Wikipedia:Reference desk/Archives/Science/2010 April 19

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April 19

Rain will clear the skies of ash, but can we artificially fill up the water by nuclear power?

1. Many submarines and some large ships use nuclear reactors for propulsion, and for all of their energy needs.
   If one of them were to anchor up off the coast of Iceland and, running its nuclear reactor on "full steam" (pun intended), used all the heat energy available, then how much sea water could theoretically be evaporated per 24 hours?
2. Nuclear power plants often use seawater for cooling.
   If one of the power plants on the coast of Europe were to be solely employed to evaporate water, then how well would it do per 24 hours?

All I have heard about rain-making, earlier, is the Cloud seeding, but at least that part of the job is allready well and surely taken care of by the volcano Eyjafjallajökull on Iceland. Now, if only we could get some millions of Cubic metre of extra water up in the skies, to soak the volcanic ash...
--Seren-dipper (talk) 00:16, 19 April 2010 (UTC)

It would be insignificant. Even if you could get together a gigawatt of electricity generation to devote to evaporating water (and that corresponds to several nuclear power plants) it would only be equivalent to the energy from the sun on about 4 square kilometres of ocean (can someone check my arithmetic?). The sun is so much more powerful than anything we can create that there is really no point us trying to help it along. --Tango (talk) 00:26, 19 April 2010 (UTC)

That's correct. it would be completely insignificant. Besides, lack of humidity in the air is not the limiting factor that prevents rain. Atmospheric lift is the main controlling factor. BTW cloud seeding doesn't work either. Dauto (talk) 01:27, 19 April 2010 (UTC)

I question the accuracy of the last statement. Yes the state of research is rather poor, it's difficult to prove what would have happened if you hadn't seeded and and many of those who use or promote it don't have good evidence it works (and personally I expect it doesn't work as well as many of them may like) however

Cloud seeding has been shown to be effective in altering cloud structure and size and in converting supercooled liquid water to ice particles. The amount of precipitation due to seeding is difficult to quantify. Cloud seeding may also suppress precipitation.[citation needed]

Overall, there is general expectation that winter cloud seeding over mountains will produce snow, expressed by professional organizations.[1][2][3][4] There is statistical evidence for seasonal precipitation increases of about 10% with winter seeding.[5] The World Meteorological Organization has indicated that cloud seeding produces positive results in many cases but is dependent on many factors such as specificity of clouds, wind speed and direction, and terrain.

These don't exactly suggest it doesn't work (which I take to mean there's strong evidence it hardly ever or even never works). Also:

A 2003 study[23] by the United States National Academy of Sciences urges a national research program to clear up remaining questions about weather modification's efficacy and practice.

Which while not saying it works, hardly suggests the NAS thinks it's a clear cut case with strong evidence it never works.

As I mentioned there are plenty of people, particularly developing countries who use cloud seeding and while I would agree many of them don't appear to have undertaken research or otherwise have good evidence they're doing anything useful, some of this does take place in developed, democractic countries where there's perhaps lesser ability for completely useless programmes to be undertaken and usually some requirement for evidence for such programmes. (None of this means they're immune to carrying out nearly useless programmes with little evidence to support the benefit.) E.g.

In Australia, CSIRO’s activities in Tasmania in the 1960s were successful[citation needed]. Seeding over the Hydro-Electricity Commission catchment area on the Central Plateau achieved rainfall increases as high as 30% in autumn. The Tasmanian experiments were so successful that the Commission has regularly undertaken seeding ever since in mountainous parts of the State.

While uncited, it's easy to find evidence this programme continues in Australia [1]. Some of the latest research I could find [2] (PRs [3] [4])

The Chinese do do their own research although a lot of it isn't published in peer reviewed scientific journals (or at least recognised ones) unfortunately so many would feel it's next to useless, but e.g. [5] [6] [7]

Note that even if the effect is small that many would feel it's not cost effective, or it simply changes the place or time of rainfall, or is otherwise useless for many of the purposes it's advocated and used for, this doesn't mean it doesn't work per se.

Recently of course, various geo-engineering suggestions to reduce global warming, including cloud seeding are being consider, albeit not generally to produce or reduce precipitation, e.g. [8]

Nil Einne (talk) 09:17, 19 April 2010 (UTC)

I certainly don't see how it could help. When you look at those impressive photos of the volcano (this one, in particular) the white stuff coming out of the top is steam (well, water vapor) - the dark stuff is the ash. As you can see, there is already a lot more steam than ash - and the steam isn't winning! SteveBaker (talk) 01:51, 19 April 2010 (UTC)

Surely all the ash is way above the height that generates rainfall. —Preceding unsigned comment added by 86.4.186.107 (talk) 05:48, 19 April 2010 (UTC)

Some, but not all. StuRat (talk) 14:30, 19 April 2010 (UTC)

use for nuclear waste

What articles cover using the heat generated by nuclear waste to boil water after the nuclear waste is processed by "freezing" it into ceramic or glass marbles to fill up a tank through which water is passed? 71.100.1.71 (talk) 03:45, 19 April 2010 (UTC)

I don't think there is an article. The heat given of by wast is thought of as 'low grade' heat. In economic terms, the capital investment for the plant, machinery and maintenance, that would be need to utilize this low grade heat for something, would be more than the cost of using other energy sources. In other words, with current technology, it is not worth the effort.--Aspro (talk) 08:17, 19 April 2010 (UTC)

The OP correctly spelled "waste". Cuddlyable3 (talk) 08:51, 19 April 2010 (UTC)

This article: Nuclear reprocessing. Instead of using the heat directly, the parts of the waste that still contain usable energy are separated from the ashes, and then reused. The article should also give you links to reactors that are able to burn uranium down to basically nothing, with almost no leftover (radioactive) waste at all. The article should also talk about the pros and cons of doing so. Ariel. (talk) 09:12, 19 April 2010 (UTC)

Not down to "nothing", but rather down to stable (non-radioactive) elements and isotopes. StuRat (talk) 14:17, 19 April 2010 (UTC)

Err, you still end up with fission products, which are very nasty and radioactive. You just don't end up with as much waste as you do if you don't do reprocessing (you use up the transuranics and actinides). You still have nasty waste, though. Just less of it. It still takes hundreds of years to decay (and the fact that the half-life is shorter than the transuranics is an indication that it is a higher level of waste). --Mr.98 (talk) 14:29, 19 April 2010 (UTC)

I believe that there was some thought of using radioactive isotopes as a direct source of home heating, early on, before the dangers of radioactivity became apparent. Now, we'd also have to be concerned about terrorists getting hold of the devices and releasing the radioactive material in a city as part of a "dirty bomb".

One application where it might make more sense is in long-term human space flights, where using conventional fuel for heating is out of the question. Perhaps, once a fuel rod is "used up" in the normal electricity generating reactor, it could be retained as a heat source. StuRat (talk) 14:22, 19 April 2010 (UTC)

Radioisotope thermoelectric generator does something like this. There are rather specific criteria for which isotopes are good candidates for this. I'm doubtful that the random slew of fission products you get in high-level waste would have appropriate characteristics. --Mr.98 (talk) 14:29, 19 April 2010 (UTC)

For deep space exploration Stirling engines show more promise than RTGs due to their higher efficiency. NASA have had prototypes, running faultlessly, for a couple of years at a time. Mono isotopes would again be the best option for the heat source due to shielding considerations (with perhaps additional heat supplied by a focused solar collector). Exhausted fuel rods would require lots more shielding, which is what one tries to avoid in space craft. If the Moon is used as a staging post, then a 'minimum mass' reactor may be practical using Luna sourced material for the shield. Mass Estimates of Very Small Reactor Cores Fueled by Uranium-235, U-233 and Cm-245 These reactors should also have very long operating lives. --Aspro (talk) 17:39, 19 April 2010 (UTC)

Some radioisotopes (e.g. Co-60, Sr-90, I-131, Tc-99) are used in medicine, especially for diagnosing and treating cancerous tumors. Clear skies 24.23.197.43 (talk) 21:47, 21 April 2010 (UTC)

ISS framework overbuilt?

I see that the backbone of the International Space Station weighs 147 tons on earth. Given the weightless environment of orbit, what need is there for such strength?Bobstuart (talk) 03:55, 19 April 2010 (UTC)

Spacecraft weigh a lot for a variety of reasons. The ISS is manned, so it must be pressurized - therefore, it must be built to withstand the pressure gradient between its interior and the vacuum outside. Also, the modules must be structurally supported, so there is a need for some quantity of material to connect the pieces. Finally, keep in mind that the space station components must be built on the ground (in "1-G") and survive a very vigorous shaking during launch (possibly subject to serious vibrations and accelerations). The structure has to withstand all of these conditions. In any case, I think you might underestimate just how much materials actually weigh (rather, how much mass they have). All told, 150 tons is not a whole lot of material; you might try to compare the mass of a similar-sized office-building on Earth. I've seen estimates for the mass of a house averaging out to about one to two tons per square-foot of occupied area (of course, the mass isn't uniformly distributed, with more mass in the walls than on empty floor); so the ISS weighs about as much as a small corner of your kitchen! Considering its habitable volume, it's actually pretty light. You might also want to try comparing it to an aircraft. A top-of-the-line single seat F-35 has a takeoff weight of about 30 tons - again, the ISS is pretty darned light, considering that it houses around six people "comfortably" - living areas, bathroom, work areas, laboratory, and exercise facility! Nimur (talk) 05:18, 19 April 2010 (UTC)

First, it's vanishingly unlikely that it is overbuilt: given the cost of lofting mass into orbit, you can be reasonably sure that the rocket scientists pared the weight to the bone. Somewhat per Nimur's answer, you're perhaps confusing weightless with massless. As & when the ISS' position is moved, the structural components need to get all of the mass to move in lockstep; weight is not very relevant. Mass is, and needs a structure sufficient to enable all components to accelerate and then decelerate without coming to pieces. --Tagishsimon (talk) 10:20, 19 April 2010 (UTC)

That's the key here - the impact force when (for example) a 16 tonne remote controlled resupply vessel or a 78 tonne shuttle docks with the ISS is dependent on the mass - not the weight (Force = Mass x Acceleration) - and the mass is the same whether in free-fall or on earth. Also, the ISS needs to be boosted up to a higher orbit a couple of times a year - either using the engines of a docked spacecraft - or using the limited capability provided by a couple of rocket motors on the Zvezda module. So the ISS needs a certain amount of structural strength to avoid breaking up under that (rather gentle) acceleration too. But it is also true that the plans for the space station were scaled back after initial design and the construction of some of the parts were complete before that decision was made (8 modules of the 23 that the ISS was originally designed for were cancelled) - so there may be some over-design inherent in that process. SteveBaker (talk) 13:28, 19 April 2010 (UTC)

This brings up an interesting Q: Could it be built lighter if they used a series of widely distributed, tiny, continuous booster rockets for station-keeping ? Think of flames the size of lighters. Or, this might be a good application for ion engines, which are more efficient, but have very low thrust. Docking might need to be more gentle, too, perhaps using an automated system. The only flaw I see is if the station is occasionally "knocked out of position", say by contact with a cloud of space gas or the exhaust plume from a passing rocket. StuRat (talk) 14:02, 19 April 2010 (UTC)

No. Distributing the propulsion over many small rockets would degrade performance. Two problems are: inert mass and specific impulse, probably the most important metrics for "efficiency" of a rocket engine. Smaller engines have a higher inert mass fraction - you need proportionally more tube, pipe, valve, fuel tank, and so forth, per unit of energy extracted. And smaller engines, because of size constraints, generally must use designs with poorer specific impulse, meaning "worse mileage per gallon" (specific impulse is a more accurate description). You would significantly decrease the propulsion system effectiveness per unit mass if you split it up that way. What you might gain is high-frequency maneuverability - see reaction control system for one use of "tiny boosters." As far as ion engines, there are current technological limitations and practical issues with the total impulse - so while they have great specific impulse ("fuel efficiency"), they've got very little total power (no good land-vehicle analogy exists, but think of a super-efficient engine which is constrained to only operate at a couple miles per hour - great for some applications, but terrible for moving a large vehicle). Nimur (talk) 15:34, 19 April 2010 (UTC)

That's "terrible for rapidly accelerating a large vehicle", but great for slowly moving it (or keeping it from moving, in this case), in the absence of any friction. Do you understand that I propose using the ion engines continuously, for station keeping (not just for brief periods as conventional engines are used) ? Thus, if they are used for 1000 times the duration, then 1000 times less thrust is fine. Ideally the orbit would be kept completely constant in this way, as opposed to being allowed to decay, then corrected. This would have other advantages, due to not having to deal with a variable orbital height, speed, and period. StuRat (talk) 16:54, 19 April 2010 (UTC)

Right. But it doesn't matter if they're used continuously or non-continuously. The total amount of impulse is the limit - $F\Delta t$. Measures of specific impulse (and total impulse) are already normalized so that it is easy to compare different types of burns, including fast powerful burns and slow, steady, low-intensity burns. Ion engines have higher specific impulse but less total impulse than we can pack into a chemical rocket. Perhaps technology improvements will change the maximum total impulse, as it is an engineering limit, and not a physical limit. Consequently, for a given mass budget, a chemical rocket is more capable of delivering the impulse (and therefore, for the ISS as a whole vehicle, the required delta v) necessary to station-keep. Nimur (talk) 17:01, 19 April 2010 (UTC)

Here's a good read, StuRat: Smart 1#Spacecraft design. As you can see, the Hall effect thruster was very efficient in terms of energy extracted per mass of propellant. But the total quantity of energy extracted, was actually abysmally small. Because the spacecraft was tiny (300 kg or so), this small quantity of energy was sufficient to reach 3700 m/s delta V, mostly for lunar injection; but to maintain a stable orbit to make this possible, they had to fly circles around the planet. Really, the magic was in precise mathematical analysis to optimize the gravity assist from the moon with as little energy expenditure as possible. I doubt this technology would be remotely feasible for station-keeping against gas drag. But what do I know... Nimur (talk) 17:12, 19 April 2010 (UTC)

Are you counting the reduction in the weight of the frame, which distributed, lower thrust ion engines would allow ? StuRat (talk) 17:10, 19 April 2010 (UTC)

Does anybody have some numbers? Frame weight vs other bits? Maximum accelerations? Certainly, those could be reduced by shock absorbers for the docking process and by using ion drive or smaller rockets, which might well save more structural weight than they cost in fuel. I agree that the frame might see its highest loads during the trip to space, but perhaps it is not needed in space. Very few lightweight modern vehicles use a separate frame. Aircraft have been largely monocoques since the 30s.

One of the funniest pictures I ever saw was of an (Atlas?) rocket in a museum. The pressure to the upper fuel tank had failed, and it had buckled under the weight of the payload. The ISS's occupied modules are pressure vessels, intrinsically strong and rigid. They could have been reinforced with aramid windings if any more structure was needed, and gained a lot of protection from space junk or meteorites.

Small sub-frames would suffice for mounting solar panels, radiators, etc. If those components are over-built soly to survive launching, they could be re-designed to reduce inertia loads by having packing material discarded after delivery. All connections could be designed with the minimum rigidity needed, to help localize any impact damage. —Preceding unsigned comment added by Bobstuart (talk • contribs) 08:06, 20 April 2010 (UTC)

I'm skeptical of the argument that the heavy frame is needed for the trip into space, as the components are brought up a few at a time, and can be well packed to protect them from g-forces. StuRat (talk) 13:37, 20 April 2010 (UTC)

sperm for Iceland

Seriously, for those not in the know. Icelanders want diversity in there population due to many inherited genetic flaws. Is there somewhere I can get more information on this and find possibly a contact through which I can donate my sperm? 71.100.1.71 (talk) 03:56, 19 April 2010 (UTC)

Maybe they prefer some who can spell "their"?--Lgriot (talk) 07:39, 19 April 2010 (UTC)

What? It's about the population of there, thus "there population".—Tamfang (talk) 03:40, 20 April 2010 (UTC)

...oops, I meant thar population as me kin foke would harv me say. :-{ 71.100.1.71 (talk) 07:20, 22 April 2010 (UTC)

_{no, Tamfang , it is that population, to rhyme with tw**}

Here is a link to the Iceland Directorate of Health, which could provide some leads. Ghmyrtle (talk) 08:10, 19 April 2010 (UTC)

Joke responses

You must clearly specify whether your donation will be in U.S. or Imperial gallons which are 3.785 or 4.546 liters respectively. Cuddlyable3 (talk) 09:13, 19 April 2010 (UTC)

Are you trying to be BB? The OP didn't suggest anything about donating gallons of material. Maybe the intend to donate in litres? Or more likely in samples which I suspect (somewhat supported by Sperm donation) is the normal way sperm banks take donations. (The samples then being divided into seperate vials, the number depending on sample volume and practice of the sperm bank.) Or they're flexible and would donate in whatever units the Icelandic authorities want? Nil Einne (talk) 10:23, 19 April 2010 (UTC)

Iceland enjoyed massive injections of Anglo-American sperm during the Second World War. DuncanHill (talk) 10:41, 19 April 2010 (UTC)

"Enjoyed" you say? I'd like to see a reference to back up that claim.--Rallette (talk) 12:06, 19 April 2010 (UTC)

how do you cite the wistful look on an old lady's face as she recalls the young men who used to pop round for a helping of puffin? DuncanHill (talk) 12:13, 19 April 2010 (UTC)

Indeed. The things that lie concealed behind the formulaic "personal communication with author".--Rallette (talk) 12:20, 19 April 2010 (UTC)

...Actually I was thinking in terms of drums so I could include what I saved from years long ago. 71.100.1.71 (talk) 07:37, 22 April 2010 (UTC)

Realistically, it seems that most IVF in Iceland is contracted out to other Nordic countries. Cryos International, out of Denmark, has a network of clinics and physicians. Because of the nature of this topic, they require you to register and log in in order to contact clinics; they are not looking for people who are just joking around about sperm donation. Nimur (talk) 17:22, 19 April 2010 (UTC)

being really happy ==> more brain damage?

What prevents dopamine neurotoxicity from being a problem in "naturally happy" people? For example, the intense rushes induced by naturally-produced beta-endorphins and runner's high? John Riemann Soong (talk) 04:08, 19 April 2010 (UTC)

My understanding is that dopamine neurotoxicity requires concentrations massively higher than could be achieved naturally -- it requires drugs, in other words. Also endorphins, which are related to opium, having a considerably stronger effect of suppressing the pain/suffering system than of activating the dopamine-dependent reward system. Looie496 (talk) 06:02, 19 April 2010 (UTC)

Yes, but it's possible to be really high while on an endorphin rush, to the extent that I will attest to its greater potency over alcohol or even methamphetamine. Which makes me wonder about the neurotoxicity of "natural" endorphin rushes (in general, not asking for medical advice). I know that if you combine physical exertion with a socially intense situation (like a party) the rush can be mind-blowing. John Riemann Soong (talk) 06:19, 19 April 2010 (UTC)

In addition to the levels being lower for a "natural high", the duration is also shorter. Unlike a 24-hour artificial high, a natural high probably only last a few hours, at most, and certainly not during sleep, giving the body time to reset/repair. StuRat (talk) 13:48, 19 April 2010 (UTC)

There are different kinds of "naturally happy" people. Some people go "happy" and benign after a stroke kills off some of their brain (and some do the opposite). I would not assume a naturally happy person has higher dopamine. --BozMo talk 09:29, 19 April 2010 (UTC)

Happiness is not a very precisely defined term. There is however evidence that people with extroverted personalities, who tend to be more sensitive to reward than average, generally have higher levels of brain dopamine function. I am not aware of evidence for any kind of natural motivational state giving rise to toxic levels of any brain chemical, with the exception that there is evidence for brain damage produced by stress-induced cortisol. Looie496 (talk) 22:36, 19 April 2010 (UTC)

Arterial injuries

Before I ask I should say that this is not a request for medical advice. I am not asking what one should do in the situation described, merely what medical opinion holds the prospects to be. I should also say that trying to picture this is not for the squeamish, but here goes. The article on blood squirt says that in the case of carotid arteries, "a completely severed artery will spurt blood for about 30 seconds and the blood isn't going to spurt much higher than the human head. If the artery is just nicked, on the other hand, the blood will spurt longer but will be coming out under pressure and spraying much further." If a person suffers an injury such that blood is squirting out of them under pressure like this, is there any hope for them? The mere thirty seconds until enough blood is lost that it no longer spurts suggests not to me, in the case of full severance, but I'm interested in the second scenario described in that quote. I suppose what I'm asking is whether blood can possibly clot under such high-pressure conditions, or whether applying pressure to a wound like that could possibly stem the flow. I suspect that in an operating theatre something could be done but I struggle to imagine how any victim of an injury to a major artery outside of such a favourable setting could do anything to save themselves. Am I right? Thanks in advance. — Trilobite 05:06, 19 April 2010 (UTC)

No severed major artery can clot fast enough to prevent death by exsanguination, but exsanguination can often be prevented by pressure on the wound in all major peripheral arteries, including the lower aorta. The carotids and upper aorta are a special case because the blood supply to half the brain would be immediately terminated even if pressure is applied to stop the bleeding. alteripse (talk) 10:54, 19 April 2010 (UTC)

Well, not quite -- depending on the patency of the vertebral arteries and the communicating arteries in the circle of Willis, even the complete loss of flow through a single carotid artery may not (and should not) fully interrupt the blood supply of a complete hemisphere. I know of cases where patients have both carotid arteries fully occluded (by atherosclerotic plaques) but who suffer no conspicuous symptoms — their brains are completely supplied with blood through the vertebral arteries. TenOfAllTrades(talk) 17:19, 19 April 2010 (UTC)

Perhaps, but collateral circulation is more likely benefit a gradually developing occlusion rather than a sudden complete one-sided interruption. While I would not be surprised if there have been occasional survivors I suspect those who do not suffer massive damage or death are in a small minority. alteripse (talk) 19:05, 19 April 2010 (UTC)

Oh, I agree that a slowly-developing occlusion will tend to lead to adaptation (and enlargement) of other vessels — but I would hesitate to jump to the conclusion that acute closure of a single carotid will lead to complete cessation of blood flow in one hemisphere. Part of the problem is that injuries which rapidly and completely occlude one otherwise-healthy carotid artery are quite rare; it's difficult to know exactly what would happen to a healthy individual in that situation. I do know that surgical ligation of the common carotid is indicated from time to time, but I'm having difficulty finding papers on recent cases. This paper suggests that roughly half of surgical ligations are accompanied by neurological symptoms or death, but it only deals with cases up to the early 1950s. TenOfAllTrades(talk) 21:53, 19 April 2010 (UTC)

To Alteripse & TenOfAllTrades: carotid endarterectomy involves cross-clamping the carotid artery. Axl ¤ [Talk] 07:39, 20 April 2010 (UTC)

can combine theory

DEAR SIR, GOOD DAY TO YOU.I WANT TO KNOW ABOUT SUPER STRING THEORY CAN COMBINE DNA STRUCTURE? NUCLEAR FUSION CAN COMBINE QUANTUM THEORY? PLEASE REPLY ME.THANK YOU. KOKOGYI,BURMA —Preceding unsigned comment added by 203.81.72.200 (talk) 05:53, 19 April 2010 (UTC)

First, please don't type in all caps; it is unpleasant to read. Anyway, what do you mean by "combine"? Someguy1221 (talk) 06:08, 19 April 2010 (UTC)

There can be very few connections between DNA structure and super-string theory. They are not at all the same sort of string!

Quantum mechanics does have some bearing on Nuclear fusion, but it is not essential for the basic theory.

Read our articles (linked above) for more information. I suppose that quantum theory could include nuclear fusion in its predictions, and super-strings are supposed to explain the whole universe, but they haven't got very far! Dbfirs 11:57, 19 April 2010 (UTC)

See the second comment on this blog posting Count Iblis (talk) 20:55, 19 April 2010 (UTC)

Test for swelling in knee joint

I vaguely remember a clever test for swelling in the knee, which involved the patient sitting with legs extended and the practitioner stroking the knee joint to empty it of fluid and then stroking it once more, in order for it to "fill up" again, if any swelling is indeed present.

I've tried Googling for it, but so far without joy. Can anyone point me in the right direction?

And no, this is not a request for medical advice, I'm not planning on using any information gained for diagnosis etc just assuaging curiosity. --Dweller (talk) 10:04, 19 April 2010 (UTC)

Milking the knee. Axl ¤ [Talk] 20:39, 19 April 2010 (UTC)

Thanks! --Dweller (talk) 10:19, 20 April 2010 (UTC)

Air Conditioning

is it true that split air conditioners are not capable of taking fresh air i.e. whether it recirculates the same air? if so the oxygen content will decrease in the room. 203.199.205.25 (talk) 10:21, 19 April 2010 (UTC)

This is not normally a problem when there are windows and doors to provide some air circulation, but in an overcrowded or sealed building there might be a build-up of carbon dioxide and a lack of oxygen even when the air conditioner is blowing cold air. Most countries have regulations about air changes per hour in buildings. Photosynthesising plants can help to restore the balance, but opening a window is usually more effective. Dbfirs 12:21, 19 April 2010 (UTC)

Well, think about it for a moment. It's not really any different from being in a room without any air conditioning. The oxygen depletion in such cases is hardly serious! SteveBaker (talk) 13:09, 19 April 2010 (UTC)

Circadian rhythm abnormalities in non-humans?

I recently discovered that I have delayed sleep phase syndrome, i.e. that my mind and body are biologically programmed to be most alert in the evenings and late at night and to crave sleep in the morning. I find myself wondering if natural circadian rhythm abnormalities have been observed in any other species. Does it ever happen that a member of a generally nocturnal species simply can't sleep during the day and can't stay alert at night? Or do diurnal non-human animals ever have a condition like mine? I know that species-atypical behavior is in most cases likely to get an animal in the wild killed, but has this ever been observed of animals in captivity (as the animal's natural behavior, not the result of any kind of human manipulation)? 71.104.119.240 (talk) 10:42, 19 April 2010 (UTC)

Think. You seem to be asking if a member of another species went to a doctor and complained of symptoms indicating that its sleep/activity cycle was out of synch with its peers. Or are you asking whether veterinarians ever make a diagnosis of delayed sleep phase in pets or farm or zoo animals? Or whether ethologists watching wild animals have ever diagnosed one as having an abnormal sleep cycle? Or whether the circadian rhythm pattern of a whole species fails to match some external standard derived from other species? alteripse (talk) 10:48, 19 April 2010 (UTC)

A large part of why human sleep patterns get messed up is that they can, without deadly consequences. This is also true of some other animals, like house cats. While they are naturally nocturnal, they can adjust their schedule, just like we can. Most animals, on the other hand, would stay in their nest/den during normal sleep time, whether they were actually asleep, or not, and go out to hunt for food when it's time for that. If they didn't get any sleep during the last sleep period, they would likely be sleepy enough when the next sleep period hits. Thus, unlike with humans, it's self-correcting. StuRat (talk) 13:34, 19 April 2010 (UTC)

There are lots of genetic mutations known to induce circadian rhythm abnormalities. The most extensive knowledge is for fruit flies, but there are also rhythm-altering mutations known for mice, rats, and maybe hamsters. In most studies the mutations are artificially induced, for example by subjecting fruit flies to X rays. Such mutations are bound to occur naturally to some degree, but assessing circadian rhythms is quite laborious, so there isn't very much information about their prevalence. (A caveat, though, is that the literature on circadian rhythms is vast and there may be work out there that I'm not aware of.) Looie496 (talk) 22:29, 19 April 2010 (UTC)

I wasn't aware that my question was that complex. How my question could be construed to be about anything other than human observation of abnormal patterns in an individual member of a species, I can't fathom. I'm not an idiot; I know animals don't go to the doctor and I wouldn't consider the biological patterns common to most members of a species somehow aberrant just because some other species has a different pattern. (The fact that I know the words "nocturnal" and "diurnal" perhaps ought to suggest that I'm familiar with the concept that different species often exhibit different patterns, no?) I don't care if there's any kind of formal diagnosis; I'm simply wondering if there has ever been an observation of an animal, in the wild or captivity, that had a persistent abnormal sleep cycle comparable to a human circadian rhythm sleep disorder. Looie496 gave the kind of answer I was looking for - thank you. 71.104.119.240 (talk) 03:38, 20 April 2010 (UTC)

Considering that the only way to verify that an animal is actually suffering from DSPS (the same way to verify a human is actually suffering from it) is to undergo treatment; you might ask about reports on animal studies of the various forms of treatment. Short of that, as someone else eluded to, there is no way to tell if an animal has DSPS or is simply lazy. --144.191.148.3 (talk) 17:57, 20 April 2010 (UTC)

I wasnt intending to insult you. Rather than accusing you of something silly, I was attempting to remind you that such a "sleep disorder" has a social and a subjective component that cannot exist in animals. The closest you could get would be some experimental situation where if you messed up the circadian rhythm of an expermental animal in a way that mimicked the objective features of the human sleep disorder, you might describe it as having the disorder, but even this model would have about the same relation to the human disorder as diagnosing depression in rodents. I stand by my suggestion that if you think about the components of human sleep phase disorder you will yourself recognize that it's not a question likely to have a meaningful answer. alteripse (talk) 19:14, 20 April 2010 (UTC)

Thank you, alteripse. I do understand where you're coming from, I appreciate your taking the time to respond to my question, and I'm sorry I was so touchy. I do see what you mean - that's why I used the word "abnormalities" instead of "disorder" in my question. I'm asking more about physiology than consequences. I recognize that the practical consequences will be different for humans and animals. I'm less concerned about whether the animals get to sleep or not than the observation of their circadian rhythms. Regardless of social consequences, biological systems that work in pretty much the same way can break down in pretty much the same way. A friend of mine has had hip trouble and so did one of my dogs. Another dog I know takes medication for anxiety, as do I. I presumably have some sort of abnormality of the suprachiasmic nucleus of the hypothalamus or a related structure; I wonder if any similar abnormality has been detected in members of another species on the basis of core temperature readings, unusual patterns of eating, sleeping, and/or alertness, etc. It may be an unusual question, and it's very possible that, for the reasons Looie mentioned among others, few if any scientists have taken an interest in naturally abnormal circadian rhythms among non-humans (or received a grant to research it) - but I still believe it's a legitimate question. 71.104.119.240 (talk) 20:13, 20 April 2010 (UTC)

Close. It's Suprachiasmatic nucleus --Aspro (talk) 21:59, 20 April 2010 (UTC)

Well, I told you mine wasn't quite right, didn't I?  ;-) (Thanks Aspro. I really should have caught the mistake when the link came up red.) 71.104.119.240 (talk) 03:42, 21 April 2010 (UTC)

Greenwich meridian.

Why does not the 0 deg meridian(WGS-84) pass through the Greenwich meridian?Or otherwise why is not the 0 deg meridian in WGS-84 chosen to pass through the Greenwich meridian? —Preceding unsigned comment added by 116.90.224.116 (talk) 11:14, 19 April 2010 (UTC)

You will find it explained here.--Rallette (talk) 11:54, 19 April 2010 (UTC)

Basically, an accidental difference, and since the choice is arbitrary, and the difference is only five and a half seconds of arc, it has not been necessary to standardize. Also, because of drifting tectonic plates, exact longitudes are impossible over decades or centuries. Dbfirs 12:09, 19 April 2010 (UTC)

Not "impossible" -- geographic longitude could be fixed via stellar right ascension (corrected for other variations emerging over time). Of course, the land "at" any longitude would shift over time, but the longitudes themselves could be fixed. 63.17.75.216 (talk) 04:15, 22 April 2010 (UTC)

How much ash to stop a car?

If the amount of volcanic ash kept increasing, which would be the first to stop operating - humans or cars? Thanks 89.240.44.159 (talk) 12:26, 19 April 2010 (UTC)

There are plenty of cases where people have driven cars through ash plumes - wrecking their engines in the process - yet living to tell the tale. People might well have problems breathing in dense ash - but we don't have to - we stay indoors or breathe filtered air or wear masks or whatever. Car engines can't do that. It's a bit complicated though - if the ash is fairly coarse, it clogs the air filter and the engine stops running without serious damage. If the ash is very fine (which it evidently is in the case of the current icelandic volcano) then it can bypass the filter and instead do serious damage to pistons, piston rings and cylinder liners that would probably allow the engine to continue to run - but make it burn oil and have poor compression. The ash can also work its' way into lubricated moving parts and cause rapid wear to bearings and such like. This USGS document is worth reading. "Change oil, oil filters, and air filters frequently (every 50 to 100 miles in heavy dust, i.e., less than 50 feet visibility; every 500 to 1,000 miles in light dust)." SteveBaker (talk) 13:06, 19 April 2010 (UTC)

Also note that people who must go outside in smoke/ash will take action to protect themselves, like wearing a wet rag over their mouth to act as a filter. StuRat (talk) 13:28, 19 April 2010 (UTC)

Wet rags may be better than nothing in an emergency, but this would be an opportunity to use some up of those N95 respirators which got stock-piled against the deadly swine flue epidemic (remember that?) . Recommended dust masks for protection from volcanic ash--Aspro (talk) 13:47, 19 April 2010 (UTC)

Those don't work on kids and only last from a few hours to about a day. StuRat (talk) 14:43, 19 April 2010 (UTC)

Electric cars would do quite well, as would a human wearing MOPP gear. As noted above, it is greatly going to depend on the density and size of the ash particles in question. 65.121.141.34 (talk) 20:03, 19 April 2010 (UTC)

Assuming unprotected unmodified cars and outdoors people. As the dust increases, would the cars or the human be the first to stop moving? 92.27.146.2 (talk) 23:32, 19 April 2010 (UTC)

Unless your car is a convertible, I would suspect the car would die first if it is only large ash particles, and the person would go first if they are very small, as the car itself would provide some protection from larger particles but much less against small particles. This is conjecture, and may greatly vary on what type of car you are driving, how fast you are driving it, how good your air filter is etc. Googlemeister (talk) 16:29, 20 April 2010 (UTC)

Billiard ball and slipping

I'm trying to do a question that revolves around striking a billiard ball horizontally with a cue, at a height above the centre of mass. I won't give the question, but can I have some hints on how to approach this? Physics isn't my forte. I think I want to resolve the impulse into a tangential component to find the angular velocity - but then what do I need to do to find the linear velocity? Thanks :-) 131.111.248.99 (talk) 12:57, 19 April 2010 (UTC)

If the cue strikes the ball at its center height, the ball translates across the surface of the billiard table but it doesn't rotate. If the cue strikes the ball slightly above the center, the ball rotates as well as translates. If the point of impact is exactly right, the rate of rotation will equal the linear velocity divided by the radius of the ball so that the ball will roll across the surface of the billiard table without any sliding relative to the surface. Dolphin (t) 13:10, 19 April 2010 (UTC)

I'm no physicist either. Under what circumstances would there be no rotation but also no friction? ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:39, 20 April 2010 (UTC)

Friction with the table felt will make it roll, rather than slide, if you strike the ball anywhere near that point. StuRat (talk) 13:25, 19 April 2010 (UTC)

The objective of the question is to determine the circumstances in which there is no sliding friction between the ball and the felt. Dolphin (t) 13:28, 19 April 2010 (UTC)

How do you know that ? The question isn't even listed. StuRat (talk) 14:37, 19 April 2010 (UTC)

That question is also in my physics textbook. It seems to be a universal question to accompany the chapter on angular motion, angular acceleration, polar moment of inertia etc. A billiard ball can contact the surface of a billiard table with any combination of linear velocity and angular velocity. If the ball is translating without rotating, friction quickly gives the ball an angular acceleration so that it rolls without sliding, but some energy has been lost to the friction. Conversely, the ball can be rotating without translating, but friction quickly provides traction, the ball accelerates across the surface, but some energy has been lost to the friction. There is a critical case of particular interest, and that is the case where angular velocity is equal to linear velocity divided by the radius of the ball. In this situation there is no sliding so no friction and energy is not lost (in the short term.) Dolphin (t) 07:45, 20 April 2010 (UTC)

Unfortunately, finding that point is part of the question. :-) I'm not sure how to set up my equations to begin with. 131.111.248.99 (talk) 13:12, 19 April 2010 (UTC)

The linear momentum of the ball will be the impulse provided by the cue. The angular momentum will be force x (distance above center of ball) x time. Force and time are the same in both equations. Linear momentum is mass times linear velocity; and angular momentum is polar moment of inertia times angular velocity. If you set angular velocity equal to linear velocity divided by radius, it should be possible to solve for (distance above center of ball). Dolphin (t) 13:22, 19 April 2010 (UTC)

I just don't see how this general premise can be correct. There is always going to be some degree of friction between the ball and the felt, no matter where you hit it or how it's rotating. If you have a felt surface of sufficient size, the ball is eventually going to stop, no matter where or how hard you hit it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:51, 20 April 2010 (UTC)

That's true, but we are talking here about the initial motion of the ball (first few milliseconds), and the position of strike to transfer maximum momentum to the ball. If the ball rolls without slipping, then the friction force is very much lower and can safely be ignored when considering the initial motion. (Unless someone has spread treacle on the table) Dbfirs 20:02, 20 April 2010 (UTC)

help with the seasons

I dont get it, how the earth is tilted and hence the seasons.I can only understand it if the earth moves on its axis i.e =0 degrees on the equinox and tilts back 23.5 degrees in winter and tilts forward 23.5 degrees in summer. I feel that I dont understand the diagrams that are usually given as it makes it look like the sun is moving.

I assume that the earth and the sun are in the same plane, so how is the sun moving.

Can you show me an experiment to do which will show me clearly the shadows? —Preceding unsigned comment added by 89.241.1.51 (talk) 14:39, 19 April 2010 (UTC)

The sun is not moving, but the earth is. Don't assume that they are both in the same place. Dauto (talk) 14:55, 19 April 2010 (UTC)

The OP said "same plane", not same place. Dismas|^(talk) 14:56, 19 April 2010 (UTC)

Both the Earth and the sun are moving. For simplicity, it is common to consider the sun somewhat stationary, at least relative to the motion of the planets - but we shouldn't be planting heliocentric theory into the OP's mind. Nimur (talk) 15:43, 19 April 2010 (UTC)

Does the diagram in Seasons#Astronomical help? You may have the misconception that the axis always points toward (or away from) the sun as the earth moves in its orbit. This is incorrect; as you can see in the diagram, the axis always points in the same absolute direction; as a result, the north pole sometimes points toward the sun, and sometimes away from it. -- Coneslayer (talk) 15:00, 19 April 2010 (UTC)

Okay, some words and then some sort of experiment. There are a three things going on with the earth worth mentioning. First. it rotates around its own axis (i.e. spins) once every 24 hours. That gives us days & nights, and has nothing to do with seasons. Second, it orbits the sun every 365 days or so ... think about a fixed sun, and a planet revolving around it - perhaps in terms as simple as a couple of balls on your floor. Now it so happens that the axis of the earth about which it spins every 24 hours is 23.5° off vertical, relative to the plane of motion of the earth (or the floor, in our simple analogy). What is more, the axis always points the same way irrespective of the motion of the earth around the sun (and in our example, whether it is on this side of the centre ball, or that side, the axis still point at that wall over there. So. Start with the earth in a position in which its rotational axis is pointing vaguely towards the sun. And then consider the position six months later, when the earth has travelled half way around the sun. Now, think about which part of the earth is nearest the sun in each of these two cases. In the first case, it will be a line around the top half of the earth (remember, the earth is still spinning). In the second case, a line around the bottom half of the earth.

Now, the experiment. Get a ball, mark the north & south pole on it, and set it up so they are about 23.5° off vertical. Instead of the sun, have a felt tip pen sited horizontally at about the middle of the ball. Get the axis of the earth vaguely pointing in the direction of the sun ... bring the earth to the felt tip pen, and spin it around its axis. Then move the axis so that it is pointing away from the sun. ... bring the earth to the felt tip pen, and spin it again around its axis. You should end up with a distinct pair of lines, hopefully approximating the tropics of cancer & capricorn. And the point is, half of the time it is the northern hemisphere which gets more sun than the southern; and half the time it is the other way around. And that drives the seasons. Hope that helped somewhat. --Tagishsimon (talk) 16:01, 19 April 2010 (UTC)

You don't really need an experiment...but a few minutes spent playing around with a ball and a flashlight will hopefully make this clear to you (put the flashlight over the other side of the room from the ball and do it with the room lights turned off). Ask yourself this: Why is it that in any 24 hour period, we have more hours of daylight in summer and less in winter? Why is it that there are months of continuous daylight and months of continuous night at the north and south poles? SteveBaker (talk) 18:41, 19 April 2010 (UTC)

(from OP) Got it! thx Tagi —Preceding unsigned comment added by 89.241.1.51 (talk) 21:48, 19 April 2010 (UTC)

Do royalty masturbate?

Well, do they? —Preceding unsigned comment added by 188.221.55.165 (talk) 18:28, 19 April 2010 (UTC)

They're not such a homogeneous group that a simple yes or no would suffice, even did we have access to that sort of private information. However they're humans, and so on balance, they're as likely to do so as any of us. --Tagishsimon (talk) 18:34, 19 April 2010 (UTC)

Firstly - how on earth do you think anyone would be able to answer that authoritatively? Secondly: Yes, of course. SteveBaker (talk) 18:41, 19 April 2010 (UTC)

With sources, of course, which Religious_views_on_masturbation#Orthodox_and_Conservative_Judaism lacks - but does make the claim that Egyptian pharaohs masturbated into rivers ceremonially. Pharaohs were royalty, right? Vimescarrot (talk) 18:44, 19 April 2010 (UTC)

Yes. You can safely assume that almost everyone masturbates or has masturbated at some point. 82.43.89.71 (talk) 20:59, 19 April 2010 (UTC)

With the possible exception of Edward Scissorhands. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:02, 20 April 2010 (UTC)

I suspect that if this kind of question actually interests you either need to masturbate more or masturbate less. Or better yet, you should get yourself a girlfriend, and then the last thing you will care about is other people's sex lives... --Ludwigs2 21:21, 19 April 2010 (UTC)

Ludwigs, why presume that the OP is lesbian? 63.17.75.216 (talk) 04:20, 22 April 2010 (UTC)

There are plenty of serious, academic studies about both sex and masturbation, and while I suspect that Mr. 188 probably isn't the next Alfred Kinsey, it's a valid area of inquiry. Buddy431 (talk) 21:39, 19 April 2010 (UTC)

Why not post this question here? Note that you can only do that after answering the previous question, as that's the rule for posting in that thread. Count Iblis (talk) 22:55, 19 April 2010 (UTC)

Do we dare ask why you want to know? 71.104.119.240 (talk) 03:27, 20 April 2010 (UTC)

Why wouldn't they? Vranak (talk) 06:09, 20 April 2010 (UTC)

Some might ungraciously say that all the royal family were a bunch of masterbators--79.76.130.158 (talk) 14:13, 20 April 2010 (UTC)

Of course, they don't do it exclusively, as that would interfere with them (in)breeding a new generation of royal pains. StuRat (talk) 22:22, 19 April 2010 (UTC)

Plants

I know a conker stores energy for the new plant when it first grows, before it takes root and develops leaves etc. What is the energy stored as; fat, protein, something else? Also, when the plant has fully taken root and used all the energy from the conker, would the conker be hollow? 82.43.89.71 (talk) 20:58, 19 April 2010 (UTC)

Yes, the energy is stored as; fat, protein, and something else. Wikipedia - as always - has an article about seeds. Yes, once the 'conker' (or other seed) has fully sprouted, the empty husk is left behind.--Aspro (talk) 21:17, 19 April 2010 (UTC)

Thanks. I was also wondering, would the conker actually decrease in weight as it's energy is being used, or is it more like an electric battery in that it stays the same weight when discharged? 82.43.89.71 (talk) 22:46, 19 April 2010 (UTC)

Yeah it would get lighter. Just as when humans eat food, some of the materials are used directly to build new cells in the growing plant, and the materials that gets broken down for energy end up as mostly water and carbon dioxide with some other types of waste that are also gotten rid of. Rckrone (talk) 23:10, 19 April 2010 (UTC)

Volcano - worst case scenario

How long could the volcano keep disrupting air travel if it was say, at the 90th percentile for length of time of eruption? 78.146.55.24 (talk) 22:42, 19 April 2010 (UTC)

The current disruption is unprecedented (at least in Europe), so I guess it is already well past the 90th percentile. --Tango (talk) 22:51, 19 April 2010 (UTC)

Well, wait a minute, I'm going to assert that at least one eruption in Europe has been more disruptive. Comet Tuttle (talk) 23:19, 19 April 2010 (UTC)

Actually on Island itself there have been far larger eruptions, like the eruption of Laki. Count Iblis (talk) 23:25, 19 April 2010 (UTC)

Iblisspeak to English conversion: "Island" = "Iceland". :-) StuRat (talk) 23:40, 19 April 2010 (UTC)

A pedant writes..... "Island" = what the people of Iceland call Iceland. DuncanHill (talk) 12:02, 20 April 2010 (UTC)

We're not talking about big volcanic eruptions. We're talking about big disruption to air travel caused by volcanic eruptions. The size of the eruption is just one factor that affects the amount of disruption caused. This level is disruption is unprecedented, despite the eruption itself being fairly standard. --Tango (talk) 00:15, 20 April 2010 (UTC)

Have you forgotten we are all super-pedantic? You said "disruption", not "air travel disruption". Hmph. Comet Tuttle (talk) 22:23, 20 April 2010 (UTC)

Well, the Vesuvius eruption in question downed all commercial air traffic for more than a millenium ;-). --Stephan Schulz (talk) 09:41, 20 April 2010 (UTC)

Well, Laki did shut down commercial boat traffic: "The summer of 1783 was the hottest on record[citation needed] and a rare high pressure zone over Iceland caused the winds to blow to the south-east. The poisonous cloud drifted to Bergen in Norway, then spread to Prague in the Province of Bohemia by 17 June, Berlin by 18 June, Paris by 20 June, Le Havre by 22 June, and to Great Britain by 23 June. The fog was so thick that boats stayed in port, unable to navigate, and the sun was described as "blood coloured".[6]" Count Iblis (talk) 14:51, 20 April 2010 (UTC)

OK, at the 90th percentile for Icelandic volcanos? 92.27.146.2 (talk) 23:29, 19 April 2010 (UTC)

The eruption of Eyjafjallajökull may trigger the eruption of Katla, followed by possibly decades of eruptions in Iceland. However an eruption at Yellowstone supervolcano would likely be worse than any effects from the current VEI 1 eruption or any other eruptions it may bring. ~AH1^(TCU) 00:47, 22 April 2010 (UTC)

or a repeat of the Hatepe eruption (the latest, but lesser, eruption of the Taupo Volcano), which (it is theorised) sent ash from NZ as far as Rome and China - now that really would stuff up air travel. Gwinva (talk) 05:25, 22 April 2010 (UTC)

Cockatoos and music

Has anyone advanced a theory yet as to why it is that some Cockatoos seem to have a deep appreciation of human music and even have their own particular favourite songs or genres of music? I wouldn't have thought that it was a new thing but it seems to be something that science has only just recently noticed. —Preceding unsigned comment added by 95.148.107.232 (talk) 22:49, 19 April 2010 (UTC)

Music (or birdsong, to be specific) is quite important to birds, since they use it as a method of communication, to impress mates, etc. I guess human music is close enough to qualify. That's probably why we also appreciate the songs of birds, more than, say, the sound of a laughing hyena. StuRat (talk) 23:14, 19 April 2010 (UTC)

I think we should also consider the possibility that early human ancestors evolved to pay close attention to bird song. Maybe hearing their warning cries helped us avoid dangerous predators - maybe knowing their location helped us find eggs to eat...that kind of thing. That being the case, it's very possible that our musical sense is our appreciation of their music. It wouldn't then be surprising if the birds didn't completely hate our mimicry of their songs. I have no clue whether this is true (and it would be hard to prove) - but it's a possibility. SteveBaker (talk) 01:11, 20 April 2010 (UTC)

The scientist who's been working with Snowball believes that it (the bird's desire to dance/bob his head/jump around to the music) may have something to do with a link between areas of the brain responsible for hearing and motor movement. Both humans and parrots are apparently 'vocal mimics' when it comes to learning to communicate using sound - and this creates some sort of neural pathway between the two parts that elicits a response to a musical beat in both people and parrots as an unintended consequence. Or something along those lines. I'm probably oversimplifying. --Kurt Shaped Box (talk) 01:26, 20 April 2010 (UTC)