Wikipedia:Reference desk/Archives/Science/2007 August 10

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August 10

Death - turning on back

Why do some animals and insects turn on their back when they die? Is it the death causing the turnover, or the turnover causing the death (for the insects)? PitchBlack 04:09, 10 August 2007 (UTC)

I'm hypothesising here, but I always assumed this happened in animals that weren't necessarily stable on their legs as far as a natural state. So say you spray a fly, as it's dieing it will tend to buzz and bounce around and at some stage flip onto its back, which is physically a far more stable position that its feet/legs, or it's side. As it no longer has the strength to resume it's preferred, but less stable, position on its feet, it will remain and die in this most stable position on its back. I can't imagine many animals that would die simply by being on their backs, unless they couldn't right themselves, such as with a turtle. --jjron 08:51, 10 August 2007 (UTC)

Sounds right, but it raises the question as to why are "these" animals more unstable when on their legs than on their back. I think it could be because being unstable makes moving around easier, better mobility. I may be wrong, any comments ? -- Myth (Talk) 15:19, 10 August 2007 (UTC)

Well, and think about a dead fly. Their legs contract inward. Even if they were somehow not on their back, they would quickly fall over. Insect legs most likely end up contracting like that when they dry out, for reasons I know not. In any case, I think it is pretty clear that it is not the turnover which causes the death — you can turn beetles over all day long and they won't care. --24.147.86.187 17:43, 10 August 2007 (UTC)

And the reason flies are more stable on their backs is that they are "top heavy". StuRat 05:45, 12 August 2007 (UTC)

I've seen spiders roll over and contract their legs (playing dead) when attacked. And then spread out their legs and take off a few minutes later. Surely, sometimes they actually die after attempting this, and maybe stay in that position (there may also be a reason for contracting the legs after dying, but I do not know). I always figured they were trying to make themselves look as small as possible, while simultaneously taking advantage of an instinct in many predators not to eat things that are already dead. 151.152.101.44 19:27, 10 August 2007 (UTC)

The Eastern Hognose Snake will roll onto its back and lie there defacating,with its mouth open oozing blood, playing dead, when attacked [1]. If turned onto its stomach, it rolls again onto its backs, genetic programming overcoming logic. Edison 00:10, 11 August 2007 (UTC)

Apparently, instead of using muscles, spiders force blood and other fluids into their legs to push them outward. When a spider dies, they lose the hydraulic pressure necessary to keep their legs extended, and thus they contract. I'm not sure if this is true of other anthropods, though. Vsst 18:47, 16 August 2007 (UTC)

Headaches

Headaches are of different types and have different causes - but I have always wondered - what ACTUALLY happens in our body or head so that our head starts 'aching'. For example, many times hyperacidity leads to a headache (which I have experienced myself). But what is actually happening in my head during hyperacidty so that my head starts aching? In other words why is head pain caused (thought not always and also not to everybody) due to hyperacidity?

Forml 11 04:57, 10 August 2007 (UTC)

Headache#Pathophysiology. More specific causation of pain is explained in articles on individual types of headaches, listed at headache#Types. Someguy1221 05:06, 10 August 2007 (UTC)

As for hyperacidity, are you referring to acidosis or heart burn?. Someguy1221 05:10, 10 August 2007 (UTC)

I was referring to Heart burn Forml 11 08:04, 10 August 2007 (UTC)

Heart burn can apparently irritate the sinuses (sinusitis), which can be felt as a headache, but I don't see an explanation on Wikipedia as to how this happens. Someguy1221 06:54, 10 August 2007 (UTC)

Thanks for the responses. Even I could not find any references to it. When I take medicines to prevent hyperacidity, my incidents of headaches go away. Hoever, my question is *not* about hyperacidity or about preventing hyperacidity or about medical treatment for acidity or headache. What is bugging me is this - what does the excess acid in my stomach do to my head so that it starts 'aching'? Forml 11 08:04, 10 August 2007 (UTC)

Well, there are no pain nerves in your brain or skull, it's all in the scalp. Very likely muscle cramps from unconsciously contracting your scalp muscles due to the pain in your stomach. Similar to the caffeine-withdrawal headaches, where withdrawal from caffeine causes the blood vessels in the scalp not to expand enough, causing the muscles to complain. Gzuckier 15:24, 10 August 2007 (UTC)

I've always been amazed that there are different kinds of headaches, I can feel the difference, and when I talk to my doctor about headaches, he always asks "where in your head is it?".Evilbu 18:51, 10 August 2007 (UTC)

WHICH BIRD CAN FLY IN BACKWARD DIRECTION ALSO?

BIRD WHICH FLIES IN BACKWARD DIRECTION61.11.76.116 06:01, 10 August 2007 (UTC)

Hummingbird? Make a new section if you want to ask a question using ==Title==. --antilived^{T | C | G} 06:02, 10 August 2007 (UTC)

Or use the handy "ask a new question" link at the top of the page. And don't type in all-caps, it's considered shouting. And wash your hands before you eat. --LarryMac | Talk 14:23, 10 August 2007 (UTC)

Does being able to glide backwards with wind assistance count? --Kurt Shaped Box 18:02, 10 August 2007 (UTC)

Let's take the air surrounding the bird to be our frame of reference. Anything else would just be silly. Plasticup ^T/C

I don't know about that. In the case of gulls (I'm sure that other birds can do it too - I've just noticed the gulls doing it when I feed them), they deliberately adjust the angle of their wings in relation to the wind in order that they may glide backwards (or glide backwards and upwards at the same time). It's a conscious decision to reverse - it's not as if they just go wherever the wind blows them. --Kurt Shaped Box 12:22, 11 August 2007 (UTC)

Flying backwards relative to the ground is easy with a wind strong enough. Even aircrafts can do it, with a stall speed small enough, for example the Antonov 2. Flying backwards relative to the air is something different, and the seagulls can't do it. The hummingbirds can certainly do it, as they can hover, so it' very close to a slow backwards flight. --V. Szabolcs 18:12, 11 August 2007 (UTC)

To clarify what the others just said (perhaps our reader doesn't understand frames of reference) - if the wind is blowing strongly at (say) 30mph and the bird flies into the wind at (say) 20mph then it would appear to someone standing on the ground as if it were flying 10mph backwards. I have also seen gulls doing that - but it doesn't really count as flying backwards because as far as the bird is concerned, it's still flying forwards into the air flow. Gulls can only do that when they have a reasonably strong headwind. Hummingbirds, on the other hand, can truly fly backwards even in still air because they can rotate their wings at all sorts of strange angles to direct thrust slightly forwards while hovering. This makes them fly more like a Harrier Jump Jet aircraft (well, sort-of).

Doh! Yes, I understand it *now*. Hehehe. :) --Kurt Shaped Box 19:07, 11 August 2007 (UTC)

It's my un-studied impression that all birds can hover to at least a small degree. Obviously, some birds, for example, hummingbirds, are very good at it and can do it for sustained periods of time, but for most of the birds I've seen, the have the ability to abruptly stop their forward motion in flight, hold still for a moment, and then change direction.

Atlant 11:54, 13 August 2007 (UTC)

Not exactly. Most of the larger birds even need a long runway to take off. Larger birds of prey were used to be captured in traps made by a bait and a fence around it. The bird did not have a runway long enough to take off, so it would be trapped in the fenced area. --V. Szabolcs 13:47, 14 August 2007 (UTC)

Citation? I recently watched a Great Blue Heron take off several times. No runway needed; it simply flapped downwards and lifted its feet. Perching birds certainly don't need a runway. I don't know of any North American "land-based" bird that needs a runway. And we're not talking about "takeoffs" anyway; I was talking about hovering and the original question was talking about reverse flight.

Atlant 12:14, 15 August 2007 (UTC)

Exact reason for the gender difference in essential body fat percentage

What, precisely, causes the essential percentage of body fat for women to be eight percent higher than that of men? In the body fat percentage article, it states that it's "due to the demands of childbearing and other hormonal functions", but does not elaborate; in particular, exactly what role does it play in childbearing? Does it merely serve to shield the woman's other organs from the mechanical stresses of hosting and delivering a developing fetus, or is there an additional reason (such as to serve as a source of nutrients)?

I'm asking because I'm trying to develop a fictional alien race of oviparous humanoids, and I'd like to know what, if any, adjustments I need to make to their figures because of their reproductive system.

CameoAppearance ^orate 07:19, 10 August 2007 (UTC)

Breasts and breastfeeding? An alien race is completely up to your imagination however, so you are only limited by what you can imagine. Lanfear's Bane

One of the key reasons is that fats are the most convenient way to store energy in the body. If I remember correctly (I can't find an immediate link to the figures), in the old money fats store 9 calories per gram compared to proteins and carbohydrates which only store 4 calories per gram. If you want to carry around the most energy for the least weight, you store it in fats. It takes a lot of energy to grow and sustain another human being from conception. --jjron 08:40, 10 August 2007 (UTC)

I'm a complete amateur, so take my hypothesis with great caution. I've always thought that women have a "base" or "normal" level of muscle mass and it's men who have an "abnormally higher" level due to the anabolic effects of testosterone. This sexual dimorphism is also seen in related species, and it's maybe caused by physical competition for females or more physically demanding duties, such as hunting. To sum up, I conjecture that the level of body fat in women has no particular reason for being the way it is and maybe it's men's level who has one. --Taraborn 21:01, 10 August 2007 (UTC)

Childbearing is one explanation. Indeed, having a child grow inside you, and nursing it afterwards require large energy reserves. But from an evolutionary point of view, I suppose that women were the ones who sat around raising the childring while the men were hunting. The hunting men, being outdoors, could eat as soon as they made a kill, if needed. The women would be left without any food. And any food they did have, would likely have gone to children of various ages. So the women (and therefore the children) would greatly benefit from them being able to last with little food. I think.81.83.82.123 20:56, 13 August 2007 (UTC)

light intensity

i was just generally thinking about light and its intensity, i was just wondering, about how would the intensity of light passing through a glass container containing a liquid vary when the height of the liquid in the container is changed. i really cannot understand what kind of relation would exist between the height liquid in the container and the light intensity?? please answer my queries, i have broken my head on this for quite some time and still cannot find an answer.

If the light is passing in a vertical direction then the liquid may scatter or absorb it. however it is passing horizontally then that will not differ, however you may get reflections from the top of the liquid affecting your result. Also if the glass is not a cylinder then the path length in the liquid would change as the height increases. The liquid is not fluorescent or luminescent by any chance is it? Graeme Bartlett 11:54, 10 August 2007 (UTC)

Did you mean passing through a glass horizontally (eg half full vs full), or passing vertically (up/down) though the column of liquid?87.102.35.197 11:56, 10 August 2007 (UTC)

You may find the photic zone article of use. Also try the underwater article, especially the section down near the second photo. --jjron 14:26, 10 August 2007 (UTC)

Mr. Graeme Bartlett the light is passed perpendicular to the liquid therefore the direction of the light will be parallel to the normal therefore there is no scope of reflection takeing place. And when i performed some experiment related to this i found that the intensity of light increases with the increase in height. i have no idea how to get convinced by the results i got. Can you please help me out.

Still not sure exactly of what you are looking at here - just as a guess if you are measuring the light reaching the bottom of a tall glass - could it be that increasing the fullness of the glass causes more light to be trapped in the cylinder by total internal reflection (catching light coming from the side). (this would apply if you have light coming from all around..)

If thats not what you are thinking of can you clarify again - is the light coming through the glass (sideways) or down (though the top surface and down to the bottom)?87.102.74.130 20:40, 10 August 2007 (UTC)

ya i ment that the light was coming from the top of the glass container.

If the liquid is coloured the Beer-Lambert law applies - this always means that the amount of light is reduced for longer columns.

I'm guessing that your liquid is clear - and you mentioned that the light seems to increase - in which case I'd suggest the answer I gave above - that is that the liquid filled portions are acting as a sort of funnel - since the light reflects from the inside of the glass when it's full of water - place the glass in strong sunlight and you might be able to see this effect - for example see the images in Caustic (optics) for a rough approximation of what I'm suggesting.87.102.8.162 21:34, 11 August 2007 (UTC)

For a compressible fluid, the density will increase with the depth/pressure, and the more dense the fluid, the more light it will absorb. StuRat 05:36, 12 August 2007 (UTC)

Sleeping feet

I was wondering, just what IS the condition of a "sleeping foot" (or hand, etc) called? That is, when it's under something for long enough that it starts to tingle and often be unable to be felt (and something hard to walk on it). Is there an article on this condition? ♫ Melodia Chaconne ♫ 14:08, 10 August 2007 (UTC)

Try Paresthesia. Mdwyer 14:13, 10 August 2007 (UTC)

Yes, that's it. Thanks. ♫ Melodia Chaconne ♫ 15:09, 10 August 2007 (UTC)

AIDS enquiries

Hi, I'm just wondering where does AIDS arise from? I mean, if 2 people do not initially have HIV (or at least they are not aware of it) and one of them have touched the other's bodily fluid, say, blood; is there a chance that one of them will get HIV, and subsequently AIDS?

Also, does kissing transmit AIDS/HIV?

If neither has the virus, they're not going to get it no matter what they do between them. If one has the virus and doesn't know it, that's different.... As for kissing, most reputable authorities put the possibility very very low. However, if there are open sores of some kind, such as bleeding gums, cold sores, etc. in one or both persons the likelihood goes up. (similar for actual sex; if there are sores from other STDs, for instance, likelihood of infection goes way up.) Gzuckier 15:29, 10 August 2007 (UTC)

You should consult your doctor for any medical advice, particularly when it comes to diseases. -- JSBillings 17:23, 10 August 2007 (UTC)

However, if you're speaking purely in the hypothetical, then no, you can't become infected with HIV without the presence of HIV. There are AIDS/HIV Denialists out there who might say otherwise, but there isn't any real science behind it. -- JSBillings 17:27, 10 August 2007 (UTC)

Yes, there was an early theory that AIDS was caused by repeated assaults on the immune system, such as by drugs and other venereal diseases, but that theory was discredited with the discovery of HIV. StuRat 05:30, 12 August 2007 (UTC)

Try reading our article on AIDS. Plasticup 17:57, 10 August 2007 (UTC)

Fading of photogaphic prints

Are there published data on the fading rates of the different dyes in a photographic print (over time, and under various conditions)? I believe manufacturers of photographic supplies must have done detailed studies on their own products but I couldn't find any published data. What I'm hoping to get is a quantitative characterization of the color shifting in a faded photograph. Thanks.

Digital_versus_film_photography#Archiving claims "Gold or platinum toned prints probably have a lifespan limited only by the lifespan of the base material, probably many hundreds of years." - I imagine that is the upper limit for film?

For a few values try this http://www.wilhelm-research.com/ist/WIR_ISTpaper_2002_02_HW.pdf (page 2)87.102.74.130 20:34, 10 August 2007 (UTC)

Microbiology/statistics

write the name of 100 types of bacterial,giving 10 examples of it structural types and indicate whether gram negative or gram positive.

Distinguish between Normal scale,Ordinal scale,Equal scale and Ratio scale.Show a graph interpretation of their relationship

and DO YOUR OWN HOMEWORK. --LarryMac | Talk 18:07, 10 August 2007 (UTC)

Here's what I don't get. What kind of person would be in a course that would ask that kind of question, yet be unable to read and follow simple directions? How is he/she going to be able to wade their way through microbiology textbooks? Are they planning on asking us new questions with every assignment? And for what? So they can become a microbiologist who still has to come to the reference desk every time they do research? Bizarre. Matt Deres 20:08, 10 August 2007 (UTC)

Maybe we should add "... and your own doctoral thesis" to the admonition. --Sean 13:32, 13 August 2007 (UTC)

This is the reference desk - yet the question reads like some sort of fuhrer-order. Were you aware that as it reads the question is pushing the boundarys of politeness? The main page asks that you 'do your own research'87.102.74.130 20:20, 10 August 2007 (UTC)

The page bacteria has links to lots of species, (look in the info box on the right for lists of phyla and you could easily find many from there. Also the page bacteria has info on structural types. Typing gram negative into the search box, or google etc may also help...87.102.74.130 20:23, 10 August 2007 (UTC)

Did anyone read the original question carefully? "write the name of 100 types of bacterial,giving 10 examples of it structural types and indicate whether gram negative or gram positive." That's quite a lot of useless work! --Bowlhover 22:19, 10 August 2007 (UTC)

Maybe the question is designed to increase general knowledge in the bacteriological subject area - by neccessitating a lot of background reading.??87.102.5.144 10:14, 11 August 2007 (UTC)

The Reference Desk staff is unable to do you homework for you because we are suffering from a staff infection. 05:18, 12 August 2007 (UTC)

about sea monkeys

i have some sea monkeys that are in the process of reproducing and there is a big black ball shaped thing on the bottom of the tank is that a baby sac or something different?

I'm not sure, but have you fully read Sea monkey and brine shrimp?

I seem to recall that the male sea monkey carries the fertilized eggs in a pouch, rather like a kangaroo. I don't know if this makes it a marsupial, but it would suggest that the "big black ball shaped thing" is not a sac of babies. Perhaps it is faeces. Plasticup ^T/C 02:35, 11 August 2007 (UTC)

Male seahorses keep babies in a pouch too - but they definitely aren't marsupials! In marsupials, it's the female that has the pouch - and there are nipples down inside the pouch for the baby to suckle on. Hence marsupials are all mammals. SteveBaker 18:05, 11 August 2007 (UTC)

changing the demand for electricity in a 24 hour period

how is it possible to change the demand for electricity in a certain period (either increase it or decrease it).thanx i appreciate your help 203.31.216.248 21:07, 10 August 2007 (UTC)

If you want to change demand for something, change the price. Many electrical utilities charge less for electricity used at night (when the natural demand from homes, offices, and factories is lower). Their customers (generally it's industries, but sometimes even domestic users with more sophisticated metering setups) can then choose to use electricity at night that they might otherwise use during the day. So the night shift at the steelmill might make more steel than the day shift. -- Finlay McWalter | Talk 21:13, 10 August 2007 (UTC)

If I recall my economics course, artificially changing price does not change demand (economics); it will change the quantity sold. This is a matter of semantics and the definition of "demand." To actually change demand, you will need to market or advertise the service differently, or change its quality, or otherwise affect how much people want it. Nimur 18:17, 11 August 2007 (UTC)

Or you might do your laundry during the day when prices are low rather than in the evening when prices are high. Plasticup ^T/C 02:36, 11 August 2007 (UTC)

In UK, we had this dual metering as an option for electricity customers for the past 35 years (at least) - it used to be called "White metering" because the electricity meters where white instead of the usual black. Since then it's gone through several incarnations - "Cheap rate electricity", "Off peak metering", etc. The deal is that you can opt to have white metering rather than the usual flat rate - that's your choice. If you opted for this scheme then electricity was significantly cheaper during the off-peak nighttime hours - but much more expensive than usual during normal daylight hours. The meter had two separate sets of dials and some kind of timer inside that switched over from one set of dials to the other at the prescribed time of day so it measured the amount of daytime and nighttime usage separately. Many people use them in conjunction with timers that set washing machines, dishwashers and water heaters to run during the night - and "Night Storage Radiators" for heating. Night storage radiators consist of a steel case containing a huge pile of thermal bricks threaded through with heating elements. During the night (when electricity is cheap), the radiators turn on, the bricks heat up - then in the morning, the heating coils turn off and the heat stored in the bricks gradually radiates out into the house to keep you warm. If you get it right, they are still sufficiently warm when the cheap rate cuts in again the next night. Used correctly, this system can save you a ton of money compared to normal electrical use. Used badly, it could cost you a packet! From the perspective of the electricity suppliers, this made a great deal of sense since this lightened the load on their generators during the day - and used some of the idle capacity during the night. Overall, this enabled them to operate with fewer power stations. This approach only really works in places where people aren't running air conditioning. SteveBaker 18:01, 11 August 2007 (UTC)

I seem to remember reading that the time-of-day switchover was actually triggered by a special tone embedded in the Radio 4 long-wave broadcast, and picked up by a receiver in the meter using the wiring as an aerial. Makes a certain amount of sense since independent clocks could be wrong - either accidentally, or deliberately in order to get night-rate power during the day. What wonderful things you could do in the 70s when all this stuff was run by quasi-government agencies :-) 62.56.81.182 23:47, 11 August 2007 (UTC)

Check out Economy_7 81.144.241.244 14:12, 15 August 2007 (UTC)

One advantage to encouraging solar power in homes and businesses is that energy production occurs during daylight hours, thus reducing demand for power from the grid during peak hours, especially during summer when A/C power use is at it's max. This "encouragement" can take the form of government subsidies, tax deductions, etc. StuRat 05:08, 12 August 2007 (UTC)

Melarsoprol - sorting fact from fiction

Has anyone here had experience with the drug Melarsoprol? I've been doing a bit of reading about it tonight and it sounds like pretty horrific stuff. Kills 5-10% (depending on what you read) of patients outright, may cause permanent nerve damage to those it cures, will eat straight through regular plastic IV tubing/syringes, corrodes veins, causes burning agony on administration, etc. This is of course 'stuff what I read on the internet'...

So, what's the straight dope with this stuff? Anyone ever been injected with it? --Kurt Shaped Box 23:15, 10 August 2007 (UTC)

Well, I imagine when the alternative is death, you're willing to try anything. :( I don't think it was this same compound, but I recall seeing a patient at a cancer clinic receiving an IV that sounded like it had similar effects. They had to be very careful when administering it (directly into a port instead of a conventional IV needle), and they covered the skin surrounding the port with self-adhesive plastic, to protect the patient in case of spills. I'm like you: I'm terribly curious how something so hazardous could actually be a good thing when injected! --Mdwyer 23:52, 10 August 2007 (UTC)

I think the general idea is that they inject it, cross their fingers and hope it kills off all the parasites before it kills the host... --Kurt Shaped Box 23:57, 10 August 2007 (UTC)

Yes, remember the way most tests of drugs are conducted is to determine if the outcome is on average better then the outcome without the drug. Nil Einne 10:08, 11 August 2007 (UTC)

Don't you reckon that there's just something "oldschool" about Melarsoprol, though? Reading about it kinda makes me think of a bottle of the stuff on a shelf next to the ether, leeches, blood-lettting equipment and various 'tonics' back in the day. --Kurt Shaped Box 12:38, 11 August 2007 (UTC)

My mom has blood-letting done on her. As bizarre as it sounds, it is still an accepted treatment for polycythemia caused by chronic mountain sickness. No leeches, though, thank goodness! --Mdwyer 22:58, 11 August 2007 (UTC)

It looks like Eflornithine is a much better treatment. Plasticup ^T/C 02:39, 11 August 2007 (UTC)