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February 11

What kind of tree is this?

I'm thinking of getting a tree tattooed on my back. This is the tree in which I spent a lot of my childhood; I don't want to make this particular tree my tattoo, but if I could remember what kind of tree it was, I could sort of start from there. Can anyone else ID what kind of tree I might have been playing in? It was so long ago, if I ever knew, I've forgotten ... -FisherQueen (talk · contribs) 01:34, 11 February 2010 (UTC)

A big tree to be carryin' around, an Oak by the looks of the bark but a leaf would be helpful. hydnjo (talk) 01:55, 11 February 2010 (UTC)

A closeup picture of a leaf, a flower, or a fruit would definitely help. --Dr Dima (talk) 02:02, 11 February 2010 (UTC)

I know- I suck! This is the only picture of the tree I have, and it's three hundred miles away in the backyard of a stranger... -FisherQueen (talk · contribs) 02:18, 11 February 2010 (UTC)

Judging by the lobes on the leaves, which I can kinda sorta make out, my top three guesses are, in order:

• An oak of some sort, likely in the "red oak" type, see List of Quercus species, Section Lobatae.
• A Liriodendron tulipifera, aka American tuliptree, aka Tulip poplar, aka Yellow poplar
• A Liquidambar styraciflua, aka American sweetgum, though these often have very straight trunks with no lower branches when mature; so this doesn't look much like that.

Those are my three best guesses. If we knew where this was from, or could get a better look at the leaves or seeds, it would help! --Jayron32 02:52, 11 February 2010 (UTC)

The 'where' I can do: northwestern Pennsylvania. -FisherQueen (talk · contribs) 02:55, 11 February 2010 (UTC)

In that case, throw out the Sweetgum; they are endemic in the South but their range ends hundreds of miles from any part of Pennsylvania. The tulip poplar is also doubtful, as its range kinda dies out near the Pennsylvania/Maryland line, though it may be this. I would explore some of the red oak species. --Jayron32 03:10, 11 February 2010 (UTC)

Oak, unquestionably, but likely currently covered in snow, so Quercus niveobrutus. alteripse (talk) 03:13, 11 February 2010 (UTC)

Thanks! That sounds plausible; I will look at pictures of oak trees as I seek tattoo inspiration. -FisherQueen (talk · contribs) 03:17, 11 February 2010 (UTC)

I have to issue a note of caution about tattoos: The problem with them is that they last longer than the original symbolism. Today, a peaceful oak tree is a nice statement - and if you like that kind of thing, not such a terrible thing to have on your back. But how do you know that in (say) 10 to 20 years time, the Oak tree won't become the symbol of a terrorist group or an evil mega-corporation, or perhaps some other social group that you'd prefer not to be associated with? Suppose, for example, that you're not gay and do not wish to be assumed to be so - then, if in the 1980's you'd decided that a tattoo of a rainbow over the greek letter Lambda (I dunno - maybe your name begins with an "L" and you like greek lettering). Since that pretty much says "I'm gay and I want you to know it" in the years 2000 and onwards - that would be a major problem for you. So think carefully. SteveBaker (talk) 14:10, 11 February 2010 (UTC)

It's already the symbol of an evil mega-corporation. Comet Tuttle (talk) 17:47, 11 February 2010 (UTC)

Does this group of compounds exist?

Why is it so hard to find information about these compounds?

Are they stable enough to exist in say, a bottle you would purchase from Sigma-Aldrich? What do you call these compounds?

Also, is the decarboxylation step shown possible, maybe in the presence of the appropriate catalyst, to generate carbenes? I'm just wondering why it's so hard to find discussion of aromatic cyclic carbonates, carbamates and ureas, etc. The keywords I have been using so far have been along the lines of "cyclic carbonate ester" + aromatic, etc. The molecule should be aromatic and therefore fairly stabilised, right? John Riemann Soong (talk) 03:08, 11 February 2010 (UTC)

Apparently you can buy them. See for example this.

Ben (talk) 03:53, 11 February 2010 (UTC)

Hmmm ... such unwieldy names. Why aren't these compounds more common, and why do molecules with this motif seem to always have both sites substituted? This seems to tell me that something interesting happens if there's a hydrogen on those C=C atoms! John Riemann Soong (talk) 04:59, 11 February 2010 (UTC)

I don't know off the top of my head, but I had a look on Web of Knowledge for you, and here are a few papers:

• Chem. Pharm. Bull. (1988) 36(1). 394–397
• Synth. Commun. (1992) 22(9), 1277–1282

Ben (talk) 01:50, 12 February 2010 (UTC)

Do any of the chemists here have comments? The cyclic carbonate ester is basically like a permanent "enol ester". Trying to restore a C=O results in decarboxylation ....? Or is it possible to carry out aldol reactions without decarboxylation? John Riemann Soong (talk) 17:16, 13 February 2010 (UTC)

Search for vinylene carbonates - it's listed as a synonym in the Sigma link I gave you. Use your initiative!

Ben (talk) 23:23, 13 February 2010 (UTC)

Thanks for the tip. I'm not good at finding synonyms. Why doesn't wiki have an article for it? I'm not a grad student. John Riemann Soong (talk) 18:43, 14 February 2010 (UTC)

Paxil

What happen to Paxil Official Website (http://paxilcr.com)? As for me I typed in Paxil in google and it isn't there anymore. —Preceding unsigned comment added by Mybodymyself (talk • contribs) 03:32, 11 February 2010 (UTC)

They seem to have pulled quite a lot of pages relating to this drug - but going to the http://www.gsk.com site and typing "Paroxetine", "Seroxat" or "Paxil" (which are the same drug under different names) into their search engine produces hundreds of pages on the subject - so I don't think they are supressing anything - it's possibly just a rearrangement of their site. http://www.gsk.ca/english/html/our-products/paxil.html seems to be the main entrypoint. SteveBaker (talk) 04:31, 11 February 2010 (UTC)

Thank you.--Jessica A Bruno (talk) 21:03, 11 February 2010 (UTC)

Shape of Human foot

.

Please look at the accompanying picture. On the left is normal human foot we all have (approximate shape). My question is that : is there any record of a human sub-race, living anywhere on the planet, that has the foot shaped like to that at the right ???? Unless I am terribly wrong I think I have seen men with foot like at the right ! Did I see on a long forgotton TV program or is it somewhere in my racial memory....

 Jon Ascton  (talk) 04:58, 11 February 2010 (UTC)

There are a number of genetic and developmental disorders that result in missing or fused digits. See syndactyly and ectrodactyly for example. --Dr Dima (talk) 05:12, 11 February 2010 (UTC)

I understand what you are saying but I am not talking about individual specimens rather I want to know is there any country or community where everyone has this as 'normal' condition ?  Jon Ascton  (talk) 05:42, 11 February 2010 (UTC)

I think you are asking about the Vadoma tribe. Here[1] is a photo of one of their members which I found with a Google image search. Richard Avery (talk) 07:08, 11 February 2010 (UTC)

Wow! That's interesting. I wonder whether the improved ability to climb trees that's mentioned in our article has resulted in some kind of selection pressure for that particular gene? Are we actually seeing an evolutionary event? SteveBaker (talk) 14:01, 11 February 2010 (UTC)

Parapatric speciation? Possible, but not very likely. Even under conditions ideal for speciation it would take many, many generations before the 5-toe and 2-toe Homo species can no longer produce fertile children with each-other. Also, as noted by Comet (see below), claim of the improved ability to climb trees lacks verifiable reference so may be inaccurate. --Dr Dima (talk) 18:04, 11 February 2010 (UTC)

You can have evolution without speciation. Lactose tolerance and alcohol tolerance both evolved in humans fairly recently, but lactose intolerant people and those that experience the Alcohol flush reaction have no difficulty breeding with the rest of us. That doesn't mean it wasn't evolution. (I don't know if the people mentioned actually lack that tolerance due to not having a certain mutation, rather than due to having a different mutation, but it's entirely plausible.) --Tango (talk) 19:14, 11 February 2010 (UTC)

You can certainly have evolution without speciation. However, that usually requires an existence of selection pressure on the entire species (predator-prey coevolution, changing environment, etc); although a random genetic drift is also possible. In the case of foot ectrodactyly I understood that SteveBaker is asking specifically about speciation, as the selection pressure to climb trees (if true) only exists for a particular sub-population of the Homo sapiens species. Indeed, majority of H. sapiens experience zero or negative evolutionary pressure to climb trees; and, more generally, for the majority of H. sapiens the foot ectrodactyly offers no reproductory advantage I can think of. --Dr Dima (talk) 17:45, 12 February 2010 (UTC)

I fact-tagged the uncited claim that the condition may help in tree climbing. Comet Tuttle (talk) 17:45, 11 February 2010 (UTC)

Aside from the actual point of your question, there's no such thing as racial memory. Comet Tuttle (talk) 17:45, 11 February 2010 (UTC)

Right. Now that is proved beyond doubt - I saw it on TV etc. long ago that's why had problem recalling actual source of information. I was mentioning racial memory just because I had serious doubt about contemporary existance of these people. But they do exist. Wikipedia is wonderful thing....

 Jon Ascton  (talk) 21:31, 12 February 2010 (UTC)

Probably in reports of cryptid mermen. :-) ~AH1^(TCU) 23:54, 13 February 2010 (UTC)

how do ants get into a house

and can thety damage fiberglass insulation and make a house drafty? —Preceding unsigned comment added by 67.246.254.35 (talk) 05:53, 11 February 2010 (UTC)

Well, when they get into my house they either walk in under the back door or they slip through a crevice where the pipe for the outdoor faucet comes through the brick. Any little opening like that will do. Fiberglass is inedible and I can't imagine ants being large enough to damage it by pushing it around, though other intruders like squirrels and raccoons certainly can. --Anonymous, 06:58 UTC, February 11, 2010.

An entire ant nest (the kind that form a mound maybe a foot across and half as high) can push fiberglass insulation around - and I suppose a subsequent abandonment of the nest might make it collapse and thereby cause a draft - but it's a bit of a stretch. But fibreglass insulation isn't there to stop drafts anyway - it's merely a thermal barrier and air can certainly pass through it. Draft protection is what the actual walls are supposed to do. SteveBaker (talk) 13:23, 11 February 2010 (UTC)

stages of urine decomposition

where can i find info on stages of urine decomposition i tried google —Preceding unsigned comment added by 67.246.254.35 (talk) 07:48, 11 February 2010 (UTC)

Urine is a simple aqueous solution. The term decomposition is not very applicable, since most of the components are not degradable. There are very small amounts of protein in normal urine and the term might be used for the further breakdown of these components by bacteria in sewage or soil (depending on where you pee). Or am I not understanding your question? alteripse (talk) 17:39, 11 February 2010 (UTC)

Urine mainly has Urea and water in it. Everything else is just trace amounts. So read about Urea to find out more. Ariel. (talk) 04:24, 12 February 2010 (UTC)

h1n1 swine flu

what is the reason of swine flu? —Preceding unsigned comment added by BHADAW SOREN (talk • contribs) 08:18, 11 February 2010 (UTC)

Are you asking about the Influenza A virus subtype H1N1? 58.147.58.179 (talk) 10:31, 11 February 2010 (UTC)

See swine flu; not everything has a reason.--Shantavira|^{feed me} 11:56, 11 February 2010 (UTC)

. . . but most things have a cause. If there were no production of meat we would not have seasonal flu or several other diseases. -Craig Pemberton 19:13, 11 February 2010 (UTC)

What is the basis for your claim that flu does not exist where there is no meat production? -- kainaw™ 19:17, 11 February 2010 (UTC)

Well, there is very strong evidence that domestication of animals resulted in the introduction of a lot of diseases to early humans. I don't think getting rid of animals bred for meat now would get rid of seasonal flu, though, we would need to go back in time and do it. --Tango (talk) 19:26, 11 February 2010 (UTC)

There is evidence that past strains and current strains of flus have come from animals. It appears that Craig Pemberton is claiming that all strains of flu have come from meat production. Claims of "all" or "none" really need to be backed up. -- kainaw™ 19:34, 11 February 2010 (UTC)

Hmm I seem to recall seeing a study that traced the origin of most seasonal mutations in the flu back to nations where people raise chickens domestically and have poor sanitation (Philippines seems to ring a bell?) but I can't seem to find it. I could be mistaken. But a lot of disease comes from meat. The zoonosis page is interesting. Even AIDs may have come through the consumption of bushmeat but that's just a theory. -Craig Pemberton 20:13, 11 February 2010 (UTC)

This is not quite right, but it describes Asia as a flu "reservoir". -Craig Pemberton 20:17, 11 February 2010 (UTC)

Close association of domesticated birds and men does aid the development of strains that are more virulent and transmissible in humans, but type A influenza is endemic in the wild waterfowl communities of Southeast Asia and even is we all stopped eating birds, the flu wouldn't simply go away. Dragons flight (talk) 20:59, 11 February 2010 (UTC)

The OP's claim that "AIDS may have come through the consumption of bushmeat" really needs to be backed up with hard evidence -- the AIDS virus is not transmitted through food consumption. 24.23.197.43 (talk) 08:15, 12 February 2010 (UTC)

I think the theory is that it came from butchering the animal and all the blood that is released. And AIDS can be transmitted through food if you consider blood to be food. Probably raw meat will transmit it too. Ariel. (talk) 09:15, 12 February 2010 (UTC)

Consumption is the wrong word, but the general belief is bushmeat is the most likely cause, as supported by our Simian immunodeficiency virus and Origin of AIDS. Whether this was from butchering the animal or injuries sustained while hunting the animals, we will likely never know, just as we can never be sure bushmeat is the cause, but it is one of the simplest and most plausible explainations. More details are discussed in the articles particularly the later one. Nil Einne (talk) 17:23, 12 February 2010 (UTC)

146.74.231.39 (talk) 22:51, 12 February 2010 (UTC)

Why ask Ariel when I already provided an article with citations? Nil Einne (talk) 18:18, 13 February 2010 (UTC)

How do the satellites move on their orbits?

how do the satellites move on their orbits after being launched from earth?

how do they get into their orbits?

thank you —Preceding unsigned comment added by 117.197.244.248 (talk) 13:17, 11 February 2010 (UTC)

They are launched on large rockets (I'm betting you knew that!) that push the satellites so high that there is (almost) no air resistance to slow them down - and so fast that they reach a point where they are falling back towards the earth at exactly the same rate that the curvature of the earth makes the ground be further away beneath them. They fall continually - but because they are going so fast sideways they end up going in a complete circle. This is why we call the "zero-g" environment inside the International Space Station "free fall" because strictly speaking, there is gravity there - but the space station and the astronauts inside it are falling freely around the earth. Our article Newton's cannonball illustrates this rather nicely. SteveBaker (talk) 13:30, 11 February 2010 (UTC)

Despite everyday experience, objects will continue to move unless something stops them (in our lives there is always friction and air resistance stopping things). In space there is nothing to stop the satellites moving so, once they are in orbit, they stay there going round and round (satellites in Low Earth Orbit do need to be boosted occasionally because of the tenuous atmosphere that is still at those altitudes). Getting the satellite up to the right altitude and moving fast enough not to fall back requires a big rocket. --Tango (talk) 13:39, 11 February 2010 (UTC)

The rockets steer themselves into the speed and direction the sat need to stay in orbit, let the sat go and then steer back to earth. There's a fine point here. If you just "threw" the sats up above the atmosphere they would not enter orbit, you need to steer the rockets. EverGreg (talk) 19:02, 11 February 2010 (UTC)

As per Kepler's laws of planetary motion, all satellites (wherever natural [i.e. moons around a planet, or planets around a star], or man-made), will orbit in an eclipse around the parent object. One of the foci(focuses) will be the centre of mass of the combined system. As most satellites are far smaller than their parent, this is the centre of parent. A beam of light emerging from one foci of an eclipse will converge on the other. Also, if you draw an eclipse by hammering two nails into a bit of wood, looping a string around them, and then draw by a pen pulling the string tight, then the nails are at the foci. CS Miller (talk) 14:52, 13 February 2010 (UTC)

Time Travel

I know this wudnt qualify as time travel in the scientific sense but Im sure we all face this while travelling behind in time zones I left Dubai International Airport at 18:05 on one given day and reached Doha International Airport at 18:00 on the same day. Does this mean, i travelled back in time? Technically speaking yes?? —Preceding unsigned comment added by 213.130.123.12 (talk) 14:35, 11 February 2010 (UTC)

No, you haven't traveled back in time. You've simply changed your watch. — Lomn 14:37, 11 February 2010 (UTC)

Indeed, when you left dubai it was 17:05 in doha, and when you arrived it was 18:00. That is 55 minutes forward in time by all accounts. —Preceding unsigned comment added by 129.67.116.217 (talk) 14:44, 11 February 2010 (UTC)

It is only "time travel" in the sense that our conception of the hours of the day are correlated with one's position on the Earth. If you rapidly change your position on the Earth (say, by jet), then you affect what hour of the day it is. You have not in any meaningful scientific sense "traveled in time," but you have changed what time, say, the Sun will be observable directly over head, as compared to your previous location. Time zones are just a way to standardize and simplify that issue so that every town doesn't have it's own arbitrary definition of what "noon" is. --Mr.98 (talk) 14:53, 11 February 2010 (UTC)

I guess if it makes you feel cool you could say you "traveled backwards through time-of-day". It'd be a strange way of describing the act of traveling east. APL (talk) 15:08, 11 February 2010 (UTC)

(You want "west", in most cases, including from Dubai to Doha.) --Tardis (talk) 15:45, 11 February 2010 (UTC)

Yes. West, not east. I get those two confused. APL (talk) 16:44, 11 February 2010 (UTC)

thanks for the answers, i knew I hadnt travelled back in time, however that day for what it was worth, I experience 18:00, 18:01, 18:03, 18:04 and 18:05 twice. which was a funny feeling. call it resetting the watch or whatever... —Preceding unsigned comment added by 213.130.123.30 (talk) 15:53, 11 February 2010 (UTC)

When you say that you "experienced" 18:00 twice, you don't mean that there was any similarity between those two minutes (other than what the nearby clocks said, and that's because you had changed to a different set of nearby clocks). What you really mean is that you assigned the same name ("18:00") to two different minutes of time. The use of the label, not the time, is what was repeated, and as it's a purely artificial construction it's no surprise that we can use a label repeatedly if we want to. --Tardis (talk) 16:22, 11 February 2010 (UTC)

Well, I'd argue this goes a little too far by calling it purely artificial. The sun was in exactly the same position relative to his head for a long time that day. That counts for something. Comet Tuttle (talk) 17:40, 11 February 2010 (UTC)

And it was in other positions relative to his head for much less time than normal. We should also note that it wasn't even the same "1800" twice; one was "1800 (UTC+X)" and one was "1800 (UTC+[X+1])". — Lomn 18:24, 11 February 2010 (UTC)

If you live somewhere with daylight saving time then you experience an hour repeated like that once a year anyway. It happens in the early hours of the morning, so you probably sleep through it, but it's the same basic idea. --Tango (talk) 19:07, 11 February 2010 (UTC)

The point is that the idea of changing your watch every time you move around the planet is merely a human quirk. If the world operated by GMT then nothing odd would have happened. We don't do that because some people find it confusing to have to get up and go to bed at different times depending on where they happen to be living - but, as I said, that's just an odd human quirk. Someone from another planet might find that a VERY strange thing to do. (And don't get me started on Daylight Savings time!) Anyway - if you are a lover of your particular form of time travel, take a trip to the south pole and walk around the pole in circle. You can cross 24 time zones in as many seconds...just think how young you'll get then! (HINT: No, you won't.) SteveBaker (talk) 21:11, 11 February 2010 (UTC)

If you try the experiment Steve suggested, remember that the Ceremonial South Pole is actually a short ways off from the real pole.

This is one of those great disappointing truths of science. APL (talk) 22:14, 11 February 2010 (UTC)

Steve, it's not "merely a human quirk" but a quirk of nearly every complex lifeform that lives where the sun ever shines. The sun regulates almost everything on the Earth's surface, and there's really nothing artificial about that. As much as we like to believe that we don't have to bow to the whims of mother nature anymore, we still get up when the sun rises and go to bed when the sun sets (well, most of us do). I agree with Mr. Tuttle; the position of the sun counts for something, though maybe not exactly time travel. Buddy431 (talk) 00:36, 12 February 2010 (UTC)

Ok, but it would be entirely possible to use GMT entirely and just remember that local sunrise is at roughly 1:30am or something. Or simply not bother with any sort of absolute timekeeping. Choosing to handle this with clock changing is entirely a human thing. Certainly polar bears wouldn't have any sensation of going back in time if it happened to cross a couple of timezones. Farther from the poles, the dateline is a inevitable consequence of setting our watches to match the sun, but animals (Ok, fish) presumably don't think they're backwards a day when they cross it. APL (talk) 00:56, 12 February 2010 (UTC)

Yep - if we simply numbered the GMT hours 1 through 24 then you'd just need to get used to getting up at 20 and going to bed at 8 or getting up at 12 and heading to bed at 24 - or whatever times got you to work in daylight and home in time for supper. The quirk is to insist that you choose the same numbers on the clock no matter where you happen to live. We can easily set our alarm clocks for any arbitary number - you'd be used to the 'new' numbering in a week. SteveBaker (talk) 02:35, 12 February 2010 (UTC)

I would bet that other animals probably do suffer from jetlag too if they travel fast enough. I'd consider that the "traveling in time" sensation. I don't think it's a human quirk that it throws our systems off a bit to travel that rapidly. I find it quite physically disconcerting to travel many time zones, so that my body's rhythms think it should be dark and sleepy time, but everyone else thinks it is the middle of the day. I would say that puts it just beyond quirk or assigning of arbitrary numbers to phenomena. The numbers themselves are at this point arbitrary (noon no longer means when the sun is at its zenith), but what they symbolize more broadly is not (changing position of sun). --Mr.98 (talk) 02:39, 12 February 2010 (UTC)

On this theme, Richard Brautigan wrote a poem called "Land of the Rising Sun" (referenced in the title of the collection containing it, "June 30th, June 30th") after flying home from Japan; part of it reads:

I greet the sunrise of July 1st
for my Japanese friends,
wishing them a pleasant day.
The sun is on its
way.

Tokyo
June 30th again
above the Pacific
across the international date line
heading home to America
Thanks for all the answers. Appreciated.

Gravitomagnetic guage conditions

http://scitation.aip.org/getpdf/servlet/GetPDFServlet?filetype=pdf&id=AJPIAS000059000005000421000001&idtype=cvips&prog=normal

Sorry, I am not well acquainted with tensor notation, but in this paper, the author instigates a guage condition to the gravitomagnetic field in equation 10. I was wondering what this equation is, and what it symmetry it is preserving. Thank you. —Preceding unsigned comment added by 129.67.116.217 (talk) 14:41, 11 February 2010 (UTC)

For anyone who can't access the paper, equation (10) is $\partial _{\alpha }h_{\beta }^{\alpha }-\partial _{\beta }h_{\mu }^{\mu }/2=0$, where h is the h from linearized gravity. I hadn't seen this before, but it seems to be the linearized form of the harmonic coordinate condition. Like any gauge condition it has no physical significance; what it does is restrict your choice of coordinates in some way, in this case to harmonic coordinates. The electromagnetic counterpart of this is the Lorenz gauge condition, which lets you simplify $J_{\mu }=\partial _{\mu }\partial _{\alpha }A^{\alpha }-\partial ^{\beta }\partial _{\beta }A_{\mu }\,\!$ by dropping the first term on the right hand side. In the gravitational case, without the gauge condition you would have

$16\pi (T_{\mu \nu }-\eta _{\mu \nu }T/2)=\partial _{\mu }\partial _{\alpha }h_{\nu }^{\alpha }+\partial _{\nu }\partial _{\alpha }h_{\mu }^{\alpha }-\partial _{\mu }\partial _{\nu }h-\partial ^{\beta }\partial _{\beta }h_{\mu \nu }$

(I got this from linearized gravity#Derivation for the Minkowski metric and rewrote it in notation closer to the paper's; note that indices are raised and lowered with η, not g). With the harmonic gauge condition the first three terms on the right side cancel, leaving only the fourth. -- BenRG (talk) 23:10, 11 February 2010 (UTC)

Question on Photography

Need answers from people who can give me a comparison of two cameras and their performance. I googled it but the details are very specific and technical. I need explanation in lay man's terms. Essentially Im comparing Nikon D90 and Canon IXUS. We are planning our first trip to Europe, we would be traavelling from England, Scotland, France, Austria, Netherlands, Germany, Switzerland and Italy. We would be travelling to some exotic locaales which I would like to capture on my cam forever. Though I have a DVD camcorder which can click still pics I also bought another 12 MegaPixel Camera the Canon IXUS. Im not a photography expert (Im a medical doctor) and Im just picking up the camera to click decent pics that I can preserve forever as a digital copy to remind me of our European Holiday. Money isnt the issue and I could buy a Nikon D90 as well. But will the Nikon D90 be of any further use to an ameteur like me, or can I still get good pics with my Canon? —Preceding unsigned comment added by 213.130.123.12 (talk) 17:42, 11 February 2010 (UTC)

For casual pics on a holiday you don't really need a DSLR. It's more expensive and prone to damage and theft. Without investing about 15 hours learning the basics of photography you run the risk of actually taking worse images than a point-and-shoot. That said, we own the D300 and absolutely love it. Wish it took video but otherwise it's great. We went with Nikon because they are backwards compatible with our old lenses. If you feel like you might one day soon get into macro or telephoto photography or something then consider springing for the fancy ones but be ready to make a small investment of time. -Craig Pemberton 19:19, 11 February 2010 (UTC)

The biggest advantage of a DSLR for an amateur is that they take better pictures in low light, because the sensor is much larger. If that matters to you, the D90 might be worth it. Otherwise, probably not.

You mentioned megapixels, so I'll mention that you shouldn't buy based on megapixels. When they increase the pixel count without increasing the sensor size, it reduces the amount of light hitting each pixel, which increases noise, which they compensate for with aggressive digital noise reduction, which reduces the effective image resolution, leaving you with questionable overall benefit. The only reason pixel counts keep increasing is that they have to increase something to make the cameras seem better than the previous generation. This is not such a problem with DSLRs because of the larger sensor, but anything more than 5 megapixels is not much use anyway unless you plan to crop the images or make huge prints. -- BenRG (talk) 20:31, 11 February 2010 (UTC)

How many megapixels you need depends on the purpose you are going to put the photos too. If you want to make posters out of them, you need really high resolution. If you just want to view them on a computer screen, bare in mind that a typical screen resolution is 1280x800. That is about 1 megapixel. That means you won't be able to tell the difference between any resolutions greater than 1 megapixel (without zooming in, anyway). --Tango (talk) 22:17, 11 February 2010 (UTC)

Another benefit of DSLR is its distinctive "look". From what I have seen a photo taken from a DSLR will look far more natural than one with a point and shoot, and much closer to film and to your eye. (much higher dynamic range perhaps?) Also modern compact cameras often sacrifice light sensitivity for megapixels, which drives up noise and necessitating aggressive de-noising algorithms. This means high frequency signals (the fine details) are all obliterated and smeared, giving it a painting like effect. Don't rely on your DSLR to replace both your IXUS and video cam though, video recording on DSLRs aren't very practical (they are, however, good for proper, controlled, theatrical work). --antilived^{T | C | G} 06:31, 12 February 2010 (UTC)

I think it's a combination of the high dynamic range (producing nicer colors), and the fact that higher-quality sensors produce prettier noise (which gives you the DSLR "texture" on solid areas). 210.254.117.185 (talk) 12:50, 12 February 2010 (UTC)

I would add shallow depth of field to the list of contributors to the "DSLR look", due to the larger sensor and generally faster lenses. -- Coneslayer (talk) 13:18, 12 February 2010 (UTC)

Are you going during winter or summer? The current European winter storms of 2009-2010 are severe enough to hamper travel in many of those countries currently. ~AH1^(TCU) 23:47, 13 February 2010 (UTC)

Thanks guys for all the answers. Truely appreciated. I went ahead and bought the D90. I will handle the fancy big one while wifey will handle the easier to use Canon IXUS. I have a feeling my wife will end up taking better pics though ;)) we are going in spring - April May we would like to check out the bloom of Tulips in Keukenhoff gardens in Amsterdam and the snow or whatever is left behind in the Swiss Alps and the hustle and bustle of Rome, London and Paris. Thanks for the answers and I hope I have some good pictures to remember and some pleasant memories

Mains transformer with open circuit

I have a mains transformer which used to power a doorbell, but is now disconnected on the doorbell side. The other end of the transformer is still connected to the mains, 220 volts, 50Hz. How much energy is the transformer likely to be using up per year? Thanks 89.243.182.24 (talk) 18:04, 11 February 2010 (UTC)

It depends on the transformer. You'll need to actually measure the current being drawn. Doing that on something connected to the mains sounds dangerous to me (if it is connected by a regular plug, there are devices to do it, but if that were the case I'm sure you would just unplug it). If you can touch the transformer (through appropriate insulation, of course) then you can get an idea from the heat it gives off. If it is very hot, it is using lots of power. --Tango (talk) 19:03, 11 February 2010 (UTC)

Noting the heat is a fine way to get an approximate idea of the energy given off. It is even better than measuring the current, since volts times amps will be greater than actual watts for a transformer only drawing its exciting current. I expect that the energy consumed per year by a disconnected doorbell is extremely close to the consumed by a doorbell in normal use, exclusive of perhaps a lighted doorbell. A doorbell in standby mode (just energizing the transformer) draws 2.1 to 2.2 watts, for an annual electric use of 19 kilowatt hours or less. Where I live, that would cost under $1.90 (US) per year, actually much less because I have time of use billing, so the nighttime and weekend usage is very cheap. Standby electric use, page 8/16. Edison (talk) 19:47, 11 February 2010 (UTC)

A transformer with an open circuit secondary winding will just draw magnetic core magnetising current. If this is a cheap and nasty transformer (with low primary inductance i.e not many primary turns), this current may be appreciable. The power dissipated in the primary winding will, of course, be I^2 * R where R is the primary wdg resistance and I is the mag current. If we neglect core losses in the transformer, then this will be equal to the total power loss. It is definitely true to say that all the energy dissipated in the transformer will be given off as heat (maybe plus some sound), so if you can fry an egg on it, its probably worth disconnecting from the mains. —Preceding unsigned comment added by 79.76.205.40 (talk) 23:48, 12 February 2010 (UTC)

I doubt that you can fry an egg with 2.1 watts. Maybe you could keep it warm enough to hatch a chick if it were fertile, but only in a well insulated incubator. Edison (talk) 01:33, 13 February 2010 (UTC)

Bread made with yeast

According to the article Leavening agent, the yeast used to make bread has ethanol as a waste product. Although not all bread is made with yeast. 1) How much alcohol is there in yeast-made bread, when consumed fresh? 2) If your recipe says put half a teaspoon of (dried) yeast in your bread dough, but you put in say two teaspoonfuls full, what will happen? Will the extra yeast be wasted because the higher concentration of waste ethanol or carbon dioxide will simply kill it off? Does a law of diminishing return apply? Or will you get extra-fluffy bread? 3) Does yeast have a taste? When I first started using bread yeast, it seemed to have a chemical taste. But now it seems to have no taste at all. Was the early yeast batch defective, or have I habituated to the taste? Thanks 89.243.182.24 (talk) 21:28, 11 February 2010 (UTC)

Alcohol, being a volatile liquid, evaporates pretty readily. So, the process of baking evaporates almost 100% of the alcohol out of bread. Residual flavor may still be present, but I'd be surprised if there's even trace quantities of ethanol in the bread (the same is true for many other usages of alcohol in cooking, e.g. cooking wine, beer batter, and beer chicken, for example). Yeast certainly does have a taste; in addition, commercially available yeasts sometimes also contain other substances (e.g. nutrients or pH balancing chemicals) which also have a flavor. Adding too much yeast will possibly have negative consequences to flavor, and may cause undesirable rise characteristics for the dough (typically, rising too fast - but in some cases, the yeast consume the food too quickly, bloom, and die rapidly - resulting in not enough rise). Nimur (talk) 21:44, 11 February 2010 (UTC)

The amount of alcohol that "survives" cooking is probably higher than most people expect; see Cooking with alcohol#Alcohol_in_finished_food. -- Coneslayer (talk) 13:14, 12 February 2010 (UTC)

Non-sodium baking powder

Contains monocalcium phosphate and potassium bicarbonate. Are there any known health-risk associated with these ingredients please? Apart from the carbon dioxide, what chemicals are left over after use in cooking? 89.243.182.24 (talk) 21:47, 11 February 2010 (UTC)

The chemicals left over are carbon dioxide, water, potassium ions, calcium ions, and inorganic phosphates. Potassium ions can have some toxic effects at high doses (see this archive, as well as potassium cations in the body and hyperkalemia), but if your kidneys are working fine, the little amount in the baking powder won't matter. Humans get way more phosphates than they need, and usually this isn't a problem. Again, if the kidneys don't work, some problems can develop, but most people don't need to worry about this. Calcium's even less problematic, and most people could do to get more of it. If are getting too much calcium (which is unlikely), hypercalcaemia may develop (which our article suggests isn't a big deal in itself, but if you do have it you'd better see a doctor to find out what the underlying cause is), and you may increase your risk of getting kidney stones, though this is disputed. Buddy431 (talk) 02:38, 12 February 2010 (UTC)

Plotting lines of force (computer graphics)

Lines of force

A vector field

I want to plot lines of magnetic force near structures such as a solenoid. The lines show the direction of force on a tiny isolated magnetic North pole and the spacing between the lines is proportional to the magnitude of the force. It looks like the lines of force in the figure at left are hand drawn and not calculated. I can describe the vector field by calculating by integration the force vector at each pixel. But how do I go from a field of vectors to lines of force? Cuddlyable3 (talk) 22:16, 11 February 2010 (UTC)

The vector field points in the same direction as the lines of force, so you can draw a line of force by starting at any arbitrary point and adding increments of some mutiplier delta times the vector field at the current point. The only tricky thing is to get a reasonable spacing between lines of force -- the usual method is to space them evenly across some chosen line, and then let them go whither they choose from there. Looie496 (talk) 22:28, 11 February 2010 (UTC)

(ec) The brute force approach is numerical integration. You start at any arbitrary point, and move by a small increment whose direction and step size if proportional to the vector field at that point. Repeat ad naseum and you will eventually trace out a field line. You need to make the step size small though if you want to have a good approximation of coming back to where you started without numerical error getting in the way. To draw additional lines, integrate the vector field intensities while moving perpendicular to your initial point. Once your integrated intensity reaches some preset increment for your spacing factor, start a new field line at your new location. In this way the density of lines is determined by local intensity.

Of course that is all rather messy. I'm sure there is a much neater way to draw 2-D magnetic field lines, but I don't recall what it is at the moment. Something like the level sets of the z-component of the magnetic vector potential or something. Dragons flight (talk) 22:44, 11 February 2010 (UTC)

The trouble is that numerical integration may be unstable - i.e. your result if you simply apply Euler integration may not converge and your magnetic field lines will not close themselves (i.e. $\nabla B$ ≠ 0, violating Maxwell's equations). You may need some fancier integration math. In fact, this is a known problem for integration of paths along 1/r^2 vector fields - even though the solution is analytically stable, its numerical approximation by Euler method is not. We discussed this a while back but I can't find it in the archives. Nimur (talk) 23:05, 11 February 2010 (UTC)

August 9, 2009 - regarding planetary dynamics. Again, here is a nice demo of the failure to converge in even simple problems. It can be proven that the integral of certain 1/r^2 vector fields will not converge for any step-length. I'm not 100% certain if that's the case for the magnetic field setup Cuddlyable has started with, but it's an issue to be aware of. Nimur (talk) 23:10, 11 February 2010 (UTC)

For this problem I hope to develop a pixel-by-pixel algorithm similar to Bresenham's line algorithm. Cuddlyable3 (talk) 13:58, 12 February 2010 (UTC)

There is a program now at Wikimedia Commons, which performs the task of producing fieldline plots. It uses the Runge-Kutta method. See VectorFieldPlot. Geek1337 (talk) 17:33, 12 June 2010 (UTC)

Square Wave

Imagine a generator produces a square wave. Does the signal switch from no voltage to a certain voltage, or does the voltage go from positive to negative? —Preceding unsigned comment added by 173.179.59.66 (talk) 23:00, 11 February 2010 (UTC)

That is a matter of preference; it's a specification of the type of square wave. Technically, that would be called the DC bias: if the signal switches from +MAX to -MAX with 50% duty cycle, it has 0 DC bias. If it switches from 0 to +MAX, then it has MAX/2 dc bias. Nimur (talk) 23:17, 11 February 2010 (UTC)

It is unnecessary to say 50% duty cycle because that is in the definition of a square wave (as opposed to a general rectangular wave). Cuddlyable3 (talk) 23:41, 11 February 2010 (UTC)

(I was being pedantic to preempt any nitpickers, but I failed!) Nimur (talk) 00:11, 12 February 2010 (UTC)

Has anyone seen a nitpicker here? File:Ape shaking head.gif Cuddlyable3 (talk) 00:22, 12 February 2010 (UTC)

Okay cool, that makes sense. Another question: imagine an RC circuit is attached to a square-wave generator (as was the case in my signal processing lab). Would having a DC bias affect the change in current when the voltage switched from max to min? I would guess not, because the lab manual doesn't mention DC bias, but I can't see why it would be true. —Preceding unsigned comment added by 173.179.59.66 (talk) 03:09, 12 February 2010 (UTC)

You guess right. The DC bias is there "all" the time which is much longer than the time for the voltage on the capacitor C to settle.Cuddlyable3 (talk) 13:51, 12 February 2010 (UTC)

Possible to make a small quantity of harmless "smoke" for assessment of PC airflow?

Is it possible to safely produce a quantity of smoke/condensed vapour as might come from dry ice, so that it may be sucked into my PC and observed from a window in the side? Dry ice and smoke machines aren't really options. Would one of these ultrasonic foggers work without potentially damaging the computer? If the computer has been running continuously and is therefore warm, I figure that the vapour ought not to condense on anything. ----Seans Potato Business 23:47, 11 February 2010 (UTC)

Maybe try the canned smoke used for testing smoke detectors. I have no information on whether that will do anything bad to the internals of the PC. Don't use a (hot) fogging machine - the fog is made from oil, which will coat your computer. But water poured on top of dry ice will work. Ariel. (talk) 23:53, 11 February 2010 (UTC)

Maybe what you need is something called a "smoke pencil". Look it up and see if it's suitable for your purpose. --173.49.16.103 (talk) 00:34, 12 February 2010 (UTC)

Careful - some smoke pencils use glycol or gycerin (a kind of oil). I wouldn't put it in a computer, particularly near the hard drives. Ariel. (talk) 05:44, 12 February 2010 (UTC)

A stick or two of incense?--Shantavira|^{feed me} 08:59, 12 February 2010 (UTC)

Buy a cigarette. One wont harm you! —Preceding unsigned comment added by 79.76.205.40 (talk) 23:30, 12 February 2010 (UTC)

...except the one that gives you cancer. As well as heart disease, stroke, and other circulation problems. 89.240.201.172 (talk) 12:41, 15 February 2010 (UTC)

February 12

Apollo 13 and teflon

The article on Apollo 13 says:

"...Damaged Teflon insulation on the wires to the stirrer motor in oxygen tank 2 allowed them to short and ignite the insulation. The resulting fire ..."

"...power passed through the bare wires which apparently shorted, producing sparks and igniting the Teflon."

First of all teflon will not burn. Even in an oxygen atmosphere. So that can't be true.

Now, while teflon does decompose at about 350 °C, the analysis said that:

"... This raised the temperature of the heater to an estimated 1,000 °F (540 °C)."

So if the teflon was going to do anything it already did, and a spark is not going to have any additional effect.

So what actually happened? A short maybe? I have a hard time believing they had no fuses though. Ariel. (talk) 00:00, 12 February 2010 (UTC)

NASA Spacecraft Incident Investigation, Panel 1, MSC Apollo 13 Investigation Team (June 1970) report states: "The first short-circuit might have contained as much as 160 joules of energy, which is within the current-protection level of the fan circuits. Tests have shown that two orders of magnitude less energy than this is sufficient to ignite the polytetrafluoroethylene insulation on the fan circuits in the tank." Your assertions about Teflon do not match the statements made by the official accident report, or any of its followups. As far as circuit-breakers or fuses, as just cited, the energy was sufficiently low as to not trip a fuse or over-current sensor, but still enough to ignite the fire. If you're interested in details, these accident reports are a great place to start - they are publicly available in their entirety, and you can see all the ground test data, recorded telemetry and spacecraft measurements, and speculations to fill in the rest of the gaps. Some amount of uncertainty will forever plague all accident investigations, but NASA spent a lot of effort tracking down what happened here, and had the good forethought to instrument everything possible on their Apollo spacecraft to assist in diagnostics. Nimur (talk) 00:16, 12 February 2010 (UTC)

Well, that calls for a test. So I took some teflon put it in a fire on my stove - and it doesn't burn (it does decompose and glow, but it doesn't burn). Obviously they said what they said, but it doesn't make sense. Just by looking at the chemistry of teflon you can see that trying to burn it consumes energy, it doesn't release it. And if there was anything flammable there (besides the teflon), why didn't it burn when the tank was heated to 1000 °F? Ariel. (talk) 00:27, 12 February 2010 (UTC)

I wonder why you've completely ignored the previous answer by Nimur which says that Teflon was not involved? 89.243.182.24 (talk) 00:50, 12 February 2010 (UTC)

Hu? Where did he say that? If teflon was not involved that would moslty answer my question - but he didn't say that. Perhaps you don't know that polytetrafluoroethylene and teflon are the same thing. Ariel. (talk) 01:04, 12 February 2010 (UTC)

My apologies for misunderstanding. Sorry. 92.29.136.128 (talk) 15:33, 12 February 2010 (UTC)

That's right - PTFE is teflon. As far as your experiments, I hardly advocate burning teflon, or even trying - because it can release some really toxic fumes - but if you're going to test this, you need to get yourself a supercritical oxygen tank at high pressure to replicate the conditions at hand. I've said it before and I'll say it again (only lightly exaggerated) - everything burns in the presence of strong oxidizer. Do you want to look at the room-temperature chicken combustion video again? Now imagine that oxidizer at thousands of psi instead of atmospheric pressure. Strong oxidizers have very unusual, unintuitive chemical behaviors. At some point, after igniting the teflon insulation, it seems that the tank walls also ignited. It may seem "impossible" to you, but this is a major problem for spacecraft or any other oxidizer-carrying tank. When you have 100% cryo oxygen at high pressure, solid steel burns like gasoline. All it takes is a small spark. Nimur (talk) 01:08, 12 February 2010 (UTC)

You are right that I need an oxygen environment to test this properly. But you are ignoring something: teflon will not burn! Teflon is carbon burned with fluorine. Oxygen will do nothing to it. Fluorine is much more electronegative than oxygen (4 vs 3.44). Ariel. (talk) 01:14, 12 February 2010 (UTC)

(ec)It occurs to me that your argument is addressing whether the oxygen would replace fluorine, but it doesn't address whether oxygen would attack the C-C bonds. Why shouldn't (CF₂)_n react with oxygen, giving carbonyl fluoride? I'm not a chemist and this could easily be nonsense, but if it is, I'd like to know why it's nonsense. --Trovatore (talk) 01:27, 12 February 2010 (UTC)

The exothermic reaction is replacing the carbon-carbon bonds with carbon-oxygen bonds. You can do that quite easily with liquid oxygen, but generally doesn't happen spontaneously in air because the rate at which oxygen gets around the fluorine to attack the carbon backbone is too low at atmospheric pressures. Dragons flight (talk) 01:23, 12 February 2010 (UTC)

So much for my being sure teflon will not burn. Thank you (both of you). Ariel. (talk) 01:35, 12 February 2010 (UTC)

Maybe the teflon is not 100% PTFE - it may contain any number of binders, polymers, adhesives, etc. In any case, unless you have a sample of the exact material used on the Apollo 13 Service Module, (which WAS tested by NASA, and DID burn in post-accident tests), your test results are of limited use for comparison. As the accident report spells out, the teflon (or whatever the insulation was actually made of) burned for about 80 seconds; after this, the inconel began to burn (yes, that's not something we typically think of as flammable, but it did burn), and ultimately, the vacuum dome failed structurally (a combination of burnthrough and overpressure) - even though the heat was insufficient to over-pressure an intact tank, the structurally damaged tank was less sturdy and may have had a gas leak as a result of the fire at the insulator entrypoint to the tank interior. Nimur (talk) 01:19, 12 February 2010 (UTC)

Page 82 of the accident report I linked above goes through a very rigorous breakdown of every likely, possible, and unlikely burn source, ignition source, mechanical stress, etc. If you're unconvinced of the teflon burning, there are dozens of other "unlikely" options to choose from, and a few "possible" options; it will be productive to read through that report and bring yourself up to speed on what NASA concluded was possible/probable. These guys are counting the number of milli-Joules of energy available from every possible source - chemical, mechanical, propulsion, RF... in order to account for every wobble measured by the spacecraft's roll, pitch, and yaw sensors. If you're absolutely sure that teflon is chemically inert, you'd best check your numbers against the extraordinarily thorough accident report. After Apollo 13's disaster, NASA sunk a lot of man-hours in to this investigation. Nimur (talk) 01:24, 12 February 2010 (UTC)

I wasn't trying to challenge, I was trying to understand. And yes, I'm quite sure teflon is inert. I'll have to read the report when I have a bit more time. When I asked this I thought it was an error in the article, not something from the report. Ariel. (talk) 01:30, 12 February 2010 (UTC)

I hope I'm not sounding dismissive. It's good that you're scientifically skeptical. I wouldn't expect you to take NASA's word on faith alone - but the report really is a good read. It will give you some perspective about how many decimal-points-after-the-zero they investigated. For example, the spacecraft was observed from at least three independent ground observatories (optical telescopes!) who measured a brightness change corresponding to the nebulous cloud of oxygen that was vented; from this, a rate and quantity of vented oxygen were calculated. These images were compared with a 1/6th scale model which was suspended and photographed with a variety of different damage simulations. The strength of the RF signal from the high gain antenna (destroyed) was used to tweak the numbers on the roll and pitch rate and extrapolate data following the loss of telemetry. I would hope that with all this diligence, with so much investigation into miniscule details, that something as obvious as "that material wouldn't burn" has not been overlooked. If it does turn out that teflon will not burn under any such circumstances, then I would apply Occam's razor and suggest that the terminology "teflon" refers instead to "a mostly teflon-based insulator which contains other materials, that, as a whole, can burn, and burns with a measured rate confirmed by ground experiment." Nimur (talk) 01:41, 12 February 2010 (UTC)

Turn out I was wrong about teflon not burning. (See higher up in this question.) I still might read the report. Ariel. (talk) 01:47, 12 February 2010 (UTC)

Time Travel question

I was booking a flight recently and i noticed that one on of the sites i could pick a return flight that was earlier than my departing flight this seem to create paradox in that i can return before depart and prevent self from departing in the first place (Dr hursday (talk) 00:07, 12 February 2010 (UTC))

What exactly is your question? If you are wondering how this could be, it is because of time zones. For example, 12pm in the eastern US is exactly equivalent to 5pm in England - they are the same time. Things going on in New York at this time are not occurring before those in London, it is just the local expressions of time being normalized to the daylight. (I renamed the section since there has already been a time travel section recently) —Akrabbim^talk 00:16, 12 February 2010 (UTC)

Isn't the answer simply that flight booking software is stupid? Dragons flight (talk) 01:03, 12 February 2010 (UTC)

To avoid confusion, flight depart/arrive times are always printed in local time. So, I wouldn't call it stupid. It is just to avoid confusion. -- kainaw™ 01:19, 12 February 2010 (UTC)

I'm not sure what the original post is referring to, but I took it to mean that when taking a return flight on the same day as the outgoing flight, the user may be presented with flights that are genuinely earlier than the original flight arrives. I've seen this happen with day trips on regional flights (i.e. my intent is to fly into LA in the morning and fly out in the evening, but the software will happily inform me about the very cheap flights leaving LA at 6 AM even though my incoming flight doesn't get there until 9 AM.) Dragons flight (talk) 05:02, 12 February 2010 (UTC)

Oh, on second read, it seems you are right. Never mind my answer then. —Akrabbim^talk 15:09, 12 February 2010 (UTC)

Moon Question

astronaunts traveling to the moon in a spacecraft that travels at the rate of 6,260 km per hour, at this rate, how long will it take for the astronaunts to reach the moon, while assuming a straight line and average distance. —Preceding unsigned comment added by 72.85.214.110 (talk) 00:29, 12 February 2010 (UTC)

Sorry, we don't do homework questions. APL (talk) 00:57, 12 February 2010 (UTC)

Two options:

• • find out how far the Moon is away (look it up; try Moon) and find out (look it up; your math(s) teacher may be available) how to calculate a time from a velocity over a given distance.
  • Give the answer "about 162 years" (then complain about the complete uselessness of Wikipedia as a research tool).

By the way, it's "astronauts". An astronaunt is your mother's cosmic sister. Tonywalton ^Talk 02:09, 12 February 2010 (UTC)

Well, if the Moon were 12,520 km away (2 X 6,260) it would take about 2 hours to get there, assuming we didn't stop too many times at rest areas for peanut butter and jelly sandwiches. How far away is the Moon? Answer: I don't know. But if we could find out how far away the Moon is, we could divide that distance by 6,260 (assuming that distance were expressed in units of kilometers). The answer (to that calculation) will be the number of hours (possibly including a fraction of an hour) of travel time. What we really need to know is how many kilometers the Moon is away as an average distance. Bus stop (talk) 02:25, 12 February 2010 (UTC)

While we're at it, assuming a straight line and constant velocity for travel from the earth to the moon is a bad approximation - even if it is the homework assignment. Orbit makes such a trajectory very difficult - not impossible, but very difficult to achieve in practice. Nimur (talk) 04:07, 12 February 2010 (UTC)

Don't let these smart people and their sandwiches distract you. You will get the answer by dividing one number by another number, and you already have one of the numbers. Good luck. Cuddlyable3 (talk) 13:35, 12 February 2010 (UTC)

It will depend on where you are. If you are sitting on the launchpad, then you would never get there, and if you were 2 miles from the moon, you will reach it momentarily. Even if we wanted to answer this HW question for you, we don't have enough information. Googlemeister (talk) 13:59, 12 February 2010 (UTC)

The indicated speed would be under the Earth's escape velocity assuming that the spacecraft is travelling at a near-constant velocity, and you'd never get off the Earth. To escape from the Earth's gravity requires a speed of over 40,000 km/h. ~AH1^(TCU) 23:44, 13 February 2010 (UTC)

No, the OP specified the velocity, not that it was a ballistic trajectory after a rocket motor had shut off. Perhaps God or Xenu or Lex Luthor is maintaining the spacecraft at a constant velocity from the beginning to the end of the voyage. The article Moon confuses the issue. Did the astronaunts depart from the center of the Earth to go to the center of the Moon? Then they have to travel 384,403 km. If they left from the surface of the Earth to travel to the surface of the Moon, then the distance will be decreased by the mean radius of the Earth (6,371 km) and the mean radius of the Moon (1737 km). If they departed from the highest or lowest point on the Earth's surface and arrived at the highest or lowest point on the Moon's surface, that would require a small correction. Edison (talk) 05:03, 14 February 2010 (UTC)

Capacitors

Yes, this is a homework question, but I have no idea where to even begin. Can someone at least point me in the right direction and give me a few useful equations please?

Two 13.0 cm -diameter electrodes 0.59 cm apart form a parallel-plate capacitor. The electrodes are attached by metal wires to the terminals of a 15 V battery. What is the charge on each electrode while the capacitor is attached to the battery? --24.207.225.13 (talk) 01:26, 12 February 2010 (UTC)

This is nothing that Capacitor doesn't answer. It really isn't all that complicated, so giving you an equation directly would practically be akin to doing the problem for you. —Akrabbim^talk 01:29, 12 February 2010 (UTC)

First, you need to figure out the capacitance of the capacitor from its geometry and the dielectric constant of the material separating the plates. In a steady state, the voltage across the terminals of the capacitor must equal that of the battery—that's how you get zero current flow in a steady state. With that knowledge, you can use the relationship between stored charge and voltage in a capacitor to work out the answer you're looking for. --173.49.16.103 (talk) 02:05, 12 February 2010 (UTC)

You will certainly be expected to assume for simplicity that the area of the plates is so much larger than the space between them that edge effects can be ignored. Treat the electrical field as though it is uniform over the whole plate area. Cuddlyable3 (talk) 13:30, 12 February 2010 (UTC)

The charge on one electrode is minus the charge on the other electrode.. —Preceding unsigned comment added by 79.76.205.40 (talk) 23:33, 12 February 2010 (UTC)

What tickles my fancy is what happens to the voltage across the capacitor if the battery is disconnected after charging the capacitor, and the spacing between the plates is changed to 10 times or 1/10 the original spacing. Quite amazing, and there are demo devices which do this. (Assume charge is conserved, since there is no path for current between the plates). Edison (talk) 04:50, 14 February 2010 (UTC)

Yes, this appears to be the principle of operation of the condenser microphone —Preceding unsigned comment added by 79.76.197.2 (talk) 11:42, 14 February 2010 (UTC)

It is also the principle of the Electrophorus which could tickle Edison's fancy. Cuddlyable3 (talk) 23:26, 14 February 2010 (UTC)

mic

i wanna know how does a mic work? or just tell me how to change sond energy into electrical energy.? does mic contains piso crystle( a crystal that can change pressure into electricity)? cant this idea be used to change sound energy aroun' us into electrical energy- put mics on the muffer tip of car or infront of horn. ^{- answer my first question dont start telling me about piso crystle! i dont want to know abot it now}-§§§§§§§

Have you checked microphone? -- kainaw™ 03:25, 12 February 2010 (UTC)

Also, microphones do not create energy. They alter an electrical signal according to sound waves. -- kainaw™ 03:27, 12 February 2010 (UTC)

Some microphones use piezoelectric crystals, but others use a solenoid or a mass-spring system, and still others use a capacitor diaphragm. Each of these has advantages and disadvantages; each works according to a different principle; but in general the idea is to convert pressure changes in the air (sound waves) into a time-varying electric signal. Most microphones also need an amplifier to boost and condition that electric signal for later use and eventual playback. Nimur (talk) 04:11, 12 February 2010 (UTC)

Kainaw: Some microphones do create electricity. You can use a mic to generate electricity from the sound around you - but not very much. It's not enough to be worth it. If you scream into headphones you can measure electricity in the jack. Ariel. (talk) 04:22, 12 February 2010 (UTC)

Yes, they all create electricity, but they do not create energy. Kainaw was referring to conservation of energy; it's unlikely that a microphone could harness waste energy from a car's exhaust or air-drag in any meaningful or productive way. Nimur (talk) 04:40, 12 February 2010 (UTC)

Mics do harness energy, i.e. convert energy from sound to electricity. I assumed Kainaw was saying mics only vary resistance (meaning they must be externally powered), and I was saying some can generate their own signal. Maybe that's not what he was saying, sorry if I misunderstood him.

Anyway, the energy they convert is in tiny amounts. Mainly because the mic is very small. Wave power is exactly the same thing, except with water instead of air. Ariel. (talk) 05:35, 12 February 2010 (UTC)

See also Carbon microphone which works on the principle of slightly varying resistance, so requiring a current to be supplied to them to work. —220.101.28.25 (talk) 07:10, 12 February 2010 (UTC)

In every case a microphone absorbs some energy from the sound. Yes, microphones could extract tiny amounts of power (energy) from noisy parts of cars. The power would be tiny but it could be maximised if the microphone resonated at a frequency related to the engine r.p.m. Similar attempts are made to extract power from a radio antenna. Cuddlyable3 (talk) 13:23, 12 February 2010 (UTC)

The complete answer here is that yes, it should be possible to harness energy from sound as you describe...and yes, with some (but not all) kinds of microphone, you could do that. However, the amount of energy would be so amazingly tiny - and the efficiency with which it could be converted would be so poor that it would certainly not be worth the effort to do so. There just isn't much energy there to be had in the first place. SteveBaker (talk) 17:13, 12 February 2010 (UTC)

Thomas Edison in the 1870's built a device called the "Phonomotor," which collected sound energy in a horn, cause a diaphragm to vibrate, used the vibration to operate a fine gear train via a ratchet to create rotary motion. It got some press around the world, with humorous comments about the power of a mother-in-law's voice to bore a hole in a piece of wood, but had no practical application. (Maybe people lost interest because it was a "boring machine"). If you had a device which converted sound to electricity with 100% efficiency, and it had a 1 square meter collector, it would require 138dB (deafeningly loud) to power a 60 watt light bulb, per [2], which says that would require the combined voices of a million people. Edison (talk) 03:01, 13 February 2010 (UTC)

Strategically placed Phonomotor's could convert noise pol-pol-pol-pollution into useful energy. Cuddlyable3 (talk) 18:08, 13 February 2010 (UTC)

Sunscreen and acne

Does sunscreen increase acne? My dermatologist told me not to use sunscreen and he told it increase acne. Don't want to seek any medical advice, just want to know the scientific basis behind this claim and the physiological mechanism through which sunscreen increases acne. --Qoklp (talk) 04:09, 12 February 2010 (UTC)

Oil-based sunscreens can increase acne. It isn't complicated. Putting oil on your face can increase acne if you are already prone to it. There are many oil-free sunscreens that will have a noticeably less increase in acne compared to the oil-based ones. How your specific face will react to any specific sunscreen will not be known until you try it. -- kainaw™ 04:13, 12 February 2010 (UTC)

The term to look for is "noncomedogenic". (Hmm, it looks like we don't have that page yet. Okay, try Comedogenic instead.) -- 174.21.247.23 (talk) 04:17, 12 February 2010 (UTC)

Hmm, Comedogenic redirects to Acne cosmetica. Perhaps Noncomedogenic and Non-comedogenic should as well. 58.147.58.179 (talk) 04:42, 12 February 2010 (UTC)

Dr Kevorkian

where can i watch i tried google when he videotaped himself performing a lethal injection on some old dude on 60 Minutes, he was charged and convicted with murder in the second degree. —Preceding unsigned comment added by 67.246.254.35 (talk) 05:24, 12 February 2010 (UTC)

The 60 Minutes video and reactions from the MDA and in comedy(1), comedy(2) Cuddlyable3 (talk) 13:10, 12 February 2010 (UTC)

Scar removal/ Erase Scars

Hi,not medical advice, but is it absolutely impossible to remove a scar.

A while ago, about ten years back, I went to touch a pie but the filling got stuck on my hand and when my hand went back as a natural jerk reaction the pie filling stuck to it and was flung on my face, leaving a small scar.

I was wondering if there was anyway to remove a scar in the future or will it be impossible forever.

Also, I what causes scars to be scars and normal skin doesn't form after injury.

Scar should contain an explanation for why you get scars and not normal skin. There are certainly methods to reduce scarring, but I believe it's on a case-by-case basis - your doctor will certainly be able to give you the information you need. Vimescarrot (talk) 06:46, 12 February 2010 (UTC)

You already asked about removed on on the 8th. Was there are problem with TenOfAllTrade's answer? You're certainly not going to get anyone here to comment on your specific case. APL (talk) 08:09, 12 February 2010 (UTC)

About burden of proof and scientific method

Burden of proof#Burden of proof in epistemology and scientific methodology says that it is "the responsibility of the person who is making the bold claim to prove it".

On the other hand, Scientific method#Introduction to scientific method says that "Note that this method can never absolutely verify (prove the truth of) 2. It can only falsify 2.[8] (This is what Einstein meant when he said "No amount of experimentation can ever prove me right; a single experiment can prove me wrong."[9])"

It seems to me that there is a mismatch between two. Like sushi (talk) 08:22, 12 February 2010 (UTC)

Your confusion stems from two different interpretations of the word "proof". In the first sentence, it doesn't mean "proof" in the absolute, mathematical sense, but rather "provide sufficient evidence for his claim". On the other hand, a single experiment can indeed disprove (in the absolute mathematical sense) a hypothesis. (note that theories that have been proven wrong in this way do not always lose their usefulness, not if they were good theories that had lots of "proof" in the first place, classical physics being the prime example of this) —Preceding unsigned comment added by 157.193.173.205 (talk) 08:31, 12 February 2010 (UTC)

Thank you. Then it is that the defender must provide enough evidence, while the accuser must disprove it (in the absplute sense). Like sushi (talk) 09:00, 12 February 2010 (UTC)

You might also be interested to know that when a "single experiment" appeared to prove Einstein wrong (I think it was some measurement of the transit of Mercury, or something), he wrote, and I quote loosely from memory: "I can't understand why some people are so impressed by these measurements and figures; the elegance of the theory is enough to convince me it must be right." And of course, we now know Einstein was right and the measurement was in some way wrong, but at the time it was a serious result that a lot of serious scientists thought meant serious trouble for relativity. That is to say, it's never really very clear-cut what constitutes a disproof and what can be simply brushed aside, and many scientific theories have been abandoned without ever being "absolutely" disproved. There are also any number of other possible complications that violate supposedly sacrosanct principles of scientific inquiry: sometimes an experiment is so expensive it can't be freely reproduced elsewhere (detecting neutrinos with a giant underground tank); sometimes the mathematics is so dense that even many experts get it wrong or just take it on faith (as in the early days of general relativity, and possibly string theory today?), etc. etc. All in all: any very broad generalization in the philosophy of science should be taken with a pinch of salt. But they can still serve as useful guides.--Rallette (talk) 10:01, 12 February 2010 (UTC)

(edit conflict) When someone makes a claim to truth, it is their responsibility to offer some evidence or justification that makes the claim seem reasonable - that is the 'burden of proof' in the first case. it doesn't mean they have to 'definitively' prove it (in fact, it's impossible to definitively prove anything outside of pure mathematics), it just means they have to do something more than say it's true, so that other people might be convinced by it. --Ludwigs2 10:06, 12 February 2010 (UTC)

"a pinch of salt", and "so that other people might be convinced by it".

How can I become able to say so? I seem to have to learn a lot to convince other people, and the amount of salt is so difficult (I don't still have something to convince other people of, in the first place). Well, it is just a useless complaint, never mind!

Like sushi (talk) 10:45, 12 February 2010 (UTC)

Like sushi, yours is not a useless complaint. "How can I be able to say (that the person has provided sufficient evidence for his claim)" is a question that deserves an answer. In order of priority the claim should 1) be demonstrable by repeatable experiments with unambiguous interpretations, 2) have an impact on the current theories in an explicable way, 3) add to the total understanding of the field and 4) achieve this in a way that is "elegant" in the sense of Occam's razor. Cuddlyable3 (talk) 12:42, 12 February 2010 (UTC)

Rallette's response is absolutely excellent. These are broad guidelines that serve to shape some kinds of activity and belief, but are more often applied in retrospect than they are at the time. We tell very nice compact histories of science in which a single experiment disproves a century's worth of theory, but this is the exception, not the rule, and even when that does happen, it can take a long, long time for everybody to agree that is what happened. Example: August Weismann cuts the tails off rats, disproves Lamarckism, etc. Problem: True Lamarckians would never have thought that what Weismann was doing actually violates Lamarckism—it only falsifies a very straw-man version of the theory. Example: John Snow shows with a single map that cholera is obviously water-borne. Problem: Almost no doctors actually believed that Snow's experiment was correct, and after a century of coming up with other complicated explanations for cholera (misasma, morality, etc.), they dismissed Snow's theory and evidence very easily. It took a good generation for the turn-over in thinking about cholera to happen, great evidence be damned.

All of which brings up the quotation of Max Planck: "A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it." None of which says that falsification is incorrect or that the burden of proof shouldn't lie with those making the stronger claim. But in practice, disagreement about whether something has truly be falsified, and these question of who is making the stronger claim, are both somewhat subjective properties. Scientists are not pure logic in vats—they are human beings, organized into professional communities, and bear all of the handicaps of psychology and sociology just like the rest of us. --Mr.98 (talk) 13:22, 12 February 2010 (UTC)

I agree that there are two meanings of the word 'proof' being used here. If you have a totally wild and crazy hypothesis - then it is without doubt your reponsibility to provide enough proof to convince other people to take you seriously. So, for example, if you claim that you can teleport objects across the room with the power of thought alone - then serious scientists are not even going to bother to talk to you until you can provide a pretty serious demonstration of that happening. But if you are an established astronomer and you claim to have found yet another extrasolar planet orbiting some distant star - then there would be only a small amount of skepticism and you could probably get other astronomers to double-check your results so you can publish your findings in a serious journal and have them come to be accepted as fact. A better way to think about this is "Extraordinary claims require extraordinary evidence". The more outrageous the thing you're claiming, the harder it is to get the attention of others and the better the evidence you have to provide. But this doesn't have to be mathematically perfect proof. If you walk into the office of a serious scientist and demonstrate your ability to teleport a pencil from one end of his desk to another - then that's probably enough proof to get him interested enough to do a controlled experiment and either prove or disprove it to a higher standard.

A practical example was the case of the Mpemba effect - which is the very odd finding that cold water freezes more SLOWLY than warm water. This is a pretty outrageous claim - and worse still, it was made by a high school student in Tanzania. It took six years of work to just to get that result published - and it's still not widely accepted.

On the other side though - it is true that there is very rarely absolute proof of anything. Einstein was right - it would only take one scientist to demonstrate how to make a golfball travel 10% faster than the speed of light to demolish relativity theory overnight. However, each experiment that confirms relativity pushes it asymptotically towards complete acceptance. But this does happen. Prior to Einstein, everyone assumed that Newton's centuries old laws of motion were correct - but one experiment which established the constant speed of light (plus a good deal of clever thinking on behalf of Einstein) was all it took to demolish it utterly in a matter of just a few years. Newton's laws were never proved conclusively - they never could be because at any time, one more experiment could bust them wide open.

However, what gives us confidence in well-established laws (Thermodynamics, Evolution, etc) is that if they are wrong - then just like Newton's laws of motion, they can only be a little bit wrong over the domain that they've been tested. Maybe thermodynamics breaks down inside a black hole - maybe evolution turns out not to be true amongst yet-to-be-discovered life under the ice of Europa - but that doesn't make them useless. Sure, Newton was wrong - but he was sufficiently right to allow almost all of modern technology to successfully rely on his laws.

SteveBaker (talk) 17:05, 12 February 2010 (UTC)

Strictly speaking, a golf ball traveling at 1.1c would not disprove relativity (it requires infinite energy to accelerate a massive particle from sub-light speed to the speed of light, but there is no instantly obvious reason it couldn't always have gone faster than the speed of light). But it would have other highly problematic consequences, assuming relativity still worked. The one you seem to be hung up on is that the usual formulas would imply that its rest mass was an imaginary number (assuming its energy is a real number) — that one doesn't much bother me; the derivations for the energy-mass relationship don't go through above the speed of light anyway, or at least none of the ones I've seen go through, so maybe it's just a different equation in that regime.

The more serious consequence is that if you could modify the behavior of such golf balls, and detect the effect of someone else's modification, and assuming relativity were still true (so that all this worked the same in every reference frame), then you could send signals back in time, as per the tachyonic antitelephone. Then you get the grandfather paradox and all that. These are seriously counterintuitive consequences. But I would not take them as "disproving relativity" in and of themselves. --Trovatore (talk) 05:03, 13 February 2010 (UTC)

Theory of justification might be worth a look. Quite a lot of people in this thread are being justificationists, I think, and Karl Popper would probably disapprove. I'm never very at ease with trying to guess what he would say, but he might propose a burden of showing how your new theory could be disproved if it was wrong, rather than a burden of proof. This is certainly the case in Occam's razor situations like the celestial teapot, where the problem with theory is not a lack of proof but a lack of testability. Epistemology is a work in progress, anyway, so it's not all that surprising if wikipedia articles contradict each other. 213.122.51.100 (talk) 04:41, 13 February 2010 (UTC)

Also, it is worth noting that epistemologically speaking, people often arrive at "truths" through different modes of understanding. On a personal level, there are certainly experiential truths, that is stuff that you know to be true because you personally expienced or witnessed them. But there are also truths "by proxy", or "by authority", that is truths we personally accept as true because we trust the person who asserts them. Most of us never performed or witnessed the experiments which supported "General Relativity", but on a personal level we accept them as true because we place trust in the source of those facts, either the person who taught us about them or the books they were recorded in, or whatever.

Take the example of crossing a street. Most people accept that there is a proper method of crossing the street (The Truth) which is to, say, cross at a crosswalk, look both ways, obey the traffic signals, etc. etc. However, many people may arrive at this personal truth by differing means:

• They were taught to do so by their parents
• They have read and obey local traffic laws
• They were hit by a car when they didn't obey the rules

Each person constructs their own truth-seeking aparatus, and as such, sets their own requirements for "proof" of a true fact. The same person often sets differing standards for different modes as well (for example, seperating scientific truths from behavioral truths or moral truths or religious truths or legal truths), each having their own standards of "proof". --Jayron32 20:49, 14 February 2010 (UTC)

Popping ears

If you inhale, block your nostrils and wait, there is a sensation of 'popping' from both ears, not necessarily simultaneously. What is happening please? If, in fact, one ear does not 'pop', over a long period, does that indicate a blockage? How does that relate to hearing ability? With many thanks. —Preceding unsigned comment added by 93.24.238.214 (talk) 08:39, 12 February 2010 (UTC)

Ears pop to equalize the pressure between the outside of the ear and the inner ear. Unequal pressure can potentially lead to damage in the ear, along with general discomfort, so ear popping is the body's way of resolving the pressure difference before it becomes an issue. Colds can cause ear popping because mucus secretions block the Eustachian tubes, making it difficult to normalize the pressure. When someone with a cold blows his or her nose, clearing the sinuses of mucus, the Eustachian tubes can open up so that the pressure will normalize and the ears pop. Incidentally, it is a very bad idea to pinch the nose shut and blow hard to pop ears if they are uncomfortable, because this can cause mucus to blow up the Eustachian tubes, causing an infection in the ear. Source: Wisegeek. -^Avicenna_sis @ 09:02, 12 February 2010 (UTC)

See also Valsalva maneuver. TenOfAllTrades(talk) 14:48, 12 February 2010 (UTC)

--79.173.235.183 (talk) 18:14, 12 February 2010 (UTC)

Civil Engineers Only .....reinforced concrete column behavior under load

we all know how to reinforce a concrete column by arranging steel bars around the perimeter and confining steel bars using stirupps ..the question is how steel work in columns ... i tried to figure it out and this is the result :

when start loading the column it respond by getting short,by other words its began to shrink and as we all know strain could'nt happen in one direction (poissons ratio) so the concrete must expand horizontally in order to allow vertical shortening ... so that in order to stop vertical strain we have to prevent lateral strain .

now let's think about it ... steel bars around the perimeter can resist compression loads alot more than concrete which leeds to the same relation between strain value for both materials ... according to that steel will held the concrete around it in position depending on adhesion between concrete and steel forming something like a fence wich can hold the concrete within as the load increased the concrete in the middle is subjected to a big load and is forcing the fence to deform so the inner concrete can expand laterally .... here where stirupps can work .... it transfer the lateral deforming in the fence into tensile strain in the stirupps so it helds the fence in position preventing lateral strain which preventing vertical strain which in the result will prevent the column to collapse ....

will ... the question is ... am i right ...? and anthor question why is there a maximum reinforcement ratio for column...? --Mjaafreh2008 (talk) 09:58, 12 February 2010 (UTC)

Remember that concrete is strong under compression. The steel reinforcement is there to provide strength under tension. Astronaut (talk) 15:16, 12 February 2010 (UTC)

Incidentally: Insisting that a question is only answered by Civil Engineers pretty much guarantees you'd get no answers because the odds of there being such people here on any given day is small. However, the questions you are asking could be answered by almost anyone with an engineering background. SteveBaker (talk) 16:29, 12 February 2010 (UTC)

Maybe he just wants the engineers to be well behaved? Googlemeister (talk) 21:35, 12 February 2010 (UTC)

Hi there .... I look for the answer in other places , and in some civil eng sites without any good .... I'am already thankful for any help i can get .--79.173.235.183 (talk) 18:14, 12 February 2010 (UTC)

Could be something to do with the shear strength of concrete! —Preceding unsigned comment added by 79.76.205.40 (talk) 00:57, 13 February 2010 (UTC)

Does a flame cast a shadow?

Well, does it? It's kinda hard to tell because the flame itself generates a lot of light that would tend to light up any area that it would shadow - but just how opaque is the flame itself to (say) sunlight? SteveBaker (talk) 16:31, 12 February 2010 (UTC)

Well it depends on the relative brightness of the two light sources. I have certainly seen the shadow of a candle flame cast by bright sunlight, but it's a kind of translucent shadow. It's very easy to check this out for yourself if the sun is shining and you have a candle.--Shantavira|^{feed me} 16:46, 12 February 2010 (UTC)

I guess the question here is this: does flame absorb light? This is an excellent question, and I suspect that the answer is yes, but this is pretty far out of my comfort zone. Is there a plasma physicist in the house? – ClockworkSoul 16:54, 12 February 2010 (UTC)

A yellow flame consists of glowing soot. Soot is black. Go figure. Cuddlyable3 (talk) 16:57, 12 February 2010 (UTC)

I've observed the "shadow" from a flame as well. I assumed it was not from the flame blocking light, but from the hot gas inside the flame acting as a lens, redirecting the light. Whatever portion of light is not absorbed should certainly be refracted. If you take a flame into bright sunlight, look for a brighter fringe of light around the flame's "shadow." 146.186.131.95 (talk) 17:05, 12 February 2010 (UTC)

A fundamental law of physics says that probabilities of absorption and emission of a photon are strictly related. Anything that can emit light can also absorb light at the same wavelengths. Anything that can absorb light can also emit light at the same wavelengths. Flame -- hot mixture of chemically reacting gases -- emits light (mostly in infrared and in visible range), therefore it also absorbs visible and infrared light. So yes, any flame can cast a shadow. It may not always easy to technically visualize and record that shadow, though; but it can always be done in principle. Steve certainly knows this, but for the general audience it is important to make the science clear first. Now, if you want to visualize the shadow of the flame, you can take a candle out into the sunlight - it will make a clear shadow of the flame. Some of that shadow will be because of the refraction rather than absorption, though. --Dr Dima (talk) 18:07, 12 February 2010 (UTC)

Steve, you should be ashamed of yourself... get a candle and a torch and find out for yourself... (The answer, however, is "yes" - a flame is a plasma, meaning there are lots of free electrons floating around. Those electrons will absorb light.) --Tango (talk) 20:30, 12 February 2010 (UTC)

It does depend if the flame is sooty and yellow versus premixed and blue so I think it is the soot not the electrons which do most of the absortion. Certainly if you pick the right laser there is enough transparency in premixed flames for laser tomography. Flames also have a massive temp difference therefore density difference across them. I have seen the flame and violin demo a few times (sound has a huge impact on flame structure) and even tried probing flames ultrasonically. The violin one you could do in a school lab with a big floppy bunsen I reckon. --BozMo talk 20:48, 12 February 2010 (UTC)

I don't have a candle anywhere in the house...but in any case, I was hoping perhaps for some kind of quantitative feel for how much a flame is likely to attenuate the light passing through it...sooty yellow and unsooty blue flames are both interesting. FWIW, I'm doing some computer graphics fires and things like rocket exhausts and trying to understand at what 'density' to draw the shadow of a flame (if at all). If it were possible to estimate the ratio of light emitted by the flame to that passing transparently through it, I could make a call as to when the shadow would be negligably visible and save a bunch of computer time by not drawing it when it's too tenuous to be noticable. The smoke produced by the flame is a different matter - that obviously does cast a shadow - and I have that much nailed. I just can't think of any source that tells me the transmissivity of a flame...and it's insanely difficult to measure (even assuming I could set a building on fire to get a nice BIG flame to measure)! SteveBaker (talk) 05:15, 13 February 2010 (UTC)

You can have the entire range of absorption, from fully opaque flame of poorly burning oil to practically invisible flame of pure ethanol. As you said, experiment is crazy hard, but it may be the only option. Take a green laser pointer and try to measure if something comes through. There is not much green in the flame (unless you add some copper compound to the fuel), but the eye is most sensitive to the green; so shadow for green is like shadow for white. You will need to find a bandpass filter for your photovoltaic cell that blocks most light from the flame but allows the green to pass. And a cell big enough to compensate for the refraction of light by flame. I never tried this, so I'm not sure it will work at all. --Dr Dima (talk) 06:11, 13 February 2010 (UTC)

Since eclipsing binary stars cause a dimming of the overall brightness of the system when one star passes in front of the other, I'd say that the opacity of fire and plasma are enough as to cause a "shadow" in the way that it blocks some of the light from the other light source. ~AH1^(TCU) 23:34, 13 February 2010 (UTC)

thoracentesis

As a practicing general surgeon, I am asked to do thoracentesis regularly. I go for a complete drainage of the pleural space, removing all the fluid I can, safely. This is often amounts over the 1 liter your article notes. This causes consternation among my patients. Your article does not describe the cough reflex associated with reinflation of the alveoli (as a newborn does during the immediate inflation of the lungs (wah wah cough cough, waaahhh), a native, protective reflex to airbreathers, nor does it mention the pleuritic pain associated with reapproximation of the separated pleural surfaces. It is that second pain that caused the patient most recent in my memory to look at your article and come in all hot and bothered. The chest x-ray showed persistent clearing of the pleural effusion with no infiltration or pneumothorax. Exam did show decreased inspiratory effort (pain) and slight rb. I ask that your editors make some mild changes. That business of "removing more than 1 liter at a time associated with complications" needs modifier that not removing all means having to repeat the procedure, also at increased risk. —Preceding unsigned comment added by Tlfmd (talk • contribs) 17:41, 12 February 2010 (UTC)

We have a guideline here called Be Bold, which says: Go ahead and make the changes yourself! You're the expert. Click "edit this page" at the top of any article and go ahead and make any changes that are needed. Normally we want "inline citations" on every claim. Formally it is preferred that articles have inline citations from top to bottom, but in practice on Wikipedia this is rare — though it's needed if the article is to be considered high enough quality to be a "Good Article" or a "Featured Article". Comet Tuttle (talk) 17:52, 12 February 2010 (UTC)

I'd just like to add a note that Wikipedia Talk:WikiProject Medicine (aka WT:MED) is an excellent place to bring up concerns of this sort. Looie496 (talk) 19:03, 12 February 2010 (UTC)

Tlfmd, thanks for pointing that out. Although I'm surprised that you, as a general surgeon, are performing thoracentesis. My experience (in the UK) is that general surgeons do not deal with pleural effusions (indeed they shouldn't deal with pleural effusions). Axl ¤ [Talk] 09:43, 13 February 2010 (UTC)

From the British Thoracic Society guidelines: "The amount of fluid evacuated will be guided by patient symptoms (cough, chest discomfort) and should be limited to 1–1.5 litres." "Large pleural effusions should be drained in a controlled fashion to reduce the risk of re-expansion pulmonary oedema." Axl ¤ [Talk] 09:54, 13 February 2010 (UTC)

ant poison methanol

im allergic to boric acid i have a ant problem can i use methanol to kill them i heard it tastes sweet i dont want to use any regular ant poison —Preceding unsigned comment added by Thekiller35789 (talk • contribs) 20:18, 12 February 2010 (UTC)

can i get an answer please i dont want to call an exterminator —Preceding unsigned comment added by Thekiller35789 (talk • contribs) 21:09, 12 February 2010 (UTC)

Methanol? As in the poisonous alcohol (AKA wood alcohol)? Do you mean menthol maybe? Either way, get some bait traps instead. Or remove the food source. Ants are attracted to food. You can use tons of traps and poison and they'll keep coming back till you get rid of the food source. Ariel. (talk) 21:45, 12 February 2010 (UTC)

yes i mean Methanol, As in the poisonous alcohol. i already removed the food source. im not going to use bait traps i want to use methanol will it work , is it toxic to ants? and will they eat it? —Preceding unsigned comment added by Thekiller35789 (talk • contribs) 21:52, 12 February 2010 (UTC)

Perhaps you'd like to tell us why you think it might be poisonous to ants? And by the way, demanding an answer from the volunteers who frequent this desk fifty-one minutes after you originally posed the question is not a good strategy for encouraging people to answer you. --ColinFine (talk) 23:12, 12 February 2010 (UTC)

Please sign your posts. It's the sweet thing to do. Cuddlyable3 (talk) 23:21, 12 February 2010 (UTC)

The practicality of methanol will be limited because it is volatile and will quickly evaporate. I think it is highly unlikely that they will eat it anyway. If you are insistent on using methanol, your best results will come from simply drowning them in it. (But don't inhale the vapors due to the toxicity!) —Preceding unsigned comment added by 72.94.164.21 (talk) 23:24, 12 February 2010 (UTC)

WILL THEY EAT IT —Preceding unsigned comment added by Thekiller35789 (talk • contribs) 23:39, 12 February 2010 (UTC)

Orange oil and neem oil are far safer than methanol, and may work better, too. Of the two oils, orange oil smells much better :) . However, you will absolutely need to inquire if any one of those oils are recommended for use against ant infestations. I do not and can not give you an advice what to use; but I strongly suggest you do NOT use methanol indoors. --Dr Dima (talk) 23:49, 12 February 2010 (UTC)

I second that. Methanol is not only highly toxic, but its volatility is troublesome for this application -- its vapor pressure is high enough to allow it to give off hazardous toxic vapors (and to evaporate too quickly to have any effect on ants), but low enough to allow traces of the stuff to persist for a long time. (I know this firsthand, we use methanol at the refinery to scrub sulfur out of the flue gases, and we actually have to wear gas masks any time we're working with the stuff!) Worse, it's also water-soluble and can soak into the soil, so using it anywhere near water supplies or even household plants (or even on your lawn) is a very bad idea (quite apart from the fact that it's a violation of at least three EPA and OSHA regulations). Also, methanol is highly flammable -- not quite as flammable as gasoline, but pretty close -- so you should be careful using it around electrical equipment, because it's particularly prone to ignition by sparks. My advice to you and to everyone else is, don't screw around with methanol unless you REALLY know what you're doing. And last but not least, it prob'ly won't even work against ants because (1) it will evaporate too quickly, and (2) its toxicity to humans is due to it oxidizing to formic acid, which ants make naturally and therefore have immunity to it. Oh, and did I mention that it could damage furniture and wood floors by dissolving the lacquer coating? 24.23.197.43 (talk) 00:29, 13 February 2010 (UTC)

Firstly, even if they are inside your house - they don't live there. If you can wipe out the nest (which is outdoors someplace) then within a day or two, there won't be any more ants indoors. Knowing that gives you more treatment options. Sure, you're allergic to boric acid - but if you wear a mask and gloves, you can apply it outdoors without coming into contact with it. There are many other options too. I had good luck with vicious Texas fire ants by kicking the top off of the nest and pouring a gallon of boiling water mixed with washing up liquid (to help it get into the small burrows). Merely warm water won't do. And, yes, you need to be sure that all of your food is in proper containers or they'll come back. SteveBaker (talk) 02:52, 13 February 2010 (UTC)

i dont want advice on other things to use just will methanol kill them —Preceding unsigned comment added by Thekiller35789 (talk • contribs) 04:49, 13 February 2010 (UTC)

It seems like you already got a clear "NO!" on that - we're just trying to offer alternatives that you may not have thought of. SteveBaker (talk) 05:05, 13 February 2010 (UTC)

or, as pointed out above, the answer could be "yes" if you pick up the ants and hold them under the surface of your methanol. Plain water would be safer but would take longer. Seriously, though, take advice and look for alternatives. We think that methanol might do you more harm than real ant killer, despite your allergy. Dbfirs 22:14, 13 February 2010 (UTC)

If methanol vapor were so deadly, I doubt Sterno would be so widely used in chafing dishes or alcohol lamps supplied in chemistry sets. Just don't try to drink it. Edison (talk) 04:44, 14 February 2010 (UTC)

In the days before photocopiers, methanol was widely used in schools for "spirit duplicators" (no, they worked using merhanol spirit, they didn't duplicate spirits in any form!). Good ventilation was advised, but the vapour was not considered dangerous for occasional use. As pointed out above, because methanol evaporates rapidly, it would be necessary to use a large quantity to maintain a supply for the ants, and, even if it did work, this might be dangerous to humans with prolonged breathing of the vapour in a confined space. Perhaps a greater problem would be the fire risk in leaving large quantities of a flammable liquid lying around in open containers. Dbfirs 08:01, 14 February 2010 (UTC)

Human field of view

How many degrees of view can humans see horizontally and vertically? 92.29.82.48 (talk) 20:48, 12 February 2010 (UTC)

Our Field of view article claims it's about 180 degrees horizontally, and that "it varies" vertically. The article could use some improvement. Comet Tuttle (talk) 22:29, 12 February 2010 (UTC)

The article Peripheral vision is in poor shape too.Cuddlyable3 (talk) 23:19, 12 February 2010 (UTC)

180 degrees is the statistical average for most people, but some folks can see as many as 240 degrees horizontally. (My own field of view, BTW, is about 220 degrees.) FWiW 24.23.197.43 (talk) 00:33, 13 February 2010 (UTC)

Our area of distinct vision, in which we can see details or read normal print, without eye movements, is tiny, confined to the Fovea of the eye, subtending less than 2 degrees of visual angle horizontally (or about twice the width of the thumbnail at arm's length) and less vertically. The edges of the claimed 180 degree field would be nearly blind, only to detect things like movement of objects or flashing lights, whereupon we would normally direct the fovea to that region of visual space by eye and head movements. The horizontal field of view is obviously greater if you combine the fields of view of the two eyes. Prey animals like rabbits or horses have their eyes set more to the side than to predator aniimals like cats, so they have a 360 degree horizontal field of view, at the expense of depth perception in the forward direction the predators enjoy. As an experiment, look at the computer screen with your two thumbs extended next to each other, at arms length, below a line of text. Without eye movements, can you read words to the left and right of the thumbs? Now turn your chair at a 90 degree angle to the computer screen, and move your fingers in front of the screen, at about 90 degrees from your visual fixation point. Rotate until the movement disappears. You have mapped your visual field. Eye doctors do tests for the extremes of the visual field called Perimetry. Some diseases cause the visual field to shrink. Edison (talk) 02:16, 13 February 2010 (UTC)

There are many numbers here because there are many ways to measure it. From extreme head-turn plus eye swivel to opposite head turn plus eye swivel is very close to 360 degrees. With eye motion only, it's more like the 220 that '24 suggests. Without eye motion - and including the outer regions of the retina where we can only see in monochrome (but are very sensitive to motion), it's more like 90 degrees - and for full color vision, more like 50 to 60 degrees. But our ability to conentrate our gaze on a smaller region still comes from brain function rather than actual vision so it's possible to concentrate only on (say) the middle 10 degrees - without noticing what's going on outside of that small region (eg when reading). These numbers are all slightly variable from individual to individual - and also depend on your eyesight (and whether you wear glasses). SteveBaker (talk) 02:08, 13 February 2010 (UTC)

At 90 degrees or so from fixation, only gross changes are seen, so glasses are less important than in the areas nearer fixation. The lens does not focus that sharply nor is the retinal that acute at visual angles far from fixation. Edison (talk) 02:29, 13 February 2010 (UTC)

Your coloured field of view is also smaller than your black and white field of view. You don't normally notice as your brain is very good at making up what colours things in you peripheral vision are. To test this, take a few coloured pens or pencils, hold one behind someone so that they don't know which colour you are using, then with the person still looking forwards bring the pencil round slowly round the side of their head towards the front of their head. You can only accurately describe the colour when its about 45 degrees away from your front. If you do the same thing but show someone which pencil you're using they'll be able to tell you the colour much sooner than before. Maybe someone can remind me as to why this happens. Smartse (talk) 17:42, 13 February 2010 (UTC)

Chemistry diagrams

http://en.wikipedia.org/wiki/Penicillin

On the right hand side of the page there is a diagram depicting the structure of penicillin. Between the HN and C atoms there is a black shaped wedge. Between the c and H bond (top middle) and the C and C bond (bottom right) there are wedges with parallel lines. Please could you explain the meaning of these bonds - I can't find reference to them anywhere90.216.189.67 (talk) 20:56, 12 February 2010 (UTC)

Thank you

Our article Skeletal formula describes how this type of chemical structure depiction can be interpreted. -- Ed (Edgar181) 21:03, 12 February 2010 (UTC)

Put simply the black wedge shows that the molecule is 3D and that that bond is coming out of the paper/screen towards you. Smartse (talk) 17:44, 13 February 2010 (UTC)

Minor quibble - all molecules are 3D. The wedges are there to indicate chirality - that is, how the molecule is structured around the atom with the wedges matters. Chiral compounds can have very different properties from their mirror image compounds. The classic example is thalidomide, where one compound is effective against morning sickness, where the other causes severe birth defects. -- 174.21.247.23 (talk) 19:25, 13 February 2010 (UTC)

Cryogenics

Hello i was wondering what has been in the field of cryogentics sucessfully done have scientist been able to freeze mice and revive with full function? i read article on cryogentic but did not see information about current ability our science is in area? (Dr hursday (talk) 22:53, 12 February 2010 (UTC))

The article you want is Cryonics.Cuddlyable3 (talk) 23:14, 12 February 2010 (UTC)

The short answer to your question is "No". The reason is, when mice are frozen, all the water in the tissues freezes and forms ice crystals -- and since ice expands during freezing, those crystals usually poke holes in cell membranes, killing the cells. It's the same reason why you don't put fruits and veggies in your freezer -- the ice crystals destroy the cells and make the veggies (or fruits) soften when thawed. In the case of mice or other animals, the blood also freezes and its expansion bursts blood vessels -- sort of like a water main bursting in sub-zero weather. You could of course put chemicals into the blood that would keep it from freezing, but the problem is, those chemicals are toxic enough to kill or to cause irreversible damage. So far, the only living organism to have been successfully frozen in dry ice and revived with full function is Han Solo in Star Wars; but it's only a movie, it's not anything like real life. 24.23.197.43 (talk) 00:55, 13 February 2010 (UTC)

Wood Frogs freeze solid and thaw out with no apparent ill effects all the time. Perhaps we could learn from them. Edison (talk) 01:49, 13 February 2010 (UTC)

I have fixed your link, Edison - internal links inside of external links confuse the MediaWiki engine. Nimur (talk) 16:49, 13 February 2010 (UTC)

Well, those few animals that can do this have a natural antifreeze in their bodies. It might be possible to do some genetic engineering and gain that benefit. However, it's not clear how well things like higher brain functions would survive, for example. If a frog lost all of it's memories through the process, it wouldn't really matter a damn - but with humans...not so good! I don't think it's impossible that we could do that one day - but don't bank on it. SteveBaker (talk) 02:03, 13 February 2010 (UTC)

There are quite a few memories I would not mind losing. Edison (talk) 04:37, 14 February 2010 (UTC)

I have seen no references that say the wood frogs lose their memories each time they freeze and thaw. If the memories are stored as new synapses, they might survive. Edison (talk) 04:39, 14 February 2010 (UTC)

This article in 2008 discussed work that Israeli scientists were doing on pig livers that could be frozen and then still functioned in another pig. Maybe read some papers in Rejuvination research if you want more up to date information. Smartse (talk) 17:55, 13 February 2010 (UTC)

As Steve says, it's the brain that's the tricky bit. Livers have amazing regenerative capabilities. --Tango (talk) 19:31, 13 February 2010 (UTC)

You be be thinking about the successful cloning from a frozen mouse, which was reported a few years back. [3] See also this interesting, if somewhat tangential, story about super-cold squirrels. [4] Rockpocket 02:21, 14 February 2010 (UTC)

21 years ago?? There simply must be more on this matter. 77.18.91.253 (talk) 19:41, 14 February 2010 (UTC)

Cloning from a frozen animal is entirely possible - you don't need to revive the animal - all you have to find is some intact DNA. In all of those trillions of cells, you only have to find one that didn't get destroyed. If 1% of the cells survived, you could clone without difficulties - but if 99% of your cells are ruptured then you're very, very dead! There are serious discussions of cloning a mammoth from frozen tissues found in northern siberia. SteveBaker (talk) 23:17, 14 February 2010 (UTC)

You can read more about it here. Rockpocket 19:20, 15 February 2010 (UTC)

February 13

Travelling to the future

I believe that the following is correct:

• If you approach the speed of light, then relative to a slower moving body, time will seem to move more slowly
• Therefore, if you circled the Earth at close to the speed of light, time on Earth would appear to pass more quickly than time on your "spaceship"
• So, if you left now, got up to the speed of light quickly and then can back in five years, far more than five years could have elapsed on Earth (so you are in a sense travelling into the future)

Also:

• With the lack of friction in space, you could potentially use a form of propulsion to gradually accelerate yourself to the speed of light
• It would be within the reach of current technology to create a spaceship that could withstand being accelerated to close to the speed of light (because the accelaration forces would be very low) - although if it hit anything it could be destroyed
• With the like of ion drives and a nuclear power source it is feasible to build a propulsion system that could accelate the spacecraft to close to the speed of light

My questions are:

• Are all of the above assumptions correct?
• Is there anything else that makes this completely unfeasible?
• If it is unfeasible, what kind of technological advances would be needed to make it feasible? (or will it likely always be impossible)?
• Could the spacecraft be accelerated close enough to the speed of light, quickly enough to mean that somebody launching tomorrow, would be able to travel a significant way into the future, and how far could they travel?
  • For example, if a 20 year old man, with a life expectancy of 80, left today, how far could he travel into the future, taking into account that he would have to accelerate and decelerate again, with the 60 years of his remaining lifespan.

Any thoughts on this would be really appreciated. Thanks Blooper Watcher (talk) 01:23, 13 February 2010 (UTC)

I did some quick calculations myself, based upon a thrust figure of 88,000 mN (which seems to be the highest achieved by an ion engine). Assuming a mass of 10,000 kg for the spacecraft, I reckon that over 1,000 years you would accelarate to approximately 283,000 km/s (which is just shy of the speed of light). The calculation being:

(88 N * (1,000 * 365 * 24 * 60 * 60)) / 10,000 = 283,824,000 m/s

Obviously that is too long for a human lifespan (although I am not sure how close you need to get to the speed of light to see significant variations in relative time), and the engine would need to be 100 times more powerful to get to the speed of light in 10 years (and 10 more years to decelerate). But a 100 fold increase in power does not seem beyond the realms of possibility. Blooper Watcher (talk) 01:42, 13 February 2010 (UTC)

There is no doubt that if you could somehow accelerate yourself to somewhere close to the speed of light - then return to Earth again - then you would have "travelled to the future" - the faster you went, and the longer you stayed at that speed, the further into the future you'd go. In as much as you would seem to others to have lived more than your expected lifespan - and you would be "in the future" - complete with flying cars, personal rocket packs and a small fortune sitting in your bank account thanks to the one penny you left in there and the actions of compound interest!

That's a scientific fact that almost all scientists would agree on.

However, we don't have a way to get something as large as a human up to anything remotely close to that speed...just look at the hardware in the Large Hadron Collider, needed just to get some teeny-tiny sub-atomic particle up to close to light speed! But it's been calculated that the Apollo astronauts (who travelled faster than anyone else on earth ever has) did travel a tiny amount into the future. Apollo 8 astronaut Frank Borman is said to have actually demanded 400 microseconds of overtime pay from NASA because of the time dilation incurred in his trip.

So yeah - we have the technology to push someone 400 microsecond into The World Of The Future! SteveBaker (talk) 01:54, 13 February 2010 (UTC)

Thanks Steve. Do my figures for the acceleration using the most powerful current ion drive look correct? It would seem to me that a 100 improvement in the technology would be feasible which, again, if my figures are correct would be acceleration up to the speed of light in 10 years, and then decelarating back down in another 10 years. The thing is, how close do you need to get to the speed of light to get a noticable effect?

Let's say that we used the current drive, and over 10 years got up to 1% of the speed of light, stayed there for 40 years and then decelrated back down to stationary. How far, beyond the 60 year journey, would we have travelled? If we could accelarate up to 99% using a more powerful drive, and did the same 10 year accelarate, 40 years travel, 10 years decelerate, how much time travelling would we have done?

Also, aside from getting up to speed. Is there anything else that would always make this unfeasible? Blooper Watcher (talk) 02:04, 13 February 2010 (UTC)

One more thing, shouldn't NASA have been chasing Borman to pay some money back? Seems to me that he worked 400 microseconds *less* than the guys on the ground. Blooper Watcher (talk) 02:08, 13 February 2010 (UTC)

You should remember that mass is also relative. As you accelerate, the mass increases and you'll need more force to achieve the same acceleration (that's why you cannot reach the speed of light - see Speed of light#Upper limit on speeds about that). Your calculations do not seem to take that into account. Also, about "Therefore, if you circled the Earth at close to the speed of light, time on Earth would appear to pass more quickly than time on your "spaceship"" - it is going to be very hard to circle the Earth at such speed as it is going to be much higher than the escape velocity... --Martynas Patasius (talk) 02:42, 13 February 2010 (UTC)

For sure there is no way you could do this in orbit. The effects of relativity as you approach the speed of light make it increasingly difficult to push your speed that little bit faster. Even ion drives require reaction mass - and if you made them 100 times better, they'd need 100 times the amount of reaction mass - which would drastically increase the mass of your spacecraft and thereby eat most of the benefit you got from better engines. This has been thought about many times before by many smarter people than us - and it's quite utterly impractical. SteveBaker (talk) 05:03, 13 February 2010 (UTC)

As you say, there would be a big problem if the spacecraft hit anything when going at relativistic velocities. Unfortunately, it is guaranteed to hit something - the interstellar medium. In the vicinity of the Sun, the interstellar medium contains about 50,000 atoms (we'll assume they are all atoms of hydrogen, which is close enough to the truth) per metre cubed. If we assume a speed of 0.99c, that's a gamma factor of about 7. That means that, from the perspective of the spacecraft 50,000*7=350,000 atoms per metre cubed (due to length contraction) and each has a mass of 7 times that of hydrogen (due to relativistic mass) and they are all travelling at 0.99c. That means that, in every second, for every metre squared of cross sectional area, the ship will hit 350,000*300,000,000*7 u of gas moving as 0.99c, that applies a force of 0.00037 N. That compares to a car travelling at 30 m/s (70mph) having air resistance of 1080 N. Clearly, that isn't a big problem (although it is still a problem, since ion drives typically produce far far less force than a car's engine), but if we increase the velocity to 0.999999997c, it becomes roughly the same resistance as the car. So, as you can see, the resistance from the interstellar medium does provide a limit to how fast you can travel, although that limit is pretty high. (All of these calculations are assuming perfectly elastic collisions - if the hydrogen doesn't just bounce off the ship then you need to look at the energy of the atoms, which is extremely high since it is proportional to velocity squared, so we would probably find the ship being significantly eroded by the constant collisions.) --Tango (talk) 13:26, 13 February 2010 (UTC)

Tango, all that hydrogen can be seen as an aset instead of a liability. In principle it could be collected and used to power a fusion reactor that suplies energy to the ion drive. Dauto (talk) 15:40, 13 February 2010 (UTC)

Bussard ramjet perhaps? 220.101.28.25 (talk) 16:36, 13 February 2010 (UTC)

That article discusses the feasibility. Most studies seem to show that it wouldn't work (you get greater drag from the collector than you can generate thrust). Our article gives an example where it would work, but assumes an extremely high exhaust velocity with no justification for it being possible. --Tango (talk) 17:09, 13 February 2010 (UTC)

The now-cancelled Project Orion was to get a spacecraft to a theoretical upper limit of 10% of the speed of light. ~AH1^(TCU) 23:25, 13 February 2010 (UTC)

As a torchship scuts through space at near the speed of light, a scoop on the front funnels any molecules encountered into the reaction chamber where they are accelerated to provide additional thrust. The scoop and the channel the molecules pass through are made of Unobtanium, a metal which is not readily available at present (but neither is Plutonium), but which has 157 hits at Google Book Search. Edison (talk) 04:35, 14 February 2010 (UTC)

See Unobtainium. Amazing the things we have articles on! --220.101.28.25 (talk) 06:00, 14 February 2010 (UTC)

Carbon dioxide and plants at night

A question has come up on a sleep forum, in regard to plants in the bedroom. I've tried to read the photosynthesis articles (difficult here, too simple at simple), and haven't found an answer. Do (some? all?) plants release carbon dioxide in the dark? Thank you. - Hordaland (talk) 10:36, 13 February 2010 (UTC)

Plants release carbon dioxide continuously, since they respire in the same way animals do. However, during the day (when they are in light) they also photosynthesise, and this converts carbon dioxide to oxygen. Therefore, it is generally true that the amount of carbon dioxide they take in during the day exceeds the amount they give out. This is not true at night time. However, the amount of CO2 they release should not be enough to cause any problems to people in the same room. --Phil Holmes (talk) 11:20, 13 February 2010 (UTC)

Yes, all plants do this - but the amount they produce is completely negligable compared to the amount a person sleeping in that room would produce. There are families in poorer countries who sleep 10 people to a room - and they don't suffocate! This is SO far from being a possible problem that might concern a "sleep forum" that it's almost laughable - so tell the people there "Don't worry - it's such a tiny effect that it's completely unimportant." SteveBaker (talk) 15:09, 13 February 2010 (UTC)

Thank you both! The forum (listserve, actually) is for sufferers of severe Delayed sleep phase syndrome, and we take each others' questions seriously. There is no effective treatment, so we question any little thing that might help -- or not. I will politely explain that the questioner needn't consider the CO2 from the "humungus bamboo tree" next to the bed. Thanks again! Hordaland (talk) 16:24, 13 February 2010 (UTC)

Steve, "suffocate" is your word. We haven't contemplated any such thing. Hordaland (talk) 16:31, 13 February 2010 (UTC)

The room would have to be airtight if something like hypercapnia were to occur. ~AH1^(TCU) 23:20, 13 February 2010 (UTC)

That's the point. Virtually no rooms are airtight, also due to building regulations. --Ayacop (talk) 18:15, 14 February 2010 (UTC)

I have seen architectural plans of hospitals from the 1920's which had a "plant room" on each floor. Plants from patient rooms were stored in the plant room at night for fear they might deprive the patient of some oxygen if left in the patient room. I do not know what year this practice arose or when it was phased out. Schaum's Outline of Biology(2009) Q. 20.3 says that plant removal from hospital rooms at night is still done in some locations. Edison (talk) 20:59, 14 February 2010 (UTC)

magnetic vector potential actual meaning?

whats exactly ment by magnetic vector potential?is it only a conceptual idea? what tha physical meaning of magnetic vector potential. —Preceding unsigned comment added by Dakshu (talk • contribs) 10:51, 13 February 2010 (UTC)

The vector potential is definatly real. read for instance Aharonov–Bohm effect. Dauto (talk) 13:54, 13 February 2010 (UTC)

Well... the Aharonov–Bohm effect depends only on the integral of A around a closed loop. E and B tell you the integral of A around all infinitesimal loops. Assuming space is simply connected, you can integrate the infinitesimal loops inside the finite loop to get the integral around the finite loop, unless there's a singularity inside. So the only case in which the Aharonov–Bohm effect depends on something beyond the E and B fields is when there's a singularity in the field. Even then you can get it from the E and B fields alone if you treat them as generalized functions.

On the other hand, to calculate the Aharonov–Bohm effect from the E and B fields you have to integrate them over a region where the electron doesn't go. This isn't even a quantum-mechanical takes-all-paths situation, because this region is excluded from the path integral too—the electron really isn't there. But if you use A, the effect depends only on the region where the electron does go. In that sense, A is closer to the reality. But A has a large gauge freedom, meaning that only part of it is real, while the E and B fields do a perfect job of capturing the part of A that's real. What Aharonov–Bohm shows is that they capture it in a way that's nonlocal with respect to (some of) the physics.

There's a GR counterpart to Aharonov–Bohm in lensing around cosmic strings. The exterior gravitational field of a cosmic string is zero. Spacetime is flat around the string; objects do not fall towards the string. But if two objects moving in parallel pass on opposite sides of a cosmic string, they'll end up heading towards each other on the other side, because the integral of the metric on a loop around the string is less than a full circle. Instead of using the metric, you can get the same result by integrating the scalar curvature over a surface that intersects the cosmic string, as long as you don't mind that you're integrating over a region where the particles don't go. -- BenRG (talk) 23:07, 13 February 2010 (UTC)

Think of it as the magnetic field's version of a voltage (or, electric potential). As the voltage is just a mathematically different way to express an electric field, the vector potential is simply another way to represent the magnetic field, in terms of relative potential energy. Then there are just different mathematical conveniences and uses than the B and H fields. Magnetic potential goes into more detail with math and stuff if you haven't read it yet. —Akrabbim^talk 14:15, 13 February 2010 (UTC)

The reason a magnetic field's energy must be described with a vector potential, as opposed to a scalar potential, is because the force imparted by a magnetic field does not only depend on position (it also depends on relative velocities and orientations). In order to quantify this field in a way that satisfies conservation of energy, the potential field must be described by a vector. This is a direct consequence of the Lorentz force law, which is empircally observed. It helps to thoroughly understand what a potential field means in general before trying to apply that mathematical concept to the somewhat pathological case of magnetism (whose force is defined by a vector cross product and a time derivative - not difficult concepts, but enough to make the math much harder than the electrostatic potential case!) Nimur (talk) 16:44, 13 February 2010 (UTC)

Nimur, does an isolated positive electric charge move if you place it in a scalar electric potential field? Cuddlyable3 (talk) 17:49, 13 February 2010 (UTC)

A meaning of pathological is Relating to or caused by a physical or mental disorder.[5]. Nimur, is there another word you could use to characterise the case of magnetism? Cuddlyable3 (talk) 17:19, 13 February 2010 (UTC)

Sorry. I meant it in the sense that the mathematical convention seriously breaks from the normal form of a scalar potential field. I use "pathological" in the sense of any instance that diverges from the norm in a way that breaks simplifications. I think this usage is very common in math, physics, and computer programming - it has evolved and is distinct from the meaning in the medical field. I don't think I'm coining a neologism - let me find some prior usage. Nimur (talk) 17:27, 13 February 2010 (UTC)

See pathological (mathematics). -- BenRG (talk) 23:07, 13 February 2010 (UTC)

There's nothing wrong with using the word 'pathological' per si. But I don't agree with what Nimur is saying since the electric field expression also depends on the vector potential. Dauto (talk) 17:25, 13 February 2010 (UTC)

Sure - but we can construct a totally scalar electric potential field - that's the simplification I'm referring to above. It is possible (although it limits the situations you can consider) to construct the electric potential in scalar form. No possible simplification exists to represent the magnetic potential in scalar form. Nimur (talk) 17:29, 13 February 2010 (UTC)

$\mathbf {E} =-\nabla \phi -{\frac {\partial \mathbf {A} }{\partial t}}.$

Dauto (talk) 17:29, 13 February 2010 (UTC)

Electrostatics - therefore, there is no time variation. I think I mentioned this before. Nimur (talk) 17:30, 13 February 2010 (UTC)

Read Magnetic potential#Magnetic scalar potential.Dauto (talk) 17:43, 13 February 2010 (UTC)

Nimur, does an isolated positive charge move if you place it in a scalar electric potential field? Cuddlyable3 (talk) 17:49, 13 February 2010 (UTC)

Yes. That does not mean the field is time-varying - that does not mean a full electrodynamics treatment is necessary. See test particle if you don't understand why. This is called electrostatics and it is a well-developed, mathematically rigorous approach. Obviously, it is inapplicable in situations where the time-variance is non-negligible - that is, by definition, electrodynamics - and it is more general, requires harder math, and requires the vector potential Dauto has spelled out above. Nimur (talk) 00:07, 14 February 2010 (UTC)

Nimur, I read Test particle#Test particles in plasma physics or electrodynamics and don't understand how there can be a force to move the positive charge without a vector to define the force direction. Is not every electric potential field a vector field? Cuddlyable3 (talk) 18:42, 14 February 2010 (UTC)

Force is the gradient of the scalar potential. The gradient operator can create a vector field out of a scalar field. This is a very common formulation of energy-force relationships, even outside the realm of electricity and magnetism. The extension of the potential to a full vector field throws some non-trivial kinks into the matter, which is what the OP was asking about in the first place. As I've mentioned above, because magnetic force is defined by the lorentz force (which involves a vector cross product and a time derivative), the corresponding potential field is most succinctly described as a vector potential. Dauto has listed above a magnetic scalar potential - I have never seen this used in practice. But, what do I know, I'm only a professional numerical physicist... Nimur (talk) 18:46, 14 February 2010 (UTC)

Thus an electric potential field (except in the degenerate case of a uniform field where all points have the same or zero potential) is inseparable from a vector field. Yes the vectors are the gradients of the potentials at each point. This is we agree a common formulation. So Nimur I don't know how you claim "we can construct a totally scalar electric potential field". Cuddlyable3 (talk) 23:18, 14 February 2010 (UTC)

I think you should review the gradient article. Nimur (talk) 03:41, 15 February 2010 (UTC)

The vector potential does have a physical meaning, but it's somewhat difficult to visualize. I'll try to explain it by a toy example. Imagine you have a cylinder of wire mesh, kind of like this. But it's twisted: the circles are still circles, and they're still parallel to each other, but they've been rotated relative to each other so the wires running between them aren't straight any more. No matter how twisted the cylinder is, you can always untwist it if you're strong enough. Now imagine you have a torus of wire mesh, kind of like this. Again, it's twisted. You can always locally untwist any part of it, but in contrast to the cylinder, you can't necessarily untwist the whole thing. If the sum of all the relative rotations of adjacent circles all the way around the torus is zero, then you can untwist the whole thing; otherwise, you can't.

This "freedom to twist" is called "gauge freedom". The only properties of the wire mesh that we care about are those that you can't untwist. This means that in the case of the cylinder, none of the twisting matters; it's all "just gauge". In the case of the torus, the only thing that matters is a single number giving the total amount of twist around the whole torus.

Now (here's where it gets hard) increase the number of dimensions. You can think of it this way: if you take a line and replace each point with a circle, you get a cylinder. If you take a loop and replace each point with a circle, you get a torus. What you want to do now is take space and replace each point with a circle. As you go from point to point in space, there's a corresponding twisting of the circles, and the question is to what extent you can untwist them and to what extent you can't. The answer is that what you can't untwist is completely captured by the total twist around all closed loops in space (the total twist around the loop being defined in the same way as it was for the torus). You can get the twist around large loops by adding the twist around smaller loops inside the large loop, as illustrated at Stokes' theorem#Underlying principle. This means that if you know the twisting around infinitesimal loops then you can find the twisting around all loops, and hence you know everything there is to know about the twisting. This is what the B field tells you. The magnitude of the B field at a point is the maximal amount of twisting of any infinitesimal loop at that point, and the direction of the B field tells you which loop is maximally twisted (namely, the one in the plane perpendicular to the field).

What the A field tells you is the amount of twisting as you move from one point to another. The direction of the A field at a point is the direction in which the twisting is maximal, and the magnitude of the A field is the amount of twisting in that direction. The A field has a gauge freedom corresponding to your freedom to twist. The B field doesn't; it tells you just the part of A that matters.

This analogy is much closer to reality than it might seem. If you imagine there really is a circle at every point in spacetime, twisted in the way I described, and write down the general relativistic equations for 5D gravity in that 5D space, you actually get Maxwell's equations and 4D gravity, the A and B fields literally mean what I just said they mean, and electric charge corresponds to momentum around the extra dimension. This idea dates back to the 1920s and is called Kaluza–Klein theory. -- BenRG (talk) 23:07, 13 February 2010 (UTC)

Paranormal

Did Jung have any faith in supernatural ? As far as I know Freud did not beleive that any entity does survive bodily death. But Jung's collective unconscious is some what near and dear to spooks...no ?

 Jon Ascton  (talk) 11:39, 13 February 2010 (UTC)

Many interpretations of Jung's writing do exist - it wouldn't be too far to consider his archetypal unconscious as a "supernatural" concept - even though he surely considered it "science". Because the collective unconscious was not based on empircal evidence, though, it's not really a scientific conclusion. Later generations of psychologists categorically discredit that line of reasoning in favor of observation-based theories of psychology. Nimur (talk) 16:39, 13 February 2010 (UTC)

See our article on synchronicity -- most people think of that as supernatural. Looie496 (talk) 18:15, 13 February 2010 (UTC)

Also look at collective unconscious. ~AH1^(TCU) 23:17, 13 February 2010 (UTC)

Why did the Challenger shuttle explode in a white cloud?

When watching the explosion again recently, I was struck by the fact that the "smoke" was all white, rather than black/grey that I would expect to see from an explosion. Is this because the white stuff is actually refrigerated fuel that did not combust and instead turned to a ball of vapour that obscured any of the smoke? Blooper Watcher (talk) 14:42, 13 February 2010 (UTC)

The fuel in the external tank is about 800 tons of liquid hydrogen and liquid oxygen. When that exploded, the reaction produced 800 tons of water vapor - which is white. What you're seeing is a small cloud - in the sense of a "rain cloud". (Um - actually, less than 800 tons - it would have used a good chunk of that during the launch sequence - but still a heck of a lot.) SteveBaker (talk) 15:00, 13 February 2010 (UTC)

(ec)Small quibble. The Shuttle itself did not explode, it was the external fuel tank that exploded 'deflagrated'(?). Aerodynamic forces broke up the orbiter. See Shuttle challenger disaster. The long continuous trails are exhaust from the solid rocket boosters. As per SteveBaker & cloud See Shuttle_challenger_disaster#Post-breakup_flight_controller_dialog 220.101.28.25 (talk) 15:09, 13 February 2010 (UTC)

This NASA link can probably answer any questions about the Challenger STS-511 --220.101.28.25 (talk) 15:19, 13 February 2010 (UTC)

As an interesting aside, since it produces so much water, the launches of shuttles like these cause sudden downpours a few hours later. Vimescarrot (talk) 16:27, 13 February 2010 (UTC)

^{(citation needed?)} Eight hundred tons of water spread over a path 100 km long and 100 meters wide (let's say) works out to a lousy 80 grams per square meter -- less than a tenth of a millimeter of liquid water, so I don't imagine it's just the Shuttle exhaust falling out of the sky. What I could believe is that the long trail of water vapour could nucleate cloud formation and trigger rainfall that way.... TenOfAllTrades(talk) 17:02, 13 February 2010 (UTC)

A (probably overly-dramatic) show presented by James May. Probably James May's 20th Century. Vimescarrot (talk) 17:07, 13 February 2010 (UTC)

Even smaller quibble. Water vapor itself is basically colorless in the visible spectrum. The white stuff, like any cloud, is condensed water (i.e. tiny droplets of liquid). Buddy431 (talk) 16:33, 13 February 2010 (UTC)

drag vs Reynolds #

There is a relationship between coefficient of drag and Reynolds number. When the object is sphere, the relationship can be pictured like this. I've seen versions of this figure in a number of chemical engineering textbooks. What I haven't been able to find out is whether this relationship is an empirical correlation, or an analytical solution, i.e. is this a relationship that is just observed to be true in experiments, or is it a relationship that must be just so according to the theory in this area? ike9898 (talk) 19:23, 13 February 2010 (UTC)

The limiting behavior (i.e. the behavior at very high and very low Reynolds number) can be derived analytically. The intermediate regimes can probably be modeled computationally for idealized fluids, but are more likely to be measured empirically for any actual fluid. Dragons flight (talk) 08:11, 14 February 2010 (UTC)

February 14

boiling

when water and milk are boiled, water boils but milk overflows. why?? —Preceding unsigned comment added by 59.96.24.220 (talk) 05:43, 14 February 2010 (UTC)

The milk's cream forms a layer at the top. When the milk boils the steam pushes that layer up making a mess. Dauto (talk) 05:47, 14 February 2010 (UTC)

But is it the increase in the tensile strength of the bubble walls by the protein+fat film on the surface, or the reduction in surface tension? BTW I am not the OP; sorry for hijacking the question this way.--Dr Dima (talk) 05:55, 14 February 2010 (UTC)

It is probably complex. There is probably more than one factor in play. Milk is a complex substance. Probably the bubbles break less easily, thereby they hold their volume, propelling the liquid portion of the substance over the rim of the pot. Bus stop (talk) 06:00, 14 February 2010 (UTC)

... so what is the mechanism for preventing boiling over by placing a ribbed circular metal device at the bottom of the pan? It causes the milk to boil almost like water. How does it work? Dbfirs 07:47, 14 February 2010 (UTC)

All your questions are answered at milk watcher.--Shantavira|^{feed me} 08:17, 14 February 2010 (UTC)

Thanks. I didn't know what they were called. I've never seen the ceramic and glass versions. Dbfirs 08:56, 14 February 2010 (UTC)

Signal White Now - Why?

There is a new product called that makes your teeth instantly white. The manufacturer offer following explanation of its effect: "Signal White Now, our latest innovation, transfers optical-effect technology developed by Unilever’s laundry team to the field of oral care, using a blue pigment to make yellow teeth appear whiter." My question is, why would blue on yellow make your teeth white? (even if it is only for a while). Shouldn't it make the teeth actually green? —Preceding unsigned comment added by Quest09 (talk • contribs) 11:38, 14 February 2010 (UTC)

Yes, it should make them green. Blue+Yellow=White for light, but not for pigments, for pigments it makes green (see additive colour and subtractive colour for details). --Tango (talk) 12:51, 14 February 2010 (UTC)

The OP may be referring to some sort of optical brightener which are commonly used for clothes and do I believe work with the article offering some explaination for how. Or perhaps it is just some simple blue dye as with bluing (fabric) agents such as Mrs. Stewart's Bluing which also work although according to our article have now been largely replaced with optical brighteners. Our article mentions some cosmetic uses for both, particularly for hair. This [6] offers some, not extremely scientific (and obviously not an unbiased source but I don't think there is any real dispute that it works) explaination of why dying white/offwhite blue can make them seem more white. If you overuse the dye, then it's likely to look too blue and if it's something extremely yellow then it's going to look green but this isn't how bluing is done. As an aside bluing agents are also useful for growing rock crystal gardens [7] [8] (also mentioned in the article) although I never found any in Malaysia when I was looking in around 2000 as a suggestion for a friends project. Nil Einne (talk) 14:31, 14 February 2010 (UTC)

Most Americans see something that's truly white as a bit yellowish (I don't have a source, other than my father). My dad helps manufacture plastics, and it's customery to add just a bit of blue coloring to white plastics to make them more attractive. He says that in plastics destined for certain other parts of the world, though, they add different colors. I don't recall what colors get added for what areas, but it's interesting that it appears to be a cultural thing, rather than something hardwired into us. Buddy431 (talk) 17:16, 14 February 2010 (UTC)

This is not exactly how color vision works. The spectrum of light that reaches the eye depends both on the emission properties (such as intensity as a function of wavelength) of the illuminant and the reflection properties (such as reflection coefficient as a function of wavelength) of the surface. The photographic film registers faithfully the light that arrives: use yellow-rich illuminant and the picture will have mostly shades of yellow, use blue-rich illuminant and the picture will have mostly shades of blue. Not so for the human eye. We have a "built-in" color constancy mechanism that allows us to discard (or at least to separate out) the illuminant information and to infer the reflectance of the objects, so that the colors of objects that we see look roughly the same under different illuminants. A gray piece of cloth will look gray both at midday, at sunset, under incandescent lights, and under the fluorescent lights; all the same. The white point therefore is not only subjective, but also depends strongly on the choice of illuminant. Now, yellow and blue are opposite each-other on the color wheel. Thus, adding more blue to the reflection spectrum is indeed making an object look less yellow (more white), as yellowish objects have relatively more yellow and less blue in their reflection spectrum. Oxidation tends to render paper, fabric, and plastics yellow; thus, at least in the past, it was customary to add a small quantity of a blue dye to the laundry rinse water and such. I am not entirely sure, but this is not AFAIK a cultural thing. Color naming is a cultural thing; but color perception is universal among humans with normal trichromatic color vision (which is the vast majority of mankind). And, regarding the question whether you get white or green when you mix blue and yellow, it is explained very well in our Color mixing article. --Dr Dima (talk) 22:42, 14 February 2010 (UTC)

heat loss

a vertical sq. plate 30 cm on a side is maintained at 50 c and exposed to room air at 20 c(temperature) the surface emmisity is 0.8 calculate total heat loss by both sides of plate?

It says at the top of the page, "If your question is homework, show that you have attempted an answer first". This looks like a homework question to me.Heat transfer might help. --ColinFine (talk) 17:22, 14 February 2010 (UTC)

(ec) This looks like a homework question to me, and we don't do people's homework for them. If you have a go at it and get stuck, we'll try and help you out, but you need to show you have tried and tell us precisely where you are getting stuck. --Tango (talk) 17:24, 14 February 2010 (UTC)

Malicious pigeon

The silly title refers to this question: From how high up can one (say: pigeon) drop an object (say: poop) and be certain that it will fall exactly on a given target (say: victim). Let us assume the object is a smooth sphere dropped in still air and we may choose its diameter and weight. Initial velocity is zero. I believe that its trajectory is predictable until either A) due to its increasing velocity the Reynolds number exceeds Re = 0.1 whereupon the path will be deviated unpredictably by turbulence, or B) it reaches terminal velocity while still in laminar flow. I lack an equation for the Reynolds number of a sphere falling in air. I shall assume the pigeon is a perfect marksbird but wonder whether the ultimate bombing accuracy is set by Brownian motion of the surrounding air which would impact accuracy less on a cold day than a hot day. Can anyone help put numbers to these considerations? Cuddlyable3 (talk) 18:26, 14 February 2010 (UTC)

Before you even begin discussing turbulence, brownian motion, and chaos theory, let's start out with an even simpler problem in predicting the actual impact location. Wind can be described (with great simplification) as a vector field for every x,y,z point. At each point <x,y,z>, there is a vector, <wx,wy,wz>(t) - a time-varying windspeed. Assuming you can estimate this 7-degree-of-freedom vector field, you can estimate the force on the falling object at all times. How do you plan to estimate those parameters? Once you have that problem solved, turbulence will be a minor perturbation. The trajectory is predictable only insofar as you know the wind speed at the time that the object passes through all points in its trajectory. I think you will find that people who spend their days laying targets for ballistic objects are satisfied to assume an "exact targeted location, with a point spread". Some will even account for an average wind speed and time-of-flight estimate, to give a first-order correction to impact position. The error caused because you can't estimate wind speed is much larger than any error due to turbulence. If you had, for example, by advanced doppler radar, a reasonably accurate estimate of the wind speed in your volume of interest, you might refine your estimates and need to start worrying about turbulence and nonlaminar flow to increase your accuracy. A better way to phrase your problem would be to ask about the order-of-magnitude error that is due to wind, vs. due to turbulence. On all but the very calmest of days inside the most carefully controlled wind tunnel, I think we could safely say your pigeon would need to worry much more about the former (wind-speed estimation error) than the latter (trajectory estimation error due to non-laminar flow). Nimur (talk) 20:46, 14 February 2010 (UTC)

Nimur your information would have been relevant if I had not said in still air. Cuddlyable3 (talk) 22:58, 14 February 2010 (UTC)

Turbulence happens in still air anytime the object is falling too fast to be in laminar air flow. Turbulence is a chaotic process - hence Nimurs information is highly relevant. SteveBaker (talk) 23:25, 14 February 2010 (UTC)

The Mathematics of Exterior Ballistics, The American Mathematical Monthly (1940), provides an analytic and numerical integral solution based on the Siacci method. The presented model may include any number of parameters, each increasing theoretical accuracy, while practically introducing huge estimation errors. The model includes, in no particular order, gravity, aerodynamic drag that linearly depends on velocity, non-flatness of trajectory, estimation of initial velocity, estimation of air density and air temperature structure, approximation of the projectile as a constant/standard weight, assumption of negligible wind, neglection of the Coriolis force, and finally, error due to numerical integration. Turbulence probably falls into the category of air density and air temperature effects, though it is not mentioned explicitly in this paper. Trajectory Models for Heavy Particles in Atmospheric Turbulence: Comparison with Observations, (2000), Journal of Applied Meteorology, details some more modern methods and mathematics; again, though, "the Langevin model estimated the location and width of the bead deposit swath very well and fixed the peak deposit density to within (at worst) about 100% error" and "uncertainties in the treatment of deposition proved more significant than nuances of the trajectory algorithm." Your insistence on modeling turbulence will categorically put you on a path to a very error-prone subset of all possible models - it would be much more useful to assume turbulence is a statistical perturbation on an otherwise ballistic trajectory, and model the more relevant ballistic effects. In any case, these papers can help "put numbers to these considerations." You might also find the Wikipedia article on external ballistics informative. It presents a large number of common models and some realistic numerical parameters to feed into them. Finally, as you found my earlier comment irrelevant, I'd just follow up and suggest that my response is tailored by experience here - so with all due respect, I may be a better judge of relevance than you're giving me credit for. Your question is asking about a marginal perturbation and neglecting a much more important and realistic effect. It's equivalent to asking the impact of brownian motion on gravity. An effect surely exists - but it's so far below the noise floor, that in anything except a staged, theoretical problem, you would never need to worry about it. Air temperature will have more of an effect on air density and air stratification - which will both affect trajectory - and any effect of brownian motion will be dwarfed by those effects. In any case, today's pigeons are rarely dropping ballistic packages - between precision-guided munition and simple passive aerodynamic munitions, the targeting accuracy is defined by a much more heavily engineered, complicated algorithm than a simple trajectory. Nimur (talk) 03:19, 15 February 2010 (UTC)

good alternative to chess?

I love chess, its depth and balance are awesome, but it is very frustrating for me that high-level play implies huge amounts of memorization instead of creativity or mind power, you know what I mean... So does anyone know a comparable game but without that disadvantage? --Belchman (talk) 20:11, 14 February 2010 (UTC)

Go (game)? There have been varients of Go, such as Othello (game), Gomoku, or Pente. Go, and all of the varients, are about as simple to play as Tic-Tac-Toe (or Crosses and Naughts for our Britishy readers) but have very complex and intellectually deep strategies. --Jayron32 20:28, 14 February 2010 (UTC)

[It's "Noughts and Crosses" (or "Naughts..."), for the record, Jayron.] To alter the set-up completely, perhaps Bridge might interest you. Admittedly it's four player, but once you get past a beginner level, it requires the sort of thinking you want (there are several variants which make it almost completely skill and not chance). - Jarry1250 ^{[Humorous? Discuss.]} 20:32, 14 February 2010 (UTC)

Bridge up to the club level, maybe. Beyond that, unfortunately, the contemporary game has become a lot about memorization, as the natural bid has almost disappeared. The first natural bid you make in one of these systems may very well be the contract you intend to play. Defensive signaling is similarly baroque. At an academic level these systems are interesting; in actual play I just find it an annoyance.

I would like to see more Individual events. Without any artificial restrictions on systems. The way I'd run an Individual is, you get to find out who your partner is and talk to him for three minutes. Anything you can agree on in three minutes is kosher, but you have to be able to accurately explain it to the opponents, and if you can't, the risk is on you. --Trovatore (talk) 21:49, 14 February 2010 (UTC)

I agree, the whole "bidding system" stinks of being a way to circumvent the rules - and all manner of meta-rules end up being imposed. I couldn't recommend bridge to someone who wished to avoid memorization. SteveBaker (talk) 23:06, 14 February 2010 (UTC)

The rules do require you to explain your system to your opponents (although usually that's just done by saying "We use the X system with Y variation" or similar). I really don't get the appeal of bridge for the simple reason that I am sure I could write a computer program that would play better than I can, and probably better than most experienced bridge players. Bidding is, as you say, formulaic and the actual play is extremely easy as long as you are capable of memorising the cards that have already been played and all the information you received during the bidding stage. Following algorithms and memorising things are precisely what computers were invented for. --Tango (talk) 23:19, 14 February 2010 (UTC)

Oh no, the play of the hand is not by any means easy. At least finding the best play is not. Granted, on a large percentage of hands, the best play will be found by any player who understands the basic principles and remembers the available information, but that still leaves lots of hands where that isn't true, more than enough to swing a tournament if the bidding is equal.

To me the play of the hand, whether as declarer or as defender, is the soul of the game, and I wish the bidding phase were less important. But it is what it is. The amount of effort put into bidding by the most successful players indicates that that must be where the tournaments are largely to be won or lost. --Trovatore (talk) 00:44, 15 February 2010 (UTC)

I disagree. The first few tricks may have some challenge in them, but after that you have so much information available that it becomes fairly predictable. The problems with the game are evidenced by the prevalence of duplicate bridge in tournaments - there is so little skill in the game (for experienced players) that you can only tell who has the most skill by removing (almost) all the luck. Most games with comparable randomness (eg. poker and Magic: The Gathering, to name two that I have played a significant amount of) you can determine the more skillful players just by playing a reasonable number of games, but that isn't the case for bridge. --Tango (talk) 00:59, 15 February 2010 (UTC)

Well, if you disagree, it means you don't know the game. The play of the has great subtlety and complexity. As I say, it doesn't show up on every hand, but it does on lots of hands.

If you want to find out what I'm talking about, you can't do better than Louis Watson's masterpiece The Play of the Hand at Bridge. You can get it from Amazon UK for about eight pounds. --Trovatore (talk) 01:06, 15 February 2010 (UTC)

I second the vote for "Go". We have computers that can play chess better than the best humans alive - but Go is so difficult that computer Go players are scarcely able to approach the level of professional players. The beauty of it is that there is no memorization of openings - no memorization of end games - and the rules are spectacularly simple. IMHO, it's a much 'purer' game than chess. I think you'll like it. SteveBaker (talk) 23:02, 14 February 2010 (UTC)

Chess computers don't play chess the way people do; the fact that those techniques fail for go doesn't reflect on go's difficulty for human beings. Not that that's an argument against learning go, unless you wanted to learn by playing a computer opponent. -- BenRG (talk) 02:16, 15 February 2010 (UTC)

Or there are variants of chess itself, which are not played at professional level so they don't have that much official and well-researched sequences one has to memorize. Two popular of them in my former high school were:

• White moves once, black moves two times, white moves three times, and so on, always increasing the number by one. Chess is allowed only as the last move in the sequence, and in this case the adversary's first move has to be stopping the chess in one move or being defeated by checkmate. One can win by checkmate or capturing everything except for the enemy king. As the later is much more common, in a tournament the checkmate win can be worth more points than the "simple win". The game is usually over in around 12-13 moves.
• For 4 players, have two chess sets, preferably of similar size. It is played by teams of two, each playing with different colors, side by side. After capturing an enemy piece, you give it to your teammate, who can place it on his/her own board. The rules are:
  • Captured pieces are given to the teammate.
  • When the opponent ended his turn, you can take all the pieces given by your teammate (while your opponent was thinking) in your hand. After this no other captured pieces given by your teammate can be used in this turn, only those already in your hand. (This is to avoid deadlocks which could occur by refusing to make a move until your teammate can capture something you need.)
  • You can choose to place a piece from your hand on the board instead of a normal move. You are not allowed to place something that would put your opponents king instantly in chess, neither can pawns be placed on the last row. Pawns reaching the last row do not promote, they are instantly captured by your opponent. This does not limit the usefulness of the pawns, as a double row of pawns are a very god defense or a good support of an attack, sometimes players ask their teammate to sacrifice a minor piece for a much needed pawn.
  • Achieving checkmate or stalemate on one board instantly ends the game and the situation on the other board becomes irrelevant in scoring.
  • There is a common variant where blocking a chess by placing a captured piece is not allowed.
  • There are other minor variants reducing the chaos in the game, such as only allowing the placement of captured pieces on your own side (first 4 rows) or even more restricting, only on that piece's starting position.

These two game variants are much more chaotic than the original chess, so quick tactical decisions are much more important than lengthy studies and thousands of memorized openings. --131.188.3.21 (talk) 00:39, 15 February 2010 (UTC)

I think you mean "check", not "chess", several times in that post. --Tango (talk) 00:44, 15 February 2010 (UTC)

You are right, I rushed the writing a bit and was not paying enough attention. Not to mention in my native language the two are spelled the same way. I'm sorry, and I hope it's still understandable. I forgot one important rule from the first game variant: "Pawns are only allowed to promote to pieces already captured. In the rare occasion nothing has been captured yet, the pawn is simply lost." And i hope it was clear enough that the second, team based game is completely different, with normal "one move per turn" rules. Enjoy! :) --131.188.3.21 (talk) 00:50, 15 February 2010 (UTC)

There's also Chess960 where the opening positions of the pieces are randomised. This makes it very difficult to memorise openings. - Akamad (talk) 01:49, 15 February 2010 (UTC)

In fact, Chess 960 was developed for that very reason. It's not as fun as ordinary Chess though. There are many other Chess variants to choose from. Zain Ebrahim (talk) 08:10, 15 February 2010 (UTC)

Cribbage and a special favourite of mine, Stratego. --Dweller (talk) 10:46, 15 February 2010 (UTC)

why is formic acid so much more toxic than acetic acid?

I don't really get it ... does formic acid have a greater affinity for dissolving into biological tissues? John Riemann Soong (talk) 21:23, 14 February 2010 (UTC)

I believe the pH level of formic acid is 2 (more toxic), and acetic acid is 3. -^Avic_ennasis @ {{subst:CURRENTTIME}}, {{subst:#time: xjj xjF xjY }} / @ 21:38, 14 February 2010 (UTC)

I went to google, typed in "formic acid" toxicity and on the very first page of hits was an except of an article "Formic acid (or formate) is apparently more toxic than other fatty acids, possibly owing to its enzyme-inhibiting activity". The wikipedia article formic acid states that it specifically affects a certain biological structure--that would be another useful search-term to help you find your information. DMacks (talk) 21:44, 14 February 2010 (UTC)

Miller-Urey

Miller-Urey experiments with better predictions of Earth's early atmosphere produce most (not all) amino acids and other organic compounds. However, they also produce toxins like formaldehyde and hydrogen cyanide which would kill any life which did happen to form. How are these experiments considered evidence for abiogenesis/evolution when they fail to produce all of the necessary compounds, and they also produce horrible poisons? --70.129.187.17 (talk) 21:59, 14 February 2010 (UTC)

All "necessary compounds" for what purpose? Remember, life doesn't have to be something we recognize to match our current life-forms in terms of their complete biochemical makeup. Likewise "toxins" is only in your current experience of certain biochemical processes. See for example, Hydrogen cyanide#HCN and the origin of life. DMacks (talk) 22:23, 14 February 2010 (UTC)

What is toxic to you may not be toxic to early life. There are plenty of extremophiles that live in places inhospitable to human yet it is still life. Also something to note is that evolution has nothing to do with abiogenesis. Evolution describes a continuous adaptation of life to its environments; it does not nor does it attempt to explain the origin of life itself (Darwin's book is called "On the Origin of Species" for a reason). --antilived^{T | C | G} 22:30, 14 February 2010 (UTC)

(ec) The primitive life forms which would have hypothetically arrived during Miller-Urey type conditions would be far too basic for HCN and formaldehyde to be "toxic" to them. I'm guessing they would just be a membrane with some nucleotides inside. HCN is toxic to us due to interactions with mitochondrial enzymes, I believe. It also should be noted that there is a hypothesis for the role of polycyclic aromatic hydrocarbons (which are carcinogenic) in the origin of life (see PAH world). This is another example which shows how fallacious it is to assume that "chemicals toxic to current organisms = chemicals toxic to primitive organisms". --Mark PEA (talk) 22:34, 14 February 2010 (UTC)

Firstly, (as our article points out) subsequent recreations of the Miller-Urey experiment produced all 22 standard amino acids. Secondly, the experiment is supposed to prove that it's possible for these compounds to have formed spontaneously from a plausible set of initial conditions. It is emphatically NOT claimed that "this is how it happened". There are a trillion possible variations of temperature, pressure, chemical precursors and energy sources that could have produced the actual abiogenesis event - and it's unlikely that we'll ever know precisely what happened because conditions changed repeatedly and dramatically over the billion years between the formation of the Earth and the first fossilised lifeforms that we have discovered.

This experiment should be viewed as a "proof of plausibility" rather than a "recreation". In dozens of other experiments with wildly different starting conditions, we get very similar results, showing that even if the conditions were quite different from the Miller-Urey experiment, there can be no doubt that these compounds would have been present in early earth history.

As for the poisons - we know that life can survive and evolve in an amazing variety of conditions (see Extremophiles) and it's no stretch at all to imagine that it could have formed despite those seemingly nasty compounds.

• This site suggests that cyanide was actually part of the chemical pathway to make Purine Adenine.
• This PBS documentary described how extremophiles survive in cave with normally lethal doses of formaldehyde.

So it's perfectly plausible that life could have formed even in such a seemingly-toxic environment. Also, we do not know what other reactions or physical separations were going on that could have subsequently eliminated these other compounds. Since we know that life most definitely exists and that it certainly evolves, it's really only necessary to find a plausible path to that initial abiogenesis event to complete the story to an acceptable degree of scientific proof. SteveBaker (talk) 22:56, 14 February 2010 (UTC)

February 15

Cooking rice under pressure

Electric rice cooker including scoop, containing uncooked rice

Inexpensive electric rice cooker containing cooked rice

• Rice cooker

The two pictures used by the article rice cooker provide an interesting contrast:

• The more expensive one on the left has a valve in the lid. It is a pressure cooker.
• The cheaper one on the right, as you can see, has a small opening in its thick glass lid. It cooks under normal air pressure and steam is not retained in the cooker.

I think people who eat sticky rice mainly use pressure cookers. Even if you are not using these advanced computerized models, the less expensive cookers use a very heavy lid as a pressure valve. I have seen some traditional wood-burning rice cookers in eastern Asian countries. They use over-sized heavy wooden lids. Some high-end sushi restaurants still use these traditional cookers because they are simply GREAT!

• http://www.quickspice.com/scstore/images/cookware-ricecooker-national-nsr42hn_lg.jpg

I guess the one on the right is generally used to cook non-sticky long grain rice (e.g., Basmati rice). I am not really sure about it. If steam can easily escape the cooker, how do they cook the rice? -- Toytoy (talk) 02:11, 15 February 2010 (UTC)

The difference is rice being cooked at around 100 degrees C and 1 atmospheres pressure; and rice being cooked at say 125 degress C and 1.5-ish atmospheres pressure. In both cases the rice is cooked; in the latter case, more quickly. See Pressure cooking. --Tagishsimon (talk) 02:25, 15 February 2010 (UTC)

How would a heavy lid act as a pressure valve? I have an old Panasonic rice cooker from the 80s, and there's no pressure cooking involved. It just has a small hole in the big plastic hinged lid. The steam escapes, yes, but at a much slower rate than if there were no lid at all. By the time the rice is finished cooking, there's still plenty of steam left in the pot.

AFAIK, it doesn't take any kind of fancy rice-cooker to make sticky rice. You just need some glutinous rice. Indeterminate (talk) 03:38, 15 February 2010 (UTC)

Certainly you can cook using a pot and a light-weight lid. The rice shall be edible but it may not be tasty. I have been told not to open the lid while cooking and "resting" countless times. That's why I thought keeping steam inside the cooker must be a way to make rice taste good. Failure to do so may compromise the taste. The heavy lid does not increase the pressure as much as a pressure cooker. However, the heavy lid without a hole may still retain steam much more than the lid-with-a-hole cookers. -- Toytoy (talk) 04:53, 15 February 2010 (UTC)

Is this girl lying to me?

I have been talking to this girl for quite some time, and she has been telling me she weighs 125-130 lbs. A month and a half ago she went into to hospital for an emergency appendectomy and was released the same day. 3 weeks ago she had to go to the ER twice because of bleeding in her esophagus and had to have stitches put in to stop bleeding. She said she was given some pills to gain weight as well as some other medicine, at this time she tells me she weighed 140 lbs. This weekend I saw her for the first time and she was FAT. She tells me she gained 40 lbs in 3 weeks (to 180 lbs) and that it is a result of her medical treatment and largely "just water" whatever the hell that means...

1) Is this at all plausible--can someone gain 40 lbs in 3 weeks?

2) what is "water weight"

3) Will she revert back to her previous size (if she is being truthful) and if so how long will it take and will her skin be all stretched and stuff?

4) Are there any ways I can tell if she is being truthful or lying?

XM (talk) 02:20, 15 February 2010 (UTC)

• I deleted this as a medical question. The OP disagrees, and has reposted it. Another opinion, please. -- Flyguy649 ^talk 03:56, 15 February 2010 (UTC)

He's not technically asking for medical advice. Well, he technically is asking for medical advice. I don't see the problem with this one though, he isn't seeking treatment or anything like that. Beach drifter (talk) 03:59, 15 February 2010 (UTC)

What I am asking is not medical advice. No medical decisions will be made based on whatever information I get here. I am asking for advice on whether or not a situation is medically possible and if so, how long it will take to resolve back to the previous state. XM (talk) 04:04, 15 February 2010 (UTC)

This girl is not going to become skinny, if that is want you want to hear. Beach drifter (talk) 04:05, 15 February 2010 (UTC)

AFTER EDIT CONFLICT:

Well I was hoping for a bit more depth in an answer. Do you think she actually gained the weight rapidly, or was just fat all along and lying to me? If it is the former, could she lose it once she resumes her normal lifestyle along with some aggressive exersize? XM (talk) 04:11, 15 February 2010 (UTC)

But it seems it would be pretty impossible to squarely address the question without entering the realm of analyzing a medical condition, and the big problem with that is all the missing pieces that we know nothing about. In my opinion it is an unanswerable question, and any attempt to respond to it entails giving out medical opinions in a reckless fashion. Bus stop (talk) 04:08, 15 February 2010 (UTC)

Again, nothing said here is going to effect (or is it affect) any medical decisions at all. I just want to know if something is medically possible. Medical opinions in this situation would not be reckless as they arent going to have any medical affect whatsoever. XM (talk) 04:18, 15 February 2010 (UTC)

1. yes, it's possible, depending on the kind of medication she's been given
2. 'water weight' usually means that the body is retaining excess water rather than excreting it. This can happen because of hormonal imbalances, kidney problems, certain medications, or other causes. 40 lbs of water weight gain strikes me as an awful lot, but I'm not a doctor.
3. She may or may not lose the excess weight - without knowing the cause, the medicines she's on, what her natural weight is, or other information there is no way to tell
4. why is it important? she's probably struggling with her own self image (whether the weight is natural or recently gained makes no difference); you're struggling with your own self image (you're apparently more worried about what she'll look like on your arm than what she's like as a person). If you're going to be a jerk and reject her because she's heavy, then go ahead and be an honest jerk; don't try to put the blame on her by making her into a liar. --Ludwigs2 04:12, 15 February 2010 (UTC)

Ludwigs, which is more likely, that she will lose the weight, or that she wont? And to answer your forth question there are two possible explainations for this situation, in one the girl is honest and her weight is temporary in the other the girl isn't and she is going to be permanently fat. I am okay with one of those explainations, not with the other. But I do need to find out which it is, or at least which is most likely XM (talk) 04:23, 15 February 2010 (UTC)

That question is literally impossible for us to answer. Ludwigs is speaking in purely general terms. It is possible for a person to gain weight due to water retention; it is possible for a person to gain weight due to medical treatments, and it is possible for a person to gain a large amount of weight in a short amount of time. Those are all possibilities based on biology, and without any real comment on the specifics of any one particular case, especially on the one you cite. Wikipedia's reference desk contributors are unable to make specific comments on a specific case as that would constitute a form of medical advice. No one here, or indeed anywhere on the internet, can make any comments as to the specifics of your friends case, as to why she may have gained weight, whether she is telling the truth or not, how she may lose it, etc. etc. All of that is between her and her doctors, we can only answer the general biological questions, not on her case. It will be up to you to decide what it all means in her case. --Jayron32 04:52, 15 February 2010 (UTC)

Jayron, So it is possible to gain that much in such a short time? If what she is telling me is medically possible, then I am inclined to believe her until other evidence presents itself. But 40 lbs in 3 weeks seems like a lot to me. XM (talk) 04:59, 15 February 2010 (UTC)

I have no idea if that specific amount in that specific time is actually possible. What you should do is read the Wikipedia article weight gain and follow any links from that article, including external links, and arrive at your own conclusions. This is not an endorsement of any information contained in either that article or especially in any of those links. I have no idea if the information is valid or reliable, but if you want some information, its a better start than asking for medical advice from random strangers on teh intrewebz. If you want a poorly informed and unverifiable medical opinion, at least make it your own poorly informed and unverifiable opinion, and don't rely on someone elses. --Jayron32 05:14, 15 February 2010 (UTC)

@ jayron: This isn't a medical question, it's an emotional one. XM is trying to find some excuse to be pissed off at this girl because she's violated his heartfelt expectations. He has all the medical information he needs to decide whether he can realistically work himself up to an effective level of self-righteous indignation; I suggest we leave him to explore his inner self on his own. --Ludwigs2 07:22, 15 February 2010 (UTC)

You know, Ludwigs, your condescending comments aren't really appericiated by me or probably anyone else on the Ref desk. I find your comments extremely rude, emotionally charged, and without basis. I asked if the claim of someone was within the realm of possibility, because if they aren't then that means I have been lied to. Additionally, in the event that she is being truthful, I want to know the likelihood that she will revert to an attractive state. Evidently this is what you have a problem with causing you refer to me as self-righteous. I'm sorry if someone decided they didn't want to be with you because of your physical appearance, but comments like yours are simply uncalled for and most unwelcome. XM (talk) 07:51, 15 February 2010 (UTC)

Fujiwhara effect

The Fujiwhara effect says that "When cyclones approach each other, their centers will begin orbiting cyclonically about a point between the two systems." This is all fine except for one thing: How would it affect two storms in opposite hemispheres, say at 5°0′0″N 170°0′0″W and 5°0′0″S 170°0′0″W? If the two cyclones began to orbit, it would result in them crossing the equator, which I seem to recall tropical cyclones cannot do. Does this mean that the Fujiwhara effect would kill the two storms, or would it just not affect them at all? Ks0stm ^(T•C•G) 04:19, 15 February 2010 (UTC)

I have fixed your coordinate template. Nimur (talk) 04:24, 15 February 2010 (UTC)

Thanks. Ks0stm ^(T•C•G) 04:29, 15 February 2010 (UTC)

There's not a hard rule about a tropical cyclone crossing the equator. The coriolis force tends to push storms away from the equator and towards the poles, but climate and storm dynamics are complicated things - if a local pressure perturbation was strong enough to suck a storm across the equator, it could happen. I suspect that since both the Fujiwhara effect and the internal cyclone spiral are both consequences of the coriolis effect, which is weaker near the equator, the tendency for this spiraling to impact storms that happen to be close the equator (which are rare to begin with) would be low. If two storms were on opposite sides of the equator simultaneously (which would be very rare), then the effect would still be weak-to-non-present - again, with the caveat that local conditions can behave counter to the global-scale trends. Nimur (talk) 04:39, 15 February 2010 (UTC)

In thousands of examples, no cyclone has ever crossed the equator. [9] Dragons flight (talk) 06:39, 15 February 2010 (UTC)

Relative temperature of fabrics

Why do different fabrics feel colder than others? For instance, I have flannel sheets as well as some (probably) nylon/cotton blend sheets. The flannel "feels" warmer when getting into bed than the other sheets yet my room is the same temperature. Or another example would be when you slip on a coat or jacket that has a nylon lining in the sleeves. The nylon feels cooler than if you were to put on a flannel shirt. Why? Dismas|^(talk) 05:03, 15 February 2010 (UTC)

This has nothing to do with temperature, and everything to do with specific heat. The temperatures may be identical, but what is different is the rate at which different materials will conduct heat away from your skin. Your perception of the temperature of the fabiric really isn't a perception of temperature, its a perception of heat flow either into or out of your skin, which is dependent not only on the relative temperature difference between your skin and the fabric, but also on the relative difference in properties between the materials involved with regard to how heat energy affects them, aka specific heat. --Jayron32 05:09, 15 February 2010 (UTC)

about the wounds

why the wounds get,s dark blue coulour after ome time?? —Preceding unsigned comment added by 200.55.135.211 (talk) 05:16, 15 February 2010 (UTC)

Wikipedia contributors cannot provide medical advice. The best we can do is direct you to articles like bruise which may contain information on the topic, but we can only tell you that you should not act on any information you find at Wikipedia, but should instead seek the direct advice of a qualified physician or other medical professional. --Jayron32 05:18, 15 February 2010 (UTC)

Another cause for wound discoloration is gangrene or necrosis. That is a very serious condition and would definitely need medical attention. Nimur (talk) 05:29, 15 February 2010 (UTC)

torro ant poison

i have carpenter ants. i got torro ant poison BAIT TRAPS there not eating it thou why —Preceding unsigned comment added by 67.246.254.35 (talk) 05:59, 15 February 2010 (UTC)

If you are not having success using store-bought pest control products to control the ants, you should call in a professional. Carpenter ants, like termites and some other pests, can cause structural damage and should not be taken lightly. I would recommend that you look up "pest control" in your local phone book, and seek a qualified professional. --Jayron32 06:08, 15 February 2010 (UTC)

Terro is a sweet bait. I suspect that carpenter ants are more interested in wood than fruit or carrion. -Craig Pemberton 06:44, 15 February 2010 (UTC)

do carpenter ants like sweet bait or greasy bait--Thekiller35789 (talk) 07:10, 15 February 2010 (UTC)

Is clear a color?

??? 69.77.247.18 (talk) 06:03, 15 February 2010 (UTC)

Not really. In computer graphics, opacity is measured on a separate channel from color - see alpha compositing. Whether this meets your definition for "color" is a matter of semantics. Outside of the realm of computers, most people use color to mean that quality which is the perceptual representation of the wavelength of light in the visible spectrum. Again, opacity is a separate quality from color in this context - it has to do with the transmission coefficient or transmittance of a material. Nimur (talk) 06:08, 15 February 2010 (UTC)

It also depends on how you define "color". In some applications, and under some definitions, it may. Color is a nebulous quantity, and without knowing what context we are talking about, it is hard to discuss it in detail. Though Nimur's answer is pretty good. --Jayron32 06:11, 15 February 2010 (UTC)

Can't hardy wait for Steve to weigh in on this one ;) hydnjo (talk) 06:43, 15 February 2010 (UTC)

Java loving roaches

Hi

I don't know if it's just me, but has anyone ever noticed (those of you who've had problems with cockroaches in your homes) that they seem to have a love for either coffee or something that's inside the coffee. A lot of times when someone has left half a cup of coffee or less overnight, we'd find the next morning that they're inside the cup floating on the coffee... dead and at times there would be more than one in a cup. Now I don't know if they like the coffee that much, but are unaware of something inside the coffee that can kill them or if they like the coffee so much that they drink themselves to death.

Thanks, NirocFX 41.193.16.234 (talk) 10:34, 15 February 2010 (UTC)

I suspect they drown, rather than drink themselves to death or have adverse reactions. Sounds like you have a solution to your roach problem, too. --Tagishsimon (talk) 10:38, 15 February 2010 (UTC)

No, luckily we sorted them out (for good) in a different manner otherwise they would have probably opened their own Starbucks in our house sooner or later.

Thanks, NirocFX 41.193.16.234 (talk) 11:23, 15 February 2010 (UTC)