Wikipedia:Reference desk/Archives/Science/2006 October 28

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[edit] October 28

[edit] Helium

According to the Helium article, it the 2nd most abundant element in the universe, but not really very abundant at all on Earth. Why? Is simply because molecular helium tends to rise in the atmosphere and escape into space? Or is there some deeper reason for scarcity of He on Earth? ike9898 03:40, 28 October 2006 (UTC)

Earth's gravity is not strong enough to hold on to a hydrogen/helium atmosphere. Before life even originated, the hydrogen/helium atmosphere was blown off by the Sun's solar wind. Right now though, the helium generated by radioactive decay does escape into space (as you said). The heterosphere actually has a lot of helium. --Bowlhover 03:49, 28 October 2006 (UTC)
It is also chemically very inert so it can't get trapped like other light atoms like Hydrogen. Hydrogen is very abundant because it is trapped as much heavier water. it would be interesting to also see how much Helium is "trapped" in radioactive atoms that undergo alpha particle decay. --OpusPenguin 03:50, 28 October 2006 (UTC)

[edit] observing stars other than the sun

I know that it is possible to take pictures of the sun that actually some 'detail', that is, they show 'surface ripples' rather than just a featureless disk of light. My question is, with any existing equipment (including the Hubbel telescope), could you produce an image of a star, other than the sun, that actually shows some of this detail? If not, would this be possible with any instrument that could be built within, say, the next 25 years? ike9898 04:36, 28 October 2006 (UTC)

Yes, it is possible. For example, here are 3 pictures of the surface of Betelgeuse. I don't know if any other star's surface has been imaged, though; I'll be curious to find out. --Bowlhover 04:54, 28 October 2006 (UTC)
The fourth picture on that page looks curiously close to something done with Crayola colored pencils. Hyenaste (tell) 23:34, 28 October 2006 (UTC)
Easy, with the right budget. If the scientific world had the budget of the military such telescopes (and better) would have been commonplace now. We'd have permanent stations on other planets and all that star trek stuff. But in the real world, you'd have to wait a few years, for the Herschel Space Observatory or a few more for the James Webb Space Telescope. Not sure how much detail they will show, though. There are also plans to send multiple telescopes into space somewhere in the 2020's, that work in unison, thus getting the resolution of a much bigger telescope (albeit not the light sensitivity). With that, we could even study the surface of planets orbiting stars (provided they are not too far away). DirkvdM 12:25, 28 October 2006 (UTC)

[edit] Gel-based ice packs - removing dried contents?

I've left an ice pack in the back of my car for a while, and not only has it burst, it's dried out. The remaining contents are some kind of crystalline-type stuff, and where they've "set" in the carpet they're damned difficult to remove. Does anybody know a) what the stuff is, and b) any suggestions for removing it more effectively than water? --Robert Merkel 05:23, 28 October 2006 (UTC)

It would depend on the ice pack, but for the one I found first on Google, you can vacuum it, and it's also water soluable. What brand was your ice pack? I believe there are more than one gel used for them. --Wirbelwindヴィルヴェルヴィント (talk) 06:03, 28 October 2006 (UTC)
It really depends on the brand. Some are water-soluble, some aren't, some are toxic, some are less toxic. I'd be careful when cleaning it up. Virogtheconq 07:05, 28 October 2006 (UTC)

[edit] Questions about salt water

I am writing about salt water. Questions:

  • Is salt water suitable for bathing (on a consistent basis)? Will soap and shampoo lather in salt water?
  • Is salt water be suitable for cleaning benches, cooking implements, and crockery?
  • Aside from the problems of installing dual reticulation where it doesn't presently exist, would there be issues in transporting salt water to homes (i.e., in corrosion of pipes/machinery - but I think most reticulation pipes are concrete or plastic, not metal...)? BenC7 07:06, 28 October 2006 (UTC)
If there is no problem of corrosion on the way to the homes, there would be huge problems within the home. Most taps, piping etc. are made of metal. --liquidGhoul 07:20, 28 October 2006 (UTC)
Soap is rather ineffective in salt water, which is why it makes sense to pre-rinse clothes you've been sweating in before you wash them (sweat is salty). There is a special kind of soap for salt water that I tried once, but I wasn't impressed at all. Apart from the soap not working properly, if you rinse something with salt water and let it dry, some of the drying will be through evaporation, leaving a salt layer, which will not be desirable in most cases. DirkvdM 12:39, 28 October 2006 (UTC)
Some soaps do fairly well. The "Joy" brand of detergent is a favorite among sailors, and being one myself I can personally attest to it working fairly decently in seawater. Not that there's much you'd want to clean in salt-water apart from dishes. --BluePlatypus 18:12, 28 October 2006 (UTC)

All (nice) salt water beaches have fresh water showers. Salt is yucky on the skin. The new trend is for saline swimming pools, but this concentration is much less than ocean water. --Zeizmic 14:40, 28 October 2006 (UTC)

Soap does not lather in saltwater. I've heard that Ivory is best - but that is likely because it floats so it is hard to lose it when bathing in the ocean. As for transport, saltwater can be effectively transported. The University of Hawaii is expanding a project that transports cold saltwater from deep in the ocean to the surface where it is used to cool buildings before being sent back to the depths of the ocean again. --Kainaw (talk) 15:11, 28 October 2006 (UTC)

In places where fresh water is scarce, one approach is to bathe or wash clothes or dishes in salt water, but then rinse in fresh water, to eliminate the salt water residue. Food may also be cooked in salt water. Note that salt water from the sea has life forms and debris in it, too, which can clog pipes. Filtering the water helps, but the filters will soon clog, as well. One approach is to clean the pipes using a "pig", a large slug rammed down the pipe to scrape the sides clean, on a regular basis. StuRat 15:26, 28 October 2006 (UTC)

Food can be cooked in salt water? What? Doesn't the food (say, rice) absorb a lot of the salt, making the food extremely salty? BenC7 01:34, 29 October 2006 (UTC)
Yea, it wouldn't work for some foods that absorb lots of water; like pasta, rice, and hot cereal. But you could boil meat, fowl, fish, potatoes, eggs, etc. in salt water without making them too terribly salty. StuRat 03:07, 29 October 2006 (UTC)
I add salt to water when I'm cooking rice or pasta, maybe not as much as to make it like sea water but I'm not sure it would make it overly salty. I would have a problem with constantly salty hair though, that would not be nice. Vespine 00:42, 30 October 2006 (UTC)
Yes, that's why you need to rinse in fresh water. StuRat 05:29, 30 October 2006 (UTC)

[edit] looking for the name of a thing used to view still photos moved by a crank

Hello,

Could somebody please help me with the name of a picture viewing machine, widely prevalent in India in the 1960s and 70s (maybe earlier and in other places too) where a record used to be played on a grammophone and kids looked through peepholes, 5 or 6 of them around a cylindrical (or polygonal) base. inside were pictures pasted on a coaxial polygon which rotated as the operator turned a crank. the whole thing rested on a table or tripod and could be packed and carried on the head.

will a picture along with the name be too much to ask for?

i have tried bioscopes but the images i'm getting on the net are not the ones i mean.

thanks in advance for the trouble.

regards

Kushal, Chennai, India

a zoetrope. Xcomradex 10:01, 28 October 2006 (UTC)
A Mutoscope is probably closer to what you're thinking of.
Atlant 21:26, 28 October 2006 (UTC)
Yes thats what I was thinking, but I called it an orthoscope. (which doesnt exist)--Light current 21:48, 28 October 2006 (UTC)

thanks for taking the trouble, though i'm afraid i'm still searching. am adding a few more clarifications that might help. > it was always (at least all i've seen) topped with a victrola - so its more of a fairground kinda machine than a serious photo viewing device. > it was larigish, lets say about a 3/4m across. > the pics seen were definitely still iamges(and meant to be so) > the peepholes had lenses on them and were covered with a lid on the outside when not in use> and finally its the theme in the latest compaq ad by shah rukh khan as being shown on tv channels in india

sorry again for the trouble, but its driving me nuts!

[edit] Papain, Bromelain, Ficin and Actindin

I am doing an experiment where I am seeing what enzyme will tenderize meat the fastest. I need a concentration/percentage that is very close. For example, if the sample of papain contains 97% of papain as the main ingredient,then ficin should be very close to that amount.

I would appreciate if anyone would know where I could purchase these digestive enzymes:

Papain (Papaya), Bromelain (Pineapple), Ficin (Figs) and Actinidin (Kiwi). Preferrably in powder form, since it would be hard to know the amount of the enzyme in each piece of fruit.

The problem I am finding is that the Health Stores only carry Papain and Bromelain and some of the biochemical companies sell only industrial size.

Would any universities carry them?

Thanks,

JDC

This was already responded to on the 27th. If you want to study the activity of the enzymes, you'll need to get them in an active form, usually frozen or (sometimes) freeze dried. Your school may be able to arrange a purchase of small amounts of the enzyme from Sigma-Aldrich (which is where I go for most of my various enzymatic needs). Good luck! – ClockworkSoul 14:00, 28 October 2006 (UTC)

[edit] Neutrinos and Antineutrinos

Hello, I was reading the Wikipedia article on the neutrino and noticed the mention that it might be the same particle as the antineutrino. There wasn't a very good explanation as to why this would be so that I could find, so I was wondering if someone could give an explanation. Thanks! Andromeda321 16:00, 28 October 2006 (UTC)

This is difficult ton understand without some background in particle physics and special relativity. Assuming that you know a little bit about it, I'll give it a try: According to the principle of C-symmetry, every elementary particle has a corresponding antiparticle, which has the same mass, but differs from the former in that all charge-like quantum numbers have opposite sign. A electron, for example, has only electromagnetic charge, of value -1, and its antiparticle, the positron hence has electric charge +1. An up quark has electric charge +2/3 and colour charge red, green or blue, and an anti up quark hence electric charge -1/3 and colour charge antired, antigreen or antiblue. Now take the photon, which has no charge with respect to any of the fundamental interaction electromagnetism, weak interaction and strong interaction. Reversing the sign of 0 (no charge) gives 0, so there is no contradiction in assuming that it is indistinguishable from its antiparticle: as it turns out the photon is its own antiparticle. Now, is the same true for the neutrino, which also has no electric or strong charge? The weak interaction has the strange feature of CP violation: it can distinguish between a neutrino "spinning clockwise" (having helicity -1) and one "spinning anticlockwise". Now oe wonders whether the difference between neutrino and antineutrino is really due to them being different particles or only because they have different helicity. One possibility is called Dirac neutrino, the other one Majorana neutrino. This difference becomes meaningless when the neutrino is massless because then it travels at the speed of light, and its helicity is the same in all frames of reference, while now, that we know that neutrinos have mass, one can imagine "overtaking" them by a Lorentz boost and see how they interact as seen from that fram of reference. About here, my memory of my particle physics course taken years ago gets a bit too fuzzy and I better stop and let somebody else continue. Simon A. 16:36, 28 October 2006 (UTC)
"The weak interaction has the strange feature of CP violation" Is that a deliberate pun? If so, it's one of the best puns I've ever heard. Very funny!

[edit] Variables

Hi there

is there a simple and clear way of understanding dependent variables and independent variables? I am 49 years of age, studying for a Single Hons Degree in Psychology, but Research Methods defeats me - especially understanding what these variables are and how to use them. Have had discussions with fellow students and a one to one session with a student taking his Phd. Am tearing my hair out, given so many examples but do not understand any of them. Please somebody help this thick old woman!!!!!!!!! Carole D

Did you try reading dependent variable and independent variable? Independent variables are ones you set for experiements. For example, if you want to use placebo, that's an independent variable. The result from using placebo, is the dependent variable. --Wirbelwindヴィルヴェルヴィント (talk) 17:28, 28 October 2006 (UTC)
Suppose you want to test the hypothesis that people who study more obtain better grades for their exams. You know that students spend on the average 25 hours or so per week on their study, but some spend much less time and some spend more time. So you randomly select a group of students, and find out for each: (A) how much time per week they studied, and (B) what grade they got. These two data are variables. So for each student you have two variables: X = hours/week and Y = grade. The hypothesis is that Y depends on X: a higher value of X gives rise to a higher value for Y. Then, for the purpose of testing your hypothesis, Y is called the dependent variable. (Maybe it turns out that the hypothesis is rejected, and that the value of Y does not depend on X. Still, for your test, it is the dependent variable.) The other variable, X, is the independent variable.
In this example there is only one independent variable. But perhaps you have also collected data about how long the students sleep each night, because you also think that you need enough sleep to get good grades. Then you have two independent variables.
See for more information also Variable#In applied statistics, Control variable, and Experimental design.  --LambiamTalk 17:36, 28 October 2006 (UTC)

[edit] control system

even though i could get lot of information about control system but the subjects which are in continution to it like Discrete Control System,Optimal control system, Adaptive Control System,Computer Adied Designe Of Control System , i am unable to get information about these subjects. can you suggest me how to get the notes of these subjects.

202.63.109.234 16:52, 28 October 2006 (UTC)imran (A.C.E.T)

Those sound like master and Ph.D. level topics, as I am an engineering student and the senior level courses only go up to systems and control. Your best bet is at a university library. --Wirbelwindヴィルヴェルヴィント (talk) 17:30, 28 October 2006 (UTC)
I agree. It is really a vast field, and you should try to find texts corresponding to your needs, interests, and background. I assume you are familiar with the material on Control Systems at Wikibooks. Perhaps our articles on Digital Control, Control theory, Real-time control, Optimal control, Adaptive control, Control engineering, and MATLAB, also following promising links in the "See also" and "External links" sections, give you some material to mull over in the meantime, and suggest some pointers to follow.  --LambiamTalk 17:58, 28 October 2006 (UTC)

[edit] how to create an artificial force field

respected sir, im an engineering student and i would like to know how to create an artificial force field. for many good reasons keeping in view the defence system of every country.by using artificial force fieldis it possible to convert the energy grabbed by the object to the potential energy of the system and can be re imparted energy to thre object.its a very typical question.so i would be needing ur help to get out of this problem.hope to seek the answer soon. —The preceding unsigned comment was added by Punitmalpani007 (talk • contribs) .

Did you read our page on force fields? There is a section called "Research and development" that answers your question. And please sign your stuff with 4 tildes, or ~~~~. --Wirbelwindヴィルヴェルヴィント (talk) 17:33, 28 October 2006 (UTC)
In a practical sense, there's no real way to create a force field that might repel/capture objects on a scale that could defend a country (at least for the next twenty years or so). The energy requirements for (see magnetic levitation for a not-very-applicable example) are just too darn high. If you're more interested in the theory of trapping matter, laser trapping might be a good article to look at too. Virogtheconq 20:45, 28 October 2006 (UTC)

[edit] Weight

I'm thinking about making yeast bread, but I like to buy my food by price-per-unit-weight. How much mass does yeast consume in producing carbon dioxide, assuming the standard practice of letting the dough double in volume? What would be the most cost-effective way to do this? Black Carrot 18:52, 28 October 2006 (UTC)

I think you can safely assume that the yeast consumes a negligible amount of the sugars in the hour or two that it is actively fermenting.
Atlant 21:30, 28 October 2006 (UTC)
Agreed. The gases which are given off by the yeast and exit the bread (after the "bread squeeze" phases) would be the only source of lost mass in the bread. I'm thinking that weight would be under one gram. StuRat 02:45, 29 October 2006 (UTC)

[edit] Complete proteins

I have often heard that soy is the only vegetable source of complete protein; however, I have also heard this claim made for certain grains such as buckwheat, quinoa, and amaranth. I found a ref for quinoa, but am having trouble for the others. Does anybody know of any reliable sources that can tell me once and for all which, if any, vegetable proteins are complete? --Ginkgo100 talk · e@ 20:58, 28 October 2006 (UTC)

To clarify, I am also looking for a ref for soy, because all I can find on the Internet is commercial bodybuilder website. --Ginkgo100 talk · e@ 21:00, 28 October 2006 (UTC)
If you don't find your answer elsewhere, then you might want to try to find a copy of Diet for a Small Planet by Frances Moore Lappé; this book discusses which foods combine well together to provide complete nutrition.
Atlant 21:32, 28 October 2006 (UTC)

For clarification, may we assume in a dietary context a "complete protein" is one which contains all essential amino acids? alteripse 14:40, 29 October 2006 (UTC)

Hmm, while I'm not completely certain, I believe most vegetables contain all amino acids. What they don't contain is enough of all of them. --BluePlatypus 16:51, 29 October 2006 (UTC)
A food with complete protein contains all essential amino acids in more or less the proper ratio. Thanks for the book reference, Atlant, I will look it up next time I'm at the library. --Ginkgo100 talk · e@ 22:03, 29 October 2006 (UTC)

[edit] Valence Electrons

How many valence electrons does oxygen have? 71.97.11.77 21:25, 28 October 2006 (UTC)nicholassayshi

Six. Why do you ask? Theresa Knott | Taste the Korn 21:51, 28 October 2006 (UTC)

It doesn't say in the web site. 71.97.11.77 22:08, 28 October 2006 (UTC)nicholassayshi

Here's how you find out: Look at the table for valence shells. Find the number of electrons in element (8 for oxygen). So 8 minus the number of electrons in shell one is 8-2 = 6. So you have a full first shell, with 6 electrons left. The 6 remaining electrons is less than the max of the second shell, thus it doesn't go to a third shell, thus the valence shell is the second shell, with 6 electrons. Hope that makes remotely some sort of sense. --Wirbelwindヴィルヴェルヴィント (talk) 22:40, 28 October 2006 (UTC)

[edit] Shimmering tarmac on a hot day

Who can explain to me why, when you look along a tarmac or asphalt road on a hot day, you see a shimmering, mirrored effect in the distance. I presume its heat related and is the same effect that produces shimmering in the desert, but what is the exact mechanism? Thanks. Rockpocket 21:26, 28 October 2006 (UTC)

See Mirage; that article is pretty complete and speaks directly to your question.
Atlant 21:33, 28 October 2006 (UTC)
Amazing. Thank you, i never realised that was what the word 'mirage' referred to. Rockpocket 21:36, 28 October 2006 (UTC)