Wikipedia:Reference desk/Archives/Science/2010 March 16

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March 16

3,3-Dimethylmalic acid

I'm looking for a reference for the acid dissociation constants for 3,3-Dimethylmalic acid. I checked my usual source, the CRC, which didn't have it. I did a google search, where I only found a little bit about the compound at all, and nothing about the acid constant (here, for example). I have access to a lot of journals at my university, so any citation would be welcome. Thanks. Buddy431 (talk) 01:21, 16 March 2010 (UTC)

SciFinder reports a value of the pKa as 3.41±0.15 (no information on the second or further deprotonations). This was calculated using ACD/Labs Software V8.14. The 7 references that SciFinder has for this compound (CAS Registry Number: 73522-92-6) don't appear to be studying the physical properties. 24.150.18.30 (talk) 01:51, 16 March 2010 (UTC)

since it is a fairly simple compound, I think that the calculated pKa would be fairly trustworthy. Anyone have any other opinions on ACD predictions?. 24.150.18.30 (talk) 01:51, 16 March 2010 (UTC)

Thanks for the quick response. That's better then nothing, I guess. I'd rather have experimental results, and I'd really like the second dissociation constant, if possible. Buddy431 (talk) 02:02, 16 March 2010 (UTC)

Any reason to believe the methyl groups would change the pKas? AFAIK intramolecular hydrogen-bond stabilisation increases the acidity and I don't see how the methyl groups would interfere (if anything it would enhance). John Riemann Soong (talk) 06:24, 17 March 2010 (UTC)

Squirrel identification

Hi, can anybody identify either of these two squirrels for me. It should be easy since they only get a few species. I'll add them to the species articles upon response, thanks in advance. --Benjamint 06:00, 16 March 2010 (UTC)

• 
  Taken at the base of Bukit Timah hill, Singapore
• 

It looks at first shot to be a Plantain squirrel, (Callosciurus notatus), another pic [1] Richard Avery (talk) 08:33, 16 March 2010 (UTC)

So I guess by elimination the other is a Slender Squirrel? I'll go ahead and change it. Thanks --Benjamint 05:29, 17 March 2010 (UTC)

Compression of purely digitally animated films

Consider a purely digitally animated film such as shrek or Finding Nemo. I wonder what the difference is between the file size of the film (stored in some sufficiently-high-resolution pixel-based format) and the size of the original dataset used by the software to render the film (in which the characters are described as a set of coordinates that presumably need to be stored only once, their movements can be described using instructions like "move a certain joint by a certain amount of degrees"). 83.134.160.19 (talk) 06:44, 16 March 2010 (UTC)

Useful stats can be gathered from open movie projects such as Elephants Dream and Big Buck Bunny. For Elephants Dream it's available at 1080p resolution at 815MB for a 11 minute film, compressed with MPEG4. In contrast the production files (texture, models, animation, sound, etc.) are split across 2 DVD's. I do not have an exact figure but 2 DVD's are about 9GB worth of data. For Big Buck Bunny the 1080p MPEG4 compressed version is 890MB, but the entire studio backup is over 200GB. --antilived^{T | C | G} 07:01, 16 March 2010 (UTC)

Thanks! I'm surprised the original data is actually larger than the film itself. I would have expected the opposite. 83.134.160.19 (talk) 07:08, 16 March 2010 (UTC)

The uncompressed number for Elephant's dream is 246 Gbytes. 1080p format is 1920x1080 pixels at 60 frames per second and at (as a minimum) 3 bytes per pixel - so 1920x1080x60x3x11x60= 246,343,680,000 bytes. If they used high-dynamic-range rendering, then it might be as much as four times that amount. Adding in the models, textures, etc is really cheating because that would include the means for MAKING the movie - not the movie itself. Anyway - that yields a fairly typical MPEG compression ratio of about 300:1. SteveBaker (talk) 12:48, 16 March 2010 (UTC)

Would they really render at 60 fps? Blu-ray Disc only supports 1080p at 24–25 fps, and according to Digital_cinema#Digital_projection, the 2K projection spec is 48 fps max. (And I suspect that 24 fps is far more common.) -- Coneslayer (talk) 12:57, 16 March 2010 (UTC)

a question about light

can we move an object using light... —Preceding unsigned comment added by Avinashmani (talk • contribs) 09:12, 16 March 2010 (UTC)

Yes. solar sail, radiation pressure 157.193.173.205 (talk) 09:22, 16 March 2010 (UTC)

Also Beam-powered propulsion, but note that some of the craft in that article have only been proposed, not successfully built. AlmostReadytoFly (talk) 12:18, 16 March 2010 (UTC)

Interesting article, I remember hearing about a team trying to develop a sustainable idea for a space elevator using a similar concept using a ground based laser as a power source for the elevator on the cable. Regards, --—Cyclonenim | Chat  13:19, 16 March 2010 (UTC)

That wasn't moving the object directly using light - it was using solar panels, lit by the laser to charge batteries that the motors would use to propel the robot up the cable. That's not really the same thing. SteveBaker (talk) 13:56, 16 March 2010 (UTC)

For something a little more abstract, see optogenetics. Nice demonstration video here. N.B. The OP doesn't specifically state that light is the source of energy of movement, just that an object can be moved by light. --Mark PEA (talk) 17:58, 16 March 2010 (UTC)

I read a science book when I was a kid that explained how to make some kind of little pinwheel thing with four blades that were shiny on one side and black on the other. You'd put it in a glass jar in the sunlight and it would spin (I think because of uneven heating). Either Wikipedia doesn't have an article on this thing, or, more likely, I'm not able to come up with the right name for it. —Bkell (talk) 18:15, 16 March 2010 (UTC)

Crookes radiometer. Compare to Nichols radiometer, which is what Crookes thought was happening. DMacks (talk) 18:59, 16 March 2010 (UTC)

Those things are always being sold as gizmo's that are rotated by photon pressure - but it's not true. The problem is that there is not a solid vacuum inside the globe and the air resistance (and probably the friction on the central spindle) is more than enough to overcome the photon pressure. The reason they spin when left in sunlight is that the black side of the vanes are heated slightly by the sunlight and that causes air to convect upwards which lowers the pressure on that side of the vane causing it to rotate (or something like that). When I last read about this, it was pointed out that these gizmo's actually rotate in the opposite direction than they would if it were light pressure that was moving them. SteveBaker (talk) 20:40, 16 March 2010 (UTC)

Yup. Our articles are pretty explicit about what's actually happening in the Crookes one...exactly how Bkell described it. DMacks (talk) 20:51, 16 March 2010 (UTC)

I like those things you get at the geek store that are black on one side and white on the other and spin when you put them in the light. We should expand the concept to train-sized models. —Preceding unsigned comment added by 99.254.8.208 (talk) 05:22, 18 March 2010 (UTC)

Don't forget Optical tweezers. -84user (talk) 18:33, 19 March 2010 (UTC)

Scientific results on animal telepathy?

Where can I find reliable information about animal telepathy? GerardLP (talk) 11:10, 16 March 2010 (UTC)

I know where to reply unreliable information: Google "animal telepathy". This paper, critical of animal telepathy advocate Rupert Sheldrake, is by academic psychologists who unsurprisingly find no evidence for psychic dogs. The article here on Rupert Sheldrake is also quite detailed. This article and this one from skepdic.com have some useful information and links, including responses from Sheldrake. The Clever Hans phenomenon is also relevant.[2] If you Google and work your way through the results you should find more. --Normansmithy (talk) 12:24, 16 March 2010 (UTC)

Let's be comepletely, 100% clear on this: There is absolutely zero proper scientific evidence for telepathy of any kind - animal, vegetable or mineral. However, dogs (in particular) often seem "telepathic" to humans because they have (non-psychic) senses that are more sensitive than ours. For example, my dog is able to tell from body language alone when I'm about to take him for a walk. This isn't telepathy - this is an animal that (in the wild) cannot rely on speech to know when the pack is about to go off hunting - and has to learn from subtle details of body posture. A pet dog uses those same skills to make seemingly impossible judgements from data that's too subtle for humans to notice. Those who seem to seek psychic explanations for everything are only too happy to interpret this behaviour to "telepathy" - which is a ridiculous assumption in the absence of controlled experiments. SteveBaker (talk) 12:39, 16 March 2010 (UTC)

Or the dog barks at the door before somebody knocks, not because they're psychic, but just because they heard them walking up the sidewalk, and we didn't, because they have better hearing. StuRat (talk) 14:18, 16 March 2010 (UTC)

Check out paramecium. Bus stop (talk) 14:20, 16 March 2010 (UTC)

The paper Bus stop is referring to does not imply telepathy but rather a possible communication system based on production of photons. There are plenty of species with bioluminescence, so how is this relevant to a discussion about telepathy? One might also notice that the article in question was published on April 1, 2009... I'd be rather surprised if PlosONE was playing an April Fool's joke, but it wouldn't be the first time someone made a gag in the scientific literature. --- Medical geneticist (talk) 16:44, 16 March 2010 (UTC)

They also have a "formal correction" to that article, and it is dated 21 July 2009, a date also known for its practical jokes. I find it here. Bus stop (talk) 16:51, 16 March 2010 (UTC)

Interspecies communication may be relevant. ~AH1^(TCU) 17:27, 16 March 2010 (UTC)

Treadmill vs uphill

What gives the most efficient exercise: Running on a treadmill that simulates movement uphill, or running up an actual hill with the exact same steepness? HenriT2 (talk) 11:34, 16 March 2010 (UTC)

I suppose it depends on your definition of "efficient". If both are at the same slope and all else is equal, then it's hard to imagine how there would be a difference. However, if your definition of "efficiency" is something like "calories burned per time expended" then if the treadmill is at home and the equivalent hill is a 10 mile drive from home - then the treadmill is "more efficient" just because you waste less time getting there and back. But then if things are not equal, it might be that the weather outdoors produces different air temperatures and humidity than where the treadmill is - so you'd be burning different amounts of energy because of that. SteveBaker (talk) 12:29, 16 March 2010 (UTC)

Steve seems to have forgotten the fact that in a treadmill you're not actually going up and the person's potential energy won't change. That makes a difference. Dauto (talk) 12:39, 16 March 2010 (UTC)

Your potential energy doesn't increase, but you have to expend energy to prevent it from decreasing. If you just stood there, you'd slide downhill (even with the treadmill off). If (and it's a big if) the treadmill offers minimal frictional resistance to sliding downhill, then walking/running an inclined treadmill should require the same power output as going up the same slope at the same speed. --Trovatore (talk) 20:00, 16 March 2010 (UTC)

Hmm -- now that I think about it, if there weren't any friction, you couldn't avoid sliding down no matter how hard you ran. So I guess the relationship is more complicated. Just the same, increasing the slope will make you work harder, even if it doesn't exactly track the effect of the same slope on a trail. --Trovatore (talk) 20:08, 16 March 2010 (UTC)

I'm not sure that case is actually achievable. I disagree about spending energy to prevent sliding - you just need decent grip on your running shoes for that. It's just like a weightlifter holding weights above his head - he doesn't require any energy to hold them there (under idealised assumptions, anyway - some energy is used to keep the arms rigid, but that's biology, not physics, and biology is far too complicated for me!), energy is only needed to lift them. The energy is used to counter the treadmill moving downwards, the friction between your feet and the treadmill should always be static friction. --Tango (talk) 20:31, 16 March 2010 (UTC)

I hadn't seen this paragraph — no, I'm afraid you've missed the point here. It's not about the friction between your feet and the treadmill; it's about the friction in the rollers.

Think of the treadmill going a constant 3 mi/hr or something, at an incline of 0. Now tilt it up. If you don't increase your power output, you will slide downhill. Not because your feet slip on the rubber — in general, they won't — but because the rollers of the treadmill itself will speed up, under the influence of the gravitational force. --Trovatore (talk) 20:53, 16 March 2010 (UTC)

Wait a minute -- no, I think as Stephan says below, it doesn't depend on whether the rollers speed up; you have to expend extra energy in any case. Have to think about this more carefully. Reminds me of the "airplane on a treadmill" thing that Cecil had to straighten out. --Trovatore (talk) 23:36, 16 March 2010 (UTC)

As StuRat says below, you have to look at the route taken, not just the endpoints. This is because the forces involved are non-conservative. If you watch someone on an inclined treadmill closely, I expect you will see them move up and down as the take a step up, then get carried down, then take another step up, etc.. As far as the vertical movement is concerned, the step up will be the same on a treadmill as in the real world, I think. The being carried down shouldn't have any effect on the energy used by the person. The horizontal movement will be different due to air resistance, as has already been mentioned, but that shouldn't be a significant factor for vertical movement because it is so slow (even a high incline is much less than 45 degrees). --Tango (talk) 20:19, 16 March 2010 (UTC)

Sure, but I'm thinking about the case where you move your legs smoothly, keeping your hips (and therefore your center of mass) at roughly the same height at all times. You still have to expend extra energy with increasing slope, to prevent sliding downhill. --Trovatore (talk) 20:23, 16 March 2010 (UTC) (Of course, hanging onto the handrails is cheating.) --Trovatore (talk) 20:25, 16 March 2010 (UTC)

I'm not sure that's right. If the person climbs up a step, then slides back down (without retrieving any of the energy lost in the climb), then the total energy use could be the same as a real hill. StuRat (talk) 12:57, 16 March 2010 (UTC)

Indeed, that is so (always assuming the usual abstractions). If you put on a pair of blind goggles, you cannot distinguish between running on a treadmill and running up a really smooth really long hill. Movement is relative. --Stephan Schulz (talk) 20:34, 16 March 2010 (UTC)

I also disagree with SteveBaker, for other reasons. According to a detailed article at Peak Performance, running on an inclined treadmill is easier than running on a real hill, due partly to the absence of air resistance which is important when running at speed but negligible on a treadmill, and partly to the fact that people on treadmills use different running styles from the real world; measures of oxygen consumption (which indicates how hard an athlete is working) are lower on a treadmill.[3]

In addition, a real hill may be slippery, uneven, or otherwise provide a harder workout. But when planning an exercise regime you shouldn't ignore the psychological factors: while some people find it easier to run on a treadmill (it's dry, you can watch TV), others find it more rewarding to run outside. --Normansmithy (talk) 12:46, 16 March 2010 (UTC)

Air resistance at a few miles per hour for a body with the cross-sectional area of a human is pretty much negligable anyway. SteveBaker (talk) 13:54, 16 March 2010 (UTC)

I don't think that's true. This page (from google) references an old study (Journal of Physiology, vol 207, pp 823-835, 1970) and says:

"the energy cost of overcoming air resistance during track running at a speed of 21.5k/hour (about six metres per second, or 67 seconds per 400m) is about 8% of the total energy cost. By contrast, the air-resistance cost doubles to 16% of total expenditure when running speed goes up to 10m/sec (100m in 10 seconds)."

So if the OP intends to run fairly quickly, air resistance might be a factor. Zain Ebrahim (talk) 14:19, 16 March 2010 (UTC)

10 m/s (22 mi/hr) will win the 100m dash against any but the most elite competition; there's not a person on the planet who can keep it up for a mile. Even 6 m/s is a 4:30 mile. I don't think this is what we're really talking about. --Trovatore (talk) 21:40, 16 March 2010 (UTC)

Yes, but that was just the data from the first google result I tried. The speeds I mention correspond to air resistance accounting for 10% - 16% of energy output. Even at speeds where it accounts for 2% - 4%, it would still be a relevant factor given the wording of this question. Zain Ebrahim (talk) 07:36, 17 March 2010 (UTC)

I would imagine, more generally as the time you spend exercising increases, running on a treadmill would be more efficient as you'd be maintaining a constant speed in order to keep up with the machine. If you're running in real life, you're likely to fluctuate your speed significantly over distance. Regards, --—Cyclonenim | Chat  13:17, 16 March 2010 (UTC)

Another vote for "it depends what 'efficient' means". Running on real ground involves many small supporting muscles in your legs that get less of a workout on the even and steady treadmill. If your goal is to get strong and useful legs, get on the real road. A similar thing happens in lifting free weights versus using weightlifting machines. --Sean 13:38, 16 March 2010 (UTC)

If by "efficient", you mean calories expended per session, then running outside will be more effective. Although there will be some air resistance, the excellent Bicycling Science by David Gordon Wilson explains that, for bicycles at least, the air flow over an outside cyclist rather than one on an exercise bike has a significant cooling effect. They can therefore maintain a moderate-to-high power output for up to three times as long as the person 'cycling' inside (if I recall correctly) before they overheat. There's also a chapter on aerodynamicity of cyclists and a little bit of data scattered throughout comparing other modes of transport, such as running and horseriding. Brammers (talk) 19:50, 16 March 2010 (UTC)

Of course the heating problem could in principle be overcome by putting a sufficiently powerful fan in front of the machine. That said, I really dislike exercise bikes, precisely because they seem like such a parody of real cycling. Exercise machines do have an advantage in terms of being able to use them on a regular schedule, without having to worry about weather and such, but I'd much rather use an upright cross-trainer that works arms and legs at the same time. --Trovatore (talk) 19:57, 16 March 2010 (UTC)

Me too. I ride a real bicycle every day - exercise bicycles are, by comparison, boring and uncomfortable. I much enjoy a good cross-trainer (especially if I get to watch good TV while on it). --Stephan Schulz (talk) 20:28, 16 March 2010 (UTC)

Psychological tests, job interviews

Which psychological tests are most commonly used in job interviews in Western Europe? How reliable are the test results when not interpreted by professional expertise?

First, please sign your posts by typing four tildes afterwards. This webpage [4] gives a good overview of psychological tests commonly used in the UK, together with a history, the evolution of personality classification, and how they work. I recommend you follow the links at the bottom to see things like leadership style tests, which is a common application of such tests in employment situations. --TammyMoet (talk) 17:39, 16 March 2010 (UTC)

They are about as validated as one of the those place mats in a chinese restaurant where you can see if you are a rat, pig, dragon, etc by year of birth. See Barbara Ehrenreich's disturbing book, Bait and Switch, for the way they are misused in the hiring process. alteripse (talk) 02:03, 17 March 2010 (UTC)

I generally find those place mats in organic save the planet health food restaurants. Bus stop (talk) 02:16, 17 March 2010 (UTC)

Are you claimin' you eat healthier than me? alteripse (talk) 02:37, 17 March 2010 (UTC)

Wow -- I had no idea Chinese placemats were used (much less mis-) in the hiring process. --Trovatore (talk) 19:00, 17 March 2010 (UTC)

It would totally explain how my boss got his job, though. 68.51.78.238 (talk) 04:08, 18 March 2010 (UTC)

Photon

When viewing a photon with for example the earth as a frame of reference, the photon is moving at the speed of light with respect to the earth. However, when the photon is used as a frame of reference, the earth - a massive object - seems to be moving at the speed of light with respect to the photon. A massive object should not be able to move at the speed of light, yet all frames of reference are supposed to be valid ones. Could you please explain how this works? Oliver009 (talk) 12:56, 16 March 2010 (UTC)

One of the central points of relativity is that light cannot be used as a frame of reference. In order to be a frame of reference, an actual object would have to be moving at the speed of light. Since that cannot happen, nothing could act as the frame of reference at the speed of light. Photons don't have a perspective. --Jayron32 13:12, 16 March 2010 (UTC)

Because the Earth is not moving 'at the speed of light' but it is the 'difference' in the speed between the Earth and the photon that equals 2.99 10^8 km per second. In other words it is the 'relative speed'.It would just 'appear' that the Earth is moving at the speed of light. This is the point that Einstein managed to explain mathematically, that whatever the observer's view point. the speed of light 'appears' to be constant -regardless of the speed that the observers going.--Aspro (talk) 13:18, 16 March 2010 (UTC)

Light's not that fast. :) Zain Ebrahim (talk) 13:30, 16 March 2010 (UTC)

Whoops: 2.99 10^8 metres per second. Also, in our every day experience this is not a familiar phenomena, so it just needs a bit of time to read through the theory several times to be able to make sense of it. --Aspro (talk) 13:34, 16 March 2010 (UTC)

Jayron is correct. If you allow an inertial frame of reference B that is moving at the speed of light relative to another inertial frame of reference A, then the Lorentz factor for B becomes infinite. An observer stationary in B attempting to measure the speed of an object O stationary in A would find that the proper time between any two observations of O is zero, but so is the proper length travelled by O between those observations. Therefore the speed of O relative to the observer in B would be 0/0, which is indeterminate. Gandalf61 (talk) 13:41, 16 March 2010 (UTC)

From the perspective of the photon, the mass, space and time dilation effects become literally infinite. Making any kind of conclusion from data that is multiplied by infinity is impossible - so "viewing things from the point of view of a photon" is an exceedingly tricky business. Also, the photon is special in other ways - it's speed appears constant no matter the state of motion of the observer...arguably, that means that you can't imagine things from a situation where the photon is stationary and the universe is moving. The photon also has a zero rest-mass, so does it even exist "from it's own perspective"? I think it's safe to say that you aren't allowed to do your thought experiment! SteveBaker (talk) 13:49, 16 March 2010 (UTC)

Economical preference gene?

Has some scientist ever speculated about an economical preference gene? A gene which would make females prefer males in a good - or at least stable - economical situation? --Quest09 (talk) 13:52, 16 March 2010 (UTC)

I don't think "economic" is quite the right word, but a "good provider" is certainly one of the things females look for. StuRat (talk) 14:06, 16 March 2010 (UTC)

Well, it won't be a single gene, most likely. Behaviour is very complex and governed by the interactions of many genes (any learned behaviours, very importantly). It is certainly true that women tend to look for a mate that will be able to support them and their children. --Tango (talk) 14:14, 16 March 2010 (UTC)

And don't forget epigenetic effects. There's lots of good recent research to show that environment can actually affect DNA expression, which is just as important as DNA code itself, and it can do so several generations out. So, a woman may show a higher preference for economic concerns because her great-grandmother nearly starved to death. Time magazine did a recent article on several studies which show that epigenetic information can be passed down to future generations as well, making the entire nature-nurture soup entirely more complex. --Jayron32 14:20, 16 March 2010 (UTC)

Do have a link to that article? It sounds interesting - a new kind of Lamarckism. --Tango (talk) 14:48, 16 March 2010 (UTC)

Question - Jayron, I don't quite understand your example (or epigenetics for that matter). How would the person's gene expression have been influenced by their great-grandparent being starved to death (their grandparent would have been born before the starvation)? If the great-grandmother survived a period of very low resources (due to e.g. not having someone to provide for her) and then reproduced, does the research you mention state that that experience could influence her female descendents to express their genes in such a way so as to make them more likely to have a preference for economic concerns? Zain Ebrahim (talk) 15:32, 16 March 2010 (UTC)

See [5]. Zain Ebrahim is about right. I was speaking in the hypothetical, I don't know if that specific behavioral expression would be controlled in that specific way, but hypothetically, yes environmental pressures on one generation can result in actual biological change in future generations. Environmental effects on a person before they pass on genetic information is found to express itself several generations out. In the article I link above, a study was done on people whose grandparents lived through a "feast and famine" cycle in the Swedish village of Overkalix. It turns out the grandsons of people who lived through famine times had measurably different lifespans than the grandsons of people who lived through feast times. I'll let you read all of the details, but the research seems to conclusively show that environmental pressures can cause inherited epigenetic traits to be passed on to future generations through means other than the DNA code. So inheritance is also environmentally controlled, and not just 100% based on DNA. You can pass on epigenetic traits to your children and grandchildren, even if those epigenetic traits are environmentally determined. --Jayron32 15:41, 16 March 2010 (UTC)

(after EC)<rant>NO NO NO... Epigenetics is NOT a new kind of Lamarckism. I absolutely hate this analogy, which is ALWAYS brought up in the popular press, as though this "new" science of epigenetics somehow dispels Darwinian evolution and suggests that Lamarck might have been on to something. Jayron, the Time magazine article is very interesting, true, but also highly overblown. Yes, some transgenerational effects have been observed, yes epigenetic mechanisms are possible, but the papers they discuss (mostly the ones about the apparent effect of famine on the health of subsequent generations) have nothing in the way of a scientific demonstration that those effects must have been due to epigenetics. There are other plausible explanations, but since "epigenetics" was one of them the popular press seems to have amped up these papers. Note, I'm not saying epigenetics is NOT involved, just that it isn't proven by those papers. Better studies have been done in mice, but even then we're talking about pretty specific changes at specific loci that increases the species' ability to adapt over the short term to ever-changing nutritional quality -- as though the capacity for transgenerational epigenetic influences has evolved through natural selection. </rant>

That being said, Tango's earlier answer about behavior being too complex to be governed by a single gene is almost certainly correct. The evolution of sexual reproduction is a fascinating topic and one of the side-products of the process is the selection for any number of sex-specific specializations (including provision of "economic" benefits) that allow individuals to evaluate the possible "fitness" of their prospective mates, many of which are likely to be complex, multi-gene processes with environmental/learned influences. --- Medical geneticist (talk) 15:57, 16 March 2010 (UTC)

I didn't mean that epigenetics was claiming to replace Mendelian inheritance, but the idea that you can inherit changes in your ancestors caused by their environment is at the very heart of Lamarckism. Sure, this is Lamarckism playing a minor role in predominantly Mendelian inheritance, but it is still essentially Lamarckism. --Tango (talk) 17:05, 16 March 2010 (UTC)

To respond to MG... I understand that the scope of the study cited in the Time article was rather small, and therefore it would be hard to place theory-smashing emphasis on it. However, it does help to provide an impetus to study in that direction. Even if it is 100% accurate and environmental effects can be passed on to future generations epigentically, such a possibility would not fundementally alter the current understanding of Mendelian genetics or of DNAs role in heredity. It would add to the complexity of inheritance, for sure, but such a revelation, if true, wouldn't mean an end to current genetic theory, only a modification of it. And isn't that the idea behind scientific study, to constantly refine and improve our models and theories? --Jayron32 04:29, 17 March 2010 (UTC)

My problem with the analogy is the "Darwinism versus Lamarckism" spin that gets put on this phenomenon in the popular press. The Time Magazine article is a great example. I read it a few months ago so I can't remember the exact phrasing, but they kept talking as though epigenetics was a way to "escape" from the "tyranny" of Darwin. Don't get me wrong -- I'm a huge fan of epigenetics -- but sometimes the importance of epigenetics gets a bit overblown. I understand that Lamarck's ideas have been caricaturized (i.e. the giraffe stretching it's neck in order to give it's offspring longer necks), and of course neither Darwnin nor Lamarck would have had any clue about the molecular mechanisms at play. I totally agree that epigenetics is just another layer on top of the A/C/T/G's that adds to the complexity of the weave. However, epigenetic effects still adhere to mechanisms of natural selection: the genes that encode the proteins that perform these functions, and the DNA letters that are acted upon, can both be selected for. If transgenerational epigenetic effects were maladaptive, they would be selected against in the same way as any other trait. The Lamarck analogy misses the point that the capacity of organisms to be affected by epigenetic transgenerational effects has been selected for because it is adaptive under certain conditions. --- Medical geneticist (talk) 17:59, 16 March 2010 (UTC)

Noise in MRI scan

3D MRI scan

What causes the apparent noise around the head in this image (found on the Neroimaging page)?
Surely this would be simple to remove programatically? Is it normally removed? If so why not in this example? Capuchin (talk) 14:12, 16 March 2010 (UTC)

Googling around MRI noise sources, there appear to be a number of possible culprits. However in this case the positioning of the noise makes me wonder if it isn't some kind of headphones on the patient, which are apparently sometimes used to either cut down on the loudness of the machine, or to pipe in other sound. I'm not sure if the plastic of the headphones itself would generate the noise, but it might be reflecting heat in a strange way, which apparently can create noise (as I gather from Googling). One might also imagine it some kind of brace (I had an MRI a long time ago, and they had my head in all sorts of padding to keep it straight) that might also be reflecting heat in some funny way. This is just speculation on my part, definitely not authoritative! --Mr.98 (talk) 14:20, 16 March 2010 (UTC)

From the square angles, I'd say it's a brace to keep the patient from moving during the scan. StuRat (talk) 14:25, 16 March 2010 (UTC)

Headphones/braces do not contain water, so why would they show up on an MRI? MRI simply aligns hydrogen atoms in water. Regards, --—Cyclonenim | Chat  15:42, 16 March 2010 (UTC)

If the brace is cold and the person's breath is warmer in comparison, it could be some condensation, particularly if the area isn't well ventilated and if the humidity is high. StuRat (talk) 14:33, 17 March 2010 (UTC)

They have barely shown up, so there doesn't need to be much water involved. Perhaps it's the lack of air (which does contain water) that is showing up, rather than the plastic. --Tango (talk) 17:07, 16 March 2010 (UTC)

MRI doesn't literally see water, it sees RF/magnetic effects of it. So all you need is something that perturbs the magnetic field or is susceptible a little differently and you can get a ghost. Our MRI article has several comments about artifacts at solid/liquid boundaries and other field-inhomogeneities. DMacks (talk) 17:37, 16 March 2010 (UTC)

I'm not a radiologist, but it looks like a data glitch to me and not a real physical object.

Don't MRI machines scan one line at a time? If so, that perfectly square interference could easily be explained by some sort of background interference halfway through the scan. (The square shape probably indicates the outer limits of the scan. So really you're looking at noise contained by two planes.) APL (talk) 18:01, 16 March 2010 (UTC)

It could be a halo but those typically have metal screws in them, I don't think a patient with one would be taking an MRI. Livewireo (talk) 18:09, 16 March 2010 (UTC)

I agree with APL. Not only do the vertical lines appear to penetrate through the head, but the pattern continues above and below where the scan cuts off. Unless they were scanning an actual slice of head held in a rack, I don't think that stuff is a real object. Rckrone (talk) 19:43, 16 March 2010 (UTC)

Capuchin, I am not sure which exact image feature you are referring to, since there are two possible candidates:

1. If you are referring to the rod-like structures seen on either side and above the head, they are almost surely (as StuRat suggested above) a physical brace/frame attached to the subject's head. Unfortunately the image uploader hasn't specified the provenance and acquisition protocol for these images, so it we can only guess the purpose: it could either be to keep the head still, or for contrast or co-ordinate calibration (see Stereotactic surgery).
2. If you are referring to the cuboidal volume which contains some noisy pixels (even outside the physical head), that is simply the MR imaging volume (the rest "completely back" volume is generated by the visualization software that converts a stack of images to a 3D animated gif). The noisy pixels outside the head are the result of signal noise in MR data, that arises from both the electronic instrumentation, and the subject/environment.

Both of these features could be quite easily removed by post-processing the images but the visibility of the rods was almost certainly a desired feature in this dataset (since, it is pretty easy to make them MR invisible by using a purely plastic frame). The noise outside the head can also be cleaned up, but it is not usual to do so since, (1) radiologists can mentally discard that noise and it doesn't affect the images' diagnostic value, (2) it gives the examiner a rough visual idea of the noise present within the head portion of the image (which cannot be trivially cleaned up), and thus they can know how much to "trust" small variations in the anatomical images. Abecedare (talk) 03:28, 20 March 2010 (UTC)

Avocado pit use and safety

Are avocado pits safe for heating? I am making heating packs for self-care use at home and wonder if they are safe to use? If so, do they need to be prepared in any special manner first, i.e. dried,cooked,etc.? —Preceding unsigned comment added by Mehndihum (talk • contribs) 16:24, 16 March 2010 (UTC)

Why use an avocado pit for heating packs? Wouldn't other similar sized and hard objects, which are not perishible, be useful, such as maybe old golfballs or something? I'm not sure there is anything wrong with the avocado pit per se (but don't take my word on THAT), however if there is any doubt, couldn't some alternative object which is about the same size, shape, and hardness work better and leave less doubt of creating problems? Perhaps with more details as to what the old pits would be used for may be helpful in answering your question. --Jayron32 05:16, 17 March 2010 (UTC)

Isn't barley the seed of choice for heat packs? --Polysylabic Pseudonym (talk) 07:29, 17 March 2010 (UTC)

Heating hard-shelled objects with moisture at the center is generally an iffy proposition--think whole eggs in a microwave, or tin cans in the campfire, or--for an example neither fundamentally messy or dangerous, popcorn. The safety issue would depend largely on variables within the pit itself and the temperature to which you're heating it--popping an un-punctured avocado pit into a microwave and hitting START seems like it could go very wrong, depending on the moisture content and any variations in the structure of the pit's walls. 68.51.78.238 (talk) 04:06, 18 March 2010 (UTC)

Programmable food

Since taste, like smell, is perceived based largely on the shape of surface molecules on the food, and since smell is a big part of the tasting experience (compare eating with a stuffed nose to eating without a stuffed nose), have any researchers published papers (preferably in open journals) on the possibility of developing edible molecules with customizable shapes for the purpose of having customizable taste? I think it might be interesting if you could first buy a device like a microwave, and from then on, buy blocks of product which you could put in the device and activate programs which could be downloaded from (definitely trusted) sources or alternatively programmed yourself if you become a programmer/chef hybrid? 20.137.18.50 (talk) 17:34, 16 March 2010 (UTC)

Well, there is a lot of work on manufacturing chemicals that makes things taste a certain way. See Flavorist. Whether some kind of home-made device would ever let you do this, it's a long way off. You're essentially describing a Molecular assembler that is just tailored to food molecules. I think it would be pretty easy to poison yourself if you didn't know quite a bit of chemistry (just as it is with "traditional" means of chemical experimentation). --Mr.98 (talk) 19:02, 16 March 2010 (UTC)

"Te voy a llevar a un pinche vaile!"

This question has been moved to the Language Desk. Nimur (talk) 18:24, 16 March 2010 (UTC)

Flow through a pipe

Engineering. with a given pressure and the area of a pipe and without the velocity is it possible to find the flow rate by calcultion? If there is a calculation available, pls. let me know. —Preceding unsigned comment added by 212.100.212.214 (talk) 17:39, 16 March 2010 (UTC)

I think you need to know something about either the fluid itself (like viscosity) or the pressure drop for the pipe length. DMacks (talk) 18:00, 16 March 2010 (UTC)

The simplest approximation is the fluid continuity equation. You can see which parameters are needed to relate flux (the generalization of linear flow rate to 3 dimensions). In this case, the net velocity flux is zero - or, in laymans terms, "the flow rate is exactly equal everywhere in the pipe, and is determined by how much fluid as you squish in on the supply-end." (That is, your problem is totally determined by its boundary conditions). Note that increasing pressure does not necessarily equate to increasing the mass flow rate - but in practice, these effects are commonly related (because you probably use a pump as your fluid supply, which works by pressurizing the fluid). It should be possible to approximate your flow in a pipe scenario under some more complex circumstances. More complete treatments, like Navier-Stokes equations, relate pressure, velocity, compressibility/density change, fluid shear, etc.; and while more complicated, they are applicable in a wider array of situations. Nimur (talk) 18:29, 16 March 2010 (UTC)

Are you talking about a gas or a liquid? I know that you can measure the speed of gas flow through a pipe if you can get a differential pressure across an orifice plate if the gas properties are known. Googlemeister (talk) 18:33, 16 March 2010 (UTC)

That would be the venturi effect. Nimur (talk) 18:34, 16 March 2010 (UTC)

The properties of the pipe would also be important. The cross section should ideally be circular, and the pipe should be straight for best flow, yielding a cylinder. Also, some surfaces will be smoother and thus have less drag. StuRat (talk) 14:13, 17 March 2010 (UTC)

The Hagen-Poiseuille equation models laminar flow through a straight tube. Axl ¤ [Talk] 08:22, 19 March 2010 (UTC)

...with a circular cross-section. StuRat (talk) 08:46, 19 March 2010 (UTC)

Er, yes. That's what I meant by "tube". Axl ¤ [Talk] 12:12, 19 March 2010 (UTC)

A tube is usually, but not always, circular: [6]. StuRat (talk) 14:40, 19 March 2010 (UTC)

Well, I don't regard that website as a reliable source for the definition of the word "tube". How about Wiktionary? Axl ¤ [Talk] 19:30, 19 March 2010 (UTC)

I would think those who manufacture tubes would know what they are, better than Wiktionary, but even Wiktionary includes the shape of a toothpaste tube, which is more elliptical than circular is cross section. If you want another dictionary source which uses the "usually cylindrical" def, as opposed to "always", here you go: [7]. Then there's the "tube"/subway, with a rectangular cross section, and the cathode ray tube, which isn't even close to being a cylinder. StuRat (talk) 21:45, 19 March 2010 (UTC)

"I would think those who manufacture tubes would know what they are, better than Wiktionary." I disagree. Moreover, that website uses the word "tube" because it is a convenient simple word that conveys a meaning close to their product. By qualifying the description as "irregular tube shapes" and "complex tube profiles", together with the photos, the context of the use of the word "tube" here is clear, i.e. not the traditional cylinder. From The Concise Oxford English Dictionary: "Tube: 1. A long, hollow cylinder used for conveying or holding liquids or gases." Thanks for pointing out other uses of the word "tube"; we wouldn't want the original questioner to become confused with the London underground. Axl ¤ [Talk] 16:06, 24 March 2010 (UTC)

Well, I've provided a dictionary that says "usually cylindrical". Also, I suspect that other definitions in The Concise Oxford English Dictionary will include non-cylindrical shapes. So, when specifying a tube, it's not entirely redundant to specify that you mean a cylindrical tube, versus one of the other forms. StuRat (talk) 16:21, 24 March 2010 (UTC)

Okay. [The Concise Oxford English Dictionary includes the "other" definitions of tube as you suggest: Cathode ray tube, London underground, Fallopian tube. It doesn't include a generic "usually cylindrical" definition.] We seem to arguing about a trivial point. Let's leave it at that. Axl ¤ [Talk] 16:32, 24 March 2010 (UTC)

Electrode potential of ethanol

What is the standard electrode potential of the oxidation of ethanol to ethanoic acid, hydrogen ions and electrons, as found in modern day breathalysers?

I have tried googling this question but could not find a suitable answer, I am just looking for a value.

Thanks 86.164.85.183 (talk) 18:20, 16 March 2010 (UTC)

Most electrode potentials are listed as reductions and not oxidations, so you'd want to phrase your search for reduction potentials of acetic acid or ethanoic acid or CH3COOH or HC2H3O2 (all synonyms) rather than oxidation potentials for ethanol. The value will have the same sign and opposite magnitude. --Jayron32 20:36, 16 March 2010 (UTC)

Thanks 86.164.85.183 (talk) 22:37, 16 March 2010 (UTC)

Bee Flies

Hello, I live in Langley, BC, and I saw these two (right) Bee flies mating on the ground. Can anyone tell me what species they are? --The High Fin Sperm Whale 18:59, 16 March 2010 (UTC)

I just looked at a bunch of bee flies here and here, and most of them looked quite a bit more bee-like than your critters. How do you know they are in fact bee flies? There are ~4500 species and I'm ignorant of all of them, so they may well be, I'm just wondering how you reached that conclusion. --Sean 19:54, 16 March 2010 (UTC)

These were quite a bit larger than most flies, about ¾ inch long. But maybe they weren't bee flies. Anyone know what they are? --The High Fin Sperm Whale 21:35, 16 March 2010 (UTC)

Horse fly first came to mind. Beyond that, I don't know. --Kvasir (talk) 22:54, 16 March 2010 (UTC)

I'm pretty sure that these are Tachinid flies, not bee flies.174.97.22.101 (talk) 05:22, 17 March 2010 (UTC)

Looking under Family Tachinidae and even its Superfamily Oestroidea definitely looks a lot closer to the OP's picture. --Sean 16:36, 17 March 2010 (UTC)

I've made an ID request over here. --Sean 16:50, 17 March 2010 (UTC)

most effective footrace training?

If I was to start training for a 3 mile footrace and wanted to complete it at a pace of 6 min a mile which would be a more effective means of training

A. Run as far as possible at the 6 min/mile pace and gradually increase the distance

B. jog 3 miles at a slower pace and gradually speed up to the 6 min/mile pace?

Googlemeister (talk) 19:27, 16 March 2010 (UTC)

Definitely B if you're starting from no running at all. Option A is a recipe for self-injury and then you'll have a huge time-out in your training. --Sean 19:39, 16 March 2010 (UTC)

You may want to look into LSD training and Interval training and Fartlek for information on different training styles for running. You may also want to consider contacting a coach or a physical trainer in your area. A local running club may be able to provide some training guidelines as well. --Jayron32 20:11, 16 March 2010 (UTC)

Flour from Grasses

Why is wheat and spelt flour so high in carbs when they just come from grass? Are there any edible grassess or seeds (not counting the nut flours) that are low in carbs and taste good that can be made into flour? Also, is it the seed of the wheat plant that is ground up and made into flour? —Preceding unsigned comment added by 71.137.244.162 (talk) 19:58, 16 March 2010 (UTC)

It is the seed of the wheat plant that is made into flour. I don't know low carb flour. Googlemeister (talk) 20:01, 16 March 2010 (UTC)

Information about flour can be found, unsurprisingly, in the article titled Flour and in links from that article. Start there, read that article, follow some blue links and read THOSE articles. They answer all of your questions and more. --Jayron32 20:07, 16 March 2010 (UTC)

(ec) Yes, it is the seeds of wheat that we use for food (the stalks are used as straw). I think any seed will be high in carbs, it's the easiest way to store energy for the new plant to grow with. You can make flour out of all kinds of things (see Flour#Other flours for a list), but I think they will all have a fairly high proportion of carbohydrates. --Tango (talk) 20:08, 16 March 2010 (UTC)

Would it be possible to make flour from just about any seed? For example, I just saw that there is a grapeseed flour that you can use to cook with what about the seeds from pomegranites or avocadoes or goji, could you make a flour from those? —Preceding unsigned comment added by 71.137.244.162 (talk) 21:53, 16 March 2010 (UTC)

Probably. It wouldn't necessarily taste very nice, though, and it may not behave well when cooking. --Tango (talk) 23:20, 16 March 2010 (UTC)

Soy flour is about 40-50% protein [8] [9] [10] . However, I never tried to cook with it, so caveat emptor. --Dr Dima (talk) 23:36, 16 March 2010 (UTC)

Caveant cucinator et cenator. --Trovatore (talk) 23:46, 16 March 2010 (UTC)

Chemistry

What do you get if iron(III) oxide reacts with hydrogen? --70.250.214.164 (talk) 20:38, 16 March 2010 (UTC)

Iron is higher up on the reactivity series than hydrogen, so there would be no reaction. --The High Fin Sperm Whale 21:33, 16 March 2010 (UTC)

I would be really surprised if you couldn't reduce it to elemental iron by passing hydrogen over it. You might have to heat it, and maybe you'd need a continuous flow, so that the moisture gets carried away and can't re-react with the iron. --Trovatore (talk) 23:39, 16 March 2010 (UTC)

Iron(III) is a catalyst used for making lithium and sodium amide: Li+NH₃→LiNH₂+H₂ in the presence of (NO₃)₃ below 0 °C but doesn't occur at all without the iron even at higher temps. I assume the iron is an electron shuttle, which would mean something like Fe(II)→Fe(III) strongly overcomes H₂→H⁺ under these conditions. And the Haber process tells us that at high temp and pressure, iron(III) transfers electrons from H₂ onto nitrogen gas, so again "just reducing to iron" is pretty difficult vs reducing other things. DMacks (talk) 00:05, 17 March 2010 (UTC)

Hmm -- well, maybe I get to be surprised, then. Still, surely the reaction coefficient isn't zero? If you remove the reaction products, it ought to go to completion? --Trovatore (talk) 00:48, 17 March 2010 (UTC)

strontium iodide

Does strontium iodide decompose by itself (without oxygen or other chemicals)? --70.250.214.164 (talk) 21:03, 16 March 2010 (UTC)

I don't think so. --The High Fin Sperm Whale 21:31, 16 March 2010 (UTC)

The compound Strontium iodide is stable. Some iodine compounds react when UV radiation is present. A yellow tint is what I would expect. --Stone (talk) 22:23, 16 March 2010 (UTC)

According to our article, on Strontium iodide, the yellow tint comes from being exposed to air. 70.250.214.164 asked if it would decay without oxygen. --The High Fin Sperm Whale 22:44, 16 March 2010 (UTC)

I am sure that UV also would do the trick without oxygen. --Stone (talk) 22:50, 16 March 2010 (UTC)