Wikipedia:Reference desk/Archives/Science/2011 April 17

= April 17 =

Does FRET work on IGE?
Does Förster resonance energy transfer work on induced gamma emission? Specifically, for purposes of sci-fi, I'd like to rely on "metatope batteries" in which covalent or ionic compounds of elements with nuclear isomers are used to break up the energy from one into another in diminishing steps until fissionable energy is broken down to a usable chemical scale. (I think that the range, which varies by the sixth power of distance, is a function of the virtual photons, rather than the size of the emitting/receiving particles, but I'm not 100% sure) Wnt (talk) 03:27, 17 April 2011 (UTC)


 * N.B. Someone at Wikipedia talk:WikiProject Physics (where I asked this and other related questions) said he thought this was unlikely because "it's an electrical dipole-dipole interaction, but nuclei must have very small electrical dipole moments, because they're so small physically" But I don't know what the dipole is... Wnt (talk) 17:32, 20 April 2011 (UTC)

How to cheat reading eye chart?
I'll start with lenghtly explenation, if you don't want to read it all just cut to the question in the end :) I have nystagmus, I did some research on it and noticed that many people with it can't drive just because they need to be able to read number plate from 20 meters away. Now I don't intend to get drivers licence any time soon, but I don't think my vision is so bad that I wouldn't be able to drive. I also believe that eye charts are crapy way to test visual acuity. So I did some research - in my country you need acuity if no less than 0.5 to be able to drive, pretty sure they use eye chart for testing. I recently got myself contact lenses (I also got astigmatic myopia), so I developed a theory on how I could cheat the eye test. I imagine nobody would ask to check the power of my contact lenses and you can buy any contact lenses you want online. The big idea is that using viciously owerpowered lenses for duration of the test would turn my eyes into binoculars. The problem, besides widely known tale that wrong glasses can make you ill, is that I noticed that my current contact lenses make things look slightly smaler, I'm not sure if it is from blurrines reduced or because of lenses themselves - you know how things look smaler when you look trough magnifying glass from distance - which is making me question my theory - maybe overpowered lenses would instead make chart appear mycroscopic. The question - is there any way to shortly improve vision for sole purpose of reading as much of the eye chart as possible? —Preceding unsigned comment added by 46.109.116.140 (talk) 03:23, 17 April 2011 (UTC)


 * Overpowered lenses will give you blurry vision, not zoomed in vision. Lenses adjust where the focus of light is inside your eye. For most people, it does not fall directly on the retina. Your prescription will be the focus in or out to place the focus directly on the retina. If you increase the power of your lens, you will move the focus too far and end up with blurry vision. -- k a i n a w &trade; 03:26, 17 April 2011 (UTC)

Hear's an idea. Why don't you take a real pair of binoculas with you to the eye test. probably nobody would notice.190.148.132.157 (talk) 04:10, 17 April 2011 (UTC)
 * The point is that you have to wear corrective eyewear you had for test at all times when driving. There is a piece of equpiment for testing the power of glasses, but they wouldn't ask to remove contacts for testing (probably wouldn't even notice they are present). So I need binoculars in form of contacts 46.109.116.140 (talk) 04:47, 17 April 2011 (UTC)
 * Wikipedia has an article about pathologic nystagmus that describes actual therapies - I'd say I hope you've explored those, but actually, I suppose it would be better if you haven't since then you have an obvious alternative to cheating the test. Best to be able to read the speed limit signs, road construction, etc. I don't know if there are specific stimuli that trigger the vibration for you - might there be some alteration to the test environment you might be able to request, so that you can pass the test that way? Wnt (talk) 03:36, 17 April 2011 (UTC)


 * I don't know the laws in Latvia (which is what the bot says your IP is from), but in the U.S. either a license requires lenses or not. It doesn't say you have to use glasses rather than contacts, even if you tested with glasses.  With 20/40 vision and nystagmus, do you really want to drive around without contacts at all, when you're wearing them now? Wnt (talk) 06:19, 17 April 2011 (UTC)


 * Generations of people have passed some eye tests just by remembering
 * E
 * FP
 * TOZ
 * LPED
 * PECFD


 * Just saying. The doofuses do not make sufficient variation in the tests. Edison (talk) 04:19, 17 April 2011 (UTC)


 * Doofi ? :-) StuRat (talk) 05:59, 17 April 2011 (UTC)


 * When I took my drivers's eye test here in USA, the letters were on mechanical wheels like a mechanical digital clock. Everyone got a different sequence of letters to read. APL (talk) 07:32, 17 April 2011 (UTC)


 * There are various eye charts, I'm not sure what they are using here (and some places could still have ancient C charts). I tested at home from 3m distance, which is kind of hard to interpet, but it appears my acuity could be half the normal, which is 0.5. I might need about one extra line. The nystagmus mostly isn't issue, except it acts up in stresfull situations.
 * I never seen stronger power lens giving me blur, which is why I think that even if it doesn't work infinite, there still could be room for improvement, especialy when it doesn't have to be long term improvement 46.109.116.140 (talk) 04:32, 17 April 2011 (UTC)


 * Well, it wouldn't be the first time, or the tenth, that I've heard people complaining about an incompetent optometrist. Spherical contact lenses aren't perfect, but you should be able to walk out of an office with a pair of eyeglasses that lets you read much BETTER than 20/20, at least if the nystagmus isn't really so big of an issue as you say and there's nothing else the matter. Wnt (talk) 05:05, 17 April 2011 (UTC)

Maybe a friend could go into the office and check out the chart for you.190.148.132.157 (talk) 05:01, 17 April 2011 (UTC)
 * For reference, Visual acuity and Snellen chart describe the above. But everyone deserves to actually have high quality visual correction available to them, not just make-believe. Wnt (talk) 06:00, 17 April 2011 (UTC)


 * Lenses for myopia do not magnify. They actually reduce. If you want to make things bigger you actually need reading glasses. But those will make the chart blurry. There's no way to put binoculars into contact lens form.
 * Anyway, I would not want anyone who couldn't pass the test to drive. Even if, (like you seem to incorrectly believe) the test only tested your ability to read it would not be safe for a driver to not be able to see the signs.  Speed limit signs alone should be enough to convince you of this.  (Also : "BRIDGE OUT" ) APL (talk) 07:32, 17 April 2011 (UTC)


 * Most people who need glasses here are allowed to drive only if they wear glasses or lenses (and even carry a spare pair of glasses). The police, however, rarely checks whether they really wear glasses or lenses, and they have no way to check whether the glasses they wear are actually suitable for them, so many people get away without effectively seeing well while driving.  (Of course, people also cheat to get a driving license in other ways, like paying to a doctor.)  &#x2013; b_jonas 10:11, 17 April 2011 (UTC)
 * The road signs are hudge and easy to grasp, the only problem I have is indeed reading - I've tried, but on moving vehicles, I can't read the direction signs and such, not because I don't see them, but because they drive past too soon (probably I myself could slow down). You all seem to be ignoring the fact that I said that I don't intend to get drivers license any time soon. I just want to explore posibilities in theory. Now how about glases+contacts? Binoculars seem to only have two (times two) lenses 46.109.116.140 (talk) 12:12, 17 April 2011 (UTC)
 * That is a very interesting question. Theoretically, could glasses and contacts be used together to form binoculars? -- 110.49.248.2 (talk) 15:41, 17 April 2011 (UTC)
 * I suspect this might be possible. Contact lenses don't seem like they make the world seem larger or smaller, but eyeglasses change the apparent size of the area they cover.  I think you could get a quite modest magnification using contact lenses for an excessive amount of nearsightedness and eyeglasses for farsightedness.  But contact lenses only go so high, and you don't have control over the distance between the lenses ... I suspect you'd get a rather modest effect. Wnt (talk) 16:42, 17 April 2011 (UTC)
 * You're fooling yourself if you think your eyes make it impossible to read, but do not impact your performance otherwise. Picking out details out in the distance, and in your mirrors, is an important part of driving. For example, you wouldn't spot a bicycle, until you were much closer than a normal driver. You'd still have time to swerve by the time you saw it, but if you'd seen it sooner you could have gradually adjusted your speed so that you weren't next to a giant truck when you needed to swerve.  For another example, you might miss hand-signals other drivers are giving you. You might not be able to pick out street name signs soon enough to be useful (So you'd drive dangerously slow, or make dangerous sudden turns.) Even something as simple as making sure no one's coming up on you in your mirror when you open your door would be difficult without good vision.  I'm not saying that you'd crash your first time out, but you'd crash way more often than a properly sighted driver. APL (talk) 22:49, 17 April 2011 (UTC)

It may be easier to visit some third world country and get your driving licence from there. Count Iblis (talk) 14:45, 17 April 2011 (UTC)
 * We Latvians tend to think that we already live in some third world country ;) but indeed - simply put I just wish to know what 110.49.248.2 was saying (or any other optical/fun means to do it). I mentioned the reason I am asking just in case someone would come up with practical way to apply it to everyday life and because I want to know how bad could stronger lenses be (as I mentioned mine allready make things smaller) 46.109.116.140 (talk) 16:53, 17 April 2011 (UTC)

molten earth heaviest elements where
In a molten earth, shouldn't the heaviest elements have gravitated to the centre. Or would the centrifugal force of earth's rotation have thrown them out to the crust? — Preceding unsigned comment added by Phalcor (talk • contribs) 07:07, 17 April 2011 (UTC)


 * Of course there's no data that far back but if the earth was very fluid then convection currents could have carried heavier elements to the surface.190.148.135.18 (talk) 07:42, 17 April 2011 (UTC)


 * Some thoughts:


 * A) Gravity is far stronger, so heavier things should sink.


 * B) More dense elements, as opposed to more massive elements, should sink to the center. So, an atom that is twice as heavy but 3 times the volume wouldn't sink below the other.


 * C) Many elements form molecules, so the density of the entire molecule must be considered.


 * D) The Earth was only fully molten for a short period at the beginning, and significant mass was added later, in the form of meteorites, so much of that would have been blocked from dropping straight to the center of the Earth.


 * E) Plate tectonics provides a mechanism whereby things on the surface of the Earth may eventually be submerged to the molten portion. However, this depends greatly on the proximity to a subduction zone. StuRat (talk) 08:22, 17 April 2011 (UTC)

Thank's a bunch sturat. Several points of info. there.Phalcor (talk) 09:29, 17 April 2011 (UTC)


 * See planetary differentiation. Denser minerals do sink.  Minerals can be broadly classified as lithophiles, chalcophiles, and siderophiles by the Goldschmidt classification.  Lithophiles tend to form mineral complexes in association with oxygen and other light weight elements, and hence they would be relatively low-density as a group and tended to stay near the surface (on average).  By contrast, siderophile elements tend to bond with iron and other metals, which leads to high density and tendancy to be depleted near the surface.  The Earth's core is mostly iron with some nickel and other things.  Dragons flight (talk) 17:55, 17 April 2011 (UTC)

Modern mammals nocturnal?
According to this, http://www.bbc.co.uk/news/science-environment-13083990, modern mammals are typically nocturnal. Is that really true? Thanks 92.15.8.229 (talk) 09:52, 17 April 2011 (UTC)


 * It says they're predominantly (i.e. mostly) nocturnal, not "typically" nocturnal, which is rather different.--Shantavira|feed me 13:10, 17 April 2011 (UTC)

Alright, is it really true that modern mammels are predominantly noturnal? 92.24.177.71 (talk) 15:49, 17 April 2011 (UTC)
 * What exactly makes you think otherwise? If you take a look at Mammal you'll see that largest orders of mammals are rodents, bats and moles, if you break it down to species in these orders you'll probably find that most are nocturnal and/or live in dark environment Xil  (talk) 17:19, 17 April 2011 (UTC)


 * When you see weird statements like that, often they refer to 'predominant' in terms of number of species, which says nothing about distribution, number of individuals, biomass, etc. Bats alone make up 20% of mammal species, and the vast majority of them are nocturnal. Rodents make up 40% of mammal species, and many (>60%?) of them are nocturnal too. Really, though large diurnal mammal species are salient to human culture, I see no reason to disbelieve that at least 51% of mammal species are nocturnal. SemanticMantis (talk) 17:24, 17 April 2011 (UTC)

Bats at 20% and 60% of rodents at 40% only makes up 44% of mammals in total. I would expect "predominantly" to mean 80% or more. So there is a large gap to fill before I could believe the BBC article assertion. 92.15.15.88 (talk) 08:37, 19 April 2011 (UTC)

Late-leafing trees in southern England
Why don't trees in southern England come into leaf earlier? (I can only speak from my personal experience, so I'm only commenting about southern England). Herbaceous plants have been in leaf months earlier. Why do trees not come into leaf in February or March rather than leaving it till late April? Wouldnt they benefit from growing more? In a wild woodland or scrub situation, would not the earlier-leafing young tree be able to out-grow its nearby rivals and thus caputure the sunlight at the canopy? Thanks 92.15.8.229 (talk) 09:59, 17 April 2011 (UTC)


 * I suspect that late-leafing has evolved to avoid damage from late frosts. However, why elder and hawthorn can leaf a couple of months earlier than oak and ash I don't know. This page has some information on the leafing dates of oak and how it relates to temperature; it seems to be not clearly understood. Alansplodge (talk) 12:02, 17 April 2011 (UTC)


 * I was actually thinking of asking about this myself. Has global warming actually created a new season?  I always thought of spring as running from Easter to May Day, bud to flower.  But it seemed like thirty years ago the winter held on more strongly, at least past the end of March, and that the tender young buds were always at real risk of frost; whereas nowadays it seems like there are two or three weeks of above-freezing weather before the plants respond.  I assume some climate scientists looking at the global warming problem must have measured such a thing, if it's not just a trick of memory and time. Wnt (talk) 16:26, 17 April 2011 (UTC)
 * Easter (24 April) to May Day (1 May) is only six days this year! Alansplodge (talk) 17:09, 17 April 2011 (UTC)
 * I don't agree with the seasons being different in the past that what they are now. I can remember, for example, a winter without snow when I was a child; as well as a winter with lots of snow. I can also remember warm sunny days in November. I conclude that weather varies more from year to year than people suppose: when you get a random run of one extreme or the other, then people mistakenly believe that its due to changes in the seasons. If people move further south or to a lower altitude than in the past then they may also mistake the improvement in weather to climate change. 92.24.177.71 (talk) 17:00, 17 April 2011 (UTC)
 * I have a weeping ash that usually doesn't come into leaf until mid-June because we sometimes get sharp frosts here in northern England at the start of June. Spring certainly seems much warmer than usual this year, so I'll watch to see if it responds.  I'm surprised that anyone thinks that spring can start as late as Easter, especially this year, but I suppose it depends on what you mean by "spring".     D b f i r s   16:47, 17 April 2011 (UTC)
 * Since the date of Easter varies from year to year, then Wnt would have to be more precise than that. 92.24.177.71 (talk) 17:05, 17 April 2011 (UTC)
 * This thread suggests that oak is temperature responsive, whereas ash is photoperiodic; ie it responds to the change in daylight hours. Alansplodge (talk) 17:03, 17 April 2011 (UTC)
 * I think leaves appear in mid spring after ground plants are already out of ground and even after tree blossom. As far I remember in previous years all this happened much sooner, so it doesn't form a pattern, which could be interpreted as result of climate change, it is just that this year winter was longer Xil  (talk) 17:27, 17 April 2011 (UTC)

Failure due to mechanical vibrations
Hi,

I was wondering if anyone knew of any intersesting/dramatic examples (other than Tacoma Narrows!) of a device or structure failing due to mechanical vibration? Thanks for any suggestions! --58.175.32.140 (talk) 11:31, 17 April 2011 (UTC)


 * Many aircraft have been destroyed in flight, or seriously damaged, due to aeroelastic flutter, often simply called flutter. This is a form of mechanical vibration, just like the Tacoma Narrows Bridge.  Dolphin  ( t ) 12:20, 17 April 2011 (UTC)


 * You want dramatic? This is worth the wait.--Shantavira|feed me 13:17, 17 April 2011 (UTC)


 * That seems incredibly dangerous. Look how much kinetic energy the motor imparts: enough to flip a two-hundred-pound washing machine.  If the brick had been ejected through the open front-door and had hit the experimenter, it would certainly have been fatal.  "Don't try at home."  Things like this make me worry that regular people should not be permitted access to powerful machinery; they have a total lack of respect for the amount of power in the motors and engines that are readily available in today's vehicles and appliances.  Nimur (talk) 15:58, 17 April 2011 (UTC)


 * What do you propose, robots? Anyway, it's hard to picture the brick gaining that kind of lateral momentum in the opposite direction.  And the video is an important third-party test of what it takes for the washer to become dangerous during use (unless you trust the government to think of every possible failure?) Wnt (talk) 16:21, 17 April 2011 (UTC)


 * I suppose by that logic, we should encourage people to film themselves playing recklessly with other dangerous tools, like motor vehicles and firearms, to test the limits of government regulatory power? I can't see your statement as anything but a non-sequitur.  Some activities are inherently dangerous and should be discouraged.  Regarding robots, I have worked in several robotics laboratories; and lab-safety has always been one of the first things we had drilled into our heads.  The alternative, of course, would be a 300-pound robot arm drilling into our heads, because our robots had motors that were strong enough to kill a human.  Electric motors are very strong and very stupid; they require intelligent instructions from smart humans to operate safely.  Nimur (talk) 16:35, 17 April 2011 (UTC)


 * Fire Marshall Bill was always willing to personally demonstrate how dangerous things were. StuRat (talk) 20:53, 17 April 2011 (UTC)


 * Spike TV isn't my favorite channel, but yes, it's good for a laugh. Regarding lab safety, well, I'm not saying you shouldn't be permitted to make your own safety decisions.  I'm OK with it if we delay the beta release of SkyNet by a few months... Wnt (talk) 22:37, 17 April 2011 (UTC)


 * Regarding the original question: you might read our articles on earthquake engineering, earthquake simulation, etc. For the less dramatic, more common case - a lot of consumer electronics solder joints will crack or fail during vigorous vibration.  Everyone worries about this: mobile phone manufacturers, aircraft electronics, even NASA analyzes vibrational failure.  While this usually doesn't result in a catastrophic and dramatic collapse, it often causes "invisible" electronic problems, which are very bad.  Nimur (talk) 16:51, 17 April 2011 (UTC)


 * Resonance can greatly magnify the damage caused by vibration. StuRat (talk) 20:53, 17 April 2011 (UTC)

@Nimur, Evolution works in mysterious ways ;-) Richard Avery (talk) 21:58, 17 April 2011 (UTC)
 * Not sure if it is exactly what you are after but helicopters can experience an effect called Ground resonance which can lead to catastrophic failure due to mechanical vibration. Vespine (talk) 05:32, 18 April 2011 (UTC)

Thanks everyone for your suggestions, they have been quite helpful. Just to clarify my question a bit in case I get some more suggestions, I'm after industrial examples so while the exploding washing machine was humourous it wasn't exactly what I was after! :) --58.175.32.140 (talk) 12:09, 18 April 2011 (UTC)


 * There is also the example that marching troops can supposedly cause a bridge to collapse if it's at the proper resonance frequency. Mythbusters did a segment on this (I forget if they were able to confirm it).  So, troops may be told to walk across normally rather than marching in step, to prevent this. StuRat (talk) 17:24, 18 April 2011 (UTC)
 * Regarding which, see Broughton Suspension Bridge and, for a related problem, Millennium Bridge (London). {The poster formerly known as 87.81.230.195} 90.197.66.111 (talk) 19:04, 18 April 2011 (UTC)


 * Battle of Jericho? Mitch Ames (talk) 13:06, 22 April 2011 (UTC)

Is there a theory about the stuff called "Significant Atomic Mass"?
Today I saw something called "Significant Atomic Mass" in this web archive, but I did not find any other references, so is it a well-known scientific concept? — Preceding unsigned comment added by Inspector (talk • contribs) 11:56, 17 April 2011 (UTC)


 * I have never heard of the term, and I can't find any respectable-looking sites that use it. The site you linked to seems to be quite poorly written: maybe it is a mistranslation from another language? 81.98.38.48 (talk) 14:00, 17 April 2011 (UTC)


 * I believe what they mean is that they're giving a round number (334) rather than an exact mass. Except for carbon-12, defined at 12, all isotopes are just a little bit off from an integer because of various bits of energy involved in their composition.  These bits of energy, though small, turn out to be extremely meaningful during fusion and fission reactions and such - thus the need for an embarrassed disclaimer.  With so little of this element available, an exact mass could only be simulated guesswork. Wnt (talk) 16:15, 17 April 2011 (UTC)
 * The technical term for what WNT has described is Mass number. Compare the following:
 * atomic number, Z, an integer number specifying the number of protons,
 * neutron number, N, an integer number specifying the number of neutrons,
 * mass number, A ≡ Z + N, the integer number of baryons (neutrons + protons) in the atom
 * atomic mass, an exact value which can be measured in kilograms (or eV or daltons or your favorite convenient mass unit), that accounts for the binding energy (mass defect) (and also accounts for the fact that neither one proton nor one neutron weigh exactly one atomic mass unit)
 * Standard atomic mass, (also called "atomic weight" for historical reasons), which averages over the natural abundance and individual atomic mass for each isotope.
 * That's basically the rundown of the standard terminology. Anything else is "non-standard" terminology and should be interpreted with caution.  Nimur (talk) 16:25, 17 April 2011 (UTC)


 * Contrariwise. Standard atomic weight can't be suitable for this isotope. The problem with elements that don't occur naturally is that one can't calculate an average. --Aspro (talk) 19:17, 17 April 2011 (UTC)


 * I know about the atomic number and binding energy already. But I am still curious about how they find the formula which was used to predict the mass of unknown elements(even up to 218).--Inspector (talk) 09:25, 18 April 2011 (UTC)

Lewis structure standard
Is there an IUPAC standard for what side of the element symbol to start on and draw up to two dots as the s orbital and in what order to place the dots for the other p orbitals? 76.27.175.80 (talk) 16:39, 17 April 2011 (UTC)
 * No, there is not. In fact, there are several "standards" for drawing lewis structures for single atoms; some of which have you place the "s" electrons on one side (usually the top) and some of which have you ignore the "s" and "p" nature and just draw the electrons individually around the atom one at a time on all 4 sides, and then double up after.  People who espouse the first standard (first 2 "s" electrons, then one of each "p" around the other three sides, then double up the "p"s) claim that it better represents the electron configuration of the element.  I happen to usually teach students the second method, as lewis structures are primarly about learning how atoms bond in molecules, and the second method (ignore s and p, and draw dots one at a time around the outside) is a better representation of the orbital hybridization in bond formation.  The difference between the two methods shows up in the dot diagram for Carbon most starkly: If you use the "s" and "p" method, you get two dots on top, one on the right, and one on the bottom.  That would seem to indicate that carbon can form 2 bonds; to match each of its unpaired electrons.  In reality, carbon most readily forms 4 bonds; best explained by having 4 "hybrid" sp3 orbitals.  As a teacher, being able to use dot diagrams as a bridge to drawing the lewis structure of molecules (i.e. connecting the dots around Carbon to the 4 bonds that Carbon makes in in a molecule) is more important than correctly modelling the "s" and "p" organization in unbonded carbon.  Indeed, so many other models do that better and more obviously than the dot diagram that it doesn't serve much purpose to make the dot diagram do that as well.  If you look at this google image search and this google image search and this one as well you'll see that most people use the "one dot per side" method.  However, you should do whatever your teacher tells you to; they are grading the test.  Understand that different teachers have different reasons (pedagogically) to teach one model or another, and that one or the other is not wrong (i.e., your teacher is not wrong because they favor a different model than I do).  Understanding the limitations of each model is more important.  -- Jayron  32  02:19, 18 April 2011 (UTC)

Most reflective mirror
What type of mirror is the most reflective? --75.40.204.106 (talk) 16:40, 17 April 2011 (UTC)


 * For most purposes, aluminum on silica glass has the peak reflectivity. If you have special needs, you should check with your optics vendor.  Nimur (talk) 16:44, 17 April 2011 (UTC)
 * You are mistaken. Silver has better reflectivity than plain aluminum through nearly all the visible band, and out into the IR. Unless you are working with violet or ultraviolet light, a silver mirror will beat aluminum. Silver mirrors are more expensive, both because it's a precious metal and because a coating is required to protect the silver from oxidation. As noted below, though, a dielectric mirror can be more reflective than any metal mirror, and can closely approach 100% over a narrow range of wavelengths. You may have been misled by the "enhanced aluminum" curve on the page you linked to. An "enhanced aluminum" mirror is an aluminum mirror with a multilayer dielectric reflector deposited on top; it is kind of a hybrid between a metal mirror and a dielectric one.--Srleffler (talk) 17:02, 20 April 2011 (UTC)
 * See dielectric mirror. Red Act (talk) 17:11, 17 April 2011 (UTC)


 * I don't know if you would call it a "mirror", but many optical devices like binoculars and periscopes use total internal reflection to redirect light with minimal losses. -- 174.21.254.3 (talk) 18:37, 17 April 2011 (UTC)
 * Found this link up the page a bit Perfect mirror. -- 174.21.254.3 (talk) 18:41, 17 April 2011 (UTC)
 * Prism as a mirror?--78.150.239.71 (talk) 09:17, 18 April 2011 (UTC)
 * Yup. While people are probably most familiar with dispersive prisms, which are the ones which separate white light into rainbows, there are also reflective prisms, such as the Porro prism. -- 174.21.254.3 (talk) 15:56, 18 April 2011 (UTC)

Antimatter explosion
What would an an antimatter explosion look like? --75.40.204.106 (talk) 16:40, 17 April 2011 (UTC)
 * See the answers from when the same question was asked last month. Red Act (talk) 16:53, 17 April 2011 (UTC)


 * (ec) It depends entirely on how much antimatter is annihilated. In practice, usual lab experiments involve minuscule amounts of antimatter - so the actual annihilation looks like nothing at all.  Photons are produced, and effects are measured; experimental high energy physicists analyze volumes of experiment data and determine a statistical presence of one or more particle trajectories that corresponds to a matter-antimatter annihilation energy.  So, in practice, the "explosion" looks like numbers in a database.  Nimur (talk) 16:55, 17 April 2011 (UTC)


 * It would look like gamma radiation. Photons. Light.  Collect (talk) 17:40, 17 April 2011 (UTC)


 * Lots of discussion of this here. To the naked eye it would look much like any other explosion — it would generate a considerable amount of heat in a short amount of time, which is what most explosions "look like". --Mr.98 (talk) 17:52, 17 April 2011 (UTC)


 * It could range anywhere between a crackling flash over in less than a fraction of a second for a relatively small amount, to a brilliant, magnesium white, expanding ball of ionised air hot enough to vaporise everything in its path. The sky itself will burn from the radiation, and flare different colours as the components of the air would fluoresce, this is accompanied by aurora. Although anyone, who witnesses such a fireball will receive a deadly dose of gamma radiation, to kill in seconds. Of course, these are two extremes, depending on the amount of antimatter. Plasmic Physics (talk) 23:26, 17 April 2011 (UTC)


 * It would look like a nuclear explosion, really. Dauto (talk) 14:32, 18 April 2011 (UTC)
 * And those look pretty much like a very large conventional explosion. Googlemeister (talk) 19:02, 18 April 2011 (UTC)

Keystone species
Is the human a kind of keystone species? How about their pets? I see on the talk page for that article that somebody has removed the domestic cat from the list of examples, reasoning that they are artificially high in abundance and only harm other populations. Given that they are artificially high in abundance because of the actions of humans, which are a kind of animal, and given that all keystone species manage, that is to say, eat, other populations, and that there is no inherent balance of nature, does either argument for the exclusion of pet cats have merit? Is it merely that humans are not part of nature by definition, and therefore every human effect is termed an artificial effect? Card Zero (talk) 18:29, 17 April 2011 (UTC)


 * The notion of keystone species is somewhat nebulous and subjective by nature (as are many ecological concepts). Most ecological studies make a distinction between ecosystems with strong anthropogenic influence and more 'natural' communities. However, this distinction is basically a convenience, because we know that humans and all their their domesticated and commensal species radically change ecosystems. The human species is definitely 'keystone' if the definition is 'disproportionate effect on its environment relative to its biomass.' The same is true for our cats: they can radically effect the ecosystem, for instance when introduced to islands. That being said, the more common usage for keystone species is indicated by the examples in our our article. Other good examples of keystone species are ecosystem engineers such as many ant and termite species. SemanticMantis (talk) 19:21, 17 April 2011 (UTC)

Glasses that correct for higher order aberrations
Are glasses that correct for higher order aberrations (spherical aberration, trefoil etc.) for sale? I think that my night vision is not so sharp because my glasses only have a diopter and a cylindrical correction. Count Iblis (talk) 20:10, 17 April 2011 (UTC)
 * Yes, but why do you think it is caused by higher order aberration? It sounds more like Nyctalopia, which can have causes other than astigmatism. Besides visual acuity is reduced by about 90% in night, you should worry if you don't see anything at all or if it is not sharp in day Xil  (talk) 20:36, 17 April 2011 (UTC)


 * Well, I actualy have very good vision at night compared to most other people. E.g. if I go outside during half moon, after a while it looks like dusk to me, I can see everything around me, while the people I'm with are complaining about not being able to see where they step well. But what I see looks like dusk, but with me not wearing my glasses. Now,  I like to do observing at night and I have read e.g. here, the last message by Brian Skiff that getting the eye correction sorted out precisely could make a difference.  Count Iblis (talk) 21:06, 17 April 2011 (UTC)
 * Everybody's night vision is less sharp than their daylight vision. This is because the sharpness of the image that is formed on the retina is partly controlled by the diameter (or aperture) of the eye's pupil - the smaller this is, the sharper the image. At night (and in any other low-light situation) the pupil expands to its widest to allow in as much light as possible, in order to make the image as bright as possible, but this has the unavoidable effect of unsharpening the image.
 * If you have exceptionally good night vision in terms of brightness, your pupils are probably able to open wider than average (and than those of older people, since maximum pupil size declines with age), so the unsharpening you experience will also be greater than average.
 * Atropine used to be used to widen the pupil to improve night vision in critical situations (such as night combat in warfare). There are doubtless some drugs that would have the opposite side effect of shrinking the pupil, sharpening but dimming your night vision, but this marginal benefit would probably be outweighed by their less desirable main effects on your body and system (whatever those might be) so this would not be safe method to pursue. {The poster formerly known as 87.81.230.195 - who also has short sight and astigmatism, and used to practise astronomy} 90.197.66.111 (talk) 23:53, 17 April 2011 (UTC)


 * Because I've been wearing glasses for such a long time (since I was 7 years old), I don't remember the characteristics of normal vision anymore. So, whenever I am not seeing sharp, I tend to blame my glasses :) . Count Iblis (talk) 14:42, 18 April 2011 (UTC)
 * Heh, that sounds like a very screwed up understanding about vision :) First of all -1 astigmatism is not all that bad vision, it is fairly close to normal, the guy on yahoo groups is saying he needs much stronger correction than you. Secondly reffractive error occurs due to shape of the eye and how light is focused in the eye, I think it is something an eye care specialist should see when checking your eyes. Lastly - why don`t you do a vision test at home - take an eye chart, and write down what you see in it from distance (writing down will produce better results and ensure you don`t memorize the chart), then try to do the same in darker conditions - you`ll know what your vision is in normal conditions and how good it is in darkness (as I said 90% reduction is considered normal). I would say that ``normal`` is what you get removing glasses and allowing eyes to adjust for a while, technicaly ``normal`` is 20/20 for which you might need glasses  Xil  (talk) 20:10, 18 April 2011 (UTC)


 * I found the specification of my glasses. The right one is -6.25, astigmatism is -1.75, the left one is -4.75, astigmatism is -3.00. This suggests to me that higher order corrections may be important for my left eye and that I should perhaps visit one of these specialized optometrists that do real measurements of the eye, instead of the regular ones that try to fit the standard glasses and ask you if you see things clearer or less clear. Count Iblis (talk) 21:45, 19 April 2011 (UTC)
 * That`s interesting idea, what tests exactly are you thinking of taking? A suggestion based on personal expierience - I recently got RGP lenses, during eye examination the optometrist did a certain test stating it wouldn`t be possible to prescribe contact lenses without it, I didn`t ask what the test was, but judging from the results I saw on her computer screen she took photograps to calculate shape of my corneas. Since the refraction errors you are intrested in are largely caused by mishapen cornea, it might be cheaper to pay a visit to any optometrist with stated goal of geting contacts and then bombarding them with gazillion of questions about your test results Xil  (talk) 22:41, 19 April 2011 (UTC)
 * A so-called "wavefront map" can be made. One problem may be that the higher order aberrations are not so stable over time. I'm still doing some reading on this isses. E.g. I read here that adaptive optics have been used to correct vision almost perfectly, but it may be that you can't do without adaptive optics, even if you want to correct the vision for one particular person. Count Iblis (talk) 18:02, 20 April 2011 (UTC)
 * WOW, that's a neat reference! Visualizing single cells in the retina!  This would seem to have all kinds of applications - detecting the first signs of diabetic retinopathy before diabetes is diagnosed (i.e. using it to diagnose diabetes), getting to the bottom of the full explanation about macular wrinkles and holes, all sorts of stuff that should have been done but so far as I know hasn't (though they're starting).  It sounds like some people haven't getting the full funding they deserve to save our planet a just amazing amount of money, not to mention anguish. Wnt (talk) 00:11, 22 April 2011 (UTC)

Getting cheese moldy?
I have an old cook book, it has a recipe for cheese, which pretty much is a way to utilize old, molded quark. I want to try it, but I only have fresh quark. A recipe for another somewhat similar cheese clarifies that it will get moldy if left in warm place for 3-4 days. Unfortunately I don't have the patience to look on ball of quark left on table, showing no sign of aging. Is there any way to speed this up? I was thinking I could find mold somewhere, but I figure I need some specific fungi, is there any way to identify suitable mold species? Xil (talk) 20:11, 17 April 2011 (UTC)


 * Yes, but part of that would involve using a microscope and maybe growing cultures and exposing them to various agents to see if they promote or retard growth. The wrong kind of mold can certainly be dangerous.  I suggest you buy a professionally made moldy cheese, like blue cheese, and use that instead. StuRat (talk) 20:58, 17 April 2011 (UTC)


 * But not this professionally made cheese, I presume? Count Iblis (talk) 21:14, 17 April 2011 (UTC)


 * Just don't forget your goggles ! StuRat (talk) 22:28, 17 April 2011 (UTC)


 * Proffesional, but illegal? :D Older members of my family know how this cheese should turn out, so I think I am not at risk. I don't know why, but it is absoultely imposible to get less known food of local origin in my country, so I have no choice, but to make it myself to get it. I had moldy philadelphia cheese, which is similar product, hence the idea to introduce it from some other food, I am not taking stuff that grows ln walls ofcourse :) What are good conditions for mold anyway? It says warm, but not exact temperature, besides it also suggests to cover it (but that appears to be for the part where you allready have mold) - wouldn't covering it keep mold away? Xil  (talk) 22:41, 17 April 2011 (UTC)


 * Yes, covering it is to keep other toxic molds away, once you have introduced the safe mold strain.  Also, you need to keep the moisture in, and covering helps with that.  As for temperature, you can certainly grow mold just find at room temp.  Warmer might grow faster, though, as long as it's not so hot as to drive the moisture out or kill the mold. StuRat (talk) 00:57, 18 April 2011 (UTC)


 * Brie has an edible mold casing. Bbuy some of that and put it in the same container as the cheese you want to get moldy. —Preceding unsigned comment added by 165.212.189.187 (talk) 12:53, 18 April 2011 (UTC)


 * Are you sure you are not confusing blue cheese with moldy cheese? The former is safe to eat (or at least I assume so as it is sold in shops etc); but many molds are carcinogenic so the later should be avoided. Decaying cheese may also produce harmful bacteria such as listeria. 92.28.241.233 (talk) 18:11, 18 April 2011 (UTC)
 * Of course I am sure that a particular sort of cheese is not some other cheese, which is why I am not very sure about introducing mold from another cheese. On top of that - there is no particular strain of mold identified for use of this, I figure it is naturaly occuring in this region, brie or blue cheese strains would be imported. There is one other thing I am unsure about - the recipe discribes the mold as ``a slimy layer covering the cheese``, no particular color or anything, at the time the average man wouldn`t go check his cheese with microscope, so maybe it isn`t mold, but something else that happens with old quark (note that it essentialy is just milk gone sour and boiled, so maybe it is whey coming out of it or some other proccess that occurs in old milk). According to google the end result is this (the black dots are caraway seeds, not mould), there is also this though, which is from article giving recipes for two diffrent cheeses, it looks moldy, but it also looks much like the other cheese described in the article  Xil  (talk) 19:35, 18 April 2011 (UTC)
 * There are a great many different species of mold, you are far more likely to obtain something harmful to eat than good to eat. 92.29.122.67 (talk) 20:40, 18 April 2011 (UTC)
 * Allright, but leave the decision to eat or not to up to me :) let`s consider this an experiment in culturing mold Xil  (talk) 21:11, 18 April 2011 (UTC)
 * Please read Mold_health_issues etc. 92.15.15.88 (talk) 08:45, 19 April 2011 (UTC)
 * Thanks, that mostly answers my question about introduction - apparently most bread and fruit molds are harmfull, note that health concerns mostly are allergies and opportunistic infections, thus mostly dangerous for people who are allergic or have weak imune system. Plus I found a site clearly stating that the mold should be transperent and white Xil  (talk) 18:02, 19 April 2011 (UTC)
 * I do not think that "white" mold is any indication that it is safe. 92.24.189.51 (talk) 10:24, 21 April 2011 (UTC)
 * Brie has a white edible mold casing. Buy some of that and put it in the same container as the cheese you want to get moldy. —Preceding unsigned comment added by 165.212.189.187 (talk) 18:55, 19 April 2011 (UTC)

Spray to clean dog feces
Does it exist? I've got the idea from Envy_(2004_film). I've also found some poop freezing sprays, but they were more of a specific solution, for dogs with diarrhea, and not for daily use. Some chemicals can indeed process feces, so it's not so crazy to think that it exists. Quest09 (talk) 21:59, 17 April 2011 (UTC)


 * It's not clear what you want the spray to do. Some possibilities:


 * 1) Sterilize the feces, so they don't spread disease.


 * 2) Remove feces stains from carpet, etc.


 * 3) Harden the feces for easier removal.


 * Of these, I don't know if 3 is feasible (fece-able ?). 1 and 2 certainly are, but only after the bulk of the feces has been removed. StuRat (talk) 22:27, 17 April 2011 (UTC)


 * None of the above. I want that they disappear, and that the owner does not have to collect them. Could a chemical simply decompose them into powder? Quest09 (talk) 23:43, 17 April 2011 (UTC)


 * No, not just powder, since they are mostly water. You could pour some kind of strong acid on them which might turn them into a sludge that sinks into grass, then add a base, like baking soda, to cancel the acidity, but this doesn't seem like a reasonable way to deal with them. StuRat (talk) 00:53, 18 April 2011 (UTC)


 * But, what is the residual remainder of a chemical toilet, after formaldehyde, glutaraldehyde or quaternary ammonium compounds are applied to our feces? Quest09 (talk)


 * The mass and volume will be the same as the original feces, plus the mass and volume of the chemicals which react with them. It could be turned into a liquid, or even a gas with the addition of lots of energy, but the mass never decreases.  The volume wouldn't decrease, either, and would dramatically increase if you turned it into a gas.  Also consider that chemical reactions are far simpler in a container than in the open, where the reactants all flow away. StuRat (talk) 01:21, 18 April 2011 (UTC)


 * Yes, the mass + volume won't change, but it could be in a form that's easier to handle, or even in a form that does not have to be treated. Quest09 (talk) 10:53, 18 April 2011 (UTC)


 * Assuming the poop is on the lawn,there was a time when I used to solve the problemm by simply squirting it with a heavy jet from a water hose. Of course it wasn,t really gone but it couldn't be seen and in such tiny particles that decomposition would be very rapid.Phalcor (talk) 01:39, 18 April 2011 (UTC)


 * Let's hope you didn't have kids or pets rolling on that grass right after. You could also get it splashed all over yourself, too. StuRat (talk) 02:07, 18 April 2011 (UTC)


 * Thank you sturat, no kids one dog and I stood well back. but if somebody did manage to touch those tiny particles hidden deep in the grass it might be less harmful than any chemical that could do the job.Phalcor (talk) 02:31, 18 April 2011 (UTC)


 * One thing to remember is that whatever chemicals you put on your lawn will be there in some form (reacted with the feces or not) for a time. There's a chance that the dog may go back to sniff whatever you've put on the feces and ingest it.  Even if this isn't your dog (think pesky neighbor's dog), many including myself wouldn't think too highly of a dog being poisoned, accidentally or not.
 * If this is your dog, you may want to consider a raw diet. I feed all my dogs (5) raw chicken and their feces just crumbles into a fine powder once it dries.  I think nothing of stepping on it while mowing the lawn since it just crushes into the soil.  And since it's a powder, I don't really track it into the house especially after walking around finishing all the other lawn chores.  Dismas |(talk) 02:38, 18 April 2011 (UTC)


 * Yes. Plus automatic nutrients for a healthy lawn.Phalcor (talk) 03:00, 18 April 2011 (UTC)