Wikipedia:Reference desk/Archives/Science/2012 April 12

= April 12 =

will aluminum foil scratch a lens or its coating?
I use it as an impromptu lens cap (while I order a new one) but will the creases cause any scratches if it comes into contact into the lens? 216.197.66.61 (talk) 00:28, 12 April 2012 (UTC)


 * Aluminum can scratch plastic. Aluminum will rarely scratch silicate glass.  Even steel will rarely scratch a quartz glass or a good mixed silicate glass.  The Mohs scale quantifies the material hardness; it's sort of a hierarchy of what each material can scratch.  In practical, real-world terms, though, you should not assume that a scratch is impossible just because metal is softer than glass.  It's better to think of it this way: if there's a hard strike or contact, both materials will be damaged by abrasion, but the glass will cause more damage to the metal.  And of course, if you have any thin-film optical coating - often a plastic or polymer or even an oil film - that can be easily damaged.
 * If the lenses are glass, the coating will not be plastic or polymer. Magnesium fluoride is a common, inexpensive optical coating material. Better quality coatings will be made from alternating layers of silicon dioxide and some other durable oxide material.--Srleffler (talk) 04:20, 14 April 2012 (UTC)
 * I worry much more about sand than metal when I take my camera and telescope gear out in to the field. Sand is often harder than glass.  Nimur (talk) 00:55, 12 April 2012 (UTC)
 * If you're already thinking of using aluminum foil, could you also use a layer of clingfilm on one side? I'm overly careful with my lenses and mirrors too; what I recommend is buy a UV filter that can screw onto the front of your lens, that way the worst thing that can happen is you get a scratch on your relatively cheap replacable filter. Vespine (talk) 01:59, 12 April 2012 (UTC)
 * I'd be concerned about the oxide coating that inevitably covers aluminum (because it reacts with air). The coating is very thin, but it's aluminum oxide, with a hardness potentially like sapphire.  I don't know how much force it can really apply, though; obviously it doesn't protect the foil from scratching. Wnt (talk) 02:28, 12 April 2012 (UTC)
 * Astronomers grinding /lapping their own lenses or mirrors use aluminium oxide as abrasive, so that would be my worry as well. Also, it has been said that fingerprints on lenses (can) damage the anti-reflection coating because they're oily and acidic. With a non-absorbant surface like aluminium foil, any grease on there will transfer to the lens surface if they touch... Ssscienccce (talk) 17:20, 12 April 2012 (UTC)
 * Since the 1940's lenses are commonly coated with a thin and easily scratched anti reflection coating, which increases the contrast available in the image. Aluminum foil could easily scratch this coating and lower the image quality of the lens. Cling plastic as a lens cover would remove the scratch issue, but when the plastic is pulled off the lens, it might leave a static charge on the glass which would attract dust, at least until the lens is cleaned. Edison (talk) 18:48, 12 April 2012 (UTC)

Boyle temperature of Argon
What is the Boyle temperature of Argon (experimentally determined)? All the Google results I find just give me the definition (where B2 is 0), or point to journal articles I don't have access to -- atropos235 ✄ (blah blah, my past) 06:46, 12 April 2012 (UTC)
 * I think you can calculate it from the experimental data and calculations in this paper . 1.155.24.19 (talk) 09:42, 12 April 2012 (UTC)
 * Google books gave me 410°K (Physical chemistry By David Warren Ball, 2011) Ssscienccce (talk) 17:45, 12 April 2012 (UTC)

Just calculated it as a part of my Physical Chemistry Vacation Work for my degree. The answer I got is 409.96K hence 410K is correct :)

unhealthy food combination
This article only provides one example of food combination that will make you sick. Aside from the one given, what else? Thank you. — Preceding unsigned comment added by 203.240.243.100 (talk) 10:46, 12 April 2012 (UTC)
 * I'm inclined to say, having read the article, that it's a load of unreferenced old tosh. I have had experience of combining ackee and alcohol which made me very ill indeed, and a West Indian friend of mine said that's a well-known interaction in their community, but I can't find any references for it. --TammyMoet (talk) 11:01, 12 April 2012 (UTC)
 * I suspect the problem there is that both the ackee fruit and alcohol are capable of causing hypoglycemia, and that the combination of two hypoglycemic agents (which produce that effect via different mechanisms) is likely to be synergistic rather than merely additive. So yes, not a good pair to combine. - Nunh-huh 05:11, 15 April 2012 (UTC)
 * To get everything down here for convenience (though I remember I raised hackles the last time I did this - this is NOT an endorsement), the article claims:
 * Cucumbers contain an enzyme that breaks down vitamin C in strawberry, orange, or tomato. Later it says carrots "damage the vitamin C" in kiwis.
 * describes ascorbic acid oxidase which is apparently present in many foods and can degrade vitamin C on standing. For instance lemon peel has several times the vitamin C of the rest of the lemon, but can lose it.  That said ... when actually eaten enzymes are not long for this world; pH 2 will stop all this, and if you're not a Prilosec addict your pH should be lower than that.  See  for a more technical discussion of this and a range of other antinutritives.
 * onion and honey together are "bad for your eyes".
 * This one has evaded me. I see people taking these two together with alleged benefits.   Another set of... claims ... at  (including that tofu and honey will make one deaf).
 * shrimp and watermelon together "lowers your immunity".
 * That site above says "prawn and pumpkin" cause "food poisoning". Mixing sweets and uncooked meat is indeed a way to grow salmonella; is that what they mean?  But it's not going to happen after eating.
 * milk and chocolate together cause "dry hair (건성모발), diarrhea, and loss of calcium".
 * pumpkin "damages the nutrition in strawberries".
 * No idea if this is more ascorbic acid oxidase trouble. Like somebody with this diet is short on vitamin C!
 * sweet potato and persimmon "causes vomiting (구토".
 * This claim is repeated at and, which look 'taxonomically distinct' from this first claim.  Hmmm...  the second claims "gastrectasia, abdominal pain, vomiting, and so on.  It may even cause stomach bleeding..."  I'm seeing more about this because of "glue" in the persimmon blocking the pylorus; apparently it's also bad on an empty stomach?   Hmmm, I tried NCBI and got a paper about endoscopic injection of patients with Coca-Cola.  Will the march of technology never cease?  No word on Pepsi, or why it comes up with this search for that matter.  Ah, persimmon is causing phytobenzoars!    High stomach pH or interference with emptying are reasons cited ... I'm beginning to see a path to plausibility, though I haven't found any confirmation so far.
 * The oxalic acid in spinach "removes the calcium from tofu".
 * Now clearly the author is not being very precise here. You can't remove calcium from anything!  But admittedly some things can decrease absorption.  Note many of the terms are given hangul (Korean) translations if you mouseover; I've copied two above from the page source.  My overall feeling is that if you're worried about mixing all these healthy fruits and vegetables rather than, say, potato chips and ice cream, you're already ahead of the curve, at least in the U.S.! Wnt (talk) 11:27, 12 April 2012 (UTC)
 * (NOTE: Nobody eats kiwis. They're an endangered species of flightless bird. It's also a slang name for people from New Zealand. Nobody eats them these days either. I suspect you mean Kiwi fruit.) HiLo48 (talk) 20:44, 12 April 2012 (UTC)
 * Apparently the kiwi population dropped significantly do to overhunting for the manufacture of boot polish. Although I might have that wrong: It might be New Zealanders who were overhunted. ←Baseball Bugs What's up, Doc? carrots→ 21:48, 15 April 2012 (UTC)

Fluid properties of blood
How does the fluid property of blood, in terms of fluid mechanics, change as it travels around the body and depending on its biochemical contents? 82.132.139.77 (talk) 14:40, 12 April 2012 (UTC)


 * When you get down to capillary size, individual red blood cells can block the flow of the plasma. So, it behaves like a much thicker fluid. StuRat (talk) 17:31, 12 April 2012 (UTC)
 * Not sure about that, they do line up behind one another in capillaries, but according to blood: whole blood (plasma and cells) exhibits non-Newtonian fluid dynamics; its flow properties are adapted to flow effectively through tiny capillary blood vessels with less resistance than plasma by itself.
 * Maybe they keep the capillaries open, prevent them from closing completely due to outside pressure... Ssscienccce (talk) 19:21, 12 April 2012 (UTC)


 * Blood has the property of shear thinning which is a type of Non-Newtonian fluid.  Spinning Spark  19:32, 12 April 2012 (UTC)

replacing wheels with balls in a car.
an obvious problem with cars is that they can only really go in two directions-forward or back. steering only makes a relatively small change in direction which is why its so difficult to get out of tight spaces.

a simple solution would be to give all 4 wheels the ability to turn 360 degrees, but this would meen that the engine, gears or some part of the mechanical system would also need to turn with the wheels. also it would take a significant amount of energy to overcome the friction stopping the wheels moving. the car would need a spherical design to remain aerodynamic. also the car may end up turning rather than the wheels.

to solve these problems, what would be the ramifications of having a spherical car with three balls instead of wheels. each ball could be driven be a belt similiar to that in an electric sander which would push the ball around. these three belts could be driven by a single engine, and the belts would be lifted off the balls, rotated, and then come into contact with the wheels again to change the direction of the car. neither the balls or the car would actually rotate, just the direction in which the balls are spinning.

Is this possible and are there any other advantages/disadvantages to the design.

ps. i dont intend to create this any time soon (oddly enough), so i'm not interested in the practicalities of actually making it. its more a thought experiment on an alternative design of motor transport-perhaps how an alien's car might look for example. — Preceding unsigned comment added by 86.176.18.18 (talk) 14:46, 12 April 2012 (UTC)
 * Spherical wheels on cars get asked about on the Science reference desk from time to time. Here are a couple previous threads on the topic:    Red Act (talk) 15:23, 12 April 2012 (UTC)
 * Mecanum wheels are what you want ;) --15:41, 12 April 2012 (UTC)
 * Three balls would have significantly less surface contact with the road, compared to four wheels. This would make braking more difficult, and skidding a bigger problem. Goodbye Galaxy (talk) 17:11, 12 April 2012 (UTC)
 * Friction is a very, very complicated subject. Depending on size, inflation pressure, materials, and many other factors, it's possible to design a three-ball system with more, less, or exactly the same traction as a four-wheel system. --Carnildo (talk) 23:02, 12 April 2012 (UTC)

Honda's Asimo robotics lab created the UX-3 Personal Mobility prototype - a wacky toy that evolved out of their research lab's good-faith engineering effort to reinvent the automobile wheel. Nimur (talk) 17:17, 12 April 2012 (UTC)


 * With electric cars, each wheel can be driven individually by a small electric motor which turns with the wheel. This should provide better mobility than when the wheels must be attached to a central drive shaft. StuRat (talk) 17:28, 12 April 2012 (UTC)


 * Peugeot MoVille  Spinning Spark  17:33, 12 April 2012 (UTC)

Some great answers and refs above. I like the similarity between the UX-3 wheel and the mecanum device. I'll add in some terminology that you might find helpful for investigating this type of issue. Steering an automobile is a form of Non-holonomic transport. This type of transport is especially difficult to design control systems for, so people are especially concerned with wheel alternative for robots. See Holonomic, which lead me to Ballbot. SemanticMantis (talk) 17:39, 12 April 2012 (UTC)


 * What strikes me about balls is that, if you think of them like big hemispherical custom hubcaps, you're bolting on a lot of inertia, for the part of the ball that isn't touching the ground. But - in modern hybrids and electric cars, regenerative braking can recover most of that energy.  Maybe this is an idea that is worth looking at again for the new generation of vehicles. Wnt (talk) 20:28, 12 April 2012 (UTC)


 * The OP asks "...are there any other advantages/disadvantages to the design?" I'd suggest that 90% of car design is fashion. It's the part that involves making the customer think they've bought an attractive car. A totally revolutionary shape would have a huge disadvantage on that front. You still have to sell it! HiLo48 (talk) 20:38, 12 April 2012 (UTC)


 * HiLO, that argument is completely counterintuitive. Usually a "revolutionary shape" is what does attract buyers or we would still have cars that look like the model T.165.212.189.187 (talk) 12:53, 13 April 2012 (UTC)
 * Cars do still look essentially like the Model T; four wheels, front mounted internal combustion engine, storage in the rear, direction controled by the two front wheels using a steering wheel, foot pedals for accelerator, breaks and clutch, two headlights, etc. 203.27.72.5 (talk) 20:18, 13 April 2012 (UTC)
 * OK, Hilo was addressing "fashion" and "attractiveness" not function and practicality.165.212.189.187 (talk) 18:56, 17 April 2012 (UTC)


 * How long would it take for such wheels to get gunked up by the grit and grime that exists on every road? I'm guessing not very. ←Baseball Bugs What's up, Doc? carrots→ 04:26, 14 April 2012 (UTC)

What is the expected operating lifetime of a modern coal-fired power station??
I read over the wiki entry for "Fossil-fuel power station," but did Not see any mention of lifetimes. I have the impression that many American coal-fired plants now in operation were built in the 1960s and 70s: so that's my idea of "modern." I assume that the limiting component in these plants is the Boiler. Thanks for responses. 98.225.64.151 (talk) 18:53, 12 April 2012 (UTC)


 * Planned lifetime is 50 years for new builds according to and  says at least some are achieving this in practice.  Spinning  Spark  19:40, 12 April 2012 (UTC)
 * Man, just like SimCity 2000! I guess maybe we'll have fusion power in 2050 after all...Paul (Stansifer) 01:30, 13 April 2012 (UTC)
 * We need a "like" function for the reference desk. That was my first thought too! :D - Running On Brains (talk) 05:34, 16 April 2012 (UTC)
 * The 50 years round number cited by Spinningspark sounds very reasonable for the mid 20th century and after. A "fossil fuel power station" can be kept in operation indefinitely. I know of one which is still in operation after over a century. We should distinguish between the "plant" and specific pieces of equipment (turbines, pumps, generators, boilers, transformers, circuit breakers). What usually happens is it opens with "Unit one" in operation. As demand increases, more and larger generators are added along with the necessary steam production and coal/oil handling equipment, and the transmission substation is expanded. The newer units are more efficient, so the initial units may be retired long before the 50 years is up, or they may be used only as "peakers" to spin up relatively quickly and handle daily peak or seasonal peak demand. If a unit is still economical to operate after decades of use, it can be given repairs and rehab and used for many more decades. An incentive to keep renewing and using an old plant is that it already satisfies zoning issues and it already has rail lines, pipelines, barge canals, river access, and transmission lines which would be prohibitively expensive to acquire in virgin territory near businesses, schools, or residences. Some utilities have done incremental rehab so that the unit is "grandfathered" as still being the old original unit, and does not have to meet the latest pollution standards, which would kick in if the rehab cost over some fraction of the value of the unit. . The "Not In My Back Yard" view even works against introducing wind generators in farm country or in the sea near the coast, because people would have to look at them, let alone large conventional power plants and transmission lines. Edison (talk) 15:42, 13 April 2012 (UTC)
 * People in the Midwestern Plains want PIMBY wind power -- Please, In My Backyard! Because the horizons are so flat and boring. 70.59.20.190 (talk) 07:12, 14 April 2012 (UTC)
 * Well, I have worked for the power company in my city. They had coal fired power stations dating back to the 1930's still going strong, original turbines, alternators, everthing.  They had been retrofitted with precipitators to reduce pollution, and some mordern instrumentation.  They have now been decommisioned, but not because they were worn out or no longer performed well.  They were phased out because when they were new, 40 MW was a good size, but as the population has grown, and the use of electricity has spread from just lighting to all manner of things, and the grid spread out from the city, they have build addition power stations of ever increasing size, and against their current complement of about six 400 MW and 600 MW sites, an old 40 MW site doesn't make a worthwhile contribution anymore.  Ratbone124.182.183.204 (talk) 15:40, 13 April 2012 (UTC)

Identify rabbit photos
I think this rabbit that I was originally told was a white-tailed jackrabbit is actually a snowshoe hare. Can anyone confirm this, please? (Images: 1, 2, 3, 4, 5, 6) —Arctic Gnome (talk • contribs) 19:57, 12 April 2012 (UTC)
 * I'm not finding this as easy to settle as I expected. The snowshoe hare is supposed to have dark only at the tips of its ears, not the whole ear.   On the other hand, your photo 6 does seem to have a black tip within the larger dark region ... and because the whole pelage changes yearly, there might be some intermediate coloration seldom remarked about.  Looking up white-tailed jackrabbit and snowshoe hare, Edmonton is within the known range only of the latter.  And the feet, well... snowshoe hares are supposed to have big feet, hence the name, but I'm not seeing the difference in the pictures.  I invite more eyes. Wnt (talk) 20:26, 12 April 2012 (UTC)
 * The feet shape seems to be the biggest difference, but I still can't guess based on the feet of these individuals. Looking at the range won't help; I've found a provincial and municipal webpage mentioning both species living in the city. These rabbits were all on the university campus, and they all look the same, so someone must know the species of the campus's population, but I can't find it. —Arctic Gnome (talk • contribs) 00:27, 13 April 2012 (UTC)
 * Uh-oh. Sounds like our article on the jackrabbit has a wrong illustration then.  Somehow this doesn't surprise me though... I have the impression that a third of range illustrations are bunkum, two-thirds on Wikipedia) Wnt (talk) 00:52, 13 April 2012 (UTC)

Brodatz texture dataset
Hi. Within image processing the Brodatz texture dataset is quite a famous dataset, and yet I can't seem to find any information about its origin. From searching around, it appears as though there's various different versions, some with 111 class, some with fewer, some with multiple samples per class, some with just one. This site shows nine samples for all 111 textures, but there is no information on what those textures are. Other sites state what small subsets of the textures are (e.g. herringbone) but I don't know what their source is for this. Does anyone know any resources that will tie all these loose ends together? --Iae (talk) 21:26, 12 April 2012 (UTC)


 * After more searching it appears the original book contains 111 classes, each with one sample. Later datasets containing multiple samples presumably were generated by rotating, adding noise etc. the original sample. I've also discovered a site with each of the 111 samples downloadable. However, the identity of each of these samples is not given. Presumably this is supplied in the original book? Is there no online listing of the identity of each of the textures? This doesn't seem very conducive to research, which surprises me, given its popularity. --Iae (talk) 22:13, 12 April 2012 (UTC)


 * First web-link I found was Filter and Filter Bank Design for Image Texture Recognition - the doctoral thesis of one Trygve Randen. Per rigorous academic standards, he cites his source: P. Brodatz.  Textures: A Photographic Album for Artists and Designers.  Dover, NY, 1966.  Perhaps someone can locate an ISBN for the book.  Nimur (talk) 22:21, 12 April 2012 (UTC)
 * Google indicates that it has been published under two ISBNs, 0844617458 (1966) and 9780844617459 (1981). It looks like an academic review of the work was published in the first issue of an otherwise anonymous MIT imagery journal in 1968, still available on JSTOR.  According to that review, the photographer released his work for free reproduction (probably explaining why the dataset is used widely in academic circles).  It also notes: "In a brief introductory text, Brodatz explains how the photos came to be taken, provides technical details on how they were made for photographers anxious to try their own luck, and suggests ways and means in which they can be used and/or enjoyed."  Nimur (talk) 22:29, 12 April 2012 (UTC)
 * Can you tell me if it gives a listing of the identity of each of the textures? The link you've given does take me to an MIT journal from 1968, but it's apparently on Leonardo? And I am unable to access it with my institutional login. I've a feeling I'm going to have to hunt down the original book in order to find out what each of the textures are sadly. Thanks for the help! --Iae (talk) 22:37, 12 April 2012 (UTC)
 * The Leonardo review is only a few paragraphs; you want the full book. I'd recommend hunting down the original book, which doesn't seem available for sale at any major online resellers.  I found a different book by Brodatz at Stanford Green Library, but no Textures in their any of the research-library collection of 6.3 million texts.  The United States Library of Congress lists:  and .  It has even been re-published as recently as 1999.  It exists!  Somewhere!  Perhaps your closest research library can request a loan.  Nimur (talk) 22:50, 12 April 2012 (UTC)
 * You can get it on Amazon for £20. They have a second hand copy for £1.33 (cheaper than an inter-library loan).  I can confirm that the review article probably does not have much to interest you, but I will send you a copy if you drop me an e-mail.  Spinning  Spark  23:30, 12 April 2012 (UTC)


 * Thanks both of you! --Iae (talk) 00:39, 13 April 2012 (UTC)


 * I don't know what this, but to be clear, the images themselves can be downloaded at http://www.ux.uis.no/~tranden/brodatz.html . If this is indeed a public domain resource we should get it on Commons and link them from an article Brodatz Texture, with more explanation than I know, for sure. Wnt (talk) 00:47, 13 April 2012 (UTC)


 * Seems to be published also under another ISBN:  &#x2013; b_jonas 09:19, 15 April 2012 (UTC)

The glue binding new and unused staples together. What is it?
What type of glue - i.e., what is the glue made of that - holds new and unused staples together, in a pack of new staples? 82.31.133.165 (talk) 23:26, 12 April 2012 (UTC)
 * staple pins glue? My guess is that you won't get much more specific then that.. I doubt there is one specific kind of glue, it's probably more a case of various proprietry concoctions made specifically for that purpose. Vespine (talk) 01:58, 13 April 2012 (UTC)
 * It seems to be heat or light cured glue (they come out of what looks like an oven or a bright light in the video "How Its Made 106 Nails and Staples", see youtube) Ssscienccce (talk) 20:15, 13 April 2012 (UTC)

how hot does it take for Titan to heat up to completely lose its atmosphere
I always been told when sun becomes a RGB in 6 or 7 billion years living on Titan will be like living on the moon today. But This source said when Titan gets to -70 C or -90 F roughly puts at Mars current temperature, Titan can retain its substantial atmosphere. Could it be because of greenhouse effect which may protect the atmosphere from eroding? Titan living a atmosphere on Marslike surface temperature could it be the greenhouse effect makes the surface temeprature much warmer than it needs to. In 6 billion years without the greenhouse? effect, could Titan at that era be much colder? if greenhouse effect depletes can Titan's atmosphere just erode quickly? If it starts eroding can Titan's atmosphere completely or mostly erode in just 1/2 of billion years? At the tip of sun's RGB is Titan's surface temperature suppose to be like Earth's today? On a Earthlike temperature on Titan, can Titan still retain its atmosphere? --69.226.43.137 (talk) 23:48, 12 April 2012 (UTC)

Apparently the jury was still out as of 2008. Part of it concerns Saturn's magnetic field, which it comes out of for part of each orbit, but which somehow lingers temporarily for part of that time... Wnt (talk) 00:41, 13 April 2012 (UTC)


 * Marsdon't have a magnetic field but it said the greenhouse effect and frozen gases beneath the surface as the sun warms up in 1 billion years, it can actually acquire a more substantial atmosphere. Mars does not have a magnetic field, I don't know what will protect the atmosphere.--69.226.43.137 (talk) 01:02, 13 April 2012 (UTC)


 * The article said that even when solar wind (mass flux) will be highest, Titan will lose less than 2% of its atmosphere per Gyr to it, so I guess at that distance from the sun Titan doesn't need a magnetic field, at least not for the solar wind (it does lose gasses due to photochemical escape that would be prevented by a magnetic field). With it smaller gravity, thermal escape is likely the main loss, dependent on temperature and on the atmospheric composition. Higher temperatures give single atoms more chance to escape gravity, and hydrodynamic escape where the difference in density drives larger masses of gas upward becomes important with higher hydrogen concentrations. Other gasses are pulled up with the hydrogen and reach escape velocity. The article does suggest that after 12.15 Gyr the consequences of the sun pulsating will be likely catastrophic, but I'm sure we'll have terraformed it long before that happens. As to how long an atmosphere would last with earthlike temperatures, I haven't found a definite the answer, only some 'rules': if the escape velocity is 5 times the average speed of a gas particle in the exosphere, then that gas will escape with a time period of about 100 Myr. If the ratio is 6, then well over 10 Gyrs, if only 4 then less than a million years, 3: less than 10 kyrs.. Problem is knowing the temperature in the exosphere since that and the particle mass gives the mean particle velocity. That would I'm guessing partly depend on the greenhouse gasses, temperature gradient in the atmosphere, atmospheric composition, and then calculate for the lightest molecule or atom... Ssscienccce (talk) 02:07, 14 April 2012 (UTC)