Wikipedia:Reference desk/Archives/Science/2009 June 15

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June 15

natural refraction of sound?

I read that that sound refraction often happens in the morning over bodies of water, where the water and lower air are still cold, and the higher air is warmer. The claim was made that this allowed people to hear further than they normally would and amplified the sound. There are then claims that people have had normal conversations from incredible distances, like 400 meters. Can the curved refraction actually focus the sound to create amplification at certain points? Or are these stories just made up? I would have thought that the refracted sound would not travel any further than normal sound during the day when all the air was heated - so how could people be talking in normal voices 400m away? Also does anyone know of any other situations in sound refraction occurs naturally or situations where sound is amplified (ie. focused so that the amplitude is above what would expect) naturally?--Dacium (talk) 01:07, 15 June 2009 (UTC)

Whispering gallery ~ R.T.G 01:21, 15 June 2009 (UTC)

No - that's not correct. Whispering galleries work by reflection, not refraction. SteveBaker (talk) 03:07, 15 June 2009 (UTC)

Certainly sound refracts through air of different densities (and therefore temperatures). In uniform air, the energy of the sound wave expands outwards in a sphere (think ripples on a pond - but in 3D) - as the sound waves move outwards, the radius of the sphere grows and the energy is spread out over an ever increasing area. As the distance from the source doubles - the area quadruples - so the sound becomes four times quieter. One mechanism by which a particular temperature profile over water could increase the volume of the sound would be if the sound were refracted from layers above the water - and bounced back off of the water surface - such that the sound waves would expand outwards in a cylinder. That would mean that doubling the distance would only halve the volume of the sound - so it would travel MUCH further and still be heard. This is somewhat like a 'waveguide' or 'optical fiber' or laser works for radio/light. By constraining the way that the waves can spread out, the energy can travel further. SteveBaker (talk) 03:51, 15 June 2009 (UTC)

In principle, sound waves can experience total internal reflection at the air/water or the cold-air/hot air interface and reach places where they might not have reached otherwise. The reflected wave can also add to the directly receive sound and (possibly) amplify the received signal - however there will be considerable phase difference (delay) between the direct and reflected waves, which means that we will hear an "echo" rather than an amplified sound. We will need to plug in the exact temperature profile (and the consequent changes in the refractive index), to determine if this "in principle phenomenon" is actually observed in practical settings. Abecedare (talk) 04:05, 15 June 2009 (UTC)

I believe the refraction and long distance surface propagation of sound occurs when the air is generally cooler than the water resulting in a gradient of warm air near the surface. The cooler air is slightly more dense and thus conducts sound slightly faster, resulting in the wave tending to focus back towards the surface. This would result in the cylinder-like propagation described by SteveBaker above. This is also why this effect is often observed in the late evening as the air cools, but the water remains warm. -- Tcncv (talk) 04:29, 15 June 2009 (UTC)

Hmmm, "cooler air is slightly more dense and thus conducts sound slightly faster" is not true. Speed of sound in air, increases with temperature (proportional to ${\sqrt {T}}$), so we need the colder air layer to be near the water surface in order for the sound to refract back down. Abecedare (talk) 04:54, 15 June 2009 (UTC)

Abecedare is right, the sound speed increases with the temperature. Hot air at the bottom and cold air on top would have the opposite effect (which sometimes is actually observed in deserts). The sound ends up deflected upwards and it becomes almost impossible to hear anything more than just a few dozen meters away. It's the silence of the desert! —Preceding unsigned comment added by Dauto (talk • contribs) 06:18, 15 June 2009 (UTC)

If you were in a desert at night, with no real wind, you could quite easily holler over a long distance. Bodies of water are often in a valley, shielded from much noise outside a specific area. It is probably a little quieter a couple of hours before morning starts. I don't know if that helps. ~ R.T.G 09:04, 15 June 2009 (UTC)

No - as Dauto points out deserts tend to be quiet because their temperature profile is the opposite of that over water. The air above the ground refracts the sound away from the ground...something that it also does to light...hence mirages. Plus, if it's a sandy desert, the ground will absorb sound rather than reflect it back up...if it's a rocky desert then the sound will likely be scattered by the rocks. The deserts I've visited in Arizona and New Mexico do indeed seem very quiet places. What makes water (particularly calm water) so effective at doing this is that it has a smooth, predominantly horizontal surface that reflects the sound back upwards. With the air diffracting the sound downwards and the water reflecting it back up - you produce this 'wave-guide' effect that prevents the sound from propagating in three dimensions - and by constraining it to two dimensions (well, kinda), allows it to propagate further. A very narrow canyon with smooth, near-vertical walls might maybe produce the same effect - but a gentler valley would not...particularly if it's predominantly lined with softer, sound-absorbing materials like grass and other vegetation. SteveBaker (talk) 12:42, 15 June 2009 (UTC)

Dang! (Kick self.) Wrong agiin. Sorry about that. I guess I need to do some better fact checking before I speak. -- Tcncv (talk) 23:14, 15 June 2009 (UTC)

Should I turn on the lights at night when using my computer?

Does it depend on personal preference, or is one option preferable to the alternative? Thanks. Imagine Reason (talk) 03:03, 15 June 2009 (UTC)

I'm not aware of any conclusive studies. Opinion is widely divided amongst computer programmers and other long-term computer users. Personally, I like light - but it's gotta be arranged so it doesn't glare off of the screen. I don't think it matters. Avoiding eye-strain is certainly important - but the best thing you can do is to take at least a couple of 5 minute breaks every hour...focus on something far from the screen - take a walk - stretch - etc. SteveBaker (talk) 04:00, 15 June 2009 (UTC)

Many scientific studies have produced conflicting results about the long-term impacts of eyestrain on vision. It seems to be inconclusive. It is not even clear whether light or dark in the periphery of your computer monitor has any effect on eyestrain, let alone whether that induces any vision trouble. Take a look at Myopia#Theories - see the cited sources there, and note that there is not a consensus among scientists and medical doctors. Nimur (talk) 04:07, 15 June 2009 (UTC)

Yes, turn them on. It will help prevent you from tripping on wires, barking your shins, and putting things down in the wrong place. Can't tell you anything about eyestrain, though. (I prefer them on, FWIW.) B00P (talk) 03:05, 16 June 2009 (UTC)

There's an article in today's Onion about how 90% of waking hours are spent staring at glowing rectangles. For those who don't know, The Onion is satire, but this one sounds depressingly close to being accurate. One would really have to expect there to be consequences of some sort from that. --Trovatore (talk) 03:12, 16 June 2009 (UTC)

supplier for polyvinyl alcohol & dextrin adhesive

Research shows me that the above adhesive ( polyvinyl alcohol & dextrin)is that which is used on postage stamps. I believe this may be the same adhesive used on self sealing envelopes. I am in need for a supplier for an ultra peelable adhesive similar to the postage stamp adhesive.

I have exhausted my search options for that particular adhesive supplier.

Thanks for the help. 72.71.31.118 (talk) 03:23, 15 June 2009 (UTC)

3M markets post it adhesive in spray cans [1] There may be similar products out there and most office supply stores or arts suppliers would have s.th. like it. The chemical composition is not what you were looking for and you should use this product in a well ventilated area. Hope this helps. 71.236.26.74 (talk) 06:16, 16 June 2009 (UTC)

The term for the glue is Mucilage and if I remember right, we used Legumes glue or Peanut glue when I was in school to make stamps. Mind you these are for the lick-and-stick type, not the self-adhesive. ZabMilenko^{How am I driving?} 10:48, 16 June 2009 (UTC)

QUANTUM MECHANICS -AS POPULAR SCIENCE

INTERESTED TO KNOW MORE ABOUT QUANTUM MECHANICS WITHOUT MATHEMATICS . —Preceding unsigned comment added by 59.184.254.55 (talk) 04:18, 15 June 2009 (UTC)

At the top of our main article, quantum mechanics, there is this message:

For a generally accessible and less technical introduction to the topic, see Introduction to quantum mechanics.

Have you read either of those articles? If they are too difficult, try the Simple English versions. Nimur (talk) 04:22, 15 June 2009 (UTC)

Why would you tie your hands behind your back like that? Quantum Mechanics is already hard enought even with mathematics.Dauto (talk) 06:23, 15 June 2009 (UTC)

I think it depends on the interest level of the student and his free time available for this. If he/she is not a serious student, then i don't think learning with all the mathematics is necessary, just the principle, as learning the mathematics itself would take considerable amount of time. Personally, I would recommend the Vignettes in Physics, Quantum Revolution by G.Venkataraman, a set of three books, which beautifully explain in qualitative terms the implications of Quantum Theory - Look for it in your local book store. I read it and thoroughly enjoyed it. Rkr1991 (talk) 07:02, 15 June 2009 (UTC)

Take a look at QED: The Strange Theory of Light and Matter, by Richard Feynman. --A. di M. (formerly Army1987) — Deeds, not words. 17:21, 16 June 2009 (UTC)

Computer Keyboard

Why is the keys of a keyboard arranged in a particular fashion and not alphabetically??Shraktu (talk) 04:29, 15 June 2009 (UTC)

From our article, QWERTY:

The QWERTY keyboard layout was devised and created in the early 1870s by Christopher Sholes, a newspaper editor and printer who lived in Milwaukee. ... His "Type Writer" had its printing point located beneath the paper carriage, and so was invisible to the operator. Consequently, the tendency of the typebars to clash and jam if struck in rapid succession was an especially serious problem, in that the mishap would only be discovered when the typist raised the carriage to inspect what had been typed. ... Sholes struggled for the next six years to perfect his invention, making many trial-and-error rearrangements of the original machine's alphabetical key arrangement in an effort to reduce the frequency of typebar clashes... Eventually he arrived at a four-row, upper case keyboard approaching the modern QWERTY standard.

You might also be interested in Dvorak keyboard layout. Nimur (talk) 04:37, 15 June 2009 (UTC)

(ec)They mimic the positions of typewriter keys - and those were originally laid out in an effort to improve typing speeds by limiting the distances your fingers have to move to hit the most frequent English word spellings. See QWERTY for details. Someone here will probably tell you that the keyboard layout was actually designed to slow down typists - but that's an urban legend. Someone will also probably try to tell us that "Dvorak Simplified Keyboard" layout is faster - but that's also untrue. SteveBaker (talk) 04:44, 15 June 2009 (UTC)

Dvorak may or may not be faster (is it for me), but it sure is more comfortable. :-) -- Aeluwas (talk) 07:54, 15 June 2009 (UTC)

A lot of the early studies on Dvorak were either faked, rigged or just so poorly run as to be meaningless. Their results caused quite a few people to switch - and given the effort required to do that, those adopters continue to support it with great fervor - mostly because of the urban legend about QWERTY being specifically designed to slow typists down in order to avoid jamming the early typewriters - which turns out to be very far from the truth - or that it was designed so that typewriter salesmen could type the word "typewriter" using only the top row of keys without moving their fingers. However, more recent, carefully run studies show zero benefits of any kind for Dvorak. As a result, it's just a pain in the neck to have to support it. Users of it have to suffer the difficulties of being unable to use other people's keyboards efficiently - and having to switch back to QWERTY for things like PDA keyboards and the like. It's a nasty con trick perpetrated on the community - and it needs to die. SteveBaker (talk) 12:29, 15 June 2009 (UTC)

Obligatory xkcd link. — DanielLC 14:28, 15 June 2009 (UTC)

Without questioning the fact that there are many urban legends surrounding QWERTY's origins and Dvorak's advantages, I'll disagree with you on your conclusion, Steve. I have typed with both keyboards for over a decade - QWERTY at work, Dvorak at home - and I'll testify that Dvorak is more comfortable & ergonomic. For me, that translates to a little faster, but that's not generalizable. But I (and my wife, who also is ambikeyboardous) don't suffer any of your supposed nasty effects of this "con". jeffjon (talk) 20:19, 15 June 2009 (UTC)

I don't understand how the Dvorak keyboard is more comfortable and ergonomic than the QWERTY keyboard. Dauto (talk) 22:47, 15 June 2009 (UTC)

Well, it has more common letters on the home row; J is among the rarest. If I were designing a layout from scratch, the first thing I'd do is partition the letters so that common digraphs like ED are split between the hands ... —Tamfang (talk) 19:41, 16 June 2009 (UTC)

But if the layout of Dvorak were that much superior from a statistical letter placement perspective, it would be faster - not just "more comfortable" - and studies done over the past few years have shown conclusively that they aren't faster. SteveBaker (talk) 20:20, 16 June 2009 (UTC)

Comfort counts, though. —Tamfang (talk) 23:30, 7 October 2023 (UTC)

Recently I learned that the hot trick in modern layout design is not to split common digraphs between hands but to put the letters beside each other, so that you "roll" these keys as if drumming with your fingers. —Tamfang (talk) 22:31, 7 October 2023 (UTC)

See also Kezboard, or the QWERTZ layout. God I hate those things... Aaadddaaammm (talk) 17:03, 16 June 2009 (UTC)

Yeah - they are amazingly difficult to type on if you aren't used to them. I've used a French AZERTY keyboard for a couple of weeks and I swear it's harder than Dvorak...it's just enough like QWERTY to fool you into thinking you can type quickly! SteveBaker (talk) 20:20, 16 June 2009 (UTC)

http://www.reason.com/news/show/29944.html has a great summary of the Dvorak versus QWERTY fiasco. SteveBaker (talk) 03:56, 18 June 2009 (UTC)

scientists own writings

How can i get important thesis of sientists in their own word with full mathematical details . —Preceding unsigned comment added by 119.154.26.19 (talk) 07:31, 15 June 2009 (UTC)

By subscribing to a scientific journal. Algebraist 07:58, 15 June 2009 (UTC)

It depends. Many articles are online, both significant older ones, but in particular newer ones, e.g. via arXiv or simply from the authors home page. "Full mathematical details" are usually in PhD theses, which can be online or available via a good scientific library, possibly via Interlibrary loan. --Stephan Schulz (talk) 11:22, 15 June 2009 (UTC)

If you live near a university (or are a student of one) they should have journal papers that you can have a look at (you probably won't be allowed to borrow them). Also, the university may have online access to journal papers that you can download. - Akamad (talk) 12:41, 15 June 2009 (UTC)

The original questioner asked for the thesis specifically - did you mean the doctoral dissertation? These are published by the original university, and may be available for free through a research library. You may also be able to access them online (for free or for a charge, depending on may factors). Universities in the United States publish doctoral dissertations through a clearinghouse, ProQuest, which is the distributor for almost all archived dissertations. You can search through 125 billion digital documents, including dissertations, from ProQuest's online access page (you may need to pay a fee or visit a library or research institution with a subscription). ProQuest republishes doctoral dissertations from all accredited universities in the United States, and has online archives of all dissertations since 1938 and a large percentage of all U.S. dissertations since the early 19th century. The original research institution and the author also usually retain the rights to republish their dissertations in other formats as well - so you may be able to find the thesis elsewhere. Nimur (talk) 16:09, 15 June 2009 (UTC) Note that this company is not merely another opportunistic Web 2.0 data aggregator - it is the official repository for dissertations by government contract to the Library of Congress. Nimur (talk) 16:15, 15 June 2009 (UTC)

Number of Synapses in Newborns

I've searched - but was not able to find - the number of synapses in newborns (or number of avarage synapses per neuron). Adults (as well as newborns) have about 10¹¹ neurons with (in adults) about 10¹⁴ synapses (1000 S./N.). For 3-year-olds I have found numbers of 15.000 S./N. and for newborns about 2500 S./N. (synaptic plasticity). Can this be confirmed (i.e. large number in the beginning, then even an increase, and finally settling to an "operational number" of about 1000 S./N.) with references? Curious ... --Grey Geezer 11:57, 15 June 2009 (UTC) —Preceding unsigned comment added by Grey Geezer (talk • contribs)

The best source I can find regarding this is the "Synaptogenesis" chapter of the book Neural Plasticity by Peter Huttenlocher. You can read a lot of it at Google Books. Looie496 (talk) 15:34, 15 June 2009 (UTC)

Thanks for the reference. Numbers are different, however, the tendency seems to be the same. Will read. --Grey Geezer 16:14, 15 June 2009 (UTC) —Preceding unsigned comment added by Grey Geezer (talk • contribs)

Weird Street Drug

My friend is trying to convince me that in the early '90's, there was this street drug that made you sexually orgasm almost instantly. He said that it was originally developed for astronauts whose stay in space is long term. Did/does such a drug ever exist/ed? --Reticuli88 (talk) 13:23, 15 June 2009 (UTC)

Clomipramine. Have fun!Sealedinskin (talk) 13:34, 15 June 2009 (UTC)

Unless you have a reference, don't make that claim. There is evidence that clomipramine can cause yawning-induced orgasms, but this is only in a small number of depressed patients [2][3]. It would be good if others can find more references for this, specifically with a larger sample and in a more reputable journal. On another note, clomipramine isn't a street-drug, and I haven't a clue what it has to do with astronauts. In the majority of cases, clomipramine (and other TCAs/SSRIs) actually causes sexual dysfunction. (EDIT: 1641GMT: Here are a couple of SD refs (but every pharmacology textbook will mention it): [4][5], sorry for lateness, I had to leave immediately so didn't have time to find refs at first). --Mark PEA (talk) 14:34, 15 June 2009 (UTC)

You are right to be skeptical. The astronaut claim is silly. You should present him with a sign like this: [6] Tempshill (talk) 14:35, 15 June 2009 (UTC)

omg, I just read about this [Scopolamine]. I wonder if this is what my friend was talking about. --Reticuli88 (talk) 14:53, 15 June 2009 (UTC)

Our article Scopolamine seems to have better and more information than that link, for what it's worth. Tempshill (talk) 20:07, 15 June 2009 (UTC)

The odor emanating from the long net stinkhorn mushroom is known to induce orgasm in females. It's probably not hard to come by, but I doubt it was ever a "street drug". ~Amatulić (talk) 00:51, 16 June 2009 (UTC)

Sun's gravity on Mercury vs Pluto

When astronauts head into space the effect of Earth's gravity tails of pretty quickly I believe. Earth is over 12000km in diameter and is 5.9736 × 10²⁴ kg but just 400km above the surface gravity tails off about 10%. With this is mind I can't get my head around why Mercury, being so close to the Sun hasn't been pulled in when the Sun still has enough gravitational force to keep Pluto in orbit when it's so far away. If it's possible to keep the explanation simple I'd appreciate it, I know very little about physics :-) Thanks all --16:19, 15 June 2009 (UTC)Contributions/87.115.23.15 (talk)

Basically the answer is that Mercury moves a lot faster than Pluto. It spins around the Sun so fast that the gravitational force from the Sun is just enough to counterbalance Mercury's tendency to go shooting off into space. Looie496 (talk) 16:38, 15 June 2009 (UTC)

(EC) Two points:

• First: Your understanding of how quickly earth's gravity tails off is inacurate. Gravity actually follows an inverse square law (That is, the strength of a body's gravitational pull is proportinal to the inverse of the square of the distace to that body). So at 400 km above the ground earth's gravity is still 88.5% as strong as at ground level.
• Second (and more important): Both Mercury and Pluto are in orbit around the sun. its true that the sun's tug on mercury is much stronger than on Pluto, but it is also true that Pluto is moving more slowly around the sun. In both situations the sun's gravitational tug is just right to provide the centripetal force necessary to keep the planets on a (approximately) circular orbit. Circular motion might be a good read for you. Dauto (talk) 16:49, 15 June 2009 (UTC)

My understanding of the OP's phrase "gravity tails off about 10%" is that the gravity is reduced by 10%, not to 10%, so s/he is approximately correct. --Sean 17:07, 15 June 2009 (UTC)

Thanks for quick replies all, seems obvious now you've explained it :-) That circular motion link was a bit much for me Dauto but I might read it again when I'm more awake, and thanks Sean, I did mean reduced by 10%. Could I ask for an expansion on the original question... I take it that when the universe solar system was forming the planets achieved a natural equilibrium? Matter closer to the Sun (accretion disc?) was orbiting faster, matter further away orbiting more slowly so that as the planets formed they naturally fell into the 'appropriate' orbit according to velocity, mass and distance from the Sun? (EDIT): What I mean is the planets didn't form and then fall into their current orbits, they actually formed apprximately where they are now? --Contributions/87.115.23.15 (talk) 17:37, 15 June 2009 (UTC)

Yes, that's correct. The planets were formed already in orbit around the (young) sun. They did not necessarily form exactly where they are now because at those early times there was a lot of debris floating around the solar system and interaction with all that debris is believed to have made the plats wander away from their original orbits. But once most of that debris was cleared away the planets orbits have remained pretty much stable ever since. Dauto (talk) 18:43, 15 June 2009 (UTC)

Tx again Dauto :-) --87.115.23.15 (talk) 22:06, 15 June 2009 (UTC)

A more simple explanation - both Mercury and Pluto constantly falling toward Sun. But because they both also have speed vector that is perpendicular to direction of the fall, they could not actually get closer to Sun. So when Mercury fall 100km toward Sun, a perpendicular velocity make up for that 100km(assuming circular orbit for simplicity, elliptic orbit bit more complicated, but general principle is the same). And since Mercury falling faster, his perpendicular speed(excuse my English, there might be a name for it but idk it) also bigger then Pluto's one. That have some interesting consequence. When Space Shuttle moving away from ISS to lower orbit in preparation for descend, it actually start to fly faster. Which is counterintuitive. And if period of extrasolar planet is known(and it known for majority of planets, due to the way they discovered) it is possible to tell distance from planet to star(sure, mass of the star should also be know, but that is usually not a problem). DeadlyPenguin (talk) 20:22, 19 June 2009 (UTC)

Recoil Upward Motion - Firearms

Why does the barrel of a pistol or rifle rise - as opposed to jerking any which way, down, left, right, etc. when fired? I understand recoil, but not why a barrel moves upward when fired. Contributions/167.153.5.107 (talk) 16:50, 15 June 2009 (UTC)

I would imagine it's because the bullet, when it fires, pushes against the upper part of the weapon closet to your body. Therefore, it's not so much going up as it is pivoting around your hand. -- MacAddct1984 ^{(talk • contribs)} 17:08, 15 June 2009 (UTC)

This is exactly right. If you fire a gun upside down, it'll jerk down, as seen in this clip. If the barrel was located exactly in the center of your grip, then it wouldn't jerk up or down, it'd just push against your hand. -- Captain Disdain (talk) 23:32, 15 June 2009 (UTC)

...and the shock of that would hurt. The pivoting of your wrist acts as a shock absorber. A barrel at the center of the grip, when fired, would feel like slamming your hand into a wall. I believe the reason a rifle doesn't exert the same level of shock is because the rifle has a lot more mass. ~Amatulić (talk) 00:48, 16 June 2009 (UTC)

Yeah, it would hurt (and it could even do actual damage). It'd also make aiming a little more difficult (proper sights would help, of course, but with varying distances, things would get problematic), and handgun design in general would become more complicated, at least with modern semi-automatics, because right now the slide has room to move freely back with each shot. If that movement took place in the center of the grip, you'd have to do a lot of re-design, because of course you couldn't have the slide hitting the user's hand. -- Captain Disdain (talk) 05:55, 16 June 2009 (UTC)

An interesting side note is that in the military, and police force, they teach you to shoot a pistol with your arms locked, instead of elbows bent. Doing this reduces the amount of muscle it takes to get the pistol back into firing position, thus enabling you to fire faster. The reason this works is that with your arms locked, your entire arm moves upwards. Then, gravity takes effect, and begins to bring te pistol back down for you. With your elbow bent, however, the recoil would make your arm bend further, pushing your elbow down, and your wrist up. This creates the added exertion of bringing your elbow back up, and extending your elbow again. Drew Smith What I've done 13:10, 16 June 2009 (UTC)

OR: Many moons ago one of my professors came to work with a bandage in the middle of his forehead. He'd been at the firing range the prior evening firing his .38 when the person next to him let him fire their .44 magnum. My professor habitually (based on his experience with the .38) bent his elbows when he fired the .44 - and the dramatic recoil brought the pistol to his forehead with embarassing and somewhat painful results. --Scray (talk) 20:19, 16 June 2009 (UTC)

question about stability of ecamsule

For a while now I’ve been searching for information on the stability of sunscreens containing avobenzone when exposed to makeup containing titanium dioxide and iron oxides. I found one article online: see http://www.koboproductsinc.com/Downloads/NYSCC-Avobenzone.pdf However, I don’t know if the information found in that article applies to ecamsule. I’ve read, for example, that since the avobenzone in la roche posay’s anthelios xl is stabilized, it won’t degrade in the presence of mineral makeups, but I can’t find anything definitive on this subject. Since most women wear makeup and since it’s almost impossible to find makeup that doesn’t contain titanium dioxide and iron oxides, I wonder why more studies have not been done regarding this issue. My big question is, does wearing makeup degrade the ecamsule or the form of avobenzone used in mexoryl sunscreens?Lunaeva (talk) 17:41, 15 June 2009 (UTC) comment added by Lunaeva (talk • contribs) 17:36, 15 June 2009 (UTC)

Shouldn't be a problem, avobenzone is not degraded to any significant extent by titanium or iron compounds. It may, however, bind reversibly to transition metal ions (such as Ti4+ in TiO2, or Fe2+/Fe3+ in iron oxides), forming colored coordination complexes that might change the color of your makeup (but the sunscreen will still protect you just the same as before). If you're still in doubt, try it and see.

76.21.37.87 (talk) 06:10, 18 June 2009 (UTC)

post-splenectomy immunication schedule

I know splenectomy patients (with no part of the spleen remaining) need vaccinations periodically for the rest of their lives, but what vaccinations and how often, please? (Later readers of responses hereto should note that they are general and not intended as personal advice, for which you should consult your physician (or osteopath).)—msh210℠ 17:42, 15 June 2009 (UTC)

The vaccinations required after a splenectomy are explained in asplenia. SpinningSpark 18:12, 15 June 2009 (UTC)

I don't see it there, actually. Where are you seeing it? (What I do see there is vaccinations needed immediately after a splenectomy (or before), but I asked about recurrent immunizations for life.)—msh210℠ 21:14, 16 June 2009 (UTC)

How do I give a ferret an orgasm?

Please help (it's a male ferret)

I would let a female ferret handle that personally. Contributions/65.121.141.34 (talk) 18:11, 15 June 2009 (UTC)

I don't want them to breed, I need to collect a ferret sperm sample for reasons best not discussed here. —Preceding unsigned comment added by 91.105.85.222 (talk) 18:34, 15 June 2009 (UTC)

It's basically the same for all mammals. This page will give you some details, and shows an artificial vagina for harvesting rabbit semen, which might be about the right size for a ferret (I'm not familiar with ferret cock, personally). --Sean 18:40, 15 June 2009 (UTC)

I'm a little concerned about any application of ferret sperm which a) does not involve making more ferrets and b) which cannot be discussed in public... --Jayron32.talk.contribs 17:41, 16 June 2009 (UTC)

Yes, it reminds me somewhat of National_Lampoon's_Van_Wilder 'In one infamous scene, Van and his friends replace the cream inside some cannoli with dog semen and send them to Richard's fraternity, where the frat brothers begin eating and don't realize what it really is until it's too late'. Hoping I'm wrong! --87.115.23.15 (talk) 17:49, 16 June 2009 (UTC)

In all seriousness, if its a prank like that, there are methods at hand which can obtain mammalian sperm which don't involve very complex procedures. I'm not sure that, culinarily speaking, ferret sperm and say, your sperm, are all that different... Don't know though, I haven't really tried that particular application of either of them. --Jayron32.talk.contribs 18:27, 16 June 2009 (UTC)

I think that "Black Footed" ferrets are being repopulated artificially, so you might be able to find some paper describing how it's done. I can't find it with a quick Google though, only articles that gloss over that important step. APL (talk) 18:11, 16 June 2009 (UTC)

By electroejaculation, of course. According to Shump et al (yes, that really is his or her name, PMID 1018477):

Semen was obtained from 40 of 62 attempted electro-ejaculations of nine anesthetized male ferrets. The ejaculations were performed using a bi-polar rectal electrode and an electrical stimulus of about 4 V and 0.35 mA applied for approximately 4 seconds and repeated at 10-second intervals. The mean number of stimuli required to obtain an ejaculation was 12.3.... the mean volume of semen per ejaculate was 0.026 ml.

Rockpocket 01:57, 18 June 2009 (UTC)

I hereby award Rockpocket the "highly relevant and informative answer to improbable question" award. :-) Great job. Dcoetzee 23:28, 19 June 2009 (UTC)

Maybe Rebecca Loos could help? Axl ¤ [Talk] 23:11, 19 June 2009 (UTC)

First ensure its still intact (hob) by checking to see if it has testicles, then masterbate it, or insert finger into anus and push up against the Ferrets prostate. --Timon b (talk) 07:19, 29 October 2009 (UTC)

parasitic worms

Would it be genetically modified parasitic worms (mainly by limiting lifespan and reproduction) be useful as a weight loss aid, or would they not steal enough nutrients to have an effect if there are only a few worms? Contributions/65.121.141.34 (talk) 20:00, 15 June 2009 (UTC)

I believe similar Q's were asked here previously, and the answer was that it's a bad idea because they steal vitamins and minerals, not just calories. So, you would risk malnutrition with such a "treatment". StuRat (talk) 20:15, 15 June 2009 (UTC)

Your body's immune response in trying to get rid of the intruder might be another point worth mentioning. Such results are highly individual, unpredictable and if they result in an Allergy can be almost impossible to reverse once primed. Contributions/71.236.26.74 (talk) 20:48, 15 June 2009 (UTC)

Yep, Stu - have a look at Wikipedia:Reference_desk/Archives/Science/2008_May_14#Tapeworms_as_a_weight-loss_aid.3F. This is the question I asked on a similar subject last year. The OP might find this useful... --Kurt Shaped Box (talk) 21:22, 15 June 2009 (UTC)

...Not to mention that the worms might still be able to reproduce more than you might want them to, and that they would be VERY hard to get rid of once you no longer need to lose weight. (E.g. tapeworms, they're the very devil to get rid of once they're inside the body). Plus, they might cause other undesirable side effects like diarrhea, or even organ damage. Very bad idea, in general. 76.21.37.87 (talk) 05:32, 18 June 2009 (UTC)

Smoked cylinder

I just watched the movie Something the Lord Made, set during the 1930's, in which a doctor berated his research assistant for failing to record a medical experiment on a "smoked cylinder". What is it, how was it used, and what info did it record ? StuRat (talk) 20:12, 15 June 2009 (UTC)

googling gave several results (including a couple that are more relevant to the ferret Q above:-) This looks like one of the more relevant ones [7] The device seems to work similarly to an old Seismometer. I'm not sure it would be worth a page, but there should be some mention in a paragraph on history of medicine somewhere. (volunteers step forward, please)Contributions/71.236.26.74 (talk) 20:31, 15 June 2009 (UTC)

Yes - they were used like pen recorders. You'd coat a class cylinder with smoke and use a sharp needle to scrape a line through the smoke as the cylinder slowly rotated. Just the thing for a seisemometer, certainly. SteveBaker (talk) 23:46, 15 June 2009 (UTC)

In general an ink pen could similarly record data on a paper chart, though perhaps with more friction. A smoked cylinder could have been used in a spirometer, to record the volume of exhaled air, indexing lung capacity. Asmoked cilinder was used in 19th century reaction time experiments, as by Donders, and in pre-phonograph sound recordings, as the Phonautograph. Edison (talk) 01:26, 16 June 2009 (UTC)

A stylus capable of scratching smoke from a rotating cylinder could have lower mass than a siphon ink pen, and thus a higher frequency response. Edison (talk) 16:02, 16 June 2009 (UTC)

I also find myself wondering why a smoked cylinder would have been preferable to ink and paper. Perhaps before the invention of the ball point pen it wasn't easy to get a continuous flow of ink from the pen to the paper ? Since the modern ball point wasn't invented until 1938, and didn't become widely available until after WW2, maybe that would explain the use of smoked cylinders in the 1930s.StuRat (talk) 19:28, 16 June 2009 (UTC)

I wondered about that too. The classic twitching needle things don't look that high-tech by 1930's standards. When I was a kid in school, we had one that had a little ink reservoir for each pen and ink that travelled to the tip via capilliary action like a fountain pen. That technology would have been around in the tenth century - so it would hardly have been difficult in the 1930's! One thing I wondered was whether they might want to take multiple permanent copies from the drum by wrapping it with a piece of photographic film and placing a light inside the glass cylinder to expose it. In an era before photocopiers - I suppose that might have made sense. But it's hard to say why this technique was used. SteveBaker (talk) 19:54, 16 June 2009 (UTC)

I can imagine a tension between the stroke being thin enough for fine lines, but thick enough that the capillary action was fast enough to keep up with a strong temblor. --Sean 23:35, 16 June 2009 (UTC)

Yeah - that's a good thought. I could easily imagine getting more sensitivity from the smoked glass widget. SteveBaker (talk) 00:05, 17 June 2009 (UTC)

Remembering my first couple of Fountain pens, they leaked, the ink kept clogging and they were quite unreliable. This was quite a few decades after they were first marketed but before we got those with ink cartridges. Just because a technology is available doesn't mean it's a good choice. 68.208.122.33 (talk) 01:32, 17 June 2009 (UTC)

Fountain pens have been around for 150 years - even the kind with replaceable cartridges. Quite a few decades! What I think changed in our lifetimes is that the price of reasonable quality pens has steadily dropped with mass-production and modern plastics. I have a really nice German fountain pen that belonged to my grandfather. It's close to 100 years old - and it's every bit as good as a high quality modern pen...but it probably cost a fortune even when it was new. Sadly, I'm left-handed - and writing with a fountain pen is pretty much out of the question! SteveBaker (talk) 02:30, 17 June 2009 (UTC)

! sdrawkcab etirw ot nrael ot deen tsuj uoy ,esnesnoN StuRat (talk) 11:28, 17 June 2009 (UTC)

immovable object and irresistable force - revisited

A while back there was some discussion about the immovable object/irresistable force paradigm. The original poster wondered if such an event were to occur, wouldn't they just cancel each other out. Anyway, while I was in my Aikido class I had a thought: what if we think differently? In other words, in pondering this question, we think in terms of either the irresistable force being stopped by the immovable object or the immovable object diffusing the irresistable force. What about the idea of redirecting? In other words, what if the imovable object turned on it's axis and redirected the irresistable force? We tend to think of moving as back and forth or sideways; therefore, simply rotating on it's axis is not really "moving" in the classical sense. Also, we tend to think of "resisting" as stopping all movement rather than redirecting it. I am suggesting that if this paradigm could exist then the idea of rotation/redirection would maintain the purity of both immovable and irresistable. What do others think? —Preceding unsigned comment added by 69.77.185.91 (talk) 21:48, 15 June 2009 (UTC)

As stated at Irresistible force paradox, this is meant to be an exercise in logic and/or in semantics. Your proposal doesn't resolve the paradox. Tempshill (talk) 21:58, 15 June 2009 (UTC)

The paradox isn't a real one since no object is immovable. (Interestingly, all forces are irresistible, though.) In the real world, an object can often redirect a force and a force can often redirect an object. StuRat (talk) 22:19, 15 June 2009 (UTC)

This reminds me I once felt I had a solution to the paradox. I'm sure it needs tightening up, and it may (almost inevitably) be flawed, but here it is:

Imagine object, something like a ray, moving through space. A ray doesn't have mass, but this object may - the point is it can exert a force and some may insist that this requires mass. Imagine it is moving through space at some speed - the amount is irrelevant, but for the purpose of concreteness, assume 1 m/s. When the head of the ray hits a small object, it just pushes it aside. When it encounters a larger object, it "piles up" behind the object, until the accumulated force moves the object. For any movable object, the ray encounters the object and the head of the ray is stopped for a time, until it amasses enough force to move the object. We can assume that the length of time is proportional to the resistive force. Note that while the head of the ray stops for a finite period of time when it encounters an object, the weighed average of the mass continues to move at 1 m/s, as almost all (in the mathematical sense) of the ray is still moving. (I realize I just calculated a weighed average over an infinite length, at that may get me in trouble.)

So we have defined an object that is irresistible. When it encounters a normal object, a finite portion of the object comes to rest for a finite period of time, but the overall object does not stop, and eventually moves the object.

So now what happens when the irresistible force meets an immovable object? The head of the ray is stopped, and begins piling up. But while the object never moves, the ray (arguably) never stops.

I don't fully expect anyone to decide this paradox has now been convincingly resolved, but it's my stab at it - in my mind, I've defined an irresistible object, and immovable object, and described what happens when they meet. The result doesn't cause one to re-assess the label of immovable, because the object doesn't move. Nor does it cause one to re-assess the label of irresistible, as it has moved every other object it encounters, and even after encountering this object, it is still moving. --SPhilbrickT 22:45, 15 June 2009 (UTC)

The fact that the trailing parts of this ray are still moving doesn't make it irresistible. It's only that if it can move the object, and in your example, it doesn't. Clarityfiend (talk) 23:26, 15 June 2009 (UTC)

I guess it depends on what you mean by "resisting" the irresistable. I would argue that merely changing the path of it would constitute resistance. But this is a stupid argument - it's not a paradox - it's just wrong. There is not - nor cannot possibly be - either an irresistable force or an immovable object. So no paradox. SteveBaker (talk) 23:44, 15 June 2009 (UTC)

The whole universe is an immovable object - as far as we know, that's not going anywhere. SpinningSpark 23:50, 15 June 2009 (UTC)

Relativity disagrees. Either the concept of the universe not moving is meaningless (which I believe is truly the case) - or if you could somehow show that its "not moving" - then I could pick a frame of references where it's moving along just fine. SteveBaker (talk) 01:29, 16 June 2009 (UTC)

You don't defeat it that easily, "immovable" in this context means that its motion cannot be changed relative to the frame of reference chosen. Changing the frame of reference has not changed the motion by applying a force. By that argument, even supposing a truly immovable object within the universe, one could "move" it by switching co-ordinates, an obvious cheat. SpinningSpark 06:30, 16 June 2009 (UTC)

I disagree with your summary. There cannot be BOTH an irresistible force and an immovable object, but there is no paradox if one or the other exists.--SPhilbrickT 00:18, 16 June 2009 (UTC)

Just because there is no paradox - doesn't mean that either can exist. A purple, elephant juggling mongoose isn't a paradox - and there aren't any of those either! SteveBaker (talk) 01:26, 16 June 2009 (UTC)

Fair enough. But simply asserting something isn't proof. In fact, I'll argue the opposite. Classify all objects in the universe by how hard they are to move. Consider the object with the largest value. Is there a force in the universe that can move it? If no, it is immovable. If yes, then the force is irresistible.--SPhilbrickT 12:33, 16 June 2009 (UTC)

You mean currently immovable and currently irresistible. Tempshill (talk) 17:52, 16 June 2009 (UTC)

A real world diversion

This question made me wonder, what is the most immovable object in reality and how would it fair against the most irresistible force. For an "object", I want something that is a coherent single entity, so I choose a supermassive black hole. For a force, I'd prefer a "contact" force in the spirit of things that push. A supernova jet seems like a logical choice. So, today's bonus round question, how large a change in velocity would the black hole experience if it ate a supernova jet? Dragons flight (talk) 05:48, 16 June 2009 (UTC)

A supermassive blackhole could eat the whole star, jet and all and would barely feel it. Dauto (talk) 06:05, 16 June 2009 (UTC)

I nominate another supermassive black hole, travelling at the speed of the oh my god particle, as the unstoppable force. --Sean 12:37, 16 June 2009 (UTC)

A black hole is in no way immovable or irresistible. It has finite mass, just like anything else, and a=f/m applies just like it does to anything else. Two black holes colliding will conserve momentum, and the characteristics of the resulting black hole will not mirror either of its progenitors. — Lomn 13:01, 16 June 2009 (UTC)

Of course, but this subsection discusses most immovable and most irresistible objects. --Sean 13:54, 16 June 2009 (UTC)

There is no distinction! A black hole, like all matter, is movable, which is to say that it is not immovable. As StuRat correctly notes above, all forces are irresistible, which is to say that none are in any fashion resisted. There are no degrees or shades of grey. There are many cases where the effect of a force is so small as to be unmeasurable, but unmeasurable is not a synonym for nonexistent. — Lomn 14:15, 16 June 2009 (UTC)

With this more reasonable question, I think we can reason it out using proper science and logic and stuff:

Because we have relativity to consider, you can't say that any object is not moving ("immovable") because that just depends on your choice of reference frame. What we mean when when we say that an object is "the most immovable" is really that it's "the most difficult to accelerate". Furthermore, the hypothetical "irresistable" object has to have the same property - it can't be slowed down or deflected...so there is really no difference between an immovable object and an irresistable one - it just depends on your frame of reference. That narrows our search. We only have to find the object that's hardest to accelerate - and it must be both the most irresistable and the most immovable.

F=ma - Force equals mass times acceleration. So the 'most' unacceleratable object is either the most massive one - or one which somehow is most successful at avoiding having forces imposed upon it.

So we have two routes to trying to pick our candidate - either something insanely massive - or something which is somehow immune to the most forces:

• If you go the "heavy" route then a super-massive black hole pretty much has to be it - because any reasonably compact object that is more massive than a super-massive black hole will inevitably become a black hole (perhaps a 'super-duper-massive black hole'!) An object like a galaxy is quite likely to be heavier than a black hole - but it's hardly something you'd count as an "object" in the terms of something immovable or irresistable because it's parts are so loosely connected. So without doubt - the answer on this side of the argument is the most supermassive black hole we can lay our hands on...nothing else is possible.

• If you go for "immune to forces" - then you can perhaps think of things like the neutrino - which has no electric charge - so it's immune to magnetism and such like - it does have a TINY mass, so affected by gravity and (IIRC) it ignores the 'strong' force. So it's really only significantly affected by gravity and the weak force...which is (guess what!) weak.

If you were to try to move a stationary neutrino by shooting lasers at it - or trying to move it with magnets - you'd be out of luck. You could try whacking it with something impressive - like, say, an entire planet moving at close to the speed of light - and it would hardly move at all...so it's pretty amazingly 'immovable' - and if you slam a neutrino into an entire planet at close to the speed of light - the neutrino hardly ever notices - which makes it fairly 'irresistable'. But the same could be said for a supermassive black hole.

So you get to choose - Neutrino or super-massive black hole? Neither is completely immovable/irresistable - but both are impressively close!

SteveBaker (talk) 14:28, 16 June 2009 (UTC)

Steve, I think the miscommunication is that when you say it's impossible to have either an immovable object or an irresistible force, you mean physically impossible. What the paradox shows is that to have both at the same time (at least, if the force acts on the object) is logically impossible; this is a different notion, or at least there's a widely accepted current of thought that considers it a different notion. --Trovatore (talk) 02:10, 17 June 2009 (UTC)

Sot the famous question can be simplified as "what happens when a neutrino meets another neutrino?" :) --131.188.3.21 (talk) 22:02, 17 June 2009 (UTC)

No - it most certainly cannot! We are now answering the alternative question: "Which objects are the most immovable/irresistable?". Neutrinos certainly can be both resisted and moved - albeit a lot less so than most other kinds of objects. The original "paradox" is still an entirely stupid question. I'm not sure we know what happens if two neutrinos happen to collide. In the time it takes you to read this sentence, 100 trillion neutrinos have passed through your body. But a typical neutrino detector is a vast machine containing 50,000 tons of very pure water - and with good luck, it can detect a couple of neutrinos each day! If you consider how many neutrinos pass through that water each day - and that it only stops a few of them - now consider the odds of a neutrino being stopped by another neutrino...the odds are very tiny indeed! SteveBaker (talk) 13:44, 18 June 2009 (UTC)