Wikipedia:Reference desk/Archives/Science/2010 February 11

= 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!  -- Jayron  32  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. -- Jayron  32  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?


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 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. :-) ~ A H  1 (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? -- k a i n a w &trade; 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. --  k a i n a w &trade; 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. &mdash; 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])". &mdash; 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 $$\partial_\alpha h^\alpha_\beta - \partial_\beta h^\mu_\mu/2 = 0$$, 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
 * $$ 16\pi (T_{\mu\nu} - \eta_{\mu\nu} T/2) = \partial_\mu \partial_\alpha h^\alpha_\nu + \partial_\nu \partial_\alpha h^\alpha_\mu - \partial_\mu \partial_\nu h - \partial^\beta \partial_\beta h_{\mu\nu}$$
 * (I got this from linearized gravity 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). --antilivedT 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. ~ A H  1 (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. -- 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)


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? 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)