Wikipedia:Reference desk/Archives/Science/2009 June 30

= June 30 =

How to estimate calories required daily?
I want to create a gradual weight loss by reducing my calorie intake slightly below the amount of calories that would make me neither fatter or thinner. How can I estimate this amount? It must be related to body size etc. 92.27.159.22 (talk) 01:46, 30 June 2009 (UTC)


 * That would be the Harris-Benedict equation. SteveBaker (talk) 01:56, 30 June 2009 (UTC)


 * Also, there are websites that will take a lot of info from you (what kind of exercise you do, how far you walk per day, etc.) and tell you exactly what the additional caloric burning/cutback you'd need to burn a pound a week or something along those lines. Obviously they are not precise but they give an estimate. Doing that made it clear to met that switching to diet soft drinks (if soft drinks must be drunk) would make sure things seriously, seriously easier! An extra few thousand calories out of one's weekly intake makes quite a difference, and it's an incredibly easy way to do it... --98.217.14.211 (talk) 03:01, 30 June 2009 (UTC)


 * I don't think this approach will work. It's almost impossible to estimate either your caloric intake or caloric output with an accuracy better than 10% -- even 20% is very hard -- hell, even 30% is hard.  If you get it wrong, it will take weeks before you get enough feedback to tell you so.  The only workable way to lose weight by dieting, I believe, is to cut your calorie intake to 3/4 or less of what you estimate you are expending.
 * I agree, it also seems that even with accurate inputs, there is generally a more than 10% error on this: "A review of the data reveals that the methods and conclusions of Harris and Benedict appear valid and reasonable, albeit not error free. All of the variables used in the equations have sound physiologic basis for use in predicting BEE," from but also "Harris-Benedict  equation overestimated basal energy requirements by 10 to 15% in 201 studies of healthy men and women. These results raise  questions regarding the accuracy of predicting an individual's energy  requirements." from  and "overestimation of 10% to 15% is normally found" from, and "Calculated resting metabolic rate was more than 10% different in 33%" from http://linkinghub.elsevier.com/retrieve/pii/S0002822303009829. Basically even the most complicated equations and perfect input of caloric intake and excercise only give a rough estimate.YobMod 17:28, 30 June 2009 (UTC)

Thanks. I had in the past tried a harsh diet of 2000c during weekdays and 2500c at the weekend that dropped my weight in a few weeks. But, like most dieters, as soon as you stop the diet, your weight soon returns to what it was previously. Currently I am on a milder diet of 2500c per day, which is undoubtedly less than what I ate before when unrestrained, since normal processed foods have too many calories in them to be eaten except as rare treats. I have been eating lots of vegetables and fruit and so far have not felt particularly hungary except mildly late in the evenings. 89.240.105.155 (talk) 19:47, 30 June 2009 (UTC)

You might like the online book The Hacker's Diet. 208.70.31.206 (talk) 07:37, 2 July 2009 (UTC)

simulating finger prints
How might I fabricate a material that could simulate human finger prints, i.e. very small grooves on the surface of a smooth rubbery? skin-like surface. Obviously you can't really replicate real fingers 100%, but what might be a reasonable material to simulate the skin? And how might I get the fingerprint "grooves"? I'm thinking some sort of rubber that I can harden into a cast after imprinting my own finger prints, and then use that mold to create the outer skin layer which I will cover the replica fingers with. Any idea what sort of rubber I could use to do this? Or does anyone know of a better way? Thanks! 124.154.253.146 (talk) 02:53, 30 June 2009 (UTC)


 * That sounds like a difficult problem. But I wouldn't be surprised if there were answers out there. My mind immediately turns to gloves -- made of vinyl, latex, or nitrile. See the work of Duane Hanson, not that I know how he made his wonderful sculptures. Finally, if you can get your hands on the DVD for the movie Click (film), there happens to be an amazing segment on that DVD, not part of the movie, which describes and shows how some of the body transformative makeup is produced and applied. (It won't really answer your question, but it shows the amazing things that can be done in the general realm of transforming the face and body.) The people working in that field (Make-up artists) would seem to be the most knowledgeable people I can imagine for coming up with a solution to the problem you pose. Bus stop (talk) 03:10, 30 June 2009 (UTC)


 * It's possible that a process used in make-up art will suffice, but since I'm more looking for functional similarity than visual similarity, I'm not sure if that's the right direction to go look. Wax sculptures, after all, can be frighteningly real, but they serve no real scientific purpose. Then again, functionality is sometimes an issue when making movies (the actors after all, sometimes have to use their hands, even if they're latex), so I could be wrong. 124.154.253.146 (talk) 03:37, 30 June 2009 (UTC)
 * In an episode of Mythbusters they were able to fool a fingerprint sensor with just a piece of ballistic gelatin which had been chemically etched with a scan of a fingerprint, though fooling a forensic scientist may be a bit more difficult.- Running On Brains (talk page) 04:01, 30 June 2009 (UTC)


 * Notably, if you actually want to leave fingerprints on surfaces, your fake finger has to have oil on it, like the kind emitted by human skin. Dcoetzee 04:09, 30 June 2009 (UTC)


 * I guess I should have mentioned that the point is to simulate the amount of grip fingerprints add (or don't) to your finger. 124.154.253.146 (talk) 06:01, 30 June 2009 (UTC)


 * It may be tough to find a material that mimics skin well enough to make that direct comparison. However, you could probably get some idea whether you're on the right track or not by comparing smooth gelatin against gelatin with a fingerprint pattern. http://www.antionline.com/archive/index.php/t-241708.html describes how to make a gelatin fingerprint. See also: http://www.realtechnews.com/posts/3129 SteveBaker (talk) 16:09, 30 June 2009 (UTC)
 * This recent study asserts that fingerprints do not improve grip. --Sean 13:15, 1 July 2009 (UTC)
 * I believe the current theory is that it improves our sensitivity to subtle surface textures. As your finger moves over a bump or an edge, the tiny ridges in the fingerprint briefly lock onto it and the skin is deflected to a larger degree than smooth skin would be - this provides a bigger signal to the nerve endings in the fingertip. The fact that someone already did the 'grip' experiment should in no way deter our OP - for science to proceed, many people have to repeat an experiment before the results of it will be widely accepted as "the truth". SteveBaker (talk) 11:33, 2 July 2009 (UTC)

It really Works !!!
Remember I had asked a question a few days back, here. Well what do you know, It really works !! It responds to light just fine on the breadboard, and it is as sensitive as it can get... I think there must be something in IR emitters after all which would enable them to detect light, and do it quite well... But thanks for helping out, guys...Rkr1991 (talk) 08:12, 30 June 2009 (UTC)
 * Thanks very much for testing that out, and good luck with the rest of the project. Any special trick you can see used to get it to work like putting a bias voltage onto it? I though there was a good chance of success but when I tried a red LEDs with an ohmmeter I couldn't get anything when going out in the sun. Are you sure it is the IR emitter? If so I'll be able to blow a raspberry to a very valued contributor ;-) Dmcq (talk) 08:57, 30 June 2009 (UTC)


 * Yep, you bet, it's the IR emitter all right. There is in fact a line in the book which I used, which I am quoting : We can't use the detectors, they're too weak. And we don't want our device to be too mousey. I didn't know what to understand from that statement. If the detectors were too weak, I suspected the emitters would be even weaker, which is why I asked the question. And its not clear what he means by too mousey. But who cares about all that, all that matters is that it works ! In fact, the detectors are even more sensitive. And yes, I did reverse bias the emitters. That was given in the book, I'm not very good in the logic part yet, we're just beginners... But overall, I guess that the fact that the emitters work would be saying something to our expert here.. Rkr1991 (talk) 11:06, 30 June 2009 (UTC)
 * I would guess mousey = "like a mouse". So you don't want it to be only as sensitive as a computer mouse, which needs high proximity or even contact to detect.YobMod 16:04, 30 June 2009 (UTC)


 * So may I just say neah-neah-ne-neah-neah to There is no way a light emitter can be used as a detector. Your book is wrong. If it's not a misprint then the author is an idiot...which is actually possible - many of these books are written by enthusiastic amateurs who are sloppy with scientific terms
 * :-P Dmcq (talk) 21:22, 30 June 2009 (UTC)


 * I'm surprised nobody has found this article yet: LED as light sensor.  "A LED is simply a diode that has been doped specifically for efficient light emission and has been packaged in a transparent case. Therefore, if inserted into a circuit in the same way as a photodiode, which is essentially the same thing, the LED will perform the same function."


 * Even more interestingly: "LEDs can be used as both emitters and detectors of light, which means that a device having only a single LED can be used to achieve bidirectional communications with another device meeting these requirements. Using this technology, any of the ubiquitous LEDs connected to household appliances, computers and other electronic devices can be used as a bidirectional communications port."  --Bowlhover (talk) 00:13, 1 July 2009 (UTC)


 * No, User 76.11.230.33 in fact pointed out this article to Steve saying it disagreed with him. But Steve's point was that why use the emitters to detect when you've already got two very specialized detectors, which still remains fuzzy... Maybe the detectors would make it too sensitive... Rkr1991 (talk) 04:52, 1 July 2009 (UTC)

Where is Steve hiding, by the way ? He did contribute at 17:30 June 30th at the Miscellaneous desk.. Rkr1991 (talk) 04:57, 1 July 2009 (UTC)
 * And on July 1st at 12:22... Rkr1991 (talk) 15:14, 1 July 2009 (UTC)

thermodynamics equilibrium constant
the equilibrium constant of a reaction depended only on temperature. At what condition equilibrium constant not change with temperature?Rikichowdhury (talk) 09:01, 30 June 2009 (UTC)


 * From the Vant Hoff equation, if ΔH for the reaction is zero, then the equilibrium constant is independent of temperature. Rkr1991 (talk) 11:09, 30 June 2009 (UTC)
 * In fact, our article on Equilibrium constant gives the link. Please do try to read the relevant articles. Rkr1991 (talk) 11:10, 30 June 2009 (UTC)

Hypotension
Can low blood pressure cause cold hands or cold extremeties? How does it cause that? --Mudupie (talk) 13:45, 30 June 2009 (UTC)


 * It is not a cause. There may be a correlation.  However, I've never seen a study on hypotension and cold extremities.  I've only seen studies on the correlation between hypertension and cold extremities.  Many find a stronger correlation between use of beta blockers and cold extremities. --  k a i n a w &trade; 13:50, 30 June 2009 (UTC)


 * See vasoconstriction, vasodilation, and total peripheral resistance for articles on how the peripheral vasculature (not the big arteries of the body) can affect blood pressure and perception of "cold" or "warm" extremities. The perception of "cold extremities" is generally due to vasoconstriction of the peripheral blood vessels, which could be due to the body trying to preserve the core body temperature and prevent hypothermia, or could be due to the body trying to preserve blood flow to critical organs (i.e. prevent hypotension) in a state of dehydration, hypovolemia, or blood loss.
 * As Kainaw said, it isn't really a cause-effect relationship, although one could imagine a situation in which acute hypotension led to peripheral vasoconstriction (and the accompanying perception of cold extremities). One could also imagine the reverse situation, in which there was acute vasodilation (accompanied by a sensation of "warmth" or "flushing") with resulting hypotension due to decreased peripheral resistence.  So not a direct cause or effect, but a correlation. --- Medical geneticist (talk) 15:10, 30 June 2009 (UTC)

To Mudupie: yes. See "Shock (circulatory)". Hypovolemic shock, cardiogenic shock and obstructive shock will all lead to cool peripheries. Distributive shock leads to warm peripheries. Axl ¤  [Talk]  17:00, 1 July 2009 (UTC)

Nitrogen enhanced gasoline
I have been reading up a bit on the new Sell gasoline that is nitrogen enhanced. I find a lot of controversy and contradiction re: the legitimacy of this enhanement. So, can anyone shed some light on whether or not nitrogen enhanced gasoline really is beneficial and if so in what way? —Preceding unsigned comment added by 209.161.211.158 (talk) 14:11, 30 June 2009 (UTC)


 * I have always been suspicious of this claim. The addition of nitrogen-containing compounds MAY have some effect on altering the octane rating of the gasoline, and thus improve performance.  It also may reduce the incomplete combustion of the gasoline, which would reduce the accumulation of soot along vital engine parts.  However, enhancing the nitrogen content of gasoline can ONLY lead to increased nitrogen oxides production, and nitrogen oxides are universally recognized as a serious contributor to air pollution, especially smog.  So what you are probably getting is a cleaner burning fuel, from your engine's point of view, but this is at the cost of increasing polutant levels in the air.  Presumably, the gasoline still meets federal clean-air requirements in the U.S., but I cannot see how it does not increase polution over non-enhanced gasoline.  --Jayron32. talk . contribs  14:37, 30 June 2009 (UTC)


 * It's probably beneficial in that it has cleaning additives. However, there are a couple of key points that don't get mentioned.  One, most major gas brands have some form of cleaning additive.  One-A, you don't need the cleaning additives every single time you fill up.  Most people, without ever thinking about it, have sufficiently clean valves and the like.  Two, it has no impact on the gasoline itself.  Your fuel economy filling at one reputable gas station will not meaningfully differ from your fuel economy filling at another. &mdash; Lomn 14:39, 30 June 2009 (UTC)

Nitrogen compounds as cleaning additives?! Come on people, get real! I've done some research on shale oil (which has LOTS of nitrogen compounds in it), and I know for a fact that those compounds are definitely harmful to fuel quality: they have a strong tendency to spontaneously polymerize and form huge amounts of disgusting sticky black sludge that clogs engine components in no time flat! In fact, in the case of shale oil, nitrogen compounds must be completely removed from the fuel, and to the best of my knowledge, they must also be removed from conventional petroleum that happens for some reason to have too much nitrogen in it. Sounds to me like Shell is trying to charge extra for low-quality gasoline by trying to market it as something good for your car, when really it's nothing of the kind. FWiW 76.21.37.87 (talk) 06:50, 1 July 2009 (UTC)
 * Have you considered the thought that Nitrogen forms more than one compound? It is entirely possible, even likely, that some compounds are harmful while other are beneficial.APL (talk) 22:38, 1 July 2009 (UTC)

APL -- I am perfectly aware of that; however, I know for a fact that most amines and nitrogen-containing heterocyclic compounds such as pyridines and pyrroles are harmful to fuel quality. Furthermore, to the best of my knowledge, it is precisely the compounds listed above that are most likely to be found in Shell "nitrogen-enhanced" gasoline, because most other nitrogen compounds are rarely, if ever, found in petroleum and petroleum products. I also reiterate that from what I know about petroleum refining (which is quite a lot), high nitrogen levels in petroleum are in general undesirable and are (if excessive) lowered by hydroprocessing. Therefore, I stand by my position that "nitrogen-enhanced" gasoline is of a lower quality than conventional gasoline. FWIW 76.21.37.87 (talk) 04:19, 2 July 2009 (UTC)

Chai - laxative qualities?
My local bagel shop serves a chai latte'. I'm not a tea drinker but this stuff is outstanding! A couple other people and I have noticed that we have to defecate soon after drinking it. So, we're wondering, does whatever version of chai that this most likely is have any laxative qualities? Note: I am not seeking medical advice. We have just noticed this pattern in three non-genetically related people. Again, this is not a request for medical advice. Dismas |(talk) 14:46, 30 June 2009 (UTC)


 * I think the general answer is no. Chai latte that i've had (Starbucks?) is just chai-style tea made with the latte milk steaming machine. There is nothing in this combination that would be any more laxitive than the two things alone. But as chai usually have a secret mix of spices in, it is possible that this one example does have an unknown ingredient with this effect (if so, it should occur without the Latte).YobMod 15:25, 30 June 2009 (UTC)


 * By the way, the three people that have noticed this live in two separate households, in two different states, and have noticed this from different bagel shops. Dismas |(talk) 17:01, 30 June 2009 (UTC)


 * Perhaps a Pavlovian response. 65.121.141.34 (talk) 18:07, 30 June 2009 (UTC)


 * Could just be the caffeine, though our tea article says there's much more caffeine in a cup of coffee. Tempshill (talk) 18:49, 30 June 2009 (UTC)


 * Since caffeine is a diuretic, shouldn't it have the opposite effect and cause constipation due to lost water? 213.122.68.63 (talk) 14:54, 1 July 2009 (UTC)


 * Caffeine is actually not a significant diuretic except in very special circumstances (this topic has been discussed ad nauseum at Talk:caffeine), but tea -- ordinary tea -- is a pretty strong diuretic. Looie496 (talk) 01:22, 2 July 2009 (UTC)


 * I've noticed from personal experience that tea in general is a laxative. 89.240.105.155 (talk) 19:35, 30 June 2009 (UTC)

Yeah? Try some native teas boys. There's one for every purpose. Take the time to learn them from an elder and you would be surprised by the results! Me??? I'm fond of spotted joe pyeweed tea or comfrey tea. Tastes horrible, hard on the taste buds and the liver but good for the brain! Experiment but BE CAREFUL! B.T.W. J-weed ...stay away from it, Salvia likewise. 67.193.179.241 (talk) 21:08, 30 June 2009 (UTC)Rana sylvatica

Strange plant in northeast Kansas.
I was hacking down plants with a machete in my brothers backyard today and I came across a very tall, non-woody-stemmed plant (about the size of a small tree). It has a reddish-purple stem and huge, long, pointed ovoid leaves. The stem is very thick (two or three inches at the base)and when I hack it open, the pith inside is divided into little segments all the way up by little white membranes. The tiny, white flowers near the top have five petals and seem to be in the process of turning into little green berries. I don't have the slightest clue what this plant might be and I'd really like to find out. Any help would be appreciated. 76.250.254.192 (talk) 17:11, 30 June 2009 (UTC)


 * Sounds like something in buckwheat genus, Fagopyrum; or related. Still, very hard to tell without a picture. --Dr Dima (talk) 18:54, 30 June 2009 (UTC)


 * When in doubt, suggest it's Phytolacca americana, the American Pokeweed. Seems to be the most commonly asked after plant this time of year. The description sounds accurate. Not sure about the stem section, though. --Rkitko (talk) 18:58, 30 June 2009 (UTC)


 * Yes, that's a good call. American Pokeweed is posionous, so caution should be exercised when dealing with it. --Dr Dima (talk) 19:57, 30 June 2009 (UTC)

I concurr, but when young, the plant is not toxic. "pokeweed salad" anyone? 67.193.179.241 (talk) 21:12, 30 June 2009 (UTC)Rana sylvatica
 * It's still toxic unless properly prepared, and it's a little bit toxic even then. See Poke salad. -Arch dude (talk) 02:25, 1 July 2009 (UTC)


 * My first guess based on the text description was pokeweed as well. It is somewhat poisonous if directly consumed, but you should be fine to touch it; its not like poison ivy or anything.  The most annoying thing is the purple berries it puts out which stain your clothes.  When in doubt, call Annie.  She'll know what to do with it.  --Jayron32. talk . contribs  03:53, 1 July 2009 (UTC)

OP here, posting from a different IP address. I just wanted to confirm that what I found was indeed Pokeweed. Thanks a lot for the help! 63.245.144.68 (talk) 22:18, 1 July 2009 (UTC)


 * Thanks for the confirmation post. Glad we could help! :-) Rkitko (talk) 02:21, 3 July 2009 (UTC)

Diffraction of sound over a wall
You have a solid heavy wall which is two metres high. 50 metres away from the wall is a point source of noise of n decibels. Although practically none of this noise gets through the wall itself, the noise will diffract over the top of the wall. Is there any way to estimate what the decibels of noise will be at various positions (x,y) on the quiet side of the wall? This is not a homework question, but I'm just trying to estimate to what extent building a walled enclosure in my garden would reduce traffic noise. Thanks. 89.240.105.155 (talk) 20:05, 30 June 2009 (UTC)


 * Have you read about diffraction? It will depend on the wavelength of the sound.  Since traffic noise covers a wide range of wavelengths, different regions (close to the wall, far from the wall), will have varying degrees of damping for different tones.  Also, you should reconsider whether the wall will completely block transmitted sound - in reality, it will reflect much energy and attenuate much energy, but some energy will pass through as well.  A non-negligible quantity of sound energy can also be transmitted underground.  Nimur (talk) 21:01, 30 June 2009 (UTC)


 * A number of companies sell sound wall caps designed to alter the diffraction of road sound over roadway noise barriers; these vary in construction from simple concrete I-caps to complex arrangements of horizontal vanes. Which is suitable depends on the traffic (particularly its speed) and the relative locations; this maker of soundwalls recommends an acoustic engineer be consulted. 87.115.68.24 (talk) 00:02, 1 July 2009 (UTC)


 * Would a row of tall, evergreen bushes be effective? Perhaps two rows would be better, with the bushes staggered from the bushes in the other row. I think the leaves would vibrate slightly from the sound and convert it to a small amount of heat. - GlowWorm.  —Preceding unsigned comment added by 98.17.43.38 (talk) 00:53, 1 July 2009 (UTC)
 * I wouldn't think that it would overcome the fact that more sound would travel through the bushes than a solid wall. &mdash;Akrabbimtalk 19:41, 1 July 2009 (UTC)

Blue giant
Is blue giant a main sequence star, or blue giant is not entirely dissimilar from blue supergiant. What is a yellow supergiant. Does yellow supergiant evolve from blue or white supergiant. Then what blue type is main seqeunce, is it blue dwarf or blue ginat?--69.229.111.118 (talk) 21:21, 30 June 2009 (UTC)
 * These sound a lot like homework questions. They can all be answered by reading the main sequence, yellow supergiant, and supergiant articles.  Red Act (talk) 22:21, 30 June 2009 (UTC)

Antartica shifting away from South Pole?
After continous moving of plate tectonics, is Antartica suppose to move away from South Pole one day. Is Australia suppose to collide with Asia one day? I thought Africa just continues to drift north. Alot of diagram shos in 200 million years Kenya will lie to like 35 degrees North liatitude, and North Africa suppose to be more or less to Artic Circle.--69.229.111.118 (talk) 21:26, 30 June 2009 (UTC)


 * This is a pretty cool animation if you have a fast enough connection to view it. Looie496 (talk) 03:09, 1 July 2009 (UTC)
 * Does anyone else find it ironic that you need a fast connection to view a process that ordinarily takes 200 million years to unfold!?! SteveBaker (talk) 12:25, 1 July 2009 (UTC)


 * Any guess as to how that video justifies that the movement of the plates will instantly go into reverse at some point in the future? -- k a i n a w &trade; 15:43, 1 July 2009 (UTC)


 * That's the Pangaea Ultima scenario. It assumes that the Atlantic oceanic crust at the margin of the North American plate eventually ruptures and becomes a subduction zone that then consumes the Atlantic.  It's not entirely crazy since this is among the oldest oceanic crust in the world; however, other people suggest the Amasia scenario (without that reversal) is more likely.  Dragons flight (talk) 17:37, 1 July 2009 (UTC)