. I'm going to keep monitoring this question for any new feedback. The Masked Booby (talk) 07:40, 6 October 2010 (UTC)

That clothes drying and showers could certainly supply enough moisture. If you could exhaust the air from the shower while using it, that would be some progress. Otherwise you may need a heat exchanger to draw in outside air and heat it with air leaving, but it sounds as if you need to filter this air too. This is hard to fit in an apartment. Electric dehumidifiers can work, but make sure they drip their water down a drain. Graeme Bartlett (talk) 09:54, 6 October 2010 (UTC)

Getting some sort of small clothes dryer and venting it outside, as well as venting moist air from the shower outside via a small exhaust fan in the bathroom window, would greatly lower the relative humidity. A mechanical wringer ($100 to $150 US) would be a green way of reducing the moisture evaporated into the air by sending more of the clothes dampness down the drain immediately after washing. There are also little clothes dryers for under $100 (US) which dry small loads on the countertop mechanically by spinning, like a centrifugal extractor. Edison (talk) 19:44, 6 October 2010 (UTC)

The problem with many of the suggestions is that they require a)access to enough money b)access to enough supplies c)access to lots of cheap electricity d)lots of room e)ownership of the apartment, allowing changes to be made f)supervision of constantly-running electrical equipment. I'm guessing you do not have these. Opening as high a window as possible when showering and leaving it open for 10 minutes might help. Improving the windows or adding something to drain or absorb water as it drips down might help, as long as you drain that water out of the apartment fairly regularly. Treating the surface with bleach after you scrub the mould off might help. Passive chemical dehumidifiers, if you can get them, can be left to work when you are at work or asleep, although they probably won't be enough by themselves. Reducing the water in your clothes, either with a mangle or by giving them an extra spin in the washing machine (if you have one) will help. 109.155.37.180 (talk) 00:05, 7 October 2010 (UTC)

There are no problems with running most electric dehummifiers running unsupervised. --Gr8xoz (talk) 08:25, 7 October 2010 (UTC)

Install double- or even triple-glazing to the windows. This means that the inside surface of the windows will be less cold, so there will be less condesation. The glazing does not have to be glass, it could be a thin sheet of plastic such as cling-film. And you could use a squeegee or sponge to collect the condesation instead of towels, so that you get liquid water that you can pour down a drain. 92.15.10.67 (talk) 22:29, 7 October 2010 (UTC)

While in general this is a good suggestion, it may be problematic. In Germany, where very high quality glazing now is the normal case, people found out the hard way that now the walls are colder than the windows, and humidity that used to condense on the window now sometimes condenses on the wall, leading to mold on the walls. The solution is to mobilize another many thousand Euros and also isolate the walls...assuming you have the money, and control over the building, of course. --Stephan Schulz (talk) 14:39, 8 October 2010 (UTC)

HIV infection through childbirth?

I've heard that most infants whose mothers are HIV-positive contract HIV through childbirth, which confuses me. Wouldn't they contract it in utero? During gestation, the mother shares nutrients, etc. with the fetus through the umbilical chord. Isn't it likely that during those 9 months, the child would contract HIV, instead of at childbirth? --- cymru lass ^{(hit me up)}⁄_{(background check)} 14:01, 5 October 2010 (UTC)

The placenta blocks transmission in utero in most cases, but during passage through the birth canal there is a risk of transmission. --14:10, 5 October 2010 (UTC) —Preceding unsigned comment added by 81.153.109.200 (talk)

This was discussed just above. The placenta blocks the HIV virus from passing in most cases. Regards, --—Cyclonenim | Chat  14:18, 5 October 2010 (UTC)

Paleontology

Mostly to get new knowledge (I am a retired teacher of math- phys,M.Sc) I am at present reading T. S. Kemp: The Origin and Evolution of Mammals. After that I would like to learn about anapsid and diapsid animals in the Permian —Preceding unsigned comment added by 87.54.145.241 (talk) 14:13, 5 October 2010 (UTC)

Okay, so what would you like us to do? Find books on anapsid and diapsid animals in the Permian for you? Regards, --—Cyclonenim | Chat  14:19, 5 October 2010 (UTC)

Chatter deleted here. Cuddlyable3 (talk) 14:31, 8 October 2010 (UTC)

We have articles on both anapsids and diapsids that should give you a starting point. Mikenorton (talk) 14:26, 5 October 2010 (UTC)

I think there is a good chance the OP meant to ask about synapsids (the group that includes mammals) rather than anapsids (a group that mainly includes turtles). Looie496 (talk) 14:52, 5 October 2010 (UTC)

In-line duct heater

Why is something like this [3] so expensive? I don't think it is anything except a section of tubing, an element, a thermostat and a cut-out, i.e. the same set of components as an electric kettle but more crudely made? I have an existing heater like this but it isn't working. It was always a bit prone to cut out and then difficult to reset, and now it doesn't want to reset at all. Would a competent electrician be able to repair it? Could a DIY enthusiast realistically make one? I don't want simply to order this at the price, but the winter is coming... (We don't seem to have an article on duct heater). Itsmejudith (talk) 15:28, 5 October 2010 (UTC)

In theory, you could stick an electric kettle in your vents, crank it up to max heat, and use it to heat your place. In practice, you will most likely burn your home down. The big difference is safety - which is important when placing a very hot heating element in a confined space. As for what is wrong with your heater, we don't know. Perhaps the heating element is burned out. Without knowing what is wrong with it, it is impossible to determine if it can be repaired at a cheaper price than purchasing a new one. As for repairing it yourself, I wouldn't suggest that a person should mess with something that has the potential of electrocuting them and/or burning down their house. But, that is just my opinion. -- kainaw™ 16:28, 5 October 2010 (UTC)

Why is it so expensive:

1) It comes with on site warranty.

2) The retailer is selling slow moving inventory from stock and promising fast delivery, good service and with technical backup by phone. All that is included in the price

3) It is made by a firm known for its quality.

4) As above, and if you should buy this brand more cheaply from a suppler without the on-site warranty (and service etc.) and a bit eventually needs replacing, you will be able to just buy a spare without having to but a whole new unit like with some cheaper other manufactures of the same type of heater.

5) The heating elements are much larger than in a kettle and it needs to be built to a higher standard for commercial installations. There is a lot more material also. So its not a fair comparison.

6) In a commercial environment is cheaper than buying a cheaper one which will need replacing every few years.

If you still think its expensive, just imagine how much it would cost if your dentist was selling them! Have had experience of buying and using products from both companies--Aspro (talk) 17:11, 5 October 2010 (UTC)

Perhaps 4) above applies though. Perhaps just one component of the existing one needs replacing (it is the same make as this). Is it worth asking a qualified electrician to have a look at it? Itsmejudith (talk) 17:35, 5 October 2010 (UTC)

This is how I would go about it. Redring is now part of the Applied Energy group. It looks like the duct heater is a re-branded Xpelair design Inline Duct Heater. There is no need for Redring to redesign from scratch if there exists a good design already, so the part numbers and everything should be the same I expect. I would find that out for sure by first making it safe electrically. It will likely have its own fuse on the switch board. Take precautions to prevent anybody re-establishing the current whilst I'm working on it. The take the whole unit out and have a look. It might just need a ruddy good clean. With some cut-outs, dust gets behind the switch and stops it re-setting. Blow it out and its OK again. A high street stockist (Applied Energy website will tell me my closest one) will probably want to sell me a whole new unit if I just take it into them. So I would have a look at the thermal cut out and meter the heating element as well to see if that's OK. Bung the sensor into hot water to see if that works too. Then phone up and see if they stock the individual spares. If they do and I don't feel competent to put it all back together again. That is when I would say to a qualified electrician: I've got all the bits can you reinstall it? A lot depends on how good the electrician is. It is more messing about for him to buy the parts himself and he might end up charging you more that it would cost to buy a new unit because of the hourly labour charge. So you will have to play that by ear. Alternatively, you could start of by saying you have a 'Redring' in-line heating duct so he knows it not a cheap and crappy one. Then say you might get it repaired if it ain't too much. Then ask if his quote will be any less if you got the parts yourself. If you can find electrician that works on ducting all of the time he may already have a small stock of spares. A heating and ventilation installation company, may employ an electrician who is keen to take on a bit of private work. Then there is the cost of your own time to consider verses his etc. Hope this give you some ideas. --Aspro (talk) 19:32, 5 October 2010 (UTC)

BTW, to answer your question (rather than give you good advice like the other posters) the reason this (and other items, like cabinets, countertops, furniture) are so expensive is that they are hand made domestically (for whatever definition of domestic applies to you). The high prices usually continue until someone in China decides it's worth copying the item and flooding the market with cheap, but serviceable versions. This usually works better in trades where it's not a tradesman who installs the item, since they resist lower prices until they have no choice. Ariel. (talk) 19:47, 5 October 2010 (UTC)

Aspro, thanks very much, incredibly helpful. I will take the unit out, dust it down and see if that does the trick. Because the problem has always seemed to be with the cut-out. Dust inside is a likely hypothesis. At least now I know it's worth taking it out and having a look at it before splashing out on a new one. Itsmejudith (talk) 21:37, 5 October 2010 (UTC)

Percentage of common genes

What does that mean? "Fraternal (dizygotic) twins," (...) "roughly 50% of their genes are the same". If a human and an ape share 98% of their genes, how does it come that fraternal twins share only roughly 50%?--Quest09 (talk) 16:17, 5 October 2010 (UTC)

In the twins context, it's talking about them being the same allele. --81.153.109.200 (talk) 16:32, 5 October 2010 (UTC)

(after EC) These are two different ways of describing genes and genetic similarity. Dizygotic twins are no different than any other pair of full siblings -- they each inherit one copy of every autosomal gene from each parent. By chance, they will inherit the same versions (alleles) of roughly 50% of their genes. When making comparisons to other species, we are really talking about genetic homology. The genes "shared" by different species are "orthologs" -- highly similar genes that encode nearly identical proteins. In this "phylogenetic" use of the term, humans and other primates have nearly the same complement of genes, with a few hundred genes that are only found in humans and a few hundred genes that are only found in other primates. Many of the genes that are not "shared" are probably "paralogs", or gene copies that only arose during the evolution of one or the other species. --- Medical geneticist (talk) 16:45, 5 October 2010 (UTC)

Physical meaning of 1 Farad = 1 Second/Ohm

What is the physical meaning of the unit of capacitance, the Farad, being equivalent to 1 second / ohm, in a short sentence? What does a one-farad capacitor do with one ohm in one second (one second of what even?)? 20.137.18.50 (talk) 16:33, 5 October 2010 (UTC)

I am unable to confirm your assertion that 1 F = 1 s/Ω. Can you explain why you think this is so? Jc3s5h (talk) 16:42, 5 October 2010 (UTC)

http://en.wikipedia.org/wiki/Farad#Definition —Preceding unsigned comment added by 20.137.18.50 (talk) 16:45, 5 October 2010 (UTC)

It takes one second after voltage is applied to a circuit consisting of a one farad capacitor in series with a one ohm resistor for the capacitor to charge up to 1-e^-1 ≈ 63% of its final charge. See RC time constant. -- 111.84.119.217 (talk) 16:47, 5 October 2010 (UTC)

(EC) To answer the last question first, one second of time. As 111.84.119.217 says, one way to think about your question is to consider the time constant of an RC circuit, which is given by $RC$. To go into a little more detail, this is the timescale on which the charge stored drops to $1/e$ when discharging, or the charge being built up rises to $1-1/e$ when charging. So 1 F = 1 s/Ω in the sense that a 1F capacitor in an RC circuit would give you a time constant equal in seconds to the resistance of the resistor in Ohms. (Or, thinking about it the other way round, for a fixed resistance in the circuit, you would have to increase the capacitance you put in to get a longer time constant.)

To prove that $RC$ does give something in units of time, consider the basic definitions of the quantities, and what their units are expressed in slightly different terms than we usually consider them:

Charge Q is measured in in Coulombs (C).

Voltage V is measured in Volts (V), but they're really Joules/Coulomb (J/C).

Current I is measured in Amps (A) but they can also be considered Coulombs/second (C/s). [Strictly speaking, the Amp is the base unit and the Coulomb is an Amp-second, but that doesn't get to the key concepts of what's going on in a circuit quite so readily, to my way of thinking.] We'll need both of these for the two definitions we need to get to the question:

Capacitance C is Q/V so it's measured in C/V or, C²/J when you replace Volts with Joules per Coulomb. That is, 1 F = 1 C²/J.

Meanwhile, Resistance R is V/I so it's measured in Js/C² -- that is, 1 Ω = 1 Js/C².

Comparing the last two, it's fairly clear that the units of RC are seconds, and thus that 1 F = 1 s/Ω. (Incidentally, I'm convinced there's some way to consider resistance in terms of action-per-charge-squared, but I've never quite managed to grasp it intuitively. Am I just barking up the wrong tree there, ref-deskers?) --81.153.109.200 (talk) 16:59, 5 October 2010 (UTC)

OK, I agree with parts of that. In particular, I agree that the RC time constant is measured in seconds. Here is how I would reason from that:

resistance ⋅ charge = time (quantities)

ΩF = s (units)

F = s/Ω

F = s[(sC²) / (m²kg)]

F = (s²C²) / (m²kg)

Jc3s5h (talk) 17:22, 5 October 2010 (UTC)

It may also help to consider electrical impedance, which is the conceptual extension of electrical resistance to the time-varying (equivalently, frequency-varying) domain. The capacitor provides a relationship between voltage and current, similar to a resistor; but this "extension" to Ohm's Law requires a unit of frequency. It so happens that the defining equation for the capacitor's impedance could be re-arranged in an "ohm's law-like" form, where (R = V/I), so by extension, Z_cap = V/I = 1/(jωC); so a capacitance should be measured in units of time over resistance. Nimur (talk) 17:56, 5 October 2010 (UTC)

I think we can tackle this without introducing additional concepts. Let's start from the identity C=Q/V:

• C = Q/V = It/V (capacitance is the number of ampere-seconds you have to pass through a capacitor to charge it up to one volt)

Dividing numerator and denominator by amperes, you get:

• C = t / (V/I), i.e. capacitance is the number of seconds it takes to charge a capacitor up to one volt with a constant current of one ampere flowing through it.

In other words (I claim; but this is OR), 1 farad is the capacitance that would charge to 1 volt per ampere (i.e. 1 ohm) in 1 second. --Heron (talk) 18:24, 5 October 2010 (UTC)

Neither V nor I are constant as you're charging/discharging. That's where all the exponential/time constant stuff comes in. --81.153.109.200 (talk) 18:39, 5 October 2010 (UTC)

I is constant because I defined it so. V of course isn't, but my reasoning doesn't require that. --Heron (talk) 18:51, 5 October 2010 (UTC)

Your defining it to be constant does not somehow magically change the results of an experiment to measure it over time as a capacitor is charged. The only way to achieve constant I would be to constantly fine-tune the emf in the circuit as time went on. Either way, the maths gets hairier than your presentation. --81.153.109.200 (talk) 05:22, 6 October 2010 (UTC)

You just use a constant current source. Of course you can't run this for millions of seconds to get millions of volts. The opposite proposed that a constant EMF is applied to the capacitor is just as impossible, as the current influx would have to be infinite to match the charge Q=CV to the voltage. Graeme Bartlett (talk) 09:23, 6 October 2010 (UTC)

Heron and Graeme are right. The exponential time constant does not come into the definition of capacitance, it only arises when a capacitor is connected to a resistor. There are practical ways to construct a source of constant I. One way is to make a feedback circuit that keeps the input side of a 1 ohm resistor always 1 volt higher than the output side of the resistor. No hairy math is needed to do that and the voltage on the capacitor will rise linearly not exponentially. Some people enjoy the Hydraulic analogy concept of capacitance as a pipe blocked by a rubber sheet. If water (current) flows at a constant rate in the pipe (wire), the pressure difference (voltage) across the rubber sheet increases linearly. Admittedly we can't keep that going forever but 1 second is not asking much. Cuddlyable3 (talk) 12:55, 6 October 2010 (UTC)

Permanganate reaction with heat

Does any chemical reaction occur when potassium permanganate is boiled? --Chemicalinterest (talk) 17:07, 5 October 2010 (UTC)

Assuming you mean heated, not boiled (it'd have to be liquid first and I suspect this reaction happens while still in the sold phase), I suspect it decomposes via 2KMnO₄(s) → K₂MnO₄(s) + MnO₂(s)+O₂(g), just as it does on exposure to light. At which point it's no longer permanganate (there's only half a manganate ion to each potassium ion), so ... --81.153.109.200 (talk) 17:12, 5 October 2010 (UTC)

I mean boiled in a solution, sorry for the ambiguation. This is the scenario. There is a solution of sodium permanganate and sodium chloride in water. I want to remove the sodium chloride. I know sodium chloride is much less soluble in water than sodium permanganate. I want to boil the solution to concentrate the sodium permanganate and filter the sodium chloride. I wanted to know whether the permanganate decomposes when boiled for a while. --Chemicalinterest (talk) 17:19, 5 October 2010 (UTC)

irish tornadoes

Resolved

How frequent do tornadoes occur in ireland and what is our peak season is it the same as britain or somewhere else. --213.94.235.26 (talk) 19:03, 5 October 2010 (UTC)

I do not have a specific answer for you yet, but your question reminds me of a related one about tornadoes in Ireland that was asked here recently. And if I may, I thought it might address some of your interest here for me to quote from Lomn's excellent response to that question: "...however, our list of European tornadoes and tornado outbreaks notes that Ireland was home to the first recorded European tornado." WikiDao ☯ (talk) 19:45, 5 October 2010 (UTC)

Its okay I just found an article from torro after i googled it said tha 9 approsminately tornadoes touch down higher numbers are recorded in summer months but for some reason the most severe ones happen in winter and summer. --213.94.235.26 (talk) 20:57, 5 October 2010 (UTC)

Interesting. Well thanks for the question and answer both, then! Cheers, WikiDao ☯ (talk) 21:31, 5 October 2010 (UTC)

Video clips stuff for science articles

This may belong to the help desk, but I thought the science ref desk is more constructive and responsive.
I am considering producing a number of video clips (after adequate research, as I am a bear of little brain) which can be added to relevant scientific articles. Attached are some examples I have been working on. As per the guidelines, the format is .ogv in all clips. Sorry about the voice over. I did not realise that I sound like a dim-witted upper class twit straight out of Monty Python.
Please provide feed back as to the (un)suitability of the clips. I am aware that details will have to be corrected and optimized. Thank you for any help.
--Cookatoo.ergo.ZooM (talk) 19:06, 5 October 2010 (UTC) Warning: Not to be used via dialup connections. --Cookatoo.ergo.ZooM (talk) 22:17, 5 October 2010 (UTC)

Sample video clips for evaluation

Amino acids, 32 MB

DNA packing, 13 MB

Nuclear decay and nuclear fission, 13 MB

Mitosis, 12 MB

The solar system, 5 MB

Neat videos, CeZoom. :) I'm sure there are all sorts of wikilaws about this sort of thing, and someone more knowledgeable of those intricacies may come along and go into them in detail here soon. But I thought I'd mention that it might be a good idea to try to do this in a way somewhat more along the lines of the Spoken Wikipedia Project. That is, keep the visuals to strictly pertaining to the text of the article (just the same way one does with static images), and then restrict the voice-over to some version of the content of the article. Regards, WikiDao ☯ (talk) 19:59, 5 October 2010 (UTC)

Did you make these animations? They are very cool! I'm not so certain about the content though, to me it's just naming a few concepts without explaining them. You have two questions here: 1: Does wikipedia want videos explaining subjects, 2: The content of the videos. Regarding 1: as far as I know most videos on wikipedia are to illuminate a certain concept in an article, but do not try to explain the content, just show a concept. However this question is a policy question and you should ask on the Wikipedia:Village pump. Regarding 2: we can evaluate the technical accuracy of the videos heres. Ariel. (talk) 19:59, 5 October 2010 (UTC)

I'm sorry to be critical, but I think you are putting too much emphasis on being impressive and too little on being clear. In a scientific video, there should only be one thing happening at any given moment, and it should be the thing that the audio is talking about, and the connection between sight and sound should be obvious to viewers. For what it's worth, there is at least two neuroscience articles, chemical synapse and action potential, where short videos could be very helpful to readers, and I would love to work with you on creating one if you would be interested in that. —Preceding unsigned comment added by Looie496 (talk • contribs) 16:07, October 5, 2010

Oops, thanks for signing for me, Ariel. As I understand it, the bot only autosigns for new editors. Looie496 (talk) 20:23, 5 October 2010 (UTC)

Thank you WikiDao, Ariel, Looie et al.
As a comment, these are not meant to be "finished" products but simply a sort of showcase as a "scratch and sniff" exercise. I fully realise that these clips have to be diligently researched and should either concentrate on a single matter or be published in a "drill down" method where a general overview is followed by increasingly detailed clips.
As all of the above are entirely my own work (with some marginal help from my late countryman, W. A. Mozart), I assume that legal matters should be manageable.
--Cookatoo.ergo.ZooM (talk) 20:45, 5 October 2010 (UTC)

I watched the nuclear decay one. I would dispense with the sparkles, and perhaps add subtitles for those without headphones/hearing. Neat idea, though. This could be an enormous contribution. Some of our animated GIFs of simple machines are wonderful and would presumably be improved in this format. --Sean 21:13, 5 October 2010 (UTC)

Not for me on dialup they won't. (Unless the movies are in fact smaller than the gifs they replace.) Also there is the point that not everybody has or can have the ogv plugin (if browsing on a public computer, for instance). 213.122.11.251 (talk) 22:00, 5 October 2010 (UTC)

I suspected that dialup won´t work. The files are 5 to 30 MB in size. --Cookatoo.ergo.ZooM (talk) 22:05, 5 October 2010 (UTC)

30 MB takes me roughly 2 hours. :) I am an anachronism, though. Still, mobile devices sometimes get horribly slow connections, and they're not doing it on purpose just to be awkward like I am. 213.122.11.251 (talk) 22:09, 5 October 2010 (UTC)

I just watched the "Amino acids" (also labeled "protein folding") and "DNA Packing" videos, subjects that I know pretty well. Neither was informative, both were very flashy and displayed many sophisticated animation widgets. The latter only distracted from the content, which was also inaccurate. The videos display very little sophistication in content or design, but they do demonstrate availability of tools and skill in applying those. I suggest you partner with someone who knows the content. -- Scray (talk) 23:57, 5 October 2010 (UTC)

Those look pretty but from a frankly professional point of view, I have some issues with the nuclear one.

"Nuclear fission is a reaction in which the nucleus of an atom splits into smaller nuclei, or emits other particles."

Yes, but then you go right into beta decay and gamma radiation, which are not the same thing. It makes it look like you are calling gamma radiation a form of nuclear fission. Both are forms of nuclear decay, but you don't say that in the voice over. Nuclear fission comes off as the overarching category, which it is not. This is not helped by the fact that when talking about fission, gamma decay is shown. (And alpha decay is spelled wrong.)

Frankly on the whole nuclear one I'm not sure that very much information is conveyed that would make more sense than just having it written out. The graphics are kind of generic in this respect: just some balls emitting more balls. If I were making one about nuclear fission, I'd have something a tiny bit more in depth that illustrated the following aspects, in the following order:

1. Nuclei are the heavy centers of atoms, and are a mix of protons and neutrons

2. Very heavy nuclei are often unstable

3. U-235 is unstable enough that if it absorbs another neutron, it starts to wobble

4. This wobbling can cause it to split

5. This splitting (nuclear fission) releases energy and more neutrons (recommended sound effect: a Geiger counter blip)

6. If one of these neutrons continues the reaction, it is a chain reaction (blip blip)

7. If two or more neutrons continue the reaction, it is an exponential chain reaction, like in a nuclear reactor or a nuclear bomb

8. Zoom out to show a huge chain reaction (blip blip blip blip blip)

Showing all of the above in a video might actually convey some information that is harder to convey in text or a static illustration. I would honestly not do videos for nuclear decay in general — the video just doesn't add anything, doesn't help you visualize it any more than a static illustration. I would also drop the music, which sounds pretentious to my ear. Putting classical music with anything scientific just makes it sound like it takes itself too seriously.

From a general point of view, the goal of a video explanation is to do something better than what you can do in text or a static diagram. That means something where the inclusion of movement and sound materially improve the final product. In some cases this is obvious: a video of a parrot talking conveys so much more than a photograph or a textual description ever could to someone who has never heard a parrot talk before. In some cases, this is important but less obvious: a video of a machine working intuitively shows us how things go together better than a set of static diagrams. But in a lot of cases this does not help: it just becomes a way to read or display something that is already well-represented in text or static illustration. Your trick is to figure out what's the best use of your time in this respect, what really would improve the article and not just be an illustrated reading of it. For nuclear fission, things that are hard to convey in diagrams include things like the wobbling or the speed of a big chain reaction (exponential growth is a hard thing for most people to grok, I have found). So a video which had those in it would be useful.

I'm not trying to be overly critical here, just trying to give some constructive criticism. --Mr.98 (talk) 12:02, 6 October 2010 (UTC)

The Ref Desk is not the place for reviewing video work in progress, which is like an article content discussion. I suggest that you A) place your videos on a video server and in a format that is as quick and universally accessible as possible. Would YouTube and FLV work for you? Then B) send a note to some editors that have been active on the relevant Wikipedia article (see its history) personally or on the article discussion page saying you would welcome their comment on a particular video. Cuddlyable3 (talk) 12:14, 6 October 2010 (UTC)

It's not a bad place though to get collaborative feedback. This is not just about article content editing, and it's broader than the content of the article (it's about presentation more than it is content). --Mr.98 (talk) 12:16, 6 October 2010 (UTC)

I think that these videos need to be improved to be useful for the reader

• I think it's very important to avoid extraneous elements in the videos. For example, the first video throws a gaggle of spheres at the video; the second has a sphere moving down the middle of the DNA for some odd reason; the third has some kind of waves around the nucleus (unless they're supposed to be orbitals? but the "electrons" are then closer).
• It's going to be very easy to end up with technical quibbles about the content shown. For example, the demonstration of DNA winding around nucleosomes shows a free end moving all over the map. But in DNA there's practically never a free end - it has to wind around them in place. So it'll take some doing to get a video that seems right to everyone.
• I just can't believe how slowly these videos load. Despite being thumbnail-sized and only a minute long, they're exasperating to load on a cable connection that has no trouble with the standard YouTube fare.

In general, I find myself more interested in how you made these videos, and I think that until we get the making of such videos into a common collaborative space, it'll be hard to make them optimal resources. As they say, give a man a fish and he has a meal for a day, but teach him how to fish and he can permanently deplete the natural resource. Wnt (talk) 16:07, 6 October 2010 (UTC)

They are not thumbnail-sized, they are 720x540. However they are somewhat undercompressed. They have 192 kbit audio, when they probably only need 32 kbit. The video compression seems fine though (although it could go a somewhat tighter). To the uploader: Reduce the audio bitrate because for speech and background music you don't need high quality, then do two encodes: and low bitrate video (i.e. compress just to the point of visible blocking), and a higher quality one. Ariel. (talk) 19:51, 6 October 2010 (UTC)

I should have made it clear that these were not meant to be serious scientific / finished video clips, as I am not a scientist. They are meant to be experiments (simplistic and partly incorrect due to my lack of knowledge) which show what can be done.
Clearly, compiling a scientific clip would require cooperating with experts in the relevant field and significant communication to arrive at a useful final product.
I am basically asking if editors in scientific areas have an interest in such a teamwork to make video clips available to WP users. Thanks to everybody who has answered. --Cookatoo.ergo.ZooM (talk) 07:30, 7 October 2010 (UTC)

I think that yes, there's interest in such a teamwork. But in order to function well as a team, editors will need to know more — what the software is, how objects are created and simulated in it, what the difficulty level is. By posting the five videos you give the impression it's a rather off-the-cuff process, yet it looks like it must have been very complicated to set up... how long did it take to make one of these? Editors should know how the video is made so they know what information to specify and what is involved in following through with a request, making a change, etc. Wnt (talk) 13:20, 7 October 2010 (UTC)

The 3D modeling software used is Cheetah 3D (as I am a Mac user of the above mentioned little brain). The generated .mov documents are imported into iMovie, fitted with titles, optional music (via iTunes) and optional voice over (via GarageBand). iMovie allows various export modes, depending on the resolution required. Clearly, the size of the resulting files (and the response via accessing those in WP) differ. The generated m4v documents are then recoded to .theora.ogv documents as per WP file upload requirements.
The time for creating (and rendering) a video clip varies widely. If there are preexisting models (for a neuron, an atomic nucleus, etc; they accumulate naturally during modeling), it may be a matter of some hours. If a model has to be build from scratch (eg a human heart for a simulation) this may be days. Of course, the rendering also depends on the hardware deployed (iMac 27 inch, i7). Architectural renderings (with glass, steel and other reflective surfaces, complex lighting and materials etc. may be 12 hours or more).
The attached video clip, 8.4 MB, on chemical synapse (designed in cooperation with a WP editor with a neuroscience background) has been created today between 15:00 (3 PM) and 24:00 (midnight), which makes 9:00 hours. This is work in progress and still has to be modified / improved according to the specs of the aforementioned editor. --Cookatoo.ergo.ZooM (talk) 22:15, 7 October 2010 (UTC)

Is E=mc^2 an approximation?

Here http://www.fourmilab.ch/etexts/einstein/E_mc2/e_mc2.pdf the formula just prior to E=mc^2 is obtained by "Neglecting magnitudes of fourth and higher orders". Would E=mc^2 be different if you did not ignore fourth powers and above? Say you went up to tenth powers for example? I claim my Nobel Prize. 92.29.115.43 (talk) 19:11, 5 October 2010 (UTC)

No: those terms are relativistic corrections to the kinetic energy, and Einstein's point is that the kinetic energy changes (never mind its precise value). He uses the convenient, low-speed case where the classical formula applies, but the full formula works if you also include the Doppler effect in the energy of the light emitted. --Tardis (talk) 19:28, 5 October 2010 (UTC)

Celebrity endorsement - scientific name of?

What is the name of the psychological or sociological process(es) involved in the celebrity endorsement of a product? Its not peer pressure, since the celeb is not a peer. Thanks 92.29.115.43 (talk) 19:38, 5 October 2010 (UTC)

Social climbing? Bus stop (talk) 19:43, 5 October 2010 (UTC)

It sounds like you are referring to the logical fallacy called Appeal to Celebrity. Interestingly, the Wikipedia article listing Fallacies does not include it. Somewhat related though is Argumentum ad populum and Argument from authority. --Zerozal (talk) 19:48, 5 October 2010 (UTC)

Ad hominem#Inverse ad hominem Hcobb (talk) 19:52, 5 October 2010 (UTC)

Association fallacy? Clarityfiend (talk) 20:56, 5 October 2010 (UTC)

But surely "peer pressure" does apply? Are you saying, OP, that celebrities have no peers? Since obviously they do, then in fact: yes, that pressure is likely to apply here in the same way that it applies in any other situation. WikiDao ☯ (talk) 22:13, 5 October 2010 (UTC)

Its not peer pressure, since the celeb is not a peer of the person being influenced. 92.28.240.84 (talk) 22:51, 5 October 2010 (UTC)

Oh, I see. (There was a question not long ago about why celebs engage in "charity work" – I mistook your question to be about that, which does involve peer pressure).

The "Measuring the use of celebrities in marketing programs" section of the "Celebrity endorsement" article says that ad people use some metric that "enables advertisers and ad-agency personnel to determine if a particular public figure will motivate consumers who see them in an ad to purchase the product advertised." And you are asking why that happens, right? And that's a good question; I'll give that some thought. Sorry for the misunderstanding :) WikiDao ☯ (talk) 23:16, 5 October 2010 (UTC)

Having now given this some thought: I still think it's just peer pressure. ;) WikiDao ☯ (talk) 02:55, 8 October 2010 (UTC)

Argument from authority is probably the most spot-on logical fallacy, though the psychological reasons we find celebrities to be "authorities" in these contexts are surely more complicated than a logical fallacy can explain. I think most people are savvy enough on a rational level to say, "Just because Tiger Woods golfs in an ad for a mutual fund, doesn't mean that the mutual fund is any good, just that it has a large ad budget." But on a psychological level, these kinds of ads do seem to work pretty well — branding does matter a huge amount, and celebrities are a large part of that. It's too bad our own celebrity endorsement article is so anemic, as I am sure there has been good work done on this by psychologists, media studies people, business people, etc. Boorstin's The Image has a lot on the rise of celebrity endorsements as a form of advertising, if I recall. --Mr.98 (talk) 13:20, 6 October 2010 (UTC)

Ethanethiol production

Can ethanethiol be made by reacting hydrogen sulphide with ethanol? Like this:
H₂S + CH₃CH₂OH → H₂O + C₂H₅SH
--The High Fin Sperm Whale 20:45, 5 October 2010 (UTC)

Fixed formula for ethanol, if you don't mind. (A CH₄ cluster would be it's own methane and not attached by any strong bonds.) Hcobb (talk) 21:34, 5 October 2010 (UTC)

Yes, but the reaction is slow. It is more normal to use a basic environment to deprotonate the hydrogen sulfide, which speeds up the reaction:

HS⁻ + CH₃CH₂OH → OH⁻ + C₂H₅SH

Physchim62 (talk) 22:00, 5 October 2010 (UTC)

I suspect that would lead to an equilibrium that favours the ethanol. Or the creation of diethyl ether -- the sulfur would act as a nucleophilic catalyst. (basically the sulfide may be a good nucleophile -- but it's also a good leaving group. there are some similarities to potassium iodide.) Unless in a protic solvent deprotonated sulfide is a stronger nucleophile than hydroxide? :Another possibility is triethylamine + ethanol + hydrogen sulfide, but here you again risk making diethyl ether. There are some reagents that will convert the -OH group to a good leaving group but it's much cheaper to start from ethylene instead! John Riemann Soong (talk) 00:16, 7 October 2010 (UTC)

Although, since ethanethiol has a lower boiling point than ethanol, run the reaction with base carefully at about 65-75C. The ethanethiol will boil off and you can collect it in a distillation flask via Le Chatelier. I am not sure if you want it to actually run it in mostly ethanol or whether you want a strong polar (and protic) solvent like water or even formamide (will DMF work?). I didn't know sulfide could displace hydroxide leaving groups, but maybe if the hydroxide is more strongly coordinated than the sulfide, it isn't such a terrible leaving group kinetically. John Riemann Soong (talk) 00:44, 7 October 2010 (UTC)

Why do parrots mimic human speech?

Why do parrots mimic human speech? The article at Talking birds only provides a list of birds that do this, without explaining the phenomenon. 86.161.31.85 (talk) 21:32, 5 October 2010 (UTC)

Bird vocalization#Learning All bird songs are learned. Hcobb (talk) 21:37, 5 October 2010 (UTC)

Probably because many parrots are domesticated, and those that are learn to "speak" words in the language of the human for communication. ~AH1^(TCU) 23:57, 5 October 2010 (UTC)

Some birds mimic sounds in their environment, and particularly unusual sounds. This may be to attract and impress prospective mates. I recall a TV documentary narrated by Sir David Attenborough in which a forest-dwelling bird did a spectacular impersonation of a chain saw, and another bird mimicked the click of a camera shutter! Mimicking of human speech occurs simply because human speech is an unusual sound in that bird's environment. Dolphin (t) 01:45, 6 October 2010 (UTC)

Northern Mockingbird are attested to mimic car alarms, among other urban sounds. It is mentioned, but uncited in the article, but running a google search on "mockingbird car alarms" will turn up plenty of anecdotes and even a few videos. --Jayron32 01:54, 6 October 2010 (UTC)

Throughout each summer, I witness the "car alarm" birds every morning. I think it is especially prevalent with the mocking birds around my house because I live two blocks away from the "auto mile" - over a mile of car lot after car lot. -- kainaw™ 11:40, 6 October 2010 (UTC)

@Dolphin51: The bird in question, for both the camera sounds and the chain saw (and a car alarm, and an auto-focus camera, and...) is the Superb Lyrebird, from the sixth episode of Attenborough's series, "The Life of Birds". Matt Deres (talk) 14:12, 6 October 2010 (UTC)

Thanks Matt. That's the one. Dolphin (t) 21:37, 7 October 2010 (UTC)

When a bird mimics human speech it gets lots of attention and affection from its master, which may be rewarding to a bird, thereby increasing the frequency of the bird emitting the operant. See Operant conditioning and the older Law of effect. Edison (talk) 04:07, 6 October 2010 (UTC)

Youl'll find more about mimicry in our article on perhaps the best vocal mimic of the bird world - the Lyrebird. Mattopaedia ^{Say G'Day!} 08:22, 6 October 2010 (UTC)

The Wikipedia article Parrot notes that the question why parrots imitate sounds is open. I have assumed they do it to deceive predators that one is of the same species or to deceive prey that one is not a predator. However the article cites only one parrot breed that is observed imitating other birds, and the article Talking bird says an Arielle Macaw speaks coherently enough to disprove the cliché “Parrots just imitate what they hear”. Still speculating, a parrot in the wild may communicate sounds that it has heard elsewhere to other parrots in the same way as a bee communicates its floral findings to other bees by means of a special dance. There are various jokes about embarrassing dialogs reiterated by parrots. Cuddlyable3 (talk) 11:40, 6 October 2010 (UTC)

It's worth noting that parrots can figure out the right context for certain words. I know of parrots who know to say "hello" when someone new enters a room, to say "shut up" when there is a loud noise, and to say "bad bird" when they are doing something that they know is against the rules. —Arctic Gnome (talk • contribs) 05:14, 7 October 2010 (UTC)

5' on sense strand corresponds to C or N terminal on protein?

For 500 points: 5' on sense strand corresponds to C- or N-terminal on protein? --178.98.126.128 (talk) 22:18, 5 October 2010 (UTC)

Have you looked at Sense (molecular biology)#Antisense_DNA?Smallman12q (talk) 23:00, 5 October 2010 (UTC)

Yipes! Even knowing the answer a person couldn't figure it out from that article.

• First, mRNAs are always translated from 5' to 3' — this is the way that ribosomes work in all organisms, and I truly mean all organisms capable of making proteins as directed by a nucleic acid; in many organisms mRNA is first recognized at a special 5' cap.
• Next, translation always, and I mean always, adds amino acids to the C-terminus of a protein chain. (there's also a special fMet structure in bacteria, which should remind you that you don't have a free NH2 to play with even if you were so minded) I should note that this is true even for nonribosomal peptides and polyketide synthase. All these processes, including preparation of amino acids by aminoacyl-tRNA synthetase,[4] involve a common step where the -SH group of coenzyme A (or at least pantetheine) binds to the C-terminal spot of the protein, peptide, or polyketide — you're actually seeing an aspect of how life functioned before the 'invention' of proteins with CoA at the C-terminus ready to act as a leaving group as each new component is added there.

For these reasons, it is always 5' to 3' codes N to C, with proteins synthesized in that direction by addition to the free C terminus. Wnt (talk) 14:06, 7 October 2010 (UTC)

"treated merino wool

what is "treated merino wool" what do they treat it with. ie. smart wool —Preceding unsigned comment added by Kj650 (talk • contribs) 23:35, 5 October 2010 (UTC)

It is more a case of Smartwool treating Merino wool. Obviously, I can't tell you what the secret process is, otherwise you could copy it and become rich beyond your wildest dreams, which may coarse you to become very unhappy and sad. But fulling process does not involve the usual treatment with chlorine... Oh dear! Have I let the cat out the bag and kicked over the pot?--Aspro (talk) 00:43, 6 October 2010 (UTC)

Interestingly, several of the properties claimed for "Smartwool" are possessed by merino wool anyway - non-itch, moisture-wicking, and odour-reducing. Indeed, apart from the non-itch, all wool is like this. DuncanHill (talk) 01:02, 6 October 2010 (UTC)

Merino wool isn't itch free. I'm not saying smart wool is any better in this regard but I know people who do find merino wool is still itchy even if not even close to being as bad as normal wool Nil Einne (talk) 07:04, 6 October 2010 (UTC)

Personally, I don't find any wool itchy. DuncanHill (talk) 13:33, 6 October 2010 (UTC)

do they treat it will perm press chemicals? —Preceding unsigned comment added by Kj650 (talk • contribs) 01:52, 6 October 2010 (UTC)

I doubt anyone here knows how the specific wool you are referring to has been treated, particularly given we don't even know what product or brand you are referring to, where you bought it etc. If you have concerns, I suggest you ask the manufacturer of the product what they used to treat the wool. Nil Einne (talk) 08:58, 6 October 2010 (UTC)

The Wikipedia article Wool notes that Wool treated with lanolin is water resistant, air permeable, and slightly antibacterial, so it resists the buildup of odor. It is also possible to make wool washable by treating the fibers by removing their "scales" or by coating with a polymer, see the cited article. Such wool is used for wool socks[5]. There is a collection of articles about wool here (it includes the Wikipedia article) that gives more information on wool production. Cuddlyable3 (talk) 09:53, 6 October 2010 (UTC)

Wool treated with lanolin? So they put back the lanolin they've already removed from the wool? Wool is washable anyway, you just need to use a low temperature and a gentle soap rather than a biological detergent. DuncanHill (talk) 13:33, 6 October 2010 (UTC)