Wikipedia:Reference desk/Archives/Science/2012 September 16

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September 16

So-called "stealth" aircraft

Why has the military been foolish enough to swallow aircraft marketers' claims that their aircraft are invisible to radar? Even if the aircraft is made totally invisible to active radar, there is no way to make it invisible to passive radar. Even if the aircraft has no radar equipment on board, it can still be detected by passive radar due to the radio waves generated by its onboard electronics. And, in any case, no manufacturer in his or her right mind would design an aircraft with no onboard radar, as such an aircraft would be totally blind. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 00:35, 16 September 2012 (UTC)

Have you read our policy on not asking for opinions or starting debates? Do you have a source that backs up your claims that marketers claim "that their aircraft are invisible to radar?" Do we need to ask you formally not to contribute such nonsense? Have you even read Stealth Bomber#Stealth? Is there any reason this should not be marked closed? μηδείς (talk) 00:58, 16 September 2012 (UTC)

The military has never simply swallowed such claims. In the case of the F-117 for instance, the military required each participant in the competition that lead to its creation to submit a model for radar testing, described briefly in Lockheed Have Blue#Experimental Survival Testbed. Our articles on the Northrop Grumman B-2 Spirit and the F-22 don't describe the selection process, but I assume radar testing was involved. The military also required flight tests of aircraft at various stages of the pre-production process, and following the aircraft with radar would have been a natural part of that process. And you're wrong on your last point. The F-117 stealth fighter has no active radar, described at Lockheed F-117 Nighthawk#Design. But it seems to work nonetheless. Six F-117s and two prototypes were lost in accidents, which is kind of pitiful when only 64 were ever built, but only one was ever lost in combat. Someguy1221 (talk) 01:07, 16 September 2012 (UTC)

As far as alternatives to using active radar, they can get info broadcast to them from ship or ground radar, AWACs, satellites, other (non-stealth planes), UAVs, etc. StuRat (talk) 01:15, 16 September 2012 (UTC)

As a methodological note, when you find yourself thinking that you're smarter than the people who build actual stealth bombers, you may wish to question your hubris, or at leasts do a little more research. Either you're wrong or they're wrong. I suspect you're wrong. --Mr.98 (talk) 02:36, 16 September 2012 (UTC)

However, the US military acquisition process is susceptible to influence peddling, sometimes resulting in rather unwise multi-billion dollar defense contracts. StuRat (talk) 02:43, 16 September 2012 (UTC)

The greatest influence peddling over military acquisitions that I'm aware of is actually coming from congressional representatives seeking pork for their state, rather than manufacturers trying to get their products purchased. This is the case, for instance, with the Boeing C-17 Globemaster III (see the "orders and deliveries" section), where congress consistently orders more planes even though the Air Force has stated they don't need any. It's a wonderful plane, however. As far as compromising actual quality, there was also a New York Times article years back, can't remember the exact link, that was criticizing the process by which the Federal Government chose where to build the Navy's ships. Rather than having manufacturers compete for contracts based on price and quality, congress was simply handing the contracts out to benefit the home states of whoever was on the relevant committees. There have certainly been some boneheaded decisions by the military in the past, but I don't think corruption had anything to do with it. The problems documented in the comical but allegedly accurate The Pentagon Wars can be blamed entirely on Generals' being unrealistic (at least that's the accusation). Going back to WWII, the Mark 14 torpedo didn't work as advertised, and in fact the Navy never tested the final product, but ordered it for the entire fleet nonetheless. More examples of simply boneheaded ideas can be found, largely centered on skepticism over repeating rifle technology, if you go back to the eras of the Spanish American war and the American Civil War. But my point is, the military does not need corruption to help them make bad decisions. Someguy1221 (talk) 03:11, 16 September 2012 (UTC)

I would classify pork-barrel projects as a form of corruption. StuRat (talk) 03:58, 16 September 2012 (UTC)

So the modern-day U.S. military is a hive of corrupt boneheads? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 05:14, 16 September 2012 (UTC)

I don't think so. You will find stupidity wherever you look, and shouldn't take a few examples as evidence of a larger problem. Congress is a hive of corrupt boneheads. Someguy1221 (talk) 05:18, 16 September 2012 (UTC)

You are wrong when you say that an aircraft without radar would be wrong. You can have an electronic map and use it to navigate. Second point: how does say this aircraft is sold as such? It is presented to the tax paying citizens as such, but operators are surely quite aware of its capabilities. OsmanRF34 (talk) 20:24, 16 September 2012 (UTC)

Should also keep in mind that on-board radar was only developed in the 1940s, but planes were flying just fine for decades prior. See Radar in World War II#Centimetric. Someguy1221 (talk) 21:42, 16 September 2012 (UTC)

Chirality in spiders

Recently I observed a spider spinning a vertical orb-type web. I noticed that while it was laying the concentric strands, it moved in a clockwise direction (from its perspective relative to the plane of the web) and consistently used its right leg to hook the silk onto the long radial strands. Do spiders in general display a preference one way or another for clockwise or widdershins movement, or for one leg over another? If so, which way? 71.248.115.187 (talk) 01:32, 16 September 2012 (UTC)

Is Chirality the Chirality you're talking about? ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:48, 16 September 2012 (UTC)

Yeah, he just means handedness; that is directionality: clockwise and counterclockwise are chiral directions. I did some searching, and this Google Scholar search turns up lots of results. There doesn't appear to be any general trends among orb-weaver spiders, from what I can see from those searches many spiders build their web in alternating directions: first clockwise and then return counterclockise; though others work in spirals, either clockwise or counterclockwise. Scanning several of the abstracts, I can't find any general trends, but if you're more interested, perhaps that search could aid you in finding more information. --Jayron32 03:03, 16 September 2012 (UTC)

This is really what biologists would call laterality. This paper from 2002 describes a lateralized behavior in a species of spider. The Introduction states that the authors were not aware of any other report of lateralization in arachnids. If anything had been published in the meantime, I expect that it would have cited this paper, but Google Scholar shows nothing that does. In short, it is plausible but apparently nobody has looked into it. Looie496 (talk) 03:02, 16 September 2012 (UTC)

Cavitating bubbles party trick

Re: http://www.youtube.com/watch?v=cOeNxkksruo&feature=related

I'm pretty sure I understand the physics behind this. But at the beginning of the video, they mention that there has to be a fair bit of air at the top of the bottle, and I'm wondering why this is. As far as I can tell it shouldn't matter, but I've seen another video saying the same thing. 65.92.7.148 (talk) 02:09, 16 September 2012 (UTC)

Here's a description of what's happening at Discovery.com. The way I would describe it myself is that the water is in effect stretched away from the bottom (and hence it needs the compressible space of the air above to move into) and then violently bouncing back against the bottom. Without the space above, the liquid would have no where to move into, away from the bottom. μηδείς (talk) 02:36, 16 September 2012 (UTC)

The air gap is needed to give the water someplace to go. Since air is far more compressible than water, the air becomes compressed at the top while the water moves upward (relative to the bottle), and cavitation bubbles form at the bottom. StuRat (talk) 02:41, 16 September 2012 (UTC)

sondern lasst uns angenehmere anstimmen, und zitatlosere? μηδείς (talk) 03:53, 16 September 2012 (UTC)

No, Fawlty! It's: Alle Menschen werden Brüder, wo dein sanfter Flügel weilt. [JackofOz]

That's a quote from a famous Sci-Fi film: Plan Ninth from Outer Space. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:52, 16 September 2012 (UTC)

Later used as the theme music for the TV show Gunfight at the OK Choral. -- ♬ Jack of Oz ♬ ^{[your turn]} 05:45, 16 September 2012 (UTC)

We're probably sickening the readers with all this trivia. Some of them might even Earp. Ya know, Old Ludwig's sanity was always fragile, but after he finished the first movement of the Ninth he went scherzoid. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:01, 16 September 2012 (UTC)

Well, blame the writer of the first bit, whatever it means. Oh, I see they've signed their name now. Are you gonna let us into the secret, Medeis? -- ♬ Jack of Oz ♬ ^{[your turn]} 07:25, 16 September 2012 (UTC)

Figure out what I have changed in the German and how that comment then applies to the comparison of the two posts above it. μηδείς (talk) 18:17, 16 September 2012 (UTC)

I assume the idea is that the air space means that first you move the bottle, while the liquid stays more or less still; then the liquid hits the top of the bottle and is also jolted into motion; then the bottle stops (because you're pulling back on it) and as a result the liquid has a chance to be fast moving and slam into and break the bottom of the bottle. Wnt (talk) 04:08, 16 September 2012 (UTC)

If the top of the bottle were hitting the liquid that hard, the top would break. What's really happening is that the water never loses contact with the bottom. Rather, in effect, it "stretches" so much that it cavitates, giving a very strong vacuum at the bottom and a much larger compressed area at the top. The net change in pressure per volume is necessarily equal above and below. But the air volume above is greater so the change in pressure it experiences is less. The cavitated volume is much, much less, so the relevant pressure is much greater, causing the "stretched" water to slam back down into it with much greater force. Effectively almost all the force of the blow is focused downward, while the air above acts like a shock absorber. μηδείς (talk) 04:20, 16 September 2012 (UTC)

I'm thinking that when the hand strikes the top of the bottle, it starts a pressure wave that travels down through bottle and then is "reflected" off the bottom into the liquid. When the pressure transfers from the bottom of the bottle to the liquid, it causes some of the liquid to separate from the glass, resulting in discrete cavities. When these cavities refill with liquid, the force that had been distributed over the bottom of the glass is focused into a few small bubbles, creating sufficient pressure to break the glass.

I'm not sure if the air space at the top is to allow the liquid to travel upwards off the bottom - the hand is probably compressible enough to allow this. I think the air space is to ensure that the pressure wave travels down to the bottom through the glass and not the liquid. It might also be to prevent the same cavitation breakage from happening at the top, which would lead to a cut hand.--Wikimedes (talk) 04:55, 16 September 2012 (UTC)

The video is actually quite clear on this. The bottle doesn't break due to the initial downward blow, and it won't break if you don't remove some liquid from the top, since the cavitation won't occur, there being no space for the all but incompressible liquid to move into. The cavities don't so much refill with liquid as recompress. A relative of mine started as a pipe fitter by trade and ended building nuclear plants and oil pipelines. Cavitation shock is a favorite subject of discussion, actually. μηδείς (talk) 18:13, 16 September 2012 (UTC)

"The net change in pressure per volume is necessarily equal above and below." Sorry, but you could you explain this in a little bit more detail? I don't really understand. 65.92.7.148 (talk) 22:23, 16 September 2012 (UTC)

Yeah, there are two bodies of gas, the air at the top of the bottle and the cavitated bubbles at the bottom. By the gas laws, at a constant temperature, the pressure times the volume must be a constant (PV=nRT). The lowered pressure of the bubbles at the bottom, times their volume, has to equally offset the raised pressure of the air at the top, times its volume. (Water is basically incompressible, so neither the volume of the bottle or the water will change, requiring the total pressure to remain constant.) Hence, if the air at the top has 100 times the volume of the bubbles at the bottom (watch the video, the bubbles are quite small) its change in pressure will only be 100th the change in pressure of the bubbles. When those bubbles collapse, they will do so with much more violence in a small space than the expanding air at the top, shocking the glass and breaking it at the bottom as the water "snaps back" into place, knocking the bottom off the bottle. μηδείς (talk) 00:15, 17 September 2012 (UTC)

It sounds like you're saying that if the bubbles were infinitely small they could generate infinite amounts of force. Though I think you may have a point that the irregular pattern of the bubbles leads to localized excesses in the force as the water descends, I think the math must work differently than that... Wnt (talk) 16:07, 17 September 2012 (UTC)

The bubbles aren't really generating a force, it is the reexpansion of the air above that drives the water back downward. There's no bubble size x force = constant equation implying infinite force at infinitesimal size, but rather (negative pressure x volume of bubbles) + (pressure x volume of air) = 0 which means the bubble "force" could only be infinite if the air pressure at the top were infinite. Obviously thats not what's going on.

Consider a thought experiment. Fill a bottle 2/3 of the way with ball bearings and strike it as is done in the video. The bottle will travel downward faster than the ball bearings, which will stay in place due to inertia. The balls will then fall back to the bottom, potentially breaking the bottom off the bottle. This is pretty much what's going on with the liquid filled body, except that with the ball bearings, air flows freely around then and they all move upwards, freely separating from the bottom of the bottle. When the bearings fall back down, it is gravity drawing them downward.

In the case of the liquid filled bottle, the liquid cannot freely separate from the bottom of the bottle, because the air cannot flow freely in to fill that space. The air above has to compress, since it has nowhere to go either, it cannot flow down around the water molecules the way it flows around the ball bearings. Likewise, the body of liquid is in effect stretched apart as if it were elastic, and the cavitation occurs where the water "breaks" when it is torn apart. The liquid below the cavitation actually stays in place, because it cannot separate from the surface of the glass, while all the ball bearings fly upward, since they are not bound to the glass and air can flow freely past them.

Simplifying a bit, in the case of the ball bearings, it is their crashing weight that breaks the bottle. In the case of the liquid, it is the rebound of the blow itself, perfectly conserved, in accord with the gas law, that breaks the bottle, not the weight of the water. μηδείς (talk) 17:54, 17 September 2012 (UTC)

Intelligence and reproduction

Why do smart people reproduce less than other people? --128.42.223.7 (talk) 05:07, 16 September 2012 (UTC)

Because of the KCM principle - Kids Cost Money. Ratbone124.182.32.79 (talk) 05:10, 16 September 2012 (UTC)

Isn't it evolutionarily harmful? --168.7.232.115 (talk) 05:15, 16 September 2012 (UTC)

[Note that both IP's are from Houston] Are you asking whether the percentage of morons in the world is continually increasing? ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:21, 16 September 2012 (UTC)

There is a solution to this problem. Clarityfiend (talk) 05:48, 16 September 2012 (UTC)

Wikipedia has an article on fertility and intelligence. I can't vouch for its quality, but it has a lot of references... -- BenRG (talk) 05:22, 16 September 2012 (UTC)

It really has nothing to do with fertility - it has to do with personal choices... which, I can virtually guarantee you, have nothing whatsoever to do with concerns about evolutionary harm. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:24, 16 September 2012 (UTC)

"Fertility" in that article refers to the number of children people actually have at a given age, not some theoretical capacity to have children, which would presumably be impossible to measure. -- BenRG (talk) 23:47, 16 September 2012 (UTC)

There is a correlation between the education of women and the number of children they have. See for example this paper and this paper. So it appears to be education that is the key rather than intelligence to reproduction. --TammyMoet (talk) 10:30, 16 September 2012 (UTC)

Perhaps they have other things to do, or are less successful in their attempts?Smallman12q (talk) 13:01, 16 September 2012 (UTC)

A movie called Idiocracy approached this issue with surprising accuracy. Vespine (talk) 22:54, 16 September 2012 (UTC)

Oddly enough, the same basic plot element was used at around the same time for the movie Wall-E. --Jayron32 04:01, 17 September 2012 (UTC)

Indeed; "Bed is the poor man's opera" http://wiki.answers.com/Q/What_does_Bed_is_the_poor_man's_opera_mean .Gzuckier (talk) 04:28, 17 September 2012 (UTC)

Three Sisters

We unexpectedly acquired 4 cats back in June. A very pregnant mother made her way into our garden shed and delivered 3 kittens, all females. We fed them, they decided to stay, and that was that. The mother's since been run over or returned whence she came or been eaten by wandering behemoths (or beastorns), but the three kids are still with us.

One has always been noticeably larger than the other two. She's got sandy/lion colouring, while the smaller ones are grey/dappled. My partner is convinced she was the first born. He says the first born comes out about half an hour before the others, has no competition for milk, and has a better headstart in life. He knows a lot more about animals than I do, but my gut tells me that the relative sizes of animals in a litter has nothing to do with birth order. I mean, on Day 1, she was already bigger. That surely must have been determined way back at conception, and can't be attributed to the transitory benefits of being born first.

We'll never know for absolute certain, but is there a reasonable likelihood he's right about this? Thank you.

Btw, I thought you'd like to know that I see myself in the Uncle Vanya role, so I've named them collectively the Three Sisters, and individually Tolstoy, Pushkin, and Frankie (because she has beautiful blue eyes). All male names for female creatures. Purrfect. -- ♬ Jack of Oz ♬ ^{[your turn]} 06:56, 16 September 2012 (UTC)

The birth order can't determine size, but perhaps size could determine birth order. The runt of the litter is renowned for coming out last, so perhaps the Goliath also can come out first ? What was the coloration of the mother ? And did you see a male lynx creeping around ? :-) StuRat (talk) 07:11, 16 September 2012 (UTC)

Googling for runt litter born last finds a lot of people saying there is no relation between order of birth and being the smallest of the litter. 88.112.47.131 (talk) 07:42, 16 September 2012 (UTC)

Cats are subject to superfecundation. The story behind your litter is that your ginger kitten is most likely the product of a different father to the other two, and she gets her colouring and size from the father. Apparently cats can "collect" fetuses over a period of time from different fathers. They all get born at the same time though. I once had a cat who was the runt of the litter, and the vet told me all about this when we adopted him and took him for a check up. Cats fertility is a fascinating subject. By the way, get them all spayed at about 4 months old, won't you? They can reproduce astoundingly quickly. --TammyMoet (talk) 10:25, 16 September 2012 (UTC)

Ah, that has the ring of truth to it. This ginger Tolstoy also has a markedly different personality to the smaller two; much more timid, extremely evasive, only comes anywhere near us when it's feeding time, and hardly ever plays with the other two, while they spend all day playing with each other. But they're all timid. None of them like to be touched, which is something we've hardly managed to do to any of them in 3 months. We thought of giving them to the RSPCA, but they required us to bring them in, which is a tough call when they're virtually uncatchable. You're probably wondering how we know their sexes if we've had almost no physical contact with them. Our plan was to give them to a good home, and we spread the word. One person came around, claiming to be an experienced cat catcher. He caught them, thoroughly traumatised them in the process, discovered they were all females, then said he only wanted a male. The legacy is 3 very skittish animals who distrust us totally, except for feeding time. They are all v-e-r-y gradually learning that we're not threats. Yes, we are aware that they mature sexually quickly, and time is getting on. Thanks, Tammy. -- ♬ Jack of Oz ♬ ^{[your turn]} 12:26, 16 September 2012 (UTC)

Back to my question. I'm getting that, without direct observation of the birth, it's not possible to tell which cat was first-born. Correct? -- ♬ Jack of Oz ♬ ^{[your turn]} 12:26, 16 September 2012 (UTC)

Yep, I think you're right Jack. And you were right not to go russian to conclusions! Richard Avery (talk) 13:13, 16 September 2012 (UTC)

Give that man a pirozhok and a blin to sustain him on the weary lonely road ahead.  :) -- ♬ Jack of Oz ♬ ^{[your turn]} 21:53, 16 September 2012 (UTC)

Yes I think you're right about the order of the birth. Here in the UK, my vet will hire out traps (as will Cats Protection League) and you can leave food in the traps which will then shut on the cat when they are inside eating. Maybe if you approach a local vet, or a different organisation, they can help you trap them and maybe take them in if you'd prefer. --TammyMoet (talk) 14:57, 16 September 2012 (UTC)

Such a trap might work on the first kitten, but wouldn't the other 2 see the trap spring, and stay the heck away ? StuRat (talk) 17:40, 16 September 2012 (UTC)

If you are feeding them regularly it should work, but possibly over a period of time rather than all at once. It's how the professionals do it. --TammyMoet (talk) 18:59, 16 September 2012 (UTC)

Did you not - long ago - mention you were born (also long ago) in Katoomba? Calling them the three sisters may have little to do with the Prozorovas. --Cookatoo.ergo.ZooM (talk) 18:32, 16 September 2012 (UTC)

Enough with the "long ago"s.  :) But wow, what a memory, and what an almost spooky connection, one that hadn't occurred to me! No, I never claimed to have been born in Cat Katoomba. I was born in Albury, or so I'm told (I wasn't there, except by definition). But I have very good reason to believe I was conceived in Katoomba. My parents had a holiday there to celebrate their 2nd wedding anniversary. I was born 9 months and 5 days after that happy event, so ... I guess I should now rename the cats Meehni, Wimlah and Gunnedoo, but I prefer my names. -- ♬ Jack of Oz ♬ ^{[your turn]} 21:53, 16 September 2012 (UTC)

So, where have you posted the pix? —Tamfang (talk) 22:09, 16 September 2012 (UTC)

On my Facebook page. Just look up Murgatroyd Seraphicus Smith.  :) -- ♬ Jack of Oz ♬ ^{[your turn]} 00:21, 17 September 2012 (UTC)

Cute, Jack. How did you get the orangey one to stay in that pose? ;>)Bielle (talk) 00:45, 17 September 2012 (UTC)

A purely serendipitous and fleeting confluence of events, over which we had no control. A split-second later would have been too late. -- ♬ Jack of Oz ♬ ^{[your turn]} 01:37, 17 September 2012 (UTC)

I took home two cats from the local animal rescue centre earlier this year. We were told they are sisters, and they look very alike except for the fact that one was larger than the other. Coming from the rescue, they were on the skinny side, so it wasn't much of a difference. It was only after they'd settled in after 3 months or so that they put on weight and the size difference became much more noticable. The larger cat is more bold & friendly, the smaller cat more shy & timid (although just as friendly when here sister is not around). 5 months down the line, I'd feeding them both in the morning as usual, and instead of going off to get ready for work, I hang around with a coffee. I watch the smaller cat eat quite slowly. I watch the bigger cat next to her, eat quite quickly and finish her food first. The bigger cat then barges the smaller cat out of the way and eats the rest of her food too. I watch this for a few days to confirm my suspicions - sure enough, the larger, bolder cat is eating 1.5 bowls of food every meal time, and the smaller, timid cat is getting 0.5 bowls of food every meal time. My solution was to lock the cats in seperate rooms during meal times and open the doors again when they're done. Sure enough, the smaller cat has put on a lot of weight, and the larger cat isn't so tubby. As an interesting aside, these two cats are the best hunters of all the cats I've owned and they bring in around 5 dead animals per day (unfortunate for the vegetarian wife, who's lucky enough to clean up these "presents" when she gets home from work)- anyway, after discovering the mealtime habits, I also realised the smaller, timid cat is the better hunter and eats most of her prey instead of giving it as a present to the wife. I'm guessing she was topping up her 0.5 bowl with the mice/rats/shrews/moles/bats/rabbitts/squirrels/birds in our garden. Thanks for reading this so far, just thought I'd add my experience with cat personalities vs feeding habits vs hunting habits. Might be worth keeping an eye on your cats during feeding to see if the larger one gets the (fe)lions share of the food.

Thanks. If anything, the biggest cat eats the least. The runt is always, always the first on the scene when the food comes out, and gets stuck straight in. The middle one turns up next, and Tolstoy, the biggest but by far the scarediest, is last. They always leave food, and they all come back later and graze when there's no competition. There's no question of their being underfed. What they eat outside of formal meal times is anyone's guess; they scavenge the compost heap, and are always on the lookout for mice, birds, insects etc. When the mother was still with us, she brought home a rabbit and a rat one day and dumped their bleeding carcasses on the back doorstop, leaving what seems to be a permanent stain on the wooden patio. No such events have occurred since she's skipped town. -- ♬ Jack of Oz ♬ ^{[your turn]} 21:30, 20 September 2012 (UTC)

Barium Wiki page

Would these be good references to the barium, and maybe chemtrails wiki pages.

Patent Title: "ROCKET HAVING BARIUM RELEASE SYSTEM TO CREATION ION CLOUDS IN THE UPPER ATMOSPHERE" http://www.sciechimiche.org/scie_chimiche/images/stories/Download/usp_3813875.pdf Test by NASA Referenced in the Patent http://naca.larc.nasa.gov/search.jsp?R=19690026282&qs=Ns%3DLoaded-Date%7C0%26N%3D4294885036

It seems the patent falls under the weapon category, mentioned as "chemtrails" in the Space Reservation Act 2001. Space Reservation Act 2001: http://www.fas.org/sgp/congress/2001/hr2977.html — Preceding unsigned comment added by 87.63.80.234 (talk) 09:19, 16 September 2012 (UTC)

Distribution of translational and rotational kinetic energy in a gas

If I understand correctly the Kinetic Theory of Gasses with respect to thermal capacity / specific heat, it works as follows. The molar specific heat at constant volume, C_V is given by:

C_V = 0.5 N_F N_A k_B

where N_F is the number of degrees or freedom;

N_A is Avagrado's number, the number of molecules in one mole of gas;

k_B is Botzman's constant, essentially relating kinetic energy to the temperature for one molecule.

For a monatomic gas (eg He), the possible degrees of freedom is three, as each molecule/atom can go flying about in three translational dimensions. For a diatomic molecule (eg O₂) there are two additional degrees of freedom, as kinetic energy can be stored by rotating the molecule about two orthogonal axes at right angles to its length. For more complex molecules, additional kinetic energy can be usually be stored by rotating about all three axes, as such molecules will usually not be symmetrical about any axis. I think this is right so far - am I? In an unreacting homogenous quantity of gas, how much energy is stored in any one molecule in any one degree of freedom (translational, and rotational as is possible for the molecule) is random. However, over the whole quantity of gas, the root mean square of all three translational axes will be a constant depending on the molecular mass and the temperature. Similarly for the rotational axes, if any. However, over the whole quantity of gas, the sum of kinetic energy for each translational and rotational axis will be the same. Is this correct? Fo any given molecule, at temperature too low to stretch bonds, there will be a random allocation of energy between translational and rotational? So some molecules will be moving fast and rotating slow, and others moving slow and rotating fast? (and some slow and slow, and some fast and fast) No textbook or internet site I've looked at actually says this. Floda121.221.80.195 (talk) 13:05, 16 September 2012

Yes, you are right basically. Ruslik_Zero 11:38, 17 September 2012 (UTC) (UTC)

sound to electrical energy conversion (part 2)

i just asked a ques. related to same topic... i.e.sound is a form of energy. each day we speak a lot i.e we waste a lot of energy. i want to use this energy. as well as there is a lot of noise in surrounding. how can we utilize this? atleast we can charge our cell phone. so, how can i convert this energy into electrical energy? http://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Science#sound_to_electrical_energy_conversion in fact, the answer was quit satisfactory. but can't we use microphone or some transducer like balanced transducers for this purpose. the main fact of answer was, as Hcobb (talk), the energy of sound is 10-12 w/m2. (Compare with the roughly one kilowatt per meter squared of sunlight). so how do we use microphones for sound to electrical energy conversion. — Preceding unsigned comment added by 14.102.26.13 (talk) 14:30, 16 September 2012 (UTC)

The ouput of even the most efficient microphones designed for speech & music purposes is of the order of 110 picowatts with close talking - output with typical ambient noise is even less. Contrast that with the radio frequency output of a handheld cellphone, 200 millwatts, 2,000,000 times greater. That's why your cellphone MUST run on a battery. Or contrast it with a small torch globe - around 3V at 300mA: around 1 watt, 10 million times greater. You could build a very large microphone - with a bigger "capture" area, you could get more output. Let's say you make a microphone with a diapharm 1 m² in area - that's an immense microphone, having a diaphram about 10,000 times bigger than a standard balanced armature phone type (about 30 mm diameter). The associated magnet would need to weigh 100's of kg. You'd still only get around 0.01 watts. As you were informed in your previous question, the energy in typical sounds is just way way too small to be usable. Ratbone124.182.134.223 (talk) 14:55, 16 September 2012 (UTC)

An electronic amplifier with another power source is the answer. As long as the signal is enough to detect at all, and the signal-to-noise ratio is high enough, then it can be amplified to the point where it becomes usable. StuRat (talk) 17:34, 16 September 2012 (UTC)

So why bother with the amplifier and microphone? The OP wants energy - he might as well just use the power source directly. That will be a more efficient. Ratbone58.164.237.102 (talk) 00:06, 17 September 2012 (UTC)

I was answering as to how we can get enough energy from sound to make a microphone usable. I agree that trying to collect energy in this manner is not feasible. StuRat (talk) 03:09, 18 September 2012 (UTC)

I changed your question title to distinguish it from the last one. StuRat (talk) 17:35, 16 September 2012 (UTC)

Aha! I see the problem!

As hcobb said, sound intensity level is 10^-12 w/m². That means "10 to the power of negative 12 watts per square meter". Or 1 trillionth of a watt. Unfortunately, its not the same thing as 10-12 w/m² which would be quite a lot of power. Airplanes talk that loud, but _most people don't.--Robert Keiden (talk) 03:56, 17 September 2012 (UTC)

What does Unsexed mean?

i.e. [Betta splendens page on fishbase]
I kind of guess unsexed means 'no differences between the 2 sexes' but the male Betta is easily distinguishable from the female (brighter colors, larger fins). What's the deal? Ebaychatter0 (talk) 15:31, 16 September 2012 (UTC)

That word appears on the page in the context of the maximum length of the fish. It seems to say that the longest recorded individual was "male/unsexed". I think that's got to mean that no sexing was carried out on the fish beyond noting that it looked male. It links to a source [1], where you can download a book and, if you wish, search for "6.5 cm" in the context of "Betta splendens" to see if I'm right.  Card Zero  (talk) 16:14, 16 September 2012 (UTC)

Googling indicates that determining the sex of some fish is difficult / impossible prior to their sexual maturity (excluding DNA analysis) as there is no early sexual dimorphism. Juvenile fish are then described as "unsexed", as they may be males or females when mature. Essentially it seems to mean "we don´t know until they tell us". --Cookatoo.ergo.ZooM (talk) 18:11, 16 September 2012 (UTC)

The verb "to sex" can mean "to determine the sex of", so if something is "unsexed" it doesn't mean that it doesn't have a sex, it just means that the sex wasn't determined. See Chick sexing for a use of the verb "to sex" meaning "to determine the sex of". --Jayron32 18:44, 16 September 2012 (UTC)

Chick sexing. Another word combination nobody should ever try googling (Did you mean "Chick sexting"?), along with dating method and, if you can't beat that game, "Tiger Woods" cheats... - ¡Ouch! (^{hurt me} / _{more pain}) 06:54, 19 September 2012 (UTC)

ok, I think I understand now. It's still rather odd that the technician/scientist performing the measurement has to mention the word "Unsexed" for this particular species. The difference between the genders is like day and night. Ebaychatter0 (talk) 04:09, 18 September 2012 (UTC)

To unsex can also mean to make impotent, as in "She unsexed him with her contemptuous stare." But in this case it just means not having been sexed, as in Jayron's response. μηδείς (talk) 19:15, 16 September 2012 (UTC)

As a long married man, I have been frequently unsexed. Children will do that to you... --Jayron32 00:07, 17 September 2012 (UTC)

Gruoch reportedly asked to be unsexed, but I don't know that her request was meant literally, or actually granted. {The poster formerly known as 87.89.230.195} 84.21.143.150 (talk) 13:28, 17 September 2012 (UTC)

She meant she wanted to have the resolve of a man, not the mercy of a woman. See also hysteria.μηδείς (talk) 17:27, 17 September 2012 (UTC)

Resolved

Thank you all Ebaychatter0 (talk) 04:15, 18 September 2012 (UTC)

Blood vs sperm

Which of the following uses more energy -
blood cells formation or sperm formation? Sunny Singh (DAV) (talk) 15:40, 16 September 2012 (UTC)

There are all sorts of intutive reasons to believe sperm will be the higher energy drain. The body makes more blood, so probably does it more efficiently, the nuclei of red blood cells are recycled, sperm require mitosis and meiosis to be made, sperm need to be motile and carry power on board, and so on. A good work around is to compare the calories in each:

Human blood, 450 calories/500ml http://www.maynardlifeoutdoors.com/2010/09/calories-in-human-blood_15.html

Sperm 5-7 calories per (5 ml) teaspoon all sorts of "spam" links

so they are actually quite close at just under 1 cal/ml for blood and just over for sperm. I suspect that would be a bigger gap if we took all the variables into account. μηδείς (talk) 18:03, 16 September 2012 (UTC)

Lagrangian_mechanics#Pendulum_on_a_movable_support

I'm trying to get a hang of deriving Equations_of_motion with Lagrangian formulation. So I've tried to derive to pendulum with movable support. Unlike in the article Lagrangian_mechanics#Pendulum_on_a_movable_support I have allowed for motion of the support in y direction also. I ended up with (ignore the signs; my axes are different)(also ignored quite a lot product of small angles)

${\ddot {\theta }}=-(g+{\ddot {y}}).\theta -{\dot {y}}.{\dot {\theta }}-{\ddot {x}}$ I'm able resolve and justify the first and last terms. The middle term looks like some sort of viscous term which depends on the velocity of the system. I assume my results should be independent of velocity (assuming no drag/viscouds force/friction) since I'm doing stuff in inertial frame. Is it the coriolis term?

Here is my logic : Suppose the system was moving in y direction with uniform velocity. and I force a small velocity on the bob. Instead of going round and round in circles around the center (which itself is moving with unform velocity in y axis) it will now slowly come to some angle and stop. That doesn't seem very intuitive. Where is this (pseudo) drag coming from? Can you shed some light on this?

I assume that if there was a bob diametrically opposite to the existing pendulum (now center of mass of system will be on the support point in the middle) I would be able split my system into (1)translation of center of mass and (2)rotation around it and this term will then disappear(haven't tried it yet). Am I right? Cplusplusboy (talk) 18:15, 16 September 2012 (UTC)

Wavy paper

Looking at the books in my library from the side it appears that in some of them the paper appears wavy (corrugated?) with wavelength of about 2 cm or so. Why is that? Is it connected to the type of binding, the paper, humidity,... ? bamse (talk) 18:27, 16 September 2012 (UTC)

I have in my collection an omnibus edition of the Hitchikers Guide to the galaxy which has this effect after being fished out of a swimming pool so I can only presume the same effect (water spillage) has happened here.--Gilderien Chat|List of good deeds 18:41, 16 September 2012 (UTC)

Do you mean deckle edging, which can be much more wavy than sawtoothed as in the picture in the article? If so, it used to be a normal effect of the binding process and nowadays is an affectation of certain modern printings. μηδείς (talk) 19:12, 16 September 2012 (UTC)

I agree with Gilderien. Is it possible some amateur effort at conservation involved cleaning the books with water, which then warped in this fashion ? I wouldn't think it would be the result of humidity, as then you'd expect mold, too. Or are the people who check these books out just prone to dropping them in swimming pools ? StuRat (talk) 20:29, 16 September 2012 (UTC)

Thanks for the repleis. I don't mean deckle edging and no conservation effort has been involved either. It also happens in rather new books and more often with thin hardcover books. Compared to deckle edging, the wave goes in the perpendicular direction, i.e. each single sheet of paper is wavy along the longer side of the paper. bamse (talk) 21:27, 16 September 2012 (UTC)

In that case, I bet the paper was defective when delivered to the book binder. In the process of paper making, it comes out wet to begin with. A quality paper maker will ensure that the paper is fully flattened while drying, by running it through a series of rollers. However, it sounds like they might have let it dry without enough rollers, which will leave stresses in the paper later resulting in this type of warping. StuRat (talk) 23:09, 16 September 2012 (UTC)

Another possibility is that the book binder uses some type of water-based glue, which then wets the paper while the glue dries. In this case, I'd expect the warping to be worse near the binding, but this doesn't seem to match your symptoms. StuRat (talk) 23:10, 16 September 2012 (UTC)

In any case, you might want to tell a librarian, as they may be able to identify the book binder making the defective books, and demand better quality from them. StuRat (talk) 23:13, 16 September 2012 (UTC)

I have seen this often in heavy textbooks with very thin paper. I always assumed it had to do with improper drying after printing. μηδείς (talk) 02:11, 18 September 2012 (UTC)

I wouldn't expect a regular printed page to get very wet. A full page illustration, on the other hand, quite possibly could. StuRat (talk) 03:05, 18 September 2012 (UTC)

Purely anecdotal, but when I do see this it is almost always with very heavy thin-paged textbooks with glossy pages. μηδείς (talk) 18:28, 18 September 2012 (UTC)

Chemistry: How to remove H2O and impurities from an ammonium formate mixture?

When mixing 5.3 parts Ammonia (12%) and 1 part Formic Acid (85%) a mixture of Ammonium formate and Water is formed. NH3 + CH2O2 + H2O = CH5NO2 + H2O

Assuming the Ammonia residue evaporates completely from the mixture and by using slightly more ammonia (5.5 parts) that the Formic Acid residue will be very minimal. Which would be the best way to remove the H2O from the mixture? Distillation seems dangerous since heating it may form HCN and it may turn into formamide. Would Electrolysis be an option or are there other alternatives?

Thanks in advance for you suggestions 83.134.92.226 (talk) 18:47, 16 September 2012 (UTC)

Wikipedia contains a List of purification methods in chemistry, perhaps something there meets your needs. --Jayron32 18:50, 16 September 2012 (UTC)

If you want to remove water, try this: add excess pure ethanol to the mixture, followed by silica gell or an appropriate dessicator. The silica gell should remove all traces of water from the mixture, however the solute (predominantly ammonium formate) will need to be kept separate from the silica gell to facilitate the removal of the gell from the mixture. This can be accomplished by using a semipermeable membrane, such as occurs in reverse-osmosis. Plasmic Physics (talk) 03:22, 17 September 2012 (UTC)

Before you remove water, I suggest that you first address other impurities by fractional crystalisation, using water's property as a universal solvent. Plasmic Physics (talk) 03:44, 17 September 2012 (UTC)

The typical way to remove water from a solid is a Desiccator. If you have more delicate things that you need to remove water from (i.e. proteins) you can use lyophilisation, but that's probably unnecessary in this case. Common desicants are Calcium sulfate, or if you really want to go crazy, P2O5. Buddy431 (talk) 21:37, 17 September 2012 (UTC)

True, but the mixture post evaporation, will contain water of crystalisation. Plasmic Physics (talk) 23:40, 17 September 2012 (UTC)

You sure? From my cursory search, I haven't found anything about hydrated salts. I'll look a little harder this evening. Buddy431 (talk) 23:53, 17 September 2012 (UTC)

In a 1921 prep I found (JACS, 43, 1470, (1921)), they recrystallized ammonium formate from absolute alcohol, and then dried it in a vacuum desiccator over 99% sulfuric acid. They make it just by bubbling ammonia gas through 90% formic acid though, so they have a lot less water hanging around than you will. The salt's still pretty soluble in ethanol, but I bet you could use absolute isopropanol to precipitate out the salt, filter that, and then worry about drying that. Buddy431 (talk) 01:29, 18 September 2012 (UTC)

"You" as in me, or as in the OP? Plasmic Physics (talk) 22:15, 20 September 2012 (UTC)

Whoever wants to make ammonium formate with aqueous ammonia. Buddy431 (talk) 00:21, 21 September 2012 (UTC)

Is the method you propose more effective than my method? I'm asking because that seems counterintuitive to me - your method air dries it (in a manner of speaking), while mine is a more direct approach: bringing dissolved water in direct contact with with the dessicator. Plasmic Physics (talk) 00:36, 21 September 2012 (UTC)

Biology/Genetics: The minimal male/female ratio for genetic diversity?

Imagine this hypothetical situation: there is a world inhabited by humans. If there are 1 million women on this world. If the men were used solely for the purposes of reproduction and contributed nothing else to society, how many men would you need in order to avoid genetic defects within the population? — Preceding unsigned comment added by 142.109.127.37 (talk) 19:31, 16 September 2012 (UTC)

A higher number will imply a better chance, but you can never avoid completely genetic defects. Take into accoutn that the children of one men with different women would be just half siblings and therefore had some chance of not having genetic disorders. OsmanRF34 (talk) 20:20, 16 September 2012 (UTC)

And if you can examine the genes in each sperm before you decide how to use it, then fertilize a specific ovum with that sperm and implant it in the womb, you can avoid any descendents getting duplicate genes. In that case one (rather busy) man should suffice. StuRat (talk) 20:23, 16 September 2012 (UTC)

StuRat, if you can tell me how you are going to examine the genes in a single sperm without killing it you will get the Nobel prizes in both Chemistry and Medicine, and pretty much be crowned God incarnate. You need to step back, put down the petri dish, and aim the syringe in a different direction. μηδείς (talk) 20:28, 16 September 2012 (UTC)

I don't see any reason why this is beyond the realm of possibility. These genes are large enough not to be subject to the Heisenberg Uncertainty Principle, so all that's needed is something like an MRI/CAT/PET scan machine, with sufficient resolution. StuRat (talk) 20:32, 16 September 2012 (UTC)

Back to reality, there is a way, medeis, but it's not on sperm. In the 8-cell stage of an embryo, a single cell can be safely removed without causing any birth defects to the child that will result from the now 7-cell embryo. There are in-vitro fertilization companies that perform this procedure as part of a genetic screening - they look for ~500 known genetic disorders, but do not fully sequence the genome, although that is technically possible from a single cell. Someguy1221 (talk) 20:36, 16 September 2012 (UTC) Addendum, this is called "Cleavage-stage biopsy", and is described at Preimplantation genetic diagnosis. Someguy1221 (talk) 21:33, 16 September 2012 (UTC)

Your reality comment should be addressed to StuRat, Someguy, he's the one apparently unaware of the exigencies here. Although only one of my undergraduate honors majors was biology. μηδείς (talk) 03:28, 17 September 2012 (UTC)

Ah! I was unclear, wasn't I? "Back to reality [from Stu's comments], there is a way [that you might be interested to know about], medeis". Sometimes what reaches the keyboard isn't 100% of what was going through my head. Someguy1221 (talk) 03:35, 17 September 2012 (UTC)

Just curious: why must they wait for 8 cells ? StuRat (talk) 22:10, 16 September 2012 (UTC)

After EC:

you could also analyse the embryo, fetus, baby still in the belly and abort mal-formed ones. No science fiction scenario. OsmanRF34 (talk) 20:39, 16 September 2012 (UTC)

I'm not sure about StuRat's 1st reply about scanning sperm's genes.. 50% of the man's genes will be in each sperm, so beyond the 1st 2 sperms that can theoreticaly share no common genes, what else are you going to scan? Vespine (talk) 22:51, 16 September 2012 (UTC)

The point is to ensure that each generation avoids repeated, defective, recessive genes carried by the one male. One approach is to never use any sperm which contain those genes. However, if the male has a case where both copies of a gene are defective, but in a different way, in his DNA, then you are forced to use one or both of the defective copies. In that case, you can use genetic testing to ensure that any of his offspring which share the same version of the defective gene either don't breed, or don't produce a defective offspring, by genetic testing of the embryo (or sperm/ovum).

More generally, you might want to avoid any repeated copies of genes, whether healthy or not, in order to maintain genetic diversity. StuRat (talk) 23:03, 16 September 2012 (UTC)

There is no way to read a specific cell's genes without destroying that cell. Polymerase chain reaction requires denaturing and cutting up the DNA into bits to make copies to analyze. You can remove one cell to test from an eight-celled or more mature embryo and it will survive. A sperm is a single cell. We murder to dissect. μηδείς (talk) 23:19, 16 September 2012 (UTC)

You are talking about with current technology, while I am talking about the future. StuRat (talk) 23:22, 16 September 2012 (UTC)

I see, you're saying to avoid genetic defects resulting from a fauly gene in the sperm donated by the male. I understood the OP's question slightly differently, I assumed they meant if you extrapolate into the future, the genetic defects that would result from the inbreeding that necessarily would have to occur if ALL the children were fathered by one man. Vespine (talk) 23:29, 16 September 2012 (UTC)

Yes, but I assumed that genetic testing will be even more available in the future. StuRat (talk) 23:34, 16 September 2012 (UTC)

Right, but if you let it get to that stage you aren't avoiding genetic defects, you're aborting them. I'm not making a judgment about that, i'm just saying I don't think it's really what the OP was asking for. I think an actual answer to this question is very complicated and after a bit of googling I can not find a consensus answer, I think the answer is somewhere between 6 and 500, depending on your definition of "avoid". Vespine (talk) 23:59, 16 September 2012 (UTC)

Well, no, StuRat. Not unless you are talking Star Trek teleporter "technology". A cell is an extremely delicate mechanism of nested membranes and organs, a sperm cell especially so. The only way to "read" the DNA is to chemically analyze (i.e., react with) it--you cannot "just" look at it with light and tell what it is. That's why the PCR test was such a huge breakthrough--and it only works on denatured DNA. Any such test would destroy the integrity you are trying to maintain. It's literally the biological analog of the Heisenberg Uncertainty Principle. If you are going to test, you test the father's genome in one of his somatic cells or you test a somatic cell of the embryo itself once it has reached an advanced enough stage. Testing the DNA of a sperm and reconstituting it is on the order of difficulty of dissolving the Mona Lisa in a solvent, doing a full analysis of its chemical makeup, and reconstituting it without causing any difference visible to a forensic art expert. μηδείς (talk) 23:59, 16 September 2012 (UTC)

Actually, the U.S. Army has been funding research to see whether narrow bands of terahertz can detect sequence specific interactions with DNA, which would be usable for a variety of things ranging from very bad to much worse, one of which might be DNA sequencing (though true, right now they say they just want to recognize anthrax in the air). It was posted here somewhere... Wnt (talk) 16:12, 17 September 2012 (UTC)

• To the original question: humanity has survived with FAR less than 1,000,000 females. See Toba catastrophe theory which may have reduced the human population to MUCH smaller amounts (estimates range from between 100,000 down to as few as 1,000 breeding pairs). One of the great mysteries of human biology is why humanity shows far less genetic diversity than it should, and one hypothesis is that there was, at some point, a population bottleneck that greatly reduced that diversity. If humanity survived that, there's no reason it couldn't survive as bad, or even worse, a restriction on genetic diversity, given that we have the benefit of knowing what we are doing. It wouldn't even require fancy genetic engineering; just careful management of breeding. --Jayron32 00:05, 17 September 2012 (UTC)

The BBC source given in that article for 1,000 breeding pairs says nothing about "1,000, thousand," or "pair". I remember reading 30 breeding adults. Obviously the source is unconfirmed as quoted. Is their some reliable and verifiable source somewhere? This article desperately needs fixing--and it's quoted all over the interweb. μηδείς (talk) 03:35, 17 September 2012 (UTC)

I really don't know how you can write an article about a scientific study and not mention who published it, where it was published, when it was published, or even what the title of the paper is. So that was 5 minutes wasted finding this, which is the actual source for anyone who wants to look. Someguy1221 (talk) 03:40, 17 September 2012 (UTC)

If I'm reading the conclusions of that study correctly, they come up with a population size at the bottleneck of around 2,700 individuals. Did I read that right? --Jayron32 04:52, 17 September 2012 (UTC)

I am unable to come up with that number exactly as 2,700 in the abstract or first several paragraphs. Can you give the exact page and paragraph or a ctrl effable number? μηδείς (talk) 05:10, 17 September 2012 (UTC)

Page down to the section titled "An Evolutionary Scenario for Ancient Expansion of Modern Humans", first paragraph, last sentence states "Fifth, an effective population size of, at most, 2,700 is required in order to account for the maximal value of the variance in repeat scores (3.45 at 271 tetranucleotide loci) observed in the contemporary hunter-gatherer populations." They later, in the next paragraph, give a number "the effective size of the ancestor population might have been as low as 700," and also cite studies which have arrived at numbers as high as 10,000. The number 2,700 comes up later in that section as well, though they seem to vasilate as to whether that is a reasonable number. --Jayron32 05:39, 17 September 2012 (UTC)

I haven't read the whole paper either. Do they ever speculate as to how few breeding pairs there were at one time, or are they only talking about effective population size the entire time? Population genetics was never my strong suit, but to make the one equal the other, I think you have to at least fail to census the members of to-be-extinct clades at the time you count the breeding pairs. Someguy1221 (talk) 06:02, 17 September 2012 (UTC)

AFAIK, pre-sperm cells (don't know the exact name) have a full (double) genome and split into 4 sperm cells, each of which has a non-redundant set of genes. So, 2 sets ofgenes are copied to give 4, one per sperm.

So if you are serious about scanning sperm cells, you have to (horribly OR)...

-scan the genome to find if it has any bad genes (any cell will do)

-if / WHEN you find a defect, check if the other gene is good (if not, you're out of luck)

Now suppose that the male has some defects but they are recoverable because the "other" genes are good.

-extract a pre-sperm cell and keep it alive until it splits into 4 sperm,

-test the sperm cells until you have exhausted 3 of 4, or have found 2 copies of every bad gene.

-If you have found 2 bad copies each, the remaining sperm(s) is/are the good one(s) by exclusion. If not, try another pre-sperm cell.

Should work, but won't be one bit of fun for the male involved. Literally, - ¡Ouch! (^{hurt me} / _{more pain}) 07:42, 17 September 2012 (UTC)

The OP's premise is flawed in two respects.

Firstly: parental genomes are not the only source of genetic defects. Everyone is born with something like 50 to 100 new genetic mutations, derived not from their parents but from imperfections in the genetic replication process. I read a reference to this yesterday, in the lead article of last week's (dead tree) New Scientist magazine (doubtless it's readily findable in the on-line version), but it (and the number is necessarily only approximate, that article gave 100, others I have read gave 50) is frequently mentioned in relevant literature. Most of these mutations are of course neutral, but a few might be either advantageous or deleterious.

Secondly: what might be a genetic 'defect' in one context, a particular genome with all its other genes (etc) and/or a particular environment (the OP spoke of "a world"), might not be a defect, or might even be beneficial, in another – think Sickle cell anaemia. {The poster formerly known as 87.81.230.195} 84.21.143.150 (talk) 14:08, 17 September 2012 (UTC)

• I don't think the sex ratio has that much of an effect. Suppose you had one male and 50 females and he happily sires two offspring from each. In such an instance, most (75%) of the genome of each female is represented in some offspring and thus gets past the bottleneck. The male's genome gets spammed, sure, but the other genes remain available at about half the frequency that they would have if they had originally been carried by other males. If the population remains small this increases the risk of fixation (population genetics) somewhat, but if it remains small long enough that can happen anyway. There is a chance of various terrible birth defects, and if they kill the offspring then this reduces the number and that matters, but otherwise they'd get past it in time. (Except for a few rare traits that cause DNA damage, like helicase mutations I suppose) Wnt (talk) 15:53, 17 September 2012 (UTC)

@ Wnt, do you have a ref for the army program? Somehow I am guessing it is meant to detect the viral envelope. @ Ouch, you're talking about spermatocytes and spermatogenesis. μηδείς (talk) 02:09, 18 September 2012 (UTC)

I found some free reference before, a grant application or something, but for now see [2]. Also [3] and [4] are of interest (just search "terahertz DNA" on Google Scholar and NCBI for many more of various degrees of relevance) Wnt (talk) 06:27, 18 September 2012 (UTC)

That third article seems to be on a different topic, and the first two are behind paywalls--and have really unhelpful abstracts. I'll have to see if I can get access to the first two with one of my sign-ons. μηδείς (talk) 17:29, 19 September 2012 (UTC)

Running Everywhere

I frequently hear about the importance of physical activity and its salutary effects, but I hardly have any time to practice it. As a partial solution I thought of running or fast-walking to places instead of walking, e.g. fast-walking to the bus station and running to the refrigerator and back. However, before starting such a strange habit I wanted to check what disadvantages it may have – after all, evolution made it highly uncommon (I suppose it's because our body needs to reserve its energy for emergences, which isn't so relevant in the modern era, but perhaps there are other reasons as well). Additionally, there would be an invigorating influence before going to sleep and stomach aches after eating (both can be solved by not doing so all the time), but is what else? Have any doctors studied this king of lifestyle? Thanks a lot, 109.65.197.85 (talk) 22:01, 16 September 2012 (UTC)

I can think of several disadvantages:

1) You'd be more likely to fall, and the severity is likely to be worse.

2) You are more likely to run into other pedestrians.

3) You are more likely to be hit by a car.

4) You are more likely to run into objects, like trees.

5) You are more likely to be seen as a threat by animals, such as dogs, and hence attacked.

6) In certain circumstances, running may look suspicious. For example, running out of a bank may result in a policeman stopping you.

7) There's also the need to warm-up and cool-down before and after exercise, to minimize the risk of pulling muscles, having a heart attack, etc. This would be difficult to do if you run sporadically throughout the day. StuRat (talk) 22:07, 16 September 2012 (UTC)

You might want to try one thing I do: I never try to find the closest parking space (well, maybe during foul weather). Instead I park far away, in the shade if I can find it, and have a long walk in and back out. I leave the close parking spaces for the lazy and infirm. As a bonus, my car has no door dings, and I find it much easier to find a space, locate my car, and navigate out of the parking lot in a crowd. I find it particularly ironic when people fight for the closest parking space at the gym. :-) StuRat (talk) 22:12, 16 September 2012 (UTC)

Unless you routinely wear gym clothes around, and change a few times a day, I think the sweat and eventually the smell would be a problem, for your own comfort and the comfort of others. Vespine (talk) 22:32, 16 September 2012 (UTC)

Depending on your clothing and the temperature, yes, this could be a problem. StuRat (talk) 23:04, 16 September 2012 (UTC)

"I frequently hear about the importance of physical activity and its salutary effects, but I hardly have any time to practice it."

Not having enough time is an independent factor causing health problems, apart from lack of exercise. If you don't have enough time, you are likely not getting enough sleep, work way to hard etc. etc. Count Iblis (talk) 23:07, 16 September 2012 (UTC)

Here are the exercise guidelines from the UK's National Health Service. "One way to do your recommended 150 minutes of weekly physical activity is to do 30 minutes on 5 days a week." They suggest "walking fast" as one way of getting "moderate-intensity aerobic activity". I don't think "running to the fridge" is going to help much. Alansplodge (talk) 23:12, 16 September 2012 (UTC)

Rope jumping, 15 minutes each day could be more than enough. OsmanRF34 (talk) 23:34, 16 September 2012 (UTC)

Rope jumping is only useful to get fit if you are a couch potato, or if you're over 60 years old. Otherwise, you should do fast running for at least 30 minutes, 5 times per week, exercise on a bike or on a hometrainer. You are fit if the power you can generate for half a hour divided by your weight is higher than 3 Watt/kg. So, if you weigh 70 kg, you should be able to do at least 210 Watts for half an hour. My power to weight ratio is above 4 Watt/Kg. I routinely exercise at a power of 240 Watts for 40 minutes and I only weigh 60 kg. Since this is just exercise, I could do a lot more is pressed to the limit, but I don't want to do that. Count Iblis (talk) 23:57, 16 September 2012 (UTC)

I agree with StuRat's method. That's what I have done, walking about 2km/day. A company I worked for gave regular free health checks - blood pressure, pulse rate, when at rest and when on an exercise bike. Some workmates brought their cars right in and did no exercise. Some brought their cars right in and worked out in a gym. Some had walking machines at home. But I consistently tested as fit as the best. And even though I walked about 2 km a day due to parking on the city outskirts (where there's plenty of free parking), due to city traffic lights and traffic density, the total time I took in getting to work and getting home was about the same. Ratbone58.164.237.102 (talk) 00:12, 17 September 2012 (UTC)

109.65.197.85, your comments tell me you are the perfect (ideal even) candidate for the Fitbit. I highly recommend it for you based on your query. Combined with the Fitbit Aria Wi-Fi Smart Scale, I think you will be able to measure your progress. Good luck. Viriditas (talk) 02:37, 17 September 2012 (UTC)

• I respectfully suggest that the OP simply try out the idea. The reasons why it doesn't work will be apparent very quickly, probably within minutes. There is no teacher like experience. Looie496 (talk) 03:50, 17 September 2012 (UTC)

(Disclaimer: I don't have actual references for the following, it's just info I've read again and again) Running can lead to degradation of the knees, hips, ankles, etc. over time, particularly if no attempt is made to avoid wear and tear; also, the amount of calories consumed for a specific distance doesn't increase that much if you run than if you walk, evolution favoring efficiency, so unless you used the time saved by running to run some more you're not really getting any more exercise than if you walked. That said, I've noted in movies and such that Australian aborigines and African tribesmen, etc. trying to get from place to place are often portrayed as loping along rather than just strolling, so it would seem that such behavior is not foreign to the natural human. However, in reference to the digression above, I've also seen it mentioned a few times that the most effective strategy for maintaining a healthy physique is, indeed, to park approx 2 miles from one's place of employment, or other such frequent destination. Variables here being not just effectiveness of the exercise, but the probability of sticking to it over time, etc., which is of course notoriously low for gym memberships, etc.. Gzuckier (talk) 04:45, 17 September 2012 (UTC)

• We can't give you medical advice here (or other advice), and obviously any lifestyle choice can have risks. Alas, our article on couriers is very incomplete about those in ancient times who made a lifestyle of running from place to place (and certainly I know nothing about it) - but of course, their situation wouldn't be the same as someone from the modern day, for example due to increases in overall body size and perhaps related epigenetic considerations. Wnt (talk) 15:40, 17 September 2012 (UTC)

Good news! Count Iblis (talk) 15:45, 17 September 2012 (UTC)

I have to laugh at that pic. Why would anyone put a stationary bike outside ? Now you have all the disadvantages of a real bike, like weather, bird crap, bugs, etc., without the advantage of actually going somewhere. StuRat (talk) 03:01, 18 September 2012 (UTC)