Wikipedia:Reference desk/Archives/Science/2007 October 17

= October 17 =

silver + potassium nitrate
what happens when i add silver to a solution of potassium nitrate? thanks —Preceding unsigned comment added by Karkaputto (talk • contribs) 00:54, 17 October 2007 (UTC)


 * The chunk of metal sinks to the bottom, because its density is much greater than the (presumably aqueous) KNO3 solution? Or is there something you didn't explain clearly here? DMacks 03:19, 17 October 2007 (UTC)


 * While silver nitrate is quite soluble, potassium is a much stronger reducing agent, and so won't be displaced the silver. In short, nothing.  Someguy1221 03:27, 17 October 2007 (UTC)


 * I am certain that the nitrate will oxidize the silver (but with what results is my question), so that is a moot point--Karkaputto 03:52, 17 October 2007 (UTC)


 * Make the solution highly acidic and nitrate will dissolve the silver very happily. Someguy1221 04:05, 17 October 2007 (UTC)
 * unfortunately, that is not my situation--Karkaputto 13:55, 17 October 2007 (UTC)
 * You need a table of elctrode potentials for nitrate reductions (and adjust to neutral conditions) (Ag > Ag+ -.8V see Table_of_standard_electrode_potentials) then find reductions of nitrate that have potentials at a higher value (note if using standard elecrode potentials the value will be reduced since in your solution [H+] << 1 .Does any of that need more explaining?
 * However I guess that even if a reaction could occur - it will most likely be very slow (acid usually speeds things up) - most reductions of nitrate need H+ to proceed so if a reaction does occur the solution will become basic - further complicating things..87.102.123.108 19:42, 17 October 2007 (UTC)
 * The barrier for nitrate oxidizing is high because the only way to go is to nitrogen N2 and this is complicated. You need an relative high activation energy and this is not possible in reasonable time in water at room temperature--Stone 13:54, 17 October 2007 (UTC)
 * Nitrate can be reduced to ammonia, nitrite as well - what are you on about?87.102.123.108 19:26, 17 October 2007 (UTC)
 * I cant think of a reaction between Silver and nitrate in the absence of acid, in the presence of acid silver will be oxidised by thee nitric acid formed.87.102.123.108 19:29, 17 October 2007 (UTC)

Light for plants
Can plants grow under normal light bulbs (household lights) or do they need to have sunlight? Hyper Girl 10:14, 17 October 2007 (UTC)


 * They only use certain frequencies (which couple energy best to the chlorophyll molecules), but they will grow under practically any source of light that we'd deem as "white"; it's just a question of efficiency -- sunlight is free while artificial light costs various amounts depending on its source.


 * Atlant 12:30, 17 October 2007 (UTC)


 * Also, sunlight is immensely brighter than artificial light. We tend not to notice that because our vision system is easily able to adjust to the brightness or dimness of the lighting - but plants really do notice that because light is what "powers" them.   However, it's certainly possible to grow plants in artificial lighting - people who engage in illicit Indoor Cannabis cultivation use massive amounts of halogen lighting (the article talks about 1000 Watt bulbs) to give the plants what they need.  So a typical 40 Watt table lamp isn't going to cut it because the plant is only getting 4% of the energy it needs.  (Our coverage of Cannabis (drug) cultivation techniques is truly alarmingly comprehensive! It's a real "How To" kind of a guide with lots of sub-pages and an entire WikiProject all of it's own!) SteveBaker 14:14, 17 October 2007 (UTC)


 * Cannibis cultivators are reputed to use metal halide lighting, not tungsten-halogen.


 * Atlant 16:34, 17 October 2007 (UTC)


 * Actually the old (not warm white - but cool white) fluorescent tubes have sufficient colour temp (enough blue and red light) for some plants to survive . An incadescent bulb won't help much - not enough blue.. Hopefully someone will come along and tell us about plants that have evolved to survive in low light conditions ivy perhaps - anything with very dark leaves is a good sign..87.102.12.215 15:41, 17 October 2007 (UTC)


 * I guess the plants that live on rainforest floors (where very little sunlight filters through) would be a good choice. Lots of those are carniverous...and I presume there is a reason for that! SteveBaker 20:15, 17 October 2007 (UTC)


 * I thought being carnivorous (for a plant) was more to do with the lack of nutrients in the soil than the energy? Skittle 23:05, 17 October 2007 (UTC)


 * Carniverous plants tend to grow in nitrogen-poor environments and have their nitrogen fix delivered to them.


 * Atlant 12:36, 18 October 2007 (UTC)


 * I highly recommend the book How to Grow Fresh Air: 50 House Plants that Purify Your Home or Office --M @ r ē ino 21:32, 17 October 2007 (UTC)


 * Note that indoor cannabis growing doesn't have to be illicit. I did some of that and of course researched it. Ed Rosenthal's excellent Marijuana Growers Handbook has some quite extensive info on this, but I can't find the book now (probably lent it out to some dopehead :) ). What I can tell you is that two 58 W Fluorescent lamps were enough for two good harvests per year (for a total of about 50 g, precisely enough to cover my 'need' (which is sleep)). This came from about four or five plants (per harvest) on half a square metre of soil. So about 50 W should be enough to let a plant grow. Note, though, that cannabis is a very tough plant and that the lamps were very strategically placed. They weren't used to light the room, so most of the light went to the plants. Also note that I did this because the only alternative I had was the windowsill, which puts to the northwest, so the plants only got some direct sunlight for a few hours in the evening (if any). The lamps did much better. Then again, I didn't put them in as much soil on the sill, so I don't know how big of a factor that was. Ok, the real reason for growing under lamps was that I couldn't look out into the street anymore. Was a shame for the tourists on the boats passing by going "Wow, look at that - marijuana growing in broad daylight." (note the pun). DirkvdM 06:56, 18 October 2007 (UTC)


 * I can't speak for cannibis growth, but I can assure you that some pretty mighty rubber trees and jade plants grow fine under 4x40W of "cool white" fluorescent lighting; I did that for years.


 * Atlant 12:36, 18 October 2007 (UTC)

coloring your eyes
In reference to an earlier question about black contact lenses, can one die the color of their eyes? Would something like food coloring be harmful to put into the eye? Obviously pen ink might, but are there any alternatives? Thanks and bunch Picture of a cloud 10:19, 17 October 2007 (UTC)
 * My mother would tell you not to put anything in your eyes. She would also advise against putting things in your ears or up your nose. Don't run with scissors, either. --Milkbreath 10:57, 17 October 2007 (UTC)
 * Mums are always out to stop kids having fun. Mine (well my nanna - she brought me up) told me not to play with fire or throw stones at stuff too. Gawd, what else is there to do when you're that age and have no money? :) --Kurt Shaped Box 11:03, 17 October 2007 (UTC)
 * Please take a seat, remove your contact lenses and I will be with you shortly. Lanfear&#39;s Bane 11:47, 17 October 2007 (UTC)
 * N.B. Nothing in your ears smaller than your elbow please.
 * Even if there was a dye that would stain the iris but not the lens, how would you get it in there? The coloured part is down underneath the cornea and is washed in the aqueous humor.  Any kind of dye that you could inject in there would tend to dissolve in the aqueous humor - and that would really mess up your vision.  The answer has got to be a big "No". SteveBaker 14:04, 17 October 2007 (UTC)
 * I'm reasonably sure that some sort of yellow die is used to test Intraocular pressure, but it apparently wears off pretty quickly. I've never come out of the doctor's office looking like a kidney patient... --Mdwyer 19:04, 17 October 2007 (UTC)
 * Some treatments for glaucoma, such as prostaglandin analogs, are known to change the eye colour in maybe 10% of patients. These combat glaucoma by increasing drainage of intraocular fluid, thereby lowering pressure. It was thought that prostaglandin acts on eye colour by mimicking a natural hormone that mediates melanin production. However recent research suggests that this hormone does not regulate uveal melanin after all, leaving the mechanism of action a bit of a mystery. Note, however, that this isn't a dye, but a bioactive compound. There are lots of dyes that will stain the eye, including indocyanine green, trypan blue, gentian violet, and methylene blue. However these are temporary, would severely disrupt your vision, and are mainly used for medical purposes during surgery. They are generally also non specific, so would leave you looking very weird for a time. Please don't put any substance in your eye - certainly not a dye - unless instructed to do so by a professional. It would, if you'll excuse the pun, end in tears. Rockpock  e  t  00:31, 18 October 2007 (UTC)


 * Yes, that sounds familiar. A relative used to have a rabbit that had something wrong with its eyes - some sort of chronic condition. Every couple of weeks, the veterinarian would drip a yellow/orange dye into each of its eyes to see how it was getting on. It would come back with the whites of its eyes stained whatever colour the dye had been. IIRC (it was a long time ago now), it wore off fairly quickly. --Kurt Shaped Box 01:14, 18 October 2007 (UTC)


 * Consuming melange can color your eyes blue. I wouldn't recommend it for this purpose though, as contact lenses are both cheaper and have less other effects.  &#x2013; b_jonas 20:27, 18 October 2007 (UTC)

Gulls and Botulinum toxin...
I've just been reading this thread over at the misc. desk and it reminded me of something that the local amateur wildlife rehabber once mentioned to me WRT gulls (the large ones, at least). Apparently, they have an *extraordinary* resistance to Botulinum toxin and can tolerate a dose that would kill a human with no apparent ill effects. Even the birds that do come down with botulism paralysis and end up with him are very often save-able (provided that the lungs are not affected), by simply keeping them warm and forcing them to drink enough fluids (his own formula) to flush the toxins out of their systems - then they just get right back up. Next time he gets one brought in, he's going to let me go round to watch the process and help out.

So, anyone have any more info on the mechanism by which gulls have managed to develop such a high tolerance to the bad stuff? I find this kind of thing absolutely fascinating. --Kurt Shaped Box 11:00, 17 October 2007 (UTC)


 * The mechanism by which they developed it is easy - evolution - gulls that had some kind of resistance to the nasty consequences of their ikky diets survived - those that didn't died. Hence they evolved.  What mechanism they developed to do that...I have no clue. According to our article, Botulinum toxin blocks the release of acetylcholine from nerve endings thus arresting their function, and there is an anti-toxin that's "derived from Horses" (how?).  Perhaps whatever this natural anti-toxin is - it's produced naturally by Horses...and perhaps also by Gulls?   But I really don't know.  Another possibility is that somehow the gull doesn't let the toxin reach it's important nerve endings.   After all, humans don't get sick from Botox injections - and Botox is just a nice, sanitized shorthand for "BOtulism TOXin". SteveBaker 13:57, 17 October 2007 (UTC)

carbon resistor
1.How can i interpret a carbon resistor with 2 gold bands.plz give one example?Roar2lion 12:06, 17 October 2007 (UTC) 2.how can i interpret a resistor with 5 colour bands.which type is it of?Roar2lion 12:06, 17 October 2007 (UTC)
 * All your homework questions are answered in the article on resistors. Lanfear&#39;s Bane 12:17, 17 October 2007 (UTC)


 * (edit conflict) Here is a picture that explains color coding for resistors better than any words of mine could. If you still have questions after looking at that, please do ask here. --Milkbreath 12:26, 17 October 2007 (UTC)

In brief, remember that gold is used in two different contexts. It can be the "multiplier" (where it means x0.1) or it can mean the "tolerance" where it means 5%.

Atlant 12:33, 17 October 2007 (UTC)

The strongest material?
If you wanted the strongest material ( for building/construction material, armor, etc), what would you want maximized/minimized ideally? For example, ductility should be maximized, tensile strength should be maximized, brittleness should be minimized, melting point should be high, heat conduction should be low, etc. Those are some I can think of, what else? 64.236.121.129 13:20, 17 October 2007 (UTC)


 * It's not that simple - the properties you desire depend on what you are using it for. You need a totally different material for (say) the foundations of a bridge pier than you need for the cables holding up the roadway.  One needs to be strong in compression - the other strong in tension.  Since no material is good at both - you end up with two different sets of needs for two different applications.  There are times when high stiffness is required - there are other times when flexibility is needed.   I don't think there is a meaningful answer to your question. SteveBaker 13:43, 17 October 2007 (UTC)


 * Steel is perfectly happy in both tension and compression, it just doesn't tend to be the most economical material for carrying many compressive loads.


 * Atlant 16:37, 17 October 2007 (UTC)


 * Hmm, I'm talking hypothetically. I'm not looking for any particular real world examples. Like for example, we use reinforced concrete in buildings because it has high compression strength, low heat conduction, among others. But if there was a material that possessed all those attributes while also having high tension strength, it would be even better.


 * So I'm talking hypothetically. You mention where high stiffness is needed, and other times flexibility (I'm assuming you mean ductility) is needed. But an ideal material would have a strong resistance to stress before deforming, but when it does deform, it is highly ductile. Ignore the fact that such materials don't exist. Ideally, what should be maximized/minimized. 64.236.121.129 14:36, 17 October 2007 (UTC)
 * I get that - the answer is - all the measures of strength should be maximise eg tensile strength, yield or breaking strength, compressive strength, and also toughness.. you'll also want high melting point and the effect of temperature on strength should be minimised. Intersetingly ductility isn't a measure of strength - a very ductile material would be very weak.87.102.12.215 14:47, 17 October 2007 (UTC)


 * Thank you, but I think you are mistaken on a ductile material being weak. Of course you want the material to maximize strength while subjected to stress, but all materials will be unable to hold up against stress at a certain point so at that point it has two options. It can either fracture, or it can deform. Ideally, you want it to deform rather than fracture. If it always fractures past its initial maximum holding strength, that means it's brittle, which is undesireable. A highly ductile material will undergo elastic and plastic deformation before it completely fractures. Ideally, a material should maximize all the strengths you mention, while also being high ductile.
 * Yes and no. a ductile material will deform though.. not good - that's why I prefer toughness as a measure rather than ductilty.87.102.123.108 17:34, 17 October 2007 (UTC)
 * ie a material could be tough, non ductile and non brittle..87.102.123.108 17:39, 17 October 2007 (UTC)
 * Plus if your material is starting to undego plastic deformation - it's broken - and you would need to go back to the drawing board as an engineer!87.102.123.108 17:43, 17 October 2007 (UTC)
 * A material can be tough, no doubt, but if it were tough, non ductile, and non brittle, it's effectively invincible right? Once a material subjected to stress beyond it's strength to sustain it, it has to either fracture, or deform. Plastic deformation is acceptable if the material is being used as armor. It's certainly preferable over fracture. 64.236.121.129 16:56, 22 October 2007 (UTC)
 * These might be useful Elastic modulus Elastic modulus Tensile strength Resilience Yield (engineering) Specific strength Compressive strength
 * Note Specific strength which requires the material to also be light in weight.87.102.12.215 14:51, 17 October 2007 (UTC)


 * I suppose you also want this hypothetical material to have minimal weight and minimal cost as well ? I imagine carbon fiber reinforced plastic is going to be a strong contender in all dimensions apart from cost - so if you constructed a whole building from it, it would be enormously expensive, as well as overengineered. For bulk use ECC might be a better choice. Gandalf61 16:07, 17 October 2007 (UTC)


 * Is this the article you seek? Strength of materials also includes "fatigue strength".87.102.123.108 17:45, 17 October 2007 (UTC)
 * There also are the articles Fracture_mechanics which may help you reverse engineer a perfect material87.102.123.108 17:48, 17 October 2007 (UTC)


 * But surely there are lots of conflicting goals. There are bound to be some applications for construction materials where rigidity is valued - and others where flexibility is key.  You can't have both - so there can't be a single perfect construction material.  To take an extreme example - suppose nanotechnology is someday able to deliver arbitarily large structures made of diamond for the same cost as lumps of coal.  This is (virtually) the hardest material known to mankind - it would be cheap, life would be good...until someone wants to hang a shelf inside the building and no drill known to mankind can cut a hole in the darned stuff!  So sometimes we WANT a hard material - sometimes that's the last thing we need.  You'll always need a range of materials with different properties - so there can never be a single "best" - not even hypothetically.  —Preceding unsigned comment added by SteveBaker (talk • contribs) 20:12, 17 October 2007 (UTC)


 * Glue? DirkvdM 07:03, 18 October 2007 (UTC)


 * Except I wasn't asking for the "best". What is best, is subjective to what the task is. As for your first point, you CAN have something strong and ductile. There's nothing in physics that doesn't allow this. 64.236.121.129 13:30, 18 October 2007 (UTC)
 * I'm surprised that in this discussion about material strength no one has considered shear. Often, a material can have a high modulus of elasticity, and its shear modulus can suck. Wood comes to mind about this. Tito xd (?!? - cool stuff) 09:13, 19 October 2007 (UTC)

Five-Point-Palm Exploding Heart Technique
Is it possible to kill someone with the technique above? --WonderFran 15:09, 17 October 2007 (UTC)
 * No, as Bill is dead and I doubt Beatrix or Pai Mei will teach you. Lanfear&#39;s Bane 15:20, 17 October 2007 (UTC)
 * Pai Mei is also dead, IIRC. Algebraist 15:49, 17 October 2007 (UTC)
 * A good point, my bad. Poisoned fish heads. Lanfear&#39;s Bane 15:58, 17 October 2007 (UTC)
 * Beatrix also gave up fighting to live with BB. It dies with her.  —Preceding unsigned comment added by 128.101.53.151 (talk) 00:08, 18 October 2007 (UTC)

Use of human excrement as manure in farming
A farm near to where I live in Grafton, Wiltshire has just started to use Human excrement as a manure on two of it's crop fields. Is this a prevalent practice? Does it come from a sewage treatment plant and has it been processed in some way? Is there any difference between the use of human and animal excrement in manure and are there any chemical properties of human excrement that would make it an ideal growing aid? Nanonic 15:09, 17 October 2007 (UTC)


 * The articles Night soil and humanure should start to answer you. DuncanHill 15:16, 17 October 2007 (UTC)


 * In my part of the world, it's common to spread the sludge that remains after sewage processing on agricultural fields, but it is not permitted to spread it on crops meant for human consumption. --Sean 17:08, 17 October 2007 (UTC)


 * I read (and therefore it's Original Research) of a family who spread human manure on their front lawn, only to find that tomatoes began growing there, as the seeds had not been filtered out of the manure. Corvus cornix 20:23, 17 October 2007 (UTC)
 * I imagine you'd get strawberries as well as tomatoes? —Tamfang 01:07, 21 October 2007 (UTC)


 * Hi. I heard that in some countries, they use human feces or urine (or both) in their crops. however, I've never heard of this being used in farming, as mass-production of human waste is ... eww. However, they might use it in their gardens where they are growing vegetables. As I am not so sure about this, I think you should check with someone else before you start putting human feces in your crops. If I remember correctly, urine contains ammonia, which could be used as an anti-acidizer, which also contains the element nitrogen, which is found in many fertilizers. Again, check with someone else before you actually start doing so. Hope this helps. ~ A H  1 (TCU) 20:50, 17 October 2007 (UTC)


 * If you do this, be careful to keep any pets or livestock away. Human manure is more likely to contain diseases that can infect humans than animal manure is.  --M @ r ē ino 21:36, 17 October 2007 (UTC)


 * Manure generally wants to be composted before use anyway. --Sean 00:37, 18 October 2007 (UTC)


 * He isn't planning to do this - his neighbours are doing it.
 * Anyway, three thoughts on this. First, human excrement can carry and thus transmit human diseases (eg cholera spreads this way), so I suppose it would certainly need special treatment for that. The humanure article only briefly mentions this (the article could do with some expansion). Second, what happens to human excrement if it is not recycled like this? Does it all go through the sewers to the oceans, thus slowly depriving the land of nutrients and feeding mass cultures of algae or something in the oceans? Third, excrement is the leftover from food after the body has depleted it of all the stuff that that body needs. So wouldn't human excrement be very bad manure for human foodcrops? DirkvdM 07:15, 18 October 2007 (UTC)


 * Dirk, as to your third question -- there's two factors at work. First off, excrement is the leftover after the body depletes it of most, not all, of the stuff that the body needs.  The better-fed the animal, the richer the manure -- I remember reading a fascinating piece a while back (sorry, can't remember the source) claiming that human excrement had become larger in the last century or so b/c we now eat more, and that in particular the protein content had gone way up.  Second off, good manure supplies the nutrients that the plant needs.  For inorganic material like minerals, that tends to be the same thing as what the human needs because life is very bad at making its own inorganic molecules, but both plants and animals are skilled at chemically converting most organic material into the molecules that they need.  --M @ r ē ino 14:00, 18 October 2007 (UTC)


 * Ok, plants make nutrients that humans need. But what about the required elements? Some are taken from the air, notably carbon, but many are supplied by the soil. If you remove the plants from the field and eat them and then put the excrement and the body after it dies back into the ground, you've got a full circle. But if you let part of that drain away into the oceans and you keep that up long enough, then there will be less and less of the nutrients in the soil. This has been bugging me for years. Is this why we need artificial fertilisers? Btw, why do you bullet your posts? DirkvdM 09:02, 19 October 2007 (UTC)

Activation energy
When two particles collide, in order to react do they both need the actication energy or would it suffice for their combined or average energy to be greater than the activation energy, i.e. if one particle has an energy siginficantly greater than the activation energy and the other has an energy only just below the activation energy? asyndeton 15:29, 17 October 2007 (UTC)
 * Almost certainly the sum of both energies. (though sometimes the situation can be complex - requiring the 'atom' to be in a specific energy state to react - rather than just having Energy > x )87.102.12.215 15:37, 17 October 2007 (UTC)

Mobile phone on the moon
The earthward face of the moon is in line of sight of mobile phone transmitters. So would a phone work on the moon, or are the signals just way too small? -- SGBailey 15:39, 17 October 2007 (UTC)
 * Normaly they do not work in airplanes so the moon is simply a few miles too far. They also only collect and transmit horizontally!--Stone 15:51, 17 October 2007 (UTC)
 * I'd argue that, and agree with it.  A GSM phone would NOT work on the moon due to limitations in Timing advance.  A CDMA phone would probably not work on the moon due to the low power and antenna limitations.  An analog phone might have the power, but the signal from the moon would engage EVERY cell tower it could see, which would just mangle the whole system.  (THAT, incidently, it why you can't use a phone in an airplane.  It has little to do with safety.  Your phone is only licensed to be used on the ground.)  Stone's comment about antenna is also apt -- most modern cell towers use antennas that put beams near the groun of the service area.  Radio waves going up to space would be wasted, so they are damped.  Finally, see EME (communications) to learn about proper ways to reach the moon with radio signals. --Mdwyer 17:30, 17 October 2007 (UTC)
 * Radio signals drop off in intensity with the square of the range. Your nearest cell tower is usually no more than about 15km away - the moon is 400,000km away - 27,000 times as far.  So your cellphone signal would be 730 million times fainter than it would be at your longest distance here on earth.  No...it's NOT going to work! SteveBaker 19:59, 17 October 2007 (UTC)


 * Follow-up question -- would an Iridium phone work, or are the satellites positioned to only detect earth-based signals? --M @ r ē ino 21:41, 17 October 2007 (UTC)


 * Same problem - the Iridium satellites are in a very low orbit (just 780km) and there are lots of them - so you're still only going to be a thousand or perhaps two thousand kilometers away from the nearest one. At 400,000km, the moon is still 200 to 400 times as far away as the nearest satellite - which means that (because of that inverse square law problem) you need a transmitter that's 40,000 to 160,000 times more powerful than the one in your Iridium phone.  (And of course the transmitter in the satellite would have to be similarly more powerful - and it's not!).  There are probably lots and lots of other reasons why it wouldn't work - but signal strength alone is a killer problem - so we need look no further. SteveBaker 22:42, 17 October 2007 (UTC)


 * Again, take a look at EME (communications). It says that even with current technology, it takes 100 watts and large directional antennas to bounce off the moon.  That assumes an out-and-back bounce, of course, but it certainly lends a lot to Steve's explanation.  Also, the Iridium sats will have the same antenna-pattern problem as the ground-based stations, except with even tighter patterns.  The satellite flare page suggests that the Iridium antennas are "door sized" -- and that just to reach 780km! --Mdwyer 02:12, 18 October 2007 (UTC)


 * If you do want to communicate cheaply with the moon, a laser is probably your best bet AFAIK Nil Einne 16:08, 18 October 2007 (UTC)

Sacrificing mice
When the time comes, what methods are used to kill laboratory mice? --Seans Potato Business 16:09, 17 October 2007 (UTC)


 * "Bite they little heads off, nibble on they tiny feet"?


 * The method doubtless varies depending on what you're hoping to analyze ex-post-mouso. You don't want the killing method to perturb the data (add stress hormones, etc.).


 * Atlant —Preceding comment was added at 16:42, 17 October 2007 (UTC)


 * Thoracic puncture, exsanguination, decapitation, cervical dislocation, CO2…lots of possibilities, which is important as Atlant notes, to avoid interfering with whatever you hope to study after dispatching them. See also . DMacks 16:52, 17 October 2007 (UTC)


 * I once had a girlfriend who was a biochemist. When I visited her lab, she proudly showed me the guillotine they used for decapitating live mice.  In some cases they used the CO2 method instead...it depended on what they wanted to measure.  Urgh!  SteveBaker 19:54, 17 October 2007 (UTC)
 * Just curious: How did that relationship end?  Well, I take it? :) --Mdwyer 02:05, 18 October 2007 (UTC)
 * Is CO2 much cheaper than N2? Seems the latter would be less stressful for the victim, if that makes any sense. —Tamfang 01:14, 21 October 2007 (UTC)


 * In some countries, the UK for example, the manner in which one kills mice is regulated by law, specifically Schedule 1 of the Animals (Scientific Procedures) Act 1986 . In other countries there is no legal restriction, though local IACUCs may restrict the use of some methods. Other methods include an overdose of anesthetic or, in the case of baby mice, decapitation with a pair of scissors. It can be quite disturbing decapitating newborns in that manner (especially when they keep crawling for a while after their head has been removed).  Rockpock  e  t  00:00, 18 October 2007 (UTC)


 * Other documented methods scientists have used include, "dissolving mice in acid, spinning them in centrifuges, blowing them up in vacuum chambers, and forcing them to navigate exit-free mazes" One scientist "Dr. Thomas Huber, author of the 1996 study Mouse Elasticity And Kinetic Rebound In High-Acceleration Collisions" found a novel method: "...when I have the time, I like to send them flying into walls." (note to ALF, this is a parody and no mice were harmed in its creation)  Rockpock  e  t  00:11, 18 October 2007 (UTC)


 * Homogenizer Delmlsfan 00:24, 18 October 2007 (UTC)


 * Man - you can see why the animal rights campaigners freak out over things like this. I know that most of it is necessary - but it certainly sounds harsh when taken out of context and listed. Newspeek-like terms such as 'Sacrificing' and 'Homogenizer' probably don't help either... --Kurt Shaped Box 09:53, 18 October 2007 (UTC)
 * Yeah, but I really have to appreciate DMacks' use of words. "Thoracic puncture, exsanguination, decapitation..." is a pretty neat way of saying "poke holes in 'em, bleed 'em, lop their heads off..."  If you get a chance, you've got to hear Henry Rollins talking about his job in a animal lab.  It is disturbing, awe-inspiring, and funny all at the same time. --Mdwyer 16:03, 18 October 2007 (UTC)


 * Rotfl. &#x2013; b_jonas 20:06, 18 October 2007 (UTC)


 * Hah! Yeah, sometimes it's just more polite to say that you "prepared ex vivo cardiac muscle" than that you "ripped out its still-beating heart". DMacks 18:54, 19 October 2007 (UTC)


 * What's the polite, acceptable euphemism for "...and then summoned Hellfire"? --Kurt Shaped Box 12:11, 20 October 2007 (UTC)


 * "Subsequently initiated Hadeopyre protocol." —Tamfang 01:11, 21 October 2007 (UTC)


 * nodnod* --Kurt Shaped Box 05:05, 21 October 2007 (UTC)

One friend of mine had the job of giving mice lethal injections before they died of a radiation overdose from the experimental radioactive fluids they contained for medical imaging studies. moink 18:26, 19 October 2007 (UTC)

Heat-deactivated FCS and deliberate hypotonic lysis
We discussed an article about the involvement of C/EBPa in granulocyte differentiation. In the method, they used 10% heat-deactivated fetal calf serum; since I thought the whole idea behind FCS was that its growth factors can stimulate the growth of cells, what is the point in using heat-deactivated FCS?

They also say that "normal murine marrow cells were obtained from the femurs of mice after hypotonic lysis and enrichment for lineage-negative hematopoetic precursor cells using the standard StemSep protocol" - what is the purpose of the hypotonic lysis? Is this part of the enrichment process? Are certain cells perhaps more susceptible to hypotonic lysis than others? --Seans Potato Business 16:31, 17 October 2007 (UTC)


 * Can you identify the article? Is it Transcription activation function of C/EBPalpha is required for induction of granulocytic differentiation? People routinely heat inactivate horse serum to remove complement, but I've never heat inactivated fetal calf serum. (see) Maybe there are heat-sensitive growth factors in FCS that influence granulocyte differentiation. They seem to indicate that the lysis step can selectively remove red blood cells and help purification via the StemSep protocol. --JWSchmidt 20:52, 17 October 2007 (UTC)

Why Two LEDs in a remote control.
Most remotes have two Infrared LEDs to transmit the codes to the receiver on the controlled device. Why two instead of just one? —Preceding unsigned comment added by 160.42.234.85 (talk) 17:00, 17 October 2007 (UTC)
 * I can make a guess: Once would be the pattern.  A single led throws a circular spot of light.  Two of them would throw a wider oval of light, making it easier to aim.  --Mdwyer 17:24, 17 October 2007 (UTC)

I don't think this is right - most I'm aware of only have one LED - see this image ..?87.102.123.108 17:29, 17 October 2007 (UTC)
 * Most only have one LED, but I have seen ones with multiple LEDs. Here's another theory:  A universal remote might need to have two different LEDs to make two different wavelengths of IR light for different receivers. --Mdwyer 18:52, 17 October 2007 (UTC)

I googled this before posting the question here, and couldn't find anything explicitly answering the question, but I got the idea it might be for increased range because two would be brighter, but then why not just use a brighter one to begin with, so I dunno. —Preceding unsigned comment added by 160.42.234.85 (talk) 18:43, 17 October 2007 (UTC)


 * Mdwyer has it correct: better remote controls use two LEDs for the wider "throw pattern" that is produced. Alternatively, the two LEDs can each be focused more narrowly allowing greater range for the same "pattern width".


 * Atlant 19:23, 17 October 2007 (UTC)


 * Thats funny Atlant!. I always thought that more elements produced a narrower, directional beam, as in YAGI antennas or other arrays for instance.--88.109.65.125 01:24, 19 October 2007 (UTC)


 * But unlike the elements in a Yagi, these multiple LEDs aren't coherent with each other so there's no possibility of employing constructive interference.


 * Atlant 16:40, 19 October 2007 (UTC)


 * Touche! Therefore there must be another reason. What about the power/efficiency of early IR leds vs that of older ones? Our page does not seem to mention efficiency/efficacy


 * Most modern video cameras see far enough into the InfraRed to see the flashes from a TV remote in a darkened room. You could do an experiment to see what's going on.  If they are indeed widening the throw pattern (which would certainly be my guess) - then you should be able to aim the thing off to one side of the camera and only see one of them flash when you push a button (use one of the 'continuous' functions like volume because they keep flashing as long as you hold the button down).  Then if you aim directly at the camera, it should be possible to see both of them flashing together.  (It might be that from off to the side, you see one brightly lit and the other very dimly lit...it's hard to predict) SteveBaker 19:51, 17 October 2007 (UTC)
 * Cell phone cameras work great for seeing infrared remotes. Sancho 22:26, 17 October 2007 (UTC)


 * Good advice, both of you! Also, Radio Shack used to sell a cute little "Infrared test strip" that could reveal infrared light and so could also be used to reveal the pattern of infrared light emitted by a remote control. It wasn't strictly a phosphor but instead had to be charged from visible light first; a little infrared than triggered the emission of the stored energy. I don't know the technical name for that effect (but would welcome it if someone else did!) but it was obviously a form of stimulated emission.


 * Atlant 12:20, 18 October 2007 (UTC)

double hearing
you know how you can see double for whatever reason (maybe a blunt trauma to the head). can the same thing happen with your two ears, to where they aren't coordinated and you hear one sound source as two? Why not?

Also, am I smart or what. Thank you. —Preceding unsigned comment added by 77.234.80.106 (talk) 17:57, 17 October 2007 (UTC)
 * Ignoring your second question for the moment, the eyes and ears aren't really comparable in this way. You see double because your eye muscles lose coordination, and are unable to correctly do Fixational eye movement.  The eyes literally *are* seeing two different images.  Problems with the ears usually don't show up as audio problems.  They usually show up as balance problems.  See Ménière's disease for an example. --Mdwyer 18:58, 17 October 2007 (UTC)
 * What about some condition that results in somebody hearing a single sound twice, in succession? Has something like this ever been reported? My first guess is that this might happen when taking certain drugs. Sancho 19:08, 17 October 2007 (UTC)
 * Nitrous oxide causes a flanging effect on inhalation. In my own personal experience, I would call it echoing.   —Preceding unsigned comment added by Mdwyer (talk • contribs) 19:25, 17 October 2007 (UTC)
 * The problem is that your ears are on two sides of the head so what ends up happening is that if there's a problem with hearing, it ends up with the perception of the origin of the sound being incorrect. It would have to be a dramatic difference in processing times for the two ears to give a doubled signal. If it were caused by drugs, it would be something happening in the brain rather than a difference in signals from the ears. Donald Hosek 19:20, 17 October 2007 (UTC)
 * Yeah, I meant a doubled signal coming from one ear, not from any physical causes at the eardrum, but with the perception in the brain. Sancho 23:51, 17 October 2007 (UTC)
 * You're definitely not going to get a doubled signal from ONE ear any more than you get a double-image from one eye. If you are seeing double - close one eye and everything will immediately sort itself out. SteveBaker 18:35, 18 October 2007 (UTC)


 * When I flinch from a sudden noise, the flinch seems to me to come first, impossible though that is. I take this to mean that memory of the two events moves on two different neural paths. I can imagine that a related effect could cause an illusory echo (which, it strikes me, is a common way in movies to suggest that the viewpoint character is concussed). — Can't resist mentioning the time I was on the phone to someone three blocks away when a train went by: I heard its toot twice. —Tamfang 01:21, 21 October 2007 (UTC)


 * I don't think it can happen with your ears. With your eyes, you have to point each eye very precisely at the 'target' object so that the two images 'line up' - and your brain calculates the distance to the object by measuring the difference in the angle that the eyes are pointing when everything is properly lined up.  When your eyes won't point where they are told to the very great precision needed (perhaps because the muscles are tired) - you see two images.
 * Your ears don't swivel (you may have noticed that) - you detect the direction the sound is coming from by the relative delay in the sound arriving at the two ears - plus some really complicated stuff to do with how the sound reverberates around inside your skull. There is no way for there to be a 'delay' between the two ears that's consistent with two nearly identical sounds coming from different directions.  That's something that it's virtually impossible for us to pick out anyway - let alone by accident.  Most hearing 'errors' come down to lack of accurate direction determination.
 * There was some interesting research done recently that shows that our noses also work in 'stereo' - just like our ears - to enable us to detect where smells are coming from. For the same reason, we don't get double-smelling problems either.
 * SteveBaker 19:43, 17 October 2007 (UTC)


 * As to your second question, see IQ test. If you do find an answer please come back and tell us what you find out. :) --S.dedalus 23:36, 17 October 2007 (UTC)

Insect identification
A dull one today. I have one iridescent blue fly, one black housefly-looking one, and one black-and-orange one (second photo of #3). What are they? I'm guessing the last is some form of bee...

All photos taken yesterday morning in South England. (Bonus points if you know what the plant is. I have no idea) Shimgray | talk | 18:09, 17 October 2007 (UTC)


 * The third is a European dark bee, on examination. Well, one down. Shimgray | talk | 19:09, 17 October 2007 (UTC)


 * The first one is a Blow-fly. SteveBaker 19:33, 17 October 2007 (UTC)


 * The insects are on Ivy flowers, probably English Ivy, Hedera helix.--Eriastrum 21:29, 17 October 2007 (UTC)


 * Er, Shimgray, are you sure the third one is a bee? It looks like a fly to me, though I don't know what kind. Flies have only two wings, which is what it looks like in your photo. Hence the name for the order of flies, Diptera.--Eriastrum 21:37, 17 October 2007 (UTC)
 * This photo is of a 'dark bee' too - you have to look pretty hard to see that second set of wings!  They are a little more obvious in the side-view photo we have at European dark bee - but still - you've gotta agree they aren't exactly prominant.  Worse still for the "Not a Bee" theory, the photos clearly orange fur and stripes on the thorax - and I don't think I ever saw a fly that looked like that.  I wish we had a photo with a clearer view of the legs - pollen sacs would have clinched the deal.  But I have to agree with Shimgray, it's a "European Dark Bee". SteveBaker 22:28, 17 October 2007 (UTC)
 * Eh, I think it is a bit ambiguous. The "fur" is not very distinct. There are a number of bee-flies that look very similar; the genus Exoprosopa in particular has a lot of very similar look candidates (lots of photos here). (Like this guy or this guy.) Anyway, if it is a bee, it doesn't look much like the European dark bee to me. --24.147.86.187 22:43, 17 October 2007 (UTC)


 * I'm certainly not wedded to the dark-bee theory, but it did look v. plausible. A slightly sharper photo - with a just-visible foreleg! - is here. I'll see if I can get any more photos of them from slightly closer in the next day or two; I'm curious now, and it certainly doesn't look like the "normal" big fat bees I'm used to seeing. Shimgray | talk | 20:18, 18 October 2007 (UTC)


 * Shimgray, I think you are right on about the second photo. It does indeed look like a house fly--quite possibly good old Musca domestica.--Eriastrum 21:44, 17 October 2007 (UTC)


 * The third/fourth pictures are definitely not a bee. The angle of the resting wings are wrong, there is an absence of hair and the abdominal shape is not bee-like. This is a species of hover-fly, (English colloquial name) possibly Rhingia campestris, but it is always difficult to identify exactly from photos and there are many species of hover-flies. Most hover-flies used protective bee or wasp mimicry which naturally can cause some difficulty in initial identification. Very nice photograph. Richard Avery 09:10, 18 October 2007 (UTC)


 * A photo of the (not-)bee from side-on, this morning - not desperately well-focused, sadly - here. And am I right in assuming A and B are normal, common-or-garden, wasps? Shimgray | talk | 22:37, 18 October 2007 (UTC)


 * I agree with Richard Avery. The side photo of the insect is certainly a fly, probably a hover fly, Family Syrphidae. Here's a quote from a guide to insects: "Hover Flies. Family Syrphidae....often brightly colored. They bear a resemblance to bees or wasps and almost always are without bristles,...also are called 'flower flies,' because they commonly visit flowers for nectar." The other two photos are of Vespids, in other words "normal, common-or-garden, wasps", though I don't know what specific kind.--Eriastrum 01:10, 21 October 2007 (UTC)

An Interesting Event with a Credit Card
There was a lineup in the mall because someone's card didn't work on the machine. However, after the cashier wrapped it in plastic, it worked! (It was swiped with the plastic on!) Can someone tell me the science behind this? Is it something with electromagnetism? Thanks. --JDitto 18:36, 17 October 2007 (UTC)


 * I've seen that, too! The reader is using a magnetic tape head to read pulses off the card.  The only thing I can think of is that the head is somehow out of alignment with the data track on the card.  The plastic might change things just enough to get a good read.  Another possibility is that the data on the card is recorded too 'loudly', and the plastic attenuates the signal enough for it to be read.  The truth is, I have no idea. :) But I *have* seen it work! --Mdwyer 18:55, 17 October 2007 (UTC)


 * I can add a bit of data: the cashier who did that to one of my credit cards actually taped over the magnetic stripe with a piece of what you probably call Scotch tape if you live in North America or Sellotape if you live in England. The tape stayed on there until the card expired and never seemed to cause me any problems.  --Anonymous, 23:33 UTC, October 17.


 * Funny that scotch is used in two ways in the US that are not used in England. Do I detect some animosity between the neighbouring countries? DirkvdM 07:33, 18 October 2007 (UTC)


 * What is the second way ? If you ask for a "Scotch" in an English pub you will get a Scotch whisky. The key point to remember is that the adjective "Scotch" should never be applied to people, who are always "Scottish". Gandalf61 10:06, 18 October 2007 (UTC)


 * Animosity? The opposite, sort of.  The American usage of "Scotch" in "Scotch Tape" is used to mean "cheap".  It is offensive to the Scottish people.  I imagine if you want to sell Scottish people tape, you're going to want to rename it.  In my part of the US, at least, that particular meaning has disappeared.  "Scotch" to me means whiskey, tartan-patterned, tape, or something containing butterscotch. --Mdwyer 15:59, 18 October 2007 (UTC)


 * It could be worse - I'm told that the leading brand of adhesive tape in Australia is 'Durex' - which unfortunately is the leading brand of condom in the UK. I'll leave you to imagine what happens when a Brit goes into an Aussie drug store and asks for "Some Durex" - or what happens when an Aussie tries to buy Durex by the roll in a British chemist shop!  Of course if an American goes into a British chemist shop and tries to buy some "Rubbers" he's going to get a surprise too. SteveBaker 18:32, 18 October 2007 (UTC)


 * Unless the ditch is larger than I think, I doubt that´s true, since I´ve never heard any Aussie talk about ¨Durex¨ while referring to Sellotape. --antilivedT 05:56, 19 October 2007 (UTC)
 * Hmmm...Durex says that the adhesive tape of that name is manufactured in Mexico and popular in Brazil. I'd heard it was popular in Australia - but perhaps not. SteveBaker 11:21, 19 October 2007 (UTC)


 * For another similar story, someone asked for a 'cola' in Colombia. After a very long time he got a dish of 'bull's tail' ('cola' is Spanish for 'tail). I wonder what would have happened if he had specified a brand and asked for a 'coke'. :) DirkvdM 09:11, 19 October 2007 (UTC)


 * This subthread really belongs more on the Language desk, but... although the story is that "Scotch" was first applied to tape in an insulting way as Mdwyer describes, the company (3M) went on to adopt it as their brand name, presumably implying that a sensibly thrifty person would use their product. It's a stereotype that cuts both ways.  In any case, when people speak of  "Scotch tape" they're mostly just alluding to the best-known brand name in a false generic way, or else referring explicitly to the brand name, and not using a stereotype at all. --Anon, 23:30 UTC, October 18.


 * Indeed, I called it "scotch tape" for mumblety years before noticing that the name, and the tartan on the package, had something to do with Scotland! The derogatory stereotype, so far as I know, is mostly forgotten here in the rebellious colonies.  (Legend says that an early customer for 3M masking tape complained that "your Scotch engineers" didn't put enough adhesive on it.) —Tamfang 01:31, 21 October 2007 (UTC)


 * According to [Dr Karl] (an Australian science presenter) the tape or plastic bag trick works because as credit cards get old or are damaged the magnetic strip can get "noisy", that is spurious data appears. The noise is "quieter" than the data, but the magnetic strip reader can see it and so the data is not clearly readable. If you add some space between the card and the reader, though, the quieter noise becomes unreadable, but the data remains readable. The tape or plastic bag add that space. --203.22.236.14 11:46, 18 October 2007 (UTC)


 * Thanks! --Anon, 23:30 UTC, October 18.

So it has nothing to do with static? Cool. The website only gives his personal information, could I get the URL for what he actually said about the matter? Or did you hear him at a conference? Thanks. --JDitto 15:15, 18 October 2007 (UTC)

Steam Freezing?
I recently watched a steampunk sci-fi movie,(Memory isn't functioning...) and at a point in the film this machine started blowing steam all over a city, the steam was creazing ice/extremely cold tempuratutes because the steam comes out so hot it sucks in all the cold air into itself and freezes, is this a factual phenomena or fiction? —Preceding unsigned comment added by 72.183.196.100 (talk) 20:39, 17 October 2007 (UTC)
 * Fiction. The second law of thermodynamics dictates that putting a hot object with a cold object will (with no external intervention) cause the two to equalize temperatures, not further differentiate. &mdash; Lomn 21:24, 17 October 2007 (UTC)
 * In case there's a misunderstanding, though, blowing steam over very cold surfaces can certainly cause it to freeze out as ice. It's not creating the cold temperature, however. &mdash; Lomn 21:26, 17 October 2007 (UTC)


 * Maybe the steam was not hot water, but evaporating dry ice? That could be quite cold indeed (sublimation of minus 78.5 °C), and it would look a lot like water steam.  --M @ r ē ino 21:45, 17 October 2007 (UTC)
 * To be terribly pedantic, the 'steam' caused by dry ice isn't the CO2 released from the dry ice. It is water vapor.  The vapor is nowhere near as cold as the dry ice is.   There are some other options, though -- liquid gasses are often terribly cold when they are boiling away.  For example, liquid butane and flourocarbons found in air duster cans. --Mdwyer 02:02, 18 October 2007 (UTC)


 * If by chance the movie was Steamboy, which has great releases of steam freezing parts of London, then the reason, as I understand it, is that the sci-fi "steam ball" was under extreme pressure. Gas released from extreme pressure turns very cold, no? Pfly 07:30, 18 October 2007 (UTC)


 * Well, it certainly cools down. That's adiabatic expansion. But if heat is the (sole) reason for the pressure then the net effect will be (close to?) zero. If, however, the compressed gas is at ambient temperature (eg room temperature) then releasing it will cause a cooling. Like with an aerosol spray - try spraying on your hand and feel the cold. Do this over a city and you will get something steamy, except it's not steam but mist - same thing, but under different temperatures. The water in the air condenses because its concentration is too high for that new temperature. DirkvdM 07:42, 18 October 2007 (UTC)


 * If I recall correctly, Michael Faraday did a pneumatic experiment with a spherical copper vessel which involved heating it, probably with water in it turning to steam, and making ice as the pressure was released. Read the original acount a couple of years ago, don't remember all the details. Edison 00:22, 19 October 2007 (UTC)

Virtual Photon
A few questions which my physics teacher wasn't able to answer:

What is the main difference between a virtual photon and a 'real' photon? Does this make any practical difference to how the virtual photon behaves?

Also, when a virtual photon is exchanged in electrostatic repulsion, does this mean that energy is exchanged between the two (in this example, electrons). I have also read somewhere, that there is some way in which the conservation of mass/energy law is broken Is this true?

Thanks,  Ai y  da  21:47, 17 October 2007 (UTC)
 * Does virtual particle help with your questions? (I should emphasise that I am not familiar with this topic and have not read the article) Algebraist 22:08, 17 October 2007 (UTC)

A real photon is described as on-shell. It's rest mass is exactly 0. A virtual photon can have a different effective mass, but this means it must be absorbed, it can not travel as a free particle. This is a consequence of a Heisenberg Uncertainty Principle kind of borrowing of energy, but only for a limited time, which in effect limits the range of the force. Energy is exchanged between two electrons if they exchange a photon, yes. The mass/energy relation you refer too is probably that the virtual photon doesn't have 0 mass enforced as in a real photon. Energy is conserved both when the photon is emitted and absorbed, it is not conservation that is broken, but the relation between energy and mass. This is hard to put into words I hope the article does a better job. Cyta 07:47, 18 October 2007 (UTC) Yes looking at it quickly the article seems quite comprehensive, although I am not sure about the stuff in the intro about some scientists not believing in virtual particles, I have never heard that view anywhere before. Cyta 07:49, 18 October 2007 (UTC)

Carbon-oxygen backbone polymer
Does a polymer with an alternating carbon-oxygen backbone exist, for example H-[CH2-O]n-CH3? If so, what are they called? These are similar to the silicones, but with carbon in place of silicon. Thanks, AxelBoldt 21:52, 17 October 2007 (UTC)
 * Maybe polyoxymethylene. --JWSchmidt 23:33, 17 October 2007 (UTC)


 * The Delrin page has a lot of applications for polyoxymethylene, in case you're interested. Delmlsfan 00:28, 18 October 2007 (UTC)