Wikipedia:Reference desk/Archives/Science/2007 April 6

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April 6

shit

Is shit flammable?

Yes, but not in wet form. It needs to be dried first, before being lit. DDB 08:45, 6 April 2007 (UTC)

Dried Cow dung is sometimes used as a fuel in the Third World. — QuantumEleven 11:40, 6 April 2007 (UTC)

Of course dried cow dung burns so well because it is mostly plant fiber. —The preceding unsigned comment was added by Czmtzc (talk • contribs) 12:45, 6 April 2007 (UTC).

I read an article a couple years ago about a power plant in Russia using retirement home used diapers as a fuel source (instead of coal). --Kainaw ^(talk) 13:53, 6 April 2007 (UTC)

Thats a whole load of shit and I find it a bit hard to believe!  :-)

I believe dried camel dung can also be used for fuel in the deserts. —The preceding unsigned comment was added by 88.110.208.218 (talk) 18:04, 6 April 2007 (UTC).

And bison dung was used by the Native Americans on the Plains. Corvus cornix 18:33, 9 April 2007 (UTC)

Do birds reject sick offspring

Baby birds are often found on the ground. Do they fall from the nest or were they pushed? Is there any evidence that adult birds can detect illness or deformity in chicks and reject them? A practical reason to know the answer is for use when deciding whether to try to reunite a wild chick with its parents, when for instance you have cared for it for a brief time.—The preceding unsigned comment was added by Haulpak (talk • contribs) 07:43, 6 April 2007 (UTC).

I think it's rather the siblings. Their chance of survival increases if they have less siblings to share the food with, and hence, a very strong one might push a weak one out of the nest. From the point of evolution, this makes sense, but don't ask for a reference as I can't remember where I read this. Simon A. 08:20, 6 April 2007 (UTC)

Here is a nice overview of this behaviour in cockatiels. Rockpocket 08:17, 6 April 2007 (UTC)

They were probably pushed. The culprit could have been a brood parasite, a selfish sibling, or a mother. See also, bruce effect. Are baby birds really often found on the ground? I've never seen any. --JianLi 01:16, 8 April 2007 (UTC)

The bruce effect describes a mammalian behaviour (birds are not mammals). Rockpocket 18:55, 8 April 2007 (UTC)

Oops, my mistake. But it still is a good example of a situation where a mother's and baby's interests are in conflict. --JianLi 19:08, 8 April 2007 (UTC)

Bouyancy in dead sea

In the dead sea, we can float without any equipment by "lying" on the surface. What will happen if we "stand" on the surface of the water? Will we float? IF no, what must be the desity of the sea water? Is it possible to achieve such density in nature/ by human?Invisiblebug590 10:21, 6 April 2007 (UTC)

Your posture is irrelevant to floating, what matters is the "amount" of you above the water's surface. If you were to "stand up" in the Dead Sea, you would still float, but the only bit of you above the water's surface would likely be the top of your head. Take a look at our article on buoyancy - if you increase the density of the water you're swimming in, more of you would protrude from the surface of the liquid. As far as I know, the water in the Dead Sea has the highest density of any body of water on Earth, however, there are other liquids with higher densities, such as mercury - but you certainly don't to go swimming in mercury, as it's poisonous! Does that answer your question? — QuantumEleven 11:38, 6 April 2007 (UTC)

I've seen a picture (an old picture!) of a worker in a mercury mine lying on -- not in -- a pool of mercury. —Steve Summit (talk) 22:59, 6 April 2007 (UTC)

Do you mean this one (scroll down a tenth of the way)?

No, but that's a nice one, too. —scs

Mercury has tremendous surface tension, so I wouldn't be surprised if someone could stand on it without sinking in. --Bowlhover 04:29, 7 April 2007 (UTC)

More than just the top of your head would stick out, even in fresh water. In Dead Sea water I believe the head and shoulders stick out. Note that the denser the liquid, the harder it would be to "stand up", as you become top-heavy. Because the lack of friction with the liquid allows your feet to slide out from under you, it would be impossible to stand up in mercury. StuRat 13:10, 6 April 2007 (UTC)

Anecdotal data point - it's impossible to stand up in the Dead Sea (with only your head above the water), as your legs rise to the surface every time you try to put them below you. To answer the OP, you still need a surface between yourself and the water to float standing upright on the Dead Sea - it's not just about the bouyancy but about the distribution of weight on the surface. Feet aren't wide enough to keep you upright on the water, at its current bouyancy. Natgoo 14:25, 6 April 2007 (UTC)

I don't buy User:Natgoo's explanation. The density of your body is pretty constant - there shouldn't be a net force pushing your legs to the surface unless they are less dense than your torso. Furthermore, in the Mythbusters episode where they attempted to show whether quicksand really sucked you down (as per bad movies!) they created a 'fluidised bed' of fine sand by pumping water up from beneath. The resulting "liquid" was a suspension of sand in water that had a considerable density - more than the dead sea - but still liquid enough to permit swimming in the stuff. One of their presenters was easily able to 'stand' in the artificial quicksand and he floated around with the liquid only just reaching his chest. You might be amused to watch this demonstration of a 'non-newtonian fluid' which evidently has pretty high density...[1]. SteveBaker 15:24, 6 April 2007 (UTC)

The density of your legs and your torso should be roughly the same, which is why buoyancy dictates that your legs should follow your torso to the surface (your torso is already there; the force pushing your legs up is that which is already holding up your torso). The only way you can remain vertical in the Dead Sea is by keeping your body ramrod straight, and even then you can only hold it for a few seconds. Perhaps the difference between the Dead Sea and the Mythbusters experiment is the complex chemical composition, and the flow, of the DS water? Natgoo 18:05, 6 April 2007 (UTC)

Doods... you're stuck on buoyancy and you're forgetting about gravity, which acts as a destabilising force on upright objects in fluid (think of a bowling pin or a log in water). The fact that people in Mythbusters could stay upright in quicksand is probably because the particulate made it easier to resist tipping over. Anchoress 18:43, 6 April 2007 (UTC)

Right. As anyone who's tried to design a boat knows, something floating in water is stable only if its center of gravity is below its center of buoyancy. But that's obviously not so for a biped standing in a liquid so dense that only the legs are submerged! —Steve Summit (talk) 22:57, 6 April 2007 (UTC)

Yeah - but look at this picture of someone actually floating in the dead sea (see right). It's clearly not dense enough that the guy's center of gravity is above the surface of the water. We're not thinking of someone floating up to their knees or something - that's completely the wrong mental image. 16:37, 7 April 2007 (UTC)

Nice pic! Thank you.

The side discussion about CG/CB had to do with Natgoo's statement that "it's impossible to stand up in the Dead Sea (with only your head above the water), as your legs rise to the surface every time you try to put them below you." If you were in a fluid so dense that the volume displaced by just your shins and feet were sufficient to support you, you could try to stand, but it would be very difficult -- you would have to (as Natgoo also suggested) try to "keep your body ramrod straight". It's not that your legs would tend to fly up due to higher buoyancy or anything, it's just that your body would tend to fall down. —Steve Summit (talk) 18:36, 7 April 2007 (UTC)

shit

What is the chemical formula of human shit(faeces)? Invisiblebug590 10:26, 6 April 2007 (UTC)

What is the chemical formula of the human diet? What comes out is just as complex and varied a combination of things. There is no single chemical formula. alteripse 10:48, 6 April 2007 (UTC)

The color is mostly due to bilirubin and biliverdin. Cellulose is a major component, depending on your diet (much healthy plants with low nutritional value). Some mucus also, so it doesn't go 'clank, clank' when dropped. 84.160.225.164 11:01, 6 April 2007 (UTC)

Chemical formulae are for describing chemical compounds, but faeces is a mixture of different substances. Hence there is no singular formula. - SpLoT // 14:49, 6 April 2007 (UTC)

There's gases, dead intestinal cells, dead bacteria, digested organic matter, nondigested matter, and other mentioned things. bibliomaniac15 20:37, 7 April 2007 (UTC)

Electron Microscopes

Can anyone explain in terms of Higher Tier GCSE level how an electron microscope works, surely you would end up seeing the atoms in the lens and not the object/atom you want? —The preceding unsigned comment was added by 84.13.132.232 (talk) 11:51, 6 April 2007 (UTC).

All "seeing" works by bouncing a smaller particle off of a bigger particle — I see a stapler on my desk because tiny photons are reflecting off of it and hitting my eye. The problem is that when you want to see very small things, the size of a photon of visible light becomes relevant — blue light has a resolution of 400 nm which is pretty small but when we are talking about things like the size of an E. coli bacteria (1 nm µm across or so) that ends up not being enough to really see very much. So instead of using photons, an electron microscope uses electrons as the particle that is bounced off of the object; electrons can have much smaller wavelengths depending on how fast you shoot them (de Broglie's formula relates a particle's wavelength to its velocity), and thus can make out objects that are much finer. As for seeing individual atoms, you can do it, if you set the wavelength of the electrons to be small enough (.1 nm or so). But in any case what's important is that you can adjust the resolution by varying the velocity of the electrons. That's my understanding of it, anyway. --24.147.86.187 12:06, 6 April 2007 (UTC)

It might be useful to compare an electron microscope with the computer monitor you are viewing now. It doesn't ever really show an object, like a sphere, but rather shows a series of 2D dots which approximate the object. Our brains fill in the missing data (usually, but not always, correctly). Our brains are actually quite good at filling in missing visual info, as the signal that comes in from the retina is much worse than you would think. In addition to the blind spot in each eye, there are also numerous locations where you looked at the Sun or a flash bulb where damage was done. Yet our brains fill in those spots with whatever's around them without us noticing. Normally this is good, but it's sometimes bad, as when a hidden car is in the blind spot. StuRat 13:02, 6 April 2007 (UTC)

No bacterium is just a nanometer across; E. coli is about a half-micron across. 1 E-9 m says that DNA is already 2 nanometers across. But optical microscopes still have problems because the wavelength of visible light is not much smaller than the target, creating all sorts of image-distorting wave behavior. --Tardis 16:03, 6 April 2007 (UTC)

My bad — I misread the Greek script on the image. --140.247.251.165 16:20, 6 April 2007 (UTC)

The answer to your question depends on the type of electron microscope that you're talking about. The type that most closely mirrors a conventional optical microscope is a transmission electron microscope, which passes a beam of electrons through a sample and forms an image out of the electrons which reach the other side. In such a microscope, there are no physical lenses of the type that you would find in an optical microscope; as you've intuited, the electron beam would hit the glass and be absorbed or scattered, leaving nothing with which to form an image of the sample. Instead, the beam of electrons in an electron microscope is focused, bent, and manipulated using electric and magnetic fields. Carefully shaped electromagnetic fields can have the same types of effects on an electron beam as cut and polished glass does on a beam of light—and electromagnetic fields propagate perfectly well inside the vacuum of an electron microscope. (Our article on electron optics, unfortunately, is still a stub—experts in the field are invited and encouraged to flesh it out.) TenOfAllTrades(talk) 14:39, 6 April 2007 (UTC)

Static Electricity

Sometimes, when you go to bed at night and you move your feet around quickly against the sheets, you see an interesting effect. What is happening? --Mayfare 12:33, 6 April 2007 (UTC)

You seem to know the answer already, you're seeing a static electricity discharge between your feet and the sheets. I've noticed this happens when the sheets are just out of the dryer, and hence full of static charge. StuRat 13:05, 6 April 2007 (UTC)

The charge may come from yourself, as you walk on cheap carpet, you may build a charge which you discharge getting into bed. Also, some blankets and some sheets can collect charge as Stu suggested DDB 14:12, 6 April 2007 (UTC)

Thanks for your responses. --Mayfare 17:36, 6 April 2007 (UTC)

graphing forces

forces can be indicated on a graph paper by the use of? —Preceding unsigned comment added by Deasedanielle (talk • contribs) 14:49, 6 April 2007

Floating vectors ? StuRat 00:57, 7 April 2007 (UTC)

A pencil?--Shantavira 08:01, 7 April 2007 (UTC)

Disciplined mental effort, coupled with sound education and a little luck, given that your teachers really were right. DDB 11:33, 7 April 2007 (UTC)

Geriatrics

Hi, I have a question: would anyone, especially a geriatric doctor or someone who works in an elder care setting be able to provide a comprehensive and high school level list of vocabulary terms that would apply to general elder care and the problems associated with it. I have a few terms like reluctant patient and I know the basics but a good advanced list would really help my score. Thanks in advance! --Uchihah 15:01, 6 April 2007 (UTC) Uchihah

Sponge bath? :P Vitriol 16:14, 6 April 2007 (UTC)

Try asking a Personal Support Worker and/or a geriatric doctor. --Mayfare 17:38, 6 April 2007 (UTC)

a topic related to taxonomy of angiosperm

please give me details about a topic related to taxonomic tools that is, COMPUTERS AND GIS (Geogrophical information system)59.94.115.227 16:00, 6 April 2007 (UTC)

Belly button problem

In the human or other mammals, where does the umbiliacal cord connect to inside the baby before birth. And how is this pathway shut off after birth? —The preceding unsigned comment was added by 88.110.208.218 (talk)

See the articles about the umbilical vein and umbilical artery. DMacks 19:26, 6 April 2007 (UTC)

So in other words you mean:

Inside the fetus, the vein courses alongside the falciform ligament and then to the liver's underside. At the transverse fissure, the vein divides into two vessels, one larger than the other. The larger of the two is joined by the portal vein, and together they enter the right lobe of the liver. The smaller vessel, now called the ductus venosus, diverges away from the liver and joins with the inferior vena cava. Whatever that means!

Why didnt you say so? —The preceding unsigned comment was added by 88.110.128.130 (talk) 23:33, 6 April 2007 (UTC).

Because DMacks assumed you could read on your own. Which, apparently, you can. − Twas Now ( talk • contribs • e-mail ) 04:40, 7 April 2007 (UTC)

Composition

What is the composition of the isotope C-12? —The preceding unsigned comment was added by 76.64.52.108 (talk) 18:59, 6 April 2007 (UTC).

Carbon, specifically the isotope with 6 neutrons. DMacks 19:09, 6 April 2007 (UTC)

And 6 protons Czmtzc 19:21, 6 April 2007 (UTC)

And 12 electrons. − Twas Now ( talk • contribs • e-mail ) 04:39, 7 April 2007 (UTC)

Six electrons, not twelve. But in addition to the six protons and six neutrons, there are bunch of thingees in the nucleus that hold it together. These are the virtual particles that embody the nuclear strong force. Of course, this force may be a mere artifact of deeper interaction amongst the quarks and gluons the comprise the protons and neutrons. -Arch dude 05:12, 7 April 2007 (UTC)

Oh damnit, what was I thinking? There goes my university degree in biochemistry… − Twas Now ( talk • contribs • e-mail ) 09:09, 7 April 2007 (UTC)

relative atomic mass

Explain why the relative atomic mass of carbon, referenced on the periodic table, is not exactly 12? —The preceding unsigned comment was added by 76.64.52.108 (talk) 19:01, 6 April 2007 (UTC).

Explain why we should do your homework for you. Please at least try to use this bazillion-page encyclopedia to look up answers for yourself and then ask about what's confusing. DMacks 19:10, 6 April 2007 (UTC)

It is not homework. Don Mustafa

The atomic mass of an element is the average mass of all of the isotopes for that element weighted by the relative abundance of each isotope. --Czmtzc 19:17, 6 April 2007 (UTC)

Ironically, the mass of carbon 12 is exactly 12 amu, since the definition of atomic mass unit is one-twelfth of a carbon-12 nucleus. Now that I think about it, I'm not sure if it's the nucleus or the whole atom with electrons too, but that should be reasonably negligible, less than one percent. The original question, though, is referencing isotopes. Nimur 20:15, 6 April 2007 (UTC)

Made-up example: if I have 50% Cl-34 and 50% Cl-35, the average atomic mass of the chlorine atoms I have would be 34.5 --Bowlhover 05:36, 8 April 2007 (UTC)

mass of fractions

Why would you want to avoid calculating the mass of fraction of an atom? —The preceding unsigned comment was added by 76.64.52.108 (talk)

Why would you want to avoid doing your own homework? --LarryMac 19:49, 6 April 2007 (UTC)

It is not homework --Don Mustafa

—The preceding unsigned comment was added by 76.64.133.10 (talk) 13:36, 7 April 2007 (UTC).

I would guess because it probably isn't much use to you—most of the atom is empty space anyway, and all but the nucleus is ignored. So you would be finding the mass of part of the nucleus, and that would be unnecessary since you already known the masses of the nucleons. [Mαc Δαvιs] (How's my driving?) ❖ 23:20, 6 April 2007 (UTC)

But the mass of the atom is less than the mass of the nucleons, because of the energy needed to bind them together. —The preceding unsigned comment was added by 68.117.135.99 (talk) 04:58, 7 April 2007 (UTC).

Binding energy increases the mass of the atom, does it not? --Bowlhover 04:39, 8 April 2007 (UTC)

Some people spend huge energies on finding a prime number larger than the largest known one, or the 10 zillionth number in the decimal expansion of π. These aren't of much practical use either, but they're justified on scientific grounds. JackofOz 06:25, 8 April 2007 (UTC)

Normalized Mean Square Error

I am instructed, without further context, to calculate a normalized mean squared error for one of my data processing projects.

I am struggling to decide which is a better "normalization":

$error={\frac {1}{N}}\sum _{i=1}^{N}(x_{i}-x_{exact})^{2}$

or

$error={\frac {1}{N}}\sum _{i=1}^{N}({\frac {x_{i}-x_{exact}}{x_{exact}}})^{2}$

I will be comparing several different fast methods for calculating the $x_{i}$. I know the $x_{exact}$ and want to obtain relative errors for each method, to determine which is "optimal." Which normalization technique will result in a more straightforward comparison between different values? Any other suggestions? Any suggestions? Nimur 20:25, 6 April 2007 (UTC)

The two values will differ by a constant factor of ${x_{exact}}^{2}$. In a sense, it's really just a unit conversion issue: for example, if $x$ is measured in meters, then the former value will be units of meters², while the latter will be in units of ${x_{exact}}^{2}$. It would seem to me that, if the instructions explicitly call for a normalized value, then what they mean is probably the latter; if they meant the former, they would just say "mean squared error" without any additional qualifiers. —Ilmari Karonen (talk) 01:13, 8 April 2007 (UTC)

Heat transfer in space

If i was to be closer to the sun in space and I was to be standing in the shadow the temperture would be cold and if I was to step out in the sunlight I would burn, on earth the shadow would still be warm but in space does the heat travel into shadow AT ALL? Wuld there be a definitive line of hold and cold? —The preceding unsigned comment was added by 86.136.246.197 (talk) 23:25, 6 April 2007 (UTC).

There is a much more dramatic difference between shadow and light when close to the Sun in a place without an atmosphere, yes. With no atmosphere to transport the heat to you from the bright areas, the only heating would be from the blocking object, which would eventually warm up and radiate heat onto you (although still less than you would get from direct sunlight). Also, space around the Sun isn't quite empty, and particles might still strike you on the far side of the object, if you are in turbulent currents of the solar wind, for example. StuRat 00:49, 7 April 2007 (UTC)

Heat is transferred by: Radiation, Conduction or Convection. Without air or water or some other fluid, there is no convection - so we're left with radiation and conduction. No air means less conduction of heat into the air. If you imagine a big rock on (say) Mercury - then how does heat get from the sunlit areas to the shadows? Well, bright light reflecting off the surrounding landscape will slightly illuminate the shadows - so some radiation does make it into the shadow, not as much as on earth because we aren't getting any light scattered from the atmosphere. But unless we're looking really deep under the rock or in a cave or something we're getting some radiation from the brightly lit surroundings. Then there is conduction - so some heat from the sunlit side of the rock will be conducted through the rock and will warm the shadowed side. But rock doesn't conduct heat all that well - so heat is coming in there rather slowly. However, temperature is also determined by energy loss - so our rock will lose heat as well as gain it - no air means that the shadowed side of the rock isn't losing as much heat as it would on earth because heat isn't being conducted/convected away by the air. It's a complicated question - but undoubtedly it's going to be a heck of a lot colder in shadows and a heck of a lot hotter in sunlight when there is no atmosphere. SteveBaker 16:29, 7 April 2007 (UTC)

Proof of global warming

Does this not underline (get it?) today's events?

71.100.6.150 23:34, 6 April 2007 (UTC)

OK those are your underpants, now what about the females?

What makes you so sure I can't darn well pack a bra? Be 'shamed your self young feller! 71.100.6.150 00:18, 7 April 2007 (UTC)

I like how it goes from 18th century (1700s) to 1900. Skipped the whole 19th century there! --24.147.86.187 00:20, 7 April 2007 (UTC)

Yep, them peoples back then were a lot closer to the Victorian age and wearing less bulky clothes did not occur to them somehow to be the right solution. That's were the saying "... just don't seem right somehow..." comes from. 71.100.6.150 00:33, 7 April 2007 (UTC)

So the moral is "don't get your panties all in a bunch over global warming" ? StuRat 00:42, 7 April 2007 (UTC)

Don't quote me but its probably more like "Take you panties off over global warming." 71.100.6.150 00:48, 7 April 2007 (UTC)

Yeah will we all be wearing no panties at all in a few years if global warming continues?

Yes. It will be the garment industry versus global warming. 71.100.6.150 01:10, 7 April 2007 (UTC)

See also: Microkini], post hoc ergo propter hoc. [Mαc Δαvιs] (How's my driving?) ❖ 01:31, 7 April 2007 (UTC)

A Google image search on Microkini, reveals that more than one women has found that a reduction in clothing size can provide relief from heat caused during Ovulation by basal body temperature which can be exaggerated by Global warming. Nebraska bob 03:52, 7 April 2007 (UTC)

Greenhouse Gases

I am interested in the partition of greenhouse gas emissions by sectors, and the only reference I found within Wikipedia is this diagram:

Are the numbers in this diagram totally agreed upon? Or is there much variance between different sources? Does the emission from vehicles account really to only 14% of the total emission? Gidip 23:57, 6 April 2007 (UTC)

I don't know, but I know it does not seem almost anything is totally agreed upon regarding things having to do with the anthropogenic global warming hypothesis. Sometimes they can get more precision than order of magnitude estimates for global carbon producers and reservoirs, and I would not be surprised if that chart was based on only the US. [Mαc Δαvιs] (How's my driving?) ❖ 01:26, 7 April 2007 (UTC)

Thanks Gidip 01:19, 8 April 2007 (UTC)