Wikipedia:Reference desk/Archives/Science/2009 October 17

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October 17

Spin quantum number

Why do they have the two possible values for the spin quantum number be -1/2 and 1/2 rather than -1 and 1? --76.211.91.59 (talk) 00:43, 17 October 2009 (UTC)

Spin quantum numbers are a measure of a particle's intrinsic angular momentum, in units of ħ, the reduced Planck constant. In other words, the component of an electron's intrinsic angular momentum, as measured along any direction, can be either +1/2 ħ or -1/2 ħ. That begs the question of why the reduced Planck constant was chosen to be defined as it is, instead of defining a unit of angular momentum that's half as big. Why that happened was really a matter of notational convenience in other places in quantum mechanics where ħ shows up. I'm not sure of the original equation(s) for which ħ were historically used first, but as an example, the energy of a photon with angular frequency ω is given by E=ħω. If instead of ħ, a constant was instead defined which had the value of ħ/2, then the equation for the energy of a photon as expressed using that different constant would have to have an extra factor of 2 in it. Red Act (talk) 03:15, 17 October 2009 (UTC)

Masturbation and a teen

Hi, if a 17 year old boy masturbates, could that affect his physical growth? --FromSouthAmerica (talk) 02:04, 17 October 2009 (UTC)

No. Masturbation is a normal, healthy practice, and even has some health and psychological benefits. See Masturbation#Benefits. Red Act (talk) 02:23, 17 October 2009 (UTC)

Yes but the growth is only temporary. Cuddlyable3 (talk) 10:46, 17 October 2009 (UTC)

What Red Act said goes for 17 year old girls too. Unfortunately many so called "civilized" cultures have indoctrinated us with various moral taboos on this subject (and sex in general) resulting in taking a 100% natural part of life and adding in artificial components of guilt, shame, and even horror to the idea of masturbation. Thus we get wive's tales of "If you do that it will stunt your growth". As we enter the 21st century we are just now (as a society) beginning to finally realize that such negative components are psychologically harmful and that masturbation (in moderate use) has physically and mentally beneficial effects. 66.102.199.179 (talk) 14:00, 17 October 2009 (UTC)

The primary factor behind stunted growth, worldwide, is malnutrition. Masturbation doesn't have anything to do with it. --Mr.98 (talk) 15:20, 17 October 2009 (UTC)

Why do some people so eagerly promote a self abuse (that was an accepted term) that is indisputably debilitating, un(repro)ductive, messy and not the sort of thing a competitive athlete does before the Olympics? Cuddlyable3 (talk) 16:32, 17 October 2009 (UTC)

I don't think I'd promote it, but it's a bit like defecation: don't talk about it in polite society, but don't deny that it exists or that it happens or that it's a perfectly normal part of the human experience. SDY (talk) 16:37, 17 October 2009 (UTC)

I'd promote it, sure. I think people coming to terms with their own sexuality, the reality of orgasm, and things of that nature are perfectly healthy. It is not debilitating in the slightest, it is not much messier than blowing one's nose, and does in fact relieve quite a bit of mental stress and allows many a young man to focus on things other than trying to have actual sex. Compared to teenage intercourse, masturbation is downright healthy and a social good. I promote it, sure, why not? I don't see any evidence that moderate masturbation does any harm, whereas self-denial, self-shame, fear-of-sexuality, marrying-at-too-early-an-age, having-children-at-too-early-an-age, and many of the mental and social activities that have gone along with the discouragement of masturbation have done legions of harm across the ages. If you don't want to do it, then don't, but don't make it out like it is not a perfectly natural human activity. --Mr.98 (talk) 23:23, 17 October 2009 (UTC)

Something to keep in mind next time you're in the Olympics. APL (talk) 23:22, 18 October 2009 (UTC)

I should remind all posters of the Ref Desk prohibition on giving medical advice - some of the above comments are getting dangerously close to it... Tevildo (talk) 20:31, 17 October 2009 (UTC)

Stating factual information isn't media advice. —Preceding unsigned comment added by 82.44.55.2 (talk) 20:43, 17 October 2009 (UTC)

This is common sex education information that anyone who paid attention in health class should know. It's not medical advice in the slightest. --Mr.98 (talk) 23:23, 17 October 2009 (UTC)

I still think there's a difference between "Masturbation doesn't stunt your growth/make you blind/put hair on the palms of your hands" and "Masturbation is good/bad for you" - however, the line has not been crossed, and I withdraw my remark. Tevildo (talk) 00:32, 18 October 2009 (UTC)

There must be nearly 98 strawman arguments in Mr.98's promotion. Masturbation is also socially preferable to running naked through the streets molesting little children but so what? Mr.98 seems to have discovered Sigmund Freud's once-liberating model of Psychosexual development a century late. Mr.98's claim that (his?) masturbating does not delibilitate in the slightest sounds more like a boast of solo virility than a prowess that can stand up to testing. IMHO Tevildo's line has been crossed and I agree with Tevildo's original post. Cuddlyable3 (talk) 13:17, 18 October 2009 (UTC)

Go back to the 16th century. —Preceding unsigned comment added by 129.67.39.44 (talk) 14:32, 18 October 2009 (UTC)

Cuddlyable, you seem to be arguing from old fashioned superstition and/or ignorance. And are definitely assuming bad faith. The Masturbation article has four separate references providing scientific data that frequent ejaculation increases fertility, not decreases it. It also has a reference indicating that masturbation can lower blood pressure. And a couple of conflicting reports that it may (or may not) reduce the likelihood of prostate cancer. And that's just for males. There a couple of other references to health benefits for females.

If you're going to go around pushing old fashioned prejudices (ie:"that was an accepted term"), then you could at least provide a modern reference that back up your claims. This is the reference desk. APL (talk) 23:37, 18 October 2009 (UTC)

You ask for a modern reference. Please click here. Among 5 agreeing English dictionaries you may find American Heritage 4th Edition copyright 2009. I hope that is modern enough for you. You may also digest the fact that I wrote WAS accepted. Having satisfied your demand for a WP:RS for what is factual information, I reject your incivil accusation that to do so is to "push old fashioned prejudices". I won't question your belief that frequent ejaculation will do you good. If masturbating is the way you want to obtain it then don't let the reference desk, which you gratuitously remind us this is, distract you from your important work. Hanlon's Razor gives a charitable view of a person who issues insults believing such is justified by their conviction that they are the vanguard of social liberation and not just a common Wanker. Cuddlyable3 (talk) 08:48, 21 October 2009 (UTC)

17th Century was part of the modern era, so I guess I get your point.

Cuddlyable3: How about some modern references for the two parts of your comment above which I flagged with a FACT tag? To wit: "indisputably debilitating" and "not the sort of thing a competitive athlete does before the Olympics"? I know this is only talk and not the article but these are strong assertions you have made and they need to be supported. I assume good faith but now you need to show your sources. Also I think you meant to type "un(re)productive". Finally to return to your initial question: "Why ... so eagerly ... ?" perhaps, IMHO, the answer lies in the fact that reproduction is one of the major biological drives in all animals, including humans. Opposing such a natural process is, well, unnatural. Something to consider. 66.102.199.179 (talk) 20:13, 23 October 2009 (UTC)

Dear 66.102 on my planet men know these things. Having read your grandiose manifesto As we enter the 21st century we are just now (as a society) beginning to finally realize that such negative components[sic] are psychologically blah blah... above I am content to wait until whoever you think are "we as a society" catches up with the sexual liberations of the 20th century. You correctly spotted my typo "un(re)productive". Understanding that means you understand the irrelevance of masturbation to actual reproduction. I refuse to engage in discussion with you who want to use this Desk to promote masturbation for 17 year old girls. Cuddlyable3 (talk) 11:34, 28 October 2009 (UTC)

(indent shifted left for readability)

Dear Cuddly, I'm not quite sure what planet you are from but this is Planet Wikipedia where simply saying "men know these things" does not meet the required standard. I politely challenge you to find any reliable sources that can confirm your assertions, noting that by your own statement, "...[masturbation] is indisputably debilitating..." (emphasis added), you are asserting this to be current fact. 66.102.199.116 (talk) 03:56, 29 October 2009 (UTC)

Set of 4 questions: Nanotech, astrophysics, and structural engineering related.

This is basically a set of mostly math-based questions but to answer them also requires knowledge of other advanced scientific subjects (see the Subject above).

The core of this question set is based on a hypothetical proposal, to wit:

Build a simplified Niven ring made entirely of carbon nanotubes and set it in an equatorial orbit around the Earth.

Two major types of nanotubes are required:

• Type One are to be engineered for use as a rigid frame for the ring structure, perhaps formed like a belt of interlocked large (2m) triangular or hexagonal cells).
• Type Two are to be engineered for use as a optical screen mesh mounted across the frame in panels.

Dimensionally the "belt" must be wide enough to fully shadow the Thermal equator during peak periods of insolation. That dimension will in turn depend on the belt's diameter which is open for discussion (see below).

So here is my question set...

1. Ideally this belt would be located in the upper atmosphere between 100km and 300km above sea-level. However, at that altitude the belt would be exposed to a large amount of atmospheric turbulence and might not be able to sustain orbit. Nanotubes should be well suited to such stresses but in the event that this is not a practical location what is the next best location (altitude/radius) to accomplish the desired shadow area?

2. Having selected an altitude what is the full set of dimensions for such a belt? Thickness obviously will be negligible unless structural design mandates a frame depth of more than nano dimension.

3. Based on the answer to #2, what is a rough estimate of the total mass of the ring? That is, how much nano carbon material would be needed to build this structure?

4. According to the WP article on optical properties of carbon nanotubes, it states:

"Their unique feature is not the efficiency, which is yet relatively low, but the narrow selectivity in the wavelength of emission and detection of light and the possibility of its fine tuning through the nanotube structure."

So, assuming you couold create the Type Two nanomaterial to filter only certain frequencies, what optical frequencies would need to be filtered to create a shadow effect that reduces the thermal energy of insolation by approximately 2% in the belt's shadow zone, but leaves the visible and botanically important sunlight frequencies unaffected?

66.102.199.179 (talk) 06:02, 17 October 2009 (UTC)

I don't see why you need carbon nanotubes. The Ringworld needs to be really strong because it rotates really fast to create artificial gravity. Your ring could rotate at orbital velocity, so there would be no forces on it at all (beyond the turbulence, etc., that you mention, but that is manageable). The problem with your idea is that the visible and botanically important sunlight frequencies make up the vast majority of the sun's emissions - that is why our eyes and plants have evolved to use those frequencies. You can't block out the thermal energy without blocking those frequencies because the energy is carried by those frequencies. --Tango (talk) 09:18, 17 October 2009 (UTC)

... and don't forget (a) to account for tidal forces due to Moon and (b) you'll need some sort of stabilising mechanism. Gandalf61 (talk) 11:14, 17 October 2009 (UTC)

I'm not sure it would be too unstable - you can consider each molecule separately as being in a stable orbit, the forces within the body will be fairly small (how big they are depends largely on the size of the body) and shouldn't affect the stability. --Tango (talk) 11:34, 17 October 2009 (UTC)

For a discussion of the dynamic instability of Niven rings see Why Niven rings are unstable by Erik Max Francis. Gandalf61 (talk) 14:17, 17 October 2009 (UTC)

Yes, but this isn't a Niven ring - it would be travelling at orbital velocity, which should make a difference. If a regular satellite can orbit stably then lots of them joined together should be able to - is the problem that the orbit needs to be able to become elliptical? If so, I've made some suggestions below to allow that. --Tango (talk) 13:40, 18 October 2009 (UTC)

Tango: As for "why nanotubes?", simply because I believe that (or some other nano structure) would be the material that would be lightest and least resource consuming yet still able to maintain structural integrity (thus my interest in answering Q#3). The inspiration for its use came from Bradley C. Edwards' idea of using a nanotube ribbon for a space elevator cable. 66.102.199.179 (talk) 13:28, 17 October 2009 (UTC)

Since making nanotubes is so difficult, I don't think it would be the best choice. They are necessary for a space elevator because of the tensions involved, there shouldn't be any tension in your design. --Tango (talk) 13:38, 18 October 2009 (UTC)

My understanding is that there are several new technologies in the final stages of development for mass production of CNTs. I expect manufacturing would be the least of the issues. I would also think a ring of that size would experience significant stresses along the circumference from centrifugal forces and from gravitic tensions (but I am not a structural engineer so someone else would need to say). CNTs are preferable for a couple more reasons... besides the reduction in mass (which will assist in lowering the needed forces both for lift-to-orbit and for station keeping) one should also consider that using an abundant material like carbon would minimize the impact on planetary resources. Finally, molecular carbon bonds should be highly resistant to disruption by minor high-velocity debris like space dust and micro asteroids. 66.102.199.179 (talk) 19:48, 23 October 2009 (UTC)

On Q#4: If we are only trying to reduce thermal energy, what about reducing of the infrared and/or the ultraviolet? What about selectively filtering out a motled sampling of the spectrum using a wide variety of freqency atuned nano-devices in low quantities? Recognize that we only need to filter about 2% of the energy, not all of it. The end-intent should be to ensure we don't make the days "always grey" and piss off the local tourist industries. :) 66.102.199.179 (talk) 13:28, 17 October 2009 (UTC)

Both infra-red and ultra-violet do serve a purpose (for example, UV is used in producing vitamin D in humans). I think blocking them entirely would be a bad idea. Just reducing intensity throughout the spectrum by 2% would probably be easiest - it is a fairly small amount compared to natural variations due to latitude and weather. --Tango (talk) 13:38, 18 October 2009 (UTC)

Gandalf61: Agreed, the belt would need a set of basic attitude actuators just as any satelite does for station keeping. This may be a huge belt shaped object but it is still an artificial satelite in the end. The issue of orbital stability does however have great bearing on the answer to Q#1. 66.102.199.179 (talk) 13:28, 17 October 2009 (UTC)

It might be best to have lots of co-orbital satellites rather than a continuous ring - that might improve the stability. Alternatively, having the ring be reasonably flexible could help. I think the instability, if there is any, would be a result of the orbit not being able to become elliptical - a series of individual satellites or a flexible ring would be able to. --Tango (talk) 13:38, 18 October 2009 (UTC)

Certainly separate satellites have better stability than a ring. The problem with a ring is that if it moves off-center by a tiny amount, the gravitational force on the side that is now nearer to the planet is greater than it was - and the gravitation on the side further from the planet is weaker - so the ring tends to move even more off-center. The inverse-square law makes this a worse-than-linear issue, so things get bad quickly. Furthermore, if the ring is even moderately rigid, parts of the ring are now under nasty stresses that are going to be tough to control. There are modes of lateral instability too - the ring can start to wobble, and again, there are feedback effects to consider that make it very tough to control. With computerized thrusters, running somewhat continuously - you could MAYBE avoid these problems - but then you have to consider where the energy and reaction mass is coming from. Solar panels would get you plenty of energy - and some kind of ion drive would minimise (but not eliminate) the amount of reaction mass needed. The killer is that with the sun and (especially) the moon involved, the tidal forces on a rigid ring would be spectacular - fighting the tides would require vast expenditure of energy. SteveBaker (talk) 15:49, 18 October 2009 (UTC)

indeed, a ring has NO orbital stability whatsoever, and thus shows no advantages over just flying a bunch of planes or balloons or some such, since it would need to be actively steered all the time. it's nothing like a satellite which just needs a nudge every now and then. the closest thing would be a couple of satellites at the Trojan points which probably wouldn't supply what you need.Gzuckier (talk) 20:45, 18 October 2009 (UTC)

Would these issues of orbital stablity be significant if the belt was significantly larger than previously was proposed. What if the orbit altitude was about 15,000km which would put it in the heart of the Van Allen belt "safe zone". Obviously that would seriously increase the construction dimensions (the ring diameter would be approx 4-5 Earth radii (R_E) and I am not sure how large the "width" of the belt would need to be at that distance) but the bottom line is would the added size significantly help with stabilizing (minimizing needed corrections to) the orbit? 66.102.199.179 (talk) 19:29, 23 October 2009 (UTC)

Before this scrolls off the reference desk I just wanted to say thank you to everyone. Not sure that I got my "math" part of these questions answered but I do feel I learned a lot. For those of you who didn't figure it out, this was about exploring an idea for a different kind of space sunshade. I would call it a Niven SunBelt. Thanks again. 66.102.199.179 (talk) 19:52, 23 October 2009 (UTC)

Could Alain Robert have escaped the Twin Towers?

The survival prospects of those above the Twin Towers explosion were limited. Would someone with the "French Spiderman" Alain Robert's near superhuman climbing skills have escaped by climbing down the outside of the building, rather than take the lethal alternative of jumping?Trevor Loughlin (talk) 08:32, 17 October 2009 (UTC)

We can only speculate and the ref desk doesn't do speculation. Sorry. --Tango (talk) 09:20, 17 October 2009 (UTC)

Ask him. His website has a contact page. Cuddlyable3 (talk) 10:36, 17 October 2009 (UTC)

If he had been in the building above the burning portion, there would be absolutely no way that he could have climbed down through the fires. If he had been below the burning portion, he could have taken the stairs down like the other survivors. 72.94.164.21 (talk) 10:44, 17 October 2009 (UTC)

I would be hesitant to rule it out as impossible. There may well have been a path around or through the fires, any reply we can give would be guesswork. --Tango (talk) 11:32, 17 October 2009 (UTC)

Philippe Petit might have stood more chance, but...--Shantavira|^{feed me} 12:27, 17 October 2009 (UTC)

On September 11, 2001 this could have happened: 8:46 a.m. plane hits WTC North Tower. Philippe Petit rushes to the roof and throws a line and anchor that he happened to have stored "just in case" to WTC South Tower. By 8:55 a.m. he is balancing on the line between the towers. Just before 9:03 a.m. he arrives on the roof of WTC South Tower and breathes a sigh of relief "Mon dieu, I am - how you say - out of zat frying pan! Cuddlyable3 (talk) 16:25, 17 October 2009 (UTC)

One question would be whether he would have time: the South tower lasted 55 minutes after the impact, the north tower about 100 minutes. Climbers like this seem mainly to go up buildings not down, although Robert has been up and down a few, e.g. the RBS Tower in Sydney, but it's hard to estimate how long it would take to climb down (especially as he normally stops to chat on the way). --82.41.11.134 (talk) 13:58, 17 October 2009 (UTC)

Right, this is what I imagine the question is. How far could he have gone in 55 minutes? The towers are pretty tall—I doubt he could do them from the very top. If one had some idea of what his speed is climbing down, you could calculate around where the cutoff would be for feasibility. --Mr.98 (talk) 15:24, 17 October 2009 (UTC)

I thought about the timing too as well but once finding out the time it took for the buildings to collapse I decided it was impossible to rule it out with that. No one said it had to be the south tower right? According to Alain Robert it took him about 100 minutes to climb the Petronas Twin Towers. This is climbing up not down but I don't see any reason to presume he would definitely take longer to climb down, in fact it's possible it would be faster therefore it seems you can't rule it out Nil Einne (talk) 15:44, 17 October 2009 (UTC)

I would personally suspect down to take longer, but I don't really know. Climbing up a tree is easy. Climbing down is hard—you've got to limit your own momentum, and you are somewhat going against the orientation of your body (you can't use your upper arms as well, and you can't see what your feet are doing as well). But I'm no climber. --Mr.98 (talk) 16:40, 17 October 2009 (UTC)

I don't know much about climbing buildings, but it seems like the facade of the trade towers would be difficult. I don't think there were any horizontal elements to grip. Rckrone (talk) 16:54, 17 October 2009 (UTC)

Take a look at his photo gallery, he doesn't actually need very much to hold on to at all. A rock climbing friend of mine can lift himself up holding on to a beam with just the tips of the fingers of one hand. This is a difficult thing to do but possible with training. SpinningSpark 14:26, 18 October 2009 (UTC)

The so-called skyscraper climbers usually just use a dedicated window washing equipment track. Descending would be far faster than ascending, and if there were a track not swept by flame or enveloped in extreme heat, it would have been a piece of cake to make the descent. Once below the fire, he could have broken a window, entered the building, and run down the stairs. Easy-peasy. Edison (talk) 00:11, 19 October 2009 (UTC)

Cold Fire

Hello I'm looking for info on cold fires i.e. fires that have unusually low temperature they don't burn, just glow. I could not find anything about it in Fire. I've been told that such fires are possible but how? Aurora sword (talk) 12:29, 17 October 2009 (UTC)

will o the wisp or ghost light is a natural kind. Does cold fire have anything? (No) Graeme Bartlett (talk) 12:33, 17 October 2009 (UTC)

Burning methane clathrate is a sort of cold fire. It's like burning ice. It does have a regular flame, though, not just glowing. Red Act (talk) 12:41, 17 October 2009 (UTC)

Interesting, is this the kind of thing commonly used in chemistry demos? Aurora sword (talk) 12:46, 17 October 2009 (UTC)

"Fire" is just a self sustaining reaction between something and oxygen which generally generates heat. It self sustained by the local diffusion of both heat and radicals, but there is no reason why in absolute terms it has to be hotter than room temperature say. The heat generated will tend to heat things up but if the starting material is naturally cool (for example has latent heat associated with a phase transition at a cool temperature) then it is possible for the fire to stay cold. But it needs to be fairly reactive to burn cold. So if you burn something which boils at body temp (Diethyl ether for example) the liquid under the flame will not get to above its boiling point, and you can pour it over your hands and light it without burning yourself (although not recommended, jugglers use it but it needs skill to avoid the flame itself burning you). A solid which sublimes but is reactive enough could surface burn cold but personally I cannot name one. Methane Clathrate seems a plausible candidate. --BozMo talk 12:53, 17 October 2009 (UTC)

In that case, what is actually burning is just methane so it is just like any other methane flame - the source of the methane is cold, but the fire itself is hot. --Tango (talk) 13:02, 17 October 2009 (UTC)

The light from a flame is usually because it is hot, so you're not going to get a bright orange flame like you get with a candle without it being hot. Any light will be from chemical emissions, like the blue flame you get from complete combustion of natural gas (eg. a gas cooker or Bunsen burner). I don't know of any chemical reactions that result in emissions at low temperatures. --Tango (talk) 13:02, 17 October 2009 (UTC)

Well, there's bioluminescence and other chemiluminescence. Red Act (talk) 13:13, 17 October 2009 (UTC)

Have a look at "pyrophoricity". Plutonium is one of the classic examples. Axl ¤ [Talk] 13:25, 17 October 2009 (UTC)

To have a visible flame - you need enough temperature for the blackbody radiation to be in the visible range. When the temperature is below the 'Draper point' (Huh! No article?!?) - which is at about 500 degrees Centigrade - there is no light emitted. So that's pretty much the coldest a visible flame can possibly be. There may be other chemical reactions that produce light as a byproduct that could kinda look like a flame - but those aren't properly 'flames'. There may be cooler oxidation reactions that produce the characteristic plume of a flame - but with no visible light. Methane clathrates look like a lump of ice - if you set light to it, it looks like you're burning an ice-cube - which is surprising and interesting - but the flame is just a normal methane flame - it's plenty hot! SteveBaker (talk) 13:26, 17 October 2009 (UTC)

I thought the OP asked for no visible flame but surface burning? So why are you suddenly all talking about flames? Surface burn cold was the request, my flame bit was intended to be an analogy. --BozMo talk 14:07, 17 October 2009 (UTC)

No no I asked for the reverse. Visible flame, but no burning. Aurora sword (talk) 03:56, 21 October 2009 (UTC)

I think the glow from white phosphorus in damp air pretty much fits the bill of what is being asked for. The reaction is essentially a kind of fire, in that it's ultimately a gas phase oxidation process, but it merely glows instead of burning normally with a flame. And the reaction is cold, because it's a form of chemiluminescence, not a form of incandescence, in which the Draper point of black body radiation would be a consideration. Red Act (talk) 14:16, 17 October 2009 (UTC)

I may be interpreting the OP's question incorrectly, but perhaps they'd be interested in coal seam fires that often simply smoulder for years and years, but don't "flame up" in the usual manner. Smoulder has more information on that kind of topic. Matt Deres (talk) 21:15, 17 October 2009 (UTC)

The OP specifically asks about COLD fires. The combustion of Coal requires more temperature than that. Recall the Fire triangle. For a fire to be maintained requires heat, oxygen and fuel. Remove the heat and the fire goes out. Even smoldering (which is just a small fire) requires - and produces - heat. So - either what you have is some kind of exotic combustion at temperatures so cool that no light is produced (below the Draper point) - or it's some other luminescent chemical reaction which would not normally be described as a "fire". SteveBaker (talk) 15:35, 18 October 2009 (UTC)

I was actually curious about the Holy Fire, where in one of the references a person tried to explain the flames by some sort of strange chemical that produce flames that are safe to touch. The original page was in Russian probably. I used Google translate to read it but the translation is not ideal. Here's an excerpt:

Chemistry, this option is different. From memory recall one way in which too can make this experience at home. Cold fire have many esters of organic and inorganic acids. In particular, one of these esters (ethyl ester of boric acid) can be easily obtained at home.

Ingredients: - Dry boric acid, teaspoon - Ethyl alcohol, teaspoon - Concentrated sulfuric or hydrochloric acid, one drop

All this is placed in a saucer, mix and gently heated on a warm (so you can hold your hand), a water bath. Produces esters of boric acid can burn (not putting the match close to the saucer, so as not to light the alcohol).

Ether boric acid burns very voluminous, slightly greenish flame, which not only does not burn, but did not warm significantly, it can safely hold your hand.

from: http://www.skeptik.net/miracles/pasfire.htm

I'm looking for further explanation of the experiment that he is describing. Aurora sword (talk) 03:56, 21 October 2009 (UTC)

How do deleaved trees breathe?

How do trees that have lost all their leaves in the fall breathe through the winter? 71.161.59.133 (talk) 15:36, 17 October 2009 (UTC)

Trees don't breathe like you or me. See the article Leaf. During tree growth, leaves absorb carbon dioxide from the air. When the tree is not growing it needs little or no carbon dioxide, and the article implies that if the concentration of carbon dioxide in the atmosphere were higher than it is now, a tree could absorb all its needs through its branches or roots. Cuddlyable3 (talk) 16:06, 17 October 2009 (UTC)

Trees only use CO2 for photosynthesizing. The rest of the cells consume oxygen.

The living tissue of the woody stems (the cambium) breath through organs in the bark called lenticels. --SB_Johnny | ^talk 16:26, 17 October 2009 (UTC)

I'm not entirely sure but perhaps this interesting [1] conference paper I found yesterday about common misconceptions taught in school including on the difference between breathing and respiration will help. While it's directed at educators it may help clear up any misconceptions Nil Einne (talk) 10:17, 18 October 2009 (UTC)

How to make my doorbell ring for longer

I find that people tend to politely press doorbell buttons for just a microsecond, which is difficult to hear. Is there any simple circuitry that could turn a brief closing of the circuit into a ten-second bell ring? My doorbell is I think 6 volts, off a mains transformer. I'd prefer somthing with rugged relays rather than transistors. This explains why bad-taste musical doorbells are popular. Thanks 92.29.130.77 (talk) 17:31, 17 October 2009 (UTC)

You could put together something using a 555 timer IC, a couple of resistors and capacitors, and a relay. See the "Monostable mode" section of the article for the circuit diagram. If your transformer is AC/AC, you'll also need a rectifier pack and voltage regulator. A good introductory electronics project. :) Tevildo (talk) 20:36, 17 October 2009 (UTC)

No need to mess around building electronics. You can buy a timer relay that does the job straight away. You can get different voltages ac/dc and timing ranges so there's bound to be one that suites your doorbell. Here's a data sheet. Tevildo's idea is a more interesting project though, if you are trying to learn electronics. SpinningSpark 21:09, 17 October 2009 (UTC)

That is a nice data sheet but none of the relays shown are rated for control by 6V. It is unsafe to connect mains voltage to a doorbell button. Cuddlyable3 (talk) 21:25, 17 October 2009 (UTC)

Ah, I missed the OP requires 6V. Those ones go down to 12V and I certainly was not suggesting connecting it to the mains (as a paperboy while still at school I once got a shock from someones doorbell) agreed that is highly dangerous. 6V is a lot less common for relays but I will see if I can find something, are you sure you need 6V? SpinningSpark 22:21, 17 October 2009 (UTC)

To press a button for literally a microsecond or 10^-6 second is practically impossible. Cuddlyable3 (talk) 21:15, 17 October 2009 (UTC)

You and your pointy-eared logic, Spock.[[Special:Contributions/Dr. Leonard McCoy|209.244.187.155]] (talk) 00:04, 18 October 2009 (UTC)

Maybe the gross motion of the button mechanical system is slower than a single microsecond event; but the electrical contact may be as short as 1 microsecond, and may actually twitter back and forth on that sort of timescale (usually due to micromechanical behavior of the switch contact plate or spring). Digital samplers often need to correct for this on any mechanical user-interface button. Nimur (talk) 21:44, 17 October 2009 (UTC)

How about a little sign that says "Please press the doorbell for at least 10 seconds". Low-tech, but effective! SteveBaker (talk) 22:16, 17 October 2009 (UTC)

Obvious answer - replace the chime with one that plays for much longer - common ones here in the UK play the opening chimes of Big Ben for instance - around 6 seconds. Exxolon (talk) 04:30, 18 October 2009 (UTC)

I am reminded of the TV show WKRP in Cincinnati, where the character Jennifer had a doorbell that played the opening notes of Fly Me to the Moon. --Anonymous, 07:02 UTC, October 18, 2009.

I've had a closer look at the old "Friedland" transformer and it has a choice of 4v, 8v, or 12v. Currently it is set up for 8v, which I recall is the current required by the bell itself. So it could be possible to draw off 12v, although the transformer does have fuses on the low-voltage side which I expect are far too old to be replaceable. Thanks 78.151.108.233 (talk) 12:05, 18 October 2009 (UTC)

That is the voltage required by the bell. The current is something else. Cuddlyable3 (talk) 12:27, 18 October 2009 (UTC)

Thoughtless typing error. The "microsecond" above was hyperbole. Relax, do not take everything so literally. You must have great difficulty reading novels or magazines. Jokes must be completely meaningless. 78.151.108.233 (talk) 12:36, 18 October 2009 (UTC)

In that case you should have used the correct technical term, which is tick, as in the expression "just a tick". You want this to be increased to "just a mo". SpinningSpark 14:38, 18 October 2009 (UTC)

That was an unfortunate choice of link! For many people, a tick has a very specific meaning. SteveBaker (talk) 15:27, 18 October 2009 (UTC)

Mixing up current and voltage is a good way to get electrocuted. And stating the time duration with six orders of magnitude error is a good way to confuse us if you're asking a technical question about circuitry (where such time units are very common). As Steve has just pointed out, these are technical terms which mean something - if you don't know what they mean, we will gladly explain them or point you to the articles - but you can't fault us for correctly interpreting the words which were actually written by the OP. We have no a priori knowledge of the OP's expertise level or technical background. Nimur (talk) 15:37, 18 October 2009 (UTC)

So, ignoring the ridiculous pedants for a moment (you know who you are!). In order to stretch the amount of time that the existing bell rings for a brief press on the button requires the addition of some sort of a timer.

You could build a piece of electronic circuit with something like a 555 timer chip - but that's likely to be difficult for anyone who actually needed to ask this question. You would change the system so that instead of directly powering the bell, the button would trigger a circuit which would count down the 10 seconds and keep applying power to the bell for all of that time. You can google "Monostable multivibrator" or check out this site. If you understand enough to build this, you can use the 555 timer output to drive a small relay and use the relay to power the doorbell - and you're done. It would be more elegant to do this without the relay and use a power transistor or something to drive the bell - but for that, you need to know a lot more about the voltage & current that the bell mechanism needs. Relays are better because they aren't so fussy about the nature of what they are switching.

If you don't have the skills for electronics but like to tinker with mechanical systems - why not build a crazy mechanical system? Have a ball-bearing balanced on a little wooden platform at the top of a ramp - pushing the doorbell mechanically nudges the ball so it rolls down the ramp. The ramp has a v-shaped cross-section with the two arms of the V made of metal strips which don't touch and which are connected to the wires where the old door bell button was connected - as the ball bearing rolls down the ramp - it connects the two metal strips just as if the button was being pressed. Make the slope of the ramp gentle enough that the ball takes 10 seconds to roll down and fall off the end. After you answer the door, pick up the ball-bearing and put it back at the top of the ramp. I'm sure you could use your imagination to make a yet cooler mechanism.

But if you are one of those sad (but all too common) people who couldn't build anything to save their lives - then you're going to have to do what you do when anything else goes wrong...spend money. Go buy a new doorbell...it's your only option.

SteveBaker (talk) 15:27, 18 October 2009 (UTC)

Dear Steve, Thank you for your question "Why not build a crazy mechanical system?". It is an excellent question for the Ref. Desk. What happens in your proposed ramp system after someone rings the bell while the OP is not at home? Signed Sad-too-common-ridiculous pedant. Cuddlyable3 (talk) 14:18, 19 October 2009 (UTC)

Bah! Anyone with an ounce of mechanical imagination could come up with a fix for that. A tube filled with about a hundred ball-bearings sits above the button - you push it, the bottommost ball bearing rolls down the ramp, ringing the bell and when the person releases the (spring loaded) button, another ball drops down to replace the first one and you're ready to go for the next visitor...easy! Plus you can count the ball bearings on the floor when you get home and figure out how many visitors you had while you were away! Vastly superior than some crummy electronic system.  :-P Come to think of it - you could dispense with the electric bell and place a series of carefully spaced and tuned chimes alongside the ramp where the rolling ball would just gently tap them on the way down - you could have it play a tune just like an electronic doorbell. A simple rearrangement of the chimes would allow a wide range of tunes to be programmed when you get bored with "La Cucaracha". Think "wind chimes".

When I was a kid, my parents had a clockwork doorbell - it had a big round bell with a couple of bulges in it that rotated against a small hammer when it rang. You wound it up by rotating the bell a dozen or so turns. All that the button did was to release the ratchet on the clockwork. However, it did have the problem you describe - if you had more than a handful of visitors while you were out - nothing. SteveBaker (talk) 02:10, 20 October 2009 (UTC)

More than one ounce of mechanical imagination. Cuddlyable3 (talk) 18:39, 20 October 2009 (UTC)

What I need is something that, when the button is pushed, will close another path in parallel with the button, and then open it again after a few seconds. (Hmmmn, electro-magnet, leaking capacitor....) 78.151.108.233 (talk) 18:14, 18 October 2009 (UTC)

That won't work if your bell is AC, and, even if it's DC, getting a reasonably accurate 10 second delay with a simple RC circuit is going to be quite tricky. You're going to need some sort of active electronic/mechanical compoments, as discussed above - or just buy a new doorbell. :) Tevildo (talk) 18:27, 18 October 2009 (UTC)

It would be extremely difficult. You're expecting the capacitor to charge up sufficiently in the tiny fraction of a second that the button is pressed to sustain powering the bell for 10 seconds! That would take a pretty huge capacitor - and the current required to charge it in a fraction of a second would be impressive! SteveBaker (talk) 19:54, 18 October 2009 (UTC)

Well, the capacitor would just be discharging through the relay coil, not through the bell itself - it _could_ be done, but a 555 would be more reliable and cheaper (because big capacitors are expensive). Tevildo (talk) 19:58, 18 October 2009 (UTC)

Trying to drag this conversation away from the 555-timer-home-electronics-enthusiasts (guys, not everyone thinks its fun to spend their evening soldering minuscule bits together, some people just want the answers). The answer in this case being a pneumatic time delay switch example, example, example. Sorry, I could not find a slimline version suitable for fitting on a door jamb, but I think they exist. Make sure you buy a pneumatic or mechanical version, the electronic models are no good to you as they will require mains powering. SpinningSpark 20:29, 18 October 2009 (UTC)

i believe there are mechanical, or at least "black box" timed relays available that will stay closed for a set period when triggered; whether they can be used with your voltages is another question. if you don't get lucky that way, then getting some high school kid to throw something together with a 555 is the second easiest bet. if not that, then get a yappy dog. if not that, then a doorbell that plays "la cucaracha" or whatever.

another point: the OP hasn't specified whether his/her doorbell is something that buzzes/rings continuously, or is the bing.....bong type ubiquitous in the US. Gzuckier (talk) 20:38, 18 October 2009 (UTC)

Oh a 555 timer, what a great idea, I wonder why no one else mentioned that. Obviously it won't work with a bing-bong, but the whole context of the OPs post is that it is a continuous bell. Of course, if you are going to use a 555 timer, you could build a timed multivibrator, which would work with a bing-bong. SpinningSpark 00:21, 19 October 2009 (UTC)

The doorbell is a continuous one. Bear in mind that the button and the bell could be on two seperate parallel circuits powered from the transformer, only connected by some sort of relay. What I was thinking of above was something like this: 1) button pressed briefly 2) electromagnet relay closes, which starts bell ringing 3) hazy fog obscuring what happens next 4) capacitor charge leaks away through a resistor, which means the electromagnetic opens, so the bell stops ringing. The capacitor and the relay could have a diode etc to overcome the AC problem. The capacitor could be powered by another cicuit from the transformer. Are there not any simple low-voltage relays available that are designed to open after a delay? 78.151.114.229 (talk) 10:19, 19 October 2009 (UTC)

Well, the timer relays in the data sheet above have coil voltages down to 12V, and the existing transformer can be stepped up to provide the 12V needed by the relay. You can just run the bell off of the same 12V, with a resistor in series with the bell in order to drop the voltage down to the 8V it needs. You'd only need to wind up buying two parts. Red Act (talk) 10:48, 19 October 2009 (UTC)

                           \
        |Co                :\
        |Co--------------^   o-------------------        C = Electrolytic capacitor
        |Co   |                                 |        D = Silicon diode 1N4003-6
        |C    |___|\|____                    -------     RL= Small relay 
-------c|C        |/|+ | V                   | bell |          with DPDT contacts
       C|C         D   |  \                  |______|          & 1000 ohm coil
mains  C|C     ________|   \                    |
       C|C    |            :\                   |
-------c|C_   |___   ____î   o--------          |
           |     ----- |             |          |
           |       |   |             |+         |
           |     push  |___        ----- C      |
           |               C       |___| 4700µF |
           |               C             25V    |
           |           RL  C       -----        |
           |               C         |          |
           |_______________C_________|__________|

Cuddlyable3 (talk) 15:03, 19 October 2009 (UTC)

It might be an idea to put a small resistor (10R should be enough) between the supply rail and the diode, but otherwise that circuit would be adequate. Make sure you get the diode and capacitor the right way round. :) Tevildo (talk) 17:16, 19 October 2009 (UTC)

In the above circuit, there's nothing limiting the current while the capacitor is charging. My guess is the diode would get smoked, although the transformer's at risk, too. Also, with only half-wave rectification, you're basically counting on the relay's operate time being less than 1/2 cycle (about 8ms), whereas a typical operate time of a relay is actually about 20ms. You could fix those problems by sticking in an extra resistor to limit the current through the capacitor while it's charging, and change to use full-wave rectification. But both of those add to the circuit complexity. It's easier to just buy a timer relay. Red Act (talk) 17:29, 19 October 2009 (UTC)

At switch-on the current in the diode is limited by the secondary resistance of the transformer but adding a resistor as Tevildo suggests can add some safety margin. Charging time for the capacitor is too short to cause significant heating of the transformer. The drive that energises the relay is initially about 12V from the charged capacitor. The half-wave rectified supply sustains current in the relay after it has built up enough magnetic field to set the contacts in motion. Inertia of the contact armature and the relay coil inductance together ensure that both contacts close. I tweaked the artwork slightly to clarify the lower relay contact. Cuddlyable3 (talk) 23:36, 19 October 2009 (UTC)

I'm still a little dubious about inertia being enough to keep the armature moving long enough to ensure the NO contacts close. Assuming the relay is the more common break-before-make, the charged capacitor wouldn't help between the time the NC contacts open and the NO contacts close. However, there are a couple simple ways to avoid any possible problem in that regard, without needing to go to full-wave rectification as I had earlier suggested. One possibility would be to simply specify the relay as being make-before-break. Another simple possibility would be to have the side of the pushbutton that's connected to the diode in the diagram instead connect to the + lead of the capacitor. That second option would also have the advantage of the ring duration always being the chosen duration (as long as the button isn't pushed longer than the chosen duration), instead of the ring duration varying depending on how long the button is pushed.

I still think just buying a timer relay would be the simpler, more reliable way to go. But the circuit above does have the advantage of only needing parts that can be readily picked up at Radio Shack, instead of having to be ordered. Red Act (talk) 02:58, 20 October 2009 (UTC)

Here is a little relay. Note that the nc (normally closed) contact arm is a spring that is slightly deflected in the rest state. Therefore the iron armature accelerates through some distance before that contact opens. As I stated, there is a persisting magnetic field as well as inertia to keep it moving. (The picture shows SPDT not DPDT contacts). When the pushbutton is connected as shown, the bell is guaranteed to ring for the defined period after the last push. If the pushbutton is connected directly to the capacitor, a second push any time during the ring is effectively ignored. I don't know whether callers can hear the bell but if not the second case might mislead them. Cuddlyable3 (talk) 18:32, 20 October 2009 (UTC)

Thanks for all the above. I would like to really make and install this. I do not know anything about electronics. I have used a soldering iron once or twice in the distant past. What would be the parts list I would need to order the components online from somewhere like Maplin Electronics please? There seem to be two competing designs: I'd appreciate a parts list for both if possible please. In the wonderful diagram above, is "push" the button? And are the diagonal lines part of the relay? Does this design have to be manually reset after a ring? This is an interesting example of something like collective intelligence applied to designing something. 92.29.141.85 (talk) 11:49, 21 October 2009 (UTC)

For Cuddlyable3's circuit, the Maplin part numbers are:

K1 (Relay) - N18AW (see note)

D1 (Diode) - QL75S1

C1 (Capacitor) - AT24B

R1 (Resistor - put between transformer and D1) - M10R

Note - the relay listed above is 12V nominal, with a 720R coil. With an 8V AC supply, half-wave rectified, you'll get about 11V DC (8√2, to be precise). That _should_ be enough to give you a reasonable length of ring, although you probably won't get the full 10 seconds. You'll also need to connect the components together. Apart from the relay, you could put the diode, capacitor and resistor on a bit of chock-block (Maplin L96AR) - you could solder some wires from the relay and connect to the chock-block that way. Alternatively, you could get a piece of Veroboard (Maplin JP46A - note that Maplin's prices for Veroboard are positively extortionate, but needs must) and solder all the components on to it. You'll then need to connect the existing wiring to the Veroboard - you can try soldering the wires directly on to it (although, if you're not experienced with soldering, this might be a bit tricky), or get a PCB-mounted terminal block (Maplin RH80B, 3 off) and solder that to the board instead. You might want to put the whole thing in a box, as well - but that's a question of aesthetics rather than practicality. Should I list the components for a 555-based solution, as well? Tevildo (talk) 23:49, 21 October 2009 (UTC)

Modifying a mobile phone / cell phone to use only as a computing device.

I do not like mobile phones. But some mobile phones can be used as a miniture computer. Is it possible to tinker with its insides and stop it being usable as a mobile phone but keeping it working as a computing device? 92.29.130.77 (talk) 17:39, 17 October 2009 (UTC)

Why not just put it in airplane mode? --Cameron Scott (talk) 17:44, 17 October 2009 (UTC)

Not OP, but not all phones have "airplane mode". Indeed, I've never seen a phone that had that, although I've not seen many newer model phones recently. —Preceding unsigned comment added by 82.44.55.2 (talk) 17:47, 17 October 2009 (UTC)

Well, many do. Mine does, and I use the feature frequently. See flight mode --NorwegianBlue ^talk 18:21, 17 October 2009 (UTC)

Actually I suspect most phones probably have airplane mode or something similar. It's not actually new at all, or uncommon. My bet is that your phones have had it but you didn't know how to use it. --Mr.98 (talk) 19:07, 17 October 2009 (UTC)

Pretty sure they don't, then again I'm talking about very old (5 years) phones here.

My 3.5 year old phone (Panasonic VS2) did not have a flight mode although it supported (limited) video playback, most audio formats, had a 1.3 MP camera, infrared, a good (for the time and price) colour 320x240 screen and had 32mb of memory. I would expect most new model phones in that price range to have a flight mode but I'm pretty sure it wasn't unusual for the time and it was in the low mid to mid price range (IMHO). It didn't have bluetooth, 3G, or expandle memory (the later being the biggest limitation). The ~2 year old Nokia 1110 I use occasionally since my Panasonic VS2 broke which is a fairly basic phone with a monochrome screen, no camera etc also lacks a flight mode. It's replacement model, the Nokia 1200 also does not have a flight mode I'm pretty sure. The usefulness of a flight mode for such a basic phone is of course fairly questionable. Of course if you're intending to use your phone as a computer you're unlikely to be using either a basic phone or a 3+ year old model however I would suspect when we think in world wide terms they do represent a substanial percentage of the market so I think it's questionable if 'most phones' have an flight mode Nil Einne (talk) 07:32, 18 October 2009 (UTC)

Actually something else occured to me... I don't know for sure but I would presume in a number of developing countries e.g. China and India no name and home brands (I know China has a lot) would dominate the market. I wonder if these might often have a flight mode even if it's not that useful since the developers may just include it as it costs nothing (since they like to advertise/show off all their features). Many Chinese phones have stuff rare in much of the developed work of course, e.g. dual sim cards, TV reception and ubiqitious touch screens (although this may be because using a stylus is an easier way to input Chinese characters) even in not really smart phones with normal numberpads. I've also noticed they have 'security' features like SMS blocking and stuff. However I haven't really looked much at the low end of the market which I guess is where most of the phones sold in China are so not sure what things are like there. Nil Einne (talk) 21:46, 22 October 2009 (UTC)

Probably... but the phone's computer is NOT very powerful. It strikes me that anything you might want to do on a cell phone could be EASILY better done on a machine better suited to that purpose. I mean, I use mine as a calculator. It's not the best calculator and it's a pain to use. It is ONLY convenient as a calculator because it is also a phone, and I am already bringing the phone with me. If I didn't have a phone, and I needed a calculator, I'd just carry a regular calculator around—it'd be a lot easier to use. --Mr.98 (talk) 19:07, 17 October 2009 (UTC)

The phone indicated by NorwegianBlue above has a higher memory and storage spec than a DOS laptop I had a few years ago. If it has an operating system that allows the introduction of other programs, then it should be able to do a lot. Perhaps the drawback would be the difficulty of using the tiny 'keyboard'. 92.29.130.77 (talk) 19:35, 17 October 2009 (UTC)

Perhaps, but for the price of the phone (probably a few hundred dollars) you can just get a netbook and skip all of the hassle and the very tiny monitor, no? --Mr.98 (talk) 20:04, 17 October 2009 (UTC)

It might help if you explained why you don't want it to work as a phone. You can choose not to make any phone calls without disabling the feature. --Tango (talk) 19:52, 17 October 2009 (UTC)

Obviously for situations like being on an airplane or not wanting a phone without a sim card to radiate you with signals when it's not being used for calls. —Preceding unsigned comment added by 82.44.55.2 (talk) 20:05, 17 October 2009 (UTC)

Obviously for situations like being on an airplane which if it is powerful enough to add as a small computer is going to have an aircraft mode for.. --Cameron Scott (talk) 20:10, 17 October 2009 (UTC)

The OP hasn't mentioned aircraft and there can be other motives for disabling the call function on a mobile phone, such as lending it to child for game playing only. Cuddlyable3 (talk) 20:55, 17 October 2009 (UTC)

Rather than modify a phone, why not just get a PDA? Does about the same thing... SDY (talk) 20:17, 17 October 2009 (UTC)

For those who wonder why anyone would want to do this, mobile phones have a very good performance / power consumption ratio so it could be seen as some kind of a green act and a cheap way to waste time to build a cluster of recycled phones. Why you would want to disable calling I do not know. --194.197.235.240 (talk) 20:48, 17 October 2009 (UTC)

If I just threw away the "sim" card, would that be the solution? Do all these phones have sim cards? I'd like to use such a device because its probably easy to get one cheaply or perhaps even for free as people upgrade, and because they are very light. PDAs or netbooks weigh 500g+ (weight of a jar of jam) as far as I recall and would be no fun to carry around in your pocket for any length of time. And because its fun getting something to work like that, particularly for little or no cost. I like to work things to the max. 92.29.130.77 (talk) 21:29, 17 October 2009 (UTC)

I'm not sure what you think of when you think "PDA", but most PDAs are the size of a phone. A PDA is something like a PalmOS device. PDAs are not the same thing as a netbook. APL (talk) 22:52, 17 October 2009 (UTC)

If I just threw away the "sim" card, would that be the solution? Depends, you are in the UK, so yes, you could just remove the SIM card, the only problem is that some smartphones will not operate for long without the presence of a SIM card. As for the weight and size, well as the size decreases, so does the screen size. --Cameron Scott (talk) 21:32, 17 October 2009 (UTC)

Actually some phones won't operate at all without a sim card (well they will just say "no sim card" or "emergency calls only" and won't let you do anything). You can get wiped sim cards from places like Deal Extreme may avert this problem however if the phone is sim locked they probably won't work. Also this won't necessarily stop the phone from transmitting so there may still be battery life and other such issues. So I have to agree a PDA of some sort would be a better bet. Why get something with the phone part if you don't want it? Nil Einne (talk) 07:36, 18 October 2009 (UTC)

I'm surprised the no one has mentioned the iTouch yet. It's essentially an iPhone without the telephone stuff.

I'd also like to mention the Open Pandora which will eventually ship its first unit. That's going to be the size of a NintendoDS which can fit your pocket, depending on the kind of pockets you have. APL (talk) 22:52, 17 October 2009 (UTC)

One of the reasons why I'd like to try using a mobile phone as a computing device is for the same reason that I keep a minature radio all the time in my bag: the radio is extremely light so I do not notice the weight, it is very small so takes up no space, and it is very cheap so I'm not worried about it being lost damaged or stolen. If I find I've got some time to waste while on a journey then the radio is there if I want to play with it. For similar reasons I wear a cheap digital watch rather than walking around with an antique grandfather clock strapped on my back. 78.151.108.233 (talk) 12:20, 18 October 2009 (UTC)

There are a number of PDAs on the market that are the same size as a phone. Those would be far better options than buying a phone and disabling the telephone. Obviously the iTouch is the same size as the iPhone. Personally I like PalmOS for PDAs. here is one current offering in that line. APL (talk) 17:17, 18 October 2009 (UTC)

Thanks, but thats at least ten times more than what I would want to spend. As I mentioned above - and surprisingly nobody here seems to "get it" - is that it would be fun to get an old phone for very little from eBay or for nothing from Freecycle, and do a "mod" (probably involving soldering irons)to get it to do what I want at little or no cost. Someone is trying to get a very old computer to run in the Computer section of the Referance Desk in the same spirit. 78.151.108.233 (talk) 18:22, 18 October 2009 (UTC)

Um, folks..... the default state of a cell phone is to be only a computing device with no phone capabilities unless you do a bunch of things including, but not limited to, paying a cell phone bill every month. I keep my old retired cell phones as free calculator/cameras, without doing anything special other than not having them on an account with a cell phone provider. Gzuckier (talk) 20:34, 18 October 2009 (UTC)

Ah. I see what you mean now. I had the impression that you were trying to buy a new phone for use as a pda, which would be crazy. I think Gzuckier is mostly right here, most phones you won't have to do anything special as long as their subscription is canceled. (Though, in my experience, they seem to keep the radio circuits turned on, apparently just to update the current time. Perhaps some tinkering could save you some electricity there.)

Don't be surprised if you need to purchase a new battery for the thing. (Perhaps it could be modded to take a battery you have on hand.) APL (talk) 21:16, 18 October 2009 (UTC)

Sorry, I don't meen to keep harping on PDAs, but I just noticed that used older model Palm devices are really cheap on ebay. [2] [3] APL (talk) 21:18, 18 October 2009 (UTC)

Gosh, you are right, thanks. I've asked a question about the best old PDAs for my old-fashioned preferances on the Computing desk. I'd appreciate people's expertise there. 78.144.243.47 (talk) 19:50, 19 October 2009 (UTC)

stomach pressure in vomiting

What pressure (mm/Hg) is needed for the stomach to eject its contents? Please cite authoritative reference. —Preceding unsigned comment added by 72.75.125.231 (talk) 23:43, 17 October 2009 (UTC)

The stomach must merely apply positive pressure to its contents while the pyloric sphincter is tensed and the esophageal sphincter is relaxed. Stomach contents will then be brought to the oropharynx via esophageal reverse peristalsis. It's not as though the stomach has to pump its contents through a conduit of static/merely elastic vessels like the heart must do to sustain blood pressure. DRosenbach ^{(Talk | Contribs)} 00:29, 18 October 2009 (UTC)

Physiology and pharmacology of vomiting, (1953), discusses the ability to induce vomiting by applying pressures to various sections of the gastrointestinal tract. Vomiting was induced by 300 mm-Hg applied to the biliary ducts; or 30 to 35 mm-Hg applied to the pyloric pouches. These experiments were conducted on dogs. Nimur (talk) 00:45, 18 October 2009 (UTC)

Respiratory mechanics of vomiting in decerebrate cats, (1974), states that "the respiratory muscles provide the motive force in vomiting..." and that "the retching pulses were generally 0.5 s or less in duration, and at their peak amplitude often exceeded minus 75 mmHg in the thorax coincident with 125 mmHg in the abdomen, adding up to transdiaphragmatic pressures greater than 200 mmHg." This paper presents time-versus-pressure plots, as well as EMG plots of the control signal, so you can actually see the vomiting process as a dynamic event (rather than an approximate average pressure). It also might explain why human studies are more or less impossible - decerebrate cats were used in this study. I would like to comment for the record that the procedures described in this paper are not necessarily pleasant. We can hope that the useful scientific data may help (or may have already helped) the medical and biological community; hopefully, assisting our understanding of the neurological issues which motivated the original research and spurning medical progress. Nimur (talk) 00:52, 18 October 2009 (UTC)