Wikipedia:Reference desk/Archives/Science/2009 May 21

Science desk
< May 20	<< Apr | May | Jun >>	May 22 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

May 21

Coraline and Real-D

Coraline was easily one of my favourite films of the past year. Even after seeing it in normal 2-D, it was well worth the price of seeing it again in Real-D (if only for the folded paper mice at the very, very end, after the theatre was empty!). Our article says that the DVD release will include both versions, but our article about Real D Cinema indicates that that process requires some pretty heavy duty specs to show in 3-D. Are those specs only applicable to projected films (i.e. a theatre) or will the normal DVD/Blu-Ray versions be the same quality as the film? Matt Deres (talk) 01:38, 21 May 2009 (UTC)

I don't see how they can show the 3D version on a standard or HD TV screen. In movie theatres, the 3D effect is produced by displaying the left eye and right eye images with different planes of polarization - and the 3D glasses filter out the undesired image for each eye. But a TV screen can't do that. There are 3D technologies that do work with TV - for example by drawing the left-eye image in red and the right-eye image in cyan and using glasses with colored lenses - but that produces nasty flicker and weird color fringing. Alternatively, they can display left and right eye images in alternate frames and use rather expensive 'LCD shutter glasses' which alternately blank out the left and right eye images alternately - but those have to be synchronised to the video stream somehow - which entails special electronics in the video player (or in the cable between the video player and the TV) to send a signal to the glasses (typically via infra-red) to tell it which eye to blank out for the following 1/60th second (1/50th in the UK). Some company once did a similar thing with a little gadget with a rubber suction cup that you stick onto the bottom-left corner of your TV screen that picks up light from a flickering black or white square and relays it to the glasses. But the cost of shutter glasses is pretty steep - and the red/cyan glasses suck - so I can't see how they plan to do this for the DVD/BluRay market. SteveBaker (talk) 12:50, 21 May 2009 (UTC)

It will probably be red/cyan. Other films shot in the Real-d process have been released to Blu-ray in red/cyan. (example: My Bloody Valentine 3D)

Personally, I enjoy movies in red/cyan, but a lot of people have trouble converging the image, get headaches, etc. APL (talk) 16:45, 21 May 2009 (UTC)

It seems as though doing polarization-based 3D on an LCD screen would be pretty easy. LCDs require an outer polarizing layer anyway, and if you replaced it with alternating horizontal and vertical polarizers then ordinary viewing would be unaffected but H-V polarized sunglasses would send each pixel to only one eye. If they'd shipped LCDs like that from the beginning then there'd be a huge installed base of 3D ready screens now. Seems like a sad missed opportunity. -- BenRG (talk) 20:40, 21 May 2009 (UTC)

It would be pretty expensive to do that in the absence of a market demand. So many good technological ideas fail because of this kind of chicken-and-egg situation. There are no 3D TV's - so there are no 3D movies for TV - so there are no 3D TV's. It's not that we don't want 3D movies on TV - it's that we can't figure out how to get there from here. Personally, I think the LCD shutter approach is a better one for the home - it requires no change to the TV whatever - so you don't have to throw away your $3,000 80" flatscreen plasma in order to see 3D movies. But it does require an IR transmitter (about $10) and actively switching glasses (maybe $30 a pair). That would be relatively expensive if you want a lot of people to be able to watch the movie at the same time (which is why they don't do that in the 3D movie theatres) - but much MUCH cheaper than a new TV set for situations where only 3 or 4 people need to be able to watch at the same time. Also they work equally well for non-LCD TV's such as plasma, DLP, CRT, OLED, etc. But it's still a chicken-and-egg situation. Unless a whole bunch of movie-makers release video's in that format on the same day that the hardware manufacturers release the glasses - it's just not going to happen. SteveBaker (talk) 14:50, 22 May 2009 (UTC)

There are already LCD monitors (not TVs) that do that. E.g. iZ3D and the Zalman Trimon. See also [1]. There is also a small number of movies released in field sequential or sensio 3D, see [2]. You may also be interested in the Meant to be Seen 3D forums although primarily about gaming, they do have a forum for movies [3]. Most 3D rendered games can of course be played in (stereo) 3D albeit with some potential issues such as related to aiming, mouse cursors and 2D interfaces. For a long time nVidia had semi decent drivers (which they inhereted from someone I forget at the moment) supporting a variety of 3D modes. They didn't survive the Vista switch nor the switch to general purposes shaders i.e. Geforce8/9 very well and were relaunched eventually along with nVidia's shutter glasses with more limited hardware support. However now that nVidia is actually paying some attention perhaps game developers will too. There are also some decent drivers for shutter glasses from iZ3D for both ATI and nVidia although these are not free. Previously there were a variety of poor quality drivers from others that sometimes worked with ATI. Nil Einne (talk) 21:39, 22 May 2009 (UTC)

Yeah - it's really tough to do that well without help from the game programmers - the driver just doesn't have enough information to get it right. But adding it into a game isn't tough - the real problem is that it halves your frame rate - and serious gamers don't like that. Casual gamers might go for it - but they don't generally want to pay the money for high-end hardware. As games programmers, we'd rather use that horsepower to make a nicer non-stereo game than to make a 3D game for 1% of the market. Of course there is always the Virtual Boy. SteveBaker (talk) 23:32, 22 May 2009 (UTC)

Red/Cyan glasses work for me - but the color is a problem. Either you have to have very monochromatic video - or you have to strongly avoid putting bright red or cyan color into the image. If you draw a bright red bouncing ball against a black background and view it with Red/Cyan glasses, the left eye sees the ball OK - but the right eye sees nothing and the 3D effect is destroyed. Worse still, if there is (say) a flashing red light in the scene - it can make things alternately pop into and out of 3D which is enough to make you want to puke! The solution is to desaturate the video so that red becomes pink...that reduces the 3D artifacts - but makes for a less vibrant image. Red/Cyan is a gimmick - it's not a proper solution to the problem. SteveBaker (talk) 14:50, 22 May 2009 (UTC)

Well, this is depressing. :P I was really hoping the answer was going to be different. With regards to the red/cyan "solution", I wonder if the foresight of that eventuality influenced the colour-palette used in the film. There aren't very many bright colours used at all; a lot of the film is set in the dark, or the fog, and has fairly neutral colours overall. Matt Deres (talk) 14:02, 24 May 2009 (UTC)

Velocity profile of typical 12V DC electric motor

Hi, I'm wondering what the velocity profile is of a typical 12V electric motor? I've noticed (just empirically) that relatively low speed electric motors get up to speed pretty much straight away but I'd like a slightly more quantified estimate if possible. I think this question is best expressed in an example. So lets say I buy this motor and use it to run a little car. Approx how long would it take to get to its maximum speed of ~500 RPM? For arguments sake the load is approx 2kg.

Also on a related note, how do you convert the torque specification of 5 kg-cm to Nm?

Thanks --118.139.3.77 (talk) 03:02, 21 May 2009 (UTC)

Consider the moment of angular momentum versus the torque. This should answer your question. If a motor were trying to spin up a rotor of large moment, it would take longer than if the motor were spinning free of any load. More torque would get the system up to a given rotational velocity quicker. Edison (talk) 04:55, 21 May 2009 (UTC)

Would the load make that much difference? Wouldn't the load just make it run slower? At any rate I'm not sure on how you relate the moment of angular momentum to the torque of the motor to work out the time it would take to get to the maximum speed. Because say the output shaft of the motor was attached to a solid cylinder with a moment of inertia of 1 kgm^2, wouldn't that give a constant angular acceleration: T_motor = I_cyl*alpha_cyl => alpha_cyl = T_motor/I_cyl. And since the alpha is constant wouldn't that mean it would keep on spinning at ever increasing angular velocity? When surely it has to peak out at 500RPM? And it wouldn't really make sense to say it accelerates according to alpha_cyl until it reaches 500RPM and then suddenly stops because then what is balancing out the torque of the motor? Thanks, --118.138.152.143 (talk) 07:27, 21 May 2009 (UTC)

The motor isn't lifting the weight of the vehicle vertically. Assuming you're on level ground: You need to know the frictional forces (both static and dynamic) and the air resistance (if it's significant at the speeds you expect to travel). Once you know how much force the motor has to apply to overcome those things - you can take the torque and the wheel diameter and figure out how much force there is left over to accelerate the vehicle. You know the mass of the vehicle and the force available from the motor - so you can calculate that acceleration. Then you can turn linear acceleration back into rotational acceleration (again, knowing the wheel diameter) and you'll know the rate of rpm increase. SteveBaker (talk) 12:38, 21 May 2009 (UTC)

Was the ice age cold enough?

According to Quaternary_glaciation, The earth was 8 degrees (C) cooler at the peak of the last ice age. This sent glaciers all the way down into in Upper Midwest. But such a temperature change doesn't seem to me to be enough to cause such glacial expansion. Consider Minneapolis, for instance, whose geology is influenced by past glaciation. According to Minneapolis#Geography_and_climate the average high in July is 29 C. If it were 8 degrees cooler it would still be a warm 21 C, more than enough for the snow to melt through the year. The average year-round temperature would fall to -1 C. Seems cold enough, but Fairbanks, Alaska is colder at -3C [4] and is not currently covered by glaciers. What am I missing?

140.247.125.9 (talk) 04:27, 21 May 2009 (UTC)

Who in Minneapolis talks about temperature in centigrade/Celsius? Edison (talk) 05:44, 21 May 2009 (UTC)

nobody, but Wikipedia's graphs are all in celsius. 140.247.125.15 (talk) 17:06, 21 May 2009 (UTC)

The temperature changes more at the poles than at the equator so currently the poles are melting whereas the temperature has only changed a little at mid to equitorial latitudes. In an ice age the poles get much colder and the effect spreads down but the equator isn't all that much colder. The big expanse of ice causes a feedback effect cooling the area that is iced up. Dmcq (talk) 07:50, 21 May 2009 (UTC)

(edit conflict) Temperature change is not uniform. The number you reference, presumably from the plot, was for Central Antarctica. The global average change during the ice age was ~3 C, with the tropic changing much less than the poles. Central Greenland, by way of contrast saw a temperature change of ~30 C. Ice sheets grow by starting at places that are very cold and spreading outward. As they spread, the effect of covering more areas with ice and snow for more of the year often causes further cooling by reflecting sunlight into space (an albedo feedback). In addition, ice sheet growth also requires an available supply of moisture to allow for regular snowfall. Fairbanks, to use your example, is far enough North that the prevailing winds are polar easterlies. This means most of its weather comes from dry Canadian air rather than from the Pacific. As a result it is harder to form glacier there than on the East coast of North America at similar latitude, where one will get snow from Atlantic moisture. Hence ice sheet in North America start in the far northeast and grow out and down as temperatures fall. Dragons flight (talk) 07:52, 21 May 2009 (UTC)

When birds sleep...

Why do they usually turn their heads through 180 and tuck their beaks into their back feathers? Is it just to keep their faces warm, or is there a physiological reason for it? —Preceding unsigned comment added by 81.77.140.54 (talk) 08:42, 21 May 2009 (UTC)

Perhaps, it acts as a natural and ready to use pillow for them, which provides comfort (in the sense of softness) and warmth both. - DSachan (talk) 09:23, 21 May 2009 (UTC)

In Britain, for example, during the winter a large proportion of birds are killed during the nights from the cold, particularly when they are short of food and hence the energy to keep them warm. Anything that reduces their surface area will help them survive. (I remember hearing or reading that the dawn chorus intensity is in proportion to the left-over energy budget from the night). Plus, I imagine that they save energy by being able to relax the neck muscles which are no longer working to hold up the head. And like humans, when they sleep their head would droop if not supported. 78.146.67.27 (talk) 10:53, 21 May 2009 (UTC)

I suspect that it helps keep the biting insects at bay. If you've ever seen a bird on the nest being swarmed by mosquitoes and black fly. You would understand. 67.193.179.241 (talk) 20:44, 21 May 2009 (UTC) Rana sylvatica

On the topic of thunderstorms and humans

I am personally very fond of thunderstorms. They bring about a certain "charged" smell in the air, a heated and moist atmosphere and indeed, the rumbling from afar is tad soothing. I know a dozen more of my friends share this with me, and while lightning striking nearby does affect us all in similar way, I was keen on asking a question more related to thunderstorms from afar: Shouldn't I feel less enthusiastic when I know a thunderstorm is about to come? Most animals seek shelter, I can't imagine too many of them enjoy the ordeal, but while some humans retain the fright of thunderstorms, many (most, according to my original research) don't. The precautionary signs come off in a comfortable way. What is to be attributed for my experiences? Simply that I've never experienced anything to teach me otherwise, or that a more built-in switch has been dulled over generations of having shelter? Thank you in advance. 90.149.144.55 (talk) 10:34, 21 May 2009 (UTC)

I'm just speculating here, but it seems to me that if you're a human-sized animal, you really don't worry about thunderstorms too much. The chance of encountering a lightning strike in our natural habitat (the savannahs) is very small, and there isn't much shelter to speak of around. It's probably even a good time to hunt for certain animals. Dcoetzee 10:39, 21 May 2009 (UTC)

Well, one of the cool (and really comparatively advanced) things about us humans is that we are capable of ignoring or overriding our instincts based on the circumstances and rational thinking. Animals aren't very good at that. I mean, when we get angry, horny or scared, we can still function properly -- we don't start fighting, screwing or running away at the drop of a hat as soon as the urge strikes us. (Well, some people do, but people with that poor impulse control are generally trouble, and in trouble.) I was a little scared of thunderstorms when I was a kid; these days, like you, I love 'em. A part of it is probably the fact that I know I'm safe, and while I haven't examined my feelings very closely, I wouldn't be surprised to find that I'm still a little scared somewhere deep inside, but knowing that I'm safe, I can enjoy the thrill -- not unlike going on a roller coaster ride at an amusement park. -- Captain Disdain (talk) 11:17, 21 May 2009 (UTC)

Captain, i respectfully disagree with "animals aren't very good at that". Any plant or animal can be aclimatized, habituated or get used to, any stimulus within thier physiological limits. Again, HUMANS ain't so special. 67.193.179.241 (talk) 20:51, 21 May 2009 (UTC)Rana sylvatica

Sure, animals can get used to all kinds of things, but there's a great conceptual -- and cognitive -- difference between becoming acclimatized to something and making an actual case-by-case decision to disobey the instinct. The latter tends to require abstract reasoning skills. -- Captain Disdain (talk) 23:32, 21 May 2009 (UTC)

I suspect (without evidence) that we're 'wired' to seek shelter in the case of storms - which means that something in our brains makes us feel uncomfortable out in bad weather and comfortable when we reach shelter. If our emotional systems "reward" us for achieving an instinctual goal, that would be no surprise. We feel similarly comfortable after eating, sex and other such activities. It seems reasonable then that when we hear a storm and are sheltered - that we feel good about that. SteveBaker (talk) 12:31, 21 May 2009 (UTC)

Maybe I'm not like other people, but personally I like being outside rather than in when a big storm is coming. Then again, I also want to go tornado chasing, so I think my fight-or-flight instinct is broken.-RunningOnBrains^{(talk page)} 14:18, 21 May 2009 (UTC)

I just got myself thinking: maybe more of us are adrenaline junkies than we give ourselves credit for. Maybe that sense of impending danger is what gives you a pleasurable rush. -RunningOnBrains^{(talk page)} 14:22, 21 May 2009 (UTC)

I think all the answers above are very good. I would only add that thunderstorms may engage our higher brain functions as well. We live in an age that allows us unprecedented communications abilities; we can vicariously experience almost anything we care to imagine, but there's something to be said for the first hand, totally immersive experience of being within a powerful thunderstorm. For an old atheist like myself, it's probably as close as I'll ever come to experiencing something of that kind of terrible power. The kind of awe that power can elicit is probably not too far from an old-time fire-n-brimstone religious experience. Matt Deres (talk) 13:38, 21 May 2009 (UTC)

The "charged" smell you sense is probably ozone. It is said that some people react positively to the ionised air before thunderstorms. Cuddlyable3 (talk) 14:04, 21 May 2009 (UTC)

The fear factor is partly situational, I think. I ordinarily don't have any fear of thunderstorms, but I've been caught in exposed positions a couple of times -- once on a mountain pass with lightning striking all around and numerous lightning-blasted trees beside the trail -- and it definitely got my adrenaline going. Regarding the smell, I think it comes more from rain on dry ground than from ozone. Looie496 (talk) 16:31, 21 May 2009 (UTC)

Rain on dry ground happens in any sudden downpour. If the smell is unique to thunderstorms then it is more likely from the ozone. That would require lightning to be nearby, though, you wouldn't get any ozone from a thunderstorm several miles away. --Tango (talk) 23:25, 21 May 2009 (UTC)

There is some element of instinct going on here. When the weather outside is utterly diabolical - storm, rain, etc. I feel very good about curling up on the sofa with a good book or vegging out watching TV. When it's gorgeous weather outside, I find it very difficult to do those things - even though I have no intention of going outside. That's not the rational part of my mind doing that - because if you're indoors anyway, what the heck does it matter what's going on outside? SteveBaker (talk) 14:36, 22 May 2009 (UTC)

Avoiding sexual arousal

I'm not sure if this is science or not. I took a guess. Anyway, my friend has two problems. One, she gets aroused very easily by vibrating buses - something which she finds intensely uncomfortable, especially as she has to take a bus to university every day. Secondly, she has wet dreams, which again, she doesn't enjoy. Is there any way to control or prevent either of these? Vimescarrot (talk) 10:28, 21 May 2009 (UTC)

Some people just happen to be very easily sexually stimulated by certain stimuli. I'm not aware of any treatment for this, although she can talk to her doctor about it if she feels comfortable doing so (I do know that there are some drugs that decrease libido - this is generally listed as a negative side effect - but I don't know if she'd want it to be impeded all the time). Generally, we can't give medical advice here. The only suggestion I can think of is to bring along a book or a music player or something to help divert her attention, and if possible to seek a more comfortable alternative to the bus. Dcoetzee 10:35, 21 May 2009 (UTC)

Maybe she just needs more sex, duo or solo? Or does she have religious reasons for abstaining? If you are a male friend, are you sure this is genuine and isnt just a come-on? 78.146.67.27 (talk) 10:56, 21 May 2009 (UTC)

She has reasons for abstaining, but she won't tell me what they are. Vimescarrot (talk) 11:09, 21 May 2009 (UTC)

Generally, if someone is abstaining from sex for reasons they aren't willing or able to disclose and gets very disturbed by arousal or wet dreams, I would consider that a kind of a warning sign. I could speculate, but what with the information available to us being second-hand and especially that whole medical advice thing, I'm gonna pass. Instead, I would recommend that she talk to a good therapist. -- Captain Disdain (talk) 11:23, 21 May 2009 (UTC)

Why the hell wouldn't she enjoy sexual dreams?? As for the bus thing,, see PSAS —Preceding unsigned comment added by 82.44.54.169 (talk) 11:23, 21 May 2009 (UTC)

82.44 - Just because you enjoy your sexuality, doesn't mean everyone does. Vimescarrot (talk) 11:33, 21 May 2009 (UTC)

True enough, but when the body and mind are at odds, it's an indication that one side or the other needs to be brought into alignment. The one requires a therapist, the other requires a physician; neither would benefit particularly from strangers on the internet making guesses based on second-hand information. The anon's comment was a little insensitive, but speaks to the general truth that the mind is often confused while the body seldom is. Matt Deres (talk) 13:43, 21 May 2009 (UTC)

I have heard two advices given to celibate monks troubled by sexual desire: A) Imagine that everyone is your brother or sister, and B) Picture everyone without their skin. Cuddlyable3 (talk) 13:42, 21 May 2009 (UTC)

The OP's friend isn't being aroused by specific people, though. Avoiding being sexually stimulated by the bus could be as simple as sitting it a different position. Cross or uncross your legs, maybe. Being made uncomfortable by wet dreams isn't something we can help with, though, that needs a therapist. --Tango (talk) 14:29, 21 May 2009 (UTC)

Check to see if she's figiting with her legs; bouncing one leg up and down is a common indication that someone is sexually aroused. It's considered by some to be an almost unconscious form of masturbation. If she's moving her legs all the time then she's likely sexually aroused more often than just on her way to school, and it's not just the bus (although that would indicate that the bus does a better job at pleasing her than her own legs). -Pete5x5 (talk) 16:07, 21 May 2009 (UTC)

Restless leg syndrome, though an invented reason to sell a drug, is not an unconscious form of masturbation. Tempshill (talk) 16:08, 21 May 2009 (UTC)

Unconsciously figiting is not restless leg syndrome. --Tango (talk) 16:27, 21 May 2009 (UTC)

Check to see if she's figiting with her legs; bouncing one leg up and down is a common indication that someone is sexually aroused. It's considered by some to be an almost unconscious form of masturbation.

Wikipedia articles are fine. Vimescarrot (talk)

Actually, I don't know why I responded to that. I don't need to know when she's sexually aroused (she tells me anyway), and we already know why. I was just after how to stop it. Thanks for trying, though. Vimescarrot (talk) 17:02, 21 May 2009 (UTC)

To me, this looks like a request for medical advice, right? Axl ¤ [Talk] 21:09, 21 May 2009 (UTC)

At least partially, yes, which is why people have been suggesting going to a therapist. --Tango (talk) 23:23, 21 May 2009 (UTC)

Becoming physically aroused without being mentally aroused or "interested" is not a bother to me, nor is it something I prefer. Perhaps she should be a bit more comfortable with herself. If she dislikes the dreams because they are sexual, not because the interfere in her normal life or they are scary dreams, then she should also be comfortable with her own mind. Also see lucid dreaming. Mac Davis (talk) 18:42, 23 May 2009 (UTC)

Rules of thumb to identify wildflowers?

The rules of thumb I know are that if its got four petals, its a member of the mustard/cabbage family, and if its got five petals then its a member of the Mallow family. Are these two rules of thumb reliable, and are there any more? I am in the UK, but such rules of thumb might apply worldwide. 78.146.67.27 (talk) 11:01, 21 May 2009 (UTC)

No, they are not reliable in that form. For example, a flower with four petals may belong to a plant in Papaveraceae and not only in Brassicaceae (=Cruciferae), and a flower with five petals may belong to a plant in Rosaceae, Oxalidaceae, Violaceae, Geraniaceae, etc., and not only Malvaceae. --Dr Dima (talk) 19:58, 21 May 2009 (UTC)

Those are not reliable rules and to each rule there are exceptions, BUT if the flower consists of many "florets" it is generally in the composite family. If the stem of the plant is roughly squared, then it is usually in the mint family. Can't think of exceptions to either rule but learning to use botanical keys quickly, is learning to cheat. That is, if you recognize that a plant is in family "X" then you can go to the index and find where that family is in the key. Good luck and have fun. 67.193.179.241 (talk) 21:19, 21 May 2009 (UTC) Rana sylvatica.

Thanks. "The family Asteraceae or Compositae (known as the aster, daisy, or sunflower family) is the second largest family of flowering plants, in terms of number of species." Cleavers or Goose grass is one of the exceptions to the square-stem rule. 78.146.162.232 (talk) 11:30, 22 May 2009 (UTC)

Biology - water

In cold countries such as Alaska, the surface of the sea freezes first or becomes solid ice, while the bottom of the surface still remains in liquid state. Why? —Preceding unsigned comment added by 60.53.212.205 (talk) 11:12, 21 May 2009 (UTC)

Because ice floats. 78.146.67.27 (talk) 12:07, 21 May 2009 (UTC)Rkr1991 (talk) 13:04, 21 May 2009 (UTC)

Exactly. Ice has a density of only approximately 9/10th of water, and hence when water freezes, ice being lighter rises to the top. This is of vital importance to the survival of fish and other aquatic animals. If ice had frozen from the bottom, they would have been pushed to the top, an a more dangerous environment. Now since ice freezes from the top, they can swim underneath the ice sheet. Also, don't forget to sign your posts by typing 4 '~' signs at the end :) Rkr1991 (talk) 13:04, 21 May 2009 (UTC)

Also, the sheet of ice on the top tends to insulate the water underneath and prevents total freezing. If it froze from the bottom up you would end up with the whole thing frozen. This peculiar feature of water (most substances constantly contract as they cool, water has a little bump in the graph near its freezing point) is one of the things that makes it so good for life. They have been theories about life on the moons of the outer planets based on ammonia, but ammonia doesn't have this advantage (it also lacks certain other advantages). --Tango (talk) 14:33, 21 May 2009 (UTC)

A crucial point is that (for fresh water) the maximum density of water occurs at 3.98 °C (39.16 °F), that is, several degrees above freezing. This means that the deep water is never colder than that, because colder water will rise. The same thing holds for sea water, except that the temperatures are different. Looie496 (talk) 16:40, 21 May 2009 (UTC)

Is that point of maximum density universal, or does it depend on pressure? --Tango (talk) 16:43, 21 May 2009 (UTC)

Here is a graph of water density vs. temperature and pressure and based on the maximums, the point of greatest density does indeed depend on pressure. Regarding ice density, there are some other forms of ice made using varied temperatures and pressures which have higher densities than liquid water like Ice III (1.16g/cm3 (at 350 MPa)). I'm not sure if Ice III is more dense than water at 350 MPa though. Sifaka ^talk 00:35, 22 May 2009 (UTC)

No, the same thing does not hold for sea water. For sea water, due to its salt content, the maximum density of the liquid is at the freezing point. Dragons flight (talk) 17:31, 21 May 2009 (UTC)

Interesting. I didn't know that. I wonder what's the minimum amount of salt necessary in order to make the point of maximun density coincide with the freezing point. Dauto (talk) 23:01, 21 May 2009 (UTC)

If what you are saying is true D.F., I'm not sure that implies that saltwater ice is equally or more dense than the saltwater it's in. To rule out the brine effect (the tendency for ice to exclude solutes as it freezes), I'm making a solid icecube of 125mM NaCl and I'm going to see if it floats or sinks in the same liquid solution it is made from. I'll report the results once the cube freezes entirely solid. (Later Edit:) I went and spilled my liquid solution and was too lazy to make some more so I tested my salty ice cube in tap water and it still floated, just barely. Sifaka ^talk 00:35, 22 May 2009 (UTC)

The solid is still less dense than liquid. It is just that the point of maximum density of the liquid shifts to the freezing point of the liquid rather than several degrees above the freezing point as is seen for pure water. It is also worth noting that the solid-to-liquid density shift is very large in all cases. By contrast the temperature dependence of density within the liquid state is relatively quite small. Dragons flight (talk) 00:51, 22 May 2009 (UTC)

DF, are you saying tha the maximum density of saltwater is precisely at the freezing point, or just much nearer the freezing point than freshwater? Is there a graph for the salinity/density/freezing point relationship? I'm asking because of my fascination with the very weird properties of water in all its phases. Franamax (talk) 09:34, 22 May 2009 (UTC)

AFAIK Freezing also changes the concentration of salt because it gets squeezed into channels and oozes out. You then get water with less salt in it which again floats. Drift ice. 71.236.24.129 (talk) 09:49, 22 May 2009 (UTC)

Self-suggestibility - link to confabulation?

I'm sure I'm not the first person to say the suggestibility article reads poorly and looks to be mostly about hypnotic suggestibility. (Or, maybe the editors are just very suggestible and have been told it's god like it is. :-) )

I was wondering how it was that some - especially children - are able to think that things they imagine are actually real. Is this self-suggestibility due to confabulation? Do their minds naturally envision that, "Since I thought/envisioned it, it must be true?" What about adults? I'm not talking necessarily about the criminal who - desipte all the evidence they did it - convinces him or herself they didn't, though that may be part of it.

I would even be tempted to try to edit the article to include mention of confabulation, but I wouldn't have real sources. But, there has to be more to suggestibility than hypnotic states, doesn't there? 209.244.30.221 (talk) 13:29, 21 May 2009 (UTC)

I'll give this a shot. First off, when you say above that editors have been "told it's god" - have you been staring at any rotating coins lately? ;)

The confabulation article seems to be about manifestations of neurological impairment. This is not the case with children, rather there is an ongoing process of distinguishing imagination from reality. Recall that for the first several months of a human life, the baby is not able to even recognize the difference between itself and its environment. For many years, one depends on one's parents to explain that your dreams were only that, that the scary movie you watched was all made up, and that it's OK to walk down the stairs into a dark basement. It takes a long time for a brain to settle down and get on with the boring process of plain old living a life. Even then, many people are still compelled by their imagination and they imagine crazy realities like light bulbs and microprocessors. That's just normal neural development,

Looking at the Suggestibility article, I'm struck by the section discussing the differences between suggestible, susceptible and gullible. Confabulation may play a part there too as a pathological manifestation, but yes, you would need to assemble some sources. If you do find them, please be bold and edit away! Franamax (talk) 08:54, 22 May 2009 (UTC)

Carbon Monoxide Poisoning

Hi, I've always been curious about some of the specific points relating to carbon monoxide poisoning and have been unable to find answers elsewhere, I have five questions, any help or answers would be greatly appreciated:

1. Many of the long term effects of co poisoning(CoP) can take several weeks to show up, I've read that this is due to the long term effects being caused by CO debinding from hemoglobin, then becoming toxic. Is it true that this is the cause of longterm effects, and if so would being treated with hyperbaric oxygen after 48 hours, but prior to several weeks, have any benefit?(HBO has a large benefit if administered within 48 hours)
2. CoP can have permenant/long term effects of cognition and memory formation; in the event that these effects occur, how often are they permenant?
3. Related to the above, I've read that some cases of CoP present mild symptoms so that the victim is unaware that have been poisoned; supposing that such a case did cause cognitive/memory problems, would the victim be aware that they had such problems? In other words, would the person be able to tell that they something was wrong, or would they be oblivous to such things, perhaps thinking that they have become somewhat absented minded...in short, how obvious are the brain based effects of CoP?
4. Again relating to the above; I've read that CoP causes demylination to occur in the white matter of the brain, and I've also read that their are medicines for other disorders that can reverse the effects of demylination; given that this medicine was developed for other disorders, would it be effective in reversing the effects of CoP also?
5. My final question, again related to the above; in the event of long term cognitive impairments would a CT/MRI be able to detect such damage? Are there any means to estimate the ammount of damage, the possiblity of recovery, or the chance of further degradation? I've read that in the first few weeks after exposure that small pockets of atrophy can be detected in the brain, though I would imagine that in time these atrophied cells would be removed by the body; is this accurate?

Thank you for any help. P.S. I do realize that this question could be considered "medical" in nature, to avoid giving the wrong impression; I am asking out of curiousity, not because I think I may have CoP or any other such thing:) Phoenix1177 (talk) 14:43, 21 May 2009 (UTC)

I have adjusted the formatting of your question slightly, I hope you don't mind! --Tango (talk) 16:30, 21 May 2009 (UTC)

To answer question 1: Carbon monoxide washout follows a biphasic pattern due to myoglobin binding. From this article, half times while breathing air are 236 minutes and 302 minutes; breathing 100% oxygen they are 87 minutes and 160 minutes. The CO level will be back to baseline within a couple of days. Our article "Carbon monoxide poisoning" describes the mechanisms of toxicity. The main effect is binding to haemoglobin, which reduces the oxygen-carrying capacity of blood, leading to tissue hypoxia. The other mechanisms are (probably) less important. Release of CO bound to myoglobin does indeed slow the rate at which CO in the blood falls. However this is not enough to actually raise the blood CO level. I am unconvinced that hyperbaric oxygen has "a large benefit". This study did not demonstrate superiority over high flow oxygen (FiO₂ 100%) at normal barometric pressure. Axl ¤ [Talk] 21:42, 21 May 2009 (UTC)

Scanning western blots randomises results...

Is there an advantage to using built-for purpose gel/blot scanners from biotech companies over a regular scanner for the purpose of scanning in western blots stained with AEC stain?

We've been using an ordinary scanner, and then quantifying the bands but I notice that the same band from two different scans of the same blot divided by the first band in the blot (for normalisation purposes) can differ by as much as two-fold. It depends on the contrast settings used. Default settings don't always result in fair representations of the actual blot. How does one overcome this? ----Seans Potato Business 15:03, 21 May 2009 (UTC)

If you mean an ordinary scanner in the sense of an off-the-shelf document scanner, I think that's a remarkably bad idea. Their nonlinearities are hideous. Looie496 (talk) 16:47, 21 May 2009 (UTC)

You shouldn't need anything fancy to scan in your gels and quantitate the bands. The commercial scanners are usually bundled with software that facilitates the analysis process and they come with other bells and whistles that make it worthwhile for some people to buy them. You can test for nonlinearity by just scanning the same gel a few different times and checking to make sure that you're getting similar results. Granted, if you're doing ultrasensitive measurements, Looie has a good point.

However, I think you already have a clue about why you're getting disparate results -- it sounds to me that the software you're using to adjust contrast is actually changing the information content of the image instead of just representing it differently on your display. This can be a huge problem because you're basically saturating the darkest bands to be able to see the lightest ones. If your image software is doing this, you need to either perform the quantitation on the unmodified image (you may not be able to see the band very well but the computer will be able to count up the gray levels for each pixel without a problem), or get new software!

If you just want to contrast the blot for the purpose of presentation or publication, you can do so but you should be honest and report that the image was contrasted using such-and-such program. Image manipulation can be very misleading and is pretty rampant in the scientific literature! --- Medical geneticist (talk) 16:57, 21 May 2009 (UTC)

Energy from walking feet

I read somewhere that now-a-days, many scientists have developed methods to produce and use energy in many forms, from walking human steps! Can anyone tell me how is this done? many thanks. 59.103.63.74 (talk) 23:08, 21 May 2009 (UTC)

I'm not sure what you are talking about, but I know that some wrist-watches use energy from a person's movement to self wind. This is not a new technology. Dauto (talk) 23:17, 21 May 2009 (UTC)

There are two technologies you could be describing. There are some devices that are powered by being shaken as a person moves. I also recall a design for a floor that uses the vibrations caused by people walking over it to generate power (possibly the floor of a subway station...). Which one are you interested in? --Tango (talk) 23:21, 21 May 2009 (UTC)

I think he is thinking of piezoelectrics which generate a tiny amount of electricity when mechanically compressed. Placed in everyday areas subject to compression, such as the sole of your shoe, and rectified in the right way this can be used to do small amounts so work. The available energy is usually quite small though. See also: Energy harvesting. Dragons flight (talk) 00:58, 22 May 2009 (UTC)

There are also floors that generate energy from the friction of those walking around on it. http://www.groovygreen.com/groove/?p=1867 has more info on them. 194.221.133.226 (talk) 09:08, 22 May 2009 (UTC)

It's not friction, it's impact. That's the kind of thing I was trying to describe above. --Tango (talk) 11:08, 22 May 2009 (UTC)

The compression technique is one method, but the questioner might have been think about something like the backpack that generates power. There were a bunch of news stories about this a couple of years ago. Looie496 (talk) 17:48, 22 May 2009 (UTC)

The anon I replied to gave a link to a description of what they were talking about, it is clearly talking about piezoelectrics. --Tango (talk) 18:23, 22 May 2009 (UTC)