Wikipedia:Reference desk/Archives/Science/2011 May 13

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May 13

What is the role of the autonomic nervous system in uterine contraction?

129.78.32.21 (talk) 01:06, 13 May 2011 (UTC)

Try starting with Uterine contraction . Vespine (talk) 01:47, 13 May 2011 (UTC)

Hi. The page doesn't really specify the type of nervous system control over uterine contraction. 129.78.32.21 (talk) 01:55, 13 May 2011 (UTC)

in which case I have to ask is this a homework question? Were you assigned course text? Vespine (talk) 02:11, 13 May 2011 (UTC)

You could also try Google Scholar or our article on autonomic nervous system. ~AH1 ^(discuss!) 18:40, 14 May 2011 (UTC)

Spider path

I just saw a spider walking around my ceiling, steadily moving inward in a spiral. I've seen them follow a similar pattern when making a web. So, what was it doing on the ceiling ? Does this particular spider lay web on a surface, in the hopes of catching crawling insects ? Or was it perhaps establishing supports from which it would next build a normal suspended web ? (Unfortunately, the spider is now a collection of guts and quivering severed legs, so I don't expect to finish the experiment anytime soon.) StuRat (talk) 06:26, 13 May 2011 (UTC)

If you'd only taken a picture of your spider before you squashed it, perhaps we could have determined the type of web that it produces. It sounds interesting behaviour. Could you not have waited an hour or two before succumbing to arachnophobia? It might now be too late to answer your question, but perhaps we have some spider experts ... ? Dbfirs 12:56, 13 May 2011 (UTC)

"And he that breaks a thing to find out what it is has left the path of wisdom" --Gandalf SemanticMantis (talk) 15:52, 13 May 2011 (UTC)

More seriously, several spiders do build horizontal webs, but usually these are across the top of a plant canopy. Did you actually see web filaments emerging from the spider? How fast was the motion? If it was quick, it might have been a hunting spider 'lassoing' prey (which may have been to small to notice in moment of giant spider panic). SemanticMantis (talk) 15:52, 13 May 2011 (UTC)

It was moving at top speed. It was maybe a half inch long, and it's color varied from clear to pale yellow. I didn't see a web filament, but I would expect it to be impossible to see that flat against a white ceiling. Why would it move in a spiral, if doing something other than web building ? StuRat (talk) 17:44, 13 May 2011 (UTC)

Usually body, leg, and mandible shape are the most useful characteristics for figuring out a spider's family. Species of wolf spider or jumping spider can rapidly run in circles around prey, stringing web to ensnare it. See an example here [1]. The prey (if present) might have been easy to miss. If there was no prey, then 90.197 mentions some alternative strategies below. I suppose it could have been an anchoring mechanism, but all the web styles I know of use point contacts, not spirals. SemanticMantis (talk) 01:33, 14 May 2011 (UTC)

It was making a big rope in order to abseil from the ceiling. Count Iblis (talk) 22:53, 13 May 2011 (UTC)

Less alarmingly, some house-dwelling spiders actively hunt other insects rather than making passive web traps, and some of these lay loose networks of silk - usually invisible to humans until they build up enough and gather enough dust to become classic cobwebs - on walls and ceilings to provide them with surer footing. {The poster formerly known as 87.81.230.195} 90.197.66.60 (talk) 23:17, 13 May 2011 (UTC)

Nephrotic syndrome in children

Sir please provide me a simple flowchart on pathophysiology of nephrotic syndrome in children Jisaj (talk) 09:30, 13 May 2011 (UTC)

This search found many sources of information about nephrotic syndrome that may be useful to you. Cuddlyable3 (talk) 13:11, 13 May 2011 (UTC)

Waste of Mir Deorbiting

Please correct my admittedly limited understanding of orbital mechanics wherever necessary. I'm wrestling with why the russians chose to deorbit Mir, rather than either pushing it to a more stable orbit around earth from it's Low Earth Orbit, or use a Hohmann Transfer to a stable lunar orbit, to be used later as good space materials/metal for Moon colonization.

I get that Russia wanted it out of its current orbit which required regular orbital maintenance of about 25 m/s delta-v per year. It seemed they had to choose the deorbit path carefully as to not cause deaths, and had to launch up a module to dock with Mir to deorbit it. Even with this cost, they missed their mark and some remnants hit western Australia. From my calculations, it would require a little over half the power of a Space Shuttle Main Engine (there are three on any one space shuttle), which is roughly equivalent to the Soviet RD-0120 engine.

LEO - Lunar Orbit: 4.04 km/s delta-v Delta V Budget

Mir - 129,700 kg Mir

RD-0120 - 1.961 MN Thrust(vac), 3,449 kg, Isp(vac) = 455 seconds RD-0120

1.961 MN = 1,961,000 kg * m / s^2 * 455 s / (129,700 kg + 3,449 kg) = 6,701.176 m/s delta-v = 6.701 km/s delta-v

This means one RD-0120 could have set it in a nice lunar orbit - where at least if it crashed, big deal. However there are four inclinations about the moon where the orbit requires ZERO maintenance due to gravitational heterogeneity: 27deg, 50deg, 76deg, 86deg ( http://science.nasa.gov/science-news/science-at-nasa/2006/06nov_loworbit/ ). This could have been useful after so many years of accumulating material in orbit for... the first moon base, or landed on the moon for 1/2 million pounds of building material for future colonization.

Was it not this easy? Am I missing something? —Preceding unsigned comment added by Ehryk (talk • contribs) 09:36, 13 May 2011 (UTC)

There are a million technical reasons why they couldn't do this, for example Mir's communications system would probably not work from lunar orbit, and the attitude determination system used Earth horizon sensors which would probably not work in lunar orbit either, and your SSME-sized engine would produce accelerations and vibrations that would tear Mir to pieces. But the main reason I'm sure is cost: It would cost millions of Rubles (maybe billions?) to design, build, and launch a system to send Mir to lunar orbit; and once there it would serve no purpose. There's simply no use for it, even as materials, in lunar orbit. So they did the economical and practical thing: Deorbited Mir into the Pacific Ocean. anonymous6494 20:20, 13 May 2011 (UTC)

You are forgetting the fuel consumption, 3449 kg is just the engine. Isp=455 s is not the maximum burn time but the ratio of lifting capacity in one g and the fuel consumption in kg/s.

The engine uses 1,961,000 (kg m/s/s)/(9.82 (m/s/s))/(455 s) = 425 kg/s

The engine normally runs 480 to 500 s in a launch but it can run in 1670 s, if we use your number 455 s then it need 425*455= 193 400 kg fuel.

This makes the spacecraft heavier and reduce the deltaV to 455 s*9.82 m/s*ln((193400 kg+129700 kg+3449 kg)/(129 700 kg + 3 449 kg)) = 4 008 m/s, very close to the needed 4040 m/s (1670 s burn needs 710 000 kg fuel and gives a deltaV of 8247 m/s)

To lift these 193 400 + 3 449 kg to LEO 25 times the fuel is needed so the start mass becomes 4 900 000 kg, almost two Seturn V (3,039,000 kg) would be needed. That is just to expensive. A Saturn V can take 45 000 kg to lunar orbit all the way from the earth's surface.--Gr8xoz (talk) 21:44, 13 May 2011 (UTC)

I made a mistake in the latest number it was 47,000 kg to translunar trajectory, to low lunar orbit it was probably about 30 000 to 35 000 kg.

--Gr8xoz (talk) 07:35, 14 May 2011 (UTC)

Bonding problem

I'm learning chemistry on my own from a free book on iBooks and it's good but the end-of-chapter problems don't have answers. One problem states: "Scientists in the lab are able to make the Cl₃^- ion but not the F₃^- ion. Give an explanation why this might be the case." My idea is that in the case of chlorine, the amount of energy needed to promote two electrons to make three half-filled hybridized orbitals is made up for by the energy released when the covalent bonds are made, but in the case of fluorine, it would take more energy to promote the electrons than would be released by the bonding, so it doesn't happen. Does this sound right? Thanks. 20.137.18.50 (talk) 12:14, 13 May 2011 (UTC)

I would say that it is related to the fact that unlike chlorine, fluorine does not have access to its d orbitals (or the 3s orbital in this case) to accomodate hypervalency structures. Plasmic Physics (talk) 12:38, 13 May 2011 (UTC)

I hate these sorts of problems because they are so often wrong (I'll WP:AGF and charitably say "authors did not consult the literature but rather wrote from their gut feeling or only superficial ideas"). F₃^– was made and studied since the mid-1970s...see doi:10.1021/ic50174a040. One could say "why is it less stable" or something and not look as poor when someone finds it's already been done or become obsolete when someone does eventually do it. DMacks (talk) 14:18, 14 May 2011 (UTC)

d orbitals are not required for hypervalency. Consider FHF^-, for instance. I suspect that the instability of F₃^- relative to Cl₃^- can be explained in part by the same reasoning that explains the instability of F₂ relative to Cl₂.--Atemperman (talk) 07:10, 17 May 2011 (UTC)

Sodium silicate

Bronze casting: Is waterglass used in strengthening moulding sand for foundry work? Would it be suitable for small scale (5/6 kilo)bronze casting provided mould was completely dried?

It is a strong sand binder and OK for heavy alloys like bronze. It and the right type of sand with instructions should be obtainable from a hobby store. As a tip: you can speed up the chemical reaction with CO2 as shown in this video. http://www.youtube.com/watch?v=UPQmgeTFHEc&feature=player_embedded --Aspro (talk) 16:54, 13 May 2011 (UTC)

I should add, that if you haven't done any very high temperature casting before you really need to go on a course first, to learn about how to do casting safely.--Aspro (talk) 16:59, 13 May 2011 (UTC)

Cognitive bias relating to extrapolating from initial conditions

I've looked over List of cognitive biases, but I don't see the cognitive bias I'm looking for. I'm not sure it exists, but I hope so. Namely, it's the bias whereby a person generally assumes the initial conditions, or especially the initial trajectory, are indicative of future performance. e.g. think of price fluctuations, early childhood aptitude being extrapolated to genius, early athletic ability being extrapolated into the future, etc. That sort of thing. Does anyone know if this is an actual named bias? Thanks in advance! --Rajah (talk) 16:50, 13 May 2011 (UTC)

I'm not sure of the formal name, if any. When people give investment advice, it's common to say "Past performance does not guarantee future results", i.e. here, at the bottom, as a disclaimer, or even as the main topic. The phrase has also been adopted for uses not related to investment: in politics, for example, or sports. Unfortunately, I'm having trouble finding the origin of the term. Buddy431 (talk) 21:09, 13 May 2011 (UTC)

This could be the primacy effect or expectation bias, and possibly black swan theory, normalcy bias, or estimator bias depending on the context. 173.8.151.126 (talk) 04:52, 14 May 2011 (UTC)

A common effect when examining preliminary data. ~AH1 ^(discuss!) 18:37, 14 May 2011 (UTC)

Try Confirmation_bias#Preference_for_early_information and elsewhere in that article. 92.15.1.9 (talk) 14:54, 17 May 2011 (UTC)

BIrds & Monarch butterflies.

I read that monarch butterfly caterpillars eat milkweed plants in order to build up toxins that will dissuade birds from eating them. Have the birds that prey on them now evolved to avoid eating the monarchs - or must each bird eat at least one monarch, dislike the taste/get sick, and then learn not to eat anymore? TIA smart guys! 216.136.51.242 (talk) 17:02, 13 May 2011 (UTC)

See Mimicry#M.C3.BCllerian. A bird may learn to not eat a Monarch because it had previously eaten a Viceroy. As for whether the avoidance is instinctual or learned, it could in principle be either, and likely depends on the species in question. SemanticMantis (talk) 17:59, 13 May 2011 (UTC)

Many thanks! That seems to answer it. They learn. 216.136.51.242 (talk) 19:05, 13 May 2011 (UTC)

There would need to be an evolutionary pressure in order for a species to develop an instinct to avoid eating another. Thus, the poison would need to be strong enough to at least occasionally cause death. If it only tasted bad, then, since those that ate the caterpillars would still live, they would continue to pass on their genes and instincts. StuRat (talk) 18:09, 13 May 2011 (UTC)

It wouldn't have to cause death surely? If the bird is simply too sick to mate for a day or two after eating the monarch, then over enough time, they might evolve. 216.136.51.242 (talk) 19:05, 13 May 2011 (UTC)

If the evolutionary pressure is low enough, then natural genetic drift will be the more powerful force. StuRat (talk) 21:52, 13 May 2011 (UTC)

Yes, apparently they have to learn from experience. However there is very strong evidence that rats and other animals can learn to avoid foods based on observing other animals's responses to them, so I'm not sure we can rule out that something of the same sort may happen in birds. Looie496 (talk) 18:13, 13 May 2011 (UTC)

One odd thing is that human babies don't do that. You'd expect them to only eat food provided by their parents, unless starving. But, in reality, they seem to try to eat anything that will fit in their mouths. StuRat (talk) 18:34, 13 May 2011 (UTC)

I remember hearing an explanation for this: babies are programmed from birth to consume food, it's the second thing they do after being born and it's the second most important thing (breathing of course being the most important thing). Their world is, therefore, defined by the sensations they receive through their mouth. A baby's eyesight is apparently extremely weak for about 6 weeks, and all the other senses have yet to fully develop. I suppose you'll want a reference for this. I'll have a look and be back later.--TammyMoet (talk) 08:03, 14 May 2011 (UTC)

That doesn't really say why babies evolved to behave like that. My own theory is that, back when most babies wouldn't survive, they could still help out the group if they did manage to find something new that was edible. Thus, the risk of this behavior causing them to not pass on their genes was relatively low (since they probably wouldn't, in any case), while the evolutionary benefit of increasing the chances of related individuals passing on their genes (by finding a new food source) was higher. StuRat (talk) 05:19, 16 May 2011 (UTC)

Rather than simply mimicry, it's likely that monarchs also use aposematism (the use of warning colours) to dissuade birds. Brightly coloured animals (especially involving bands of red/orange/yellow on black) are frequently poisonous or venomous; avoiding eating such things would be a very strong evolutionary pressure as it can be reinforced so frequently. As with most things in nature, it's probably a complicated combination of both these strategies where one strategy reinforces the other - and vice versa. Matt Deres (talk) 21:12, 14 May 2011 (UTC)

See https://www.monarchlab.org/Lab/Expert/AddExpertQuestion.aspx.

—Wavelength (talk) 22:17, 14 May 2011 (UTC)

Multiverses beginnings

Maybe I wasn't reading it properly, but the Multiverse doesn't seem to answer this query…

For the scientists who theorise about there being a Multiverse, is there a consensus about when constituent (parallel) universes began: did they all start when our Universe started at the Big Bang, or do they think some may have started before and some after?

Regards, -- PhantomSteve.alt/talk\^{[alternative account of Phantomsteve]} 19:30, 13 May 2011 (UTC)

"Multiverse" covers a huge number of different ideas, which have nothing in common except that there's more out there than the visible universe. Often, the other worlds are temporally disconnected from this one, meaning that you can't compare times in one to times in another to say which was "first". In traditional eternal inflation, there are a lot of independent big bangs one of which gave the cosmos that we see, and they are all "connected" inasmuch as they come from a common inflationary state, but I think the inflationary state is symmetric enough that you can't assign a time ordering to them (I may be wrong). In the many worlds interpretation of quantum mechanics, you start with one world which splits later into independently evolving parallel worlds, which then split again, etc. There will never be any consensus on the existence or properties of other worlds until we find some way to investigate them experimentally, which will probably never happen. -- BenRG (talk) 00:25, 14 May 2011 (UTC)

Other theories suggest that a multiverse is created/destroyed by black holes, during a quantum wavefunction collapse or during any scenario similar to Schrodinger's cat. ~AH1 ^(discuss!) 18:35, 14 May 2011 (UTC)

Help identifying plant

Hi. There's a shrub in my back yard that I've been trying to identify for a while. In the past, I asked here, and was told that I should get pictures of it flowering, because it's easier to identify that way. What I've got now are the closest things I've seen to flowers on it. Here are some photos:

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Thanks in advance if anyone can help me. If any more photos would be helpful please let me know; I can probably take them. I am in Denton, Texas, and the plant seems to grow wild here. -GTBacchus^(talk) 21:01, 13 May 2011 (UTC)

Looks to me very like privet, probably Oval-leaved privet Ligustrum ovalifolium, or a close relative, which though of Japanese origin has been introduced worldwide as a garden hedging plant (and of course comes in many cultivated varieties - I have at least three in my own UK garden). As the article says, in the US it has escaped domesticity and become invasive. {The poster formerly known as 87.81.230.195} 90.197.66.60 (talk) 22:43, 13 May 2011 (UTC)

That's awesome; thank you very much! :) -GTBacchus^(talk) 03:27, 14 May 2011 (UTC)