Wikipedia:Reference desk/Archives/Science/2008 December 17

= December 17 =

The Vagina and an imperforate hymen
I can't seem to get clarity on this - if you have an imperforate hymen, then fluids would not be able to escape from the vagina, so most articles that touch on this simply say "so a procedure is needed" - but it doesn't explain the consequences of what would happen if a procedure was not performed...

In other words:

If you have an imperforate hymen would the fluids get reabsorbed into the blood stream, would the menstrual cycle just discontinue, or would the whole thing burst ?

Rfwoolf (talk) 01:44, 17 December 2008 (UTC)
 * I think I found the answer here: "The fluid gets backed up inside the vagina and causes a condition called hematocolpos -- a big wad of blood". I assume that when this happens the menstrual cycle stops, but I do wonder if there's any re-absorption into the system or what, and assuming the menstrual cycle did not discontinue it would probably eventually burst. Interesting... Rfwoolf (talk) 01:59, 17 December 2008 (UTC)


 * I believe that symptoms and signs would occur long before any 'bursting' occurred. It would be very likely that pain due to the haematocolpos would be felt which would draw attention to the problem. 86.4.182.202 (talk) 08:54, 18 December 2008 (UTC)

When discussing the most important organ, care must be taken to spell everything correctly: "hæmatocolpos".

Does human hair change color while decomposing in water?
I know that hair decomposes very slowly under normal circumstances. But, can loss or change of pigmentation occur during say, 6 months of death and decomposition? If so, how much difference would it make, if any, if the body was submerged in fresh, warm water? The body in question is one making headlines in Florida currently, so was in a somewhat tropical climate. Thanks so much. MoeJade (talk) 02:10, 17 December 2008 (UTC)
 * Sunlight (if it was present) causes depigmentation. That's all I know. Rfwoolf (talk) 02:24, 17 December 2008 (UTC)


 * That stone-age guy they found mummified in deep snow in the Italian alps had hair that retained it's color over maybe 100,000 years...so depigmentation doesn't happen in the dark under ice.
 * Human hair wigs seem to last for many decades (at least) - so air and sunlight isn't really enough. I suppose submersion could make a big difference - but that doesn't seem likely to me. SteveBaker (talk) 03:12, 17 December 2008 (UTC)

See New York Medical Journal, 1870, p.412, which cites the observations of a Dr. Hauptmann, that a man who had dark brown hair during life, was found to have red hair when dug up after 20 years in the ground. A Prof. Sononschein said that dark hair becomes red after long burial due to an acid reaction. When it is claimed hair "retained its color" we can't ascertain the truth of the statement without knowing the original color. The Hauptmann finding was cited in "A Treatise on Diseases of the Hair"(1912) by Jackson, p. 71. Hair which has been dyed can certainly change color if the dye washes out or reacts chemically with the water. Old and credulous sources say the hair color can change post-mortem, but their reliabliity is called into question by the repeated claim that hair and fingernails continue growingto great lengths after death. This is even seen in encyclopedias and medical books from the first 2 decades of the 20th century.Publications of the Body Farm should provide a modern answer to the question of the effect of submersion after death on hair color, but I did not find the specfic information. "Advances in Forensic Taphonomy" (2001) p 123 says"Hair color is usually modified as a result of burial and early decomposition" Melanin (dark hair) becomes lighter, and hair of those buried a long time (archeological samples) tends to make it "ginger" or reddish. P383 says wool (which is hair of a sort) turns "honey brown" in "waterlogged anoxic conditions." Edison (talk) 16:02, 17 December 2008 (UTC)

Liquid light
Can high density photons turn into liquids or solids ? Can they be consumed ? 69.157.229.14 (talk) 03:04, 17 December 2008 (UTC)
 * No, they can't be turned into liquids or solids. They can be absorbed though - when you shine a light on a black surface - the surface is "consuming" the photons - making the surface a little warmer. SteveBaker (talk) 03:18, 17 December 2008 (UTC)

What about electrons ? This is a could question, meaning with various futuristic technologies ? 69.157.229.14 (talk) 03:26, 17 December 2008 (UTC)


 * Electrons can also be absorbed by liquids or solids. Just think of the old computer monitors and tvs. Their absorbtion, just like light, also makes things warmer. Sjschen (talk) 03:41, 17 December 2008 (UTC)


 * The only elementary particle that could be a liquid or solid as far as I know is a neutron. See neutron star. --98.217.8.46 (talk) 04:15, 17 December 2008 (UTC)


 * That is of course, stretching the definition of "liquid" and "solid" beyond the bounds of creditibility. The standard three-phase model of matter (solid-liquid-gas) presupposes atomic matter at standard room conditions.  Once you start to mess with those conditions (i.e. non-atomic or subatomic particles) or raise the temperature to very high levels, the three-phase model breaks down.  --Jayron32. talk . contribs  05:51, 17 December 2008 (UTC)


 * I'm utterly out of my depth in this subject, but I discovered by Googling "photonium" that there is a posited entity - I don't know if you could call it matter - that might result from virtual electron/positron pairs if you could persuade them to remain stable (see here for a serious example). Make sure you put on your tinfoil hat before searching for this stuff, however, because some of it is fringe science or science fiction. --Heron (talk) 13:25, 17 December 2008 (UTC)
 * Just because a concept has a name and google hits in no way makes it credible. Do a Google search for 'teleport' and you get 6.1 million hits - does that make it real/possible? No. SteveBaker (talk) 19:37, 17 December 2008 (UTC)
 * I know. That's why I provided a link to a (speculative) statement by a professional physicist. He could still be wrong, of course. --Heron (talk) 20:35, 17 December 2008 (UTC)
 * Isn't a stable virtual particle something of a contradiction in terms? --Tango (talk) 14:13, 17 December 2008 (UTC)
 * I probably misunderstood the page I linked to. In some places it talks about creating virtual e+e- pairs and in other places it seems to imply that they are real particles. I don't know how they change from virtual to real, if indeed they do, and neither do I know whether the 'photonium' of which he speaks is composed of these particles or is just the field in which they sit. I was hoping that one of you boffins could sort it out for me, but you don't seem to be biting. :) --Heron (talk) 20:35, 17 December 2008 (UTC)


 * Yes photons can turn into liquids in a sense. Two photons can be made to collide, producing elementary particles which may or may not then form part of a liquid. Most likely they'd be a plasma. Photons themselves cannot form a liquid because the particles that form a liquid need to be able to bump into each other. Photons can't bump into each other. EverGreg (talk) 14:35, 17 December 2008 (UTC)
 * That's just saying "photons can turn into things that in turn can form liquids and solids" - the photons themselves can't do that. SteveBaker (talk) 19:37, 17 December 2008 (UTC)
 * I think you've just refuted my speculation above, Steve. I'll stop arguing now. -Heron (talk) 20:40, 17 December 2008 (UTC)
 * Photons can bump into each other (redlink?! try the literature), so a photon gas could be interacting, but they can't have attractive interactions, so they can't be condensed matter.  --Tardis (talk) 19:11, 18 December 2008 (UTC)


 * An electron and positron in "orbit" around each other form an "atom" referred to as positronium, which has been generated in the lab. Some versions of it can actually stick around for a fraction of a second before decaying, too. Confusing Manifestation (Say hi!) 22:09, 17 December 2008 (UTC)

Surely light can't form a plasma? A Bose-Einstein Condensate seems more likely than any of the more conventional forms of matter. I don't know if it's possible, but at least you'd be heading along the right lines. 81.174.226.229 (talk) 14:32, 18 December 2008 (UTC)

speed of sound
Assume that sound is traveling through a medium of x density.

How does the speed of sound tend as x approaches 0? —Preceding unsigned comment added by 24.251.110.126 (talk) 04:04, 17 December 2008 (UTC)


 * I don't know the answer off-the-cuff, but reading the speed of sound article may help. --Scray (talk) 04:13, 17 December 2008 (UTC)


 * The speed of sound when x=0 is 0, so isn't that the answer? --99.237.96.81 (talk) 04:29, 17 December 2008 (UTC)


 * We weren't asked what the speed of sound is at x=0, but how it behaves as x approaches 0. This is a slightly different question, and has to do with Limit (mathematics), specifically Limit of a function. Mathematically speaking, the limit of a function as x->a does not have to be the same as the value of the function when x=a. For example the limit of the function f(x) = (3x-6)/(x-2) as x approaches 2 is 3, even though the value of f(2) is undefined. -- 128.104.112.113 (talk) 19:07, 17 December 2008 (UTC)

The speed of sound is inversely proportional to the square root of the density, so as density approaches 0, speed approaches infinity. Of course the medium cannot be changed in this way without changing the stiffness, so your result will differ. Graeme Bartlett (talk) 04:54, 17 December 2008 (UTC)


 * Also, as the density approaches 0 (think of very diffuse gas, approaching vacuum conditions), the material will no longer sustain a sound wave, and the pressure and energy wavefront will lose coherence and dissipate. Nimur (talk) 15:39, 17 December 2008 (UTC)

plants
because plants breath co2 like we breath o2, would adding co2 to a plant in.....(lets say a box)...make it grow faster? —Preceding unsigned comment added by 76.14.124.175 (talk) 04:21, 17 December 2008 (UTC)


 * Yes, and in fact glasshouses often have CO2 added in the form of decomposing organic matter to make the plants grow quicker. Graeme Bartlett (talk) 04:44, 17 December 2008 (UTC)


 * (edit conflict) A news release from Stanford University dated December of 2002 indicates that it's not that simple. Yes, it seems that increasing CO2 increases growth, all else being equal, but in combination with increased temperature, water, or soil nitrogen, an elevated ambient level of CO2 can actually retard growth. --Milkbreath (talk) 04:50, 17 December 2008 (UTC)


 * Yes, but only if lack of CO2 is the limiting factor holding back growth. If lack of water, sunlight, or minerals are the issue, then more CO2 won't help until those other shortages are addresed. StuRat (talk) 15:01, 17 December 2008 (UTC)


 * Also keep in mind that plants only use CO2 during photosynthesis. They produce CO2 during regular Cellular respiration.  Increased CO2 wouldn't be useful at night, for example.  Some plants have evolved special carbon fixation cycles that allow the photosynthesis to use CO2 produced by respiration. (See CAM photosynthesis and C4 carbon fixation)--  JSBillings  16:11, 17 December 2008 (UTC)


 * Certainly it can help - but as JSBillings says - plants only consume CO2 during daylight - in the dark, they actually PRODUCE CO2 - just like us animals. Another issue that's come up as a part of the global warming debate is that it seems that quite often the weeds that compete with our crop plants do even better with increases CO2 than the plants we're trying to encourage - so I guess in some situations, it might result in a shift in the 'balance of power' between competing species that could be counter-productive. SteveBaker (talk) 19:28, 17 December 2008 (UTC)

Indian apple
I've been trying to find out the scientific name for the spiny fruit shown in this picture (bottom right side, on the table). In Tonga, it's known as the "Indian apple", but I can't find any references explaining what the scientific name is, or if it has any other names. Anyone know the answer? Thanks! ··· 日本穣 ? · Talk to Nihonjoe 05:54, 17 December 2008 (UTC)

Still unclear, Julia Rossi (talk) 09:40, 17 December 2008 (UTC)


 * Oh, bottom right on the table is a "star fruit" or Carambola... as per the handwritten name tag, : ) Julia Rossi (talk) 09:42, 17 December 2008 (UTC)


 * Yeah, I read that tag, but it's not by the fruit in question (as you noticed below). Thanks, though. :) ··· 日本穣 ? · Talk to Nihonjoe 03:47, 18 December 2008 (UTC)


 * I think it is a Annona muricata, which is a type of custard apple. (another picture). Apparently, it is called apele ‘initia in Tonga, which could have been vulgarized into "Indian apple" (speculating here!) Abecedare (talk) 10:07, 17 December 2008 (UTC)


 * That's the fruit. I think you are probably right about the "Indian apple" part. Thanks! ··· 日本穣 ? · Talk to Nihonjoe 03:47, 18 December 2008 (UTC)


 * Julia, I don't think you were seeing the whole image. --Sean 15:30, 17 December 2008 (UTC)
 * Arg, you're right, Sean – there's nothing like having the whole picture. Annona M. it is. :-P Julia Rossi (talk) 21:02, 17 December 2008 (UTC)
 * You might be interested in the excellent image zoom extension to Firefox. --Sean 15:12, 18 December 2008 (UTC)
 * Thanks for the tip. Just upgraded firefox and it looks to have a built in pic zoom using the text-shrink keys (apple -). That's better! 8-) Julia Rossi (talk) 08:42, 20 December 2008 (UTC)

Hiroshima Peace Memorial
I just wanted to be clear on the reason that the building that became the Hiroshima Peace Memorial survived the A-bomb as well as it did.

The story I was given was:
 * The building was almost directly below the hypocenter.
 * Therefore the shockwaves that hit the structure were traveling almost vertically.
 * Therefore its horizontal structures (e.g. ceilings) were largely destroyed while its vertical structures (e.g. walls) were largely preserved.

Is this correct? Joaq99 (talk) 11:20, 17 December 2008 (UTC)


 * That sounds reasonably correct, but keep in mind that only a small portion of the building actually "survived as well as it did" (compare before and after). It's also worth noting that reinforced structures can do okay depending on the conditions of the shock wave. If it had been a wooden house that had been right underneath, it would have been smashed flat, no problem. --98.217.8.46 (talk) 14:48, 17 December 2008 (UTC)


 * The dome was 150m from the hypocenter and the bomb was detonated 600m above ground. This gives a blast 15 degrees off vertical. But the article links to this page: [] It states that the dome and surrounding ruins was part of some larger complex, so even close to the hypocenter, walls were not generally spared. You'd have to look at more ruins to say if they'r statistically more likely to withstand at the hypocenter, but remember that a nuclear explosion also creates a strong "backdraft" feeding the rising mushroom stem. In films from nuclear test explosions, it can be seen that this backdraft is almost equally devastating on buildings and it probably didn't have the exact same direction as the blast. So my answear would be no, the explanation you got is not quite good enough. EverGreg (talk) 14:51, 17 December 2008 (UTC)


 * The explanation seems a bit ad hoc. Was it based on any computer simulations of how the blast would affect the structure, based on the actual plans? Edison (talk) 15:32, 17 December 2008 (UTC)


 * Could be an example of survivor bias here. Some building has to be the closest surviving building to the hypocenter; people want to believe this is due to something other than pure chance (or, at least, the complex and unpredictable interaction of many different factors), so they invent various post hoc explanations. Gandalf61 (talk) 13:56, 18 December 2008 (UTC)


 * That building is by no means the only one to survive in similar condition (see this, this, and this) - many modern iron, steel, and concrete buildings "survived" (in that they remained recognisable husks). The reason that so few buildings are evident in the post-bomb photographs is because, like the centres of most Japanese cities of the era, most buildings were constructed of wood. By this late in the war the centres of most cities had been gutted by bombing or firebombing (and most of their stock of wooden buildings consumed); Hiroshima and Nagasaki were spared at the behest of the Conant committee (the manhattan project's political sponsors) which had explicitly asked Curtis LeMay to refrain from bombing either city (see Atomic bombings of Hiroshima and Nagasaki).  So we can attribute the extremity of the devastation in both cities to the incendiary effect of both bombs. The memorial building, and those few like it, survived firstly because they were more modern and more solidly constructed (so they withstood the pressures) and secondly because they were constructed of materials that didn't burn. 87.114.130.249 (talk) 18:52, 18 December 2008 (UTC)

What is the difference between a male seed and a female seed?
''Please note, I found this question at CAT:CSD/What is the differance between a male seed abd a female seed?. I've deleted the page, but decided to AGF and redirect the questioning to here. Below is the text from that deleted article -Andrew c [talk] 15:38, 17 December 2008 (UTC)''

Does anyone know what the differance between a male seed in an orange and a female seed in an orange? please write something about it on wikipedia please I need to know because I am trying to grow an Orange tree so please help if you can and i will only take answers that are the most relible to me so please send in thanks alot from your fellow Wikipedia user.

Susan E. Summers User:Dumplin97


 * Believe it or not, we have a pretty good article on this. See Plant sexuality.  Good luck!  --Jayron32. talk . contribs  21:06, 17 December 2008 (UTC)
 * There's no such thing as a "female" or "male" seed.  bibliomaniac 1  5  21:25, 17 December 2008 (UTC)
 * Are you sure that's that true? Some Dioecious plants (Holly, for example) have distinct male and female plants - surely they grew from distinctly male or female seeds?  Certainly SOME plants (Monoecious and Hermaphrodite) have just one 'sex' that has both male and female flowers - in THOSE cases, there is presumably no sexual difference evident in the seeds. (But I could be wrong - I'm not an expert!) SteveBaker (talk) 22:00, 17 December 2008 (UTC)
 * Anyone care to guess what the top results are when you search for male seeds or female seeds? In that case, there is no apparent way to tell the seeds apart simply by looking at them (can't say I'm surprised. Actually I'd be more surprised if the opposite is true) Nil Einne (talk) 13:09, 18 December 2008 (UTC)
 * That doesn't sound all that different from animal development, where physical differentiation between the sexes actually comes quite late to the game. It can be several weeks in humans before physical differences exist.  --Jayron32. talk . contribs  19:24, 18 December 2008 (UTC)
 * Indeed - I'd be very surprised if you could tell the difference between a boy holly-tree seed and a girl holly tree seed without doing some kind of genetic testing on them. However, I believe that a genetic difference must exist inside the seed for these Dioecious plants - it just doesn't manifest itself as a difference in the appearance of the seeds. SteveBaker (talk) 20:43, 18 December 2008 (UTC)

Researching Invention for child's project
My daughter has to create an invention that will help humanity etc. She wanted to create some kind of shield that people could buy to add to their existing outdoor lighting to block the light so that sea turtles would not be drawn to it, yet allow the lighting to still shine on the deck etc where people would only see it. Has this been already done? I have searched and found lights that come with special lighting for sea turtles but have not been able to find out if an actual shield for garden or light posts have been invented.

Thank you for your help.

Dee Ingham —Preceding unsigned comment added by 76.97.57.168 (talk) 17:20, 17 December 2008 (UTC)


 * Use something like this to determine what frequencies of light the sea turtle can see. Then, get a filter to block whatever frequencies the sea turtle sees.  The light will be very dim on those frequencies, but bright in all others. --  k a i n a w &trade; 17:46, 17 December 2008 (UTC)


 * You might also investigate the various efforts made by astronomers to avoid light pollution. The International Dark Sky organization (http://www.darksky.org/) might also be a source of relevant information.  Click on the 'approved fixtures' button to see a list of companies that make outdoor lighting that is less polluting.  There are many things people can do to help - certainly employing reflectors behind the bulb to direct the light only in the direction it's needed.  Using MUCH dimmer bulbs (our eyes will adapt perfectly well to seeing by candle-light - we don't need multiple 100W bulbs).  Use light absorbing (ie flat-black) paint in areas where the light strikes but is not needed - avoid reflections in water surfaces, etc. SteveBaker (talk) 19:22, 17 December 2008 (UTC)


 * Typical office lighting where I live is ceiling fixtures consisting of a box with two or four fluorescent tubes inside, and a sheet of translucent plastic that keeps you from seeing the bare tubes but lets the light out freely. However, there is an alternative version where the plastic sheet is replaced with something that only lets light out in a narrow range of directions, the light is concentrated downward on the area below the fixture and if you look at the fixture from another part of the room it does not look bright.  As far as office lighting is concerned I personally hate this effect (along with the notion that it is all right to use less light overall), but it sounds exactly like what you want for this purpose.  Unfortunately I don't know what these fittings are called or even exactly how they work: my impression is that the sheet is constructed from of a large number of small lenses, each maybe 1 or 2 cm across.  --Anonymous, 21:44 UTC, December 17, 2008.

Disseminated Intravascular Coagulation Question
Is there any connection between DIC and long past surgeries?

The case I'm concerned with most likely got started with vasculitis (thank you, Wiki community for the information by the way) but another party was told the DIC resulted from a surgery 20 years ago. The surgery was a vascular transplant (femoral artery was replaced with anothe vessle from the patient). We can find information on the causes of DIC but nothing yet on association between DIC and past surgeries. Thank you for any help in understanding this. - Jill —Preceding unsigned comment added by 71.193.169.115 (talk) 17:48, 17 December 2008 (UTC)
 * One strong risk factor for DIC is major trauma, infection or sepsis. Surgery has the possibility to cause all of these but only you will know if it applies to your case or not. The supposed pathophysiology of this is the release of inflammatory or infected tissue into the blood circulation triggers the cytokine network and coagulation pathway. So in conclusion, there could be a link, but I'm pushing the boat out a bit far speculating whether this is the cause or not. —Cyclonenim (talk · contribs · email) 19:37, 17 December 2008 (UTC)


 * There's no significant association between DIC and a history of long-past surgery. One might argue that DIC can be a reaction to a foreign body surgically implanted into someone in the distant past, but the surgery you mention above doesn't seem to fall into that class of operation (it used the patient's own tissue rather than, say, a dacron vascular graft.). - Nunh-huh 19:42, 17 December 2008 (UTC)
 * Agree with Nunh-huh - Draeco (talk) 01:07, 18 December 2008 (UTC)

Helium latex Balloon Questions
How much does a standard (in the US) latex balloon weigh, what is a safe volume to fill it up to, and if I fill it up to that volume with the type of helium typically used at dollar stores that sells balloons, what would be the amount of weight that it could lift (or at least cancel out so that it would just float) before it falls?

Any good guesses?

A few of the things we need to know to answer this question is-

1) what is the average volume of a latex balloon in the US, and

2) how much weight does helium offset.

Scofield Boy (talk • contribs)y 19:40, 17 December 2008 (UTC)


 * 2 is easy: just check the relative densities of helium and air. At STP, you get about 1.1 g/L of lift in dry air.  Since volume increases more quickly than surface area, larger balloons will have more lifting power.  However, I've got no idea what an average latex balloon's volume is (or even what a latex balloon is).  Do you mean the basic inflate-via-lung-power balloons used at birthday parties and the like? &mdash; Lomn 20:45, 17 December 2008 (UTC)


 * Yeh, that's what I mean. The rubber-like ones.  Scofield Boy 21:27, 17 December 2008 (UTC)  —Preceding unsigned comment added by Scofield Boy (talk • contribs)


 * It may not be as simple as Lomn indicates. I've read that "the type of helium typically used at dollar stores that sells balloons" is not pure helium but is diluted with air, because this is cheaper and provides sufficient lift to keep the balloon off the ground (for some hours until the gas leaks out, that is).  However, I don't have a reliable source to cite for this.  --Anonymous, 21:48 UTC, December 17, 2008.


 * Also, Lomn's estimate for the lifting power is incorrect. The pressure of the gas inside the balloon is higher than the ambient air pressure because it has to counteract the inward force of the rubber.  One reason that the mylar foil balloons work so well is that the balloon itself doesn't have to be stretched much - so lower pressure helium (and therefore, LESS helium) may be used - both saving money and increasing lift
 * SteveBaker (talk), 17 December 2008 (UTC)


 * Lomn's estimate is plenty good enough for back-of-the-envelope work, though. The excess pressure inside a typical latex balloon is only about ten percent over ambient atmospheric pressure: .  Ten percent higher helium pressure makes for about a 1.5% decrease in lifting power per unit volume &mdash; barely noticeable.  (Since Lomn only gave his answer to two significant figures, the effect of elevated pressure would probably be lost in the rounding....)
 * That's not to say that there aren't other benefits to the mylar balloons. The balloon material is typically lighter, giving more apparent lifting power.  I believe that metallized mylar is less permeable than latex is to helium gas, giving the balloon a longer floating lifetime.  Since the helium isn't under excess pressure, you do still save about 10% on your filling costs, and the balloon doesn't make a scary noise if it bursts.  Finally, a lot of people have a natural latex allergy while mylar is hypoallergenic. TenOfAllTrades(talk) 23:09, 17 December 2008 (UTC)


 * From personal experience as a kid, a freshly-filled birthday-party balloon has a net lift of between 1 and 4 grams, decreasing to 0 over the course of about 48 hours. --Carnildo (talk) 22:51, 17 December 2008 (UTC)


 * Lift is a force and should be measured in newtons (or pounds), not in grams. The statement "a balloon has a net life of between 1 and 4 grams" is incorrect.  That balloon has enough lift to maintain a 1 to 4 gram object at equilibrium (or to accelerate it upward at some approximately fixed acceleration).  Nimur (talk) 16:23, 18 December 2008 (UTC)


 * Thanks for that: that knowledge might come in handy. But the technicalities really don't matter much to me. Carnildo statisfyed my question.  I was mostly interested in how practical it would be to lift a certain weight wigh a balloon, and his personal experience was excactly what I was looking for.    Scofield Boy (talk • contribs) 19:25, 19 December 2008 (UTC)


 * Pounds and grams are both mass units in strict usage (contrary to what some of us were taught in school) and both are commonly used as force units (because here on the Earth, in many practical contexts the distinction is not important and it's easier to work with them). --Anonymous, 23:15 UTC, December 18, 2008.

"Good" Chemical
My teacher has assigned our class to write a letter to a company thanking them for using a "good" chemical. Normally I'd rant about how this is forcing a political opinion on someone, but you have to pick your battles. I'm having difficulties finding a suitable example. Does anyone else know of something?Tuesday42 (talk) 20:05, 17 December 2008 (UTC)
 * Everything is a chemical, and an argument could be made for any one of them. What makes a chemical "good" in your opinion? What is something you find useful in your life? What is a time you have chosen one chemical product over another, and why? DMacks (talk) 20:10, 17 December 2008 (UTC)
 * I once read a newspaper article lambasting tinned peaches (or somesuch) for having added chemicals - the one the columnist picked out for especial opprobium was ascorbic acid. DuncanHill (talk) 20:16, 17 December 2008 (UTC)
 * Personally, I would write to my local water authority. Dihydrogen monoxide is a pretty useful chemical, even if it is highly addictive! – ClockworkSoul 20:21, 17 December 2008 (UTC)


 * There are various additives that have value. Calcium in orange juice. Iron in breakfast cereal. Fluoride in water.  Iodine in salt. etc.
 * That would meet the requirement without seeming like a gimmick.
 * Even additives that people complain about usually serve a useful purpose and could arguably be "good". Commercial bread lasts a lot longer in your pantry than freshly baked bread. You could thank them for adding preservatives.
 * That may be the point of the exercise, anyway : To get you to understand that you're not living in a Captain Planet cartoon. Nobody uses a chemical just to be evil, they use it because it serves a useful purpose. So just about any substance ever used by any company ever would qualify. It's all in how you frame it. APL (talk) 20:59, 17 December 2008 (UTC)


 * DMack's is right, you need to define "good" before you can get anywhere. Do you mean useful? Environmentally friendly? Abundant? Cheap to make? Pretty looking? Nice smelling? Once you've done that, you need to decide what you're comparing it to, since any reasonable definition of "good" will be relative. You need to find a company which is using a "good" chemical as opposed to a "bad" chemical which they could have used. --Tango (talk) 21:02, 17 December 2008 (UTC)


 * All of these additives are "good" when considered from one perspective or another - even the melamine that was added to baby formula in China (killing who-knows-how-many kids along the way) - was "good" from the point of view of the evil bastards who added it - it increased the protein content measurement reading and was cheaper than actual protein. From THEIR warped perspective, it was a good additive or else they wouldn't have done it.  No matter what chemical you pick, it's going to be good for some people and bad for others.  Consider vitamin E to heat treated milk to replace the natural vitamin that got trashed when the milk was pasteurized - that's "A Good Thing" for the health of the people who consume milk - but it must increase production cost somewhere down the line - so that vitamin supplement is pushing up the cost of the milk.  People who already get plenty of vitamin E in their diet might well regard the cost of that addition to be "A Bad Thing".  So - you may calm your moral outrage with the knowledge that every single one of the chemicals that are added will be good for some set of people and bad for others...so knowing that, you can just pick one and write the letter. SteveBaker (talk) 21:48, 17 December 2008 (UTC)


 * I dissagree with that fluoride in drinking water is a good thing. A chemical that is only supposed to help your teeth shouldn't have to travel through your bloodstream to get there. New studies have suggested adverse health effects. ~ A H  1 (TCU) 21:57, 17 December 2008 (UTC)
 * Old studies have suggested that too. Which is why we have a whole Water fluoridation article with all sorts of cites:) Any chemical can be problematic, any can be well-intentioned but have what (some, few, many, most, all) (have, do, will someday) deem to be unacceptibly high drawbacks compared to the advantages and available alternatives. Your rationale is either poorly explained or poorly considered among similar routes of administration: "shouldn't have to" only becomes "therefore shouldn't do it" if there's a better way to accomplish the goal. Otherwise people wouldn't swallow antibiotics for localized infections. DMacks (talk) 22:36, 17 December 2008 (UTC)
 * Bah. I just knew someone was going to say that. That's sort of my point. Even the additives that are complained about, and may have side effects, can still be considered "good" because they serve a purpose. So, an easy way to complete the assignment was to pick an additive, more or less at random, look up what it's for, and thank whoever put it there for putting it there. Assignment done.
 * (Of course, Steve took this one step farther and talked about chemicals that kill babies for profit. But no one argued that. Either I'm not very good at communicating my point, or fluoride evokes automatic knee-jerk replies.  Or likely both.  ) APL (talk) 01:41, 18 December 2008 (UTC)


 * DDT has saved millions of lives, and yet water has killed millions more. I'm sure you know which one is a "good" chemical :-D - Running  On  Brains  22:28, 17 December 2008 (UTC)


 * You could write to the Stolichnaya folks and thank them for using ethanol. That's what I'd do. Deor (talk) 22:31, 17 December 2008 (UTC)
 * ... as opposed to using methanol ... 93.132.182.39 (talk) 07:49, 18 December 2008 (UTC)


 * I notice that a lot of the answers above equate 'chemical' (in the context of food) with 'additive'. Everything in your food is a chemical or a mixture thereof.  Write a nice letter to a manufacturer of sugar for giving us sucrose.  Send a note to a table salt company acknowledging their delivery of sodium chloride.  Congratulate your local bread company for their brilliant use of polysaccharides, gliadin, and glutenin.  All those 'natural' foodstuffs?  They're full of evil, dirty 'chemicals' like fructose, or palmitic acid and hydroxytyrosol.
 * Moving beyond the world of foods, my sarcastic side urges you to thank your local fertility clinic for their efforts with deoxyribonucleic acid. TenOfAllTrades(talk) 23:20, 17 December 2008 (UTC)
 * In formal science, it is true that any substance that's made of atoms is a 'chemical'. However, many English dictionaries offer an alternative, less formal definition which is a better fit for what our OP is clearly asking.  Wiktionary (for example) provides three definitions:
 * chemical
 * Any specific chemical element or compound.
 * An artificial chemical.
 * "I color my hair with henna, not chemicals."
 * An addictive drug.
 * We have to assume that this assignment implies the second definition.
 * Personally - I love the elegant definition in the American Heritage Science Dictionary:
 * A substance having a specific molecular composition, obtained by or used in a chemical process.
 * The implication being that it's a chemical if it has a simple, pure composition - so pure, distilled, water is a chemical - but sea water isn't. That's a much better fit to the way most of us use the word.
 * SteveBaker (talk) 23:34, 17 December 2008 (UTC)
 * I was more-or-less imagining a strict reading of the first definition with my answer. (ie: Sugar is a "chemical", but Flour is a substance made up of a multitude of chemicals.) My examples were additives, because it would be weird (to me) to thank a company for some particular chemical unless they were using it specifically and purposely. APL (talk) 01:34, 18 December 2008 (UTC)

Other chemicals to be thankful for : Caffeine, Ethanol. APL (talk) 01:43, 18 December 2008 (UTC)

I apologize for not specifying what I was asking for. The assignment wasn't quite as ambiguous, it wanted a chemical that a company was using for something that most other companies in the same field weren't. As for the political opinion aside, it isn't really evident when you look at the assignment out of context, but this teacher... let's just say I'm looking forward to the end of this term.Tuesday42 (talk) 03:57, 18 December 2008 (UTC)


 * So, to clarify ... you're looking for an example of a company voluntarily switching from some dangerous chemical to a safer chemical that serves the same function even if the safer one is higher cost? APL (talk) 06:19, 18 December 2008 (UTC)


 * How about this? I should caution you, however, that since this article was published the FDA has given its official approval so I'm sure other competitors will jump on the bandwagon.  216.239.234.196 (talk) 13:45, 18 December 2008 (UTC)


 * Have you checked the websites for big chem companies like Dow, Exxon, Oxy or BASF? I'm sure they have numerous press releases touting how they wuv the planet and how they are doing good? Have you seen the "green" Exxon PR commercials lately? --70.167.58.6 (talk) 20:20, 18 December 2008 (UTC)
 * Yeah - "We've found a way to continue to fill the air with Carbon Dioxide even after the oil runs out. Yay!  Gas-to-liquid technology! (Oh - and could you please buy some of our stock because we aren't doing so good now that the price of oil has tanked. K'Thnks!)" ...argh! SteveBaker (talk) 20:36, 18 December 2008 (UTC)

Does anyone else think it's stupid that every definition for the word "chemical" uses the word chemical? Mac Davis (talk) 21:12, 18 December 2008 (UTC)


 * Yeah, that pretty much sucks. The condensed OED, here defines it as "noun a distinct compound or substance, especially one which has been artificially prepared or purified."  There ya go...  --Jayron32. talk . contribs  00:56, 19 December 2008 (UTC)

Evolution of the liver
Are there any clues as to the original function of the liver? How it could have evolved? What changes in the digestive system would have led to the first primitive liver, and what evolutionary advantages the most primitive adaptations to the digestive system on the way to a liver would have have been given the host creature? Jooler (talk) 21:20, 17 December 2008 (UTC)
 * I can't find any references so I'm just going to go on speculation. I think it's likely that in some animal in the past, certain cells started to produce enzymes which broke down certain substances and helped the creature gain an evolutionary advantage by being able to eat something which others could not, because they could not break down that substance. This probably advanced further and further until many enzymes could break down many substances. —Cyclonenim (talk · contribs · email) 22:25, 17 December 2008 (UTC)


 * The wording makes it sound like a homework question. We don't do your homework, but we do try to help with specifics and hints. I'm not a biologist, but here's how I would approach this: Look at our articles on the more primitive animal phyla. Based on that, what simple organs with some functions similar to liver functions arise? After you have found some obvious ones, go "back" to "more primitive" phyla to see if you can find homologus organs. You can probably create a plausible evolutionary path. -Arch dude (talk) 01:07, 18 December 2008 (UTC)


 * I don't get the homework vibe; what red flags do you see? —Tamfang (talk) 20:02, 28 December 2008 (UTC)


 * The vertebrate liver evolved from the hepatic diverticulum of the gut of an amphioxus-like ancestor during early chordate evolution. The amphioxus hepatic diverticulum has been found to synthesize several substances that are similarly synthesized in the vertebrate liver. - Nunh-huh 01:20, 18 December 2008 (UTC)

@Arch dude. It's not homework. Its a very a long time since I left school. Jooler (talk) 15:20, 19 December 2008 (UTC)

Copurification, Pull-down assays, and co-immunoprecipitation
What is the relationship of these three terms? My best guess so far is that copurification = pull-down assays, while co-immunoprecipitation is a particular type of copurification/pull-down assay (as well as a type of immunoprecipitation). Is that at all accurate? Unfortunately copurification is currently a red link, and pull-down assay just redirects to immunoprecipitation even though it is mentioned nowhere in the article. Kaldari (talk) 23:20, 17 December 2008 (UTC)


 * Looks like your red has magically turned to blue. Isn't it great when a question has positive consequences? --Scray (talk) 12:18, 18 December 2008 (UTC)

Unfortunately, the link doesn't really address the OP's question. A "pull-down assay" is a generic term for a biochemical protein purification in which a target protein is isolated from a soup of other proteins (usually some type of cell lysate or extract).

"Immunoprecipitation" implies that a specific antibody against the target protein is used to achieve the "pull-down".

"Co-immunoprecipitation" is when you look for other proteins (or in the case of chromatin immunoprecipitation, a piece of DNA) that also purify along with your targeted protein, thus implying a physical interaction between the two entities.

There are also non-antibody means of achieving a "co-purification" including: Fusion proteins can be engineered to contain the preferred tag -- this is then expressed in bacteria, yeast or cell culture to be used in a "pull-down" experiment to see what else binds to the fusion protein. ---Medical geneticist (talk) 00:28, 19 December 2008 (UTC)
 * His-tag, which can be purified with nickel-coated beads
 * GST-tag, which can be purified with glutathione-coated beads
 * Maltose binding protein, which can be purified with maltose-coated beads
 * Thanks. That is very helpful information. Kaldari (talk) 20:26, 19 December 2008 (UTC)