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March 6

Silent Supernovae

Is it right to say that when a star goes supernova, it is an acoustically silent event, even if one could (hypothetically) witness it from a close distance? And because sound cannot travel through space, this would also apply to events such as Gamma Ray bursts, and even the Big Bang itself, correct?Honeyman2010 (talk) 04:50, 6 March 2013 (UTC)[reply]

This seems to be a common question. Sound can and does travel through space, as it is not a complete vacuum. However, due to it being a pretty good vacuum, the sound propagated is not what human ears could detect, even if the human could function in that vaccuum. You would need absolutely immense ears. Go to the top of this page, and try "sound in space" and similar strings in the Search Reference Desk archives field, and you'll be entertained for quite a while. Wickwack 120.145.35.223 (talk) 05:17, 6 March 2013 (UTC)[reply]

And, when the particles blasted off during the supernova hit you, they would make quite a racket, indeed. StuRat (talk) 05:29, 6 March 2013 (UTC)[reply]

Not to mention, vapourise you in the process. I mean planets in orbit have a difficult time surviving such an event, what chance have a mere human? If our sun were to go supernova, Jupiter would be stripped entirely of its atmosphere and be left a metallic white-hot cinder only just larger than earth. The outer gas giants beyond should fare better. Plasmic Physics (talk) 08:06, 6 March 2013 (UTC)[reply]

If you were in that star system, sure. But if you were far enough away, you're spaceship would just get noisy when the particles hit. StuRat (talk) 16:30, 6 March 2013 (UTC)[reply]

Or do it the Native American way: touch your ear to the dark side of a planet. The chances of survival are still somewhat low... ;) - ¡Ouch! (^{hurt me} / _{more pain}) 08:04, 8 March 2013 (UTC)[reply]

As for the Big Bang, yes, you would hear it, but it would not sound like a bang. It would sound more like a very, very ,very loud, high pitched hum, which would decay both in volume and pitch in an exponential way. You'd hear it because space was not as vacuous as it is today. Plasmic Physics (talk) 07:24, 6 March 2013 (UTC)[reply]

After this much time, it has decayed to such an extent, that it is not discernable from background noise. The sound would initially have been audible for millions of years. Plasmic Physics (talk) 07:28, 6 March 2013 (UTC)[reply]

Considering a gamma ray burst, would it not create secondary sound as it irradiates the listening device, creating a large amount of static. Plasmic Physics (talk) 08:09, 6 March 2013 (UTC)[reply]

Big Bang and light

Is it true that all matter can be converted into light? If so, is the coverse true? If that is also true, could the primeval atom have been pure light in a metastable state, which spontaneously condensed into matter, such as particle-antiparticle production from gamma radiation. How many electron volts would a single photon have to represent to contain the total universal energy and all its mass. Plasmic Physics (talk) 07:51, 6 March 2013 (UTC) "Let there be light." Plasmic Physics (talk) 07:54, 6 March 2013 (UTC)[reply]

If matter fell into a black hole, or quantum tunneled into a black hole, the hole may then decay into Hawking Radiation, which may be mostly photons. So the future of matter may the formation of cool photons. You will have to say how big is the universe to get an answer to the total energy in the universe. As the universe ages the visible universe expands, so we do not actually know the size or mass of the universe. Graeme Bartlett (talk) 09:33, 6 March 2013 (UTC)[reply]

Well, the most obvious problem is that there's no such thing as light before electroweak symmetry breaking. If you believe inflation, the energy of all the particles in the universe came from the energy of the field that caused inflation, which is similar to the present-day Higgs field or dark energy. So they did come from pure energy, in a way.

According to Google the density of the universe is around 5·10⁻³⁰ g/cm³, and the radius of the visible universe is about 46 billion light years, and it's spatially flat, so the total mass in the visible universe is around (5·10⁻³⁰ g/cm³) (4/3) π (46 Gly)³ ≈ 10⁹⁰ eV/c². But that's just the part we can see. -- BenRG (talk) 22:13, 6 March 2013 (UTC)[reply]

What would happen to such an energetic photon if released into our universe today? Plasmic Physics (talk) 08:14, 7 March 2013 (UTC)[reply]

Some questions about the Universe

I have some questions about the Universe.

1. Is the Universe finite or infinite? Universe is the sum total of all matter and energy. The unknown part of the Universe, i.e. the part that extends beyond the observable universe, may be finite or may be infinite. What are the current opinion regarding this?

2. If the Universe is finite, then it must have edges or boundaries. I want to know what is beyond that boundary? Is that pure vacuum?

3. If the Universe is infinite, then why is it said that the Universe is flat. An infinite object is not supposed to have any shape.

4. According to the Big Bang theory, the Universe, at its beginning (the very early Universe), was rapidly expanding and cooling, and then expanded gradually. I want to know is there any explanation how did this very early Universe originate? --PlanetEditor (talk) 13:31, 6 March 2013 (UTC)[reply]

(Q4) If I'm not wrong, Stephen Hawking said something like at the very very early stages of the Universe, it (the Universe) was just like a very small balck hole. As time does not exist in a black hole, there was no time before the Big Bang. There is no cause or origination for the Universe because there was not time for a cause to exist in. It just "popped up" like a proton, which IS possible according to some elaborate Science laws. ☯ Bonkers The Clown \(^_^)/ Nonsensical Babble ☯ 13:44, 6 March 2013 (UTC)[reply]

If you're talking about the stuff in A Brief History of Time, that was never mainstream; it was just a description of his own (highly speculative) research. -- BenRG (talk) 21:53, 6 March 2013 (UTC)[reply]

re Q2: finite does not imply edges or boundaries. The surface area of the earth is finite, for instance, but has no edges, (according to modern theories). Imagine a 4th dimensional sphere analog that we're on the 3d surface of. Now imagine that sphere expanding, and now you have the expanding universe we experience, where there is no particular center to the expansion which is uniform all over. Gzuckier (talk) 18:15, 6 March 2013 (UTC)[reply]

(Q1) According to the Shape of the universe article, the infinite flat model is currently the most popular of the models of the universe that fit the currently available data. Red Act (talk) 21:54, 6 March 2013 (UTC)[reply]

1. Nobody knows. If you asked cosmologists to guess, I suspect a majority of them would say infinite, but that doesn't mean much. 2. As Gzuckier said, it doesn't imply there's a boundary, but there could be a boundary. There would be nothing outside of it, which is not the same as vacuum. Light can't propagate through nothing. 3. An infinitely large object can have a shape. For example an infinite plane and an infinite paraboloid have different shapes. 4. Nobody knows, but if you asked cosmologists to guess, most of them would guess some kind of inflation. -- BenRG (talk) 21:53, 6 March 2013 (UTC)[reply]

Thank you everyone. --PlanetEditor (talk) 10:12, 7 March 2013 (UTC)[reply]

However I would have liked a bit more explanation of Q4. The religionists use this issue as an excuse to prove the existence of God. --PlanetEditor (talk) 10:20, 7 March 2013 (UTC)[reply]

If you haven't seen it already, Big_Bang#Speculative_physics_beyond_Big_Bang_theory. You really are stuck in a bind, there. Either you have something exist before the Big Bang, and then have to explain where that came from; or you have a theory such as Hawking's where a beginning is (allegedly) not required. Neither class of theories is likely to satisfy. Someguy1221 (talk) 10:45, 7 March 2013 (UTC)[reply]

Hawkins' explanation that time is compressed inside a black hole - and that's (effectively) what the early universe was like - may or may not be correct, but at least it offers one possible explanation for the "Origin of Everything" question that doesn't result in an infinite regress. The idea that this is an argument for the existence of God is a silly one because one only has to ask the question "So...what created God then?" to demonstrate that adding a supernatural being as the creator of the universe doesn't help to answer the ultimate question If the early universe was "caused" by something, then you're in the infinite regress of asking what that cause was and what was the cause of the cause and so forth. Hawkins' approach is elegant in that by pointing out that time inside a black hole is crunched into nothingness and therefore there is no "Before" in the case of the big bang - it was there for a literally infinity amount of time. He might not be right - but at least there are possible "ultimate origin" explanations that do not require gods and other mystical junk to make them work. SteveBaker (talk) 22:04, 7 March 2013 (UTC)[reply]

Thank you Someguy and Steve. --PlanetEditor (talk) 09:07, 8 March 2013 (UTC)[reply]

Statistics of hysterectomies

Why are hysterectomies so common in women above tha age of 50 if its such a major operation? Clover345 (talk) 14:48, 6 March 2013 (UTC)[reply]

I think the article on Hysterectomy actually does a good job of going into some of the issues. The major downside of the surgery (aside from risk) is loss of the ability to bear children, which is usually a moot point by the age of 50. The upshot to the surgery, such as benefiting cancer risk or severe pain, will often outweigh that downside, although for sure there are a lot of these being performed. ~ Amory (u • t • c) 15:24, 6 March 2013 (UTC)[reply]

From personal experience in the UK, if there is no good reason to remove a uterus then they won't. Fibroids or adenomyosis stop responding to oestrogen as less and less is being produced, and shrink of their own accord. I'd like to see up to date statistics on this. --TammyMoet (talk) 16:23, 6 March 2013 (UTC)[reply]

Prove relation

Given $P(x,t)=|\Psi (x,t)|^{2}$ ,

and $J(x,t)=-{\frac {ih}{2m}}\left(\Psi ^{*}(x,t){\frac {\partial }{\partial x}}\Psi (x,t)-\Psi (x,t){\frac {\partial }{\partial x}}\Psi ^{*}(x,t)\right)$

I want to prove the following relation

${\frac {\partial }{\partial t}}P(x,t)+{\frac {\partial }{\partial x}}J(x,t)=0$

I denote complex conjugate with asterisk. I believe I can think of examples of functions Psi for which it's not true. Here is my working so far anyway.

$={\frac {\partial }{\partial t}}|\Psi (x,t)|^{2}-{\frac {ih}{2m}}{\frac {\partial }{\partial x}}\left(\Psi ^{*}(x,t){\frac {\partial }{\partial x}}\Psi (x,t)-\Psi (x,t){\frac {\partial }{\partial x}}\Psi ^{*}(x,t)\right)$

$={\frac {\partial }{\partial t}}\left(\Psi (x,t)\Psi ^{*}(x,t)\right)-{\frac {ih}{2m}}{\frac {\partial }{\partial x}}\left(\Psi ^{*}(x,t){\frac {\partial }{\partial x}}\Psi (x,t)-\Psi (x,t){\frac {\partial }{\partial x}}\Psi ^{*}(x,t)\right)$

$=\Psi ^{*}(x,t){\frac {\partial }{\partial t}}\Psi (x,t)+\Psi (x,t){\frac {\partial }{\partial t}}\Psi ^{*}(x,t)-{\frac {ih}{2m}}{\frac {\partial }{\partial x}}\left(\Psi ^{*}(x,t){\frac {\partial }{\partial x}}\Psi (x,t)-\Psi (x,t){\frac {\partial }{\partial x}}\Psi ^{*}(x,t)\right)$

It's not clear at all that this is zero to me.

150.203.115.98 (talk) 15:19, 6 March 2013 (UTC)[reply]

maybe this is a homework question, so we should be wary. I don't know much about this area, but I'd try integrating J first. Let me know if I'm out on a limb. IBE (talk) 17:19, 6 March 2013 (UTC)[reply]

You should differentiate the expression in parentheses (by x) then you should substitute derivatives by time from the 1D Schrodinger equation in free space. After that everything will be obvious. Ruslik_Zero 18:15, 6 March 2013 (UTC)[reply]

Reverse osmosis semipermeable membranes

Semi-permeable_membrane says that membranes used in reverse osmosis are made of polyimide while Thin-film composite membrane says that they are made of polyamide.

What's correct?--Gauravjuvekar (talk) 16:42, 6 March 2013 (UTC)[reply]

Looking through a number of suppliers of such membranes, most just describe them as "Thin Film", but Dow's datasheet states that their membranes are polyamide. On the other hand, this patent is for a polyimide membrane. I think it's safe to say that both _can_ be used. Tevildo (talk) 22:36, 6 March 2013 (UTC)[reply]

This site lists lots of polyamide membranes, a few "Thin Film" membranes, and a few cellulose acetate membranes. Polyamide seems to be the most common material. Tevildo (talk) 22:45, 6 March 2013 (UTC)[reply]

Meteor fragments and aircraft

There is LOTS of discussion about meteors/comets/etc impacting the Earth, the History of the big ones, etc. HOWEVER, I heard somewhere that 40 TONS of material impact on the Earth's atmosphere daily. ALL discussions I've read say something like "most" of this material burns up in the Earth's atmosphere, leaving particles "smaller than grains of sand" etc. When most folks read this phrase, they say "no problem". HOWEVER, I would imagine that a particle not much bigger than a grain of sand could have a disastrous effect should it strike the wing of a flying aircraft. How come there aren't more recorded (or hypothesized) cases of aircraft being affected by meteor fragments? Thanks, Jack Murray p.s.- This is a WORLDWIDE question p.p.s. - How do I know what to search on in Wikipedia to find out if anyone addressed this? — Preceding unsigned comment added by Jaqmur (talk • contribs) 17:14, 6 March 2013 (UTC)[reply]

Regarding your last question, "How do I know what to search on in Wikipedia to find out if anyone addressed this?", knowing what search terms to use to finds the answer to a question is known as Google-fu, and it's a skill you learn through practice. If you meant where do you search, there's a search bar at the top of every reference desk page where you can search the desk archives. 90.193.232.228 (talk) 17:43, 6 March 2013 (UTC)[reply]

Particles the size of a grain of sand will rapidly decelerate to free-fall speed, due to air resistance. A grain of sand at that speed is not a problem for an aircraft. However, many such grains of sand are, and we get those by flying through a volcanic plume. StuRat (talk) 18:00, 6 March 2013 (UTC)[reply]

Just in case you're still struggling with Google, I had a go myself. I typed aircraft "meteor strike" into the search bar (the words within the "quote marks" means that Google will only show an exact match for that phrase). I found a data analysis blog called Revolutions - How much of a threat are meteors to aviation? Using some complicated calculations, the author states that the chance of a meteor strike on a single aircraft are "about 1 in a billion, give or take". However, given the number of aircraft using the sky, "there's about a 4.3% chance of a meteor strike on at least one airliner in the next 20 years". Alansplodge (talk) 18:16, 6 March 2013 (UTC)[reply]

It's called terminal velocity, not "free fall speed". μηδείς (talk) 23:28, 6 March 2013 (UTC)[reply]

"Free fall speed" is a synonym for "terminal velocity". StuRat (talk) 05:08, 7 March 2013 (UTC)[reply]

Aircraft regularly encounter hail stones. Hail is capable of stripping paint and abrading windshields so pilots use their weather radars to avoid heavy rain and hail. Despite that, damage more serious than stripped paint and abraded windshields occurs occasionally. A meteor fragment the size of a grain of sand, falling at its terminal velocity, is nowhere near as hazardous to an aircraft as a hail stone falling at its terminal velocity. Dolphin (t) 00:14, 7 March 2013 (UTC)[reply]

How do we know the fragments would be at terminal velocity? Objects only reach terminal velocity in free fall; a meteor may strike the earth at many orders of magnitude faster than its terminal free-fall velocity, and it may take some distance to slow down to terminal velocity. A meteor could be moving quite fast when it strikes the plane; there's no requirement that it be moving as slow as terminal velocity. --Jayron32 06:05, 7 March 2013 (UTC)[reply]

The OP has prefaced the question with most of this material burns up in the Earth's atmosphere, leaving particles smaller than grains of sand. The question excludes particles much larger than grains of sand. Meteors disintegrate in the Earth's upper atmosphere. By the time a fragment the size of a grain of sand falls to the altitude at which aircraft operate, a long time will have elapsed and it will be at its terminal velocity. True, the geological record shows evidence of very large meteors having reached the Earth's surface, leaving large craters, but the question doesn't extend to consideration of such large meteors. Dolphin (t) 06:17, 7 March 2013 (UTC)[reply]

Gotcha. Yeah, in that case a grain of sand at its terminal velocity is still a grain of sand at terminal velocity, and carries very little energy, certainly not enough to damage anything on an aircraft. The origin if the sand itself is irrelevant. If the sand were really hauling ass, then maybe, but sand in free fall is still sand in free fall, even if it came from space. --Jayron32 06:23, 7 March 2013 (UTC)[reply]

I interpreted the OP to be asking about a high-speed aircraft striking a particle that has no horizontal velocity and almost zero vertical velocity. Dolphin (t) 06:37, 7 March 2013 (UTC)[reply]

Re your last question. I read that as "How do I find out if anyone has answered this very question I'm asking here?". You just search for this page by its name, Wikipedia:Reference desk/Science, using the search function. Then scroll down to find the right thread. -- Jack of Oz ^[Talk] 00:41, 7 March 2013 (UTC)[reply]

From playing around with numbers at this impact simulator, it looks like any meteor smaller than about 50 cm in diameter is going to be moving at its terminal velocity by the time it reaches the typical airplane. For a piece of sand, that terminal velocity is a few miles per hour, so most of the impact speed will come from the airplane's movement, not the rock's movement. --Carnildo (talk) 01:56, 7 March 2013 (UTC)[reply]

Thanks for all the info. Jaqmur (talk) 14:35, 7 March 2013 (UTC)[reply]

The thing to bear in mind when thinking about meteors and such is that if you halve the diameter of a roughly symmetrical object, you reduce it's cross-sectional area by a factor of four and it's mass by a factor of eight. So the aerodynamic drag forces on small particles (which depends on their cross-sectional area and not on their mass) are much larger compared to their initial kinetic energy (which depends on their mass) than for big rocks. So these sand-grain sized meteors slow down to their terminal velocity very quickly - where a mountain-sized meteor hardly slows down at all.

Do a mental experiment - take a rock the size of your fist and imagine how far you can throw it - 20 feet maybe? How far do you think you could throw a grain of sand? A couple of feet maybe? Both objects leave your hand at about the same speed just as large and small meteors are entering the atmosphere at about the same speed.

So for meteor dust, it's going to be moving at terminal velocity - which is when the gravitational force (which is proportional to its mass) balances the drag force (which is proportional to it's cross-sectional area) - with very tiny mass and less tiny cross-section, it's moving very slowly. But the hailstone is obviously moving a lot faster because the ratio of mass to cross-sectional area is much higher than for the dust. More importantly, since kinetic energy (which is what goes into damaging the plane) is proportional to the SQUARE of the speed multiplied by the mass - these low-mass, low-speed sand-grains don't have enough energy to do much damage...and as Carnildo pointed out - the speed of the airplane is by far the biggest contributor in terms of relative velocity.

Hitting meteor dust is much less damaging than hitting even a raindrop or a snowflake...it's about as bad as hitting the smoke particles from the airplane a mile or two ahead of you.

SteveBaker (talk) 13:21, 8 March 2013 (UTC)[reply]

Film problems

Not sure if this should go here or on the entertainment desk, but...

While watching The Aztecs (Doctor Who), I noticed two problems:

1. In episode 1, the image jerks upwards for a fraction of a second and then returns to normal.

2. There is considerable background noise, sounding a lot like rain.

Why do these effects occur? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 20:19, 6 March 2013 (UTC)[reply]

1) This sounds like a problem I've sometimes seen when projecting a film. Presumably it was copied into a digital format, but, if that process involves using a film projector, and the operator is rather careless, this could be the result. Or, perhaps that happened when filming. Were they doing any hand cranking: [1] ? (This techniques was sometimes used to change the recording speed of the film, manually.)

2) This might be an original issue with the sound recording. Wind noise can sound like that, if they don't cram the microphone inside a dead cat to prevent it. British TV of that era had notoriously low production values, so it wouldn't surprise me if this happened. StuRat (talk) 20:34, 6 March 2013 (UTC)[reply]

1) Then why is the image stable for the entire episode with the exception of that momentary jerk? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 20:39, 6 March 2013 (UTC)[reply]

1) Probably a torn sprocket hole or two messed up the timing, then it was able to recover. This type of thing happens more often than you might think. It's just that in a Hollywood production, as bad as the plots are, they do an extraordinary job of fixing any production quality problems like this which crop up. Watching foreign films and TV, I've been surprised to see microphones repeatedly in the frame, characters calling each other by the wrong names (possibly by the actor's name), and worse mistakes, all making it onto the final film. In a Hollywood production, this type of thing ends up on the blooper reel. StuRat (talk) 20:43, 6 March 2013 (UTC)[reply]

A 1964 Dr. Who? I wouldn't be surprised to see one of the crew wandering around the back of the frame eating a sandwich. Gzuckier (talk) 21:03, 6 March 2013 (UTC)[reply]

In Terrence Malick's The Thin Red Line, if you watch the DVD copy on a computer, you can see a crew member standing about staring at the camera holding a clipboard on the far edge of the frame in one of the love scenes. Can't be seen on a TV. – Kerαunoςcopia^◁_galaxies 03:15, 7 March 2013 (UTC)[reply]

<coughs> No period after "Dr". See Dr. Who (the Peter Cushing Dalek movies). Tevildo (talk) 22:53, 6 March 2013 (UTC)[reply]

Our article on negative cutting doesn't say anything, but sometimes a negative cutter will foobar a splice. Projectionists have been known to cut out single frames of their favorite shots, using cheap splicing tape or cement to piece the film back together. Also damage happens to film, sometimes a single frame or sprocket can become damaged and either cut or, if unnoticed, left in the film. If the Dr Who episode was made from a print, rather than a negative, this could be what happened, though a solid jump up and down probably means there was a splice. (The thickness of the cement/tape jerks the film about in the telecine or projector.) By the way, regarding projectionists cutting out frames, there shouldn't be a problem with sound sync anymore (it's been a while) since I think sound CDs are now synchronized to code printed on the actual film edge. In the old days, though, if someone cut out a splice, you would hear a pop/jump in the sound about a second later. – Kerαunoςcopia^◁_galaxies 03:15, 7 March 2013 (UTC)[reply]

Did the BBC actually spend the money in 1964 to shoot Dr who on film? It would have been cheaper to shoot on video tape. The first programs were lost, and The Aztecs is from several months later. I just watched it on Netflix, and it had the look of videotape. Perhaps it got converted to film at some point for distribution and rebroadcast. Doctor Who (series 1) says that the series only transitioned from videotape to film in the 2005 relaunch, which they perversely call "Series 1." Edison (talk) 04:23, 7 March 2013 (UTC)[reply]

Our article on that episode makes it clear that it was first recorded using videotape, then converted to film so that the tape could be reused (because video tape was extremely expensive at that time), then later converted back to a video format using the VidFIRE process. Looie496 (talk) 06:22, 7 March 2013 (UTC)[reply]

Genetic disorders that come out due to inbreeding.

The article on the Amish states

Since almost all Amish descend from about 200 18th-century founders, genetic disorders that come out due to inbreeding exist in more isolated districts (an example of the founder effect).

I have always thought that inbreeding, while it does increase the incidence of certain disorders, does not create new ones by itself. Am I correct? If not, can anyone of you provide examples of genetic disorders that come out due to inbreeding? --190.19.83.213 (talk) 02:19, 7 March 2013 (UTC)[reply]

You are correct, but I think you are misreading that quotation. It is basically saying the same thing you did. StuRat (talk) 02:29, 7 March 2013 (UTC)[reply]

"Come out" is a misleading term. By far the most common type of genetic disease associated with inbreeding is autosomal recessive enzyme or other protein deficiencies. If the carrier (heterozygote) rate in the US population for an autosomal recessive mutation that causes blue hair disease in homozygotes is 1%, but the carrier rate in an intermarrying subpopulation, like Amish, or Ashkenazi Jews, or Yupik Eskimos, is 6%, then the likelihood of a carrier marrying another carrier is 6x higher, and the rate of homozygous blue hair births in that population will be 36x higher than in the general US population. alteripse (talk) 02:41, 7 March 2013 (UTC)[reply]

Jumping from a airplane with wingtip sails

This picture is taken from the humanities.

My question is:

Is it safer to jump out from an airplane with wingtip sails because of reduced wingtip vortices? -- Toytoy (talk) 03:18, 7 March 2013 (UTC)[reply]

Maybe if the chutes are going to open immediately, as they seem to in the pic. On the other hand, if the chutes wait a bit to open, then they will be clear of the vortices before opening. StuRat (talk) 03:23, 7 March 2013 (UTC)[reply]

Our article, Wake turbulence, doesn't mention hazards to parachutes, but does say that vortices are generated when the wings are creating lift. I suspect that the pilot would take this into account when people are jumping out of his or her aircraft, but perhaps another editor has some experience in this field. Note that the RAF has been dropping paratroopers since 1941, but has never possessed one with wingtip devices until it acquired some C-17s in 2002. Alansplodge (talk) 18:01, 7 March 2013 (UTC)[reply]

On large aircraft such as the one pictured here, the wingtip vortices are too far outboard in any case to affect parachutists jumping out of that aircraft. FWIW 24.23.196.85 (talk) 04:57, 9 March 2013 (UTC)[reply]

March 7

could you compare a hot air balloon with a plane and helicopter?

Let's say we want something to get to 10,000 feet from ground while expending as little energy as possible. Three ways of doing it are: the something is a plane. The something is a helicopter. The something is a hot-air balloon. All of these require energy to get up to their heights. Can you give me an idea of how these energies compare? (for the same weight). I would think that the hot-air version is least efficient as you are basically heating a huge volume of air. But then again you only do it ONCE and then just "float" up. Whereas the other two require continual energy even to just maintain level flight. Still, how do these three compare in terms of total energy required to lift to 5000 feet from ground? 91.120.48.242 (talk) 07:46, 7 March 2013 (UTC)[reply]

I think the answer will depend on whether "for the same weight" means "for the same total weight" or "for the same payload". Lifting the total weight of a small plane or helicopter using a hot air balloon sounds quite inefficient (hand waving theoretical justification: considered as a heat engine, the operating temperature of the balloon is lower than the plane or helipcopter engine so its theoretical maximum efficiency is lower). But for the same payload (say five people), the balloon could be more efficent because it has no heavy engines/wings/rotors. Gandalf61 (talk) 09:19, 7 March 2013 (UTC)[reply]

Could you be a bit more precise or explain your reasoning further? In particular I don't understand your argument about "the operating temperature of the balloon is lower than the plane or helipcopter engine so its theoretical maximum efficiency is lower". What does the plane or helicopter have in its favor?

Also, is there some theoretical argument to be made about kinetic energy here? I can imagine some kind of theoretical proof that heating the air around an object and encapsulating it is guaranteed to be the most efficient use of those joules of power. On the other hand, I can imagine that there is a theoretical argument to be made based on air resistance (how lift is generated). Any ideas? 91.120.48.242 (talk) 10:20, 7 March 2013 (UTC)[reply]

See heat engine, fuel economy in aircraft, aerodynamic drag and drag coefficient. I don't think there is going to be a clear cut answer. If this is a homework question then the point of it is probably to see how many different arguments and variable factors you can come up with, to show that you understand the complexities that may lie behind an apparently simple question. Gandalf61 (talk)

The wiki article suggests a hot air balloon will mass 3.5 tonnes for 5 passengers. That surprised me. So perhaps you could do your calculations based on 5 people as a payload. FWIW the helicopter will almost certainly be the worst possible choice, and I have a suspicion that rather expensive aircraft might be the best. Greglocock (talk) 22:41, 7 March 2013 (UTC)[reply]

The answer (not one of the choices given) is almost certainly the glider. It needs a tow to get off the ground, but after that there is no energy expenditure at all. It only relies on the pilot's ability to find suitable thermals to get to height. Spinning Spark 23:11, 7 March 2013 (UTC)[reply]

I strongly disagree. You're conveniently ignoring the energy cost of towing the glider to an altitude high enough to be able to reach the first thermal before it hits the ground again. That's most definitely not a zero energy cost! The (powered) airplane, the helicopter and the hot-air balloon can (and will) benefit from those very same thermals. As a practical issue, navigating the hot air balloon to get to where they are might not be possible...and a high speed fixed wing aircraft might have trouble staying inside the thermal - but a powered airplane could be designed to be just as good at catching thermals as the glider, yet get into the air more efficiently than your gliders' towing system can.

Location matters though. If you were starting the experiment near to the base of a 10,000 foot tall mountain - on the side where the wind is blowing gently up-slope - then a hang-glider could probably make it to the top without a tow, using slope-lift and truly zero energy. But if you're on a flat, featureless, windless, uniform surface (hence no thermals and no slope-lift) then your best bet is probably the fixed wing aircraft. If you're on a flat surface and there is plenty of wind - then maybe a kite is what you need?

I suspect that a rocket would be the best option. According to rocket engine, chemical rockets can be 60% efficient...that's better than either jet or piston engines. Also, a fixed-wing aircraft has massive drag due to those big wings - the rocket can be designed to be almost any shape you like - so it can be aerodynamically optimal. Fixed-wing aircraft have to travel quickly in the horizontal direction in order to get enough lift to gain altitude - so they need to spend more time getting to altitude than the rocket does - and therefore they expend more energy overcoming drag and gravity.

Calculating "energy costs" is tricky though. An airplane is re-usable, but the rocket probably isn't...so do we include the construction costs into the calculation? If we don't then we can use a hydrogen balloon...the hydrogen "cost" is a part of the construction cost - but if that's not included then this technology can do the job at zero energy cost. Sadly, you either have to throw away some of the hydrogen at altitude in order to get back down again - or you have to expend energy in some other way to get back down...so unless this is a one-shot mission, then that's another consideration.

Without tighter rules, this debate can get silly. Suppose we put the payload onto a large spring so it's flung into the air with enough speed to get to 10,000 feet. The energy cost is now that of compressing the spring. We can do that using a very slow, highly geared solar powered motor that takes an entire year to slowly compress the spring. If the glider is allowed to get "free energy" from thermals, then my spring launcher can certainly get "free energy" from sunlight. What's more, since my payload is the only thing I have to get to 10,000 feet - I don't have to waste energy launching some kind of vehicle along with it. For some payloads, this makes a lot of sense.

SteveBaker (talk) 13:59, 8 March 2013 (UTC)[reply]

A good glider pilot can make use of the thermal rising from a plowed field. That won't get you much height, but it can you enough to get somewhere else. I'm not saying you can get to 10,000 feet from a low height in every circumstance, but an experienced pilot has at least a possibility of doing it, even starting from a flat landscape. Spinning Spark 18:54, 8 March 2013 (UTC)[reply]

OP here. Thanks for the response guys :) You guys went off in your own direction, which is fine and interesting, but actually only prompted by my "topic-setting" sentence which seemed general. The rest of my comment mentioned in specific the three things I was interested in comparing the theoretical energy requirements of: a hot-air balloon, an airplane, and a helicopter. Perhaps we can add that the hot-air balloon is assumed to be inflated by ambient-temperature air at ground. So while of course a helium balloon can get there for "free", and so can a glider riding thermals, what I'm really interested in is helicopter and airplane craft "powered" by an engine versus using those joules simply to heat a balloon. I agree that perhaps there are no clear-cut or theoretical arguments to be made here. I was hoping some argument about air density at different temperatures, versus a coefficient of friction argument about air, could be combined to come to a theoretical proof that of the three proposed things we are comparing, one has a better theoretical limit. 86.101.32.82 (talk) 11:55, 9 March 2013 (UTC)[reply]

Mean from a wavefunction

Thanks for your help with the previous question. Now I would like to prove this identity:

$\int _{-\infty }^{\infty }p|{\tilde {\Psi }}(p)|^{2}dp=\int _{-\infty }^{\infty }\Psi ^{*}(x)(-ih{\frac {\partial }{\partial x}})\Psi (x)dx$

Working

$\int _{-\infty }^{\infty }p|{\tilde {\Psi }}(p)|^{2}dp$

$=\int _{-\infty }^{\infty }p\left|{\frac {1}{\sqrt {2\pi h}}}\int _{-\infty }^{\infty }\Psi (x)e^{-ipx/h}dx\right|^{2}dp$

$=\int _{-\infty }^{\infty }p{\frac {1}{2\pi h}}\left|\int _{-\infty }^{\infty }\Psi (x)e^{-ipx/h}dx\right|^{2}dp$

$=\int _{-\infty }^{\infty }p{\frac {1}{2\pi h}}\left(\int _{-\infty }^{\infty }\Psi (x)e^{-ipx/h}dx\right)\left(\int _{-\infty }^{\infty }\Psi (x)e^{-ipx/h}dx\right)^{*}dp$

$=\int _{-\infty }^{\infty }p{\frac {1}{2\pi h}}\left(\int _{-\infty }^{\infty }\Psi (x)e^{-ipx/h}dx\right)\left(\int _{-\infty }^{\infty }\Psi ^{*}(x)e^{ipx/h}dx\right)dp$

$=\int _{-\infty }^{\infty }p{\frac {1}{2\pi h}}\left(\int _{-\infty }^{\infty }\int _{-\infty }^{\infty }\Psi (x)\Psi ^{*}(y)e^{-ip(x-y)/h}dxdy\right)dp$

$={\frac {1}{2\pi h}}\int _{-\infty }^{\infty }\int _{-\infty }^{\infty }\int _{-\infty }^{\infty }p\Psi (x)\Psi ^{*}(y)e^{-ip(x-y)/h}dpdxdy$

But, the inner integral does not converge ! ! !

150.203.115.98 (talk) 10:46, 7 March 2013 (UTC)[reply]

Shouldn't this be at Wikipedia:Reference desk/Mathematics? --Guy Macon (talk) 12:10, 7 March 2013 (UTC)[reply]

That inner integral is the Dirac delta function; if you want a more rigorous derivation that avoids invoking the delta function, you have to use (and prove) the fact that transforming to momentum space and back is a unitary tranform. In general:

<psi|A|psi> = <psi|U-dagger U|A|U-dagger U|psi>

for U some arbitrary unitary transform. U-dagger denotes the Hermitian conjugate (which is equal to the inverse of U because U is unitary). Then the state |psi> transformed under U is |psi'>= U|psi>, and thus <psi'| = <psi|U-dagger, and the transformed operator A is

A' = U|A|U-dagger, so we indeed have:

<psi|A|psi> = <psi'|A'|psi'>

In your problem the momentum operator p = -ihbar d/dx is diagonal in the momentum representation, so you can take it out of the Dirac brakets. Count Iblis (talk) 12:58, 7 March 2013 (UTC)[reply]

How is the inner integral a dirac delta function? 150.203.115.98 (talk) 13:49, 7 March 2013 (UTC)[reply]

It's the derivative of the Dirac delta; to see this, differentiate the integral identity for the Dirac delta w.r.t. its argument. Count Iblis (talk) 15:44, 7 March 2013 (UTC)[reply]

Are you sure? I thought

\delta (y-x)={\frac {1}{2\pi }}\int _{-\infty }^{\infty }e^{ip(y-x)}dp

. This one is

{\frac {1}{2\pi }}\int _{-\infty }^{\infty }pe^{ip(y-x)}dp

. 150.203.115.98 (talk) 16:10, 7 March 2013 (UTC)[reply]

Yes, the derivative of the delta. So, if you put z = x-y and differentiate both sides w.r.t. z, and move the derivative under the integration sign, you'll get a factor p in the integrand as a result fo taking that derivative. Count Iblis (talk) 16:30, 7 March 2013 (UTC)[reply]

And then you would have to make a integration by parts to move the derivative over to one of the PSI functions and finally use the delta function to get rid of one of the outside integrations completing the desired proof. The only thing to keep in mind is that some of the steps of this proof need to be further explained (if you care for mathematical rigor), specially the reversal of the order os derivative and integration mentioned by the Count in his last post. A rigorous proof requires special treatment for the delta function because it is not a normal kind of function. Dauto (talk) 17:17, 7 March 2013 (UTC)[reply]

Hydrogen solubility in copper

What is the hydrogen solubility in alpha-copper at 100 kPa and 25 °C? Values should be stable up to 50 MPa. Plasmic Physics (talk) 12:32, 7 March 2013 (UTC)[reply]

Growth between 18 and 24

Do any significant changes or growth occur between 18 and 24 years of age? Most people can't tell the age differences in this age group. — Preceding unsigned comment added by Clover345 (talk • contribs) 13:05, 7 March 2013 (UTC)[reply]

We've had a previous instance of a similar question here. Have a look at the links there and get back to us if you need further. --TammyMoet (talk) 13:12, 7 March 2013 (UTC)[reply]

−

thanks. Do you think these statistics change though. Most people think that young people looked older 20 years ago. Why is this? Clover345 (talk) 13:36, 7 March 2013 (UTC)[reply]

Well, we know that the onset of puberty has shifted (at least in developed countries) over the last 200 years, and we know that average human height changes with respect to environmental conditions and the like, so yes, these statistics can certainly change. As for "people looking older": that's highly subjective and speculative, and I doubt we can verify it, much less meaningfully extrapolate to "why". — Lomn 14:14, 7 March 2013 (UTC)[reply]

“Most people think that young people looked older 20 years ago.” I think every generation has this perception. Looking through my family photograph albums, people clearly tend to stay with the clothes, hairstyles and social etiquette they became accustomed to in their younger years – thus that style become thought of as looking mature by the later generation. Actors and actresses often dress in the latest styles for the reason that it makes them (they think) look younger and use modern jargon. I've noticed on some recent American films (if you can call 1990 recent), such as the Memphis_Belle_(film), that the director and makeup artists went to lengths, to have the actors playing the air crew, appear to conform to image of modern youths of that age – to emphasis just how young the original crew of the Memphis Bell really were. It is more striking when you look at World War II RAF officers with their short-back-and-side haircuts, neatly trimmed moustaches and panache for voicing understatements. So it is not really a perception of 'older in age' but recognition of older cultural values. --Aspro (talk) 15:06, 7 March 2013 (UTC)[reply]

There are real differences though which may make new generations look relatively younger. Decreased tobacco, alcohol, and other drug use, decreased time working as youths/increased time spent in school, decreased time in the sun, higher sunscreen use, decreased manual labour, better hygiene, and better diets, can all increase youthfulness. I think many of these things are working to make newer generations appear younger, minus those who use tanning beds to an extreme and those who are overweight. 70.48.212.115 (talk) 16:01, 8 March 2013 (UTC)[reply]

Unfortunately the answer offered to that September question is astonishingly bad. The answerer clearly did not know what he was talking about and did not read the relevant article: puberty clearly says there is a relationship between timing of puberty and completion of growth because both are dependent on several years of estrogen and androgen. Aspro is closer than Lomn to answering this current question, in the sense that perception of age of young adults is more influenced by clothing and hairstyles than by actual earlier pubertal onset. The degree of earlier puberty in this century is much smaller than popularly supposed. The late changes of puberty have not changed as much as the early changes. Surveys of boys and girls suggest menarche is occurring perhaps 3 mos earlier now than in the late 1960s, but thelarche may be occurring as much as 1-2 years earlier. The nature of the widening gap in uncertain; one possible explanation is that the early changes come from environmental estrogens and are not true puberty, which has been only slightly hastened. The phenomenon in boys is even smaller. Progression and timing of late stages of puberty do not seem to have changed much in the last 50 years. On average maximum adult height is reached at average ages of about 15 and 18 y for girls and boys (wide individual variation of course). The outward changes of facial appearance in late teens and early twenties that serve as age cues to us involve thickening of the skin, recession of the frontal hairline, slight thinning of the hair in both sexes, but increasing facial hair, especially in men. Men's beards continue to get heavier throughout this period-- but again with large inter-ethnic and inter-individual variation. Men also continue to have some increase in shoulder musculature and width in late teens as height growth is finishing. Acne often improves. But all of these changes have been far smaller over the last century than the changes of hairstyle and dress and I vote with aspro that our questioner's impression was entirely based on those features. alteripse (talk) 16:21, 7 March 2013 (UTC)[reply]

Plane lens?

Can a "lens" be plane, meaning not being curved at all? 117.227.203.61 (talk) 13:28, 7 March 2013 (UTC)[reply]

You might be interested in fresnel lens. They are flat at the gross scale, but have tiny ridges at the fine scale. SemanticMantis (talk) 13:34, 7 March 2013 (UTC)[reply]

not being curved at all? 117.227.203.61 (talk) 13:38, 7 March 2013 (UTC)[reply]

Well, a Fresnel lens can either have the individual segments be curved ([2]) or flat ([3]). The curved segment version focuses more clearly, but the flat segmented kind has application where you don't need a clear image, such as focusing sunlight for solar energy. StuRat (talk) 15:25, 7 March 2013 (UTC)[reply]

If the material has a uniform refractive index throughout the plane, no, that can't be a lens. 131.251.133.27 (talk) 14:10, 7 March 2013 (UTC)[reply]

then what it is called? — Preceding unsigned comment added by 59.161.101.17 (talk) 14:26, 7 March 2013 (UTC)[reply]

Ah, a window? TenOfAllTrades(talk) 14:32, 7 March 2013 (UTC)[reply]

If the faces are plane but non-parallel, it will be a prism. If they are it may be called a plate (as in plate glass and photographic plate). Note that TOAT's suggestion of 'window' is not (I presume) whimsical - apertures sealed by flat glass (or other materials) in scientific instruments may also be called windows: one that springs to mind is the mica window used in the designs of Geiger Counters I was taught about in school (which are probably now obsolescent, like myself). {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 14:41, 7 March 2013 (UTC)[reply]

Mica windowed Geiger Counters are not obsolescent, in fact I have one sitting behind me in my lab as I write this (used for contamination monitoring during and after biological radiolabeling experiments). Equisetum (talk | contributions) 16:42, 7 March 2013 (UTC)[reply]

Though if you're allowed to vary the material composition (specifically, its refractive index) across the plane, then you can build GRIN devices (see gradient-index optics). TenOfAllTrades(talk) 14:34, 7 March 2013 (UTC)[reply]

There's also a pinhole lens, which can be a planar material with a small hole. Note that they reduce the brightness of the object considerably, so are most useful for focusing bright objects, like the Sun, or with time exposures. StuRat (talk) 16:16, 7 March 2013 (UTC)[reply]

There are also plain lenses made of a material with negative refraction index. Ruslik_Zero 18:52, 7 March 2013 (UTC)[reply]

Isn't space itself curved? Aren't all so-called straight or plane objects intrinsically curved? -- Jack of Oz ^[Talk] 23:05, 7 March 2013 (UTC)[reply]

See Geodesic and Geodesics in general relativity for the concept of straight lines in curved spacetime. --Carnildo (talk) 00:37, 8 March 2013 (UTC)[reply]

See gravitational lens. Spinning Spark 06:51, 8 March 2013 (UTC)[reply]

Russian MBT Designs

It is known that Russian tanks are smaller and have a less area exposed to fire , but does that make a big difficulty for opponents to hit it ? in other words does it worth to exhaust the tank crew for this reason ? — Preceding unsigned comment added by Tank Designer (talk • contribs) 15:18, 7 March 2013 (UTC)[reply]

Yes and no. The T-90 is about a foot lower than the M1 Abrams, but their guns are roughly the same distance below turret top. So in the open, the T-90 presents a slightly smaller target. In a hull-down position, this distinction in height doesn't matter, though the T-90 turret is also somewhat smaller. Our article there further notes that US tanks can typically depress their main gun farther than Russian designs, which results in the Russian design potentially exposing more of the tank body (particularly if using a natural slope). For aerial threats, the two tanks have roughly the same size.

As for the last, the Gulf War demonstrated a clear advantage for US-manned M1s with air superiority against Iraqi-manned T-72s. For the rest, I refer once again to the evidence of design philosophy: each military fields the tanks they believe best match their doctrine and probable opponents, but unless and until it comes to open warfare, anything further would be conjecture. — Lomn 16:04, 7 March 2013 (UTC)[reply]

Having talked with a Gulf War tank crew veteran, he claimed that the US advantage in tank-to-tank combat was due to their automatic targeting system, allowing US tanks to hit the target with the first shot, while Iraqi tanks averaged about 3 (for those which managed to survive that long). StuRat (talk) 18:01, 7 March 2013 (UTC)[reply]

I've read quite a bit about the Persian Gulf War (of 1991), and talked to a few veterans, and it is my opinion that the chief American advantage in tank-to-tank combat was avoiding it. From the Combined Arms Research Library, here are the memoirs of one Captain Enloe, an officer in a mechanized infantry brigade, Persian Gulf War: 2d Battalion, 18th Infantry Regiment (Mechanized), 197th Infantry Brigade. "At 280515 Feb 91, all elements were ordered to stop all movement, a temporary cease fire was immediately in effect throughout the entire theater of operations. In absolute disbelief, we came to a halt and formed into a Task Force Tactical Assembly Area." Ground operations in Desert Storm famously lasted less than one hundred hours, most of which were spent driving from formation assembly areas to to other formation assembly areas.

Our original poster may find the digital library collection full of interesting information about modern armored doctrine. Nimur (talk) 18:21, 7 March 2013 (UTC)[reply]

Thank you very much Mr. Lomn

Filter paper to concentrate interesting things for microscope viewing?

Hi Folks, I have a pretty good microscope (1000x oil immersion) but am a total amateur as a scientist. I live on the ocean and would like to see interesting things like tardigrades, nematodes, plankton, etc. I'm not that interested in things at the bacterial level. Looking at plain seawater it takes a long time to find neat stuff so I was wondering if I could run a bunch of seawater through filter paper to concentrate creatures. What kind of filter paper should I use? Maybe a coffee filter would work but I don't mind buying the real thing. Any other suggestions for easy interesting things to see? Thanks! — Preceding unsigned comment added by 72.165.55.147 (talk) 17:46, 7 March 2013 (UTC)[reply]

The problem with filters is that the critters will all be stuck in the filter, and you'd need to use more water to flush them back out. Swamp water seems to be crawling with critters, so you might try that instead of ocean water. I also suggest starting a slide on a low magnification, then finding something of interest, before zooming in to max res.StuRat (talk) 17:53, 7 March 2013 (UTC)[reply]

First, usually freshwater is used for this type of thing: there are plenty of freshwater tardigrades (and nematodes and plankton too). I've found water bears in wet moss, on the edge of ponds, etc. It's easiest to find the bigger things, of course, and tardigrades can get up to 1 mm. However, I am not sure if the reason fresh water is more common is because there are more critters to see, or if it's just more widely available...

I think your idea is worth trying. As Stu says, some critters will get caught on the filter, but if you filter e.g. 1 L and then use 0.1 L to flush them back, you'll presumably have a 10X concentration, which could make your hunting up to 10X easier. I'd start with a filter of about 0.4 mm and see how it goes from there. You could also filter out coarse debris first with a 2mm sieve. As for other interesting thing to see (in freshwater/pond scum), bdelloid rotifers, hydras and volvox are all pretty cool. In ocean water you'll probably find more (and more interesting) diatoms, though they are also in fresh water. SemanticMantis (talk) 19:19, 7 March 2013 (UTC)[reply]

I think the best way to concentrate these critter is to use patients. I may take a long time to go through a bucket full of sea water with an eye dropper drip-by-drip but that the best way IMHO. You can take advantage of sea water stratifying. Not easy close to shore, because the wave action mixes it up. However, go a little off shore and you have the photosynthesising hungry stuff in the upper surface areas and the bottom dwelling stuff ... err... on or within the bottom sediments – like nematodes . Text books should tell you their natural habitat and all you need to do is take sample from those areas. For instance, a suitably weighted metal tube, hack-sawed off like a giant hypodermic syringe, with a cord attached for retrieval, can by used to get bottom sediment samples. This hunt (a male trait) makes microscopy more satisfying then just going mindlessly through the mechanics of preparing a slide and peering down the lens. A good cook book, can also help to solve the disposal problem of most sea life that is too big to go on the microscope stage. This alone, can only add pleasure to your hobby. I’m salivating at the thought. Don't forget also, many seaweeds are edible too and they have microscopic life crawling all over them. Go down to you local Japanese delicatessen and you'll have to pay good dollars for seaweed. Collect your own and its a double win situation. Forget filter paper - unless it for coffee. --Aspro (talk) 20:06, 7 March 2013 (UTC)[reply]

I would suggest using patience, as using patients might be considered unethical, although you could use patients to grow some parasitic organisms into an easier to see size. :-) StuRat (talk) 03:29, 8 March 2013 (UTC) [reply]

P.S. For other interesting thing to see, go down to the landings an buy some of the stuff that comes up in the nets that are not of commercial value. Some critters that the fishermen bring in make Alien look like a loveable puppy. With a few sharp dissecting tools, there are things that would take more than a life time to explore. A good book on the microscopic dissection of marine zoology would help to give you an idea of how to slice them up for best viewing under the 'scope. These critter also often have tiny little parasites on them so inspect them carefully, as they make for good viewing too... Also, whilst you may have never seen some off these critters on the supermarket fish counter, what’s left over from your dissections are very probably edible as well. It's a crying shame that it usually only goes into cat food. --Aspro (talk) 20:39, 7 March 2013 (UTC)[reply]

Regulatory genes that account for monocot physiology

Is there some sort of regulatory gene regime like the homeobox genes in animals that accounts for differences between monocots and (eu)dicots as a suite? Or are things like parallel venation and monocotyledony separate, unrelated innovations? Thanks. μηδείς (talk) 20:40, 7 March 2013 (UTC)[reply]

I don't know. But I found this reference in the homeobox article: A Comprehensive Classification and Evolutionary Analysis of Plant Homeobox Genes. Mol Biol Evol. 2009 December; 26(12) (open access here [4]) - A quick glance leads me to believe it would answer your question, but I can't really read that stuff. SemanticMantis (talk) 20:51, 7 March 2013 (UTC)[reply]

That source basically says that analogs of the homeobox genes exist broadly in plants from algae to flowering, but it doesn't focus on flowering plants or answer the question as to whether monocot innovations are a suite of characteristics due to one regulatory system or not. μηδείς (talk) 21:03, 7 March 2013 (UTC)[reply]

Flirting

If flirting a subconscious human behaviour? Do animals do it or only humans? Clover345 (talk) 22:57, 7 March 2013 (UTC)[reply]

Flirting behavior is by definition a human behavior; it can be conscious or subconscious. For (slightly) analogous behavior in animals, see courtship display and courtship_in_animals. SemanticMantis (talk) 23:46, 7 March 2013 (UTC)[reply]

if its subconscious, is it an emotional response? — Preceding unsigned comment added by Clover345 (talk • contribs) 23:51, 7 March 2013 (UTC)[reply]

Flirting in primates does not brake down into simple conscious or sub-conscious behaviour. The opposite sex can often detect conscious willful manipulation. However, if the basic animal instinct of sexual attraction is satisfied (emotional) then the higher intellectual demands requiring compatibility come into play. In the past, when people often did not travel far from their village and and expectations were less, like-married-like. Now, in the modern age, with cheap travel... like still marry like (so they hope) – but from further afield, because they have been brought up to be more fussy. The down side is that in the US and some other countries, singletons are chasing the impossible dream. Many animals flirt as part of their courtship.--Aspro (talk) 00:41, 8 March 2013 (UTC)[reply]

For specifically subconscious flirting behavior, see Proteans. Evanh2008 ^{(talk|contribs)} 22:57, 8 March 2013 (UTC)[reply]

Psycho-acoustics

are the explanations of psycho-acoustic simulation per the Hank Risan article consistent with science in this area? --_nonsense ferret 23:33, 7 March 2013 (UTC)[reply]

Wikipedia has an article on Psychoacoustics with references. You could use that to help your research. --Jayron32 02:13, 8 March 2013 (UTC)[reply]

March 8

Radiative transport?

Does the "Radiative transport" linked in the Sievert integral article mean the same thing as "Radiative transfer"? Or is this "Radiative transport" referring to some physiological aspect of radioactivity? I can't tell from the references. Thank you. Praemonitus (talk) 00:21, 8 March 2013 (UTC)[reply]

The former. The integral pertains to a layered medium, with

\varphi =0

normal to the layers, such that

x\sec \varphi

is the distance along a line at angle

\varphi

to the normal to a point x away in the normal direction. Then the exponential decay of radiation over distance (in the simple case) is invoked. I'm not sure what should be taken from the weighting by angle; there may be compensating terms involving solid angle subtended at each end of the line segment. I think "radiation transport" (as it says: note the first word) is a common synonym for "radiative transfer"; it might deserve a redirect. --Tardis (talk) 03:08, 8 March 2013 (UTC)[reply]

Thank you for the clarification, Tardis. Praemonitus (talk) 05:23, 9 March 2013 (UTC)[reply]

Mixing chemicals

Hello. Can you tell me what would complete the following reaction, which I added together into a beaker. I have noted the solution is both black, and very acidic.:

C3H6O + H20 + NaCl + HCL + C3H8O + KCL + BaCl2 + HNO3 + CoCl2 + K2Cr2O7 + K2CrO4 + H2SO4 + K4Fe(C2O4)4·2H2O → ?

Thanks, Albacore (talk) 03:07, 8 March 2013 (UTC)[reply]

It depends on the initial concentration of the hydrochloric and nitric acids, many of the reagents in that reaction aren't reagents at all, and may only at best act as catalysts. The final solution is black because of colloidal carbon. Plasmic Physics (talk) 03:41, 8 March 2013 (UTC)[reply]

Also, barium sulfate may crash out of the solution, and if the chromate/dichromate is concentrated enough, they may oxidize the isopropyl alcohol to acetone. Of course, if the sulfuric acid is concentrated enough, it will dehydrate all organic compounds in the mixture to carbon like Plasmic said -- but if the nitric acid is highly concentrated, then it might in turn oxidize the carbon to CO2 (which will bubble out of the solution because of its low solubility in acid)! So if I had to guess, I'd say your solution contains the following: H2O (solvent), C(s), C3H6O(aq), Na+(aq), Cl-(aq), H3O+(aq) (lots of), K+(aq), BaSO4(s), NO3-(aq), Co+2(aq), Cr2O7(aq), HSO4-(aq), CO2(g), and Fe+2(aq). 24.23.196.85 (talk) 06:43, 8 March 2013 (UTC)[reply]

Oh, I forgot the oxalic acid H2C2O4(aq) (which will be fully protonated because of the acidity). 24.23.196.85 (talk) 06:48, 8 March 2013 (UTC)[reply]

A biological question about myself

we cannot offer diagnosis or medical advice

The following discussion has been closed. Please do not modify it.

I once took an otc pill was for Common coldness (it was in 2011) and contained:

Dexchlorpheniramine maleate Pseudoephedrine

for an unkown reason, it maid my hand-skin very dry !!!, so much so, that after 5 days some of the skin on the middle of the upper hand (next 2 where the fingers start-out), and also, in some cushions of the hand, skin could be easily ripped off from this areas (and it wasn't painful). other Antihistamine drugs didn't do that 2 me (except 2 one which i think contains the same AH molecule mentioned above, but don't take my word for it).

could you at least try 2 tell me about this very interesting mechanism?

thanks 4 your time. Ben-Natan (talk) 05:50, 8 March 2013 (UTC)[reply]

The drug is a common antihistamine decongestant combination. Your skin changes were either (1) an effect of the respiratory infection for which you took the drug-- several of them can cause late skin desquamation and peeling; (2) an allergic reaction to either component of the drug; or (3) due to something completely unrelated. Note that an allergic reaction to a drug is different than a "side effect"-- what you describe is not a recognized side effect of either drug. I suspect the first possibility is most likely. The only way I can think of for you to determine whether it was a drug effect would be to take it again for a few days: if it didnt happen again, it probably wasnt the drug. Note that this is speculation because you asked for it and not medical advice. alteripse (talk) 12:41, 8 March 2013 (UTC)[reply]

This is a one-off trial with a sample size of one person and no double-blind control. Literally nothing can be deduced from it. Without other information, there is zero reason to assume that the effect on your skin had anything whatever to do with the medication - rather than some chance encounter with some chemical or biological agent over some several days before you skin condition popped up - or as a side effect of the disease that caused you to take the drug in the first place.

To even credit the question as something worth answering, you'd first have to take a thousand people, give half of them the medication and the other half a placebo, count the number that have skin problems and see if the result is higher for those taking the medication than those that didn't. If that's a big enough difference, then it's a side effect and you can start to ask why it happens. But if not...then this is not a meaningful question. Since the manufacturers most certainly did some kind of a trial like this for all of the active ingredients, then if this were a reasonably common side-effect, it would be printed on the label someplace.

So check the label - and if it describes this symptom, then we can probably find the cause somehow. If not - then it was almost certainly something else that caused your skin issues.

SteveBaker (talk) 14:20, 8 March 2013 (UTC)[reply]

Hi. For the first answerer, anytime i take the drug, the exact thing happen, i took it again before and after the aforementioned time. thanks. Ben-Natan (talk) 17:16, 8 March 2013 (UTC)[reply]

the human singing voice - effects of age

Until age 50, I had a soprano voice and could sing a high A without difficulty. In the 15 years since, it has dropped an octave. I now sing (croak) lower than my husband does. I am aware that voices change over time and that women's voice generally get lower. What physical changes account for this please? And does it matter? There have been no illnesses which might explain it and my speaking voice has not much changed. Thank you. — Preceding unsigned comment added by 109.12.62.161 (talk) 07:59, 8 March 2013 (UTC)[reply]

One of the illnesses that affect voice, and that affects many females over the age of 50, is hypothyroidism. I presume you've ruled that out. --TammyMoet (talk) 10:25, 8 March 2013 (UTC)[reply]

Firstly, we're not allowed to diagnose medical issues here on the Wikipedia reference desk - that's a huge "No-no" for use! So our advice has to be limited to "Go see a doctor"...and something like this does have the potential to be indicative of medical issues that you might not otherwise have noticed (see Vocal cord dysfunction for a range of alarming possibilities), so that's especially good advice in this case.

Our vocal cord article suggests that menopause can specifically change a woman's singing voice, and since this evidently happened in your early 50's (which is plausibly the age when menopause happened for you) the timing is right for that to be the cause here.

If all else fails...there is always helium! :-)

SteveBaker (talk) 14:37, 8 March 2013 (UTC)[reply]

And menopause causes a lowering in the voice frequency due to changing hormone levels (a higher testosterone to estrogen ratio, which also can cause facial hair). I wonder if anyone has studied if hormone replacement therapy reduces or reverses this effect ? StuRat (talk) 16:14, 8 March 2013 (UTC)[reply]

Does the concept of a "quantum speed" make any sense?

I am currently taking a Quantum Chemistry class at university and to test our knowledge on quantum mechanics, the professor just posted a rather interesting question. The question is:

"Does the concept of a 'quantum speed' make any sense?"

I thought this question in two ways:

1) Speed as a continuous variable is not quantizable. This means a "quantum of speed" doesn't exist, and therefore the concept of a "quantum speed" does not make any sense.

2) Since speed is the magnitude of velocity and velocity is the time derivative of position, the speed of a particle trapped in a box (say, a 1-D infinite square well potential) is represented by || d/dt [xΨ(x,t)] ||. Taking the position operator on the wave function yields a position with an imaginary part, and taking the magnitude of the time derivative of a complex position should be able to yield a real solution. Would the real solution represent the "quantum speed"

Am I at all on the right track with these two approaches? Hope to hear you guys' insights! — Preceding unsigned comment added by 169.232.187.44 (talk) 08:28, 8 March 2013 (UTC)[reply]

What evidence do you have to support your theory that "speed as a continuous variable is not quantizable"? It might be true, but is it established as a fact? See Planck length and Chronon. Also see [ http://arxiv.org/pdf/quant-ph/0004086.pdf ]. --Guy Macon (talk) 10:19, 8 March 2013 (UTC)[reply]

The Planck length is just a distance at which quantum gravitational effects should become large. There's no particular reason to think that distances are quantized in units of the Planck length. Anyway, there's no Planck speed—or rather the Planck speed is c, which isn't particularly helpful in this context. -- BenRG (talk) 23:09, 8 March 2013 (UTC)[reply]

Perhaps an overly simple approach: aren't speed and temperature essentially the same thing, on a quantum scale? Isn't temperature quantized? --Mr.98 (talk) 12:50, 8 March 2013 (UTC)[reply]

Sorry for the digression, but no, absolutely not. Speed and temperature are not remotely the same thing. In fact temperature has nothing directly to do with kinetic energy. Temperature is a measurement of the relationship between entropy and internal energy. This is the statistical mechanics approach to temperature, and it is far more fundamental than the kinetic approach. Temperature can even be negative, that is, below absolute zero, which is obviously not possible for speed or kinetic energy. --Trovatore (talk) 17:13, 8 March 2013 (UTC)[reply]

Define a linear speed operator S by defining it on the functions exp(i k x) (which form a complete set), as

S exp(i k x) = hbar |k|/m exp(i k x)

Then S is defined for all states. You then need to check to see if S is a Hermitian operator. Count Iblis (talk) 15:51, 8 March 2013 (UTC)[reply]

In physics, I believe there are some massless particles which can only go the speed of light, while particles with rest mass can go speeds below, or, theoretically, above the speed of light, but not precisely that speed, as getting there would require infinite energy. A complicating factor is that the speed of light itself varies, depending on the medium. StuRat (talk) 16:04, 8 March 2013 (UTC)[reply]

If you're implying that particles can't travel faster than the speed of light in a medium, that's absolutely wrong. They can and do break the "light barrier" in water all the time, and the result is Cerenkov radiation. --140.180.243.114 (talk) 18:53, 8 March 2013 (UTC)[reply]

(Mostly responding to StuRat) The speed of light in a medium is just the speed of light in a medium and has nothing intrinsically to do with the speed of anything else. The universal constant c has nothing intrinsically to do with light, even though it's often called "the speed of light in vacuum" or even just "the speed of light". So your second sentence isn't a complicating factor in any physical sense. It's just a pun on the phrase "the speed of light". -- BenRG (talk) 23:09, 8 March 2013 (UTC)[reply]

To the OP: maybe I'm missing something here, but why can't you apply the momentum operator to the wavefunction, calculate the inner product of the result and the wavefunction, and integrate over all space? That would give you the expectation value of momentum. Divide that by mass and you'll get the classical analogue of velocity for a wavefunction. --140.180.243.114 (talk) 18:53, 8 March 2013 (UTC)[reply]

I wonder if this question had some specific context—i.e. there was something in the lectures or readings recently that looked like it was about "quantum speed", and the question is whether that's accurate or misleading. Without context it's hard to know what to say. Speed is an observable in quantum mechanics, as other people have already said. It's not quantized in general (though it can be in particular cases like the particle in a box), but not being quantized doesn't mean it's not quantum—"quantum X" and "quantized X" generally mean different things. -- BenRG (talk) 23:09, 8 March 2013 (UTC)[reply]

There isn't a really specific context that I can provide I'm afraid. We just wrapped up 3D particle-in-a-box and moved onto the harmonic oscillator approximation. The professor is pretty big on the interpretation of Quantum Mechanics though. I suppose the context for a "quantum speed" comes frmo the latest Verizon adverts where they allow the users to upgrade to a faster internet speed called "quantum." I think that's where he based the problem off of. In regards to 140.180.243.114, taking the momentum operator and then dividing it by the mass does seem to be a much quicker way to determining the velocity! — Preceding unsigned comment added by 169.232.187.164 (talk) 00:22, 9 March 2013 (UTC)[reply]

Something about coelomates

In here (page 95), the classification chart of animals into different phyla is given. I'm having trouble understanding how coelomates are further divided. Can anybody help? Thank you. --Yashowardhani (talk) 09:30, 8 March 2013 (UTC)[reply]

The chart on that page clearly shows that coelomates are divided into Annelida, Mollusca and Arthropoda on one branch and Echinodermata and Chordata on the other. Wikipedia uses a 'superphylum' notation to name those two branches - so the Echiondermata and Chordata are both "Deuterostomes" (with a couple of other phyla tossed in that your chart doesn't mention) and the Annelida and Mollusca are all in the super-phylum "Lophotrochozoa". Wikipedia's chosen classification places the arthropoda in the "Ecdysozoa" super-phylum.

The trouble with these classifications is that they are changing rapidly as we discover more about the animals involved - and the entire structure of the tree is a matter of heavy debate with some biologists preferring a DNA-based approach, others an evolutionary approach - and with both laboring under some horrific mis-classifications made by observation of body structure alone dating back to Victorian times. Your book looks like it was probably published about 8 years ago...and things are changing faster than that!

SteveBaker (talk) 15:04, 8 March 2013 (UTC)[reply]

Some of the clades you mention, are fairly certain and stable such as the crown deuterostomes and the ecdysozoans. The big problem is the protostome/deuterostome dichotomy has turned out to be as flawed as the dicot/monocot dichotomy, with protostomy and dicotyledony turning out to be non-diagnostic symplesiomorphies. The linked information Yashowardhani provided would have been considered simplistic and out of date decades ago--it's basically suitable merely as an introduction to the fact that such concepts exist, as might be okay for non-science majors. There are plenty of popular books like Assembling the Tree of Life that are slightly more updated and at least bring up the issues that are at question. (Even that will be outdated, however--the field is in a huge flux, see Afrotheria for an unexpected recent yet now undoubted grouping.) μηδείς (talk) 01:25, 9 March 2013 (UTC)[reply]

The solubility of francium hydroxide: is it OR?

In Chinese article of francium hydroxide it is claimed that francium hydroxide is soluble in water along with this source:Maddock, A. G. (1951). "Radioactivity of the heavy elements". Q. Rev., Chem. Soc. 3 (3): 270–314. doi:10.1039/QR9510500270.. In English article of francium there is a similar claim using the same source says"Nearly all francium salts are water-soluble." But in the DOI page all I can say is an abstract of the research focusing mainly on the actinium series. So does this article actually describe the solubility of francium salts?

The article says "nearly all francium salts are soluble". That's it; no further details are given. It doesn't say water-soluble, though this is implied by the context. Chris (talk) 15:29, 8 March 2013 (UTC)[reply]

After all, the article might mean "soluble in molten tungsten"... :) --Guy Macon (talk) 17:05, 8 March 2013 (UTC)[reply]

What??? The wikipedia article did say water-soluble. You mean the doi article?--Inspector (talk) 23:57, 8 March 2013 (UTC)[reply]

Cinnamon Wattle

Hi!

How has the plant Cinnamon Wattle got its scientific name Acacia leprosa? Does it have something to do with leprosy? --213.214.155.24 (talk) 12:13, 8 March 2013 (UTC)[reply]

The word indeed derives from the original Latin word for leprosy (as of course does the English word itself), and in biological nomenclature is sometimes used to indicate a spotted or blotched appearance (as a sufferer of leprosy might have). Although it's not obvious in the pictures in our article on the Cinnamon Wattle, it looks as if the 'leaves' do have a slightly mottled appearance due to their texture. {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 14:42, 8 March 2013 (UTC)[reply]

This says: "Acacia; from Greek acis, a thorn. leprosa; having a whitish, mealy or scaly surface, presumably referring to the phylodes.". And according to leprosy: "The word leprosy comes from ancient Greek Λέπρα [léprā], "a disease that makes the skin scaly"". So the name basically refers to the scaly nature of the plant - and both "leprosa" and "leprosy" come from a common base term for scaliness. The plant itself has nothing whatever to do with leprosy. SteveBaker (talk) 14:45, 8 March 2013 (UTC)[reply]

Drat, I misread the title, and now I'm hungry for cinnamon waffles. StuRat (talk) 16:10, 8 March 2013 (UTC) [reply]

This here's the wattle, the emblem of our land,
you can stick it in a bottle, or hold it in your hand
— Monty Python

Amen. -- Jack of Oz ^[Talk] 04:27, 9 March 2013 (UTC) [reply]

specilization of the cell wall of epethilia

please i want it very soon

specilization of the cell wall of epethilia — Preceding unsigned comment added by 41.37.24.186 (talk) 16:07, 8 March 2013 (UTC)[reply]

See Epithelium, but "the epithelia" includes every type of tissue in the body, apart from muscles, nerves, and tendons. Without knowing the specific type of epithelium you need information about, it's not really possible to answer the question. Tevildo (talk) 18:07, 8 March 2013 (UTC)[reply]

Why azane, not nitrane?

All the examples listed at Substitutive nomenclature are constructed as main part of element name + "ane": borane, oxidane, phosphane. So why is azane not called "nitrane"? — Sebastian 16:44, 8 March 2013 (UTC)[reply]

It's named after azote which is an alternate name for nitrogen which has now fallen out of use. Dauto (talk) 18:58, 8 March 2013 (UTC)[reply]

Cool, thanks! BTW, German "Stickstoff" expresses the same idea, meaning "suffocating substance". — Sebastian 19:33, 8 March 2013 (UTC)[reply]

There's also Guns 'n' Roses copyright. μηδείς (talk) 01:13, 9 March 2013 (UTC)[reply]

Which they stole from Roy Acuff. 24.23.196.85 (talk) 03:37, 9 March 2013 (UTC)[reply]

Weird chemistry dream: The scent of a proton

I had an odd dream last night in which I was back in chemistry class. The teacher had a device which could strip the electron from atoms of hydrogen, leaving positively charged protons, which we sniffed via a tube stuck up the nose. They had an unpleasant acrid smell. Now in reality, would such a gas of low energy low density hydrogen atom stripped of electrons have a smell? I know that normal hydrogen is odorless. This is quite distinct from proton beam therapy. The Proton article in the section "Interaction of free protons with ordinary matter" says that such protons might combine with another atom or molecule to make "Bronsted acids," which makes the "acrid" scent in the dream plausible. Is such an experiment possible (however inadvisable)? Edison (talk) 17:56, 8 March 2013 (UTC)[reply]

It must have been an awesome dream! 140.254.121.60 (talk) 19:30, 8 March 2013 (UTC) [reply]

Maybe you were smelling ozone. The protons can also be called ionized hydrogen, and ions are generated during lighting storms which also makes ozone, which you can smell. Ariel. (talk) 20:18, 8 March 2013 (UTC)[reply]

Acrid: "Smells like Akron". :-) StuRat (talk) 22:51, 8 March 2013 (UTC) [reply]

Didn't you mean this Akron? 24.23.196.85 (talk) 03:40, 9 March 2013 (UTC)[reply]

Nope, Akron, Ohio, with that lovely rubber volcanization scent. StuRat (talk) 04:20, 9 March 2013 (UTC) [reply]

To be smellable, a substance must be volatile and soluble. (Volatile to get to your nose, soluble to penetrate the aqueous and lipid layers that surround the olfactory nerve cells.) I'm guessing that by the time a proton reaches your olfactory receptors, it's hydrogen, though as you point out other substances might be possible. - Nunh-huh 03:48, 9 March 2013 (UTC)[reply]

If a number of low energy protons were introduced to the olfactory area of the nose, they might steal an electron and become odorless hydrogen as you suggest. They might also latch onto another atom or molecule and share its electrons. The stray low energy proton would likely not combine with the nucleus of another atom, increasing its atomic number. Most air molecules would be nitrogen, followed by oxygen. What compound would nitrogen or oxygen plus a proton be? (For me, a chemistry or physics dream is interesting and thought provoking, while a math dream is literally a nightmare). Edison (talk) 03:20, 10 March 2013 (UTC)[reply]

A protonated oxygen molecule O₂H⁺ is called the hydroperoxyl ion.[5][6][7] The hydroperoxyl anion is O₂H^- the opposite charge. (but this may also just be called the hydroperoxyl ion too, casuing confusion) N₂H⁺ is rather boringly called protonated nitrogen.[8][9] The links I provided also list some reactions. There is also a protonated nitrogen dimer: N₂H⁺N₂ with two nitrogen molecules bridged by a proton.[10] There looks to be just enough material to justify articles. Graeme Bartlett (talk) 04:21, 10 March 2013 (UTC)[reply]

caffeine ==> adenosine receptors

Is caffeine a competitive agonist for ATP on the adenosine receptors? ATP stands for adenosine triphosphate, and it is used by cells as an energy source. Similarly, caffeine somehow gives you energy. Is it possible that they work the same way? 140.254.121.60 (talk) 19:27, 8 March 2013 (UTC)[reply]

The chemical that activates adenosine receptors is adenosine, not adenosine triphosphate. I am unaware of any evidence that ATP acts as an agonist at adenosine receptors. So I believe the answer to all these questions is no. You can look at our article on caffeine for more information. Looie496 (talk) 23:23, 8 March 2013 (UTC)[reply]

Adding water causes liquid soap to gel

We decant liquid dish soap from a large commercial bottle into a pump-action dispenser beside the kitchen sink. Recently in rinsing out the liquid remaining in the bottle by adding water, I found the resulting diluted soap lathered up well on the sponge and was then easier to rinse off the dish being washed. However, when I added water to the dish soap in the dispenser (about 1:3 ratio), I was dismayed to discover the lower part in the dispenser turned into a gel that resists dilution with water. What's going on here? -- Deborahjay (talk) 19:49, 8 March 2013 (UTC)[reply]

If you put the dispenser in warm water for a while, does the gel dissolve? --Guy Macon (talk) 20:00, 8 March 2013 (UTC)[reply]

I can't try that without recreating the original problem - I poured the entire contents of the dispenser into a large bowl and combined it with my fingers, then added much more water so it's highly diluted now. -- Deborahjay (talk) 20:23, 8 March 2013 (UTC)[reply]

I think what Guy is getting at is that the water temperature might make a big difference, with the water mixing much better if hot. Was the water a uniform temperature in both cases ? The other big difference might be the surface area. Presumable, on the plate, there was much more surface area available for mixing than in the dispenser. Next time, you might want to just add a little hot water to the dispenser, mix that in, then add a bit more, until it's all mixed. StuRat (talk) 22:48, 8 March 2013 (UTC)[reply]

March 9

Why do ceiling and walls get darker except for the corners

My room used to be white but darkened because of smoke, etc. Except for the very corners that seem to be unaffected. A professional painter tells me this is very common. How would smoke even know it's in a corner? Joepnl (talk) 00:00, 9 March 2013 (UTC)[reply]

Just a WAG, but my guess is that it has something to do with the way that air currents distribute the smoke around the house; the corners may present perturbations to air flow that prevent as much smoke from getting into the corners as along the surface. --Jayron32 00:05, 9 March 2013 (UTC)[reply]

In that case I'd expect a big white spot in the "very 3D-corners", where there are three angles at the same time giving reason to the smoke to not stick to the wall. The white stripe seeminglingy has the same width everywhere. I was thinking that it might have to do with the way the paint was applied (using a paint roller for the large areas and a brush for the corners), but the white stripe also appears next to lights that were installed after the painting was done. Joepnl (talk) 01:19, 9 March 2013 (UTC)[reply]

Doesn't laminar flow decrease exponentially with proximity to a surface? Wouldn't that imply airflow in room corners is minimal, and that wsmoke would more likely escape a room before getting into its extreme corners? I am reminded of H. P. Lovecraft. μηδείς (talk) 02:03, 9 March 2013 (UTC)[reply]

It's an effect called ambient occlusion. SteveBaker (talk) 05:00, 9 March 2013 (UTC)[reply]

An optical illusion? ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:29, 9 March 2013 (UTC)[reply]

No, neither of these. I've observed exactly the same effect and it is real and independent of paint and light (it happens to wallpaper, too). Jayron's and Medeis' answer of airflow must be correct one, though there will sometimes be a bit of turbulence. I'm not sure how airflow behaves at the intersection of room right-angles, but presumably one could make some deductions from the lighter areas. The pattern might depend on the temperature difference between the room air and the walls, thus creating constant convection currents unless the walls are really well insulated. Dbfirs 15:50, 9 March 2013 (UTC)[reply]

science writing

Why is science writing usually done in the third person, passive, past tense? — Preceding unsigned comment added by 99.146.124.35 (talk) 02:52, 9 March 2013 (UTC)[reply]

Because it's always done that way. I'm serious. That's what my high school science teachers told me almost 50 years ago. Oh, there's also the fact that we lost marks if we did it any other way. HiLo48 (talk) 02:59, 9 March 2013 (UTC)[reply]

Well, there is actually a reason: to maximize objectivity. First-person writing brings ego into the picture, and when ego comes in, objectivity goes out. Looie496 (talk) 03:10, 9 March 2013 (UTC)[reply]

My impression is that most papers are written in the present tense, first person plural (even if there's only one author). Popular books about science are written in the past tense insofar as they're histories, in the third person insofar as the author wasn't involved, and in the first person insofar as he/she was involved. I think the passive voice is used mainly where the subject would otherwise be "scientists in our (sub)discipline" and it would be silly to keep repeating it. You do often see "our results are summarized below" instead of "we summarize our results below", but there's nothing wrote with that. -- BenRG (talk) 04:58, 9 March 2013 (UTC)[reply]

This does actually vary a little. A friend told me in psychology, the first person is becoming more common, even (I think) normal or expected in some journals. This is true of qualitative and quantitative research. I do not mean to suggest applies across the board in psychology, and it was just what one psych PhD told me. In IT I was told to use the third person, but the reason given was just because my supervisor had seen things done that way himself, not because he had any ideology about it. I think those that have strong feelings get their opinions heard, and others play along. In science, as might be suggested by Looie's post, more people are strongly against the "I" than strongly in favour. I'm in favour, but wouldn't make a drama over it. Also, past tense for your methods section (this is what you did) and present for the conclusions (where the conclusions apply to a general case, rather than reasoning about specific factors in the experiment). So "Method: 33 subjects were recruited....Discussion: It seems from the data that some of the results may have been confounded by the subjects talking on mobile phones and drinking too much beer ... even so, it seems (present tense) that safety lessons improve driver behaviour... " etc IBE (talk) 02:04, 10 March 2013 (UTC)[reply]

About 1970 my high school biology teacher said to write up the lab report in the "third person". He meant "passive voice". So I wrote things like "he made the incision in the frog". "She saw the intestines." To address the original question, I think that it is because it is more about the object and procedures than the person doing them. Bubba73 ^{You talkin' to me?} 04:23, 10 March 2013 (UTC)[reply]

Papers in the natural sciences usually have a number of authors. Using "I" would be weird: which of the authors is speaking. And using "we" would also jar, because it was actually just one person minding the experiment in the lab, another one crunching the results on the computer, etc. In the social sciences and humanities most papers have one or two authors, so it sounds more natural to write "I" or "we". Itsmejudith (talk) 10:00, 10 March 2013 (UTC)[reply]

Glomerular Pore Radius

Hello. Given the filtration coefficient, how can one find the pore radius in order to calculate the "pore surface area to pore length" ratio? I am referring to the formula: $K_{f}={\frac {r_{0}^{2}S}{8\mu l}}$ where $r_{0}$ is the pore radius and ${\frac {S}{l}}$ is the ratio. A link to a journal article would be appreciated. Thanks in advance. --Mayfare (talk) 03:28, 9 March 2013 (UTC)[reply]

Eggs and potatoes

Eggs and meat cook from the outside in, but potatoes and root vegetables cook evenly (if that's the right way to put it). I suppose that it has something to do with the fact that eggs and meat contain more protein, but what is the reason for that difference? Sjö (talk) 08:27, 9 March 2013 (UTC)[reply]

There might be a small difference in thermal conductivity as you suggest, but the main difference is that potatoes and root vegetables are normally cooked for much longer at only 100C, so the difference between inside and outside is not really significant because the whole object has been at a constant temperature for a long time. Eggs are normally cooked for a short time so delays in heat flow are noticeable, with the yolk never reaching 100C in some cases. Meat is normally cooked for longer, but at a higher temperature, and not covered in water, so low thermal conductivity and restricted heat flow becomes very important. Those who like their meat "rare" never allow the inside to reach 100C, even if the outside has reached several hundred degrees. If you try grilling potatoes and root vegetables, you will see that they also cook from the outside in. Dbfirs 09:44, 9 March 2013 (UTC)[reply]

I can assure you that potatoes and root vegetables do indeed cook from the outside in, and I really have no idea where you got the notion that the inside of a potato cooks at the same rate as the outside. Do you have any references to that effect? --TammyMoet (talk) 10:53, 9 March 2013 (UTC)[reply]

As Dbfirs notes above, while they do cook from the outside in, the difference in cooking time between the outside and inside is small, relative to the overall cooking time. I've cooked potatoes, carrots, etc., for hours, while that would ruin eggs or meat, in many cases. In the case of exceptions, like a pot roast, where meat is cooked for a long time, you don't find a noticeable difference in how well the inside and outside are cooked. StuRat (talk) 15:46, 9 March 2013 (UTC)[reply]

... and as Tammy mentioned, if you try boiling a large potato for less than five minutes, you will see that the inside is still starchy and uncooked. Dbfirs 15:57, 9 March 2013 (UTC)[reply]

Does vitamin D insufficiency known as a potential Obesity cause?

My Nutritionist told me that there may be a connection. my endocrinologist told me: "take at least 10 drops !!! (off 400 IEA)"). is there a connection between being with bmi like 29 (near obese) to this vitamin? thanks Ben-Natan (talk) 08:49, 9 March 2013 (UTC)[reply]

That seems unlikely. New Zealand is pretty close to the ozone hole, and apparently we're the sixth fatest country in the world. Plasmic Physics (talk) 10:38, 9 March 2013 (UTC)[reply]

Vitamin D is involved in many more process than bone health. E.g. without enough vitamin D, your muscles will have a more difficult time accessing energy, see here:

"Conclusions: Cholecalciferol therapy augments muscle mitochondrial maximal oxidative phosphorylation after exercise in symptomatic, vitamin D-deficient individuals. This finding suggests that changes in mitochondrial oxidative phosphorylation in skeletal muscle could at least be partly responsible for the fatigue experienced by these patients. For the first time, we demonstrate a link between vitamin D and the mitochondria in human skeletal muscle."

Count Iblis (talk) 13:48, 9 March 2013 (UTC)[reply]

Also note that just about any vitamin or mineral deficiency may be linked with obesity, in the Western world, as the most frequent cause of such deficiencies (where food is plentiful) is solely eating junk food, which also causes obesity.

In the case of a vitamin D deficiency, since this vitamin is produced by exposure to sunlight, as well as obtained from nutritional sources, a lack of D also implies a lack of time spent outside, which can mean a lack of exercise, which is also linked to obesity.

So, a vitamin D deficiency may or may not cause obesity, but may also indicate an unhealthy lifestyle which is associated with obesity. StuRat (talk) 16:34, 9 March 2013 (UTC)[reply]

The likelihood of finding vit D deficiency in obese adolescents and young adults is >90%. The association of vit D deficiency and obesity is strong. However association does not prove causation, and there not yet strong evidence that vit D deficiency actually causes obesity. alteripse (talk) 16:45, 9 March 2013 (UTC)[reply]

Both StuRat and alteripse need to provide some sources, especially as they are in disagreement with each other. Bielle (talk) 17:09, 9 March 2013 (UTC)[reply]

Read our posts again. We're both saying that, while there's a correlation, that doesn't necessarily means it's the cause. StuRat (talk) 17:12, 9 March 2013 (UTC)[reply]

No disagreement. Just emphasis that association does not prove direct causation. alteripse (talk) 17:24, 9 March 2013 (UTC)[reply]

Exactly, we're fat, and we don't have a D deficiency, if anything, have a D surplus. Plasmic Physics (talk) 22:44, 9 March 2013 (UTC)[reply]

Unless you take something of the order of 5,000 IU/day of vitamin D or if you happen to live in some African tribe in the wild, you are vitamin D deficient, if not severely vitamin D deficient. See here for some actual measuremnts of vitamin D levels of people who live in the way we all lived until about 10,000 years ago. Count Iblis (talk) 23:33, 9 March 2013 (UTC)[reply]

OK, so we are deficient, but certainly less so than most other areas. Plasmic Physics (talk) 23:41, 9 March 2013 (UTC)[reply]

what is Nec?

in many scientific words like Necrosis, Adiponectin, and also in such as Necromancer there is the morpheme Nec. what is the meaning? Ben-Natan (talk) 10:15, 9 March 2013 (UTC)[reply]

It comes from the Greek prefix necro, meaning death. Don't know whether Adiponectin uses that particular meaning though. --TammyMoet (talk) 10:46, 9 March 2013 (UTC)[reply]

The etymology of the nect element in adiponectin is from Latin nectere meaning to connect or to bind. Spinning Spark 11:47, 9 March 2013 (UTC)[reply]

How can we predict properties of an element and its compounds when that element is not available or too unstable to experiment?

One early example of those might be Mendeleev's prediction for germanium and its compounds, which includes some densities and melting points. How are those kinds of predictions made? Just simple linear regression, and in some cases by theoratically calculating the Van der Waals Force? Do we know how accurate it can be? Can we apply such methods to other elements and their compounds? Is it original research to make such predictions?--Inspector (talk) 10:10, 9 March 2013 (UTC)[reply]

For putative properties that we don't measure but derive, this is the realm of disciplines such as computational chemistry. The modern methods are more rigorous (as we have more data and better equations) than Mendeleev used in filling in the holes in his table, but the principles are the same. The prediction of these properties is roughly the field of Ab initio quantum chemistry methods, which basically involves deriving putative properties from purely mathematical principles: You start with what you know of the laws of physics as they apply to all smaller atoms you already know, then you extrapolate that data (it's probably a LOT more complex extrapolation than mere linear regression) and predict the likely properties of the unknown element. --Jayron32 16:14, 9 March 2013 (UTC)[reply]

Planck derived units

What is the difference between one Planck length per Planck time; and one Planck length per second? Isn't the latter one meaningful when describing quantum speed? Plasmic Physics (talk) 10:49, 9 March 2013 (UTC)[reply]

One Planck length per Planck time is simply another way of saying C: the speed of light in a vacuum. It is the equivalent of measuring speed in light-years per year. --Guy Macon (talk) 14:25, 9 March 2013 (UTC)[reply]

So, one is the fastest speed, and the other is the slowest measureable speed? Plasmic Physics (talk) 21:47, 9 March 2013 (UTC)[reply]

The latter is not the slowest measurable speed. It can't be, because the second is a human invention, and there's no reason for the universe to depend it. Since momentum is not quantized, there's no such thing as a slowest speed. --140.180.243.114 (talk) 21:53, 9 March 2013 (UTC)[reply]

Note, I adjectived 'measureable'. Plasmic Physics (talk) 22:01, 9 March 2013 (UTC)[reply]

It's important not to get hung up on the Planck units as imposing some sort of limitation on physical phenomena. The Planck mass is a perfectly ordinary macroscopic mass, well within the measurement capabilities of, if not a set of kitchen scales, certainly a cheap education-grade analytical balance. Nothing special happens at that mass - it's not a lower or upper limit to anything. The Planck length and Planck time are outside the range of (practically) measureable quantities, but they have no special significance otherwise. Tevildo (talk) 22:51, 9 March 2013 (UTC)[reply]

The Answer to "Relaxing Voices"

This is from January 2011; my original question was deleted because it was too "medical" sounding, and my follow-up question was therefore poorly explained on my part because I didn't want it removed. Anyway, from this thread: "Why do some voices, e.g., Bob Ross's, cause people to relax? I've read on other forums that people will watch his show to help them fall asleep." I didn't know how else to explain this. well just now, some random video on YouTube was being pushed on me ("featured"?), so finally I watched it and I noticed all these "ASMR" videos that seem to be a thing now. I Googled ASMR and it took me to Autonomous sensory meridian response—that's precisely what I've been looking for for decades (long before people discovered this on the Internet). It's a "dizzy" feeling one experiences when certain individuals talk quietly.Reflectionsinglass (talk) 11:59, 9 March 2013 (UTC)[reply]

You should look at Bitching Betty. Shadowjams (talk) 12:33, 9 March 2013 (UTC)[reply]

Venus flytrap and meteors

Is it true that following meteor impacts, large numbers of venus flytraps can often be found growing around the craters and no-one is really sure how they got there? And that their main habitat is located near what was once a crater left by a huge meteor strike from millions of years ago? — Preceding unsigned comment added by 87.113.139.192 (talk) 17:41, 9 March 2013 (UTC)[reply]

Carnivorous plants typically grow where the soil is missing some needed nutrient, which they then get from whatever they digest. I suppose the area where a meteor has struck might be depleted in some nutrients, if it blew away the topsoil. This would make it difficult for normal plants to grow there, but the Venus flytrap could survive. StuRat (talk) 17:56, 9 March 2013 (UTC)[reply]

However, none of that answers the question about venus flytraps being mysteriously co-located with impact craters. The answer to that question is firmly "no". Flytraps are native (only) to the Carolinas, which are not notable impact basins, and are not natively found elsewhere. — Lomn 18:04, 9 March 2013 (UTC)[reply]

I think we need to link to Little Shop of Horrors. Rmhermen (talk) 20:18, 9 March 2013 (UTC)[reply]

March 10

Social interaction and levels of cognitive activity

I read an interview with French neurologist Pierre Bustany that neural activity was greatly heightened in social interaction, much more than, say, when doing a crossword. The conclusion was that social interaction is much better for the mind than puzzle solving. That last part may be obvious anyway, but I'm not so curious about that - I just want to know if anyone can point me to any interesting references (books or key papers) that establish the claim about the level of neural activity/ excitement in social interaction, especially compared to puzzles/ games/ etc. Thanks in advance, IBE (talk) 02:09, 10 March 2013 (UTC)[reply]

The entire concept of doing a brain scan, then assuming, because glucose is being used in many areas of the brain, that that somehow indicates more thought is occurring, seems like a stretch, to me. I suspect that glucose is used for other things, too, like repairing damage. Or, even when it does indicate brain cells "working", it's not necessarily useful thinking. For example, an epileptic seizure probably lights up the scan, but this doesn't indicate that quality thought is occurring. StuRat (talk) 02:51, 10 March 2013 (UTC)[reply]

No worries, and by all means point me to a reference on this line of thinking. It's for a PhD lit review, although there is only a marginal chance I'll be able to squeeze it all in anyway. Totally peripheral aspect, but I like to paint a broad picture, even at the risk of sounding frightfully amateurish. IBE (talk) 03:26, 10 March 2013 (UTC)[reply]

I'm skeptical of that statement, and it doesn't seem to be a topic that he has actually worked on. As far as I know the greatest difference in brain activity is between sleep and waking, and across the range of normal waking states the variations in activity level are pretty limited. Also as far as I can see the literature, such as PMID 18381770, does not give any support, although of course there are specific brain areas that are activated by social cognition. Looie496 (talk) 03:59, 10 March 2013 (UTC)[reply]

I think you're right that he hasn't worked on this area, or at least my own googling says it isn't his primary field at all. I was under the impression it was something that was maybe generally well known, but you have convinced me otherwise. At any rate, it isn't going in the "lit" review ;) IBE (talk) 04:32, 10 March 2013 (UTC)[reply]

I highly doubt that any non-crackpot neurologist would draw a conclusion like "social interaction is much better for the mind", as if the mind were a monolithic entity instead of a collection of interacting components with different functions. That simply doesn't follow from "more brain areas are active". --140.180.243.114 (talk) 08:42, 10 March 2013 (UTC)[reply]

It turns out I've overstated it slightly. I was just looking for a paper on it, and assuming it was some well known thing, so I wasn't too precise about it. The full quote is this (French with my Fr-2 translation, interview in Ca M'Interesse, Jun 2012):

Les cablages formes dans la jeunesse sont-ils effectifs toute la vie?

Ces associations de neurones se maintiennent a peu pres vingt ans. Apres, si elles ne sont pas utilisees, elles disparaissent.

......

Comment eviter cette impasse?

Il faut stimuler son cerveau a toute age. Pour cela, rien de mieux que les relations sociales. Avoir des contacts avec les autres impose de devoir discuter, echanger, decrypter les non-dits, les gestes, les hesitations...Et aussi d'anticiper, de s'organiser pour arriver a l'heure a un rendezvous. Tout cela met en jeu des reseaux de neurones differents. Bien plus nombreux que lorsque vous faites des mot croises! Rien de pire, a la retraite, que de quitter le lieu ou l'on a toujours vecu pour se retirer sur la Cote ou l'on ne connait personne. C'est l'atrophie cerebrale assuree.

My translation:

Are the neuronal connections formed in our youth effective throughout the lifespan?

These connections last for about 20 years. After that, if they are not used, they disappear.

How do you avoid this?

One must stimulate one's brain throughout one's whole life. For that, nothing is better than social relationships. Social contact imposes the need to discuss, interact, and interpret non-verbal cues...And also to anticipate, to prepare oneself to arrive on time for a meeting. All this activates a variety of networks of neurons. Many more than when you do a crossword puzzle! There is nothing worse, upon retirement, that leaving the place where you have always lived, to retire to the Cote (d'Azure?) where you know no one. That is guaranteed to produce cerebral atrophy.

So I had overstated it, partly from trying to weave it into my own knowledge/ interests. Does it sound more reasonable in this form? IBE (talk) 18:12, 10 March 2013 (UTC)[reply]

Can plants grow on lunar soil given enough water and air?

--Inspector (talk) 04:33, 10 March 2013 (UTC)[reply]

No, because lunar soil has no organic matter, and therefore no nutrients needed for growth. See [11]. In fact, even on Earth, plants will die if the concentrations of the 6 macronutrients and 8 micronutrients are too high or too low, or if the soil is too coarse/tight, or if the soil PH is too low or high.

It is possible to grow plants on the Moon if you provide the required nutrients, using hydroponics. If you plan to do that, you might as well ditch the soil, because it doesn't help. --140.180.243.114 (talk) 08:35, 10 March 2013 (UTC)[reply]

This appears to disagree with the above. --Guy Macon (talk) 09:04, 10 March 2013 (UTC)[reply]

In that experiment they added bacteria to the lunar soil simulant, which by the looks of it leached nutrients from the rock. It notes that the plants "fared very badly" in neat soil simulant. Fgf10 (talk) 09:37, 10 March 2013 (UTC)[reply]

Also lunar night is too long (354 hours). This makes moon unsuitable for Earth's plant life. --PlanetEditor (talk) 08:45, 10 March 2013 (UTC)[reply]

The OP may find the Soil article useful. ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:02, 10 March 2013 (UTC)[reply]

What is happening here?

what is happening here?112.209.165.87 (talk) 11:29, 10 March 2013 (UTC)[reply]

It's an electric fence. The first four people are insulated from the ground, so don't get shocked. As soon as the last guy joins the chain, a connection is made to earth, current flows, and everybody gets zapped. Rojomoke (talk) 13:25, 10 March 2013 (UTC)[reply]

inactive ingredients (excipients) in prescription and otc drugs

I have a question not writing an article: individuals who have celiac disease or other sensitivities such as milk allergy such as myself find it very difficult without a physicians desk reference to determine what the binders are in drugs when they are being manufactured. When researching the drug Ultram for a friend I determined per the site www.ehow.com: (I am copying and pasting)"The starch ingredients in Ultram are used in the manufacturing process. Grain Processing Corporation indicates that various starches are used for thickening and binding applications as well as water absorption. Individuals with allergies could have an adverse reaction to tablets containing starches. One example is patients with celiac disease, an allergy to gluten that results in intestinal inflammation. According to Steven Plogsted, clinical pharmacist, the U.S. Food and Drug Administration is not as strict about inactive ingredients, called excipients. They dictate which ingredients may be used but do not stipulate the quantity and type. Lactose, milk sugar and microcrystalline cellulose from fibrous plants are also used as filler." I cannot find any information on wikipedia any information re excipients in any drugs or information re any binders. Can you suggest a better way for me to search your site for further information. Thank you. — Preceding unsigned comment added by 68.61.198.89 (talk) 14:16, 10 March 2013 (UTC)[reply]