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December 11

What kind of machine is used to sew patches over holes in the middle of the roof of a M.A.S.H. tent?

I can't find anything on how to use a sewing machine to sew a patch in the middle of a large sheet of fabric (50' x 50').

The problem I'm running into is that there isn't enough room between the needle and the base of the sewing machine for that much fabric.

But I've seen patches done in large tents, tarps, sails, blankets, etc.

What's the secret?

(Is there another type of machine that is used for this?)

Simple Simon Ate the Pieman (talk) 03:52, 11 December 2009 (UTC)

There are special "long arm" machines for that kind of thing. Like this one, for example. SteveBaker (talk) 05:56, 11 December 2009 (UTC)

The example machine is said ominously to have "All fear driven hook mechanism". Cuddlyable3 (talk) 21:02, 11 December 2009 (UTC)

The thing I need to sew is a GP Medium (M.A.S.H. tent). See http://www.youtube.com/watch?v=lAlYK3W7FAA The thing is huge, and the rips are in the middle of the roof. I would need a sewing machine with an arm 6 feet or more long just to pull enough of the fabric past the needle to be able to reach the holes!

Is there a machine that can sew a lockstich from one side of the fabric? Or without an arm? If so, what is it called?

Simple Simon Ate the Pieman (talk) 00:49, 16 December 2009 (UTC)

On the number of exoplanets that transit their stars in the milky way

I'm a pretty avid observer of the amateur transit watch community and I was just wondering something. Obviously, astronomers looking for transits are hoping that the rotational plane of the observing planetary system will coincide with our line of sight, thus having planets crossing the light of the star every once in a while giving us much more direct evidence for their existence. To measure the radial velocity of stars we watch how quickly the star moves towards and away from us, and thus, a similar transiting orbital orientation works best for radial velocity measurements as well.

Now my question is, is there a tendency for planetary ecliptic planes to orient themselves in a certain way relative to the orbital plane of the galaxy? Obviously this comes down to the rotation of the star in its early stages, so I could ask then do the rotations of stars in any way reflect their orbit around the galaxy? I couldn't find out the planar angle of the solar system relative to the milky way, but from visual memory it doesn't seem to be very close, which means that this will be much help to astronomers looking for transiting stars, but I guess it's also possible that local planetary systems will have similar planes, due to similar environment, age, etc.

Does anyone have any insight on this? Thanks! 219.102.221.182 (talk) 05:02, 11 December 2009 (UTC)

I doubt there is any special tendency for the plane of the stellar ecliptic to line up with the galactic ecliptic. So the probability of an exoplanet eclipsing it's parent star basically comes down to it's orbital radius and the diameter of the star (and to a much, much lesser extent, the diameter of the planet). The angle through which the orbit will occlude the star is arctan(starRadius/planetaryOrbitRadius)x2.0 - if the angle of the star's ecliptic is random then you can easily figure the probability that it'll happen to line up with the position of the earth. So to answer your question - we'd need to know the distribution of diameters of the stars in our galaxy - but we'd also need to know the statistics of the planetary orbital radius...and there's the problem. We haven't got that information until we've already found the exo-planets! We could probably make a guesstimate.

So if we said that our sun was typical - and we were looking for planets out as far as (say) Saturn - then that eclipse is only visible over an angle of about 0.06 degrees...out of 180 degrees. That's about a one in 3,200 chance. There are a lot of stars out there - so there are a lot of chances - and lots of planets are a lot closer to their stars than Saturn - so the odds are probably a lot better than that. This is a worst-case - where the plane of the stellar ecliptic is completely random. If there is some tendency for the stellar ecliptic to line up with the galactic ecliptic - then for more distant stars - that greatly increases the probability of eclipses - but for closer ones - it decreases the probability. SteveBaker (talk) 05:36, 11 December 2009 (UTC)

Thanks! 1 in 3200 chance, that would actually be quite a bit better than I had expected (for random planes). Is there any particular reason you feel that the planes should be random? The fact that the solar system, earth, and most satellites occur on the same plane would seem to hint at a trend, and I have no reason to assume in the other direction. Though I have to say I totally didn't realize the consequences this would have for near star systems... I guess I was thinking too 2-dimensionally. Also it's worth noting that if the sol system isn't nearly planar with the galaxy, but there indeed is a general trend for other planetary systems to be, that could also lower the odds of catching a transiting planet considerably. 219.102.221.182 (talk) 06:34, 11 December 2009 (UTC)

It is also worth mentioning that gravitational microlensing techniques such as the proposed The Galactic Exoplanet Survey Telescope (GEST) are expected to be good for small planets some distance from the star. Both observed transits and radial velocity techniques require a large planet close to the star (which microlensing in not very good for), hence microlensing is expected to find many more planets and of a smaller size than previous methods. SpinningSpark 10:46, 11 December 2009 (UTC)

I agree that one in 3200 seems like unexpectedly good odds - I tried to make it come out worse - but the numbers insisted and we must obey! It's not so much that I have a reason to believe that the ecliptic planes of stars should be random with respect to the plane of the galactic ecliptic - so much as that I can't think of any reason why they shouldn't be random. (Maybe that's the same thing?!) The plane of the Milky Way galaxy is at 60 degrees to the Sun's ecliptic - so unless we're rather special - I'm pretty sure there is no correlation. However, if there is a preferred direction then that's a problem. The deal is that the galactic spiral is quite thick - maybe 1000 light-years. So all of the stars within about 1000 light years of us are much more likely to be above or below us as than they are to lie in the same plane. If there is some tendency for planetary disks to lie in the galactic plane (meaning that our sun is weird in that regard) - then we'd be unable to see any eclipses for almost all of the stars within about 1000 ly. That would be bad news for astronomers because the really nice, easy-to-measure stars are going to be the closest ones...and those would be the problematic kind. However - as I've said - there doesn't seem to be a good reason for them all to line up like that (and the Sun certainly doesn't) - so I think the 1:3200 number is about right...at least for stars the size of the sun with planets at the distance of Saturn. Of course, exo-planets that are closer to the parent star will be seen to eclipse their star over a wider angle - and planets further from their star - less so...so the 1:3200 number is just a ballpark figure based on our Solar System. Also - some of those eclipses will be briefer in duration than others if the planet only just eclipses the very edge of the star - so nice long-duration eclipses would be rarer. SteveBaker (talk) 13:48, 11 December 2009 (UTC)

Check out Methods of detecting extrasolar planets#Transit method - it has some of the probabilities. For an Earth-like planet in an Earth-like orbit (which are the most interesting), it's about 1 in 200. Pretty good odds. --Tango (talk) 14:00, 11 December 2009 (UTC)

Binoculars in Games & Movies.

When game makers and movie makers want to depict the idea that we're seeing the world through a pair of binoculars - they often use the trick of masking off the edges of the screen with a pair of overlapping circles kinda like this:

  #################################
  #######      #######       ######
  ####            #            ####
  ###                           ###
  ###                           ###
  ####            #            ####
  ######       #######       ######
  #################################

I'm pretty sure that out here in the real world, binoculars don't look like that when they are properly set up (sadly, I don't own a pair to try) - it's really just a single circle. Is this a true statement? ...and (because I need to convince some people about it today) is there a cogent explanation as to why that is the case.

Finally - is there a name for this kind of mask - maybe some kind of movie jargon?

TIA SteveBaker (talk) 13:32, 11 December 2009 (UTC)

You are correct that only a single circle is seen in the real world, however that would waste a lot of screen real estate (cf a "gun scope / crosshairs" view as seen in any typical James Bond film opening.) As far as terminology, in Final Cut Pro, they just use the term "binoculars filter". --LarryMac | Talk 13:50, 11 December 2009 (UTC)

Yeah - and the 'real-estate' issue is under debate too. I'm building a computer graphics simulation where realism is very important - so loss of screen real-estate is taking second place to "getting it right". What I may do is to use a single circle that's only a little bit narrower than the screen - and let it cut off at the top and bottom. A compromise solution.

So what is a convincing explanation (to my Producer - who also doesn't have a set of binoculars at hand right now - and who wants a double-circle) of why we only see one circle?

SteveBaker (talk) 14:09, 11 December 2009 (UTC)

Steve, if this is for work, this is the perfect occasion to buy a pair of binoculars on company expense ;-). --Stephan Schulz (talk) 14:13, 11 December 2009 (UTC)

It's all about frame of reference... The point of looking through binoculars is so that both of your eyes can experience the visual of the down-field magnification. Your brain, doing what it always does with information from your eyes, stitches the two circles together to form one stereoscopic view. A looking glass, spotting scope, monocular, etc. are all single optic versions of the same thing, if you aren't interested in the stereoscopic view. The answer that I am getting to is that there is no good computer screen approximation for the function of binoculars, unless you have a stereoscopic display of some sort, so "getting it right" with binoculars is kind of out of the question. If you want my opinion, either go for the movie cheeze double bubble view, change the device in the game to a monocular and make it a circle, or make it a computerized spotting device of some sort that doesn't use discrete optics but still has the wide form factor of binoculars, so that the onscreen representation can be 4:3 or 16:9 or whatever it is that you are going for. --66.195.232.121 (talk) 14:29, 11 December 2009 (UTC)

Actually, I can't change the device. What we do at is "Serious Games" - using games technology and game development techniques to produce simulations for training real people for the jobs they actually do. They could be firefighters, county sheriffs, black-ops guys, campus security people...you name it. But if what they carry is binoculars - we have to simulate binoculars - the actual binoculars they'd really have with the right field of view, depth of field and magnification. We don't have the luxury of being able to make it into some kind of futuristic gadget. Whatever that person would be issued with in reality is what we'll give them...to the degree of fidelity possible with the computer we're running on. SteveBaker (talk) 22:44, 11 December 2009 (UTC)

...and therefore no good computer screen approximation for the function of eyes. 81.131.32.17 (talk) 17:21, 11 December 2009 (UTC)

(ec) Try this one on for size — even without special equipment, you already have binocular vision. You're looking through two eyes, but you only see one image. The brain is very good at fusing two images into one, and the same merging process happens when you use a pair of binoculars.

If you don't have a pair of binoculars handy, then you can do a quick and dirty demo with a matched pair of hollow tubes. (Note - this is original research. I just tested this with a toilet paper tube cut in half, as it was the only tubular object I had handy.) Hold the tubes side-by-side, directly in front of your eyes. You want the center of the tubes to be as close as possible to being in line with the pupils of your eyes.

Now, focus your eyes on an object in the distance. Notice how the inner surfaces of the tubes (as seen from each eye) get merged together, and you have an apparently circular field of view? Presto! You may have to wiggle the tubes a bit to get the positioning right, but without a pair of binoculars it's probably the most convincing demo you're going to get. That said, if your boss wants the double-bubble silhouette, just give it to him/her. Or try to persuade him to equip the in-game character with a spotting scope, telescope, or other single-eyepiece device. TenOfAllTrades(talk) 14:37, 11 December 2009 (UTC)

I think the important point is not so much that your eyes can fuse the two images, since that doesn't preclude the sort of "double-bubble" effect, but that the fields of vision provided by the binoculars to each eye is nearly identical; they almost completely overlap. In contrast, your normal vision without binoculars is much closer to this double-bubble thing, since the left side of your field of vision is only seen by the left eye and the same with the right. Only the center area is in the overlap seen by both. With binoculars you adjust the position of the two telescopes specifically so that they provide each eye the same view in order to get binocular vision of what you're looking at. Rckrone (talk) 15:28, 11 December 2009 (UTC)

Surely the why-for is so that it is instantly clear to (most) people that the vision we are seeing on screen is (as if) 'through binoculars'. Binoculars defintely show just a single-circle when used - though if you adjust the 'width' you can make it look more like a side-ways laid number 8 (infinity sign?) too. I'd imagine it's a simple short-cut by film-crews to make it clear what we're supposed to be seeing, and as others not it takes away less of the view on screen than a circle would. 194.221.133.226 (talk) 15:32, 11 December 2009 (UTC)

To answer the question of what this is called in cinematography, if it is done with "soft" edges, as it invariably is, it is called a "vignette" (and the technique is called "vignetting"). If the edges are hard it is simply called mask/masking. SpinningSpark 16:06, 11 December 2009 (UTC)

The problem with the game/movie thing is that with real binoculars you can actually see depth, and know the difference between a binocular image and a spyglass image. In a game/movie, you cannot, and cannot know the difference otherwise. So you're already going to have to sacrifice the biggest "reality" aspect of binoculars for your game (seeing in 3-D) just by the nature of it (unless you are working on something a bit more cool than I am guessing). At some level, the amount of "reality" is somewhat arbitrary, given how much you are already abstracting. --Mr.98 (talk) 16:15, 11 December 2009 (UTC)

You might try showing a movie clip of an accurate depiction, the only one i can recall is from The Missouri Breaks.—eric 17:08, 11 December 2009 (UTC)

This problem is equally as challenging as asking somebody to describe the "shape" of their field of view without binoculars. Nimur (talk) 17:21, 11 December 2009 (UTC)

Well, I learned from this pseudo-educational host segment from MST3k, they're called "Gobos" or "Camera Masks". WP's articles don't seem to fully back this up. But google shows me that that "gobo" is at least sometimes used in this context. Google also seems to suggest "Binocular masks" APL (talk) 17:54, 11 December 2009 (UTC)

As a compromise, when you switch to the binocular view, you could start with two separate circular images (arranged like a MasterCard logo, with the two images identical) that converge to a single circular field. The action should be sort of irregular, with some jerkiness and overshoot. This would mimic someone picking up binoculars and adjusting the interpupillary distance to their eyes, and I think it would clearly depict "binoculars" to the user. -- Coneslayer (talk) 18:57, 11 December 2009 (UTC)

What a touching lament "sadly, I don't own a pair to try" so close to Christmas.... Cuddlyable3 (talk) 20:58, 11 December 2009 (UTC)

(No,no,no! Do NOT confuse Santa. I carefully wrote my Xmas list (in my best handwriting) and shoved it up the chimney already - what I want is a Kindle - I don't own binoculars because I neither want nor need binoculars! I have not been naughty this year - at all - ever.  :-) SteveBaker (talk) 22:44, 11 December 2009 (UTC)

What never? If you ask for a pair of binoculars Santa won't think of an unauthorised verse sung to the melody of the Eton Boating Song

It was Christmas eve at the harem

All of the eunuchs were there

watching the beautiful houris

combing their pubic hair

Just then from the regal apartment

the sexy old sultan calls

What do you want for Christmas boys?

The eunuchs as one shouted Balls.

Cuddlyable3 (talk) 00:02, 13 December 2009 (UTC)

You shoved a piece of paper up the chimney? You won't get a Kindle, you're getting kindling! -- 128.104.112.87 (talk) 15:59, 14 December 2009 (UTC)

Coneslayer's idea sounds good. I could also suggest that at the edges of the circles you blur it a bit and darken. You could even have the whole picture go out and in focus a couple of times, increase the chance of missing something in the view. And don't forget to ray trace the internal reflections off the lenses if you are looking near something very bright! And there would be a little bit of unsteady shaking. Graeme Bartlett (talk) 21:54, 11 December 2009 (UTC)

I like the idea of doing a quick bit of faked "adjustment" - but maybe only the first time you use the binoculars in the game...it wouldn't be cool to do that every time they picked them up though! There is a fine line between "cool effect" and "bloody annoying"! SteveBaker (talk) 22:44, 11 December 2009 (UTC)

Although if you are going for realism "bloody annoying" may be more realistic than the "cool effect". Ideally (i.e. for maximum realism) anytime the binoculars are used straight out of their case (i.e. from folded) the faked adjustment should happen. Also there should be a little bit of focusing delay when shifting views to objects at different distances - similar to what Graeme suggests. Reading about what you do (cool job by the way) simulating this usage delay could be fairly critical for some stuff. For example, if a police officer gets in the habit of keeping multiple people in view just by swinging their binoculars around, they are going to be unprepared for the need to constantly refocus when doing this in the real world. I speak from birdwatching experience, keeping multiple subjects at different distances "under surveillance" is quite challenging. Putting focus delay into the simulation would train people to consider carefully how many subjects they can watch at once, an annoying but important real world limitation. Apologies if you are way ahead of me on this one or I am getting too pedantic. 131.111.8.99 (talk) 01:12, 12 December 2009 (UTC)

We have 'subject matter experts' who we consult about small details like this. It's always interesting to discover what features matter and what don't. For example - play one of the very latest combat games: Call of Duty: Modern Warfare 2 - as you're walking around in "first person" mode - look for your shadow. You'll be surprised to find that while every other character in the game casts a shadow - you don't! It may not be immediately obvious why this is important - but if you are hiding around the corner of a building - hoping that the bad guy doesn't know you're there - in the real world, your shadow can give you away...if you have a shadow! You'd like someone who is trying to do that to pay attention to where their shadow is falling - so CoD isn't a great training aid (for lots of reasons - not just this). It's actually surprisingly difficult to produce a good shadow in a first person game because the animation of your avatar is hard to get right when you're doing joystick/mouse-driven actions while the pre-scripted "run", "walk", "shoot" animations are playing...so they just don't bother! We don't have that luxury to just ignore things when they are difficult. SteveBaker (talk) 04:10, 12 December 2009 (UTC)

He is right though, and I think an animation is the only solution to this. There have been games in the past that go for pseudo-realism using similar tricks. Heck, Counter-Strike tries to make the whole "pull a machine gun out of your pocket" thing a little more realistic by varying the time it takes to get the gun loaded and ready, although the animations can generally be overridden by shooting. If annoyance is something you want to avoid, then you could always just shorten the animation after the first use. I don't see any reason it would be that annoying though, as long as the zoom settings don't reset every time you use it, it shouldn't take that long to get ready. 219.102.221.182 (talk) 23:48, 13 December 2009 (UTC)

Need a reliable value for the sun's illumination under variable Earth conditions

Firstly, I am after approximate ranges for the sun's illumination on earth and in orbit under various conditions (clear day, overcast, etc.) for the purpose of calibrating CG lights in a 3d computer application. The confusion has arisen as a result of trying to research a good value for an overcast day; I tried using Google for that and encountered wildly varying values with some surprising implications. I have already looked at the Wiki article on Sunlight for these values. The opening section of the article gives an (uncited) value for the sun's illumination of 100,000 lux at the Earth's surface. Now, this sounds all well and good adn would match the default ranges for sun objects in the doftware package I am using. However, I then ran into, for example, these values on this page; the value given for 'direct sunlight' is indeed 100,000 lux, but it then describes 'full daylight' as 10,000 lux, and an overcast day as 1000 lux. This page gives the same values without specifying the 10,000 lux value for 'full daylight'. The implications of the first page are that, if direct sunlight is 100,000 lux, and 'full daylight' 10,000 lux, then the Earth's atmosphere absorbs or reflects 9/10ths of the sun's light on a clear day (!), and that an astronaut in orbit would be receiving 10 times the amount of light as someone on the Earth's surface; and that a cloudy overcast day provides around 1/10th or 1/100th the illumination of a sunny day (depending on which figures you look at), and 1/100th the illumination in orbit. . . All this sounds surely wrong to me. Firstly I was under the impression that, as the Wiki article suggests, the 100,000 figure is roughly correct for Earth's surface on a clear day, although I am a bit puzzled by the figure of 1/100th that for an overcast day - that sounds a bit too dark. Similarly, I would have assumed that the amount of visible light absorbed or reflected by the atmosphere is comparatively slight (given, for example, Earth's average albedo of around 0.31, ie. 3/10ths), and that lighting conditions in orbit aren't too far off those at Earth's surface on a clear day - brighter yes, but not that bright. Please help if you can, I seriously need some reliable values for these conditions, and with pages contradicting each other I don't know which values I'm supposed to follow. Thanks in advance for any helpful answers. LSmok3 ^Talk 17:14, 11 December 2009 (UTC)

Insolation is usually measured in Watts per Square Meter. The solar constant is pretty clearly measured at about 1370 watts per square meter at the top of the atmosphere (reliable sources are cited in our article); depending on conditions, anywhere from ~ 100 to 1000 watts per square meter reach the Earth's surface; but since you need a luminosity and not an incident power (irradiance), you might want to look at lux and see the conversion procedure. Nimur (talk) 17:26, 11 December 2009 (UTC)

The albedo of cloud is betwen 0.5 to 0.8 (see albedo). So we'd expect the total amount of sunlight reflected back out on a cloudy day to be 50% to 80% of the total sunlight. All that isn't reflected is either absorbed by the cloud - or scattered around so that it ends up down here on the ground as ambient sky-light - so we'd discounting absorption by the cloud - you'd expect the ratio of light on a clear-day to an overcast day to be between 2:1 and 4:1 - with multiple layers of cloud and some idea of what is being absorbed - I could easily believe the 1/10th of sunny day illumination. The 1/100th value seems more dubious...perhaps they are talking about the light coming fron the direction of the sun itself - neglecting the scattered light...that could easily explain the 1/100th number. For patchy cloud conditions between those two extremes, it all depends on whether the sun happens to be behind a cloud or not from wherever you happen to be standing.

Some of the confusion may arise from the fact that the sky isn't black. If you measure the light coming from the direction of the sun alone - you get a much lower value than if you average it over the entire sky. —Preceding unsigned comment added by SteveBaker (talk • contribs)

Okay, thanks for the quick answers, but I'm afriad I'm still a bit lost. Firstly, the watts to lux conversion is a bit beyond me - I'm an artist, not a mathematician: the lux page directs me to the page for the luminosity function, which is required to make any such calculation, and that specifies variables I don't have, like the actual wavelength. Secondly, all I'm after are guideline ranges and averages for a few conditions - Earth orbit, clear day at surface (noon - sunrise/set), and fully overcast (noon - sunrise/set), from which I can approximate all I need. The point about ignoring cloud absorption seems a bit odd, as that is a determining factor in surface illumination based on cloud cover, ie. exactly what makes an overcast day, (and remember, I was only quoting the average albedo of the Earth). I also seem to have run into the same trouble here as I encountered on other pages, namely a lack of any clear definition of terms and contradictory figures. Helpfully, the lux page gives various values for different conditions, but makes a distinction between 'full daylight' and 'direct sunlight' (10-25k and 32-130k respectively) and gives the value of 1000 lux for overcast: without any actual definition, I would assume that 'full daylight' refers to the brightest Earth-surface conditions, and 'direct sunlight' to unfiltered, non-atmospheric, ie. orbital conditions. This matches the pages I had found which caused me the confusion in the first place, and suggests that the sun lights in the application I'm using default to outer-space conditions (which is a bit silly; and to quote from the documentation: "Intensity: The intensity of the sunlight. The color swatch to the right of the spinner opens the Color Selector to set the color of the light. Typical intensities in a clear sky are around 90,000 lux."). However, the daylight value links to the Wiki page on Daylight, which also provides guideline values; it doesn't use the term 'Direct sunlight', but gives similar values for 'bright sunlight' and 'brightest sunlight', and gives the value of 10,000 - 25,000 lux for an overcast day: 10-25 times higher than the lux article. So, what am I supposed to follow? LSmok3 ^Talk 18:46, 11 December 2009 (UTC)

Among the problems in converting solar radiant flux into an equivalent "candela" is the difference between specular and diffuse lighting. "Candela" really only applies to an approximately point-source light - but sunlight, whether the day is cloudy or clear, is illuminating the ground diffusely - in other words, the entire sky "glows" and lights the object. So, trying to model the lighting as a single point-source (the sun) is obviously flawed - there is no equivalent brightness or luminosity for the sun which would result in equivalent lighting conditions. In computer graphics, this is usually dealt with by applying an ambient lighting condition - a "uniform" illumination from a particular direction. Alternately, you can model the sun as a point-source at a great distance, and then model the atmospheric diffusion - but that will be very computationally intense, and will yield about the same visual effect as an ambient lighting source. Nimur (talk) 19:58, 11 December 2009 (UTC)

Yes, I am well aware of that issue. And no, I'm not looking for the candle power of the Sun. Indeed, in modeling a daylight system (including the IES Sun and Sky system I quoted the documentation for above), two lights are generally used, one to represent the contibution from the sun as a point source (ideally Photometric) light (although in recent years that's tended to be an area light purely to allow for the modelling of realistic shadows due to scale and diffusion), and another to represent diffuse scattered 'fill' from the sky. But that doesn't mean I don't need realistic values, especially given that the systems may mix photometric with non-physical lighting, and with global photometric controls the relationships between all lights in a scene are affected (for example, street lighting at dusk would feature a sun and sky system in combination with artificial lighting, so the relationships must be correct). (And in fact, the reason I was originally looking for realistic lux values for an overcast day - the whole thing - was to calibrate just such a fill to realistic proportions, bearing in mind that it may also be photometric; again, if the relationships aren't accurate, not only is it bad practice, but problems would also occur if, say, I was animating a shift from clear to overcast conditions.) Also, don't assume I am only interested in Earth surface figures; as I already said, I also need realistic values for space scenes. So are there no reliable values that actually agree for sunlight in lux? That seems a bit strange. It should be possible for just about anyone to get such figures by going outside under the given conditions armed with a light meter set to give values in lux and measuring at exposed ground - I'd do it myself but I don't own one, and can't help assuming those values must surely be well-established; for some reason my documentation suggests values that Wikipedia claims are burn-your-retina space lighting and the reason why astronauts where mirror-visors, and no one seems able to agree on overcast values. LSmok3 ^Talk 20:50, 11 December 2009 (UTC)

Okay, how about Reference luminous solar constant and solar luminance for illuminance calculations, (J. Solar Energy, 2005), or Determination of vertical daylight illuminance under non-overcast sky conditions, (Building & Environment 2009)? Table 2 in the first article specifies a lot of parameters, including luminance of about 1.9x10⁹ cd/m². For the very detailed cases you are considering, you may want to read the entire articles, since you are particularly clear that their assumptions differ from yours. There is an entire section devoted to the assumptions made and the impact these have. Nimur (talk) 22:20, 11 December 2009 (UTC)

Well, I'm afraid the problem with that is the principle of having to pay around $60 for the information, which as I say I would have thought would be pretty well-established. The whole point of Wiki is that information is free, and as it is, I don't even own a credit card or have a paypal account to buy it, especially without being sure it actually contains what I need. Having said that, I did find this link through Google to the same site, which suggests that the values quoted in my software are correct and the ones on Wiki are wrong. So never mind. LSmok3 ^Talk 07:43, 12 December 2009 (UTC)

If you don't have access to the online journals (which are not free), then you can try requesting hard copies of those journals through a library. Unfortunately, not all information is published under a free license, so immediate access to download over the internet is not always possible. Alternately, you can ask your school or library to purchase a web subscription to those journals so you can have immediate access in the future. Nimur (talk) 20:32, 12 December 2009 (UTC)

I actually wouldn't be that surprised if direct sunlight really was 100 times more "bright" then on an overcast day. The sun is literally blindingly bright. And anyway, isn't it one of those logarithmic scales? Something with 10 times the energy only looks twice as bright? So 100 times it appears 4 times as bright? If you are really interested in getting good results, I would be borrowing a light meter and taking measurements myself. Vespine (talk) 03:10, 14 December 2009 (UTC)

trialkyloxonium salts and beta elimination

Most of these are unstable, right? My question is, what happens if you have no beta proton on the oxonium salt? It can't possibly eliminate via the Hoffman mechanism? Will it decompose onto ether + carbocation anyway?

Also, can you undergo transalkylation with ethers and an alkyl halide via SN2?

Are carbamates prone to beta elimination?John Riemann Soong (talk) 22:52, 11 December 2009 (UTC)

Triethyloxonium tetrafluoroborate is pretty stable. Graeme Bartlett (talk) 23:47, 11 December 2009 (UTC)

How does it decompose in water? Does water act like a base? John Riemann Soong (talk) 02:01, 12 December 2009 (UTC)

It would appear that water is acting as a Lewis base. If you do the electron pushing for this reaction:

• [(CH₃CH₂)₃O]⁺BF₄⁻ + H₂O → (CH₃CH₂)₂O + CH₃CH₂OH + HBF₄

You can see pretty easily how an electron pair from water "grabs" an ethyl group from the trialkyloxonium and then loses a proton to the tetraflouroborate anion. --Jayron32 05:28, 12 December 2009 (UTC)

Can tetraalkyl ammonium salts undergo SN2 substitution with a nucleophile instead of beta-elimination? An alkene product seems to be favoured for ammonium salts, but an alkane-alcohol product for oxonium salts? John Riemann Soong (talk) 06:04, 12 December 2009 (UTC)

Both types of reactions are possible. Depends (as usual) on sterics and electronics of the tetraalkylammonium structure and sterics and electronics of the "other" reactant, solvent effects, etc. All the usual concerns for deciding between these two competing reaction modes. DMacks (talk) 07:50, 13 December 2009 (UTC)

I know ammonia is a pretty bad leaving group, but is it a worse leaving group than hydroxide? John Riemann Soong (talk) 18:27, 13 December 2009 (UTC)

Ammonia (NH₃) is stable, so it's a plausible LG. Hydroxide (OH^–) is not stable, so it would only be a viable LG if there were some other large gain in stability in the reaction. DMacks (talk) 04:59, 15 December 2009 (UTC)

December 12

Hedgehog exercise

This BBC News article discusses an obese hedgehog.

• Fat albino hedgehog put on weight-loss regime.

To exercise him, the veterinarians have put the hedgehog in a bathtub to swim around as part of his weight-loss regimen. Is this standard procedure for exercising a hedgehog? I would have expected a "hamster-wheel" would be more common. Anyway, I know there's a few hedgehog experts on the desk, so I figured I'd solicit their input on this unusual exercise regimen. Nimur (talk) 00:39, 12 December 2009 (UTC)

Domesticated hedgehog may have some useful information. There are also external links to follow, you may be able to find more by poking around some of those. --Jayron32 01:19, 12 December 2009 (UTC)

A standard hamster/mouse wheel is unacceptable for a hedgehog. They often step into the gaps between the spokes and suffer injury (including broken toes). Instead, a hedgehog wheel is commonly referred to as a "bucket wheel" because it is like a shallow bucket placed on its side. Many people actually make their own from buckets. On average, a hedgehog will run about 3 miles each night. The bathtub regimen is not extremely common. Many hedgehogs are afraid of water. Those that like water will spend hours swimming around. Those that are scared of it do nothing except fight to get out of the water (I've got some pretty good claw marks as scared hedgehogs have clawed right up my arm to my shoulder). Some hedgehogs are scared of water and won't run in a wheel. For them, they need exploring activities. It is common to hide their food in a lot of hard-to-reach places. Then, they have to run around and try to figure out how to get their food. All in all - there isn't such thing as a single hedgehog personality. Like all other animals, each has its own personality. -- kainaw™ 01:36, 12 December 2009 (UTC)

Ah. The hazard of getting feet trapped in wheels seems like a motive for finding alternative exercise ideas. From the news story, there are several other news articles linked about obese hedgehogs, [1], [2]. Is this a common problem, or is it just getting disproportionate media attention because of the "weird" factor? Nimur (talk) 01:47, 12 December 2009 (UTC)

In captivity, hedgehogs regularly become obese. Hypertension, diabetes, and hypercholesterolemia are common. This leads to heart attacks, stroke, liver failure, and high rates of cancer. The issue isn't simply captivity. It is that the hedgehogs get plenty of food (most of it rather unhealthy food) and very little exercise. In the wild, hedgehogs span many miles searching for food every night. Relatively, imagine if your main purpose each day was to run a marathon to get a good meal. Sure - you have all day to run the marathon, but the meal won't do much to offset the calories burned getting to it. There is another issue - winter. Hedgehogs are said to hibernate. They don't truly hibernate, but they do spend most of winter holed up and waiting for the weather to get warmer. To last a long time, they need to fatten up. So, this is the time of year that European hedgehogs tend to get rather plump. -- kainaw™ 02:24, 12 December 2009 (UTC)

nitromethane

Is the pka given for this substance the value of nitromethane as an acid, or its conjugate acid (nitromethane is acting like a base)? I really can't see an acidic proton in nitromethane ... unless nitromethide carbanion is really that stable? John Riemann Soong (talk) 02:19, 12 December 2009 (UTC)

It is the pKa of losing a C-H hydrogen. If you read the article on nitromethane, the acidity of the compound and its uses specifically because of this acidity are discussed in the Uses section. The Nitroaldol reaction makes use of this acidity of nitromethane. --Jayron32 05:23, 12 December 2009 (UTC)

How was the international prototype for the metre made?

How was the 1889 version of international prototype for the metre made? —Preceding unsigned comment added by 173.49.9.184 (talk) 04:06, 12 December 2009 (UTC)

The French version of the article explains this in detail. In short, they kept making copies of the 1799 prototype until they got one whose length could not be distinguished from that of the original. --Heron (talk) 15:06, 12 December 2009 (UTC)

Thanks. --173.49.9.184 (talk) 15:53, 12 December 2009 (UTC)

"Bleeding like a stuck pig"

Do hogs bleed more easily than other animals? Or is this phrase a vague allusion to something literary or historic? 24.93.116.128 (talk) 05:14, 12 December 2009 (UTC)

It refers to the practice of Exsanguination in the slaughter of an animal. When you want to kill a pig, it is common practice to drain the blood as fast as possible from the meat, the article on Slaughterhouse describes the process in some detail. So when you "bleed like a stuck pig", it means you are bleeding like you are being drained of your blood in a slaughterhouse. --Jayron32 05:20, 12 December 2009 (UTC)

There is a passage in Jude the Obscure in which a character (Jude's unsympathetic wife) instructs Jude that the swine's blood vessel should be lightly nicked, so that the blood would drain slowly, resulting in less blood in the meat. Jude cannot stand to see the animal suffer and kills it quickly, enraging his wife. --Trovatore (talk) 23:22, 12 December 2009 (UTC)

There's some weird sex stuff going on in that book. There's the scene towards the begining where the chicks who are butchering the pig pelt him with the pigs penis. Thomas Hardy was not a stable dude. --Jayron32 05:02, 13 December 2009 (UTC)

Due to the sizes of the animals, it was more common to send cattle to a slaughterhouse for butchering, while smaller animals like chickens, sheep and even pigs you could do yourself at home. So the "average joe" may be more familiar with seeing stuck pigs. It may also have to do with the spiked club once used to kill pigs. The only people I know who have home butchered cows used bullets for the first step. Rmhermen (talk) 14:26, 12 December 2009 (UTC)

According to Jewish law and to Muslim law, animals must be slaughtered by a single cut to the throat while the animal is still conscious, see this article, Cuddlyable3 (talk) 23:14, 12 December 2009 (UTC)

According to Jewish law and to Muslim law, you can't eat pigs! --Dweller (talk) 16:45, 14 December 2009 (UTC)

Perhaps it is "bleating" like stuck pig. I never heard the phrase. But a pig that is "stuck" in some way probably complains loudly. Only problem is that "bleating like a stuck pig" gets zero Google hits. Bus stop (talk) 22:11, 14 December 2009 (UTC)

Pigs don't bleat; they squeal. "Squealing like a stuck pig" gets hits, but it may be an eggcorn. AlmostReadytoFly (talk) 15:33, 15 December 2009 (UTC)

Enzymes

I was under the impression that enzymes simply increase the rate of a reaction (my college bio text book says this). However denaturing certain enzymes can result in certain products from not being produced. But if they only increase the rate, shouldn't the products be formed without the enzyme, but only at a slower rate? So I'm a bit confused as to the nature of enzymes. ScienceApe (talk) 08:32, 12 December 2009 (UTC)

Yes, sometimes the uncatalysed reaction is just REALLY slow, so slow that in a biological system it basically doesn't occur. And also, some enzymes couple 2 reactions - 1 thermodynamically favourable with an unfavourable reaction, in essence driving the second reaction against the direction it would proceed without an enzyme, and using the first reaction to provide the "fuel" to do this. Aaadddaaammm (talk) 09:33, 12 December 2009 (UTC)

To expand on what Aaaddaammm is saying, the uncatalyzed reaction may occur so slowly as to take thousands or millions of years under uncatalyzed reaction conditions. So essentially, enzymes do "make" reactions occur which would otherwise be impossible (or, at least, impossible to work in a living system). --Jayron32 15:16, 12 December 2009 (UTC)

I see, thank you. But what about something like RNA polymerase for example. From what I understand it's the only way to make RNA. Can RNA be produced without RNA polymerase, just very slowly? ScienceApe (talk) 17:13, 12 December 2009 (UTC)

RNA polymerase is special stuff in that it takes a template DNA strand, and uses it to specifically reduce the activation energy barrier to sequentially adding an appropriate RNA base (A, G, C, or U) to the growing RNA strand. (That's a bit of a simplification, because the addition is a multistep process which includes a host of other enzymes, too.) For just random concatenation of RNA bases, you can drive the process using nothing more complicated than ultraviolet light. (See, for example, RNA world hypothesis.) Of course, once you start to have lots of complicated RNA floating around, it can do some simply marvellous stuff — including catalyze the formation of more RNA polymers. Modern RNA still forms a number of important enzymes, collectively called ribozymes. TenOfAllTrades(talk) 17:46, 12 December 2009 (UTC) (expanded, TenOfAllTrades(talk) 00:26, 13 December 2009 (UTC))

So you can transcribe RNA using just ultraviolet light? ScienceApe (talk) 01:21, 13 December 2009 (UTC)

"Transcribe" implies that you can control the order of bases in the created RNA, and that's not what TenOfAllTrades said. With UV light you just get some random RNA (think monkeys with typewriters). If you're really lucky it will turn out to be a ribozyme that does something interesting, and if you're really really lucky, "something interesting" will involve catalyzing transcription of RNA. Once you get there, you're golden. –Henning Makholm (talk) 02:04, 13 December 2009 (UTC)

So then for all intents and purposes, RNA polymerase, an enzyme, makes messenger RNA. ScienceApe (talk) 07:06, 13 December 2009 (UTC)

Yes. Both this example and the fact provided Adam above hit on extremely important concepts in biochemistry. We always say that enzymes accelerate a particular reaction, but when you are trying to consider what happens in the absence of the enzyme, you have to think about all the other reactions that can happen. In the case of RNA polymerization, the mRNA product of transcription is one possible product of the polymerization of N ribonucleotide triphosphates. There are, in fact, N⁴ conceivable products. In the case of an ATP hydrolysis driven reaction, a conceivable set or products is ADP plus inorganic phosphate, with the enzyme's substrate left unaltered. An enzyme "makes a reaction happen" by lowering the activation energy for one particular reaction amongst the many reactions possible with a given set of reactants. Someguy1221 (talk) 07:19, 13 December 2009 (UTC)

The templated polymerization of ribonucleotides (i.e. the reaction which RNA polymerase catalyzes) will occur on it's own (theoretically). The problem is that it is *so* slow uncatalyzed that all the other reactions which can conceivably occur to the substrates (such as hydrolysis, Maillard reactions, non-specific polymerization, etc., etc.) will go to completion thousands of years before you'll get appreciable amounts of desired product. It's not just that enzymes increase the rates of reaction, but they increase the rates of *specific* reactions, while leaving the other, undesirable reactions slow. -- 128.104.112.87 (talk) 15:55, 14 December 2009 (UTC)

Russian rocket failure

Is this for real? http://www.nzherald.co.nz/world/news/video.cfm?c_id=2&gal_cid=2&gallery_id=108562 Aaadddaaammm (talk) 09:38, 12 December 2009 (UTC)

Yes. The spiral was seen by hundreds of people in northern Europe. The most likely explanation is a Russian ICBM test where the rocket went out of control. spaceweather.com has a write up on it, and the rocket plume of the boost phase of the rocket is visible and normal in at least one photo of the spiral. --121.127.200.51 (talk) 10:10, 12 December 2009 (UTC)

There was a discussion on this earlier. We have an article 2009 Norwegian spiral anomaly Nil Einne (talk) 13:03, 12 December 2009 (UTC)

And just as a note, "spiral in the sky" seems odd if you haven't seen something like that before, but many failed missile tests look like that and produce distinctive spiral smoke shapes. E.g. [3] and [4]—when you have one part of a missile spewing out heat and it gets off-center, you easily get spiral-like activity. What's interesting in the Norway case is how high it was and how the period of the spiral looks so perfect, but you'll notice in the videos that most are showing a clip of just a second or two in length—it disperses immediately afterwards. It is fairly what you'd expect it to look like if, say, the third-stage of an SLBM failed to detach from the main body and spun it around. --Mr.98 (talk) 14:18, 12 December 2009 (UTC)

And just another note... another possibility that has not been discussed seriously, but doesn't quite fall into "conspiracy theory" territory, is that this is a test or failure of a different type of weapon. In their book Nuclear Express, Thomas C. Reed and Danny B. Stillman (the latter of whom was a Los Alamos scientist), report on a mysterious, not-fully-understood weapon that the USSR and China had both been developing, that they term "domes of light". Some of the description from their book, and the photos they reproduced, are visible here. The spiral on the Norwegian thing says "missile test gone awry" to me, but I remember reading about the "domes of light" sometime back and finding them pretty odd as well. Just putting that out there! --Mr.98 (talk) 14:30, 12 December 2009 (UTC)

That sounds vaguely like the conspiracy theories surrounding HAARP and its Russian counterpart SURA (neither of which is at all near Norway or the White Sea). But then what use is a sci-fi death ray if you can't blow up far away things (like test missiles over the White Sea). 87.115.47.74 (talk) 00:08, 13 December 2009 (UTC)

Vaguely, maybe, but it's not, and the source of it is much better than the normal conspiracy nonsense. The authors of that particular book are not kooks, and the book itself has been well-reviewed all over the place. One sign that this particular theory is not just kook-land is the fact that the authors readily admit they aren't really sure how it works (rather than spinning out endless Tesla-based theories). --Mr.98 (talk) 18:40, 13 December 2009 (UTC)

Cavity Preparations-Dentistry

What are the recent modifications made in outline form of class 1 cavities (with faciolingual extentions)n class 2 cavities for amalgam restorations? <ref>Fundamentals in cavity preparations</ref>—Preceding unsigned comment added by DOC PANU (talk • contribs)

Is this homework? Fences&Windows 14:41, 12 December 2009 (UTC)

You may find the information here. Cuddlyable3 (talk) 23:03, 12 December 2009 (UTC)

Your question is very vague -- could you be more specific, please? DRosenbach ^{(Talk | Contribs)} 14:12, 13 December 2009 (UTC)

no transmission for a car?

Why does a car need a transmission and an airplane doesn't? I'm not sure, but it looks like propeller aircraft have propellers somehow attached to the engines' crankshaft; would it possible to do the same with a car so engine speed would be directly proportional to car speed? 70.144.137.239 (talk) 14:36, 12 December 2009 (UTC)

A modern propeller driven plane will generally have a variable pitch propeller - and that is (in effect) a continuously variable transmission - when the propeller blades are parallel to the circle in which they travel, the blades generate almost zero thrust - as you increase the pitch of the blades, the 'gear ratio' gets higher - suitable for flying at higher speeds. Prop planes that don't have that are essentially "stuck in one gear" - which is a compromise between performance and idle. But aircraft don't have much problems with stop-and-go traffic - once they are moving, their power needs are over a fairly small band - and the range of RPM's they need isn't that great. Also, you can't stall a plane's engine in the way that you can stall a car engine. If you bring your car to a dead stop using the brakes in a high gear - the engine RPM will drop so low that the engine will be unable to keep running. In an airplane, on the ground, the propeller can continue to rotate when the brakes are on and the plane is stationary - so you don't need a clutch or a neutral gear either.

Having said that - I recall that at least one design of Russian or maybe Czech fighter from the WWII era did actually have a gearbox. Sadly, I can't recall the model number - so no link.

SteveBaker (talk) 15:21, 12 December 2009 (UTC)

As far as I know cars with electric motors (e.g. Tesla Roadster) actually go all the way down to zero RPM, they don't have the stalling or motor starting issues that regular engines have that would necessitate the need for a clutch, torque converter or gearbox. In principle they could couple the the motor directly onto the crankshaft (especially in the case of the Tesla which has a 1-speed gearbox). However there are practical considerations and advantages to have at least a neutral gear (free-wheeling downhill without excessive engine braking is one) as well as several gears. As Steve points out, a plane or boat operates in a VERY limited RPM range. If you had to stick with only 1 gear in a (electric) car it would simultaneously need to be short enough to pull away from standstill (while loaded to its maximum allowable weight) and at the same time long enough to cruise at top speed within the engine's operating range (typically 12,000 RPM for an electric motor). The Tesla can do this because it is a light sports car with no boot space and only 2 seats. The max. weight is not excessive so the gearing isn't TOO compromised on the "short" side. Zunaid 16:04, 12 December 2009 (UTC)

Our turbofan article has a very brief section discussing gearboxes for aircraft engines. The gearing is very different from a car transmission. Nimur (talk) 17:31, 12 December 2009 (UTC)

Yeah - some planes do have gearing - but it's not a shiftable gearbox - it's just a way to get the engine RPM down to a reasonable fan/propeller speed. Helicopters have much fancier gearboxes - but again, they aren't shiftable - they are a constant ratio. SteveBaker (talk) 22:16, 12 December 2009 (UTC)

I'll digress into trains and talk about diesel ones. Most of these are actually diesel-electric: the diesel engine drives a generator, at a narrow range of speeds, and electric motors drive the wheels. No gearbox needed since the electric motors can handle the full range of speeds needed. But there have been some diesel-hydraulic trains, based on a torque converter like in an automatic-transmission car; the Budd Rail Diesel Cars once common on secondary passenger services in Canada and the US are one example. And there have even been "diesel-mechanical" trains with a gearbox; these used to be common on secondary passenger routes in Britain. --Anonymous, 20:47 UTC, December 12, 2009.

Yeah - electric motors have a very flat torque-versus-rpm curve - gasoline & diesel engines typically don't. Hence the need for a gearbox to get the gasoline engine to run at the optimum RPM to get the best torque (or the lowest fuel consumption or whatever) at a range of vehicle speeds. With an electric motor, it's not really necessary to shift gears because the torque output is pretty much the same no matter the RPM. Having said that - some electric cars do use a simple two-speed gearbox with a 'starting gear' and a 'running gear'. Hybrid cars (and diesel-electric railroad locomotives) take advantage of that by running the internal-combustion engine at it's absolute best RPM - use the engine to generate electricity - and use the electricity to drive electric motors. That's a neat trick - and it's how hybrid cars get such good gas mileage. But you just don't need that range of RPM's in a low-cost light aircraft. High end prop planes use that variable-pitch prop trick - so they can alter the torque demands at a wide range of speeds without altering the engine RPM by more than it can cope with. SteveBaker (talk) 22:16, 12 December 2009 (UTC)

What happens when a cold-blooded animal gets an infection.

When warm-blooded animals (well, humans, dogs, etc at least) get an infection - their temperature goes up in a fever as their bodies try to kill off the bacteria/virus by making things too hot for them.

How do cold-blooded animals cope under these circumstances? Is there evidence that they'll bask in the sun for longer in an effort to create a hotter situation?

SteveBaker (talk) 15:26, 12 December 2009 (UTC)

Apprently that is the case.[5] There is something called 'behavioral fever' in reptiles, birds, fish and amphibians and it seems to be effective in increasing survival rates following infection. Mikenorton (talk) 17:09, 12 December 2009 (UTC)

It should be noted that the idea that fever is a useful survival technique has been questioned by some researchers. See Fever#Usefulness_of_fever which notes that the notion is not universally accepted that fever is beneficial to the organism as described by SteveBaker. --Jayron32 17:12, 12 December 2009 (UTC)

As a further pedantic note, the main function of fever isn't to make things too hot for the infectious agent, it is to ramp up the activity of the immune system. Looie496 (talk) 17:59, 12 December 2009 (UTC)

Wow! Thanks for the link Mike. So they got snakes to want to be in a warmer place by injecting them with DEAD bacteria?! How did the snakes know they needed to do that if they didn't get sick? (Presuming they didn't get sick from dead bacteria.) That's an interesting result! I'm glad I asked. SteveBaker (talk) 22:05, 12 December 2009 (UTC)

Well the dead bacteria would still contain the antigens which would bind to immunoglobulins. --Mark PEA (talk) 22:12, 12 December 2009 (UTC)

I have not read that study, but I doubt it was due to immunoglobulins, which are generally produced by the adaptive immune system and therefore would only be generated in large amounts if the animal had had that infection before. More likely it's an innate response mediated by LPS and other PAMPs from the bacterial cell, binding to PRRs like TLR4. According to this (free) publication the sensing of bacterial PAMPs by PRRs is conserved throughout vertebrate evolution. -- Scray (talk) 00:36, 13 December 2009 (UTC)

On a more general level than which antigens bind to what, "getting sick" is generally not something the invading bacteria actively do. It is simply the body's reaction to something foreign being there. Feeling sick is how we perceive the immune system's being activated to flush out the invaders before they get many enough to do damage of their own. It seems to work well for modifying our behavior to support the immune reaction; being miserable tends to make the patient lie down, bury himself in blankets and generally conserve as much energy as possible to fighting the infection (as opposed to things that can wait, such as locomotion, gathering food, or preparing for winter). Snakes probably feel it similarly. –Henning Makholm (talk) 01:10, 13 December 2009 (UTC)

M&M

Why are there two "m"s in Mmgy? SpinningSpark 16:48, 12 December 2009 (UTC)

According to our article on the barrel, where a million barrels is sometimes rendered as 1MMbbls, this arises from the use of M to represent a thousand (derived from 'mille'). Mikenorton (talk) 16:56, 12 December 2009 (UTC)

It's worth noting that neither Mmgy and MMbbls are SI units, so they do not abide by SI standard prefixes. Nimur (talk) 17:33, 12 December 2009 (UTC)

Thanks Mike, and thanks also to Nimur, although I did not think for one minute that this was an SI unit. SpinningSpark 18:57, 12 December 2009 (UTC)

December 13

Bleach Reactions

Ive had a mouse(or mouses) crawling around my room lately and i didnt really notice untill i saw one of the buggers the other night. Theres mouse excretions all over the carpet and places where it could hide where its especially concentrated.

Is it safe to spray the carpets with bleach or will this have some kind of reaction with the (presumably small?) amounts of ammonia in the mouse waste and ultimately kill me?

Cheers, kp —Preceding unsigned comment added by 121.220.22.118 (talk) 06:28, 13 December 2009 (UTC)

Urine + bleach --> chloramines, which are toxic. Probably it will be a small amount if you're cleaning a small spot, but it's still not the approach you should take. Go for an enzymatic cleaner (you can find it in pet stores, as it's used to clean up litter boxes and dog and cat urine or poop stains.) It is more likely to remove the smell, and won't turn your carpet white. - Nunh-huh 07:29, 13 December 2009 (UTC)

Bleach will oxidise ureas? Ureas already seem oxidised to me ... what will bleach do, convert urea to nitrogen dioxide, carbon dioxide and water? :S John Riemann Soong (talk) 01:02, 14 December 2009 (UTC)

I thought that since people have been putting bleach down toilets for years, this wouldn't be a problem, but it seems I was wrong. The Chlorine institute says not to mix chlorine bleach with urea or ammonia, and this NJ health factsheet warns about cleaning cat litter trays or diaper pails with it. You could try using borax, which is recommended by many for removing urine[6][7] --Pleasantman (talk) 13:34, 14 December 2009 (UTC)

Nitrogen Trichloride IED?

Would it be possible to build an improvised explosive device using urine and chlorine based cleaning products? —Preceding unsigned comment added by Trevor Loughlin (talk • contribs) 13:28, 13 December 2009 (UTC)

• I'm not going to look up how to make a bomb, but: "[NCl₃ is] formed in swimming pools when the chlorine gas used to disinfect the water reacts with nitrogen compounds found in urine, and can be a health risk to people like lifeguards who work continuously around the water. NCl₃ can be formed when chlorine reacts with nitrogen compounds in wastewater treatment plants. The particular danger associated with the formation of NCl₃ under these conditions is that a combination of its sensitive nature and low solubility in water leads to explosive droplets of NCl₃."[8] It's also very unstable, so don't try to make any: Nitrogen trichloride#Safety. Fences&Windows 17:04, 13 December 2009 (UTC)

Autophagy in bacteria

In eukaryotes specialized organelles - lysozomes - are used to mediate autophagy. Since bacteria lack organelles, they obviously can not take that approach. Even so, are there processes comparable to autophagy that occur in bacteria? Specifically, can a bacteria that finds itself in a low nutrient environment break down it's own proteins and structures to provide a temporary emergency supply of energy? Dragons flight (talk) 13:45, 13 December 2009 (UTC)

As you said, prokaryotes do not possess membrane-bound organelles. It's a great question. DRosenbach ^{(Talk | Contribs)} 14:21, 13 December 2009 (UTC)

Yes. Under starvation conditions bacteria will break down, or lyse, their macromolecules, and then many form resistant endospores. Fences&Windows 16:59, 13 December 2009 (UTC)

Don't suppose you can back your assertion with a reference? I specifically want to know about the consumption of macromolecules as a food source, which I'm having trouble finding references to for bacteria. Simply breaking down macromolecules wouldn't be interesting to me unless they can also utilize the associated energy for other activities. Dragons flight (talk) 21:28, 13 December 2009 (UTC)

There are tons of research studies on it, just Google "bacteria starvation proteolysis". Here's a recent study: [9]. Fences&Windows 20:42, 14 December 2009 (UTC)

on average how many pounds of fish are under a square meter of ocean?

On average, how many pounds of fish are under a square meter of ocean? 85.181.144.117 (talk) 14:30, 13 December 2009 (UTC)

Ocean biomass has some aggregate total mass of marine fish for the entire ocean; you can divide that by an estimate of total ocean surface area. However, fish are not uniformly distributed, so the merit of this average value, at least constructed in such a simple way, is dubious. Nimur (talk) 16:18, 13 December 2009 (UTC)

Google tells me that in January of this year a team estimated that the total mass of bony fish in the ocean is between 812 and 2050 million tons, therefore between 1.6 and 4 trillion pounds (1.6x10¹²—4x10¹² pounds). Our ocean article gives the surface area of the ocean as 3.6x10¹⁴ square meters. Dividing, you get somewhere around a hundredth of a pound per square meter. The distribution is extremely inhomogeneous though -- the vast bulk of fish are found on continental shelves. Also note that the figure leaves out squid, which might boost the number by 25% or more if included. Looie496 (talk) 16:35, 13 December 2009 (UTC)

what if you include the mass of all living things in the sea, including single-celled organisms? Then how much is under each square meter of water? 85.181.144.117 (talk) 16:57, 13 December 2009 (UTC)

[10] gives several estimates for the total mass of living things in the ocean - but the bottom line seems to be between 3 and 4x10⁹ metric tons - so let's split the difference and go with 3.6x10¹²kg - dividing that by the 3.6x10¹⁴ square meters of ocean surface gives us a handy 0.01kg/m². Given the size of the likely errors in our assumptions - this is a very similar kind of a number to the one Looie496 gives above - so you could assume that about half of that mass is fish and the other half algae, plants, etc. SteveBaker (talk) 17:22, 13 December 2009 (UTC)

Europe and Asia

Where does the boundary between Asia and Europe between Ural mountain and Ural river meet each other? —Preceding unsigned comment added by 113.199.185.146 (talk) 16:06, 13 December 2009 (UTC)

There is no fixed boundary. See Europe-Asia border and Borders of the continents#Europe and Asia. PrimeHunter (talk) 16:16, 13 December 2009 (UTC)

There are also several politicized slants on where the border is and where it should be, in both a political and cultural sense. The Caucasus has no shortage of conflict over this - see Dagestan (Invasion of Dagestan (1999)), Ossetia (2008 South Ossetia war), Chechnya, (First Chechen War and Second Chechen War). With such a disputed cultural and political boundary, and in the absence of a clear geographical barrier like a river or coastline, the boundary is very poorly defined and its location depends on who you ask. I think the Ural region has had less conflict over the boundary, historically, but the line is similarly ambiguous. Nimur (talk) 17:09, 13 December 2009 (UTC)

The border of Asia and Europe is not a political issue.It has nothing to do with the politics.It is purely an issue of geographical nature.So my question was also of geographical nature. —Preceding unsigned comment added by 113.199.157.236 (talk) 03:22, 14 December 2009 (UTC)

As explained in numerous articles including those linked to I presume, geographically the concept of Europe and Asia is questionable or even meaningless Nil Einne (talk) 11:54, 14 December 2009 (UTC)

Radon

How do I test for radon in water? I would prefer something I can find in a basic laboratory, if not something I could find in a store. I'm doing a science fair project on it. THX --Richard —Preceding unsigned comment added by 76.230.211.192 (talk) 16:18, 13 December 2009 (UTC)

[11][12][13] Fences&Windows 16:52, 13 December 2009 (UTC)

It's a shame that F&W provided no description of those links - the second one is highly applicable and contains an excellent discussion of air/water partitioning of radon, with a method of on-site radon testing of water. -- Scray (talk) 17:35, 13 December 2009 (UTC)

Hmmm - tricky. Radon is a nobel gas - like Neon or Argon - so simple chemical tests are unlikely to be available. It does form a compound with fluorine to form Radon difluoride - but that sounds like a tough thing to do.

Radon is radioactive - and decays with a half-life of 3.8 days - so you could instead test for the decay product. Unfortunately, the commonest isotope of Radon decays to Polonium - perhaps you could detect the polonium instead - but sadly, the test for Polonium requires fancy spectrographic techniques - which are almost certainly beyond your "basic laboratory". So I think you have to test for radiation. If you can get a hold of one - I'd start testing the water with a geiger counter - if that indicates that the water is radioactive to a higher degree than background radiation - then the odds are very high that it's radon rather than some other radioactive substance. I don't know whether a gieger counter falls within your definition of a "basic laboratory".

Our article on Radon says that tests for radon in air are done using a Lucas cell - but again, that's measuring radiation, not a direct test for the chemical element itself. Our article says that radon test kits are cheap "and in some cases, free" - so perhaps you should talk to the manufacturers of the test kits and see if they'll send you a freebie - if you get a hold of the right person and explain what it's for, they'll probably be very helpful (it's free advertising!). However, I suspect that they are talking about radon in the air - not in the water. Also - if you're doing a science fair - remember that the half-life of Radon is just a few days - so you'll need to get a fresh sample on the day of the fair if you need to demonstrate the testing 'live'. SteveBaker (talk) 17:04, 13 December 2009 (UTC)

It's not chemically difficult to purify extract and purify polonium, even at very small amounts (isolated microgram quantities from several liters of urine!). Once it's pure, it's easy to quantify by measuring the radioactivity. But it's α, so you need a scintillation counter not a Geiger-counter. If you've got a scintillation counter already though, easier to just monitor radon directly with it instead of waiting for its daughter-nuclei. DMacks (talk) 18:08, 13 December 2009 (UTC)

Yes - but the radon only hangs around for a matter of days to weeks. The polonium that it decays into is much less radioactive and stays around for years. Hence, if you could easily do a chemical test for polonium, that would be a good thing to do because radon is a noble gas and will be extremely hard to test for chemically. But evidently, you can't chemically test for polonium either. So you're back to testing for radioactivity - and if you're going to do that then you might as well try to deduce how much radon is present from that.

You could presumably take a fresh water sample - measure the radioactivity - then wait (say) 3.8 days (the half-life of the most common radon isotope) - then measure the radioactivity of that same sample again. The amount by which the radiation levels have dropped would be an measure of how much radon was present in the original sample. Doing it that way, you're more directly measuring the radon content because (if present) it's radioactivity should completely dominate all of the other potential sources in the water.

Test kits for radon are easily obtainable - and cheap (http://www.free-radon-test-kits.com/ for example!) - but the problem with that is that the test kits only test the air - not the water. That makes our OP's task kinda tricky. I suppose you could boil away the water and somehow separate out the radon gas (it's really heavy) and then use an airborn test...but it's not clear whether you'd get enough radon from a small enough sample of water to make that feasible on an amateur scale (boiling away even a couple of gallons of water is TOUGH!). The second and third of the links that User:Fences and windows linked to seem to say that there are direct tests one can do on water - but since both are pay-to-read pages, I can't tell what the actual tests entail.

So - our OP has to measure radiation - not attempt difficult chemical or spectroscopic tests. Using the "test, wait 3.8 days, retest approach", you'd get a pretty good idea of the amount of radon in the sample...but that requires that our OP can find either a scintillation counter or a geiger counter or something similar.

I suppose - if you didn't have access to a geiger counter - you could try to McGyver a radiation counter somehow. Maybe get a household smoke detector and (carefully!) remove the Americium radiation source from it - then use the alpha particle detector to measure the radioactivity from the water. If you could pull it off - it would be an amazingly cool science fair project! Googling "homemade Geiger counter" produced a bunch of interesting pages. SteveBaker (talk) 19:26, 13 December 2009 (UTC)

Again, you can isolate incredibly minute amounts of polonium quantitatively. The problem isn't "no chemical test" (you just weigh the recovered material) but actually doing it on such a small scale. The amount of radon in the air (even dangerously-high levels in a poorly ventilated basement) is really a very small number. See Radon#Concentration units. But isn't polonium's half-life very short also? DMacks (talk) 19:50, 13 December 2009 (UTC)

Oh - you're right. ²²²Rn (the commonest Radon isotope) decays to Polonium - but all of the commonly found isotopes of Po are long-lived. What I didn't check was exactly which isotope of Polonium you get. Our article says: ²¹⁸Po - which has a half-life of just a few minutes. Decay chain says that the first stable decay product is ²¹⁰Pb - lead. Darn. You can't find that chemically because there will be plenty of regular lead in the water anyway. OK - so definitely you're going to need a radiation counter. SteveBaker (talk) 02:01, 14 December 2009 (UTC)

5' Cap and Poly-A Tail

Hello. If the 5' cap of mRNA is indigestible by nucleases since it resembles the 3' end, then why is the poly-A tail at the 3' end digestible? Thanks in advance. --Mayfare (talk) 19:36, 13 December 2009 (UTC)

What is your source for the 5' cap being indigestible and the 3' poly-A tail being digestable? In essence, they need not be digestable beyond being able to be cleaved from the mRNA at their points of attachment, which I am sure they are, or else they would remain indefinately. On second thought, does it really matter if it stays indefinately? The AUG "primer," so to speak, is the point at which translation will begin either way, but I do think the 5' cap is cleaved. DRosenbach ^{(Talk | Contribs)} 21:18, 13 December 2009 (UTC)

The 5' cap doesn't mimic the poly-A tail, the cap is simply a methylated guanine attached in an odd way. Together they prevent digestion, but there are decapping enzymes (names escape me) which can remove the cap. ~ Amory (u • t • c) 01:28, 14 December 2009 (UTC)

Aaaaand of course there's an article. 5' cap ~ Amory (u • t • c) 01:28, 14 December 2009 (UTC)

According to the 5' cap article, "the 5' cap looks like the 3' end of an RNA molecule (the 5' carbon of the cap ribose is bonded, and the 3' unbonded). This provides significant resistance to 5' exonucleases." According to the polyadenylation article, "in eukaryotic somatic cells, the poly(A) tail of most mRNAs in the cytoplasm gradually get shorter, and mRNAs with shorter poly(A) tail are translated less and degraded sooner." --Mayfare (talk) 10:30, 15 December 2009 (UTC)

Identify species from unusual shell

left-handed shell

shell

I found this shell on the east coast of the US (Atlantic Ocean). It is the only one I've found that opens on this side - all others I've found go around the other way and open on the other side. Can anyone identify it? Bubba73 ^{(Who's attacking me now?)}, 22:14, 13 December 2009 (UTC)

Are there some species that are left-handed? Or is this one a mutation or something? Bubba73 ^{(Who's attacking me now?)}, 23:43, 13 December 2009 (UTC)

It may be a Lightning whelk. Bubba73 ^{(Who's attacking me now?)}, 00:00, 14 December 2009 (UTC)

We appear to be missing our article on the chirality of shells, but taking Gastropod shell as an example, most "are dextral (right-handed) in their coiling, but a small minority of species and genera are virtually always sinistral (left-handed), and a very few species (for example Amphidromus perversus[) show an even mixture of dextral and sinistral individuals." --Tagishsimon (talk) 00:37, 14 December 2009 (UTC)

The times had an article about this a little while ago. Again, snails. ~ Amory (u • t • c) 01:24, 14 December 2009 (UTC)

And sex. And snakes. Excellent article. --Tagishsimon (talk) 01:55, 14 December 2009 (UTC)

Stephen Jay Gould has written an essay titled 'Left snails and right minds' about that subject in chapter 16 of his book 'Dinosaur in a haystack: reflections in natural history'. Dauto (talk) 01:49, 14 December 2009 (UTC)

Thanks, these pretty much tell me what I wanted to know (except for the specific species). (And I've ordered Gould's book.) Bubba73 ^{(Who's attacking me now?)}, 01:51, 14 December 2009 (UTC)

Resolved

Identified as a Lightning whelk. Bubba73 ^{(Who's attacking me now?)}, 16:07, 14 December 2009 (UTC)

Hunter-gatherers

Hunter-gatherer societies (such as Africans) were largely peaceful and in touch with nature. They only hunted what they needed to survive, and as a result they didn't cause any extinction. Then the Europeans came with technology and changed everything. Now, as a result of European technology, Africa is one of the most violent regions on the planet, with constant extinction, attempted genocide, etc. Other hunter-gatherer societies were largely peaceful as well, but then they turned violent and destructive once technology arrived. Why is it that technological societies have so much more problems than "primitive" hunter-gatherer societies? --70.129.184.254 (talk) 23:03, 13 December 2009 (UTC)

I just feel the need to say citation needed! Who told you hunter gatherers were peaceful? Were Africans hunter gatherers? Were they peaceful? Where did you get that they only hunted for survival? Have technological societies mopre problems with violence? Citation needed! Dmcq (talk) 23:19, 13 December 2009 (UTC)

There is little evidence that hunter-gatherer societies are necessarily more peaceful or more sustainable. You might, for example, take a look at John Keeley's War Before Civilization: The Myth of the Peaceful Savage. There are also some good books (the titles evade me at the moment) on the ways in which indigenous societies in the Americas often did agricultural and earth-works projects that had vast effects on their ecosystems. The overall premise that technological societies have more problems than primitive societies is fairly unsustainable. The problems are often different, to be sure. And we lack much record of much of life in a pre-modern period. But social problems hardly seem to be new, nor would one necessarily expect them to be. --Mr.98 (talk) 23:34, 13 December 2009 (UTC)

Try also Jared Diamond's Guns, Germs, and Steel: The Fates of Human Societies. While I won't go into details, the gist of the author's thesis is that the differences between societies (especially those which made the transition from hunter-gatherer societies to intensive agriculture versus those which did not) can be laid almost entirely at the feet of differences in the availability of domesticable plant and animal species in various regions. He makes a very persuasive argument that the innate character or characteristics of each region's native peoples had no appreciable effect.

On the issue of the relative peacefulness of hunter-gatherer societies, Diamond notes that in areas with low population densities, if your more powerful neighbour wants your land or hunting grounds, then you can just move further away. In small groups (family groups of hunter-gatherers, or small villages of early agricultural societies) it is possible to every person to know every other person in the group; any violence is directed solely at 'outsiders' and there is a vested interest in (indeed, an evolutionary imperative for) getting along. As you move to higher population densities and larger groupings, there's no way to escape your neighbors, and you have to deal with strangers even within your own society. Both factors lead to increased conflict not due to a change in the nature of the individuals involved, but due to a change in circumstance.

On the issue of extinctions, technologically-primitive peoples lacked the tools to efficiently eradicate entire species or (in general) to generate significant change in the environment. Hunter-gatherer populations were generallly very low-density, making it difficult for them to exceed the carrying capacity of the land. In other words, they lacked the numbers and the tools to render (many) species extinct; it had nothing to do with being 'in touch with nature'. They raped and pillaged as best they could, though they probably didn't succeed in wiping out entire species very often. (One very big exception may be the mammoth and other Pleistocene megafauna. See Quaternary extinction event#Hunting hypothesis.) TenOfAllTrades(talk) 00:58, 14 December 2009 (UTC)

We have Guns, Germs, and Steel, btw. so watch out... --Tagishsimon (talk) 01:02, 14 December 2009 (UTC)

(ec) There is evidence that Hunter-gatherers caused the extinction of several sub-species of the Mammoth - so, yeah - they probably caused extinctions. Tribes of modern hunter-gatherers have wars - there is no reason to believe that this didn't also happen back in prehistory. Were they in touch with nature? Probably. So this kind of wishful thinking really isn't true - which means that we can't answer your question because it's based on an obviously false premise. SteveBaker (talk) 01:37, 14 December 2009 (UTC)

What does "in touch with nature" even mean in this context? APL (talk) 01:40, 14 December 2009 (UTC)

The Native Americans managed to keep bison alive and thriving for millennia. The Europeans showed up and bison were nearly extinct in a matter of years. That shows that the Native Americans were more in touch with nature than the Europeans. --71.153.45.118 (talk) 01:53, 14 December 2009 (UTC)

It's certainly true that they didn't destroy the buffalo. On the other hand the Indians had neither economic incentives nor technological means to accomplish the eradication of the buffalo. So it doesn't really tell us anything. I have never killed a T-rex, but that's not proof I love and respect them. I think a good case can be made that many Native Americans did in fact treat living things with greater respect than the typical European settler, but to make that case one needs to look at legitimate lines of evidence and behavior and not impossible counter-factuals. For example, their religious and cultural traditions, their (small-scale) hunting practices, and their response to different hunting practices introduced by Europeans. Dragons flight (talk) 02:19, 14 December 2009 (UTC)

What does "in touch with nature" mean? You have to define it before you can use it in any sort of arguments at all. As far as I can tell it's nothing more than a feel-good phrase. APL (talk) 17:53, 14 December 2009 (UTC)

It's also commonly believe that humans were the ultimate cause of extinction of much of Australian megafauna possibly both due to hunting and their use of fire. Our article briefly discusses this and the evidence available and this appears to be even more recent [14]. In any case, it is well accepted that the Māori are responsible for the extinction of the Moa and indirectly therefore of the Haast's Eagle which preyed on Moa and also the Adzebill and other species, although of course they weren't necessarily all hunter-gathers. Holocene extinction may also be of interest. In terms of this 'in touch with nature' thing there is IMHO some suggestion that recent human arrivals were commonly not particularly in touch with nature and it was only with the development of more sophisticated culture and in some cases agriculture that they began to realise they should take more care with what they killed to avoid wiping out species in the area they were living in (which was generally a disadvantage to them). Even then, their limitations in tools etc was also likely a limiting factor. Those humans who were completely inept at taking care of nature were likely to make themselves extinct Nil Einne (talk) 03:28, 14 December 2009 (UTC)

Head-Smashed-In Buffalo Jump shows that Indians did everything they could to kill buffalo and probably harvested more than they could use at time. 75.41.110.200 (talk) 03:37, 14 December 2009 (UTC)

And the Easter Islanders were sufficiently "in touch with nature" that they made every tree on their island extinct...two for the price of one! SteveBaker (talk) 05:05, 14 December 2009 (UTC)

There is evidence that the settlement of polynesia, 3000 years ago, caused mass-extinctions and depletion of resources. From recent archeological studies of the island Vanuatu, east of Australia, we know that giant tortoises and many other species disappeared within the first century after human settlement. Excavated household waste also showed that seashells got progressively smaller over the years, indicating that the harvesting of the seashell population was done in a non-sustainable way. Consider for a moment that these ecological catastrophes were brought on not by consumerism or extravagant cultures but simply by people collecting food to eat. EverGreg (talk) 08:00, 14 December 2009 (UTC)

The Nazca cut down all their best trees. [15] Then again, they were farmers, so this doesn't count. I note though that the reason for farming is to solve the problem of not having enough food. This leads (without foresight) to the problem of deforestation, but the alternative (population control by letting people starve) is still a problem. Also, problems come in two kinds, those which cause heartache and pain and those which cause interest and fulfillment, depending I think on the learning curve or the condition of flow (psychology). Happy states of flow are I suppose more likely to be found in technological societies, where the idea that "nothing is impossible" is present, while hunter-gatherers are presumably stuck behind a kind of learning cliff which they haven't even thought about scaling, and are highly vulnerable to famine and flood and disease (and war). 81.131.39.3 (talk) 09:11, 14 December 2009 (UTC)

The reasons for the "primitive people were in touch with nature, modern people are not" fallacy are pretty easy to see. They come from our own deep-seated reservations about modernity, about a desire to see our own problems as part of a kicked-out-of-Eden story. But there is not much evidence for this view at all—it is more poetic and literary than it is historical and literal. What we can take away from this, I think, is not that Native peoples were bad, or that the European way of dealing with life is "the same" as theirs. It is more a deeper quality about how humans interact with their environments in general, and in this sense, the technological ability does have real importance—technology allows us to amplify our more exploitive side quite a bit. "Pre-civilized" nations definitely lacked the MEANS to be as destructive to either themselves or their lands on a scale comparable with the Europeans, for the most part, even if they did not actually lack the WILL to do so. In such an analysis, it is a problem of quantity and not quality of difference. --Mr.98 (talk) 14:58, 14 December 2009 (UTC)

We had almost this exact discussion last week, here. I suggest you read that. Once again, the question is based on a false assumption. There is plenty of evidence that hunter-gatherer societies caused mass extinctions, usually when moving to a new place where the native large animals weren't used to humans and thus made easy prey. You don't need any technology beyond a spear to kill an animal that doesn't know to run away from you. --Tango (talk) 15:03, 14 December 2009 (UTC)

December 14

are imine groups stabilised by base?

My class always seemed to discuss imine in terms of equilibrium (e.g. excess HOH ==> hydrolysis; distillation of HOH and excess amine allows formation of imines), but it seems to me that an imine group would survive in water without being deaminated under basic conditions, whereas hydrolysis would be catalysed by acid. (Ignoring the fact that acid prolly changes the equilibrium by deactivating the amine.)

In neutral solution, assuming equal abundance of HOH and amine, would a C=N bond tend to equilibrate to 50% C=O and 50% C=N? I know the bond energies are different but NH2- is a bad leaving group, NH3 is a decent leaving group (sorta?), whereas HOH is only formed as a leaving group under much rarer conditions and certainly much rarer in base! John Riemann Soong (talk) 00:56, 14 December 2009 (UTC)

If you know there is a stability difference, it would be silly to assume there is an equal distribution at equilibrium. Thermodynamic equilibrium is the same as the balance of the forward and reverse reaction rates. General equilibrium direction is stated in the very first paragraph of the imine article. DMacks (talk) 14:06, 14 December 2009 (UTC)

Well yes, but mass action principles often seem to overrule enthalpy considerations. I'm wondering just looking at leaving group principles. John Riemann Soong (talk) 00:49, 15 December 2009 (UTC)

time/temperature formula

Is there a formula to convert cooking time sufficient to kill pathogens such as cooking chicken for 20 minutes at 170 to the time required to kill all pathogens at a temperature of only 120? 71.100.0.206 (talk) 02:03, 14 December 2009 (UTC)

Is that degrees Fahrenheit or degrees Celsius? You can't kill all pathogens at all at normal atmospheric pressure (except by burning the food); you need a pressure cooker to do that. Certain temperatures from 140 °F (60 °C) to 180 °F (82 °C), depending on the variety of food, will prevent the growth of bacteria and/or destroy any toxins that might have already been produced by bacteria, over the period of time food is normally held between cooking and serving (no more than 4 hours). Below 140 °F (60 °C) bacteria can grow and the heat can do more harm than good. --Jc3s5h (talk) 02:20, 14 December 2009 (UTC)

Fahrenheit. I read somewhere that vegetarians cook at 118 deg F so maybe the reason is only flavor? 71.100.0.206 (talk) 02:48, 14 December 2009 (UTC)

I would not recommend cooking chicken at either 170°F or 120°F. My meat thermometer says that, for poultry to be cooked it should reach a temperature of 190°F, and you're clearly not doing that if you're cooking at a temperature below that. Cooking chicken in an oven would typically be done at 200°C (~400°F) so trying to cook at the very low temperatures you're talking about seems an impossibility. --Phil Holmes (talk) 15:15, 14 December 2009 (UTC)

The 118°F thing may be a reference to a raw food diet, not an ordinary vegetarian diet, but the number is a little different than what our article says. For cooking meats at a low temperature for a long time, see sous-vide. And I don't want to eat chicken that's been cooked to 190°F. 165°F is plenty. -- Coneslayer (talk) 15:30, 14 December 2009 (UTC)

200 F sounds way too low, and it would take a very long time for the internal temp to creep up to 190. My old 1981 "Better Homes and Gardens Cookbook" says to roast chickens at 375, under 2 pound chickens at 400, turkey at 375, goose at 350, and foil wrapped turkey at 400. It calls for an internal temperature of 185 in the thigh meat as a doneness test. Edison (talk) 19:54, 14 December 2009 (UTC)

depurination

Why isn't depurination a much larger problem than it seems to be? I know there's BER, but I mean, a purine glycosidically linked to a sugar seems to be quite problematic, because purine seems to be a good leaving group, and that anomeric carbon is all the more reactive to SN2. John Riemann Soong (talk) 02:50, 14 December 2009 (UTC)

Also why isn't depyrimidination also a mutation regime? Glycosidic-bonded pyrimidines have a carbonyl at the 2' position, effectively making a 2N-nitrogen an amide (negative charge can be delocalised onto the oxygen) so a pyridine lone pair could be similarly delocalised. John Riemann Soong (talk) 03:09, 14 December 2009 (UTC)

Scanning for a lost cellphone

Hi, I've lost my cellphone. It might have been stolen (it's now blocked for outgoing calls, just in case) but it's on and I suspect it's in my house. I can call it and I get the "calling" sound in the phone I call from but I can't hear it ringing (if it's in the house, the sound must be off or it's surrounded by pillows or something). It's an iPhone but I think the WLAN is not transmitting when it's not being actively used. Is there any way I can "scan" my house for it using simple equipment, like a small radio? Would it be feasible to call the phone while walking around with a radio to see if I hear interference on the radio? If so, would anything other than a radio (just a small speaker, for example) be more likely to work? I'm of course also looking by conventional methods but I just moved and there's a lot of cardboard boxes it could potentially have fallen into (as well as the possibility that it is indeed not in the house). Thanks! Jørgen (talk) 11:23, 14 December 2009 (UTC)

It turned up without any scanning. But I still think it was an interesting idea... :-) Jørgen (talk) 19:38, 14 December 2009 (UTC)

Both wifi and bluetooth have RSSI that indicate roughly how close the transceiver is. If you have set your iPhone to automatically connect with a laptop or something you could maybe do some sort of triangulation, although it won't be very accurate. --antilived^{T | C | G} 23:22, 14 December 2009 (UTC)

The connection between blonde people and intelligence

I have a question, are blonde people really stupid? I mean, does being blonde affect your intelligence? —Preceding unsigned comment added by RocketMaster (talk • contribs) 13:35, 14 December 2009 (UTC)

Off course not. It is also not true that the chiken crossed the road to get to the other side. Dauto (talk) 14:40, 14 December 2009 (UTC)

But it is true that silly people post nonsense in Wikipedia at times. JamesBWatson (talk) 15:39, 14 December 2009 (UTC)

It's a perfectly reasonable question. Sometimes conventional wisdom is right, sometimes it is wrong. Determining which is the case for a particular piece of wisdom is a job for science, not for assuming it must be nonsense because you've been brought up with the dogma of equality. So, how about we try and actually find some references for the OP? --Tango (talk) 15:57, 14 December 2009 (UTC)

Indeed: intelligence is a combination of nature and nurture, and part of the nurture is attributable to one's appearance. A number of studies have shown that unattractive children receive poorer treatment from their parents, for example, which could lead to lower educational opportunities. --Sean 16:18, 14 December 2009 (UTC)

There could also be a case of self fulfilling prophecy. If culture views blonds as dumb, then smart women who do not wish to have such a stereotype may dye their hair a different color, resulting in a higher proportion of "dumb blonds". 65.121.141.34 (talk) 16:24, 14 December 2009 (UTC)

It is not a reasonable question. There is NO conventional wisdom about blonds being dumber. Just dumb jokes about it. Dauto (talk) 17:40, 14 December 2009 (UTC)

Perhaps "conventional wisdom" is the wrong term, but there certainly are people that believe blondes have a lower average intelligence. Jokes don't exist in a vacuum. Even if nobody believed it, it would still be a reasonable question. Empirically verifying things that everybody believes to be true is an important part of science. The refusal to even consider that your assumption could be wrong is the defining characteristic of a dogma, and dogma has no place in science. --Tango (talk) 17:54, 14 December 2009 (UTC)

Are you asserting, Dauto, that you are a master of every single one of the thousands of cultural enclaves that exist in all of the 192 countries in the world and that you are positive that nobody believes this? You're overstating. Please stop; this is the Reference Desk. Tango is correct. Let's find some citations. This link isn't one, but its hypotheses touch on why physical features and intelligence might theoretically be correlated (the claim is that genes set an upper limit for intelligence and that "genetic clustering occurs due to geographical isolation over long periods of time, and continues through inheritance", so you could see how, say, hair color and intelligence might be correlated because one particular group happens to be of a certain hair color and of a certain intelligence range. This is surely controversial but that's something to debunk with a link to a study, not by trying to shout it down). Comet Tuttle (talk) 18:00, 14 December 2009 (UTC)

We do have a dumb blonde which says "This stereotype (and the associated cognitive bias) may have some negative consequences and it can also damage a blonde person's career prospects. [16]" which I think calls into question the idea it's simply dumb jokes. Conciously the people may say it's a dumb jokes but the study here suggests subconciously at least they are being influenced. I have read of other studies before that have been summarised as "blondes really do have more fun" specifically they've found that people (or women?) who dye their hair blonde start to behave differently and also induce different responses from people IIRC. To put it a different way, as with many stereotypes, whether they have any truth or not, people subconciously at least respond to them. And in fact I agree with Tango here, as with many stereotypes there are certainly people who do conciously believe them to some extent.

And repeating what has been said above, it seems likely to me there will be some influence therefore on the blonde's 'intelligence'. To clarify, I should say I'm not referring to intelligence as defined by some IQ score but more generally in terms of knowledge and other things which make the difference between a 'smart' person and a 'dumb' person. Anyway if other people have lower expectations of that person and therefore the person is not pushed so hard to achieve and is given less opportunities to succeed (the study for example) it seems likely this will often negatively influence their intelligence. And conversely since when the person does have to do something they may have to put in less effort to succeed again that's likely to negatively influence their intelligence. Nil Einne (talk) 19:24, 14 December 2009 (UTC)

Tango, Equality is not a dogma. You seem to be confusing it with a virtually nonexistent belief that there are no differences between people. Equality is simply not taking one person's observed behavior or intelligence and attributing it to trivial factors such as appearance (i.e. blonde hair) with no non-biased attempt to find any actual evidence of a cause-effect relationship between said blonde hair and the specific behavior or intelligence, thereby wrongly assuming that all people with the same appearance (i.e. blonde hair) are less intelligent then non-blondes. --Itwilltakeoff (talk) 00:17, 15 December 2009 (UTC)

Equality is dogmatic for some people (like Dauto). Of course it isn't for everyone, for plenty of people it is just an assumption based on evidence, or lack thereof. The difference is whether or not you are willing to consider that it might be wrong. --Tango (talk) 00:53, 15 December 2009 (UTC)

Also, the Stereotype threat article may interest the OP.

Which leads to the vastly more interesting question of whether or not blondes have more fun. ~ Amory (u • t • c) 01:38, 15 December 2009 (UTC)

I mentioned the study earlier. I found some mention of it here [17] [18]. I couldn't find if it was published or where, one of the articles links to a press release which doesn't work, I didn't try that hard. Some obvious flaws occured to me when reading this study and when writing about it above which I didn't bother mention but found this which does a resonably job of highlighting them [19]. The second ref and [20] mentions some other studies with more ambigious results and [21] [22] suggests blondes may have more fun, unless they want to get married/settle down. It's apparently also a question which interested Darwin [23] [24] so I guess you're in good company for wanting to know. I also noticed this mostly unrelated thing about improvements in modelling blonde hair and the reasons it's difficult [25] which perhaps SB can help clarify if anyone is interested. Nil Einne (talk) 10:10, 15 December 2009 (UTC)

What medicine stops the itchiness inside of nose?

Template:RD medadvice -- Scray (talk) 03:05, 15 December 2009 (UTC)

Irritation

Why does a body part become red when its irritated?Accdude92 (talk to me!) (sign) 14:43, 14 December 2009 (UTC)

I believe it is a histamine response. The redness is due to increased blood flow to the area. --Tango (talk) 15:06, 14 December 2009 (UTC)

Yes -- check out rubor. DRosenbach ^{(Talk | Contribs)} 03:10, 15 December 2009 (UTC)

Faroe Islands tunnels/civil engineering.

What are the main civil engineering companies, or company, in the faroe islands? I mean for instance who builds the most tunnels? —Preceding unsigned comment added by 188.74.72.115 (talk) 16:04, 14 December 2009 (UTC)

We have a List of tunnels of the Faroe Islands - there aren't that many of them. 75.41.110.200 (talk) 21:57, 14 December 2009 (UTC)

See the Miscellaneous section. By the way that's a real lot of tunnels for only 49,000 people to use. The Danish taxpayers have spent more than a billion Euros on them and now they want independance[26]. Alansplodge (talk) 23:25, 14 December 2009 (UTC)

Following a link in the Norðoyatunnilin article (the only one linked in the "list of" page), I find this page: http://www.tunnil.fo/Default.asp?sida=565 . From what I can read from it (Norwegian and Faroese separated some 700 to 1000 years ago, so not much) it seems NCC constructed that tunnel. In general I would expect most or all tunnels on the Faroes to have been constructed by foreign companies. Jørgen (talk) 07:33, 15 December 2009 (UTC)

Google also gave me this (only part of an article, but one more (or the same) example of NCC building a tunnel there) Jørgen (talk) 07:36, 15 December 2009 (UTC)

Tail on Human

Could this be true that some humans were born with a tail? This is video of a woman showing her tail note: it is a porn video. with a tail. —Preceding unsigned comment added by 74.14.119.246 (talk) 16:24, 14 December 2009 (UTC)

Well, who knows about the video—one should never look for reality in porn. But our article on Tail covers the possibility of human tails quite well, check it out. --Mr.98 (talk) 16:28, 14 December 2009 (UTC)

To put 98's comment in a different way, humans can have tails, but while I haven't looked at the video it's quite doubtful IMHO that the woman in the video really has a tail Nil Einne (talk) 19:21, 14 December 2009 (UTC)

I watched it and it was obviously fake. --Sean 22:12, 14 December 2009 (UTC)

Both my nephews were born with tails - instead of curving inwards, the coccyx curves outwards. --TammyMoet (talk) 18:42, 14 December 2009 (UTC)

See also our Atavism article. 87.81.230.195 (talk) 21:17, 14 December 2009 (UTC)

And Human tails and this [27] and [28] Alansplodge (talk) 23:19, 14 December 2009 (UTC)

Theories vs. laws (Re: Einstein)

Hi. I've been trying to figure why Einstein's theories of Relativity are still widely considered theories and not laws, and how there aren't even aspects of those theories that are considered laws per se. I know there have been discussions about the subject here already. What I want to know is if what I found at the Physical laws article is true (and would therefore explain calling Relativity a theory and not a law):

Physical laws are distinguished from scientific theories by their simplicity. Scientific theories are generally more complex than laws; they have many component parts, and are more likely to be changed as the body of available experimental data and analysis develops. This is because a physical law is a summary observation of strictly empirical matters, whereas a theory is a model that accounts for the observation, explains it, relates it to other observations, and makes testable predictions based upon it. Simply stated, while a law notes that something happens, a theory explains why and how something happens.

So, is this really true? Even if it is, I could argue that certain formulas or concepts within the theories of relativity could be isolated and named "laws", right? PS. I found it very curious to know that Relativity is the only item in the List of laws in science article that is still a theory... 190.157.136.97 (talk) 16:42, 14 December 2009 (UTC)

This issue has been discussed many times on the RD before. You may want to read those discussions first and then come back with anything that still confuses you Nil Einne (talk) 16:59, 14 December 2009 (UTC)

Some of the many discussions pertaining to theories and laws that I was referring to Wikipedia:Reference desk/Archives/Science/2009 July 17#Theory vs. law; Wikipedia:Reference desk/Archives/Science/2008 February 29#Question about scientific theory vs. law; Wikipedia:Reference desk/Archives/Science/2008 May 6#The Law of Gravity; Wikipedia:Reference desk/Archives/Miscellaneous/2009 April 20#Possible Einstein quote? Else who?; Wikipedia:Reference desk/Archives/Science/2009 May 25#scientific method and evolution*; Wikipedia:Reference desk/Archives/Science/2008 November 3#Are there any legitimate scientific alternatives to evolution?; Wikipedia:Reference desk/Archives/Miscellaneous/2009 March 16#Government plans for ET contact; Wikipedia:Reference desk/Archives/Science/2009 July 18#Gravity; Wikipedia:Reference desk/Archives/Science/2009 July 14#Big Bang, how did it happen?; Wikipedia:Reference desk/Archives/Science/2009 February 12#Darwin mechanism of evolution?; Wikipedia:Reference desk/Archives/Science/2008 February 15#What exactly is a magnetic field? Nil Einne (talk) 18:07, 14 December 2009 (UTC)

Yes, that definition is correct. "Still a theory" is nonsense - a theory is a good as it gets. "Theory" in science doesn't mean "something that hasn't been proven", as it does in everyday usage, since there is no concept of proof in science. Something like "E=mc²" could be described as a law, I suppose, as could "the speed of light is constant". They are simple statements that have been empirically demonstrated. The idea that theories become laws is just not how science works and is generally nonsense spread by creationists trying to discredit the theory of evolution. --Tango (talk) 17:02, 14 December 2009 (UTC)

For example, the Lorentz transform is a law which governs the composition of velocities in the theory of special relativity. However, this law only describes a small portion of the total class of phenomena which might be explained in a special relativitistic treatment. Compare, for example, how Ohm's law is the simplified governing equation for a more general theory of electrical conductivity and an even more general quantum theory of conductivity. Not only is the theory more complex, but it includes the law(s) as special-case simplifications of the general physics. Furthermore, different theories can support some of the same law(s), as is the case when a simpler theory is a proper subset of more generalized theory. Nimur (talk) 17:50, 14 December 2009 (UTC)

E=mc² is a law: it is a description of mass-energy equivalence. I suppose we could name it something like "the law of mass-energy equivalence". There are two different theories of relativity "special relativity" and "general relativity". --Jayron32 18:56, 14 December 2009 (UTC)

Don't forget Galilean relativity. Einstein wasn't the first to theorise about things being relative. --Tango (talk) 18:59, 14 December 2009 (UTC)

This is a very good article comparing evolution with gravity: Evolution as theory and fact. --Mark PEA (talk) 19:35, 14 December 2009 (UTC)

Actually, that article is not even a Good Article, much less a "very good article". Comet Tuttle (talk) 19:42, 14 December 2009 (UTC)

No, no, no! Nonsense. An article can be extremely good in every regard - but if nobody offers it to the WP:GA crew to check out, it'll never become a Wikipedia:Good article. SteveBaker (talk) 01:34, 15 December 2009 (UTC)

foggy car windows

What atmospehric conditions must there be for a car's window to fog up?Accdude92 (talk to me!) (sign) 20:19, 14 December 2009 (UTC)

The basic cause is that the glass is colder than the air on one side of the glass. Based on the humidity of the air, there is a dew point (a certain temperature) below which the water evaporated in the air will condense into liquid. If the window is colder than the dew point of the air, water will condense on the glass in very small droplets, which is what makes it foggy. —Akrabbim^talk 20:27, 14 December 2009 (UTC)

Further to this subject, is there a good, cheap way to minimise the condensation that forms on the inside of a car's windows when it's parked outside during an overcast British winter? My car lacks air conditioning and the windscreen's air blowers (using engine heat to warm cold but humid exterior air) take a considerable time to clear it, as does the rear window's heating element. I have latterly resorted to driving with the side windows half-open for 10 minutes, which works but is no fun in the cold and impractical when it's raining. 87.81.230.195 (talk) 21:12, 14 December 2009 (UTC)

Clean windows fog up much less than dirty ones. I proved this to a coworker who refused to believe it because it meant that he had to do a minor amount of physical labor. I cleaned the passenger side of the windshield. Then, the next week, I saw him driving down the road leaning over so he could look out the passenger side of the car while the driver side was all fogged up. -- kainaw™ 21:15, 14 December 2009 (UTC)

In order to fog up, the window needs Nucleation sites. Basically, in order to change phase from a gas to a liquid, the water molecules need some rough areas to "stick" to first. That's why dirty windows fog up so fast, the particles of dirt provide lots of good nucleation sites. If cleaning the window really well does not work, there are anti-fog coatings and sprays that you can buy at any auto supply store, or the automotive department at your local supermegamart. These are usually surfactants (i.e. soap) that prevents the water from forming tiny droplets. Window fog is essentially lots of little droplets, so by lowering the surface tension of the water, the water forms a thin sheet instead of droplets, and a sheet of water is much easier to see through than lots of droplets are. --Jayron32 21:29, 14 December 2009 (UTC)

As I remember from my (mispent) youth, a cut potato rubbed over the window helps - also it's not bad if your wiper dies and you want to drive in the rain (Mr. Plod might not approve). Way back in the 60-70's there was a product for the rear window called (I think) GnoMist - a thin sheet of plastic which clung to the screen (like some of those window stickers that aren't sticky), that helped to keep the back window clear, I assume the water did not like forming droplets on the surface. Make a mental note for your next car to get one with a heated front window - my Mondeo is just great in keeping the windows clear.  Ronhjones  ^(Talk) 21:49, 14 December 2009 (UTC)

I've never heard of GnoMist, but Rain-X and Aquapel are water repellent products available in the US which are supposed to reduce the amount of fogging on windshields. -- 128.104.112.87 (talk) 00:17, 15 December 2009 (UTC)

between large vision acuity

This is possible to say 20/100-1 or 20/200+1? What what does this mean? Is 20/100-1 mean like 20/120 and 20/200+1 mean like 20/170 or so? Doctors can do like 20/x+3 if vision is between 20/200 and 20/300, this do happen.--209.129.85.4 (talk) 22:02, 14 December 2009 (UTC)

I've never seen visual acuity quoted like that. Where did you see it? --Tango (talk) 22:25, 14 December 2009 (UTC)

Last doctor's visit one eye is 20/100-1 that's what the doctor wrote.--209.129.85.4 (talk) 22:29, 14 December 2009 (UTC)

Any changes the one is actually a lower-case L? Jc3s5h (talk) 22:36, 14 December 2009 (UTC)

For "Left eye"? Opticians usually use "S" (from the Latin for left) rather than "L", but I suppose it is possible. --Tango (talk) 00:49, 15 December 2009 (UTC)

It could be possible that the numbers are actually separate things. The first number (ex. 20/20 or 20/100) might represent the visual acuity expression, and the other number (ex. -1 or 0.5) might represent the number of diopters that the optometrist has prescribed for corrective lenses. 152.16.15.144 (talk) 00:48, 15 December 2009 (UTC)

December 15

Why isn't t-butyl (as a carboxylate protecting group) sensitive to base?

It seems to me you could perform an E2 elimination and kick out carboxylate as a decent leaving group .... John Riemann Soong (talk) 00:24, 15 December 2009 (UTC)

Boiling water simply by adding kinetic energy?

Is it possible in principle to bring water from room temperature to a boil simply by adding kinetic energy via something like an egg beater? If yes, is it possible given the tools available in the average home, or would you need some serious manufacturing/industrial class hardware? Just curious as I gently stir my morning coffee... 218.25.32.210 (talk) 00:40, 15 December 2009 (UTC)

In theory yes, but it'd be very impractical. A major problem is heat dissipation. (At some point the water will lose more heat than you are adding to it.) And efficiency. An egg-beater is way too weak ... a major problem is that you'll just end up heating the room air instead. If you completely insulated the boiling apparatus in question, and ensured very little heat flow between the container and the outside environment, and dropped in an agitator, you could prolly theoretically boil it. The heat capacity of water (or any solvent for that matter -- even hexane) is kinda large though. John Riemann Soong (talk) 00:46, 15 December 2009 (UTC)

Given the right circumstances - certainly. If you take an electric drill with a really blunt wood-bit - and try to drill your way into a small chunk of stainless steel - after a couple of minutes of fruitless drilling, squirt a small amount of water into the area and it'll boil immediately. Now, admittedly - we took the kinetic energy of the drill - and used friction to convert that to heat - but the intermediate step is merely a convenience. The question is really whether you can figure out a way to get from motion to convert directly into heat in the liquid. In principle, it's certainly possible - and with a sensitive enough thermometer you'd certainly be able to measure a small, slow heat increase from a fast electric mixing machine or such like. But as John said - the problem is to get the heat into the liquid faster than it'll lose heat to the environment. So you need to agitate the water as fast as possible to get the heat in faster than it's losing it. You'd want an insulated container...that kind of thing. It's got to be possible though - it's just a matter of figuring out a way to do the experiment. SteveBaker (talk) 01:31, 15 December 2009 (UTC)

My favourite candidate so far is to use a magnetic stirbar. No moving parts, and you could theoretically seal up the container with lots of insulation, then just apply a changing magnetic field! =D Better yet, drop fine magnetic powder and turn on the field. The big thing you see is surface area. If you do some simple calculations, you find your agitator is adding very little energy (most of the energy doesn't end up in the water, even without the water losing anything). Very fine particles being moved about means more surface area ===> more friction ===> greater heating efficiency. John Riemann Soong (talk) 01:36, 15 December 2009 (UTC)

Nod, keep in mind that 'heat energy' is for all intents and purposes just kinetic energy on a small scale, IE the energetic movements of atoms unless I was deceived as a child. Unomi (talk) 01:44, 15 December 2009 (UTC)

An interesting extension is to use something with an electric dipole or that is ionic...apply an oscillating electric field and the molecules vibrate and collide with each other to heat the material. 173.79.45.179 (talk) 05:17, 15 December 2009 (UTC)

Related: frictional heating from the mixing is an important factor when kneading bread dough mechanically. --Sean —Preceding unsigned comment added by 76.182.94.172 (talk) 01:34, 15 December 2009 (UTC)

Car windows again

The above question from yesterday reminds me of a related question that I have long puzzled over. Several people have assured me that setting the blowers to cold will clear condensation from the inside of a windscreen quicker than if they were set to warm. This does seem to be true, even though it goes against what I would intuit: shouldn't warm air perform this function more efficiently?--Shantavira|^{feed me} 08:25, 15 December 2009 (UTC)

The condensation is there because the car is warm inside while it's cold outside. So why do warm blowers work at all? 213.122.69.70 (talk) 08:50, 15 December 2009 (UTC)

Did you even bother to read the answers from yesterday? Warm blowers work because the problem is cold windows in wet air. If you warm up the windows (by blowing warm air on them), the condensation will get slower and slower until it stops, and in addition, the warm air will evaporate the drops that are already there, because warm air can "store" more water vapor than cold air (and the flow of air helps, too). --TheMaster17 (talk) 09:19, 15 December 2009 (UTC)

You may be misunderstanding the advice... if you turn on the air conditioning, it will dry the air and improve evaporation. But even with the air conditioning on, you should have the heater set to warm, so the air that blows is warm and dry. -- Coneslayer (talk) 12:31, 15 December 2009 (UTC)

There are two effects going on here. The amount of water that the air can hold depends on temperature. Warm air can hold lots of water - cold air, much less. So - when your car is cold, the water in the warm air in your breath hits the cold windshield and cools rapidly. At that point, the water can't stay in the air so it forms as droplets on the windshield. Hence:

• The A/C cools the air - but also dries it (it's not an "air refrigerator" - it's an "air conditioner" - it "conditions" the air - removing dust and moisture as well as cooling it down). Drying the air reduces the water content (irrespective of temperature) and without water in the air, there is nothing to condense.
• The heater warms up all of the air in the car - but since that air was formerly cold - it didn't have much water in it. So now the car is warm (and dry) and your breath can dissipate water into all of the other warm air in the car which (being dry) is easily able to hold it. Also, the warm air heats up the windshield so that when warm, moist air does touch it, it's not cooling the air down enough to allow the water to condense.

Hence either heating or cooling the car will eliminate mist from the glass. In fact, because the main source of all of this water is your body - simply turning on the fan and replacing the air inside the car with outside air will remove much of the moisture and prevent misting. Just blowing the air onto the windshield will maintain a barrier of drier air and thereby prevent your moist breath from getting in contact with it.

Hence, almost anything you do with the car's heating/cooling controls will help to demist it. However, the airconditioner (on cold) works best because it's literally removing the water - not just moving it around. SteveBaker (talk) 14:44, 15 December 2009 (UTC)

Shatika

Where can I find more information on Shatika? Regards-Shahab (talk) 09:07, 15 December 2009 (UTC)

My guess would be that the snake oil article would be a good place to start. Keep in mind that these sorts of products are rarely regulated, so their claims of efficacy may be totally fictional. Nimur (talk) 13:16, 15 December 2009 (UTC)

Don't be too hard here. The product is Ayurvedic rather than allopathic. Sometimes I think we're guilty of judging one culture by another culture's lights. I know that's heresy on a science reference desk, but what the hey. --TammyMoet (talk) 13:51, 15 December 2009 (UTC)

Oh - yes, we can be that hard! This is the science desk and we don't stick our heads in the sand and say things are OK just because it comes from another culture and therefore we must respect it somehow. That is 100% not how science works - we judge things by the facts - and culture simply doesn't enter into the equation. What you just said is beyond heresy - it's completely f**king stupid.

So - let's do this properly. Let's examine the claims made for the stuff: It says that it "Relieves pain" - OK - maybe. Much of pain is psychosomatic and any placebo can do that. So - yeah - maybe.

But it also says that it cures: Arthritis(Osteoarthritis,rhumetoid arthritis),Spondylitis and Migraine. Pick any one of those: Osteoarthritis let's say. This is a disease that's caused by physical wearing and degradation of cartilage around the joints. Unless this oil somehow causes a magical regeneration of cartilage (something completely unknown in humans) - then it can't "cure" osteoarthritis - at best it might relieve the pain - but they already said it relieves pain in general, so they must be talking about something more specific. We don't say "Tylanol cures Osteoarthritis" - although it does help the pain. Spondylitis isn't even a specific disease - it's a symptom of many possible diseases...curing it would require fixing all sorts of odd problems - none of which seem to be listed?!? Curing migrane would require getting involved with seratonin inhibitors in the brain...this would have to be a substance capable of crossing the blood-brain barrier. Such a substance should be regarded with EXTREME caution! In short - if this stuff did what it said - it would be capable of doing untold amounts of harm too! If you used it to cure your Arthritis and it started leaching into your brain and messing with your seratonin levels - the consequences would be horrific!

Where is the list of side-effects. No change that you do to the body comes without changes elsewhere. If it's curing one thing (say your migrane) then whatever effect it has on stimulating the growth of new cartilage in osteoarthritis would cause who-knows-what joint changes in people who have no cartilage problems to start with!

If this stuff works as advertised - it's lethally dangerous and I wouldn't want to be within 50 feet of an opened bottle! If it doesn't work (as I STRONGLY suspect) - then don't buy it because it's snake-oil.

At best, this is a mild pain reliever - probably more for psychosomatic reasons than anything else. My mother uses 'witch hazel' to relieve her migranes - it's very clear that it's not doing anything but acting as a credible placebo for her - so I'm not going to tell her that it's useless. This stuff is likely doing the same thing.

Sorry - but science CAN discuss these kinds of matter.

SteveBaker (talk) 14:27, 15 December 2009 (UTC)

Out of curiosity several Shell lubricants contain salicylates (Alexia has the most check Google) and we did sometimes come across people abroad massaging it into arthritic joints apparently with some benefit (obviously, this is not medically safe, but aspirin is a salicylate of course). Conventional analgesics can be absorbed by the skin, and do occur in tree bark etc but as I think Steve's said before the ones which work are sold as medicine and the ones which don't work are snake oil. --BozMo talk 14:46, 15 December 2009 (UTC)

Acetone/Water Mixtures: Flammability

Greetings! Acetone is a flammable liquid. 1 % acetone in water is not flammable. At what concentration (v/v or w/w) are liquid water/acetone mixtures flammable? And at what liquid mixture ratio is the vapor flammable? (everything under standard conditions). I have been searching, but these data seem to be hard to find. Thanks for help! Grey Geezer 09:21, 15 December 2009 (UTC) —Preceding unsigned comment added by Grey Geezer (talk • contribs)

One type of answer (which leads to more questions!) is "whatever liquid ratios give acetone vapor concentration between the lower flammability limit and the upper flammability limit". Assuming it's actually the evaporating (and rapidly so, given the heat of the flame) acetone that's burning, you need to know the Lower flammability limit. The added water means some of the heat is used to evaporate that rather than acetone (reduces the efficiency of the self-perpetuating flame) and to dilute the air/acetone vapor with water vapor (affects the lean/rich mixture required to burn). I have no idea the specifics for acetone, but those are "one level deeper" into how I understand the issues involved. DMacks (talk) 09:40, 15 December 2009 (UTC)

Depends on the liquid temparature too. My copy of the rubber company handbook has vapour pressure curves for acetone above mixtures of acetone water but in practice it is going to be tough to calculate, and flash points etc in reality depend heavily on geometry however we try to standardise them. The only help I can think of is that these kind of numbers are easily obtained for ethanol and ballpark acetone might be similar. Cold brandy is hard to burn warm brandy will sustain a flame easily. So brandy at say 20C (and 40 degrees proof which is 20% alcohol is marginal). Guess acetone might be something similar? --BozMo talk 10:06, 15 December 2009 (UTC)

What are the arm blades of a preying mantis made from?

I've seen videos of the large preying mantises stabbing or slashing open rodents and birds with them. I suppose that they're probably made from a similar substance to the rest of the mantis's exoskeleton, but are they toughened or hardened somehow? Also, does the mantis have to do anything to keep them sharp? --95.148.104.205 (talk) 09:23, 15 December 2009 (UTC)

It may have been done initially with pun intended, but the proper spelling is praying, referring to the folded arms/prayer-like stance. DRosenbach ^{(Talk | Contribs)} 14:17, 15 December 2009 (UTC)

AFAIK, "blades" of the grasping forelegs are made of the same thing all insect exoskeletons are made of: chitin + protein matrix + calcium carbonate. Chitin by itself is somewhat similar to cellulose, but the addition of the other two components makes it much more rigid. Now, as far as the sharpening goes, mantises spend really a lot of time grooming their forelegs; but I am not sure at all if that contributes to the sharpness of the spines on the forelegs or is just meant to keep them clean. Anyway, keep in mind that any mantis molts a number of times before it reaches adulthood, and the entire exoskeleton is replaced every molt. --Dr Dima (talk) 10:34, 15 December 2009 (UTC)

Tree question

I am ok at felling trees in a given direction but I have a tricky one. The tree is on the bank of my moat, and is leaning over the moat by about 30 degrees (slowly falling). The moat is 6 m wide and the main tree truck is about 18m high (most of the canopy is gone so it approximates to just a trunk). I do not want to be fishing a tree trunk weighing a number of tonnes out of a 2m deep moat so I want to fell the tree so that the bottom of the fallen trunk is at a good distance from the stump. If I cut the tree at a given height above the ground how far away from the tree stump will the bottom of the trunk be at impact on the ground? Can I improve this by varying the slope of the cut? Any other ideas on how to get the trunk well over the moat?--BozMo talk 10:17, 15 December 2009 (UTC)

A photograph would help!

It doesn't matter how high up you cut it - the tree rotates about the point where you cut it until it's pretty much horizontal - and then pretty much falls vertically. If the fibreous wood doesn't break cleanly - then the trunk may even stay attached to the top of the stump and cutting it up higher just makes for a lot more grief - and makes what I'm about to suggest even more difficult. But a lot depends on how clean the break is and how top-heavy the tree is. IMHO, you're not going to get the trunk to fall more than maybe half a meter from the stump, no matter what you do.

If the geometry of the situation is as you say then you need to fell the tree so that if falls at right angles to this 'moat' - cutting it as close to the ground as is reasonable. If it's already leaning by as much as you say - you have no chance of making it fall in any other direction anyway.

If you're right about the dimensions then about 12 meters of tree will be on the far side of the moat with 6 meters dangling in fresh air across the moat. In theory - if the tree were of uniform thickness - the 12 meters out there on dry land would be plenty heavy enough to stop the other 6 meters from falling into the water. However - if the tree tapers strongly then it's possible that the bottom 6 meters will be heavier than the topmost 12 meters - and then the heavier bit might dip into the water - but at least you could loop a rope over the top of the tree and with a modest amount of weight - pull it down so it's horizontal.

Once it's down - if you don't have heavy machinery to haul the trunk 6 more meters until it's all on level ground - then I suggest that you prepare some rollers (maybe some nice round logs) on the far side of the moat for the tree to land on that would make it easier to pull it away from the water. If the tree's trunk is nice and smooth and round - you could probably use a fulcrum close to the water's edge to rotate the tree so that it's almost all on land anyway.

Whatever you do, don't start cutting the top of the tree into logs until the bottom is pulled clear of the water because as soon as you remove weight from the top of the tree - the bottom will be more likely to fall in!

Also, I would prepare for the worst by tying some heavy ropes or chains to the base of the tree a few feet above where you intend to cut it - BEFORE you cut it down - so that if it does end up in the water - you at least have something to haul it out by.

Good luck!

SteveBaker (talk) 14:06, 15 December 2009 (UTC)

The real worry about tree felling as far as I'm aware is if the tree doesn't just angle over still connected to the stump but breaks away, in which case the base of the tree would come towards you rather than go further over the water. So yes the best you can do is cut it near the base. If you can strip off the branches for the first 6 meters it mightn't be too hard to winch it out after you're finished. Or there may be some heavy canvas or a board you could put down to make it slide over the other bank easier. The only advantage I can see of cutting it higher up is that the bit over the moat will be lighter. Dmcq (talk) 14:21, 15 December 2009 (UTC)

Yep, its a big Ash and will split violently. But by the time it does the canopy must have momentum away from the bank. Perhaps if I undercut the far side and over cut the bank side second I can get the whip to go the right way. My guess is there is at least six or seven metric tonnes of trunk there though so the sliding bit ain't going to be easy. --BozMo talk 14:50, 15 December 2009 (UTC)

The base of the tree can indeed kick backwards (because the tree would 'naturally' try to rotate about it's center of gravity - not about the bottom of the trunk) - but if you do it right, you don't cut all the way through the trunk - you leave enough wood there to act as a "hinge" to prevent that from happening - and to give you enough time to shut your chainsaw off and get far enough away from the falling trunk! But that hinge also ensures that the tree rotates about the top of the stump - so that end of the trunk will end up close to (if not still attached to) the stump. When you get it right, that hinge breaks through completely just as the tree gets horizontal. The angle of cut of the "notch" that you cut on the side where you want the thing to fall is what makes that happen. The depth of the cut on the opposite side (which actually brings the tree down) is what ensures that the "hinge" is the right strength. There is an art to doing it right. I suppose the if the hinge broke through before the tree got horizontal - it might slide a little away from the stump - but I can't imagine that being anywhere near far enough to make a difference here. SteveBaker (talk) 14:54, 15 December 2009 (UTC)

Movement of the sun and moon around the sky

So, in the Northern hemisphere, the sun rises in the east, moves in a clockwise direction through the sky (and is at its midday peak in the south) and sets in the west. The moon does the same. Am I right so far? So what happens in the southern hemisphere? Does the sun still rise in the east? Is it at the north at midday? Does it go in an anti/counter-clockwise direction to set in the west (if it sets in the west?)? And what happens on the equator?

In the Northern hemisphere, stars move around the Pole Star - but what direction do they circle in - clockwise or anti/counter-clockwise?

Thank you for helping.81.159.89.69 (talk) 11:44, 15 December 2009 (UTC)

The cause for all these apparent motions, including star movement, sun rise, and sunset, is Earth's rotation. (The moon also adds a non-negligible extra detail due to its orbit around us, and the Sun also adds a smaller variation because of our orbit around it). But the most important factor here is Earth's rotation. Since Earth's rotation direction is the same everywhere on Earth, the apparent rise of the sun and moon are always in the east; the apparent direction is always the same - counterclockwise if you're facing north (clockwise if you're facing south). In the unique case of polar regions, the midnight sun throws another neat variation, in that the summertime sun never gets low enough to sink below the horizon; but it still "wobbles" in a circular path. The equator doesn't really behave very specially, except that the sun is directly overhead, approximately at the zenith, on noon of the equinoxes. As far as where the sun is at its midday peak, this depends on your latitude and the current season. Nimur (talk) 13:25, 15 December 2009 (UTC)

edit conflict Because, from a bird's eye perspective of the plane, so to speak, of our solar system, the earth rotates on its axis in a counter-clockwise fashion, the celestial entities (sun, moon, planets, stars) seem to orbit us in a clockwise fashion. Therefor, things rise in the east and set in the west. For one living in the northern hemisphere, solar/lunar "orbits" manifest as short days, with rising and setting occurring south of due-east and -west and the celestial entities don't travel too much into the southern sky. For the same northern hemispherer, summer manifests as long days, with the celestial bodies rising way north of due-east and setting way north of due-west and traveling three sides of the sky (east, south + west). Mid-day, by definition, presents as the sun in the exact middle of the sky in an east-west dimension, but the north-south aspect of the suns position at mid-day will depend upon the time of year (n.b. mid-day here is defined as the time from sunrise to sunset divided by 2). I will not speculate about what occurs in the southern hemisphere, because its quite easy to allow a minor error in calculation to become a tremendous error in conjecture. DRosenbach ^{(Talk | Contribs)} 13:30, 15 December 2009 (UTC)

Another interesting bit about latitude and the sun's midday position: it's a generalizable rule that the sun is southward in the northern hemisphere and northward in the southern hemisphere, unless you're in the tropics. Between the Tropic of Cancer and the Tropic of Capricorn (those lines of latitude equal to the Earth's angle to the ecliptic), this rule can be broken. At the northern summer solstice, all of the northern hemisphere south of the Tropic of Cancer sees the sun to the north at midday. In fact, at the equator, the expected lengths of day and such get extremely odd: the sun is highest in the sky near the equinoxes, lowest at each solstice. At Quito, Ecuador, the longest day of the year is near the December solstice (no surprise), but there's another maximum at the June solstice, and the minima are in April and August.[29] I expect that shift from the equinoxes is driven by the Earth's orbital eccentricity (the Earth is farther from the sun in June than in December). — Lomn 14:07, 15 December 2009 (UTC)

It's altogether easier to imagine that you're standing on the surface of a spinning ball - with everything else being more or less stationary! The ball takes 24 hours to spin once. (Which is unsurprising - because that's really what's happening.) SteveBaker (talk) 13:45, 15 December 2009 (UTC)

What happens when you mix hydrogen peroxide and liver?

Biology