Wikipedia:Reference desk/Archives/Science/2008 December 23

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December 23[edit]

Material with highest melting point?[edit]

Hello -- what material has the highest melting point? I've found listings for the melting points of various pure elements by melting points, but nothing which describes what happens to the melting point when you create alloys, etc. Is there anything that has a higher melting point than carbon in amorphous or graphite forms? -- (talk) 00:51, 23 December 2008 (UTC)

The melting point article you cited lists Tantalum hafnium carbide as having an extremely high melting point. The article for Tantalum hafnium carbide says that it is the compound with the highest known melting point. --Scray (talk) 00:54, 23 December 2008 (UTC)
Wow! That's impressive - it's about 80% of the temperature of the surface of the sun! SteveBaker (talk) 21:17, 23 December 2008 (UTC)
So, what's a refractory compound? — Sebastian 22:33, 23 December 2008 (UTC)
Never mind, found it: Refraction (metallurgy). — Sebastian 22:35, 23 December 2008 (UTC)
I thought that maybe liquid tungsten (boiling point 5828 K according to the article, but I don't think it is known that accurately) could exist in the photosphere - but the pressure is probably too low. Icek (talk) 10:32, 28 December 2008 (UTC)


Why do we not get a sweet taste when we already had a sweet dish before it? As it is not in the case sour tasteM.meghajain (talk) 02:14, 23 December 2008 (UTC)

See "Neural adaptation" and "Habituation", and don't type in all caps. Our senses grow dull to a constant input. We stop feeling our clothes soon after we put them on, and we don't smell the pig farm next door after a week or two. --Milkbreath (talk) 02:25, 23 December 2008 (UTC)
I'm not an expert, but if I remember correctly sour taste is caused by a low (=acidic) pH inside certain receptor cells, I guess that internal pH is regulated by the cell with only short delays, while sweet substances stick to receptors on the outside for a longer time. Regarding sweetness, an interesting substance to look up is miraculin. Icek (talk) 06:21, 23 December 2008 (UTC)

Science/Humanities question on Egypt's buried tombs[edit]

"70 percent of Egypt's ancient monuments remain buried under sand," a news article on two 4300-year-old tombs quotes an official as saying. Was it desertification? Thanks in advance. Imagine Reason (talk) 03:13, 23 December 2008 (UTC)

In any case it is a policy of modern archaeology not to exploit completely an archaeological site. The idea is that in the future more advanced tools and techniques will be available, and doing all the job today would destroy important elements that tomorrow we could be able to detect. This is indeed what has happened in the past: many Egyptian lefts passed 4000 years in perfect state to their end by the enthusiastic hands of archaeologists.--PMajer (talk) 12:34, 23 December 2008 (UTC)
The ancient Egyptians placed tombs and burial pyramids in areas that were desert at the time, since that allows both buildings and bodies to last longer. They lived in moister areas, however. StuRat (talk) 14:44, 23 December 2008 (UTC)

Why is the static between channels loud?[edit]

Tuning an analog radio with the knob, one hears static between stations. The static typically has a loudness about equal to the stations themselves. But how is this possible, when the real stations have the same noise layered onto the transmission, and yet manage to produce silences in the programming that are much quieter than the sound heard when there's no transmission at all?-- (talk) 03:49, 23 December 2008 (UTC)

See Automatic gain control for a start--GreenSpigot (talk) 04:41, 23 December 2008 (UTC)
In short, when you hear static the radio is trying to pick up a weak signal and not really finding one. When you hear silence in a program, it has found the carrier signal and "knows" how loud a broadcast it could carry and therefore that the silence is desired. --Anonymous, 06:09 UTC, December 23, 2008.
AGC reduces the sensitivity of an AM radio receiver when a broadcast signal is being received. The AM RF signal is constantly varying in strength (amplitude) due to the sound modulation imposed on the RF. The AGC circuit smooths the amplitude variations to provide a DC voltage whose amplitude is determined by the average strength of the received signal.(The smoothing capacitors in a simple power supply similarly smooth the AC ripples superimposed on the rectified DC.) The smoothed AGC voltage is used to decrease receiver sensitivity. The stronger the received signal, the higher the AGC voltage and the more the sensitivity is reduced. Silent moments in a signal stay silent because receiver sensitivity remains reduced; that is because the carrier wave (unmodulated signal) is still being received and the carrier wave produces AGC voltage. AGC not only prevents atmospheric noise (white-noise static) from marring a received signal, it also prevents overloading of audio stages when a strong signal is received. Overloading would cause audio distortion. — GlowWorm
Yes - exactly. The radio needs 'AGC' (Automatic Gain Control) because the amount of radio energy received by the radio depends dramatically on how far you are from the transmitter (amongst a bunch of other factors). If you are 1 mile from the transmitter, you get about four times as much energy than if you are 2 miles away and a hundred times more than if you are 10 miles away. This HUGE variation in the amount of signal the radio receives would result in the volume produced by the radio varying by perhaps a factor of ten thousand depending on how close to the transmitter you are, etc. So the radio has to automatically alter the 'gain' (volume) of the signal to try to keep the same audio levels no matter where you are. As GlowWorm says - that circuit has to monitor the level of the 'carrier' wave and use that to adjust the sound volume. When there is no carrier (ie, between stations), the AGC circuit has nothing meaningful to latch onto - and the result is a lot of random noise with the AGC turning up the volume as far as possible in the hope of picking up some very faint signal. With many modern radios, there is additional circuitry to turn the volume down to zero when there is no carrier detected - and in that case you don't get any noise between channels. But that kind of sophistication has not always been present - and cheaper/older radios don't have it. SteveBaker (talk) 13:37, 23 December 2008 (UTC)
Ah yes: squelch (ouch!)--GreenSpigot (talk) 06:58, 24 December 2008 (UTC)
Note that this effect is not present in digital audio or digital television broadcasts. Nimur (talk) 19:16, 24 December 2008 (UTC)

Ion slowing down in plasma[edit]

What electrical effect, if any, would cause an ion to slow down in a sparse cloud of ions i.e. outer space? I want to figure out how well the Earth would hold a charge. In case anyone's wondering, I am not a geocidal maniac planing on causing the Earth to spiral into the sun by putting electron guns on the top of a launch loop to build up a charge of over 8*1017 Coulombs and letting the Abraham-Lorentz force take care of the rest. That would just be silly. Why would you even bring it up? — DanielLC 06:47, 23 December 2008 (UTC)

Short and not-in-depth answer: You have to take into account the magnetic fields in space - homogeneous magnetic change only the direction of the velocity vector (except for the Abraham-Lorentz force of course), but inhomogeneous fields also cause a change in kinetic energy. Icek (talk) 15:09, 23 December 2008 (UTC)
Hmm - the magnetic field never changes the total kinetic energy of a charged particle, regardless of any inhomogeneity. I think what the OP is looking for is Coulomb scattering. An ion traveling through a "cloud of ions" (see plasma) interacts with the background ions via the coulomb interaction, thus transferring some of its kinetic energy to the background ions. This leads to an exponential decay of momentum and energy of the incident ion. I won't comment on the rest of the plans you don't have. --Bmk (talk) 05:35, 24 December 2008 (UTC)
You're right about Coulomb scattering, but the kinetic energy of charged particles is changed by inhomogeneous magnetic fields because in the particle's tangential inertial frame of reference, the magnetic field is varying with time. Time-varying magnetic fields create electric fields (Faraday's law of induction). Icek (talk) 06:50, 25 December 2008 (UTC)
You're right that the particle's tangential and perpendicular (to the B-field) kinetic energies can be changed, but the particle's total kinetic energy is not altered by the field. In a way, your answer was really accurate, since a particle entering a region of higher magnetic field will be slowed in its forward motion, but its total kinetic energy will remain constant (since its gyro kinetic energy, or perpendicular kinetic energy will increase). Here's the proof:
(electric field in this frame is zero)
(dotting both sides with v)
(reverse chain rule, and noting that the v dotted with the cross product of v and something else is zero)
(thus the rate of change of the total kinetic energy is zero if there are only magnetic fields) --Bmk (talk) 16:55, 26 December 2008 (UTC)
I made an error by not taking into account how the magnetic fields are properly transformed - but your proof assumes classical mechanics and the Lorentz force. In special relativity, force does no longer equal , but the relation is, with accelerations parallel and perpendicular with respect to velocity:
But you are still correct, as the force is perpendicular to the velocity, the acceleration is, too.
The only kinetic energy changing interactions with the magnetic field are thus those from the magnetic field that the charged particle itself creates by its movement (if it doesn't have an intrinsic magnetic moment), and that is just the Abraham-Lorentz force (I think). An important effect is that particles are repelled from regions of larger magnetic field strength (see magnetic mirror), another one is that they lose energy even while circling in a homogeneous magnetic field due to cyclotron radiation. Icek (talk) 08:17, 27 December 2008 (UTC)
True enough - non-classical effects can result in energy loss in magnetic fields alone :) --Bmk (talk) 23:00, 27 December 2008 (UTC)

What happens to sexual desire after penectomy?[edit]

Are there any reliable studies about sexual desire in men after a penectomy, particularly if so much has been removed that orgasm is impossible (or at least nearly impossible)? Without being able to orgasm do they go crazy from not being able to orgasm or lose their sexual desire completely? If not reliable studies have been conducted, anecdotal evidence is fine. (talk) 06:54, 23 December 2008 (UTC)

I don't know but I strongly discourage original research. (talk) 07:56, 23 December 2008 (UTC)
Many things[1]... Julia Rossi (talk) 09:54, 23 December 2008 (UTC)

nutrition facts[edit]

If a jar of pickles contains 10 pickles and each pickle contains 500 mg of sodium, if one eats all the pickles and drinks the juice does one consume 5000mg sodium. In other words is the juice factored in when computing sodium in such things as pickles,olives, or canned tuna for that matter. (talk) 11:50, 23 December 2008 (UTC)

Probably not in the case of pickles or olives. The nutrition 'panel' on the side of the jar tells you only the content of one "serving" - which is likely to be 1 pickle - not 1 pickle and 3 tablespoons of liquid (which is probably more 'brine' - used as a preservative - than 'juice' from the pickles) I suspect they leave out the information about the content of the liquid. That's probably NOT the case for canned tuna because it's much harder to separate liquid from solid)...but it's hard to know for sure. One has to be VERY careful reading those nutrition panels because very often their estimate of 'serving size' is very small indeed! SteveBaker (talk) 13:26, 23 December 2008 (UTC)
In canada, which shouldn't be different in the us, one serving is one actual serving for you day. So say if for you sex and age, you require 3 meat and meat alternatives, and the nutrition panel says 30 g's of tuna is one serving, when you eat 30 g's of tuna, you should only eat 2 more servings of meat and meat alternatives (still considering your sex and age); in canada, the food guide (our food guide) factors in exercise, so don't eat more than your recommended, unless your mike phelps, then you can eat as much and whatever you want!
In your case (of pickles), if the label says, "per pickle" it does not factor in juice. And don't be like steve here. if the serving's size is small, that's just subjective, and follow the food guide, or you'll be obese lol. And exercise. (talk) 09:24, 28 December 2008 (UTC)
In the US, the extra pickle juice isn't included in the nutritional information. According to the Code of Federal Regulations, Part 101 - Food Labeling, section 101.9, paragraph (b)(9), for "foods that are packed or canned in water, brine, or oil but whose liquid packing medium is not customarily consumed (e.g., canned fish, maraschino cherries, pickled fruits, and pickled vegetables)", the "[d]eclaration of the nutrient and food component content [...] shall be based on the drained solids." --Bavi H (talk) 09:10, 31 December 2008 (UTC)

Genetic Misogyny and sex war?[edit]

Could the counter-instinctual mistreatment (to Western eyes) of women and girls in the tribal areas of Pakistan, Afghanistan and the Middle east have some genetic component, and would it ever be acceptable to test this theory on a large scale with DNA analysis? Also could a sex war ever break out, given that women even in secular insurgency groups such as the Tamil Tigers can be a ruthless fighting force? —Preceding unsigned comment added by (talk) 13:24, 23 December 2008 (UTC) (talk) 13:29, 23 December 2008 (UTC) Trevor Loughlin

Not a genetic component, no. However, despite the claims of those who throw acid on women that "the Koran tells us to do it", it says no such thing. It says that both men and women should "dress modestly", but it's a long way from that to "you should throw acid on any woman who shows her face in public". It's strictly a cultural belief, which they use their religion to justify. As for a gender war with actual shooting, I'd say women would lose that war unless they outnumbered the men considerably, as they would have to tend the children, as well, and wouldn't have weapons or military training. Striking women who deny men sex and food is one possibility, but only after the possibility of violence against the strikers has been removed from the table. StuRat (talk) 14:37, 23 December 2008 (UTC)
Was "striking" an adjective, and if so which sense of "striking," or a verb in that last sentence? Edison (talk) 17:32, 23 December 2008 (UTC)
I meant it as "going on strike". However, such striking would be more effective if the women were strikingly beautiful, and less effective if the men were striking them down. StuRat (talk) 19:34, 23 December 2008 (UTC)
A "sex war", or even widespread dissatisfaction, can only break out if (1) the women believe they are being mistreated and (2) the women are not willing to tolerate the mistreatment. I don't think either criterion is fulfilled as of now; a person's beliefs are heavily influenced by her upbringing, and the Muslims are no exception. --Bowlhover (talk) 18:06, 23 December 2008 (UTC)
Have a search for the pink vigilantes in India to see how women can overcome such obstacles. There's many other less extreme examples in India also where women are getting more control of their fate. Dmcq (talk) 22:05, 23 December 2008 (UTC)
The article here is Sampat Pal Devi for the Pink Saree Gang, and there's the late Phoolan Devi, dacoit leader. The less extreme measures include microfinance for women. Julia Rossi (talk) 22:57, 23 December 2008 (UTC)
Modern India is very different from Afghanistan, Iran, and most other Muslim countries in that its laws attempt to guarantee equality for women. Its government is actively trying to educate girls, one example of the way it's breaking down traditional stereotypes. Many females in India grow up being aware that gender equality is being promoted by the government and that it is at least reasonable, not just a crazy idea. The bias against women is not promoted by the courts like it is in many Muslim countries. India obviously offers an environment very conducive to feminism, which is exactly why Indian feminist activists were mentioned here instead of Saudi Arabian or Iranian ones.
I'd be very surprised if more than a small minority of women in countries like Iran believe their husbands have no right to control them. I'm not claiming, mind you, that such independent thought is absolutely impossible. It's just very unlikely and thus cannot be prevalent. --Bowlhover (talk) 05:53, 24 December 2008 (UTC)
You mean like Shahla Sherkat, Parvin Ardalan, Shirin Ebadi, Mehrangiz Kar and Shadi Sadr? Nil Einne (talk) 11:26, 26 December 2008 (UTC)
I'm suprprised no one linked to Lysistrata for the dramatic interpretation of a sex strike. (Oh, wait, this is the Science Desk; "two cultures" still divide and separate?) And see the articles on feminism and Islamic feminism. BrainyBabe (talk) 20:41, 30 December 2008 (UTC)

Not so bright question...[edit]

How do I compare the brightness of a TV projector, given as lumens, with an LCD TV, given as cd/m2 ? Obviously, the first step is to figure out the area of the projected image and do some math and conversions. But the second step is to figure out what portion of the lumens produced by the bulb actually makes it to the screen. How do I do that ? StuRat (talk) 14:29, 23 December 2008 (UTC)

Assuming the thing is focussed and aimed correctly, you can assume that all of the lumens produced by the projector make it to the screen (after all - where else would they go?) - but the complication is in how efficient the screen is. There is a trade-off between viewing angle and brightness to be made in the actual material of the screen. Some screens are covered with tiny retro-reflectors that push most of the light back out towards the projector - giving the screen a very narrow visibility angle - but a heck of a lot of brightness within that angle. Others are closer to perfect lambertian reflectors and they spread the light out equally in all directions - so you can see the image equally well from any place in the room - but it's going to be rather dim. Similar considerations apply with your LCD TV - many LCD's have very tight viewing constraints - others don't - so the number of candelas being emitted by each square meter of the screen can be identical between two devices - and yet one appear much brighter than the other. Remember - a one milliwatt laser can take out your eye - a 10 watt light bulb is scarcely bright enough to read by! The light bulb is visible through 360 degrees - the laser through some tiny fraction of a degree. SteveBaker (talk) 14:48, 23 December 2008 (UTC)
Surely there isn't a 100% efficiency at the projector, and much of the light generated becomes heat. Some might also be absorbed or scattered by dust particle in the air between the projector and screen. StuRat (talk) 14:58, 23 December 2008 (UTC)
The scattering due to dust is negligable and the light that is absorbed inside the projector ought not to have been counted in the lumens value you got from the manufacturer (they ought to be stating the brightness on the output side of the final lens - not the brightness of the light source) - so it's only light absorbed by the air (which is pretty transparent over the distance a projector is likely to be used!) or in the screen itself (which ought to be designed to reflect a large percentage of the incoming light - not absorb it as heat). I think you can ignore those concerns. The screen, however, is a critical part of the equation here. SteveBaker (talk) 17:07, 23 December 2008 (UTC)
Sure they should give the actual output lumens of the device, but it's in each manufacturer's interest to be deceptive and instead list the output of the bulb, as that will make it appear that they have a brighter image. So, unless you have a source that confirms that they do the right thing, I'd tend to doubt that they would. StuRat (talk) 17:32, 23 December 2008 (UTC)

Also, what's the range of brightnesses for TVs by type (LCD, plasma, DLP, projector), etc. ? StuRat (talk) 14:58, 23 December 2008 (UTC)

Also, what is the range of brightness between between the white and black areas of various types of screen? For LCD and CRT screens, it varies with the width of the black area. Text, which has narrow lines, is dark grey rather than black. Wider black areas are a darker grey, approaching full black. It would much improve readability if text could be made jet black. I once had a black-and-white CRT computer monitor - the contrast for lettering was much better than on a color LCD or CRT monitor. – GlowWorm —Preceding unsigned comment added by (talk) 15:55, 23 December 2008 (UTC)
The range of brightness (usually called "The Contrast Ratio") is indeed an important concern for overall image quality. If the image is nice and bright - but the contrast ratio is crap - the colors will be very 'pastel' and the black areas will be grey...not a very appealing image. For bright, vibrant colors and deep blacks you need a high constrast ratio AND a bright image. This is where you see a big difference between LCD projectors (where a bright light is shone through an LCD panel to form the image) versus the DLP projectors where the light shines onto about a million tiny mirrors that can be moved such as to either reflect light out through the lens to the screen - or off to the side somewhere. For a long time, DLP's had vastly better contrast ratios than LCD projectors - but I've been out of that business for a couple of years now and things may have changed since then.
The issue of displaying thin vertical lines is to do with the rate at which the display can go from dark to light along the scanline - and that's 'bandwidth' - and 'modulation depth' - which are generally rolled into one "resolution" figure in the spec sheets for the display - but the measurement of it is something of a black art and comparing two monitors on the basis of this number is a bit more subjective. If you can get a set of test patterns displayed on the thing (like a TV 'test card') you should be able to directly compare resolutions. Horizontal lines are a different problem and relate more directly to the monitor's raw screen resolution and have nothing to do with bandwidth. However, StuRat isn't asking about any of those things.
SteveBaker (talk) 17:07, 23 December 2008 (UTC)

I've got a phillips widescreen CRT and I still think they can't be beat on contrast and colour reproduction, even if it's not HD and takes up a lot of room. I've heard a system called SED might achieve the same (but in HD this time) but until then I am sticking with this "obsolete" technology. (talk) 10:06, 25 December 2008 (UTC)

A tool for measuring cubic volume[edit]

Hi. I would like to measure the cubic volume of some irregular shaped products, specifically folded clothing (think of a folded up pair of jeans with a belt, or a folded t-shirt with a hanger). Does anyone know of a commercially available device that is suitable for this task? Thanks for your help. sparkl!sm hey! 16:27, 23 December 2008 (UTC)

I don't know of any machine for doing this - but you hardly need one. Archemedes principle applies here.
For most irregular shapes - take a large, utterly full, container of water - push the item completely below the surface (water will of course overflow the sides of the container) - then remove the object and measure the amount of water that it takes to completely refill the container (using a kitchen measuring jug for example). The volume of water you have to add to restore the level is the volume of the item. Sadly, for folded up clothing, this is a little tricky since the object is absorbant - and the 'volume' of something like cloth is a little hard to define because it's full of microscopic holes. Probably - you're interested in the volume of the irregular shape surrounding the cloth - ignoring the spaces between the folds and between the fibres of the cloth - in which case you're going to have to seal the item in a waterproof plastic bag having compressed the clothing to the desired degree. The difficulty isn't so much in the measuring as knowing exactly WHAT you're trying to measure! For items that you really can't immerse in water like that (eg because they float or compress too much under the water pressure - or if you really DID want to take account of the space between the folds of cloth, etc) then you could replace the water in the experiment above with some other fluid - perhaps a heavier-than-air gas like can put that stuff into something like a large aquarium tank and use an air-filled balloon as a float to tell you the level of the gas. Put a mark on the balloon and a scale up the side of the tank. Partly fill the tank with SF6 - note where the balloon floats. Drop in the item of clothing and see how much the balloon rises. Multiply the area of the bottom of the tank by the amount the balloon rises to get the volume of the item. SteveBaker (talk) 16:50, 23 December 2008 (UTC)
Funny, we did think of rigging up a displacement theory solution, but it isn't really practical.
You are correct, the actual volume I am interested in is the volume taken up by the garments when they are stacked - so the space in the folds of the cloth etc is also included in the calculation. You are also correct in suggesting that there will be a degree of compression of the garments, but I can perhaps factor this into the measurement. What I am looking for is something like this, a tool that can be used accurately on an industrial level. That one isn't suitable though, the garments exceed 18 inches in some cases. sparkl!sm hey! 17:19, 23 December 2008 (UTC)
I'm guessing you want to know how much storage space is required per item. In this case, as mentioned above, the clothing can be compressed to varying degrees, but you most likely want to know how much space it takes up without being compressed at all, if you want to avoid wrinkles. I suggest taking a storage unit of known volume, like a box, and pack in as many identical items as fit comfortably. Then divide the container's volume by the number of items to determine the volume per item. StuRat (talk) 17:22, 23 December 2008 (UTC)
(ec)There might be some standard test for the volume of clothing. We could devise several different methods, which would yield different volumes. Water displacement in a plastic bag would yield a different volume from SF6 displacement because the gas could fill much more of the space between the fibers of the garment, yielding a smaller volume. Another way would be to place the garment in a container and fill it to the top with beans, marbles, rice, styrofoam peanuts, or any other small defined particles which would not soak into the fabric as a liquid or gas would, noting the volume of the filler when the garment is removed. The smaller the filler particles, the smaller the measured volume. Another approach would be to take a box of a certain size, like 1 cubic foot, and see how many of the garments fit in the one box. The variation here would be how much force you apply if any to pack them in. This is the "volume" that would be of interest to a shipper or manufacturer. Edison (talk) 17:26, 23 December 2008 (UTC)

The idea of filling a standard size box is a really good one, particularly as the garments are in a warehouse, and will be order picked into a standard plastic tray. However, the measurement method needs to be fairly accurate as well as simple, and there is a problem when the cubic volume of the garment is not a factor of the cubic volume of the tray. For example, the tray is 1.5 cubic feet, and I can fit 1 folded coat into the tray. The coat fills just over half of the tray, meaning that I cannot fit 2 coats into the tray. What is the cubic volume of the coat? Well, it is less than 1.5 cubic feet, but more than 0.75 cubic feet - this is not an accurate enough method for what is required. sparkl!sm hey! 17:43, 23 December 2008 (UTC)

If your use case is stacking the coats in that 1.5 cubic foot box, then it would be accurate enough for your purposes. If you're looking to fit the coats in a 10 cubic foot box, however, then it wouldn't be. For what it's worth, the volume-in-a-box-divided-by-number-in-a-box technique can be made more accurate by increasing the size of a box. A 0.8 ft3 coat measured with a 1.5 ft3 box gives you a size in the 0.75-1.5 ft3 range, but measured with a 15 ft3 box yields ~0.79-0.83 ft3 (between 18 and 19 coats per box). -- (talk) 17:58, 23 December 2008 (UTC)
Exactly. If 10 garments fit in the box, the accuracy is within 10%. If 100 fit, the accuracy is within 1%. Here we're getting below the variation you would get from trial to trial. Also note that larger sizes of the same garment will, of course, take up more room. If you want the average for all sizes, ensure that you have a representative sample (with more of the most common sizes) in the trial box. StuRat (talk) 19:26, 23 December 2008 (UTC)
The tool in the link you gave us looks like it's measuring the height and width of the object as it passes under that archway. If I were building something like that I'd have a camera looking down on the object while the object moves through a scanning laser in some well-defined manner. Thats something a person with the right knowledge could rig up spectacularly easily with a PC (or even something like an Arduin microprocessor board), a laser pointer, a barcode-scanner lens and a web-cam. The precision of the device would depend on the speed of the measurements you require and resolution of the camera - both of which should be easy to control. If your garments are already passing along a conveyor of some kind - it would be really simple to make a machine to do it.
You may wonder how I know this: Well, a couple of years ago, I actually built something to scan 3D objects (You can read about it on my personal Wiki: Here). It used a Lego(!) turntable, a $25 web cam, a $10 laser pointer and a lens bought on eBay in a pack of miscellaneous lenses for $5. My objective was to make 3D models by sampling the position of the reflected laser light on the surface of the object and slowly rotating the object to get a "radial point cloud" (to use a technical term) which could then be turned into polygons and rendered as a 3D image. But using the 'point cloud' to calculate the volume from the 3D model is pretty simple - and for folded clothing - a linear conveyor belt with TWO cameras and TWO lasers (one red, one green) would do a better job. There are restrictions about things like measuring deep concavities - and the machine works best in the dark - but you could probably handle that in most industrial situations either by enclosing that section of the conveyor belt or by using much brighter lasers. The cost of the parts to make the thing would be under $100 - plus the cost of a computer to drive do the actual work - but if you only need one of these machines then the software and development costs would be your issue here. The image processing software needed to extract the coordinate information from the image on the camera is a little tricky - especially for something like clothing which might have a lot of different surface colors - if you want to discuss it in more detail - my email address can be found via my User: page. SteveBaker (talk) 20:48, 23 December 2008 (UTC)
That's pretty impressive, I must admit!
To put things into context here: this is a BIG warehouse where I need to measure (clothing) products accurately. When I say big, I mean there are 15000 different products stored there, and each week there are 1000+ new products added. Each new product must be measured. Storage in the warehouse is not a problem (the stock is palletised in large storage boxes). However, when the stock is picked for despatch to store, it is picked as individual garments into plastic trays of 1 ft3. Any combination of garment mix could be picked into the plastic tray i.e. there might be 1 t-shirt, 1 coat and 6 pairs of jeans per tray. In order to maximise the shipping operation, there must be minimal gaps left in the tray once the product is picked into it. This is achieved by accurately measuring the products when they first arrive at the warehouse (goods in). Presently, the method is to measure each product with a ruler, and treat each pack as a cuboid. This is wildly inaccurate for many different reasons - the net result is that my lorries are stacked with half-full trays and I am "shipping air". This costs a LOT of money in an operation of this scale. What I am looking for is a tool that will easily, accurately and consistently measure the cubic volume of this product mix - I am surprised there isn't a commercially available tool to do this with - SteveBaker, there is a gap in the market here, you could make millions!!
Thanks for your responses guys! sparkl!sm hey! 21:32, 23 December 2008 (UTC)
You said "the stock is palletised in large storage boxes". Don't you know the number of items in each box ? Is the stock in each item identical ? Do you know the volume of each box (or can you get it from H×W×L) ? If so, it seems like all that is needed is some very simple math to determine the volume per item. If you need a program to determine which items can be packed together, based on the volumes of each, to fit into a given volume, that could be done, too. Beware that you don't want to get too terribly efficient at packing, though, or you'll pack the clothes so closely they will get wrinkled. Also, are there combos that shouldn't be packed together, like fragile clothes and clothes with hooks ? StuRat (talk) 01:01, 24 December 2008 (UTC)
Interesting. The problem that you have is – at least tangentially – related to a classic optimization problem in mathematics: the aptly-named bin packing problem. That problem deals with objects of known size which must be packed into a minimum number of standard bins. TenOfAllTrades(talk) 01:13, 24 December 2008 (UTC)
I wonder - isn't cloth of sufficiently reliable density to at least ESTIMATE the volume by weighing it? If your boxes are literally half full - wouldn't you get at least somewhere close by weighing it? SteveBaker (talk) 02:06, 24 December 2008 (UTC)
Since your target volume is the 1 ft3 tray you can define your clothes as occupying a portion thereof rather simply. Tape a tapemeasure each, to one side and crosswise to the bottom of your tray. Then you get a couple of plexi glass strips. Fold a sample garment. Put one strip on top of the garment, note the measurement, put one on the side of your garment (if it doesn't fill the bottom entirely. Note measurement. Repeat with the 3rd dimension if it isn't the tray's length. Since the way you fold the garment will influence the volume occupied by the garment (OR: crupmpled up laundry takes up more space than folded.) you should try various ways of folding it, unless it's pre-folded and your staff doesn't do any folding. There are a limited number of ways to fold your garments, so you'll end up with a limited number of volumes measured for each garment. (Make sure your staff knows what folding method to use when.) You could probably rig some thingamyjig to do the measuring for you, but I assume, since you only have to do it once when the garment is entered into the inventory, you wouldn't save that much manpower vs. doing it manually. The measurements are also more useful to you than the volume, because, even if 2 leather coats would fit your tray by volume, you might not be able to fold them in a way to occupy the space the way you'd need to. Thus volume is only one parameter you'd have to consider. (Your socks might have enough volume to fit in the L shaped space left between the coats and the Jeans, but I doubt your clients would appreciate if you'd deliver them crunched in there.) (talk) 02:57, 24 December 2008 (UTC)

Firstly, I am overwhelmed by the response to the OP, thanks again! There are so many questions you guys have asked above, I'll try to answer some of them now, sorry if this seems a bit disjointed. Weighing is a good idea, but the densities are a bit too varied (we have cotton, wool, leather, denim, silk etc). I do know the volume of each storage box (well, I can easily measure HxWxL), but the suppliers do not necessarily fill the box with the product, so the method of using storage box volumes is not suitable. The product mix in each tray is already calculated by a terrifically clever program, so no need to worry about that. Any products which are not suitable for mixing are also already easily dealt with. Calibrating the tray is a good solution, but will only work effectively for cuboids, and it is the irregularity of the products that is the fundamental problem here (I also manage large non-clothing warehouses, where the products are regular cuboids, and this problem does not exist in those environments).
Let's get back to a very simple level: I work in a warehouse, it is my job to measure the volume of irregular products - what is the simplest and most accurate way to do this, and is there a tool that I can use? Thanks sparkl!sm hey! 08:44, 24 December 2008 (UTC)

Another option is to just give the packers more discretion to pack things best. That is, instead of telling them how much of what to put in each tray, let them figure it out themselves. Perhaps you could implement a bonus system for the most they pack in without wrinkles (you could just weigh the trays when packed to determine the bonus). I suspect they could pack things better, but have no incentive to do so, at present. StuRat (talk) 18:47, 24 December 2008 (UTC)

Non-lethal weapon against gangs[edit]

What non-lethal weapons are there against a street gang attack? Mr.K. (talk) 17:47, 23 December 2008 (UTC)

See Less-lethal weapons for more information, there's a whole list of links you can follow from there. 18:06, 23 December 2008 (UTC)
There is nothing there that I could order through the internet. :( --Mr.K. (talk) 18:20, 23 December 2008 (UTC)
Well, you didn't ask about that, did you? There is an interesting article about something the Israelis have been working on: Skunk. Perhaps you could get ahold of some scent at a hunting supply store, or google on "skunk scent" and pick a purveyor. "Deer scent" isn't much nicer-smelling. --Milkbreath (talk) 18:50, 23 December 2008 (UTC)
If it's an entire gang - you'd be very unlikely to take them all out non-lethally without also doing yourself some kind of injury. Those whom you don't incapacitate are going to be VERY upset with you and the consequences may well end up being a whole lot worse than if you'd done nothing. So this may not turn out to be such a great idea. A cellphone with a GPS and a one-button 911 dialler has to be your best defense. For just one attacker - a Tazer is probably the answer - and even against a gang, waving a Tazer around threateningly with your back to a wall may be enough to hold them off until the cops show up. A multi-shot tazer might even keep back a handful of them. Sadly, they too may have thought of this so there are never any guarantees. SteveBaker (talk) 21:15, 23 December 2008 (UTC)
I personally doubt street gangs would be intimidated by a tazer. It's not quite the same level of threat as an actual gun—it's not quite as much as an investment to take one for the team in such a situation. Frankly, you're better of not trying to violently confront street gangs, if you care about your own health. -- (talk) 02:57, 24 December 2008 (UTC)
A few stink bombs may be effective if they aren't very determined. It is a non-aggressive way of getting them to go away. Dmcq (talk) 21:55, 23 December 2008 (UTC)
Are tear gas grenades obtainable? Though of course you would need a protective mask. Exxolon (talk) 22:43, 23 December 2008 (UTC)
Air bazooka would have the advantage of not being immediately recognizable as a "weapon". A Water cannon would probably also be available online somewhere. When dealing with a gang, though I'd also like to strongly advise against any vigilante action. They are very likely to sneak up on you next time and not to repay you "in kind" either. Call the cops, that's what they are there for. (talk) 03:09, 24 December 2008 (UTC)

This isn't really a science question, is it? It's a mix between a policy debate and a request for web-search help. Nimur (talk) 19:20, 24 December 2008 (UTC)

Yeah, especially since the first thing I thought of was very loud classical music. (talk) 20:45, 24 December 2008 (UTC)

Perhaps a bulletproof inflatable suit that turned the potential victim into a mitchelin man would mean you didn't get hurt as they gave you a kicking, and they would be laughing too much to try. I have been thinking along these lines, and I think on Star Wars I saw a sort of segmented metal hood that instantly sprung up and over (from the back of the neck) protecting the head and face of someone about to be attacked. This might be practical in real life, because whilst body armour can be worn discretly, an armoured helmet kept on all the time would be unsocial. —Preceding unsigned comment added by (talk) 10:20, 25 December 2008 (UTC) -Trevor Loughlin

How about calling the cops? --Shaggorama (talk) 07:46, 26 December 2008 (UTC)

No guarantee they are a non lethal weapon (incidentally I agree this isn't a science question0 Nil Einne (talk) 11:15, 26 December 2008 (UTC)
A gun can be a non-lethal weapon if you're lucky and a good shot. Just like any other weapon can be a lethal weapon if you're unlucky. An unloaded gun is another fairly nonlethal weapon with good scare effect. Unfortunately, numerous studies have shown that people who wave guns around are far more likely to get shot than unarmed people. general you're probably going to get less injured if you are unarmed than if you start threatening people with weapons. --Bmk (talk) 17:03, 26 December 2008 (UTC)

AeroGarden gizmo.[edit]

My wife has been afflicted by the TV adverts for a gadget called 'AeroGarden' ( and wanted one for Xmas. This is a gadget that lets you grow stuff like lettuce and baby tomatoes indoors, hydroponically. Leaving it to the last minute - I wandered into the local store that sells them and was shocked...SHOCKED to see that these things cost $ other crap. Figuring that a lettuce costs about $1 and the machine takes several weeks to grow one - I figure we'd save about $12 a year on food - so this gadget might maybe pay for itself in 10 years...oh - but you need 'supplies' and it eats 60W of probably more like 20 years.

But not being one to disappoint - I've been wondering if I can make one...tomorrow (I have the day off and nothing better to do than to sit and chat to you guys!).

It looks like the thing consists of a container for the plant with water and nutrients underneath - and a pair of CFL lamps with a timer to do day/night some stuff to tell you when to add water and nutrient tablets - which can only be some other kind of timer hooked up to an LED. I'm thinking that a couple of nested plastic popcorn serving bowls with some light fittings and such plus a regular 24 hour timer would get me something functionally identical for about $10 plus lightbulbs...which at least stands a chance of reducing the payback period to something close to the 'novelty-wearing-off' period which historically has been under 6 months for this kind of gadget. (cf Breadmaker, Icecream Maker, Pizza cooker).

Does anyone here actually have one of these machines? Or some insight as to how the plant and the water make contact? Our hydroponics article offers loads of suggestions - mostly that there needs to be some kind of substrate to bring the water up to the roots by capillary action...I'm guessing that stuff like that could be found in a gardening store.

Any information that would increase the probability of it actually growing something would help. Failing that I'm just going to have to buy lettuces of steadily increasing size at the store and sneak them into the container at dead of night in order to convey the impression that whatever I make actually works! SteveBaker (talk) 21:05, 23 December 2008 (UTC)

I'm under the impression (I don't have one) that they actually use aeroponics rather than hydroponics. Same general concept, different technical implication. (Might be relevant if trying to build one yourself.) -- (talk) 22:04, 23 December 2008 (UTC)
My first piece of advice is to grown an herb like basil, which picked fresh will add flavor not found in dried seasoning. There are a dozen varieties of basil so you'll feel like a gourmet in selecting the right blend for your pizza or spaghetti. Herbs can be harvested at any point in their life cycle and tend to be low maintenance. My second piece of advice is spend the $140 and spare yourself some grief. --Digrpat (talk) 22:12, 23 December 2008 (UTC)
Although grief may set in later when it's gathering dust. Julia Rossi (talk) 22:50, 23 December 2008 (UTC)
"Hydroponics" and "aeroponics" in ebay list over 2,700 items for growing plants indoors in artificial medium. There is equipment, lights, books, chemicals, and more. "Marijuana" also lists stuff of that kind – for educational purposes only, of course. – GlowWorm
To answer SteveBaker's question of repaying costs, a sizable portion of the hydroponic/aeroponic/indoor gardening market is people who want to grow wacky tobacky in their basement, where it is not easily detectable by authorities. There's probably a small market for people who genuinely want to grow some tomatoes and summer squash in January, but for the most part the entire industry exists to support Mary Jane production. And a crop of said weed will likely pay for the entire operation in the very first growing season. So yeah, go ahead and get the set-up for those greenhouse tomatoes in February, but also understand that you aren't really the target market for this equipment. People buying this stuff are the same people who are buying "tobacco pipes" and "rolling papers"... 00:35, 24 December 2008 (UTC)
You've listed the financial aspects, so let me say outright that this gizmo isn't about saving money. Why else grow food at home then ? Here's some reasons:
1) If you have small kids it's a good lesson on where food comes from (and far less likely to make your kids run away from home than if you start slaughtering your own livestock). Why not just grow it in a garden then ? Well, you could, but isn't that where the neighbor's cat likes to tinkle ?
2) It enables you to control what goes into the food, so you really know it's "organic", as opposed to trusting some combination agricultural company and chemical company that claims their food is organic (even though you've seen their food glowing in the dark).
3) It's fun. OK, you're not likely to to die from excitement, but it's still a bit of a thrill to grow something yourself.
4) You have to give some piece of crap gift to everyone to honor the Holy Day of Commercialism, so why not give this ? StuRat (talk) 00:51, 24 December 2008 (UTC)
Oh, no, I think its a great idea. I mean, we do LOTS of things just for fun, and this one seems like quite a cool adventure. I wasn't disparaging the idea of gardening, just noting that SteveBaker's frustration over the cost was likely misplaced, as he's not really the target market for this product. But still, I think this is an AWESOME gift, for the record... 01:00, 24 December 2008 (UTC)
It's not that I don't think you should grow things like herbs indoors - it's handy in the winter - the stuff comes out clean (no soil), etc. It would make my wife happy, etc. But $140 for what appears to be two CFL's and a timer is nuts - it's a complete ripoff. So I plan to make a 'clone' - but (to reiterate my actual question) - I don't know what kind of 'substrate' to put the plants in - or what fertiliser/chemicals are needed.
Right now - I'm thinking of buying three white plastic 'popcorn' bowls (there are heavy plastic - about 18" across by about 6" deep - and nearly hemispherical). These are $1 each in the 'everything's a dollar' store. I plan to drill a dozen 1" holes in the bottom of one of the bowls and stack it inside one of the others with some kind of 'substrate' trapped between them (coconut matting perhaps) which will be kept wet - and onto which seeds will be dropped. The third bowl will be inverted and will have two 30W broad spectrum CFL's mounted inside - plugged into a 24 hour programmable timer. Two pieces of concentric plumbing pipe will run vertically up through the center of all three bowls with a pipe clamp on the inner one so it can slide up and down so that the top bowl plus lights can be moved as the plant grows. The outer pipe will have holes drilled around the base so that you can replenish water and 'chemicals' by pouring them down the center of the pipe from the top.
I figure I can buy the parts for $20 or less and assemble it in an hour...but the problem is that I don't know whether I've got enough of the salient details right to make it actually 'work'. Hence my request for help.
SteveBaker (talk) 16:16, 24 December 2008 (UTC)
From my experience with friends who grow "herbs": rockwool is a very good substrate (but make sure that you only cut it while it's wetted); if you are using pure hydroponic, you need to pay attention to oxygenation of the roots, so you need a bubbler or use the ebb-and-flow method, where the rockwool sits in a pan that is periodically drained. A more advanced design uses a rotating wheel where the rockwool enters the pan of nutrient & water every hour or so. The lights are placed at the centre and this maximizes absorption from the light, while also providing the necessary aeration (and also produces compact plants, but likely wouldn't work for tomatoes). The single biggest factor is light intensity, and a proper nutrient mix and aeration/circulation are also important. Depending on how often you replace the water, you might need a UV sterilizer too.
I've seen those same ads for the AeroGarden and my impression is also that it's a "gizmo" whose best effect is to separate the public from their money. (Hint: do they offer to throw in a set of knives? :) But you certainly can build a very effective hydroponic system for not a lot of money. You need some tubing, some rockwool, some PVC pipe, timer & pump, and your budget will be constrained by the light intensity. Franamax (talk) 02:53, 25 December 2008 (UTC)

Sail all wet?[edit]

Why do submarines have sails? It looks to me like it would add drag and weaken the structure. Clarityfiend (talk) 21:22, 23 December 2008 (UTC)

According to Conning tower (which is part of the 'sail'): "A conning tower is a raised platform on a ship or submarine, often armored, from which an officer can con the vessel; i.e., give directions to the helmsman. It is usually located as high on the ship as practical, to give the conning team good visibility.". The 'sail' is there to get the conning tower up as high as possible. SteveBaker (talk) 21:27, 23 December 2008 (UTC)
Wheres on a sailing ship giving directions to the helmsman from the conning tower makes lots of sense, on a sub I suppose it's more to do with keeping your feet dry. (The bridge being downstairs, inside the sub) If you wouldn't have the sail you'd have to raise the entire top of the sub out of the water to go "topside" for a look-see. In calm sea that wouldn't be that big a deal, but give it a bit of a chop and you'd be real happy to be a bit farther up. Apart from making the sub as easy to spot as a boat from afar, if you'd raise the whole thing up above the waves, it would add all sort of engineering challenges as to the shape of the hull where to put the ballast and pump outlets etc. (talk) 22:27, 23 December 2008 (UTC)
Looking up that article led me to the question: Why was a French submarine called "Casabianca (Q183)" in 1935? — Sebastian 22:52, 23 December 2008 (UTC)
Well, just looking at the Casabianca disambiguation page, the obvious thing would be that it was named after the place.
Incidentally, there has been a movie named after this submarine, which means that there have been movies named Casabianca and Casablanca. Hard to tell those words apart in some typefaces! --Anonymous, 07:07 UTC, December 24, 2008.
Not quite. Looking at the lede of the sub's article makes it quite clear that the vessel was named for the person, not the place (and it's not the only French vessel to have been so named). As for why they'd name a sub after him, my best guess would be the rather poignant death of he and his son in battle -- but that's purely guesswork. — Lomn 13:59, 24 December 2008 (UTC)
In addition to giving the commander a dry place to stand, it provides a handy place to put communications antennas, radar equipment, and other stuff that you want to have high up and clear of the water when the boat is surfaced (or nearly surfaced). It also makes it easier for crew to board and exit the craft in less-than-perfectly calm weather. (If you opened a hatch that was flush with the top of the rest of the hull in any sort of wave action then you'd very quickly get a sub full of water.) TenOfAllTrades(talk) 00:27, 24 December 2008 (UTC)
This is sort of a kid's site from the Office of Naval Research, but it also explains that the Sail houses some control surfaces, and has historically been the location for steering and other controls. My guess is that before the digital era, placing controls for periscopes, control-surfaces, etc, far from the locations of the actual instruments was much more difficult. Nimur (talk) 19:39, 24 December 2008 (UTC)

Red Panda, Giant Panda thumb.[edit]

The Red Panda articles says "[The Red Panda and the Giant Panda] are only very distantly related by remote common ancestry from the Early Tertiary Period." Is the specialised thumb (extra digit formed formed at the wrist), which they both have, derived from their common ancestry, or is it a case of convergent evolution? Jooler (talk) 22:39, 23 December 2008 (UTC)

Convergent evolution indeed, according to this paper. Nice! --Dr Dima (talk) 00:21, 24 December 2008 (UTC)
My understanding is that the Red Panda is closely related to racoons, while the Giant Panda is closer related to the bears. 00:29, 24 December 2008 (UTC)
Correct. According to Flynn et. al. (2005) Syst. Biol. 54(2) pp. 317–337 (see figure 3 therein if you have full access), Red Panda's closest living relatives are Mephitidae (skunks) and Procyonidae (raccoons, coatis, kinkajous, and the like) of Musteloidea (weasel) superfamily; while the Giant Panda is closely related to bears and hence is placed in Ursidae (bear) family, superfamily Ursoidea. Happy Holidays! --Dr Dima (talk) 02:02, 24 December 2008 (UTC)
Great answer Dr Dima. Jooler (talk) 14:06, 24 December 2008 (UTC)