Wikipedia:Reference desk/Archives/Science/2011 March 9

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March 9

dust mite covers and bed bugs

Will a special mattress cover designed to keep out dust mites (for those who are allergic) also keep out bed bugs, so that if bed bugs appear in the apartment, the person who lived there wouldn't have to throw out the mattress after eliminating the bed bugs? I guess I want to find out if a dust mite mattress cover could be part of preventative measures. I'm not asking medical advice. Thanks, 74.14.13.241 (talk) 00:02, 9 March 2011 (UTC)

Well it might act as a partial barrier, but bed bugs are particularly resourceful in gaining access to the sleeping body. There are accounts of them climbing up the bedroom wall and jumping off onto the bed, having calculated the appropriate parabolic trajectory! (No, I don't believe that, but I do believe that they will find their way round most obstacles to gain access to their food.) Treatment with insecticide is much more effective, but even that is not guaranteed. Dbfirs 00:11, 9 March 2011 (UTC)

Are you actually asking if the cover will keep them in? i.e. the bed bugs will be locked under the cover and can't reinfect the room? Assuming you kill all the ones in the room? It seems unnecessary to me - killing the bugs in the mattress is pretty easy compared to killing the ones hiding in the room. Also they can live for a year without food, even under that cover. As a general answer, the cover will do nothing, since the bed bugs can live in the room and then walk over to the person on the mattress. (Unlike mites they don't live inside the mattress, they hide on the mattress in seams.) And they can also hide in cracks in the floor or walls, etc. Ariel. (talk) 00:58, 9 March 2011 (UTC)

Antimatter explosion

Is it possible to determine/make an educated guess as to what a (hypothetical) antimatter explosion in air would actually look like? Would it appear similar to a nuclear bomb going off - but larger for the given mass of 'explosive' material? Would there be a mushroom cloud? Would the explosion be the same colour? --Kurt Shaped Box (talk) 00:25, 9 March 2011 (UTC)

It should look more or less like a nuclear explosion, which itself (from a superficial point of view) is just the creation of a gigantic expanding ball of heated air. The mushroom cloud is caused by it being close to the ground, and is not unique to a nuclear explosion (any explosion of a sufficient size will cause one if it is close enough to the ground to suck up dirt). I don't know about the color — nuclear explosions generally just look like the standard black body spectrum (a ball of fire), but you do get weird cloud colors because of the radiation involved, ionization of the air, etc. I don't know what kinds of things you'd get from an antimatter explosion but I'd imagine they would mostly look pretty similar, since the essential thing responsible for the appearance of a nuclear explosion (lots of heat energy all at once) is essentially the same. (I would not expect all of the effects to be the same, mind you. But you can't see neutrons, for example, so the fact that nukes let out gobs of neutrons doesn't really change how they look.) --Mr.98 (talk) 00:31, 9 March 2011 (UTC)

As a point of clarification, while a nuclear mushroom cloud can contain particulate material pulled up (and/or vaporized) from the ground, this is not required to form the cloud. When warm, moisture-laden low-altitude air is rapidly lifted up by the fireball and then cools, fine droplets of water condense out, forming the cap of the mushroom. (Even in the absence of soil and dust from the ground, the vaporized remains of the bomb and its casing rapidly condense to provide a rich supply of condensation nuclei for water droplet formation.) While very-high-altitude bursts won't form explosions, it is because they are unable to draw up enough warm, humid, air from lower altitudes—not because they can't suck up dirt. TenOfAllTrades(talk) 01:12, 9 March 2011 (UTC)

Well, you have to suck up something to get that mushroom stem. If you have an aerial burst (not even high altitude), you get a cloud, but not a "mushroom", like this.--Mr.98 (talk) 12:41, 9 March 2011 (UTC)

If you are reacting exactly equal amounts of the same element (rather than anti-matter in air) it will make almost 100% gamma rays (assuming you can mix the two fast enough, which is NOT easy). That type of explosion will not look like a normal explosion. It will ionize air to a tremendous distance, and will look more like an aurora than a fire. If you just drop anti matter through the air it will look either like a meteor, or a series of explosions (probably depending on how fast it moves through the air). It won't explode all at once, since the initial explosion will push away all the matter, leaving nothing to react with the antimatter. The explosion will then stop, letting matter back in, and it will cycle. If it's moving fast, then the fresh air arriving at the front will constantly provide matter to react with, and it will leave a trail of light. (But because most of the energy is being released in the front, it will rapidly slow down.) I am assuming it will take the form of fire because the two elements being reacted are not the same, so you have residual particles to carry energy as heat. If things match up however (perhaps you pick anti-silicon which has twice the atomic number of nitrogen in air), then you'll get mostly gamma rays and bursts of auroras (aurorae?). Ariel. (talk) 01:08, 9 March 2011 (UTC)

Are you sure it would look like an aurora? What I'm imagining would happen is that said gamma rays would collide with said air and heat them up (e.g. via Compton scattering), making it look like a pretty regular explosion to the naked eye. Similarly the bulk output of energy from a nuke is in the form of neutrons and rapidly moving fission products, which looks, to the naked eye, just like fire when it is done in an atmosphere. The only place you'd notice the difference is if you did it in a vacuum, with a nuke. But I'm not a physicist; this is just my understanding of the visible effects. --Mr.98 (talk) 12:41, 9 March 2011 (UTC)

No, I am not sure (I never got a chance to test the one we built in StuRats lab). But Compton scattering does not heat up air - rather it makes light that looks pretty much like an aurora. And unlike a nuke there aren't any neutrons or other particles left to cause heat effects. It's all neutrinos and photons. Ariel. (talk) 13:15, 9 March 2011 (UTC)

That's completely wrong. Gamma rays don't release their energy by Compton effect. They release it by pair creation that produces a particle shower which efficiently delivers the energy to the medium. I don't think your aurora-like explosion makes any sense whatsoever. The result would be very much like a nuclear explosion. Dauto (talk) 14:33, 9 March 2011 (UTC)

I'm not convinced. Because you have anti-matter (either from the original or the pair production) you can't have a proper particle shower - the shower is annihilated. Maybe some of it heats up the matter, but most will end up as gamma rays again. As further evidence, I heave never read anywhere (and I just checked again) that actual gamma rays from Gamma-ray bursts cause particle showers. If they did then the Compton Gamma Ray Observatory would not need to be in space, they could do it on the ground. Cosmic rays, i.e. protons do. But not gamma rays. Ariel. (talk) 21:51, 9 March 2011 (UTC)

You got it upside down. The observatory must be in space because the gamma rays are effectively blocked by the atmosphere. Read Gamma ray#Matter interaction for more details. notice that pair production becomes the dominant mode of interaction with matter for gamma rays with energy above 10 MeV. A proton-antiproton reaction releases roughly 2000 MeV. The point is moot because most of the energy is released in mesons, not gamma rays, and mesons interact with matter even more promptly than gamma rays do. Dauto (talk) 16:34, 11 March 2011 (UTC)

For further evidence, read Gamma-ray astronomy. Read the caption of the first picture which states "Gamma rays are absorbed by the atmosphere and must be studied from a space telescope.". Dauto (talk) 19:40, 11 March 2011 (UTC)

When I wrote my question, I was thinking something along the lines of an antimatter bomb of comparable physical size to that of a nuke, dropped on an enemy city from a B-52 (or whatever). I suppose that merely allowing the bomb to hit the ground and break open, exposing the antimatter (hitherto contained by a magnetic field in vacuum) to the air would be sufficient for the purposes of mass destruction? That said, what physical effect would a bomb that worked by colliding an equal quantity of elemental matter and anti-matter have on a city and its population - supposing that this massive 'gamma aurora' (and little else) was produced upon detonation? --Kurt Shaped Box (talk) 01:32, 9 March 2011 (UTC)

See Gamma-ray burst. It would sterilize all life. It probably would not do a lot of destruction, because while all those gamma rays eventually end up as heat, they travel quite far and the energy would be spread out. The ground right under the bomb would get hot, but again, the gamma rays would travel deep underground. Note: I'm speaking relatively - it would still be a massive bomb, just not as big as the energy calculations might lead you to expect. If I were designing an anti-matter bomb I would make two types. In both of them I would place the anti-matter in many small containment structures, and place matter right near each structure. The idea it to try to get the two to mix as thoroughly and rapidly as possible. In one type that would be all. I would let them mix, and let the gamma rays sterilize all life. In the second type I would surround the bomb with a tamper designed to absorb as much gamma ray energy as possible. This will turn it into heat and cause a massive physical explosion. This is good for attacking fortifications. StuRat can I join your lab? Ariel. (talk) 02:05, 9 March 2011 (UTC)

Sure, I'm always looking for new henchmen, since they occasional make mistakes and thus must be liquidated. StuRat (talk) 04:15, 9 March 2011 (UTC)

Rough plot of Earth's atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation, including visible light.

I'm not so sure about your speculation here, Ariel. The graph at right suggests gamma rays are absorbed by (transfer their energy to) the atmosphere pretty well. It's hard to say exactly what would happen, but I see no reason to doubt an antimatter weapon would be far more destructive by weight than a thermonuclear weapon no matter where or how you set it off. Please cite a source if you really believe otherwise.WikiDao ☯ 02:44, 9 March 2011 (UTC)

Well by weight no question at all. I was saying by energy. By total energy released, an anti-matter bomb would be less effective than a nuclear one, which in turn is less effective than a chemical bomb. But of course the available energy is far higher so that outweighs it. As far as the graph, that's for the entire depth of the atmosphere. Gamma rays are able to travel in air. Ariel. (talk) 02:58, 9 March 2011 (UTC)

This seems to imply a kilometer for gamma rays, which I guess isn't much. Ariel. (talk) 03:10, 9 March 2011 (UTC)

Your assumption that it's almost 100% gamma rays is incorrect; a significant amount of energy will be carried away by neutrinos. Nucleons and anti-nucleons create pions. While the neutral pions decay largely into gamma rays, the charged pions decay mostly into muons and muon antineutrinos; the muons in turn decay into muon neutrinos, electron antineutrinos and electrons. Icek (talk) 03:29, 9 March 2011 (UTC)

Addendum: And I forgot the positively charged pions, which decay into antimuons and muon neutrinos; the antimuons decay into muon antineutrinos, electron neutrinos and positrons, which can annihilate with the electrons. But the neutrinos will carry away some energy, as they hardly interact with matter. Icek (talk) 03:32, 9 March 2011 (UTC)

Our Antimatter weapon article says: "The effect of a large antimatter bomb would likely be similar to that of a nuclear explosion of similar size." WikiDao ☯ 01:41, 9 March 2011 (UTC)

That is correct. As Icek explained above, the matter-antimatter reaction produces mostly mesons, not gamma rays, and as I explained further above, gamma rays are absorbed by air just fine. Dauto (talk) 14:49, 9 March 2011 (UTC)

As others have said, the explosion should look similar to a nuclear explosion, but if you want a different looking explosion, an impact from a large object like an asteroid should produce a different looking explosion since the fireball would have a tendency to be sucked up into the ionized wake created by the asteroid as it traveled through the atmosphere. See, http://www.stardestroyer.net/Empire/Essays/Planet-Killers.html#Asteroid ScienceApe (talk) 18:29, 9 March 2011 (UTC)

Gamma ray emissions have already been detected at high altitudes in thunderstorms. ~AH1^(TCU) 02:31, 13 March 2011 (UTC)

Aftertaste

Why does chocolate have such an unpleasant aftertaste? Some other sweet foods have similar, but not quite as strong, aftertastes, as well. --75.15.161.185 (talk) 01:07, 9 March 2011 (UTC)

Try a different brand of chocolate. Also, personally, if I eat too much chocolate in a short period of time it starts tasting sour, so perhaps let your tongue rest first. Ariel. (talk) 01:13, 9 March 2011 (UTC)

But it's happened with other foods too, not just chocolate. Most foods with sugar or (to a lesser extent) starch also seem to have a bad aftertaste. Do the carbohydrates break down into acid? --75.15.161.185 (talk) 01:18, 9 March 2011 (UTC)

I find that an aftertaste is usually a sign that they added some nasty chemicals. Read the ingredients. If there are things in the list you can't pronounce, try a different brand without all the nasty added chemicals. StuRat (talk) 03:56, 9 March 2011 (UTC)

I can't rule out that some (thin) person gets an aftertaste from sugar. But U.S. chocolate lovers should beware: believe it or not, there are grinches making chocolate out of castor oil! (See PGPR) I'm talking about the main brands you see in the store aisle - check the ingredients.

Actually, what I really wonder is, what do they do with all the leftover ricin? Where do they farm all those plants? They must have accumulated enough to wipe out a large country by now, if they didn't throw it all out... Wnt (talk) 05:22, 9 March 2011 (UTC)

It really depends what kind of "unpleasant aftertaste" you're talking about. Cacao itself has a complex and bitter flavor, and so high quality chocolates with a high percentage of cocoa mass have a sharp bitterness that is considered part of the complexity of the flavor. Milk chocolate, especially of the Hershey's variety, has a somewhat sour taste which is considered characteristic of its process of production. Some of this is just how chocolate tastes — it is not a simple "sweet" flavor, but a mix of lots and lots of complicated (natural) chemicals that makes cacao such an interesting appeal flavor. --Mr.98 (talk) 17:31, 9 March 2011 (UTC)

I get unpleasant aftertastes and sometimes tongue pain from various foods (chocolate being one of them). But, I have geographic tongue, so it is just a side effect. If I continue to eat bad foods, I get tiny white bumps all over my tongue and it takes many hours for them to go away. -- kainaw™ 17:40, 9 March 2011 (UTC)

The story I heard was that American chocolate has a bad taste because the milk supplied by rail to an early factory would go rancid on its way there. This bitter taste became stuck as the flavour Americans expected in chocolate. European chocolate does not have a bitter taste, although european brands sold in North American have the bitter taste that Americans expect. I remember when out of curiosity I bought a Hershey bar being sold as a novelty here in the UK - I thought it had gone bad. I've never seen any other American chocolate being sold on this side of the Atlantic. 92.28.254.54 (talk) 13:36, 10 March 2011 (UTC)

That sounds plausible (an early processing method introduced a bitter flavour that is now expected by the consumer in modern equivalents). Unlike any other country I've been to, I find it more difficult in the US to find chocolate I like. Hershey's being particularly nasty I agree. M&M's are ok though and seem to taste the same as they do in the UK. Best place for chocolate? Belgium. Even the cheapest most generic chocolate based confectionary I could find (bought in their equivalent of Aldi or Lidl) was absolutely gorgeous! 213.120.209.248 (talk) 14:45, 10 March 2011 (UTC)

The rancid milk sounds like an urban legend, but Hershey is famous for having developed a cheap alternative process. There are many steps involved in making a good chocolate - the kind of cocoa bean, the kind of processing, and the ways in which greedy manufacturers try to replace the cocoa butter; whenever possible, American manufacturers choose the worst possible option. I suppose the real mystery is why Americans haven't learned to import chocolate like we do everything else. Wnt (talk) 21:04, 10 March 2011 (UTC)

I believe cocoa is bitter to start with, then some is "processed with alkali", which can only make it worse. It's only by adding massive quantities of fat and sugar to a tiny amount of cocoa that it becomes good tasting. StuRat (talk) 05:34, 12 March 2011 (UTC)

Activity series

Hey all. I am a first-year chemistry student and right now we are studying single-replacement reactions (example: AgNO₃+Na→Ag+NaNO₃, Na "replaces" Ag) and predicting products. In the reactivity series the teacher gave us, lithium is listed first before all the other metals; this version is also widespread around the internet ([1], [2], [3]). But, why is lithium above sodium and potassium? I thought metals lose electrons more easily as one moves down the table, and thus potassium should be more reactive than sodium should be more reactive than lithiu,m, and a professional chemist concurs with my reasoning. However my teacher insists her table is correct. Who is right? Thanks. 72.128.95.0 (talk) 02:28, 9 March 2011 (UTC)

Reactivity series has a quite different order. It also mentions that there are three different ways to define the order, so perhaps that explains the difference. (The article should really clarify which order the chart at the top uses, and ideally include 3 charts, one for each.) Ariel. (talk) 03:30, 9 March 2011 (UTC)

Equivalence at Inflection

Hello. Why is the equivalence at the point of inflection on a titration curve? Thanks in advance. --Mayfare (talk) 06:42, 9 March 2011 (UTC)

Tagishsimon (talk) 11:37, 9 March 2011 (UTC)

When you have a neutral solution and you start adding 3M base, the solution becomes basic, but no matter how much of the base you add, the solution will never exceed 3M - the more you add, the slower it approaches that concentration. Similarly, you can add a 3M acid and watch the solutions pH lower, but never quite reach that of the original acid. Titration is taking this process in reverse, so the equivalence point is also the point where adding just a bit of acid or base makes the largest change in pH - the change slows down from there - hence the point of inflection. SamuelRiv (talk) 19:45, 10 March 2011 (UTC)

aransremen

aransremen Penulisan lagu untuk menyingkat APA Yang disebut bertujuan Penulisan? —Preceding unsigned comment added by 118.97.15.21 (talk) 10:52, 9 March 2011 (UTC)

Google translate reckons this is Indonesian, and translates it as "aransremen Writing songs to abbreviate the APA The so-called -objective writing?" --Tagishsimon (talk) 11:37, 9 March 2011 (UTC)

There is a Indonesian reference desk. 118.97.15.21 might be better asking there. Or, if he can write in English, ask on the Humanities desk if the question is about music. CS Miller (talk) 12:35, 9 March 2011 (UTC)

Ah. The Indonesian desk appears not to be used often. CS Miller (talk) 12:38, 9 March 2011 (UTC)

It sounds like the question is something like what's the purpose of abbrevating/condensing song arrangements but I'm not really sure. Although I don't speak Indonesian it's not that dissimilar from Malay and while my Malay isn't that great, the grammar and sentence structure seems wrong. It doesn't even seem like the sort of informal language you may expect on the internet, it's almost like half the question is missing. BTW aransremen probably means wiktionary:aransemen and I'm pretty sure the apa is probably just wiktionary:apa i.e. what. I'm not sure why the 'yang' (that/the) and 'penulisan' (writing) are capitalised either. Nil Einne (talk) 14:11, 9 March 2011 (UTC)

Life expectancy according to age

Is the life expectancy is 80 years, what can an 80 years old expect? 80.58.205.34 (talk) 12:56, 9 March 2011 (UTC)

The article on Life expectancy might be reasonably useful for you to look at, but the article on Life table may be even more so (and the pictures and graphs used there-in). If I am reading the table correctly on the 'Life table' article, then it suggests that if you were a 66-67 year old living in the US, you would have a 0.01624% chance of dying before your next birthday, and would be expected to live for a further 17.7 years. I know that you asked specifically about somebody at age 80, but the table only goes to the 66-67 range.

Also, I believe that in the context of your question, the life expectency of 80 years is the life expectency at birth, not at the point when somebody is 80 years old. Hope that helps to a certain extent. Darigan (talk) 13:07, 9 March 2011 (UTC)

Yes, I supposed that the life expectancy is at birth, not when you turn 80. 80.58.205.34 (talk) 13:26, 9 March 2011 (UTC)

Hi again, as a further reference - There is a complete table here http://www.ssa.gov/oact/STATS/table4c6.html (goes up to 119 years old) that gives the expected life expectency for US males and females from ages 0-119. So, a direct answer to your query - In the US, 80 year-old-males have a life expectency of 87.78 years (At birth it is 75.1), and females of 89.33 (at birth, 80.21). Those tables are quite interesting, thanks for asking that question (I wouldn't have come across them if you hadn't). Darigan (talk) 13:44, 9 March 2011 (UTC)

I doubt if many 80-year old males would expect to live for a further 87.78 years. Perhaps a further 7.78. Ghmyrtle (talk) 14:09, 9 March 2011 (UTC)

I believe the meaning was understood, I wasn't aware that by saying that an 80 year old US male had a life expectancy of 87.78 years meant that I was suggesting that he would live to counts fingers... not enough, shoes and socks come off.... be 167.78 years old - But happy to be corrected if that was the case. Darigan (talk) 14:20, 9 March 2011 (UTC)

According to life expectancy (as linked above) it does mean that, the source you used does also apparently use it with the same meaning. Nil Einne (talk) 18:21, 9 March 2011 (UTC)

Yes, I think the term is widely mis-used to mean "expected age at death". I was interested to see that the life expectancy of a US 80-year-old male was almost exactly the same (at just under six years) in 1950 as it was in 1850, and has subsequently risen by less than three years, so the answer to the OP's question is "less than nine years" for a male, and "about ten years" for a female American. Dbfirs 22:16, 9 March 2011 (UTC)

Ants that like sweat or human sweat?

This problem has bugged me for months: ants swarming my hands and feet for my sweat. Just today my laptop keyboard was intruded for that reason (I'm aware there's something like a keyboard sheet/protector but I like to touch the keyboard directly, and this isn't the main point), and I've tried doing Google search and searched archive here for an answer but no avail (unrelated: found sweat bee though, what an interesting world). A friend suggested it could be termite since the table-cupboard is made of wood, but I don't think they look like termites, and I've tried Googling termite sweat but no relevant results as well.

Situation: My campus hostel had a renovation and I moved in after, we got a new table-cupboard (err table + cupboard above, 2-in-1) and I'm using it. On the first few days I noticed ants were swarming the floor even after we cleaned the room. Sometimes they swarmed my feet when they're on the floor, and you know, you'd kill the ants without a second thought - that's when I realised they smell bad. The odour resembles one that's secreted by some other insects perhaps, I'm not sure. You'd definitely get the strong odour if you try killing like 5+ at once, and killing a swarm will definitely make you go "uuuuuuurghh".

These ants are black, with whitish yellow abdomen. They're quite aggressive towards me, but I'm sure it's because of my sweat that they bite me all the time.

How do I find out they're after my sweat is a long story... but an interesting point to note: while trying to find out, I purposely left my cup unwashed after drinking Milo (Nestle product, chocolate drink). After a week, only 2 ordinary black ants came, 1 of which I left it there for hours to see if it'd call its friends, but it looked like it just kept it to itself lol.

I've also tasted my sweat to make sure it doesn't taste sweet, and yes it's very salty as expected (fortunately!).

Now actually I'm just curious if they're an undiscovered species or if there's a new discovery for ants' behaviour.

Any thought is welcomed, thanks. — Yurei-eggtart 15:32, 9 March 2011 (UTC)

Assuming you are in Malaysia, this may be helpful. Malaysian ghost ants stink and are heavily attracted to water sources. -- kainaw™ 16:27, 9 March 2011 (UTC)

Yes I am from Malaysia. Thanks a lot for the link, I think this is the one, except the fact that I'm not used to seeing them up close. The ones I have here seem to be darker (oh my, does that mean they're more experienced?). I'm just a little bit disappointed they're already discovered and even known as pest. — Yurei-eggtart 16:55, 9 March 2011 (UTC)

Yes, they're very likely to be Tapinoma melanocephalum. A keyboard sheet/protector won't help. Your best bet is to do what other ant species do and use chemical interference. Since they rely on a hydrocarbon based trail system a giant wet soapy cloth washing away their lines of communication causes havoc. Sean.hoyland - talk 09:31, 10 March 2011 (UTC)

How many human species coexisted with eachother?

How many different human species lived during the same time period. I know the Homo Neanderthalis and the Homa sapien sapien were around at the same time. Except I am wondering if there are any others. Matthew Goldsmith 19:07, 9 March 2011 (UTC) — Preceding unsigned comment added by Lightylight (talk • contribs) 19:06, 9 March 2011 (UTC)

Our homo article covers this thoroughly. The picture I've attaching shows the most important species but leaves out a lot of minor ones. Looie496 (talk) 19:28, 9 March 2011 (UTC)

The nice graph at Human evolution says it's just the Neanderthals. Comet Tuttle (talk) 19:30, 9 March 2011 (UTC)

The graph leaves out both homo floresiensis and the Denisova hominin, though. Looie496 (talk) 19:36, 9 March 2011 (UTC)

(Edit Conflict) I don't think that that nice graph is meant to be comprehensive, Comet Tuttle. From the figure attached by Looie496, plus generally available information, it seems likely that Homo neanderthalensis in Europe and early Homo sapiens in Africa and beyond coexisted in time with late Homo erectus in Asia, and perhaps Homo rhodesiensis in Africa. To these we can add the disputed Homo floresiensis and the recently discovered Homo denisovan, if they prove valid taxons. It seems quite possible that further new human species also coexisting in time with H sapiens will be discovered in the future. Bear in mind, Lightyearlight, that since various of these species emerged from various others and there are no agreed on sharp boundaries between some of them, there may be valid disagreement over which ones certain coexisting individuals belong to. {The poster formerly known as 87.81.230.195} 90.201.110.135 (talk) 19:50, 9 March 2011 (UTC)

If we include Australopithecines in the definition of "human" then there were several species sharing the plains of Eastern and Southern Africa too. Roger (talk) 20:05, 9 March 2011 (UTC)

Couldn't various of these different "species" likely have interbred and had fertile offspring, such as modern humans and neanderthals, if not for geographical isolation from each other? Edison (talk) 19:32, 10 March 2011 (UTC)

I don't think that's known - and might never be. Matt Deres (talk) 14:38, 11 March 2011 (UTC)

Premature babies

Why isn't it yet possible to set up artificial transfer of oxygen and nutrients to a premature baby through its umbilical chord? Or even by setting up transfer through the placenta? Since they stick breathing tubes in and try to get the babies breathing with their under-developed lungs, I assume it's completely impossible at the moment. But, on the face of it, it would seem quite feasible given current technology, even if the complete artificial womb is a long way away.

So, what is specifically so difficult about this? 86.163.4.134 (talk) 21:20, 9 March 2011 (UTC)

I've wondered this too. The umbilical cord would not be possible (it closes), nor the placenta. But you can set things up just like in dialysis except with oxygenation instead of filtering. After some searching I found: Extracorporeal membrane oxygenation, which says: "Newborns cannot be placed on ECMO if they are under 4.5 pounds (2 kg), because they have extremely small vessels for cannulation, thus hindering adequate flow because of limitations from cannula size and subsequent higher resistance to blood flow". Seems to me this should be solvable, but I guess it isn't possible now. Ariel. (talk) 22:36, 9 March 2011 (UTC)

Why would they fool with tiny blood vessels when a premie is dying? Why not put in a PIC line like they do for an adult when the peripheral lines aren't adequate? Edison (talk) 19:29, 10 March 2011 (UTC)

N.B. We have an article PIC line. Wnt (talk) 20:59, 10 March 2011 (UTC)

I recently came acrros a documentary series called Baby ER on Zone Reality. Among other things medical personell was collecting blood for testing from a baby and explained that as the blood vessels are small their needles get cloged pretty fast, so they may need to take blood for testing from several sites. I guess drawing blood dosen`t take much time, so it might be yet another reason why they prefer ventilation and feeding tubes over trying to enrich blood with something ~~Xil (talk) 01:37, 11 March 2011 (UTC)

Seems there is another problem: "In infants aged less than 34 weeks of gestation several physiologic systems are not well-developed, specially the cerebral vasculature and germinal matrix, resulting in high sensitivity to slight changes in pH, PaO₂, and intracranial pressure. Preterm infants are at unacceptably high risk for intraventricular hemorrhage (IVH) if administered ECMO at a gestational age less than 32 weeks." Ariel. (talk) 08:09, 11 March 2011 (UTC)

Airbus 321, air speed

Resolved

 – thanks to Dolphin

When I was flying an A321 I observed a sharp shift in the refractive index of the air around the plane on two occasions.

1. In normal flight in a vertical line above the wing near the leading edge.
2. Outside the front of the engine when in glide flight before landing.

I assume that this is a shock waves indicating that the flow on one side is supersonic relative to the air plain. Is the flow supersonic before or after the shock wave?--Gr8xoz (talk) 23:18, 9 March 2011 (UTC)

Why do you assume it's supersonic? I don't know what caused it, but two other possibilities come to mind: The air is being compression heated, or the air is being compressed (or both). Either of those would cause a change in the refractive index. Ariel. (talk) 02:16, 10 March 2011 (UTC)

Gr8xoz is correct. This phenomenon is readily visible when travelling on any of the swept-wing jet airliners, providing you are sitting in a position that allows you to look along the wing, parallel to the leading edge. These aircraft are not supersonic but when flying at their cruising altitude they are transonic. This means the aircraft itself is not supersonic but as the air flows over the top surface of the wing at high speed, for a short distance it is supersonic relative to the wing. The air accelerates progressively as it passes the leading edge of the wing but it does not decelerate progressively. A shock forms, and as the air flows through the shock its speed (relative to the wing and the shock) suddenly decelerates to subsonic. Any gas, including air, approaches a shock at supersonic speed but the instant it emerges from the other side of the shock it is moving at a slower speed. The flow downstream of a normal shock is subsonic. (The flow downstream of an oblique shock is still supersonic but it has changed direction and is slower than the speed at which it approached the shock.) On either side of the shock there are different speeds, pressures, temperatures and densities. The difference in density on either side of the shock explains why the shock is sometimes visible, looking like a crack in a pane of glass. Dolphin (t) 02:35, 10 March 2011 (UTC)

OK so the speed is supersonic in front of the shock wave.(Relative to the wing) Thanks.--Gr8xoz (talk) 16:33, 10 March 2011 (UTC)