Wikipedia:Reference desk/Archives/Science/2010 April 9

= April 9 =

Use of imaging in cancer diagnosis
How can imaging alone determine the source of cancer in the body? I've just learned that an elderly distant relative has been diagnosed with cancer in two different parts of the body; based on imaging alone, the oncologist believes that it originated in one part of the body, even though it's apparently no more pronounced there than in the other part. Please don't take this as a request for medical advice; I simply can't understand how images can reveal that one spot of cancer is the source and a similar spot of cancer is the result of metastatis. Nyttend (talk) 01:09, 9 April 2010 (UTC)
 * Not necessarily images, but certain tests of immunohistochemistry can identify metastases. 76.235.109.131 (talk) 01:15, 9 April 2010 (UTC)
 * (after EC) The oncologist is probably using additional sources of information (clinical judgment and knowledge of typical patterns of cancer incidence and metastasis) in conjunction with the imaging to come to a "most likely" explanation. Additional confirmatory tests, such as a biopsy (and the aforementioned pathology studies), are generally involved in making a definitive diagnosis. --- Medical geneticist (talk) 01:18, 9 April 2010 (UTC)
 * Too add to that, the cancer may have particular characteristics (shape, rate of growth, density on a CT scan etc.) that identify it as probably originating from a particular organ/part of the body. 131.111.185.75 (talk) 09:22, 9 April 2010 (UTC)
 * If the tumor is avascular (which I think all if not most are, someone clarify that for me) then PET scans can look for high concentrations of radioactive glucose given to a patient and see where it builds up. Avascular tumors can't respire aerobically. Presumably you can see where the biggest build up of glucose is to see where the cancer originated, as the tumor should be largest there? I'm not sure of this, so I'll let someone with formal medical training check it :) Regards, --— Cyclonenim | Chat 17:46, 10 April 2010 (UTC)

Imaging alone is very helpful in determining the source of cancer, although not 100% definitive. CT scans and FDG-PET scans are the most helpful. Radiologists are specifically trained to look out for characteristic patterns associated with different cancers. With the clinical context, the radiologist can often give the likely diagnosis.

Certain cancers are more common than others; common ones include breast cancer, lung cancer, prostate cancer and colorectal cancer. If, for example, a scan shows an abnormal mass in the lung and an abnormal mass in the adrenal gland, this is far more likely to be a primary lung cancer with metastasis to the adrenal, rather than a primary adrenal cancer with metastasis to the lung. Axl ¤  [Talk]  01:13, 11 April 2010 (UTC)

Imaging alone by itself cannot determine if something is cancerous, however it can identify abnormal growth that should not be present in the body of a person. These abnormal growths can appear with different colour or intensity as opposed to the other tissue that surrounds it in the medical image. Using the image, a biopsy may be performed to determine if the abnormal tissue actually is cancerous, or a radiologist with experience in diagnosing patients through medical images can state whether the images looks like a cancer and recommend a medical procedure. Different types of medical images (MRI, CT, ultrasound) are good for imaging different types of tissues/cancerous growth. CT is good for denser tissues (bone), MRI is good for softer tissues as is ultrasound. Of course you can also use contrast medium to enhance your images. Sjschen (talk) 19:10, 13 April 2010 (UTC)

Causality
How does information travelling faster than the speed of light disrupt causality? I've read this mentioned many times, but I haven't seen any justification for it. Thanks. 173.179.59.66 (talk) 02:41, 9 April 2010 (UTC)
 * Basically, if you can send a signal faster than the speed of light, and if the means of doing so works the same in all reference frames, then you can also send information back in time. So then someone from 2100 could send you a signal telling you to kill his grandfather, and you get the grandfather paradox.  See tachyonic antitelephone for how this would work. --Trovatore (talk) 02:44, 9 April 2010 (UTC)


 * (ec) I'm no Gandhi but I bet it is because there is no single "now" but only frames of "now" and if you could send information faster than light then you could disrupt all into someone's frame. 82.113.121.111 (talk) 02:47, 9 April 2010 (UTC)
 * reading the above (first to post in edit conflict) it seems I was right :) maybe I am a gandhi... 82.113.121.111 (talk) 02:47, 9 April 2010 (UTC)


 * I live on Alpha Centauri and have your cat under my care. Your cat dies, and I send a faster-than-light message to you (on Earth) telling you that it died.  That message--the effect of the cat dying--would arrive before you would see the cat die if you had an enormous telescope.  That can't happen; the effect cannot precede the cause in any reference frame.  --99.237.234.104 (talk) 03:02, 9 April 2010 (UTC)


 * Trovatore's answer is correct but may not be clear enought. The point is that for any faster than light movement there is always some reference frames in which that movement is seen as motion backwards in time which violates causality. That happens because of the relativity of simultaneity. In other words, if you can move faster than light then you also can move backwards in time. Dauto (talk) 03:24, 9 April 2010 (UTC)
 * It's a little subtler than that. Just going backwards in time in someone's coordinate system isn't enough in itself.  Suppose I can send a signal that, in your coordinate system, leaves from Earth in January, 2012, and arrives at Alpha Centauri, around 4 light-years away, in January, 2011.
 * That doesn't get you the grandfather paradox, because if you send the signal back to Earth the normal way, it won't arrive until sometime in 2015. So you can't send a signal back to cause it not to be sent.
 * To close the loop, you have to repeat the trick, and send the signal back to Earth, if not backwards in time, then at least at four times the speed of light or better.
 * That's why I specified frame-invariance. It's logically possible that there might be a distinguished frame of reference in which you could send a signal faster than light, but because the method is not frame-invariant, you still would not be able to get causal loops.  That would, of course, contradict relativity, but only in regimes where it's never been tested. --Trovatore (talk) 05:30, 9 April 2010 (UTC)
 * @99.237.234.104: Wouldn't you be able to account for the speed of the message and, correcting for it, see that cause didn't precede effect?
 * @Dauto: Would you be able to show me how you get that mathematically? Otherwise I'd just be taking your word for it. 173.179.59.66 (talk) 04:37, 9 April 2010 (UTC)


 * The relevant equation is the Lorentz transformation. Specifically, Assuming the faster than light signal started from space-time origin - that is x=0, and t=0, and endded at x=X, and t=T where X>cT, and plugging these values at the lorentz transformation $$t' = \gamma (t - \frac {u}{c^2}x)$$ you find that the same signal is seen from the point of view of the second observer as also starting from space-time origin and anding at $$t' = \gamma (T - \frac {u}{c^2}X)$$ which may be negative for some values of u<c which is the relative speed between the two observers. Dauto (talk) 14:25, 9 April 2010 (UTC)


 * The Lorentz transform article explains both the simple formula and the experimental justification for the mathematical description of different refernce frames. Nimur (talk) 11:51, 9 April 2010 (UTC)


 * Right, thanks. 173.179.59.66 (talk) 15:03, 9 April 2010 (UTC)

crash landing fatality rates - higher for helicopters or fixed-wing aircraft?
Seeing the news that a NATO helicopter in Afghanistan went down overnight with 4 presumed deaths got me wondering about crash-landing survival rates - if I'm military personnel, so I have a better chance of surviving a helicopter being shot out from under me / suffering severe mechanical failure or a fixed-wing aircraft? Numbers please, not speculation. I can do that myself! 218.25.32.210 (talk) 06:38, 9 April 2010 (UTC)


 * You would not believe what we have. To compile these statistics, however, one would need to go over those numbers to set up one's own graph. What we are looking for is the survival rate of crashed aircraft, rotary versus fixed. You do not explicitly state if you would like to discriminate based on "crash landing"; some aircraft that are shot at do explode in the air. I have been able to locate a source for your desired information: This forum's second poster has a lot of sources posted, and may be able to help you.

Please note these are statistics for one year, and, in addition, concern the civillian market. What should be clear, however, is that the accident rate (not casualty rate) with helicopters is so vastly higher than airliners, that it would take great statistical deviance to suggest there is not also an accompanying casualty rate. This is speculation, of course, but it is educated. I could not produce numbers for helicopter accident fatalities/casualties versus fixed wing numbers, but I think these should be easy to gather from some of the sources mentioned in that link. 88.90.16.251 (talk) 08:21, 9 April 2010 (UTC)
 * The bit about "great statistical deviance" does not make sense. There is no particular statistical reason to expect the accident rate, and the survivability rate when accidents do happen, to be correlated.  --Anonymous, 23:05 UTC, April 9, 2010.


 * You might want to compare helicopters with single engine planes, as they are similar in being unable to fly after an engine failure (even twin rotor choppers crash if either fails). This would allow you to compare the difference in the airframe only. StuRat (talk) 12:14, 9 April 2010 (UTC)
 * Many single-rotor helicopters, however, are multi-engine aircraft. 64.238.255.250 (talk) 14:11, 9 April 2010 (UTC)
 * An engine failure in either an airplane (even a single-engine type) or a helicopter would not necessarily result in a crash with damage and/or injuries: an airplane can glide down for a dead-stick landing, even in the case of a complete engine failure, and a helicopter can autorotate to a more-or-less controlled landing. In both cases, much depends on the skill of the pilot in dealing with this type of in-flight emergency.
 * Speaking of pilot skill, I strongly suspect that the much higher accident rate of helicopters vs. airplanes has to do in large part with the fact that a helicopter is much harder to fly than an airplane -- it's got four primary controls (cyclic, collective, rudder pedals, and throttle) vs. an airplane's three (stick, rudder pedals, and throttle), and what's even more important, it's not inherently stable like an airplane, so you can't fly it "hands off", you have to positively control it at all times and correct for any incipient divergence in the flight path. If you're flying a chopper, you can't ever let your attention wander, or you're as good as dead. 24.23.197.43 (talk) 05:25, 10 April 2010 (UTC)


 * In the case of engine failure in a helicopter or single-engine plane, you'd better have a good landing spot nearby. If you're over water, mountains, forest, etc., you may be SOL.  And, you also need a certain amount of altitude for the auto-rotate function of a chopper to kick in. StuRat (talk) 05:43, 10 April 2010 (UTC)


 * Yeah, that too. My point is, an engine failure doesn't turn an aircraft into a pile of scrap metal falling from the sky -- it turns an airplane into a glider, and a helicopter into an autogyro, so a pilot (often) has a chance to make a safe engine-out landing.  BTW, engine failure over water is no problem if you're flying a seaplane or amphibian aircraft. 24.23.197.43 (talk) 06:19, 10 April 2010 (UTC)

Re-focusing photographs
Could it be possible for an out-of-focus photo to be brought into focus by some kind of algorithm or equipment? It seems to me that all the necessary information must be in the photo, and although the information is scrambled up, the scrambling must occur in a predictable way. Presumably I'm wrong? "Sharpen" filters that work by edge-detection are not at all what I mean. 81.131.18.168 (talk) 10:44, 9 April 2010 (UTC)


 * See deconvolution microscopy, and more generally deconvolution for the theoretical basis of this approach. My impression is that detailed information is required about the whole optical system for this to work effectively, making it impractical for normal photography, however I am no expert on optics. I know that one approach in biological microscopy is to image a perfectly spherical bead of known diameter, and use this to work out the deconvolution parameters needed. 131.111.185.69 (talk) 11:19, 9 April 2010 (UTC)


 * (ec) Computational photography studies that problem. Here are a few links you might find interesting: Light fields and computational photography, Synthetic Aperture Focusing using a Shear-Warp Factorization of the Viewing Transform, and the MultiCamera.  It really helps to have redundant information, (for example,  many separate photographs - though there are other ways to have redundant information), so that an algorithm can extract additional information to help focus the image.  This video, Synthetic Aperture focusing, shows a series of processed results from a "single image" generated by the multi-camera (you can consider this a single camera with a huge synthetic aperture, or you can consider it 128 cameras with normal apertures).  In either case, though, these algorithms require additional (redundant) information which is not contained in an ordinary photograph - your post implies that de-focusing is "information scrambling" (which is correct, but your terminology is a bit imprecise.) However, your assumption that this "scrambling" is predictable is not exactly right - it's only predictable if we have additional information - how the image was defocused, or some knowledge about the 3D setup of the scene, etc.
 * If you have a fairly powerful computer (~ 1 GB of RAM and a pretty fast processor), you can use this browser-based demo to play with synthetic-aperture focusing on a series of test photographs. If you're a programmer, the project source code is available, so you don't have to run this inside a web-browser (for obvious performance reasons!)  Nimur (talk) 11:23, 9 April 2010 (UTC)


 * If you know exactly how the blur occurred then you can calculate a point spread function, and do the inverse convolution. However there is still a problem of noise.  Any noise will be amplified.  compression artifacts will be counted as noise too, so you need to perform this on a non compressed and high quality image.  Without knowing the way the picture was corrupted, you can attempt blind deconvolution.  As far as I know there were not any stable algorithms or methods using a limited CPU to get a good result. Graeme Bartlett (talk) 12:41, 9 April 2010 (UTC)


 * Adaptive optics may also be relevant. StuRat (talk) 13:01, 9 April 2010 (UTC)


 * Yes, by deconvolution or Blind deconvolution. There is or was some free software on the internet somewhere that does this. This link seems to relate to non-free software http://www.quarktet.com/BlindDecon.html 78.147.131.74 (talk) 21:00, 9 April 2010 (UTC)


 * Decon will take out motion blur, but it will fail abysmally in most cases because depth-of-field blurring is non-linear with respect to pixel x-y location (it is dependent on depth of field (z), which is an external variable which we have no knowledge about from a single image). In other words, the convolution filter is not invertible (or requires nonlinear inversion).  To put another way, consider this example.  Imagine you photograph an object with a fuzzy edge (like a diffuse mist).  Even when focused, you still image a fuzzy edge.  An equivalent point-like object in the same photograph, but out-of-focus, will look exactly the same in terms of x-y pixel locations and intensities.  So, how can you construct a decon filter to preferentially "point-ify" the point, and preserve the mist's fuzzy edge condition?  You need to know something about the scene - the actual distance to each object; and you also need to know something about the optics - the focal depth of field.  This information isn't available from a single image.  Nimur (talk) 21:16, 9 April 2010 (UTC)
 * The blind deconvolution software has a bash at it anyway. 84.13.21.95 (talk) 23:16, 9 April 2010 (UTC)


 * Using a coded aperture in the lens can help reduce some of the ambiguity and make the deconvolution a little less ill-posed. See here for some dynamic refocusing samples and a paper:  http://groups.csail.mit.edu/graphics/CodedAperture/ .  128.12.174.253 (talk) 18:31, 10 April 2010 (UTC)

Realistically it can't be done. Unblurring is an example of what mathematicians call an ill-posed problem, meaning a transformation that isn't invertible. The difficulty is that blurring an image results in a loss of information, and even if the way the information is lost is totally understood, there is no way to get it back. (This answer oversimplifies the story a bit, but the reality is that there are no good unblurring algorithms that work in a broad range of situations.) Looie496 (talk) 05:28, 10 April 2010 (UTC)
 * I saw some before and after photos of deconvolution of blurred images in a textbook once, so I have to disagree - I believe it can be done, especially when you know or can estimate (or use trial and error) the quantitative extent of the blurring. 84.13.169.129 (talk) 10:38, 11 April 2010 (UTC)
 * Nimur is correct that depth-of-field blur cannot be reversed. However the other sources of blur that can be corrected by deconvolving a point-spread function may be lens imperfections, simple defocus (not depth-of-field variation), or limited scan (e.g. TV) bandwidth. This is theoretically possible assuming analog (not digitised) information with sufficient signal-to-noise ratio. A 2-D point spread function must be used, which is not possible close to the image borders or for blur of objects in relative motion. Cuddlyable3 (talk) 11:09, 11 April 2010 (UTC)

why are car wheels the size that they are?
Why are car wheels the size that they are, instead of much bigger or much smaller?

why are car wheels the size that they are... I don't understand it, as to my mind, there are two possibilities: - the graph of "size" (x) versus whatever you're optimizing (y) slopes like this: / up until the size of the car Then the wheels should be as tall as the car. If the sloping continues, the wheels should be much taller than the car, maybe as tall as a person.

- the graph of "size" (x) versus whatever you're optimizing (y) slopes like this: |\ where the initial jump happens when you get above the size of pieces of gravel or microholes in the pavement or whatever

In that case the wheels should be tiny, like wheels on rollerblades, although you may need more of them to support the car.

Either way, to my mathematical, binary inclined mind, I can only imagine "bigger is better" or "smaller is better" -- I can't imagine what, if anything, the current wheel size can POSSIBLY optimize.

Does anyone know? What would happen if the wheel size were slightly bigger or slightly smaller? (ie whatever y axis you're optimizing must have a smaller value when x - the wheel size - is even slightly smaller or bigger; hence the fact that it is the size that it is: at the point of the current actual wheel size, the graph must look like this: /\ where if you make it (x, the wheel size) either bigger or smaller, the y-value (whatever you're optimizing) is reduced.  Can someone tell me what exactly the y really IS?  Thank you.84.153.199.127 (talk) 12:04, 9 April 2010 (UTC)


 * This is exactly why every instance of a claim of "designed without compromise" - a car industry favourite - boils my piss. Tyres (like most things) are optimised against a basket of variables and the sweet spot is a compromise. Some example factors for car tyres: size affects rolling resistance; gearing choices; axle speeds; weight; cost; space required to accommodate the four wheels and the spare; ability of the wheel to lend suspension/damping to the vehicle; ability to negotiate defects in road surfaces &c&c&c. None of this is enough to pin why the sizes are as we're familiar, but merely to suggest that there's a lot of complexity, and probably a lot of pragmatism, in the choices. And that being the case, a simple x versus y analysis will be insufficient to answer the question. --Tagishsimon (talk) 12:43, 9 April 2010 (UTC)


 * The way this type of thing usually works out is that there are some advantages to being bigger, but most of that advantage comes in at the initial increases in size, with diminishing returns for further increases, and the same is true for being smaller. The result is that there's some optimal size or range of sizes in the middle.  But let's look at some of the advantages of small wheels and large wheels:


 * Small Wheel Advantages:


 * 1) Less expensive.


 * 2) Easier to carry a spare.


 * 3) Easier to change.


 * 4) Less rotational inertia, which makes turning and stopping easier.


 * Large Wheel Advantages:


 * A) More suspension, for a softer ride.


 * B) Better at going over obstacles.


 * C) They "look cool".


 * D) Since they average out the friction over a larger contact area, they tend to slip less.


 * Of those, perhaps not being able to change a wheel over about 30 inches pretty much sets an absolute limit on sizes. There are wheels larger than that, on industrial equipment, but those require a team of workers and maybe some specialized machinery to change, so aren't practical for a normal car. StuRat (talk) 12:47, 9 April 2010 (UTC)


 * I think the simplest explanation would be that they are designed to optimize versatility for cars of a certain size. People use cars under a lot of conditions and different speeds. You don't want something that is only optimized to one set of conditions that fails under others. You want something that is a good generalist. The only times you want super-optimized wheels are for very constrained conditions—like Formula One tires, which are meant to do basically one thing and one thing only under controlled conditions. Extreme optimization for specific situations is not always an advantage unless the conditions are entirely predictable. (Human beings are, incidentally, pretty well optimized for versatility. We can do a lot of things pretty well. Most animals are by comparison optimized for specific ecological niches. Humans can go basically anywhere.) --Mr.98 (talk) 15:53, 9 April 2010 (UTC)


 * I tried living with the giant tube worms on an undersea volcanic black smoker, but I didn't care for it. :-) StuRat (talk) 16:03, 9 April 2010 (UTC)

Two more points. Large wheels simply weigh more. And, more important, they get in the way of things. For many cars today, if the wheel diameter was increased about 30-40% they'd need to poke above the hood (but they'd still neet to be covered for safety reasons). Do that a little and it looks weird; do it much and you increase aerodynamic drag. Also, the front wheels also need to pivot to angle sideways for steering, so larger wheels would mean you'd lose available width in the engine compartment. (Similarly, on vehicles like buses and streetcars, especially the low-floor, wheelchair-accessible types, a limiting factor for wheel size is how far the wheel wells can protrude into the passenger compartment without interfering too much which where the seats can be put.) --Anonymous, 23:17 UTC, April 9, 2010.

And what about the trend, too?
There's another facet to the original question as well. Look at vehicle tyres from 1920s, you see basically upsized bicycle wheels and tyres -- lots of wheel, not much rubber. 1950s, you see smallish wheels and lots of rubber, and the ratio of height to width is .80 or .75 on just about every passenger sedan in the world.

Mid-to-late 80s or thereabouts, the pendulum began to swing back, wheels got bigger / rubber got smaller, and a 60-series tyre was considered "low-profile" -- and it was probably mounted on a 16- or 17-inch rim, even for passenger cars.

Today 18-19-inch rims are not uncommon, and it really doesn't look like there's more than 3 inches of sidewall showing -- in other words, except for the width needed to support the weight, we're back to bicycle tyres. Aspect ratio 45 -- what's up with that?

Clearly, the trend is to larger and larger wheels, and less and less air volume. Anybody want to bet on whether 22-inch wheels and 2-inch sidewalls are commonplace in another 5 years?

If 20-inch rims and 3-inch tyres are wonderful, why didn't we just keep using them for the past 40 years??

(Part of the answer will probably have to do with improvements in suspensions, which shifts "responsibility" for pavement bumps away from the tyres and onto the struts, but that can't be the whole story, can it?)

DaHorsesMouth (talk) 22:46, 9 April 2010 (UTC)

Making hybrid fruit trees
Last year, I planted a couple dwarf peach trees on my parents farm. Basically, they're just normally sized peaches grafted on to a dwarfing rootstock. I knew they were supposed to be small, but to my surprise, they're already making blossoms this year and by June or July, we should have some peaches. The farm is also covered in thousands of wild plums that start blooming this time of year too. Plums and peaches are closely related and they've made hybrids before. So that gave me a crazy mad scientist idea.

I found a healthy looking blossom on the largest peach tree and before it opened, I carefully tied a plastic bag over it with a twist-tie (being careful not to damage the plant). This should keep foreign pollen out of the blossom. It just opened up today and my plan is to transfer pollen from one of the plums into the peach blossom to make a hybrid plant. If all goes well, sometime in the next decade I'll find out what my frankenstien fruit tastes like.

I just want to know if I'm doing anything wrong here. Are peaches able to pollinate themselves from the same flower? If so, that will throw a wrench in my whole plan. Also, I'm concerned about growing my new fruit from a seed which I hear doesn't always work well with fruit trees since they've been crossed and selectively bred so extensively.

Does the reference desk have any advice for a newbie mad scientist attempting to make a new species?

63.245.168.34 (talk) 14:40, 9 April 2010 (UTC)


 * I suspect that something as common as those two would have already been cross-bred, if it's both possible and desirable to do so. StuRat (talk) 15:58, 9 April 2010 (UTC)


 * There are a number of stone fruit (Prunus) hybrids, including the pluot, the plumcot, the aprium, the nectacotum and the peacotum. I'm not sure if there is a name for it, but doing a Google search for "plum peach hybrid" reveals a number of sites, including some indicating that a variety called "Tri-Lite" is commercially available. Regarding crossing, a quick Google search indicates that most varieties of peach are self-fertile, however there are some which are self-sterile and some which are male sterile. One possibility is to attempt to excise (pluck) the stamens from the flowers you want to cross after they become visible, but before they mature. If you're able to catch them before they drop pollen, your plastic bag trick might work. -- 140.142.20.229 (talk) 17:02, 9 April 2010 (UTC)


 * Uh oh. I better do that ASAP. I actually covered two flowers with a bag and only one has opened yet. There's dozens of flowers on the tree, though, so if I need to try again, I can start with another flower. Thanks for the heads up! 63.245.168.34 (talk) 23:26, 9 April 2010 (UTC)
 * The statement "attempting to make a new species" requires addressing. It is unlikely that you will be able to produce a new species. Speciation occurs over many generations, and is a result of selection and evolution rather than a one-time cross. The offspring will, more likely than not, be infertile due to chromosomal imbalances or other issues. While it is possible with plants, and certainly some species are a result of hybridisation, your experiment will probably fail to produce a distinct species.  Intelligent  sium  03:38, 10 April 2010 (UTC)


 * I was aware of that. I know that I'm not going to make the textbook definition of "species", but it'll at least be making something completely new an unheard of. If the offspring is infertile, will it still make fruits? I don't mind if it's infertile, I can propagate it by grafting. 63.245.168.34 (talk) 06:13, 10 April 2010 (UTC)

Darwin's Origin of Species contains a pretty extensive discussion of what happens when plants are crossbred. A newbie mad scientist could probably benefit from reading it. Looie496 (talk) 05:21, 10 April 2010 (UTC)

Collision
Suppose there's an elastic collision involving two billiard balls. How would we write out the conservation of energy in this case? Would we have two seperate equations, one for kinetic energy and one for rotational energy, or would the sum of the two be conserved? 173.179.59.66 (talk) 15:14, 9 April 2010 (UTC)


 * The sum of the two is conserved. In practice, when solving problems, it is not wise to write down the conservation of energy equation as that will yield messy equations. Instead, you should transform to the center of mass frame where energy conservation can be automatically implemented in the conservation of momentum equations: The magnitude of the momenta stay the same. Count Iblis (talk) 15:32, 9 April 2010 (UTC)


 * The physics of billiards is more complex in the penal regime of The Mikado where: ''The billiard sharp who any one catches,

''His doom's extremely hard —

''He's made to dwell —

''In a dungeon cell

''On a spot that's always barred.

''And there he plays extravagant matches

''In fitless finger-stalls

''On a cloth untrue

''With a twisted cue

And elliptical billiard balls!
 * Cuddlyable3 (talk) 17:28, 9 April 2010 (UTC)

@the Count: How does that work? In the centre of mass frame, conservation of linear momentum gives m1v1 + m2v2 = 0 before and after the collision, and conservation of angular momentum gives I1ω1 + I2ω2 = constant (can I have confirmation that this doesn't equal zero?). Where would energy come in? 173.179.59.66 (talk) 18:30, 9 April 2010 (UTC)


 * You may also have to include orbital angular momentum to have an accurate prediction of the outcome of a shot. The energy equation is E = 1/2 * (m1v12+m2v22+I1ω12+I2ω22). Note that a) It can get very messy to solve the equations, b) Assuming conservation of energy might lead to imprecise results, and c) You still need to stipulate some contact condition. (may be a non-slip condition). Dauto (talk) 18:49, 9 April 2010 (UTC)
 * Fine, but how do you get that the magnitude of the momenta will be the same? 173.179.59.66 (talk) 00:46, 10 April 2010 (UTC)
 * Perhaps if it makes my question clearer, how were equations (1a) - (2b) determined? 173.179.59.66 (talk) 02:43, 10 April 2010 (UTC)
 * lol I forgot to link my document: http://www.cns.brown.edu/physics/userpages/staff/Gerald_Zani/billiards/billiard1.pdf. 173.179.59.66 (talk) 05:46, 10 April 2010 (UTC)

Physiological diplopia
I'm curious about the prevalence of the ability to (consciously) see both eyes' images of an object not in the plane of the object upon which one's gaze is directed (more precisely, the Panum's fusional area or horopter). Most people I've checked with have this property, but a few report not being able to see two copies of anything ever, such that (for instance) they can hold up two thumbs, one at arm's length in front of the face and one near the nose, and fully obstruct the far thumb with the near despite having both eyes open. Others report that the near thumb is somehow indistinct or transparent such that the far thumb is visible, so that it seems they are constructing one image from the two eyes but which combines what is visible to each. (That is of course normal for the object one is regarding, but not so much for objects that are much closer.)

An optometrist I consulted called the normal tendency to see double in this fashion physiological diplopia, which does seem to be an accepted term for it, but he didn't know of any studies of or figures about how many people don't exhibit it normally. I think having an article on this would be wonderful, but I haven't found anything online other than that it is considered normal, so any actual references on the subject would be appreciated (as would be just the numbers). --Tardis (talk) 15:47, 9 April 2010 (UTC)


 * To your survey of perceptions of near and far thumbs I can add a category: one has interest focussed on the near thumb and the far thumb becomes two thumbs on either side of the near thumb. Wikipedia has articles on Diplopia, and Binocular vision that describes tests for disorders of binocular vision such as the tropias. Useful references may be a tutorial on Binocular Vision and the neuroscience of binocular rivalry. Cuddlyable3 (talk) 17:14, 9 April 2010 (UTC)
 * Two copies of each thumb when focused on the other is part of the standard behavior. I'll look at those references, thanks; have they anything about the proportions?  --Tardis (talk) 17:32, 9 April 2010 (UTC)

Obviously this is not to be mistaken for a medical diagnosis, but what the question made me think of is amblyopia. --Anonymous, 23:22 UTC, April 9, 2010.

Coordinate system
What is the reference coordinate system in our universe with respect of which acceleration of moving bodies is measured? —Preceding unsigned comment added by Amrahs (talk • contribs) 16:22, 9 April 2010 (UTC)
 * Any inertial coordinate system will do. Taking the first derivative of position destroys the knowledge of the origin of the coordinate system (making it an affine space), and so velocities do not depend on the origin.  Taking another derivative destroys the knowledge of the (uniform, inertial) motion of the coordinate system (or, equivalently, the origin of the velocity space), and so accelerations do not depend on one's reference frame so long as it is not accelerating.  Of course, if you're speaking relativistically (even in SR) then things like time dilation interfere with this constancy.  --Tardis (talk) 16:33, 9 April 2010 (UTC)
 * The idea of an inertial coordinate system doesn't really exist in General Relativity. An accelerating object is equivalent to a non-accelerating object in a gravitational field. If you want to define a coordinate system, you basically have to choose an object to do everything relative to. Any object will work, but some may be more convenient than others for certain problems. Alternatively, you can work relative to the cosmic microwave background, which isn't an object, per se, but can be used in the same way. --Tango (talk) 19:53, 9 April 2010 (UTC)

Adiabatic Expansion
Suppose air at pressure P1 and sp. volume v1 is adiabatically expanded under STP to P2 and v2. Now, using adiabatic process formula, P1v1k=P2v2k (Initial conditions are known.) Which value to be used as final condition? Either value of P2=101325N/m2 to be used or density=1.2256kg/m3? —Preceding unsigned comment added by Giganticvis (talk • contribs) 16:22, 9 April 2010 (UTC)
 * Both, assuming that by "under STP" you meant "to STP". If this makes the equation overspecified, then you have a mistake somewhere, possibly in the statement that the expansion was adiabatic (not all initial states can be changed adiabatically to STP).  --Tardis (talk) 16:31, 9 April 2010 (UTC)
 * I should add that specifying the temperature and pressure of an ideal gas determines its density; that's why you can use the density at all. Perhaps you knew that.  --Tardis (talk) 16:36, 9 April 2010 (UTC)

Chemistry question
Hellow! Could you tell me the stoichiometric requirement of lime(Cao) for neutralizing Sulphurdioxide gas please along with chemical equation? —Preceding unsigned comment added by Krishvanamali (talk • contribs) 17:47, 9 April 2010 (UTC)


 * See Calcium Oxide and Sulfur dioxide for chemical formulas, and stoichiometry and Chemical_equation for a description of how to calculate stoichiometric ratios. -- Jayron  32  17:52, 9 April 2010 (UTC)


 * The chemical equation for this reaction is CaO+SO2→CaSO3. You can calculate the mass ratio from there. 24.23.197.43 (talk) 05:38, 10 April 2010 (UTC)

Can I drink dishwashing liquid?
Gene Weingarten was asking a similar question in one of his columns devoted to customer support experiences.

Specifically, if I need to use a cup, glass or mug right away after washing it because I've run out of clean ones, and despite my best efforts to rinse out what I washed, it still has soap in it, I can't ever recall any ill effects. What I'm drinking tastes kind of soapy.

Normally I turn the item upside down where the dishes dry. sometimes it doesn't drain because it tipped over, and the same thing happens.Vchimpanzee ·  talk  ·  contributions  · 18:10, 9 April 2010 (UTC)


 * Drinking enough dish-washing liquid would probably make you vomit or even kill you, but the tiny amount left on the dishes isn't likely to do any harm. In fact, one of the main ingredients, phosphates, is found in many foods and drinks. StuRat (talk) 18:15, 9 April 2010 (UTC)


 * Soaps can be both a purgative and a laxative, so eating sizable quantities of detergent may not kill you, but it may give you diarrhea or make you puke. However, its a matter of degree.  Small amounts of residue left on the dishes will have no effect at all on your health; while downing an entire bottle at a draught may result in some ruined underwear.  -- Jayron  32  18:50, 9 April 2010 (UTC)


 * Or, while not killing you, it may make you wish you were dead. Googlemeister (talk) 18:52, 9 April 2010 (UTC)


 * Purely original research, but I can tell you with absolute certainty that, from personal experience, in sufficient quantities it acts as a strong purgative. AlexHOUSE (talk) 19:22, 9 April 2010 (UTC)


 * And what possessed you to drink large quantities of dish-washing detergent ? StuRat (talk) 17:18, 10 April 2010 (UTC)

The bottle of dishwashing liquid in my kitchen has warning notices saying to keep it away from children and not to mix it with bleach, get it in your eyes, or use it in a dishwasher. It doesn't say anything about hazards from consuming the stuff. Assuming that the Colgate-Palmolive company has a normal degree of concern for liability, I would conclude that it's not particularly dangerous to ingest it. Of course, that doesn't mean it wouldn't make you sick. --Anonymous, 23:26 UTC, April 9, 2010.


 * This that make you usually aren't very dangerous, since they don't stay in your system long enough to do much harm. --Tango (talk) 00:34, 10 April 2010 (UTC)


 * Permit me to add a Tangoese to English translation: "This that make you..." = "Things that make you sick...". :-) StuRat (talk) 00:52, 10 April 2010 (UTC)
 * In my experience adding dishwashing liquid has very amusing results--Jac 16888 Talk 02:41, 10 April 2010 (UTC)
 * I was going to quibble with this by mentioning Mussolini's use of castor oil on his political enemies, but to my surprise the article notes that the victims "rarely died". 213.122.59.14 (talk) 07:43, 10 April 2010 (UTC)
 * Purified castor oil doesn't kill you -- it only makes you dirty your pants. The only dangerous toxin in castor beans is ricin, which is present in raw castor oil, but is removed during purification before the castor oil is marketed. 24.23.197.43 (talk) 02:15, 11 April 2010 (UTC)

I was about to jump in to this with a big NO when I saw the title on my watchlist...that had me alarmed for a moment. Anyway, if you want to be able to use a glass right away after washing it, the way we used to do that in boy scouts was washing in warm soapy water, then rinsing in bleach water, then in normal water...after drying with a cloth they were good to go. Ks0stm (T•C•G) 23:48, 9 April 2010 (UTC)

If you accidentally swallow a poison, the emergency procedure MAY (not always) be to vomit it up. One way to do this is to swallow a teaspoon of dish detergent with a glass of water, so I would say that it can make you vomit.24.150.18.30 (talk) 02:25, 10 April 2010 (UTC)


 * Getting back to the original topic, the reason this is a problem is that I decided to have the plumber take out that gadget people normally use to rinse, the one that has been the source of several America's Funniest Home Videos pranks, when the faucet got old and needed replacing. I had just never seen the need for it. And as for cloths--well, I never feel confident that a cloth is clean enough, and once it's used, then there's the matter of getting it clean enough again. The wool cleaning pads I use are another matter entirely and I should probably replace them more often. No, not steel wool, because some of the items I clean are non-stick.Vchimpanzee ·  talk  ·  contributions  · 20:17, 12 April 2010 (UTC)

do bodybuilders get blind or have poor eyesight from overexertion?
This is not a request for medical advice, and I am not a bodybuilder, but my friend told me bodybuilders get blind at a very young age or at least get very poor eyesight due to overexertion. However I don't see the relationship - maybe if they take some kind of weird steroids that put their blood pressure through the roof or something, but just from "overexertion"? Is there anything to what my friend said? 82.113.121.93 (talk) 19:48, 9 April 2010 (UTC)


 * Sounds like an old wive's tale to me. Googling does not turn up anything compelling. --Mr.98 (talk) 21:44, 9 April 2010 (UTC)
 * The story I heard when I was younger was that straining to lift weights can put undue stress on capillaries, and those at the back of the eye are particularly fragile. Rupture of these capillaries could produce a bleed which disrupts the retina, resulting in partial or total blindness in the affected eye. I have no evidence that this is in fact the case. --TammyMoet (talk) 08:20, 10 April 2010 (UTC)
 * In the movie La Strada the strongman performer Zampanò warns onlookers that the feat he will attempt may go wrong and make him blind. Cuddlyable3 (talk) 11:42, 11 April 2010 (UTC)

Enzyme for digesting pork?
Yesterday someone told me they had been raised vegetarian and so had trouble digesting pork because they didn't produce a necessary digestive enzyme. What enzyme would that be? RJFJR (talk) 19:53, 9 April 2010 (UTC)


 * I've heard vegetarians claim this too, but this and this would both indicate that it's not true; that your body generates the requisite digestive enzymes regardless of your diet. In the unlikely case that your friend is a panda, she can still digest meat, but may have lost the taste for it. -- Finlay McWalter • Talk 20:06, 9 April 2010 (UTC)
 * The gut bacteria will be different. And it takes a while before you change the colony composition. So you need to change your diet slowly to let the bacteria adjust. Ariel. (talk) 20:23, 9 April 2010 (UTC)
 * Digestion of meat (protein) is mostly done by proteases in the stomach at low pH. Intestinal bacteria may play a secondary role, but it is a minor one.  See Gut flora for a run-down of their major roles in the human digestive tract. These bacteria are more relevant to the digestion of carbohydrates, starches and to some extent even cellulose; but protein is pretty much chemically digested by gastric acid.  Nimur (talk) 21:21, 9 April 2010 (UTC)
 * Gastric acid starts the process, but trypsin and other pancreatic proteases do the main job of digesting all proteins, either plant or animal source. Vegetarians can certainly digest pork: they just notice a change in stool appearance and composition related to a different set of undigestible excreta. alteripse (talk) 02:49, 10 April 2010 (UTC)
 * Your body will not lose the ability to produce certain digestive enzymes over time (except milk-digesting ones) but it does change the amount it produces depending on the "usual" diet of a person. Just as vegetarians become less able to digest large amount of consumed meat after being vegetarians for a while, meat-eaters are less able to digest certain carbohydrates if it is not part of their usual diet, for example beans and cabbage. When your body does not digest and absorb the nutrients from the food the bacteria in the lower-gut essentially gets a very rich meal, thus causing possible changes in bacterial types, populations and growth, which can lead to indigestion and "gas". Sjschen (talk) 18:56, 13 April 2010 (UTC)

Baby teeth
Why do children lose their Deciduous teeth when growing up? Why is one set of teeth not enough for one's entire life? 71.178.44.93 (talk) 20:14, 9 April 2010 (UTC)


 * For one, it's a matter of scale. The original teeth are designed for a smaller mouth, and you need to grow additional teeth anyway to fill in the gaps with age. Historically, poor dental hygiene and unprocessed foods caused more wear and tear on teeth, so having the initial set swap out was also handy. This way you have small teeth when you can't fit more, and larger, stronger teeth to take over as the first set wear out and/or become too small. &mdash;ShadowRanger (talk 20:24, 9 April 2010 (UTC)


 * I think the main issue is size. A child's mouth is much smaller than an adult, so the child's set of 20 mostly smaller teeth is replaced by the larger set of 32 adult teeth.  It makes sense to have a smaller set of smaller teath for a smaller head.  -- Jayron  32  20:31, 9 April 2010 (UTC)


 * I think it's important to remember that this did not evolve first with humans; it is a general mammal trait. Looking for an explanation that relies entirely on human experience is going to likely be incorrect. Generally speaking, the evolutionary question seems to be why don't mammals lose and replace their teeth more regularly, like most fish and reptiles. Retaining a permanent set of teeth is the special evolutionary development, not the loss of teeth. --Mr.98 (talk) 21:10, 9 April 2010 (UTC)


 * An equally valid question is why we don't replace any tooth which falls out due to decay or injury; this would be a great evolutionary advantage. It seems to be pretty unfortunate that we do not have this capability.  See regeneration (biology) for some related processes.  Nimur (talk) 21:24, 9 April 2010 (UTC)


 * Sometimes we do - my grandfather lost most of his adult teeth in his childhood due to malnutrition and grew a third set. It's unusual, though. --Tango (talk) 22:04, 9 April 2010 (UTC)


 * Wonder if this could be artificially stimulated, that would be nifty. 213.122.59.14 (talk) 07:46, 10 April 2010 (UTC)


 * Or more interestingly I wonder if any of your grandparents offspring inherited the trait. The embryo teeth would probably be visible by radiological examination. We could then start breeding a race of people with replaceable teeth! Caesar&#39;s Daddy (talk) 08:00, 10 April 2010 (UTC)


 * Some babies are born with a set of teeth; these fall out and are replaced during normal teething. As for why primates don't have continuously growing teeth - in rodents (which are reasonably close to primates) they do have this, but their teeth don't fit well together, which is OK for tearing your food, but not good for grinding it. CS Miller (talk) 10:36, 10 April 2010 (UTC)


 * In that case, wouldn't replacing all teeth but the molars (used for grinding) and maybe bicuspids, make sense ? StuRat (talk) 12:38, 10 April 2010 (UTC)
 * Rodents' teeth aren't replaced, they just grow continuously. That's why you have to give pet rodents something to gnaw on so they can wear their teeth down. --Tango (talk) 14:38, 10 April 2010 (UTC)
 * That would be interesting to know, but (un)fortunately my Grandad managed to pull himself out of poverty, so none of his children or grandchildren (or great-grandchildren, although they're all still on baby teeth, I think) have been malnourished (also, the welfare state arrived, so they wouldn't have been anyway). --Tango (talk) 14:38, 10 April 2010 (UTC)

From a completely individualized, non-evolutionistic perspective, one would lose his or her baby teeth because the adult teeth exist deeper in the bone and being erupting into the space occupied by the baby teeth's roots. The baby teeth roots resorb under the pressure (this can perhaps be referred to as pressure necrosis) and without proper support from the surrounding bone (as the roots are all but gone after said resorption), the baby tooth crowns either fall out or are pulled out by children, parents, dentists, etc. When people have congenitally missing succedaneous (adult, in that they succeed the baby teeth) teeth, they will very likely retain their baby teeth well into adulthood, if not retain them for life. I've treated 35-year-olds with baby maxillary lateral incisors and canines because they never had the adult teeth to cause them to fall out.  DRosenbach  ( Talk 02:28, 11 April 2010 (UTC)

bride selection
In the movie, "Mongol" about the creation of Genghis Khan the Mongols are depicted as following the custom of an 8 or 9 year old son of a Khan (no pun intended) selecting his bride from girls near his own age. Was this custom for everyone or just the Khan's son and in either case what other cultures have this custom and does it exist in other societies like those religious groups that live in Montana or anywhere else? 71.100.3.207 (talk) 23:47, 9 April 2010 (UTC)


 * If by "Those religious groups that live in Montana" you mean the Mormons (who actually are headquartered in Utah), then no, they do not practice that nowadays, although I don't know if they did in the past. Ks0stm (T•C•G) 23:52, 9 April 2010 (UTC)


 * There is a small fringe group of the Mormon church, the Fundamentalist Church of Jesus Christ of Latter Day Saints, or FLDS church, which still practices both polygamy and childhood betrothal. They kidna flew under the radar until a few years ago, during the Raid on the YFZ Ranch.  However, this group does not represent a significant part of the Morman church.  The vast majority of LDS church members have family practices which generally fall into the norm of Western cultural expectations. -- Jayron  32  04:55, 10 April 2010 (UTC)


 * In Arab countries, it's pretty darn common for girls to be given in marriage (without any semblance of consent) at a very young age, often as young as 6 years. In what is possibly the most notorious example of this barbaric practice, Muhammed married his wife Aisha when she was six years old, and screwed her for the first time when she was ONLY NINE.  (Some prophet!) 24.23.197.43 (talk) 05:48, 10 April 2010 (UTC)


 * Child marriages were common in a number of cultures. BTW 'prophet' simply means messenger of God. Given that in Abrahamic religions, be it Judaism, Christianity or Islam, God was guilty of genocide, biological warfare, terrorism and numerous other things and directly advocated a father murder his child we perhaps should be surprised with whatever evils his messengers may or may not have commited. It's perhaps also worthwhile remembering that whatever we may think of historic practices, they were often quite different from what we regard as morally acceptable nowadays. After all Mary the allegedly virgin mother to God was bethored to Joseph at sometime between 12 or 14, the norm at the time . Nil Einne (talk) 16:42, 10 April 2010 (UTC)


 * 14 years old is, physiologically speaking, not too young to marry (though right on the borderline) -- 9 or 10 years old certainly is. And what makes you think that marriage before puberty can ever be acceptable in any historical context? 24.23.197.43 (talk) 01:55, 11 April 2010 (UTC)


 * "Given that in Abrahamic religions, be it Judaism, Christianity or Islam, God was guilty of genocide, biological warfare, terrorism and numerous other things and directly advocated a father murder his child we perhaps should be surprised with whatever evils his messengers may or may not have commited." -- Your take on the binding of Isaac is completely bassackwards vs. what is actually said to have happened -- in the Biblical story (Genesis 22:1-20), it's made clear that God had only commanded Abraham to sacrifice Isaac to test his faith, and then expressly commanded Abraham not to do it. In fact, these verses are in themselves the first of God's commandments to be revealed to mankind -- a commandment to not sacrifice humans to God.  And as for "whatever evils [God's] messengers may have committed": you haven't provided one single shred of evidence that any of God's messengers other than Muhammad had actually committed any evil acts, so until and unless you do, this claim of yours is absolutely baseless.  And since in an earlier thread I have provided, at your request, evidence that "stealth jihad" is indeed happening in some parts of the USA, I likewise challenge you to provide evidence that Moses or Jesus have committed evil, or else to take back your claim that they ever did so. 24.23.197.43 (talk) 04:17, 11 April 2010 (UTC)


 * "Evil" is a subjectively defined word, but personally I'd consider the following two behaviors to be "evil": 1) Leading a lynch mob that stones someone TO DEATH for bundling sticks on a Saturday; 2) Encouraging people to reject and abandon their families if their families don't agree with your religious/political philosophy. Moses did the first, Jesus the second. 63.17.75.69 (talk) 03:56, 12 April 2010 (UTC)
 * I need the chapter and verse numbers for both of these claims. 24.23.197.43 (talk) 07:40, 12 April 2010 (UTC)

I meant to return sooner an move this to the humanities section where I intended to put it in the first place but its really great to know the science section is so well monitored by those who are at least knowledgeable of the Faith. Anyway, The way the marriage selection is depicted in the movie is quite attractive to me. One year older girl asks Son of Khan to pick her and stops father from taking him to another camp to select a bride and selects her instead. Hot stuff. They had to wait five years and ended up waiting even longer. As for the Mormons marrying young girls to old men that is a different story. Its not hot but disgusting and should be outlawed secularly and in the Mormon Church. actually I was thinking about another group that moved from Switzerland. Is there a list of religions which practice same age youthful commitments? 71.100.3.207 (talk) 06:27, 11 April 2010 (UTC)


 * Marriages arranged between children (usually with couples selected by adults) are still seen in India. In the middle ages such marriages, even between infants, were considered permanent and binding.  In general the "wife" would continue living in her parents' house, and the relationship unconsummated till 12-16.  Currently such marriages are not legally binding, but there may still be social or religious pressure to honor commitments arranged in childhood.  Dragons flight (talk) 20:00, 11 April 2010 (UTC)