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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! — Preceding unsigned comment added by 121.247.87.206 (talk) 09:21, 28 July 2015‎

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)

• Many things could interfere with such presumptions. I generally carry heavy things with whichever arm has less joint pain that day. When I'm at my computer and not typing, my right hand generally rests on the arrow keys and my left hand on the mouse, so that my mousing hand has less far to move to reach the letter keys. When I shoot a pistol one-handed, my ‘wrong’ hand is steadier. — There is a faint difference between my middle fingers, but nothing like the very obvious groove I had at age 16; I no longer grip a pen with such force! —Tamfang (talk) 06:58, 31 July 2015 (UTC)

These arguments are anecdotes vs data. Suppose I take a million computer users. I identify a spread in the wrist bones on 90% of them due to mouse use and verify that the hand use for their mouse is the hand they normally use for everything. I can then state that, after identifying a spread in the wrist bones, I am about 90% confident in identifying the handedness of the person. I work with this type of argument every day. For example, over 99% of people who have an HbA1c>6.5% are diabetic. Still, people want to talk about an anecdote about some guy they heard of who had an HbA1c of 8%, but wasn't diabetic. Therefore, they think they've invalidated the millions of other data points that support using HbA1c to identify diabetes. They are wrong, very wrong. In other words, the plural of anecdotes is not data. 209.149.113.45 (talk) 16:55, 31 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)

Sure, if we can only find a cost-effective and safe way to obtain a statistically-significant number of demons! I'm still looking for a cost-effective and safe way to obtain a statistically-significant number of neutrons, which I consider to have more interesting thermodynamic properties... regrettably, the best I can find is a one-of-a-kind spallation source on the opposite side of this continent - but it's available to anyone with any experience or credential level, so long as the research proposal is meritous! Nimur (talk) 16:25, 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)

@Nimur: I'm surprised if there isn't a formula for the efficiency, but to give an example: today I had to deal with a car issue and was waiting for a long time in a room with a soda pop vending machine. (For some inexplicable reason, the supposed pleasure of having a cooled soda pop outweighs the prolonged and annoying noise of the contraption; as I don't actually refrigerate soda, it is all very mysterious to me) Anyway, the point is, I'd like to rip out the condenser and coils and replace it with a sort of refrigerator magnet lining the box that has a thin layer of water in it and many, many demons that put the hot water to one end of the layer and the cold to the other, so as to act as a heat pump and do the refrigeration. My understanding is that the power consumption of these demons is linked to the number of times that it measures the temperature (speed) of a water molecule approaching the gate, opens or shuts it, and then has to forget what it decided to do - that last part, oddly enough, is where the entropy is charged. So just like a refrigerator, there has to be a plug in the wall to keep it running; but fortunately one expects not to hear those bazillion gates clattering open and shut every second. And so the efficiency should be absolutely, directly comparable; but it can be written either as Carnot efficiency assuming that the demon can't power some kind of steam engine that powers the demon, or as the cost of erasing a whole bunch of bits of data. I think someone somewhere might have explained the relationship of those two means of calculation in terms even I can understand. Wnt (talk) 18:46, 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)

Agreed. Note that these bubbles are too small to see, and that the large surface area to volume ratio of such microscopic bubbles allows the water vapor to instantly cool below the boiling temperature and become liquid water again, which takes up much less room, causing the bubbles to collapse. The bubbles get larger as the heating continues, and you might be able to see them collapse briefly, or at least get smaller as they rise. StuRat (talk) 14:17, 30 July 2015 (UTC)

The fancy science term for this is cavitation. Notably, it's also caused by things other than heating, like surfaces passing through a fluid at a high speed. This is an issue for things like propellers and turbines. And when cavitation bubbles form, they are indeed noisy, which is one way you can tell that it's happening to a propeller, pump, etc. --108.38.204.15 (talk) 15:45, 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 hit 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)

The problem is that the environment on Earth is 'chaotic' (in the mathematical sense of Chaos theory) - epitomised by the idea that the flapping of a butterfly wing might cause a hurricane halfway around the world a year from now. This effect (which is very real by the way) means that the most insignificant change (one atom displaced by a nanometer or so) is more than sufficient over the very long term to cause extinction or failure to evolve of an entire species. There is no lower limit beneath which you shouldn't care.

Imagine a single cosmic ray misplacing a single atom in the DNA of the sperm that was to become Richard Nixon. That resulting in it swimming 0.1% more slowly than it otherwise might - and resulting in a different sperm making it to the egg, Richard Nixon never existed but instead we got Sandra Nixon. Despite an unprecedentedly great political career, and a reputation for honesty and a high ethical standard - in 1968, America simply wasn't ready for it's first female president and Hubert Humphrey got the job instead. Being obsessed with solving the Vietnam problem, Humphrey failed in Cold War engagement with the Soviet Union. The resulting nuclear holocaust caused in the extinction of 90% of the species on earth and resulted in the eventual evolution of super-intelligent giant cockroaches who farmed genetically engineered fungi over 80% of the land area of Earth - and that caused the extinction of the wheat plant on earth. One cosmic ray - one nanometer to the left.

So, no - it's not sufficient to assume that one misplaced atom cannot make a difference!

SteveBaker (talk) 17:47, 30 July 2015 (UTC)

That is very funny. Sagittarian Milky Way (talk) 12:57, 31 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)

I have lots to say about this, as my research specialty is theoretical ecology of plant communities. Unfortunately I don't have much time work for free today :) The big thing everyone seems to be ignoring is that the number viable plant species depend on the community context, competition, dispersal, life history, predation, disturbance, and many other factors. The number of possible genetic combinations has nothing to do with the number of species you might expect to find in a given situation. For starters, see Chesson (2000 a,b), freely accessible here [10]. The main idea is that number of coexisting species that a system can support is limited by resident-invader differences in the covariances between environmental and competitive effects. The papers go into great detail on this if you can handle the math and follow some basic ecological terminology. If you're still interested next week, drop a line on my talk page and I'll be happy to discuss further. SemanticMantis (talk) 15:22, 30 July 2015 (UTC)

They don't seem to be asking about how many plant species can survive in one particular environment (E), but rather how many could exists (n) in every possible Earth environment (P). It's probably not as simple as n = E×P, either, as E varies widely, P is unknown, and there will be many species that could exist in multiple environments. Also note that in plants (as well as animals, etc.) with asexual reproduction, defining a species is even trickier. StuRat (talk) 15:52, 30 July 2015 (UTC)

Funny, I would have thought that every possible Earth environment would include all specific and particular Earth environments. Please don't try to teach me to suck eggs until you've gotten a relevant PhD and published at least a few peer-reviewed papers about plant ecology ;) SemanticMantis (talk) 16:49, 30 July 2015 (UTC)

Nice argument from authority fallacy. I hardly need a PhD in plant biology to be able to read a question correctly. Specifically, "randomize the shapes of the continents and their topography and when and where asteroids hits and the like" means the OP wants to know about all possible Earth environments, not merely those which currently exist. StuRat (talk) 17:25, 30 July 2015 (UTC)

If you'd taken the time to read and understand the research I linked above, you'd have seen that the framework allows for descriptions of species coexistence in environments that don't exist on Earth, as well as plants that don't exist on Earth. You seem to think I'm interpreting the question incorrectly but don't seem to be understanding what I'm saying. Whether the OP thinks my refs and responses relevant is not for you to decide. Finally, I did not appeal to my authority to support my claims, my refs do that just fine. Rather, I appealed to a well-known saying, and implied that you're trying to give your opinion to an expert in the field, who most likely knows more about this than you do. Whatever, I'm happy to discuss this with OP further as I said above, but I have no more time for you today. SemanticMantis (talk) 17:39, 30 July 2015 (UTC)

You don't seem to understand what I said. Say you determine that environment X₁ can support n₁ species, and environment X₂ can support n₂ species. You can not then conclude that the total number of species environments X₁ and X₂ can support is n₁+n₂, because you don't know how many are in common. When you have thousands or millions of possible environments, the overlapping Venn diagrams become absurdly complex. So, how do you propose to calculate the total for all possible Earth environments ? Finding the number for an individual environment is interesting, but simply doesn't lead to an answer to this Q. Then there would be the issue of determining the number of possible environments that could possibly exist on Earth. And, again, no PhD is required to read the Q, and see that it's not what you are answering. StuRat (talk) 17:58, 30 July 2015 (UTC)

I never said we'd sum the numbers of species. The relevant thing to get at overlaps in species distributions and overlapping environmental properties is Beta diversity. There's actually an entire body of research that explicitly addresses your sentences "Say" to "complex". Ok, now I'm done, have a nice day. SemanticMantis (talk) 18:27, 30 July 2015 (UTC)

Thanks for the offer. Sagittarian Milky Way (talk) 13:32, 31 July 2015 (UTC)

vital advances in plant evolution

• How many species are physically possible is a meaningless question, since species can be genetically isolated due to differences in ploidy (chromosome number) but otherwise be indistinguishable. What really matters is the number of niches available and occupied.

Looking at the question ecologically, there are several different breakthroughs in plant evolution.

The first big question is photosynthesis in eukaryotes, assuming we are going to exclude bacteria from our definition of plants. There are plenty of different routes that evolution could have gone down to produce multicellular photosynthetic land organisms. It so happens that this has only really happened with the green plant phylum. But land plants could certainly have evolved from the red algae and green algae had the green algae not beat them to it. The former are still very important in the ocean, with kelp an example of a brown alga. There are several thousands of species of red and brown algae, and other types of algae, the classification is in flux.

The next two major advances on land were the development of vascular tissue, which allowed tall upright forms like ferns, rather than mosses, and of seeds, which allowed evolution independnt of the need of spores to swim through rain water to cause fertilization. These events caused the evolution of forests and the colonization of arid lands. Forests had evolved before amphibians and insects appeared on land, and there were seed plants by the time of the dinosaurs. During this time, however, plant diversity was much lower than it is today due to the vagaries of fertilization. Plant species tended to cover large areas of similar terrane such as todays boreal forests given distribution of pollen and seeds by the wind doesn't tend towards locally specialized species.

It was the development of the flower, and the mutual feedback between pollinators and food plants that allowed the huge boom in plant evolution that occurred with the arrival of guided fertilization. While there are only about 630 species of conifer, a very ancient group, there are some 25,000 species of orchid, a very small but highly specialized branch within the flowering plants. Many plants such as orchids have their own unique species of animal polinator. This means they can become highly specialized to microhabitats that are totally unavailable to plants like conifers. Some orchids are found only on specific mountains. Such evolution doesn't happen with more primitive plants; small ranges in them indicate either relict populations only found on certain islands or species headed toward extinction.

Even then, the total number of flowering plant species, which far outnumbers all other plants combined, is estimated to be only a few hundred thousand species.

In the end it comes down to what ecological niches are available to and accessible by plants. There are parasitic flowering plants, carnivorous flowering plants, flowering plants (e.g., bromeliads) that live in the branches of other flowering plants, flowering plants that are only fertilized by one species of flying organism, and flowering plants that are going extinct because the megafauna that ate their seeds, allowing them to germinate, have been hunted to extinction. μηδείς (talk) 00:53, 31 July 2015 (UTC)

I guess we could've had a red world then, and human connotations of red being the color of bloodshed and war might be merged with peaceful Edenity. That would be more efficient though, sunlight peaks near the color that leaves reflect. And if red algae, which I think can live near the surface, is any good at absorbing blue light then it should be able to photosynthesize deeper than any other algae and be more likely to discover the mutation first cause it can live in more of the ocean. I don't know why we didn't go that route? Sagittarian Milky Way (talk) 13:32, 31 July 2015 (UTC)

Leaves are green because they absorb red and blue light more strongly than they absorb green. See also: purple bacteria. The real point about the "possible" number of plants is that many specialized species exist only because their niches have co-evolved with other organisms. There'd be no mistletoe without birds and oak trees, no orchids without certain insect pollinators. μηδείς (talk) 16:10, 31 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)

Incidentally, this week's Cosmic Video from Keck Observatory was Black Holes and the Fate of the Universe, presented by Dr. Günther Hasinger, directory of the Institute for Astronomy at University of Hawaii. This is part of the Keck Cosmic Summer School, and the videos are available at no cost. These videos are a great way to hear real scientists talking about cutting-edge research: it will help you see how they actually frame their questions.

Attention physics students: note that in his only slide with equations, the Director has conflated orbital velocity with escape velocity. Astronomers are the only scientists who can get away with such errors - a minor factor of 2x or 10x or 100x is just a "practical detail" in the field of astrophysics. Directors can get away with this type of thing, but when you calculate orbit velocity for your rocket, don't use the equation for escape velocity!.

The presentation discusses "mergers" of massive black holes, and black holes eating galaxy-sized masses, around 30 to 40 minutes into the video.

Nimur (talk) 13:38, 30 July 2015 (UTC)

Might want to be a little careful. At the event horizon, the orbital velocity is the speed of light. It's also the escape velocity as it creates Hawking radiation. Ta daaa! --DHeyward (talk) 02:51, 31 July 2015 (UTC)

Watch the video carefully. His statement, which I quote here verbatim, adding wikipedia article links is:

"When we are trying to send a rocket to the moon or even to the International Space Station, we have to give the rocket a certain speed in order for it to leave the earth... If I could throw a stone, the stone would go up and it would come down again. But if I could throw the stone with a velocity faster than the escape velocity, then it would leave the earth and go into orbit. Now, this velocity on the Earth is 11 kilometers per second."

Now do you see why I say he conflates escape- and orbit- velocity? He's talking about low earth orbit and he even specifically calls out the International Space Station, whose orbital speed is closer to 7 kilometers per second. In fact, it is possible to throw a stone with a speed slower than escape velocity, and the stone can enter a stable orbit - it may never fall back down again, provided that it is thrown in the right direction (your added velocity must impart the correct angular momentum to achieve a stable orbit)!

This is one of those cases where we need to understand conventional physics in order to describe what it is about black hole physics that makes them actually weird! The escape velocity of a black hole, measured relative to a point inside the Schwarzschild radius, is greater than the speed of light. At a different radius, the orbital speed is equal to the speed of light: this is exactly 1.5 times the Schwarzschild radius and it is called the photon sphere. Photon escape by Hawking radiation - which is a real phenomenon - defies the mathematics of conventional orbital mechanics, and is usually treated in a statistical fashion! Photons emitted by Hawking radiation are neither exceeding the escape velocity nor are they even exceeding the speed of light: they are photons, and they always travel at c - yet they are emitted! There is the novel physics of a black hole, and that is the reason that Hawking radiation is so groundbreaking. It is a different process that we cannot describe using only the equations of general relativity.

Nimur (talk) 14:42, 31 July 2015 (UTC)

To elaborate a bit, you seem to be exhibiting a common misconception about black holes: that they're all-consuming monsters that want to devour everything. Black holes are just objects that obey the same laws of physics as everything else. The only point of difference is we aren't currently quite sure what happens inside their event horizons. For that, we need a full-fledged theory of quantum gravity. But outside the event horizon, the gravitational force of a black hole works the same as that of anything else, including you. Large (meaning "having a high mass") black holes are just very very massive, so they have a correspondingly strong gravitational pull, but things on the right trajectories will still orbit a black hole just like they orbit stars and planets—indeed, we are orbiting the black hole at the center of the galaxy right now. If our Sun were replaced by a black hole of equivalent mass, the whole Solar System would continue orbiting it just the same. Of course, most life on Earth would die since it's ultimately powered by the Sun, but nothing would change Earth's orbit. --108.38.204.15 (talk) 15:32, 30 July 2015 (UTC)

It's probably a little early to say it's quantum gravity that is missing. All physics is a mathematical representation of observation. At the end of the 19th century, theoretical physics was "being wrapped up" as Newton and Maxwell had described evreything and there were just some small details that didn't fit. Those small details turned into quantum mechanics and relativity. We were wrong at both ends of the spectrum. Black holes appear as a singularity and I suspect the mathematics needed to describe will be as revolutionary as QM and GR. Planck time and all the things that currently defy the rules (or rather the things that make our observable approximations follow our models) --DHeyward (talk) 02:51, 31 July 2015 (UTC)

What will happen will depend on how much angular momentum they have, and the relative orientation of the spin. The binary black hole that comes about will orbit faster and faster. When a merger takes place an apparent non conservation of momentum can happen with a "kick' where the result can be pushed out at 1000km/second, gravitational waves carry the complementary momentum. Maybe the black hole will be ejected from the galaxy. Perhaps 5% of the mass will be lost as gravitational waves. Material taken for a ride may be ejected at high velocity, so stars may be sprayed in all directions from the merging core. Graeme Bartlett (talk) 01:19, 31 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 [11]].

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)

Does Dr. Oetker's actually sell plain oatmeal ? A Google search yielded products containing oatmeal, but not the oatmeal itself. Here's their oatmeal muffin mix nutrition: [12]. At only 2% RDA iron, they apparently haven't added any.

And note that when iron is added, it's just to make their numbers look better, they don't actually care if it can be absorbed or not. StuRat (talk) 14:06, 30 July 2015 (UTC)

Note that you're just being cynical and not doing any research or citing any references. Most forms of iron fortification do get absorbed by the body Human_iron_metabolism#Dietary_iron_uptake explains quite clearly that the common form of added iron is absorbed by the body at a rate of 10%-20% of intake. Animal sources of iron are absorbed at 15%-35% intake, but that is easily compensated by ingesting a bit more iron salts (Iron(II)_sulfate#Nutritional_supplement). Other forms of iron used for food fortification include Ferrous gluconate. Here's a nice report from the WHO that covers the use of food fortified with iron [13]. OP might like to take a look at that last link, it does list several foods and compounds that interfere with iron absorption. Finally, you don't even need fancy iron compounds if you get enough total iron, the Lucky Iron Fish [14] has already made huge improvements in anaemia levels, and that's just a simple lump of iron that you boil with your soup. Anemia#Oral_iron also has some good info on some of the common supplements and food additives. SemanticMantis (talk) 15:01, 30 July 2015 (UTC)

I included a reference listing the iron content of one of their products. StuRat (talk) 15:24, 30 July 2015 (UTC)

Duly noted, I should have said "any references that support your final claim" ;) SemanticMantis (talk) 15:27, 30 July 2015 (UTC)

Also, in many countries, including the U.S., the government requires that refined grains be fortified with nutrients, including iron, that are found in the bran and cereal germ, which are removed during processing. Whole grains retain these, so they aren't required to be fortified. --108.38.204.15 (talk) 15:19, 30 July 2015 (UTC)

Train deceleration

Why do trains in Asian countries such as Japan and South Korea accelerate and decelerate so fast? — Preceding unsigned comment added by 176.251.146.3 (talk) 17:41, 30 July 2015 (UTC)

Because they can? Fast acceleration gets the train up to its very high maximum velocity quicker, and fast deceleration permits it to continue at maximum speed longer before stopping. Robert McClenon (talk) 17:44, 30 July 2015 (UTC)

Hmm, let's look at some factors:

PROS:

1) Reduces total trip time.

CONS:

A) Uses up more energy, particularly in the rapid decel (as opposed to allowing the train to slowly decelerate due to friction). Some type of regenerative braking could reduce that.

B) In the case of traditional brakes, rapid decel causes wear on brake pads. However, in a maglev train, probably not, although heating might cause wear.

C) Can be uncomfortable for the passengers to undergo either rapid accel or decel, although depending on if the seat faces forwards or backwards, one of those should be easier on them than the other. Getting caught walking with a cup of coffee would be bad, too, so some warning would be appreciated. StuRat (talk) 18:09, 30 July 2015 (UTC)

So, they must feel the pros outweigh the cons. The main factor that might vary in Asian nations is more maglev trains, reducing concern over B. StuRat (talk) 18:09, 30 July 2015 (UTC)

It doesn't actually use more energy for the acceleration or deceleration itself. It uses more power, but uses that for a shorter time. It also uses more energy due to the higher air resistance at the higher speeds achieved earlier, of course. Regenerative braking should be fairly standard for electric trains in most advanced countries today. --Stephan Schulz (talk) 18:19, 30 July 2015 (UTC)

Of course, that's assuming that the energy-efficiency for the train's power plant is uniform at all power levels. Is this accurate for, say, the Shinkansen bullet train? Nimur (talk) 18:46, 30 July 2015 (UTC)

I believe, at least in the case of rapid braking, that it does use more energy, since more of the braking is done by the train, and less by air resistance and rolling resistance (in the case of trains with wheels). StuRat (talk) 14:15, 31 July 2015 (UTC)

In reply to StuRat's C), the comfort of passengers is determined mainly by the rate of change of acceleration (see Jerk (physics)). This can be high even on slow British trains, and is regularly felt on slow buses especially if badly driven. Dbfirs 20:08, 30 July 2015 (UTC)

To take a slightly different epistemological angle, countries like Japan and South Korea have invested heavily in high-speed rail. This means the rail infrastructure tends to be designed for higher speeds. High-speed rail also generally is designed to allow trains to accelerate and decelerate more rapidly, since the whole point is to get people to their destinations quickly. It's kind of a waste if your train has a high top speed but it takes forever to get to that speed! Designing for high top speed and rapid velocity changes generally goes hand-in-hand anyway. Tracks need to be sturdy, level, and as straight as possible, trains need to be able to withstand high stresses and have powerful engines, etc. --108.38.204.15 (talk) 18:28, 30 July 2015 (UTC)

They can accelerate and decelerate because each axle is a traction motor (see Electrical multiple unit). By distributing the traction engine, the train isn't limited by a central traction system. Every car is driven and the distributed mass and drive improves both acceleration and deceleration. It's all electrically driven. By contrast, diesel electric trains have electric motors only on the locomotive. Synchronizing all the axles is not trivial and is why it's not done everywhere and is one of the reasons high speed trains in Europe don't accelerate or decelerate as fast (see AVE Class 102 for example of high speed train in Spain that has only 2 drive units). Most braking is done using with either regenerative brakes or more commonly, Eddy current brakes so pad wear isn't an issue. --DHeyward (talk) 21:06, 30 July 2015 (UTC)

No, this is quite wrong. Provided that there is sufficient weight on the powered axles for the necessary traction to be achieved, the maximum acceleration of a train is determined by its power-to-weight ratio. It doesn't matter if there are a large number of small motors or a small number of large ones. The two "power cars" (locomotives) of that AVE class 102 have a total of 8 motors developing 1,000 kW each, and the train weighs 322 t (metric tons), so that's a ratio of 8,000/322 = about 25 kW/t. The N700 Series Shinkansen, built about the same time, has 56 small motors developing 305 kW each, and weighs 716 t, giving almost the same ratio at 17,080/716 = 24 kW/t. The acceleration capacity of the two trains should be about the same, provided that the AVE locomotives are heavy enough for the force from the motors to be practically used. Multiple-unit trains do have two big advantages (against a downside that is mostly in cost): they're easier on the track (no heavy locomotives) and they can be made to divide into shorter trains by simply uncoupling. But they don't have an advantage in performance. Also, there is no need to "synchronize the axles". --65.94.50.73 (talk) 04:50, 31 July 2015 (UTC)

The original question implies that trains in Asian countries DO accelerate and decelerate at a greater rate than similar trains outside Asian countries. I'm skeptical. What is the evidence before us that there IS a significant difference in rates of acceleration and deceleration? Dolphin (t) 06:44, 31 July 2015 (UTC)

Go ride them :). Japan most certainly accelerates faster. Spain acknowledges it in their design docs but it's not an issue on a long run, only when there are lots of stops. --DHeyward (talk) 07:23, 31 July 2015 (UTC)

Your caveat is why it's not equal (and also why a car with wide driving tires accelerates quicker than narrow tires for the same power to weight ratio). In practical high-speed trains power to the motor is regulated and measures slippage and creep. Power has to be reduced when wheels starts slipping too much but slippage is required for maximum acceleration. By distributing the weight and a driving motor each with it's own power control, the available torque is much higher. There's much more driving wheel surface in contact with the rail, all the weight of the train is on driving wheels (it's all the normal force of the full train weight, not just normal force of the mover weight), and each motor is driving with the optimum slippage. Top end speeds are the same but acceleration is much greater in the distributed case because the motors are running with maximum tractive force throughout the acceleration cycle. Japan has many stations and stops so they use distributed motors to maximize acceleration but it doesn't help top speed. When acceleration is a significant factor in trip time, distributed is better. For that reason, N700 Series Shinkansen accelerates to top speed much quicker than the AVE class 102 even though top speed is about the same and your power to weight is about the same. Distributed power delivery and control must be coordinated (synchronized was a bad word considering its meaning wrt motors) and it is more complicated with EMU's and is not simple and it's more expensive. --DHeyward (talk) 07:23, 31 July 2015 (UTC)

As a peripheral observation, this was also why the Southern Railway was in the forefront of electrification in the UK: it had the largest proportion of urban, suburban and rural commuter traffic (mostly to/from London) the associated high number of stations and stops, the passenger-driven motivation to minimize journey times, and the ever-present desire to minimize energy costs. Electrification enabled both better acceleration and improved efficiency (over coal/diesel). {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 13:33, 31 July 2015 (UTC)

July 31

What do the galaxies, galaxy clusters and galaxy superclusters revolve around? Do they change place?

The Moon revolves around the Earth, the Earth revolves around the Sun, the Sun revolves around the supermassive black hole at the center of the Milky Way.

Now a question will arise. What does the Milky Way revolve around? Is it that, like binary star system or triple star system, the Milky Way and other nearby galaxies revolve around themselves?

Do the galaxy groups also revolve around themselves? Do the galaxy superclusters also revolve around themselves?

But even if the galaxies, galaxy groups and galaxy superclusters revolve around themselves, this means they are fixed at a particular location in the Universe, they are not moving away from that place. The Sun is changing place within the Milky Way because it is revolving around the galactic center. But the galaxies, galaxy groups and galaxy superclusters are not revolving around something at the center of the Universe. So they are in a fixed place, right? --IEditEncyclopedia (talk) 02:30, 31 July 2015 (UTC)

The thing is, the moon doesn't technically orbit "the earth". The moon and the earth both orbit their common Barycenter. As far as galaxies go, they are definitely not "stationary", the discovery of this being one of the greatest discoveries of modern cosmology. , Vespine (talk) 04:22, 31 July 2015 (UTC)

It's all an illusion. Everything moves in a straight line. Mass and energy warp space to create the illusion. The 2D example is to travel on a great circle on the surface of the earth. You travel due east and eventually "orbit" to your origin but that doesn't change the straight line motion. The 2D plane you travel in is warped around a 3D sphere. Gravity warps 3D into at least 4D to appear to orbit. --DHeyward (talk) 04:40, 31 July 2015 (UTC)

... and there is no known unique centre of the universe: Earth is the centre, along with every other point in spacetime. See Dark flow for a possible non-rotational drift. Dbfirs 12:50, 31 July 2015 (UTC)