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How long does it take for a new habitat to change an organism's DNA?

I'm not sure if my question makes sense. I was wondering if, theoretically speaking; my ancestors and I reside in Norway for the last 300 years or so (light-skinned and blue -eyed) and travelled to a warmer climate like Dominican Republic or Africa, how long and what mechanisms by which a person's DNA is changed to look like the current inhabitants? — Preceding unsigned comment added by 67.142.96.127 (talk • contribs)

• How much sex are you having with the natives? --Jayron32 01:57, 26 July 2015 (UTC)
• The DNA itself doesn't change. What happens is that certain organisms reproduce and others don't, and the recombined DNA of those that reproduce is passed on. Imagine if there's a comet that strikes the earth, and only aquatic creatures and those that live buried in underground dens survive, while those that live above ground are roasted to death. (KT event). Then all the elephants will go extinct in a few days, if not hours. That is a drastic "change" in the organism's DNA. For human evolution, disease (think smallpox in the Americas) is the biggest game changer. Other traits like hair color can change very slowly within a population. What matters is the selection pressure. μηδείς (talk) 02:07, 26 July 2015 (UTC)

(edit conflict × 2) Assuming no interbreeding with the locals (so, assuming a large number of Norwegians accompany you) and ignoring tanning, the skin changes would be the result of Natural selection. One of your descendents could be born with a genetic mutation (not like sci-fi super powers, but a benign mistake in combining the parents' DNA) that causes them to produce more melanin than their ancestors (or their immediate ancestors at any rate). That descendent would be less likely to develop skin cancer and have more resistance to sunburning, so s/he would lead a healthier life and so be more likely to reproduce. A mutation could also occur to make them produce less melanin, which would make them more prone to sunburning and skin cancer, and so make it harder for them to survive long enough to reproduce as much as the darker-skinned descendent. The darker skinned descendent would have their own children, and some of their descendents could have a similar mutation, increasing melanin and so their chances of survivability. It is theoretically possible (though practically impossible) that the change could happen after a single generation (i.e. you have a kid who blends right in with the Khoisan). What would be more likely is that it'd take many generations. I'd guess that 1,000 years would still be theoretically possibly but practically impossible, 10,000 years as possible but remarkably fast, and that it could definitely happen in about 100,000 years. Of course, this is based on reversing how long it took African colonists in Europe to lose their melanin (giving them more vitamin D), a number that might have been thrown off by interbreeding with neanderthals. Ian.thomson (talk) 02:16, 26 July 2015 (UTC)

I don't think it took nearly 100,000 years for white skin to develop when Homo Sapiens Sapiens moved to Europe. According to Europe#Prehistory, modern humans appeared there some 40-43 thousand years ago. Not sure if we know how long it took for skin color to lighten after that. Does the earliest European modern human artwork from which color could be determined show black skin ? If so, when did it change ? StuRat (talk) 04:19, 26 July 2015 (UTC)

Why use artwork when you can use genetics? See Human_skin_color#Light_skin, Light_skin#Evolution. It's also not just time, one hypothesis is that there was relatively little selection towards lighter skin in Europe until about 6-10k years ago, roughly when certain behavioral and agricultural changes occurred. It seems from the research linked there that there were few if any light-skinned Europeans before ~20k years ago. SemanticMantis (talk) 14:19, 26 July 2015 (UTC)

July 26

Scar and hair biology

If someone has a small scar on the chin that makes a beard clearing... Can he transplant hair on the scar? If there are some Dermatologists that claim that they can transplant hair on this scar with about 60% success, are they talking the truth from a biological perspective? Can hair really grow on scars?... Maybe they mean that only some areas in the scar are living skin? What is your final conclusion on this? Thank you!!! Ben-Yeudith (talk) 04:42, 26 July 2015 (UTC)

If you are talking about hair transplant in scar area then answer is "yes". but one should have enough blood supply at that particular area..turbo 05:20, 26 July 2015 (UTC)

Turbo, Could you please elaborate even more? Can you give more details of what of the sub-questions the "yes" applies? Thank you. Ben-Yeudith (talk) 13:31, 26 July 2015 (UTC)

Can we have speed greater than c ?

In Michelson-Morley experiment, we saw that the speed of light in space is equal in all inertial frames and in relativity, light speed is defined to be the maximum. Is it really impossible to get speed slightly greater but equivalent to light speed such that if we calculate that speed as light speed, we won't be wrong?Sayan19ghosh99 (talk) 07:52, 26 July 2015 (UTC)

Are you asking how sure we are that nothing travels slightly faster than c? Experimentally I think all we can do is measure approximate masses. The mass of the photon is known to be very close to zero, but I suppose that leaves open the possibility that it's a tiny imaginary number (which would make it a tachyon). Theoretically, in quantum field theory, tachyonic particles make the vacuum unstable, which is a very strong reason to think they don't exist. (See Tachyonic field#Interpretation.) -- BenRG (talk) 08:57, 26 July 2015 (UTC)

My (non-expert) understanding is that the true c, from the viewpoint of relativity, is the velocity that can be attained only by truly massless particles. If photons had a tiny bit of (non-imaginary) mass, they would necessarily have to travel a bit slower than the relativistic c. However, this would also mean that c_photon, unlike the true c, would no longer be a constant in all frames, which would be quite easy to detect: experiments that measure this are thus experiments which can put the masslessness of the photon to the test.

There are also more sensitive tests available: for more on these, see John Baez' page here, and Photon#Experimental checks on photon mass -- The Anome (talk) 13:38, 26 July 2015 (UTC)

I might be wrong, but I think the OP is saying something like "What if we accelerate something to light speed, and keep on accelerating it ... even if it is still calculated as moving at the speed of light, couldn't it be going faster?" And the answer there is that it takes an infinite amount of energy to accelerate any object with mass to lightspeed, and it would have infinite relativistic mass; if you could apply two infinities of energy it would have two infinities of relativistic mass, but that doesn't really mean anything, and it doesn't ever happen, because if it happened even once we'd have all been sucked away by the infinite gravity of the object, no matter where it is in the observable universe.

That said, photons experience a phenomenon that is sort of like deceleration, in the red shift that occurs as space expands. After all, a galaxy that is coming at us at a slower speed might seem to decelerate and eventually turn back and move away from us as billions of years pass. The photons can't go slower than light speed, but they do lose energy. You might compare this to the difference in overall energy in them going from 0 * infinity to 0 * infinity / 2 (or whatever the redshift is at their source), but that of course isn't really proper mathematics. Wnt (talk) 14:59, 26 July 2015 (UTC)

Just to be clear, you CAN have 'speed' grater than C, quite easily depending how you define "speed". What you can't have is information faster than C. Our article Faster-than-light which no one has linked yet, is quite good! Vespine (talk) 22:40, 26 July 2015 (UTC)

A shadow can travel faster than C. But of course a shadow is not a thing. Void burn (talk) 23:36, 27 July 2015 (UTC)

Shadows are indeed mentioned in the article Vespine linked. Along with many other classic examples. Someguy1221 (talk) 00:01, 28 July 2015 (UTC)

Why in Bohr's stationary orbits an electron completes integer wavelengths?

Why mvr=nh/2π and 2πr=nλ ?Sayan19ghosh99 (talk) 07:53, 26 July 2015 (UTC)

In the Bohr model it was just assumed to be that way. The only justification for it was that it led to a correct formula for the spectral lines of hydrogen.

In real quantum mechanics with the Schrödinger equation, it's for more or less the same reason that musical instruments have discrete harmonics. -- BenRG (talk) 08:36, 26 July 2015 (UTC)

To continue a bit with the above, look at the Schrödinger equation article itself, specifically the first time-dependent formula: iħ multiplied by the partial derivative over time of the wave function is equal to the Hamiltonian of the wave function. Solutions to that equation always (???) seem to take the form e^{iħ [phase]}, so the wave function ends up as a three-dimensional loop in space, generally with a positive lobe and a negative lobe, as shown. I'll admit that one of the little mysteries I missed is where the negative end of an 1s orbital is, but I think it must be tucked in there somewhere... anyway, the point is that the wave function has to go "all the way round" in a way that ends up quantizing its angular momentum in units of ħ. Wnt (talk) 10:55, 26 July 2015 (UTC)

How much can ice reduce the temperature in a room.

If you put two liters of ice in 20 cm3 room, how much degrees will the temperature drop, when the ice melts?--Scicurious (talk) 17:03, 26 July 2015 (UTC)

20 cm3 is a very small room. You couldn't even fit 2 L of ice in there.

Assuming you meant 20 m3, you can work it out easily. Density of ice is about 0.92 kg/L, latent heat of fusion is about 335 J/kg, density of air under typical conditions is 1.2 kg m-3, specific heat of air is 1004 J/(kg K). The rest is just arithmetic.

If the ice is colder than 0 C you need to take account of the heat absorbed by warming up the ice to the freezing point. Short Brigade Harvester Boris (talk) 17:17, 26 July 2015 (UTC)

However, the adjustment for the ice being below 0 C is not large, because the latent heat of fusion is large compared to the heat capacity of ice. Robert McClenon (talk) 17:52, 26 July 2015 (UTC)

Generally true, which gives me the opportunity to correct my units: latent heat of fusion is about 335 J/g, not 335 J/kg. Short Brigade Harvester Boris (talk) 21:53, 26 July 2015 (UTC)

How did we get images of asteroid 2011 UW 158?

A week or two ago it came screaming by the Earth and the radio telescope in Puerto Rico took some pictures. Cool, radio pictures of screaming asteroids, but how was it done? One report said they used a 20 tw signal. How do you generate 20 tw of anything, much less a microwave? So they generate this signal, and point it at the asteroid, and the signal bounces back, but how do you make an image out of returns? Are they scanning the asteroid, pixel by pixel? Or are they somehow able to focus the return signal and get an image all at once, like a camera? 50.43.33.62 (talk) 19:14, 26 July 2015 (UTC)

Generating 20TW of (peak) power is actually quite easy: you really only need a very short pulse. When this pulse is scattered its temporal profile and spectrum change. From these you can reconstruct the shape of the surface. Ruslik_Zero 20:07, 26 July 2015 (UTC)

The technique of synthetic aperture radar is used to image objects. Twenty Terra Watts is not really a lot of energy, since a watt is defined by joules per second. I.E. If one was to release (transmit) one joule in a nano-second that would would equate to a 100,000,000 watts.. should the transmit power last for a full second.--Aspro (talk) 20:48, 26 July 2015 (UTC)

Easy? Sure it is, but with what? (Watt?) I can imagine all kinds of equipment that could be used for this, like capacitors and batteries and transformers, but what are they actually using? Tin cans? Diesel generators?

I can see how the temporal profile can tell you that some parts are farther away, and spectrum change can tell you if something is moving closer or away, but how do you turn that kind of info into an image? 50.43.33.62 (talk) 02:22, 27 July 2015 (UTC)

If you assume that the object is rigidly rotating, the timing and Doppler data alone should give some inferences about shape, even without any fancier tricks such as are presumably described in the article that I haven't looked at yet. —Tamfang (talk) 06:25, 30 July 2015 (UTC)

What report quoted twenty terawatts? Are you certain they didn't mean effective radiated power? Power is a complicated parameter for RADAR! Start by reading RADAR signal characteristics.

https://en.wikipedia.org/wiki/Arecibo_Observatory#General_information50.43.33.62 (talk) 06:17, 29 July 2015 (UTC)

"The Radio Telescope" mentioned in the original question probably refers to the Arecibo Observatory. Arecibo usually operates passively, but for some experiments it can transmit as a true RADAR, as well: read about how the transmitter works; when it does so, it typically uses about 150 kilowatts of average power - that is how much power the electrical generator is providing. (That website is a bit old, citing an operations manual from year 2001, and there have been many facility upgrades at Arecibo since then - so use all of these numbers with caution)! The transmitter is often used to send a pulsed RADAR signal; so at any given fraction of a second, either zero watts or 2.5 megawatts are being transmitted.

That peak pulse number provides true instantaneous power. To compute peak ERP, you multiply the power with the antenna gain to derive a (fictitious) equivalent as if the energy was transmitted in all directions. This allows us to use simplfications in the RADAR equation. In actual fact, the energy is directed by the RADAR antenna: it is not a spherically-isotropic source. Radio astronomers like ERP because it's the amount of power that an equivalent spherical cow would emit.

In specific, you can read about the high priority NEO survey conducted by Arecibo to image 2011 UW 158: Current NEO surveys from the Solar System Sudies group at Arecibo Observatory. Their nominal operational power was scheduled to operate at 900 kilowatts for the survey.

For big antenna facilities like Arecibo, antenna gain is enormous - so you can get very strange values when you look at "effective" radiated power. The physical quantity of energy per unit time, on average, is still only the amount supplied by the electricity source, and is not "terawatts."

Nimur (talk) 14:29, 27 July 2015 (UTC)

Excellent reply from Nimur, as always. To answer the OP's specific question, the transmitter device is a klystron. Tevildo (talk) 22:12, 27 July 2015 (UTC)

One way to boost the power in a pulse, but keep the same energy, is to generate a sweeping frequency. Then the signal is put through dispersion so that the earlier frequency comes out at the same time as the latter frequency, and all the power piles up into a very short pulse. Graeme Bartlett (talk) 22:57, 27 July 2015 (UTC)

July 27

What chemical properties make soap useful for cleaning?

Why is soap good at cleaning things? What chemical processes underlie the effectiveness of all soaps and detergents? I remember pondering this question during organic chemistry in college, and I vaguely recall coming up with something about "micelles" being especially good at isolating dirt and making it capable of being scrubbed away by physical force or washed away by water, but I feel like there is more to it than that. Why does soap create useful micelles when other compounds with hydrophobic epitopes don't? Is it perhaps related to the reason why soap makes long-lived bubbles with proper agitation?

Also, how is a soap's effectiveness increased or decreased by time and temperature? Does hot water really make certain soaps and detergents more effective than if they were used with cold water? Is there an ideal amount of time for which a given dirty item should be exposed to soap's chemistry, for maximum cleaning power? Thanks for your help! PJsg1011 (talk) 06:39, 27 July 2015 (UTC)

Regarding the chemical processes, this is due to the fact that one end of the molecule is hydrophobic, whereas the other is hydrophilic -- so the hydrophobic end sticks to the greasy dirt, whereas the hydrophilic end is attracted to water and pulls the grease away from the surface being cleaned. In effect, this makes the surface of the grease particles hydrophilic as well (by coating it with hydrophilic molecules), which makes them miscible with water when normally they're immiscible. One end hydrophobic, the other hydrophilic -- THAT is the key. And yes, higher temperatures usually increase soap's effectiveness -- but this is due to the normal increase in solubility with temperature. 2601:646:8E01:9089:F88D:DE34:7772:8E5B (talk) 08:58, 27 July 2015 (UTC)

Surfactants make the water grap nonsolvable stuff. Cheap kitchen cleaners use lactic acid to remove fat and oil. Surfactants are more expensive and some you do not taste or smell them. For that reason such cleaners have added parfume or substances we can detect by smalling them. Whe getting enging oils on your hands and use soap, the oils part is removed by water and soap but your hands feel like sill put into vinegar which is not beeing removed by the soap. Then the soap contains some glycerol which is a part of soap production, the ester can solve in water. For that reason shower gels or shampoo might be more effective aginst engine oil on the hands. Todays full synthetic engine oils are based on hydrcracked substances, some very stable compared to mineral oil are esters. Calcite is being removed by citric acid oder formic acid. This show you the major difference between bath and kitchen cleaners. --Hans Haase (有问题吗) 09:14, 27 July 2015 (UTC)

ESV

What rescue equipment and capabilities does a modern oilfield ESV (Emergency Support Vessel) like the Iolair have? 2601:646:8E01:9089:F88D:DE34:7772:8E5B (talk) 08:50, 27 July 2015 (UTC)

Anyone? 2601:646:8E01:9089:F88D:DE34:7772:8E5B (talk) 05:46, 29 July 2015 (UTC)

End of domino impulse

Is it possible to estimate how many dominoes it would take to completely stop the impulse imparted by finger or hand to the first domino? This states that 3,847,295 dominoes is still insufficient to completely exhaust the impulse, resembling a perpetual motion. By impulse I mean standard force to provide watchable collapse speed, not too strong and not too slow. Brandmeister^talk 14:45, 27 July 2015 (UTC)

Each domino contains gravitational potential energy. That means that it releases energy when it falls down. That energy goes into knocking down the next domino. You can even have each domino get slightly larger than the previous one, since the gravitational potential energy of the smaller one is more than the force required to tip over the larger one. So, there is no theoretically limit to the number of dominoes that can be knocked down. (There is a practical limit, though, as the more you have the greater the chance of them being knocked down prematurely or being misaligned so they don't all fall down.) StuRat (talk) 15:07, 27 July 2015 (UTC)

I saw a this video of a chain of dominoes of increasing size just the other day. AndrewWTaylor (talk) 16:34, 27 July 2015 (UTC)

And there are some even bigger ones here. AndrewWTaylor (talk) 18:13, 27 July 2015 (UTC)

This is an example of a chain reaction. To achieve perpetual motion, each domino would have to bounce back up into its upright state after it had toppled. You could then create a circle of dominos that repeatedly toppled and bounced back up - but this is, of course, impossible. Gandalf61 (talk) 15:14, 27 July 2015 (UTC)

Or just have an infinite number of dominoes. That could take a while to set up, though. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:13, 27 July 2015 (UTC)

Not if you have an infinite number of people to do it! --65.94.50.73 (talk) 19:33, 27 July 2015 (UTC)

That is a genuinely brilliant response to a (no offense to Bugs who was clearly just trying to make light) nonsensical statement. Snow ^{let's rap} 12:59, 28 July 2015 (UTC)

An infinite number of dominoes lined up would continue to fall, one by one, without ever ending. Any extremely large but finite number will likewise continue to fall until the last one, barring the application of some external force. But it doesn't qualify as a perpetual motion machine, given all the work expended just to get them set up. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:52, 28 July 2015 (UTC)

What tickled me about the response is that "infinity" is a conceptual construct, not a real number, so outside of certain mathematical principles, any practical application of the term to represent physical phenomena defies both sense and the basic principles of the nature of the universe. Which is why I assumed, especially with the inclusion of the second statement, that you were going for humour. Regardless, the IP responded in a way that I felt hilighted the dubious usage, but did so by replicating it in a statement which "played by the same rules" even as it underscored how such usages lead to obvious paradoxes. I'm not even sure that was entirely the intent, but it made me laugh in any event. :) Snow ^{let's rap} 09:31, 29 July 2015 (UTC)

It's a bit of both. And it's kind of a variant on the "turtles all the way down" story. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:13, 29 July 2015 (UTC)

Desert chimney

I wonder if this concept has ever been tried. In a desert, where the outside is hot but dry, if you use an inside evaporative cooler, that makes the inside air cool but potentially overly humid. If a chimney was added, wouldn't that let the humidity out of the house, but not the cool air, since cool air sinks ? You would need to arrange the chimney so sand wouldn't blow in and fall down it, and some convolutions would also reduce radiative heating. The flue on the chimney could then be opened or closed, to control the house humidity level. So, is this approach ever used ? (I realize there are also swamp coolers that evaporate outside the house, then circulate the coolant inside the house, but I'm not asking about those.) StuRat (talk) 16:27, 27 July 2015 (UTC)

See qanat, windcatcher ... there may be more useful terms for this tech, which has been used a very long time in the Middle East. Wnt (talk) 18:52, 27 July 2015 (UTC)

That's a bit different, in that they use wind to replace the air, while I'm talking about not replacing the air, but only allowing the humidity in it to diffuse away, even without winds. (In fact, in my design, you might want to close the flue when windy, to prevent replacing cool, inside air with hot, outside air.) StuRat (talk) 18:58, 27 July 2015 (UTC)

Desert termite mounds are humid and cool. They are basically very tall chimneys. The termites make them humid. They don't have swamp coolers in them, but I mention this because they remain humid and cool even though they are of the design you mention. 209.149.113.45 (talk) 19:21, 27 July 2015 (UTC)

Certainly the interior would remain somewhat more humid than outside, and, in a desert, that would be a good thing. The idea is just to keep it from becoming oppressively humid, to the point where water no longer evaporates and evaporative cooling fails to work. StuRat (talk) 19:32, 27 July 2015 (UTC)

Enthalpy_of_vaporization, latent heat, sensible heat, adiabatic cooling, relative humidity, Evaporative_cooler#Physical_principles. Evaporative cooling works until the relative humidity is 100%. You can't let out "humidity" without letting out the cooler air. The air has less sensible heat because it has higher latent heat. That's how evaporative cooling works. SemanticMantis (talk) 23:00, 27 July 2015 (UTC)

Precisely. You can't "unmix" the humidity from the cool air unless you add another processing step (e.g., an air conditioner). Short Brigade Harvester Boris (talk) 00:53, 28 July 2015 (UTC)

This runs contrary to my experience. When it's cold and humid outside, and hot and dry inside, just opening the windows seems to make it hot and humid inside. I believe the water vapor achieves equilibrium much faster than the temperature does, and in this Q's scenario, the "unwillingness" of cold air to rise up the chimney should exaggerate this effect even more. And it's not "unmixing" the air, but really mixing it, with regards to water vapor, more quickly than with regards to temperature. StuRat (talk) 12:01, 28 July 2015 (UTC)

It's physically impossible that "water vapor achieves equilibrium [i.e., complete mixing] much faster than the temperature" or for water vapor to mix more quickly than heat, except in perfectly laminar flow (where the molecular diffusivity of water vapor in air is slightly higher than the thermal diffusivity of air). And I can guarantee that your example is not laminar. It may feel worse because human comfort can be more sensitive to humidity than to temperature. Short Brigade Harvester Boris (talk) 14:00, 28 July 2015 (UTC)

Sounds like we need a chemist's input here. I recall from chemistry class that different molecules diffuse through the air at very different rates. Can we find a chart listing the diffusion rates of water vapor, diatomic oxygen and nitrogen in air ? StuRat (talk) 14:18, 28 July 2015 (UTC)

The molecular diffusivity of water vapor in air is slightly higher than the thermal diffusivity of air, but that's utterly irrelevant because the situation you're describing is nowhere close to laminar (i.e., the Reynolds number is >>1). Short Brigade Harvester Boris (talk) 14:59, 28 July 2015 (UTC)

So you think there will be turbulent flow up the chimney ? Why ? There should be little or no flow, only diffusion. We could even add baffles to ensure that, if necessary. BTW, what are those "diffusivity" numbers, and does the heat diffusivity take into account the tendency of heat to rise ? StuRat (talk) 15:06, 28 July 2015 (UTC)

For conditions distinguishing between laminar and turbulent flow, see Reynolds number, which you can calculate. (TL;DR version -- it's challenging to create laminar flow even in laboratory conditions.) Regarding the definition of the various diffusivities, I have been told that there is a large online encyclopedia that has articles on such topics. (smiley) Diffusivity is a molecular process and takes no account of buoyancy (which in any case promotes mixing). Short Brigade Harvester Boris (talk) 15:31, 28 July 2015 (UTC)

I've looked, but I haven't found a table, only equations. Surely somebody has done the math already ? It's not like I'm asking about the diffusivity of some rare gases in each other, after all. As for the tendency of hot air to rise promoting mixing, I have to disagree with that, as that mixing would result in an even distribution of heat in the air, but air is measurably hotter in upper floors of a house, or just by the ceiling of a single story, where it is blocked from rising further. StuRat (talk) 15:38, 28 July 2015 (UTC)

As the saying goes, Google is your friend.

OK, I'll tell you the secret: the thermal diffusivity of air is about 1.9*10-5 m2/s and the diffusivity of water vapor in air is about 2.5*10-5 m2/s. With these values we can use scaling arguments to show that a significant role for molecular diffusivity in transporting heat up the chimney is falsified by comparison to observations. The thermal diffusivity of air is about K = 1.9 * 10-5 m2/s. Then the distance that heat diffuses in time T can be scaled as d ~ sqrt(KT), or conversely the time T to diffuse by a distance d would be T ~ (d^2)/K. So the time for heat to diffuse up a 3 m (10 ft) chimney would be order T ~ (9 m2) / (1.9 * 10-5 m2/s) ~ 474,000 s or about 5.5 days.

Does it take nearly a week for heat to travel up your chimney? I doubt it. The dominant heat transfer process in the atmosphere is bulk turbulent motion, not molecular diffusion. Short Brigade Harvester Boris (talk) 15:52, 28 July 2015 (UTC)

Great info, thanks. Do you have a source for those diffusivity rates ? (Not that I doubt your numbers, I just want direct access for the future.) StuRat (talk) 15:59, 28 July 2015 (UTC)

Meant to respond to this earlier, but ran out of time; it's a bit redundant on SM's comments now, but I'll comment briefly anyway. The thing is, unless I have misunderstood you in some way, the system which you describe is basically the standard implementation for a swamp cooler. That is to say, the system is almost always more efficient and effective if you allow the space to vent. A flue is probably an atypical means of achieving this in the context of a small domicile, but a window serves just as well under most circumstances; there might be some minimal advantage to this end-point being at elevation, but usually the cooling unit itself (which is typically set at the other end of the system in a stream-lined setup) employs a powerful fan as part of the evacuation mechanic, so any propensity for hot air to rise is going to have very little total effect on either the total heat or humidity of the system as a whole. There are variations on evaporative cooling (and hybrid approaches which employ air conditioning) in which a closed system would be more optimal, but the system you describe is generally the most energy-efficient and common form, especially in the arid context you stipulate. Snow ^{let's rap} 00:20, 28 July 2015 (UTC)

I think you are picturing the swamp cooler venting directly into the chimney, while I had in mind something like a misting system venting right into the living space, with a separate chimney elsewhere to let the excess humidity out. StuRat (talk) 12:09, 28 July 2015 (UTC)

No, if you review my post you will see that I understand that the living space is situated between the cooling unit and the chimney. Indeed, it would be a virtually useless setup in any other configuration. But again, the scenario you propose is the typical way in which a swamp cooler system is employed. And in this regard it doesn't mater whether your use a misting system or a conventional swamp cooler; the two vary in how quickly they will cool a given space, but that is a quality derived from the unit, not from the venting you propose, which I assure you is very much the typical manner in which venting is configured in a structure that employs a swamp cooler (again, other than the fact that for small domiciles an open window is usually employed rather than a chimney/flue). Snow ^{let's rap} 12:50, 28 July 2015 (UTC)

From my reading of our swamp cooler article, it sounds like they use a fan to blow air into the house, and then vent the house air back to the outside. Hence there is a high rate of air exchange. A disadvantage of this is that cool air is blowing back out of the house at the vents. My idea is to not force any air into or out of the house. Instead, the mister creates mist without pulling in any outside air, and only the excess humidity goes up the chimney. (A regular open window wouldn't work, as here hot outside air would indeed mix with the cool inside air.) StuRat (talk) 13:02, 28 July 2015 (UTC)

Sure, you can vent with a chimney, and it may make more sense to do that with a given architecture, but there is no way that you'll be letting humidity out without also letting cool air out. It is true the outdraft of a chimney may be less cool than the outdraft from a window. SemanticMantis (talk) 13:37, 28 July 2015 (UTC)

I realize that 100% of the humidity won't be vented nor that 0% of the cool air will be vented, but as long as more of the humidity is vented than the cool air, that seems like a successful design to me. StuRat (talk) 13:42, 28 July 2015 (UTC)

I don't think you get it. Cool air and humidity are not separate things. When the water evaporates, it cools the air by converting sensible heat to latent heat. I don't know how many other ways to say it. Your design is in fact very similar to things the Persians worked out a thousand years ago. I don't think anyone is saying your idea is bad, only that can't selectively exhaust humidity that way. You need a condenser for that. SemanticMantis (talk) 14:43, 28 July 2015 (UTC)

I don't understand why you think cool air is the same as humid air. You can have hot air which is either humid or dry, or cool air which is either humid or dry (although extremely cold air can't hold much humidity). This shows they can be separated, by natural processes. While water vapor itself carries heat, the water vapor is only a small portion of the total air, and hence that heat is only a small portion of the total. The water vapor is left cool from evaporation, but the heat from the inside air should quickly warm the water vapor back up, and in the process cool the rest of the air down. After that, it would be nice to be able to remove the now warmer water vapor. This is my goal. StuRat (talk) 14:50, 28 July 2015 (UTC)

Of course temperature and humidity can vary. But when you use an evaporative cooler, you are making the air both cooler and more humid. This is because of the latent heat of evaporation. I don't know what else to say, maybe someone else can put it in a way that you will understand. I think your explanation of how you think it works means you're not fully understanding latent heat, but I can't explain it any better than our article already does. It is true that a chimney will tend to let out the hotter portion of air in a room, if it is ducted properly. SemanticMantis (talk) 15:09, 28 July 2015 (UTC)

Let's try this. I will lay out all the logical steps, and you can point out which steps contain errors:

1) A mister sprays water droplets into the house air. No outside air is brought in.

2) Flash evaporation of water droplets into water vapor lowers the temperature of the water vapor molecules.

3) The water vapor mixes freely with the house air, and thus each reaches the same equilibrium temperature.

4) The chimney is arranged in such a way (perhaps with baffles) as to prevent turbulent motion of air. The lack of air blowing into or out of the house elsewhere prevents rapid movement of air up or down the chimney.

5) Since "The molecular diffusivity of water vapor in air is slightly higher than the thermal diffusivity of air" (2.5 vs 1.9*10-5 m2/s) per Short Brigade Harvester Boris, more water vapor will vent up the chimney than heat.

6) The fact that heat tends to rise and the air inside the house is cooler than that in the chimney will tend to retard the flow of heat even more. Specifically, hotter patches of air in the chimney will rise up and out the chimney, while cooler patches will stay in the house. Placing the chimney opening in the highest point of the house, distant from the mister, will also help to ensure that the air there is hotter than the rest of the house, so the air that is vented isn't cool air. StuRat (talk) 15:26, 28 July 2015 (UTC)

You seem to have invented a system which vents hot air out of the house without letting new air in. How long do you expect it to carry on doing that? AndyTheGrump (talk) 15:32, 28 July 2015 (UTC)

That would be a very slight flow, and all houses are "leaky" to air, so the air would come into the house through the normal leaks (around doors, etc.). This happens without a chimney, too, to ventilate the home. Presumably air is blown into such tiny leaks on the windward side and sucked out on the other side, although with this chimney design, perhaps it would no longer be sucked out by those leaks, but instead go up the chimney. StuRat (talk) 15:40, 28 July 2015 (UTC)

And you are expecting a 'very slight flow' to be sufficient to cool the inside of the house to a significant degree? AndyTheGrump (talk) 15:47, 28 July 2015 (UTC)

No. The airflow doesn't provide the cooling, the evaporation of the misted water does (step 2 above). StuRat (talk) 15:49, 28 July 2015 (UTC)

I don't have time to go in to this any more today, but I think your step 2) may be wrong. "Evaporative cooling therefore causes a drop in the temperature of air proportional to the sensible heat drop and an increase in humidity proportional to the latent heat gain." This is all about latent heat vs. sensible heat. I'm not sure, but I don't think the water itself loses sensible heat. For step 4) as pointed out above, truly laminar flow is very hard to achieve. Turbulence occurs at all scales. It may be useful to approximate this flow as laminar, it may not. As for step 6), this will be air that was once cooled by the mister, even if it is warmer than the air that is lower. You might want to look at Psychrometrics#Psychrometric_charts, and recall that evaporation is isenthalpic, i.e. it occurs at constant enthalpy. What you really need is thermodynamics here, not chemistry, but I've said all I can on the topic at present. SemanticMantis (talk) 17:35, 28 July 2015 (UTC)

The above seems too complicated to follow, so tell me if this gets the gist:

1) You have air that you pass over a wet pad (the "swampy" smell in the swamp cooler, which ironically enough doesn't work in a swamp). That can come from inside or outside, doesn't matter. 2) The evaporation of the water makes the pad, and the air passing over it, cooler. The humidity makes it heavier. Therefore, the wet air should tend to sink rather than rise. 3) Given an unlimited supply of water (indeed a fortunate thing in the desert!) one can therefore constantly cool the air passing over it to a degree determined by the starting humidity and temperature. 4) The need for air flow is dictated by the amount of heat the cooled air/water is called upon to absorb; the evaporative cooling of the water must equal that, which determines the air flow and thus the water consumption. Essentially, the moistened air can be seen as a stream of coolant at a certain temperature, and as you get arbitrarily close to that temperature the flow becomes arbitrarily large. 5) A chimney next to the house will indeed release some "coolth" through the wall for the inhabitants, but only to a limited degree. All the usual designs of car radiators and such would seem to apply - cooling fins, multiple ducts, countercurrent exchange and so forth. 6) However, that said, nothing is quite as efficient as simply releasing the cooled air into the house, together with its humidity, and if the desert is dry enough, that might bring few complaints. This system, together with a windcatcher to suck out hot air from the top of the building, would seem to be the usual Middle East installation AFAIK. Wnt (talk) 18:47, 28 July 2015 (UTC)

"The humidity makes it heavier." A common misconception. At a given temperature and pressure, humid air is less dense than dry air. Short Brigade Harvester Boris (talk) 01:34, 29 July 2015 (UTC)

D'oh! You're absolutely right, and if I'd been thinking instead of typing I would have realized it, since the ideal gas law still applies (more or less), and H2O is a lighter molecule than O2. [1] details this explanation. Wnt (talk) 13:38, 29 July 2015 (UTC)

Humid air feels "heavier", even though it isn't. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:11, 29 July 2015 (UTC)

July 28

Multi-cylinder IC engine

Can the same cylinder design for an IC engine be used in multiple engines, with different number of cylinders? For instance, design a 250cc cylinder, and use it in 1, 2, 3, and 4-cylinder configurations for 250cc, 500cc, 750cc and 1000cc engines? Thanks!

Yes, to some extent. For instance it wasn't unheard of for manufacturers to chop two cylinders off a V8 to make a disgusting V6, and I was involved in a project that took a 4 cylinder and turned it into a 3 cylinder, but that did not go into production. But really you only reuse the con rod and piston and perhaps valves and liner, everything else is redesigned. Greglocock (talk) 09:48, 28 July 2015 (UTC)

According to something I read yesterday somewhere on the BBC website's current coverage of Formula 1, one of the engine manufacturers is currently testing a potential improvement on a single-cylinder setup (presumably a bench setup) which, if successful, will be incorporated in a forthcoming engine upgrade. This suggests that elements of the OP's scenario are valid. {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 12:37, 28 July 2015 (UTC)

yes, research engines are often single cylinder engines. Greglocock (talk) 06:30, 29 July 2015 (UTC)

I remember in the late 1980s some people would bolt two Yamaha RD250 engines together to create a 4 cylinder 500cc bike. A few were featured as reader specials in Motorcycle Mechanics/Performance Bikes. Hesketh Motorcycles use the same cylinder, piston and conrod for both sides of the V (unlike say a Ducati Darmah SD900 which has different cylinder casting). --TrogWoolley (talk) 13:19, 28 July 2015 (UTC)

A significant problem that must be solved when taking a mature engine and converting it into one with a different number of cylinders is engine balance. To achieve satisfactory freedom from vibration requires much more than a new crankshaft and adding or subtracting a cylinder and piston. See balancing of rotating masses, Internal combustion engine#Cylinder configuration and balance shaft. For a high-speed engine, re-balancing with a non-optimal number of cylinders will require more effort and expense than balancing the original engine, and will deliver a poorer result. Dolphin (t) 06:42, 29 July 2015 (UTC)

When drinking sweetened drink (such as cola) is it coming to the kidneys as water molecules?

18:19, 28 July 2015 (UTC)

Water molecules among others, yes. It is delivered to the kidneys, with other waste products, through the bloodstream, after having been absorbed through the intestinal walls, and, in the case of sugars, etc., metabolized into waste products. Some of the water also leaves the body in sweat, respiration, tears, etc. StuRat (talk) 18:48, 28 July 2015 (UTC)

In most people (excluding diabetics with glucosuria) the body is pretty good about extracting as much energy from sugar as possible, which means that the carbons in the sugar leave as exhaled carbon dioxide. But the hydrogens in it go out the kidneys (and other places) as water, having found some oxygen (ultimately from the lungs) in the meantime. The other components are more complex - for example, if you read caffeine you'll see the various metabolites produced. (oxygen is involved there too, but CYP1A2 isn't trying to produce energy, but just to break stuff down into a form that hopefully will leave the body) The caffeine and all metabolites slowly go out in the urine, because urine is basically just blood that is filtered through a membrane and has a lot of different things the body wants to keep taken back out of it into the body, until whatever is left is peed away. Caramel color so far as I know is still mostly sugar and I'd expect is metabolized much like sugar. Wnt (talk) 19:26, 28 July 2015 (UTC)

Thanks. So can I understand that it doesn't matter what you drink for the kidneys (of course for the short term), always just the liquid that comes into the kidney is almost the same thing? 213.57.14.75 (talk) 19:30, 28 July 2015 (UTC)

I'm not sure what you're asking exactly. The kidney filtrate is just your blood plasma minus the large or highly-charged molecules that can't pass through the glomerulus. So whatever's in your blood will generally make it into the filtrate. I recommend CrashCourse Biology's video on the kidneys for an introduction. --108.38.204.15 (talk) 19:56, 28 July 2015 (UTC)

The general recommendation is to drink lots of water (except for people with kidney failure), as that dilutes the urine and makes kidney stone formation less likely. A high protein diet puts more strain on the kidneys, as does lots of tea (tannins) and a few other things. If you are asking about yourself, then you should consult a doctor for your specific case. StuRat (talk) 02:06, 29 July 2015 (UTC)

Well, almost. Urine is always mostly water, but there are a lot of substances dissolved in that water (see Urine#Characteristics for more information). The mixture of substances will vary, depending among other things on what you eat and some diseases that will change the composition. Two well-known examples are diabetes which will make the urine high in glucose, and asparagus which will give urine a peculiar smell. Both of these are because the blood holds a higher level than normal of a compound that is then excreted through the kidneys. Sjö (talk) 08:56, 29 July 2015 (UTC)

Has any serious effort been made to build a robotic sandworm?

Sandworms come in two types: the giant kind in fantasy that infest the deserts of Dune and some town in Nevada, and the kind that actually live and burrow through (wet) sand. I'm not too clear about what can be done in between, though. Are there factors of scale that limit how large an annelid can be and burrow through sand, and could machines get around them? What would happen if you tried to make a huge metal tube with a slightly pointed end around an intake, which gathers the sand it takes in and uses a hydraulic ram to push it backward out and the rear? Has such engineering been explored seriously? Wnt (talk) 19:13, 28 July 2015 (UTC)

Seems like it would be quite slow and use a lot of energy. What would be the goal, just to imitate nature ? In that case expanding and contracting, with a surface that grabs sand in one direction and slides in another, might be closer to that. Of course, this only works on a small scale, as you don't see Dune sized sandworms in nature. StuRat (talk) 19:18, 28 July 2015 (UTC)

Microchaetus_rappi seems to be the largest Annelid. This [2] page says max diameter is 2cm. I would not suppose that this is hard physical limit to how large of a worm can burrow, but rather a limit based upon ecological niche that also incorporates life history, resource competition, predation, general body plan, etc. etc. SemanticMantis (talk) 19:53, 28 July 2015 (UTC)

There should be a low limit on diameter, since sand or soil can only compact so much to make tunnels, and beyond that it needs to be removed to make room. As for the length, the limit on that, if there is one, should be far greater. Worms have multiple "hearts" to circulate blood, so could just add more. They breathe through their skin, so length isn't a problem there. As for nerve impulses, the various parts could operate only knowing what the parts on either side of them are doing, much like a centipede or millipede, so that's no issue either. The inability to hide from predators might be the limiting factor on length. Or the energy needed to send food through the long digestion tract could be a limit, but there the anus could just be moved to the side somewhere (which would leave open the Q of what would be left in the "tail"...maybe the reproductive tract ?). StuRat (talk) 21:30, 28 July 2015 (UTC)

There are lizards that "swim" in dry desert sand [3], and lizardy robots inspired by them [4]. --Amble (talk) 20:22, 28 July 2015 (UTC)

Here's two research papers on worm-bots [5] [6]. SemanticMantis (talk) 21:05, 28 July 2015 (UTC)

There's also the sidewinder, which "swims" through sand, but only on the surface. This has led to attempts to replicate it with a snakebot. StuRat (talk) 21:35, 28 July 2015 (UTC)

• It's rather insane to swim through sand. The golden mole does it in a way to find its food. The naked mole rat burrows in hard soil for safety and to find the tubers it eats. Herbert's sandworms used friction to power an unexplained chemical process that created Spice and oxygen. It can be discounted as unsupported fiction. The energy required is pretty much prohibitive without a huge ecological advantage. μηδείς (talk) 01:53, 29 July 2015 (UTC)±

This sounds a lot like the approximate fact that most animals that are not specialized for jumping can do a standing jump to a height of about a foot off the ground. Elephants, humans and mice...all about the same. This happens because the weight of an animal increases as the cube of it's size, but the cross-sectional area of their muscles only grows as the square of their size - so when you double the size of an animal, you don't double the height it can jump. I'd expect a similar problem with scaling up a worm - and I'd speculate that a giant sand-worm would only be able to move at the same speed as a pencil-sized sand-worm...which would seem excruciatingly slow. A robotic sand-worm could (perhaps) have a more efficient power supply - but even so, I'd expect it to have difficulties with moving at any speed.

According to this, "Bertha" (the world's largest tunnel-boring machine) manages to travel 35 feet per day - according to this, a typical earthworm manages 27 feet per hour. Bertha doesn't carry it's own power source - but has to install concrete liners into the tunnel it makes rather than allowing it to collapse behind it. Be we could perhaps imagine that a machine that's optimised for sand - and which is more interested in forward speed than in tunnel construction might maybe be able to go ten or twenty times faster - but that would only be about the same speed as an earthworm. All of which fits rather well with my intuition that all sandworms would move at about the same speed, regardless of size. SteveBaker (talk) 14:39, 29 July 2015 (UTC)

July 29

Merger

The question is straightforward: should inventory control be merged with Inventory control system?Lbertolotti (talk) 01:29, 29 July 2015 (UTC)

Have you tried discussing that on those articles' talk pages? ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:00, 29 July 2015 (UTC)

Yes, so far nobody said anything.Lbertolotti (talk) 03:13, 29 July 2015 (UTC)

@Lbertolotti: Although there is no real harm in raising the issue here, the Ref desks are not really the ideal means to solicit additional opinions as relates to the best policy approach to an issue on an article. I would recommend you explore Wikipedia:Proposed mergers, WP:RfC, and (for this particular case) Wikipedia talk:WikiProject Business. The first is a noticeboard to promote merger discussions, the second is a process page which will guide you in how to attract outside input to article talk page via a method known as a "request for comment", and the third is the talk page for a Wikiproject (collection of editors with a common interest) for business-related articles. One of these methods should surely attract some attention to your request for additional input. And, of course, if you feel very confident that you have reviewed the relevant policies and that a merger would be warranted in this instance, you could always WP:BEBOLD and institute the change yourself (since no one has commented despite your best efforts to raise the issue on the talk Page) and then if someone objects or reverts the change, you can invite them via their user talk page to comment on the article talk page so you can get their views and a better feeling of how to proceed. Regardless of which route you choose, I applaud your efforts to approach the change in a slow and cautious manner and to go above and beyond to seek additional input and consensus.  :) I will give my own opinion on the talk page shortly, but you should keep the above methods for outreach in mind for the future. Snow ^{let's rap} 09:51, 29 July 2015 (UTC)

Wikipedia:Reference_desk/Archives/Science/2015_July_21#Wild_animal_photos

I'm updating the pictures description, if there's no objection. Lbertolotti (talk) 01:34, 29 July 2015 (UTC)

The handedness of a dead body

Could a coroner tell if the person was left-handed or right-handed? Anna Frodesiak (talk) 06:13, 29 July 2015 (UTC)

It is possible if the dominant hand was used in repetitive activities, such as archery or metalworking, as the musculature will develop more and produce bone deformities. I'd say (not being a coroner but being a physical therapist) that modern life in general doesn't produce such gross deformities, the evidence would be more nuanced. --TammyMoet (talk) 08:42, 29 July 2015 (UTC)

I am not a coroner, but if I were asked I'd check the middle fingers for calluses. There is likely to be one on the dominant hand, caused by writing. DuncanHill (talk) 08:50, 29 July 2015 (UTC)

That might be harder to do these days, with people doing less writing: I can't see any obvious external differences between my middle fingers, though perhaps an export could. According to this, "[Forensic anthropologists] can tell whether the person was right or left-handed. There would be more muscle attachment on the bones on the dominant side". By the way, a coroner is a legal officer (at least in the UK), so they would not be the one doing the physical investigation. AndrewWTaylor (talk) 08:57, 29 July 2015 (UTC)

Use of a mouse on a computer affects the wrist, indicating handedness. Constantly moving a finger over a screen causes a callus, indicating handedness. That does not include muscle mass. Most people are stronger in their dominant arm. In boot camp, everyone had to work out. It was easy to identify the left handers because they had trouble lifting weights in the right hand that were easy in their left. For everyone else, lifting weights in the left hand was harder (except for the two who were body builders previous to boot camp, one put on weight control specifically to lose muscle mass). 209.149.113.45 (talk) 16:11, 29 July 2015 (UTC)

Not sure this would be deterministic. My father is left handed and before wireless mice made switching easier, he simply used his right hand. I am right handed but left eye dominant so some things like shooting a rifle is left handed, while a pistol is right handed. I use the wireless mouse on the right side, but the dot mouse on the laptop I use my left index finger. Not sure why, it's just natural for me and it's not ambidextrous where I can use my right finger for the dot mouse or my left hand for the wireless mouse. Could be just training. rather than handedness. --DHeyward (talk) 21:21, 29 July 2015 (UTC)

This book [7] has a chapter titled "Skeletal indicators of handedness". SemanticMantis (talk) 14:55, 29 July 2015 (UTC)

Sink your teeth into this! There is another way to find a deceased's handedness which I found out just 2 hours ago! I took my sister to the dentist today and had a good chat with her (the dentist). I was telling her that I had heard right-hemisphere dominant people chew on the left side of the mouth and vice versa. She told me it was true, and this affects the distribution of cavities. She then went on to tell me that right-handed people brush the teeth on the right of their mouth harder (better) than on the left (and vice versa). So, right-handed people have fewer cavities and less plaque on the teeth of the right side of their mouth! Elementary my dear Watson!DrChrissy ^(talk) 17:22, 29 July 2015 (UTC)

Was this what she was reporting the dentist had told her, or was it her own opinion? Is she a dentist herself? -- Jack of Oz ^{[pleasantries]} 19:30, 29 July 2015 (UTC)

Apologies for my unclear posting. This was what the dentist was saying to me. (My sister's input to the conversation was "Arrrggggh", "Ugggguuuuuhhh" and "thank God that's over".DrChrissy ^(talk) 20:48, 29 July 2015 (UTC)

Are you sure that you have not reversed right and left for brushing. A comment by my dentist implied that it was the other way round. Dbfirs 06:55, 30 July 2015 (UTC)

In my excitement at hearing the relationship, I might have mistaken it. However, I am right handed, and it feels like I put more pressure on the teeth on the right side of my mouth. (sample size N=1 !)DrChrissy ^(talk) 12:00, 30 July 2015 (UTC)

A person who writes with the left hand is more likely to use the right hand to support the right cheek, which as a result will likely tend to be more concave than the left cheek. (I searched for a reference, but found none.) This question is relevant to Wikipedia:WikiProject Medicine/Participants (including User:Doc James, User:Bluerasberry, User:Jfdwolff, User:Mattopaedia, User:Richardcavell, User:Looie496, User:Ozzie10aaaa, User:CFCF, and User:Peter.C).

—Wavelength (talk) 23:35, 29 July 2015 (UTC)

Thank you all!! Very, very interesting indeed!!! Pity, though, that I can't see the book with the "Skeletal indicators of handedness" chapter. Anna Frodesiak (talk) 05:51, 30 July 2015 (UTC)

Late to the party, but FWIW, in both the novel and film In the Heat of the Night, Police Detective Vergil Tibbs determines that a suspect is left-handed (and therefore likely not the perpetrator) simply by feeling the musculature of his forearms. Unless the author John Ball thought this up off his own bat (is that a USA-known term?), it's presumably possible to do the same to a corpse. {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 13:25, 30 July 2015 (UTC)

Maxwell's demon and the Carnot efficiency

I'm curious whether there is a simple, straightforward way to relate the maximum efficiency of a Maxwell's demon to the maximum efficiency of a Heat engine, i.e. 1-Tc/Th. There is an impressive paper that does so [8][9] but it is somewhat difficult for the non-expert to process, and I'm not sure if the quantum mechanical features they focus on there are important for making this connection or just a distraction. Also there's a discrepancy between that paper and our entropy article on one hand and the Landauer's principle article on the other; the former use k_B ln 2 for the entropy that must be produced elsewhere and/or energy cost, while the latter uses kT ln 2. I'm thinking the latter is measuring entropy in terms of joules and the former two doing something else but I'm not quite sure why. Is there a straightforward derivation by which you can start with this expression (whichever one) for the cost of erasing a bit and end up showing that the demon has the same maximum efficiency as a heat pump for reservoirs of the same temperatures? Wnt (talk) 23:46, 29 July 2015 (UTC)

Sorry, Wnt, there's no formal definition for the efficiency of a demon, so there's no meaningful way to compare it to the efficiency of a heat engine. Nimur (talk) 00:03, 30 July 2015 (UTC)

But surely it could be measured empirically? {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 13:33, 30 July 2015 (UTC)

Not sure it's applicable but see here Bose–Einstein condensate#Superfluidity of BEC and Landau criterion. Using lasers to cool through coherence seems pretty neat. QED and QM seem fundamental. For some reason, Maxwells demon seems like the simple aerator on my pool. The hot molecules leave as evaporation, cold molecules stay and the pool is cooled. It's not a closed system though but the "demon" is a pump. At some point the demon would have too many collisions with the door (i.e. similar to space-charge region in a plasma where the atom has so much less velocity than electrons at a given temperature that a charge region forms until the collisions balance and the current is zero). I would think that barrier could be QM related distance with tunneling and other effects. Black hole formation and evaporation may also have relevance. Just a thought. --DHeyward (talk) 04:02, 30 July 2015 (UTC)

July 30

Why does water get loud before it boils?

I notice that when boiling water in a metal or glass kettle or metal pot, a noise slowly builds before the water actually boils. Once the water reaches a rolling boil, the noise lessens. What is causing the noise? The water? The expansion of the glass or metal kettle? --Navstar (talk) 02:05, 30 July 2015 (UTC)

It says here that the explanation is that in the hottest area of the kettle the water is boiling, but the bubbles collapse as they rise into water below the boiling point. The collapsing is what makes the noise, and it stops happening when all the water is at the boiling point. --65.94.50.73 (talk) 03:54, 30 July 2015 (UTC)

How many Earth plant species are physically possible?

If we could simulate Earth's entire history octillions of times with different random DNA mutations until we exhaust every possible species how many would there be? Is this even estimatable any time soon? Sagittarian Milky Way (talk) 02:36, 30 July 2015 (UTC)

And also randomize the shapes of the continents and their topography and when and where asteroids hits and the like cause those were random accidents. Sagittarian Milky Way (talk) 02:43, 30 July 2015 (UTC)

It's not possible to do this in a meaningful way. The largest plant genome is 150gb long. There are 4^{150,000,000,000} possible genomes of this size (such a big number I can't find a math program that will even display it in scientific notation). We can think about any particular variation of this genome, but without creating it, we have no way of knowing whether it would be viable in a given environment (or ever), whether it would constitute a species distinct from any other particular variation, or even whether it would classify as a plant. There's also no reason to suspect that 150gb is the upper bound for the size of a plant genome. So while we can imagine all the variations of a genome, we can't know anything useful about most of them - certainly not enough to answer your question. Someguy1221 (talk) 03:04, 30 July 2015 (UTC)

To convert a power of A into a power of B, just multiply the exponent by log A / log B (using logarithms to the same base for both numbers). log 4 / log 10 is just over 0.6, so 4^{150,000,000,000} is about 10^{90,000,000,000}. --65.94.50.73 (talk) 04:01, 30 July 2015 (UTC)

As for the continents...the number of possible outcomes depends on how different two 'shapes' have to be. If a single misplaced atom makes two topographies "different" then the answer is some kind of factorial involving the number of atoms in the earth's crust from somewhere above the height of everest to the bottom of the marianas trench. That's a truly ungodly number. I don't see much value in attempting to estimate it - the mathematical notations for such numbers start to get fairly incomprehensible.

If "different" required a difference of (say) a kilometer in the shape of a continent or the path of a river - then the number is still insanely large - but more manageable. But it's arbitrary - why one limit for "different" rather than another? That's really the problem with these "curiosity" kinds of question. Does it matter how big the number is? I can't imagine why you'd need the answer. Why bother even asking it?

It's really the same deal with the plants - there are an insane number of changes in the DNA of an Oak Tree that would still produce a viable, recognisable Oak Tree - so why count the number of possible DNA strands when it really tells you nothing about how much meaningful variation there might be.

So the best answer here is "Don't Know" - and "Don't Care" comes a close second. SteveBaker (talk) 04:19, 30 July 2015 (UTC)

I meant changes big enough to affect the evolution of species, a kilometer probably wouldn't do it. If the dinosaurs got to evolve for longer or got killed off sooner maybe plants that never existed would happen, though. I'm kind of also wondering how many Earthlike planets would have to gain DNA-based vegetation of the correct amino acid chirality to make a wheat species that could interbreed with the Earth kind. Sagittarian Milky Way (talk) 04:50, 30 July 2015 (UTC)

All of them. (BTW, besides being a flip answer, there are DNA changes that aren't meaningful for species. The human genome is fairly narrow that produces lots of variability without a "species change." I'm not sure how you can specify "species change" with DNA variation. Eye color, skin color, gender, etc, etc, are all DNA differences without species implications and there are genomes that aren't so narrow and allow "inter species" creation (i.e. Ligar) as well large variation within a species such as Dogs.) --DHeyward (talk) 04:28, 30 July 2015 (UTC)

Galaxy merger - Andromeda and Milky Way

What will happen to the two supermassive black holes at the centers of the two galaxies when these two galaxies will merge? Will these two black holes merge to from a single black hole? --IEditEncyclopedia (talk) 05:28, 30 July 2015 (UTC)

yes Void burn (talk) 05:30, 30 July 2015 (UTC)

But supermassive black holes are much more powerful. Will not they engulf all the matter if they are disturbed? --IEditEncyclopedia (talk) 05:33, 30 July 2015 (UTC)

Why would they engulf all matter? Black holes obey the same laws of gravity as anything else. Putting two of them together will release a great deal of energy in the merger, but the gravity won't be any stronger than the sum of the two black holes. Someguy1221 (talk) 05:51, 30 July 2015 (UTC)

Why guess what could happen, when astronomers have already been studying it happen: let my type super massive black hole merger into google for you. 209.149.113.45 (talk) 13:25, 30 July 2015 (UTC)

Does eating oatmeal increase or decrease the iron in the human body?

Oatmeal is rich in iron, but it seems that it hinders the absorption of iron by the body (see [10]].

Would consuming regularly some commercial product as Dr. Oetker's Oatmeal increase or decrease the iron level in the blood? Do producers enrich the product with iron to avoid a decrease of iron in the body?--Yppieyei (talk) 10:10, 30 July 2015 (UTC)