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December 6

Restriction endonuclease - etymology

What meaning is the word 'restriction' supposed to convey in the term 'restriction enzyme' or 'restriction endonuclease'? --90.219.114.59 (talk) 00:45, 6 December 2010 (UTC)

See Restriction enzyme.Smallman12q (talk) 00:55, 6 December 2010 (UTC)

Before the actual function of restriction enzymes was identified, it was known that many strains of bacteria contained factors that restricted which viruses could successfully infect them. This was late determined to occur as a result of enzymatic cleavage of viral DNA, in research that eventually yielded the first restriction enzymes. See restriction modification system for more information. Someguy1221 (talk) 00:56, 6 December 2010 (UTC)

Bladder - when you're empty, are you really empty?

I just read the article on urinary bladder. It was lacking the one thing I was interested in learning - just after you pee, when you feel empty, are you really empty? How much urine remains if you aren't? I'm guessing this could be estimated with some careful ultrasound work... If you know the answer, please also add it to the article! Thank you! The Masked Booby (talk) 02:23, 6 December 2010 (UTC)

I think the bladder really is empty, as gravity and the opening being at the bottom allows it all to drain out (with the exception of a few drops that adhere to the walls, due to surface tension). However, I've noticed that when I really have to urinate badly, I finish up and then a few minutes later there's more, maybe 1/3 the original amount. I attribute this to urine accumulating in the kidneys, which probably isn't good, as it could lead to kidney stones.[1] Once the bladder is emptied and the back pressure eliminated, the urine is free to quickly drain into the bladder. StuRat (talk) 02:39, 6 December 2010 (UTC)

Hence the phrase, "breaking the seal". Dismas|^(talk) 02:52, 6 December 2010 (UTC)

. . . but on the other hand don't believe everything your read on the internet. Richard Avery (talk) 08:15, 6 December 2010 (UTC)

Inability to urinate properly (start and stop) when wished are common symptoms of Benign prostatic hyperplasia, evident in over a third of men over age 80 years. Cuddlyable3 (talk) 08:16, 6 December 2010 (UTC)

I recall long beer drinking sessions of my youth (totally reformed now, of course!) when the lengths of time between needing to urinate shrank remarkably. Obviously new urine is being produced all the time, so within seconds after urinating a few new drops will appear. HiLo48 (talk) 21:45, 6 December 2010 (UTC)

Alcohol is also a diuretic, so it will tend to increase the frequency of urination. --Jayron32 21:50, 6 December 2010 (UTC)

The bladder is presumably compressed by muscles to empty it, rather than being the equivalent of a stretchy balloon which releases liquid smoothly when the outlet valve is opened. In addition I expect there is a controllable outlet valve equivalent. Is it possible that the described process of "1)pee freely until no more comes out, 2) wait 60 seconds or whatever, 3)pee freely an additional 1/3 or so of the original amount " could result from one mode of contraction (one set of muscles, or one mode of folding) following a different and initial mode? It seems to ask a lot of the kidneys for them to suddenly process such a large amount of urine. As for the "enlarged prostate" theory, if a balloon full of liquid has an outlet tube, and a clamp is tightened slightly on that tube, it do4es not result in an initial free flow of a lot of liquid, followed by a pause with no flow, followed by a second smaller phase of free flow. (This post should probably be signed "I.P. Freely") Edison (talk) 17:44, 7 December 2010 (UTC)

Is there even such a thing as a hybrid motorcycle?

The last time I looked at Harley-Davidson's product line, I didn't see such a motorbike.

I think I should help the environment even better than a Prius by having a hybrid motorcycle, but what marques have one? Thanks. --Let Us Update Wikipedia: Dusty Articles 06:01, 6 December 2010 (UTC)

According to this article from 2008, Honda is developing one which should be out in the next two years. So they have 25 days left to make good on their promises! Dismas|^(talk) 06:05, 6 December 2010 (UTC)

This slightly newer source suggests Yamaha is also supposed to have a hybrid motorcycle by 2010 (the above source also mentions Yamaha). They showed something at the 2009 [2] Tokyo AutoMoto Show but no sign since then that I saw. Nil Einne (talk) 07:27, 6 December 2010 (UTC)

A Motorized bicycle is a class of hybrid vehicle. For devoted friends of the environment, electric bicycles are making a comeback, see Hybrid vehicle#Two-wheeled and cycle-type vehicles. Cuddlyable3 (talk) 08:03, 6 December 2010 (UTC)

You would help the environment the most by cycling to work etc. Noodle snacks (talk) 10:38, 6 December 2010 (UTC)

I'm CLEARLY alive-and-well. Why am I STILL barred from donating blood/plasma?

It's only because I lived in Germany in my toddlerhood. They're afraid that I could develop CJD from possibly having eaten contaminated meat there. I thought CJD forms just MONTHS after eating such meat.

I haven't been in Germany in 20 years. I'm obviously still alive-and-well, with no signs of CJD. How long should I be alive & well to prove to a blood bank that I am fit to donate blood or plasma?

(I've been wondering about what could happen from lying about where I've been at some new blood/plasma bank somewhere because I know no harm could possibly come out of my donations. Sure, they'll conduct blood tests, but if I have stayed alive & well for 20 years since being in Germany, there's no way in hell that CJD viroxins will be found in my blood. Anyway, how could they find out about my lie, and what could happen if I did so?)

If there's no way to prove blood banks in the US that I truly am fit to donate, then what other countries would allow me to donate blood or plasma for money? Thanks. --70.179.178.5 (talk) 08:21, 6 December 2010 (UTC)

When was the last time you checked to see if you were eligible? Although the original 2002 restriction was on anyone who has spent more than six months in certain European countries such as Germany, the restriction has since been relaxed to only include people who have spent more than five years there.

Blood tests cannot ensure the safety of your blood, because there is no test to determine if a blood donor is infected while in the latent phase of vCJD.

I'm getting all this information from Creutzfeldt–Jakob disease#Blood donor restrictions. Red Act (talk) 08:48, 6 December 2010 (UTC)

Variant CJD is generally fatal after about a year from when symptoms arise, but some studies have suggested that this or similar prion diseases can have a very long latency period between the exposure and the onset of symptoms. For example, this points to a latency possibly as long as 50 years in some cases. Other researchers think the time is probably relatively short. Without knowing for sure though, it probably makes sense to err on the conservative side, and assume that people possibly exposed to CJD might remain asymptomatic for a long time. Dragons flight (talk) 09:05, 6 December 2010 (UTC)

The incubation period varies depending on how the infection occurs. According to page 85 of this paper, the estimated incubation period in individuals that acquired vCJD from a blood transfusion is 5 or 6 years, but the estimated incubation period in individuals that acquired vCJD by eating contaminated beef is between 13 and 40 years. Red Act (talk) 09:24, 6 December 2010 (UTC)

You might want to look up the source of the restriction in PubMed if you can find it, then email the corresponding author for advice. If anyone knows whether that cost/benefit analysis is still producing the same sign, they would. You can lie, but the penalties might be severe in some cases, including stiff liabilities if you're wrong. I would do a PubMed search for the corresponding author(s)' email address if I didn't have other work at the moment. Maybe someone else trying to answer can find it. Ginger Conspiracy (talk) 09:02, 6 December 2010 (UTC)

Please don't second-guess the established safety standards, and please don't lie to the screeners. This report from the US GAO found that paid donors of plasma products were 1.5 times more likely to donate an infectious unit than unpaid donors. Note also that the viral inactivation/removal strategies used to partly eliminate HIV, HBV, and HCV from pooled plasma products are of limited or unknown efficacy against prion particles. TenOfAllTrades(talk) 13:51, 6 December 2010 (UTC)

My boss lived in Scotland for some time and he is still not allowed to donate blood in Germany. This is really cool. In the US a German is not allowed to donate while in Germany anybody from Great Britain is not allowed. A solution might be donate for a British medical company. You might be a smaller risk than a native UK person--Stone (talk) 18:28, 6 December 2010 (UTC)

I had the same thing happen in Spain. Because I had been resident in the UK they deemed that the risk that I might have CJD was too high. There was not bovine spongiform encephalitis in Spain at that time. Ironically it arrived within 1 year of my refusal. I hate the term 'mad cow disease' because it is so inaccurate. It is a neurological disease not a psychiatric disorder. Richard Avery (talk) 19:58, 6 December 2010 (UTC)

Of course, if they donate in the UK they won't be paid, which they seem to want. 86.161.208.185 (talk) 23:35, 6 December 2010 (UTC)

This is not the language desk and English is my second or third language but are not a donation per definition unpaid, in other cases the blood is sold not donated or am I missing something? --Gr8xoz (talk) 04:22, 7 December 2010 (UTC)

Blood donations by paid donors are still referred to as donations. Blood_donation#Benefits_and_incentives has some information about the distribution of paid/unpaid donation. Sean.hoyland - talk 04:50, 7 December 2010 (UTC)

BSE is a serious risk, but given its risks, it's still a bit of a mystery. There are other possible vectors other than beef, including chronic wasting disease, which is a real concern for wild game. Shadowjams (talk) 11:00, 7 December 2010 (UTC)

I find it odd that I can't give blood in the UK now because I had a transfusion in 1981. Surely anything I caught would have become evident by now?Zzubnik (talk) 14:50, 7 December 2010 (UTC)

See the comments above about prion diseases. The latency period is poorly characterized and probably variable, but may run into decades — and there isn't any sort of reliable blood test, so we can't screen for it in donated blood. TenOfAllTrades(talk) 15:31, 7 December 2010 (UTC)

Normal decibel level in an office?

Are there any studies showing the average decibel level if you are sitting in the middle of an open-plan office filled with 50 people? My Iphone app shows an average of 55 decibels even when it is very quiet (by my own standard), that seems a very high number. I was expecting to read 25 or 35 at most. --Lgriot (talk) 12:52, 6 December 2010 (UTC)

According to this, 55 is just about right. Page 15 of this source lends credence to that figure as well. And finally, this agrees with the 50 db figure. Dismas|^(talk) 13:00, 6 December 2010 (UTC)

The table of examples in our article on sound pressure says that a "very calm" room is 20-30 dB and normal conversation at a distance of 1m is 40-60 dB. Gandalf61 (talk) 13:08, 6 December 2010 (UTC)

Thanks to both! So a conversation is a little lower than half the painful level! My iphone reading is accurate then. --Lgriot (talk) 14:08, 6 December 2010 (UTC)

In decibel scale, a 3dB increase is a doubling of the power, however the human ears exhibit a logarithmic response. CS Miller (talk) 14:53, 6 December 2010 (UTC)

Makes sense, so 60 db isn't half as intensive as 120 db, it is 20 times halved!!! Thanks --Lgriot (talk) 16:34, 6 December 2010 (UTC)

... or, slightly more accurately, one millionth of the power, because one "bel" represents a factor of ten in the power. Dbfirs 17:12, 6 December 2010 (UTC)

Brine instead of broth

Let's say I'm making a soup or bisque or something in which one of the main dry ingredients is olives. Rather than boil them in chicken/vegetable broth, would it be acceptable to substitute olive brine? Or would the chemical properties be different? I understand that broth generally has some fat in it, so maybe it would behave differently. LANTZY^TALK 13:39, 6 December 2010 (UTC)

Broth also usually contains stock as well, since most broths are made with bones as well as meat (technically, broth is made from meat, and stock is made from bones) and so broths often contain a sizable amount of gelatin. Many times, the "fatty" taste of broths are actually not fat at all, but gelatin, as gelatin adds that "slick" or "unctuous"(to use the chef's term) mouthfeel without adding fat. Also, since cured olives tend to be very salty, one of the purposes of reconstituting them in chicken broth would be to dilute the saltiness; reconstituting them in brine wouldn't accomplish this. The excess saltiness of the brine (which is likely much more salty than broth) may throw off the salt balance in the final dish, so be careful. --Jayron32 14:02, 6 December 2010 (UTC)

In that case, perhaps a half-and-half of broth and brine... LANTZY^TALK 17:48, 6 December 2010 (UTC)

Seriously, go for it. A big part of cooking is experimentation; if you have an idea for a dish, try it out. If it comes out awful, then you know your changes to the recipe may have been to blame. If it tastes good, then you just discovered something as well. I myself am an avid cook, and I will say for the record that some of my dishes have resulted in ordering pizza for the night. It happens. --Jayron32 17:51, 6 December 2010 (UTC)

Of course. Where's my spirit of adventure? I just hate the idea of wasting ingredients. In this case I'll go ahead and try it, because olives aren't an extravagance, and brine would just be dumped down the drain anyway. LANTZY^TALK 18:00, 6 December 2010 (UTC)

I think you'll find that if you use enough to taste the olives, the final result will be way too salty. But there is no harm in experimenting, if the ingredients are not too expensive. Looie496 (talk) 22:58, 6 December 2010 (UTC)

Eyeball judder

I'm fairly sure there's a name for this - when one's eyeballs briefly judder, like an underdamped robotic arm. What's it called? 81.131.24.249 (talk) 13:57, 6 December 2010 (UTC)

Saccade, or Physiologic nystagmus. 92.24.184.218 (talk) 14:15, 6 December 2010 (UTC)

Thanks! 81.131.24.249 (talk) 14:25, 6 December 2010 (UTC)

Bismuth oxychloride appearance

Is it shiny (pearlescent) and pale yellow-white? --Chemicalinterest (talk) 14:06, 6 December 2010 (UTC)

Just ordinary white powder. But it's usually tinted beige to darker skin tones in makeup. Ginger Conspiracy (talk) 10:40, 7 December 2010 (UTC)

Sources of gas and electric in the UK

I'm wondering where a) the gas I'm using is coming from - what proportion from Russia, what from the North Sea, etc? b) What proportion of the electricity I'm using is nuclear, wind-power, etc? Thanks 92.24.184.218 (talk) 14:36, 6 December 2010 (UTC)

For electricity, the National Grid show year-average figures on their site at http://www.fuelmix.co.uk/fuel_mix_info.htm/. CS Miller (talk) 15:57, 6 December 2010 (UTC)

Actually, that data seem to be out-of-date. CS Miller (talk) 16:16, 6 December 2010 (UTC)

The latest figures are here[3]. Alansplodge (talk) 10:37, 7 December 2010 (UTC)

A large chunk of the UK's gas supply comes from the Ormen Lange (gas field) in mid-Norway via the Langeled pipeline, potentially supplying 20% of the country's needs on its own. Mikenorton (talk) 23:51, 6 December 2010 (UTC)

This article[4] says that imported gas exceeded home production for the first time in 2010. Alansplodge (talk) 10:37, 7 December 2010 (UTC)

This graph[5] (on page 7 / 17) gives a projection of imports by type to 2024.

The very rough figures for 2009/2010 are:

50% - UKCS = UK Continental Shelf,

25% - Norway

15% - LNG = Liquefied natural gas imported by ship from the Americas and Middle East.

10% - BBL = Balgzand (Netherlands) to Bacton Line, which links to Nord Stream, the Russo–German gas pipeline. Alansplodge (talk) 11:56, 7 December 2010 (UTC)

simple:Halophile

Under the life style section, do I have the osmosis description correct? Thanks, Albacore (talk) 14:44, 6 December 2010 (UTC)

You may want to put a little clarifying statement at the front, something like "In osmosis, water tends to move from inside the cell to outside, in order to balance the salt concentrations on both sides of the cell membrane" or something like that. Your statement is correct, but may be unclear for someone who has never heard of osmosis. --Jayron32 15:03, 6 December 2010 (UTC)

I've looked for examples of slight halophiles, moderate halophiles, and extreme halophiles, but couldn't find any specific examples. What are some examples of each? Albacore (talk) 17:48, 11 December 2010 (UTC)

Color in anodization

How does color in anodization change the recyclability of aluminum components? /130.236.40.119 (talk) 14:53, 6 December 2010 (UTC)

Probably the way that your textbook tells you that it does. Or, perhaps, the way your teacher told you that it does in lecture. --Jayron32 15:04, 6 December 2010 (UTC)

Considering your quirky response I'm assuming you think this is some kind of homework, since this isn't the case I'd appreciate a serious response or non at all, thank you./90.239.94.250 (talk) 20:04, 6 December 2010 (UTC)

I don't believe it makes any difference. The color is various organic dyes that will just burn off when the aluminium is melted. The anodize article mentions that tin can be used as well, but I don't think that will be a problem - in general recyclers are geared up to handle mixed metals (no batch can possibly be perfect after all). Ariel. (talk) 21:40, 6 December 2010 (UTC)

Why Lorentz Transformation (LT) is correct?

The Reference Desk is not a forum for presenting novel physics theories. Please stop reposting your original work. TenOfAllTrades(talk) 15:44, 6 December 2010 (UTC)
The following discussion has been closed. Please do not modify it.
I think it is because Lorentz is very lucky. Why? I have at least three reasons: 1. Because there is a Galilean Transformation (GT) ready for him so that he did not have to establish his famous theory from scratch. 2. When he applied “ruler contraction” to GT and established x'=γ(x-vt), he was correct by pure luck. You see, before the origin point O’ of the moving system S’ meets the origin point O of the rest system S, we have x’-OO’ = x and after that we have x’+OO’ = x; so that based on OO’ = v|t’| as measured in S’ we should have x’= γx-vt’, not x'=γ(x-vt). But then why LT is correct? 3. Lorentz is so lucky that I can show you t’= γt is always true if we apply “ruler contraction” to GT, so that x'= γx-vγt=γ(x-vt) and then x'=γ(x-vt) must be correct! Here is my way to establish t’= γt. 3-1. Let B (b,0,0) be a point in S. When b<0, let observers in S record the time that the origin point O' of S' moves from B to O by Δt = (0-t) and the distance between B and O by BO, we have BO = |v|Δt; let observers in S' measure the time O' moves from B to O by Δt' = (0-t') then we can calculate the distance between B and O as measured in S' by (BO)' = |-v|Δt'. 3-2. Based on hypothesis of ruler contraction, we have (BO)' = γBO so that |-v|Δt' = γ|v|Δt, then we have △t’=γ△t. Since it is the same as (0-t')=γ(0-t) so that t’=γt. That means when O' is at B, the time relationship between S' and S is t’=γt. 3-3. Let us go through quite the same procedure for the rest scenario. When O' is at B while b>0, t’=γt is also true. When b=0, t'=t=0, so that t’=γt. That means we have now derived that for any location of O', t’=γt is always true.Jh17710 (talk) 15:40, 6 December 2010 (UTC) Why Lorentz Transformation (LT) is useful? I think the main reason that we like to keep LT is because most of contemporary physicists believe that LT is correct. If you check all textbooks introduced LT and currently recommended by teachers, you will find out most of them confirmed that LT is correct. However, in the real world, I think LT is useless, why? 1. If we apply the time equation in LT to the spatial equation in LT, we will get the spatial equation of inverse LT, x=γ(x'+vt'). That means, both of LT and inverse LT are coexist at the same time. 2. It is not easy to understand what will happen if constant velocity v and constant velocity –v coexist at the same time. We may think, it will be v=0, but not sue about it. There is a better way to see it clearly. If we put the missing time equation in LT, t’=γt, and the missing time equation in inverse LT, t=γt’, together; let them to coexist, then we can derive γ=1. That means, mathematically we can derive v=0 from γ=1. 3. Since the relative velocity must be zero in LT and in the inverse LT, LT is almost useless in the real world.Jh17710 (talk) 15:18, 6 December 2010 (UTC) Is there a question here? Wikipedia's reference desks are not for making general statements or starting general discussions. If you wish to ask a factual question we can answer for you, then ask. If you wish to invent your own system of physics, please do so elsewhere. --Jayron32 15:33, 6 December 2010 (UTC) I will ask real question next time. Thanks. This is not an obvious question. My question is behind the characters which is "Do you know any textbook states LT is wrong?", I should ask question like that. Sorry for my mistake.Jh17710 (talk) 15:47, 6 December 2010 (UTC) Why Special Relativity (SR) is wrong? I think there are at least two reasons: 1.The main reason is because of LT is correct. Since the missing time equation in LT, t’=γt, must be correct if LT is correct so that the time equation that SR claimed, t’=t/γ, must be wrong. 2. The second reason is interesting. If we assume two clocks A and B have same model number and exactly same clock speed. Then we put them to run at same speed v on two circles of the same radius on one plane with the closest point Pa and Pb apart from each other 0.1 meter away. We also assume that whenever A is at Pa, B is at Pb. Now, we have created a “paradox of clock” in SR. When A is at Pa, we can compare the time of clock A and B; the problem is, since the relative speed between A and B is about 2v, according to SR, their clock speeds should be different so that we have a conflict scenario at Pa and Pb that the clock A runs slower than B and the clock B runs slower than A at the same time.Jh17710 (talk) 15:18, 6 December 2010 (UTC) Look, as I stated above, this is not the place to start a debate or a discussion. In the previous three or four times you have started this exact same discussion, many different editors have explained to you where your initial assumptions were incorrect. Everytime this has been done, you have ignored them and started a new discussion with the exact same incorrect statements. Please stop this, it is becoming disruptive. If you have a factual question that we can answer for you, please ask it. This reference desk is not the appropriate forum to propose wild ideas or to start debates over the validity of established physics. --Jayron32 15:36, 6 December 2010 (UTC)

Thanks for your kindly response. I will stop doing this. I will just ask question.Jh17710 (talk) 15:54, 6 December 2010 (UTC)

I encourage you to read the article Twin paradox that is relevant to your "paradox of clock". Cuddlyable3 (talk) 00:01, 7 December 2010 (UTC)

Physics Textbook

Do you know any textbook states Lorentz Transformation (LT) is wrong? If yes, what is it and what is the main reason? Thanks.Jh17710 (talk) 16:02, 6 December 2010 (UTC)

What you don't understand is that the Lorentz transform is mathematically correct but physically wrong. might help. I do not know LT but google helps.--Stone (talk) 16:25, 6 December 2010 (UTC)

Thanks. Is this a textbook? Do you know any teacher used it as a textbook since year 2005?Jh17710 (talk) 17:44, 6 December 2010 (UTC)

An advanced Google search for the exact phrase "Storm in Physics" (the name of the book) in the .edu domain doesn't turn up one single hit.[6] A search for the exact phrase "Ricardo Carezani" (the author) in the .edu domain[7] only turns up four pages: a page of links in which Carezani is listed in the "Fringe Science" section,[8] a page of links that includes him under a section entitled "UFOs, Fringe Science and Others",[9] a rant by Carezani about how the 126 authors of a paper in Physical Review Letters describing an experiment that showed that neutrinos exist (contrary to Carezani's beliefs) are a kind of "Secret Society" that's publishing wrong and misleading information,[10] and the abstract of a 1982 paper Carezani coauthored describing an experiment which wound up showing that special relativity was correct and Carezani was wrong.[11][12] The search does not turn up anyone in the current educational community who treats his ideas seriously, much less anyone who uses his book for teaching a class. Red Act (talk) 23:34, 6 December 2010 (UTC)

(e/c)You state above, in the thread that has now been closed, "I will ask real question next time. Thanks. This is not an obvious question. My question is behind the characters which is 'Do you know any textbook states LT is wrong?'" How is this question now a "real question"? You do know the answer to that already, right? So what point are you trying to make? WikiDao ☯ (talk) 16:28, 6 December 2010 (UTC)

No, I really don't know. Do you know the answer? My point is, if some textbook states LT is wrong, I like to know what is the main reason that textbook provides. If no one can provide a good answer, then, I know that it is really hard to find one of such a textbook. I really appreciate the help from this open website. Thanks.Jh17710 (talk) 17:44, 6 December 2010 (UTC)

I am not aware of any physics textbook which is both generally regarded as reliable which also states that the Lorentz transformations are invalid or wrong. The world being what it is, I would not be shocked to find if someone had published something somewhere which did state this, but as an educator myself, I have not seen any such textbooks used in any classroom or educational setting. --Jayron32 17:49, 6 December 2010 (UTC)

Thanks a lot, Jayron.Jh17710 (talk) 18:34, 6 December 2010 (UTC)

A transform is not a theory or statement and therefore cannot be right or wrong. This whole section doesn't make the slightest bit of sense. Looie496 (talk) 01:30, 7 December 2010 (UTC)

It could be wrong if there was a mathematical error in it. It could also be considered wrong if it were useless; that is if applying the Lorentz Transformation resulted in incorrect physical solutions; that is if the solution it predicts disagrees with experimental results. As far as I know, neither of this is the case. That is, the Lorentz Transformation is mathematically correct, and consistent with experimental results regarding Special Relativity. --Jayron32 04:55, 7 December 2010 (UTC)

Chicken meat and pork

Does chicken meat contain more harmful microorganisms then pork? Which animal carries fewer pathogenic diseases? Thanks-Shahab (talk) 17:34, 6 December 2010 (UTC)

It would probably be hard to quantify it. If raised properly, with proper waste management and feeding, butchering, and cooking procedures, poultry and pork should be generally safe and free from harmful microorganisms. Contaminants can be introduced at any part of the life cycle of the animal or post-death, whether in the animal's diet or as a result of improper butchering or storage, but I am not aware that any particular animal is more or less susceptible to contaminants as a general matter, as long as best practices regarding raising of the animals and preparation of the meat is followed. --Jayron32 17:47, 6 December 2010 (UTC)

It used to be the case that trichinosis from improperly handled pork was a problem, but due to improved husbandry practices that is no longer the case (at least in the US). There are about 12 cases of trichinellosis reported each year. Compare that to around 140 thousand cases of salmonellosis each year, which can taint any kind of meat, eggs or plants. In short, there is nothing pork-specific that is a big threat, but there are things that can affect any food stuffs. This is different in countries where they feed their pigs meat and garbage. --Sean 19:16, 6 December 2010 (UTC)

If I recall, not all of the trichinellosis cases were caused by pork either. You can get it from improperly cooked wild game. Googlemeister (talk) 19:54, 6 December 2010 (UTC)

However, note that there are significantly more cases of illness from contaminated chicken eggs each year than from either beef eggs or pork eggs. :-) StuRat (talk) 21:31, 6 December 2010 (UTC)

Under ordinary circumstances meat of any sort continues virtually no microorganisms. They get into it only from contamination during processing, and obviously the level of contamination is determined by how the meat is processed. In chicken, however, if the skin is included, it would naturally continue some level of microbial content -- but from a healthy animal, there ought not to be any microbes in muscle-meat. Looie496 (talk) 22:52, 6 December 2010 (UTC)

Looie and StuRat can you give me sources for the above statements. Thanks to everyone-Shahab (talk) 06:20, 7 December 2010 (UTC)

I think you should re-read what StuRat wrote before asking for sources :) Ariel. (talk) 08:33, 7 December 2010 (UTC)

Oops..lol-Shahab (talk) 10:10, 7 December 2010 (UTC)

In the case of trichinosis, it's not a handling issue. The parasite larvae are actually in the flesh itself. But again, it's rare in places with good animal husbandry practices. --Sean 19:59, 7 December 2010 (UTC)

Those aren't microorganisms, though, they are little worms. Looie496 (talk) 20:46, 7 December 2010 (UTC)

In that case, the article needs to make clear (and in an explicit manor) that these are classed as parasitic micro-organisms as it took the use of a microscope to first explain causative agent of these conditions. Who can do that?--Aspro (talk) 21:26, 7 December 2010 (UTC)

I'm not sure that the line between microorganisms and macroorganisms is a sharp one. If the standard is whether or not it can be seen with the naked eye, you are still likely to have differences between the eyesight of the observer and the size of each individual within the species. If a person with extremely sharp eyesight can spot a giant of the species, does this disqualify it ? If a person with only average eyesight can't spot a dwarf or juvenile, does this make it qualify ? Whether the organism is moving, the same color as the background, and in darkness or lit at an angle (so it casts a long shadow) would also come into play. It's a more difficult line to draw than if Pluto is a planet or not. StuRat (talk) 19:00, 8 December 2010 (UTC)

Perfect machines?

Is it possible for an electric space heater to be anything but 100% efficient? If less, where does the wasted energy go? Let's assume the thing is quiet and there are no windows that would let energy escape as visible light. --Sean 19:20, 6 December 2010 (UTC)

An electric device may have a complex impedance, (equivalently, a power factor other than 1.0). Roughly stated, this represents the power that is reflected back to the electric-plant; in other words, it's related to the effect your device has on the efficiency of the transmission line. A space heater rarely has any significant inductive or capacitive component; therefore its reactance is close to zero; but let's assume otherwise for the example. If the space-heater has a non-zero reactance, it means that in addition to the heat it "burns off" inside your house, it's also forcing extra heat to be dissipated in the transmission wires from the electric power station (by reflecting some un-used power that was not burned in your house, back into the transmission wires). It does this by forcing the voltage and current out of phase: "pulling" current from the power station; not using it or burning it; and then sending it back across the transmission wires. As a consequence, it's forcing the power-station to work a little harder for no benefit to you. So, when you measure "efficiency", you need to define how big of a system you care about: if you only worry about home-efficiency, you start measuring at the circuit-box in your garage; but if you care about city-wide efficiency, you need to think about power factor correction on a massive scale. (Electric companies already do this at the power substation level). Nimur (talk) 19:43, 6 December 2010 (UTC)

However domestic electric power is not distributed on constant impedance transmission lines. Cuddlyable3 (talk) 23:47, 6 December 2010 (UTC)

OK, so for the purposes of my power bill they're perfect, but not when considered as part of the power grid. But let's imagine I have a Mr. Fusion in my home that puts off heat. If the purpose of the machine is to heat the home, then it would in fact be 100% efficient, right? I guess it's a philosophical point in that I've always understood 100% efficient machines to be impossible, but if you adjust your desires to have heat -- waste or otherwise -- as the desired result then it is possible. Thanks for the detailed response. --Sean 22:07, 6 December 2010 (UTC)

If you look "wide" enough, everything is perfectly efficient of course, but practically speaking it's not. For example to heat your house with natural gas you need to exhaust the waste products, which will steal some heat. With your Mr. Fusion you also loose some energy in the form of the waste products of the reactor. The bigger issue is how to "concentrate" the energy source. Once you have a concentrated energy source, you can probably get good efficiency, maybe even 100% - but making that energy source in the first place is not 100% efficient. Ariel. (talk) 22:39, 6 December 2010 (UTC)

I suppose that's all true, but the main thing is that the thermodynamic efficiency limit is a technical property of heat engines. It's not a broad statement about the unattainability of perfection in this corrupted world. A perfect heater is a 0% efficient heat engine, which is allowed since 0% is less than the theoretical maximum efficiency. -- BenRG (talk) 07:33, 7 December 2010 (UTC)

And of course that's 100% efficient in the sense that 100% of the energy becomes heat. Not necessarily in the sense that it uses the least possible energy for the given situation. (If it heats your home unevenly you may have to crank it way up so that no parts of your home are uncomfortably cold.) Sorry, I don't mean to keep harping on this point, but it feels important to make sure we don't equate "100% efficient" with "perfect". APL (talk) 02:24, 8 December 2010 (UTC)

(P.S. As a purely philosophical point, I'll bet most heaters make some noise, some small percentage of which would escape your home before it degraded to heat! Probably some EM interference as well? That'll take you down a fraction of a percentage point!) APL (talk) 02:24, 8 December 2010 (UTC)

Relativity and Time Dilation

Resolved

I know that relative time slows the faster one travels, e.g. the twins paradox. I'd read that a difference of nanoseconds can be realised between a transatlantic jet and a stationary atomic clock. What about the international space station? That makes around 15 and 16 orbits of the Earth per day, and clocks up speeds of around 17,500 mph. The ISS has been in orbit for 10 years and 72 days. If I'd put an atmoic clock on the ISS prior to launch, and had kept one near the lanch site. What would the differences in times be? (I'm a mathematician, so I'd like some formulas, and would rather not someone say "a lot".) — Fly by Night (talk) 22:37, 6 December 2010 (UTC)

17,500 MPH is about 0.000026c, where c is the speed of light. Plugging that into the equation for Time dilation#Time dilation due to relative velocity gives the ratio of times (the Lorentz factor) to be about γ = 1 + 3.40x10^-10, which over the course of 10 years 72 days gives a difference of about 3.92 seconds. Red Act (talk) 00:06, 7 December 2010 (UTC)

That's a perfect reference desk answer. You answered my question, and you gave me links for further reading. Thanks for that; it's appreciated! — Fly by Night (talk) 00:10, 7 December 2010 (UTC)

Follow-up

How would one calculate the time difference due to the difference in gravity, and what would that be? WikiDao ☯ (talk) 00:30, 7 December 2010 (UTC)

If I remember correctly, calculate the centrifugal force (acceleration) that is equivalent to the force of gravity you wish to calculate. The linear speed of the rotating body is the equivalent speed. Ariel. (talk) 00:43, 7 December 2010 (UTC)

Per RedAct above the ISS has a time difference of about 3.9 seconds due to special relativity. What I'm wondering is what time difference is due to the difference in gravitational field strength between ground and low-earth-orbit. WikiDao ☯ (talk) 01:11, 7 December 2010 (UTC)

The ISS has an altitude between 278 km and 460 km, so I'll take the average and use a figure of 369 km. Using the equation for Δτ_g at Hafele–Keating experiment#Equations, I calculate the time difference due to gravitational time dilation over 10 years, 72 days to be 0.013 s. Red Act (talk) 01:32, 7 December 2010 (UTC)

Interesting, thanks. :) And I found this cool graphic at Error analysis for the Global Positioning System#Relativity:

WikiDao ☯ (talk) 02:31, 7 December 2010 (UTC)

The Ariel Sharon Diet

People go to extremes to lose weight, and are often willing to seriously jeopardize their health in order to do so. Imagine this: A fat guy flies to Medellín or Bangkok and checks into a clinic, the only one of its kind in the world. He is put in a coma, for several weeks or even months, depending on his wealth and ambition. During this time he receives only a minimum of intravenous nutrition, or perhaps no nutrition at all - merely water with some vitamins. The fat steadily wastes away. That is to say, he starves. Being unconscious, he is spared the unpleasant sensations associated with starvation. No patience or "will power" is required. (Indeed, this is a major selling point of the procedure.) When the subject has reached his target weight, or when his account has been depleted (whichever comes first), his body is gradually reintroduced to solid food (so as to prevent refeeding syndrome), and only then is he revived and discharged. I imagine most western governments would frown on this kind of "therapy", hence its implementation in east Asia or South America or wherever. Never mind the legal and ethical red tape. Never mind the long-term health effects. My question is this: As a quick fix, would it be medically feasible? LANTZY^TALK 22:29, 6 December 2010 (UTC)

Being in a coma increases risks of all sort of health problems and death, from things as basic as bed sores to having health symptoms (like heart pains) they don't communicate to anyone. Wouldn't a less severe version of this therapy be to just lock the person up, and only provide them with a healthy diet, until they reach their goal weight ? Self-control wouldn't be an issue. I suppose they would feel deprived, but They would certainly feel worse upon waking from a coma to find their muscles had atrophied, their skin had deteriorated, etc. StuRat (talk) 22:54, 6 December 2010 (UTC)

"I think they'd get used to a good, healthy diet in a few days and then be OK with it." Pfft, have you never been on a diet? If you're losing weight at any significant rate, you're burning more calories than you're eating, and you feel deprived. Why do you think people yo-yo diet? 86.161.208.185 (talk) 23:21, 6 December 2010 (UTC)

I think I should expand my answer. I'm talking about a HEALTHY diet, by which I mean one that only gradually causes weight loss, say at a pound a week. Crash diets which cause rapid weight loss are neither healthy nor sustainable. Now a diet that causes the loss of a pound a week and is otherwise complete and healthy shouldn't be all that much of a burden to bear. I'm sure the patient would prefer to eat more, and less healthy, food, but being a bit hungry isn't exactly equivalent to torture. StuRat (talk) 04:52, 7 December 2010 (UTC)

The Minnesota Starvation Experiment (see article) studied a controlled weight loss of 25% by under-feeding. The article Starvation is also relevant. The Ref. Desk cannot speculate "would it be medically feasible?", noting that medical ethics demand more than just not quite killing a person.Cuddlyable3 (talk) 23:41, 6 December 2010 (UTC)

When I framed the question, did I not give specific instructions to disregard ethical considerations? I suppose my view of the word "medical" does not necessarily exclude unethical behavior. Blame my background in lexicography. Very well, I withdraw the adjective. Would the procedure I describe be biologically feasible? I do not ask if it would be healthy or conscionable or peachy-keen. And "The Ref Desk cannot speculate..."?? Honestly, Cuddles, do you suppose that I'm planning to open a Coma-Slim weight loss clinic in my basement, and all I need is technical approval from Dumbledore42 on the Wikipedia Reference Desk? LANTZY^TALK 04:33, 7 December 2010 (UTC)

If you are in a coma, and fed minimal calories, you will lose weight. Period. The rest of the procedure is an ethical question; whether the risks associated with a coma are so harmful as to outweigh the advantage from a lower weight. That is 100% an ethical question, because it asks someone to weigh values against one another and choose the least harmful path. Biologically, you lose weight if you take in less calories than you expend. --Jayron32 04:51, 7 December 2010 (UTC)

I would think they could hire people to put you through some kind of electrical workout regimen while you are in your coma to speed weight loss and prevent muscle atrophy. Googlemeister (talk) 17:31, 7 December 2010 (UTC)

the fix here is to not put you in a coma, just keep you pumped full of drugs so that you remain conscious and can eat, exercise, etc. but will have no recollection later. not sure what drugs do that. Gzuckier (talk) 13:41, 8 December 2010 (UTC)

December 7

How to identify something I had photographed in the sky this morning?

Resolved

Dear RefDeskers, this morning, using my 40D with a 24-135 mm lens, I took a shot at a bright object in the morning sky. Turns out it's probably natural in origin, not artificial, because it came out vaguely round. How to identify what it is? Will anyone be able to tell me if I tell you my geographical location and the direction I was looking in? It's Gdańsk, Poland, object almost straight due East, twentyish degrees above the plane of the horizon. Curiosity, yes, nothing more! Cheers and thanks, Ouro (blah blah) 05:01, 7 December 2010 (UTC)

Yourhorizon at Fourmilab shows Venus low on your SE horizon about now, that's probably it. Jupiter is just above it. WikiDao ☯ (talk) 05:29, 7 December 2010 (UTC)

Wow, useful tool! Would be Venus then, though it's much more E than SE over here. Brighter than stars in the sky. Thanks, WikiDao! --Ouro (blah blah) 06:04, 7 December 2010 (UTC)

Earth is about as close to Venus as it ever gets: 0.435 AU at 2010-12-07 6:35:47 UTC. This is almost the closest pass during the entire year. KStars said Venus is around a Magnitude -4.3; Sky and Telescope says -4.8. (Very bright). Nimur (talk) 06:38, 7 December 2010 (UTC)

I'm gonna go ahead and mark this as resolved. Thanks loads, guys! Was worth it getting up early today :) Ouro (blah blah) 06:57, 7 December 2010 (UTC)

There exists lots of software that can show what the sky looked like at a particular time. I like Stellarium (computer program), which is quite user friendly in allowing you to choose a location and a time to see what's in the sky. Buddy431 (talk) 15:50, 7 December 2010 (UTC)

LED Street Lights

My city (Seattle) recently installed new "energy-effecient" LED street lights on my block. They seem awfully bright and I was wondering if they'll dim over time as they get nearer their end-life or if the spectrum would likely be at all adjustable, maybe some way to reduce the "spillover" into bedroom windows and such? Definitely have their upsides it sounds like, but I do find myself suddenly nostalgic at seeing the contrasting dull yellow glow of the old sodium lights. Ah, well. —Preceding unsigned comment added by 67.160.87.224 (talk) 05:09, 7 December 2010 (UTC)

Yes, the primary failure mode of LEDs is to gradually get dimmer. However, they have a very long lifespan. See LED#Lifetime and failure and List of LED failure modes. Red Act (talk) 05:33, 7 December 2010 (UTC)

New LED streetlights may well be part of a street light control system. If you apply to your relevant local authority they may well be able to dim your nearest lights for the hours that you find most annoying. There also seems to be a feedback page at seattle.gov that you could use to register your opinion. Blakk and ekka 15:14, 7 December 2010 (UTC)

This brings up an interesting Q: Could they compensate for dimming of LEDs over time by putting in more than are needed, initially, but leave some off (or at lower light levels) at present, to keep from blinding people ... then gradually turn more on as they dim, so that the final brightness is constant, until they are scheduled to be replaced ? StuRat (talk) 04:51, 8 December 2010 (UTC)

Testing for tobacco use

Resolved

Settle an argument; how long after tobacco use would evidence still be present in a blood sample? --John (talk) 06:46, 7 December 2010 (UTC)

The in vivo half-life of nicotine is only about 2 hours. However, blood tests for tobacco usage also test for cotinine, the primary metabolite of nicotine, which has an in vivo half-life of about 20 hours, and is detectable in the blood for days (up to about a week) after the use of tobacco. See Nicotine#Detection of use and Cotinine#Measure of tobacco smoke exposure. Red Act (talk) 07:37, 7 December 2010 (UTC)

Thank you! --John (talk) 14:55, 7 December 2010 (UTC)

michael douglas

will michael douglas die —Preceding unsigned comment added by 66.66.92.152 (talk) 10:54, 7 December 2010 (UTC)

Yes. Dismas|^(talk) 11:03, 7 December 2010 (UTC)

Eventually. TomorrowTime (talk) 11:06, 7 December 2010 (UTC)

We're all dying, in some sense of the word. Shadowjams (talk) 11:08, 7 December 2010 (UTC)

For reference, this is probably in regards to Michael Douglas, who has said that he has Stage IV Throat Cancer. That is, the cancer has metastasized, or spread through the body. If I understand correctly, cancers that have metastasized are rarely curable, but, depending on the circumstances, may be treated with a varying amount of success. I don't know enough about Mr. Douglas' case to say how it's going to end, but he'll almost certainly die with the cancer, and probably because of it. How long this will take is dependent on a variety of factors. Buddy431 (talk) 15:46, 7 December 2010 (UTC)

Climate change

Resolved

From a synoposis of BBC documentary series "How the Earth Made Us": "Having documented the planetary forces that have shaped the development of civilisations, Iain Stewart discovers how this relationship has been reciprocated. He examines how the advent of farming prevented the world from slipping into a new ice age, and demonstrates why humanity unwittingly caused a catastrophic mudslide in Indonesia." I'm interested in knowing the scientific standing of the idea that the introduction of farming had an effect on global climate. It must be based on at least one scientific paper, but how recent, how established, is this idea? Itsmejudith (talk) 12:51, 7 December 2010 (UTC)

There is this paper:how did humans first alter global climate?. Also we have an article on Climate change and agriculture.--Aspro (talk) 15:15, 7 December 2010 (UTC)

Thanks. The Ruddiman paper is what I was looking for. I should have remembered we would have an article but it doesn't go into the Ruddiman hypothesis. Itsmejudith (talk) 15:40, 7 December 2010 (UTC)

Railgun vs. Coilgun efficiency

Which is more efficient at turning electric energy into kinetic energy? ScienceApe (talk) 14:40, 7 December 2010 (UTC)

My guess is coilgun, but I think these devices are too individual for any overall answer. Especially the coilgun that recycles the energy from each cycle (see the article) would be pretty efficient. Railguns waste a ton of energy as heat - but on the other hand can handle way more power. Ariel. (talk) 12:14, 8 December 2010 (UTC)

Standard practice rounding significant figures

I read in Schaum's Outline of Beginning Chemistry the following: If the first digit to be dropped is a 5, and there are no digits or only zeros after the five, we change the last digit remaining to the nearer even digit. The following numbers are rounded to one decimal place: 5.550 -> 5.6, 5.55 -> 5.6, 5.450 -> 5.4, 5.45 -> 5.4

Is this standard practice? I never heard of this before, and would have thought to make 5.450 and 5.45 change to 5.5 20.137.18.50 (talk) 16:16, 7 December 2010 (UTC)

That's the "Round half to even" method discussed in Rounding#Rounding to integer. See the associated discussion there of the other ways to do it, the pros and cons of them, etc. DMacks (talk) 16:31, 7 December 2010 (UTC)

(ec)Always rounding the mid-point ("xxx.5") up leads to a systematic error - e.g., the "apparent" average value of a collection of numbers is now slightly larger than the true average value if had been computed without rounding. This is problematic because it affects the statistical analysis of huge sets of data. It also affects numerical or computer algorithms because it introduces an error that "grows". This can turn a problem that is analytically stable into one that is computational unstable. We have a complete section at rounding to integer discussing several algorithms, such as "always round up"; "always round toward zero" (... think about what "rounding up" means for negative numbers); "always round toward the nearest even-number"; "pick a random direction to round"; and so forth. In IEEE-754 (the standard for computers to represent fractional numbers), the programmer can specify a rounding algorithm to guarantee a specific behavior. Nimur (talk) 16:32, 7 December 2010 (UTC)

That being said, this is an issue that has pretty much lost relevance in this age of ubiquitous computation -- no sensible programmer would use the rounded data for any kind of important analysis, you'd always use the actual numbers stored to the maximum precision of your database, and if rounding matters at that level, you ought not to be doing that analysis in the first place. Looie496 (talk) 17:05, 7 December 2010 (UTC)

Numerical analysis is the science off determining how to compute accurately - which means correctly accounting for the errors you describe - deciding what precision needs to be stored. In a simple case, like financial mathematics, you are right - a programmer can simply use integer-math where necessary. But in other cases, like scientific computing or controls, this issue becomes much more complicated: suppose you're building an autopilot; sampling flight-data at 10 MHz at 12 bits. If every 10th sample has a 1-bit rounding error, and you're integrating the result for a control algorithm, you accumulate an error of 1 million samples every second. If you didn't realize this, you might start pitching the plane up. Entire textbooks; entire careers, even, are made on the subject of correct numerical handling to make sure you are not running up accumulated error. Rounding Errors in Algebraic Processes, Error, Accuracy, Stability] (from the infamous Numerical Recipes). In this era of ubiquitous computing, no sensible programmer should assume that "the computer will just do math correctly" - for mission-critical systems, programmers need to actually understand the way calculations are performed and how to manage them. Nimur (talk) 18:09, 7 December 2010 (UTC)

In this day and age, I would think any analysis with a large enough amount of data for rounding rules to matter would be done by a computer. Most likely the numbers will be in binary form when the rounding is performed. So when analyzing how different rounding rules might affect a result, the radix of the number at the time of rounding must be considered. Jc3s5h (talk) 17:16, 7 December 2010 (UTC)

This has the interesting(?) side effect that, in Windows, UNIX and OpenVMS at least, if you add 2⁵² (4,503,599,627,370,496) to a number then subtract it again, the result is the number rounded to the nearest whole integer. Gzuckier (talk) 13:52, 8 December 2010 (UTC)

Transduction, transformation and transfection

Do these terms actually apply only to particular cell types (e.g. pro- vs eukaryotic)? If so, is there a pragmatic reason? --129.215.47.59 (talk) 21:44, 7 December 2010 (UTC)

Our transfection article explains these distinctions right at the top. Looie496 (talk) 22:30, 7 December 2010 (UTC)

Sun-Jupiter Barycenter

How far above the surface of the sun is the Sun-Jupiter barycenter? ✍ (talk) 21:58, 7 December 2010 (UTC)

About fifty thousand kilometres, as I just calculated but is anyway stated at barycenter. Algebraist 22:04, 7 December 2010 (UTC)

I don't see it. ✍ (talk) 14:35, 9 December 2010 (UTC)

The examples table at barycenter has a Sun-Jupiter row where r₁ - R₁ = 742,000 km - 696,000 km = 46,000 km. By the way, it seems the center of mass of the whole Solar system moves between inside and outside the Sun (where is it now?). According to my quick calculations it will very rarely be on the opposite side of Jupiter inside the Sun. PrimeHunter (talk) 19:20, 9 December 2010 (UTC)

Bermuda rigs

How good are Bermuda rigs when heading directly downwind? Are lateen sails or gaff rigs any better for this? --T H F S W (T · C · E) 23:32, 7 December 2010 (UTC)

Ask a commercial concern such as http://www.riggingonly.com Ginger Conspiracy (talk) 18:56, 8 December 2010 (UTC)

December 8

tonneau cover areodynamics

A few years back, Mythbusters did a segment comparing the areodynamics of a pick up truck with the tailgate up vs. the tailgate down (with the myth of it being better to have the tailgate down getting busted). Since that time, I have wondered if there have been any studies of the areodynamics of the open truck box vs a tonneau cover vs a fibreglass truck cap. Undoubtedly there are some differences, but are they significant? 99.250.117.26 (talk) 04:13, 8 December 2010 (UTC)

I don't know about studies, but I would think a cover would have to help, because the wind whips around something fierce in an open-bed pickup. A cap is a different matter, since that puts more of the vehicle into contact with fast-moving air, possible increasing drag. StuRat (talk) 04:43, 8 December 2010 (UTC)

Why are the planets almost spherical?

Why are the planets almost spherical? —Preceding unsigned comment added by 125.21.50.214 (talk) 08:23, 8 December 2010 (UTC)

For a detailed discussion, see Hydrostatic equilibrium. The reason is that, when an object reaches a certain size, the force of gravity holding that object together will tend to act uniformly in all directions, compressing that object into a sphere. Planet-sized objects generally meet this definition (indeed, it is one of the definiting characteristics of a planet that seperates planets from other objects, like asteroids). --Jayron32 08:28, 8 December 2010 (UTC)

As long you do not have a strong rotation of a liquid object in zero gravity the sphere is the energetically most favourable form you can have.--Stone (talk) 09:36, 8 December 2010 (UTC)

Because if it's not almost spherical, it is - by definition - not a planet. Mitch Ames (talk) 10:17, 8 December 2010 (UTC)

Sorry, but that definition begs the question, since the definition reads as such because planets are normally almost spherical. If the Earth and the other planets in our solar system most closely resembled a very long cigar, you can bet that the IAU's definition of a planet would not exclude very long cigar-shaped bodies! Thus this definition does nothing to address the OP's question of why the Earth and the other planets in the solar system are nearly spherical instead of, say, most closely resembling a very long cigar. (But you already knew that, that's why your response was small  :) ) 88.182.221.18 (talk) 11:51, 8 December 2010 (UTC)

It's a matter of semantics, I guess, but it depends on how you read the OP's question. If they are wondering why it is that planets formed into rough spheres a few years back, then the hydrostatic equilibrium answer is best. If they are wondering why a planet must be spherical to be deemed a planet, then yes, it's because we are familiar with the shape and put it into the definition of what we call a planet. Dismas|^(talk) 12:02, 8 December 2010 (UTC)

Note that Mars, being smaller than the Earth, gets to have bigger mountains because gravity is less. Gzuckier (talk) 13:56, 8 December 2010 (UTC)

Does that apply to Venus or Mercury as well? If not, I would question that conclusion. Googlemeister (talk) 16:00, 8 December 2010 (UTC)

Venus is not drasticly different in mass from earth. This is confirmed as Maat Mons, the largest shield volcano on Venus is 8 km high as measured from the base. The equivalent peak on earth would be the Hawaiian volcano of Mauna Kea which is 10 km high as measured from its base. Making some allowances for random variables and differing local conditions regarding erosion and composition, these are roughly on the same scale with regard to size. Contrast this with Mars, which is much smaller than earth, at only 1/10th the size, and its equivalent largest shield volcano, Olympus Mons, is 21 km high. --Jayron32 16:17, 8 December 2010 (UTC)

So it seems that it might be correct if venus and earth are roughly equivalent with both mountains and gravity and mars with less gravity has a bigger mountain, but then wouldn't mercury have an even bigger mountain then mars, or would its proximity to the sun prevent that mountain from forming somehow? Googlemeister (talk) 17:03, 8 December 2010 (UTC)

Mercury is too small to have a motlen core or techtonic plates! Is this another blow against intelligent design? Slartibartfast or any other intelligent being would make them cubes so as to make mapping and a whole lot of other things easier. --Aspro (talk) 17:07, 8 December 2010 (UTC)

Mercury also presents interesting problems because of its proximity to the sun; it experiences something like tectonic acivity, though not from inside forces but outside ones. The surface of Mercury is buckled by tidal forces it experiences from the nearby sun. Mercury doesn't have volcanoes, per se, but it does have interesting features like buckles and escarpments and impact craters. See geology of Mercury for more. --Jayron32 17:14, 8 December 2010 (UTC)

Walking on a cubic planet might not be easier when you encountered the transition from one face of the cube to another. Those people who frequently had to cross this divider might be plagued with tendinitis of the ankle or something. Bus stop (talk) 17:12, 8 December 2010 (UTC)

Ah. Now you're trying to baffle me with science :-)--Aspro (talk) 17:23, 8 December 2010 (UTC)

Anticipating the next question. No, a planet does not need to be 'molten' in order to form into a sphere. Rock is plastic when subjected to planet forming pressures. One only has to visit a mine to see upage, downage, etc., as the rock expands in response to the overlying rock (and thus the pressure) being removed.--Aspro (talk) 17:23, 8 December 2010 (UTC)

Volcano benefits?

Do eruption of volcano have any benefits? —Preceding unsigned comment added by 125.21.50.214 (talk) 08:50, 8 December 2010 (UTC)

Volcanoes produce gaseous sulfur dioxide, which reacts with OH and water in the stratosphere to create sulfate aerosols, which contribute to global dimming for a couple years after the eruption. Global dimming helps offset global warming, so that's generally a beneficial thing. Unfortunately, sulfur dioxide and sulfates in the atmosphere also result in acid rain, so the sulfate aerosols aren't purely beneficial. Red Act (talk) 09:51, 8 December 2010 (UTC)

Do volcano play any role in the process of evolution? —Preceding unsigned comment added by 125.21.50.214 (talk) 09:55, 8 December 2010 (UTC)

Some rather basic information about the benefits of volcanoes - As well as Red Act's notes, they can also increase the fertility of land in the area surrounding the volcano and tourism, according to the source

/edit - A better source with some references you may find interesting Darigan (talk)

The Earth's earliest atmosphere came primarily from gasses produced by volcanoes[13], and volcanic gasses were an important contributor to the Earth's second atmosphere (see History of Earth#Origin of the oceans and atmosphere). The beginning of life on Earth occurred toward the beginning of Earth's second atmosphere. So volcanic gasses played an important role in the creation of the environment within which life began. It's questionable as to whether life on Earth would have even arisen at all, if it weren't for volcanic gasses. Red Act (talk) 11:08, 8 December 2010 (UTC)

Farmland near volcanoes has very good soil, and they also attract tourists. Here's a page listing some of the benefits 82.44.55.25 (talk) 12:14, 8 December 2010 (UTC)

Yes, dirt from weathered volcanic rock or ash mixed with local mud has lots of air, plenty of nutrient minerals, and energy sources for both anaerobic and aerobic bacteria; so it makes a wonderful loose richly fertile soil. See [14]. Ginger Conspiracy (talk) 14:48, 8 December 2010 (UTC)

Carbon cycle; carbon dioxide gets quasi-permanently tied up reacting with silicate minerals. When these compounds are subducted they are broken down by the heat underground, and the carbon dioxide gets released back into the atmosphere via volcanic eruption. Gzuckier (talk) 14:06, 8 December 2010 (UTC)

Volcanoes also provide scientists with a method of studying the Earth's interior (such as by sampling gases and magma/lava), and diamonds and other gems are sometimes found in extinct (or at least dormant) volcanoes. StuRat (talk) 14:34, 8 December 2010 (UTC)

I read somewhere that the steam given off by volcanoes is what formed the oceans eventually. Can anyone confirm this? ScienceApe (talk) 15:03, 8 December 2010 (UTC)

Nope, we got the volatiles pounded out of us by the Giant impact hypothesis. The oceans are all imported water. Volcanoes are good for recycling. Planets without them are lifeless. Hcobb (talk) 15:10, 8 December 2010 (UTC)

Pseudo-morning sickness

Some years ago, I would occasionally wake up in the morning too warm, though not really feverish, and nauseous at the thought of food. I was never noticeably ill apart from those symptoms, and it was always gone by midday. What might have been going on? As this isn't a current issue for me (hasn't happened in probably three years), I'm not really breaking the "no medical advice" thing, am I? ;-) — Preceding unsigned comment added by RandomLurker (talk • contribs) 13:47, 8 December 2010 (UTC)

Maybe you really were too warm. A room temperature which was fine during the day might have been too much when you were under the blankets. The other symptoms might have been a result of being overheated. You didn't list your age and gender, but if you are an older female, perhaps hot flashes due to menopause might also cause such symptoms. StuRat (talk) 13:58, 8 December 2010 (UTC)

What often baffles people (and their GP's) is when they have developed an intolerance to a commonly eaten food. Food intolerance. Some specialist still refer to this by their old names of delayed allergy or masked allergy. As it can take hours for the symptoms to come on, it is very easy to fail to make the connection. Morning fatigue, nausea, feeling hot and a host of other possible symptoms caused by this can often be dispersed by just a bit of vigorous exercise. A good sign that this is indeed the problem is if the exercise initially may one feel a lot worse before feeling better. It is common as well, that the symptoms can change overtime, which adds to the difficulty of working out the cause. Eating a very varied diet appears to help avoid it developing in the first place. --Aspro (talk) 16:55, 8 December 2010 (UTC)

Dreams

When people dream, the content of the dreams is usually stored in short term memory and discarded when the person wakes up. How might a hypothetical human brain be switched to storing dream material to long term memory? 93.85.8.58 (talk) 16:36, 8 December 2010 (UTC)

A voice recorder and/or a notepad and pencil on the nightstand plus a programmable alarm clock telling you to remember to rehearse the memories of your dream as well as you can while you reach for the recorder or pencil and paper. Set the alarm to 2-3 hours before you usually get up so you have a better chance of interrupting REM sleep. Don't be discouraged if you can't remember any dreams -- if you get awoken during non-REM sleep you might not be having any. Please remember that dreams are really strange, and the various theories ascribing meaning to dreams have never been verified. However, if you are struggling through a surrealist writing assignment, no problem! Ginger Conspiracy (talk) 17:12, 8 December 2010 (UTC)

That's the usual method, but it's conceivable that a drug could be invented for this. Current belief is that the storage of memory in the brain depends on a process called long-term potentiation, which strengthens the synaptic connections between neurons. This process has two phases, an early phase that produces a memory trace lasting only a few minutes, and a later "consolidation" phase producing memory traces that last much longer. It seems likely that the consolidation part is somehow suppressed during dreaming, although we don't understand why (it may have something to do with the drastic reduction in norepinephrine during dreaming). If a drug could be invented that would block the suppression of the consolidation phase, presumably the result would be that we would remember our dreams as well as our ordinary experiences. This is of course all very speculative... Looie496 (talk) 17:21, 8 December 2010 (UTC)

There might be a tradeoff. Might you not relegate normal wakefulness memory establishment to a status of secondary importance at the same time that you are elevating the purposeless memory establishment of the dreams that occur in sleep? We establish many memories during wakefulness that are apparently abandoned soon after they are no longer needed. It is just a guess—but our intellectual capacities may be limited to remembering things only to a limited degree. Bus stop (talk) 17:32, 8 December 2010 (UTC)

I'm certainly not saying this would be useful, just that it might be possible. Looie496 (talk) 17:42, 8 December 2010 (UTC)

Dark matter: black holes

It's dark matter awareness week \o/ I attended along with a previous series of cosmology, astronomy, and astrophysics lectures on dark matter and very closely related topics, and have been reading journal and arXiv papers and emailing various experts in the field. I've come to the conclusion that Paul Frampton is right about dark matter being mostly black holes.[15] Is there any observational evidence against this possibility at all?

I've seen so many people spending lots of money looking for nonbaryonic explanations, and they always freely admit that nobody has ever found any evidence for such new kinds of particles, I'm wondering what's going on. The evidence for nonbaryonic cold dark matter is exceptionally flimsy, but it does seem to be entrenched. Why? Ginger Conspiracy (talk) 16:41, 8 December 2010 (UTC)

I think its largely because the evidence for baryonic dark matter, or the "its just a bunch of black holes we haven't accounted for yet" theory is equally as sparse. Dark matter is pretty much an ad-hoc hypothesis to explain certain fundemental deviations from the predicted universe from the observed universe. While there are strong opinions regarding what it might be (or even if it exists at all). It seems likely to exist, given that it is the most plausible explanation for the observations, but as it has never been directly observed, any such propositions are lacking in the sort of verification which would take one proposal "over the top" to become established, accepted theory. What we are left with instead is a lot of propositions of varying likelyhood. Personally, from all of the reading I have done (which is probably not as much as you), I consider myself somewhat noncomittal on the issue. Until there exists some definitive way to verify one of these theories, none seems to be worth "believing in". --Jayron32 16:54, 8 December 2010 (UTC)

There's zero evidence for the new particles, but at least the intermediate-mass black holes have GCIRS 13E and M82 X-1. I think we need microlensing sky surveys (looking for arc and crescent shapes in sky survey data) and better names for these things than GCRIS 13E and M82 X-1. Ginger Conspiracy (talk) 17:10, 8 December 2010 (UTC)

Most physicists accept the conclusions of big bang nucleosynthesis, which models the population of primordial atoms as a consequence of the Big Bang. By looking at the concentrations of hydrogen, helium, beryllium, lithium, and their isotopes, scientists can place constraints on the amount of baryonic matter existing immediately after the Big Bang. The measurements of ~8 different isotopes are mutually consistent with theoretical expectations only if we assume that baryons make up about 3.5 to 5% of the closure density. Estimates of total matter are currently about 28% of the closure density, which is far larger than the uncertainties reported for nucleosynthesis. If most of the total matter were baryonic then nucleosynthesis would predict primordial concentrations of deuterium and lithium that differ by more than an order of magnitude from their observed values. Of course it is always possible that something is wrong with either the theory or the measurements, but because it is a relatively simple theory constrained by multiple independent measurements, most people give it a lot of credence. The implication though is that most of the mass in the universe must be in some form other than baryons. Whether that is WIMPs, primordial black holes, sterile neutrinos, axions, or something else is still a matter of debate and active searches. (Note: Primordial black holes are consistent with the nucleosynthesis results only if they form before nucleosynthesis. Black holes created afterwards wouldn't be able to explain dark matter in a way that is consistent with nucleosynthesis.) Dragons flight (talk) 17:18, 8 December 2010 (UTC)

After more than a month of searching, I haven't been able to find the source for the deuterium and lithium predictions. Do you know where that comes from? If it is from [16] then which passages in it actually support the assertion? Ginger Conspiracy (talk) 17:48, 8 December 2010 (UTC)

Many places. For a recent review, you might try: [17] For an older, and somewhat more technical discussion, perhaps: [18] Dragons flight (talk) 18:04, 8 December 2010 (UTC)

Thank you! Ginger Conspiracy (talk) 18:46, 8 December 2010 (UTC)

Cheapest source of ethanol for sterlisation

At my institute, from the "Stores" department, which stocks most commonly used materials, we can get 2.5l 96% ethanol for just over £8 or 2.5l absolute ethanol for just over £6. Obviously there's something wrong if the prices are that way around. Does someone know a cheaper source of ethanol (for sterilisation purposes), taking into account delivery charges? ----Seans Potato Business 17:21, 8 December 2010 (UTC)

Well, you could check the local drug store, er, chemist. That seems like a pretty low price, though, considering all the higher expenses involved in running a lab. Looie496 (talk) 17:29, 8 December 2010 (UTC)

Depends what you are trying to sterilise. Industrial alcohol is used for hypodermic syringes and things. That's usaly cheaper (well it is where I am).--Aspro (talk) 17:28, 8 December 2010 (UTC)

Not necessarily. As alcohol distills as an azeotrope, absolute ethanol is usually produced by desiccating it with benzene or some other organic molecule. It would be easy enough to leave just enough benzene in the resultant product to render it denatured alcohol, unfit for human consumption. For that reason the absolute ethanol might not be subject to alcohol excise taxes, rendering it cheaper. (£1 per liter does not sound excessive for excise taxes). The cheapest alcohol you'll likely find would be methylated spirits sold by a (house) painting supplier, although whether or not that meets your requirements is another question. Usually there are enough legal and administrative hassles with the purchase of alcohol that most institutions find a single supplier policy is less expensive/easier in the long run, even if some other company has a cheaper sticker price on some item. (P.S. suppliers and shipping costs are likely going to change based on location. Use of £ indicates UK, but where in the UK? London? Glasgow? Belfast? Douglas, even?) -- 174.31.212.34 (talk) 17:39, 8 December 2010 (UTC)

Fully denatured methylated alcohol leaves a residue and so does surgical spirit. So really need to know the application. --Aspro (talk) 17:48, 8 December 2010 (UTC)

For a country like the UK you can usually get referrals. This company came up top in a Google search. Call them and see if you're in their delivery area, and if not, ask them who they recommend who is. It looks like you need to fill out a free customs form if you're a non-consumption user to avoid the £20/l tax. Ginger Conspiracy (talk) 19:01, 8 December 2010 (UTC)

This isn't what you asked, but for sterilization 70% alcohol works better than 96%. Ariel. (talk) 20:02, 8 December 2010 (UTC)

That surprised me, and I checked - it seems to be accurate. I searched for "sterilization 70% ethanol" and found this book, Disinfection, sterilization, and preservation, with a chapter comparing efficiency of sterilization with various types and grades of alcohols. It seems that in most cases, 70% ethanol kills microbes faster than 95% ethanol. In some cases, the reverse has been shown. It seems to depend on the type of substrate (glass, counter-surface, organic matter, etc.), and the species of bacteria to be destroyed. Nimur (talk) 20:41, 8 December 2010 (UTC)

I think we can safely presume that the OP already knows the strength of alcohol to use, what he's asking for is the cheapest way to achieve sterility. I was encouraged to use isopropyl alcohol when ever possible as it was the cheapest (I don't know about current prices) but in some applications its toxicity may be problematical if there is going to be some residue left behind. The NHS uses industrial alcohol and you can't go much wrong with that. --Aspro (talk) 21:01, 8 December 2010 (UTC)

Synthetic Organic Schemes for Pharmaceutical Compounds

I'm interested at looking at the synthetic reactions used to synthesize pharmaceutically relevant compounds. I'd prefer the reaction schemes used for commercial production, but schemes for the original synthesis would be fine, too. Does anyone know of a compilation (e.g. a website or a book) of the reaction pathways used to synthesize commonly used drugs, or would I have to assemble them drug-by-drug? -- 174.31.212.34 (talk) 17:24, 8 December 2010 (UTC)

There are some books with lots of them collected. K. C. Nicolaou's Classics in Total Synthesis has some ones that are significant (milestones in methodology or structure, etc.). Many recently-developed/currently-used prescription drugs are probably covered by patents and/or obscurely described and/or non-published (gotta protect that income stream!). Journals like Chemical Reviews have articles about classes of them (for example, lots of synthetic approaches towards a common type of structure). But there's no general compilation of them all...too many, too rapidly changing, to redundant or no value-added vs the individual literature for each. DMacks (talk) 18:18, 8 December 2010 (UTC)

The information you want is spread out in hundreds of journals, books, patents, and even web sites, but there are some databases which try to aggregate it. However, the Chemical Abstracts Service indexes by compound so once you get used to searching it (and there are a lot of programs to help you enter structures, substructures, and do various forms of pattern matching on structure, composition, and reaction surface geometry, even) then you still need access to a large college or university library journal subscription services if you need to do dynamic searching. If you are just starting out you might be more comfortable with SciFinder CAD searching but if you think you can handle a text interface then STN may be for you. Or maybe it sounds like you only need the SYNTHLINE database, which costs $200/hour to search plus $1.50 per bibliographic record or $40 per synthesis record. Ginger Conspiracy (talk) 18:28, 8 December 2010 (UTC)

Alternatives to silicon for computers?

Suppose that silicon were (somehow) rare and pretty expensive. What other materials could we use to make semiconductors? This is for a sci-fi story I'm working on, so I'm looking for something that could be accomplished by a culture with technology no more advanced than our own -- I thought about vacuum tubes but my understanding is it would be extremely difficult if not impossible to build modern computers that aren't the size of houses using them (and even then still pretty tough). Thanks for your help. 96.246.58.133 (talk) 18:56, 8 December 2010 (UTC)

List of semiconductor materials. You can also make transistors out of carbon nanotubes, but that's very new, expensive, and might end up being impractical or otherwise esoteric. Ginger Conspiracy (talk) 19:05, 8 December 2010 (UTC)

There is also the question of developing light-based transistor alternatives rather than semiconductor-based. --Jayron32 19:09, 8 December 2010 (UTC)

Yes, optical computing, about as far along as the carbon nanotubes these days, which isn't saying much (no x86 compatible ICs with millions of gates for at least the next 2-5 years, for both.) Ginger Conspiracy (talk) 19:24, 8 December 2010 (UTC)

Okay, wow, thanks. Useful list. Offhand do any of you guys know why silicon is preferred over anything else? I'd assumed price, but some of those don't seem like they'd be very rare. Is it just institutional, ie the first transistors were made with silicon and its just what everyone is used to? 96.246.58.133 (talk) 20:02, 8 December 2010 (UTC)

Actually, the first transistors were not silicon. The first semiconductor diodes were metal/oxide P-N junctions (anecdotally, discovered "accidentally" using oxidized/rusty nails, or delicately balancing a wire against galena or other rock/mineral); and the first practical transistors were III/V semiconductors (see History of the transistor, particularly William Shockley's germanium triode). Silicon, as a semiconductor, requires doping, and by most metrics, silicon is an inferior semiconductor to 3-5 materials. But it is cheap, and it is easy to mass-produce, and it does not "gum up the machinery" as much with impurities, so it is easier to have extremely high quality clean-room and clean-process environments. It is cheaper to acquire raw materials for silicon processing. Modern technologies (that is, things invented in the 1930s-1960s) like feedback control made it possible to deal with the crummy performance of silicon; and the adoption of CMOS over bipolar junction transistors gave silicon a distinct advantage. Finally, the semiconductor era quickly gave way to the digital VLSI era - so it became more important to pack very many small devices very densely (instead of worrying about the quality and electrical performance characteristics of each device). So silicon CMOS VLSI is now the standard for most computer electronics (though it is not the clear winner for technologies like wireless radio, optical (LED and photosensor) electronics, nor for high power systems like solid state relays and power transistors, nor for radiation hardened electronics for spacecraft or scientific applications. This introduction to integrated circuit design gives some good comparisons between bipolar and CMOS (and while you can implement either process on almost all types of semiconductor substrates, in practice, silicon is used for CMOS processes, and alternative technologies are not). Nowadays, if you want to design a semiconductor circuit, your first decision is silicon or not silicon - every performance-spec, theoretical/practical design process, software EDA tool, and even the factories or countries that you can use to manufacture your circuit, will depend on this choice. Nimur (talk) 20:59, 8 December 2010 (UTC)

When I taught basic electronic components in K-8 classes (long long long ago), I used water. A semiconductor is anything that somehow changes the flow of water. A resistor is a narrower tube. A diode is a one-way valve. A transistor is a valve controlled by pressure on a plunger. There is no reason you couldn't make micro-versions of all plumbing components and push water through them instead of electrons. Of course, water molecules are tremendously larger than electrons, so you will never achieve the same compactness. For a modern computer, you'd still be looking as a device about as large as a room. -- kainaw™ 19:19, 8 December 2010 (UTC)

I'm irresistably reminded of the MONIAC Computer. 87.81.230.195 (talk) 20:21, 8 December 2010 (UTC)

There are plenty of ways to compute mechanically, which circumvents the need for semiconductors. See e.g. Analytical engine. Using current technology, compact and powerful (though not very general) computers can be built, see e.g. [19]. SemanticMantis (talk) 20:06, 8 December 2010 (UTC)

Reed relay computers can be built, too. They are more compact than vacuum tubes, but suffer from reliability problems. Nimur (talk) 20:32, 8 December 2010 (UTC)

Water molecules (~3Å) are quite a bit smaller than the feature size of state-of-the-art CPUs (~320Å), but water is too sticky to force through a pipe that small. I suppose you could make a compact liquid-based CPU with superfluid helium, but it's not very practical. -- BenRG (talk) 02:49, 9 December 2010 (UTC)

volcanoes

i have been searching for the deration of a volcano. what is it? 24.45.91.137 (talk) 20:40, 8 December 2010 (UTC)

Do you mean duration of a volcano? Mikenorton (talk) 20:43, 8 December 2010 (UTC)

yes that is what i mean. 24.45.91.137 (talk) 20:59, 8 December 2010 (UTC) —Preceding unsigned comment added by 24.45.91.137 (talk) 20:53, 8 December 2010 (UTC)

There is no fixed duration, they can last from day to years. According to volcano: "The lifespan of a volcano can vary from months to several million years" Ariel. (talk) 20:59, 8 December 2010 (UTC)

and one more thing would 1980 eruption of mount saint helen's be cosidered one of the worlds worst volcano eruption? 24.45.91.137 (talk) 21:07, 8 December 2010 (UTC)

Far from it. See our article on Volcanic Explosivity Index and our list of largest volcanic eruptions for starting points, and note that you'll have to define the criteria for "worst" (largest? longest? most casualties? most monetary damages?). — Lomn 21:13, 8 December 2010 (UTC)

Based on any metric, Mt. St Helens isn't a superlative in any category except "Was in the continental United States", That's probably the only reason it was so memorable. It should be noted that the term "volcano" is very broad, it describes a VERY wide range of structures and events which are only very loosely related. Shield volcanos like Mauna Kea are very different than Stratovolcanos like Mount Pinatubo and Mount Vesuvius, and neither one is very much like Cinder cone. Other than the general "hole where stuff comes out of the earth" classification, none of these types of volcanoes has much in common. The erupt very differently, they have very different structures, etc. etc. In general the most destructive type of volcano is a Stratovolcano; all of the really bad "explosive" type eruptions are associated with them. On the other hand, eruptions like Kīlauea (a shield volcano) tend to be not all that destructive comparitively speaking; Kīlauea has been erupting more or less continuously since 1983, and it could best be described as a major annoyance. It does cause some considerable property damage when a lava flow takes out some structures, but it isn't "dangerous" in the sense of killing people like Stratovolcanos are. --Jayron32 21:32, 8 December 2010 (UTC)

Although a shield volcano can also do a lot of damage if the eruption is extensive enough. For example the eruption that produced the Siberian Traps is widely believed to have been responsible for the Permian–Triassic extinction event, the greatest mass extinction in geological history. Looie496 (talk) 21:58, 8 December 2010 (UTC)

Actually I heard of a one in lake toba Indonesia that when it erupted that it effected the entire human population and nearly drove us to extinction. Also other other bad eruptions was mount vesuivus at 79 AD produced its famous eruption burying the roman cities of pompeii and herculaneum. Mount Pinatubo in the philipines island of Luzon, Mountserrat in either the leeward islands, Mount Tambora in Indonesia causing the year without a summer. These are few of the famous ones but they are others. --213.94.237.14 (talk) 21:44, 8 December 2010 (UTC)

See Toba catastrophe theory. Looie496 (talk) 22:00, 8 December 2010 (UTC)

Some Large igneous provinces can last very long. Also, the Yellowstone supervolcano has been around for over 20 million years, and the Hawaii hotspot likely for over 80 million. ~AH1^(TCU) 03:45, 11 December 2010 (UTC)

In order to calculate the lifespan of a volcano, you need to know its geological pressure isosurfaces, which aren't always available from seismic studies. You may need active seismology (e.g., setting off underground explosions to listen to their echos) with a good understanding of the speed of sound in different pressures, temperatures, and compositions. That means you may need to drill for core samples to get complete information, too. It is a very difficult problem, but not insurmountable. Ginger Conspiracy (talk) 05:26, 11 December 2010 (UTC)

Multiforce members (statics)

Hello,

I did a test yesterday. Got about half way in to the question, then hit a wall. Where do I go from here? I've labelled all the external forces. A and G are hinge supports. The external reactions I am fine with. A sum of the moments at A or G combined with a sum of the x forces reveals Ax and Gx to equal 28 and 32 kN, respectively. The sum of the y forces is thus = 0 = Ay + Gy + 20 kN

EG is a two-force member, and is under 28kN of compression. And then.... I can't go further because the forces acting at D are unknown no matter which of the remaining three members I analyze. If I perform a moment equation at D, all the numbers contradict one-another.

Where do I go from here? - ʄɭoʏɗiaɲ ^τ _¢ 20:40, 8 December 2010 (UTC)

It might help if you told us what question you were supposed to answer. Looie496 (talk) 20:58, 8 December 2010 (UTC)

Standard analysis. Need to find all the internal forces acting on each of the members. - ʄɭoʏɗiaɲ ^τ _¢ 21:55, 8 December 2010 (UTC)

You seem to be ignoring gravity, is that appropriate here? Dragons flight (talk) 22:06, 8 December 2010 (UTC)

No, the weight of the members themselves is not included, and the structure is assumed to be motionless (statics). - ʄɭoʏɗiaɲ ^τ _¢ 22:19, 8 December 2010 (UTC)

Some length seems to be missing, either length AB or the distance from member CE to the axis at which the 20kN force is applied. Do you have this info anywhere ? Also, we'd like to see the calcs you did that appear to get contradictory results. StuRat (talk) 00:21, 9 December 2010 (UTC)

EG is a two-force member, so the stress on EG is purely compressive, and that compressive stress on EG is purely horizontal, so Gy=0. Setting the sum of the y forces to 0 then gives Ay=-20kN. Red Act (talk) 01:30, 9 December 2010 (UTC)

Sorry, made the diagram quick and left that measurement out. It's 0.4 m between A and B.

For member CDG:

• SumM@D = 0 = (20*0.6) - (40*1.3) + (32*1.3) - (Fc*1.2)

That means the x-component of the force acting on B of member ABC must be 26.67 kN ( 28 - 1.33 ). The 4/3 ratio of BCD means the axial force of that x-component is 5/3*26.67 = 44.44445... And if I keep going things just get worse and worse. Not to mention the sum of the x forces on CDG not equalling zero. - ʄɭoʏɗiaɲ ^τ _¢ 03:27, 9 December 2010 (UTC)

You don't seem to be considering that the 20kn Y force at the end of the member encompassing BD is not applied directly at D but 0.3m away. Arakunem^Talk 20:49, 9 December 2010 (UTC)

Yep. Got the results back today and that was exactly the problem. I should analyze BDE to find the x component at D, and then a sum of x's on the same member to get Cx. Using that, I analyze ABC to get the x and y component at B and perform a check with member BE - ʄɭoʏɗiaɲ ^τ _¢ 02:21, 10 December 2010 (UTC)

How can this ignore gravity and not be a homework problem? Are ISS astronauts posting questions these days? Ginger Conspiracy (talk) 05:27, 11 December 2010 (UTC)

Acid with nylon

What is the chemical equation for adding an acid (such as sulfuric acid) to nylon?David255 (talk) 23:57, 8 December 2010 (UTC)

There's one given in the nylon article. DMacks (talk) 00:27, 9 December 2010 (UTC)

So nylon + dilute acid -> carboxylic acid + amine via nucleophilic substitution?David255 (talk) 01:14, 9 December 2010 (UTC)

See Nucleophilic acyl substitution for the mechanism. Physchim62 (talk) 01:32, 9 December 2010 (UTC)

So I take it my equation is right? Thanks for the link...didn't realize there was an article on that!David255 (talk) 01:39, 9 December 2010 (UTC)

December 9

Math problem

I'd ask this at the Math reference desk, but I'll ask it here for two reasons:

1. The math reference desk is stagnant and

2. It's probably not that a difficult problem.

The problem states:

Your chores for the week are to cut the grass, wash the car, clean your room, clean the garage, and shine your shoes. You are to do 1 chore each day from Monday through Friday. You can do a chore on whatever day you want, except that you must wash the car either Thursday or Friday. In how many different ways can you perform the chores?

To solve the problem, I'd take 4!, 4!, 4!, 4!, (the days of the week for the 4 chores) and 1! (the days of the week for the other chore), and add those together to get 17!. Then, I'd take that 17! and divide it by the four 4!s for something like:

17×16×15×14×13×12×11×10×9×8×7×6×5×4×3×2×1

---

4×3×2×1×4×3×2×1×4×3×2×1×4×3×2×1

And would end up with 1,072,071,000 different ways. That seems a bit excessive. Where, in my work, did I go wrong? Thanks in advance, Albacore (talk) 01:42, 9 December 2010 (UTC)

It's only 2 × 4! = 48. There are two choices for when to wash the car, then for each, four choices of when to cut the grass; for each combo three choices for when to clean the room, and so on. The reasoning underlying your solution is completely opaque to me. Looie496 (talk) 01:54, 9 December 2010 (UTC)

I concur: 48 possibilities. On Monday through Wednesday, you can't wash the car, so you have only 4 chores available. That means 4 options on Monday; 3 on Tuesday; 2 options on Wednesday. On Thursday you can either wash the car or pick whatever other chore you haven't done yet - so 2 choices; and on Friday, you have no options left. So, 4×3×2×2×1 = 48. Nimur (talk) 01:56, 9 December 2010 (UTC)

I also agree with 48, but I'm curious as to why you think the Math Desk is stagnant. I just came from posting a rather elaborate answer there, source code included, so I can assure you that posts there do get attention. StuRat (talk) 08:03, 9 December 2010 (UTC)

Regarding your reasoning: you cannot add factorials in the way that you do. Consider:

$5=1+1+1+1+1=1!+1!+1!+1!+1!=5!=120$

which I think is false for obvious reasons. There are also not 4! possibilities for each day (other than Thursday/Friday). There are 4 possibilities for the first day; for each of those four, there are 3 possibilities for the second day, and so on. Repeating this for all days is why you use the factorial. The mistakes you made suggest that you need to spend a lot more time practicing combinatorics problems. --superioridad ^(discusión) 01:10, 10 December 2010 (UTC)

Reproduction and rate of erythrovirus B19

Hello everyone. I've been looking around for how Parvovirus B19, the virus that causes fifth Disease, reproduces, and at what rate. Nothing has come of. Do any of you happen to know? Buggie111 (talk) 03:29, 9 December 2010 (UTC)

This recent review article suggests that the cell cycle of the virus is unresolved. However, there is a section on replication and there are a number of references that you could track down to find out what is known about it. --- Medical geneticist (talk) 14:30, 9 December 2010 (UTC)

Potential and kinetic energy

Gravitational potential energy depends on the reference frame or base against which you measure h the height int he formula U=mgh. However you can choose a reference frame arbitrarily so if I were to drop a rock into a river 20 metres below me (pretend I'm on a bridge) rather than choose the surface of the water as is the logical choice I could in theory choose the point where I let go as the base and get a negative potential energy, but this is nonsense. I could also choose the airplane flying above me or the Great Wall of China, for that matter, and get equally nonsense results! It obviously doesn't make sense that a real quantity changes just because you change something on a piece of paper, but that seems to be what the formula implies! What is wrong? 24.92.84.83 (talk) 03:37, 9 December 2010 (UTC)

The sign of the energy is arbitrary to your perspective. If you chose the surface of the water as the "zero point" and thus have "negative energy" compared to choosing the bridge as the reference point, then all of your measurements would be sign-flipped, and the end results would be the same. Its even more arbitrary than that; absolute energy is somewhat meaningless as well, what you are usually measuring is ΔE, not E. What that means is that once you define the "zero point" for your coordinate system, all measurements become relative to that, and ΔE is invarient in absolute value, and the sign is arbitrary, but consistant across whatever system you use. For example, lets say you define the airplane overhead as your reference point. Now, the two points against which you measure the potential energy of the rock are a) the bridge and b) the ground below it. The potential energy is still calculated against that distance; so even if neither of those two points is defined as "zero potential energy", the value of ΔE is the same in all reference systems. Even more significant, the various laws of conservation of mass/energy apply even relativisticly, so that the total ΔE measured by raising or dropping the rock is the same regardless of your relative velocity, etc. --Jayron32 03:59, 9 December 2010 (UTC)

Potential energy can indeed be negative. Potential energy, like many other concepts in physics, may be viewed as a way to describe a system. Whether it's a "real" quantity is ultimately a matter of definition but it's certainly a very practical quantity for making computations of real events, for example predicting how objects will move in relation to a given point when something is done to them. By the way, the strength of a gravitational field varies with location, meaning that g in mgh is not a constant, so the formula mgh is an approximation. It works well for a small bridge on a large planet, but not in some other cases. PrimeHunter (talk) 04:10, 9 December 2010 (UTC)

In real calculations on energy, only the change in potential energy is used (as Jayron mentioned above), so the starting point is irrelevant. The same applies to temperature, where zero can be taken to be any point at or above −459.67°F. Dbfirs 08:44, 9 December 2010 (UTC)

Let's imagine there is an object of weight W newtons on the floor, and I am using the floor as the datum for determining potential energy PE. The object on the floor has potential energy of zero. Now I raise this object above my head to a height of 2 metres above the floor so that its potential energy is 2W Joules. The change in potential energy is:

PE2 — PE1 = 2W — 0 = 2W

So in the course of raising this object above my head its potential energy has changed by 2W. This is positive so its potential energy has increased.

Now let's imagine I am using the ceiling as the datum for determining potential energy. The ceiling is 3 metres above the floor. The object on the floor has potential energy of W(— 3) or — 3W Joules. When I raise this object 2 metres above the floor it is 1 metre below the ceiling so its potential energy is W(— 1) or — W Joules. The change in potential energy is:

PE2 — PE1 = — W — (— 3W) = — W + 3W = 2W

Despite the different choice of datum the change in potential energy is still an increase of 2W. Dolphin (t) 11:34, 9 December 2010 (UTC)

The OP is correct when he says "It obviously doesn't make sense that a real quantity changes just because you change something on a piece of paper". The natural answer to his question "What is wrong" is that potential energy isn't a "real quantity". Potentential energy cannot be measured. Only changes in potential energy can be measured. For advanced readers: The answers in this thread are knowingly or otherwise ignoring any general relativistic implications which make that question much trickier than those answers here would let one on. 71.101.41.73 (talk) 16:16, 11 December 2010 (UTC)

technology run wild stories

I just got an email from a friend linking a fox news report about how credit cards with RFID now make it so easy now to be ripped off by someone simply walking past you and scanning your CC with a RFID reader in the street or a crowd. And surprise! The guy promoting this scare story runs a company that sells wallets which are "scan proof" *sigh*. So I'm working on a blog post about how this is just another "technology run wild" story, and I'm using microwaves and mobile phones and the internet all as examples of technology that was going to "ruin the world" and it got me thinking, I'm quite certain that TV and probably even radio would have had the same type of technophobe movements, but that was before my time, even the printing press was going to ruin the world wasn't it? I wonder if anyone knows about any references relating to this? Stick to my question please, i don't need any more other suggestions for my story, it's pretty much done, this is just the extremely concise version. Vespine (talk) 03:49, 9 December 2010 (UTC)

See Luddite. —Bkell (talk) 04:05, 9 December 2010 (UTC)

Wow that's totally one of those things I SHOULD have known.. I sort of knew how the word Luddite was used, but had no idea how specifically it applied to exactly this situation, great ref thanks.Vespine (talk) 04:52, 9 December 2010 (UTC)

And the form of the word "neo-Luddite" is often applied to modern technophobes. StuRat (talk) 07:57, 9 December 2010 (UTC)

Earliest driven wheels

When were drive wheels or driving wheels invented? In other words, what was the historically first application of applying force to the wheels of a vehicle to provide the necessary propulsion (rather than, say, pulling the vehicle with a horse)? —Bkell (talk) 04:17, 9 December 2010 (UTC)

I thought it might have been a bicycle, but the first mechanically-driven bicycle was invented by Kirkpatrick Macmillan in 1839. Previous bicycles were basically scooters; they moved by pushing your feet against the ground. The first working model of a powered locomotive was built by either by John Fitch in 1794 or by Richard Trevithick in 1802-1804. Since the bicycle is the simplest human-powered drive wheel, and the locomotive the earliest (apparently) engine-powered drive wheel, my bet is on either Fitch's of Trevithick's locomotive. --Jayron32 04:50, 9 December 2010 (UTC)

• Before railway locomotives there was Cugnot's steam carriage. That was 1769. --Anonymous, 21:39 UTC, December 11, 2010.

Wow! Locomotives predate pedal bicycles! I wouldn't have guessed... Vespine (talk) 05:26, 9 December 2010 (UTC)

I wouldn't have either. But History of the bicycle confirms that. --Jayron32 06:49, 9 December 2010 (UTC)

Hmm, I hadn't thought of bicycles. Thanks. Tricycle#History mentions a tricycle made in 1680 that was powered by hand cranks—I assume that must mean it had a driven wheel. —Bkell (talk) 06:59, 9 December 2010 (UTC)

If you include toys, you might find older spring-powered wheel-driven vehicles. StuRat (talk) 07:53, 9 December 2010 (UTC)

I'd be interested in hearing about such toys, too, if anyone can find references to early examples. —Bkell (talk) 08:05, 9 December 2010 (UTC)

The idea of having driven wheels dates to long before that. See the Italian physician Guido da Vigevano designs, which made use of cranks and gear wheels. Crank_(mechanism)#Middle_Ages Maybe the Romans did the same.--Aspro (talk) 14:47, 9 December 2010 (UTC)

Um, humans have had mill wheels for many many centuries. It occurs that by driven wheel you might mean more specifically a wheel which turns as a means of propulsion? Googlemeister (talk) 15:56, 9 December 2010 (UTC)

It's not clear to me, but it seems likely that at least some kinds of pedalo (human driven paddle boat) probably have some form of drive wheel in them. Our article claims that Da Vinci drew one, though I have no idea what sort of pedalo it was or even he was drawing something that already existed or if it was a more hypothetical exercise, like his helicopter. Might be worth looking into, though. Matt Deres (talk) 17:48, 9 December 2010 (UTC)

Hero of Alexandria, who probably lived 10-70 AD, invented a wheeled vehicle powered by a falling weight, as described on this web page. I can't imagine that Archimedes (a few hundred years earlier) would have failed to think of this, but I can't find any explicit description -- unfortunately he himself didn't consider his mechanical inventions important enough to write about. Looie496 (talk) 22:11, 9 December 2010 (UTC)

Is there any evidence he built a working model, or was it all just speculation on his part or the part of those hundreds of years later who wrote about him without much by way of historical record? Edison (talk) 15:52, 10 December 2010 (UTC)

Hero/Heron also made a steam engine, with a rotating sphere, as described in our aeolipile article. This certainly could have been attached to a drive wheel on a vehicle, but I don't believe it ever was. StuRat (talk) 17:03, 10 December 2010 (UTC)

swiss watch

sir,the back side of this watch reads,

                                     cd 3ATM water resistant
                                     christian Daniel
                                     24k gold plated
                                     hardness crystal
                                     swiss Qartz
                                     10MIC     
                                     No.001235

pls let me know the price and manufaturer of this watch.

something i found about this on www.trademe.co.nz but not the informaton which i want with help of google.com —Preceding unsigned comment added by 121.243.158.100 (talk) 04:47, 9 December 2010 (UTC)

Honestly, there's no way that anyone at Wikipedia could appraise this watch. You need to find a reputable jeweller or appraiser if you believe the watch to be truly valuable. --Jayron32 04:52, 9 December 2010 (UTC)

They aren't very valuable -- produced in large quantities and probably worth well under 50 US dollars. Looie496 (talk) 06:38, 9 December 2010 (UTC)

Note that gold plating is different than "made of gold." The actual quantity of gold present is virtually 0 (we're talking micrograms, if even that). You can bet that even a $1 digital watch has a minuscule bit of gold-plating in some of its electronic connectors. Nimur (talk) 17:46, 9 December 2010 (UTC)

Evolution

How ocean and land formed? —Preceding unsigned comment added by 125.21.50.214 (talk) 06:35, 9 December 2010 (UTC)

Our History of the Earth article covers this. Looie496 (talk) 06:39, 9 December 2010 (UTC)

And Geological history of Earth also has some more details. Most of the time when the earth was forming in its current form, with land and oceans and all that, occured during the Hadean eon. --Jayron32 06:47, 9 December 2010 (UTC)

Note that evolution is only concerned with how life progresses after it has come into being. The origins of the first life (on Earth) is abiogenesis, the formation of the first landscapes on Earth is geology, the formation of the early Earth is in the realm of cosmology, astronomy, and cosmogony. Are you implying a reference to Kent Hovid's challenge? CS Miller (talk) 09:23, 9 December 2010 (UTC)

Not strictly true. We often use the term "evolution" to be shorthand for "biological evolution", but evolution just means "gradual change over time". See Formation and evolution of the Solar System, Evolution of the British Empire, etc. The geologic changes the Earth has experienced over time could quite properly be described as evolution. --Jayron32 13:32, 9 December 2010 (UTC)

While this is true, there are, as you know full well, also people who use "evolution" as shorthand for "godless communist soulless science used by people who will burn in Hell for denying the existence of God". TomorrowTime (talk) 14:04, 9 December 2010 (UTC)

people for whom the preferred shorthand term is "insane".--Jayron32 15:16, 9 December 2010 (UTC)

See also plate tectonics and Miller-Urey experiment. ~AH1^(TCU) 03:40, 11 December 2010 (UTC)

Cube planet

I know this is highly unlikely, but a question higher up piqued my interest. If there were such a planet, cube shaped, with an earthlike mass how would walking along it be? Would it be like the center of each panel is the bottom of a valley, and walking towards edges would be like walking uphill, since the points and edges would be furthest away from the center of gravity? Gunrun (talk) 11:19, 9 December 2010 (UTC)

Yes, with the corners being further from the center than the edges. More significantly, though, the atmosphere won't be evenly distributed. If we suppose a cube planet with an average radius equal to Earth's, then the corners will be, ballpark, a thousand miles above datum. The middle of each face will be, ballpark, several hundred miles below datum. Contrast with the Earth, where Everest is less than 6 miles high, and the Dead Sea just a few hundred feet below datum. As such, the atmosphere would distribute toward the low spots, leaving the high spots in vacuum. Most of the surface will not support human life (Note that the low spots may have too much atmo for life, leaving a ring-shaped habitable zone on each face). Additionally, you'll get some weird gravity effects going from high to low by virtue of that significant an altitude change. — Lomn 14:19, 9 December 2010 (UTC)

I would think that the gravity would not be pulling you straight down when you were near the edges, but at a 45 degree angle down and away from the edge. That might mean you are going to have a very difficult time approaching the edge, since gravity will be creating a lot of drag on your forward progress. Googlemeister (talk) 14:36, 9 December 2010 (UTC)

I had a thought after posting this. Wouldn't the shape of the planet affect the shape of its gravitational field? Your explanation (and my initial thoughts) seem to work assuming the gravity is a sphere eminating from the center of the cube, is this how it works? I'm assuming this cube planet would have a cube core and mantle, as well as the crust here, and the densities would be similar to earth. Gunrun (talk) 14:35, 9 December 2010 (UTC)

There is a book with this as the premise. 'Children of Chaos' and 'Mother of Lies' by Dave Duncan. The planet is actually dodecahedral in the books, and the books are not really about that, but the geography is treated very well, including an appendix discussing the science (and the places where he had to take some license). Ariel. (talk) 17:13, 9 December 2010 (UTC)

The gravitational field wouldn't be spherically symmetric, but it wouldn't be hugely different from being spherically symmetric. In particular, at the center of a face, the center of an edge, or at a corner, gravity would pull you precisely towards the center of the planet. Anywhere else, gravity would pull you in a direction that's mainly towards the center of the planet, but somewhat towards the nearest corner. Red Act (talk) 17:43, 9 December 2010 (UTC)

That's right: I plotted the equipotentials and guess that the local gravity vector is never more than 10° or so away from the center-ward direction. --Tardis (talk) 20:13, 9 December 2010 (UTC)

Threads like this are why I treasure Ref Desk. You do not see this in the NY Times. Edison (talk) 06:43, 10 December 2010 (UTC)

The Bizarros live on a cube-shaped world. 93.95.251.162 (talk) 18:33, 10 December 2010 (UTC) Martin.

Under normal circumstances, such a planet would approach hydrostatic equilibrium. Imagine the simultaneously reduced (further distance from core) and elevated (forces pulling you toward centres of three planes) gravity while you stand on one of the corners. ~AH1^(TCU) 03:38, 11 December 2010 (UTC)

Yogurt

My EasuYo made yogurt turns to water after 24 hours what am I doing wrong I've followed manufactures instructions and also their help line advice without success.13:44, 9 December 2010 (UTC)86.133.163.19 (talk) 13:44, 9 December 2010 (UTC)

Added a title. Vimescarrot (talk) 13:46, 9 December 2010 (UTC)

Water is one of the byprotducts of the lactobacillus cultures that make yogurt, well, yogurt. The lactobacillus eats the sugars in the milk and produces water as one of its waste products. This is normal and to be expected. The same sort of water build-up occurs with sour cream and other cultured milk products. If the package is kept in its original seal, the lactobacillus remains somewhat dormant, so you tend not to see it until after the package is opened and it is exposed to air. Its completely harmless, and a normal part of what being yogurt is all about. You can, to your preference, either stir the watery part back into the yogurt or pour it down the drain. --Jayron32 14:00, 9 December 2010 (UTC)

The metabolic water produced from the milk sugars is going to be absolutely minuscule compared to the 90+% water content from the original milk itself. My understanding is that the liquid seepage you see from cultured dairy products is due to the broken protein matrix contracting and exuding the liquid, in a similar fashion to how yogurt cheese is made. As you said, some liquid seepage from the yogurt is completely natural. However, I get the impression that the poster has a different problem, where their yogurt doesn't just exude liquid, but turns completely to liquid. I'm not sure why it would turn to liquid after a day - are you sure it was completely set to begin with? Also, is it completely liquid, or just thinner than you would like? Usually commercial makers add stiffeners (like gelatin, starch, agar, etc.) to yogurts to increase the solidity. For homemade yogurts, the usual recommendation is to add additional dry milk powder to the milk to increase the protein content and thus the stiffness of the yogurt. Another issue for liquidy homemade yogurt may be that your yogurt cultures are sick/dead, or that the temperature of incubation was off. -- 174.31.212.34 (talk) 17:40, 9 December 2010 (UTC)

Think the OP is simply expecting it to look like it does when bought ready made. Commercial yoghurt is cultured in large vats first were the whey separates. Then the liquid whey gets thoroughly mixed back in before going to fill thousands of smaller pots. If the OP just waits until the culture has fully converted all the milk, then take a fork and stir thoroughly, he will find it takes on the same smooth consistency of shop bought yoghurt. Let it stand overnight in the fridge and it will set a little and look like he expects it to look. Mix it too early and it will separate a little again. I prefer it in its natural unmixed form so as to enjoy the contrast of flavours. If the OP hasn't ever seen or tasted home-made yoghurt before, this might look really odd and the taste rather unexpected and strange.--Aspro (talk) 23:29, 9 December 2010 (UTC)

Makeup for the eyes in the form of airbrush

I mean in a Bladerunner kind of makeup. An airbrush that you spray over your eyes forming a black stripe. Mr.K. (talk) 13:46, 9 December 2010 (UTC)

Airbrushes are used for makeup. It is not easy to do it on yourself, but it is used for professional work for photo-shoots and movies. Do you have a more specific question? -- kainaw™ 13:54, 9 December 2010 (UTC)

But, are airbrushes used over the eyes? Even if they are closed, is that a safe procedure? Mr.K. (talk) 13:56, 9 December 2010 (UTC)

Yes. What is the safety concern that you have? Are you assuming that they are using extremely high-pressure spray guns designed to blow a person's eyeballs through their skull? They use just enough pressure to spray a little tint about 2 inches from the nozzle to the skin. Spray-on tanners (which are also applied to the face) likely use more pressure than that. -- kainaw™ 14:02, 9 December 2010 (UTC)

I was more concerned about any effect of the makeup entering in contact with the eyes (or in this case, the tanning solution). Mr.K. (talk) 14:07, 9 December 2010 (UTC)

You close the eyes first, obviously. Lots of makeup is applied on the eyelids and around the eyes. The airbrush used is not high pressure. --Mr.98 (talk) 15:36, 9 December 2010 (UTC)

Well, yes, if you look at it this way. It's just a different way of applying makeup, which is often applied near the eyes and that has been tested thoroughly in the eyes of some animals before... 17:34, 9 December 2010 (UTC)

Wikipedia has an article on airbrush makeup.--Shantavira|^{feed me} 17:53, 9 December 2010 (UTC)

"You know you're wife's getting old when ... she needs to use power tools to apply her make-up." :-) StuRat (talk) 01:37, 10 December 2010 (UTC)

"You know you're getting old when ... you start talking about herself in the third person." 86.161.208.185 (talk) 11:19, 10 December 2010 (UTC)

Nasal saline solution

In many places, I see the recommendation to use non-iodized salt to make a nasal saline solution at home. Why is it different to iodized salt? Mr.K. (talk) 14:04, 9 December 2010 (UTC)

Iodine will sting your nasal epithelium, so using non-iodized salt makes it less painful. Rockpocket 14:45, 9 December 2010 (UTC)

But is this stinging only painful or also unhealthy? Mr.K. (talk) 16:01, 9 December 2010 (UTC)

If it's approved for use as food, it's probably not going to be too harmful applied in moderation to nasal tissue, but you never know, so you should ask a doctor, especially if you intend to use it a lot. WikiDao ☯ (talk) 17:50, 9 December 2010 (UTC)

No, it's just curiosity. But how is the nasal epithelium more sensitive than your mouth or throat? Is it another type of skin? Mr.K. (talk) 18:08, 9 December 2010 (UTC)

They're similar but different tissues, we probably have articles about them. WikiDao ☯ (talk) 18:21, 9 December 2010 (UTC)

The nasal epithelium is not inherently more sensitive, but it is sensitive to different things. It is particularly senstitive to zinc, for example. So avoid nasal spays or washes containing zinc if you value your sense of smell. Rockpocket 18:41, 9 December 2010 (UTC)

In a food related example, pepper in your food isn't very annoying, but inhaling pepper dust sure is. StuRat (talk) 01:33, 10 December 2010 (UTC)

Some people are hyposensitive to iodine, so giving more iodine through a nasal wash, added on to that ingested through food, could cause a reaction. Having said that, iodine hyposensitivity is fairly rare, and iodized salt contains very little iodine, so most people should be able to use iodized salt for nasal washing without any problems. Physchim62 (talk) 20:44, 9 December 2010 (UTC)

I'm guessing you mean hypersensitivity rather than hyposensitivity -- "hypo" means smaller than usual. Looie496 (talk) 22:15, 9 December 2010 (UTC)

I used to make a nasal solution with about a cup of water, ¼ teaspoon of iodized salt, and ¼ teaspoon of either baking soda or baking powder (I can't remember which it's been long enough...whichever one Arm & Hammer makes in an orange box), and it didn't sting or anything beyond the feeling of having water forced through my sinuses, and actually worked quite well. This was actually done with the advice of a doctor, as the main thing I used it for was to help prevent colds from turning into sinus infections, so I don't see that iodized salt versus uniodized salt makes that huge of a difference. Ks0stm ^(T•C•G) 18:41, 10 December 2010 (UTC)

Tapiridae (Tapirs)

Could Tapiridae be surviving Meridiungulata or Notoungulata? Has anybody reputable put forth such a theory? --Eu-151 (talk) 14:33, 9 December 2010 (UTC)

I probably shouldn't respond to a question I know so little about, but the fact that tapirs were common in North America for a long time before the Great American Interchange would seem to argue pretty strongly against the idea. Looie496 (talk) 22:24, 9 December 2010 (UTC)

Another improbable planet question

Say you had an earthlike planet, and one day a thick layer of extremely dense material (say... uranium or plutonium or something) evenly covered the planet, enough of it to increase the mass of the planet by 1/4 or something. Disregarding the utter havoc this would cause to whatever was on the surface what would this do to the planet (and ignoring the possibility of the crust collapsing under the weight of this new material (if thats even possible?)), regarding its gravity? Gunrun (talk) 14:38, 9 December 2010 (UTC)

If you cover the Earth with 1.5x10²⁴ kg of either uranium or plutonium, critical mass will trivially be met, and the planet will explode in an enormous nuclear explosion. Regarding its gravity, the post-planetary vapor will easily achieve escape velocity, so the vapor will not coalesce back into a planet. Red Act (talk) 16:15, 9 December 2010 (UTC)

Actually, this rather flip answer isn't necessarily correct, depending on the isotope being used. U-238, in particular, isn't fissile. Red Act (talk) 17:08, 9 December 2010 (UTC)

Ignoring the nuclear effect described by red act, and just dealing with the added mass, The effect would be to increase the effect of gravity by the same proportion as the new mass added would. Oh, and weight IS the effect of gravity, the two terms are synonyms, so if the new material would cause crustal damage in some way, the only mechanism it would cause it by would be gravity. In otherwords, if you increased the mass of the planet by 1/4 it would exert an increase of 1/4 in the effect of gravity on nearby objects. --Jayron32 16:17, 9 December 2010 (UTC)

Yes, but the surface gravity would not increase as fast, as the radius of the planet also increases with the cube root of the mass increase, assuming the new material is the same density as the existing material. CS Miller (talk) 16:21, 9 December 2010 (UTC)

The increased radius of earth would be about 150km (for uranium) so the mass would increase 25% and the distance would increase about 2.5%, so the gravity would end up 20% higher (on the surface) Googlemeister (talk) 16:28, 9 December 2010 (UTC)

Uranium star

Would it be possible, if you had one solar mass of something very heavy and radioactive, such as Uranium, Plutonium, or Radium, or even something lighter, like lead or bismuth, would if be possible to have a star creating energy via fission? And I know the improbability of this, I was just wondering. --T H F S W (T · C · E) 17:19, 9 December 2010 (UTC)

Probably not at that size. It seems to me you have two possibilities: The temperatures and pressures would (may?) be high enough that any fission products would be fused back together, stealing any energy. Or the fission would proceed but the resulting neutrons would cause other atoms nearby to also fission, making a chain reaction that would blow the whole thing apart. Cool question though. Ariel. (talk) 17:48, 9 December 2010 (UTC)

Have a look at stellar nucleosynthesis. Based on our understanding of the way that heavy elements form, it's not probable that any star could ever reach a state where uranium is a significant constituent, by mass, volume, number of particles, or any other metric. After reaching iron fusion by "burning" lighter elements like Oxygen, the star typically can not produce heavier elements in great quantity. The neutron- and proton-capture reactions are not very efficient. So, for a star to have even a small quantity of uranium present, it necessarily requires a much larger quantity of hydrogen fusion. Uranium may fission in any star of sufficient size and age, but it will never be the dominant energy-production reaction. Also, you might have a look at fission bomb related articles: one of the biggest problems with fission of uranium is that it is often explosive. While this sounds obvious, consider the problem more carefully: a property of uranium is that once it reaches a critical density, the fission reaction occurs explosively at a speed too fast for the metal to hold together. Then the material explodes, blows apart, and the critical density no longer exists and fission can not be sustained. That's why fission bomb designers have to spend so much effort on carefully arranging parts, and working on "explosive lenses" and "neutron reflectors" and so forth. It's pretty unlikely that a natural nuclear fission reactor could ever exist. (Insert your favorite Soviet/Cold-War conspiracy-theory about West African geology here). Nimur (talk) 18:02, 9 December 2010 (UTC)

You guys pointed out that one problem is that it is explosive. This is true, but you must remember that it has to combat the massive pull of gravity. Hydrogen bombs are explosive as well, but the sun has 1,400,000,000,000 of them going off every second. I am not wondering if it would explode (trust, me it wouldn't; collapsing is more likely), I am asking if such a star could have a maintainable, energy-giving, stable reaction. --T H F S W (T · C · E) 18:40, 9 December 2010 (UTC)

I think I wasn't quite clear: the problem isn't merely that fission is explosive - anything energetic will cause expansion. Hydrogen fusion is also energetic, and also causes expansion. The problem is that specifically for uranium fission nuclear chain reaction, the rate of material expansion is faster than the rate of neutron production. This means that there will not be enough neutrons to sustain the fission over long enough time-scale to "actuate" all the uranium. The relative rates of expansion and neutron-production are "hard-coded" into the atoms, due to the energetic nature of uranium fission. (On these time-scales, size-scales, and energy-scales, gravity isn't even in the picture, so to speak - we're talking nuclear-force here, and worried about relative positions and velocities of atomic nuclei). So it is physically impossible to fission a lot of uranium unless something forcefully contains the nuclear reaction. This has been a known problem since the early 1940s, and requires an engineering solution (neutron reflectors, implosion triggers, and so on). It is unlikely that an "engineering solution" like that could naturally exist. Put another way, "we don't see a lot of uranium fission in stars, it will never be the dominant energy-production reaction." Nimur (talk) 19:17, 9 December 2010 (UTC)

THFSW: With fusion the reaction is self regulating - if it runs too fast the density goes down, slowing the reaction. Not so with fission, which has a positive feedback loop instead, and the faster it fissions, the faster it induces more fission, till the whole thing goes at once. Nimur, I'm not sure what you mean by "the rate of material expansion is faster than the rate of neutron production" - are you saying it will expand too far for it to sustain a reaction? I'm not sure that's true, unlike fusion which requires density, with fission all you need is some neutrons, and as long as you have sufficient depth of material that some neutrons inevitably will impact on the uranium, it will sustain, even at low density (at least until it expands large enough that the neutrons decay before they hit anything). i.e. that your uranium "cloud" has enough atoms in it that in any random line 10/14 light minutes long through the cloud there is at least 1 uranium atom (this is oversimplified obviously, you have to take into account cross section, etc.) Ariel. (talk) 20:06, 9 December 2010 (UTC)

Regarding "expanding so fast..." - yes, this causes a premature termination of the chain-reaction. Have a look at the discussion of Little Boy's inefficiency. Technical reports are available in the references and further reading sections of our Little Boy article. I recall a specific paper, published in 1945, that outlined the detailed physics calculations, but I can't find it at the moment. I think it used to be posted from our Nuclear Weapon Design article. In any case, you can perform and verify the calculations yourself by solving the collision kinetics of the fission-product. Nimur (talk) 20:36, 9 December 2010 (UTC)

A star is rather larger than Little Boy. It could expand a lot and still work. Or more specifically the uranium in Little Boy is not very thick, so when it expands neutrons will pass right through without hitting the uranium, but in a star - even an exploded star - the uranium would be thick enough that the neutron will still hit something. Ariel. (talk) 20:41, 9 December 2010 (UTC)

I suppose. I know less about the physics of stars than the physics of nuclear weapons. I should probably spend more time outside. Nimur (talk) 21:33, 9 December 2010 (UTC)

In any case, it strikes me that you'd want something that was more like a star-sized reactor than a star-sized bomb. It seems like of odd to assume that the uranium in question is HEU like Little Boy. I'm imagining some kind of ideal uranium-boron mix or something else that would be somewhat self-moderating and self-restricting. --Mr.98 (talk) 22:28, 9 December 2010 (UTC)

Stars that try to make heavy elements in great quantities end up with these elements decaying back to lead making a lead star. (we need an article) Even so the star s nowhere near 100% lead, but still contains hydrogen and helium, and some other elements. Graeme Bartlett (talk) 20:58, 9 December 2010 (UTC)

Here are a list of references to papers that talk about lead stars. Red Act (talk) 21:25, 9 December 2010 (UTC)

I made a wee stub for it. --Sean 22:24, 9 December 2010 (UTC)

Heavy radioactive elements are most often created in the shock waves and extreme temperatures of Type II supernovae, and any fission energy produced may contribute to the supernova. ~AH1^(TCU) 03:31, 11 December 2010 (UTC)

Neutron stars can collide, resulting in fission-like liberation of energy and mass. Ginger Conspiracy (talk) 05:30, 11 December 2010 (UTC)

touchscreen technology

how to make touch screen? — Preceding unsigned comment added by Djmyemailid (talk • contribs) 18:10, 9 December 2010 (UTC)

We have an article on Touchscreen technology. There are a variety of them, all of which seem difficult to make from scratch. Perhaps easiest is to buy a company that already produces them, or just buy one of their products if you only want one. WikiDao ☯ (talk) 18:18, 9 December 2010 (UTC)

There are touchscreen overlays you can purchase if you have an existing display that you want to add touchscreen capability to. -- kainaw™ 19:20, 9 December 2010 (UTC)

Here are instructions for one way to build your own touchscreen. Red Act (talk) 21:18, 9 December 2010 (UTC)

Electromagnetic induction and capacitance may be of background interest. Ginger Conspiracy (talk) 05:36, 11 December 2010 (UTC)

do magnetic interactions EVER change the magnitude of velocity of a charged particle

I am told that magnetism and electromagnetism are basically two sides of the same force. Now I believe I understand classical mechanics, but I don't get how the magnetic and electromagnetic forces are unified (through relativity?). If the force is unified, how does this reconcile with the observation that magnetic forces don't ever seem to change a charged particle's velocity (not in a circuit)? Can Faraday's law be applied to a beam of electrons? John Riemann Soong (talk) 21:29, 9 December 2010 (UTC)

Magnetic fields produce a force that does no work on a charged particle (by definition, the Lorentz force is perpendicular to the motion, so F_B · v is zero and thus energy is totally conserved). So in the "purist" interpretation, the magnetic field itself does not change the energy of the particle. In complex situations, such as a dense plasma, changing the particle trajectory affects things like viscous drag, collision rate with other particles, and so forth. In that case, the magnetic field can affect the particle energy, but only indirectly by steering it into a different direction, where other effects (electrodynamic, or even just thermal/collisional effects) actually negotiate the energy exchange. Nimur (talk) 21:39, 9 December 2010 (UTC)

From a relativistic perspective, the "electric field" and "magnetic field" are just different aspects of the electromagnetic field tensor. See Covariant formulation of classical electromagnetism for a unified treatment of electromagnetism. Red Act (talk) 04:03, 10 December 2010 (UTC)

A time-varying magnetic field is equivalent to an electric field, as per the Maxwell-Faraday equation. This is used for deflecting electron beams all the time. Although the electron beam in old cathode-ray oscilloscopes commonly used electrostatic deflection, the beam in modern CRT monitors and TVs all use magnetic deflection, i.e., the beam is deflected by a time-varying magnetic field generated by electromagnets; see Cathode ray tube#Overview. Red Act (talk) 05:46, 10 December 2010 (UTC)

Dear New Yorkers, why haven't I seen buildings built ABOVE your streets?

Manhattanhenge. ~AH1^(TCU) 03:25, 11 December 2010 (UTC)

The City of New York is in an EPIC land crunch, yet there is so much valuable real estate floating above your wide avenues. Apparently, there are just a few structures built above streets, but why aren't there more? Since parking is extra tough in your beloved city, why shouldn't parking garages be built above your streets?

Then there are the waterways. Hudson and East River could have buildings built on supports (that would have to be like the ones seen on arch bridges in order to provide clearance for boat traffic.)

So despite the land crunch, why doesn't New York see more of these?: http://forum.skyscraperpage.com/showthread.php?t=151423 --129.130.99.68 (talk) 21:29, 9 December 2010 (UTC)

New York isn't really in an epic land crunch. The population density of the outer boroughs is much lower than Manhattan; there are large areas of Queens and Staten Island that are essentially suburban in character. Also, there's not really a huge demand for new office towers in Manhattan itself. Some, but not so much as you imply, that demand is somehow drastically ahead of the ability to keep up with it. --Jayron32 21:36, 9 December 2010 (UTC)

ec. I can not speak for the city of New York, but there would be some engineering challenges if you want to build buildings that cover the city streets. First, you need to be able to support the building with a large tunnel going through its base. Not impossible, but it does create greater construction expenses. Second, if you are going to close off the sky above the streets, you are going to have to install adequate ventilation systems to prevent a buildup of vehicle fumes, specifically nasty things like carbon monoxide. Third, the streets are owned by the city of New York, which will add a lot of red tape to anyone wanting to build there. I am sure there are other complications, but I think that the conclusion is that we do not have much in the way of over-street buildings because the point where the engineering and bureaucratic challenges being less then the costs of simply building elsewhere has not been passed. Googlemeister (talk) 21:39, 9 December 2010 (UTC)

The simple answer is that the 1916 Zoning Resolution ensures that even the bum in the gutter can look up and see the stars above – and be so reminded, that this is the land of opportunity where a man can achieve anything he wants to.--Aspro (talk) 23:49, 9 December 2010 (UTC)

I love this answer! However, in 1916 they were unable to project planetarum displays to the underside of tunnels and therefore the resolution must be updated. Also, air quality control. Ginger Conspiracy (talk) 05:40, 11 December 2010 (UTC)

There's also the psychological aspect. Some of us enjoy the idea of having at least some feeble connection with nature, rather than being entirely surrounded by man-made structures the entire day. An outdoor walk between the office and the train station on a nice day can provide a little of that. If the sun's shining, you can help stave off seasonal affective disorder, and even synthesize some vitamin D while you're at it. Red Act (talk) 00:03, 10 December 2010 (UTC)

You'll find a few of them in Boston. For example, the Floating Hospital for Children. Paul (Stansifer) 04:32, 10 December 2010 (UTC)

Besides, it's already been done. The MetLife Building, the Helmsley Building and other buildings on the Park Avenue axis are built above the extensive rail yards north of Grand Central Terminal. Madison Square Garden's built over the late lamented Pennsylvania Station (New York City).Acroterion _(talk) 04:38, 10 December 2010 (UTC)

Also, the very page you linked to, original poster, contains a number of examples from New York City. As for the East River and Hudson River, a significant portion of the Manhattan shoreline is landfill. Instead of building into the water "on supports", they simply filled the water in, especially in the downtown area. Further, both waterways are very deep and impractical to build over completely without resorting to suspension bridges and the like. Also, as others have said, there's is not currently a land crunch. Pfly (talk) 04:47, 10 December 2010 (UTC)

Syd Mead had a good idea related to this in his plan for replacing the World Trade Center. Comet Tuttle (talk) 18:12, 10 December 2010 (UTC)

December 10

Physics trouble

I'm having trouble solving a physics problem:

A 2kg weight is hanging in a rope inside a car accelerating at 4 m/s^2, what is the angle on the rope?

Just a pointer to what formula I should use is most appreciated since I'm at a total loss at the moment. 95.80.22.142 (talk) 10:45, 10 December 2010 (UTC)

F = ma ;) Intuition should tell you that the rope will be at an angle from the vertical, hanging backwards. Now solve for the force of the rope on the weight – because it is at an angle, there will be two components which sum to the gravitation force on the weight. The horizontal componant has to be 2 kg × 4 m/s² = 8 N to accelerate the weight at the same rate as the rest of the car, so calculate the angle for which the horizontal component is 8 N. Physchim62 (talk) 11:13, 10 December 2010 (UTC)

You don't need a formula, you just need to understand what you're doing. This is, I guess, why you don't have a specific formula in your notes. Start by drawing a diagram and marking on all your forces. Okay, you need an equation that links force and mass, but I'm pretty sure you know one ;) Then let us know if you need more pointers, when you've done that. Don't just use something someone gives you, because then you'll be lost on the next question! 86.161.208.185 (talk) 11:16, 10 December 2010 (UTC)

When you are satisfied you have worked out the correct method, and have the correct answer, it will be very revealing to contemplate what the angle on the rope will be if the object at the end of the rope is not 2kg, but 3kg. Dolphin (t) 11:42, 10 December 2010 (UTC)

... and also the angle when the acceleration of the car is equal to the acceleration due to gravity ! :-) - WikiCheng | Talk 12:43, 10 December 2010 (UTC)

Another fun experiment is to see just how close to horizontal you can possibly get the rope by accelerating it faster in the horizontal direction. In cartoon physics, you often see a 90-degree angle when a road-runner or something starts accelerating really fast, dragging a rope behind them or whatnot. In practice, this is not possible - there will always be some vertical displacement (unless another, different force exists to counteract the effect of gravity). Nimur (talk) 18:33, 10 December 2010 (UTC)

How can this not be {{homework}}? Ginger Conspiracy (talk) 05:42, 11 December 2010 (UTC)

Of course it's homework. Have you read our guidelines on homework? This section mostly conforms nicely. Not much to moan about here. 86.161.208.185 (talk) 11:59, 11 December 2010 (UTC)

Turbocharging in motorcycles..

I want to know as we use turbochargers in diesel engines... can we do the same in powerful bikes to improve it's performance..? —Preceding unsigned comment added by 220.225.96.217 (talk) 13:25, 10 December 2010 (UTC)

Typing "Turbo motorcycle engine" into Google confirms that motorcycle engines can be (and are) turbocharged. --Jayron32 13:33, 10 December 2010 (UTC)

ofcourse... but are they useful.. and why do we not turbocharge every motorbike..? —Preceding unsigned comment added by 220.225.96.217 (talk) 13:41, 10 December 2010 (UTC)

Turbocharging is rarer on motorcycles for a number of reasons. Motorcycles are much lighter than cars and can get away with a less powerful engine with less low end torque. Too much power and the bike becomes very difficult to ride. Sports bikes rarely have much more than 200 hp for even the most powerful superbike (With the exception of weird specials like the Dodge Tomahawk. This can be achieved with high revving normally aspirated engines. Since creating a surplus of power on a bike is easier than in a car, the disadvantages of turbocharging quickly become an issue. Turbos take up space, which is at a premium on sports bikes. They create uneven power delivery which makes the bike hard to ride. They also get very hot which can be an issue when the turbo is just inches from your body. The only place where turbo bikes are common AFAIK is on the dragstrip. --Leivick (talk) 15:42, 10 December 2010 (UTC)

Turbocharging a bike can easily result in over 300bhp, on a motorbike that is insane. For an example of a turbocharged bike, watch this. http://www.youtube.com/watch?v=r3IxSjuMUCE 81.145.247.90 (talk) 16:52, 10 December 2010 (UTC)

Two other comments to add to the points above:

1) Both turbochargers and superchargers are also used to get the same power out of a smaller engine, and you might wonder why this approach isn't also used on motorcycles. In the case of cars, a standard aspiration V8 might be replaced with a turbo 4 cylinder. However, there are limits to how small, and how few cylinders, you can put in an engine, without creating problems. While a single cylinder engine does exist, it's not ideal.

2) Turbo lag is perhaps more of limitation on a motorcycle, where low-end acceleration is more desired. Superchargers lack this problem, but have their own issues. StuRat (talk) 16:51, 10 December 2010 (UTC)

Transporting Gases....

I have seen, while transportig gases instead of using a single tank sometimes many cylinders interconnected are used.. why do they do so...? I saw it on mini truck it was assembly of near about 40 cylinders and all of them were connected with metal pipes.. are there some special kind of gases which need this type of transporting..? —Preceding unsigned comment added by 220.225.96.217 (talk) 13:31, 10 December 2010 (UTC)

A standard high pressure gas cyclinder is 50 litres in capacity and is pressurized to 200 bar when full, giving approximately 10,000 litres of gas. If you want more gas than that (but not hugh industrial quantities) you use more cylinders, because it's cheaper than constructing a larger pressure tank and then having it certified for safety. Physchim62 (talk) 14:07, 10 December 2010 (UTC)

Something like that [20] ?--Stone (talk) 15:00, 10 December 2010 (UTC)

Multi-element gas containers (MEGC) are missing from the articles on gas_cylinders and storage tanks and the effect that these tanks have on standardizing the licensing for storage and transportation of hazardous gases. It really could do with being added. The image of the MEGC battery truck shows a hazchem number for hydrogen. --Aspro (talk) 16:00, 10 December 2010 (UTC)

MEGC are constructed in a way that you can unload the whole package, while a battery vehicle like in the image above has a fixed connection and the gas containers stay on the truck al the time. [21] .--Stone (talk) 19:43, 10 December 2010 (UTC)

If the individual tanks can be disconnected and used individually, then this provides an additional flexibility. Yes, smaller tanks could be filled from a larger tank, but this takes time and labor, will lower the pressure, incur a risk of leaks, etc. Compare this with gallons of milk you buy at the store. The store could get a 10,000 gallon tank and fill the one gallon containers individually, but that method isn't as practical. StuRat (talk) 16:31, 10 December 2010 (UTC)

Volume, volume, volume. Ginger Conspiracy (talk) 05:43, 11 December 2010 (UTC)

what percent of people are using 3G technology.....in world..

i wanto to know this because i am going to purchase a mobile with 3G technology and i live in india.. i am curious that buying it would be worthful in next 2 years or not... —Preceding unsigned comment added by 220.225.96.217 (talk) 13:39, 10 December 2010 (UTC)

Not sure, but they're been selling "4G" in the U.S. for a while now. If you go with a prepaid phone (the type where you buy cards to extend them) instead of a contract, then you can more easily abandon your current phone/plan should better or cheaper ones become available.

One general comment on mobile phones, though, you need to look over the coverage map very carefully to see if the areas where you live, work, etc., are covered, especially if you are far from a major city. If you aren't covered by any of the major carriers, you might consider a satellite phone instead of cellular, although they do tend to be more expensive. StuRat (talk) 16:24, 10 December 2010 (UTC)

I don't think that the number of users has much bearing on whether 3G is worth it. Perhaps a larger number of users will lead to more coverage, but that's a loose connection. Paul (Stansifer) 00:50, 11 December 2010 (UTC)

It also depends on what you count as "worthful". What do you think the advantage will be to you of using 3G? Here in the UK there's wide 3G coverage (this gives links to maps but they don't appear to work) but 2G usage is very wide indeed. Tonywalton ^Talk 01:04, 11 December 2010 (UTC)

Hawking Radiation and negative mass

So a negative mass (or energy?) particle causes a blackhole to lose mass correct? But I was under the impression that negative mass should be repelled against gravity. Shouldn't the negative mass particle be deflected away from the black hole... Unless it's able to quantum tunnel through it... My second question is, why don't these negative mass particles destroy us or our planet? Shouldn't they be appearing all around us? Wouldn't they slowly eat away at our mass too? Or maybe even quickly... I believe a 228ton blackhole only lasts around 1 second. ScienceApe (talk) 16:42, 10 December 2010 (UTC)

There is no negative mass. What happens in Hawking radiation is that an antiparticle (which still has a positive mass!) falls into a black-hole and anihilates some small part of the black hole, while the "virtual pair" of the antiparticle escapes, resulting in a net loss of mass by the black hole. The mass lost is equal to the mass of the escaping particle, and the energy from the anihilation results in the black hole getting warmer. --Jayron32 17:00, 10 December 2010 (UTC)

I don't believe that is correct. An antiparticle annihilating inside a black hole would still add energy to it, not subtract it. The "virtual" particle is the one that falls in the black hole, while the real one escapes. This virtual particle is not a real particle, it's more of a mathematical concept. The thing with virtual particles is that they can't exist in the first place, unless the math works out. Which is why it falls in - that's the only way it can exist. And that's why even if they appear around us (which they sort of do), they can't do anything, because that would violate various laws of physics. And yes, I know this is a very fuzzy answer. Presumably the math works out, but since we have never observed it we don't really know what happens. Ariel. (talk) 18:29, 10 December 2010 (UTC)

I think you're taking the virtual-particle picture of black hole evaporation too literally. I've never entirely understood Hawking radiation, but John Baez, who is pretty knowledgeable about these things, mentions here that it was not originally derived based on virtual particles, and questions whether there even exists a correct derivation of it based on virtual particles. Virtual particles are just a funny way of doing calculations in quantum field theory, and they don't always give correct answers even in the absence of gravity. -- BenRG (talk) 18:45, 10 December 2010 (UTC)

Maybe I should have posted this video first. http://www.youtube.com/watch?v=S6srN4idq1E This is where I got the whole negative mass thing from. So it's wrong? ScienceApe (talk) 23:31, 10 December 2010 (UTC)

I only watched the first 60 seconds, but I disagreed strongly with almost every sentence uttered by the narrator in that time. The last thing he said before I gave up was that Hawking's goal was to reconcile the quantum prediction that the vacuum is full of particles with the GR prediction that "nothing exists at the edge of a black hole". This is utter nonsense. It's so random that I don't even think it's a misinterpretation of something from a reliable source. More likely it was invented out of nowhere by a scriptwriter in an attempt to make a coherent narrative out of something that he/she didn't understand at all. This particular scriptwriter doesn't even seem to understand the difference between atoms and subatomic particles. Awful, just awful. The overhead photography was kind of neat, though. -- BenRG (talk) 01:12, 11 December 2010 (UTC)

Hawking radiation occurs when particle decay/creation splits across an event horizon, or through a naked singularity. Can neutron stars evaporate this way too when at least one of the particles is a lepton? Ginger Conspiracy (talk) 05:46, 11 December 2010 (UTC)

Hawking radiation has nothing to do with singularities, naked or clothed. I think that there is no Hawking radiation without an event horizon, i.e. ordinary gravitating bodies don't Hawking-radiate at all, but I'm not at all sure about that. Of course, ordinary gravitating bodies emit blackbody radiation in the ordinary way. If you're wondering whether a virtual electron-positron pair can appear in the vacuum with the positron annihilating with a nearby object and the electron escaping to infinity, with a corresponding loss of mass from the object, the answer is yes, but this is just an ordinary electron-emission event described in a complicated way. -- BenRG (talk) 06:43, 11 December 2010 (UTC)

A naked singularity is its event horizon. Ginger Conspiracy (talk) 18:57, 11 December 2010 (UTC)

La Nina

When does it end?Accdude92 (talk) 20:16, 10 December 2010 (UTC)

The La Niña‎ article lists this reference for the end of the current one. The article only says Early 2011, though.Vchimpanzee · talk · contributions · 21:05, 10 December 2010 (UTC)

This slide presentation, updated weekly, tells you everything you could possibly want to know about the current and predicted future state of La Niña. Looie496 (talk) 21:40, 10 December 2010 (UTC)

A quarter of ENSO forecast models predict El Niño by summer 2011, and the average prediction calls for an end to La Niña by spring 2011[22]. ~AH1^(TCU) 03:17, 11 December 2010 (UTC)

I am not convinced that there are any weather patterns at this level of atmospheric CO₂ which people are able to predict. We need vastly negative atmospheric carbon concentration growth -- perhaps using http://windfuels.com -- before we will be able to predict the relative stability of tropical storm and flood magnitude conditions again. Ginger Conspiracy (talk) 05:49, 11 December 2010 (UTC)

airplanes that run on car fuel

Do we have some kind of list of airplanes that will fly just as well on the gas you put into your car as the av gas that is 2x as expensive? Googlemeister (talk) 20:22, 10 December 2010 (UTC)

It depends on what sort of engine is running the airplane. There's nothing inherantly wrong with running a prop plane on gasoline. The gas you put in planes may be twice as expensive merely because you are buying it in an airport. Location has a lot to do with price. --Jayron32 20:26, 10 December 2010 (UTC)

That is a bit of an over simplification. We have an article on Avgas which give a bit more info.--Aspro (talk) 20:34, 10 December 2010 (UTC)

I assume the OP is referring to piston driven planes not jets (as they will run on just about any flammable liquid). It is not safe or legal to fuel a piston plane designed for specialized avgas on automotive pump gas. Avgas is special high octane fuel and putting lower octane fuel in an engine designed for it can cause detonation (a bumber in a car, but a potential disaster in a plane). There are however conversion kits available to convert avgas engines to run on automotive pump fuel (probably at the expense of some performance). As for the question about a list, I don't think it exists. --Leivick (talk) 20:37, 10 December 2010 (UTC)

Here is a list of the popular planes that can run on mogas. Red Act (talk) 20:42, 10 December 2010 (UTC)

Excellent Red Act. Does anyone know if the RV-9 is cleared to run on car fuel? Googlemeister (talk) 21:08, 10 December 2010 (UTC)

Gasoline can be refined into kerosene with the excess hydrocarbons being used to run the still, with energy and/or fuel left over. Ginger Conspiracy (talk) 05:51, 11 December 2010 (UTC)

It is incorrect to talk about certain airplanes being suited to automotive gasoline and certain other airplanes not being suited. It is the ENGINE that is either suited or not suited to automotive gasoline. Instead of Googlemeister asking whether the RV-9 is cleared to run on car fuel he should be telling us what engine is installed in the airplane, and asking if that engine is suited to car fuel. The RV series are amateur-built airplanes and so they don't all have exactly the same engine. Different amateur builders choose to install different engines in the same airplane type. Dolphin (t) 12:18, 11 December 2010 (UTC)

What should I do with this jelly?

It's in a Mason jar with a Ball lid. In the eleven years I've lived alone, no one has given me one of these, so it must have been given to my father before that.Vchimpanzee · talk · contributions · 21:00, 10 December 2010 (UTC)

Unlike a tin-can, it will not have absorbed any iron or tin etc. Cannot think of anything else to be concerned about. A really good port is often much older. You could auction it on eBay. --Aspro (talk) 21:25, 10 December 2010 (UTC)

To clarify, Aspro points out that it will likely be as edible now as it was 10 years ago, and I agree. However, if it was canned improperly, there may still be a risk of botulism. SemanticMantis (talk) 21:30, 10 December 2010 (UTC)

(edit conflict) Homebrewed preserves are also more likely to have been incorrectly prepared. Your idea is good, but it should be noted that Grandma's kitchen is unlikely to have the quality control measures in place to make certain that this particular jar of preserves was prepared in a way to survive till today uncontaminated. --Jayron32 21:33, 10 December 2010 (UTC)

I can't believe that a Mason jar lid could maintain a good seal for 11 years. If the lid is still sucked on after that time (indicating a good seal), I suppose it would be edible, but I am skeptical that that would happen -- the rubber is too porous -- and if the seal is not intact, you obviously should not eat it. Looie496 (talk) 21:35, 10 December 2010 (UTC)

Thanks. I didn't expect to able to use it. I wonder if I can even open it.Vchimpanzee · talk · contributions · 21:51, 10 December 2010 (UTC)

What has the rubbers sealing capacity got to do with it? In the days before tine-cans and things, our grannies used pig bladder etc. Also: Google “egyptian tombs edible honey”. Botulism spores are a theoretical danger but a healthy immune system will cope with these (otherwise this common spore would have resulted in all of our deaths by now). --Aspro (talk) 22:31, 10 December 2010 (UTC)

Botulism poisoning is the result of the secreted botulinum toxin, which can be generated in an improperly-sealed can. A healthy immune system successfully eradicating the surviving bacteria (if any) does nothing about the already-accumulated toxin. TenOfAllTrades(talk) 22:56, 10 December 2010 (UTC)

So that's OK then, as botulism pores are only preserved in high sugar environments, rather than acting as healthy growing environments for the little wiggly things themselves. Hence, the habit developed, for using sugars for preservation! I almost feel like bidding for this blast-from-the-past myself.--Aspro (talk) 23:09, 10 December 2010 (UTC)

Responding to Aspro's previous question, to understand what the rubber has to do with it, you have to understand how home canning works. When you can something, you heat it to nearly boiling, then put the lid on it, and as the contents cool, the air inside contracts, creating a negative air pressure that holds the lid down tightly enough to create a seal. If the rubber leaks, you eventually lose the negative air pressure inside, and end up with a lid that is just sitting loosely on the jar. Once that happens, many bad things can follow. Looie496 (talk) 00:56, 11 December 2010 (UTC)

The Egyptian honey is a red herring. Honey has antibacterial properties. Jam does not. APL (talk) 05:00, 11 December 2010 (UTC)

Virginia Cooperative Extension says "although most jams and jellies can be stored safely for at least a year, they lose their flavor and color during storage" and "Home canned foods can be stored safely for up to 1 year. Do not eat foods stored longer than 1 year."[23] The University of Maine Cooperative Extension says "Jellies, jams, and spreads are best if eaten within a year. They are safe as long as the lids remain vacuum-sealed."[24] Red Act (talk) 06:25, 11 December 2010 (UTC)

Try a few milligrams first, and if you don't die in a week... BZZT! PSSHT! I'm sorry, you may not ask the Reference Desk for medical advice. Please share your jelly with a licensed physician or veterinarian. Ginger Conspiracy (talk) 05:55, 11 December 2010 (UTC)

I had several times jam which was ten to 15 years old. The taste was bad of one so I threw it away. If you are healthy an it is not meat with botulism there are only a very few things which would be capable to harm you if you try a small portion.

You may not die or even get any symptoms of illness, it doesn't mean you aren't harmed. There are plenty of toxins, particularly mycotoxins which are carcinogenic or have other cumulative/chronic exposure effects which you probably don't want and there's often no real guarantee you will taste them. Jam probably isn't so bad but I would be worried about peanut butter for example. (So yes this is somewhat OT but I strongly dislike the common but misleading claim 'if it taste's okay and you don't get sick in a few days it isn't harmful') Nil Einne (talk) 10:36, 11 December 2010 (UTC)

Plateosaurus and bipedal walking

So, we all know by now that Plateosaurus couldn't pronate its hands and had to have walked bipedally. The problem is that a lot of reconstructions of Plateosaurus I've seen walking this way look pretty goofy. If you look at that image (the hands still look weird, but that's not what I'm talking about), you'll see that the tail acts like a third leg to support the dinosaur's weight. That would be fine when standing, I'm pretty sure, but dinosaurs didn't drag their tails while walking. To walk bipedally that way with tail in the air just doesn't look right. There must be some sort of explanation to this (as they certaintly walked that way), so what is it? Crimsonraptor (talk) 22:58, 10 December 2010 (UTC)

I don't see a problem, personally. Presumably they made continual adjustments to their balance, in part by tail movements, just as their relatives the birds did and do. 87.81.230.195 (talk) 00:57, 11 December 2010 (UTC)

Maybe. It's just that a 2000 lb plus animal standing on two regular feet would probably have difficulty in some way. Not going into the whole diplodocoid-rearing-up debate, I've seen elephants go up on two legs, which sort of compares to the proportions. But that really isn't a good comparison, as they're built a lot differently. Crimsonraptor (talk) 01:07, 11 December 2010 (UTC)

The usual idea is that they walk with the head balancing the tail, pretty much horizontal, like in the silhouette picture in the Plateosaurus article. 81.131.51.70 (talk) 05:39, 11 December 2010 (UTC)

OK, the silhouette looks reasonable. A more upright stance than that, though, would likely be problematic. Crimsonraptor (talk) 14:03, 11 December 2010 (UTC)

Any chance that they used a similar approach to this Australian traffic hazard with a weighty tail? HiLo48 (talk) 06:38, 11 December 2010 (UTC)

A hopping plateosaur? A weird image comes to mind... but yeah, that could work! Crimsonraptor (talk) 14:03, 11 December 2010 (UTC)

December 11

chlorine dosing

I've been trying to find out the dosing rate for chlorine but I couldn't. Would you please help me on it? The R.O product rate [is?] 2.6GPM, the Chlorine solution strength is 0.1PPM, and I need 1 ppm on the product.

On the other hand, how to adjust the pump speed and stroke? Should i deal with it as a percentage of it's maximum?

Thanks a lot. — Preceding unsigned comment added by Dawoad0a (talk • contribs) 06:58, 11 December 2010 (UTC)

Dose is a function of time, so make sure the surface is exposed for 10 times as long with 0.1 ppm as you are supposed to expose it to a 1 ppm solution. Ginger Conspiracy (talk) 10:55, 11 December 2010 (UTC)

circuit idea

Can I get a circuit or a block diagram for a single port wireless d.c. charger? —Preceding unsigned comment added by 117.207.197.196 (talk) 07:30, 11 December 2010 (UTC)

Yes.[25][26][27][28] Ginger Conspiracy (talk) 11:05, 11 December 2010 (UTC)

Mercury sulfate

Does the dissolving of mercury in concentrated sulfuric acid produce mercury(I) sulfate or mercury(II) sulfate? Thanks, --Chemicalinterest (talk) 12:03, 11 December 2010 (UTC)

It dissolves in hot conc. sulfuric acid forming mercury(II) sulfate. But in water it dissociates forming a yellow solid.

3HgSO₄ + 2H₂O→Hg(SO₄)•2HgO + 2H₂(SO₄).

--Stone (talk) 12:40, 11 December 2010 (UTC)

How is mercury(I) sulfate produced then? Is it a metathesis reaction between a sulfate and another mercury compound like mercury(I) nitrate? Thanks, --Chemicalinterest (talk) 12:57, 11 December 2010 (UTC)

Mercury (I) is pretty exotic stuff. For the one, it's a dimolecular metal ion, which is pretty much a one-of-a-kind thing. If you read Mercury polycations, you'll see that Mercury (I) is essentially metastable in solid form. That's because of the equilibrium in solution Hg₂²⁺<--> Hg⁰ + Hg²⁺. Anything which precipitates Hg²⁺ will, by Le Chatelier's principle, cause the equilibrium to shift rapidly away from the Mercury (I) ion. You can create solutions of Mercury (I) nitrate via reduction from Mercury (II) nitrate; however it doesn't really "exist" except in solution. The solid precipitate has a hydrated cation (see the infobox in the article Mercury(I) nitrate), and any heat applied which would eliminate the water of hydration causes the Mercury (I) to disproportionate. There are other mercury (I) compounds, like calomel (mercury(I) chloride), but calomel isn't an ionic compound, it's molecular in nature; it sublimes at a relatively low temperature and forms gasseous molecules of Cl-Hg-Hg-Cl fairly easily. It's also non-polar, so it isn't much soluble in water. --Jayron32 14:22, 11 December 2010 (UTC)

This is all very interesting. But how is mercury(I) sulfate made? --Chemicalinterest (talk) 14:58, 11 December 2010 (UTC)

There are references in the article Mercury(I) sulfate. If you have access to a library, you could look these up. --Jayron32 15:18, 11 December 2010 (UTC)

Here ya go: this article from 1962 has a procedure. The procedure involves slow addition of sulfuric acid to a mixture of mercury(I) nitrate and nitric acid. And by slow I mean S....L....O....W. The procedure calls for dropwise addition of the sulfuric acid over 67 days... and then the product left to settle for 3 months, then is stored in an airtight, dark, nitrogen atmosphere before being subjected to an elaborate purification procedure. I have no idea how much time and equipment you have, but depending on how desperate you are, you could do this. (I did mention that mercury(I) compounds were exotic, didn't I?) --Jayron32 15:28, 11 December 2010 (UTC)

Is this a joke? People may revert it if I add that to our article... I do not want to do any experiments with mercury as I do not have any mercury or mercury compounds. This is just for Wikipedia article research. --Chemicalinterest (talk) 15:51, 11 December 2010 (UTC)

[29] states three methods:1) precipitation from mercury(I) nitrate solution with sulfuric acid 2) By adding an access of mercury to sulfuric acid 3) electrochemically from mercury(II) sulfate. --Stone (talk) 15:32, 11 December 2010 (UTC)

This sounds a little more practical than the above method, but probably will come out with a more impure product. Anyway, thanks for the answers; I plan to be adding them to my article on simple and your article here. --Chemicalinterest (talk) 15:53, 11 December 2010 (UTC)

I'm pretty sure that the Journal of Physical Chemistry, which published the above article, is not much into publishing "jokes" as peer reviewed articles. On the contrary, the actual practice of chemistry is usually quite tedious; getting a pure compound is not a trivial thing, and actual working chemists are used to doing some pretty long, otherwise tedious procedures to do it. --Jayron32 15:59, 11 December 2010 (UTC)

Gives plenty of "down-time" to edit Wikipedia! DMacks (talk) 20:05, 11 December 2010 (UTC)

..BURNING DIMOND....

I want to know as dimond is purest form of carbon .... would it give any product (ash) if we burn it....? would it burn or not...? I also want to know why table teniss ball, when burnt do not give any product...? —Preceding unsigned comment added by 220.225.96.217 (talk) 14:29, 11 December 2010 (UTC)

If you burned a diamond (and it does burn pretty readily, as you note, it is just carbon) you get some combination of carbon dioxide and carbon monoxide gases, in a proportion depending on how much oxygen is present. If you have enough oxygen, you get essentially carbon dioxide. In low-oxygen environments you get more carbon monoxide. There will be no "ash" left over, unless the diamond has some impurities; for example I believe that so-called "blue" diamonds contain cobalt impurities, if you burn one of those you will get a (very tiny amount) of cobalt oxides as an ash. However, if you have an essentially pure diamond, it will burn completely. --Jayron32 14:46, 11 December 2010 (UTC)

To answer your second question, a table-tennis ball is plastic, probably polyethylene. These sort of plastics are essentially just long hydrocarbon chains. That is, nothing but hydrogen and carbon. The carbon (as noted above) makes the gasses carbon monoxide and carbon dioxide. The hydrogen produces water when burned, and in the heat of a flame, it will be a gas as well. Thus, burning the table tennis ball will ALSO not leave any ash behind. When ash forms, it because burning the substances produces some sort of solid oxides; if the substance contains only elements that have gasseous oxides, you get essentially all gasses. --Jayron32 14:49, 11 December 2010 (UTC)

Most plant ashes (pot ash) are sodium or potassium carbonates and oxides. --Chemicalinterest (talk) 14:56, 11 December 2010 (UTC)

Table tennis ball is Nitrocellulose and the burning is so rapid that the little ash which is produced is going up as little fume.--Stone (talk) 15:14, 11 December 2010 (UTC)

I'm not so sure about that; nitrocellulose is notoriously unstable and flammable, it used to be used early on as a plastic when there were no other alternatives, however I don't think that many modern products that use it. --Jayron32 15:55, 11 December 2010 (UTC)

You are right, but you never have a large amount of table tennis balls at home. The last one I burned 10 years ago was still Nitrocellulose made flexible with Camphor. You smell it sometimes if you rub a table tennis ball.--Stone (talk) 16:11, 11 December 2010 (UTC)

Celluloid is what table tennis balls are. I don't know the relationship and/or difference between that stuff and nitrocellulose. 90.195.179.14 (talk) 17:03, 11 December 2010 (UTC)

The difference is the amount of nitro groups per sugar molecule. The one is soluble in acetone the other not. But in general the difference is small.--Stone (talk) 17:22, 11 December 2010 (UTC)

Another factor in if any "ash" is left is how complete the combustion is. If part of the original is left unburnt, then that will be mixed in with the ash. You might think it would be obvious if part of it is left unburnt, but it's often not. If the material is fractured and blackened, it may look just like the rest of the ash.

What leads to incomplete combustion ? It's usually a result of not enough oxygen getting to the material, such as the pages on the inside of a phone book. Increasing the surface area and air flow will help here, and a table tennis ball (ping-pong ball) has a large surface area relative to it's volume, so complete combustion is likely.

Another reason for incomplete combustion is that the temperature falls below that needed for combustion. This can be a problem for things which burn slowly, as they might not generate enough heat to maintain the fire. A large wooden log can have this problem. But, as noted previously, the table tennis ball burns quickly and generates plenty of heat to maintain combustion. StuRat (talk) 17:51, 11 December 2010 (UTC)

Musical volume

I want to know why do we call the loudness or lessloudness of music "volume" ? why don't we use technical terms such as frequency... or amplitude....? —Preceding unsigned comment added by 220.225.96.217 (talk) 16:15, 11 December 2010 (UTC)

Because loudness (or volume) isn't directly tied to a physical property, it is a perceptive property, that is it's biologically and psychologically-based, not physically-based. The human ear's response to sound is roughly logarithmic with respect to the amplitude of the sound waves, which is why the loudness scale, decibels, is a logarithmic one. For most acoustic applications, its the perception of sounds which is more important than the actual physical properties of the sound. See loudness for more information. --Jayron32 16:42, 11 December 2010 (UTC)

The closest technical term for the intrinsic property of pressure-wave is "intensity" or "power" (and they are derived from frequency and amplitude). But loudless/volume is (as Jayron32 notes) about "how you hear it", not "how it is". The pressure-change of a tornado is enough to shatter your windows, and a dog-whistle is intense enough to anger my the pets the next property over, but neither one is "loud" in the common meaning of that term. Different terms for different situations/effects/properties, even if they are all related concepts. DMacks (talk) 20:05, 11 December 2010 (UTC)

Unidentified Mineral

My nephew found some minerals that look like glass but much thicker and not as clear, more whiteish. Does anyone have any idea what it could be or how I could identify the rock or mineral?— Preceding unsigned comment added by 71.137.246.92 (talk • contribs)

If you type "identifying rocks and minerals" into Google, you get several promising websites that do just that. Without a picture of said mineral for people here to look at, it would be VERY hard to identify. --Jayron32 17:08, 11 December 2010 (UTC)

Are you sure that it isn't just quartz? Some good specimens are quite clear. Does it scratch glass (do not try this on a good window)? Then it probably is quartz, one of the most common minerals. --Chemicalinterest (talk) 17:36, 11 December 2010 (UTC)

Depending on how you found it, it might actually be glass. I once found some frosty glass pebbles in a river. Best as I can tell, they came from a broken glass bottle (old glass bottles were often much thicker than window glass) which had been in the river long enough to weather to smoothness (this also explains the frosty color). -- 174.31.218.235 (talk) 19:03, 11 December 2010 (UTC)

Examples of specific halophiles

I'm looking for specific examples of slight halophiles, moderate halophiles, and extreme halophiles, but can't seem to find any. What are some examples of each? Albacore (talk) 19:41, 11 December 2010 (UTC)

The "Lifestyle" secion of that article gives some specific species (or families, or genus, etc.) as examples of moderate and extreme ones. Might also be useful to find a copy of Dieter Häussinger and Helmut Sies (2007) Osmosensing and Osmosignaling, Academic Press, 579 pages ISBN 0123739217, which is given as the reference for the statement "The extent of halotolerance varies widely amongst different species of bacteria." in the halotolerance article. DMacks (talk) 19:55, 11 December 2010 (UTC)

High pressure = good weather

Why is high pressure associated with good sunny weather, even in winter? Thanks 92.15.28.181 (talk) 19:47, 11 December 2010 (UTC)

Our atmospheric pressure article says "See pressure system for the effects of air pressure variations on weather", but the "Local atmospheric pressure variation" section-title makes it hard to find. The linked page talks in gory detail about how high pressure relates to lack of precipitation, reduced cloud-cover, etc. DMacks (talk) 19:52, 11 December 2010 (UTC)