Wikipedia:Reference desk/Archives/Science/2008 March 29

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[edit] March 29

[edit] Canned tuna

Is canned tuna cooked? 71.100.15.236 (talk) 01:02, 29 March 2008 (UTC)

In short: yes. There's some information about it at Tuna#Canned tuna. --Masamage ♫ 01:14, 29 March 2008 (UTC)
Okay, cooked but a couple of other questions... it looks like there is no minimum amount of tuna per can to call it tuna. 90% water or oil and 10% tuna and its tuna. No one would probably buy it again but what about 10% tuna, 41% catfish and 49% water? 71.100.15.236 (talk) 02:31, 29 March 2008 (UTC)
The cans have to contain a certain weight of tuna after the liquid in the can is drained. See here for the FDA regulations on canned tuna, specifically part c. Someguy1221 (talk) 11:07, 29 March 2008 (UTC)

[edit] cd recycling

Can cd's be recycled? If so, do you put them in with normal municipal recycling? I know the procedure might vary from place to place, so fyi, in my city of Perth, my local council (Claremont) uses mixed recycling, ie. without source separation. thanx in advance, 130.95.106.128 (talk) 07:10, 29 March 2008 (UTC)

I recycle mine as coffee cup coasters. Seriously, they can be recycled. Try this [1] google search string. You will also see that there are a lot of charities that will take them to make interesting products. SpinningSpark 13:12, 29 March 2008 (UTC)

[edit] Sodium Bicarbonate Vs Constipation?

Why does Sodium Bicarbonate help in going to the toilet? I know it is an has a much higher ph than the stomach but why does this result in the need to visit the toiler 5 mins after drinking it mixed with warm water? Is it bad for the stomach to use on a regular basis?

Lopex —Preceding unsigned comment added by 86.4.182.208 (talk) 08:42, 29 March 2008 (UTC)

When you mix Sodium bicarbonate with stomach juice it foams up making carbon dioxide gas, which build up pressure in the digestive tract, that pushes the contents out. Too much will give you pH imbalance, and also too much sodium. Graeme Bartlett (talk) 22:18, 29 March 2008 (UTC)
I am not convinced that a pressure build up in the stomach will have a direct pressure-based effect on the lower bowel. They are separated by several metres of soft small bowel which would absorb the pressure and apart from that, if there is that much pressure build up (again, questionable) surely it would escape upwards through the gullet, giving a vomiting effect. Bowel movements are associated with psychological stimuli in some people and the thought that something will effect the bowels does just that. An alternative explanation may be related to the gastrocolic reflex, even so five minutes seems a bit quick. Richard Avery (talk) 07:19, 31 March 2008 (UTC)
As for regular basis, once things are back to normal, probably no need. Julia Rossi (talk) 07:53, 31 March 2008 (UTC)
I would think the more likely explanation of any laxative effect of sodium bicarbonate is induction of hyperosmotic diarrhea. On the other hand (or on the other end), sodium bicarbonate's "fizzy" effect is used in suppositories, and acts by inducing a feeling of rectal "fullness", with the expected reflex action. Bicarbonate isn't really a popular laxative - it's used more as an antacid - and of course, it's considered bad form to use any laxative regularly without consulting a physician to see if there is an underlying problem that need to be addressed.- Nunh-huh 09:53, 31 March 2008 (UTC)

[edit] What is the difference between a UPS and a inverter ?

Media:Example.ogg —Preceding unsigned comment added by 124.124.1.131 (talk) 12:17, 29 March 2008 (UTC)

An inverter is a device for converting dc power to ac power. An Uninterruptable power supply (UPS) stores energy it obtains form its input (often in a battery, but it could be something else, eg a flywheel) which it applies to its output if the primary source fails. A UPS will often contain an inverter because its output may be ac while it has stored power as dc. However, in principle, a UPS might not have an inverter if its output was required to be dc. SpinningSpark 12:29, 29 March 2008 (UTC)
SpinningSpark is right. Also, sometimes people may say "inverter" when they mean UPS. I knew someone who had a home-built UPS system, basically a inverter, a charger, and a big battery. They called it an inverter even though that was just one part of the system. -- 71.91.127.85 (talk) 16:25, 30 March 2008 (UTC)
If you remove the DC input to an inverter, the AC output will immediately go to 0VAC. If you remove the (usually AC) input to a UPS, the AC output will not change (much). A UPS includes an inverter, a battery, and a battery charging system. -Arch dude (talk) 23:41, 30 March 2008 (UTC)

[edit] blackout --- caused by global warming?

I would like to know if I got it right that global warming also has something to do in any way with having power/electrical loss or blackout. Thank you in advance for the reply. —Preceding unsigned comment added by 119.93.229.75 (talk) 12:30, 29 March 2008 (UTC)

In general no, but the drought in Australia, which could have been global warming related, nearly lead to blackouts becuase of lack of water to hydro-electric plants [2] -- Q Chris (talk) 13:11, 29 March 2008 (UTC)
Indirectly, I suppose you could say that global warming leads to more use of air conditioning leads to higher electricity usage leads to more risk of brown- or blackouts. (Contrariwise, of course, more electrical usage for air conditioning leads to more global warming...) —Steve Summit (talk) 13:43, 29 March 2008 (UTC)
Hi. I just thought of something, could the 2003 European heat wave somehow been related to the 2003 Italy blackout, even if indirectly? Thanks. ~AH1(TCU) 13:56, 29 March 2008 (UTC)


The electric company here in our city has announced a citywide blackout and giving "global warming" as a reason. —Preceding unsigned comment added by 119.93.229.75 (talk) 14:35, 29 March 2008 (UTC)

Wild guess - is this perhaps something to do with Earth Hour ? Although I thought that was supposed to be a voluntary initiative, so I don't see why a power company would announce a blackout. Anyway, there is a list of participating cities in our Earth Hour article. Gandalf61 (talk) 15:01, 29 March 2008 (UTC)

[edit] Rules for making Baryons

I'm trying to understand what are the rules for making baryons. I know baryons are made from 3 quarks (screw pentaquarks for now), any quarks. Since there are 6 different quarks, then we have 6^3 combinations of 3 quarks. However, from the Δ+ and the proton, each with quark composition u/u/d, it looks like the spin orientation has to be taken into account. Since each quark can be in +1/2 or -1/2 spin state, then we have 12 different quarks/quarkstates possible for each of the three quarks, which gives us 12^3 different combinations of three quarks. If we remove the degeneracies (such as ssd (3/2),sds(3/2),dss(3/2)), then we have 364 (12+11+10...+11+10+9...+10+9+8+...3+2+1+2+1+1) distinct combination of quarks/quarkstates.

Now I'm not sure of this, but I think that it is the modulus of the spin that is important, so particles with spin -3/2 and -1/2 really are the same than the particles with spin 3/2 and spin 1/2. Removing these degeneracies leaves us with half the particles, and thus we have 182 distinct baryons that can be made from three quarks.

Also, there seems to be some states that are forbidden - the Δ++ cannot be in spin 1/2 configuration, and there are some duplicate combinations &Lamba;0 is uds (1/2) and so is Σ0. Headbomb (talk) 16:18, 29 March 2008 (UTC)

The top quark does not form baryons, according to our article, because its lifetime is too short. Apart from that, I think any combination of three quarks gives a baryon (and the corresponding three anti-quarks gives the baryon's anti-particle). If the three quarks all have the same flavour then their spins must align (because of the symmetry of the state) and you get a spin 3/2 baryon. If the quarks do not all have the same flavour then their spins may align to give a spin 3/2 baryon, or their spins may not align, which gives a spin 1/2 baryon. Quarks can also exist in excited states within a baryon - so the spin 1/2 Σ0 is an excited state of the Λ0. See list of baryons and particle zoo. Gandalf61 (talk) 13:12, 30 March 2008 (UTC)

[edit] Top Ten Chemicals Produced

I need to find the top ten chemicals produced in any given year from 1973 to the present. I have done some online searches but have found very little data. Please help.Jdbauman283 (talk) 19:06, 29 March 2008 (UTC)

Do you mean chemicals deliberately produced by humans on the earth in a manufacturing chimcal industry process? (ass opposed to naturally produced, in space, a waste product, or grown or quarried). Graeme Bartlett (talk) 22:21, 29 March 2008 (UTC)
Obviously they meant man-made. Is that obvious? that's what I'm answering anyway - see below
Sulphuric acid is always a big one. Also see Chemical industry . " Polymers and plastics, especially polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, polystyrene and polycarbonate comprise about 80% of the industry’s output worldwide."
Also ammonia, fertilzers.
plus liquid nitrogen/oxygen
Here's a very out of date list http://pubs.acs.org/hotartcl/cenear/960624/prod.html 87.102.16.238 (talk) 11:14, 30 March 2008 (UTC)
I recall from the sulfuric acid article once, that sulfuric acid was actually the number one highest purposefully produced industrial chemical in terms of mass. Mac Davis (talk) 17:52, 30 March 2008 (UTC)

[edit] Do residential security lights reduce burglary?

In the Earth Night thread above I saw this comment: sounds like a field day for burglars, if residential security lights are turned off. And wondered whether such lights actually deter burglary. My understanding was that it is usually easier to see a person in the dark outside without lights than it is to see a person lurking behind a bright light. In other words, a smart burglar would use security lights to advantage. Am I misinformed? Pfly (talk) 19:12, 29 March 2008 (UTC)

I'd suspect you're mis-reasoning. If it is non-lighted at night it can be hard to see anything, something we forget in our current constantly-lit existence. Yes, standing behind a bright light can make it hard to be seen, but that requires 1. being able to get "behind" the light in the first place, and 2. knowing exactly whom you are hiding "behind" the light from (hence the quotation marks around "behind"—to someone on the other side of you, you're in front of the light!). I don't honestly see how even a smart burglar, much less the normal variety (which any public defender can tell you are not usually the best and the brightest), would use basic security lights to their advantage in a practical way. In any case, it's also a psychological case: someone under spotlights is probably more likely to feel like they are being seen, or at least could be seen, that someone without them, regardless of whether anyone is looking at them or whether they might also be able to be seen at night. --Captain Ref Desk (talk) 19:56, 29 March 2008 (UTC)
According to the article on light pollution, the International Dark-Sky Association (which is honestly a biased source) says that there's apparently no current scientific research supporting (or opposing) the idea that lighting increases security. And there's plenty of anecdotal evidence out there. I personally think most people overdo it. (The light pollution haze from the city actually does a better, more uniform job lighting my place than having proper security lights would). -- Consumed Crustacean (talk) 22:06, 29 March 2008 (UTC)
Hi. Security lights are so annoying because their glare prevents good observation of the night sky. Besides with all these street lights around it would already be bright enough. A good security system shoul only activate when the burgler is detected trying to enter the house and not up all night (most burgleries happen during the day). Thanks. ~AH1(TCU) 23:50, 29 March 2008 (UTC)

Ah ha, I believe I did hear this idea from someone from the International Dark-Sky Association on the radio. Biased, of course. And certainly it is easy to think up examples (and places) that are obviously one way or the other. I can imagine it would be difficult to do a good scientific study of the matter. Then again, I know certain towns and suburban areas have had "dark sky" programs for years. I'd think there would be studies of those kind of places and crime rates over time. Not that it would show causality, and would be limited to the kind of neighborhoods that would actually implement such programs. Still, I wonder.. Pfly (talk) 01:28, 30 March 2008 (UTC)

When Los Angeles had a big earthquake about a decade or two ago, the power went out and the milky way was visible. People rushed outside during the earthquake, and most have never seen the real milky way before. The reason? The Los Angeles city lights have been washing out the stars for all this time. In the past 50 years or so, stereotypes have developed about what the night sky really looks like, because most urbanites have never seen the real night sky. So, a lot of people called to ask the observatory if a sudden brightening of the milky way had caused the earthquake. The observatory workers tried to explain that this is how the night sky is supposed to look. The L.A. residents didn't believe them. Pfft. ~AH1(TCU) 21:12, 30 March 2008 (UTC)

[edit] efficiency question .

what portion of energy is wasted as a result of friction of an automobile ? how efficient will maglev train be compare to conventional vehicle ? —Preceding unsigned comment added by Shamiul (talk • contribs) 20:37, 29 March 2008 (UTC)

Pretty much all of the inefficiency in an electric car is a result of some type of friction. There is friction in the engine and transmission, rolling friction in the wheels, air resistance is a type of friction, and brakes use friction. If all friction could be eliminated, say by traveling in a vacuum, using regenerative braking, etc., then the only energy used would be in raising the elevation of the car, providing heat and A/C, running the lights, and maybe the radio. Internal combustion engines also suffer major inefficiencies due to incomplete combustion and heat bled off to the environment from the radiator. Electric cars also suffer inefficiency due to battery leakage. StuRat (talk) 21:42, 29 March 2008 (UTC)
Have you seen our engine article?. And does this answer your question? 81.93.102.185 (talk) 21:50, 29 March 2008 (UTC)

[edit] What do you see?

Do the eyes of all mammals see the same spectrum of what we call "visible light"? Seems like they do.. any particular reason? Seems like a predator who developed eyes that could react to infrared radiation would quickly dominate their environment. :D\=< (talk) 20:38, 29 March 2008 (UTC)

A very similar question was asked last December and got a lot of responses. (Just putting that out there, not trying to discourage more answers, thoughts.) --Captain Ref Desk (talk) 21:10, 29 March 2008 (UTC)
See our article on the eye and retina. It has to do with the physiology of the cells in the latter. rods and cones. Wisdom89 (T / C) 21:55, 29 March 2008 (UTC)
Let me quote Richard Dawkins in the ancestor's tale page 147. "All eyes on our planet are set up in such a way as to exploit the wavelengths of electromagnetic radiation in which our local star shines ... For an eye that has commited itself to biochemical techniques suitable for this loosely bounded range of wavelengths, the laws of physics impose sharper bounds to the portion of the electro-magnetic spectrum that can be seen using those techniques. No animal can see far into the infrared. Those that come closest are pit vipers, who have pits in the head which, while in no sense focusing a proper image with infrared rays, allow these snakes to achieve some directional sensitivity to the heat generated by their prey. And no animal can see far into the ultraviolet although some, bees for instance, can see a bit further than we can. But, on the other hand, bees can't see our red: for them it is infrared. All animals agree that 'light' is a narrow band of electormagnetic wavelengths lying somewhere between ultraviolet at the short end and infrared at the long end. Bees, people and snakes differ only slightly in where they draw the lines at each end of 'light'" emphasis and typos added by me. -- 71.91.127.85 (talk) 19:21, 30 March 2008 (UTC)
I assume its because water is only transparent within a narrow range of frequencies.Em3ryguy (talk) 21:13, 30 March 2008 (UTC)