Wikipedia:Reference desk/Archives/Science/2008 October 26

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October 26

Twins from different fathers

Is it possible to have non-identical twins with different fathers, if the mother was involved in an orgy or something? If so, has this ever been documented? --76.173.201.40 (talk) 01:58, 26 October 2008 (UTC)

Yes, it is possible to give birth to half-sibling dizygotic twins. I cannot think of any specific documented cases, but it is possible because sperm survives for about 3 days (5?) in the woman's body. If two eggs are released, and fertilized by sperm from different fathers, there will be two half-sibling twins.CalamusFortis 04:04, 26 October 2008 (UTC)

This case is rather well documented ;) but still doesn't count. --Dr Dima (talk) 05:06, 26 October 2008 (UTC)

Yes, the phenomenon is known as Superfecundation. From the article: "The first recorded case was made by John Archer, an American physician in 1810 and is discussed in Williams Obstetrics (1980). According to Archer, a white woman who had sex with a black man and a white man within a short time subsequently gave birth to twins—one white, one of mixed-race. Other cases have been reported since." Among humans this is rare, but in reptiles where sperm can be stored for long periods of time, it's not as uncommon. bibliomaniac15 05:41, 26 October 2008 (UTC)

If memory serves, the honey bee reproduces like that routinely. The queen flies around for a bit, receives sperm from a variety of drones and then lays eggs. --Tango (talk) 14:09, 26 October 2008 (UTC)

As an aside, this was the basis of one of the patient's storylines in an episode of Grey's Anatomy. Dismas|^(talk) 15:27, 26 October 2008 (UTC)

After reading the article for the episode, I see that I was a bit off in my remembrance of the episode. It seems the woman had two separate uteruses. Dismas|^(talk) 16:32, 26 October 2008 (UTC)

It is not necessary that there be separate fathers for twins to be one black and one white. See the recent Daily Mail story where one man and one woman had fraternal twins, one quite black and one quite white [1]. Its called Genetics. Edison (talk) 21:56, 26 October 2008 (UTC)

In domestic cats it is not unusual for kittens in a single litter to have a different male begetter. This can sometimes be seen in the different coloration of the kittens. —Preceding unsigned comment added by 98.17.36.129 (talk) 10:42, 27 October 2008 (UTC)

While you're correct, it's worth also bearing in mind cat coat colour can be dependent on other factors then genetics, as shown by CopyCat [2] Nil Einne (talk) 12:37, 30 October 2008 (UTC)

first nutritional supplements

What year were nutritional supplements first available to the general public for purchase in USA? And where? What was the first supplement available? —Preceding unsigned comment added by 12.215.237.58 (talk) 02:06, 26 October 2008 (UTC)

They have always been available. See snake oil for a surprisingly balanced history of that balm, which should give you an idea of the time range involved. From there, it might seem that the next choice would be to determine when the first effective supplement was marketed, but see multivitamin to see how ambiguous the results are for even modern supplements. Matt Deres (talk) 15:48, 26 October 2008 (UTC)

handwoven wool rug cleaning

ow would I clean an antique, multi colored, hand woven(with nap) wool rug myself, at home?75.36.147.148 (talk) 03:01, 26 October 2008 (UTC)

Well, If it's a Persian rug, the best and easy option is to hang it over a horizontal bar and beat the dust out (best done outside). If you choose to use a vacuum cleaner, use the bare floor setting (so the beaters do not turn). If there is a stain, it is probably best left to a professional, but if you feel brave, and you are sure it its a high quality rug (low quality Persian rugs often are ruined by washing because the colors run) you can give it a deep cleaning by laying it out on some sunny concrete, and using Orvis Horse Soap (sodium Laural sulfate) under running water (from a hose), and scrubbing with a push broom. However, this is best done in warm weater, as the rug will take several days to dry. —Preceding unsigned comment added by Hacky (talk • contribs) 18:58, 26 October 2008 (UTC)

I've heard of rugs like this being placed face down on the snow and beaten on the back to remove dirt. Face down makes sense since the heavy dirt needs to come back out rather than be forced against the rug's woven base. OR here, but I washed a small carved wool chinese style mat thinking it was quality and all the pastel colours ran out. Another time washed a filthy large oval version face down on the grass and it came out clean and original. Patch testing first might be a good idea. Julia Rossi (talk) 22:15, 26 October 2008 (UTC)

Shock waves

Is it true that during areal bombing windows and doors of the house should be open in order to "balance" out the pressure after the explosion? That used to be the rule in case of tornadoes, but National Weather Center now advises to keep the windows closed. So what about during bombing from the sky - open or close the windows and doors?

thanks!

Lana —Preceding unsigned comment added by 72.224.207.32 (talk) 04:44, 26 October 2008 (UTC)

Well, opening doors and windows certainly reduces - or perhaps even eliminates the possibility of the windows blowing out - but doing so must therefore increase the amount of 'over-pressure' entering the interior of the building - which could mean more damage inside than there would have been if the windows had withstood the initial pressure-wave for a while before breaking. That's probably why the advice over tornadoes has changed. SteveBaker (talk) 05:38, 26 October 2008 (UTC)

The tornado warning was changed because even an F5 tornado doesn't create enough of a pressure differential to cause damage; even a "closed" house will be able to breathe enough to compensate. My understanding is that the idea it helps at all is flawed, not that the net amount of damage was re-assessed. The current wisdom from the NWS is not to close or open the windows but rather, "Never mind them. The tornado will open them if it wants." IOW, get your ass to safety. If I knew/suspected that my neighborhood was going to be bombed and I already had a safe place for myself and family, I would shut and board all windows and doors; the pressure difference will be nothing compared to the blast itself. Matt Deres (talk) 15:37, 26 October 2008 (UTC)

Don't bother opening the window. The bomb or tornado will open it for you. As for boarding it up, a documentary about a controlled demolition of a building in the downtown of a city showed the contractors putting plywood over the stained glass windows of a church to reduce the chance of the pressure wave breaking them. Boardup is also encouraged when hurricanes are expected, both to protect against wing pressure and flying debris. Sturdy shutters could also be helpful. Edison (talk) 21:50, 26 October 2008 (UTC)

Controlled demolition is designed to avoid producing large shock waves...the blasts are small and contained and the only "danger to the public and neighbors" I ever hear about it from flying debris. So I call : were they really trying to protect the stained glass from a pressure wave and if so did they actually have an engineering basis for doing so, or were they just protecting from an errant brick? DMacks (talk) 13:12, 27 October 2008 (UTC)

Unfortunately I do not keep a acrd file of references for every fact presented in every TV documentary I have ever seen. They said it was to increase protection against the pressure wave, since the clearances were marginal. Better safe than sorry. Edison (talk) 19:30, 27 October 2008 (UTC)

Thanks for the info! I was curious as in Yugoslavia during bombing we used to open doors and windows as I was told that that is done to reduce the pressure. —Preceding unsigned comment added by 72.224.207.32 (talk) 05:17, 27 October 2008 (UTC)

It's perfectly possible that people in Yugoslavia thought it was a good idea - when in fact it was not. People do a lot of dumb things with the idea that they are doing some good based on 'common sense' reasoning - even when the science points the other way. Drive along any road in Texas and look at the number of pickup trucks where people have either removed or lowered the tailgate "to reduce air resistance" in an effort to get better gas mileage. It SEEMS like a perfectly rational idea - right up to the point when you put a truck into a wind tunnel and find that the manufacturers actually did their homework - and the truck's aerodynamics are better with the tailgate up. However, even though the owner's manual tells you this in words that a child could understand - that doesn't stop hundreds of thousands of truck owners going by "gut instinct" alone. SteveBaker (talk) 14:12, 27 October 2008 (UTC)

Here: http://www.fourmilab.ch/bombcalc/instructions.html we find that windows will be broken by between 0.2 and 1.0 psi of overpressure - and that walls of a typical house require between 1 and 5 psi to demolish them. That's not really surprising - a 4'x4' pane of glass contains 2300 square inches of glass - so between about 500 and 2300 pounds of force will be applied to it - that's like between 3 and 15 adults standing on it...and it doesn't surprise me that it would break!

So the question is this: If the overpressure outside the building compared to inside is going to exceed the amount needed to break windows - but not be enough to demolish the house - then will opening the doors help? The problem with answering it is this: As the pressure wave travels towards the building, does the pressure rise sharply or more slowly? This matters because if the pressure builds slowly enough, high pressure air will be able to gradually leak into the house through small gaps and equalise the pressure inside and out - thereby preventing the windows from blowing in because of the overpressure...whether the doors are open or not. (Sure, flying debris might take them out anyway - but this is a thought experiment - and I want to imagine there is no debris.) If the pressure builds really quickly then even if the doors are wide open, the high pressure air will not be able to flow through the doorway and around to the insides of the windows before the overpressure reaches 1 psi and they blow out.

Therefore, there must be some middle range of rate-of-pressure-increase at which (with doors closed) the air cannot get in through the small holes fast enough to keep the pressure difference on the two sides of the glass down below 0.2 psi - yet if the doors were opened, the reduced resistance to passage of the air into the house would allow the air to flow into the house fast enough to keep the pressure difference under 0.2 psi - so the windows will be saved. So to answer the question rigorously - we'd need a plot of the rate of change of pressure in the shockwave from whatever kind of bomb we're considering.

However - I'm pretty sure the rate of pressure increase gets less as you get further from the explosion (the actual overpressure also gets less too - but that's not the question here). I'm pretty sure this is true because of the business of low frequency sounds travelling further through the air than high frequencies - so the sharp, high-frequency leading edge of the pressure curve must get softened. So this suggests that there must be some distance from the bomb where leaving the doors open will indeed save your windows. So the idea has some merit.

The problem is though that by leaving your doors open - you are increasing the sharpness of that pressure wave on the things inside the house...such as the interior walls. The thought experiment I did for the windows applies equally to the interior walls. If the 'sharpness' of the overpressure curve is too steep - the interior walls will be destroyed - but if it's gentle enough, they won't. With the outside doors open - the interior walls will feel more sharp overpressure than if the outside doors are shut and therefore slow down the pressurization of the interior. So there is the problem - if you are at the right range from the explosion - opening the doors will save your windows - but MIGHT cause more extensive interior damage. At other ranges, your windows will blow out even with the exterior doors open - but you are making matters much worse for the interior structures of the house. So unless you somehow know in great detail how big the explosion is going to be - and how far away it is - there is no way to know whether it's worth opening your doors or not. Overall, therefore, you're better off leaving them shut.

SteveBaker (talk) 00:13, 28 October 2008 (UTC)

Diseases by Mortality Rate

NOTE: This is out of sheer interest.

Is there a list somewhere of diseases by mortality rate? Vltava 68 (talk contribs) 08:33, 26 October 2008 (UTC)

List of causes of death by rate. Axl ¤ [Talk] 10:00, 26 October 2008 (UTC)

But something by percentages? 203.188.92.70 (talk) 19:32, 26 October 2008 (UTC)

...Of the people who get the disease every year? 203.188.92.70 (talk) 19:33, 26 October 2008 (UTC)

Making a movie in PyMol

I would like to make a movie in PyMol based on "mset 1 x60" followed by "mdo 1: turn x,3; turn y,5;" but whereas this makes a rotating molecule on-screen, exporting to PNG files yields only a single file. ----Seans Potato Business 11:39, 26 October 2008 (UTC)

Can you export to .gif format? These can be animated, otherwise you will have to go to .mov or .mp4 format, and then convert to animated .gif or ogg format for use in Wikipedia. Graeme Bartlett (talk) 23:40, 26 October 2008 (UTC)

PyMol only gives me the option to export movies as a series of PNG images which then have to be put together with another program. The problem is that I am only getting a single frame when there ought to be many. ----Seans Potato Business 23:51, 26 October 2008 (UTC)

"eMovie is a free tool that makes the creation of molecular movies both easy and intuitive via a breakthrough storyboard interface, similar in nature to what is used in the creation of traditional movies. eMovie is a plug-in for PyMOL ...". Seems relevant. --Sean 13:21, 27 October 2008 (UTC)

Free energy idea needs debunking

Ever since I was a kid I've occasionally come up with free energy and wacky propulsion ideas. Ultimately they've all proved to be fatally flawed in some way, based on my misunderstanding of energy conversion. But I can't figure out what's wrong with this new idea. I'll keep it in its simplest terms.

Okay, imagine a glass tank filled with water, like a fish tank. Through electrolysis we can split the water into hydrogen and oxygen. These gases will float up, in air, right? So if we let the gases separately float up two pipes and collect them in upside-down glass jars, we have potential energy at the top. Then if we recombine that into water, suddenly we've got something that wants to run down again, down another pipe gathering momentum until it hits a turbine at the bottom at speed, driving an electric motor, before falling back into the original tank.

Now this wouldn't generate enough energy to do the electrolysis in the first place. But I don't see why we couldn't extend the height of the system to exploit gravity more, say to 10m. The gases will still float up, and the water will still run down, but now the water will gain additional speed because it's falling further, and it will hit the turbine with much more momentum, thus pushing it round much further for the same amount of water.

Why couldn't this idea be extended until the water reaches terminal velocity, to generate a simply huge amount of energy for the same amount of effort put into electrolysis? There must be something I've got wrong. Can anyone share some insight? • Anakin ^(talk) 14:33, 26 October 2008 (UTC)

Some things wrong which I notice are; when recombined, don't hydrogen and oxygen form water vapour?; why should both gasses rise to the top of the jars (hydrogen is lighter so it will rise above oxygen)? --Seans Potato Business 14:43, 26 October 2008 (UTC)

This is rather simple to debunk on your own if you like experimenting. Get an electric motor and try to split some water. Notice how much energy it takes - as a sanity check, think about the lack of hydrogen as a fuel source. If hydrogen was so eager to split away from oxygen in water, wouldn't it be possible to have hydrogen producers running on tiny batteries in our back yards? Another sanity check - if it was so easy to split water into hydrogen and oxygen and recombine into pure water, wouldn't that be used all over the world to desalinate ocean water? You will find that it takes a lot of energy to split a water molecule. Then, put a water wheel out in the rain and see if a constant rainfall can produce enough electricity to do the job. Of course, it won't. But, you can see how big the gap is between the energy needed and the energy produced. -- kainaw™ 15:07, 26 October 2008 (UTC)

Ah, but 'common sense' arguments by analogy have no place in physics. Putting a 'water wheel out in the rain' is – at its heart – essentially how all modern hydroelectric power plants operate. To make it work, we collect a lot of raindrops from a wide area, and concentrate them into lakes and rivers. It's just a question of scale. Similarly, concerns about the energy cost of electrolysis don't immediately sink the proposal — putting a fuel cell on the uphill end of the device allows us to recapture a substantial portion of the energy used for electrolysis when the hydrogen and oxygen recombine into water. Sure, electrolysis takes a lot of energy for a given amount of gas production, but the reverse process also releases a lot of energy. (There's a reason why hydrogen is used as a rocket fuel.)

What we really have in this proposal is (nominally) a method for moving water from a low altitude to a high one. In hydroelectric plants, the energy to drive this process comes from sunlight (ocean water is evaporated, this water vapor eventually condenses and falls at higher altitudes, we capture some of its gravitational potential energy as it flows back to the oceans). In this perpetual motion device, the source of energy is not immediately obvious, but (since in this house, we obey the laws of thermodynamics) we know that there must be unaccounted energy 'leaking' in somewhere. DanielLC, below, has hit on what I think is the explanation — the conditions at the top and bottom are such that the energy costs of inflating bubbles of gas against atmospheric pressure will offset the apparent energy gained by moving the liquid water to a higher altitude. TenOfAllTrades(talk) 16:16, 26 October 2008 (UTC)

The amount of energy released from burning hydrogen is the same amount used to separate it, assuming the conditions are otherwise the same. Energy is conserved, not destroyed. The problem with your idea is that the conditions aren't the same. The further down the water is, the more pressure it's under and the harder it is to separate into hydrogen and oxygen. The higher up it is, the less pressure it's under and the less energy is released burning it. — DanielLC 15:19, 26 October 2008 (UTC)

I came across a case where a person wanted to bring water up a hill by having the pipe go downwards so the water would get up speed and then rush upwards. Nonsense of course, but even something as silly as that could lead to an idea like the hydraulic ram. So keep up with the wacky ideas and then see if something else occurs to you. Dmcq (talk) 15:46, 26 October 2008 (UTC)

DanielLC, that sounded like the right explanation at first, but it seems to me that balancing the pressures is a bit of a flimsy way for the universe to ensure that we can't violate the laws of thermodynamics. I mean is it really that much harder to do electrolysis of water under an extra 10m of air pressure, compared to the increase in acceleration provided by gravity when the water falls again?

One way to rule out the pressure problem is to see if there's any conceivable way it could work in the absence of air.

Imagine, for example, a sealed room in a lab with all the air sucked out. The water tank would be the same, but this time, instead of upside-down glass jars to collect the gases in, we'll use two open tubes. The bottom end of each tube would be under the water, around the electrodes to collect the gases. The top ends would just be left open. As the gases bubble out from the electrodes, they would float out of the water then sit and float on its surface (near the bottom of the tubes). Without air in the room, they wouldn't float up any further. But if this process was given enough of a kick-start the tubes would gradually fill all the way up. A littler pipe could run between the two tubes near the top and the gases could be recombined into water again in the middle, providing a perfect stream of water to run down an open shoot again, onto the turbine to generate electricity (which would now spin faster, in the absence of air resistance!).

So I'm not sure it's debunked yet. Is there another reason this wouldn't work? • Anakin ^(talk) 18:18, 26 October 2008 (UTC)

If there were no air pressure the water would boil. Even if it didn't, the gas released wouldn't just sit there it would spread out to fill the vacuum. --Tango (talk) 18:30, 26 October 2008 (UTC)

It's very definitely debunked - because the laws of thermodynamics say it's debunked and that's enough.

If you really have to break it down, the fatal theoretical flaw is that the cost of splitting water into oxygen and hydrogen is the cost of breaking the bonds between them PLUS the cost of overcoming the pressure in the water to create the bubbles. When you recombine the gasses at the top end of the equipment, you rejoin those chemical bonds - but you only get back the energy you used to break them - not the energy you used to make the bubbles form. The energy you get back from the flowing water is the same as the additional energy used to create the bubbles in the first place. I used to have a reference for the additional electrical energy it took to do this (as a function of the temperature and pressure of the water) - but sadly, I can't find it right now so you'll have to take my word for it.

The much more obvious practical flaw is that neither electrolysis nor recombining hydrogen and oxygen are remotely close to being 100% efficient - there is friction everywhere in the system and the turbines for recovering power from the flowing water can't ever be close to recovering 100% of the kinetic energy because to do that they'd have to stop the water from flowing - which would block the output of the system.

There comes a point in your life when you've seen enough of these crazy perpetual motion machines. We have a set of thermodynamic laws that step back from the details of the mechanism and do an end-run around all of the detailed explanations. When someone suggests such a system - you may safely start from the principle that it definitely won't work. The details of why are then just an intellectual exercise with little or no practical value.

SteveBaker (talk) 18:39, 26 October 2008 (UTC)

Speaking of perpetual motion machines, can't a solar system or galaxy count as a perpetual motion machine? 67.184.14.87 (talk) 02:07, 27 October 2008 (UTC)

What extracts energy from it? —Tamfang (talk) 03:00, 27 October 2008 (UTC)

Neither a solar system or galaxy is a perpetual motion machine. Both start, last a long time, and end. The universe as a whole is debatable. It did begin. Will it end? Most theories say that it will, so it isn't perpetual. However, it is possible that it will keep going forever. -- kainaw™ 04:15, 27 October 2008 (UTC)

A perpetual motion machine is usually defined as something that moves perpetually while giving off energy. If you don't include that last bit, a pendulum in a vacuum is a perpetual motion machine (give or take the difficulties in producing a perfect vacuum). --Tango (talk) 11:40, 27 October 2008 (UTC)

It would have to be a pendulum in a perfect vacuum with a frictionless bearing - which is impossible because anything that bears the weight of the pendulum is going to produce friction of some kind. Worse still: an-anything-in-a-perfect-vacuum is impossible to start with because as soon as you put something into a vacuum - it'll shed a few molecules and you won't have a perfect vacuum anymore. If you ignore the problems of the imperfect vacuum then a simple spinning disk (in a perfect vacuum and someplace where there is no gravity) might

work - except that in our universe, there is ALWAYS some gravity from somewhere.

Solar systems clearly aren't perpetual. The star runs down and explodes or collapses or something...and a galaxy is just a bunch of solar systems - and all of them give off light that they can't get back - so they definitely aren't perpetual. The universe as a whole...well, that's a bit tricky. Entropy is going to cause the universe to change - but arguably, that's an exponential process that never actually goes to zero. (Although a lot depends on things we don't know about like dark energy/matter). However, we can discount the idea of getting 'free energy' this way because if you are considering the universe to be the 'closed system' in thermodynamic terms - then any machine that's supposedly extracting energy from it is a part of the system that the energy is being extracted from - so the laws of thermodynamics are happy about that. SteveBaker (talk) 14:02, 27 October 2008 (UTC)

Actually, in theory it does work: if your electrolysis device and fuel cell are both 100% efficient, the energy used to split the water is exactly the same as the energy gained from recombining it. You can then extract energy from the water as it flows down to the electrolysis device. It needs to be open to the atmosphere, though, because you're using the gravitational potential energy of the atmosphere to lift the gasses generated to fuel cell. --Carnildo (talk) 22:30, 27 October 2008 (UTC)

No - even in theory there has to be energy lost due to friction and heat and turbulance and things like that. You can make a thought experiment in which all of those annoying things are magically handwaved away - but that's true of even the simplest of perpetual motion ideas. Connect a magical 100% efficient motor to a magical 100% efficient generator and use magical zero friction bearings and magical zero-resistance wires - and you have a perpetual motion machine. Heck - you don't even need to go that far - pick up any object and set it spinning and in an idealized world, you have perpetual motion. But you can't justify this kind of nonsense on the basis of UTTERLY unreasonable frictionless, lossless parts. As I explained before - to extract 100% of the kinetic energy from the water as it goes through the turbine, the turbine has to utterly stop the liquid from moving. The trouble with that is that the dead stationary water now blocks the output of the turbine. So no matter how far 'out there' you want to go with your 100% efficient turbine 'thought experiment' - it can never extract 100% of the kinetic energy. So as the water enters the tank at the bottom of the machine - ready to be re-electrolysed, it has to have a tiny bit of residual motion - which ultimately leeches energy from the system and causes it to stop. The laws of thermodynamics tell us that even in the uttermost airy-fairy theory, you can't get back 100% of your energy unless you are operating it at the absolute zero of temperature - and it also says that you can't ever get to the absolute zero of temperature - so no machine can ever be 100% efficient...even in theory.

SteveBaker (talk) 23:31, 27 October 2008 (UTC)

um, the hydrolysis thing is a red herring; all you need to do is let water vapor condense and fall. in fact we do get power from such a system on a big scale, it's called hydroelectricity. Gzuckier (talk) 05:54, 1 November 2008 (UTC)

transformer

i have tried a lot but dint got a satisfiable answer,so plz tell me wat exactly happens when we apply a heavy ac signal on primary of a single phase transformer ,but keep secondary open.although power at primary is same as in normal cases because input voltage and current will be same.then where does this huge power goes.116.71.185.65 (talk) 16:43, 26 October 2008 (UTC)

Nowhere if it is all ideal. No power is drawn from the input if the output doesn't draw off any power. Dmcq (talk) 17:38, 26 October 2008 (UTC)

Input voltage is the same but, on no load, input current will be only the magnetising current. As this is 90 deg out of phase with the applied voltage, then the input power (VI cos phi) is also (very nearly) zero. --GreenSpigot (talk) 19:22, 26 October 2008 (UTC)

See Transformer. There will also be a little real power dissipated with an open secondary due to eddy currents and due to I² R losses in the primary winding, due to magnetizing current. Even the humming of an unloaded transformer means that a little power is being consumed to cause vibration of the metal. The real point of misunderstanding in the question is the mistaken assumption that "power at primary is same as in normal case." If "normal case" means a normally loaded transformer, then the comparatively low current into the primary of the unloaded transformer means that the input power is much lower than the normal case. Remember that for an ideal (lossless) transformer, "power in = power out" even though the voltage and current levels vary with the number of turns in the primary and secondary, directly for voltage and inversely for current. Edison (talk) 21:46, 26 October 2008 (UTC)

How are all sciences interrelated?

Hello, I am looking for a kind of scheme in which important topics/fields of exact science are related. Most of the articles on scientific subjects (take semiconductor devices for example) relate it to more fundamental topics (quantum physics--> solid state an semiconductor physics) and to applied topics (transistors--> chips etc), but I would like to see all that information on one (perhaps giant) picture. Any ideas?

Thanks —Preceding unsigned comment added by 87.67.44.42 (talk) 18:47, 26 October 2008 (UTC)

• http://imgs.xkcd.com/comics/purity.png SteveBaker (talk) 19:20, 26 October 2008 (UTC)

Except that in the diagram the mathematician appears to be a woman. ;-) Axl ¤ [Talk] 19:29, 26 October 2008 (UTC)

I have seen that cartoon before: it kind of made me start wondering so it's funny to get as an answer :-). I'm looking for something more in detail, though. —Preceding unsigned comment added by 87.67.44.42 (talk) 20:19, 26 October 2008 (UTC)

I suppose, at the end of the day, it all comes down to (quantum?)physics (and- not to upset the mathematicians- some maths)--GreenSpigot (talk) 19:27, 26 October 2008 (UTC)

"Some" maths? :'-( --Tango (talk) 11:41, 27 October 2008 (UTC)

What you are basically looking for is a classification of knowledge. Some people have tried to do that. It's not easy to do and it requires a lot of hand waving. One of my favorite attempts to do this comes from the Encyclopedie: Figurative system of human knowledge. --98.217.8.46 (talk) 23:43, 26 October 2008 (UTC)

I can kinda imagine the sort of diagram you're looking for - and I'm surprised I couldn't find one anywhere (I did spend a while hunting for one). I kinda imagine a diagram with the words "PHYSICS", "CHEMISTRY", "MATH", "BIOLOGY" and so on in big letters in regions of the diagram - with all of the sub-disciplines (things like "ELECTRONICS") placed in relation to the main topics (eg Electronics straddling physics and chemistry - but nowhere near biology) - perhaps with arrows between sub-disciplines showing how they relate to one-another. I think you could make a coherent diagram like that - but it would be hard to do a perfect job because most things touch mathematics - and (as the XKCD cartoon so elegantly points out), chemistry is technically a sub-field of physics and biology a sub-field of chemistry...so it's not really going to be perfect. However, I was unable to find such a thing (although I'm sure I've seen one someplace in the past). SteveBaker (talk) 13:45, 27 October 2008 (UTC)

The article The central science on chemistry's role as the "connector" between the physics-based sciences and biology-based sciences contains the exact diagram, with attribution, that you are looking for. --Jayron32.talk.contribs 17:14, 27 October 2008 (UTC)

Yeah - that's the kind of thing - but that one only has the sciences that relate directly to chemistry - I was thinking of a much denser diagram with hundreds of fields connected with arrows showing how they interrelate. The annoying thing is that I'm almost sure I've seen something like that. SteveBaker (talk) 23:20, 27 October 2008 (UTC)

That's indeed what I was looking for. Thanks for help me searching, and if you happened to stumble across something similar I would be happy to know. --Gnorkel (talk) 23:35, 27 October 2008 (UTC)

Photons released while burning?

Since photons are the carriers of light and when anything (like paper, wood, candle wicks, etc.) burns light is emitted, does this mean that photons are part of the atomic structure of all matter?Terran2034 (talk) 18:50, 26 October 2008 (UTC)

No. Photons are created whenever energy is released as electromagnetic waves (E=Mc² - the energy released is converted into the mass of the photons that are carry the energy away). They aren't tucked away inside the atoms waiting to be released. Aside from anything else, photons have to move at the local speed of light which means that they can't be stationary inside the atom. SteveBaker (talk) 19:11, 26 October 2008 (UTC)

Photons are created or absorbed when an electron in an atom loses or gains energy. In the course of burning, lots of energy is released from the breaking of chemical bonds. This energy, among many other things, causes electrons to move into higher orbitals, where they are in an "excited state". As the electrons "relax" back to their native, or "ground" state, they release photons. Its not that the photons are "part" of the electron; you need to stop thinking of sub-atomic models as having convenient macroscopic analogs. The electron "releases" the photon, but it does not "contain" the photon itself. The electron is releasing "energy", which at this scale is basically exactly the same as releasing mass. Whether you think of light as a "photon" (i.e. a "mass") or as a "wave" (i.e. "energy") depends upon which model best fits your application. Light is light, and it does what it does. Photons are a convenient model for explaining some behaviors of light, but that doesn't mean that photons behave like little billiard balls... --Jayron32.talk.contribs 17:10, 27 October 2008 (UTC)

and one more nitpicking; photons are produced whenever an electrical charge is accelerated. Electromagnectic_radiation#Speed_of_propagationGzuckier (talk) 05:58, 1 November 2008 (UTC)

Harmonic distortion in Wein bridge oscillator

What do people think is the prime source of (ie largest contributor to) harmonic distortion in a Wien bridge oscillator (Not homework Im researching low distortion oscillators ATM)--GreenSpigot (talk) 20:26, 26 October 2008 (UTC)

My guess would be due to non linear gain due to the amplifier element being not ideal. If you use ceramic capacitors you may also get non linear response. Graeme Bartlett (talk) 21:11, 26 October 2008 (UTC)

Bot of those Im sure will have some effect but what about the gain control mechanism: is that going to give an effect?--GreenSpigot (talk) 14:35, 27 October 2008 (UTC)

If you use a light bulb that should be reasonably linear as long as the oscillator is much higher frequency than the response of the filament in the bulb. At audio frequencies you may have some detectable effect. Graeme Bartlett (talk) 20:31, 27 October 2008 (UTC)

What does the 5 in Saturn 5 and Ares 5 mean?

What does the 5 in Saturn 5 and Ares 5 mean? 67.184.14.87 (talk) 23:50, 26 October 2008 (UTC)

As far as I'm aware, it just means it's the 5th version of that technology. See Saturn V#Development. --Tango (talk) 00:32, 27 October 2008 (UTC)

How about Ares? Ares 1 isn't even finished yet. Also, I don't think that there's a Ares 2, 3 or 4. Maybe NASA decided to borrow the Saturn version numbers for the Ares rocket program? 67.184.14.87 (talk) 00:39, 27 October 2008 (UTC)

I'm actually quite surprised that NASA didn't save the 'Ares' designation for future hypothetical Mars missions... --Kurt Shaped Box (talk) 00:49, 27 October 2008 (UTC)

Actually, they are planning on using Ares V as the launch vehicle for manned Mars missions. 67.184.14.87 (talk) 01:30, 27 October 2008 (UTC)

Ares IV was planned, but the project was later scrapped. I assume that the same is true of Ares II and III, though perhaps these got no further than rejected proposals. Deor (talk) 10:51, 27 October 2008 (UTC)

Indeed, it's quite common for some versions to never get past the drawing board or maybe some testing which results in strange orderings. (eg. Apollos 2-6) --Tango (talk) 11:44, 27 October 2008 (UTC)

Like Preparations A-G? Arakunem^Talk 16:56, 27 October 2008 (UTC)

Or WD-1 through WD-39. SteveBaker (talk) 05:17, 28 October 2008 (UTC)