Wikipedia:Reference desk/Archives/Science/2009 February 1

= February 1 =

How delicate is the universe?
If the universe was one millidegree cooler would it be nonexistent? Would it regret not having created me to gaze at it's wonders? One little atom out of place and the whole thing collapses? Is it that sensitive? Has a mini universe ever been created in the labratory under slightly different conditions? If so, I wonder if any scientist ever snapped and became "God" of his newly created universe?--Dr. Carefree (talk) 00:47, 1 February 2009 (UTC)


 * $$(no)^6 \,$$


 *  Sp in ni ng  Spark  01:28, 1 February 2009 (UTC)
 * If you don't have an answer - please don't answer. K'thnks. 72.183.123.248 (talk) 01:48, 1 February 2009 (UTC)


 * Well, on the bulk scale - the universe is the exact temperature it is for some reason or other (I don't know why) - if it were even a millionth of a degree different than it actually is then there would have to be something different about it at the start. The subtle difference in temperature might not be enough to make a very large difference - but the fact that things were different at the outset might be exceedingly significant.  The cosmic background temperature is around 3 degrees kelvin - so a 'millidegree' would represent an 0.3% change - that implies a pretty large change in one or more fundamental constants or one or more laws of physics.  That would cause who-knows-what consequences...maybe stars don't form or planets don't orbit.  It's really tough to speculate on (a) what might cause a one millidegree difference and (b) what the consequences of that difference might be.


 * We haven't created any other universes - we have no idea (even in principle) how to do that - and the amount of energy that might take sounds like it would be impossible for us to obtain...but who knows? Was our universe created by some little green man with a white lab coat and a petri-dish?  We don't know - we can't ever know - so it's pointless to speculate.


 * The 'anthropic principle' really does apply here. If the universe were different than how it is - then we could be different too - and we'd still be asking the exact same question of the different universe.  If the universe were different in some other ways, then perhaps sentient beings would be impossible - or perhaps stars would not form - perhaps even atoms might not exist.  In those cases, there would be nobody there to speculate.  If we buy into the idea that there are an infinite number of universes out there - then (by definition) we MUST live in one that allows us to have to evolved - so the precise conditions (however far-fetched) that are required to make a creature exactly like us MUST be the conditions in any universe in which we are present to observe it.  The anthropic principle is a less comfortable explanation than "The charge on the electron absolutely has to be such-and-such because " - but in the absence of such a reason, it is a good explanation.


 * 72.183.123.248 (talk) 01:48, 1 February 2009 (UTC)


 * Temperature isn't constant, either in time or space, so it can change without any significant consequences (depending on what caused the change, there may be other consequences in the details, but the basic structure of the universe and physics would be the same). It's more interesting to consider what would happen if various physical constants were changed. I've heard that changes to some constants of less than 1% would make it impossible for stars to form, or other consequences that preclude life as we know it. So, in that sense the universe it pretty sensitive. We do, of course, have an article: Fine-tuned Universe. --Tango (talk) 14:00, 1 February 2009 (UTC)


 * The current temperature of the Universe (which I take to be the temperature of the cosmic microwave background) is 2.725 Kelvin. As the Universe expands its temperature drops, and it will be cooler by 1 millikelvin in about 5 million years (computed with Ned Wright's cosmology calculator ). If there are astronomers around at that time, they will measure a lower temperature than we do today and there will be nothing weird about that. The actual temperature is largely a contingent feature of the Universe, it is not prescribed by any physical principles; it is more a question of when it is measured. There is presumably a time window of some sort in the history of the Universe in which intelligent life can form and exist, and that time window can be translated into a "temperature window". That window is, however, certainly much larger than the 1 Millidegree (or 5 million years) you quote. Incidentally, 1 millidegree corresponds roughly to the accuracy of our measurements of the mean temperature of the CMB. --Wrongfilter (talk) 14:25, 1 February 2009 (UTC)

How much would an outside observer (an alien scientist, if you like) be able to determine about life on Earth as a whole...
...from the study of one living earth creature? Supposing the one creature was (just an example chosen at random from the bird articles on my watchlist) a Green Cheeked Conure of the female sex. By examining just this one bird as a representative of all life, what (correct) conclusions could be drawn? --Kurt Shaped Box (talk) 02:07, 1 February 2009 (UTC)


 * Quite a lot, I would imagine. If the scientist could keep the poor creature alive (which would be very hard) he'd know something about atmosphere, temperature range, gravity, etc.  But the odds are good that the creature would be dead in short order...but even so, you'd find a lot about biochemistry.  With technology like ours, it might take a long time to figure out things like DNA - but that depends on how similar we are to them.  If (for example) they are very similar to us - then the relative differences would tell them a great deal in detail.  If they are very different from us (I dunno - silicon-based lifeforms from a high gravity, high air pressure planet where temperatures hover around 100degC all the time) - then they'd see that the spindly legs and the light build implies less gravity - and the nature of the lungs and flimsyness of the musculature for operating the lungs would suggest that there is a less dense atmosphere than they are used to.  Liquid water everywhere in the body tells them that the temperatures must be lower...there's a lot they could figure out.  But I doubt those silicon beings would be able to fathom out the function of DNA (for example) with a dead parrot. 72.183.123.248 (talk) 02:25, 1 February 2009 (UTC)
 * Nothing about life as a whole. Any generalized conclusion would be invalidated by nonprobability sampling. The only think one could infer would be that there is at least one species that can fly, has feathers, has DNA, etc. They could infer things about the earth's environment, though Rockpock  e  t  02:32, 1 February 2009 (UTC)


 * Thanks. When I posted my Q, I was actually thinking about how human astronauts would go about studying the life in the hypothetical oceans of Europa from a single specimen, or a small number of specimens that they managed to fish out by pure luck during a manned mission. --Kurt Shaped Box (talk) 02:50, 1 February 2009 (UTC)
 * First off the scientist would have more than one species in their hands. The bird is essential a viral and bacterial colony.  Furthermore by looking at the organelles of the cells they could infer a great deal out evolutionary history.  They would be sure that there was "at least one" but it would be foolish not to infer such a complex creature is at least representative of a portion of the unknown planets life.  Just from the design of GI track the scientists would know some constraints concerning its diet even if the bird had its stomach pumped before abduction.  If they could read the birds genetic structure they could probably start making extrapolations about its genetic heritage and evolution.  If I found an alien critter that couldn't live in our environment I would promptly freeze it and start looking for the things I've described above.  Of course the first thing to do would be to get a handle on its fundamental chemical make up which I didn't discuss but we haven't provided time constraints.  It would take years, huge amount of resources by our standards, and a host of researchers but it would be ultimately informative.


 * I know modern science insists on postulating that there are endless possible forms life, ie alternative biochemistry. I believe this more was developed to avoid developing a anthrocentric perspective which makes sense.  At the same time I've never heard of any molecular system that could accomplish the task that our proteins and DNA accomplish.  No one has been able to suggest anything reasonable for silicone biochemistry.  This lack of an alternative wouldn't be a big deal if there was more elements to discover but there aren't.  So it seems reasonable to expect a fair amount of convergent evolution; which we see all over the place in nature, my favorite example is social insects.  The alien very well may have the opposite chirality on a molecular level, run some metabolic process the opposite way, and have a drastically different appearance.  But odds seem high to me that they evolved to manipulate metal in a very similar way we did.  Hell even their bodies temperatures upper limits are probably governed by the temperature at which most proteins denature around 40C.  I say that with full respect for extremophiles while noting that they are all unicellular or close to it.  Multicellulars don't do real well above 40C unless its at high pressures.  Thus the qualification begins.  So I'll end there, comment please.--OMCV (talk) 03:05, 1 February 2009 (UTC)


 * I wrote my answer before the last entree you might want to check out it talks about life sense devices with the potential to be on future space missions.--OMCV (talk) 03:09, 1 February 2009 (UTC)


 * Interesting, thanks. I wonder if NASA has yet devised a 'standard procedure' for the handling and storage of extraterrestrial biological specimens, what with the manned Mars and deep-sea Europa missions possibly happening in the not-too-distant future? I can't help but wonder what they'd actually do if they chanced across something macroscopic. --Kurt Shaped Box (talk) 17:27, 1 February 2009 (UTC)


 * OMCV makes a good point, we shouldn't under-estimate how much scientific value one can obtain from a single sample. I know I said the "only thing" one could infer, but even proving that there is at least one alien species that respires, has carbon based DNA etc would without a doubt a scientific discovery of the century. Moreover, comparative studies of our vast knowledge of life on our own planet would enable many general conclusions to be drawn, many of which would probably prove to be correct. But taking these beyond the level of hypothesis would require greater sampling, though. Rockpock  e  t  03:11, 1 February 2009 (UTC)


 * If they fail to understand anything, they can safely say that Creationism has control over Earth too :) manya (talk) 04:24, 2 February 2009 (UTC)

explanation on tensors
please help me, a tenth grade student in detail abt tensors. please. i have understood the special theory of relativity but i want to do the same on general theory of relativity. --Harnithish (talk) 02:40, 1 February 2009 (UTC)


 * There is some information in the tensor article regarding applications to physics, and links from there to more detail. If you have a specific question, people here may be able to help if you state it clearly.  For some aspects of tensors, the math RefDesk may be a helpful alternative.  Best wishes for your studies - sounds like you are off to a great start! --Scray (talk) 17:17, 1 February 2009 (UTC)


 * The simple answer is that tensors are complicated beasts, and as a 10th grade student you would almost certainly have trouble understanding them. However, that doesn't mean you shouldn't try, and as such it would probably be good for you to first get a grasp of vectors and matrices, and of calculus - particularly solving differential equations. Tensors are then an extension of vectors and matrices, and then in differential geometry and GR calculus is added into the mix. You might also want to track down the book "Gravity: An Introduction to Einstein's General Relativity", by James Hartle, which takes an approach that avoids a lot of the tensor calculus and looks more at things in terms of undergraduate physics. Confusing Manifestation (Say hi!) 23:30, 1 February 2009 (UTC)

books on physics theories
is there some book which can be e-downloaded freely on quantum theory, string theory, general theory of relativity and something exciting for the students in the age group of 14-16--Harnithish (talk) 02:58, 1 February 2009 (UTC)


 * I don't know about the age range - but here are the freely downloaded "books" that I could find:


 * Wikibooks (a Wikipedia sister project) has two books on Special relativity - one at undergraduate level and another at an 'intermediate' reading level that only requires basic algebra as a prerequisite.  There is a general relativity book - that appears to be about half-finished - but it looks too complex for 14-16 year olds because it goes into tensor algebra and such.  This is alse a book on String Theory that's in the process of being written - but it's very sketchy right now.  We also have This Quantum World - which also seems a little high level - although 16 year old's might manage it if they have been doing calculus at a level similar to British 16 year-olds rather than the rather pathetic level that it's taught at in US high schools.


 * Project Gutenberg has a vast repository of free eBooks - including Einsteins' own book on Special and General relativity: (you can read it in the original German too!) - It's actually surprisingly readable. They have Lorentz's book on the same topic


 * Wikisource (yet another Wikipedia sister project) has which is Einsteins rebuffing of people who disbelieved in relativity.  It's somewhat entertaining. Wikisource also has  Einstein's book that I mentioned earlier.


 * Wikiversity (yeah - guess) has a couple of 'courses' on Quantum theory:, on Special relativity and  on General relativity.


 * Sadly, most of those things descend into a sea of equations pretty quickly. Surprisingly, perhaps, Einsteins' works are the pretty approachable if you take it slowly and work to understand each part before skipping on to the next.  Well, I'm not sure I helped very much...but that's what I found. SteveBaker (talk) 00:18, 2 February 2009 (UTC)

Hey, how do they know they've discovered methane (tm?) gas on Mars?
That's like,-way over there. And we're we're like,-down here. Were at the center of the universe (comparatively speaking). With no machinery or people on Mars, how can they tell? Sometimes I wonder if scientists are just desperate for headlines and figure we'll believe anything. Sorry.--Hey, I&#39;m Just Curious (talk) 03:28, 1 February 2009 (UTC)


 * By using NASA's Infrared Telescope Facility and W. M. Keck Observatory both in Hawaii. The scientists attached spectrometers to the telescopes to spread light into its component colors. They looked for dark areas in light spectrum where methane was absorbing sunlight reflected from the Martian surface. They found three - so-called absorption lines - which together form a definitive signature of methane. They were able to distinguish the Martian methane from that in Earth's atmosphere because the lines were disturbed in sync with the planets motion. Rockpock  e  t  03:37, 1 February 2009 (UTC)
 * There is an example of of methane's IR absorption fingerprint on Methane (data page) near the bottom of the page.--OMCV (talk) 03:42, 1 February 2009 (UTC)


 * Well, we do have quite a bit of machinery on Mars - Spirit rover and Opportunity rover for example. We also have Mars Reconnaissance Orbiter and something like four other spacecraft in orbit around Mars.  But in this case the information was obtained spectrographically from an earth-based telescope.  We routinely collect spectrographic data from stars that are millions of lightyears away - so this isn't that tough to do!  Each chemical absorbs and reflects light differently - which is why some things look different colors to others.  By splitting the light coming from Mars' atmosphere into a spectrum (a 'rainbow' if you like) there are lots of dark lines corresponding to colors that should be there in the sunlight - but aren't there in light reflected back from Mars because something is absorbing it.  Some of those missing lines evidently correspond exactly with the precise colors that methane gas absorbs.  The exciting thing is that methane cannot exist long in the atmosphere of a planet - so whatever put it up there is still making the stuff!!  Since the most common source of methane on Earth is animals - one possible reason for the methane to still be there in the Martian atmosphere is because there are still living creatures there...which would be a very exciting conclusion!  Sadly - as with the other signs of life on Mars that we've seen, this is not 100% conclusive because there are complicated non-biological processes that could possibly produce methane too. SteveBaker (talk) 04:50, 1 February 2009 (UTC)

I don't know, but we can smell the methane gas around Uranus from here. —Preceding unsigned comment added by 82.120.227.157 (talk) 14:28, 1 February 2009 (UTC)


 * Methane is an odorless gas....oh...wait...you were trying to be funny right? Oh, OK - well...um...ha,ha then. SteveBaker (talk) 14:48, 1 February 2009 (UTC)


 * Now, the next step for the scientists is to determine whether the methane was produced by biogenic or abiogenic sources. This is why the news became so exciting. ~ A H  1 (TCU) 17:54, 1 February 2009 (UTC)


 * Are you saying that there's something living on the surface of Uranus?


 * Sorry. --Kurt Shaped Box (talk) 17:59, 1 February 2009 (UTC)

Clearing Brush
I was wondering about the activity that former President Bush enjoyed at his Crawford Ranch. What does "brush" consist of? What is the purpose of clearing brush? Is it to use the soil for agriculture? Once the brush is cleared, what is usually done with it? What kinds of tools are used to clear brush? Is the process mechanized, or still done by hand? Are there people who do this as a profession? 211.109.12.170 (talk) 04:31, 1 February 2009 (UTC)


 * The brush normally consists of fallen tree branches (or entire trees), dead bushes, fallen leaves, etc., and sometimes also live trees or bushes. The primary purpose of clearing brush is to prevent fires from spreading.  A secondary purpose is to allow easy access to the property, which might otherwise become overgrown.  Some of the smaller items could be raked up, larger branches would need to be carried off individually, and the largest branches (or entire trees) would need to be cut up and then carried away.  The leaves are likely composted, while branches could possibly be burnt in a fireplace.  (Leaf-burning is usually prohibited, since it puts out a lot of smoke.) StuRat (talk) 04:43, 1 February 2009 (UTC)


 * (Hmmm - we don't really have any kind of an article on brush wood and brush (disambiguation) doesn't mention it.) Wiktionary says that 'brush' is plant growth that's larger than grasses and smaller than trees.  Once you've collected it, you can burn it - but you can also toss the stuff into a wood chipper which chops it up into teeny-tiny chunks that can be used as a mulch to help keep weeds from growing around desirable plants.  Other machinery could be anything from an axe or a Machete to a chainsaw.  There are also Brush hogs and brush mowers that chop the stuff up and leave it on the land.  These exist as large lawn-mower-like contraptions that you walk behind - or bigger ones that you tow behind a tractor.  The purpose of clearing brush on a working ranch is to allow the cattle to gain access to the grass beneath - and to reduce the risk of wildfire.  While you can use machinery out in open areas - in tight corners where there are trees, it's a mostly manual process.  There are people you can pay to clear your brush - but it's essentially an unskilled and fairly mindless task...the perfect thing to occupy the time of a US president.


 * President Bush's ranch out in Crawford (not far from where I lived until recently) probably contains a bunch of bushy texas cedar trees (they aren't true cedars) that have the annoying property of having branches that grow out parallel to the ground as the tree gets bigger - these die off - but don't fall off. So a group of these trees forms an impenetrably woven mass of thin, dead, spikey branches that even a cow won't walk through.  Getting in there with a machete (and occasionally, a chainsaw) allows you to remove all of these dead lower branches and produce a nice tree with a clean trunk and a bushy green top.  Clearing the lower branches of cedars improves an otherwise useless piece of land by allowing both humans and animals to get into it.  Since the branches are dead anyway - this does no harm to the trees and the resulting mulch is useful.  With my wife and I, a chainsaw, a couple of machetes and a gasoline powered wood-chipper, we were able to clear the lower branches from an acre and a half of cedars around our house over a couple of weekends.  Removing the dead trees also let in more light and gave us a large stock of logs to burn in our open fireplace.  10 years later, the lower branches of the cedars have not grown back and the resulting improvement of the land is well worth the effort.  SteveBaker (talk) 05:18, 1 February 2009 (UTC)


 * I think President Reagan also talked of doing brush clearing. But I think both presidents spoke of it in a double sense. Clearing away brush meant not only eliminating unwanted undergrowth, it also meant clearing away liberal ideas and negating progressive legislation. – GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 06:07, 1 February 2009 (UTC)


 * Very interesting, thanks all! I also looked at that disambiguation page without finding anything. I previously had the misconception that clearing brush involved pulling out live undergrowth.  I wonder if removing all the dead wood hurts the ecosystem?  Does one generally remove all the brush or just paths to give accessibility and act as fire breaks?  I wasn't aware of the double meaning and history of the expression - also interesting!    211.109.12.170 (talk) 06:42, 1 February 2009 (UTC)


 * Whether you'd only remove brush that's obstructing access or remove it all depends on your local fire department. In some counties fire prevention requires that you basically strip everything between the height of grass and grown trees.  The county in California we used to live in traded increased fire safety for erosion of hillsides and mudslides this way.  Controlled burning of underbrush is not practiced in residential areas, but has proven successful in some managed forests. It's not for the layman, though, and can't be done during a drought. 76.97.245.5 (talk) 10:57, 1 February 2009 (UTC)


 * I think that brush clearing might well involve removing live vegetation. If the Wiktionary definition is correct then live as well as dead material can be considered "brush".  In the context of the Crawford ranch - it's possible that there was some 'undeveloped' acreage that had a lot of live brush in it that would need to be cleared for the purposes of increasing the amount of land available for cattle.  Removing dead material certainly does hurt the ecosystem - the nutrients that were absorbed from the soil in growing that material is not being returned through the normal processes of decay - so if you did this repeatedly, the nutrient levels in the soil would indeed decline.  Also, the rotting wood acts as food and habitat for insects and such like.  In the case of the ranch, this may ultimately be a problem.  In the case of my back yard, the chipped brushwood was spread back onto the land - so there was no loss. SteveBaker (talk) 14:42, 1 February 2009 (UTC)


 * Well to my Rocky Mountain brain, brush is Sagebrush (disambiguation). He's clearing tough woody shrubs to enable edible grasses to grow.  He's making food for cattle. --Mdwyer (talk) 18:43, 1 February 2009 (UTC)

Kaiser Bill spent a lot of time chopping wood for the silent movie newsreel cameras. Any coincidence? It is mediagenic busywork. Edison (talk) 03:00, 2 February 2009 (UTC)


 * ina pasture, "brush" is basically anything except the grass, clover, and alfalfa. If a pasture is left fallow for more than about two years, brush (small woody bushes) starts to grow and crowd out the grass. The farmer must then cut down the brush before using the pasture. You typically use a bush hog for this. -Arch dude (talk) 00:14, 3 February 2009 (UTC)

About the cooling and heating of the air as an affect of clouds

 * ''Note:this question was moved from Portal:Weather by User:Runningonbrains.

About the cooling and heating of the air as an affect of clouds. It was hard for me to understand why the air is cooler when there is a clear sky and warmer when clouds are present. It has the same principals as a vacuum or a fridge. A vacuum, for example. The point is to have a space with no air in it, so that it will suck up all of the dirt you have on your floor. But if you are going to take all of the air out of an area, the excess wind has to have somewhere to go. If you feel a slight breeze on your legs while vacuuming, this is where the excess air is exiting. Perhaps a better example is a fridge, as it contains the same components, heat and cold. In order to make a refridgerator, the heat in that space must be removed. As with a vacuum, (and the air) the heat must go somewhere, so it it expelled out the back. Like both of these examples, the heat is dispelled out of the clouds. Clouds are made up of tiny ice/water droplets. These obviously are very cold. When the heat exits, it must go somewhere else, so it goes to the surrounding air. When there are no clouds in the sky, the heat that exits the clouds normally does not exit, and the cold that is captured in the clouds is not inhibited by the boundaries of the cloud, therefore spreading in the surrounding air. This is why it is generally colder when there are clouds in the sky, and generally warmer when there are no clouds in the sky.- —Preceding unsigned comment added by Smartcookie1596 (talk • contribs)


 * Even though, as you say, the clouds are made of tiny, cold ice and water droplets. Then think of them as a sort of igloo.  Despite being cold themselves, they have an insulating effect on the Earth.  Its not that clouds cause the Earth to be heated, they more effectly trap the heat that is already here than do cloudless days.  The effect is that the clouds act as a blanket of sorts.  It should also be noted that its not that simple, since the ambient temperature can affect cloud formation as well; warm air rises and warm air carries more humidity than does cold air, so rising warm air has the effect of creating more clouds.  On colder days, there is just less moisture in the air, and less "lift" bringing that moisture to altitude where it can create clouds.  --Jayron32. talk . contribs  12:14, 1 February 2009 (UTC)


 * Yes, clouds work based on the greenhouse effect. That is, like the glass in a greenhouse, they let light from the Sun in but don't let heat back out.  (Well, they let most light in and block most heat from escaping.)  So, the effect is that it warms up more quickly below the clouds during the day, and cools off more slowly during the night.  The "extra heat" is actually in the form of less heat radiated into space.  So, in other words, space (and the air above the clouds) is cooler when the Earth is covered with clouds.  Of course, there's such a small amount of heat added to the many widely spaced objects in space that it doesn't increase the temp there by a measurable amount. StuRat (talk) 14:23, 1 February 2009 (UTC)


 * This is a very complicated effect that is giving the climate change modellers headaches. On nights and winter days, low clouds trap in warm air, while when there are no clouds, the heat escapes to space. On a summer's day, clouds cool the air because they block the heat of the sun. When it's clear, however, humidity can still build up, which makes it feel even hotter than it is. High clouds during daytime can also cool temperatures: when the entire American air fleet was grounded for three days following 9/11, the average temperature of the entire continental United States rose by 1 C (1.8 F), because the cooling effects of the high clouds produced by the contrails were removed. In the same manner, some man-made pollutants are not only contributing to global warming, but they're hiding its effects as well. Soot, found in brown clouds of pollution travelling across the Indian and Pacific oceans, cause warming by absorbing heat and decreasing albedo when they land on ice in the Arctic, but they also hide the warming effect by blocking sunlight during the day. This also produces global dimming. Clouds play an important, but confusing, role in determining the effects of climate change. When factoring the possible effects of clouds and water vapour in global warming simulations by computer models, the upper limit for possible temperature rise in the next 100 years rises from 6C (11F) to 11C (20F). PS. What's your question? ~ A H  1 (TCU) 17:46, 1 February 2009 (UTC)

what is the detail standard of MS20995AB32 or NASM20995AB32
Hi, I need to know the detailed standard of these MS20995AB32 or NASM20995AB32. I cannot get free information online. Is anyone can help? —Preceding unsigned comment added by Decowire (talk • contribs) 07:37, 1 February 2009 (UTC)


 * If you have a university or engineering college nearby they usually have a reading room with all/most of the standards. Otherwise you might get lucky if you contact local manufacturers or associations. OK it's an military aircraft part, a wire to be exact. That can get tricky, doubt a reading room would have that. 76.97.245.5 (talk) 10:47, 1 February 2009 (UTC)


 * IMHO this is a very vague question, surely you could have provided some context to this question, you might know exactly why you want/need this information and what the numbers relate to but I suspect that to everyone else it is just some number. What specifications are you actually after? Googling finds: http://www.casa.gov.au/rules/1998casr/021/021c99s2c09.pdf Which states:
 * {| class="wikitable"

!Wire type !Material !Colour !Size !ID !Shear or Seal Wire for Magnesium Parts !Aluminium Alloy (Anodized) !Blue !0.032 inch !MS20995AB32 9525-01-031-1086
 * }
 * but I don't know if that has answered your question, probably not. Jdrewitt (talk) 14:25, 1 February 2009 (UTC)

Clones and lung problems
I was reading this article about the newly cloned extinct ibex (first time they've cloned a extinct animal, woot!). There is this line:


 * Sadly, the newborn ibex kid died shortly after birth due to physical defects in its lungs. Other cloned animals, including sheep, have been born with similar lung defects.

Why is this the case? (Assuming we know). Unless they somehow keep screwing up the DNA is some specific way, I would guess it has to do with the insemination process rather than the cloning process? Looks like that is what took Dolly_(sheep) down for the count too. Anythingapplied (talk) 08:44, 1 February 2009 (UTC)


 * I remember reading at the time this was first noticed that the best guess of those involved was the ageing process: in other words, the cells that had been cloned were the same age as the parent and therefore had degraded through the ageing process. --TammyMoet (talk) 09:54, 1 February 2009 (UTC)


 * Yes, in reproductive cloning, the cell nucleus from one individual is placed into an embryo which has had it's nucleus removed. The problem is that the cell nucleus has an "age", as defined by the length of it's telomeres, and thus any organism cloned from the cell will continue to age, starting from the age of the organism which contributed the nucleus.  Using a younger donor for the nucleus will help to reduce this problem. StuRat (talk) 14:05, 1 February 2009 (UTC)


 * In the future, it's quite likely that this can be fixed by increasing the length of the telomeres in the DNA before implantation. An additional problem for cloning extinct animals is finding a suitable animal to provide the womb for the developing animal.  In the case of an ibex, there are plenty of similar species around that will work - but if you were thinking in terms of 'bringing back' (say) Giant Sloths - then there would be considerable difficulties even with suitable DNA.  The problems with cloning for extinct species can also be fixed without telomere lengthening by cloning both a male and female of the species and breeding them (possibly artificially) before their short lives expire.  The lambs born to Dolly seem perfectly normal - so this appears to be a viable approach. SteveBaker (talk) 14:26, 1 February 2009 (UTC)
 * Despite the speculation, the answer is no-one really knows. Some clones appear perfectly fine, others die early. We don't really have enough of them to do the controlled experiments to determine if there is any pattern. In Dolly's case, she was probably the most abnormal sheep in history in terms of her environment, therefore we have no real way of knowing whether her lung disease was due to being a clone, due to being kept indoors, or just dumb bad luck. If and when cloning becomes commonplace, we will be able to control for these factors and answer your question. Its worth noting, though, that when IVF was first being developed there was all sorts of concerns that it was unnatural and would lead to defects and premature death. There is still debate over that subject, but the worst cases scenario never panned out and IVF is extremely well tolerated. Rockpock  e  t  19:47, 1 February 2009 (UTC)


 * In addition to the telomere length problem mentioned earlier, there is also the possibility that epigenetic plays an important role in cloning. Every cell has a pattern of silenced and activated genes in its DNA, called "epigenetic programming". In short, this means that the DNA is chemically modified to change its structure. To become a fully potent stem cell (to then develop into an embryo), these "activation marks" have to be erased to enable a "start from scratch" for the new organism (and in most cases, this works perfectly, which is still not really understood). Some studies suggest that a "faulty start up" of the genetic machinery is sometimes involved when stem cells don't really become totipotent after nuclear transfer. And one could speculate that this could also lead to minor defects, let's say in lung development, when only a fraction of genes is not properly "reset". TheMaster17 (talk) 09:16, 2 February 2009 (UTC)


 * It seems odd though that this kind of genetic problem would affect the lungs in preference to other organs in so many cases. SteveBaker (talk) 16:24, 3 February 2009 (UTC)


 * Nothin' for nothin', but it could be that they have many other defects that don't have time to kill the clones before the bum lungs do. --Milkbreath (talk) 16:31, 3 February 2009 (UTC)


 * But perhaps it's all for the best, since, as anyone familiar with bad sci-fi knows, clones are all evil and have laser beams that shoot out of their eyes. :-) StuRat (talk) 14:43, 4 February 2009 (UTC)

Day with the most number of deaths
In recorded history, on which day did the most people die? Thanks LotsOfJam (talk) 10:19, 1 February 2009 (UTC)
 * List of causes of death by rate quotes the World Health Organization as estimating that 58 million people died in 2005, and slightly less in 2002. That's 158,904 per day. We can assume that there will be some seasonal variation, especially since the world population is concentrated in the Northern Hemisphere, but I don't know how to allow for that.


 * The largest death toll in recent years caused by a disaster was the result of the 2004 Indian Ocean earthquake, with 229,866 deaths, according to our article. Almost all of these are likely to have died on the day of the earthquake, 26 December 2004. Together with the average death rate per day calculated above, that makes 388,770 deaths on that day.


 * While I don't have figures for the average daily death rate in much earlier years, the 1556 Shaanxi earthquake killed about 830,000 people. I don't know how many of these were killed in a single day; probably most of them. This places 23 January 1556 as the answer to your question. Some unknown number of people will have also died unrelated to the earthquake around the world on that day. The article World population doesn't give a population for around that date, but we can assume it was between 300 and 800 million. Someone else can provide a refinement of that range, I'm sure. You could look at Life expectancy and try to calculate an average number of deaths per day to add to the earthquake figure if you want a total number of deaths for all reasons on that day.


 * The article List of natural disasters by death toll gives a number of disasters with much higher death tolls, but these were spread out over a month or two, and probably didn't result in such a high number of deaths in any single day as the 1556 earthquake.- gadfium 11:24, 1 February 2009 (UTC)


 * For comparison, the firebombing of Tokyo on the night of March 9-10, 1945 is probably the biggest man-made catastrophe in a single 24-hour period, with an estimated 100,000 dead. That total is somewhat more than died from the immediate effects of the nuclear bombing of Hiroshima and Nagasaki (which of course occurred on separate days).  Dragons flight (talk) 11:39, 1 February 2009 (UTC)


 * Concerning daily death rate, Mortality rate gives a crude death rate (annual) of 9.6 per thousand. That would be 2.63 per day per 100,000.  The caveat here is that 9.6 per thousand is the *current* crude death rate, which was probably different hundreds of years ago.  152.16.59.190 (talk) 11:45, 1 February 2009 (UTC)

information in Dutch about Cryptosporidium parvum
Hello,

I would like to now more about Cryptosporidium parvum because we have ill animals with this illness.

Can you send us informaion in Dutch??

Thank you very mutch.

J en M Steeghs Holland.


 * Sorry, no. We're not supposed to give out medical (or even vetinary) advice.  Also, we're only able to provide advice in English.  You need to see a veterinarian.  We have an article on Cryptosporidium parvum - but it's only available in English, German, Spanish, Polish and Indonesian. SteveBaker (talk) 14:12, 1 February 2009 (UTC)
 * You could try the informatiebalie on the Dutch language wikipedia, although that seems to be a surprisingly quiet place. --Wrongfilter (talk) 14:26, 1 February 2009 (UTC)

Should my adam's apple be perfectly symmetrical?
←Sorry, but this most certain should not be answered by anyone here, Wikipedia does not provide medical advice. You stated that you were concerned about it being cancer in your original question. That's most certainly a request medical advice, and I must insist that you seek help from a medical professional rather than asking a question here. My apologies for removing the answers from other users, but I do feel this is in the OP's best interest. —Cyclonenim (talk · contribs · email) 19:10, 1 February 2009 (UTC)
 * Correct. You are right, Cyclonenim. --VanBurenen (talk) 19:24, 1 February 2009 (UTC)

Sound in Water
I have just been informed (on Mythbusters) that sound travels 5 times faster underwater than in air, due to the closer proximity of the molecules. Why, then, does it not sound at a higher pitch?--KageTora (talk) 15:44, 1 February 2009 (UTC)


 * It's easy is see why. That sound travels faster in water only means that the time it takes for sound to travel from a source to an observer is short than in air. However, peaks of successive cycles still experience the same delay traveling from the source to the observer. If they are separately by time $$\Delta t$$ at the source, after the same delay, their arrivals at the observer will still be separated by $$\Delta t$$. --98.114.146.178 (talk) 17:14, 1 February 2009 (UTC)


 * To put it succinctly,
 * $$\lambda * f = v_{sound}$$
 * wavelength times frequency = wave speed
 * In water, the wave speed has changed, and the wave length has changed, but the frequency is still the same frequency due to the source of the noise. Nimur (talk) 17:35, 1 February 2009 (UTC)


 * Air waves vibrate the ear drum. That stimulates auditory nerves to convey nerve impulses to the brain. If the air waves are at an audio frequency, the brain then experiences "sound". The actual nature of what the brain experiences is as much a mystery as the brain's experience of "color" in response to impulses on the optic nerves. With audio air waves, does the brain respond to the wavelength or frequency of the received audio signal? Is the wavelength of the nerve impulses the same as the wavelength in air? What if the ear channel was filled with water; as Nimur has pointed out,the frequency would be the same but the wavelength would be different; would the sound experienced by the brain be different? – GlowWorm.


 * Does the brain respond to the wavelength or the frequency of light? – GlowWorm —Preceding unsigned comment added by 98.17.34.148 (talk) 16:11, 2 February 2009 (UTC)


 * The brain does not respond to light directly; light is first converted by the rod cells and cone cells in the retina, and the messages are passed over the optic nerve. The cone cells, responsible for color vision, probably respond to frequency, rather than wavelength, because the detection of light is a photochemical reaction.  In any case, the eye is a fairly controlled, non-dispersive medium with a fixed index of refraction so the frequency and wavelength should be directly related.  See visual perception for a high-level overview.  Nimur (talk) 17:10, 3 February 2009 (UTC)

Setting up a temporary "cleanroom" at home
What can you do to set up a low-dust environment at home (a makeshift cleanroom of sorts) for cleaning/servicing dust-sensitive equipment (say a scanner)? --98.114.146.178 (talk) 16:53, 1 February 2009 (UTC)


 * Avoid rooms with carpet. You may be able to buy a HEPA filter but it has been my experience that these are useless.  Nimur (talk) 17:35, 1 February 2009 (UTC)


 * I would say the emptier a room the better. If you have a completely empty room, vacuum the floors, walls and ceiling and then wash them with a wet cloth. It goes without saying that you should keep the door/s (and any windows) closed at all times and turn off any fans. I would expect you'd get a reasonably dust free room although obviously not even close to enough to make microchips Nil Einne (talk) 17:39, 1 February 2009 (UTC)


 * I suppose take a look at cleanroom for a start. An air filter is a good idea. This might be excessive for your purposes, but a mycology lab used a HEPA quality airfilter to keep contaminating spores and bacteria from mucking up growth media plates. A wood turner I know uses a standard shop vac to cut down on the dust. Before you start, wash down all the surfaces of wherever you set up, including the walls, floor, and ceiling if you can get to it. Maintaining a positive air pressure in your work environment is a good idea. A lot of cleanrooms I have seen have those cleanroom sticky mats which pull dirt and dust from your shoes when you walk over them. Google cleanroom sticky mat for suppliers. As far as ersatz goes, someone from slashdot had this method for making an improv cleanroom:. Hope this gives you some ideas. 152.16.15.23 (talk) 17:48, 1 February 2009 (UTC)


 * It might be easier to make a chamber with gloves and a window rather than a room you go into yourself. Make sure theres no gap around the HEPA filter. Dmcq (talk) 18:04, 1 February 2009 (UTC)


 * If you're just trying to keep particulates off a work surface (and you're not worried about nasty fumes or biohazardous materials), the solution may be a laminar flow cabinet. The simplest models are enclosed at top, bottom, and sides.  Room air is HEPA-filtered and blown in along the back wall, over the work surface, and exhausted into the room at the front.  (The picture in our article shows a Class 2 device that is designed for biohazardous materials; it is equipped with germicidal UV lamps, and the second set of vents at the front of the cabinet collects the exhaust air to refilter it.  What you would need is a much cheaper version which exhausts direct to the room &mdash; more like this, this, or this.) TenOfAllTrades (talk) 18:36, 1 February 2009 (UTC)


 * For one off or infrequent use, things like an Atmos bag can act as a portable glove box provided you have a way to fill them with a filtered supply of air. Dragons flight (talk) 23:18, 1 February 2009 (UTC)


 * TenOfAllTrades beat me to it. Just make an enclosed workbeanch. Improvise a sealed passthrough with gloves. Air enters the top and is drawn through the bottom. Calculate the required flowrate to maintain laminar conditions.


 * Not sure if you want a medical cleanroom or a fabrication cleanroom, but the following is what I've seen in fab plants. You want smooth surfaces inside, use stainless and Polypropylene. PP is an inexpensive high purity plastic. Exposed stainless steel should be passivated (there is a certain type used in the semiconductor industry that electrochemically blows off surface impurities). In fab pants, new equipment gets a 'superclean' cycle; swab every inch with isopropyl alcohol and special towelettes (made for clean rooms). No paper or pencils allowed inside! (you can order special cleanroom paper). Also, look into a positive pressure feed and looping the air through the filter (polishing). --TungstenCarbide (talk) 00:32, 2 February 2009 (UTC)
 * PS, not sure what you want a clean room at home for but if it's to screw with your disk drive be careful, that usually requires a class 100, which takes a lot of effort to achieve. --TungstenCarbide (talk) 00:46, 2 February 2009 (UTC)


 * Back when window-modding of computer hard drives was in vogue, the recommended method for creating an ad-hoc cleanroom was to steam up the bathroom and let the steam (and hopefully any airborne dust) settle out on the walls, then work quickly while it was still humid. This would result in a working hard drive about one time in three. --Carnildo (talk) 01:05, 3 February 2009 (UTC)


 * The OP said he wanted one for cleaning a scanner. 99.50.50.41 (talk) 17:11, 3 February 2009 (UTC)

Identify plant?
Does anyone recognize the plant at (other pictures of same plant at  and )? The photos were taken in July in Connecticut. RJFJR (talk) 17:40, 1 February 2009 (UTC)


 * Is it Echium vulgare or Viper's bugloss? Julia Rossi (talk) 22:18, 1 February 2009 (UTC)
 * I read the article and it could be. Thank you.  (I'm disappointed it doesn't flower perennially, those flowers were pretty and I was wondering if I could plant some).  RJFJR (talk) 01:38, 2 February 2009 (UTC)


 * I guess it depends how you want to feature it. All by itself is too much for it as a monocarpic type of perennial, but mixed with others varieties, it would just keep coming along, if that helps. It looks quite tough, self-seeding in the roadside turf like that. I'd try taking it home to grow roots and all, or leave it on the surface of prepared soil, to shed some seeds on the spot. Julia Rossi (talk) 03:46, 2 February 2009 (UTC)

what are the best arguments for there being no objective truth?
what are the best arguments for there being no objective truth?


 * See Relativism, also it is a good idea to study objectivism. It used to be a good way to be a bright young pain in the neck and get some groupies to make out with but I think it's a bit passé now. Dmcq (talk) 21:56, 1 February 2009 (UTC)
 * What are the arguments for there being an objective truth? As far as I know its a reasonable assumption.--OMCV (talk) 21:58, 1 February 2009 (UTC)


 * It's an unfalsifiable proposition. I can never prove that there IS objective truth because you can always say that whatever evidence I offer is a figment of my imagination.  The best we could hope to offer is some kind of Occam's razor kind of thing - but even that is a bit flakey.  I don't think there can be any evidence the other way either.  If you have proof that there is no objective truth - then that, in itself would be an objective truth - so we can show by reductio ad absurdum that no such proof can exist.  Hence we might as well operate under the assumption that universe exists and we along with it because the world would be a mighty boring place otherwise. SteveBaker (talk) 23:23, 1 February 2009 (UTC)
 * (At some point in this discussion - I'm going to need to say that "Philosophers are a waste of quarks" - I thought I'd get it over with early.) SteveBaker (talk) 23:33, 1 February 2009 (UTC)


 * A lot of it comes down to defining what one means by "objective" and "truth", as well. Both of those are often presented as if they are straightforward concepts, when both can be quite difficult to nail down in a precise way. --98.217.14.211 (talk) 00:59, 2 February 2009 (UTC)

Electron configurations
For my homework (let me finish, I'm attempting it) there's the following question:


 * "If the oxidation state of Vanadium is +3 in VCl3, what is the electron configuration vanadium in VCl3 and explain why it is considered a transition metal"

I've worked out that I think the configuration is 1s22s22p63s23p64s2, but this would mean that it's not a transition metal since it has an empty 3d orbital. I'm guessing I've made a mistake with filling 4s before 3d in this case, should it be 4s13d1, or 4s03d2? Cheers. —Cyclonenim (talk · contribs · email) 21:57, 1 February 2009 (UTC)


 * Yes, your last configuration is correct (4s03d2). The common rule is that transition metal cations (but not neutral atoms) will lose their s electrons before their d electrons. (Don't worry, I made this mistake until I was well into college :) )  --Bennybp (talk) 22:25, 1 February 2009 (UTC)
 * Ah I see, thanks. So they empty first just like they fill first? —Cyclonenim (talk · contribs · email) 22:27, 1 February 2009 (UTC)
 * The statement The common rule is that transition metal cations (but not neutral atoms) will lose their s electrons before their d electrons. needs more qualification. The idea that s electrons empty first just like they fill first is "fudge" general chemistry teachers teach to avoid going into details.  Logically and experimentally it doesn't make sense.  The electron configuration model your using is accurate when the neutral transition metal is not bound to anything and in its ground state.  Finding a unbound transition in a ground state is more the exception than the rule.  Most metal centers have something that is described as a coordination sphere or they have metal metal bonds.  In solid VCl3 for example every Vanadium  bound to six chlorides (which is shares with neighbors) forming a common octahedral coordination sphere.   Once there is a coordination sphere even if the metals not oxidized such as [M(O)Ln] its best to discuss them in terms of ligand field theory or if you are old fashioned crystal field theory.  Either way the electron configuration is then described by the d electron count which fits experimental results for metals in complexes (in most situations).  With that all said most general chemistry classes are looking for the answer in the form Bennybp provided.  Good luck with your chemistry studies.--OMCV (talk) 23:10, 1 February 2009 (UTC)
 * (ec) Thanks for your expansion, but I do believe that is probably a stage ahead of what I need to know currently. I'm currently studying A level Chemistry, which is a step below an undergraduate degree in terms of scale. The 'general chemistry teacher explanation' is probably good enough for now, but it was an interesting read nonetheless :) —Cyclonenim (talk · contribs · email) 23:16, 1 February 2009 (UTC)


 * (post ec)What Bennybp said is often true for the transition metals, although you usually fill the 4s before the 3d orbitals according to the Aufbau principle. Some transition metals even in their "neutral" state will "push" electrons from the Ns to the (N-1)d if it means they will have 5 or 10 electrons in their d orbital. Common oxidation states of first series transition metals have 3, 5, or 6 electrons in their d orbital. (I speculate the reason for the 3 and 6 have to do with 3 of the d orbitals being lower energy than the other 2 in certain situations) I go by the principle the more electrons an atom has the more likely it will violate the filling order you would expect. See Atomic electron configuration table
 * In the first row transition metals the violaters in neutral are:
 * Chromium with [Ar] 3d5 4s1. Chromium (III) ([Ar] 3d3) is the most stable, Chromium (II) and (VI) come up often, while (I) is rare although it would seem to make sense.
 * Copper with [Ar] 3d10 4s1 but note that its most common oxidation state is (II) (3d9) rather than (I) (3d10) which you think would make sense
 * First row transition metals lose their 4s2 electrons before the 3ds with the following common exception: Cobalt (III) (4s1 3d5). Manganese III and Manganese VI may also have an unexpected electron configuration but I can't find a source to verify it. See for more. 152.16.15.23 (talk) 00:28, 2 February 2009 (UTC)

That last post just isn't up to speed; the author clearly doesn't understand transition metal electron configurations. The "push" idea is still based on metal center not bound to anything and in its ground state situation. As for "common oxidation states" it goes beyond speculation into imagination on the authors part. a quote from his reference. Some oxidation states, however, are more common than others. The most common oxidation states of the first series of transition metals are given in the table below. Efforts to explain the apparent pattern in this table ultimately fail for a combination of reasons. Some of these oxidation states are common because they are relatively stable. Others describe compounds that are not necessarily stable but which react slowly. Still others are common only from a historic perspective. This citation is mostly accurate but I would also say most of the M(0) oxidation state are common as well as and few other neglected configuration suchg as Co(I). Its enough to say first row transition metal centers vary from d0 to d10 and depend on many features directly tied to the specific metal center. I can personally verify that Co(III) is usually low spin diamagnetic d6. If you don't know what you are talking about don't write anything.--OMCV (talk) 01:00, 2 February 2009 (UTC)
 * Please don't criticize other editors for attempting to help, especially when they've cited a reliable source. There's always someone that knows more than you do, and the great thing about open discussion is that we all can learn if we listen (or read...).  --Scray (talk) 02:21, 2 February 2009 (UTC)
 * Ok, your right I should have just said that they were wrong and didn't read the source they cited. The personal aspect was a mistake.--OMCV (talk) 03:12, 2 February 2009 (UTC)
 * There seems to be a disconnect here. There are two ways of answering the question; the easier method is "here's a heuristic (aka rule to follow) which will produce the right answer" and the other is to explain what is really happening.  Its possible to apply the heuristic and get the right answer almost all the time, and never understand the physics behind what is going on; at the A-level a student is probably on the "heuristic" level; it is not until one gets to about 3rd year of an undergraduate chemistry degree that one begins to understand the actual bonding symmetry and nature of the metal-ligand bond to the degree that OMCV is describing.  So yes, OMCV is scrupulously correct here in his explanation, however no high school chemistry student is going to have the background to parse his explanation.  Hence, the heuristic trick of "add 4s before 3d" and "remove 4th level before 3rd level" to get the answer here.  --Jayron32. talk . contribs  04:24, 3 February 2009 (UTC)
 * Frankly I wonder why anyone teaches that form of electron configuration since its utterly meaningless and just makes things confusing latter on. I guess all the other elemental electron configurations are comparably meaningless formalisms used solely to familiarize student with quantum numbers of atomic orbitals and little more.  So what Jayron32 said is true and the configurations mentioned above are gospel truth right through the chemistry GREs (at least in the states).--OMCV (talk) 04:37, 3 February 2009 (UTC)
 * Actually, what I said was that the use of electron configurations is a "heuristic" (aka a teaching tool) as a means of preparing students who otherwise lack the background to learn such concepts. All students in the United States who go on to major in chemistry and chemical engineering degrees learn The Truth(tm) during their studies, usually in physical chemistry and advanced inorganic chemistry classes; though freshman level college chemistry almost always introduces the basics of Hybridization theory and Molecular orbital theory, which begins to deconstruct the standard "high school model" of the atom.  Rather than being confusing, it allows a student to get a cursory understanding of the quantum model of the atom, without necessily having to work with Schrodinger's equations and eigenstate functions and all that fun stuff.  For a high school student who has no interest in pursuing a career in chemistry, its probably good enough.  There's not enough time in the 4 years of high school to teach every student every fact ever learned in every discipline ever.  --Jayron32. talk . contribs  05:36, 3 February 2009 (UTC)
 * As it turns out the ACS accreditation and most universities in the US don't require a regular inorganic chemistry class let alone and "advanced" one for a chemistry degree; And d electron counts aren't covered in every pchem class either. I think pchem could easily be expanded to a year and half and still be a superficial survey of material.  My point was that I question the value of the way the atomic "electron configuration" is presented even as a "heuristic" teaching tool and wonder if it is more "historic" (like our appendix).  I think this sort of "historic" concepts is an issue in chemistry for example why is crystal field theory still taught and the language of oxidation and reduction is cumbersome?  Although I could never unlearn it, I see the value of developing more logical language?  The origin of the term "reduction" is from the mass lost when taking a metal oxide to it metallic form, "oxidation" is adding the oxygen back to the metal form to make the metal oxide.  Each term boarders on many related meanings which makes the concepts very hard for student to learn.


 * I understand people taking a survey of the field won't get all the details but it would be nice if chemists didn't waste their time with busy work. All the quantum number are good information but it seems as if the electron configurations are designed to act only as test questions.  You note that Hybridization theory and Molecular orbital theory deconstruct the "high school model", as a side note hybridization is taught in most high schools these days since its hard to talk about sigma or pi bonds with out it; Back to my point which  is that I think that your ability to see a deconstruction is mostly insight on your own part and no thanks to standard teaching methods.  My experience with undergraduates is that they have a hard time connecting what their learning with the real world.  They treat science as ritual or game that needs to be played for a year or two in college.  They don't feel the need to make chemistry self consistent.  I think it might be easier for them if they weren't taught so many contradictory models or at least identified them as contradictory models.  If you look classic general chemistry texts like Chang or Silberberg at no point does it say heads up kids now that you are using the hybridization model or MO model, carbon doesn't have the 2s2 2p2 configuration anymore.  On most general chemistry final you will find questions on each of the three subjects but never have a question asking the students to compare and contrast the hybrization model with the MO model let alone and how our understanding of atomic orbitals work into each model.  Then there is the big secret even most chemistry majors never internalize which is the Schrodinger's equations and eigenstate functions only work for a one electron system, the hydrogen like atom;  Every other application is an approximation, the value of which is often questionable.  I know it might sound like I'm missing your point but I actually appreciate you writing so that I can vent on the subject.  Have a good one.--OMCV (talk) 13:21, 3 February 2009 (UTC)

Gaur image
I've been searching tirelessly to no effect for an image that shows an average human next to a gaur. I'd like to see how big it looks, thanks. --Taraborn (talk) 22:06, 1 February 2009 (UTC)


 * Here's one next to a 4x4 http://flickr.com/photos/pixbykris/2307472690/in/photostream/ Jdrewitt (talk) 22:29, 1 February 2009 (UTC)


 * I think the gaur facing off the pickup truck is a young one or a female. Wikipedia says a gaur is larger than a bison - that's pretty big. Wiki gives weight and shoulder-height of the gaur. A full grown male can weigh more than a ton and a half. If it was me driving that pickup, I'd put it in reverse and tromp on the accelerator - fast! :) GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 23:23, 1 February 2009 (UTC)


 * Well maybe its not fully grown, but it still looks pretty heavy to me though, can easily see that one being a ton, and is the same height as the truck. Jdrewitt (talk) 10:16, 2 February 2009 (UTC)

Here's a couple, both dead. I don't think it's very safe to stand next to a live one.  Sp in ni ng  Spark  01:31, 2 February 2009 (UTC)

Testing for air tightness
Is it true that one can test a container for airtightness just by using a lamp in a darkened room to see if any light leaks out? Is so, then you are not airtight?--GreenSpigot (talk) 23:51, 1 February 2009 (UTC)


 * That method is useful for showing you gaps at edges and joints especially when the material is dark. There are problems of course if the material you used isn't opaque, or you seal edges with a transparent material like epoxy. Then the light can leak out through the epoxy, but the container may really be sealed. On the flipside, you can imagine a case where a series of switchbacks occurs which blocks the light although the material isn't airtight. I suppose it you really wanted to check for airtightness, you could pump said container to a higher pressure, seal it and see if the pressure decreases over time or stays constant. You could also fill the container with colored smoke, water, or some other gas or liquid and look for leakage that way. 152.16.15.23 (talk) 00:47, 2 February 2009 (UTC)


 * While that method may give you an indication, it is obviously not going to be definitive. Consider the inside of a camera, it is lightproof, but not usually airtight, or even watertight.  If you are just checking the hoses of a compressor, for instance, it might not be important that there is a small amount of leakage.  If you are dealing with something dangerous like silane on the other hand, you need to use a more professional method. Leaks will usually occur at joints in pipeworks, inspection covers, access plates etc.  One way to test is to slightly pressurise with air and use bubble leak detector solution on all the joints prior to letting in the working gas.  Sp in ni  ng  Spark  02:24, 2 February 2009 (UTC)


 * When building rockets, we are very concerned with quality of seals. Rather than a binary "airtight"/"not airtight", we rate a particular vessel as pressure-tested to a certain pressure.  Usually this is accomplished by hydro testing, in which the sealed vessel is filled with pressurized water and held at pressure for a specified quantity of time (e.g., "holds 1500 psi water for 10 minutes with no leak" would indicate a pretty darn good seal).  I would never trust this "lightbulb test" - light does not "leak", and is a terrible analogy for finding a gas or fluid path.  Nimur (talk) 03:52, 2 February 2009 (UTC)


 * One disadvantage to this method is that an object with a small leak that could have been fixed, or no leak initially, could be destroyed. StuRat (talk) 10:04, 2 February 2009 (UTC)
 * Sure, but you can start at lower pressure and work up to the rated pressure test. A catastrophic failure at 1500 psi may be manifested as a slow trickle leak at 800 psi.  Also, because water doesn't expand or contract volumetrically by any significant amount when depressurized, there's not a lot of danger from a hydro test (pressurizing with gas could lead to explosive decompression).  Nimur (talk) 13:26, 2 February 2009 (UTC)
 * The light test may also fail to detect materials which are gas-permeable, such as certain plastics. StuRat (talk) 10:07, 2 February 2009 (UTC)
 * Some critical structures (and one that I happen to know about is rollercoaster tracks) are pressurized with nitrogen and have continual monitoring of the gas leakage rates. Any sudden decrease in the rate of leakage can be attributed to a crack or failed weld somewhere in the system leading to it being shut down and tested.  These systems are pretty amazingly sensitive - they have to be calibrated to cope with things like the expansion of the metal as the sun shines on it - which increases the volume and temporarily decreases the pressure. SteveBaker (talk) 14:56, 2 February 2009 (UTC)
 * the optimal test for you is going to depend on the kind of container you are using and how you will be using it. Anyway, here's a leakage test that's used for gas lines: pressurize the container, then spray it's surface with a soapy solution. Bubbles will form at leak locations. --Shaggorama (talk) 19:47, 2 February 2009 (UTC)


 * To avoid further unnecessary speculation, I should say at this point that the container is a loudspeaker reflex cabinetGreenSpigot (talk) 19:46, 2 February 2009 (UTC)


 * Just be thorough. Some good tips on sealing your project can be found here. -Shaggorama (talk) 19:59, 2 February 2009 (UTC)


 * With a speaker enclosure, being perfectly gastight isn't really necessary because the high pressure impulses are of very short duration. All you need is to ensure that the 'impedance' of the leaks is sufficiently high.  Although...are you perhaps the OP who was talking to us a month or so ago about making pressurized speaker enclosures to effectively reduce the size of cabinet needed or something?  SteveBaker (talk) 16:21, 3 February 2009 (UTC)
 * SteveBaker is probably referring to the December 14, 2008 discussion. If the questioner is using a pressurized gas, such as SF6, safety precautions should dictate the seal.  Nimur (talk) 17:14, 3 February 2009 (UTC)


 * Steve:1. All the speaker books and sites say the cab must be airtight (even tho you have a hole for the port).
 * 2.I agree that the impedance of the leaks should be higher than the impedance of the port; but just how high is ::::that?
 * 3.Yes I am
 * 4.But I have reverted to a conventional design using ordinary atmospheric air because of supply and sealing
 * difficulties with SF6!--GreenSpigot (talk) 18:55, 3 February 2009 (UTC)