Wikipedia:Reference desk/Archives/Science/2010 June 16

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June 16

What value is associated with "low impedance"?

What value is associated with "low impedance"? I know that in wire, the material, gauge, and length all contribute to the impedance. I continually see references to "low impedance", but is there a quantifiable answer to the value?—Preceding unsigned comment added by Blinstedt (talk • contribs) 00:33, 16 June 2010 (UTC)

It probably depends on the application. What sort of use are thinking of? --Jayron32 01:39, 16 June 2010 (UTC)

BTW, impedance is basically resistance as applied to A/C (like sound in a speaker wire). Ariel. (talk) 01:50, 16 June 2010 (UTC)

Blinstedt's question contains a hidden error. In wire, the length and diameter, and the resistivity of the material, all influence the resistance of the wire. Resistance is the ratio of potential difference (voltage) to direct current. Impedance is the ratio of potential difference to alternating current. Inductors have significant impedance because they prevent an alternating emf from causing as high a current as would occur if the emf was steady. Capacitors have low impedance because they allow an alternating emf to drive a continuous current (albeit a sinusoidal current.) So a low-impedance circuit has high values of capacitance and/or low values of inductance, and conversely a high-impedance circuit has low capacitance and/or high values of inductance. A thick piece of copper wire might have low resistance, but when used in series with a large inductor it becomes part of a high-impedance circuit. Conversely, a thin piece of copper wire might have high resistance, but when used in series with a large capacitor it becomes part of a low-impedance circuit. Dolphin (t) 03:10, 16 June 2010 (UTC)

You are mistaken. Please read the articles: Electrical impedance, Electrical reactance.—eric 03:22, 16 June 2010 (UTC)

People often use impedance as a synonym for Electrical reactance as dolphin has, I often make this error too. and see below.87.102.18.94 (talk) 03:28, 16 June 2010 (UTC)

I'll try = for power transmission low impedence means less than 1ohm. much less. For other applications such as audio inputs and outputs the answer is a bit different.

But we need to differentiate between reactive and resistive impedance too see Electrical_impedance#Device_examples for an explanation.87.102.18.94 (talk) 03:26, 16 June 2010 (UTC)

"High" and "low" are completely relative to your application so we cannot answer the question without more information. For example, when specifying a power transformer for a substation, typically a "standard impedance" transformer has an impedance of 10% or less, whereas a high impedance transformer would be 15% or more. There is no absolute impedance value that defines "high" or "low". Zunaid 09:03, 16 June 2010 (UTC)

To give another example: in the audio world, the most common low-impedance load is a loudspeaker, which usually has a value between 4 and 150 ohms, while an input to an amplifier, typically 10 kilohms or more, is considered high impedance. There is no exact dividing line between the two. --Heron (talk) 13:27, 16 June 2010 (UTC)

The general answer is that it depends on the application. The exact threshold could be defined as the point where accounting for the exact impedance value (as opposed to approximating it as zero) causes less than a 5% error in your application. So suppose you have a 9V battery, ignoring its equivalent series resistance, and using a piece of copper wire you connect the battery to a heating element like nichrome wire which has a 10ohm resistance. The electrical power turned to heat in the heater will be (9V)^2/(10 ohm) = 8.1 Watts, assuming the resistance of the copper wire is about zero. But suppose the copper wire has a resistance of 0.26ohms, then by using the voltage divider formula and we can see that the power being transferred to the heater has decreased by 5% from our nominal value to 7.69 watts. So below 0.26ohms maybe we don't care about the value of the copper wire's resistance, and assume it is zero, and we call it "low impedance" or "negligible". But above 0.26 ohms (in this case only) ignoring the exact value will lead to a greater than 5% error. But really "low impedance" is too vague to mean anything specific. Mattski (talk) 23:51, 16 June 2010 (UTC)

In my application, I am specifically interested in draining static electricity that is built up within a DC powered device. —Preceding unsigned comment added by Blinstedt (talk • contribs) 02:29, 17 June 2010

In that case you should work out the capacitance of your device, (probably in the picofarads range) and from how long you want to discharge to a particular fraction you can calculate a resistance required. I would expect anything below 100 megaohms will do the job to discharge static. Graeme Bartlett (talk) 12:52, 17 June 2010 (UTC)

Atom with some muons

If there is an atom with a muon or two replacing the electrons, do those muons sit in the same orbital as the electron they replace, or do they have their own, non-overlapping, series? And if it's their own series, does that mean the atom would then behave chemically as something else (because the outermost electrons are in a different shell)? Ariel. (talk) 01:41, 16 June 2010 (UTC)

Did you read the article in question? The section titled "Muonic atoms" discusses the exact issue you have, as does the linked article Exotic atom#Muonic atoms and the article Muonium discusses the exact opposite (where an antimuon replaces a proton). --Jayron32 01:54, 16 June 2010 (UTC)

These articles do not however answer the question about orbitals. Graeme Bartlett (talk) 01:55, 16 June 2010 (UTC)

Ah, of course. I would suspect that the orbital organization of a muonic atom would have to be different; since a muon has 200x the mass of an electron, its angular momentum would by necessity then be different, and a key component of orbital organization is angular momentum. See quantum numbers for a brief discussion of the role of angular momentum in orbital organization, or Azimuthal quantum number for a more detailed discussion. --Jayron32 03:05, 16 June 2010 (UTC)

To first approximation, an atom with X protons and N muons replacing electrons will have the same chemistry as an atom with X-N protons and no muons (provided X >> N). The muons have an independent series of quantum numbers and occupy much tighter orbits than electron, so effectively each muon results in one proton's worth of charge being hidden from the electron cloud so that the rest of the system behaves as if the nucleus was of lower charge. Dragons flight (talk) 03:17, 16 June 2010 (UTC)

Haha Dragons, are you willing to pull out Griffiths/Shankar and go through the derivations, as my copies are in storage? SamuelRiv (talk) 09:20, 16 June 2010 (UTC)

overcharging a handycam or mobile phone battery

why do some manufacturers advice us against leaving the batteries of handycam or mobile phones connected to the chargers for too long/ What happens when you over charge a battery? Fragrantforever 06:50, 16 June 2010 (UTC) —Preceding unsigned comment added by Fragrantforever (talk • contribs)

There is a message on your talk page about signing posts that you might find helpful. ;-) Caesar's Daddy (talk) 07:30, 16 June 2010 (UTC)

If you leave a battery on a charger constantly it overheats, then dries out. The charger charges it till it's full, then the extra energy just goes to waste heating up the battery. The heat eventually dries it out, and then it doesn't work anymore. Depending on the chemistry of the battery it might damage it in other ways (rechargeable batteries are pretty delicate and are easy to damage). Lithium ion batteries especially get damaged if they overcharge even a little, so all of them include limiting circuity to prevent this. Another thing that can happen is the water in the battery gets electrolyzed into hydrogen and oxygen, which then either leaks out of the battery, causes it to swell, or (hopefully) gets recombined back to water, releasing some heat in the process.

If you want to store a battery most of them are best stored in a half charged state, except for lead acid which needs to be fully charged at all times. Ariel. (talk) 09:10, 16 June 2010 (UTC)

Note that smart chargers detect when the battery is fully charged and then stop charging it. Cell phone chargers seem to do this, for example. Unfortunately, many other chargers don't and there doesn't seem to be any standard way of labeling devices so you can tell if your charger is smart or stupid. However, if the instructions include that warning, it's probably the bad type of charger, so do as they suggest. StuRat (talk) 15:08, 16 June 2010 (UTC)

Thanks for the responses, Ceaser's daddy, I do add 4 tildes ( or whatever its called) at the end of all my posts and I thout that means signing my posts, it still says unsigned entry- which prompts you to drop a comment like that with a wink. 213.130.123.12 (talk) 10:22, 16 June 2010 (UTC)

You appear to have modified your default signature in such a way that SineBot does not recognize it. (See User:SineBot#What it looks for.) If you want to keep your linkless signature, you may wish to opt out of SineBot's scrutiny. 58.147.52.243 (talk) 10:56, 16 June 2010 (UTC)

Bad idea. See Wikipedia:Signatures#Links Nil Einne (talk) 18:33, 16 June 2010 (UTC)

yawning + stretching euphoria

why do you get euphoria when yawning + stretching in the morning (or any time of day, especially if you are a feline)? 92.224.204.156 (talk) 08:35, 16 June 2010 (UTC)

I'm not sure about the stretching, but yawning is a way of getting more oxygen into your blood which would make you more alert. Regards, --—Cyclonenim | Chat  11:21, 16 June 2010 (UTC)

That's what I thought too until I read up on this recently (trying to understand contagious yawning) and found that there is actually no data to support it. As far as I can tell, stretching feels good because it reduces muscle stiffness, and yawning may be a sort of stretching of the lungs. Looie496 (talk) 14:55, 16 June 2010 (UTC)

Evolutionarily speaking, things "feel good" which are (or were) helpful for passing on our genes. Stretching helps prevent injury and thus could keep our ancestors alive long enough to reproduce. As for yawning, the benefits there are less clear. StuRat (talk) 15:03, 16 June 2010 (UTC)

Will poppy seeds in processed horse feed test false positive for Synephrine in the urine or could slippery elm bark powder contain Synephrine.

Our race horse had a pre race urine sample taken which tested positive for Synephrine. My husband has been a trainer for thirty odd years and has never had a positive swab until now. Prior to the swab, we had started using processed feed in a pellet form, that was a bonus prize from a win we had with one of our horses. I read somewhere that poppy seeds, which were profuse here in Australia at the time and visible in unprocessed feed, can give a false positive for Synephrine and suspected that this may be the cause of the positive swab. I cannot find the article now to present to the stewards inquiry. Is this true? Will poppy seeds cause this result? Also we used slippery elm bark powder, which was guaranteed to be a legal substance that was safe to use when racing. We used this to prevent/relieve stomach ulcers that can be prevalent in race horses. —Preceding unsigned comment added by Traveloz (talk • contribs) 10:23, 16 June 2010 (UTC)

I've heard of poppy seeds giving false positives for opiate tests, but not for this. Synephrine is similar structurally to neo-synephrine which can give false positives for amphetamine/methamphetamine tests, but my previous point stands: poppy seeds shouldn't be giving false positives for synephrine, but instead for opiates. I'm not sure about slippery elm bark powder. I suspect you'd need to talk to a veterinary pharmacist for a conclusive answer. Regards, --—Cyclonenim | Chat  11:20, 16 June 2010 (UTC)

Volume of a drop

I have a tap that drips about once a second. I'm wondering how much water it is wasting a year. Drop (liquid) does not say what the volume is. Do not know if tap drops are always a particular size or if they vary. 92.28.251.43 (talk) 13:41, 16 June 2010 (UTC)

You could do an experiment... just put a liquid measuring cup under the tap, and record how long it takes to reach a certain volume. Google can make the calculation easy: example. -- Coneslayer (talk) 13:47, 16 June 2010 (UTC)

Drops will vary in size, but drops from a single source like this one should be consistent with themselves. Some of the math behind this is discussed at drop (liquid). However, you don't need that to estimate how much water you're wasting. Instead, grab a measuring cup (the one with the smallest graduations you have) and place it under the leak for a set period of time (longer is better, as long as you don't overflow the cup). You can then extrapolate annual leakage based on that short term. Suppose, for instance, that you got 1/4 cup of water in one hour's time. That would become 1/4 (cup/hour) * 24 (hours/day) * 365 (days/year) / 16 (cups/gallon) for about 140 gallons of water wasted per year. You could similarly estimate the volume of an individual drop. — Lomn 13:52, 16 June 2010 (UTC)

I agree with the previous responses. The reason is that there's a fair amount of error both in estimating the volume of a drop and in estimating the time increment between them. Collecting a larger volume over a larger time period will reduce both those errors and thus give a far more accurate total. However, use a tall, narrow container to collect the water, such as a vase. This will reduce water loss from splashing and evaporation. You can then pour it into a measuring cup. StuRat (talk) 14:54, 16 June 2010 (UTC)

Is there an approximate answer for the volume of a tap drop please? 92.28.251.43 (talk) 16:14, 16 June 2010 (UTC)

http://www.google.co.uk/search?q=volume+of+water+drop&hl=en&start=10&sa=N shows that the generally used figure is 1/20ml or 0.05ml ie 20,000 drops in a litre.87.102.92.166 (talk) 16:26, 16 June 2010 (UTC)

But, as we've noted, that doesn't mean your water drops will be 1/20 ml or anything like it. However, it would be trivial to determine this experimentally. StuRat suggests an excellent method above. — Lomn 18:39, 16 June 2010 (UTC)

WolframAlpha agrees with teh 0.05ml approximation. [1]. Aaadddaaammm (talk) 09:10, 17 June 2010 (UTC)

Thank you for your replies although I'm rather dissapointed that people seem to think I'm too stupid to have thought of the measure-it-yourself method before asking the question. I am busy. I make it 1577.88 litres a year, which is a lot. Now I'll have to find my metered water bill to see how much its costing me. 92.15.14.87 (talk) 17:15, 18 June 2010 (UTC)

It would take, what, a minute to place a measuring cup under the faucet and start a timer, a minute to read the cup and timer and put them away, and a minute to plug the values into Google? That's 3 minutes of work, and I think I'm being generous with the estimates. And you'd end up with an answer that actually meant something, and wouldn't give the impression that your time is so much more important than ours. -- Coneslayer (talk) 17:29, 18 June 2010 (UTC)

You would need an extremely small measuring jug for that, since you would only collect about 60 x 0.05ml = 0.003 litres. 92.15.4.168 (talk) 12:28, 19 June 2010 (UTC)

Um, no. You go do other things while the water is collecting in the measuring cup. You don't have to stand there watching it. At the risk of again insulting your intelligence, there's a difference between "3 minutes of work" and "the process taking 3 minutes from start to completion." -- Coneslayer (talk) 19:49, 19 June 2010 (UTC)

I don't want to play thank you, a quick estimate is better for the purpose at hand. Its charming how one gets detailed descriptions of the obvious. 92.15.4.168 (talk) 20:27, 19 June 2010 (UTC)

~ (Tobacco vs. other illegal, recreational drugs)

So if I wanted to trade my legal cigarette smoke for illegal recreational drugs instead, in order to maintain whatever utility I think I get from the tobacco smoking, while expressly making the trade (with concommitant justice risk) in order to reap certain comparative health benefits for the same level of utility, would I be able to do so? As for the utility part, I shall have to judge, but for the health part, I think you can help me. Viz.

• How do the health effects of tobacco use compare with the health effects of other, illegal, recreational drugs?

Specifically, what is most comparable in its effects both during consumption and in terms of deletirious health consequences? Note: because in my estimation there are something like a few million dollars of salaries going into Wikipedia shills, I would like to mention that I have absolutely no relationship with tobacco or any other drug other than being a simple consumer. 84.153.246.145 (talk) 13:57, 16 June 2010 (UTC)

I changed your useless title to one which actually identifies the question. StuRat (talk) 14:51, 16 June 2010 (UTC)

At what point did the OP mention cannabis? There are other illegal drugs which can be vaporised or smoked, so I've renamed again accordingly. Regards, --—Cyclonenim | Chat  15:02, 16 June 2010 (UTC)

OK, but please always leave the original title, both so they can use it as a search term and so everyone knows what I was talking about when I said the original title was useless. I've therefore added the original title (a single tilde), back in. StuRat (talk) 15:28, 16 June 2010 (UTC)

To answer your question, I recommend reading these links: Health effects of tobacco, effects of cannabis, heroin#Risks of use and cocaine#Effects and health issues. Of course, there are other drugs, and if you search for their articles you'll usually find either a separate article on their health effects, or a subsection discussing it. Regards, --—Cyclonenim | Chat  15:04, 16 June 2010 (UTC)

Thanks, I'm pretty sure heroin and cocaine are off the scale in terms of risk versus tobacco, though. Isn't there something comparable? (op here) 84.153.246.145 (talk) 15:35, 16 June 2010 (UTC)

This chart should help. Note, that while I personally am not so convinced it's accurate (for example I think solvents are more dangerous than alcohol), it's probably a good start. (My main objection is how the raw data was combined into a mean.) Anyway, based on it Khat seems like the best choice. Ariel. (talk) 15:52, 16 June 2010 (UTC)

And that proves your point. Khat causes severe psychosis. The Somali community in Leicester (where I used to teach) are campaigning to get it put on the banned list in the UK because it causes more social harm in that commmunity than any other drug, legal or otherwise. But you wouldn't know that from that chart! When I get chance (later on tonight) I'll try and find the research they've used in their campaign. --TammyMoet (talk) 16:31, 16 June 2010 (UTC) Here's one: http://informahealthcare.com/doi/abs/10.3109/00048679409075648 --TammyMoet (talk) 17:24, 16 June 2010 (UTC)

I wonder where chewing of Coca leaves falls on the chart? (It is not the same thing as doing concentrated cocaine.) Off the top of my head that seems like it is probably a similar trade-off as tobacco, perhaps even a bit better for one (similar physical effects, but without the obvious lung problems). It's not illegal everywhere, but it is in the United States, so that satisfies the "illegality" component. This is not medical advice in the slightest—there are probably long-term health risks associated with chewing Coca leaves, and how they stack up against long-term risk from cigarettes, I honestly don't know. --Mr.98 (talk) 17:23, 16 June 2010 (UTC)

Interesting - I wonder where this chart came from, and what it was designed to do? for instance, yes, chewing cocoa leaves should be far less dangerous that snorting concentrated cocaine. further, while cannabis ounce for ounce might be comparable to cigarettes in terms of toxins, no one smokes 20 cigarrette-sized joints a day. consumption is probably less that 1/20th that of tobacco even in the heaviest pot smokers. Hashish might be different, of course. I'm really curious about the positioning of LSD, though - LSD is entirely non-addictive and has negligible physiological effects on the body (I don't even think researchers have discovered a toxic dose level for it). It really should be down close to 0,0, though that's not a recommendation for use (LSD is not a drug that should be taken casually, because it has intense psychological ramifications). --Ludwigs2 19:15, 16 June 2010 (UTC)--Ludwigs2 19:15, 16 June 2010 (UTC)

Is it useful to read the chart as whatever has the lowest total score is the most desirable? Presumably if you were to try to replace one with another you would have to give one addiction in favor of another addiction, right? Assuming that the "dependence" is the reliance on the effect of the drug that you develop. If that is the case then isn't it more appropriate to think of it as dependence divided by harm? Since trying to replace a high-dependence, high-harm drug with a low-dependence, low-harm drug is likely to result in failure due to your body still craving the old drug? Remember, the OP did say that he was interested in the "utility" of the drug vs smoking which means he would have to supplant his cigarette addiction with whatever addiction this new drug offered. This is an interesting (if morbid) thought experiment. How about not being addicted to any drug? Why isn't that on the chart? --144.191.148.3 (talk) 19:27, 16 June 2010 (UTC)

Tobacco has an interesting feature that the physically addictive (and perhaps even beneficial) portion, nicotine, is completely separate from the unhealthy portion, called "tar". Unfortunately, current smokers seem to associate the tar with the "nicotine high", and thus aren't satisfied with no-tar cigarettes, called a psychological addiction. However, perhaps if no-tar cigarettes were provided to new smokers, or better yet, cheap nicotine patches, pills, etc., then they wouldn't ever associate tar with the "nicotine high" and therefore wouldn't crave it, with the additional benefit of eliminating or reducing the harm to others from second-hand smoke. StuRat (talk) 13:03, 17 June 2010 (UTC)

errr... nicotine is a neurotoxin - for the tobacco plant it's a built in insecticide. like any poison it can have beneficial uses, but... --Ludwigs2 20:00, 17 June 2010 (UTC)

The dose makes the poison. --Carnildo (talk) 01:36, 18 June 2010 (UTC)

Absolutely. Sure it's toxic at a high enough level, but so is iron and many other nutrients we need. So nicotine's toxicity is quite irrelevant, unless you plan to make yourself a belt out of nicotine patches. StuRat (talk) 14:19, 18 June 2010 (UTC)

Not true, it's toxic at any level and it's definitely not irrelevant. See nicotine poisoning. You can't compare an essential nutrient to a toxin. It's like comparing vitamin C and cyanide. Regards, --—Cyclonenim | Chat  16:40, 18 June 2010 (UTC)

I think StuRat meant, it's fatally toxic at a high enough level. And many, many things are toxic in high levels. Vitamin C happens to be pretty benign because it is water-soluble and thus flushes out easily, but many other vitamins—Vitamin A or Vitamin D for example—are indeed quite http://en.wikipedia.org/w/index.php?title=Wikipedia:Reference_desk/Science&action=edit&section=8toxic at high levels. Cyanide is much higher in toxicity, but that's not the point being discussed here. The point is that just about everything has a level of toxicity associated with it in large doses. As our article on Toxicity explains quite clearly: "A central concept of toxicology is that effects are dose-dependent; even water can lead to water intoxication when taken in large enough doses, whereas for even a very toxic substance such as snake venom there is a dose below which there is no detectable toxic effect." --Mr.98 (talk) 17:10, 18 June 2010 (UTC)

I do understand what you're saying, but my point is that water is usually not toxic because on a molecular basis it is good for you, not bad. Nicotine, whether just the one molecule or millions of molecules, is harmful. Just because we recover from small doses of nicotine very effectively doesn't mean that it's not toxic at those levels. Does that make sense? Regards, --—Cyclonenim | Chat  17:43, 18 June 2010 (UTC)

No, it doesn't make sense. There is nothing inherently "good" or "bad" about molecules. --Carnildo (talk) 23:38, 18 June 2010 (UTC)

Yes, there is. A molecule of water doesn't do any damage to your body, it just gets transported in and out of cells. A molecule of nicotine, on the other hand, competes with acetylcholine receptors. That can be harmful. Regards, --—Cyclonenim | Chat  10:56, 19 June 2010 (UTC)

Regrowing of human skin and its color

The other day I saw an African-American firefighter. He had suffered a serious burn on his face at some point in his life, but the skin was all grown back. However, the skin was nowhere close to the tone that the rest of his skin was so it looked like a mask. Just a white patch around his mouth and dark brown skin everywhere else on his face. I know that skin color has a lot to do with melanin, but I am wondering why it didn't grow back the same color that it was previously. Is there only so much melanin in the body? Thanks, The Reader who Writes (talk) 15:20, 16 June 2010 (UTC)

The same applies to skins of naturally paler colours - the new growth is even paler. I don't know the reason though, except to note that skin naturally grows darker as it ages and is exposed to UV. Dbfirs 15:43, 16 June 2010 (UTC)

It's likely that the burn was of a significant enough degree to damage the melanocytes which lie at the bottom of the epidermis. Bad first degree burns and all second and third degree burns cause this damage. I suspect that the burn was bad enough to prevent the repopulation of melanocytes to the area. Regards, --—Cyclonenim | Chat  16:19, 16 June 2010 (UTC)

The white patch may have been vitiligo which is known to sometimes occur in association with trauma to the skin. 86.4.183.90 (talk) 07:02, 17 June 2010 (UTC)

A display that doesn't suffer from glare

I was checking out some of the next gen display technologies like Laser TV, and Field Emission Displays. But one thing all these displays have in common is that bright sunlight creates large amounts of glare. Is there any display technology, present or future, that will not suffer from glare while delivering high definition/quality visuals? And I'm talking about broad sunlight, like if you had your laptop or whatever out in the park in the middle of the day.

What about holograms? Don't know how advanced this technology is, but in some sci fi games, and movies they use holograms as displays in their futuristic worlds. How well will they work in broad sunlight? 148.168.127.10 (talk) 15:46, 16 June 2010 (UTC)

This isn't an answer, more of a point to ponder, but how can you create a device which emits light, but doesn't reflect it back when it shines on it's surface? I would have thought any coating that prevents glare would also darken the image. Regards, --—Cyclonenim | Chat  16:21, 16 June 2010 (UTC)

My wife has read her Kindle on the beach in extremely glaring sunlight. So, that is one very anti-glare display. However, it is only black-and-white. -- kainaw™ 16:23, 16 June 2010 (UTC)

That's the answer. ePaper. Currently only available in monochrome, but color ePaper displays are in development. APL (talk) 16:33, 16 June 2010 (UTC)

I would think any reflective capable display would also work similarly. These are usually monochrome and of course also require ambient lighting to see which may be undesirable in some circumstances. One option is for a combined display which can operate in either reflective or transmissive modes like the OLPCs or Pixel Qi although these still operate in monochrome in reflective mode. Or perhaps a transflective liquid crystal display. Nil Einne (talk) 18:24, 16 June 2010 (UTC)

Conservation of energy

What's the difference/resemblance between the conservation of energy and the first law of thermodynamics? /Natox (talk) 17:05, 16 June 2010 (UTC)

Quoting from the article: "The first law of thermodynamics [is] an expression of the principle of conservation of energy." If you want to get picky, the FLoT addresses non-isolated systems by expanding the system in question until it's isolated. — Lomn 18:33, 16 June 2010 (UTC)

No difference. The 1st law of thermodynamics is The conservation of energy applyed to thermodynamic systems. Dauto (talk) 20:56, 16 June 2010 (UTC)

Spider indentification

what kind of granddaddy long legs spider is white with black spots, and has two front yellow fangs? —Preceding unsigned comment added by 71.50.164.12 (talk) 17:05, 16 June 2010 (UTC)

It's hopeless without a picture. If by granddaddy-long-legs you mean a harvestman, then many if not most of them (and there are over 200 species in US) have spotted or wavy patterns of dark gray or brown with white or beige, and some indeed have pale chelicerae and pedipalps. Leiobunum vittatum is fairly common and may fit the bill, but there are many others, too. However, granddaddy-long-legs may also refer to Pholcidae. Which is it? --Dr Dima (talk) 18:20, 16 June 2010 (UTC)

You also have to tell us where you saw it. --Sean 19:43, 16 June 2010 (UTC)

Protein percentage in muscle by mass

Hello. Can someone please tell me what is the percentage of protein in muscle by mass, or in other words, roughly how many grams of protein can I expect to find in 100 grammes of an average muscle. Thank you.--Leptictidium (mt) 18:12, 16 June 2010 (UTC)

You might find list of foods by protein content informative, but that lists muscles in an edible state, which presumably means cooked, so some protein loss might occur in that process. --Sean 19:45, 16 June 2010 (UTC)

Most meat (animal meat) is muscle, so it's the same as that. Ariel. (talk) 23:20, 16 June 2010 (UTC)

If that 100 grams of muscle is not dehydrated, then a significant amount will be water. Protein with make up most of the remaining amount. So, a ballpark guess is 90+% if dehydrated, but 50% or less if not dehydrated. --Rajah (talk) 18:01, 17 June 2010 (UTC)

Stronger reducing agent than azide

What is the strongest stable reducing agent? --Chemicalinterest (talk) 19:10, 16 June 2010 (UTC)

Under normal conditions probably lithium. The trick answer is a charged capacitor - stable form of stored electrons - any electrochemical potential you like ie will reduced Li+ Cs+ etc etc.87.102.92.166 (talk) 12:22, 17 June 2010 (UTC)

Lithium is the most electropositive, however be careful in air it can catch fire and melt. Graeme Bartlett (talk) 12:44, 17 June 2010 (UTC)

Electropositivity says this property "increases down groups" so sodium would beat lithium (and potassium beat sodium)? Lithium and sodium are pretty easy to handle without being too likely to burst into flame accidentally. Potassium starts to more strictly require inert atmosphere. DMacks (talk) 18:22, 17 June 2010 (UTC)

Lithium is the least electropositive, but it has the highest standard reduction potential, -3.0401. Azide is -3.09, HN₃ + e^- ⇌ ³/₂ N₂ + H⁺. --Chemicalinterest (talk) 11:30, 18 June 2010 (UTC)

Strongest base

There's a redirect at strongest acid but not at strongest base, so what's the strongest base? --76.77.139.243 (talk) 19:16, 16 June 2010 (UTC)

Tert-Butyllithium - It has a pKa of greater than 50 if my memory serves. Regards, --—Cyclonenim | Chat  20:00, 16 June 2010 (UTC)

We have an article about superbases. For example, swapping tBuLi to tBuK makes it stronger. DMacks (talk) 20:07, 16 June 2010 (UTC)

Kewl. What happens if you mix a superbase with a superacid? Are there any YouTube videos, like the ones of people pouring liquid oxygen on their charcoal grills? I suppose the reaction might be just boring; that would be too bad. --Trovatore (talk) 21:30, 16 June 2010 (UTC)

Even "moderately strong" bases (almost any organometallic) reacts rapidly when exposed to the air (humidity and/or CO2), don't even need any "extra" reactivity of a complementary strong acid. The reactions are extremely exothermic, but nothing visibly dramatic unless the heat is enough to boil a solvent or fracture a glass flask. Then it's nothing special, just "a flask explodes". It gets dramatic when there is air present, because there is enough energy released to ignite the solvents or the bases themselves (n-BuLi reacts with traces of moisture to form butane and heat, for example). And it's really easy to lose control or have even a small amount of material create a very dangerous situation (unlike a charcoal fire contained to a grill, or a thermite reaction in a flowerpot, for example) because of the volatile solvents involved. This accident was less than 50 mL total. DMacks (talk) 22:29, 16 June 2010 (UTC)

That's very sad. Not what I had in mind, of course. --Trovatore (talk) 22:46, 16 June 2010 (UTC)

Tert-Butyllithium is sold as a solution in an inert solvent, for example tetrahydrofuran or hexane. I once worked with someone who accidentally let a single drop of the solution fall on chem-wipe tissue and it instantly caught fire (everyone was fine). Just spraying it in the air on even a 'not humid' day (there is always some moisture) will apparently cause it to burst into flames (graduate schools can have some poor waste disposal options). Mixing it with strong acids will be very exothermic.Pmdove (talk) 02:09, 18 June 2010 (UTC)

How can I make it not possible to throw things

I don't want people throwing things in my apartment, how do I make it so you have to place things, you can't throw them (anything)? Note: I don't think I ever throw anything at all, but I would like the change to be reversible in case there is some bad consequence I didn't think of,l. Would I have to change inertia (inertial dampers?) air viscosity, or what, and how would you do it, 85.181.146.84 (talk) 19:50, 16 June 2010 (UTC)

You can't. Next question! — Lomn 20:07, 16 June 2010 (UTC)

Concur, you can't have inertial dampers because they don't exist in that sense, we're not in the Star Trek universe unfortunately. You can't change the air viscosity because you'd have to have a solid to prevent things from moving, thus you couldn't move either. You'd be encased! Regards, --—Cyclonenim | Chat  20:12, 16 June 2010 (UTC)

Get everyone out of the apartment. Close and lock the door from the outside. Throw away the key. Problem solved. --Sean 20:23, 16 June 2010 (UTC)

Move to an Earth-like planet with a gravitational field strong enough to make everyday objects impossible to lift. Don't expect to be walking anywhere. (Is such a planet possible, or would the increased gravity cause fundamental differences precluding Earthlikeness? 20:32, 16 June 2010 (UTC)Vimescarrot (talk)

Possibly. The Moon might not have had a chance to form if the gravity of the Earth was stronger than it is/was, and our Earth would not be as stable as it is now. It was on Discovery Channel a few nights ago, saying that when the Moon finally escapes orbit all sorts of apocalyptic scenarios will happen (but it doesn't matter because the next program was about 2012). If we hadn't had a moon in the first place, though, then those scenarios would have already happened and life possibly would have evolved anyway, as hardy as it is, just not in the same way. Also, we cannot preclude the possibility that throwing things may be a very welcome evolutionary feature, and the existing animals (or some of them) would evolve to do it anyway, such as by being stronger. Therefore we can envisage a world with no moon, no tides, no months to count, and populated by short squat people with massive biceps. --KägeTorä - (影虎) (TALK) 11:26, 17 June 2010 (UTC)

Invest in friends who don['t throw things. it will be worth the money in the long run. --Ludwigs2 20:31, 16 June 2010 (UTC)

This is an exercise in apartment design. Furnish your apartment with only objects that cannot practically be thrown. Areas that need small objects (Kitchens?) could be constructed so cramped that throwing items is impractical.

That's really the only answer, there's no way to adjust the laws of physics in your room in such a way that things can't be thrown, but they can still move when carried. (Otherwise you could fill the apartment with concrete, or Lucite.)APL (talk) 20:38, 16 June 2010 (UTC)

Recently while reading about ADX Florence I came across this lovely graphic: [2]. You can design your apartment to look like that: there will be no objects that are physically capable of being picked up, moved, or thrown. All furniture is made of concrete and is part of the floor. The only other item(s) are a monolithic toilet/sink. Nimur (talk) 22:35, 16 June 2010 (UTC)

Cover EVERYTHING with Velcro!!!!! SamuelRiv (talk) 01:12, 17 June 2010 (UTC)

I'm surprised no-one's mentioned punishment. It's impossible to change the laws of physics but not human behaviour. Next time anyone throws anything, give them a good kicking. In the end, they'll either mend their ways or move out. Either way, nobody's throwing stuff any more and nobody's getting a good kicking any more. Everyone wins. --KägeTorä - (影虎) (TALK) 01:46, 17 June 2010 (UTC)

You could have nets everywhere, so you have to walk through a maze of suspended nets to get anywhere. This would make throwing things pointless, as they would just get caught in a net. StuRat (talk) 03:58, 17 June 2010 (UTC)

Change the definition of "throw." It's just a linguistic problem. Bus stop (talk) 04:11, 17 June 2010 (UTC)

Fill the apartment with Jello and wear scuba gear when inside. I considered whether it would be possible to have a computer detect a 'thrown' object with cameras, but can't think of a device it could then activate to stop it from moving (a high speed jet of air doesn't seem effective.) RJFJR (talk) 17:41, 17 June 2010 (UTC)

Since we're getting silly, have the computer automatically fire a paint-ball gun at any one who throws something in the room? CS Miller (talk) 18:05, 17 June 2010 (UTC)

The telomeres of Turritopsis nutricula

I'm a layman with respect to biology, but from what I have read, the telomeres of chromosomes for most species get a little shorter with each cell division until a cell can't divide anymore. But at List of long-living organisms, it says "Turritopsis nutricula is capable of cycling from a mature adult stage to an immature polyp stage and back again. This means that there may be no natural limit to its life span." I know it's not certain whether there's a causal relationship between telomere length and aging, but limitless life span seems to necessarily imply limitless ability to divide. So does Turritopsis nutricula not lose any telomere length at all on each cell division, or does it keep adding as much as it loses, or something else? I saw the abstract at the link entitled "Telomerase activity is not related to life history stage in the jellyfish Cassiopea sp." at the bottom of Turritopsis nutricula but didn't really understand it. Thanks. 20.137.18.50 (talk) 19:59, 16 June 2010 (UTC)

I am also a biology layman but I believe telomere shortening isn't necessarily a "given" in cell division. For example I've heard cancer cells divide without telomere shortening, this is what allows them to grow out of control, because they don't "run their course". So it's not impossible to divide a cell without shortening telomeres. Maybe it's because we assume aging is "inevitable" so it must be the result of a inevitable process, so telomere shortening must be inevitable. But I think aging is quite probably just another evolved trait, so telomere shortening could very well be just another regular biological mechanism. Vespine (talk) 00:22, 17 June 2010 (UTC)

Our telomere article suggests other ways that organisms can get around this - some have circular DNA molecules that don't need telomeres to stop them destroying themselves. Others have enzymes that replace the missing telomeres so that they never run out. There seems to be a lot of complexity going on here. SteveBaker (talk) 00:36, 17 June 2010 (UTC)

The paper you reference [3] (subscription probably needed...) measured telomerase activity in this jellyfish. Telomerase is the enzyme that fixes the shortening of telomeres - in mammals it's only active in stem cells, cancer cells, etc. But this study found it active all the time in the jellyfish. They didn't check if the telomeres are actually maintained at the same length, but it's a pretty good suggestion that they are "adding as much as it loses". Aaadddaaammm (talk) 09:07, 17 June 2010 (UTC)

Just wanted to point out that telomeres can be resynthesized and maintained for a very long time. e.g. all the cells in your body divided from a cell that was created by your mother and father, and all of theirs, ... etc. all the way back to cell-1 a few billion years ago. Cheers! --Rajah (talk) 18:11, 17 June 2010 (UTC)

Number of deep sea oil rigs worldwide

How many deep sea oil rigs are there worldwide and how many are owned by which major oil companies.

I can not find this information in any Wikipedia articles.

Gary Tennison [email removed] —Preceding unsigned comment added by 70.168.154.204 (talk) 20:31, 16 June 2010 (UTC)

There are about 100,000 offshore wells (or holes, it's not clear). Does offshore mean deep sea to you? Anyway see [4], [5], [6], [7] Ariel. (talk) 21:27, 16 June 2010 (UTC)

Every week, Oil & Gas Journal [8] publishes a statistics list of countries operating offshore rigs, and estimated production figures. They also have a Production and Operations section in each issue. You can find these numbers week-by-week. They fluctuate based on the economics of operating the rigs. (It looks like the web/HTML current issue doesn't have these statistics available for free, but you might find a hard-copy in a library or research university). Correction: You can get these statistics for free by subscribing to the O&G Email Newsletter: [9] - be sure to check "OGJ Monthly Drilling & Production Report" and any others of interest to you. Nimur (talk) 22:26, 16 June 2010 (UTC)

I don't know about the world-wide numbers - I've seen figures suggesting about about 4000 wells operating in the Gulf of Mexico alone - and also numbers that say that there are 5600 oil rigs world-wide. The difficulty of sorting out what is a "rig" and what is a "well" - and what is "operating" and what isn't makes this a tough question. SteveBaker (talk) 00:34, 17 June 2010 (UTC)

Cumberland Slider Turtles

We recently had a turtle lay her eggs in our garden. We live on the North Fork of the Holston River in Tennessee. How long will it be before we see these hatch? —Preceding unsigned comment added by 173.105.80.255 (talk) 20:37, 16 June 2010 (UTC)

don't forget not to get your hopes up as these eggs are delicious for many predators. 92.229.12.200 (talk) 20:58, 16 June 2010 (UTC)

"Hatching usually takes place in the late summer or early fall but some sliders over winter as eggs and hatch in early spring." [10] "It takes 2 to 2.5 months for young to hatch." [11] "Young turtles hatch in 8-10 weeks, though occasionally they will spend the winter underground in the nest." [12] Ariel. (talk) 00:09, 17 June 2010 (UTC)

Is it fair to say that Nuclear Power plants are environmentally friendly?

Because we all know about nuclear waste. But can it be said that as long as the nuclear waste is either properly disposed of or recycled, that a nuclear power plant is enivronmentally friendly, and produces no negative impact to the environment? 148.168.127.10 (talk) 20:43, 16 June 2010 (UTC)

Yes, it is actually a lot easier to dispose of nuclear energy than it sounds. It is certainly much more environmentally friendly than fossil fuels, since a rice-grain size piece of ²³⁵U produce as much energy as three tons of coal or fourteen barrels of oil, so certainly a rice-sized piece of nuclear waste does much less damage to the environment than all the CO₂ produced by fossil fuels. --The High Fin Sperm Whale 20:51, 16 June 2010 (UTC)

Compared to the fossil-fuel alternatives, they are massively better. Nuclear waste issues really fall into two classes - the highly radioactive waste (which can be recycled and reused) - and low level stuff which is a pain to dispose of safely. However, coal-fired power plants take vast amounts of coal with background levels of radiation - and concentrate it down into ash - which ends up being fairly radioactive. It turns out that when you take out the recyclable waste from a nuclear plant - what's left is actually quite a bit LESS radioactive than the ash that comes from a coal plant...mega-watt for mega-watt that is. SteveBaker (talk) 21:54, 16 June 2010 (UTC)

it's one of those trade-offs. the normal consumption of fossil fuels is worse for the environment than the normal use of nuclear power, but nuclear power accidents are much worse than fossil fuel accidents. The entire Gulf 'deepwater horizon' debacle isn't going to be a fraction as damaging as the Chernobyl disaster. --Ludwigs2 22:00, 16 June 2010 (UTC)

Indeed, Belarus estimated the cost from the explosion to modern day to be around $250 billion. In comparison, the gulf oil leak is currently estimated to cost around $15 billion to clean up, plus whatever they decide/are forced to pay out in damages. Of course, the economical cost is yet unknown, but BP lost about $60 billion of it's value on the stock markets. Regards, --—Cyclonenim | Chat  22:16, 16 June 2010 (UTC)

You need to multiply damage by frequency to get any sort of reasonable comparison. We have had exactly one serious accident (not including early times when we didn't understand this stuff well) (3 mile island didn't cost much). How many oil leaks have there been? How many people were killed by coal mines? Nuclear is much safer. And less radioactive too - burning coal releases a TON of radiation into the air. Far more than nuclear plants do. Ariel. (talk) 22:28, 16 June 2010 (UTC)

There are really a couple environmental questions that would need to be disentangled:

• What are the "normal" environmental costs of nuclear power as it current operates?
• What are the "normal" environmental costs of nuclear power if it were done differently? (E.g., with fuel reprocessing, which would reduce the waste volume considerably, but has been halted in the U.S. since the 1970s because of plutonium economy fears)
• What are the likely costs from not totally rare accidents?
• What are the likely costs from one-in-a-million, worst-case-scenario accidents?
• And how do these costs and benefits stack up against the comparative risks and benefits from other energy generation schemes? (Fossil, renewables, increased conservation, etc.)

It's a big equation, and there are a lot of places where informed experts, acting in good faith, will disagree. And plenty more places where uninformed pundits, or people acting really in service of one agenda or another, will disagree. Even whether something Chernobyl should be taken into account at all is something well-informed people could dispute. Chernobyl was of a plant that was inherently more dangerous than any U.S. power plants, for example, and was being run in an exceptionally shoddy manner, and had basically no disaster mitigation done afterwards because of the dysfunctional nature of the Soviet bureaucracy at that time. Is it really a useful analog to making sense of nuclear power as a whole, or is it just a specific, weird, "one-in-a-million" case? Very smart and honest people would probably disagree on that.

I'm not saying, "it's unanswerable"—it is surely answerable within certain parameters. But the odds of getting a well-informed, balanced set of answers that everyone will agree upon is pretty unlikely. Even sorting out what the right questions are is a contentious activity. --Mr.98 (talk) 22:45, 16 June 2010 (UTC)

There are certainly modern nuclear plants that are inherently safe - but even in the case of Chernobyl, the human cost was immense - but the long term ecological damage is much more debatable. The lack of people around the plant means that wildlife has had a chance to rebound strongly. Most animals are too short-lived to suffer most of the longer term ill-effects of radiation that humans suffer from - and the presence of humans is vastly more damaging to their lives than the radiation problem. This paper says that numerous kinds of wildlife are thriving inside the 10km (human) exclusion zone - and doing considerably better than in the 30km zone where limited human return has been allowed.

But more to the point - over the lifespan of nuclear power, Chernobyl is actually the only significant accident we've had. Even Three Mile Island eventually ended fairly well. Contrast that to dozens of major oil spills from wrecked tankers - and many other drilling rig disasters. You might think the present spill in the gulf is bad - but it's not that much different from the Ixtoc I oil spill and way less than the Lakeview Gusher. Also, coal power has resulted in massive problems with ash tips subsiding, dams breaking and all manner of other major problems resulting in much MUCH more loss of life than Chernobyl...although not in such spectacular fashion. Only 35 people died directly at Chernobyl - and the 2% increased cancer risk for perhaps 200,000 people living near to the site adds 4,000 more deaths - but those people will die after happily living a considerable fraction of their lives, so it's not really fair to equate them. Many people lost their homes and jobs - but the Gulf Oil spill will cause similar disruption for fishermen and people in the tourist industry and destruction of the wetlands around the coast will cause more problems with storm surges and flooding in the future. But bear in mind - that's across the entire planet and over the entire lifetime of the industry! By comparison, the various oil/gas/coal industry disasters of just the last few year have killed WAY more people than Chernobyl. 6000 coal miners die every year in China alone! Sure, China's a long way away and so maybe you don't care - but Russia is also a long way away so why do you care about that?

There is absolutely no credible argument that nuclear power is more dangerous, more polluting, worse for the environment when compared to coal, oil and natural gas production. Add the lack of CO2 pollution and the consequent world-wide disaster that's about to befall us all and it's a no-brainer. We need nuclear power to cover the gap while we downscale our energy consumption, get wind, wave and solar up to speed - and maybe figure out how to do fusion in a practical manner. Nuclear clearly isn't the most desirable solution - but it's a pill we have to swallow for the eventual health of the planet.

SteveBaker (talk) 00:04, 17 June 2010 (UTC)

I used to be totally against it, but I researched it a bit and i've changed my mind over the last few years. I think the main stumbling block is the the common perception that each nuclear power plant is basically an atom bomb waiting to go off. Chernobyl is all the proof people need. But the fact is, plant technology today, is not only more advanced, it's completely different, they have fail SAFE operation now, not fail disaster like in Chernobyl, it means when stuff goes wrong, the reactions stop instead of going critical. As for the waste, plant technology now is so much more efficient it will produce less waste in the foreseeable future then we've already made and have to deal with. Vespine (talk) 01:01, 17 June 2010 (UTC)

It's worth noting that the US didn't have Chernobyl-like reactors then, either. It's not like people didn't know the risks that Chernobyl presented. — Lomn 01:12, 17 June 2010 (UTC)

Then there's my suggestion of building nuke plants deep underground where terrorists can't get at them, with cooling towers up above. They can also just push the nuclear waste further back into the cave and not worry about transporting it. StuRat (talk) 03:50, 17 June 2010 (UTC)

You mean like these: [13]? Rmhermen (talk) 07:50, 17 June 2010 (UTC)

Except for the "mini" part, perhaps. That one is apparently designed to be both unmanned and unguarded, allowing terrorists to steal the nuclear material and use it to make a dirty bomb. StuRat (talk) 12:37, 17 June 2010 (UTC)

The other significant thing to note about Chernobyl is that it didn't fail during normal operations. They were actually experimenting on one of the two reactors - seeing if shutting off all of the safety systems and cutting primary power to the coolant pumps would allow time for the backup systems to kick in. All it took was one actual failure of backup systems during the experiment to kill the system and cause a catastrophic cascade of events that lead to the ultimate disaster. That kind of experimentation on a live reactor was just a crazy thing to be doing. Read the timeline of events in our Chernobyl disaster article and you'll be horrified at the stupid risks those guys were taking. These days we could do much of that experimentation in software simulators and only do verification of those test results on the live reactor...and I'm sure that the protocols for doing that are much stricter than they were back then. These risks are highly manageable - unlike in coal mining and oil drilling where loss of life is seen as an inevitable part of the operation. SteveBaker (talk) 11:48, 17 June 2010 (UTC)

However, we should plan for the worst case scenario. Based on the Gulf oil spill, we should expect the following:

1) Like BP, any company running a nuclear reactor may lie to regulators about their ability to prevent an accident, their ability to stop an accident in progress, their ability to clean up after, and the magnitude of the accident, once it occurs.

2) Also assume that the company will ignore all safety rules and regulations.

3) Like now, government regulators can be assumed to be both incomptent and in the pockets of the industry they are supposed to be regulating, thus effectively shielding the private company from public scrutiny and criticism while providing zero regulatory control.

So, then, can we come up with a design for a nuclear plant which is still safe given these assumptions ? StuRat (talk) 12:50, 17 June 2010 (UTC)

The assumptions have actually not proven to be valid. American nuclear regulation is based on defense in depth, with the idea that while it's possible for things to go wrong, you'd need a huge number of things going wrong at the exact same time for a worst-case scenario. The one-in-a-million scenario is not necessarily the one that should bend the entire production line around it, if you can reasonably break the risk into discrete chunks. The one-in-a-thousand scenario, definitely. But in any case, there are many different designs for plants, some of which afford greater inherent protection against serious accidents than others, and I think that the years since TMI in the US have shown that regulation doesn't have to be a bust (we've never had anything even close to it happening happen again in the US, and even then, TMI didn't kill or harm even one person). --Mr.98 (talk) 14:13, 17 June 2010 (UTC)

Why do you say those assumptions aren't valid ? If it can happen in one industry (oil), it can happen in another. Multiple safeguards are good, but can also increase complacency. As in the Chernobyl case, people might reason "we don't have to worry about disabling that safeguard, there are others". I've noticed this myself, when I thought it would be a good idea to have spare car ready to use if my primary car fails. The reality, however, was that one of them would break down, and having another usable car took all pressure off me to fix that broken one, so I always had one broken-down car after that. Putting in too many safeguards can make people just ignore them entirely, like the extreme rules for passwords at EDS which resulted in everyone having such complex passwords that they wrote them down on a Post-It note and stuck it to the computer. Similarly, if people going in the front door of a secure building must undergo the equivalent of a full body cavity search, you will find the back door chained open, with no security at all.

I like the idea of inherently safe designs, like one where gravity will drop control rods into the reactor core in the event of a power failure. Unfortunately, one particularly stupid design had caps on the end of the control rods which reflected radiated particles, thus actually increasing the reaction rate when the control rods first started to lower. StuRat (talk) 14:14, 18 June 2010 (UTC)

Use thorium reactors. Thorium is much more common than uranium, and thorium's most common isotope can be used for fission as-is (unlike uranium). Thorium reactors also produce more power and have even less nuclear waste than uranium reactors. --76.77.139.243 (talk) 12:33, 17 June 2010 (UTC)

However, in the US we have an almost unlimited supply of refined uranium available from decommissioned nuclear weapons. StuRat (talk) 12:42, 17 June 2010 (UTC)

It's not true that thorium's most common isotope can be used for fission. In the presence of neutrons, it can be bred into U-233, which is fissile. This is analogous to the fact that U-238, in the presence of neutrons, can be bred into Plutonium. Both of these still require an existing neutron economy—you need uranium reactors to start the thorium cycle. In any case, in the US, there is no reprocessing currently undergone at all for civilian purposes, the reason being that in the 1970s people got concerned that if you scaled that up to very large volumes, the amount of fissile material loss inherent to the system (say, half of 1%) would result in literally thousands of kg of bomb-grade material not being accountable, and thus presenting incredible possibilities for diversion or theft for terrorist purposes. Now whether that could be overcome, or could just be lived with, is another question, but it's not simply case of dropping in a new technology and calling it a day. --Mr.98 (talk) 14:13, 17 June 2010 (UTC)

It's also unreasonable to assume that there would NEVER be another casualty in a nuclear power plant - every industry has it's disasters (9 people died in a beer industry disaster, 21 died in a Molasses catastrophy) - the key thing is to make them rare and to keep the danger to a minimum. Very few people care for very long when an oil rig explodes and kills a dozen people - but when it does that and dumps a million barrels of oil into the ocean, it's much more significant. When the Piper Alpha oil rig exploded in the North Sea - killing 150 people, it was a major news event - but there was no lasting consequences beyond the immediate families of the victims. But when the Ixtoc I oil spill spewed oil for nine months before it could eventually be shut down - that was a major problem. The fifty or so people who died in the Chernobyl disaster are not the problem - it's the spreading of radioactive dust over half of Europe that really needed to not happen. I don't doubt that we'll someday hear about disasters caused by wind farms and solar plants too - but so long as they don't have frequent or long-term or wide-spread consequences - we can be somewhat relaxed about the risks. What's happening in the Gulf of Mexico right now is firmly in the "Not reasonable" category. SteveBaker (talk) 19:00, 17 June 2010 (UTC)

Keep in mind that nuclear power doesn't just involve fissioning Uranium. You first have to mine Uranium ore, process it and enrich it, all of which must be done with energy, and may result in the burning of fossil fuels. But I suppose that this is not a concern if you have lots of uranium fuel available from nuclear bombs, as StuRat pointed out.Pmdove (talk) 02:25, 18 June 2010 (UTC)

There are lots of other things to take into account, to be sure, but in terms of its net carbon impact, it still beats the pants off of fossil fuels in terms of energy release for carbon cost. I don't know where it stands against other forms of energy, but uranium fission releases so much energy for so little mass/volume that it still probably does pretty well. --Mr.98 (talk) 17:14, 18 June 2010 (UTC)

Nuclear energy actually produces less CO2 per kWh than the "renewable" solar power. IIRC, nuclear power's CO2 production is comparable to that of wind energy. (Of course, all these energy production forms would be able to operate with zero carbon if they had to, just using their own power.)--Roentgenium111 (talk) 18:12, 20 June 2010 (UTC)

star classification

Could a computer scan the sky and classify stars strictly according to their spectra? 71.100.13.202 (talk) 22:46, 16 June 2010 (UTC)

Well, a computerised telescope with a spectrograph attached, yes. In fact, they do. --Tango (talk) 23:02, 16 June 2010 (UTC)

Where is the classification table? 71.100.0.224 (talk) 23:13, 16 June 2010 (UTC)

You may find some useful links within the Astronomical spectroscopy article. The one appearing as "spectral types" links to the rather relevant Stellar classification article. 87.81.230.195 (talk) 23:45, 16 June 2010 (UTC)

Spectrum (correlated to temperature) vs Luminosity is plotted in the Hertzsprung-Russel diagram (along with mass which is formulated within the axes). The "fuzziness" associated in the main sequence line is due to varying element distributions when the star is formed, which is a major bit of information determined by spectrum. Drift, rotational velocity, and at the largest scales, distance, can also be determined from redshift, so there's quite - just about everything, in fact - that one can tell from the spectra alone. SamuelRiv (talk) 01:16, 17 June 2010 (UTC)

There is not a "single" catalog or database of star classifications; every research organization is free to make and use their own system for whatever research needs they have. There are several public, free-of-charge / free-to-use astronomical catalogs. For example, the high-resolution HR diagram from our HR diagram article was made with Hipparcos Catalogue data (and other data). You can access Hipparcos online, provided by Cambridge University; you can construct queries manually or see the help-files for programming your own interface. Nimur (talk) 05:40, 17 June 2010 (UTC)