Wikipedia:Reference desk/Archives/Science/2011 August 13

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August 13

'Av a go at interpreting this liver function test

Medical advice question collapsed
The following discussion has been closed. Please do not modify it.
Strictly hypothetical of course. I really shouldn't have to point out that it's not a request for medical advice for a real case because that would be nuts... but I do anyway, just so we're all on the same page Results: Serum total bilirubin level: 7 umol/L (normal range 1-17) Serum total protein: 72 g/L (normal range 64-83) Serum albumin: 48 g/L (normal range 35-50) Serum globulin: 24 g/L (normal range 18-36) Alk Phos: 94 u/L (normal range 40-129) Serum ALT Level: 96 u/l (normal range 0-40) high Serum gamma GT level: 179 u/L (normal range 5-60) high (Serum electrolytes, glomerular filtration rate, and blood glucose level avaliable on request) Please indicate your level of expertise! Even I'm capable of clicking on each individual article and considering an indicator in isolation - although not necessarily of coming to a conclusion... other than the hypothetical patient really ought to drink less! Egg Centric 00:42, 13 August 2011 (UTC) P.S. I just looked at this and it really does look like I'm soliciting medical advice and/or some kind of homework. I absolutely promise that I am not. I can't think how to rephrase the question, without utterly altering it. And I am not a medical student, nor have I ever been one. I knew some medical students at university but they are doctors now. Not sure what else I can say! Egg Centric 00:49, 13 August 2011 (UTC) P.P.S. There is a very good reason I am using those specific numbers, but it's a long story that's a bit silly. Suffice to say it is certainly not from any real liver test. Egg Centric 00:51, 13 August 2011 (UTC) You can say that you are not requesting medical "avice" all you want, but what you are asking for is an interpretation of a medical test, which requires additional information in order to provide accurately. It would be irresponsible for us to speculate about possible explanations for the values you have given, since it would be impossible for us to know all of the relevant details. In any event, you have already linked to several articles that discuss the possible explanations for different elevated levels. That's about the best you can ask of an encyclopedia; we should not provide a more detailed discussion of this specific scenario. --- Medical geneticist (talk) 10:32, 13 August 2011 (UTC) Just as a matter of basic bandwidth, you're not likely to get a diagnosis out of these numbers - you're looking at two abnormal results and trying to assess the likelihood of a vast number of possible genetic diseases, infections, injuries, toxins, blockages, and tumors. A medical history is doubtless important to make a guess, and any guess might mean more tests to confirm it. But as a matter of personal understanding, which should encourage such a patient to obtain appropriate medical attention, the first thing to understand is that alanine aminotransferase (ALT) is an intracellular protein.[1] So when it turns up in high levels in the blood, it means that somewhere in the liver, cells are getting physically busted open and releasing their contents. The same source indicates that GGT is a confirmatory, nonspecific test for liver troubles. Note that serum bilirubin can give an indication when the bile duct is blocked, and albumin gives some indication of the overall function of the liver when chronic disease is present. Wnt (talk) 12:09, 13 August 2011 (UTC)

Space shooting

Would it be possible to fire a gun in space ? — Preceding unsigned comment added by 124.253.128.87 (talk) 06:38, 13 August 2011 (UTC)

Yes. Why not?--Shantavira|^{feed me} 07:09, 13 August 2011 (UTC)

But note that using it in a weightless environment would propel you backward, and, if you didn't have the barrel aligned with your center of gravity, would also impart a spin to your body. This would make a second shot difficult. StuRat (talk) 07:17, 13 August 2011 (UTC)

I thought firing a gun required something to ignite. Would that be possible in the absence of oxygen? Pais (talk) 07:40, 13 August 2011 (UTC)

Yes, Pais, that's what I meant... — Preceding unsigned comment added by 124.253.128.87 (talk) 07:47, 13 August 2011 (UTC)

I don't believe the ignition of gunpowder requires any additional oxygen beyond that present in the gunpowder already. See Gunpowder#Combustion_characteristics. StuRat (talk) 08:01, 13 August 2011 (UTC)

Well, there is this - Soviet laser pistol - though I seriously doubt it ever existed. (I know next to nothing about firearms, but, well, you don't have to be a theoretical Physicist to know that time is not cubic.--Shirt58 (talk) 08:08, 13 August 2011 (UTC)

The Soviets did test a gun on a space station - after the cosmonauts had safely left it, though. See Almaz#Defense measures. 75.41.110.200 (talk) 21:01, 13 August 2011 (UTC)

Potatos strapped to the wrist

This is going to sound really strange, but can you break your wrist by tying potatos to it for 8-12 hours then hitting it? I'm not looking to try it! Chemistrydegreebutnojob (talk) 07:33, 13 August 2011 (UTC)

I would think you could break your wrist by hitting it even without first tying potatoes to it, if you hit it hard enough. Pais (talk) 07:41, 13 August 2011 (UTC)

The stories I've read and heard about involve hitting with a spoon after sleeping with potato slices tied to the wrist. I just wanted to know if there was any scientific basis for this and whether it was likely to workChemistrydegreebutnojob (talk) 11:45, 13 August 2011 (UTC)

In that case, no. Plasmic Physics (talk) 11:53, 13 August 2011 (UTC)

I'd say that depends on the spoon. I've seen wooden spoons that make a pretty good Hanbō (e.g. [2]), and they can break a wrist easily. It's unlikely that the potatoes have any effect on this, though. --Stephan Schulz (talk) 12:57, 13 August 2011 (UTC)

Potato slices tied to wrist? Hitting with spoons? If there was a polite version of WTF, I feel this would be a good occasion to use it... 86.179.3.8 (talk) 13:38, 13 August 2011 (UTC)

Potatoes have nothing to do with how much force it takes to break the wrist. Plasmic Physics (talk) 14:35, 13 August 2011 (UTC)

They have as much to do with it, as the stars has to do with predicting a good investment. Plasmic Physics (talk) 14:37, 13 August 2011 (UTC)

Though if enough people thought that the stars could predict a good investment, it might create a self-fulfilling prophecy and work, at least for a while. Googlemeister (talk) 14:33, 15 August 2011 (UTC)

I cannot help but wonder where one might find stories about sleeping with potato slices tied to the wrist. Wanderer57 (talk) 14:47, 14 August 2011 (UTC)

Oddly enough, a simple Google search potato wrist break spoon gets many hits of people asking about this (or could it be the same person trying to start an urban legend?). I haven't found any claim that it is true. PrimeHunter (talk) 21:32, 14 August 2011 (UTC)

That seems very plausible. One or more bored students spamming lots of message boards trying to start some urban legend. 86.160.84.240 (talk) 11:56, 15 August 2011 (UTC)

• I feel like the following points need to be made:

• Deliberately breaking your own wrist is an extraordinarily stupid idea.
• Whether you strap a potato to it first or not.

Beeblebrox (talk) 21:39, 14 August 2011 (UTC)

escape velocity

What is the escape velocity for a galaxy? --DeeperQA (talk) 10:53, 13 August 2011 (UTC)

How big is the galaxy, what is its mass? Plasmic Physics (talk) 11:50, 13 August 2011 (UTC)

And escaping from what? Nyttend (talk) 11:52, 13 August 2011 (UTC)

It is the escape velocity from the most dense planet, unless there is a Black hole that you can't escape. Cuddlyable3 (talk) 12:20, 13 August 2011 (UTC)

No, the galaxy has a significant pull, and indeed it is hard to escape: according to escape velocity it would take 525 m/s from the Earth to escape the Milky Way, nearly 50 times what it takes to escape the Earth's gravity (though of course there are stars to stop and refuel at in the Milky Way's case). Wnt (talk) 12:30, 13 August 2011 (UTC)

For the Milky Way galaxy, in this youtube clip, physicist John C. Mather estimates ~1000 km/s. This is a lot more than the 525 km/s that the escape velocity article says, citing an article written in 1987. The reason for the discrepancy is, as Mather says, we're not very sure about how massive the Milky Way is, and estimates have steadily increased over the last few decades. This touches upon this 2010 question, which also depends on galactic mass estimates and discusses Wikipedia articles citing old papers. -- Finlay McWalter ☻ Talk 12:50, 13 August 2011 (UTC)

A few thoughts:

1) Unlike a planet or star, a galaxy really can't be treated as a point mass, meaning the location and direction would significantly impact the escape velocity.

2) We probably need to define "escape", too. Since the times involved are very long, would it count as having escaped if the universe expands more quickly than the rocket falls back towards the galaxy ?

3) Does finding the Lagrange point between the Milky Way and one of it's small satellite galaxies count as having "escaped" ? How about between the Milky Way and Andromeda ? StuRat (talk) 17:45, 13 August 2011 (UTC)

(1) is true, but becomes irrelevant once we've left the galaxy, so it might make the most sense to talk about the escape velocity of a galaxy at its edge (just as we usually talk about the escape velocity of a planet at its surface). (2) isn't really true - cosmological effects are pretty insignificant at the galactic level. There isn't really any expansion within, say, the Local Group (it's gravitationally bound). If you want to talk about the escape velocity of a galactic supercluster, then you may need to take it into account, but even then it will be minor. As for (3), I suppose galaxies will have L-points with each other, but just reaching an L-point doesn't do anything. You need to enter the right orbit at that point. It would take a hell of a lot of thrust to get from a near-escape trajectory to a periodic orbit around a galaxy. --Tango (talk) 18:45, 13 August 2011 (UTC)

How does dark matter affect an objects velocity needed to "escape" from a galaxy? Isn't it simplistic to just look at the gravitational attraction of the masses of ordinary matter on a galaxy? Isn't there something peculiar about the rotational velocity of the outer spirals of galaxies? Edison (talk) 19:52, 13 August 2011 (UTC)

It increases it because it contributes to the total mass of the galaxy. The thing is, we can calculate a galaxy's mass by looking at the orbital velocities of stars in it, as well as by working out how much mass just the matter we can see ought to have, and as you say the higher-than expected velocities observed demonstrate that dark (i.e. unseen) matter (which may be exotic or may be, at least in part, ordinary matter we can't see merely because it's cold and dark) is present (which is how it was detected in the first place). {The poster formerly known as 87.81.230.195} 90.201.110.213 (talk) 20:59, 13 August 2011 (UTC)

Bear in mind that a spherical shell of mass around you exerts no gravity. Someone ten miles from the center of the Earth, if possible, would feel the gravity of a 10-mile iron ball. Unlike the normal matter of the galaxy, the dark matter is at least roughly spherical, and makes up most of the mass. So however far you go out from the center, things feel the gravity of a mass that increases with the radius, so they're always orbiting at roughly the same rate. But this means that it's not really known quite how far you have to go out before the total mass you feel pulling you back in stops increasing - which in turn determines the escape velocity at that point. Wnt (talk) 00:49, 14 August 2011 (UTC)

Measuring atomic mass

How is atomic mass measured? Mass–energy equivalence tells me that nuclear binding energy is found by measuring atomic mass and subtracting the AMUs for the protons and neutrons, Atomic mass tells me that it's done with mass spectrometry, and Mass spectrometry tells me a lot of things about the process, but as far as I can see, it doesn't tell me how it works. Could I have just a simple layman's explanation please? I'd like to improve the atomic mass article by the addition of such an explanation to its "Measurement of atomic masses" section. Nyttend (talk) 12:06, 13 August 2011 (UTC)

May be you should read the article again. Everything you need to know is in there. Read in particular the section Mass spectrometry#Mass selection. Let us know if don't understand anything. Dauto (talk) 12:25, 13 August 2011 (UTC)

Barycenter

In a 2-body system, does the barycenter coincide with the L1 Lagrange point if, and only if, the masses of the two bodies are equal, or do other variables also figure in ? StuRat (talk) 17:59, 13 August 2011 (UTC)

The "if" is definitely true. If the two bodies are of equal mass then the barycentre and L1 point will be at the equidistant point on a line joining them, by symmetry (they are both always on the line joining them and, since there is no way to distinguish the bodies you can't work out which would be closer, so they must be the same distance away). The "only if", I'm not so sure about, but I think it will be true. The barycentre is always closer to the heavier object (it's distance to each object in inverse proportion to their masses), while I think L1 is always closer than the lighter object. --Tango (talk) 18:55, 13 August 2011 (UTC)

What Tango said is correct. The two points only coincide if the two objects have identical masses

... reply above by Dauto at 00:27, August 14, 2011

The formula for the L1 point is not simple. If $f$ is the fraction of the separation of the masses to L1 from the larger mass, and $b$ is the fraction to the barycentre, then $b={\frac {m}{(m+1)}}$ where $m$ is the ratio of the masses (small/large), and $f$ is given by $(1-f)^{2}-mf^{2}-f^{2}(1-f^{2})[(1+m)f-m]=0$ (assuming circular orbit).

I don't think there is an algebraic proof, but graphing the functions should show that $f=b$ is only possible when they are both a half. There might be a more elegant proof, but I don't know it. Dbfirs 08:25, 14 August 2011 (UTC)

It can be shown algebraically, assuming your equations above are correct (which I didn't check). Since we require$f=b$, we substitute $b={\frac {m}{m+1}}$ for $f$ in $(1-f)^{2}-mf^{2}-f^{2}(1-f^{2})[(1+m)f-m]=0$ to give, after a little algebraic simplification, ${\frac {1-m^{3}}{(m+1)^{2}}}=0$. That equation can only hold when the numerator $1-m^{3}=0$, the only real solution of which is $m=1$. (The complex solutions $m=-{\frac {1}{2}}\pm i{\frac {\sqrt {3}}{2}}$ are of course nonphysical.) Red Act (talk) 17:22, 14 August 2011 (UTC)

Thanks, I missed that -- in fact I was very lazy and didn't check because I knew there was no algebraic solution to the quintic in "f" for the L1 point. Apologies for the faulty assumption. Dbfirs 21:49, 14 August 2011 (UTC)

Thanks for the replies. So that was a "yes", as "In a 2-body system, the barycenter coincides with the L1 Lagrange point if, and only if, the masses of the two bodies are equal", right ? StuRat (talk) 21:39, 16 August 2011 (UTC)

Compound movements workout

Are compound movements - chest press, squat, dead lift etc the ony way to build muscle mass? Are machines and other free weight isolation exercises not as effective? Clover345 (talk) 18:01, 13 August 2011 (UTC)

Walking, running, jumping and climbing have done it for most of human history, long before the invention of exercise machines that people can sell you for a profit. HiLo48 (talk) 21:35, 13 August 2011 (UTC)

Isolation is useful if you want to develop one muscles group, and not others. Why would you want to do this ? Perhaps if one muscle group seems to need more work than the rest. Otherwise, I'd think good overall exercise, such as swimming, would be in order. StuRat (talk) 23:39, 13 August 2011 (UTC)

Thanks Stu. Yes, I forgot swimming. HiLo48 (talk) 23:52, 13 August 2011 (UTC)

predicting toppling

hi, i want to know how can we determine at what angle a body will topple. for example, if i'm leaning back on a chair, at what angle will i topple? — Preceding unsigned comment added by 117.192.193.90 (talk) 18:29, 13 August 2011 (UTC)

An object will topple when its centre of gravity is no longer over its base. So, for you leaning backwards on a chair, that will be when the centre of gravity of you and the chair is behind the back legs of the chair. --Tango (talk) 18:58, 13 August 2011 (UTC)

thank you tango, but what do you exactly mean by 'over its base'. also is it possible to define it mathematically, in terms of toppling moments and restoring moments? what forces will constitute each of these moments? thank you — Preceding unsigned comment added by 117.192.193.90 (talk) 19:07, 13 August 2011 (UTC)

By "base", I just mean the bit of it that should be on the ground. For a chair, that's the area between the four legs. Once your centre of gravity is not over the area between the legs, you will topple. You can view it mathematically by considering the force of gravity acting vertically down from the centre of gravity and the reactant force from the ground pushing up vertically from the points that are in contact with the ground. If those forces aren't in line with each other, there will be a moment. If gravity acts through the base (ie. the centre of gravity is over the base), then the moment will be to tilt the object so the the base touches the ground. If gravity doesn't act through the base, the moment will cause the object to topple. (This is much easier to explain standing in front of a blackboard! Sorry if I'm not making it clear.) --Tango (talk) 21:36, 13 August 2011 (UTC)

Yeah, as long as the base is flat (or concave) and the edge of the base is rigid you can just consider the outline from directly above--if the center of gravity is within that outline it will be relatively stable. The higher the center of gravity is and the close it is to an edge the less stable it will be in the face of wind or someone bumping it. If you define the parameters and ask at the math desk someone will likely give you some relevant formulae. μηδείς (talk) 22:15, 13 August 2011 (UTC)

More generally, a stationary rigid object resting on a horizontal plane and subject to no forces except for a vertical gravitational force will be unstable if the orthographic projection of the object's center of gravity onto the horizontal plane lies outside of the convex hull of all parts of the object which touch the plane. Red Act (talk) 02:13, 14 August 2011 (UTC)

Sounds definitive. Like that formulation "convex hull"--very efficient way of expressing a complex abstraction. μηδείς (talk) 02:48, 14 August 2011 (UTC)

... and the toppling or restoring moment is just the weight multiplied by the horizontal distance between its line of action (a line vertically down from the centre of gravity) and the pivot (the line joining the points of contact of the two chair legs still on the floor). This will be toppling if outside the "complex hull" (wrong side of the pivot) or restoring if inside (right side of the pivot). If your feet are on the ground, or you are holding on to something, then there are other forces contributing to the moment. Dbfirs 06:49, 14 August 2011 (UTC)

thank you guys, you guys are simply superb — Preceding unsigned comment added by 117.192.202.79 (talk) 18:20, 14 August 2011 (UTC)

Stomach anatomy

Hello. What part of the stomach lies approximately 1 inch above the belly button? Thanks. Leptictidium (mt) 20:13, 13 August 2011 (UTC)

Lots. Depending if you mean inside or outside or how picky you are at exactly how far the inch is. See Abdomen.-- Obsidi♠n Soul 20:52, 13 August 2011 (UTC)

Note thay the umbilicus is a fixed part of the abdominal wall, while the contents of the abdominal cavity are not fixed with respect to the abdominal wall, and do move about within the individual, not to mention individual variations. That said, compare the figures that I've copied. I would place the imbilicus at an inch ore two below the plane labeled d in the image to the left. This would imply that coils of small intestine are a good candidate, or possibly the Transverse colon. The great omentum may also extend down to this reagion, and be the closest anatomical structure within the abdominal cavity to your point of interest . --95.34.139.175 (talk) 21:13, 13 August 2011 (UTC)

Abdominial cavity

Male torso

200 proof alcohol sale and consumption

While on the last portion of my annual Israel summer dig/trip, I purchased the infamous Perfect 95 (Israeli Everclear) with the intention of using it as lighter fluid (My dad actually took a sip of it and was not well afterward). This plan worked, as it always does, to great affect, and got me we wondering. I read that 95% alcohol is the highest ethanol content one can purchase in the realm of simple-distilled alcohol. There are other methods of course that would allow one to get pure ethanol, but does anyone use these methods to make a commercially available beverage? I guess my question is, is there any publicly available pure ethanol spirit sold anywhere in the world? I am a teetotaller btw, so I have no intention of drinking it, as a result any jokes will most likely fall flat. Sir William Matthew Flinders Petrie | Say Shalom! 20:16, 13 August 2011 (UTC)

You can buy absolute ethanol for your chemistry lab. In the US it has a liquor tax stamp, because obviously it can't be denatured. Whether a supply house would sell it to an individual I don't know.

Despite the stamp, it could be risky to use it for beverage purposes, because benzene is used as part of the purification process, and trace amounts could remain. I have no reference for that; just going off what I've heard. --Trovatore (talk) 20:20, 13 August 2011 (UTC)

I don't believe there is any beverage that is 100% alcohol. It would taste terrible and be very dangerous. Everclear really isn't safe either, it's pretty much made for college kids to make horrible punch drinks in garbage cans and watermelons. I've never met anyone over the age of 25 who would even consider purchasing it. Beeblebrox (talk) 20:22, 13 August 2011 (UTC)

190 proof alcohol has other uses. For example some people pour it over cherries and let them sit for some weeks or so to preserve them. I make no claims as to how safe this is. --Trovatore (talk) 20:26, 13 August 2011 (UTC)

The US gov is very paranoid about people getting alcohol through any means they can't tax you a great deal on. If it's denatured, they might if you can produce good credentials I'll bet. Ah well, I'm 21 so no worries then. :p Sounds about right. I only use it for lighter fluid (and hell is it effective). Though as you say it is very dangerous, if you pour for too long on an open flame, said flame will race up into the bottle as my digmates found out last year (Then again, someone lost a finger on that dig as well after he tried to catch a low-thrown mini-boulder on a ledge, so some of our newbies weren't the brightest bulbs, especially the ones who actually drank that crap). What about using it as a disinfectant? Sir William Matthew Flinders Petrie | Say Shalom! 20:39, 13 August 2011 (UTC)

Note that 95% ethanol forms a positive azeotrope where distillation does nothing to change the ratio of ethanol to water in the vapor. For commercial scientific use 95% ethanol is substantially cheaper than 100%. Also I think there's that nagging question of what chemical process is used to remove the last 5% of water from the ethanol and whether there is a risk of contamination with something unpleasant. But the main point is nobody is going to a lot more for 5% more alcohol unless they're doing chemistry. Wnt (talk) 00:43, 14 August 2011 (UTC)

See also Ethanol purification. --Ouro (blah blah) 14:16, 14 August 2011 (UTC)

Cute little Israeli Rodent which I cannot identify

I meant to post my above question last night, so apologies for the two-for. Anyway, this little fella has been walking around the hotel portion of our kibbutz. My dad and I have been wondering what he is. Clearly a rodent, and appears to be blind. He is out during the day and the night, but seems to favour the night. Doesn't seem outwardly vicious at all and appears to be either a herbivore or insectivore. Anyone want to help me identify this fellow? Sir William Matthew Flinders Petrie | Say Shalom! 20:18, 13 August 2011 (UTC)

It's a hedgehog, not a rodent. Looks really bad off--look at the sores on the legs. How awful. See here. μηδείς (talk) 20:23, 13 August 2011 (UTC)

Ah, see that's what I told my dad first, but he thought it was another animal. Poor little guy, I wonder what did that. Thanks! I will get him some watermelon tomorrow. Sir William Matthew Flinders Petrie | Say Shalom! 20:40, 13 August 2011 (UTC)

If it's native to Israel (and not a transplant from somewhere else), it's likely to be a Southern White-breasted Hedgehog or a Desert Hedgehog. The Long-eared Hedgehog is also native to the area, but the critter in your picture doesn't look like the ones in the article. Pais (talk) 20:44, 13 August 2011 (UTC)

Desert is unlikely as the map shows the range only being in the Judean Desert and the Negev. I am in the Western Galilee, Kibbutz Lohamei HaGeta'ot to be specific. I doubt the little fella could have made it up here what with all the cars and roads that would squish him (of course a kibbutznik could have brought him up here from one of those areas). Sir William Matthew Flinders Petrie | Say Shalom! 20:52, 13 August 2011 (UTC)

Watermelon is almost nutrient free except for water (which I am sure he'll want) and not too much sugar per volume. I'd suggest some little scraps of meat, some peanut butter. You really should check on line since I am just guessing--there are tons of fan sites--but he's an omnivorous insectivore, so don't starve him on a rodent diet. You might take him to a vet who might suggest euthanizing him but will have the best advice, obviously. μηδείς (talk) 22:10, 13 August 2011 (UTC)

A pet store or fishing shop will probably have crickets, or better, earthworms or mealy worms. Some egg might work as well. Keep in mind they do transmit diseases and I am curious if rabies might be a risk. μηδείς (talk) 22:19, 13 August 2011 (UTC)

And hedgehogs are not really rodents. Googlemeister (talk) 18:44, 15 August 2011 (UTC)

Rabies in hedgehogs is extremely rare (only one case I've ever found - but it was a similar hedgehog from Budapest). Salmonella is the primary concern for human contact with hedgehogs. There are many cases of that. Also, hedgehogs anoint themselves with various things they find as they travel. So, it isn't uncommon for a wild hedgehog to be covered in various toxins. -- kainaw™ 18:50, 15 August 2011 (UTC)

Does it exist a Pyrenean Isthmus?

I am interested in doing some work which includes The Pyrenees, but not only the mountain system itself, but its surroundings too (valleys, rivers, oceans, territories, etc.). It has always appeared to me that The Pyrenees and its surroundings are a large isthmus who separates the Iberian Peninsula from the Western European continent, but when i look for references i can not find any.

I tried the link for isthmus in Wikipedia, but besides saying that isthmus is "....a narrow strip of land connecting two larger land areas usually with waterforms on either side", it never mentions or considers a Pyrenean Isthmus, as such. I believe it is an important subject to include such European territory as an isthmus due to its significant value in regard to its demography and several other factors.

I know that today, such isthmus is shared by two countries (Spain and France), but also i am aware that in the past, was shared by other different countries or their equivalent, without diminishing its importance.

I guess the clue here is on the term "narrow strip of land"....how narrow has to be a strip of land to be considered an isthmus?

I shall be looking forward for some help in this respect. Thanks in advance. — Preceding unsigned comment added by 86.196.220.164 (talk) 21:13, 13 August 2011 (UTC)

I doubt there's a hard limit on how big an isthmus can be before it's no longer an isthmus, but whether or not the Pyrenees can be labeled an isthmus shouldn't impact a discussion of the landform's importance to Western Europe. Note also that the Pyrenees are shared amongst three present-day nations: France, Spain, and Andorra. — Lomn 21:32, 13 August 2011 (UTC)

You get 59 hits for "Pyrenean Isthmus" including a blog with that name asserting an identity for the people living between the Ebro and the Garonne. Is that your blog? You get 55 hits for "Iberian Isthmus" which seems to be used in a scientific rather than cultural manner. μηδείς (talk) 22:02, 13 August 2011 (UTC)

Fernand Braudel writes, in The Mediterranean and the Mediterranean World in the Age of Philip II (volume 1), of four great European isthmuses: "It [Europe] is intersected by a series of north-south routes, natural isthmuses that are still decisive influences on exchanges today: the Russian isthmus, the Polish isthmus, the German isthmus, and the French isthmus." He describes each at length. The Russian isthmus being from the Baltic to the Black and Caspian Seas, the Polish from the Baltic to the Balkans and the Bosphorus, the German from the Baltic & North Seas to the Adriatic and Tyrrhenian Seas, and the French from "Rouen to Marseilles". He's clearly picking these specific "isthmuses" out for being important routes of trade, migration, etc, more than just for being "narrow strips of land". He also mentions west-east "routes" in the Iberian peninsula, including "Barcelona to Navarre", which is close to the notion of an isthmus at the Pyrenees. Braudel's focus on linking trade routes and isthmuses doesn't work for the Pyrenees themselves. Still, it is an example of the term "isthmus" being used with a very broad meaning. Pfly (talk) 05:56, 15 August 2011 (UTC)

Thanks you for your respective answers. Absolutely true! How could i have forgotten Andorra, being that i live there part of the year....and probably is due to the habit of considering this small country as one of those that form part of the Pyrenean Isthmus as a whole, not partially. On the other hand, among those 59 hits that one of you mention above, i have come across with a few new ones, with different opinions about the same subject which i find quite interesting; and yes, the blog mentioned is mine. And finally, but not least, it would be interesting to dicuss if the so called "French isthmus" (Rouen-Marseille) could be considered as such, even considering it as a "linking trade route", or even more, considering it as a larger trade route than the strip of land existent between the Atlantic and the Mediterranean (Pyrenean isthmus). I am not trying to push the concept that a Pyrenean isthmus should be considered as such in Wikipedia, but like me, there could be other people who would not know to consider it as such "officially" by the writers and authors of Wikipedia, or not. I believe, this matter should be left well defined in the article about isthmus, by you all and me, but i do not know the procedure to follow to make it happen. Thanks for your attention and effort.

Origin of viviparous fishes

Why some fishes are viviparous? --195.74.79.17 (talk) 21:49, 13 August 2011 (UTC)

If you're asking about the difference between viviparous and ovoviviparous when they obviously both give birth to live young: 'True' Viviparity is when nourishment is given to the embryo other than from its own yolk, the embryos are not covered in membranes. It comes in two flavors - Histotrophic viviparity (literally 'tissue-eating') is when the embryo eats other embryos or other eggs to gain nourishment while inside the mother (cannibalism). Hemotrophic viviparity ('blood-eating') is when the embryo gets its nourishment directly from the mother's own nutrients (like in placental mammals). Ovoviviparity is when the eggs are retained inside the body of the female until they develop fully but do not receive nutrition from the mother (basically they still lay eggs, but they do not let it out of their bodies, hence why they seem to give birth to live young when they hatch).

If you're asking about why they developed the ability to give live birth, that's a more difficult question to answer as it has evolved multiple times separately. Overall, it just might be that lower number of offsprings but greater survival rates is more advantageous than the hit and miss spawn-by-the-millions of egg-laying fishes (though the assumption that viviparous fishes bear less young has been challenged). Especially since fishes which [independently] evolved viviparity do not revert to egg-laying, suggesting that it is advantageous in some way (with the exception of some elasmobranchs which might have reverted, probably because their eggs are very well-protected anyway). Others propose that adapting to a pelagic mode of life may have been important (harder to lay eggs in the open ocean). Still other theories factor in internal fertilization which encourages fiercer sexual selection pressures (sexual conflict), offspring evolving to get more from their mothers since they are propagating mostly her genes anyway (fetal-maternal arms race). etc. No one really knows for sure. *shrugs* Some of those pressures may have also played a role in the evolution of external parental care, even if they aren't viviparous (e.g. mouthbrooding in cichlids, nest-building in sticklebacks, etc.)

See also:

• Life-history correlates of the evolution of live bearing in fishes (Goodwin et al., 2011)
• Evolutionary Origins of Viviparity in Fishes (Blackburn, 2005)
• Parent-Offspring Conflict in the Evolution of Vertebrate Reproductive Mode (Crespi & Semeniuk, 2004)

Lots more papers about it really. Try searching in Google Scholar. -- Obsidi♠n Soul 22:57, 13 August 2011 (UTC)

(ec) Because they are able to survive. See the section Fish#Reproductive method. By far the majority of known fish are oviparous i.e. the eggs develop outside the mother's body. Relatively few have evolved vivaporous reproduction the mother retains the eggs and nourishes the embryos. This gives survival advantages such as continual maternal protection of the embryo and the need for males to compete before mating occurs. For the female to carry the embryo to term, a structural requirement is a placenta. Cuddlyable3 (talk) 23:09, 13 August 2011 (UTC)

If viviparity is more advantageous, why such fishes constitute a minority and aren't positively selected against?--195.74.79.17 (talk) 00:15, 14 August 2011 (UTC)

They were. Again, those which did evolve viviparity did not revert (again with the possible exceptions of one or two elasmobranch lines, I haven't checked reptiles/birds). Also note that evolution is not a straight line, those that did develop viviparity were 'branches', moving on to produce wholly viviparous lineages but not affecting the rest. Lesser fecundity also made sure that even with higher survival rates, they really can't push oviparous species to extinction. The survival of their genes is more assured, but they aren't exactly going to explode in population numbers soon. It also helps if you consider that all higher vertebrates are their descendants (not directly though). In reptiles, viviparity again independently evolved multiple times. It stuck in placental mammals, who took parental care and viviparity to an extreme. Most extremely even, in humans, and we are the most successful species aren't we? -- Obsidi♠n Soul 00:42, 14 August 2011 (UTC)

It's a matter of r and K selection. Small animals like mice are subject to high predation and cannot invest too much in any one child or risk losing it. They have many large litters. Big animals like elephants can invest alot in one child who will have a higher chance of survival and can develop to a more mature physical state before leaving their mother. More than four tiny baby elephants born at once would hard to feed and corral yet much easier for lions to kill.

Which strategy, r (rate) or K (investment), is better for a species depends on many things. Rate selected species are weeds, they can quickly invade new territory when an opportunity arises but are selected out of established territories where you find it hard to get a foothold. Investment selected species can live as the stable dominant organisms of a large, complex, patchy, spatially variable, yet cyclically regular territory. While r selected animals scatter, K selected animals can have culture.

Viviparity is a K selected trait. The young are fewer but much better developed. Since the two strategies have tradeoffs--the K selected species has all its few eggs in one basket, the r selected babies are out of the nest and often depend on mere chance in numbers to survive--no one such strategy is best. μηδείς (talk) 02:00, 14 August 2011 (UTC)

Awesome explanation. Though to be fair, there can be oviparity too with significant investment (like simply laying a very large heavily armored egg, or dedicated parental care), as in the case of dinosaurs (hadrosaurians most famously), and of course, the modern dinosaurs - birds. And some of the largest animals come from tiny planktonic paralarva - giant squids, who still spawn them by the millions. All in all, evolution is really too complicated to pigeonhole neatly. μηδείς' explanation is probably the best in showing how the business of reproduction are really just different strategies all aimed at propagating the genes of the parents. It's a cutthroat game. Like manufacturers producing competing products, some cheap but easily breakable, some expensive but durable. Humans won the jackpot with sentience, but he was already armed with billions of years of genetic weaponry, some unexpressed and laying dormant for future use. BTW, OP has this anything to do with Polycotylus? :P Interestingly, that one seems to be a common thing shared by large pelagic air-breathers - extinct archosaurians, ichthyosaurs, mosasaurs, and plesiosaurs (mammals can perhaps be discounted as viviparity is the default). Though why it hasn't evolved in extant marine birds and reptilia is puzzling. Perhaps they're still too attached to land, too early in their evolution, or simply can't squeeze in a niche in the current pelagic marine ecology (thus being restricted to shorelines, they still can access land and thus have no need to be viviparous), or something. Sea snakes are though. -- Obsidi♠n Soul 03:08, 14 August 2011 (UTC)

Yes, but in the case of fish eggs I can't imagine any large armoured ones unless you look at the elasmobranchs which tend toward live birth or at the mouth brooding cichlids where the father serves as the large armoured part--and they lay no where near the number of eggs as do oviparous non-brooders.

Live bearing is the advantage of the mammals and the bearing of precocious young is what allows bats to fly and whales to swim. Marsupial whale babies would drown in the pouch. The problem with Penguins and sea turtles switching to live bearing is that the intermediate stage, young born quickly from a weaker egg, is less adaptive than young born well developed from a thick shell. There's no way to get over the hump in between the two strategies. μηδείς (talk) 04:09, 14 August 2011 (UTC)

Yeah. The sea is far more hostile than their land habitats, and penguins and sea turtles aren't exactly equipped to defend their young against predators. Unless they find a relatively benign ecology somewhere where they might slowly lose the necessity for land incubation and thick-shelled eggs, they can't really make the leap to viviparity. The oviparity of extant archosaurians is a trickier question. Why didn't they? Though while modern archosaurians don't bear live young, their extinct exclusively marine flipper-limbed counterparts might have (no evidence, possibly yet, though). It does seem to be a chicken or egg question. Did viviparity give air-breathers the edge to become truly marine and to reach large sizes, or did large sizes and a completely marine lifestyle force viviparity? Probably a little of both.-- Obsidi♠n Soul 16:18, 14 August 2011 (UTC)

Yes, I was thinking that you could probably get ovoviviparity in cold-blodded sea turtles with a relaxation in selection pressure. But an insuperable problem birds face is the oxygen demands of their high metabolism. A chick born into the water would have to be highly developed, like a post-molt juvenile, not just a newly hatched chick. But in emperor penguins, comparable in size to seals, whose eggs are incubated for 64 days, it would be hard to maintain the chicks oxygen needs inside the body as it developed from fertilised egg to newborn. Let alone to sustain it in the body for the two months it spends as a nestling and the months it spends as a crecheling until it is ready to molt and enter the sea. And of course whales can feed their newborn young with milk, while penguins would have a hard time regurgitating food to their young in the open ocean. I am afraid that for birds you simply can't get there from here. A shame, as I always loved Dougal Dixon's porpins.μηδείς (talk) 21:44, 14 August 2011 (UTC)

Leptictidium Cretaceous

Did Leptictidium live during the Cretaceous? Pinguinus (talk) 22:44, 13 August 2011 (UTC)

We can only base possible geologic time ranges on the earliest fossils known. According to our article Leptictidium, no. It existed during the Middle Eocene of the Paleogene period, Cenozoic era. Specifically from the Late Ypresian to the Middle Bartonian ages (50 to 35 million years ago). The Cretaceous period ended 61.7 million years ago, which was around 11.7 million years before the first known fossils of Leptictidium.-- Obsidi♠n Soul 00:28, 14 August 2011 (UTC)

Deep sea fish and rupture of something (I guess)...

Been watching fishing shows on TV again. These guys were fishing in deep water in the South Pacific and they pulled up a couple of big fish (from memory, I think they were Hāpuku) from the depths. When brought to the surface, these fish had something that belonged on the inside sticking out of their mouths, all ruptured and grossly inflated - it was a pink, basketball-sized lump of flesh. I think this was some sort of decompression injury caused by the sudden change in water pressure (I've read about that happening to fish, but I've never seen it before) and it was obviously fatal. Does anyone know what manner of tissue or organ this would be? An inside-out stomach? --Kurt Shaped Box (talk) 23:38, 13 August 2011 (UTC)

Probably the swim bladder, but it in turn could push out other stuff. It's called barotrauma. It's discussed in both Swim bladder and Catch and release#Deep sea fishing and catch and release.-- Obsidi♠n Soul 00:15, 14 August 2011 (UTC)

Thanks very much. That sounds like it. --Kurt Shaped Box (talk) 20:25, 14 August 2011 (UTC)

We have this same issue with rockfish here in Alaska. If you catch one when fishing for halibut you pretty much have to keep it per [3]. Beeblebrox (talk) 20:55, 14 August 2011 (UTC)

Yeah, the anglers on TV were pretty much 'oh crap, we'd better move on from here - I hate bringing these up' - they'd caught them one after the other in short order while fishing for something else. --Kurt Shaped Box (talk) 21:08, 14 August 2011 (UTC)