Wikipedia:Reference desk/Archives/Science/2010 May 7

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May 7

humanure

i knew a guy in the usa who got committed for 5 days because he practiced humanure. there was nothing wrong with him and he was eventually released. a) how can they do that and b) can he sue them and under what grounds? —Preceding unsigned comment added by Tom12350 (talk • contribs) 02:19, 7 May 2010 (UTC)

That's odd...how'd anyone know? DRosenbach ^{(Talk | Contribs)} 02:31, 7 May 2010 (UTC)

A) There may be some local laws to keep people from using human excrement as compost. Composting toilets may not be allowed where he lives due to the availability of citywide sewage systems or laws which require septic systems. Dismas|^(talk) 02:40, 7 May 2010 (UTC)

i think it was legal since he lived in the country side but thats irrelevant. if it was illegal they should have arrested him no t committed him. clearly they had no cause or legal right to commit him. —Preceding unsigned comment added by Tom12350 (talk • contribs) 03:09, 7 May 2010 (UTC)

Sounds like we aren't getting all the facts here. Also be aware that there is a difference in Humanure and Night soil. Beach drifter (talk) 03:13, 7 May 2010 (UTC)

what more facts do you need? —Preceding unsigned comment added by Tom12350 (talk • contribs) 16:27, 7 May 2010 (UTC)

If you are claiming that someone was involuntarily committed to a psychiatric facility because he was putting his excrement in a garden or yard, I do not believe you. You either do not know all the facts or are withholding or misrepresenting some of them. alteripse (talk) 16:44, 7 May 2010 (UTC)

that is really what happened. he also only bathed once a week, which they also held against him. thats all he did. they said it was "abnormal behavior" and claimed it was enough to commit him. he has the paperwork to prove it which he showed me. —Preceding unsigned comment added by Tom12350 (talk • contribs) 04:08, 8 May 2010 (UTC)

See involuntary commitment for a discussion of the rules on this in the US. Even for a brief commitment of 2 days, someone would have had to persuade the police and an admitting psychiatrist that he was a danger to himself or someone else. You dont have the whole story or you are not giving us the whole story. alteripse (talk) 04:28, 8 May 2010 (UTC)

they specifically said he was NOT a danger to himself or someone else. they claimed that because he was bathing once a week and storing urine and feces (for humanure) that he was "unable or unwilling to care for himself" despite showing the doctors he could they still kept him for 5 days. —Preceding unsigned comment added by Tom12350 (talk • contribs) 19:51, 8 May 2010 (UTC)

What did he grow with his humanure? If the answer is nothing then forget about a case. 71.100.0.29 (talk) 21:14, 8 May 2010 (UTC)

This is the sort of question that changes a LOT depending on the details. Does he live out in a farm and was using a modified outhouse to properly compost and sterelize human wastes? Or was he a city dweller keeping his crap in jars who ranted about saving the environment anytime someone questioned him about it? What you described could easily go either way.

They don't commit people "For" doing some particular thought crime, the person's mental state has to be evaluated. In that sense, it's not really about the humanure, they could commit him 'for' filling out a crossword puzzle if he was somehow doing it in a way that led people to think he was badly insane.APL (talk) 22:52, 8 May 2010 (UTC)

Good grief APL. You dont do the ref desk or the questioners any favor by giving answers about things you know nothing about. Didnt you even read the involuntary commitment article referenced above? "Insane" is neither a legal nor a medical terms and certainly not a criterion for commitment. American cities are full of people who are not just diagnosable with a serious mental illness but cannot take care of themselves, yet our laws forbid involuntary commitment unless they seem to be posing an imminent threat to themselves or others. They are called "homeless". alteripse (talk) 13:18, 9 May 2010 (UTC)

Having read the article I stand by my basic point that the question as-asked, is unanswerable because people are not committed for doing specific "things" (Like composting human waste), but because someone believes they have a dangerous state of mind. That's what makes the whole process different than arresting people on criminal grounds where there really is a giant list of specific things you can't do. APL (talk) 18:24, 9 May 2010 (UTC)

so does this guy have a case to sue them or not? he was using the humanure in his garden. —Preceding unsigned comment added by Tom12350 (talk • contribs) 18:34, 9 May 2010 (UTC)

(1) Anyone can sue anyone for anything-- that is not the same as having a good case that a lawyer would take. (2)We cannot give legal advice here and IANAL. (3) Not even the best lawyer in the country would give you a yes or no answer to your question without wanting to ask your friend a whole lot of questions. (4) I think we have about exhausted this question. alteripse (talk) 23:46, 9 May 2010 (UTC)

Don't hold your breath

I was able to hold my breath with no distress to 1:45 and after beginning to increasingly suffer, I made it to 2 minutes before I had to exhale and then inhale. Is that normal for a 28 yo healthy white male? I was very surprised, assuming that humans couldn't hold their breath for that long. Granted it's not the 30 minutes-plus of a marine mammal, but is 2 minutes for a human while sitting quietly normal? DRosenbach ^{(Talk | Contribs)} 02:30, 7 May 2010 (UTC)

Normal? Maybe. With practice, a person can train themselves to hold their breath for longer and longer times. Have you been practicing? Dismas|^(talk) 02:44, 7 May 2010 (UTC)

PS I'm in my mid-30s and was just able to make it to 1:30 without too much strain. Dismas|^(talk) 02:50, 7 May 2010 (UTC)

2 minutes is not that big a deal especially if you hyperventilate first (2 or 3 deep breaths is enough, you don't have to get dizzy or anything like that). 69.228.170.24 (talk) 02:56, 7 May 2010 (UTC)

That's exactly what I did before my attempt. I think I could go longer if I was laying down and not having to support my torso as I'm doing now sitting upright on my couch. Dismas|^(talk) 03:03, 7 May 2010 (UTC)

According to Static Apnea, the world record for breath-holding is eleven and a half minutes [1]. I had thought that it was around six! Man, sometimes I have a hard time going eleven and a half minutes between ginger snaps. (Note that the record was just eight minutes a decade ago, which suggests that being able to get anywhere close to that is highly unusual.) Paul (Stansifer) 03:23, 7 May 2010 (UTC)

It depends on if the breath hold is under water or not. Due to the mammalian diving reflex humans can hold their breath much longer if their face is in cold water. Ariel. (talk) 05:11, 7 May 2010 (UTC)

Not a scientific response, but personal experience: I sometimes find it easier if I slowly exhale as I reach the point where it starts to burn. Riffraffselbow (talk) 06:52, 7 May 2010 (UTC)

I know that with practice humans can hold their breath for several minutes, but I am very surprised by the above comments. If I'm anything like Mr. Average I struggle to hold my breath for longer than one minute, unless I practice ... a lot. Astronaut (talk) 13:06, 7 May 2010 (UTC)

With hyperventilation I can hold it for 1 1/2 minutes. I am 15. --Chemicalinterest (talk) 13:26, 7 May 2010 (UTC)

The weird thing I find is that I can't hold my breath for even a minute just sitting down doing it (I'm 54 years old - so I don't last as you young-un's) - but I can easily swim between two and three lengths of my back-yard pool underwater - and hold my breath for well over a minute to a minute and a half, despite the obvious extra exertion due to the swimming burning up oxygen faster. I don't understand that. But I suspect it's because the "rules of the game" are a bit different. When I sit here holding my breath, it somehow seems to be cheating to release air from my lungs while I'm "holding" by breath - resulting in an explosive exhalation when I finally have to give up. When swimming underwater, it seems OK to gradually release air as I swim - so long as I don't surface and take another breath. Does this somehow explain the difference in my times? I think so...but I don't understand why. When I release air underwater, it's not like I'm breathing out just the CO2 that I don't want and keeping the left-over oxygen in my lungs! What I'm breathing out has the same percentage of oxygen as what's left behind. So are you folks who can manage an impressive 2 minutes allowing yourself to exhale while doing it? SteveBaker (talk) 14:06, 7 May 2010 (UTC)

Steve, I posted about this a little higher up, the reason is the mammalian diving reflex. Even though you are exerting your mussels, they are probably working non-aerobically, at least at first, and the reflex prevents them from using up your oxygen. Ariel. (talk) 21:07, 7 May 2010 (UTC)

In my youth I once held it for over 3.5 minutes, hyperventilating first. Claims of 11.5 minutes just do not seem plausible. Most people seem to give up at the point where a "burn" or oxygen need is first sensed, which seems like a pretty healthy response in general, but if you were under water it would not end well. Edison (talk) 15:47, 7 May 2010 (UTC)

Hyperventilating before swimming under water is dangerous, because the most important stimulus for breathing is the CO₂ content of the blood, and not hypoxia. By hyperventilating, you artificially lower the CO₂ content of the blood, thereby suppressing the urge to breath, making it possible to stay under water until you pass out because of hypoxia. See shallow water blackout. --NorwegianBlue ^talk 16:59, 7 May 2010 (UTC)

What's a tumor like?

I've heard about tumors that are "inoperable" because they're wrapped around organs or whatever. So what is a tumor like? From the way that people talk about them, I guess they aren't some semi-solid mass that you can just cut bits off until you get something that is small enough to just pull out. So what are they like? Dismas|^(talk) 03:02, 7 May 2010 (UTC)

Well Tumor has the basics, as well as links to what you probably want, like Cancer. Calling a tumor inoperable usually means that it's not safe to remove the cancerous growths. Often this occurs because the cancer was detected late in the game, and has already metastasized to other parts of the body (thus making it very hard to remove). Also, cancerous tumors don't have to be wrapped around something, it can be withing something. A relative of mine, for example, currently has a tumor growing inside a kidney. Tumors inside vital organs, such as the liver or spleen, can be very tricky to remove properly. ~ Amory (u • t • c) 03:21, 7 May 2010 (UTC)

Tumors generally originate in an organ, and often invade other nearby structures. There isn't always a clear dividing line, since it infiltrates into surrounding tissue. And if vital structures are involved, it may not be possible to remove it, as Amorymeltzer points out. And yes, if a cancer has metastasized (spread), there may be no benefit to removing the primary tumor (and surgeries always carry risk). Does that help?

I would have to respectfully disagree, Amory, regarding your specific examples of inoperable tumors. In the cases you presented, the surgeons would remove the entire spleen. Inoperable tumors exist in or around crucial organs, such as the brain, in which case an operation to remove the tumor may necessarily lead to immediate loss of life/function while allowing the tumor to remain would likely lead to loss of life/function later down the line. The parotid gland, for example, exists with the facial nerve running and branching within it -- so it's a difficult task to remove the parotid because removing it en masse' would leave the patient with a unilateral facial muscle paralysis. But there are ways around this problem, such as testing each and every bit of tissue for conduction ability prior to resection. The point is that each case is different and a particular benefit/cost analysis of each and every case would need to be carried out. DRosenbach ^{(Talk | Contribs)} 13:06, 7 May 2010 (UTC)

Tumors are the result of uncontrolled cell division. As such, tumors are relatively similar in physiology to normal cells with a few exceptions. They usually have poor blood supply, and they don't differentiate to perform special functions like their normal counterparts. Instead they just grow, and grow, and grow. Some invade surrounding tissues very easily, others do not. Some metastasize (when a few cells break off and travel through the blood or lymph system) and form new tumors in other locations; again, others don't. There are no hard and fast descriptions of a tumor, but instead several different descriptions depending upon the type. Regards, --—Cyclonenim | Chat  14:25, 7 May 2010 (UTC)

Reverse dial gauge/indicator alignment

How to carry out shaft alignment using reverse dial gauge/indicator alignment method? —Preceding unsigned comment added by 202.79.203.51 (talk) 03:31, 7 May 2010 (UTC)

Please rephrase your question. I don't think anyone understood it. Ariel. (talk) 22:00, 7 May 2010 (UTC)

Does this help at all? Reverse Dial Alignment--Aspro (talk) 16:01, 8 May 2010 (UTC)

archae biotech

Biotechnologically, what are the manipulations made to some archae present deep inside the earth? —Preceding unsigned comment added by 125.21.50.214 (talk) 03:43, 7 May 2010 (UTC)

1. genome sequencing. Graeme Bartlett (talk) 12:34, 7 May 2010 (UTC)

How many slots on GEO are available for communication satellites?

Obviously a limited number, but how big is it? See also orbit allocation. 70.48.64.135 (talk) 05:09, 7 May 2010 (UTC)

The problem is not room for the satellites - there's tons of room. The problem is all the satellites use more or less the same radio frequency, and if they are too close together you will pick up signals from more than one at a time. So there is no real way to answer you question - if you stagger the frequencies you can fit more in. But maybe you need a specific frequency in a specific spot and you can't. Also, some places are better than others, for example over the ocean is not a desirable spot. Ariel. (talk) 06:25, 7 May 2010 (UTC)

It is obvious that the physical space for satellite not a problem (how could it even be? Have you have slightest idea of how big GEO?). It is also absolutely obvious that the problem restricting number of COMSATs on GEO is RFI. If you know nothing about subject, please refrain from answering the question. Reading link I provided above might also help. PS. I'm almost speechless about your remark about "spot over the ocean". Yes, while it is true that for the spot over the ocean, signal must travel longer distance, the relative overhead would be minimal, if worth of mentioning. For a country over equator signal from satellite flying directly above the country must travel ~36 000km, while from satellite that 10 000 km from the first one and "over the ocean" signal traveling distance would be 37 400km. Please also read geostationary orbit article. 70.48.64.135 (talk) 08:12, 7 May 2010 (UTC)

QUOTE from the link I provided above, before you start talking ignorant nonsense about "no real way to answer you question": The requirement to space these satellites apart to avoid harmful radio-frequency interference during operations means that there are a limited number of orbital "slots" available, thus only a limited number of satellites can be operated in geostationary orbit. This has led to conflict between different countries wishing access to the same orbital slots (countries at the same longitude but differing latitudes) and radio frequencies. These disputes are addressed through the International Telecommunication Union's allocation mechanism. 70.48.64.135 (talk) 08:24, 7 May 2010 (UTC)

Unless you know which frequencies are desired, and how many satellites overlap in a given area+frequency how are you supposed to know how many can fit? It all depends on what they want to do with them. And some satellites have more narrow broadcasting (spot beam), and others are wider. You could fit tons of spot beams, and just a few wide ones, there is no single number for how many will fit. The problem with the ocean is that it's over the horizon for your customers unless they have tall masts (and satellite communication is line of sight), it's not the distance to the satellite. Ariel. (talk) 09:07, 7 May 2010 (UTC)

To help you understand, the radio waves from the satellite dish spread out and cover a particular angle, called the main lobe. For a small satellite TV dish this could be 3 degrees. So you cannot have two satellites sending to the same area closer than 3 degrees. If you have a bigger dish, such as might see for C band satellite TV, the beam will be around 1 degree, and those satellites sending to large dishes could be closer together. There could be sidelobes as well that pickup interference, so the response from the antenna to a neighbouring satellite should be very small. However most of the money will be from pay TV on Ku band, so that will determine the economic distance. Over the mid Pacific Ocean there are very few satellites, so there are plenty of free slots, but few users. Graeme Bartlett (talk) 12:33, 7 May 2010 (UTC)

Stars

Sorry for being dumb! Why are stars born and dead without living? If they live, what life do they lead? - anandh, chennai —Preceding unsigned comment added by 125.21.50.214 (talk) 05:57, 7 May 2010 (UTC)

There are many types of stars, and they lead very different lives. Light stars would take billions or even trillions of years to run out of fuel, then slowly burn out into a cinder. Intermediate stars like the sun would take several million years to use up their fuel, and heavy stars burn out quickly then erupt in a supernova. See the article on Stellar evolution for more information. --The High Fin Sperm Whale 06:04, 7 May 2010 (UTC)

Stars like the Sun last for billions of years, not just millions. StuRat (talk) 19:49, 7 May 2010 (UTC)

Sperm Whale: his question was more etymological than scientific; In short, stars are born and die because humans, or at least western culture, think of stars as quasi-living beings. It's anthropomorphism, akin to Mother Nature or the concept of a living sea. Riffraffselbow (talk) 06:50, 7 May 2010 (UTC)

In other words, they aren't alive, they aren't born, they don't die, and they don't "live different lives" as Whale said -- we just talk about them as if they do. It's a metaphor. People also speak of places and companies and lots of other non-living things as being born and dying, when we mean they start existing and stop existing. --Anonymous, 06:55 UTC, May 7, 2010.

Yes, but... Define "life". Stars "metabolise" hydrogen into helium. They certainly react to some stimuli, and when they die, they seed the interstellar medium in a way that influences the next generation of stars. Are viruses alive? ;-) --Stephan Schulz (talk) 07:22, 7 May 2010 (UTC)

You're asking a philosophy question on the science refdesk. Scientists hate philosophy, it makes them grumpy. Riffraffselbow (talk) 07:43, 7 May 2010 (UTC)

well, thanks for making me a philosopher. All i need to know is about the duty of stars during their life time. —Preceding unsigned comment added by 125.21.50.214 (talk) 10:51, 7 May 2010 (UTC)

It's not philosophy - it's linguistics. Wiktionary has half a dozen meanings for words like "born", "life", "live", and "die" - just pick the appropriate ones and not the inappropriate ones and the problem disappears.

Anyway, the definition of "life" is fuzzy. It is increasingly clear that there is no hard boundary between things that are clearly alive (Zebras) and things that clearly aren't (Rocks) with things like Viruses being on the borderline. I think most people would put stars rather closer to the "Rock" end of the scale than the "Zebra" end - and probably somewhere lower down the scale than Viruses. However, there are some attributes of stars (like that they do, somewhat, in a sense, 'reproduce') that puts them above rocks on that scale. But you can't ask science to answer a question that only relates to the arbitary use of a fuzzy word. Stars are whatever stars are - no matter whether we call them "alive" or "inanimate".

SteveBaker (talk) 15:05, 7 May 2010 (UTC)

I echo The High Fin Sperm Whale in saying the stellar evolution article is probably what you are looking for. Comet Tuttle (talk) 19:37, 7 May 2010 (UTC)

Nitrogen in tyres

I've read a couple of things on filling tyres with nitrogen, which basically boil down to: it leaks less than air, it corrodes wheel and tyre less than air, it expands/contracts less with temperature than air. And almost all of that is due to the fact that the nitrogen sold to you is dry, whereas the air from the local service station has water vapour in it, and water vapour expands and contracts strongly with temperature change and with the help of the oxygen causes the corrosion. So filling tyres with dry air gives you all of the benefits of using nitrogen, except for the leaking thing.

So, a few questions: 1. If I fill my tyres on a cold (5°C) low humidity day do I get the same benefits? 2. Presuming I fill on such a dry day, and always top up in similar conditions, will my tyres become ever closer to being filled with pure nitrogen as oxygen leaks more quickly than nitrogen? 3. I'm a brewer, I have bottled CO₂, how does CO₂ compare? Should I use that instead to fill my tyres? 4. Should I use this as an excuse to buy a bottle of nitrogen which will also contribute to better stouts and other British beers?

I also note that the companies selling nitrogen tell you that you must never top up your tyres with air if you're using nitrogen as it will ruin any benefit - (5) does this ruin my plan, with the tiny amount of water included in low humidity air? (6) Does this ruin the tyre companies' plans if the tyre has a reasonable amount of air in it (from being installed onto the wheel in a normal air atmosphere).

Wow, a lot more questions than I had when I started thinking about and typing this question. So, one more for luck (7) If I'm stating with a tyre full of normal, wet, air, and I wanted to refill it with dry air or whatever gas, how many times would I have to deflate it to near zero net pressure and inflate it to 200kPa before I could be reasonably assured that there were no more than trace amounts of what was in the tyre before? --Psud (talk) 07:48, 7 May 2010 (UTC)

Remember, they want to sell you something. How often have you seen a tire "corroded" (from the inside) before its tread has worn down? So go by point 3 and leave your car alone ;-). --Stephan Schulz (talk) 08:21, 7 May 2010 (UTC)

Four links for you: [2] [3] [4] [5] Ariel. (talk) 10:46, 7 May 2010 (UTC)

Using carbon dioxide will cause the tyres to get hotter. This gas is has a higher molecular mass, so the work done on it by the flexing tyre will heat it more than pure nitrogen and more the normal air. You did not say what type of vehicle you were considering this for. If you are a microbrewery, then it is not worth it, but if you have a fleet of commercial lorries, then you could save because you could have the same old tyres remoulded time, after time, after time. [6] As for nitrogenated beer -sacrilege! --Aspro (talk) 11:40, 7 May 2010 (UTC)

That doesn't make sense. Higher heat capacity ==> temperature rises less quickly. John Riemann Soong (talk) 19:40, 7 May 2010 (UTC)

Uhmm. Maybe then, you are thinking still in terms of the classical experiments, with those same values that were fixed (by the design) and those values that were the variables (which aided the formulation of the laws).--Aspro (talk) 21:12, 7 May 2010 (UTC)

We discussed this issue in 2007, and brought it up peripherally in a 2009 discussion about nitrogen. Nimur (talk) 06:16, 8 May 2010 (UTC)

space objects on earth

What prevents the space objects (moving randomly) from hitting the earth? Rarely does that happen. - anandh, chennai. —Preceding unsigned comment added by 125.21.50.214 (talk) 09:51, 7 May 2010 (UTC)

Well, they're spread pretty thinly, and small objects burn up in the atmosphere before they hit the surface. Most things in the solar system are pretty comfortable in their orbit around the Sun, too. 212.219.39.146 (talk) 10:20, 7 May 2010 (UTC)

I think we have impact craters on the surface of the earth. 125.21.50.214 (talk) 10:48, 7 May 2010 (UTC)

See meteorite. The friction of the atmosphere gases vaporizes the rocks. --Chemicalinterest (talk) 11:56, 7 May 2010 (UTC)

Nothing stops space objects from hitting the Earth and many thousands of objects hit the Earth every day. The vast majority of these objects are moving very fast and are very small such that they quickly burn up in the Earth's atmosphere as meteors. On rare occasions an object might be large enough to survive its trip through the atmosphere and fall to Earth as a meteorite. On even rarer occasions the object is so large that it hits the Earth's surface with enough force to leave a crater, sometimes with devestating effects. Astronaut (talk) 12:48, 7 May 2010 (UTC)

One thing that helps us here is that most of the big things that were in orbits that would bring them close enough to the earth to impact it have already done so - hence the early history of the planet (before life formed here) was exceedingly violent with large chunks of rock and ice pummeling the planet all the time. In fact, it is generally agreed that our moon was formed from debris that resulted when another entire planet (the size of Mars!) hit the earth very early on in it's history. Fortunately, that super-violent era is over now - and even though (as User:Astronaut says) we're hit by a lot of stuff, most of it is small and the odds of a big rock hitting something important is rather small. You can see this happening at particular times of year during meteor showers. Every year, if you go out late at night (midnight until maybe 2am is good) between August 9th and 14th - in an area far from city lights and other 'light pollution' you'll be treated to a most amazing light show from the Perseids - which are bits of an old broken-up comet that cross the earth's orbit on the exact same few days every year, peppering our planet with teeny-tiny rocks and other debris. Most of those burn up in the air - making for a spectacular show of "shooting stars". There is only one recorded instance of a person being hit by a falling piece of space debris - and a mere handful of cases of buildings and cars getting hit. However, there are still gigantic rocks out there and there is always a chance of one of them hitting us and wiping out an entire city - or perhaps killing all life on earth! SteveBaker (talk) 13:52, 7 May 2010 (UTC)

Space materials-luminosity

Might be basic. What is responsible for the luminous efficacy/luminosity of sun, star and other space objects that 'glow'? Are there any reactions behind hydrogen and helium, eventually resulting in the luminosity of certain space objects? - anandh, chennai —Preceding unsigned comment added by 125.21.50.214 (talk) 11:18, 7 May 2010 (UTC)

Most people think it is nuclear fusion. See Sun and nuclear fusion. --Chemicalinterest (talk) 11:54, 7 May 2010 (UTC)

And it is very hot! Graeme Bartlett (talk) 12:23, 7 May 2010 (UTC)

It is indeed nuclear fusion. The sun's gravity is so strong that it crushes the hydrogen atoms together and turns them into helium. In the process of doing that, a tiny fraction of the mass of the hydrogen gets converted into energy - and because E=m.c², that's an enormous amount of energy! That's why the sun can burn for billions of years without running out of fuel. However, the sun has already burned through about half of it's hydrogen - and in another billion or so years, it'll have to start converting the helium that it's made...and that will result in the destruction of the earth and everything that lives on it! SteveBaker (talk) 13:40, 7 May 2010 (UTC)

That's a bit oversimplified. Stars of the size of the sun are fairly stratified, with helium "ash" accumulating in the center. When it goes red giant, a significant amount of hydrogen will still be left. The sun has gone through about half of its main sequence life, but not through half of its hydrogen. And if the Earth will be destroyed is somewhat uncertain - every few months a new study comes out claiming the opposite of the preceding one. But it will certainly become rather warm... --Stephan Schulz (talk) 14:00, 7 May 2010 (UTC)

The fusion provides the heat. Stars then glow because of Thermal radiation. It's essentially the same reason why hot iron glows red. Everything with a temperature above absolute zero will glow in this sense, but for most temperatures that we're used to, they primarily glow predominately at wavelengths longer than what we can see. Humans, for example, glow predominately in the infrared range. When you heat something up, it will emit more light of shorter wavelengths. That's why iron that's somewhat hot will emit a dull red light (the longest wavelength we can see), while it will emit orange, then yellow light when heated further. When you heat something even more (like a light bulb filament), it will emit light at all visible wavelengths, giving white light. The sun is very hot, so not only does it emit "white light" by emitting light at nearly all wavelengths in the visible range, it also emits a more generalized "white light" by emitting across nearly the entire electromagnetic spectrum, from short wavelength gamma rays to long wavelength radio waves. Buddy431 (talk) 14:34, 7 May 2010 (UTC)

Light & escape velocity

Why is light (irradiated from the surface of the earth) still on earth when it has more speed than the escape velocity of earth? If it escapes, can that be seen from/in the space? - anandh, chennai —Preceding unsigned comment added by 125.21.50.214 (talk) 11:24, 7 May 2010 (UTC)

Yes, light can escape the earth and be seen from space. -- Coneslayer (talk) 11:32, 7 May 2010 (UTC)

The Earth reflects light that is emitted from the Sun. About 30% of the light eneregy that the Earth receives from the Sun is reflected back into space - another way of expressing this is to say that the Earth has an albedo of about 0.3. This reflected light is how astronauts see the Earth (or, at least, its day side) from space stations in orbit or from the surface of the Moon. The other 70% of the light energy is absorbed by the oceans, atmosphere, soil, plants etc. (and some of it bounces off objects and is then absorbed by your eyes, which is how you see stuff). The overall effect of this absorbed energy is to keep the Earth warm - if the Earth had a higher albedo, its average temperature would be colder. Gandalf61 (talk) 11:45, 7 May 2010 (UTC)

Atmospheric diffraction and atmospheric refraction ensures that a lot of light gets bounced around before it escapes or gets absorbed.--Aspro (talk) 11:53, 7 May 2010 (UTC)

Furthermore, and more importantly, light is just another form of energy. Plenty of it does escape. What you see when you, say, turn on a lightbulb, is the conversion of electrical energy into light energy and heat energy. Riffraffselbow (talk) 12:06, 7 May 2010 (UTC)

Note that even the the classic "daytime" views of the earth (Blue Marble) are keen evidence that light escapes. Everything you can see is light that is reflecting off of Earth from the Sun. If light could not escape Earth, it would look like a Black hole. --Mr.98 (talk) 13:14, 7 May 2010 (UTC)

Light has both speed and direction. The light that bounces off of something in just the right direction and hits your eyes before it can escape the planet is what you "see" - most of the other light hits some other thing (the ground, your head, an oxygen molecule in the air) and either gets absorbed and turned into heat or maybe bounces off again. The remainder is the light that "gets away", that you don't see - and which (as you say) has enough speed to escape the earth's puny gravity and head off into space. The average "albedo" of the earth is about 0.37, which means that (very roughly) 37% of the light that comes from the sun and the stars is reflected off into space - and the remaining 63% bounces around until it's absorbed by something and turns into heat. Someone (or something) that's out there in space looking at the earth is only able to see our planet at all because of that 37% of reflected sunlight.

(I said it was "very roughly" 37% because there is a lot of complication about light that is outside of our visual range (infrared and ultraviolet) and electromagnetic radiation in general, and whether we're talking about 37% of the energy or 37% of the photons...that complicates the explanation about what "albedo" means). SteveBaker (talk) 13:34, 7 May 2010 (UTC)

In terms of energy, earth emits 100% as much light as it receives. The other 6x% is blackbody radiation in the infrared, which is invisible to our eyes but not to telescopes. In terms of particle count, earth emits far more photons than it receives. I'm thinking the ratio is about 20 (= 6000 K / 300 K), but don't quote me on that. -- BenRG (talk) 19:12, 7 May 2010 (UTC)

Surely it emits more than it receives, due to radioactive decay, as well as a general cooling of the interior? Buddy431 (talk) 19:23, 7 May 2010 (UTC)

You're right, but I think it's a small correction. Geothermal gradient says "total heat loss from the earth is [...] about 1/10,000 of solar irradiation". -- BenRG (talk) 20:33, 7 May 2010 (UTC)

Hmm... I'm surprised it's that small, but I guess it makes sense when I think about it, considering how much energy the sun dumps on us. Buddy431 (talk) 21:34, 7 May 2010 (UTC)

Light does continuously leave Earth, but more is continuously supplied by the Sun, Moon (reflected from the Sun), and stars. If they all went dark, then the Earth would, too (except for Las Vegas, of course :-) ). StuRat (talk) 20:58, 7 May 2010 (UTC)

minimum oxygen requirements and carbon dioxide toxicity

Is there a list of the minimum amount of oxygen required to sustain life for different species and the maximum amount of carbon dioxide that would not be toxic including "guesstimate" for extinct species like dinosaurs? 71.100.0.29 (talk) 17:40, 7 May 2010 (UTC)

By "amount", do you mean percentage of oxygen in the air ? The larger dinosaurs may have needed the higher oxygen levels in the air at the time, so presumably their oxygen requirements were higher than ours. StuRat (talk) 20:48, 7 May 2010 (UTC)

I recall that reptiles react to insufficient o2 while humans react to too much co2 or vice versa but yes by amount i mean percent o2 and percent co2 in the "air." Too little o2 or too much co2 will kill you and I'm looking for a list that shows what range various species can tolerate of each. Ther must be such a list somewhere. 71.100.0.29 (talk) 00:42, 8 May 2010 (UTC)

I don't understand your first sentence. Insuffient oxygen and excessive carbon dioxide are big problems for any multicellular creature. If you are looking for specifics values of how much oxygen dinosaurs needed, or how much CO₂ would be too much for a dinosaur, I think you're going to be pressed to find an accurate answer since they are, as you said, extinct. For humans, hypercapnia is defined as 45 mmHg or above CO₂ in the blood. Hypoxia is any stage down to 40 mmHg of oxygen, at which point it, roughly speaking, becomes lethal. Obviously these aren't exact values for every human, just rough averages. Regards, --—Cyclonenim | Chat  00:30, 9 May 2010 (UTC)

wear earplugs 24 hours?

do army wear earplugs 24 hours or shoot without them in war? —Preceding unsigned comment added by Tom12350 (talk • contribs) 17:46, 7 May 2010 (UTC)

This article from Army Times says that earplugs have been standard issue for the US Army since 2002, but a challenge has been getting soldiers to use them. Comet Tuttle (talk) 19:35, 7 May 2010 (UTC)

There are times when there is a much higher probability of gunshots than others. For example, someone in the "Green Zone" in Iraq is obviously safer (although not entirely safe) than someone on patrol. So, I suspect they avoid wearing them when in safer areas.

Then there's the issue of whether decreased hearing ability while the earphones are in place makes soldiers wearing them more susceptible to ambush. Perhaps a more sophisticated option is needed, like noise canceling earphones with a pickup on the gun to only counter noises it makes, not the noises the enemy makes. StuRat (talk) 20:45, 7 May 2010 (UTC)

Artillery gun crews of course wear better protection and more often than infantry. 75.41.110.200 (talk) 23:40, 10 May 2010 (UTC)

I don't know how anyone can complain about not being able to get them to wear ear protection. Hearing is an extremely important sense when you're in a warzone. Better sllightly damaged hearing than death (I bet most ipod users do more damage to their ears while listening to it on high volume than a soldier does when shooting). Besides an M16 rifle isn't very loud, the loudest weapon in a squad is likely the M249 light machine gun.--92.251.166.171 (talk) 18:23, 11 May 2010 (UTC)

Hurricane gustav

did hurricane Gustav damage Louisiana? —Preceding unsigned comment added by 169.244.148.235 (talk) 19:26, 7 May 2010 (UTC)

Yes; see our article Hurricane Gustav, which has an "Impact" section that has what you want. Comet Tuttle (talk) 19:32, 7 May 2010 (UTC)

Lung capacity vs. holding my breath

For most of my life I can hold my breath for longer than most people, but when I did what was AFAICR a lung capacity test in my doctor's office a few years ago, I did quite poorly and was recommended exercise, I think. Is holding breath a learned skill rather than a useful sign of health? Thanks. 67.243.7.245 (talk) 19:48, 7 May 2010 (UTC)

How long you can hold your breath is dependent on more than just lung capacity. Some other factors:

1) Your level of activity at the time. Obviously you need less oxygen while sitting quietly than while running a marathon.

2) Your basal metabolic rate also affects oxygen consumption.

3) Your tolerance for high carbon dioxide levels, as that's what triggers a new breath.

4) Your mass. More mass means more oxygen is needed. StuRat (talk) 20:38, 7 May 2010 (UTC)

We can't say anything about your breathing rate and the results of your lung capacity test or anything else about you. But I'd like to point out that even if holding your breath for extended periods can be learned, that doesn't mean that it's not also a useful sign of good health. For example Cardiorespiratory fitness says

"Exercise improves the respiratory system by increasing the amount of oxygen that is inhaled and distributed to body tissues"

and according to Physical exercise,

"Physical exercise is any bodily activity that enhances or maintains physical fitness and overall health".

Lung volumes says that athletes have larger volumes than non-athletes and Breathing says

"Medical respiratory data ... suggest that sick people breathe about 2-3 times more air at rest than the medical norm".

See this disclaimer. Zain Ebrahim (talk) 21:01, 7 May 2010 (UTC)

The episode of Bang Goes the Theory shown on 3 May in the UK had a segment at the start on practising breath-holding as preparation for free diving (Series 2, Episode 7 viewable online in the UK only i think). According to that "you can almost double your breath-holding ability just by practising regularly". Your body builds gets used to lower levels of oxygen and higher levels of carbon dioxide, and your brain gets better at overriding the signals to breathe without panicking. Qwfp (talk) 09:50, 8 May 2010 (UTC)

I want to destroy a culture...

Specifically, an active yogurt culture. Can they be killed off without ruining the yogurt ? Does anyone sell yogurt without "active cultures". I imagine they could be killed without affecting the product via irradiation, but I obviously can't do that at home. StuRat (talk) 20:32, 7 May 2010 (UTC)

Campden tablets (the brewer asking about nitrogen couold hav etold you this as well)--Aspro (talk) 21:15, 7 May 2010 (UTC)

So, you'd crush the tablets and stir them in ? Would it diffuse through the yogurt that way, or would it be too thick for that ? StuRat (talk) 21:56, 7 May 2010 (UTC)

Crush, stir in, then ten or twenty minutes later stir again. I think it was done because we would then add pulped raw fruit (which also so treated). During the post-war austerity period, few people had refrigeration and we did not want it to start a different type fermentation that may have given it a less than pleasant tang. However, some asthmatics are sensitive to metabisulphites and so it might be easier in the long run just to heat it in a Bain-marie or something. According to page 2 of [7] heating in a hot water bath to 65 C and holding for 3 min should do the trick. --Aspro (talk) 11:15, 8 May 2010 (UTC)

At least in my experience (UK) any yoghurt which is not in a chiller cabinet at the store will not have active cultures. I don't know if there is a way you can positively confirm this though other than writing to the manufacturer. 131.111.185.69 (talk) 21:51, 7 May 2010 (UTC)

I think it's always refrigerated here in the US. StuRat (talk) 21:56, 7 May 2010 (UTC)

In the UK, yoghurt with an active culture will say something like "live yoghurt" (or, these days "probiotic") somewhere on the tub: other yoghurts are available which do not contain active cultures. Often the yoghurt marketed to children, for example. 86.180.48.37 (talk) 20:04, 9 May 2010 (UTC)

Invasive surgery on small animals

Does anyone know what's the smallest animal that a veterinarian has been able to successfully perform complex brain/thoracic/abdominal surgery on? Is it humanly possible, to perform open heart surgery (just for example) on a mouse, or a zebra finch? --95.148.107.169 (talk) 21:19, 7 May 2010 (UTC)

I suspect that larger tumors would be more easily found and removed from smaller animals, whereas delicate surgery, like neurosurgery, would definitely be out. StuRat (talk) 22:03, 7 May 2010 (UTC)

Actually not "out", if you count surgery for experimental research reasons instead of therapeutic reasons. Lots of surgical procedures get done on mice and rats, including implantation of brain stimulators in specific nuclei. alteripse (talk) 02:42, 8 May 2010 (UTC)

Heh. Complex surgery has been performed on fruit flies (for example see PMID 20053645.) With powerful microscopes, micromanipulators, and lasters, pretty much nothing is impossible. Delicate surgery on mice is everyday stuff nowadays. Looie496 (talk) 03:14, 8 May 2010 (UTC)

Undergraduate college students have routinely done stereotaxic brain surgery on rats, mice and even frogs, doing some removal of portions of the cortex, or inserting microelectrodes to record brain potentials. Edison (talk) 03:32, 8 May 2010 (UTC)

It goes even smaller than fruit flies, in fact. Microsurgery is regularly done on Caenorhabditis elegans, which are only 1mm long as adults. Researchers can laser ablate individual cells, and surgically remove individual sensory neurons for research purposes. Someguy1221 (talk) 09:36, 8 May 2010 (UTC)

Researchers can cut open a single-celled organism, surgically remove the nucleus of the cell, and put a new nucleus in! (Nuclear transfer) It doesn't get much smaller than that! APL (talk) 22:42, 8 May 2010 (UTC)

OP here (probably with a different IP) - thanks for the replies. I didn't know that surgery on organisms that small was possible but when I asked my question, I was thinking more about a veterinarian performing surgery on small domestic/pet animals. Say if I had a zebra finch that needed open heart surgery (I don't, I'm not asking for medical advice here), would a typical veterinarian be able to perform the op these days, if he/she decided that a rough long term suvival vs. risk of death on the table vs. desire of the owner for his pet to live calculation suggested that it was worth performing? --95.148.104.246 (talk) 20:28, 9 May 2010 (UTC)

Shell Oil Company

In Fortune Magazine i believe the last issue in October of 2008 I read that Shell Oil Company has under it's control in the United States enough shale rock from which they could make oil that would supply our needs for as much as 50 years and Shell could make money doing so at $30 a barrel. Could you revue this and update these estimates. Thanks —Preceding unsigned comment added by Norwood jones (talk • contribs) 22:33, 7 May 2010 (UTC)

There is a lot of Oil shale in the US and Canada, so the time estimate is probably right, but $30 a barrel sounds wrong. The article says it's more like 70-95 (at least at first). See the article I linked, it's really good and has a ton of details. Make sure to read the sub-articles it points to as well. Ariel. (talk) 22:55, 7 May 2010 (UTC)

Note that if oil prices stay up in that area, however, then oil demand will drop, and alternative sources of energy will be used, instead. So, that "50 year supply" could last a lot longer at that reduced level of usage. StuRat (talk) 03:48, 8 May 2010 (UTC)

Reaction of metal hydrides from nickel-metal hydride cell

When the metal hydride anode of a nickel-metal hydride cell is reacted with acid, it forms an almost black solution, then changes dark green solution, fizzing all the while. I added the ammonia and the hydrogen peroxide as described in the article for cerium to test for cerium ions. I came up with a green precipitate, a little lighter than ferrous hydroxide. When it is just neutralized by ammonia, it forms a blue precipitate. What is the green precipitate? --Chemicalinterest (talk) 23:20, 7 May 2010 (UTC) A help would be that the filtrate from the neutralization with ammonia of the anode solution is blue. When it reacts with hydrogen peroxide, it turns green and fizzles. --Chemicalinterest (talk) 00:45, 8 May 2010 (UTC)