Wikipedia:Reference desk/Archives/Science/2009 March 5

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March 5

Osseous structures and soft tissue uptake in L3 vertebra

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis, prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page.

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page. --~~~~

--Milkbreath (talk) 17:46, 5 March 2009 (UTC)

The discussion about whether this is a request for medical advice is here. StuRat (talk) 05:18, 5 March 2009 (UTC)

This question may be a request for medical advice. It is against our guidelines to provide medical advice. You may find it helpful to read the article: Positron emission tomography, osteoblasts, and osseous tissue, and form your own opinion from the information there. Thank you. StuRat (talk) 19:25, 5 March 2009 (UTC) (edited to remove "contentious" statement – 74  20:40, 5 March 2009 (UTC))

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magnatizing a charged body

some one has told me that we can magnatized a uncharged body but charged body can not be magnatized.I could not understand this.Is it true ,plz explain —Preceding unsigned comment added by 119.154.28.19 (talk) 01:06, 5 March 2009 (UTC)

Not true, a magnet can be charged. Graeme Bartlett (talk) 05:14, 5 March 2009 (UTC)

There might be a misunderstanding here - in general permanent magnets cannot be made from good conductors. But being a poor conductor does not mean the material will make a good magnet. (Before anyone says - Iron which can be magnetised contains a lot of ceramic paricles in the matrix - which are respondsible for it's ability to be magnetised as well as its brittleness - any conduction of electricity is around the particles held in the matrix - pure iron which does not contain any ceramic particles does not make a permanent magnet)FengRail (talk) 13:49, 5 March 2009 (UTC)

The OP may also be confused because electric charge does exist, while magnetic charge does not. Magnetism in materials is not caused by a (magnetic) charge, but it can co-exist with an electric charge and will certainly interact with moving electric charge. It sounds like you misinterpreted someone explaining: there is no way to put a magnetic charge on an object; but it is definitely possible to put an electric charge on a magnet.. Nimur (talk) 15:34, 5 March 2009 (UTC)

It is also possible to magnetize a piece of iron after an electric charge is placed on it. Edison (talk) 19:36, 5 March 2009 (UTC)

Is it possible to magnatise the charge ? ~)

Not in the conventional sense, which is ferromagnetism. In solid matter, charge is carried by free electrons (either present in excess, as negative charge), or missing (because they moved somewhere else, leaving positive charge behind). Since the charge is carried at an atomic-sized level, and ferromagnetism is the macroscopic alignment of magnetic moments, it would not be possible to "magnetize" the free electrons. However - two more exotic forms of magnetism exist: diamagnetism and paramagnetism, which are both directly related to interaction between electron magnetic moments and an applied external field. I don't think either of these are usually observed in relation to free electrons, though; usually they interact with electrons that are bound in atomic-orbitals. Nimur (talk) 05:45, 6 March 2009 (UTC)

Either way it's definately possible to magnetise a thing that has an electric charge. As long as it's the sort of thing that can be magnetised. I've no idea if potentially magnetic things are hard to put a charge on - could this be true?FengRail (talk) 00:39, 6 March 2009 (UTC)

Many ferromagnetic materials are also conductors, which do not hold charge very well because they are hard to electrically isolate (one could be wrapped in rubber or plastic, though). Some of the more exotic ferromagnetic materials are more akin to a ceramic or glass (or a semiconductor) and are likely electrical insulators. Those should hold a static charge without too much difficulty. Yttrium iron garnet shows up in a lot of materials research because it interacts in interesting ways with light, (as polarizing filters and rotators), which of course can be explained at the atomic level as having to do with the electromagnetic interactions with the material's intrinsic atomic-scale magnetic moments and dipole moments. Nimur (talk) 05:41, 6 March 2009 (UTC)

If a metal magnet is placed on a piece of PVC pipe or glass, or hung from a silk it is easy to charge it with electricity, positively or negatively. The charge is able to move around in a conductive magnet . If it is resting on a wooden table or held by someone not insulated from the earth, the charge will naturally leak off. A nonmagnetized piece of ferromagnetic conductor or nonferromagneetivc conductor, such as copper, can also be charged the same way. An uncharged magnet or nonmagetic metal will also be attracted to a charged object. I am not sure what the uncertainty or confusion is here. Edison (talk) 18:52, 6 March 2009 (UTC)

How do we know how high the sea level was 500 million years ago?

I heard that the last time we had the same level of greenhouse gases was some 500 million years ago, and the sea level was then several hundred feet above what it is now. I checked the sea level article, which led me to sequence stratigraphy, but I must admit, I don’t understand that article well enough to get that information. The whole earth crust is continuously in motion, and some of the highest mountains contain sediments from the bottom of the sea. What does it tell us about the sea level 500 million years ago if we find sediments from what was 10,000 feet below sea level then 10,000 feet above sea level now? Mary Moor (talk) 02:03, 5 March 2009 (UTC)

That article makes precious little sense to me as well, but it appears to be mostly about methods for oil prospecting. I'm also not an expert (sad but true, I'm related to a sad number of them and they would all laugh at my pathetic attempt at a response), but rocks that are under water for extended periods are different than those that are above water. Fossils are the obvious difference (very few cnidarians on land, for example), but there are chemical and physical features as well. If you have a network of points, you can create a map from dot to dot and from known rates of continental drift, and you can give an estimate of where the land was and where the sea was. Just a guess. SDY (talk) 03:25, 5 March 2009 (UTC)

True - but the OP's question is an entirely valid one - we know that over geological timescales, mountain ranges may be formed by upward buckling of the crust as two plates are forced together (kinda like you can create an upwards ruck in a rug by sliding one end of it towards the other). So just because you find fossils 10,000 feet up a mountain - even if they were fossils of horseshoe crabs or something that could only have formed at close to sea level - that doesn't prove that the ocean was once 10,000 feet deeper than it is now. The problem here is that you should be asking: "Sea level was then several hundred feet above what it is now...relative to what??" You can't just put a mark on the side of a mountain where the sea level was then - and take a tape measure and measure down to where sea level is now - because the mountain itself has moved up or down in the meantime. The only MEANINGFUL measure would be if you could say that "The radius of the earth measured to the surface of the ocean was several hundred feet greater than it is now"...but I very much doubt that's what's being measured here. So I don't know that this measurement is terribly meaningful when you are comparing ocean levels over geological timescales. BUT when we say that global warming might raise ocean levels by 7 meters (or whatever the current estimate is) - we're talking about this happening on timescales of perhaps just 50 years - and the continents, mountains and everything else won't have moved noticiably over that amount of time. So this measure of sea level rise is entirely meaningful...it tells us how many major cities - and even entire nations will vanish beneath the waves. SteveBaker (talk) 04:52, 5 March 2009 (UTC)

I wasn't clear. Something can be 10,000 feet up or down because the plates and rocks that make up the plates are moving. If you're talking 500mya, the world looks rather different (the map is a little ways down the page). If we assume that the mountains aren't drastically steeper (et cetera), if there is FOO% less dry land then there must be BAR% more ocean therefore there must be BAZ% more water and BAZ% more water equals QUX% feet deeper. SDY (talk) 05:54, 5 March 2009 (UTC)

No - you were perfectly clear - but I don't see how you can make that equation without also knowing things like how the continents are depressed by the weight of the oceans on top of them (a not inconsiderable matter) - and also the extent of water locked up in the ice caps. I think these claims from so far in the past would be tough to substantiate. SteveBaker (talk) 13:52, 5 March 2009 (UTC)

I would say that the answer is that while some of the Earth's surface is uplifted or subsides, this is not true of all of the surface, at least over a time scale of 500 million years. So, the goal would then be to find a geologically stable area and measure historic sea levels there. StuRat (talk) 05:13, 5 March 2009 (UTC)

There is so much assumptions one is making when looking at sea level 500,000,000 years ago relative to today. Lets look at how these interfere with making a meaningful comparison.

1. There was the same amount of water (including ice and atmospheric water) on earth 500m years ago... Possibly not true. Water comes and goes as it evaporates into space (slowly) and also as more water lands on earth on meteorites, and is released from volcanic activity. On human timescales (measured in the thousands or tens of thousands of years) such effects may not be noticable, but on the multi-million-year timescale, there is likely to be marked differences in the total amount of availible water on Earth.
2. There was the same amount of availible space for that water to take up... Also possibly not true. The level of the oceans is due not only to the amount of water in them, but also their shape. Plate tectonics is a complex process, and depending on what the surface of the earth looked like; even assuming we had the same amount of total water to deal with (see above, we may not) then differences in sea level could be due almost entirely to differences in the shape of the surface of the earth; i.e. where the continents were, how low the ocean floors were in comparison to this, yada yada yada.
3. That the level of greenhouse gases is the ONLY controling factor in the Earth's temperature... Also not true. The earth's temperature can also be affected by solar output, by surface albedo, by surface area of the oceans vs. land, by overall volcanic activity, etc. etc. These factors remain relatively constant on the short term, which is why measureing greenhouse gases and their effect on climate, say over the past 10,000 years, may be useful, it isn't going to be terribly useful over 500,000,000 years, since so many other parts of the system are changing that we can't necessarily say "The temperature the earth was 500,000,000 years ago should be the same as it is today solely because the greenhouse gases are at comparible levels"...

Throw all of this stuff in, and even if we COULD actually tell what the greenhouse gas levels and the climate of earth was really like to any detail (and I am not sure we can); it still doesn't mean we can make meaningful statements about sea level based on those statements. --Jayron32.talk.contribs 06:14, 5 March 2009 (UTC)

The existence of one REALLY deep/wide ocean trench at one period in time - and it closing up or filling in some other period in time would erase any hope of appealing to any idea of the total volume of water remaining constant - and therefore the ratio of dry land to ocean surface giving you this answer. If you don't know how deep the ocean went below (or above) present day levels - you can't use the constant volume argument to say very much about overall levels. But unless you're talking about knowing the average radius of the earth measured at "sea level" half a billion years ago - to a rather impressive precision of a couple of hundred feet...you can't make this kind of statement in any meaningful way - no matter what fossil or geological evidence you have. SteveBaker (talk) 13:52, 5 March 2009 (UTC)

Global sea levels changing by hundreds of feet is not very precise at all, we're talking a couple percent change or so in average ocean depth (current average is about 10k ft/3km). Not a huge change, but not impossible precision either. SDY (talk) 16:14, 5 March 2009 (UTC)

It's much easier to find out if the sea-level was LOWER than present levels, because the evidence will exist in sedimentary rocks. But, it's complicated - the current height of the shoreline in the rock layer is not necessarily the original height of the water, because on geological timescales, rocks don't stay in the same place. The crust sort of flows and moves, and float up or down, convecting like a very very slow fluid, and occasionally collide catastrophically. Geologists can estimate how fast a vertical upwelling occurs by a number of techniques, ranging from physics-based modeling of material densities, to observations of broken layers and index fossils.

Old shore-lines and rivers still exist in geological strata and are often CLEARLY visible. In some cases, they can be exposed by erosion, like the amazing canyons carved through the American west. We can also find old geological strata by digging (impractical but possible), or by subsurface imaging. This excerpt, from Geophysical Estimation by Example, shows a marine sounding sonar used to survey the Sea of Galilee, and a bit of signal processing theory to help view what's happening: "The output of the roughening operator is an image, a filtered version of the depth, a filtered version of something real. Such filtering can enhance the appearance of interesting features. For example, scanning the shoreline of the roughened image (after missing data was filled), we see several ancient shorelines, now submerged." Nimur (talk) 15:46, 5 March 2009 (UTC)

At any rate, I'm not an expert, I'm just speculating on how it might have been done and I'm probably wrong. Note that the CO2 level was not claimed to be the cause of high sea levels, simply that it was associated with high sea levels. Chicken and egg possibilities abound, as does pure coincidence. I am, however, almost certain that it has nothing to do with sea level compared with radius of the earth, since that's such a tiny percentage (The stupendously deep Mariana trench is ~10k, radius of the earth is ~6,370 km) that I don't see how it could have been meaningfully measured, and the variability in shape of the earth's crust is such that not only is Kansas flatter than a pancake, but so is Mount Everest. Improbable research is your friend. SDY (talk) 15:55, 5 March 2009 (UTC)

In a recent paper (October 2008) Haq & Schutter [1] describe evidence for a major but gradual sea level rise throughout the Cambrian, culminating in the late Ordovician about 450 million years ago, also shown in this diagram [2]. This rise is recorded by marine transgressions across previously non-marine strata in stable cratonic areas (much as suggested by StuRat above). How accurate such estimates are compared to present day values, that's another issue. Note that 500 million years ago is not associated with an unusually high sea level on these estimates, it happens to be about half way through a 100 Ma period of gradual rise. Mikenorton (talk) 16:04, 5 March 2009 (UTC)

To go back to the original question: As far as I know nobody seriously claims that "the last time we had the same level of greenhouse gases was some 500 million years ago". This seems to be a case of Chinese whispers. We have good evidence that CO2 is higher than during the last 800000 years, and we believe it to be higher than during the last 20 million years. Not a short while, but very different from 500 million years. James Hansen's somewhat famous quote is "The last time the world was three degrees warmer than today - which is what we expect later this century - sea levels were 25m higher." Hansen was talking about a period about 3 million years ago. --Stephan Schulz (talk) 16:34, 5 March 2009 (UTC)

Thank you; it was indeed Chinese whispers. I think it originally comes from Field Notes from a Catastrophe, and I would have to get the book to see the actual numbers. But that was only the background for my question. I wanted to know how we even know how high the sea level was many years ago. The beautiful diagram Mikenorton showed us has three very different curves for the sea level, which could indicate that there is so little consensus among scientists as to render it practically useless. But then again, the diagram was funded by the oil industry, which has used precisely this argument of "there's no consensus among scientists" to persuade the last administration to do nothing about climate change. Mary Moor (talk) 17:55, 5 March 2009(UTC)

Mary, the curves in that diagram are actually very similar. The two to the left that cover the whole time interval both come from the Haq & Schutter paper and appear to be slightly different ways of presenting the same base data (with different smoothing etc.). The third curve, from a source that I haven't managed to find yet, shows a similar overall shape (at least to my eye) but rather greater short term variation. There are plenty of critics of these curves but I'd be surprised if anyone suggested that they were anything other than a genuine attempt to estimate past sea level changes. They were created to better understand observed sedimentary sequences in the geological record. Mikenorton (talk) 22:21, 6 March 2009 (UTC)

Thank you, this is very helpful! I also better understand your earlier comment now: There are areas that are so stable that we can consider them as static, correct? I now see the similarity between the two first curves. (The sudden drops of sea levels of 50m or more in the left curve were a bit scary, anyway.) As for the third curve, however, it still seems very different to me: During Sheinwoodian, the left curves experience one of their highest periods, above 200m, but the third curve varies between 50m and 0m. Mary Moor (talk) 22:11, 7 March 2009 (UTC)

The trouble is that modern estimates for sea level increase for (say) 3 degrees of global warming are not calculated by looking back in time to when we last had those temperatures. They are estimated based on several things:

• When the temperatures rise 3 degrees - any ice that's currently within 3 degrees of melting - will melt. We can pretty much know the volume of that ice. Of course floating sea ice (such as at the North Pole) doesn't count because it's already displacing its own weight of seawater. The main concern is glaciers, snow-pack and antarctica.
• Water that's more than a few degrees above freezing expands as it gets hotter. So knowing the present volume of all of the oceans - it's easy to calculate how much all of that water will expand by.

So those two things give us an idea of just how much more water (by volume) there will be in a 3 degree warmer world...and it's a heck of a lot. Divide that by the surface area of the oceans and what you have left is a rough idea of how much the ocean will rise. There are a couple of secondary effects - one is that as land is inundated by water, it's under more pressure - and that extra weight sitting on top of our continents could push them downwards - allowing yet more flooding. Secondly - (and annoyingly) the exact opposite of that effect happens in the antarctic - where the loss of ice above the land of that continent will allow antarctica to rise up somewhat because of the loss of weight pushing down on it...this displaces more water - which then floods the other continents still more.

25 meters is definitely on the upper end of scientific consensus - but even the lower estimate of 7 meters is pretty frightening if you live in a low-lying city such as New York, London, Paris...you name it. Claiming that "scientists don't agree" is a reasonable claim providing that you are quite clear on what it is that they don't agree on. It's not a matter of "Is this going to be a total disaster or not?" - it's a matter of "25 meters or only 7 meters." - or to put it more pointedly: "Do we lose 100 major cities world-wide or only 30? Are three billion people going to be made homeless or only two? Will loss of low lying fertile farmland result in 50% of humanity starving to death or only 30%." To claim that scientists can't agree on whether this is or is not the single most important thing for the world to focus on fixing - is quite incorrect. The agreement on that point is as close to unanimous as matters. SteveBaker (talk) 20:04, 5 March 2009 (UTC)

The point was that, based on what we know about the ancient situation, we can make assumptions about our time, not the other way round. I assumed that this was a finding of geology. Mary Moor (talk) 03:26, 6 March 2009 (UTC)

As an approximate estimate, melting all the ice on Earth into the ocean would raise sea levels by about 75 metres (250 ft). However, there are factors that can raise this level further, such as isostatic rebound in coastal or undersea areas (land displaces the water, forcing the global sea level to rise), thermal expansion, or a decreased atmospheric water vapor content (more of it being in the ocean). ~AH1^(TCU) 00:52, 8 March 2009 (UTC)

Also, finding the volume of all the ice at a certain melting threshold really isn't a good indicator of how much sea levels will rise. For one thing, a global temperature rise of 3C means that the poles will usually warm faster than at the equator, and land warms faster than ocean. Also, some ice shelves, especially West Antarctica, are vulnerable to being flooded from underneath, lubricating the ice and sending it into the ocean faster, and one example of where this could occur is at Pine Island Bay. ~AH1^(TCU) 01:49, 8 March 2009 (UTC)

Chlorine in tap water

How poisonous is Chlorine in tap water?--Mr.K. (talk) 13:06, 5 March 2009 (UTC)

To you or the bacteria? 76.97.245.5 (talk) 13:58, 5 March 2009 (UTC)

Sufficiently poisonous to kill the things it's supposed to kill, particularly E. coli, which, believe me, is good news for all of us. There isn't enough of it to be harmful to humans, though. -- Captain Disdain (talk) 14:05, 5 March 2009 (UTC)

Some reading material [3] - 76.97.245.5 (talk) 14:34, 5 March 2009 (UTC)

This one's better [4] and also see Risk assessment. To reduce health risks you would do better giving up commuting than water chlorination. Living is detrimental to one's health, but beats the alternative :-)76.97.245.5 (talk) 16:56, 5 March 2009 (UTC)

To answer as simply as possible, not nearly as poisonous as Cholera. --Jayron32.talk.contribs 01:43, 6 March 2009 (UTC)

Ordinary E coli are not dangerous. The reason why E coli content is used as a measure of contamination is usually because it's an indicator of the presence of other bacteria, which are not as benign. If you get sick from bacteria in your drinking water, it's statistically unlikely to be due to E Coli. --Pykk (talk) 09:27, 6 March 2009 (UTC)

Chlorine is an essential nutrient provided by tap water, as is fluoride. See Nutrients in Drinking Water, Page 3.71.30.254.216 (talk) 04:03, 6 March 2009 (UTC)

The link is actually talking about chloride, Cl^-. Chlorine in drinking water is hypochlorous acid, HOCl / OCl^-. Even if you accept them as the same, describing it as an essential nutrient is an extreme stretch in Western society. Our diet is far too rich in sodium chloride (table salt); any contribution from drinking water is vanishingly small by comparison. arimareiji (talk) 15:22, 6 March 2009 (UTC)

Chlorine in tap water is dangerous to fish. Also, see opposition to water fluoridation. ~AH1^(TCU) 00:44, 8 March 2009 (UTC)

Interchangeable left and right hand driving

Is there a car where you can interchange the wheel from left to right and back? At least, was any car designed so that this is easier to accomplish?--Mr.K. (talk) 13:12, 5 March 2009 (UTC)

There are a few cars out there that have a center steering wheel - exotic three seaters sports cars and concept cars, typically[5]. The Toyota Alessandro Volta has three seats in the front - and because it's completely drive by wire, any one of the three people can drive! But sadly, it's just another concept car. Of course there are also driving instruction cars fitted with steering wheels and pedals in both front seats...although these days those are very rare and most instructors have just a set of pedals on the passenger side. Many years ago, BMW ran a newspaper ad showing how their cars could be easily switched from left to right hand drive...and later advertised a car with no steering wheel and center console...but alas, both were just an April Fools pranks. [6]

My classic 1963 Mini has a steering wheel and pedals that can be switched sides in perhaps 4 hours with the right tools...but I suspect you're looking for something a lot more convenient than that. SteveBaker (talk) 13:42, 5 March 2009 (UTC)

Yes, 4 hours would be too much. I was thinking about something more convenient for casual drivers in Europe. The strange thing is that the auto industry doesn't offer this extra. Thousands of vehicles cross the Channel everyday and some drivers would be clearly happy of being able to drive on the proper side of the road. --Mr.K. (talk) 16:48, 5 March 2009 (UTC)

I would hope that most UK drivers, having crossed the Channel, DO drive on the "proper side of the road". Evolutionary processes will reduce the numbers of those who do not. --Cookatoo.ergo.ZooM (talk) 19:51, 5 March 2009 (UTC)

Some ways it could be done and the advantages and disadvantages of each:

1) Center driver position. This has the advantage of being safer, for the driver, as they are not close to either side of the car, making them less likely to be killed if the car is "T-boned". It has the disadvantage of making the driver slide to the center when they get in, could make using drive-through windows difficult, and could make it difficult to fit another passenger in front. A triangular-shaped car addresses some of these issues, but also brings in some stability concerns.

2) Duplicate driver positions. This is best for driver flexibility, but does increase the complexity and thus cost of the vehicle. It might be either more or less reliable, depending on whether the systems are truly independent of each other. A front seat passenger may also find the unused steering wheel and controls are "in the way".

3) Movable driver position. This would make it necessary to make the car "drive by wire", as mentioned above. This has it's own risks, as losing control of the vehicle at high speed is a distinct possibility, since electrical systems are prone to sudden, catastrophic failure, while mechanical systems more often suffer from gradual reduction in function. StuRat (talk) 20:01, 5 March 2009 (UTC)

The Unimog can be changed from LHD to RHD "in the field".195.128.251.103 (talk) 23:11, 5 March 2009 (UTC)

FWIW, British Army soldiers get posted to Germany a lot, and usually take their RHD cars with them - in fact, they often buy a new car just before going as the purchase of a new car for "export" is subject to a little less tax. Though the added difficulty (slightly reduced visibility on right-hand bends) of the driver being on the "wrong" side while driving on the Continent is not zero, in practice it doesn't seem to be sufficient to warrant temporarily switching to a LHD car, the expense of which would probably be roughly comparable to the higher cost of a car designed to be L-R convertible.

Moreover, any visibility advantage of switching from one's accustomed driving side might be more than negated by the potential danger of the gearstick and other controls being in an unaccustomed position. Otherwise, as international lorry drivers constantly move between the two driving regimes, it might be thought that their vehicles would more economically benefit from convertability, although the much improved visibility from their high cabs probably reduces what visibility problem there is.

I dimly recall that a couple or so decades ago, some model of family car built for both UK and Continental sales with the corresponding variations in driver position actually had pedal mechanisms on both sides, those on the passenger side obviously lacking the actual pedal extensions through the floor. Unfortunately the floor was over-flexible and it was found that a passenger could, when bracing a foot on the floor, operate the accelerator, with predictably interesting consequences. Probably that particular design also retained some portions of the steering-column mounting on the passenger side, and would have been more readily convertible than most cars. 87.81.230.195 (talk) 04:39, 6 March 2009 (UTC)

I've driven all four ways (RHD car on UK roads, RHD car on French and US roads, LHD car in the US and a French LHD car in the UK)...switching from one to another is EASY - and the flipping of the shifter to the opposite side takes no adaptation at all. Being on the correct side of the road is a little confusing in big areas like parking lots - but once you're out on the open road, it's not at all difficult - and after 10 minutes of driving around town - you've go it nailed. The difficulty of adapting is very overrated. The only weird thing is that even after 15 years of driving (mostly) LHD, I still occasionally walk up to the wrong side of the car when I approach it from the front in a parking lot! The hard (and dangerous) thing is that for RHD in France/USA and LHD in UK, you can't overtake safely - you have to pull so far out past the vehicle in front before you can see around it...if there is something coming the other way - you're doomed. For my restored 1963 RHD Mini here in Texas, I've turned the passenger-side door mirror around 180 degrees so I can nudge the car out just a little and then see around using the mirror. It works pretty well and I'm surprised that things like that aren't sold as accessories for Brits taking their cars across the channel to France & Belgium. SteveBaker (talk) 05:30, 6 March 2009 (UTC)

Systemic Beta Hemolysis Infection

Is it possible that one can get systemic Beta hemolysis (Beta Strep) infection? I know that some women can get a Beta Strep infection vaginally but it possible that it could spread throughout the body? Also, does anyone know why more research hasn't been done on this? --Emyn ned (talk) 14:19, 5 March 2009 (UTC)

Well, yes, it's possible. Streptococcus agalactiae is an important cause of neonatal sepsis, especially effecting premature babies. Less commonly, it can effect pregnant women or non-pregnant adults. [7] - Nunh-huh 14:24, 5 March 2009 (UTC)

We have a page for almost everything, including the beta-hemolytic streptococci, which notably include Streptococcus pyogenes. --Scray (talk) 00:16, 6 March 2009 (UTC)

Woman with 3 breasts

Warning: The video linked hereunder is sexually explicit.

The specific link is www.redtube.com/21290 Does the this unusual thoracic development shown in the linked video seem credible or faked?

I remember seeing cases of people having an extra nipple or two that are located under the standard two, and underdeveloped. I presume these are so easily removed surgically that their actual rate of occurrence is unrecorded - or does anyone know about these? Can anyone add any knowledge about the fully formed triplet exhibited by the actress in the video? Is it practical to "build" such a chest by cosmetic surgery? If her triple breasts are a genuine mutation are other internal abnormalities likely, and should all 3 breasts lactate? What can one say about human breast number and evolution? Is there evidence that human mutation is increasing? Cuddlyable3 (talk) 14:38, 5 March 2009 (UTC)

We have an article, Accessory breast, that would be a good place to start. --Tango (talk) 15:13, 5 March 2009 (UTC)

Milk lines extend from the axilla to the groin, both on the left and the right frontal side of the body (see the teats of cats or pigs). It would seem to be anatomically impossible for a mammary gland to develop in the centre. --Cookatoo.ergo.ZooM (talk) 16:53, 5 March 2009 (UTC)

The article I linked to describes cases of extra breasts growing on the feet, so I guess it is possible for them to grow pretty much anywhere. I do think the case shown in the video is rather unlikely, though - the three breasts are very symmetrical and equal in size, which I think would be extremely rare. --Tango (talk) 17:01, 5 March 2009 (UTC)

The only way I can imagine a third breast between the other two is in the case of conjoined twins, in particular, the parapagus type. However, they would likely have other duplicated body parts, as well, such as heads. StuRat (talk) 19:35, 5 March 2009 (UTC)

I was sure to have noticed a third head somewhere in this shortish documentary. --Cookatoo.ergo.ZooM (talk) 19:56, 5 March 2009 (UTC)

In another video the girl says that her two side boobs (hehe) were originally small, but she got implants to make all three about the same size. —Preceding unsigned comment added by 99.255.228.5 (talk) 00:44, 6 March 2009 (UTC)

That is so fake - the middle boob has zero jiggle factor - it's glued on there. Clever makeup work - nothing more. SteveBaker (talk) 05:16, 6 March 2009 (UTC)

I agree with Steve. Frankly, most anatomical oddities seen in porn should probably be assumed to be fake, unless they're incredibly convincing and constantly interacted with... which this one hardly is. The simple fact that she's extremely unwilling to let the middle breast just hang loose and is almost constantly holding on to it should be a an obvious hint: if she didn't do that, it'd fall off. It is a pretty good makeup job, though. -- Captain Disdain (talk) 08:48, 6 March 2009 (UTC)

"Jiggle factor" - never thought I'd hear that term outside of anime reviews. ^_~ And although I haven't seen said video, CD's argument sounds intuitively correct. arimareiji (talk) 14:32, 6 March 2009 (UTC)

I'm a computer graphics engineer and I work in the field of computer games. In my chosen profession, "jiggle factor" (as applied specifically to ridiculously oversized boobs in female game characters) is an entirely accepted term which appears in any number of serious papers published at conferences on graphics technology. It is typically scaled from 0 to 1. The person in the video has an 0.0 boob in the center - and I'd judge about an 0.6 or so on either side. "Trust me - I'm an expert!"  :-) SteveBaker (talk) 20:57, 6 March 2009 (UTC)

And what would the "jiggle factor" be in Dead or Alive Xtreme 2? 2? 3? --Carnildo (talk) 00:59, 7 March 2009 (UTC)

On a scale of 0 to 1? 11. --Tango (talk) 16:24, 7 March 2009 (UTC)

Oh so now you're a "computer graphics engineer" eh? Last time you were some mini driving texan. Just sayin'. 85.181.144.5 (talk) 19:21, 7 March 2009 (UTC)

Yeah, because no one in Texas drives a Mini and works as a computer graphics engineer. Sir, you appear to have forgotten your stupid on. -- Captain Disdain (talk) 09:50, 8 March 2009 (UTC)

LC/NE system and the ascending activating systems

Resolved

Sometimes it is hard to connect information from different sources. In the article on stress, the "LC/NE system" is mentioned. In my textbook on neuropsychology, the authors mention "the four ascending activating systems, classified by the dominant transmitter and their neurons: the cholinergic, noradrenergic, dopaminergic and serotonergic systems". My question: is the LC/NE system the same as the noradrenergic system? And if not, what is the difference? Lova Falk (talk) 17:27, 5 March 2009 (UTC)

This [8] source has: "The principal components of the stress response consist of the hypothalamic-pituitary-adrenal (HPA) system (most commonly known as the HPA axis), the locus coeruleus-norepinephrine (LC-NE) system, and the extrahypothalamic corticotropin releasing hormone (CRH) system." --Cookatoo.ergo.ZooM (talk) 18:04, 5 March 2009 (UTC)

Thank you, but that is not an answer to my question... Lova Falk (talk) 20:33, 5 March 2009 (UTC)

LC refers to the locus coeruleus, which is the primary brain stem nucleus where norepinephrine (NE) is produced. The neurons of the LC project widely throughout the brain (see the norepinephrine article for a list) and have an "activating" effect under conditions of stress. So, yes, the LC/NE is most likely the ascending activating system described by your textbook. --- Medical geneticist (talk) 23:11, 5 March 2009 (UTC)

Thank you! Personally I think that neuroscience textbooks should mention all alternative names for the structures or systems they describe. All those different names for the same thing just creates so much unnecessary confusion... Lova Falk (talk) 11:09, 6 March 2009 (UTC)

Question on mag fields and EMF

A magnetic field is perpendicular to the plane of a single-turn circular coil. The magnitude of the field is changing, so that an emf of 0.70 V and a current of 3.5 A are induced in the coil. The wire is the re-formed into a single-turn square coil, which is used in the same magnetic field (again perpendicular to the plane of the coil and with a magnitude changing at the same rate). What emf and current are induced in the square coil?

So I have no idea how to get the EMF without the area of the circle which the coil creates. I'm assuming the EMF changes due to the area of the coil. I'm also assuming that if you shape a circular coil into a square the area should be the same anyway... I know that the EMF and the current can give me the resistance of the wire. I got .2 ohms of resistance. With this, if I get the EMF of the square coil, I can get the current (I think). But I don't know how to get the EMF of the square coil. I'm really confused as to how to go about this... 98.221.85.188 (talk) 19:34, 5 March 2009 (UTC)

If you are forming it out of the same wire then the perimeter will be the same, not the area. If you know how to calculate EMF given area (unfortunately, I don't!), then do it in reverse to get the area and perimeter. You should then be able to use that, together with the formulae for area and perimeters of circles and squares to get the answer. --Tango (talk) 19:39, 5 March 2009 (UTC)

The magnetic field is changing... EMF= -(number of turns in coil)*[(change in Mag Flux)/(change in time)]. I know Magnetic flux = (Mag field) * (Area of the coil). The magnetic field is changing though, so I'm not sure how to get the Magnetic flux... 98.221.85.188 (talk) 19:45, 5 March 2009 (UTC)

You are given one more piece of information - the current. What formulae do you know with current in? --Tango (talk) 20:28, 5 March 2009 (UTC)

You don't need to compute the magnetic flux. All you need is the fact that the emf is proportional to the area. So the ratio between the two emf's (before and after) = the ratio between the two areas (before and after) which, as Tango pointed out, comes out of the formulae for the perimeters. Dauto (talk) 22:05, 5 March 2009 (UTC)

The OP describes a shorted wire loop that is extracting energy from a varying magnetic field. Energy, not emf, is proportional to the loop area. We must assume the external magnetic field is uniform except where it is perturbed close to the loop, and that the resistance is constant. The emf (to 4 sig. figs.) in the square loop is 0.5190 V and not 0.5498 V.Cuddlyable3 (talk) 23:18, 5 March 2009 (UTC)

Force meter question

Dear Wikipedians:

In the above scenario, if m is also 1 kg, then I know the force meter will register 9.8 N as the tension. However, what will the force meter register if m is 2 kg?

Thanks.

L33th4x0r (talk) 20:12, 5 March 2009 (UTC)

What will it register if M is infinite (i.e. fixed to the floor)? --Stephan Schulz (talk) 21:29, 5 March 2009 (UTC)

With the weight imbalance, the system will begin to accelerate and the tension will be just enough to keep the acceleration of the two masses equal. So the solution can be obtained by calculating the acceleration of each mass in terms of the tension T, setting the two accelerations equal, and solving for T. I don't know if this is homework or not, so I am not giving an explicit answer, but the calculations are pretty straight forward. -- Tcncv (talk) 21:42, 5 March 2009 (UTC)

But the force meter is accelerating too, so the tensions in the two cables are only equal if we assume the force meter has negligible mass. If the force meter has a non-negligible mass than the tensions are not equal - but then we need to know the mass of the force meter to solve the problem. Gandalf61 (talk) 22:19, 5 March 2009 (UTC)

This is a physics problem; real objects need not apply. Force meters are always massless — in exactly the same way that we assume that the pulleys are frictionless and have no moment of rotational inertia, and that the rope in the system is massless, and that the meter doesn't drag on the ideal frictionless physics table.... TenOfAllTrades(talk) 23:10, 5 March 2009 (UTC)

Lets start again, if m=1kg also then the force meter measures (2kg) = 19.6N

If fixed to the floor then the force meter measures (1kg) 9.8N

If the masses are 1kg and 2kg then the thing will move, the net force being (2-1)kg = 1kg = 9.8N on a total mass of 3kg... this gives you the acceleration of the masses as 9.8N/3kg = 1/3 of gravity.. can you work out the final answer from there?FengRail (talk) 00:31, 6 March 2009 (UTC)

The original stated tension of 9.8N is correct. Whether or not one end is fixed in the balanced configuration has no effect. Your third statement is correct (after minor editing for units) and is another way to get to the solution. -- Tcncv (talk) 01:51, 6 March 2009 (UTC)

Why is the tension 9.8N and not 19.6N like FengRail said?

If m is 2kg, then the apparatus is not balanced. m will descend, the 1kg mass will ascend, and the force meter will move to the left; until one of them encounters a pulley or the floor. Astronaut (talk) 02:53, 6 March 2009 (UTC)

If the tension were 19.6N, the upward force of the cable on the masses would be twice the downward force due to gravity. The result would be both masses accelerating upward (at least enough to reduce the cable tension). Another way to look at it: Consider the balanced system of two weights. Now drive a sturdy bolt through the heart of the force meter and into that frictionless table (don't let the lab manager catch you). The cable tension has not changed, but now we effectively have separate cable, pulley and weight systems both anchored at the bolt. -- Tcncv (talk) 03:53, 6 March 2009 (UTC)

I have no idea what you are on about - the tension (forces) due to a mass of 1 kg under gravity is 9.8N, there are 2 of these forces working in opposite directions, therefor the total tension is 2x9.8n

In the orginal question, it is incorrectly stated:

"In the above scenario, if m is also 1 kg, then I know the force meter will register 9.8 N as the tension"

I attempted to correct this statement.FengRail (talk) 10:58, 6 March 2009 (UTC)

No, it will register 9.8N, because there must be an equal and opposite force for the weights to be in equilibrium. Think of it this way: If m was instead a hook on the floor, what would the scale register? 124.169.174.199 (talk) 11:54, 6 March 2009 (UTC)

A force meter does not measure the sum of the forces on either side of it. The way that the hook and scale are attached to the solid body of the force meter introduces an asymmetry - it always registers the force on the hook side only. For an ideal massless force meter or for a force meter in equilibrium, the two forces will be equal in magnitude, so we often loosely say that the force meter registers "the" force, as if there were just one. For an accelerating force meter with non-negligible mass, the two forces will be unequal - but it is still just the force on the hook side that is registered on the force meter. Gandalf61 (talk) 13:49, 6 March 2009 (UTC)

Look at the diagram above, the two equal and opposite forces are on either side of the force-ometer, forces are vectors right, (so if one of the forces was zero, what would the other force have to be to give the same tension?)

Why not try an experiment - find a weight that doesn't quite cause breaking in a length of string or wire, then try to replicate the diagram with two of those weights on either side - see if the sting brakes... signed FengRail —Preceding unsigned comment added by 213.249.232.187 (talk) 14:31, 6 March 2009 (UTC)

Gandalf is right (if the hook can be considered massless, even though the forcemeter isn't). Dauto (talk) 14:12, 6 March 2009 (UTC)

Not really. Consider two people playing tug-of-war, with a force meter connecting the two ropes. Does it measure only the force of one person pulling, or two? arimareiji (talk) 14:28, 6 March 2009 (UTC)

Simpler example: Hold the top of the force meter in your hand and hang a 1kg mass from the hook. For meter will say 9.8N, obviously. Now consider the forces on the meter - there is a force of 9.8N from the mass pulling it down, and there is a force of 9.8N from your hand pulling it up. That's exactly the same forces are are on the meter in the diagram above (just rotated 90 degrees), so the meter will show the exact same value. --Tango (talk) 14:42, 6 March 2009 (UTC)

Tug-of-war - force meter registers force of only one person pulling. Exactly the same as if just one person pulling and other side of force meter attached to solid wall. Gandalf61 (talk) 16:08, 6 March 2009 (UTC)

(undent) Vaguely-related question that this reminds me of, which came up a little while ago among coworkers: Say that a person weighs too much for a scale to register. Can you accurately measure their weight by getting them to step onto two scales, one foot on each scale, and adding the registered weights? arimareiji (talk) 14:52, 6 March 2009 (UTC)

Yes, that should work. The scales measure the force required to stop them falling through the floor (which is equal to their weight), that force is the same regardless of what is applying it and forces in the same direction just add when combined. So, yes, I can't see why that wouldn't work. --Tango (talk) 15:41, 6 March 2009 (UTC)

Oh, I get it now (I think?). The purpose of the experiment is to demonstrate to students that there are two equal and opposite forces at work. The teacher first demonstrates that a 1kg weight suspended from a fixed point registers 9.8N on the force meter. The teacher explains that there are two forces - gravity pulling the weight down with a force of 9.8N, and the fixed point pulling up with an opposite 9.8N force. Some students might doubt the existence of this upwards force, so the teacher sets up the above experiment with m = 1kg. If the force meter reads the same 9.8N then it shows the upwards force must exist and be equal and opposite. Astronaut (talk) 16:22, 6 March 2009 (UTC)

Great little circle jerk, wikipedia reference desk at its best.FengRail (talk) 18:32, 6 March 2009 (UTC)

Let's write down Newton's second law of motion(EOM), for our two masses and the rope, then we can get into the answer: the resultant force acting on a mass is equal mass times of its acceleration. the magnitudes of each acceleration of the masses are equal, which relates our equations. further assumption is the negligible mass of the rope (which according to the EOM of the rope, yields: the magnitudes of two tension forces, acting on each end of it, are equal). the magnitude of acceleration becomes (abs(m2-m1)*g)/(m1+m2) , and tension becomes(in this situation) (4/3)*g . Re444 (talk) 18:55, 6 March 2009 (UTC)

Correct. In terms of force, (4/3) × 9.8N or about 13.1N. That leave a net upward force of 3.3N on the 1kg mass and a net downward force of 6.5N on the 2kg mass. Ignoring round-off errors, that gives the masses the same acceleration. -- Tcncv (talk) 01:19, 7 March 2009 (UTC)

Wow, this is soooo good! Thanks for all the response! L33th4x0r (talk) 03:25, 7 March 2009 (UTC)

Why blood groups and Rh?

I couldn't find in our article or figure out in google why blood groups are needed. What is their actual purpose, why don't we have some universal blood group? And what is the purpose of Rh? 85.132.54.6 (talk) 20:32, 5 March 2009 (UTC)

Why should they be "needed"? As with most evolutionary matters, they simply are. Also, for quick reference: blood type/ABO blood group system and Rhesus blood group system. — Lomn 21:04, 5 March 2009 (UTC)

Blood groups exist because they turned up one day and they don't do any harm, so they stuck around. Blood groups only became significant in any way when we started doing blood transfusions, which was extremely recently in evolutionary terms. (I guess there is a slight disadvantage to them since there are sometimes problems with Rh- mothers having Rh+ babies [I think it's that way around], but it's very rarely a problem because, if memory serves, it's only the second such baby that dies, and even then only if there were complications with the first one.) --Tango (talk) 21:11, 5 March 2009 (UTC)

There was (until recently) no evolutionary pressure in favour of compatibility or homogeneity (and so things just drifted apart, as they are wont to do). Right now there is a modest pressure - if someone has a group that requires transfusion with a rarer type, they run the disk of the hospital not having the right kind, and thus their dying without issue. If medicine were to remain exactly as it is for a few thousand years then you would expect to see a modest increase in the proportion of individuals who have transfusion-friendly blood when compared with those who don't. 87.115.143.223 (talk) 21:13, 5 March 2009 (UTC)

There is one modest piece of evolutionary pressure, Hemolytic disease of the newborn (HDN), which is part of why the Rh system was discovered in the first place. ABO rarely has a role in HDN. The ABO and Rh red cell antigen groups are not known to be functional, but there are some red cell antigens, such as the Duffy antigen system (usually "Fy" in shorthand) which are known to be meaningful outside of blood typing for medical or investigative purposes. In most of these cases, it's likely that no one has found out exactly what these bits of stuff on the extracellular matrix of the cell are for. SDY (talk) 21:15, 5 March 2009 (UTC)

Hmm, that's interesting. So that would imply either that human blood groups are slowly converging (from a more disparate ancestry - RH+ == grandma was a Neanderthal) or there is weak opposing pressure from some unknown utility in heterogeneity (e.g. resistance to some blood-borne disease). 87.115.143.223 (talk) 21:25, 5 March 2009 (UTC)

I'm not sure when the mutation happened which causes some people not to have the RhD antigen (I think everyone had it originally, but I may be wrong), but it wasn't necessarily that long ago. It only takes one mutation followed by the person with that mutation having lots of children for it to spread fairly widely within just a few thousand years. There may be some evolutionary pressure towards heterogeneity, but don't forget the importance of random chance. If the evolutionary pressure, in whatever direction, is very weak then random chance can end up being far more significant, even over the long term. --Tango (talk) 21:34, 5 March 2009 (UTC)

(outdent)

In general, when a genetic polymorphism is maintained in a population, some kind of balancing selection is at work. Polymorphisms that are neutral tend to disappear rather quickly. In this paper, the authors develop a model which attempts to explain the ABO gene frequencies by frequency-dependent selection (a type of balancing selection). They hypothesize that the reason is that bacteria may adapt differentially to the different carbohydrate structures of ABO antigens, and that, in addition, the natural antibodies that we have against the A and B antigens we lack, may offer protection from viruses that carry A and B antigens in their envelope derived from their previous host.

Rh proteins are believed to be ion transporters, involved in ammonia transport. I have not come accross any articles that attempt to explain the maintenance of Rh polymorphisms, although Hemolytic disease of the newborn may play a part, as suggested by SDY. --NorwegianBlue ^talk 21:40, 5 March 2009 (UTC)

[9] discusses the matter, I'm still reading it so I'm not sure what it concludes (it seems to be suggesting there must be a balancing selection of some kind). --Tango (talk) 21:50, 5 March 2009 (UTC)

Not necessarily relevant, but my favorite bit about blood is that the gene for type "O" is the gene for type "A" with single base pair different, a nonsense mutation. Tiny change in genetics, potentially lethal difference in transfusions. SDY (talk) 22:11, 5 March 2009 (UTC)

One of the mysteries in transfusion medicine is why people who have never been exposed to other ABO types have antibodies to those types. For example, a person who is type B (not to be confused with the immune system's B cells) has antibodies to type A immediately after the immune system develops (by about 3-6 months of age). Speculating: this would give a strong evolutionary advantage if both A and B "look like" viral antigens, since even if only half of the population is immune, the disease may have trouble persisting. Type "O" in this case would be the best of both worlds, since it would grant immunity to both "A-like" and "B-like" viral antigens. SDY (talk) 22:55, 5 March 2009 (UTC)

Re the paper that Tango linked to: Note that it was written at a time when the D, c/C and e/E antigens were thought to be encoded by three separate, linked genes. It has since been discovered that the c/C and e/E antigens are two epitopes on the same molecule. --NorwegianBlue ^talk 22:23, 5 March 2009 (UTC)

Didn't I read something somewhere about some mild correlation where people with blood group X were a bit more likely to get disease Y but a bit less likely to get disease Z, for suitable values of X, Y, and Z; and that the geographical distribution of the genes for different groups (if you corrected for recent migrations) could be related to the geographical distribution of the relevant diseases? This would make sense as a factor to preserve a diversity of blood types (in the ABO system) in the global population. (The practice of transfusing blood is too recent to have had any effect on this, of course.) Anyone remember reading something like this? --Anonymous, 05:48 UTC, March 6, 2009.

I don't remember a specific news item like that. In the disease associations that come to mind, negativity for an antigen is associated with resistance to a disease. This is the case for Duffy antigens (malaria), and A and B antigens (malaria and thrombosis). However, fetal A and B antigens may be protective hemolytic disease of the newborn, because anti-A or anti-B antibodies in an Rh(D) negative mother, who carries a child that is Rh(D) positive and positive for the A or B antigen that the mother lacks, protect against maternal Rh-immunisation. --NorwegianBlue ^talk 12:34, 6 March 2009 (UTC)

Moved comment by SDY that was posted in the middle of my reply. --NorwegianBlue ^talk 09:44, 6 March 2009 (UTC)

Can't give a definitive reason but the presence of Blood type (non-human) amongst numerous animals and its persistence from the apes to us indicates having blood groups must have a strong evolutionary advantage. Dmcq (talk)

Malaria: Worst. Disease. Ever?

Hi. Is there any truth to the claim that Malaria has killed about half the people who have ever lived??? --Kreachure (talk) 22:35, 5 March 2009 (UTC)

I very much doubt it. The estimates for the total number of people who have ever lived is all over the map - but 100 billion isn't a bad guesstimate. There are between 6 and 7 billion people alive today - and about half of the 100 billion are estimated to have lived before 1000 AD. This means that in order for this to be true - a CONSIDERABLE fraction of those deaths must have happened long before consistent records were kept - and VERY long before the diagnosis of diseases was good enough to be reliable. We know that half of the people who ever lived can't have died of malaria SINCE 1000 AD because for that to be true, we'd all have to be dead. List of causes of death by rate lists malaria as causing around 2% of deaths worldwide in 2005. So clearly the death rate from malaria would have had to be not just 50% in more ancient times - but VASTLY more than 50% in order to compensate for the miserable 2% rate we're seeing these days...but again, we can't be sure of numbers that far back in history because statistics were not kept - and the germ theory of disease didn't exist - so a death from malaria might be attributed to any number of bizarre causes. SteveBaker (talk) 23:31, 5 March 2009 (UTC)

I wonder (as I have heard this folk-fact before) as to whether it came from somebody saying "The number of people who have ever died as a result of malaria is equal to half the people living today". That would seem consistent with the maths. 2% of 100 billion being 2billion, but 2% being low due to modern anti-malarial drugs, so likely higher in the past. Fribbler (talk) 23:54, 5 March 2009 (UTC)

Sounds quite plausible. arimareiji (talk) 14:23, 6 March 2009 (UTC)

That's a possible reason

Alright, this is rediculous...I have in ten minutes of searching found countless forum discussions, blog postings, websites, and even a national geographic article asserting something along the lines of "some scientists believe that malaria has killed over half the people who have ever lived.] Not a single source I've found gives a citation for this, or ever elaborates on who these "scientists" or sometimes "medical historians" are. I'm starting to wonder if this is one of those factoids that got made up one day and spread around and around...like "humans only use 10% of their brain" (btw, is there a name for "facts" like that?). Someguy1221 (talk) 23:59, 5 March 2009 (UTC)

Ironically, Wikipedia is blamed for propagating false information due to anonymous contributions. In fact we're all here working our hardest to do due diligence on our facts before stating them; meanwhile, out there is a sea of even more anonymous contributors to tens of millions of random websites - and they typically don't have the same good intentions, focus, and presence of mind to evaluate information and its source. Nimur (talk) 05:56, 6 March 2009 (UTC)

Viral verbal encephalitis? --Scray (talk) 00:32, 6 March 2009 (UTC)

Thanks for the laugh. ^_^ arimareiji (talk) 14:23, 6 March 2009 (UTC)

Check out Common misconceptions. Kreachure (talk) 01:44, 6 March 2009 (UTC)

Urban legends of course! SteveBaker (talk) 02:13, 6 March 2009 (UTC)

Malaria is bad, bad news, and it wasn't until the modern era that people were able to do much about it. People still die from it because they can't get the basic care to prevent or cure it. That said, half of all people who have ever lived is a rather extreme claim. To say that half of all people who have ever lived had malaria (as opposed to directly dying from it) wouldn't be quite as ridiculous, but even that is extreme. SDY (talk) 01:16, 6 March 2009 (UTC)

Sure - it's just barely possible that this might be true (although I rather doubt it) - but what is flat out utterly impossible is to KNOW that it's true. Most of the deaths would have to have been so far in the past - that there is no way we could know the cause. SteveBaker (talk) 02:13, 6 March 2009 (UTC)

We can't even "know" the number of people that currently have it, but there are reasonable ways to estimate it. We can estimate that x percent of people with no effective prevention get malaria in an area and without effective treatment y percent of them die. If we know the percent of those people that lived in areas with similar exposure to malaria, we can apply modern case and fatality rates to create a percent of possible infections. It's an estimate, but so is the number of modern deaths from malaria given that many of the places where it takes place don't have the infrastructure to keep good records. "Cannot know" does not mean "have no clue." SDY (talk) 16:28, 6 March 2009 (UTC)

Malaria is a tropical disease, so the population of temperate regions did not get it. Also, it was not present in South America or Central America, or the Pacific islands, until brought by whites. Thus quite a few humans in those areas were beyond its influence until fairly recently. Population growth in the last couple of centuries has put a great many humans in all tropical regions in danger from it, but that is balanced by population growth in temperate regions. Malaria has, of course, been present in Africa from earliest recorded history. Malaria has also been recorded in Ancient China - but that would have to be only in southern China; the more northerly parts of China would be too cool for it. Being present in southern China, it would also undoubtedly have been present in other parts of SE Asia, and perhaps India. But all-in-all, many humans have not lived in malarial zones, so the 50 percent figure does seem too large. - GlowWorm. —Preceding unsigned comment added by 98.17.34.95 (talk) 04:58, 6 March 2009 (UTC)

And of course, the native African population (where malaria was at it's worst) had evolved a gene for resistance to malaria - but because having two copies of the gene results in sickle-cell disease - it could not have been present in 100% of the population. SteveBaker (talk) 05:08, 6 March 2009 (UTC)

Malaria may be a tropical disease but at times the tropics were obviously in civilized places like Rome, too, as at least one pope died of malaria. At least until the 20th century, Sicily was malaria-infested, and it will be the first to become that again, when the climate hits us. --Ayacop (talk) 10:23, 6 March 2009 (UTC)

Humans are basically a tropical species anyway. There were a lot more people in Egypt than there were in Norway for a large percent of human history.

While we may describe malaria as a 'tropical' disease, it's historical range has extended to some very non-tropical areas. Malaria was widespread in England, possibly since Roman times, and certainly from the fifteeth century. It was "endemic along the coasts and estuaries of south-east England, the Fenlands, and estuarine and marshland coastal areas of northern England": [10]. It took a combination of quinine antimalarials, the elimination of mosquito breeding areas, and systemic insecticide use to end local transmission of malaria in England.

Similarly, oh-so-tropical Canada enjoyed its own malaria problems: [11]. Here's a study which looks at endemic malaria in Russia, Finland, and Sweden: [12]. TenOfAllTrades(talk) 16:40, 6 March 2009 (UTC)

Hypertension

What is the reason of hypertension in the patients of Diabetes? —Preceding unsigned comment added by 201.220.215.12 (talk) 23:36, 5 March 2009 (UTC)

There are a number of reasons why hypertension and diabetes are linked. Anyone suffering from either (or both) condition need to consult health professionals in order to understand and treat their own condition. The two conditions have similar risk factors (relating to age, weight, diet, exercise), but also a number of inter-related conditions. Some common causes include insulin resistance (Metabolic syndrome) in Type II diabetes, and diabetic nephropathy. Various alterations to the vascular cells caused by hyperglycaemia can also contribute. In addition, diabetic sufferers are more prone to developing cardiovascular disease. (Note that high blood pressure is a symptom of, complication of, or contributor to a number of conditions.) Gwinva (talk) 00:38, 6 March 2009 (UTC)

It is possible that the questioner is wondering why "normal" blood pressure in a non-diabetic is commonly anything less than 140/90 while "normal" blood pressure in a diabetic is anything less than 130/80. These come from many studies that were used to create the JNC7 guidelines (available here). Of note, patients with chronic kidney disease are also considered "normal" with a BP less than 130/80. Also note that I put "normal" in quotes as it isn't actually "normal". Between 120/80 and 140/90 is prehypertensive. Most people just consider anything non-hypertensive as normal and ignore the prehypertensive category. -- kainaw™ 03:57, 6 March 2009 (UTC)

I am very thankful to Gwinva and Kainaw for ur interest. I had an idea that in patients of Diabetes, normal values of preessure are high (my friend asked to me) Iam myself a medical student but I could not get the reason(answer), so I asked u. But I failed to get some conclusion here. Basically I wanted to know the mechanisms that are responsible for the Hypertension in the patients of diabetes. —Preceding unsigned comment added by 201.220.215.12 (talk) 04:31, 6 March 2009 (UTC)

As Gwinva mentioned, you want Syndrome X; most likely the underlying mechanism is insulin resistance. - Nunh-huh 04:37, 6 March 2009 (UTC)