Wikipedia:Reference desk/Science

Welcome to the science section
of the Wikipedia reference desk.

skip to bottom

Select a section:

• Computing
• Entertainment
• Humanities
• Language
• Mathematics
• Science
• Miscellaneous
• Archives

Want a faster answer?

Main page: Help searching Wikipedia

   

How can I get my question answered?

• Select the section of the desk that best fits the general topic of your question (see the navigation column to the right).
• Post your question to only one section, providing a short header that gives the topic of your question.
• Type '~~~~' (that is, four tilde characters) at the end – this signs and dates your contribution so we know who wrote what and when.
• Don't post personal contact information – it will be removed. Any answers will be provided here.
• Please be as specific as possible, and include all relevant context – the usefulness of answers may depend on the context.
• Note:
  • We don't answer (and may remove) questions that require medical diagnosis or legal advice.
  • We don't answer requests for opinions, predictions or debate.
  • We don't do your homework for you, though we'll help you past the stuck point.
  • We don't conduct original research or provide a free source of ideas, but we'll help you find information you need.

Ready? Ask a new question!

How do I answer a question?

Main page: Wikipedia:Reference desk/Guidelines

• The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.

See also:

• Teahouse
• Help desk
• Village pump
• Help manual

May 22

If Earth was great big ball of magnetism

If the earth was magically replaced with a new earth made totally from a strong magnetic material like neodymium what sort of impact would that have on the solar system? I know that gravity is really weak compared to the other forces so i'm just curious would an earth of neodymium pull other planets towards it? Would it have any effect on the sun? Mike --87.112.183.70 (talk) 01:17, 22 May 2010 (UTC)

I don't think so -- at the sorts of interplanetary distances involved, the gravitational force would still be much more of a factor than the magnetic force. Keep in mind, too, that the other planets would still be non-magnetic. FWiW 67.170.215.166 (talk) 05:17, 22 May 2010 (UTC)

This is a terrific question that I know will have several people puzzling. I can't speak much to the change in Earth's natural magnetic field at all - I will defer to someone who knows more about it - and I'm not sure how the polarity is set up in those Nd magnets. That said, most planets have natural magnetic fields, and if the field lines from two bodies reinforce each other, they will attract according to the cube of the distance from each other. This tapers off much more quickly than gravity, but even if it didn't, Earth's field may be strong but even Jupiter's, the strongest in the solar system, is relatively weak and will likely not result in much orbital disturbance.

It takes two good fields to magnetically tango. When magnets pick up pieces of metal like paperclips they do it by inducing a temporary field in the paperclip, because the iron in a paperclip is something that can quickly align as a magnet and then fall back out of it, depending on what other fields are in the environment (so it can attract itself to either pole of a magnet by rearranging itself, for example). A planet is not made out of this "ferromagnetic material". Most of them have heavy cores of iron or nickel, but those are far too high temperature to hold an attractive arrangement together to attract itself to the Nd Earth. However, Nd magnets are strong enough to induce magnetic fields in even non-ferromagnetic materials, even humans, and thus can make for neat household tricks (try dropping one down an iron tube).

In conclusion, I don't think this giant Nd Earth will have much direct effect on other planets, though someone will probably prove me wrong. SamuelRiv (talk) 05:24, 22 May 2010 (UTC)

I think that the neat trick you're thinking of involves dropping a strong magnet down a copper tube. The magnet will simply stick to an iron tube. APL (talk) 07:42, 22 May 2010 (UTC)

Now you've got me curious. What happens? Vimescarrot (talk) 07:57, 22 May 2010 (UTC)

assuming you've not already google'd it - here's a youtube video of what happens. (http://www.youtube.com/watch?v=30oPZO_z7-4) ny156uk (talk) 09:13, 22 May 2010 (UTC)

Nifty! Vimescarrot (talk) 15:27, 22 May 2010 (UTC)

This super magnetic earth will have an impact on solar wind it will probably drag all the solar wind nearby and accelerate it to the magnetic pole. It might also attract iron asteroids - especially if given enough time. I think the first order of business is calculating just how strong the magnet would be. Ariel. (talk) 02:11, 23 May 2010 (UTC) well u see magnet can attract only magnetic substances around itself. grationational pull of earth could be the reason of its magnetic effect but not the only one . gravitational force is effective between masses, gravitones are smallest particle exchange which goes on between the masses. if earth would be a giant magnetic ball then its shape and size will deform itself under many time period(permanent magnet is always in shape of a bar). their are few forces we know so we can think of it but many more types of orce do exist whose effect we don't know.......for more questions mail me to champgamy@gmail.com

rust forceps

i bough some German stainless steel Surgical OCHSNER Forceps. i put them on my sink counter. a few weeks later a small amount of rust appeared. hows that possible. —Preceding unsigned comment added by Tom12350 (talk • contribs) 04:57, 22 May 2010 (UTC)

What's your sink counter made of? If could the rust have come from that and not the forceps? This used as a source in stainless steel only says that stainless steel rusts less easily than normal steel. I'm no chemist though, hopefully someone can explain in more detail. 131.111.30.21 (talk) 08:59, 22 May 2010 (UTC)

Stainless steel is very resistant to oxidation by oxygen gas, where it forms a thin protective layer of chromium(III) oxide. If there is acid, the coating dissolves, starting the corrosion (although the rust dissolves too). If there is strong alkali, the coating dissolves, and some rust forms which is insoluble in alkali (iron is not amphoteric). But you shouldn't have strong acids and alkalis on your sink. --Chemicalinterest (talk) 10:51, 22 May 2010 (UTC)

[1] [2] Rust spots on stainless steel happen, for a variety of reasons.77.86.62.107 (talk) 14:51, 22 May 2010 (UTC)

Weather recce

What's an aerometeorograph, and what atmospheric parameters does it measure? 67.170.215.166 (talk) 06:06, 22 May 2010 (UTC)

From here "A self-recording instrument used on aircraft for the simultaneous recording of atmospheric pressure, temperature, and humidity." APL (talk) 07:30, 22 May 2010 (UTC)

Cool, three essential parameters measured with one instrument! Now, does anyone happen to know its typical weight and size, and also whether it's a self-contained instrument or whether it has to be hooked up to the plane's static port or OAT gauge? Thanks for the info! 67.170.215.166 (talk) 02:53, 23 May 2010 (UTC)

Update: Just looked up some pictures of modern units, they're quite small (about the size of your typical battery-powered portable emergency radio). So no problem about the size; the only thing I need to know is, is it self-contained or does it hook up to the plane's instrument systems? 67.170.215.166 (talk) 07:17, 23 May 2010 (UTC)

Can the acoustic guitar hurt your hearing?

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the talk page discussion (if a link has been provided). --TenOfAllTrades(talk) 13:40, 22 May 2010 (UTC)

TenOfAllTrades(talk) 13:40, 22 May 2010 (UTC)

Too fast to be an Iridium flare... so what was it?

I sat beneath the stars tonight for about an hour. I no longer have a grasp of the night sky, so all I can say is I was facing southwest (the Big Dipper was behind me somewhat). At one point, I saw what looked like a camera flash go off, but it was a pinpoint of light. It was extremely quick, no "few seconds" or "trail" that the Satellite flare article talked about. Then I noticed something peculiar... I kept staring at that spot and there was a second, almost imperceptible flash, just a hair to the left of the original flash. Huh! Anyway, time goes on and I'm staring to the northwest, closer to the Big Dipper, and again, there is a microburst of light way up in the heavens. This time I stared and stared, hoping to corroborate the secondary flash, and sure enough, after a few seconds, and just a fraction of some unknown stellar distance from the original flash was a second "pop" of light... What's up there, and is it rotating? I've seen dozens of "normal" satellites that are a constant reflection, a dot moving slowly across the night sky. I've never seen this before in my life. Any ideas? SR-71 taking pictures of me? :D – Kerαunoςcopia^◁_galaxies 09:17, 22 May 2010 (UTC)

It might be an airplane doing combat manuevers in the air. It also could be a meteor. Firecrackers? --Chemicalinterest (talk) 11:06, 22 May 2010 (UTC)

Without having seen it, it's hard to say for certain. It's also worth remembering that one's eyes can play tricks under low-light conditions. (For example, the second 'flash' might be just some sort of afterimage that you're seeing just because you're looking very hard for it. As well, to dark-adjusted eyes an object doesn't have to be particularly bright for it to look quite bright.) A couple of guesses: a meteor following a trail aimed almost directly at you, so that it didn't appear to move appreciably as it rapidly brightened and then disappeared. If the rock happened to break into more than one fragment, you might see a second flash. Another explanation could be tumbling space debris — the solar panels on a retired or 'lost' satellite, etc. That reflection would tend to have a much faster 'rise time' than an Iridium flare, and you might get a second flash as the satellite tumbled around. TenOfAllTrades(talk) 13:12, 22 May 2010 (UTC)

A fundamental problem we have here is not knowing how high was the artefact that caused the brief flashes. It could indeed be something as simple as a plane at altitude and you caught a solar reflection, you don't say how long after sunset this occurred. However the fact that it happened again in a different part of the sky makes me believe that it was some sort of image created by your eye or optic system. There are several non-pathological causes for the effect of "seeing stars" in a medical sense and I am not inferring that you have a medical condition that requires attention, I suggest this may be a possible reason for seeing microflashes of light. Richard Avery (talk) 14:59, 22 May 2010 (UTC)

It could easily be a satellite flare, just not an iridium reflection. There are other objects tumbling rapidly that could give a flash. If it is short you wont see a trail. Graeme Bartlett (talk) 22:09, 22 May 2010 (UTC)

Could it be a plane's anti-collision strobe lights? Many civilian planes have them, and they make bright white flashes every couple seconds. And if the plane was at high altitude (like an airliner at 30000 feet), then you can see the flashes but not hear the engine noise. FWiW 67.170.215.166 (talk) 02:58, 23 May 2010 (UTC)

If you remember the exact time, check the Heavens-above website. Count Iblis (talk) 16:56, 23 May 2010 (UTC)

Thanks, all. It wasn't an eye problem, it couldn't have been an airplane because I was watching for that, and beside, the night was absolutely crystal clear pitch black loaded with stars, and nothing was moving up there, and thanks for the Heavens Above website, but unfortunately I have no clue what time it was. Anywhere between 4 and 5 in the morning, but i have no watch. – Kerαunoςcopia^◁_galaxies 19:20, 23 May 2010 (UTC)

How many carbon black add in polypropelene polymers from protection SUN LIGHT

Dear, Plese, find answer headline and give me reply. thanks, Mr. jatin —Preceding unsigned comment added by Mjhirpara (talk • contribs) 12:14, 22 May 2010 (UTC)

More carbon black produces increased uv resistance.

This product [3] uses 3% carbon black.77.86.62.107 (talk) 15:03, 22 May 2010 (UTC)

See this book [4]77.86.62.107 (talk) 15:06, 22 May 2010 (UTC)

Iodine oxidation

Is sodium hypochlorite strong enough to oxidize elemental iodine (in its dilute state as household bleach)? --Chemicalinterest (talk) 12:19, 22 May 2010 (UTC)

Look up the reduction potentials for Cl⁺¹ → Cl⁰ or Cl^–1 compared to I⁰ → I⁺¹ to see which is stronger/able to oxidize or reduce which when you have these two redox half-reactions balanced. DMacks (talk) 15:06, 22 May 2010 (UTC)

There's a number of issues with this reaction:

• hypochlorite solutions are strongly basic - so the standard electrode potentials will need converting, or may not be applicable
  • particularily : Iodine disproportionates in alkaline solution to iodide and iodate
• Additionally Iodine reacts with chloride to form I₂Cl- and other reactions.

There's some more detail on iodine redox here [5] 77.86.62.107 , the chlorine potentials are also in this book a few pages before. (talk) 15:24, 22 May 2010 (UTC)

I never find the reduction potential for OCl^- + H₂O + 2 e^- → Cl^- + 2 OH^-; only see it for reduction to Cl₂. The iodide probably will be oxidized by NaClO when it is formed. --Chemicalinterest (talk) 17:04, 22 May 2010 (UTC)

It's in the above link, page 74 section C E=0.890V (in basic solution - not at [H+] = 1mol/dm3)

Probably the reason why it's never found as a standard E is that ClO- is unstable under standard (ie acidic) electrode conditions.87.102.18.191 (talk) 17:11, 22 May 2010 (UTC)

FWIW, "put a drop of solution on starch/iodide paper" is a standard test my students use for presence of hypochlorite in solution; turns dark if there is oxidizer available. See starch indicator and iodine test for some backround on what this might mean chemically. DMacks (talk) 18:55, 22 May 2010 (UTC)

Wembley Stadium grass - too dark?

Are the problems with the Wembley Stadium pitch simply due to the fact that the design of the stadium (high walls, roof) means that the grass does not get enough sunlight to grow properly? 92.28.248.33 (talk) 13:06, 22 May 2010 (UTC)

It seems unlikely, grass doesn't require a particularly high level of photosynthetically active radiation to grow. In fact at my house, the grass grows longer in the shade since there is more water available due to less evaporation. I'm not familiar with stadiums but I can't believe that Wembley is particularly different to any others and you'd think that they would have thought about it during the design stage. Reading this it sounds like it is more of a problem with it not being laid long enough before a game is played for a strong mat of roots to grow and form a good surface. 131.111.30.21 (talk) 16:33, 22 May 2010 (UTC)

The roof of Wembley was specifically designed to maximise the sunlight on the pitch, for the grass - that's why it's retractable. Vimescarrot (talk) 17:46, 22 May 2010 (UTC)

The stadium is in London, which is on the same latitude as Newfoundland, so it would not get as much intensity of sunlight as similar designs of stadium would in most parts of the United States for example. The grass is also 4 metres lower than it used to be, and the old design was less raked and roofless as far as I recall. 92.15.9.117 (talk) 18:04, 22 May 2010 (UTC)

dimple above penis

I have noticed that some men have a slight dimple just above the spot where the penis meets the pubis (this is normally only apparent if the pubic hair is shaved). Is this a medically recognised anatomical feature, and if so, what is it's name? Little radiolarian (talk) 13:14, 22 May 2010 (UTC)

Do you mean Apollo's belt? --Jayron32 04:25, 23 May 2010 (UTC)

Jayron -- I think he refers to the dimple in the midsagittal plane. It's a space between muscles that doesn't provide the support for the skin in that region as seen in the immediately surrounding areas -- anatomically, the space will fall in the midsagittal plane and will correspond to the skin and fatty tissue superficial to the suspensory ligament of the penis, just inferior to the pubic symphysis. DRosenbach ^{(Talk | Contribs)} 04:30, 23 May 2010 (UTC)

That certainly sounds like the same spot I'm describing. Would it be correct to describe this dimple as a surface feature of the pubic symphysis? If not, how would you refer to it (on the rare occasions one might have reason to)? Little radiolarian (talk) 15:25, 23 May 2010 (UTC)

I dreamt about this question last night, graphic imagery and all. Didn't even remember until I was passing through this question. – Kerαunoςcopia^◁_galaxies 19:16, 23 May 2010 (UTC)

According to the anatomy text I'm using (Moore), the pubic symphysis is too inferior to palpate -- probably because of both a low position and the erectile tissue being too massive to poke through. DRosenbach ^{(Talk | Contribs)} 01:28, 24 May 2010 (UTC)

The origin of life!!!!!!

I want to know how it was successfully verified that life on earth has arisen from complex molecules such as methane and oxygen was not present during the initial formation of life on earth? —Preceding unsigned comment added by Hitarth21 (talk • contribs) 14:58, 22 May 2010 (UTC)

Hi, your sentence is very confusing, can you rewrite it? Thanks. Beach drifter (talk) 15:00, 22 May 2010 (UTC)

Our knowledge and understanding of abiogenesis is very limited. There are some educated guesses about how it might have happened (see that article for details), but we don't really know. --Tango (talk) 15:50, 22 May 2010 (UTC)

TWO SCIENTIST DID AN EXPERIMENT: they took a round bottom flask, put two electrodes in it,filled it half with water, and put some rare gasses in same proportion they thought would have been present at the time of origin. they kept this setup for weeks at 100degree Celsius. electrodes are used for sparking mimicking lightning. and after weeks lo and behold1 TYHEY found key compounds needed to let life exist. THIS EXPERIMENT WAS CALLED MILLER'S EXPERIMENT ON THE NAME OF ONE OF THE GEEK. GOOGLE IT --Myownid420 (talk) 15:53, 22 May 2010 (UTC)

You're thinking of the Miller-Urey experiment. It was an important step in thinking about how life came about, though people today realize that the actual composition that they used probably wasn't very representative of Earth's early atmosphere. However, similar experiments have been done using other compositions, sometimes with interesting results. Buddy431 (talk) 16:23, 22 May 2010 (UTC)

Here are some of the problems with your original post:

1) Methane and oxygen aren't complex molecules, they are simple molecules (CH₄ and O₂). Oxygen, of course, is also a chemical element, O, but isn't normally found as a single atom.

2) The "complex molecules" you were probably thinking of are amino acids, the building blocks of proteins.

3) Then when you ask about whether scientists "verified that life on earth has arisen" from this process, you must realize that scientist can only propose a hypothesis that this is how it happened, as there's no fossil record of the original life forms. StuRat (talk) 16:30, 22 May 2010 (UTC)

The initial stages of the origin of life are still not clearly understood. To me it seems most likely that deep ocean vents are where the action took place. Regardless of that, there is very strong evidence that significant oxygen levels didn't show up until about a billion years ago -- the rocks that formed at the surface prior to that are not oxidized as they would be if high levels of oxygen had been present. Looie496 (talk) 16:52, 22 May 2010 (UTC)

AFAIK it is considered that oxygen was likely poisonous to early life. Vespine (talk) 22:55, 23 May 2010 (UTC)

Germ cell tumor

Whats the prognosis of a metastatic germ cell tumor —Preceding unsigned comment added by 24.97.164.250 (talk) 15:13, 22 May 2010 (UTC)

I assume you've read "Germ cell tumor#Prognosis"? Remember that Wikipedia does not give medical advice (see WP:MEDICAL). Gabbe (talk) 17:10, 22 May 2010 (UTC)

planets coming in align

in how many years does all planets come in one line. is it even possible or not? When they will align, will not it anyhow efffect Earth's life? if so then how.

<IN MY CLASS TEST ONCE I MADE ALL THE PLANETS IN ONE LINE AND MY TEACHER ASKED ME "WHAT IS THE PROBABILITY OF THIS". I SAID "MAY NOT IN COMING THOUSANDS OF LIGHT YEARS BUT SOME DAY IT WILL HAPPEN". I WANNA KNOW I WAS CORRECT OR NOT>

See Syzygy. How often it happens depends on how precisely you want them to line up. If you're happy with them just being in the same quadrant (ie. a 90 degree wide sector) then it will happen far more often than if you require them to be within a 1 degree sector, say. As for what effect it would have - none at all. About 70% of the combined mass of the planets is Jupiter, so all the planets acting together couldn't do anything significantly more than Jupiter can do on its own, which isn't much (as far as the Earth is concerned). --Tango (talk) 15:57, 22 May 2010 (UTC)

And when you consider the relative gravitational influence of solar system bodies on the Earth, you stop caring after the moon and the sun. Jupiter isn't even the most influential planet (it's 1/10th the effect of Venus), but none of them are meaningfully relevant. — Lomn 19:44, 22 May 2010 (UTC)

Ah, yes, I forgot it's tidal forces, not direct gravitational forces, that matter, so we need the cube of distance not the square. I believe Jupiter has the largest gravitational force out of the planets on Earth, just not the largest tidal force. Thanks for the link! --Tango (talk) 21:25, 22 May 2010 (UTC)

And a light-year is a unit of length, not of time. --Магьосник (talk) 16:37, 22 May 2010 (UTC)

Isn't there a particular name for this phenomenon?--Myownid420 (talk) 02:18, 23 May 2010 (UTC)

If you count Pluto as a planet, Neptune and Pluto "align" every 492 years ("align" = conjoin in geocentric celestial longitude -- it would be better to be heliocentric, but this is just for illustration). Uranus and Pluto align every 115 and 165 years, alternating. Uranus and Neptune align every 171 years. Saturn and Uranus align every 45 years. Saturn and Pluto align every 30-plus years, as do Saturn and Neptune. Jupiter and Saturn align every 29 years. And so on. Given that the solar system has been and will be around for billions of years, it's likely that at some point all nine planets will be within one degree of each other in heliocentric "longitude" because the product of all the periods is probably much less than several billion years. However, if you want alignment to within one arc-second, it seems unliekly that even the products of the periods will realistically indicate an exact nine-planet alignment, though I don't know the math for this. Anyone else? 63.17.50.130 (talk) 02:43, 23 May 2010 (UTC)

This data is based on short term observations. The solar system is basically an n-body problem; in the short term it can be predictable, but in the long term it becomes highly chaotic. So, we can pretty easily predict how often two bodies will be in line with the sun; but once we start waiting for three and four and five bodies to align in such a way, the time frame becomes long enough between occurances that chaotic effects take over and it literally becomes impossible to predict. --Jayron32 04:22, 23 May 2010 (UTC)

This happened about 5 years ago, all the red top papers in the UK were predicting workd disaster...nothing happened, just a normal day at the office. therefore, it does happen, rarely, but is of no significance to anyone. —Preceding unsigned comment added by 62.172.58.82 (talk) 14:24, 24 May 2010 (UTC)

I don't think anyone here would be happy to accept as evidence of multiple planet alignment, the word of red-top newspapers. --Tagishsimon (talk) 14:30, 24 May 2010 (UTC)

Solid phase extraction and Chromatography

Hi, I have just read both Solid phase extraction and Chromatography pages but I haven’t found the difference between techniques. I mean, they do the same thing and exploit the same principle or not? Thanks so much in advance, I ‘m studying Forensic pathology for next month exam.--151.53.91.218 (talk) 16:51, 22 May 2010 (UTC)

SPE deals with making the desired analyte specifically soluble/extracted or insoluble/stuck-to-solid-phase, the other starts and ends with the desired analyte in solution merely passed through. The key to SPE is where that article states "either the desired analytes of interest or undesired impurities in the sample are retained on the stationary phase" (emphasis mine) as opposed to the more general idea of chromatography "passing a mixture [...] through a stationary phase, [...] Subtle differences in a compound's partition coefficient result in differential retention on the stationary phase". Differential retention causes elution time to vary vs "retained or not-retained". DMacks (talk) 18:50, 22 May 2010 (UTC)

updates based on scientific fact

Shrimp are bottom feeders meaning their diet may include toxic substances including radioactive particles. However, since 1970 shrimp have been farmed in non-toxic environments. Consequently do any of the religions which in the past have excluded them from the diet now permit such non-toxic shrimp to be labeled "Kosher"? 71.100.3.228 (talk) 19:53, 22 May 2010 (UTC)

Toxins possibly being present in food has nothing to do with the food being or not being Kosher. Beach drifter (talk) 20:00, 22 May 2010 (UTC)

I think the toxin example is a bad one because it presumes to know the intent of the law, which would not sit with a religious person terribly well. (It assumes they have secular goals behind them; that is how an outsider views such things, not an insider.) But there are modern updates to things like kosher laws—for example, there is an entire industry of appliances designed to conform with Sabbath strictures as they are interpreted to apply to modern technology. See: Sabbath mode. In Judaism, there are rabbis who get together and debate whether or not, say, flicking a switch violates the strictures against "work", or whether setting an oven to heat up violates strictures against lighting a fire, and so on. --Mr.98 (talk) 20:52, 22 May 2010 (UTC)

To elaborate on Mr.98's concise post above, the laws of Judaism are immutable and the biblical violation of eating seafood that does not possess both fins and (easily scrape-off-able) scales (Leviticus 11:9) does not hinge on the toxicity or other physical uncleanliness of these organisms. DRosenbach ^{(Talk | Contribs)} 04:37, 23 May 2010 (UTC)

Okay then I'm really stumped here trying to explain why in this modern day why such ancient rules are not arbitrary but rather mandatory, unless they are intended to be arbitrary so they can serve more as test of obedience rather than anything else. If that is THE CASE and its just a matter of proving loyalty through compliance rather than compliance serving a practical purpose then not updating such laws makes more sense. 71.100.3.228 (talk) 07:54, 23 May 2010 (UTC)

"Why a religion has a certain rule" is not a scientific question. DMacks (talk) 08:13, 23 May 2010 (UTC)

Then what in your opinion is the purpose for a religion having rules? 71.100.3.228 (talk) 20:04, 23 May 2010 (UTC)

In any case, much of Judaism in particular is about doing what the law says even though you don't understand it. It is not and does not claim to be scientific. If you'd like a humorous send-up of Orthodox Jewish thought, which nonetheless gives a great (and entertaining) primer as to the logic behind it, I highly recommend Shalom Auslander's hilarious Foreskin's Lament: A Memoir. The basic philosophy is that you do what God says because God says to do it. As for whether the origin of the laws are based in some kind of secular purpose, well, there's been a lot of speculation about that, and that would be interesting for the anthropologist, but it would not be relevant to anyone practicing the religion. And I will note that my very reform cousins did not keep kosher at all, even at their bar mitzvahs and things like that (they served Hawaiian pizza, if you can believe it). There are multiple strains of thought within any religious heading. (I write all this as a nonreligious person myself, so if I offend anyone or have grossly caricatured a complicated thing, I apologize ahead of time.) --Mr.98 (talk) 12:53, 23 May 2010 (UTC)

What comes to mind are certain religious real world physical "journeys" in which the individual believer marks out the entire journey with a prone position to show devotion to its head. In any practical sense walking would be an update or flying in a plane but since the purpose is to show devotion to the religion's head by lying prone the entire length of the journey and walking or flying would not show this level of devotion they must be ruled out. From this perspective then I can see why religious rules would not be subject to update. 71.100.3.228 (talk) 20:12, 23 May 2010 (UTC)

Religious rules are subject to update - just, usually, not for scientific reason. Christianity is Judaism 2.0 (well, actually, a bag from 2.0 to 4.5 with plenty of mutually incompatible patches ;-) and Islam is essentially a merger of both rewritten from scratch. Looking at the early history of Christianity (which essentially started out as a jewish sect) shows significant debate of which laws apply to jewish Christians, and to gentile Christians. The laws given to Noah (don't kill, don't eat blood) were deemed to apply to all Christians (although the first has been very much rationalised away, and the second largely forgotten by now), but the Kashrut and circumcision were on the table for a while, too (with Paul being one of the strongest opponents of applying them to gentiles). --Stephan Schulz (talk) 20:46, 23 May 2010 (UTC)

Thanks for the Kashrut link. I have a friend who is developing meals that comply with individual diet plans which are based on varying amounts of commonly available foods which Kashrut will help guide. For instance, farmed shrimp was on the list until now. It would be nice in some cases though if the rules were updated to include farmed shrimp. 71.100.3.228 (talk) 20:59, 23 May 2010 (UTC)

(outdent) Religious observance is one of those things that really doesn't take kindly to an outsider trying to find technicalities or adjustments in how to apply or accommodate them. If you're trying to be polite and make certain populations feel welcome, you definitely take them on their own terms, however obsolete, confusing, nit-picky, or technicality/confusing-to-you they might seem. In fact, one of the tenets of Judaism and "follow its laws" I often hear is that you shouldn't try to find loopholes to excuse why you don't want to follow an observance (the flip side being whole movements that have taken a coherent look at deciding what observances are appropriate for modern-day). Or in a milder form, better to play it safe than to accidentally actually violate a law while trying to just tread close to the edge. Really, if you're trying to host an event where keeping kosher (to some level) matters (for some guests) ask them what they feel comfortable with. There's strictly kosher, who wouldn't even eat off your dishware and wouldn't drive to your venue on Saturday, there's "pretty kosher" who would be happy with a vegetarian option rather than putting you to the effort of cooking something really kosher, there's "kosher style" who would eat non-kosher beef but not a cheeseburger, etc. Just like there's vegan, lacto-ovo-vegetarian, "no red meat", etc. Actually, having a real vegetarian option (an actual entree, not just the side-salad) is a pretty good way to solve many different special diets (health, moral, religious). DMacks (talk) 21:45, 23 May 2010 (UTC)

I suppose the question arises from the use of the word "unclean" in reference to the different kinds of plant and animal that can be eaten as the basis for using a modern scientific designation of what is actually clean. Since shrimp are unclean from only what they eat it seems that if they are farm raised on only corn meal for instance that the designation of unclean simply cannot or would not apply. I'll ask the guests though from now on as the best strategy. 71.100.8.229 (talk) 03:15, 26 May 2010 (UTC)

Kashrut has nothing to do with unclean. Kashrut for animals is based on specific lists of things the animal needs to have. For a water-dweller (not just fish) it needs to have fins and scales. Shrimp doesn't. Unclean has nothing to do with it. Ariel. (talk) 11:38, 26 May 2010 (UTC)

magnetism versus temperature

what is the formula that relates and objects temperature to its magnetism? 71.100.3.228 (talk) 20:01, 22 May 2010 (UTC)

I'm not aware of one - maybe you were thinking of the Curie temperature .87.102.18.191 (talk) 20:25, 22 May 2010 (UTC)

So the state of magnetism undergoes a similar transition as state of matter phase change in which changes occur at junctures rather than continuously? 71.100.3.228 (talk) 20:49, 23 May 2010 (UTC)

Niel ?

I keep thinking I've heard of a "Niel temperature" - but search shows nothing. (Not Niels Bohr - I think it was a surname)

Is there a similarly name temperature or point - I'm sure it was a transition or phase change temperature.87.102.18.191 (talk) 20:27, 22 May 2010 (UTC)

Annealing temperature? --BozMo talk 20:34, 22 May 2010 (UTC)

:) (no) 87.102.18.191 (talk) 21:20, 22 May 2010 (UTC)

The Néel temperature is the temperature above which an antiferromagnetic material becomes paramagnetic. Cuddlyable3 (talk) 21:29, 22 May 2010 (UTC) Cuddlyable3 (talk) 21:29, 22 May 2010 (UTC)

Yes thanks. 87.102.18.191 (talk) 21:49, 22 May 2010 (UTC)

Resolved

What metals were thrown out by the icelandic volcano?

What heavy metals were ejected by the icelandic volcano?--92.251.177.211 (talk) 20:55, 22 May 2010 (UTC)

The material ejected by the volcano would have been basically basalt, which has metals in the form of silicates and oxides but none of the heavy metals are likely to be present other than in trace amounts, as far as I know. Mikenorton (talk) 21:26, 22 May 2010 (UTC)

Heavy metals are found in only trace amounts in basalt - but the overall effect of a volcanic eruption is to increase the levels of heavy metals in the surrounding area (in general) http://www.google.co.uk/search?hl=en&q=volcano+heavy+metal+emmision&meta=

In norway no effect had been noticed expected in this report http://www.niva.no/symfoni/infoportal/publikasjon.nsf/.vieEngInterForsideNIVA/1135331028BA9759C125770E00278CE0?OpenDocument&Category=&m1=News

[6] people are measuring this, but as far as I can tell the results aren't readily available as yet.87.102.18.191 (talk) 13:21, 23 May 2010 (UTC)

Is there any animal that can 'emit' fire?

Years and years ago I saw a wildlife documentary that featured a rainforest insect of some kind which (IIRC) as a defence mechanism was able to squirt a stream of *something* from its hindquarters which then spontaneously ignited in contact with the air, producing a small jet of flame. For some reason, I ended up discussing this with someone today, who insisted that I was wrong and asserted that there is no such and never has been any such creature. I'm open to the possibility that my memory is playing tricks on me and that I've mixed up something like a bombardier beetle (I looked that up first, thinking that it may have been what I was remembering) with Pokemon, or dragons - or that I saw it in a dream, or whatever.

So, does anyone know if there really is a bug, or anything else out there that can do this? --Kurt Shaped Box (talk) 21:05, 22 May 2010 (UTC)

I think you're just thinking of the bombardier beetle. There are no fire-breathing anything (other than people). --Mr.98 (talk) 22:07, 22 May 2010 (UTC)

Dragon —Preceding unsigned comment added by 79.76.233.61 (talk) 23:44, 22 May 2010 (UTC)

Animal, mythological creature. These are not equivalent, 79. Vranak (talk) 01:59, 23 May 2010 (UTC)

Salamanders are often associated with fire, though in reality they have very little to do with it. Buddy431 (talk) 04:12, 23 May 2010 (UTC)

It used to be thought that salamanders derive from fire, but it was later shown that they merely crawl from ground detritus when fire causes them to leave. See Slifkin's Mysterious Creatures (Targum Press 2003) ISBN 1-56871-248-0 (republished as Sacred Monsters) for a thorough review. DRosenbach ^{(Talk | Contribs)} 04:40, 23 May 2010 (UTC)

Any creature capable of setting fire to its environment would have made itself extinct by now.--Shantavira|^{feed me} 06:16, 23 May 2010 (UTC)

The conclusion being, any animal capable of emitting fire would have to live in a difficult-to-ignite environment. Vimescarrot (talk) 08:54, 23 May 2010 (UTC)

Or just be careful about what they ignite. I mean, humans are animals that are capable of setting fire to their environment. Yes, we've burnt ourselves a few times doing that, but it's hardly an evolutionary impossibility! --Mr.98 (talk) 18:49, 23 May 2010 (UTC)

Yes, but we've only been around for the blink of an eye. The (non-avian) dinosaurs still have about a factor of 1000 on us, and see where they are now. --Stephan Schulz (talk) 20:50, 23 May 2010 (UTC)

Not necessarily. Certain pines (I think Jack Pines are one), for example, need fire in order to germinate. If there isn't a periodic wildfire, they can be crowded out by other trees. (This has happened in portions of the western U.S., where there has been a "suppress all wildfires" policy for several decades.) Right now they require externally initiated fires, but one could easily imagine a hypothetical situation where a pine recognizes that it's being crowded by other species, so produces copious amounts of (fire-resistant) seeds, and then sets fire to the forest. Other species will be pushed out, and the seedlings now have ash-enriched soil to grow in. This might allow them to spread to wetter climates, where wildfires are not as wide ranging. -- 174.24.200.38 (talk) 17:48, 23 May 2010 (UTC)

A 2005 forum post [7] says: "There was an article a year or two ago in the NY Times, from a number of scientists who said that a fire-breathing animal was biologically possible." I haven't found the article. PrimeHunter (talk) 00:25, 24 May 2010 (UTC)

You're not thinking of fireflies, are you? (I wish I was a firefly I never would be glum Cos how could you be gloomy When the sun shines from your bum?)--TammyMoet (talk) 09:14, 23 May 2010 (UTC)

How about Bombardier beetle? RJFJR (talk) 17:42, 24 May 2010 (UTC)

The OP already mentioned the Bombardier beetle. --Tango (talk) 18:00, 24 May 2010 (UTC)

Black hole paradox

After watching an explanation of the black hole paradox from Leonard Susskind, the explanation made first at sense, but further thought has left me only more confused. First, a quick explanation of the paradox:

• When person 1 watching person 2 enter into a black hole, person 2 appears to freeze, and time for him stops due to the gravity. Person 2 will never progress beyond the event horizon from person 1's view.
• Time, however, does not stop for person 2; from his perspective, he will sail right past the event horizon.
• Point 1 appears to conflict with point 2. Thus anything done by person 2 inside of the horizon will be irretrievably lost to the outside world - this shouldn't happen though. Physics says that, in theory, person 1, with a perfect view of what's occurring, should be able to reconstruct person 2's past perfectly.
• The solution, as explain by Susskind and apparently mostly accepted by physicists, is that the information is stored on the surface of the event horizon, an unfathomably hot place where matter is squished into a two-dimensional (or essentially two-dimensional) plane.

What I don't understand is this:

1. For person 2, time on the outside world should go faster and faster. Right before reaching the event horizon, the world will speed up to infinite time. What then to make of what person 2 observes after passing the even horizon? (this situation, by the way, is far from just theoretical: the spaghettification on a smaller sized black hole apparently won't occur on supermassive black holes).
2. What of the matter towards the center of the collapsing star that becomes a black hole? That matter has no way of being "stuck" on the event horizon and as such wouldn't be visible as the event horizon slowly evaporates.
3. What happens to matter immediately inside the event horizon upon collapse? The gravity there would insist on a field faster than the speed of light. This seems to violate the laws of nature.

Magog the Ogre (talk) 21:25, 22 May 2010 (UTC)

I'm not sure what the problem is in your first question. Somebody falling into a black hole will see the outside world sped up (and massively distorted) and will observe things happening billions of years after they crossed the line in the few hours (at most) they can survive before being ripped apart, that's just the way it is. For your other questions, I don't think the problem exists since the collapse will happen from the inside out. The centre of the star will be the densest bit, so will become a black hole first and the rest of the star will fall into it. The event horizon will start out with very tiny diameter (you probably need a theory of quantum gravity to describe that bit) and grow. Your questions seems to be based on the assumption that the event horizon forms instantly at its final size, which isn't the case. --Tango (talk) 02:23, 23 May 2010 (UTC)

1. Remember that person 2 can only see what happens in his past light cone which will not include a infinite amount of the time of person 1
2. Tango answered question 2 pretty well above.
3. I'm not sure I understand your question, but be asured that any local observer (that is person 2) doesn't see any object passing by at a speed higher than the speed of light and light always is observed to move at the speed of light. He will, for instance, observe light rays moving outwards at the speed of light.

Dauto (talk) 02:45, 23 May 2010 (UTC)

Your bullet-point summary of the information paradox isn't really correct. "Losing" information behind an event horizon isn't a problem, because you can just say the information is on the other side of the horizon. Any surface that moves towards you at the speed of light behaves as an event horizon if you never cross it, including the unbounded redshift of objects falling through, the "gravitational" attraction, and even the Hawking radiation (though it's called Unruh radiation instead of Hawking radiation in some contexts). This is true even if you're out in the middle of nowhere and the "surface" is one that you just invented with no physical meaning whatsoever. Rindler coordinates has more information about this.

The problem with black holes is that they apparently can disappear completely by Hawking radiation, leaving nowhere for the lost information to go. People have proposed various unsatisfactory solutions to this, which you can find at black hole information loss paradox. The idea that infalling objects get "squished onto the event horizon" and then leave as Hawking radiation is the one called "Information gradually leaks out during the black-hole evaporation" in the article. The problem is that there's nothing physically special about event horizons, as I said above. You can define an event horizon anywhere, so the "new" physics should show up everywhere, unless you throw away the equivalence principle.

Susskind wants to solve this by having the "new" physics (where you turn into Hawking radiation) actually be mathematically equivalent to the ordinary physics (where you just fall through the horizon and nothing special happens to you). This sounds completely crazy, but there actually is a lot of circumstantial evidence for an equivalence ("duality") like this, and it's appealing because whereas the other solutions all break some nice physical symmetry (like unitarity or the equivalence principle) this one introduces a new physical symmetry, while preserving all the old ones.

I don't know why Susskind says that all physicists agree with him on this. Only a small number of physicists are interested in black hole information loss in the first place, and I've never had the impression that they agreed about much. I guess everybody now agrees that unitary is preserved (Hawking was the holdout, but changed his mind a few years ago). -- BenRG (talk) 21:44, 24 May 2010 (UTC)

May 23

Spider behaviour

In our shared house for university we have a dead spider that's been encased in some sort of plastic or wax near the ceiling for at least a year (before we moved in, damned if I'm gonna clean it!).

Today I've seen a big, similar sized spider climb up towards the dead spider about a day ago and it seems to be staying there up until this point of writing. It looks to be moving whilst up there too, and looks relatively healthy so I don't think it's dying.

That said, what would cause this sort of clinging behaviour to a dead, very-different-to-how-it-would-have-been-a-year-ago spider? Do spiders try to rescue their kind? Do they go off to die in similar places, or hang around with their dead counterparts? Is this just a coincidence and it might move in a couple of hours? Cheers!

Regards, --—Cyclonenim | Chat  02:32, 23 May 2010 (UTC)

You're presuming incorrectly that the source of the spider's attraction to that spot is the dead spider. Its attraction is to a good place to hang out; it would have no interest in the dead spider, but rather to that part of the ceiling itself. 63.17.50.130 (talk) 02:52, 23 May 2010 (UTC)

It certainly could move in a couple of hours, maybe to someplace you wouldn't like. If you want to dispose of it, try extending your vacuum cleaner's hose attachment, and the critter's last thought will be about how life sucks. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:57, 23 May 2010 (UTC)

Ha, yes maybe. Maybe it is a good place to hang out, but it's not even in a corner or somewhere remotely comfortable. It's just sitting on top of the dead spider. Regards, --—Cyclonenim | Chat  12:13, 23 May 2010 (UTC)

Would you rather live with a dead spider on your ceiling than to clean it? Dauto (talk) 03:31, 23 May 2010 (UTC)

Well it's never really been an issue, I guess it's hard to not sound disgusting unless you've actually seen where we're living. The place is an absolute shit hole as it is, a little dead, encased-in-wax spider from the previous occupiers isn't really going to bother me. Regards, --—Cyclonenim | Chat  12:13, 23 May 2010 (UTC)

How Spiders Work Count Iblis (talk) 16:42, 23 May 2010 (UTC)

Aircraft repairs, part 2

If the same saboteur as cut the generator wires also puts emery powder into the propeller pitch-change mechanism, could the damage be repaired by replacement/repair of parts and subsequent regreasing, or does it require replacing the whole screw? (Assume that the screw in question is a two-bladed Hamilton-Standard Hydromatic, if that helps.) 67.170.215.166 (talk) 03:07, 23 May 2010 (UTC)

• Hmmm, the wikipedia has a legal disclaimer, medical disclaimer, isn't it time for a "life critical systems disclaimer"? Right, I know that 67.170.215.166 wrote about a fictional setting, not real hardware, but what if one day someone takes wiki-advice on this matter seriously? East of Borschov (talk) 04:59, 23 May 2010 (UTC)

This kind of work is only done by licensed aircraft mechanics, and they know enough to always refer to the manual, not the Wiki reference desk. So there's no chance of this advice being taken seriously. 67.170.215.166 (talk) 05:57, 23 May 2010 (UTC)

Speaking of which, this being a reference desk, I suggest that you might consider referring to an aircraft mechanic. If you have trouble locating one, give me the identifier of your nearest local airport and I can see if I can help. Falconus^{p t c} 14:13, 23 May 2010 (UTC)

I believe this question refers to a fictional novel the OP is writing in which a pilot needs to make some emergency repairs to his plane (in a rainstorm, if I remember correctly), as the second part of a question he posed on the Ref Desk a few days ago. Hence, "Part 2." OP, you might give us a quick recap so we're all on the same page here. AlexHOUSE (talk) 21:57, 24 May 2010 (UTC)

Well, the story is, the pilot and crew are making a flight around the world (which is a scientific mission to study climate change as well as a commemorative flight for Amelia Earhart), and they're forced down in Pakistan due to engine problems, and while getting the spare parts they get in trouble with the local mutaween for breaking sharia law and decide that they have to escape to India; but one of the mechanics happens to be racist against Americans (which is very common in Pakistan, by the way) so he sabotages the plane by cutting the generator wires and reattaching them in such a way that they would vibrate loose in flight (so that the pilot wouldn't notice until well under way) and also loosens one of the engine exhaust valves to make it drop into the cylinder and wreck the engine. Well, after reading a recent posting by Alex Mandel on the Amelia Earhart talk page, I got an idea to have the said anti-American mechanic also throw some emery powder into the propeller pitch change mechanism in the hope that the prop would get stuck in the wrong pitch and hopefully make the plane crash on takeoff. My idea is that he does that, but the crew catch the malfunction in time and fix the propeller; but this will be contingent on how long it will take (the flight can't be delayed too long because of the monsoon season arriving). So if the damage can be fixed by simply re-grinding the damaged parts and/or replacing them with brand-new parts and then regreasing the mechanism, then I'll go ahead and put it in the novel; but if it requires replacing the whole prop, then I'll have to skip it because it will take too long to repair. So what's your take on this? 67.170.215.166 (talk) 06:09, 25 May 2010 (UTC)

No experience with pitch-change mechanisms in particular, but I wouldn't expect emery powder (or sand, or any other abrasive) to be fast-acting enough to cause problems on the flight. Six months down the road is another matter entirely. --Carnildo (talk) 00:00, 26 May 2010 (UTC)

Stable ranges for Albedo and Emissivity of Earth

The Earth has a Global Annual Average Temperature of 14°C.
The Global Average Albedo is 0.30 and the concomitant Emissivity is 0.622.
Hence:
$T_{p}={\frac {((6.955\times 10^{8})^{2})\times (5778^{4})\times (1-0.3)}{(4\times 0.622\times 149597876600)^{2}}}={14}$
(derived from Luminosity)

So I was wondering how far that 14°C can shift and the planet still sustain some "liquid water,"
somewhere on the planet, what range is possible, and also what is range for the Albedo,
and the range for the Emissivity, for a stable habitable temperature for Earth life?
For clarity, this question is only about the Earth, as a reference point, not exo-moons.
Earth's temperature range is 60°C to -90°C, or 150 degrees.
There must be limits.
Global Annual Average Temperature Maximum: ??
Global Annual Average Temperature Minimum: ??
Minimum Albedo: ??
Minimum Emissivity: ??
Maximum Albedo: ??
Maximum Emissivity: ??
24.78.178.147 (talk) 01:30, 23 May 2010 (UTC)

I won't answer your question, but I will fix your equation.

$(T_{p}+273.15)^{4}={\frac {((6.955\times 10^{8})^{2})\times (5778^{4})\times (1-0.3)}{4\times 0.622\times (149597876600)^{2}}}=(13.78+273.15)^{4}$

T_p=13.78°C Dauto (talk) 05:48, 23 May 2010 (UTC)

Thanks, I missed that because I'm used to Excel not the code here.
((((((695500000)^2)*(5778^4)*(1-A)/(4*ε*(149597870690^2)))^0.25)-273.15) = 14.000
A=0.3
ε=0.62009
24.78.178.147 (talk) 04:42, 24 May 2010 (UTC)

Pineal gland

Is serotonin produced in the pineal gland? At present our article on this gland makes a big deal in the opening paragraph of serotonin as a product of the gland. If it's true, it's a secondary or minor function of the gland and the info needs to be moved further down. I'd rather cut it out, but need to be sure. Thank you. --Hordaland (talk) 07:14, 23 May 2010 (UTC)

I know melatonin is produced from serotonin in the pineal gland. (Melatonin in retina and in the digestive tract is a different story). Serotonin is produced from tryptophan, not sure where. --Dr Dima (talk) 08:25, 23 May 2010 (UTC)

What I mean by "not sure where" is as follows. The primary location of the serotonergic neurons in the human brain is the raphe nuclei (a part of the reticular formation) in the brainstem. What I'm not sure about is whether they produce most of their serotonin locally, or whether they "recycle" serotonin that is produced elsewhere. I'm pretty sure that serotonin is produced in the digestive tract, too. How much of it is produced in the pineal gland, how much in the raphe nuclei, and how much in the gut - I do not know. --Dr Dima (talk) 08:34, 23 May 2010 (UTC)

According to PMID 8745273, serotonin is indeed released by the pineal, although its main function there is to serve as precursor for melatonin. I believe the accepted concept is that serotonin serves as an autocrine hormone (i.e., affecting the pineal itself), rather than exerting significant effects elsewhere. Certainly the pineal, being a gland, does not send specific serotonergic projections to parts of the brain, as the Raphe nuclei do. Looie496 (talk) 16:50, 23 May 2010 (UTC)

Thank you for your answers, confirming what I suspected was the case! Meanwhile, someone else has fixed that paragraph, saving me the trouble. Hordaland (talk) 20:28, 23 May 2010 (UTC)

Intramuscular fat

I'm a bit lost here, so this could be a silly question, but I'm wondering if it's possible to sort of "target" certain types of body fat, in this case IMTG, when chosing a diet? Thinking retroactively, eating chips and french fries seems to have a larger effect on visceral fat, or at least a large effect, but is there any, healthier alternative that might have less of an effect on a certain, less desirable "unhealthy" fat types, and help to produce intramuscular fat (IMTG)? This is a bodybuilding/nutrition question! 210.254.117.185 (talk) 09:24, 23 May 2010 (UTC)

The relevant article is spot reduction, which says any kind of targeted fat loss is a myth - regrettably that article is pitifully underreferenced. -- Finlay McWalter • Talk 09:37, 23 May 2010 (UTC)

I wasn't asking about fat loss, I was asking about the increase of a certain type of fat. Even if it was related (though in reverse), IMTG and visceral fat are made by a difference process, where as the article you linked talks about the same type of fat on different parts of the body. 210.254.117.185 (talk) 10:16, 23 May 2010 (UTC)

CO2 and infrared radiation

If you double the concentration of CO₂ in a glass container, say from 0.03% to 0.06% (can't think why I chose those numbers!) what happens to the percentage of infrared radiation that will be absorbed? Does it double (i.e. it's a linear relationship) or does it only increase by say 25% (i.e. it's logarithmic). Hopefully someone has actually done an experiment to show this! 131.111.30.21 (talk) 11:07, 23 May 2010 (UTC)

The answer is given by the Beer–Lambert law - assuming that the absorbtion is linear with concentration - which I'm sure it will be. Also did you mean reflection of IR (as per global warming)?87.102.18.191 (talk) 11:22, 23 May 2010 (UTC)

So the absorption coefficient will double - this means the ratio of light passing through (before and after) will be:

e^-ax / e^-2ax = e² = 7.4 times less light after doubling the concentration.87.102.18.191 (talk) 11:32, 23 May 2010 (UTC)

Yea sorry, meant reflect. Does that change the figures above? 131.111.30.21 (talk) 12:11, 23 May 2010 (UTC)

I think so yes - will have to go and check.. (hang on)87.102.18.191 (talk) 12:33, 23 May 2010 (UTC)

Actually I think I was wrong to say that reflection of IR is the factor behind global warming.

The equations for reflected light will be those of scattering - however I'm not sure if the scattering is elastic or not - I think CO2 can reflect by Raman effect at least.

Someone else will need to answer this.87.102.18.191 (talk) 13:01, 23 May 2010 (UTC)

Clarify: That would be 7.4 times less light NOT being absorbed (ie if 93% of light was absorbed before, then 7% escapes, after doubling CO2 only 1% escapes..)87.102.18.191 (talk) 13:44, 23 May 2010 (UTC)

In the case of the atmosphere the very low concentration is already enough to absorb most of the radiation so doubling makes little difference. However temperature is not relative to zero degrees Centigrade but absolute zero at -273°C so the 'little difference' can still mean a few degrees change. Dmcq (talk) 12:38, 23 May 2010 (UTC)

Where should I start?

1. Absorption of IR by CO₂ is the cause of greenhouse effect.
2. The equation used to get the figure 7.4 is completely wrong
3. The effect of the doubling of CO₂ concentration on how much IR gets absorbed depends on how thich is the path of the light through the container. If the path is thin enough that most of the radiation does get through, then doubling the concentration does double the absorption, but if the path is so thick that most of the radiation is already getting absorbed, then doubling the concentration has little effect. Think about it. If you look up at the sky through a canopy which has just a few liefs then doubling the number of liefs does double the fraction of the sky that's is covered but if you are looking through a canopy so thick that it already covers most of the sky than doubling the number of liefs has little effect.

Dauto (talk) 03:54, 24 May 2010 (UTC)

Can you explain 2 in more detail - assuming the atmosphere stays the same thickness - as an approximation, how is the Beer-Lambert law wrong here?87.102.85.123 (talk) 11:42, 24 May 2010 (UTC)

The law is not wrong. The calculation performed is wrong. Dauto (talk) 16:36, 24 May 2010 (UTC)

I see the error - the absorption coefficient doubles (?), or in the case of the equation T=I₀e^-σlN N doubles with double concentration.

So the ratio T1/T2 =

I₀e^-σlN/I₀e^-σl2N

e^-σlN/e^-σl2N

T1/T2=e^σlN

or T2=T1e^-σlN

So if 90% of the light was originally absorbed, then after doubling the concentration, a further 90% of the remaining unabsrobed light would be absorbed, or 90% of 10% - total 99% absorbtion.

Is that right?87.102.85.123 (talk) 17:31, 24 May 2010 (UTC)

Yes. Dauto (talk) 03:22, 25 May 2010 (UTC)

No, that is wrong. For the greenhouse effect, it is not relevant how much direct transmission there is ("how much sky can I see"), but how much light is transmitted at all, including diffuse light that has already interacted with one or more leafs. The canopy is actually not too bad an analogy. Even if you cannot see the sky at all, doubling the thickness of the canopy will reduce the amount of light that reaches the ground (for any given input). --Stephan Schulz (talk) 08:13, 24 May 2010 (UTC)

Yes Schultz, you're correct. I was simplifying my description to make a point. Dauto (talk) 16:36, 24 May 2010 (UTC)

Ok that makes more sense, so it is logarithmic rather than linear? Does anyone do direct measurements of infrared reflection by the atmosphere? I.e. shine an infrared laser from somewhere like Mauna Loa Observatory to a satellite and then see how this is changing over time? 131.111.30.21 (talk) 08:49, 24 May 2010 (UTC)

IR reflection is irrelevant here. IR absorption (and re-emition) is what has to be measured. Dauto (talk) 16:36, 24 May 2010 (UTC)

Yes, overall climate sensitivity is logarithmic. In other words, doubling CO2 causes an equilibrium temperature increase of 3 degrees centigrade (roughly best current estimate, but there are fairly large error bands). Note that the earth has a lot of thermal inertia, so the effect lags the cause significantly. --Stephan Schulz (talk) 14:23, 24 May 2010 (UTC)

Sneezing during examinations

The last couple of years I've been noticing that I do a disproportionate amount of sneezing about 15 minutes into an examination, and I'm interested in why this might be. I don't suffer from hay fever, and I don't sneeze a lot generally. Could it be a reaction to the stress of exams? There's nothing to sneeze - my airway isn't blocked, for example - and once it's done I generally don't sneeze again. My other thought was a slight allergic reaction to the surroundings, but I've noticed it happening in two different examination halls. Of course, it could all be down to observation bias, or any number of other biases, but I don't think it is, and it does intrigue me, so I thought I might ask. Thanks, - Jarry1250 ^{[Humorous? Discuss.]} 13:04, 23 May 2010 (UTC)

• Was it an air-conditioned room? could be adjustment to AC or just some draft. Or, perhaps, simply adjustment to sitting (as opposed to active walking etc.). East of Borschov (talk) 13:21, 23 May 2010 (UTC)

Preparation of examination rooms often requires moving furntiture etc - maybe this produces a lot of dust?87.102.18.191 (talk) 13:45, 23 May 2010 (UTC)

Yes. Inhaling dust and sneezing are inextricably linked. I would also say, normally if a person finds themselves in a dusty room, they might open a window, or leave -- but when you're writing an exam, these are not good options ("Excuse me miss, you have to hand in your test before you leave. No you may not leave the room and then return. I can't allow that."). Unable to deal with the dust in this fashion, all they can do is keep breathing it in -- and sneezing to help keep the nasal passages clear and clean. Vranak (talk) 13:59, 23 May 2010 (UTC)

Dust seems like a good suggestion, the exam tables and whatnot must accumulate a load during the year. Previous locations may have been air-conditioned, but I'm 99% sure the place I'm sitting this years isn't (they open windows, doors, etc.) - Jarry1250 ^{[Humorous? Discuss.]} 14:29, 23 May 2010 (UTC)

At my old school they placed down canvas tarpaulins on the gymnasium floor for examinations. I'm fairly sure they got no use apart from the exams in January and June, so I suspect a lot of dust would be stirred up whenever they got moved or walked on. Always had to take an anti-histamine tablet on the day of an exam, since sniffles were a problem. Brammers (talk) 10:57, 24 May 2010 (UTC)

Another possibility: Because stress stimulates the Autonomic nervous system, for example it makes you feel like you have to pee. Maybe in your case it is something similar? 195.35.160.133 (talk) 13:16, 25 May 2010 (UTC) Martin.

Why does sugar make things less sour?

So lets say you are making lemonade. Why is it that sugar makes it less sour? Does the sugar flavor overpower the sour flavor, or does it negate it? Or I should ask, would other flavors, like salt (saltiness) for example, make it less sour as well? ScienceApe (talk) 15:56, 23 May 2010 (UTC)

Sourness is due to acidity Taste#Sourness - adding sugar doesn't affect the acidity. Lemonade sourness is in part due to the citric acid , and also due to dissolved carbon dioxide (if it's fizzy type). There's not a reaction between sugar and citric acid to be expected in lemonade (though it could possible esterify) I'm fairly certain it is a masking effect.87.102.18.191 (talk) 16:25, 23 May 2010 (UTC)

Sweetness competes with each of the other basic tastes (sour, salty, bitter), in the sense that increasing sweetness reduces the perception of the others, and increasing the others reduces the perception of sweetness. A notable example is tonic water, which doesn't seem sweet to many people even though it is almost gooey with sugar. I'm not sure whether the other basic tastes compete with each other (sour versus bitter or sour versus salty, for example). Looie496 (talk) 16:39, 23 May 2010 (UTC)

There's a significant difference between the taste of "straight" tea and coffee, which tend to be bitter, vs. adding sugar to them. The one I'm not sure you can do much about is saltiness. I can't think of any obvious way to counter saltiness other than simply diluting it (as you could with the other items as well). ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:30, 23 May 2010 (UTC)

The old wives' way of adding a potato to oversalted stews (and then discarding the potato, which will have absorbed the excess salt) does work. Never tried it for anything else, though. --TammyMoet (talk) 09:59, 24 May 2010 (UTC)

Has anyone seen Neptune with the naked eye?

Although it is commonly claimed that Neptune is too faint to be seen with the naked eye, this is not really true.

Brian skiff has tried but he failed to see it. The conditions were not optimal as Neptune was low in the sky. He claims that from the Southern Hemisphere it would be straightforward to spot. So, this suggests that there should be quite a few (amateur) astronomers with excellent eyesight who have seen it, but I haven't seen any such claims. Count Iblis (talk) 17:53, 23 May 2010 (UTC)

At a magnitude of ~8-7.78, it would require exceptional conditions to see it: an experienced astronomer who knows how to look for faint objects, exceptionally clear sky, hundreds of kilometers from any city, and knowing exactly where to look. Even if you could, by some miracle, manage to see it, I'm not sure that you could distinguish it from any other faint star out there. Do you know the positions of the tens of thousands of stars at least that bright with a high enough degree of precision to distinguish one barely visible point of light from another one? As the forum points out, even Uranus, with a magnitude of up to 5.32, and 4 Vesta, of magnitude up to 5.1, were not discovered and named until telescopes were around. I would hazard a guess that most celestial objects dimmer than magnitude 5 were not cataloged and named until after the invention of the telescope. Now granted, "named and recognized" is not the same thing as "ever seen", but if you can't recognize a faint dot as Neptune, do we really count that as "seeing" it? Buddy431 (talk) 18:22, 23 May 2010 (UTC)

Yes, "seeing Neptune" with the naked eye would be a tour de force involving detailed star charts and identifying all the brighter objects in the immediate neighborhood. But note that quite a few (amateur) astronomers do exactly this sort of a thing as a sport, but usually for spotting Messier objects with the naked eye. They keep logs of successful naked-eye observations, see e.g. here. So, given this dedicated effort, I find a bit strange that only [Brian Skiff's report] of his failure to see Neptune exists. Count Iblis (talk) 00:24, 24 May 2010 (UTC)

Incidentaly, Wikipedia doesn't have a comprehensive list of astronomical objects (or even stars) by magnitude that's very good. We have the List of brightest stars going down to magnitude 2.5. It would be nice if we could get lists for the other ranges (i.e. List of stars with magnitude 2.5-3.5, list of stars with magnitude 3.5-4.5, etc). If there are machine readable star catalogs available, such lists could be made with some sort of bot. Of course, such lists may be seen as "indiscriminate" by the deletionists here... Buddy431 (talk) 18:49, 23 May 2010 (UTC)

The problem with such a table is that the number of stars at magnitude X grows exponentially in X (there are roughly 3 times more stars with magnitude 2.5-3.5 than with magnitude 1.5-2.5, and another 3 times more with 3.5-4.5). So you get into really large numbers really fast - and I suspect for most of these stars we have very little information. --Stephan Schulz (talk) 11:41, 24 May 2010 (UTC)

I'm envisioning something along the lines of our list of minor planets. There's only about 10,000 stars in the Bright Star Catalogue (as opposed to 200 000 minor planets...), which would easily be manageable if broken into sets of 1000 or so. Even the Henry Draper Catalogue "only" has 350 000 entries: I imagine some sort of manipulatable list could be created from it too. It looks like the astronomy club here is currently trying to improve the table for their minor planets: maybe I'll drop by and try to urge them to work on stars next (I know, I know, or I could do it myself... much too lazy for that). Buddy431 (talk) 16:57, 24 May 2010 (UTC)

No fish

Is there a term for someone who eats meat, fruit and vegetables but doesn't eat any fish? Servien 18:47, 23 May 2010 (UTC)

Closest I've found so far is Pollotarianism, which excludes fish and mammals. Vimescarrot (talk) 18:53, 23 May 2010 (UTC)

Are there enough people that fit that description to warrant having a name for it? --Tango (talk) 19:17, 23 May 2010 (UTC)

I know two. They can eat mammals such as whale but are highly allergic to all fish (salt water and fresh), seafood and crustaceans. It is one of the nine most common food allergies. Kittybrewster ☎ 19:29, 23 May 2010 (UTC)

Reverse pescetarian? Clarityfiend (talk) 20:23, 23 May 2010 (UTC)

How does anti-pescatarian sound? Or just apescatarian. Vranak (talk) 21:03, 23 May 2010 (UTC)

Like they wouldn't eat fruits or vegetables either. Clarityfiend (talk) 21:09, 23 May 2010 (UTC)

Pesca- just means fish though. Apesca = no fish. Vranak (talk) 21:33, 23 May 2010 (UTC)

Heh, nice term. I guess that applies to me. I eat meat, vegetables and fruit, but I'm not a fan of fish so I don't eat it. Regards, --—Cyclonenim | Chat  22:33, 23 May 2010 (UTC)

Of course it's hard not to notice that the first part of the term forms the words ape scat. Vranak (talk) 22:47, 23 May 2010 (UTC)

Jane Brody has used the term "pescaphobia". Looie496 (talk) 22:58, 23 May 2010 (UTC)

That implies an irrational fear of fish, but if one is allergic, it's a rational fear, and if one simply doesn't like the taste of fish, that's neither irrational nor a fear, it's just personal preference. That does not preclude the possibility that there could be some having an irrational fear of fish. However, terms like vegetarian and vegan are preferred over "carniphobia" or whatever the equivalent would be. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:03, 23 May 2010 (UTC)

So there simply is no official term for a "no-fish eater"? Some time ago I thought of the term anichthyophagist the verb beeing anichthyophagia (from Latin) Sεrvιεи | T@lk page 20:51, 25 May 2010 (UTC)

Bird call

What bird is this? http://commons.wikimedia.org/wiki/File:Unknown_bird_call_MN_052210.ogg

Taken 2010-05-22 in Interstate State Park. I was not able to see the bird making this call (all weekend!).

-Ravedave (talk) 20:37, 23 May 2010 (UTC)

Dragons

Are we absolutely sure that dragons have never existed? I find it interesting that almost every part of the world has stories about dragons of some form or another. Seems strange for something that was never real. If there *were* dragons (not saying fire breating and flying, which AFAIK would be impossible - just really big carnivorous reptiles, or even the long, thin, Chinese-style water-based ones) and their numbers were declining at around the same time that humans were becoming civilized, and the last few had been wiped out before 1000AD (say), would there even be any ovbious evidence today of their existence? Just curious. --95.148.108.186 (talk) 21:06, 23 May 2010 (UTC)

If they don't breathe fire or fly, why would anybody call them dragons instead of "just really big carnivorous reptiles"? Clarityfiend (talk) 21:14, 23 May 2010 (UTC)

Because they were stories of heroism that were exaggerated in the telling and re-telling? Going from a dinosaur/big lizard-like creature, to something with borderline magical powers? Don't know really, I was just thinking on the screen. :) --95.148.105.95 (talk) 21:25, 23 May 2010 (UTC)

Really big carnivorous reptiles? Like crocodiles and alligators? Or dinosaurs? They definitely exist(ed). --Tango (talk) 21:20, 23 May 2010 (UTC)

Or Pterosaurs? ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:45, 23 May 2010 (UTC)

Or Komodo dragons? "really big carnivorous reptiles" ... check, check, and check. We even call them "dragons". -- 174.24.200.38 (talk) 01:24, 24 May 2010 (UTC)

I believe the biggest issue is that dragons have, by classical definition, six appendages (four legs and two wings), while (and correct me if I'm wrong), all other higher land-going lifeforms have four. Snakes of course don't count; they have none. But six, no, that just doesn't seem feasible from an evolutionary standpoint. And then there's the small matter of there being no fossil record of such a thing. Vranak (talk) 21:31, 23 May 2010 (UTC)

Take a look at draco (genus). Looie496 (talk) 22:54, 23 May 2010 (UTC)

Fair enough! I'll revise that 'classical definition' then -- four legs and flappable wings, for more than just gliding. Vranak (talk) 23:19, 23 May 2010 (UTC)

two points, both from Dragon

• in Origin and Etymology "Dinosaur and mammalian fossils were occasionally mistaken for the bones of dragons and other mythological creature; for example, a discovery in 300 BC in Wucheng, Sichuan, China, was labeled as such by Chang Qu...." ... more in that section
• in Dragon#Indian , after removing hyperbole, appears to be a description of a Python

Anyway , if it didn't exist you'd have to invent it .. those long cavemen evenings without TV, and kids always asking "what is there over there/below"87.102.18.191 (talk) 21:37, 23 May 2010 (UTC)

I'm also likely to believe the idea of dragons being an exaggerated folk memory (of v. big snakes and crocs) - reason - apparent absense of dragon myths in countries that do have big snakes and crocs.87.102.18.191 (talk) 21:43, 23 May 2010 (UTC)

Folk memory, yes. Perhaps as with other mythical creatures, e.g. the unicorn. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:47, 23 May 2010 (UTC)

They probably come from descriptions of rhinoceri. (original research?) --Kurt Shaped Box (talk) 21:54, 23 May 2010 (UTC)

I've heard that theory before. And there typically weren't any rhinos in Europe, just the Rhineland, which is unrelated as far as I know. There's a much more modern analogy, though, and that is the current stereotype of what flying saucer aliens look like, i.e. like the characters in Close Encounters and E.T., which apparently evolved over time from the appearance of primitive crash-test dummies used in high-stratosphere balloon tests. This contrasts with The Day the Earth Stood Still, where the aliens looked like Michael Rennie. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:00, 23 May 2010 (UTC)

Which, trust me, was a lot more scary. HalfShadow 22:01, 23 May 2010 (UTC)

Yep. Klaatu barada nikto, and all that sort of thing. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:03, 23 May 2010 (UTC)

I have to ask -- I know this phrase from Army of Darkness, but does it have any deeper/earlier meaning? Vranak (talk) 23:18, 23 May 2010 (UTC)

We have an article on it, which I've now linked. Without looking at it first, I know "Klaatu" was the name of the alien played by Michael Rennie, and the whole phrase was spoken to the robot Gort, which somehow told him where to find Klaatu. That's a lot of info to be contained in 2 words, but the robots were programmed with a series of commands which were like shorthand of some kind. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:26, 23 May 2010 (UTC)

An excellent book on the subject is The Natural History of Unicorns by Chris Lavers. The Indian rhinoceros certainly played a part in the creation of the unicorn, but it's an extremely complicated tapestry that includes several animals native to central Asia, including the chiru. The interesting thing about the unicorn is how sure everyone was that it existed. Our article on Harry Johnston notes that "[H]e was instrumental in bringing the okapi to the attention of science", but he wasn't wandering Africa looking for the okapi - he was searching for the unicorn. And why look in Africa when all the stories said it came from Asia? Because it had to live somewhere and Africa was the only place left to look... Matt Deres (talk) 01:14, 26 May 2010 (UTC)

Also note that different parts of the world having stories about "dragons" is not terribly telling. A Chinese dragon isn't all that similar to a European dragon other than the fact that they're both mythical reptiles. Do big, scary (or auspicious, depending on your point of view) exist? Absolutely. Buddy431 (talk) 23:01, 23 May 2010 (UTC)

I have heard it proposed, though not directly by the experts of the field, that it goes way back. When our mammalian ancestors were evolving, there were still dinosaurs around. It would stand to reason that early mammals would have been extraordinarily cautious about large carnivorous reptilian animals. The theory that was proposed is that the reason that many human cultures have a dragon of sorts is just because those descriptions stand out to us on residual instinct. Now is that likely after 65 million years? I have no clue, maybe someone else can comment. Falconus^{p t c} 00:27, 24 May 2010 (UTC)

Hey, this seems to be directly related to what I just said above. An Instinct for Dragons.Falconus^{p t c} 00:33, 24 May 2010 (UTC)

I try to refrain from just giving comments which don't add to the discussion, but i have to say the above is just absolutely fascinating! What an amazing hypothesis. Vespine (talk) 00:55, 24 May 2010 (UTC)

I also heard that theory long ago. I think it was termed "racial memory". It seems a little far-fetched. However, humans often show a fear and distrust of reptiles in general, including the serpent in Genesis as just one example. Whether that's "racial memory" going back to times when mammals and dinosaurs may have co-existed, or if it's just good sense, is hard to say. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:36, 24 May 2010 (UTC)

On the subject of "pre-programmed" fear or knowledge of serpents - the plant/drug Yage is commonly reported to produce hallicinations of predators such as big cats/snakes.. even in people brought up in countries with no such thing [8] (also [9]) (it was reported possibly less reliably by Terence McKenna that even eskimos hallucinate cat predators under it's influence) If that is someway related to some sort of built in DNA memory of giant reptiles is tenuous .. It's not as far as I know been shown that people with no concept of cats / snakes hallucinate them under it's influence. Probably irrelevant.87.102.18.191 (talk) 01:33, 24 May 2010 (UTC)

Right. It is highly doubtful the "genetic memory of the dinosaurs as the arch-nemesis of humans" hypothesis has any merit at all. At the time dinosaurs went extinct our ancestors were not even monkeys; actually, at the time of the last dinosaurs the lemurs and the tarsiers did not yet split into separate lines (we are on the "tarsier" line, haplorrhini, in case you wonder). Big cats, hippos, and early hominids / humans were and are until this day a much more real and a much more present threat to our ancestors. Yet we do not have much of a natural fear of cats, large herbivores, or other people. What humans usually fear are bacteria, viruses, cockroaches, snakes, and spiders. People go to the zoo to see the tiger; people run away when they see a garter snake. A flying snake should be an outright nightmare. Hence, I guess, is the dragon. --Dr Dima (talk) 01:36, 24 May 2010 (UTC)

There are plenty of tropes which tend to occur independently in all sorts of cultures and stories. Like superhuman strength - how many people do you think in the history of man have been carrying something and thought it would be really neat if they could pick up the whole load in one hand? Or flight - all kinds of legends and myths talk about people soaring through the sky, not because humans ever had the ability to fly, but because it's almost universally held that it would be awesome. ZigSaw 11:51, 24 May 2010 (UTC)

Here's the problem with dragons. It's sometimes mooted that dragons are a universal or near-universal fixture in myths around the world. For that reason, ridiculous books like the afore-mentioned An Instinct For Dragons get published to account for this "fact". The only problem is that there is no such fact - it's complete baloney. Dragons have no legs, two legs, four legs, more legs; dragons have no wings, two wings, four wings; dragons are scaly like snakes, leathery like rhinos, slimy like worms, feathered like birds; dragons are small-ish, large animal sized, huge, the size of islands; they breathe fire, they breathe poison; they have one head, they have seven heads, they have nine heads; their tail is forked, their tail is like a snake, their tail is like a fish; they're benevolent, malevolent, and indifferent. The problem is that "dragon" is a catch-all term for all sorts of vaguely reptilian monsters. If these monsters had all kept their original names, people might be less inclined to explain their universality. Matt Deres (talk) 20:28, 25 May 2010 (UTC)

Yes, that is quite true. Dragons would have been a Wastebasket taxon if they were real; them being mythological, they are just dragons :) . There were actually attempts in Middle Ages to "classify" dragons. If my memory serves me well, you can find a stealth parody of that in The Hobbit, where Tolkien goes into great detail of how Smaug is unlike the other dragons, even though Smaug is the only dragon to actually appear in The Hobbit. But yes, again, you are right, there are Chinese dragons (many kinds, always one head, mostly terrestrial or "celestial", usually benevolent), Japanese dragons (one head, mostly aquatic), Ukrainian dragons (three heads, one body, fire-breathing), Norse dragons, Biblical dragons, Hittite dragons, wyverns, and so on in the myths of the various nations. They all look more or less like flying snakes or flying crocodiles, which should be a Bad Thing in itself; but beyond that every nation or group of nations basically comes up with an idea of its own about what it may look like and what it could do. --Dr Dima (talk) 21:57, 26 May 2010 (UTC)

over eating

If a person is disabled or older they cannot do as much exercise as may be needed for weight control. Therefore weight control is dependent on not over eating. Yet because the human body requires so little food it is very easy to over eat. Is there a pill or other means of controlling appetite so that a person will not over eat due to a feeling of hunger? 71.100.3.228 (talk) 21:24, 23 May 2010 (UTC)

There are lots of appetite suppressants available. I won't comment on their efficacy or safety, but they certainly exist. --Tango (talk) 21:45, 23 May 2010 (UTC)

What about other means besides pharmaceuticals? Are their foods or other means to control or eliminate appetite? 71.100.3.228 (talk)

I've heard of the opposite effect, i.e. that places like McDonalds used to put chemicals into your food which made you feel full slower, and thus more likely to buy more food. Regards, --—Cyclonenim | Chat  22:31, 23 May 2010 (UTC)

Regards what? 71.100.3.228 (talk) 04:27, 24 May 2010 (UTC)

"Regards" is a formal way of ending a letter. I don't see it much in Web postings, but that's what Cyclonenim meant. Comet Tuttle (talk) 06:58, 24 May 2010 (UTC)

It works better for starting threads than replying to them, but it's part of the signature and I sure as hell can't be arsed to write it out every time (i.e. think when it's needed). Regards, --—Cyclonenim | Chat  07:32, 24 May 2010 (UTC)

When I see it at the end of a web post I'll continue then to append (the word) nothing. 71.100.3.228 (talk) 08:47, 24 May 2010 (UTC)

User:SqueakBox signs off with "Thanks". Kittybrewster ☎ 10:59, 25 May 2010 (UTC)

Studies have shown that the feeling of satiety comes from the bulk and weight of food, not calories. Eat lots of vegetables and fresh fruits - bulk and weight without much calories - and wheat- or oat-fibre too to fill you up. Avoid foods containing fat, especially saturated fat (although a small amount of fat is required for health). See http://www.nutritiondata.com/topics/fullness-factor After a few months you will prefer healthy food and be disgusted by fatty junk food. 92.28.255.202 (talk) 22:24, 23 May 2010 (UTC)

Byetta is a powerful appetite suppressant, which also delays emptying of the stomach. It is presently commonly used as a prescription drug for Type 2 diabetics, but might be the next big weight loss drug. The article notes some undesirable side effects of the drug. Edison (talk) 00:44, 24 May 2010 (UTC)

For severe cases of obesity, where the standard advice of diet and exercise does not work, bariatric surgery has been used to reduce the size of the stomach. A smaller stomach means that less food is needed to obtain satiety. -- 174.24.200.38 (talk) 01:20, 24 May 2010 (UTC)

The diet market is massive, so you'll hear hundreds of claims of "miracle diets" and "pills". Even moderate exercise can help though. Under normal conditions weight gain or loss is down to the amount of energy you use, minus the energy you take in from food (calories). You can increase your use of energy as well as decrease your intake and it works very well. FT2 ^{(Talk | email)} 04:17, 24 May 2010 (UTC)

This remedy is where the problem begins... exercise only increases hunger making the task to reduce intake even harder. 71.100.3.228 (talk) 04:25, 24 May 2010 (UTC)

No, I read about a study which said that although people did eat more after exercise, the extra calorie intake was still less than that expended. So there is no excuse for not exercising. Never mind the drugs - a simple thing to do, without possible bad side-effects, is to make sure you eat enough fresh vegetables and fruit each day. Something that may block this is that many people in my experience do not know how to do simple cooking, such as boiling vegetables (cut into chunks and put in a saucepan of boiling water for a few minutes until tender), and so have to buy junk food instead. 92.28.251.49 (talk) 11:13, 24 May 2010 (UTC)

The reason I disagree with this study is that walking a mile only burns about 50 calories and jogging only about 90. Only athletes able to jog 10 miles can expect to burn off 900 calories. Most people do not have the time or inclination to jog 10 miles every day so its back to not overeating as the main way to lose or not gain weight. 71.100.8.229 (talk) 20:25, 25 May 2010 (UTC)

Nevertheless, excercising is good for you. Not exercising considerably raises your chances of getting seriously ill and having a reduced lifespan. 92.28.240.102 (talk) 22:50, 25 May 2010 (UTC)

I agree that exercise is good for you and you should do a program that gets round to every single muscle but not do exercise only to burn calories. People who do exercises only to burn calories fall into the group of mammals with a higher metabolism and shorter lifespan. 71.100.8.229 (talk) 08:40, 27 May 2010 (UTC)

Hunger is a very inaccurate sensation. People tend to feel hungry if they haven't eaten what their body is used to them eating at a given time of day. The calories you actually need are a very small factor in determining hunger. That means you generally don't feel significantly more hungry if you increase your activity (of course, if you try and run a marathon you are going to notice a need for extra calories, but small changes can easily go unnoticed). --Tango (talk) 00:33, 25 May 2010 (UTC)

Compare the fact that you can easily get 105 calories from a single medium size banana which will require 2 miles of walking to burn off and you see clearly that exercise is not the solution but rather that not overeating is. 71.100.8.229 (talk) 20:28, 25 May 2010 (UTC)

I am not sure that you can write off exercise so easily. What would be the effect of walking 2 miles extra each day? I expect it would lead to an increase in muscle mass, which would increase your calorie requirements. -- Q Chris (talk) 13:33, 26 May 2010 (UTC)

help pLz \\ drugs used in managment of infusion

describe the drugs used in managment of infusion - related to side effects —Preceding unsigned comment added by Mrmr-rana (talk • contribs) 21:33, 23 May 2010 (UTC)

You're going to need to be much more specific if you want a meaningful answer. What type of infusion do you mean? Also note that we cannot give medical advice on the reference desk. If this is about a treatment you or someone you know is undergoing, you should talk to the doctor who's administering the treatment. Buddy431 (talk) 22:56, 23 May 2010 (UTC)

Possibly means "Blood infusion" ie Blood transfusion - an anticoagulant is Heparin, Paracetamol is used if minor side effects occur [10] not a medician so don't know much more.87.102.18.191 (talk) 00:32, 24 May 2010 (UTC)

This looks more like a homework question than a request for medical advice to me. AndrewWTaylor (talk) 08:18, 24 May 2010 (UTC)

I really hope it is, I'd hate for the triage nurses to have brought in a wireless laptop just to have the physician's Reference Desk question get rejected ZigSaw 11:39, 24 May 2010 (UTC)

Tiny bullet-shaped dog

I saw the tiniest dog I've ever seen being taken for a walk recently. It was white and bullet shaped, with the head forming the curved cone-like front of the bullet. Moving at walking pace, its little short legs were a blur, as its stride could only have been one or two inches. It was not a sausage-dog or a chichua. It did not behave like a puppy, but like a disciplined fully-grown dog. What breed could it have been? 92.28.255.202 (talk) 22:21, 23 May 2010 (UTC)

Sounds more like a pet guinea pig to me. 71.100.3.228 (talk) 22:38, 23 May 2010 (UTC)

or White rat on a lead ? (it happens).87.102.18.191 (talk) 22:44, 23 May 2010 (UTC)

What was its coat like? And it's not a Scottish Terrier is it? Vranak (talk) 22:46, 23 May 2010 (UTC)

It was not a guinea pig or a Scottish terrier. It had short fur. 92.28.255.202 (talk) 22:49, 23 May 2010 (UTC)

Sure it wasn't a ferret? --Kurt Shaped Box (talk) 22:51, 23 May 2010 (UTC)

It was definately a dog, and not a rat or ferret. 92.28.255.202 (talk) 22:53, 23 May 2010 (UTC)

Try teacup dog. 71.100.3.228 (talk) 23:06, 23 May 2010 (UTC)

It may have been something like a Bull Terrier (Miniature) except it had no neck, and shorter legs. Apparantly there are "designer dogs", so perhaps it had been specially bred to be super-tiny. 92.28.255.202 (talk) 23:14, 23 May 2010 (UTC)

Maybe a Pomeranian (dog)? —Preceding unsigned comment added by 86.4.186.107 (talk) 07:52, 24 May 2010 (UTC)

In case you haven't found it yet, the article on List of dog breeds gives you loads of pictures. If you were in Yorkshire, it's likely to have been a ferret.--Shantavira|^{feed me} 08:48, 24 May 2010 (UTC)

It was not a pomeranian as it did not have a fluffy coat, and a pomeranian is not bullet shaped either. Perhaps I underestimated the stride - it may have been more like three inches. I have seen ferrets being taken for a walk on one or two other another occassions, and it was definately not a ferret. If miniature Bull Terrier puppies have short legs and no neck, then it could have been one of them. As it had to concentrate on moving its little short legs as fast as propellors, then it may not have had time to indulge in the usual romping puppy behaviour. My best guess is that it was a cross between a minature Bull Terrier and some other minature dog that gave it tiny legs and no neck. 92.28.251.49 (talk) 11:00, 24 May 2010 (UTC)

These are miniature bull terrier puppies. I don't know if they're what you saw, but they I do know that they are adorable. --Mr.98 (talk) 15:51, 24 May 2010 (UTC)

Next time, ask the person who is walking the animal. Failing that, a photograph would be more useful than any verbal description. --Teratornis (talk) 19:43, 24 May 2010 (UTC)

No, really? 92.28.244.102 (talk) 10:44, 25 May 2010 (UTC)

In any case, it might not be a recognized breed at all—it could be a mixed-breed dog. --Mr.98 (talk) 21:45, 24 May 2010 (UTC)

May 24

OIL SPILLS

Technically aren't asphalt highways just oil spills mixed with dirt? 71.100.3.228 (talk) 02:26, 24 May 2010 (UTC)

No. Part of the definition of "spill" is that it is accidental. Also, asphalt is a specific component of crude oil, rather than crude oil itself. --Tango (talk) 02:32, 24 May 2010 (UTC)

That's right — fractional distillation is used to separate crude oil into things like gasoline, kerosene, and asphalt. But then the asphalt is indeed mixed with dirt; our asphalt article, in its Rolled asphalt concrete section, states that an asphalt highway is actually only 5% asphalt itself, and 95% "aggregates", meaning gravel, sand, and stones. Comet Tuttle (talk) 06:56, 24 May 2010 (UTC)

Roads and urbanization are a different form of habitat destruction than oil spills. They definitely all involve introduction of non-natural (or at least, non-local) materials into the environment, often significantly altering the local ecosystem. However, unlike oil spills, roads have a measurable benefit - improving the quality of life for humans - so there is at least some level of tradeoff to consider. Nimur (talk) 14:43, 24 May 2010 (UTC)

Asphalt is not a liquid, so it doesn't have the same effects that the liquid crude oil has on birds, fish, etc. --Chemicalinterest (talk) 14:55, 24 May 2010 (UTC)

Roads are also confined to discrete areas; their destruction is intense, but it covers only a fraction of land area. Roads generally do not move on their own, so animals have some hope of avoiding their hazard. Oil spills on water can spread widely and uncontrollably. Sea birds and other animals have trouble avoiding oil slicks. However, note that motor vehicles can drip appreciable amounts of engine oil onto road surfaces, which tends to run off during rain storms, thereby polluting the runoff. A busy roadway thus functions like a low-level oil spill that continues indefinitely. A widespread shift to battery electric vehicles and bicycles instead of the current dominance of internal combustion engine vehicles would greatly reduce oil pollution on road surfaces. --Teratornis (talk) 19:40, 24 May 2010 (UTC)

Well, if you're advocating some kind of worldwide mandate to ban automobiles and force everyone to use bicycles or glorified golf carts, then we will veto it in the United Nations before you can say "oil spill". This kind of change is absolutely out of the question for civilized, industrialized nations -- what about the eighteen-wheeler trucks that take merchandise from the warehouse to the local neighborhood store? A much better way would be to implement more frequent, more stringent and consistent mechanical inspection requirements for motor vehicles to make sure they don't drip motor oil all over the place -- this would achieve substantially the same result, but without nationwide economic upheaval that your proposal would cause. 67.170.215.166 (talk) 06:38, 25 May 2010 (UTC)

There are electric cars available today that are not remotely similar to golf carts — they have highway performance that matches up quite nicely with gasoline-powered cars. Range is a bit of a problem — the Chevy Volt has a nice interim solution, with a gasoline engine that doesn't kick in until it's needed, which except on long trips, it usually won't be.

The big problem with them, at the moment, is price. Hopefully that will come down.

But of course if/when that happens, if they're going to be our transportation solution for large numbers of people, then we're going to need a lot more generating capacity. I suspect the only realistic way of getting that much capacity, without producing lots of greenhouse gases, is to build a lot of nuclear plants. Unfortunately it takes upwards of a decade to get a nuclear plant on-line. That's why I think we need to get some in the pipeline starting now. --Trovatore (talk) 22:01, 25 May 2010 (UTC)

Excellent idea, why don't we write Congress and demand more nuclear reactors? 67.170.215.166 (talk) 01:41, 26 May 2010 (UTC)

acetone

does acetone evaporate like alcohol or does it leave a residue? can u use it on food surfaces? —Preceding unsigned comment added by Tom12350 (talk • contribs) 03:37, 24 May 2010 (UTC)

Yes, it evaporates very quickly, maybe not as quickly as most alcohols though. No, I would never use it on anything that would ever contact food. Beach drifter (talk) 03:44, 24 May 2010 (UTC)

After a little reading, it appears to be hardly toxic at all. I still see no reason you would need to use it in the kitchen. Beach drifter (talk) 03:47, 24 May 2010 (UTC)

can i use it on a plastic counter top, and a particle board kitchen table with a wood looking plastic/ vinyl vanear —Preceding unsigned comment added by Tom12350 (talk • contribs) 04:11, 24 May 2010 (UTC)

It's a solvent, so plastic-based and printed food surfaces might get damaged, or colors from packaging transfer. What would you intend to use it for? FT2 ^{(Talk | email)} 04:12, 24 May 2010 (UTC)

There are lots of products specifically designed for this use, visit your local supermarket. Vespine (talk) 04:50, 24 May 2010 (UTC)

No. Don't use it on those - it will dissolve them, then evaporate, leaving an impossible to clean mess. Not really a mess - more like a mushy smear of the veneer. It's pretty non-toxic though (it's actually legal as a food additive!), and does not leave any residue behind, so in that regard it's safe in the kitchen. I use acetone to remove stickers. But you have to work VERY fast, it evaporates very quickly - even the open bottle will evaporate. Put the acetone on a tissue, and rub the sticker - don't put the acetone on the sticker, it will dissolve the glue, then run, leaving a bigger sticky spot than when you started. Ideally have a second person to cap the bottle in between putting some on the tissue. Acetone is probably the fastest evaporating solvent commonly available. Ariel. (talk) 05:32, 24 May 2010 (UTC)

A little WD-40 will remove stickers as well and there's no bottle to close. Dismas|^(talk) 08:10, 24 May 2010 (UTC)

You dont' want to use that stuff in the kitchen, though, it leaves a mess and it can be toxic if ingested. 67.170.215.166 (talk) 06:43, 25 May 2010 (UTC)

How much are you using?! Do you lick your counter clean?! I doubt any reasonable person would A) use so much WD-40 as to be a health hazard and B) just let WD-40 sit on their counter after cleaning off sticker residue and then use that spot to make a sandwich. Dismas|^(talk) 08:06, 25 May 2010 (UTC)

I'd rather not use any petroleum distillates in my kitchen, unless absolutely necessary. 67.170.215.166 (talk) 01:57, 26 May 2010 (UTC)

how will plastic-based and printed food surfaces get damage if they use it in labs to clean plastic labware? will it help if i dilute it 50-50 w/water? —Preceding unsigned comment added by Tom12350 (talk • contribs) 06:13, 24 May 2010 (UTC)

Not every plastic is the same, some will be totally unaffected, others will dissolve into goo - there are a LOT of different kinds of plastic. I don't know what water will do, probably it will slow down the dissolving. Ariel. (talk) 08:08, 24 May 2010 (UTC)

arent there only 7 kinds of plastic? —Preceding unsigned comment added by Tom12350 (talk • contribs) 08:41, 24 May 2010 (UTC)

Category:Plastics. 212.219.39.146 (talk) 08:47, 24 May 2010 (UTC)

There are many more! I used acetone in the lab and I saw somebody cleaning a keyboard. The Grey keys like Strg And Alt got very soft and the printed letters vanished, the other white keys showed no problem and ended up very clean.--Stone (talk) 09:37, 24 May 2010 (UTC)

While there are seven classifications in the Resin identification code, the seventh is "other", and would include everything from ABS to nylon to teflon to polycarbonate. -- 174.24.200.38 (talk) 04:38, 25 May 2010 (UTC)

The better cleaning agent for you might be, what other people use for disinfection, it is a mixture of 70% isopropanol and water.--Stone (talk) 09:37, 24 May 2010 (UTC)

i already tried that. will it help if i dilute acetone 50-50 w/water? —Preceding unsigned comment added by Tom12350 (talk • contribs) 10:49, 24 May 2010 (UTC)

That would slow its evaporation, but it would also slow its cleaning abilities, so there would be no net difference. You can put it in a spray bottle, not a mist one, a squirt one. --Chemicalinterest (talk) 11:02, 24 May 2010 (UTC)

i dont understand. if i dilute it wont it be less corrosive? —Preceding unsigned comment added by Tom12350 (talk • contribs) 11:14, 24 May 2010 (UTC)

Yes diluting it will make it less likely to damage the plastic. Alchohol is a better choice though if you have it. What are you cleaning?87.102.85.123 (talk) 11:47, 24 May 2010 (UTC)

I used to be a follower of the "throwing assorted chemical compounds on a surface makes it cleaner" school of thought, I must admit, but a lot of 'em will ruin your crap if you aren't careful. The way I see it, just because something kills bacteria and viruses doesn't mean it's safe for you to eat. It's not that antiseptics and antibac soap are actually making the surface cleaner on a microscopic scale - they're simply poisons designed to kill microbes instead of humans. Which is why you're supposed to wipe away the disinfectant before you eat off something you use it on. In the same vein, just because something is caustic doesn't mean it's necessarily going to clean whatever you put it on. And if its effects are 75% "creating a goopy catastrophe" and 25% "cleaning the surface", no matter how much you dilute it you're still going to get three times as much goop as cleaning action. ZigSaw 11:46, 24 May 2010 (UTC)

I don't understand why you are so intent on using acetone in your kitchen. Did you get a hold of an industrial quantity and just trying to use it on EVERYTHING? Lol… if you absolutely insist on using it, at least try rub some on the least conspicuous spot first and leave it for a few minutes and rub it again, see if it damages the surface before making a mess of it.. My know it all uncle once used to clean his fancy hi fi with metho, one day he decided that acetone might be a better idea and it melted the face of the LCD display making a matted mess you couldn't even see through, he was gutted. Vespine (talk) 23:13, 24 May 2010 (UTC)

Crystal Violet

Hi there :) My name is Elin and I'm from Sweden. Right now I'm writing an assay about terraforming in astrobiology with chemistry and biology as "main subjects". I'm now stuck on gram staining and I really need to know how crystal violet is produced. When I read this article: http://en.wikipedia.org/wiki/Crystal_violet, I don't quite get the production. Mostly it's because I don't understand everything that is written, for example I don't get if it's ment that it is redox (gain) or oxidation (loss) that happens when you oxidize the compund in the second prodction step. And what about the last step? Is that the final step to get crystal violet, or is it a step to produce something else since it says "Hydrolysis of crystal violet gives the carbinol"? And what is a leuco? I've written about the first two steps, but I've left out what I've asked about (the oxidize-question, leuco and the third step). I feel like I should bring more to the table in order to get a higher grade and it would be sad if difficulties with language should stop me from getting the grade that I need. Please try and explain clearly and detailed. I don't mean that I want it to be simple, just that i'm thankful if you explain a lot since I don't understand all english words. Thanks a lot! /Elin —Preceding unsigned comment added by Ailithey (talk • contribs) 08:56, 24 May 2010 (UTC)

The leuco (white or colourless) form is oxidized with oxygen. The carbinol is a alcohol derived from methanol by substituting the hydrogen by something different, here the central C-OH is attached to three 4-dimethylaminopheny substituents.--Stone (talk) 09:46, 24 May 2010 (UTC)

The German article Kristallviolett has a better image what happens.--Stone (talk) 09:49, 24 May 2010 (UTC)

Gentian violet and Crystal_violet are the same substance, but the Gentian violet is about the medical use!--Stone (talk) 09:53, 24 May 2010 (UTC)

Thanks a lot, I'm starting to get it. But if you look at the article http://en.wikipedia.org/wiki/Crystal_violet, I still don't really get the production. The ast step says this: A typical oxidizing agent is manganese dioxide. Hydrolysis of crystal violet gives the carbinol: [C(C6H4N(CH3)2)3]Cl + H2O → HOC(C6H4N(CH3)2)3 + HCl Is this step part of the production of crystal violet? Do you get crystal violet by following all three steps, or is the last step the formula for the production of a carbinol? —Preceding unsigned comment added by Ailithey (talk • contribs) 10:38, 24 May 2010 (UTC)

The article was a bit confusing - I've changed it to avoid confusion - http://en.wikipedia.org/enwiki/w/index.php?title=Crystal_violet&oldid=363908374

It should be clear now. The last step was not part of production. 87.102.85.123 (talk) 12:06, 24 May 2010 (UTC)

center of mass

why does objects rotate around it's centre of mass ..? I mean as a example, when we throw a rod (something like that) in the air holding at the edge,we can see it rotates around its CM.dany (talk) 13:19, 24 May 2010 (UTC)

Try to imagine an object that does not rotate around its CoM. Then that would mean that the CoM of the object would rotate around some point (inside or outside of the body). Therefore the CoM would be accelerating toward the point of rotation (centripetal acceleration). That would require an external force. Count Iblis (talk) 14:06, 24 May 2010 (UTC)

When an object is forced to rotate around something other than its center of mass by an external force, the object will precess, and if it continues to rotate for a long enough time (e.g., low friction or low damping), it will eventually change its rotation through a precession so that the rotation aligns with its principle axes. Nimur (talk) 14:48, 24 May 2010 (UTC)

You mean principal axes. lets mantain the principle of spelling words correctly. Dauto (talk) 16:18, 24 May 2010 (UTC)

Let's punctuate our contractions correctly, and capitalize the first word in each sentence. --Teratornis (talk) 19:25, 24 May 2010 (UTC)

lets not. Dauto (talk) 02:27, 25 May 2010 (UTC)

Let's envision your example of the thrown rod. The center of mass will follow a parabolic path back to Earth, and in that respect the rod will act as if all its mass is located at the center of mass. In addition, the rod can have rotation around one or several axes, but the center of mass will still follow the same parabola. If it didn't, it would act like a thrown marble rippling up and down instead of following a parabola back toward earth. That would require energy instead of just gravity.Overjive (talk) 03:16, 26 May 2010 (UTC) —Preceding unsigned comment added by Overjive (talk • contribs)

aching muscles = laughing reflex?

Yesterday I played in an action cricket tournament. Being the most unfit person ever, today my muscles are all exacting their revenge on me and I could hardly roll myself out of bed this morning. Funny thing is, I discovered that whenever I move (and stretch some of my sore muscles) I get this urge to laugh for no apparent reason. Even thinking about it now makes me giggle. Is this a known thing or am I the only one? Could it be related to tickling (I'm VERY ticklish and laugh uncontrollably when people try to tickle me, even before they've made any contact)? I tried Googling but I'm getting false hits about laughing so much your muscles ache. Zunaid 16:28, 24 May 2010 (UTC)

The Delayed onset muscle soreness article does not mention this effect. You could ask on that article's talk page if you get no help here. --Teratornis (talk) 19:30, 24 May 2010 (UTC)

You evidently have an easily-triggered laugh reflex, so perhaps the pain in your muscles triggers this by reminding you of the fact that you find the situation amusing. Dbfirs 06:57, 25 May 2010 (UTC)

Sodium hypochlorite and Sodium acetate

I mixed solutions of sodium hypochlorite and sodium acetate together. Is the hypochlorite strong enough to oxidize the acetate ion? I noticed some gas being produced (not much), but otherwise there was no indication of a reaction. Thanks. --Chemicalinterest (talk) 17:19, 24 May 2010 (UTC)

(edit conflict with below) Oxidize it to what? Peracetic acid? Usually that's done with hydrogen peroxide, but hypochlorite isn't that much weaker of an oxidizing agent than peroxide, so I suppose it could. Even with hydrogen peroxide, the equilibrium still lies to the left, so it makes sense that only a little, if any acetic acid would be oxidized. Buddy431 (talk) 20:40, 24 May 2010 (UTC)

Did you look on a standard reduction potential table? We've linked them before, and there are many of them out there on the internet and in books as well; the numbers should tell you if it is possible for hypochlorite to oxidize acetate. The only possible products are the chloride ion and carbon dioxide, so if hypochlorite DID oxidize acetate, you'd get some bubbles. --Jayron32 20:31, 24 May 2010 (UTC)

The standard reduction table here doesn't have acetic acid, so no beans. And why do you say only that Chloride and CO₂ are the only products? It could only be reduced to chloride gas (a weaker oxidizing agent than the hypochlorite), which could be the bubbles observed. Buddy431 (talk) 20:42, 24 May 2010 (UTC)

Chloride gas doesn't exist, but hydrogen chloride might. --Chemicalinterest (talk) 21:06, 24 May 2010 (UTC)

I meant chlorine gas. Hydrogen chloride would stay in solution. Buddy431 (talk) 22:35, 24 May 2010 (UTC)

Doubtful. Chlorine gas disproportionates to hypochlorite and chloride in any basic solution, see Chlorine_bleach#Chemical_interactions. Cl2 may be an isolatable intermediate, but I think that spontaneously, the chloride ion ends up being the lowest-energy product here. Consider that the Eo for the reduction of chlorine gas is highly positive itself... --Jayron32 21:03, 24 May 2010 (UTC)

It's not clear what the reaction would be here:

Acetate oxidise to CO2 - can't find potentials either - note - acetic acid is quite resistant to oxidation - it's used as a solvent in many oxidation reaction.

Peroxide - maybe?

Reaction to form a chloroacetate - this seems quite likely - chlorite would be reduced in this reaction - so I suppose acetate must be oxidised. I'm fairly certain this reaction will go, don't know how fast.

There are simple tests to see if a reaction has happened - such as add chlorite to excess acetate, let it react, then add iodide - if chlorite remains iodine will be produced (visible), as a control compare with the control reaction (chlorite + water . no acetate) 77.86.125.207 (talk) 18:33, 25 May 2010 (UTC)

Special Relativity

One of the implications of Einstein's Theory of relativity is- If two observers are in relative motion, they will not, in general, agree as to whether two events are simultaneous. If one observer finds them to be, the other, in general, will not. Now I read this example in Halliday/Resnick, Fundamentals of Physics. Two observers Sally and Sam stand in two long spaceships. They are stationed a the midpoint of the two ships. The relative velocity of ssSally with respect to ssSam is v separating along a common x axis. They are stuck by two meteorites just when they were crossing each other, one setting off a red flare and the other blue, leaving marks at R and B on ssSam and R' and B' on ssSally. Let us suppose that Sam and Sally are positioned right in the middle of R and B and R' and B'. Sam receives the two light waves at the same time and gave the following explanation. Sam: Light from event red and light from event blue reached me at the same time. From the marks on my spaceship, I find that i was standing halfway between the two sources. Therefore, event red and event blue were simultaneous events. Sally and the expanding wavefront from event red are moving towards each other, while she and the expanding wavefront from event blue are moving in the same direction. Thus, light from event red reaches her before light from event blue. Her explanation goes as follows. Sally: Light from event red reached me before light from event blue did. From the marks on my spaceship, I find that i too was standing halfway between the two sources. Therefore, the events were not simultaneous. These reports do not agree. Nevertheless, both observers are correct.

My question goes as follows: If we observe the two spaceships from a third inertial reference frame, we will discover that the two events occurred simultaneously as they occurred at a unique instant when the two spaceships coincided on the x-axis. Does that mean Sally's explanation was wrong? If that is so, is the first postulate of the Theory of Special Relativity contradicted? Please explain the validity of Sally's explanation in this light. --Lightfreak (talk) 18:20, 24 May 2010 (UTC)

You said that Sam is equidistant from R and B and saw light from the two flares at the same time. That means that the two collisions were simultaneous in the rest frame of Sam, so your third inertial frame is the same as the rest frame of Sam. There is no unique instant when the spaceships cross because they have length; it takes a while for them to pass each other completely. There is a unique instant in a unique inertial frame when the ships occupy the same range of x coordinates, but the collisions didn't happen at that instant. (One of them may have, but not both.)

I don't think there's much insight to be gained into special relativity by looking at different reference frames. It's like checking that 5+5+5 = 3+3+3+3+3 and 7+7+7+7 = 4+4+4+4+4+4+4 and so on. What you really want to understand is why multiplication is commutative in the first place; then you don't have to try all the special cases. The best way to understand this problem is to draw a spacetime diagram showing all of the events. -- BenRG (talk) 18:51, 24 May 2010 (UTC)

What is the point of a lawn?

Besides the aesthetic aspect, is there any coherent reason to constantly trim, weed, fertilise and reseed the part of your property with nothing built on it? I can understand preventing erosion, but wouldn't regular old wild weeds do that? Does anything horrible happen when grass gets too long? It seems to me that a ludicrous amount of money goes into herbicides, mowers/gas, fertilizers and all kinds of ugly side effects of fighting natural selection to get a "good-looking lawn". Unless there's some benefit I'm not seeing... ZigSaw 20:36, 24 May 2010 (UTC)

Small animals, some of which may be pests, can hide in tall grass. Jc3s5h (talk) 20:41, 24 May 2010 (UTC)

I figured lawns were a sign of the wealthy being able to afford land and to manicure it as well. As well as for aesthetic purposes, lawns provided ample grounds for one's "constitution" I suppose. More recently, lawns are smaller and part of the package when you buy a nice house. It's probably more for aesthetic purposes now than it ever was, because most lawns (at least around where I live) are so small, you can't even play Badminton on them. Backyards usually allow for a single sport and maybe that's it... barbecues and other activities are restrained to a porch. I know that with my family's country estate, we have no "lawn", because it's all overgrown and wild and absolutely beautiful. (According to lawn, it's still a lawn.) Of course, lawns at, like, Versailles, are simply ostentatious but stunning. – Kerαunoςcopia^◁_galaxies 20:43, 24 May 2010 (UTC)

There's nothing wrong with doing things for aesthetic purposes. You either do something because you want to adhere to cultural norms, or you do it specifically to fuck with cultural norms. So, either you maintain a lawn because its expected, and your culture tells you it looks good, or you let it grow wild because you want to intentionally go against those norms. Either position is equally valid, and both have as much weight. It comes down to personal aesthetic choice and little else. --Jayron32 20:52, 24 May 2010 (UTC)

Kids and pets can play on them. They are pleasant places to sit or snooze with a beer and a good book. Grass is basically outdoor carpeting. If you don't have grass then you have...what?

1. Nothing - you live in an apartment with no outdoor space.
2. Dirt - which you can't lie on and isn't comfortable to walk on - and is unusable for days after rain.
3. Xeriscape - less work but also uncomfortable to lie on. Also, doesn't naturally absorb dog poop and is hopeless for little kids to kick a ball around on.
4. Concrete - ugly, also not very useful for all the reasons above.

If you want extra space beyond your indoor living space, a garden...and therefore a "carpeted" garden is the way to go. Grass is the natural choice because unlike most other plants it's evolved to survive being grazed by herbivores - and can therefore be mowed to keep its height in check and to maintain the density needed.

Having said all that - my house is situated out in woodland and my kid is old enough not to need to go out and play in it - so we mostly have wild grass which doesn't grow too long because of the dense trees - and doesn't get mowed because we don't live someplace where we have to conform to social norms with manicured grass.

SteveBaker (talk) 21:05, 24 May 2010 (UTC)

This probably goes back to the rise of surburban life - in the 20th century - before then people didn't have lawns - they either lived in towns (with almost certainly no garden at all) or in the countryside.. Lawns did exist prior to surburbanisation - notably common land such as the village green; the lawns would be 'mowed' mostly by sheep - which do a very good job.

The rise of surburban life meant that everyone got their own miniature village green - called a garden. (along with a miniature mock tudor mansion - or 'semi').

That is basically the origin of the grass lawn. Basically people now imitate the cutting sheep once did using lawnmowers. Strange behaviour but true. If you don't believe me ask on the humanities desk. Obviously grass is good for playing on. Doh, I just found out all this is at lawn, nobody will read it anyway. 87.102.85.123 (talk) 21:39, 24 May 2010 (UTC)

We do have a History of the lawn article: they appear to date from before the 20th century: the first lawnmower (as opposed to a scythe) was invented in 1827. Buddy431 (talk) 22:28, 24 May 2010 (UTC)

As mentioned above by many, having a lawn at the backyard is actually quite nice. I just want to point out that you don't really need to use herbicides, fertilisers or gas to have a nice lawn. I don't use any of that and still am quite happy with my lawn. Dauto (talk) 03:19, 25 May 2010 (UTC)

Some lawns have just the right amount of moisture from ground water and sun to only require mowing. Other lawns require watering and mowing. Other lawns require so many things that its better to zero-scape. If you use mulch to zero-scape then it will retain moisture and and allow the zero-scape plantings to thrive. The problem is when neighbors want to dictate whether you have grass or zeroscaping and constantly yap to the police. You should have the right to have any kind of "lawn" your heart desires that is affordable and not a hazard to others. Some people though claim that zeroscaping hampers firefighters and attracts venomous or disease carrying creatures. If the economy gets any worse though even fancy dancy bank lawns might be used to grow tomatoes. 71.100.8.229 (talk) 20:52, 25 May 2010 (UTC)

It's because lush, green grassland would have been a sign of plenty to our very distant ancestors. Food, water, and good visibility to protect against preditors. Even our eyes are structured to process horizontal objects more readily than vertical. It's a comfort factor that is bolstered by other social and cultural points raised above. 24.130.145.253 (talk) 04:33, 26 May 2010 (UTC)

Old Testament

Old Testament states "Adam has lived 930 years".How this can be explained? Real today's years, or possible short years of the old time? Does the length of years,as days,may be variable? Today 1 year=365 days, but billion years ago 1 year=15 days for example?TASDELEN (talk) 21:13, 24 May 2010 (UTC)

There's no evidence such intervals have changed that much in Earth's history. 67.243.7.245 (talk) 21:32, 24 May 2010 (UTC)

In scientific terms, it is explained by pointing out that many cultures have myths that are not scientifically accurate. Anything other than that is sheer interpretation. Creationists and others who are decidedly not scientific (in that they take their conclusions as givens and then work backwards from there) usually say things like "God let him live that long" and "since the time of the Flood people have been more and more sickly and sinful and degraded" and things of that nature. See e.g. Answers in Genesis, a young-earth creationist ministry. But there is absolutely zero scientific evidence for this and it is entirely implausible from a truly scientific standpoint. AIG happily distorts scientific evidence to fit its very literal interpretation of the Bible. Frankly I think (as a nonreligious person) that such analytical attempts miss out on the entire point of the Bible, which was not meant to be considered a science textbook. But that's a personal opinion, to be sure. --Mr.98 (talk) 21:34, 24 May 2010 (UTC)

(edit conflict with above x2) Look at this article we have: Longevity myths#Biblical. Some scholars argue that people inflate the lifespans of their important patriarchs and elders (sociological/anthropological reasons I guess, I'm not in this field, so I can't discuss that aspect any more). Note that most (i.e. all) non-religious scholars do not believe that there was a literal single first human (named Adam or otherwise). Buddy431 (talk) 21:37, 24 May 2010 (UTC)

(ECx3) I don't know why this is on the science desk since the obvious scientific answer is it's all nonsense, but AFAIK it's generally held by those who believe in those parts of the bible literally that human age was significantly reduced after the great flood. E.g. [11] [12] [13] [14] [15] [16]. The reason for this is obviously something those who do believe in such things can't agree on, since it isn't really discussed in the bible but it's either thought of as a result of direct action by god (punishment or whatever), the problems/consequences that resulted from flood or the way humans have lived since then (see the earlier links some of which include discussion). Not to do with changes in the length of years AFAIK. Nil Einne (talk) 21:38, 24 May 2010 (UTC)

Not sure where you got a billion years from, neither creationists nor evolutionists would try to argue that anything like first humans were around a billion years ago. For some actual science, a DAY is determined by how fast the Earth spins on its own axis, a YEAR is determined by how long the Earth takes to orbit the sun. Days and years are independent of each other, a planet can have a long day and a short year, or a long year and a short day, there is no correlation. For example, in the Moon's orbit around the Earth, Moon days and years are actually equal, they are both one Earth month. We're less interested in length of days for the time being. As for years, the orbital period of any object around a much more massive object, like the Earth around the Sun is directly determined by the distance between the objects. This means: how far the Earth is from the Sun. The further apart the objects are the longer the orbital year. Mercury is only 0.4 of the distance from the Sun to the Earth and it has a year of about 88 days, Venus is 0.7 of the distance from the sun to the earth, it has a year of 224 days. Earth obviously takes 365 days to orbit the sun, Mars is 1.5 the distance from the Sun to the Earth and it has a year of 780 days. So for the earth to have a shorter year it would have to be closer to the Sun. There's no evidence that the Earth shuffled around or changed places since the formation of the solar system, there may have been some catastrophic events which changed the year a bit, but there's some decent evidence that the Earth has been at least in the Habitable zone, since life arose anyway. Vespine (talk) 22:42, 24 May 2010 (UTC)

So just for completeness, for Earth's year to be 15 days, it would have to be 0.15AU away from the Sun, that's a third of the distance to Mercury which is already a hot Sun scorched rock with any hope of an atmosphere blasted away long ago, quite certainly incapable of harbouring any life. So we can be pretty certain that at no stage during evolution of life was the Earth's year as short as 15 days. Going by the habitable zone link I gave above, I think shortest possible year that the Earth with life could have is about 345 days. Vespine (talk) 23:01, 24 May 2010 (UTC)

The explanation that I am familiar with is the confusion between the lunar month and the solar year that has occurred before the stories of the Bereyschitt (Book of Genesis) were written down. I think this is the explanation Zenon Kosidowski gave in his "Biblical stories" (Russ. transl. from Polish: Библейские сказания) book. Kosidowski is almost certainly not the first one to come up with it, though; I do not know who is. Our Longevity myths#Biblical article mentions this explanation, too. --Dr Dima (talk) 22:46, 24 May 2010 (UTC)

So that means he lived 930 months which would be 77.5 years, that's much more believable, while still being very old for the time. Vespine (talk) 23:04, 24 May 2010 (UTC)

According to http://multilingualbible.com/genesis/5-9.htm, Enos (or Enosh) fathered a son at the age of 90 years. According to http://multilingualbible.com/genesis/5-12.htm, Kenan fathered a son at the age of 70 years. If a "year" was a month, then 90 "years" meant 7 years and 6 months, and 70 "years" meant 5 years and 10 months. -- Wavelength (talk) 23:22, 24 May 2010 (UTC)

We may have ended up with some ages in months and others in years. Hunter/gatherers tend to use months, while farmers tend to use years, with herders using a bit of each. Since society of the time had a mixture of farmers and herders, they may have gone back and forth between the two systems. And just as we often omit the word "years" when giving our age, so do those who give their ages in months. Also realize that many books of the Bible were told, retold, written, rewritten, compiled together from multiple accounts, etc., to make the final text. This method results in rather poor quality control and many inconsistencies. This was also common to other books from antiquity, such as the Odyssey and Iliad.StuRat (talk) 00:27, 25 May 2010 (UTC)

So Enos fathered a son at 90 years old even though he died about 15 years before? (905 months = 75.4166667 years) I never knew the bible discussed sperm preservation and artificial insemination (well not counting the virgin Mary). And to think some Christians are opposed to these sort of things despite having the clear approval of god! Nil Einne (talk) 08:39, 25 May 2010 (UTC)

There were also likely many mistakes in the Bible, such as confusing two people with the same name, or maybe people just lying about their ages. But a large portion of the ages seems to be around 12 times what would normally be expected, so confusion over months and years is the most likely explanation for most of this. StuRat (talk) 02:37, 26 May 2010 (UTC)

Five months equaled 150 days, according to http://multilingualbible.com/genesis/7-11.htm, http://multilingualbible.com/genesis/7-24.htm, http://multilingualbible.com/genesis/8-3.htm, and http://multilingualbible.com/genesis/8-4.htm. -- Wavelength (talk) 23:46, 24 May 2010 (UTC)

The modern practice of observing nature, making written records, and thinking freely and critically are recent developments. Galileo Galilei is considered to be the father of this scientific approach to thinking, and he did not do his ground-breaking work until the early 1600s. Prior to Galileo’s new approach to thinking, myth, superstition and intuition were all that was available. People were illiterate and favourite stories were passed by word-of-mouth from parents to children, generation after generation, gathering embellishment along the way. The ancient scriptures, including the Bible, were written by men in that era of myth, superstition and intuition. We should not be surprised when we find things in these ancient scriptures that are not believable. These things should be ignored. Dolphin (t) 23:50, 24 May 2010 (UTC)

That is not true. Schliemann found Troy based on the Iliad record. Archaeological sites in modern Israel, Palestinian Autonomy, and Jordan are too numerous to even start to mention, and match very well the Biblical record, at least in their location (see e.g. Temple Mount, Tel Megiddo, Tel Hazor, Tel Be'er Sheva). Timelines are far more fuzzy, as expected for the events that took place several hundred years before being written down. Regarding month / year confusion, I recall Kosidowski speaking specifically about people's ages; it may have something to do with how the human age used to be specified 3000-4000 years ago. The day and the month of the Great Flood are indeed specified, as Wavelength has mentioned; but that does not mean that Noah's age is accurately recorded. --Dr Dima (talk) 00:08, 25 May 2010 (UTC)

I didn't imply that everything found in ancient scriptures is incorrect or unsound. My view is that when we find things in these ancient scriptures that are not believable, we should not believe them. See Scientific scepticism. The alternative, to which User:TASDELEN alludes, is that the things in the ancient scriptures must be correct and therefore we need to construct an explanation that makes them believable. Dolphin (t) 04:38, 25 May 2010 (UTC)

As someone who believes in the literal truth of the Bible, I'm rather confused by the idea that "most non-religious scholars do not believe that there was a literal single first human" — wouldn't standard evolutionary theory hold that there was a point at which one organism reached the point that it would be classified as Homo sapiens? Nyttend (talk) 05:44, 25 May 2010 (UTC)

Not really, we have a Most recent common ancestor also Mitochondrial Eve and Y-chromosomal Adam. I don't think you could really pinpoint the origin or Homo Sapiens to one individual. Even if we are commonly descended through ONE of the individuals, there were thousands of other very similar individuals in the same species which just happen not have surviving descendants today. Vespine (talk) 05:55, 25 May 2010 (UTC)

(edit conflict) Not really. Speciation is a much more fuzzy and fluid concept. We don't really have a hard-and-fast definition of what makes one group of living things a distinct species. Some of the stuff is really obvious (for example, dogs are different than cats), but at the edges it becomes quite fuzzy. For every aspect of the standard "textbook" definition of distinct species, there are exceptions which are common enough to make the definition problematic. There is the Mitochondrial Eve, often cited as the ancestor of all modern humans, but that doesn't make her a single individual which was a unique species different from the other members of her community. After all, she had to be able to mate with the members of her community to have viable offspring; which would make her the same species as those other members. At a temporally zoomed-out view, we can say that the first modern humans developed sometime around, say 200,000 years ago. But its not like on Monday there were no humans, and on Tuesday there suddenly was one. AT any given point, there are a population of fully interbreedable individuals; that is usually the common definition of a species; when two populations drift genetically apart to the point where they are no longer able to produce viable offspring with each other, we generally hold that they are now different species. But its not a binary state; if we go back to the time when the populations became seperated, they likely would be considered the same species for many thousands of years before genetic drift causes them to differentiate. There isn't a single individual which represents the new species. --Jayron32 05:57, 25 May 2010 (UTC)

Postscript: Found a good link for Nyttend which discusses in more detail what I was trying to explain above. See Species problem. --Jayron32 06:10, 25 May 2010 (UTC)

See also ring species (and linear species), where there are a number of different communities of a species, each community is slightly genetically different. Each one can breed with its neighbours, but not with the neighbour's neighbour's. If the community in the middle were to be wiped out, then there would be two unique species, albeit very similar to each other. CS Miller (talk) 11:50, 25 May 2010 (UTC)

• Nice and reasonable comments!

Vespine says: "I think shortest possible year that the Earth with life could have is about 345 days". Then, if the velocity of the light has a fixed value, the definition of light-year distance should be changed to be "light-day" or 1000 LD distance, as " Days and years are independent of each other, a planet can have a long day and a short year, or a long year and a short day, there is no correlation...".I understand 1 Earth's day length is innate,is constant while 1 Earth's year length is variable. So, the distance of the Earth to the Sun is variable.GOD has not placed the planets at a fixed distance and let them orbit the Sun at these fixed distances, on a fixed elliptical orbit as said Kepler in 1609.TASDELEN (talk) 10:30, 25 May 2010 (UTC)

Sorry I'm struggling to understand what you mean by all of that.. Barring any cataclysmic events, these days both the year and the day of the Earth are quite stable. See Stability of the solar system. I was referring to the period during the formation of the Earth or when there might have been other cataclysmic events, not in the recent or even not so recent past. Vespine (talk) 11:43, 25 May 2010 (UTC)

• I meant the non Stability of the solar system; because,as you say,"I think shortest possible year that the Earth with life could have is about 345 days".So, 1 year may be=to 345 days, in an older time. Then ligth-year distance, at that old time should be = actual measurement*345/365; which is impossible.This why "the non-stability" should be considered. TASDELEN (talk) 14:04, 25 May 2010 (UTC)

No, TASDELEN, you seem to have have misunderstood some of the earlier discussions. Neither the Earth's day length nor its year length are "innately fixed" so you can't define one variable as a constant and then compare another independent variable to it. The only constant is the second, because we have (now) defined it according to another fixed value based on the invariable properties of light and independent of anything to do with the Earth's motions. We extend the defined second to a defined year by simple multiplication, and the light-year is based on that, not on any derivitive of the actually variable day length and/or year length.

The length of the day (defined as noon to noon) varies slightly through the year due to the eccentricity of the Earth's orbit around the sun: its average over the year depends (mostly) on the speed of the Earth's rotation on its axis. This has been gradually slowing since the formation of the Moon around 4.5 billion years ago, due to tidal acceleration (which both slows the Earth's rotation and moves the Moon further away), so as one tracks further back in time the days were shorter and there were more of them in the year, and also the months were slightly shorter (because the Moon was closer and orbited the Earth faster): "620 million years ago: the day was 21.9±0.4 hours, and there were 13.1±0.1 synodic months/year and 400±7 solar days/year", as that last linked article says. However, these changes are very long term, and the day and month lengths a mere few thousand years ago when the accounts preserved in the bible were formulated would not be noticeably different from today's.

The Earth's orbit, and consequently the length of the Earth's year also varies slightly over very long periods due to several factors, but not by any amount significant for everyday purposes (like measuring lifespans) over historical periods; nonetheless we no longer ultimately define any scientific measurements relative to the actual year, but instead to a year derived from the independently defined second. Vespine was alluding to a purely theoretical situation where the Earth would have fewer days (of the current length) in the year by virtue of orbiting closer to the Sun in accordance with Kepler's third law; increased insolation due to the simple inverse-square law would clearly place a lower limit on the proximity, and hence the number of days in the year, for which habitability would be possible.

None of this conflicts with the well-known fact that in the very long term the stability of the Solar System is not assured, as illuminated by Chaos theory. 87.81.230.195 (talk) 14:49, 25 May 2010 (UTC)

Note that a light-year is the distance which light travels in a vacuum in one Julian year (astronomy) which is 31,557,600 SI seconds (with each second defined as "the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom"). This measure of time is not dependent on the length of sidereal year which is not even now precisely equal to the Julian year (astronomy). 124.157.249.129 (talk) 15:05, 25 May 2010 (UTC)

• When I say "innate=constant", I consider Newton's total energy expression: Etot=Ekin+Epot=Ct, where Ekin=1/2*m*Vr^2+1/2*I*w^2. All V=Velocity related values are evaluated according the new second. So, 1/2*I*w^2 is constant, was (innate), today or 4 billion years ago and this represent what we call "day" in Newton's expression. 1 year is the time for 1 cycle of the Earth around the SUN. Practically, we say this time is 365 days. Year's lengths are "not innate" but variable according the distance of the planet to the SUN.(Kepler's period law). As a possibility of 1 year=345 days is considered, I say "light-year" distance has no sense, but ligth-second distance should be defined. Say 3600*second=1 day=innate=Constant. Then we must use Ligth-day or 1000LD distance in astronomy; not ligth-year. Now, coming back to our Adam's 930 years living, it seems that this is possible if we agree on "variable year lengths". Suppose the human life is 100 fictive Earth's years, today. 100 Earth's years=36500 today's Earth's days. If we were living on Saturn, according Kepler's period law, we will live only ....Saturn's years. Are there any old Earth's periods, where Adam has lived 930 cycles corresponding to today's 100 cycles of the Earth around the SUN? That may explain Adam's and others long life. And probably Adam (homo sapiens) has lived at a period where 930*P=36500 fictive days.Then P=39 days/ a cycle. Mathematically this is possible, but physically it looks impossible. Is it really impossible? TASDELEN (talk) 18:53, 25 May 2010 (UTC)

No, there has never been a time when the Earth revolved around the Sun 9.3 times faster than it does now (which would require it to orbit only about 30 million miles from the Sun, closer than Mercury). In any era that Homo sapiens has existed (no further back than 1.5 million years using the most generous definitions) the year length has been very close to today's value, so shorter actual years cannot in any way explain the Bible's supposed lifespan values. The fact that in the remote past the Earths axial spin was faster, so that there were more but shorter days in the year, is quite irrelevant to this question, as is the way we define the distance we choose to call a light year (which you have misunderstood, please re-read 124.157.249.129's correct explanation above). 87.81.230.195 (talk) 21:24, 25 May 2010 (UTC)

Most certainly, people back then were not thinking about velocity of photons or even the rotation of the Earth. Most of the stories where these "timing problems" are present are set in a time when people were not much more than hunter-gatherers. How could they measure years and moths? How could anyone of us, without extensive knowledge of astronomy and without the help of the organized society around us know the exact month we are in or your exact age? Especially in a region without observable change of seasons? How could you measure time frames longer than the day based on things that really interest you? Maybe after the harvest seasons of certain plants? Migration patterns of certain animals you hunt? A year could mean pretty much anything, and most stories before the time of Moses are probably set many centuries apart from each other. Besides this, many people assume the language, way of thinking and memes were exactly the same as today. It's like if you write down that you've seen dozens of something, and many centuries later someone reads it, looks up what "dozen" could have meant, does a research about the things you've seen, discovers that their number was not exactly divisible by 12, and reaches the conclusion that you were a big liar. --131.188.3.21 (talk) 22:39, 25 May 2010 (UTC)

TDS

Say one has a geophysical electric log with data for SP, short number (16), long number (64), and what one wants to do is to calculate/estimate the TDS (Total dissolved solids) -- water quality -- from that data. How does one go about doing that? Killiondude (talk) 22:14, 24 May 2010 (UTC)

This link may be of some help, although it points out that it can be used in this way provided that the analysis is tied closely to local water chemistry measurements. Mikenorton (talk) 19:32, 25 May 2010 (UTC)

May 25

Consider a satellite moving at 3.87 km/s - how much is the clock aboard the satellite affected by special relativity per day?

The calculation I did was $86400{\sqrt {1-(3870/299792458)^{2}}}-86400=-7.2\times 10^{-6}s$ meaning that the clock aboard the satellite falls behind by about 7.2 microseconds per day. Could someone please verify that this is the correct approach?220.253.221.60 (talk) 00:32, 25 May 2010 (UTC)

Could you give us the rest of your approach? It is difficult to know if it is right based on just the final answer. (I could try and calculate it myself and see if I get the same answer, but even if I do, that doesn't mean your approach was right - you might just have been lucky.) --Tango (talk) 00:54, 25 May 2010 (UTC)

(ec) It's fine, except that a day is 86400 seconds long, not 86500, and you can't realistically ignore general relativity in this situation. (Also, you're comparing your satellite clock to a clock "at infinity". If you wanted to compare to a clock on the surface, you'd have to take into account that surface clocks also move at up to 0.5 km/s relative to a nonrotating frame, depending on latitude.) -- BenRG (talk) 00:55, 25 May 2010 (UTC)

Ah, that's why I wasn't recognising the method! Now I see what the method is! --Tango (talk) 01:04, 25 May 2010 (UTC)

Global Average Annual Temperature limits

How low/high can the Global Average Annual Temperature drop/rise before it irreversibly spirals into either an snowball effect or a runaway greenhouse gas effect.24.78.167.139 (talk) 01:00, 25 May 2010 (UTC)

I don't think the scientific community has reached a consensus on that. I'm not sure there is even a consensus that either of those things would happen at all. --Tango (talk) 01:12, 25 May 2010 (UTC)

The problem with climate change is that the current climate system has been relatively stable for a long period of time. Historical records of climate show that in transitions between different stable climate states, the system becomes highly chaotic and unpredictable before establishing a new equilibrium. So, while the current rate of carbon emissions is likely to lead to a warmer, on average, equilibrium climate conditions, the path to that new equilibrium state is likely to be a wild ride, and very unpredictable. Picture several centuries of unpredictable and wild climate swings, and that is part of the big problem. Its not that we can predict what will happen that is the problem. That would actually be less of a problem, because we could at least prepare for it even if we couldn't stop it. Its that we a) know its going to be crazy and b) can't predict what kind of crazy its going to be. The problem is that this is a complex problem which has been reduced by the popular media to "global warming" or "global cooling". Then people here scientists making both predictions, and think "they don't know what they are talking about, so we can ignore whatever the scientists predict." It might be better to think of it as "global climate clusterfuck." --Jayron32 01:30, 25 May 2010 (UTC)

Y'know, climate change could go different ways in different parts of the world, too (for instance, we could have global warming in Europe and Africa but global colding in North America, among many other possibilities). FWiW 67.170.215.166 (talk) 06:53, 25 May 2010 (UTC)

You're confused about the meaning of the word 'global'. 67.243.7.245 (talk) 19:14, 25 May 2010 (UTC)

I think there is a consensus that if it somehow got so cold that the oceans froze over down to the equator, the resulting Snowball Earth state would be stable until CO2 built up to extremely high levels. I think there is also a consensus that a runaway greenhouse is not a real possibility -- CO2 levels have been over ten times higher in the past without producing such an effect. Looie496 (talk) 06:56, 25 May 2010 (UTC)

So there is no maximum temperature, and there is no minimum temperature??24.78.167.139 (talk) 07:12, 25 May 2010 (UTC)

Not so. There are probably (though not certainly) both, but we don't yet know what they are, and other factors beyond average global temperature (such as atmospheric composition, continent distribution and biosphere feedbacks) also have influence through multiple interactions more complex than we yet understand. Our current studies are focussed mainly on changes and states that are much less extreme, but which nonetheless would have serious effects on human global infrastructures and civilisation (such as sea-level changes). Looie496's second point (on the runaway greenhouse) related only to CO₂ levels, but ultimately increased insolation due to the long-term brightening of the Sun will almost certainly cause one, and one way or the other will raise the average global temperature way above survivability. 87.81.230.195 (talk) 13:33, 25 May 2010 (UTC)

The utter maximum could easily be close to the situation on Venus - 460°C!! Venus is a little closer to the sun - but not anywhere near enough to account for the difference. But the truth is that we don't know.

There is certainty in a short term (several years) rise in average global temperature and a rise in ocean levels...we're actually measuring that happen and seeing it correlate to CO2 levels. But if it levels out - and where it levels out is totally unknown.

• Firstly because we can't predict irrational human behavior...the degree to which we turn down the CO2 production rates is sensitively dependent on crazily unpredictable things like the reaction of the US public to a health-care bill pushing out the time when the climate change laws can be discussed and whether some accident in the gulf of mexico produces an oil spill and a knee-jerk reaction to pro-"green" agendas.
• Secondly, there are feedback loops - both positive and negative built into the system. Some things (like the melting of the polar ice causing the shiney white reflective surface to be replaced by dark green, heat-absorbing ocean) mean that as things get hotter, so those systems make the world hotter still - positive feedback - a 'runaway' effect that's impossible to stop once it gets started. Other things (like the increase in CO2 levels causing some kinds of plants to grow faster - enabling them to absorb yet more CO2) have the opposite effect - negative feedback.

When you get dualling run-away systems, the result is exceedingly hard to predict. If you turn on both taps on your bathtub and pull the plug out - will the bath stay more or less empty or will it eventually fill up and overflow? It's hard to guess. What if you install a device that opens the faucets up more and more the deeper the water gets? And this is a vastly over-simplified analogy. There aren't two systems (drain and faucets) fighting each other, there are hundreds of systems - and many of them have that property of positive feedback: "the worse things are, the worse they'll become".

The smart money says this: Even if the findings are 'iffy' and there is only (let's say) a 15% chance of making the planet essentially uninhabitable and an 85% chance that it's all just bad science - can we really just ignore that risk? Would you be prepared to risk the future of your child's life on the roll of a single dice? If it comes up '1', they shoot your kid...and everyone else's kid for good measure? If that was the choice then wouldn't you do absolutely everything in your power to avoid rolling that dice? The science is easily 15% reliable...probably more like 85% reliable. Roll a dice, if it doesn't come up '6' they kill your kid. Why are you waiting for a certain answer? SteveBaker (talk) 20:21, 25 May 2010 (UTC)

What makes you think that climate change has the slightest possibility of making the planet "essentially uninhabitable"? Even scientists who agree that global warming is happening don't make such outrageous claims anymore -- only Al Gore still makes these kinds of statements. 67.170.215.166 (talk) 02:04, 26 May 2010 (UTC)

I think you mean human-caused climate change. The earth itself is capable of some pretty destructive stuff all on its own, without humans. There have been some catastrophic geologic events in the past, and there's nothing to say something like the Yellowstone Supervolcano couldn't happen again, say, tomorrow. Look at the effect of the Mount Tambora eruption on climate (the Year Without a Summer, and imagine an event several orders of magnitude larger. Such eruptions exist in the geologic record. There are lots of ways the climate could change to make the Earth essentially unlivable. It is unlikely humans could do anything like that, but that isn't to say that the Earth could not become unlivable. The article Risks to civilization, humans and planet Earth contain some overview of this. --Jayron32 02:19, 26 May 2010 (UTC)

I have trouble buying anything in the foreseeable future completely destroying humans. At this point, we have the technology to survive in some pretty extreme conditions. I can imagine something wiping out 90+% of people (heck, we can even do that with nuclear weapons), but killing off everyone would be hard, even for nature. Buddy431 (talk) 03:55, 26 May 2010 (UTC)

Brewing yeast and fructose

What is the difference between yeast metabolism of glucose and fructose? Our yeast article only mentions fructose once. Specifically, I'm curious in brewing yeast whether fructose has the same conversion rate as glucose. Shadowjams (talk) 02:07, 25 May 2010 (UTC)

Most yeast uses glycolysis to convert sugars into energy (and alcohol). One of the early steps in glycolysis is the conversion of glucose-6-phosphate to fructose-6-phosphate. This reaction is easily catalyzed, and goes back and forth freely (glucose-6-phosphate isomerase is not a control point in glycolysis). The only difference between glucose and fructose utilization would be differences in efficiencies between going from free glucose to glucose-6-phosphate and free fructose to fructose-1-phosphate. -- 174.24.200.38 (talk) 04:32, 25 May 2010 (UTC)

Thank you for that, but I think glycolysis differs greatly from fructolysis and fructose-6-phosphate is quite different from molecular fructose. Do yeast have a fructolysis pathway? Shadowjams (talk) 05:37, 25 May 2010 (UTC)

Cats and newborn/infant humans

My wife and I have 4 cats and we are planning on adding a human soon. Could someone please help me find reliable sources regarding precautions and practices for newborns and cats? I am not asking for medical advice, I'm asking for help finding government health guidelines and the like - there is certainly a distinction. I'm already aware of toxoplasmosis - but that's the only reliable and well-sourced issue I can find. Help? 218.25.32.210 (talk) 03:19, 25 May 2010 (UTC)

The medical professionals you consult at various stages during the pregnancy will be able to give you advice on pets or at least tell you where to find that advice. I think they can do that better than we can. --Tango (talk) 03:22, 25 May 2010 (UTC)

When I was a baby our cat (Kitty Fisher) used to sit in my pram and guard me :) DuncanHill (talk) 07:40, 25 May 2010 (UTC)

Cats rock, but ask your doctor. The toxoplasmosis issue is relevant, but perhaps there are other issues. Shadowjams (talk) 10:13, 25 May 2010 (UTC)

Antenatal classes warned us on the risk of accidental suffocation from cats thinking babies faces were nice warm places to sit. A cot net or exclusion was advised. --BozMo talk 10:41, 25 May 2010 (UTC)

FWIW [17] looks pretty reasonable. --BozMo talk 10:48, 25 May 2010 (UTC)

Yeah, there are documented cases of that, with babies at least as old as 3 months. EverGreg (talk) 11:19, 25 May 2010 (UTC)

A study found that children who were exposed to cat-allergenes in the household dust at age two, had an increased risk of developing asthma at age 10. So cleaning would be important. cleaning, vacuuming mattresses and keeping the cats away from the bed would be a precaution. (This is from the PhD thesis of R.J. Bertelsen: "The indoor environment and childhood allergic disease; the importance of allergens and microbial components" [18])

This goes hand-in-hand with the suffocation issue. Never let the cat have access to a sleeping child and keep it out of the bedroom completely.

Confusingly, other studies have shown the opposite effect of cats and allergies, so the issue is not completely settled, though this appears to be one of the more thorough studies.

There are also issues of cat-psychology. The cat could get jeleaous or stressed and react by biting the baby or defecating indoors. Some recommend to famliarize the cat with the baby, by letting it smell the baby for instance. EverGreg (talk) 11:19, 25 May 2010 (UTC)

My sister didn't have a cat at home until she was about 3 - she is asthmatic. I had a cat in my pram from as soon as Kitty could get in there, and I'm not asthmatic. When she had her kitten (Pussy Simpkins) she'd bring Puss in by me too. DuncanHill (talk) 22:24, 25 May 2010 (UTC)

Nothing personal but I would strongly advise against this kind of anecdote. This is one of the reasons we don't give medical advice, everyone has an anecdote but for all we know, your and your sisters asthma (or lack of) could very well have nothing to do with cats. The OP was asking where to find information, not for personal experiences. Anecdotes are what superstitions, pseudoscience and quackery thrive on. Vespine (talk) 22:50, 25 May 2010 (UTC)

Nothing personal, but no. DuncanHill (talk) 22:55, 25 May 2010 (UTC)

Vespine is right. --Tango (talk) 23:41, 25 May 2010 (UTC)

You should also take in to account the personality of the cats. Babies cry, whine to be fed constantly, and puke at inopportune moments. Some cats react badly to this. We were lucky in that we had a Siamese which considered all that to be perfectly normal behaviour. As EverGreg mentioned above, jealousy can be expressed in all kinds of ways; during the first meeting, you'll want to be extremely close by to immediately correct any violent behaviour towards the infant; they'll need to learn right off the bat that attacking the new naked "cat" is unprofitable. Contrary to popular belief, cats can understand a basic social hierarchy, so long as it is presented clearly. This site suggests that some cats may "spray" in response to the new arrival (in an attempt to cover the new scent). I'm not sure what kind of precautions you can take with that, but if you've been thinking about replacing your carpets with linoleum, now might be a good time. :-) Matt Deres (talk) 23:24, 25 May 2010 (UTC)

Future computer (from IP 117.197.246.107)

if in future somebody makes a future predicting device/computer , what would be its concequences??? —Preceding unsigned comment added by 117.197.246.107 (talk) 10:03, 25 May 2010 (UTC)

This has been considered and there are results in computer science that state that such a machine is impossible. Consider: Machine #1, able to predict the future, tries to predict what will be going on inside a house. In that house there is machine #2 which can also predict the future, but it predicts the future of machine #1. That is, it knows what machine #1 will predict and then it does something that breaks with that prediction, invalidating the result of machine #1. Put in another way, a machine can't predict the outside world because you can't cram all the complexity of the outside world into a computer. EverGreg (talk) 11:03, 25 May 2010 (UTC)

Perfect future prediction being available creates causality problems, so they couldn't exist unless we are massively wrong about the way the universe works. For example, imagine that this computer predicts whether I'm going to say "apple" or "orange" next. In order for the prediction to work, I can't look at the prediction and do the opposite, but that's the very thing I want to do!

Interestingly, there's a a similar argument that the easier-sounding problem of halting problem is also unsolvable. If you could write a program (call it "H") to determine whether another program will halt or not, you could write another program that runs H on itself, and obstinately does whatever H said it wouldn't do it. It may seem like a silly trick, but this kind of thing comes up all the time in computer science. Paul (Stansifer) 12:00, 25 May 2010 (UTC)

Been done already - see weather forecasting. 92.28.244.102 (talk) 13:36, 25 May 2010 (UTC)

Perfect prediction is impossible since quantum mechanics tells use the universe isn't deterministic. Approximate prediction we already have in various ways (eg. weather forecasting, as already mentioned). --Tango (talk) 16:01, 25 May 2010 (UTC)

We have computers which predict the future! They predict the weather every day. They compute the orbits of satellites and predict where they will be. They predict solar eclipses, predict winners in baseball games, predict population growth for traffic studies, predict where an artillery shell will land, etc. anonymous6494 16:00, 25 May 2010 (UTC)

Right. You can predict "future" (trajectory) of a macroscopic system, with accuracy that decreases for longer time. If the dominant interpretation of the quantum mechanics is correct, however, you can not predict the outcome of a measurement unless the system is in an eigenstate of the operator involved; you can only predict the probabilities of all possible outcomes, but not the outcome itself. Even when you disregard the quantum-mechanical "complications", in classical mechanics most many-body systems exhibit "deterministic chaos", which essentially makes the long-term prediction of future an exercise in futility; I can go into more details if you want me to. --Dr Dima (talk) 19:40, 25 May 2010 (UTC)

They don't "predict" the future (check your dictionary!) - that would imply that they always get the answer 100% perfectly right! They estimate the future...with varying degrees of success - that's certainly possible.

Wrong. Predictions always have a finite accuracy, and are never implied to be 100% correct. That is how a prediction is defined. See Prediction interval. --Dr Dima (talk) 00:42, 26 May 2010 (UTC)

The problem with perfectly predicting the future is also a matter of thermodynamics. The computer requires energy in order to perform calculations - and that energy gets turned into (mostly) radio waves and heat. The amount of radio/thermal energy and the direction it's radiating in depends entirely on how those calculations turn out - roughly, on how many bits have to be flipped. Simplistically: if the answer to a simple piece of arithmetic changes the value in a one-byte memory location from 0 to 127 (which in binary is from 00000000 to 01111111) then the computer will consume seven times more energy than if the answer to the calculation had been just one bigger and changed the memory contents from 0 to 128 (ie from 00000000 to 10000000). Since the energy output by the computer as a part of its calculations goes out into the environment, it actually affects the very future that the computer is trying to predict (not by much...but think "butterfly effect"!). That means that to perfectly calculate the future, the computer would have to be able to perfectly calculate the effect of it's own energy output...energy that will come about from a calculation it has yet to perform! But doing that requires that the computer perform those very calculations that it has not yet performed in order to know what data to feed into those very same calculations! Hence there is an infinite regress and the computer cannot possibly predict the future accurately because any calculation it does in order to perform that prediction changes what the outcome should be. SteveBaker (talk) 19:52, 25 May 2010 (UTC)

Tyvek and Nylon

is tyvek any better than nylon —Preceding unsigned comment added by Tom12350 (talk • contribs) 10:03, 25 May 2010 (UTC)

Better than nylon at doing what? Both Tyvek and nylon have many uses. Dismas|^(talk) 10:20, 25 May 2010 (UTC)

It can be assumed that unless tyvek and nylon are controlled by regulation, that they would not both continue to be on the market, unless each had a distinct niche. Nylon has been widely made for decades, therefore it's almost certain that tyvek, a newcomer, has some inherent advantage. 24.130.145.253 (talk) 04:18, 26 May 2010 (UTC)

list

please list these in order of solvent strength. 91% alcohol, pure acetone, 3% peroxide, kerosene, turpentine, 5% vinegar, pure lemon juice (citric acid) household ammonia, 10 % hydrochloric acid, 10 % nitric acid, , ethyl ether, chlorine bleach —Preceding unsigned comment added by Tom12350 (talk • contribs) 11:10, 25 May 2010 (UTC)

Solvent strength for what? sugar, salt ?87.102.85.123 (talk) 12:20, 25 May 2010 (UTC)

Yeah it depends on what you want to dissolve: food, bacteria, plastic, goo, salt, etc. etc. --Chemicalinterest (talk) 13:52, 25 May 2010 (UTC)

For copper the 10% nitric acid is strongest, a mixture of the 3% peroxide and 10% hydrochloric acid is next, then bleach, then ammonia. --Chemicalinterest (talk) 13:53, 25 May 2010 (UTC)

to dissolve oil off surfaces —Preceding unsigned comment added by Tom12350 (talk • contribs) 15:59, 25 May 2010 (UTC)

In order

Kerosene and turpentine are oils, they will mix with other oils.

Depending on the type of oil Acetone .. ethyl ether .. 91% alcohol will have roughly the same de-oiling properties, alcohol being slightly weaker, or possibly innefective for heavier non vegetable oils.

Citric acid is a well known degreaser, vinegar to a lesser extent.

The other acids and ammonia may be slightly better than pure water. Non will have any true de-oiling effect. Neither chlorine bleach or nitric acid can be recommended and are potentially unsafe.

end

In general hot water, or water with detergent will be more effective than all except ether/acetone. Thick oils may not even dissolve in a ether acetone mixture, but hot detergent solution will work in this case.77.86.125.207 (talk) 18:19, 25 May 2010 (UTC)

An oil can still be a solvent. Edison (talk) 22:47, 25 May 2010 (UTC)

Acetone is a common choice for removing oil from surfaces. Reasonably pure acetone will leave no visible residue, and is fairly safe except for fire hazard. Alcohol is also fairly safe, but less effective for oil / fat, and is also a fire hazard. Commercial detergents (say, a liquid for manual dish-washing) should work well, too. What kind of surface are we talking about? Acetone may damage plastic surfaces. And don't even think of using nitric acid or (di)ethyl ether. --Dr Dima (talk) 20:01, 25 May 2010 (UTC)

i dont want to use a detergent. i know that Kerosene and turpentine are oils. but they are also solvents. where do they rank in that list in terms of strength? —Preceding unsigned comment added by Tom12350 (talk • contribs) 07:01, 26 May 2010 (UTC)

The relationship between the passage of time for a stationary object and the passage of time for a moving object

My understanding is that the relationship between the passage of time for a stationary object and the passage of time for a moving object is given by the formula $\Delta t'={\frac {\Delta t}{\sqrt {1-v^{2}/c^{2}}}}$

In this formula, which variable represents the passage of time for the stationary object (i.e. $\Delta t$ or $\Delta t'$) and which one represents the passage of time for the moving object?--Wikinv (talk) 12:45, 25 May 2010 (UTC)

In relativity, it's not possible to distinguish between which object is moving and which is stationary. To object A it may appear that it is stationary and object B is moving. To object B, it may appear that it is stationary but A is moving. So we can only talk about the passage of time in our frame of reference, and the other that appears to us to be moving. I beleive that $\Delta t$ refers to our frame of reference, and $\Delta t'$ refers to the frame of reference that we see to be moving. See Time dilation --Phil Holmes (talk) 16:30, 25 May 2010 (UTC)

Here's what that equation really means: if you have a bunch of clocks that are at relative rest ("comoving") and all synchronized in a certain way ("Einstein synchronisation"), and you have one clock that moves at a speed v relative to all the others (which I'll call the wandering clock), and the wandering clock passes two of the other clocks at different times, and Δt is the time ticked off by the wandering clock between those encounters, and Δt' is the difference between the readings of the two clocks it encountered, then that equation gives the relationship between Δt, Δt', and v. Don't try to remember the primes; just remember that the wandering clock always records the shorter time ("time dilation"). -- BenRG (talk) 20:41, 25 May 2010 (UTC)

...So does that mean that it takes less time for a traveling object, "C" to go from stationary objects "A" to "B" than it does for stationary objects "A" and "B" to stand still, i.e., "A" and "B" would have more ticks than "C"? 71.100.8.229 (talk) 10:24, 26 May 2010 (UTC)

Artificial microbes to help terraform Mars

Now that a semi-artificial microbe has been created, would any microbe, artificial or otherwise, be able to survive and grow on Mars? And could they help to terraform Mars, by changing the composition of the (thin) atmosphere, or raise temperatures by the greenhouse effect for example? 92.28.244.102 (talk) 14:18, 25 May 2010 (UTC)

In theory, sure. There's no reason such an organism would need to be artificial, though: current techniques could be used to encourage an existing organism to adapt to the Martian climate. As for how much change such organisms could make, and how long it would take them to make it, that's for a scientist of a different sort to answer. – ClockworkSoul 14:32, 25 May 2010 (UTC)

As I recall, one of the major problems with Mars is the lack of a magnetosphere, and the consequent exposure to solar winds. DuncanHill (talk) 14:48, 25 May 2010 (UTC)

From the description in the article, it sounds as if deinococcus radiodurans could survive on Mars. Gandalf61 (talk) 15:18, 25 May 2010 (UTC)

There is a difference between spores surviving and a microbe actually being able to grow. Nothing we know of would be able to grow on the surface of Mars without a major assist. It is barely possible that there are deep subsurface environments where liquid water exists and microbial growth could occur -- but since the crust is solid and therefore lacks mixing, any such life would quickly exhaust its resources. Looie496 (talk) 15:41, 25 May 2010 (UTC)

Radiation is not that much of a problem. If our article on Terraforming of Mars is right, even humans without shielding can survive Mars radiation levels for years. Microorganisms should be doing just fine with this. Of course, a direct hit by a coronal mass ejection is a different story. One would imagine that the said microorganisms live in the H2O and CO2 ice-rich top layer of the "soil" near the polar caps, and reproduce during summer when the temperatures go up and the ice starts to melt/sublimate. For the winter they would either freeze or form spores or endospores. The hope is mostly to increase Mars albedo in the visible range, so the surface is warmer; and, to a lesser extent, to increase Mars atmospheric pressure. I would not be surprised if many of the extant terrestrial microorganisms can survive dormant on Mars for years or longer. Coercing them to effectively grow and multiply is much harder, though. Bear in mind that the spores from Earth are probably present on Mars already, and likely in large quantities. Earth atmosphere "leaks out" into space due to the interaction with solar wind, so small airborne particles are likely to be carried with it. Some of these particles can (and will) eventually get deposited on the surface of Mars. The fact, however, is that we have not conclusively detected any microorganisms on Mars so far. This may be because (1) we did not look hard enough or in the right places, (2) the microorganisms are all dead by the time they reach the surface of Mars (e.g. killed during re-entry), (3) The conditions do not allow for any of them to multiply. As for bringing the bioengineered ones from Earth - it would me far more appropriate to thoroughly search for the local ones first. --Dr Dima (talk) 18:33, 25 May 2010 (UTC)

There is also the fact that aggressively introducing microbes to the surface of Mars could destroy any life/evidence of life previously extant on mars, or at least complicate the identification of it, so we'll probably be studying the surface of mars for at least a few more decades before anyone with the means seriously thinks about terraforming it. 210.165.30.169 (talk) 03:02, 26 May 2010 (UTC)

Effective Max speed of the international space station during interplanetary travel.

Using the Drag equation I am trying to figure out the effective max speed of the International Space Station if the pilot felt so inclined to take a joyride. Here is what I have so far:

Coefficient of drag: >2.5 (shall we assume 2.5?)

Mass density of Interplanetary medium: 5 particles / cc (5,000,000 particles / m^3) (I need help converting this to actual mass-density)

Velocity: This is my variable.

Force of drag: I want to set this equal to the force of the stabilizing engines, but I cannot find this information.

Reference Area: Since the main engines are in Zvezda, I'll use height and width instead of length for the area to give me: 108.5 m * 20 m = 2170 m^2

So can anyone help me find the force of the main engines and calculated the mass density of interplanetary medium? —Preceding unsigned comment added by Anythingapplied (talk • contribs) 15:06, 25 May 2010 (UTC)

You can ignore drag, it won't be a significant factor. It's not going to stop accelerating when drag balances thrust, it's going to stop accelerating when it runs out of fuel. I don't think the ISS's own engines would be enough to even get it out of orbit - they use the engines of docked spacecraft just to boost the orbit a bit, they would need to attach much bigger engines to get it to escape velocity. --Tango (talk) 15:58, 25 May 2010 (UTC)

But the ISS is scheduled to get a VASIMR engine. This has much better specific impulse than old-fashioned chemical rockets, so it will certainly change things. --Stephan Schulz (talk) 17:04, 25 May 2010 (UTC)

What if fuel were unlimited? I've been told by others that drag is insignificant, but at some speeds, it has got to start being significant (say 1/100 the speed of light?). Maybe you have to start getting into relativistic speeds before it matters, but I'm still really curious to what would happen if you plugged in all the right numbers... how fast you could get going? So assume fuel is infinite and that the solar system is infinite stretching on at 5 particles / cc. How fast could you get going? I guess I would like to see first hand the results of the equation that say the drag is insignificant, but am having trouble finding a complete set of numbers to plug in. Anythingapplied (talk) 18:41, 25 May 2010 (UTC)

My guess (but we await an expert on this) is that even at speeds approaching the speed of light, the drag force will still be less than that of the (reasonable powered) thrusters, so, with infinite fuel, the energy acquired (but not the velocity of course) can increase without limit (assuming that time is also infinite). As a simple, back of an envelope calculation, one could assume that the number of particles emitted by the thrusters would have to be many times greater than the number of drag particles encountered. The number of times greater would depend on the speed at which the thrusters emit particles. Dbfirs 21:50, 25 May 2010 (UTC)

I think the ISS would be destroyed by the interplanetary medium ablating the hull (which is one of the biggest problems with interstellar travel - if you go fast enough to make the trip a reasonable length, the interstellar medium destroys you) before the drag became an issue. If we ignore that, we should be able to work it out, but it would require relativistic calculations. I'll let somebody else do that. --Tango (talk) 23:17, 25 May 2010 (UTC)

Ah yes, I hadn't thought of that. Since we are dealing in unrealistic infinities, should we assume that the hull is infinitely strong? I assume that magnetic field shielding becomes ineffective at these speeds? Dbfirs 01:29, 26 May 2010 (UTC)

. How much interplanetary spaceship-destroying "interplanetary medium" is there per cubic kilometer, exclusive of asteroids? Why haven't all the previous interplanetary probes been destroyed by it? Edison (talk) 05:24, 26 May 2010 (UTC)

Because none of them travelled at relativistic speeds. --Tango (talk) 11:14, 26 May 2010 (UTC)

75% of the universe is hydrogen, so 5 particles / cc is essentially 5 amu / cc = 8.3×10⁻²¹ kg / m^-3. It is pretty trivial to show that this density results in negligible drag for anything less than highly relavitstic speeds. Dragons flight (talk) 09:15, 26 May 2010 (UTC)

Moon

Given the level of technology available in 1959, would it have been technologically possible to send people to the moon, and return them? Or to put it another way, were the materials, technology and understanding of space travel developed enough at that point? I know the moon landing is considered fact (I don't want to get into a big discussion about that) and you could just say "yes" and post the wikipedia article as proof, but I would like something more that actually adresses the question of if the technology was advanced enough. Thank you, and sorry if I've come across as rude or forceful in my asking of this. —Preceding unsigned comment added by 213.114.115.208 (talk) 15:31, 25 May 2010 (UTC)

No, it took about 10 years from 1959 to develop technology to that level. See Apollo Program. -- Coneslayer (talk) 15:41, 25 May 2010 (UTC)

(edit conflict with Coneslayer) Almost certainly not. The first artificial satellite was only launched in 1957, and it wasn't until 1961 that anyone at all was put into space (and that was one person, for one short orbit, in a space capsule that was basically designed like a submarine; way too heavy to be suitable for a moon trip). In 1959, there just weren't rockets big enough, nor the technical knowhow to send someone to the moon and back. The first probe to the moon, Luna 1, did fly by the moon in 1959. However, the first three Luna missions, in 1958, all failed. The technology was coming along, but it was nowhere near ready to launch a person to the moon at that point in time. Buddy431 (talk) 15:45, 25 May 2010 (UTC)

Do you mean 1959 or is that a typo and you actually mean 1969? The moon landing in 1969 is considered fact and is the proof that the technology was advanced enough then to do it. I can't imagine what kind of proof could possibly be better than it actually being done. If you really mean 1959 then the rest of your question doesn't really fit, but the answers already given are correct. Both the USSR and the USA were doing everything they could to get to the moon as fast as possible, so I think we can safely assume that they couldn't have done so any sooner than they did. --Tango (talk) 15:54, 25 May 2010 (UTC)

Unless it was a hoax... 82.44.55.254 (talk) 16:34, 25 May 2010 (UTC)

But it wasn't - and that's remarkably trivial to prove to all but the most recalcitrant idiot. SteveBaker (talk) 19:33, 25 May 2010 (UTC)

To be fair, they probably could have done it a year or two earlier if it hadn't been for the Apollo 1 fire. That incident – and the subsequent capsule redesign – delayed the first manned Apollo launch by 21 months. TenOfAllTrades(talk) 16:05, 25 May 2010 (UTC)

True, but I don't think it delayed the first manned lunar landing by anywhere near that much. As I understand it, they turned some of the planned manned missions into unmanned ones, but still kept going along the same timetable. There may have been a delay, but I don't think it was as much as 21 months. I can't find the original timetable... --Tango (talk) 16:21, 25 May 2010 (UTC)

I can't rule out the possibility that if President Truman had announced in 1951 (as Kennedy did a decade later) that the U.S. would land a man on the moon and return him safely within 9 years, that it might have been feasible. It would have been a prestigious program, and better intercontinental ballistic missiles and spy satellites would have been valued spinoff. Microelectronics and computer technology would seem to be major hurdles to be overcome. Giving Von Braun and company the huge funding NASA received in the 1960s would have greatly accelerated building of the Saturn V. Edison (talk) 16:48, 25 May 2010 (UTC)

Perhaps, but it would have been a crazy thing for Truman to announce. We had V2 rockets in 1951, but that was it. There was no way he could have had any idea it would work. --Tango (talk) 17:25, 25 May 2010 (UTC)

Truman certainly would have had no idea it could be done, but Von Braun and the other rocket scientists were thinking about it. They just needed a big budget for R & D and they could have gotten to the moon years earlier than 1969. Edison (talk) 21:50, 25 May 2010 (UTC)

Sort of tangentially related, I like pictures such as this one taken of the Apollo sites recently from space. They don't do much to deter the conspiricy buffs (if NASA can fake a moon landing, surely they can fake a few photographs from their own spacecraft, the Lunar Reconnaissance Orbiter), but if you do accept the moon landings as fact, it provides an interesting link to the past. Buddy431 (talk) 17:17, 25 May 2010 (UTC)

There are mirrors left on the moon that are Corner reflector. With the right equipment you can shine a laser at moon and have it bounce back back. This proves at the least that there is man made equipment on the Moon. Anythingapplied (talk) 18:50, 25 May 2010 (UTC)

The thing is that the technology to get to the moon in 1969 would not have existed unless someone had decided years earlier to develop that technology. If someone had just woken up on Jan 1st 1969 and said "Hey! Let's go to the moon next month!" then of course that would have been impossible because they would not have had all of those years of prior technological build-up. Similarly, if Obama woke up today and said "Let's go to the moon on Jan 1st 2011" - then we couldn't do it...despite "having the technology". So if someone had decided that going to the moon would be an urgent priority in (say) 1939 - then maybe we would have had the technology to do so by 1959. These kinds of "What if history had been different?" stories are impossible to resolve. SteveBaker (talk) 19:33, 25 May 2010 (UTC)

Assuming the OP means 1969, they still do have I good point. It's really quite amazing what we were able to do with the technology, especially the limited computers (2048 words of RAM?!), of the 1960s. That's not to say that we didn't land on the Moon; we most certainly did. It just means that we should admire the technical proficiency and ingenuity of the engineers, scientists, flight planners, etc. who made it happen. Buddy431 (talk) 19:57, 25 May 2010 (UTC)

In the Shadow of the Moon is a great doco made a few years ago about the moon landings as told by the people who actually went there. I really enjoyed it. Vespine (talk) 22:30, 25 May 2010 (UTC)

Indeed. The most amazing thing to me is the fact that it occurred less than 70 years after the first heavier than air flight. I'm in awe of the fact that lots of people lived their lives where in childhood they knew only balloon flight and by retirement could see folks hopping around on the moon. It's a bit like going from a Fluyt to Alvin in two generations. Matt Deres (talk) 23:33, 25 May 2010 (UTC)

If I recall correctly, the "Journal of the British Interplanetary Society" published, in 1939, fairly detailed and reasonably accurate plans for a rocket to take humans to the moon. Sadly, what I read in the journal print edition many years ago does not appear to be available online. They specified things like the consumable oxygen and water needed, the mass of the ship, and the thrust from the engines, naturally without detailed blueprints of how the engines were built. That publication was noted by the United States Army Air Corps in 1942 [19], and by many other organizations. Scientific science fiction by such writers as Heinlein and Clark had astronauts navigating with star sights and using sliderules to make calculations, and sending back Morse code communications via shortwave. In addition, they had to actually fly the thing (as the Apollo 13 astronauts had to do on the emergency return trip), rather than having autopilot control or fly by wire. An earlier start of the "space program" and a disregard for loss of life comparable to, say early arctic expeditions, or efforts to climb Everest, might have allowed a moon landing a very long time before 1969. Edison (talk) 04:31, 26 May 2010 (UTC)

2048 words of dynamic state is a lot. I imagine that the computers were given that amount of RAM because that's how much they needed to do their job. I think that would still be true today, more or less, for the same reasons it was true then. You could move to a fancy memory-hungry operating environment, but it would be much harder to validate and I'm not sure you'd gain much in return. -- BenRG (talk) 05:23, 26 May 2010 (UTC)

Pendulum question

The following is a homework question, but I don't want a solution, just some clarification. (The problem is taken from Kleppner and Kolenkow, problem 8.3): "A pendulum is at rest with its bob pointed toward the center of the earth. The support of the pendulum starts to move horizontally with a unifor acceleration a, and the pendulum starts to swing. Find the angular acceleration α' of the pendulum. Find the period for which the bob continues to point toward the center of the earth."

I'm not sure what they mean by the angular acceleration of the pendulum. Do they mean at the very instant the support starts accelerating? In that case, I would imagine the answer would be a/L, where L is the length of the pendulum. But they don't mention L, so I assume this answer is incorrect. Also, is the bob is continuously pointing towards the center of the earth, then how is it swinging? Wouldn't the period be zero in that case? And then, wouldn't the length of the pendulum have to be the same as the radius of the earth? Please, any help would be appreciated. Thanks. 173.179.59.66 (talk) 18:18, 25 May 2010 (UTC)

I don't understand the question either. I guess it means the angular acceleration as a function of time since, if it is swinging, the angular acceleration won't be constant. If it it swinging, though, the bob can't be always pointing towards the centre of the Earth... I have tried to work out what would happen in the situation described, but I've failed so far. As I'm typing, I've thought of something I can try, so I'll get back to you. --Tango (talk) 19:19, 25 May 2010 (UTC)

No, I've failed. The problem I'm having is that we have a constant acceleration, rather than a constant force, and that acceleration is of the support, not the bob, so I just can't work out what to do with it. Given no information to the contrary, I'm treating the support as massless, which means the forces on it much balance, but I have no idea what either the external force is or what the tension in the string is. I need one of them to work out the other... If anyone else is better at mechanics that me and can work this out, I would love to know you did it! --Tango (talk) 19:30, 25 May 2010 (UTC)

Confusing question (is it a difficult book?) - it seems to me that at constant acceleration of the support the equilibrium position would be at tan(theta)=a/g where theta is the angle to the vertical - thus this is your equilibrium position. note : at this equilibrium position the bob/string does not point through the centre of the earth due to the acceleration

You should be able to calculate the force (sideways) on the bob at t=0 (?) and at positions offset from the equilibrium point. I'd assume the angular acceleration is wanted as a function (either of offset or of time) - the fact that it doesn't state which is confusing.

The swinging is caused by the bob becoming offset from the equilibrium position at the time the sideways acceleration starts acting (I assume it starts abruptly) ie at t=0 the pendulum is offset by angle theta given by the equation above.

If you are setting up the equations it seems easier to use a 'flat earth' with gravity pointing down rather than attempting to model a round earth..77.86.125.207 (talk) 19:30, 25 May 2010 (UTC)

the maths desk may also be able to help77.86.125.207 (talk) 19:33, 25 May 2010 (UTC)

I couldn't understand the question either until I looked it up in the book, where there is further text and a diagram that make the meaning clear. You are meant to approximate Earth as a sphere, not a plane. The horizontal acceleration is circular (around the center of the Earth). If α' (calculated at the moment the acceleration starts) is equal to the angular acceleration of the pendulum support about the center of the Earth, then the pendulum will continue to point toward the center of the Earth. Example 8.3 ("pendulum in an accelerating car") may be helpful. -- BenRG (talk) 20:06, 25 May 2010 (UTC)

First off, sorry if I gave the impression that I was assuming the earth was flat, my fault for not clarifying. But anyhow, I did something akin to what was described above, but I got some silly answers. If the pendulum is to continue pointing to the earth, then α'/L = a/R_e, meaning that the pendulum should be the length of the radius of the earth. I used that to calculate what the pendulum's period would be were it not accelerating (2π*sqrt(R_e/g)), but still this seems wrong, because I would think that the pendulum wouldn't be moving or swinging at all, if it's pointing continuously toward the center of the earth. 173.179.59.66 (talk) 21:38, 25 May 2010 (UTC)

According to User:BenRG below length of pendulum is the same as the radius of the earth - you were right. (bit of a trick question in my opinion).. 77.86.125.207 (talk) 01:19, 26 May 2010 (UTC)

I just can't arrive at a physical understanding of how this works. When the support starts accelerating (assume in the plus X direction), the pendulum bob will obviously lag behind. If the support accelerated to some speed then moved at constant speed, clearly the bob would swing forward and pass through the line between the support and the center of the Earth. But constant acceleration of the support would seem to leave the bob always lagging behind, by an increasing angle which would depend on the acceleration versus the gravitation, in a balance between the force (in the minus X direction) due to the acceleration of the support, and a force in the plus x direction due to gravity (with due acknowledgement of resolution of forces into components parallel to and perpendicular to the ideal massless thread connection the bob to the support). If the acceleration of the support were equal to gravity, why would the bob swing back and forth through the line connecting the support to the center of the Earth, rather than settling in at, say, a lagging 45 degree angle? Edison (talk) 21:44, 25 May 2010 (UTC)

reply to last question - 'hanging' at a 45 degree angle is right (for a=g) if it starts in that position .. this would also be the rest position of a damped pendulum.. but I would assume that the acceleration started abruptly (at t=0) and previously (t<0) the acceleration of the pivot was 0, thus as the new accelerating frame comes into being at t=0 the pendulum would be in a non-equilibrium position - hence the oscillations. (the line of the pendulum string would pass through the centre of the earth at the extremity of its oscillations in this case ie when V_{bob,relative to pivot}=0)

(of course in the question nowhere does it state that explicitly - but it's what I expect it to be implying - perhaps wrongly - I still confused about wording of question)77.86.125.207 (talk) 23:02, 25 May 2010 (UTC)

I assumed that when the acceleration started, it was previously 0 and instantaneously changed - this means that initial the line of the pendulum was passing through the center of the earth - thus (as above) - I get a shift in equilibrium position to a lagging the motion orientation.. Since initially the pendulum starts with the bob not in line with the 'lagging' equilibrium position it starts to swing.

I still don't really understand the second half of the question though .. when it says Find the period for which the bob continues to point toward the center of the earth. I assume this to be a time period - but it never continues to point towards the centre of the earth.. except under odd conditions - if time period of the oscillation is P then it instantaneously points towards the centre at t=0,P,2P,3P etc.. Also Find the angular acceleration α' of the pendulum - I assumed about the pivot, and not the earth.. this must be a function (except under curious circumstances) - either I'm totally misreading it, or the authors have a curious way of asking things.experience tells me it's the former yet I still think I'm right...77.86.125.207 (talk) 22:27, 25 May 2010 (UTC)

"Period" means "pendulum period", i.e. T = 2π/ω. The angular acceleration α' is about the pivot, and you're supposed to calculate it at the moment the pivot acceleration starts. I've solved the problem and I get the answer given in the book (T ≈ 1.5 hr). I'm not sure how much of a hint to give you. -- BenRG (talk) 00:49, 26 May 2010 (UTC)

(I'm not the OP) I've got to admit I'm totally stumped (same thought process as the OP so far) - though I finally understand what the question grammar meant . thanks. 77.86.125.207 (talk) 01:09, 26 May 2010 (UTC)

Doh. 1min later - reverse engineered your answer. OP's idea was right - pendulum must be length of earth radius. (I think both of us refused to accept that it might be anything like a trick question) Thanks.77.86.125.207 (talk) 01:19, 26 May 2010 (UTC)

There's something similar here about an 'accelerating frame of reference' [20] - linear not circular though, what it doesn't explain is the apparently strange questions that are being asked in the original question.77.86.125.207 (talk) 22:46, 25 May 2010 (UTC)

Thanks guys for the help-personally I think this was a bit of a stupid question, but that's just me... 173.179.59.66 (talk) 02:36, 26 May 2010 (UTC)

OK, I can understand that the bob would start pointing to the center of the Earth, then swing up to a lagging max, and if undamped, swing back to a point once more pointing tto the center of the Earth, but that is not the end of the story unless a flat Earth is posited. The support is travelling around a spherical Earth at constant acceleration. The rotation of the support around the center of the Earth will be negligible at the beginning of the experiment, unless the acceleration is very large, like many orders of magnitude greater than G. But after a while (depending on the unspecified acceleration) it is whipping around the Earth every few seconds, eventually approaching (but not equalling) the speed of light (hope the ideal string holding the bob is ideally strong). From the point of view of the "bob," the support is eventually twirling it around and around as it circuits the Earth, like a YoYo in the hands of a pro, hence it does point toward the center of the Earth relative to the support, due to the increasingly rapid whirling of the support around the Earth, just under once per rotation eventually, possibly overwhelming whatever the (unspecified) period of the pendulum was (maybe it was several minutes, or several hours). At 1 G acceleration how long until the support is racing around the Earth once per second? How soon would it approach c? Edison (talk) 04:11, 26 May 2010 (UTC)

perkinson's disease

Explain how you would an Augumentative and Alternative Communication device with one suffering from perkinson's disease to enable effective communication —Preceding unsigned comment added by 41.204.168.3 (talk) 18:26, 25 May 2010 (UTC)

This looks like a homework question, and we aren't supposed to do those for people. Regards, Looie496 (talk) 18:38, 25 May 2010 (UTC)

We have an article Augmentative and alternative communication, at least partial answers will be found in that article. Please do your own work/research.77.86.125.207 (talk) 18:50, 25 May 2010 (UTC)

We also have an article on Parkinson's disease, which could prove helpful for links to other websites. Brammers (talk) 19:31, 25 May 2010 (UTC)

How to tell if plastic is degradable

I was reading through my science book on the last day of school (I know, how unusual for a young person to actually read a textbook when not required to by a teacher), and I saw something about a plastic fork formulated to biodegrade in a week if burried. That got me wondering if the plastic silverware at the hospital or school cafeterias could possibly be degradable plastic. Is there any to tell other than the recycle codes, which isn't present? The ones at the hospital are made by Sysco and if they're not bioplastic (which I wouldn't know because I'm not overly familiar with that type), then they seem to be polystyrene, which I do not believe is biodegradable. The ones at school are more like polyethelene or polypropyline, if not some sort of bioplastic. PCHS-NJROTC ^(Messages) 19:57, 25 May 2010 (UTC)

Probably they aren't biodegradable, but you can just do an experiment to see. Bury them in dirt and forget it for a year. Dig it up and see if it is decomposed. I an a student and I read my science book through and through whether teacher says to or not. Also plastic silverware? --Chemicalinterest (talk) 20:04, 25 May 2010 (UTC)

The only biodegradeable plastic I'm aware of in common use is Polylactic acid - there are ways to tell if it is this - notably it cannot hold a hot liquid (put in boiling water), it is also chiral which you might possibly be able to tell (if it's transparent -easier for a cup) - otherwise bury it and see (or ask).77.86.125.207 (talk) 20:16, 25 May 2010 (UTC)

Our article Biodegradable plastic mentions the use of the word "compostable" on the packaging. Comet Tuttle (talk) 20:17, 25 May 2010 (UTC)

e/c ::Good to see I'm not the only one that went to school to learn and not just to get a piece of paper. So what are the general characteristics of bioplastics, and what are their most common uses? I see that plastic bags appear to be a big one, and although bags I see almost always have a 2 or 4 resin code for polyethelene, I've see some of such that say degradable. I'm assuming that would be Bio-derived polyethylene. I sometimes see food containers that have 7 resin codes (7 other), so I'm assuming that could be PLA or some other sort of bioplastic? Are bioplastics usually labeled as such with pride, or are they often "undercover?" PCHS-NJROTC ^(Messages) 20:27, 25 May 2010 (UTC)

Thanks for the replies! PCHS-NJROTC ^(Messages) 20:27, 25 May 2010 (UTC)

See articles Biodegradable plastic and Bioplastic, which are often different things. note that bio-derived does not have to mean bio-degradable and vice versa 77.86.125.207 (talk) 20:36, 25 May 2010 (UTC)

The resin code doesn't indicate source -so they can be undercover.77.86.125.207 (talk) 20:37, 25 May 2010 (UTC)

Resin code 7 includes Polycarbonate which is/was used for bottles, could also be Styrene-acrylonitrile resin for containers (plastic cups), polylactic acid (disposable plastic cups), or many other things.77.86.125.207 (talk) 20:40, 25 May 2010 (UTC)

reducing MAC layer handoff latency

i was studying the different ways to reduce handoff latency in wlans (ieee802.1x) when i found this[21] (page18:tableII) comparison among the many popular techniques adopted. in it there is a criteria called signalling overhead. what does this "SIGNALING OVERHEAD" mean? i have given many searches regarding the topic but havn't found anything concrete. i would be very thankful if anybody can shed some light on the matter. --scoobydoo (talk) 20:18, 25 May 2010 (UTC)

The "signalling overhead" is the amount of the tranmission that is not data, but is other information required to ensure that the data arrives correctly at the right place and time.

ie consider a written letter to a friend, the 'signalling overhead' in this case would be the address written on the envolope.

More specifically it's the amount of bandwidth wasted/bandwidth disrupted, rather than the absolute data amount

You might get a better answer on the computing desk.77.86.125.207 (talk) 20:30, 25 May 2010 (UTC)

In this specific case, it's talking about all the network traffic that the different strategies discussed use. In order to be able to perform a (hopefully seamless) transition from one access-point to another, the different strategies preemptively start new (concurrent) connections to potential APs, so that if the current connection dies we're already some or all of the way through establishing a fresh connection to a better AP (so our phone call or video stream or whatever can continue unmolested). The more aggressive strategies actually establish and authenticate connections, so they're ready to go. But doing this involves extra communications to one or several nodes, using bandwidth (and placing extra stress on potentially busy nodes). This extra traffic (which mostly results in establishing connections that go unused) is wasted - it's the overhead. Less aggressive strategies impose less overhead (they don't try so hard), but are at greater risk of a material interruption if things go wrong. -- Finlay McWalter • Talk 20:46, 25 May 2010 (UTC)

Cats - gender and coat colour

This is the grandmother of the kitten. This is the colour I'm talking about.

I know that a tortoiseshell cat is very likely female, because the coats of (normal) male cats can't be black and orange at the same time. Well, a tortoiseshell cat I take care of gave birth to five kittens. One of them is grey (like the Russian Blue) with a yellow stripe on its head. Is it likely that the kitten is female? Do the genes that produce grey (blue) and orange coat act like the genes that produce black and orange coat? Surtsicna (talk) 21:17, 25 May 2010 (UTC)

Have you read the article Cat coat genetics? Cuddlyable3 (talk) 22:00, 25 May 2010 (UTC)

Yes, but I don't understand a word of it. Actually, I have understood that tortoiseshell cats can only be females but I haven't found the answer to my question.

For a cat to be tortoiseshell, calico, or one of the variants such as blue-cream or chocolate tortoiseshell, the cat must simultaneously express two alleles, O and o, which are located on the X chromosome. Males normally cannot do this, as they have only one X chromosome, and therefore only one allele, and so calico cats are normally only female. I am not sure that "blue-cream" is the colour I'm talking about. Is the cat on the photograph a "blue-cream" cat? Surtsicna (talk) 22:12, 25 May 2010 (UTC)

Can I suggest, as a practical matter, that there are easier and more reliable ways to determine the sex of your kittens? I'm aware that Googling "sex kittens" will get you quite a lot of, err, "noise", but here's a practical article (warning, pictures of kitten butts... should be safe for work, I guess, unless they prohibit kitty porn, hyuk hyuk hurrrr). --Mr.98 (talk) 01:37, 26 May 2010 (UTC)

I have book on cats wich has a list of possible coat colors depending on parents, tortoiseshell cats are capale of producing blac, blue, red, cream and red-cream males, which suggests that if your kitte indeed is blue-cream it`s a female, I`m not sure though that one stripe constitutes fur color - that may come from some diffrent gene, for example, I had a cat who had a white stripe on neck as did all her black and blue kittens regardless of gender. Speaking of which the method suggested by person before me is more efficient - take kitten by neck skin so that it curls up, draw back tail, look at its butt - both sexes have two... um... openings, the diffrence is that in females they are very close to each other and of equal size, while in males, they are further apart, lower hole is slightly smaller, plus their sexual organs form a small bump. In my expierience if you have five kittens they are not of one sex - compere and you`ll figure it out ~~Xil (talk) 09:50, 26 May 2010 (UTC)

I sugest looking at the cts genitals and then you can, hopefully, tell us what sex it is, if not you have bigger things to worry about than this —Preceding unsigned comment added by 62.172.59.90 (talk) 09:06, 26 May 2010 (UTC)

May 26

What's wrong in this picture?

According to the description of this image, the photographer had a cellulitis infection on his knee. How would he know that the knee is infected, since the only discolouration is at or below the middle of the photo, and the knee is above the top of the photo? Nyttend (talk) 02:28, 26 May 2010 (UTC)

Best guess: he meant to say "shin". --Jayron32 02:37, 26 May 2010 (UTC)

Better idea: Ask him. He doesn't appear to be active at Wikipedia any more, but you could always try the "email this user" function. --Jayron32 02:43, 26 May 2010 (UTC)

Nyttend (talk · contribs) seems pretty active to me. hydnjo (talk) 03:07, 26 May 2010 (UTC)

Nyttend didn't upload the image. He asked the question... Duh... --Jayron32 04:54, 26 May 2010 (UTC)

types of life

With the recent news about "synthetic life" I've read a couple of articles talking about the "definition of life" and how it is probably not worth arguing, but I felt that it might be useful to at least define certain limits to the description of life and non-life by attaching names to features of natural systems. I've just quickly put together a few names, if they seem off, awkward, contrary, unjustified, or irrelevant in any way let me know! I've used the suffix -ate rather arbitrarily. The point here is that each category should be necessary for the following category, so for example 2 shouldn't be possible without 1, and 3 shouldn't be possible without 2. If there are exceptions, then I'll have to scratch these and think some more lol.

• 1) syntropate (or negentropate) from "syntropathy", basically any natural system that mantains or lowers entropy. I don't know if anything exists exclusively in this category, but I think it's possible. maybe crystals could be considered syntropate?

• 2) holoplicate (holo "whole" plico "copy"), or a holoplicatic syntropate, would be a sytropate that has the ability to replicate, though no mutation is possible, either because replication is perfect (which as far as I know isn't possible), or because any flaw results in complete failure of the system (which may be the case for man-made artificial life, i.e. replicating robots, though I'm a bit unsure about this)

• 3) ateloplicate (atelio "imperfect"), or a ateloplicatic syntropate, would be a syntropate that replicates introducing flaws in its copy. all commonly recognizable life would be included in this group.

I was thinking of another group that would include systems capable of accessing it's own code and modifying it on the fly, but I'm not sure if that warrants a category because it could include some microbes as well as humans, and it might be exclusive of (3).

Any thoughts? Or anything to add? 210.165.30.169 (talk) 02:52, 26 May 2010 (UTC)

You're free to do whatever you want in your own head. Getting another person to use your system would require you to get published in a peer-reviewed journal or something like that... --Jayron32 03:04, 26 May 2010 (UTC)

Well of course, I'm just curious if a categorization such as this has any relevance towards describing the types of life/non-life that might exist in the universe! 210.165.30.169 (talk) 03:09, 26 May 2010 (UTC)

I'm fairly certain that maintenence of entropy is a common theme in attempts to define life eg eg I've seen the idea many(?) times. As far as I know the old fashioned definitions are still used. (I assume you've seen the disclaimer on Wikipedia:Reference desk/Science at the top "does not ..opinions ..debate" etc ..77.86.125.207 (talk) 03:49, 26 May 2010 (UTC)

Hmm... you're right. I'm pretty sure that rule wasn't there when I last revised the header some 6 years ago, but it's not really my place to argue. Sorry, I'll retract my question? comments? then. 210.165.30.169 (talk) 04:03, 26 May 2010 (UTC)

As far as I know nothing apart from life is capable of maintaining it's own entropy (definately not crystals) .. are further definitions really needed. Just use No.1 that's my suggestion - perhaps there is an exception.77.86.125.207 (talk) 03:55, 26 May 2010 (UTC)

What animals can use the widest range of useful light strengths?

Some animals are mostly nocturnal. Some have vision that is mostly useful in the day time. Some animals, such as cats, have vision useful both in the day, and in low nighttime light levels. Which animals have the greatest useful visual range? —Preceding unsigned comment added by 24.130.145.253 (talk) 04:13, 26 May 2010 (UTC)

Any animal which has cone vision and goes out in bright daylight can use daytime illumination,(adapting by contraction of the iris in addition to retinal adaptation) so the medal must go to one of the animals which also had nocturnal vision via rods, a large pupil, and a reflective Tapetum lucidum to maximize night vision (though there is a decrease in acuity in bright light). It would be an animal specialized for nocturnal life which can function in full daylight (one not "blinded by the light" as the Mole (animal) and Bat are sometimes claimed to be). Zoos have some scary looking animals specialized for nightlife, with really big eyes. Owls would be in the running. Huge eyed mammals like the Bushbaby, the Aye-aye and other Lemurs seems like another candidate if it can function in daylight. They lose points for having no fovea, thus poor visual acuity in daylight. Primates seem to do better in daylight with a good fovea "The topography of primate retina: a study of the human, bushbaby, and new- and old-world monkeys.". Cats, dogs and raccoons have good night vision, with the reflective tapetum, and also see pretty well in daylight. Edison (talk) 04:50, 26 May 2010 (UTC)

Uses of Stars

What are uses of stars?ugygdyowerg —Preceding unsigned comment added by 76.174.168.105 (talk) 05:04, 26 May 2010 (UTC)

There's one star we use a LOT, see Sun. Otherwise, people have used the stars to make constellations, i.e. draw pictures in the sky and tell stories about them. Stars have been used as navigation aids (see Celestial navigation). Hope that gets you started on some ideas. --Jayron32 05:28, 26 May 2010 (UTC)

I believe that stars still are used as navigation aids by many indigenous people. Many people attempt to use them to predict the future, compatibility between people and all sorts of things. -- Q Chris (talk) 09:00, 26 May 2010 (UTC)

Stars are also used to derive the calendar and to know how long a year is, and to determine where the earth is in space. Stars are also used for navigation by space ships. They have also led to some discoveries such as helium and nuclear fusion. Graeme Bartlett (talk) 10:35, 26 May 2010 (UTC)

Residual stresses in the coatings given on insetrs

What are the methods avialable to find the residual streses present in the coatings given on carbide inserts? —Preceding unsigned comment added by 122.248.132.54 (talk) 07:44, 26 May 2010 (UTC)

Is blood group a factor in organ transplantation ?

I was just waching an episode of CSI:NY in wich they speculate that crime was comited to harvest victims liver ecause she had AB+ lood type which is very rare. To my knowledge the idea of AB blood type being rare is quite popular misconception (as people with that type of blood can receive blood of all other types). So I am wondering if lood type can acctualy play any role in organ transplantation ? (I figure there wouldn`t be much blood left in the organ...)--~~Xil (talk) 08:55, 26 May 2010 (UTC)

Here's a compatibility chart. Ariel. (talk) 11:12, 26 May 2010 (UTC)

buying lemon juice

this site says "lemon juice an inexpensive, readily available acid for use in educational science experiments." but my store sells only tiny bottles 6 oz of it. its expensive too. im looking to buy it by the liter or gallon. iv looked online and cant find it either. it needs to be food grade. and not have any other chemicals or preservatives in it. —Preceding unsigned comment added by Tom12350 (talk • contribs) 09:00, 26 May 2010 (UTC)

Just buy food grade citric acid, it will likely have the same function for you. If you just want cheap, buy sulfuric acid or hydrochloric acid and dilute it, but they will not be food grade. 10:32, 26 May 2010 (UTC)Graeme Bartlett (talk)

It isn't that inexpensive, lemons are expensive too. Go with acetic acid (vinegar) or hydrochloric (muriatic) acid or even possibly food-grade phosphoric acid. --Chemicalinterest (talk) 11:04, 26 May 2010 (UTC)

I usually buy frozen Minute Maid lemon juice. Ariel. (talk) 11:07, 26 May 2010 (UTC)

how stationary is geostationary?

If someone were hanging just above the ground from a cable depending from a geostationary satellite, how much would they be moving around? Would they be swinging? bobbing up and down? racing to and fro? or would they be more or less still?

thanks Adambrowne666 (talk) 09:09, 26 May 2010 (UTC)

The satellites in these orbits move around in a figure 8 shape. The satellite operator will try to contain this inside a specified cube, while minimising fuel use. Allow for a tenth of a light millisecond (30 km) up and down each day, and with east west and north south added in. The angle should stay withing about 0.1 degree unless it is abandoned and goes into an inclined orbit. Graeme Bartlett (talk) 10:29, 26 May 2010 (UTC)

It's a bit more complicated than that. The weight of the person will change the orbit of the satellite. In order to compensate you will need to raise the orbit, but then it won't be geosynchronous. More accurately the center of mass of the satellite/person combo will (could) be in geosynchronous orbit - BUT - if the cable was rigid everything would be fine, but with a flexible cable the orbits of the person and the satellite won't match. Ariel. (talk) 11:00, 26 May 2010 (UTC)

Sagrada Familia (Barcelona)

Two triangles marked 19-1-07 and a crack in Sagrada Familia inner wall. Help needed: What is the purpose of the two triangles? Thanks! Etan J. Tal 10:19, 26 May 2010 (UTC) —Preceding unsigned comment added by Etan J. Tal (talk • contribs)

It's some sort of telltale designed to enable someone to evaluate the extent to which the crack is developing, and or the relative directions of travel of the two plates as they move relative to eachother. --Tagishsimon (talk) 10:40, 26 May 2010 (UTC)

Similar to this I think: Ariel. (talk) 11:04, 26 May 2010 (UTC)

four classes of consumables

(NOTE: This question is NOT about "calories.") Years ago I read the basic formula, Fat: 1 gram = 9 calories. Protein: 1 gram = 4 calories. Carbohydrates: 1 gram = 4 calories. Alcohol: 1 gram = 7 calories. (Again: This question is not about calories or about the preceding formula.) What's always seemed strange to me (ignorantly) is the aspect of "one of these things is not like the other": i.e., that "alcohol" seems somehow not to fit in this apparently comprehensive list. SO, Q: Is this list comprehensive, and if so, in what category? Are there other things with "calories" but which aren't digestible and so are not included? Also, three of the four are necessary, in the long run, for nutrition; is alcohol in any way necessary? Does everything we consume fit into one of the four categories (excluding bizarre things, like eating chalk or whatever). And so on, on the basic theme of this list of four and only four classes of consumables. 63.17.33.231 (talk) 11:11, 26 May 2010 (UTC)