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May 4

learning skills

On one of the Nat Geo documentaries that I watched, I saw why one messes up when they get nervous. It seems that there are two parts of the brain that learns a skill. One is a learner that is very clumsy and a learned part that executes the technique. When one needs to perform and cannot overcome their nervousness, the very clumsy "learner" part takes over and the resulting performance is bad. I think they used an amateur soccer player for this experiment and tricked him by saying that he was being watched by talent scouts. Anyone can direct me to its wiki article? --121.54.2.188 (talk) 00:39, 4 May 2010 (UTC)

I've never heard this idea before and am very sceptical. It doesn't make much sense to have your brain learning something twice, once not very well. We have an article on Anxiety and also the Yerkes–Dodson law which may be useful to you. --Tango (talk) 02:20, 4 May 2010 (UTC)

I think I wasn't very clear. One part of your brain learns the skill while the other part executes the learned skills. Anyways, it seems to be Procedural memory and messing up due to choking. I was able to get to them from muscle memory.--121.54.2.188 (talk) 02:26, 4 May 2010 (UTC)

(edit conflict)Its probably closely related to concepts like working memory vs. short-term memory vs. long-term memory. The article The Magical Number Seven, Plus or Minus Two specifically discusses on theory of Working memory and also contains some great links to related articles. I think there is a specific term related to this sort of performance-learning connection. As a teacher, you'd think I remember the term. I'll do some digging and get back to you. --Jayron32 02:22, 4 May 2010 (UTC)

The article Procedural memory also discusses learning procedures and processes, and the normal way in which procedures are learned. May offer some insight into the OP's question. --Jayron32 02:27, 4 May 2010 (UTC)

How long does that 'one part of the brain' learns? —Preceding unsigned comment added by 125.21.50.214 (talk) 11:38, 5 May 2010 (UTC)

Molar mass of Aluminium

What is the molar mass of Aluminium? Thanks in advance, --The High Fin Sperm Whale 01:45, 4 May 2010 (UTC)

It is in the article, in the infobox, under the title "Standard atomic weight". --Jayron32 01:59, 4 May 2010 (UTC)

dumbest idea in the world

So this has to be the dumbest idea in the world, but please confirm that it is. They have done various nuke tests in the desert where after the bomb goes off, the sand underneath is fused into glass, maybe dozens of feet thick. The dumb idea is: what if they do that underwater, as a way to seal the burst oil well in the gulf of Mexico? Would it exchange one environmental catastrophe for another? Radiation, tsunamis, etc.? Test ban treaty issues? There was at least one deep-water test in the 1950's (Operation Wigwam) whose effects weren't all that severe. 69.228.170.24 (talk) 01:57, 4 May 2010 (UTC)

Would the explosion fuse the sand into glass, or would it rupture the entire oil deposit, and send the entire contents of the deposit into the sea instantly, making the situation MUCH worse. Its a nice line of thinking, but beware of unintended consequences. --Jayron32 02:01, 4 May 2010 (UTC)

I think most of the heat would go into evaporating the water, rather than melting the sand. --Tango (talk) 02:06, 4 May 2010 (UTC)

Controlled frac is done all the time during drilling and enhanced oil recovery. It never needs nuclear weapon sized explosions. Most of the time, just pumping saltwater or steam down the bore is sufficient to frac the entire formation. In some cases, chemical frac (chemical fracture) is used - e.g., injecting an acidic drilling mud to intentionally break up the reservoir rock. Frac often increases permeability, rather than decreasing it - though the geomechanics is very complicated and depends on the circumstances. See, e.g., Hydro Frac at the Schlumberger oilfield glossary. Blowing stuff up in the borehole will more likely increase fluid flow; but there's a possibility of plugging the hole. Remember also that there's a pressure gradient - the oil is flowing up because it is at higher pressure than the water (and the rock) above it. That is why it blew up in the first place. Nimur (talk) 02:23, 4 May 2010 (UTC)

FYI the technical term for intentionally plugging the well to stop fluid flow is "bridging" the borehole. Nimur (talk) 02:32, 4 May 2010 (UTC)

You might find this article a good description of the likely consequences. Clear skies to you 67.170.215.166 (talk) 02:48, 4 May 2010 (UTC)

I can't believe I forgot to link to Completion (oil and gas wells). This is the term for the general set of techniques to manage a well, including casing, cementing, safety valves, and so on. I don't believe any completions use explosive of any type. Most use downhole tools and careful control of fluid/mud pumping. Nimur (talk) 14:39, 4 May 2010 (UTC)

Apparently it's not such a dumb idea, because if this article can be believed, the russians actually used nukes 5 times to seal leaks. Ariel. (talk) 19:59, 4 May 2010 (UTC)

For what it's worth, the article is from the Komsomolka, which is every bit as credible as our own National Enquirer. 67.170.215.166 (talk) 01:46, 5 May 2010 (UTC)

The U.S. government in 1964 proposed to use a series of nuclear explosions in Missisippi to excavate the "Divide Cut" portion of the Tennessee Tombigbee Waterway. These would have been excavation explosions of hydrogen bombs, which would have created ground shock waves and air blast as well as radioactive fallout according to the book cited. The Corps of Engineers at the time said there would be "[no fallout or radiation problems" because the explosions would be underground. This was part of "Plowshare," a program for the peaceful use of atomic energy, in which the U.S. government also proposed to set off nuclear explosions to dig harbors. Trying to seal up an oil leak a mile below the surface far out in the ocean sounds way more acceptable. Edison (talk) 19:46, 5 May 2010 (UTC)

It also requires a lot more precision than you get from your typical nuke -- as Jayron correctly pointed out, this method is more likely to actually make the leak worse. 67.170.215.166 (talk) 00:42, 6 May 2010 (UTC)

Would a nuclear blast be any more desirable then your traditional plastic explosives? I mean, I don't know if C-4 would operate properly at 150 atmospheres of pressure, but it would be a lot more simple to control what the explosion would do then simply dropping a nuclear warhead on it. Googlemeister (talk) 13:31, 6 May 2010 (UTC)

I think it's a good idea. Then we could write an article about the results! In fact if it was a catastrophic failure it might spawn several articles! Bus stop (talk) 13:41, 6 May 2010 (UTC)

In principle, high explosives could be used to bridge a gusher, but in this particular case just plain ole C-4 won't do -- since the well is in deep water, it requires some kind of waterproof explosive (such as Torpex). FWiW 67.170.215.166 (talk) 04:28, 8 May 2010 (UTC)

refrigerating foods

I have heard from some people that refregerating some foods spoil them.Is it true?amrahs (talk) 04:24, 4 May 2010 (UTC)

Never heard that before. See Refrigerator for details. There are some issues, such as freezer burn if meat is not packaged properly before freezing. Additionally, if the fridge is not cleaned properly, food may become contaminated through a process known as "cross contamination". But a properly maintained fridge and/or freezer should be perfectly safe for all foods, so long as the foods themselves are properly packaged before storing. --Jayron32 04:39, 4 May 2010 (UTC)

Actually, some foods will indeed spoil, not in the sense of becoming contaminated or rotten but in the sense that they will turn into something I wouldn't want to eat. Bananas, for instance become pretty disgusting when placed in the refrigerator. Dauto (talk) 04:45, 4 May 2010 (UTC)

Generally speaking, foods with a high water content (like bananas) are susceptible to "freezer burn" -- since water expands on freezing, any ice crystals that form tend to burst the cell membranes and thus degrade the food item's texture. Likewise, if frozen items (like ice cream) are thawed and then refrozen, large ice crystals can form that degrade the texture. In both these cases, however, the items involved are still safe to eat (though less appetizing). Foods made from grain, though, tend to have a different problem if refrigerated -- since they have very low inherent moisture content, they tend to exhibit hygroscopic tendencies at near-freezing temperatures, which makes them soggy and also could promote mold growth. (Incidentally, I store bananas in my fridge all the time, and I hardly ever observe any degradation in texture from it.) FWiW 67.170.215.166 (talk) 04:57, 4 May 2010 (UTC)

Correction: the phenomenon I described where ice crystals burst the cell membranes is not the same as freezer burn -- the latter is caused by dehydration from contact with the air. 67.170.215.166 (talk) 05:01, 4 May 2010 (UTC)

Not really refrigeration as much as freezing but an interesting fact is the founder of the modern method of freezing food was Clarence Birdseye, founder of the Birds Eye company. Until I discovered this I always assumed "Bird's eye" was just a arbitrary name. Vespine (talk) 05:52, 4 May 2010 (UTC)

Potatoes and other foods that are rich in starch will go off faster in a 'fridge than at room temperature. The temperature promotes the conversion of starch to sugar. CS Miller (talk) 11:08, 4 May 2010 (UTC)

Not correct. Warmth drives the starch to sugar conversion, not cold; cold temperatures put the spud into hibernation. Potatoes actually have a longer shelf life when kept near 0C (Please don't just take my word for it, but I do work in a huge foodservice distribution centre where we routinely have to store hundreds of different products to maximize shelf-life.) The problem with taters in the fridge is that they are not kept uniformly chilled; every time you open the door, you introduce more warm air and humidity and this fluctuation is what kills the spuds. If you have potatoes that you're planning on using, keep them cool, dry, and dark - slightly less than room temperature if you can. If you want to keep them for more than a couple of weeks, keep them cold, dry, and dark (you know, like in a root cellar), just let them warm up before you try to make fries with them.

It doesn't have anything to do with starch to sugar conversion, but certainly breads and other baked goods don't keep as long cool. Refrigerating breads causes them to go "stale" faster. (Staling in breads has more to due with rearrangement/recrystallization of the gluten network, rather than drying out per se.) Freezing baked goods, on the other hand, doesn't have the same problem. Cookwise and Bakewise by Shirley Corriher are good reads, if you are interested in the topic. -- 174.21.225.115 (talk) 15:25, 4 May 2010 (UTC)

You're right, placing fruits and vegetables that are grown in warm regions into the fridge damages them. It is due to their plasma membranes being susceptible to chilling. Basically the membrane stops being a fluid and turns into a gel, this creates holes in the membrane allowing the cell contents to mix. This is obvious with bananas as they go black but it also happens with tomatoes (and others - not sure which). It's not due to ice crystals forming as 67.170 says. Temperate fruit + veg are used to the cold and so are preserved by the fridge - their membrane lipids are less saturated and longer, so the Van der Waals forces between the lipid tails are weaker and the membrane remains fluid and intact at lower temperatures. 131.111.30.21 (talk) 12:34, 4 May 2010 (UTC)

See Banana#Storage_and_transport - it might only be when they are unripe that the fridge damages them. Also see Tomato#Picking_and_ripening - they remain edible but lose their taste when refridgerated. 131.111.30.21 (talk) 12:41, 4 May 2010 (UTC)

Chilling also causes decreased binding of ethene to its receptor, thereby slowing down ripening as well ([1]). It looks like this may also be the same in tomatoes. 131.111.30.21 (talk) 12:56, 4 May 2010 (UTC)

Note - "if frozen items (like ice cream) are thawed and then refrozen, large ice crystals can form that degrade the texture. In ...these cases, however, the items involved are still safe to eat" - is not true.

"The third and most important reason not to refreeze is increased risk of spoilage due to microorganisms. Many people thaw food by letting it sit at room temperature for several hours, giving the microorganisms in it time to get busy and partially spoil the food before it's refrozen. The problem is particularly pronounced in large pieces of meat such as a turkey, some parts of which may be at or near room temperature for hours during thawing. That's why turkeys should be thawed in a sink filled with water--the water equalizes the temperature and makes for faster thawing. Alternatively, you can thaw in the refrigerator, which is slower but retards spoilage by keeping the meat cool. Even so you're likely to have some multiplication of microorganisms. If you refreeze and rethaw, you've subjected the food to double the microorganism growth and double the fun.

If you must refreeze food that has been thawed in a warm place (or which has remained thawed in a cold place for a long time), you should cook the food properly first, then refreeze it. Even under the best circumstances, however, multiple freezing cycles aren't recommended. If you can't finish the food yourself, you're better off giving it to your household garbage disposal--ideally the one that barks or meows."[2] Exxolon (talk) 16:06, 4 May 2010 (UTC)

Ice cream that's been allowed to warm to a few degrees above freezing and then refrozen is no more dangerous than the food in your fridge. Clearly warmer is worse than colder (up to room temperature) but lets be reasonable. Rckrone (talk) 16:27, 4 May 2010 (UTC)

"Refrigeration" is not the same as "freezing." The OP did not ask about the freezer. Bananas turn dark quickly in the refrigerator, but refrigeration is claimed to leave them edible longer[3]. Some books claim that refrigerating tomatoes [4] and avocados [5] adversely affects the flavor and texture . A refrigerator is kept in a range of perhaps 34 to 38 degrees F (1-3 C). A freezer might be at 0 degrees F( -17C).A "self-defrosting" freezer causes worse freezer burns than older manual defrost ones, because of the low relative humidy needed to remove the frost from the walls. Edison (talk) 21:11, 4 May 2010 (UTC)

Tomatoes and bread are two things that tend to suffer from refrigeration -- tomatoes turn mealy, and bread dries out. Looie496 (talk) 00:55, 5 May 2010 (UTC)

Older refrigerators, before the "self-defrosting/no-frost" feature became so common, had higher humidity and baked goods, lettuce, etc did not dry out so quickly. An ice box was probably even better at keeping a high humidity in the refrigerator. Edison (talk) 19:33, 5 May 2010 (UTC)

Air navigation

What is an aperiodic compass, and how does it work? I've seen it mentioned by both Amelia Earhart and Charles Kingsford-Smith in their writings, but neither of them explains in any detail how it works or what advantages it has (if any) over an ordinary magnetic compass, Earth inductor compass, directional gyro or any other such device. Also, is it still used for navigation, or has it been completely replaced by other devices? Thanks in advance! 67.170.215.166 (talk) 05:12, 4 May 2010 (UTC)

Aircraft are very different to ships in that they can change heading rapidly, so ideally an aircraft compass can retain a reasonable degree of accuracy during a turn, without excessive overshoot. Prior to development of the gyroscopic compass, many aircraft were equipped with a magnetic compass specially developed for use in aircraft. This was more complex than the simple magnetic compass used for surface navigation. It was called the aperiodic compass. There is some good information available HERE. In modern aircraft the magnetic compass is used primarily as a back-up for the gyroscopic compass, and to ensure the gyroscopic compass is correctly aligned. Consequently, in modern aircraft the magnetic compass is simple and inexpensive because it is not relied on when maneuvering.Dolphin (t) 05:49, 4 May 2010 (UTC)

I wouldn't call the magnetic compass a "backup". It's the reference for the gyro, which has no sense of direction of its own. The gyro is set to the mag compass on the ground, and checked periodically when it level flight. It is, as you say, used for navigation and maneuvering, because it's easier to read and interpret that the mag compass. PhGustaf (talk) 06:19, 4 May 2010 (UTC)

So essentially it's a magnetic compass with an advanced magnetic damping system that prevents oscillation and overshoot (but also makes it lag behind the aircraft when maneuvering); and there's no longer any need for it because the gyrocompass is the primary instrument when maneuvering. Thanks for the info, and clear skies to you! 67.170.215.166 (talk) 06:14, 4 May 2010 (UTC)

I wasn't clear. All the gyro can do is point the same way all the time, with a little drift and precession. It has no idea which way is north. So the pilot sets it so it's pointing North, or whatever direction the magnetic compass says. The mag compass is the primary direction reference. The gyro has a bigger dial and is easier to interpret if the aircraft is turning, because is isn't sensitive to second-order issues, as is the mag compass. You mostly watch the gyro and check every so often to make sure it agrees with the mag. PhGustaf (talk) 00:26, 5 May 2010 (UTC)

I would imagine magnetic compasses on aircraft these days are electronic, e.g. using flux gates or other such devices. 69.228.170.24 (talk) 20:23, 4 May 2010 (UTC)

Could be. My pilot's license dates from 1976, and I might have missed stuff since. But even a plane with a flux gate compass would surely have a mag compass along: it doesn't weigh much, works even when the electric system fails, and doesn't break often. Modern pilots use GPS a lot. PhGustaf (talk) 00:26, 5 May 2010 (UTC)

It isn't correct to imagine that modern magnetic compasses in aircraft are electronic. If a modern general-aviation aircraft has a magnetic compass it will only be for orienting the gyroscopic compass. It wil be of the basic variety as used in boats, not even an aperiodic one. (Modern aircraft of the highly sophisticated jet-powered variety are likely to have no magnetic compass. Modern Inertial Reference Systems, GNSS and area navigation systems render the humble magnetic compass redundant.) Flux gates are linked to the gyroscopic compass to keep it aligned correctly - they are not linked to the magnetic compass.

Back to the original question. I believe the word aperiodic was intended to refer to the expectation that the compass needle would not follow the aircraft as it maneuvered but would remain accurately in the north-south alignment. Dolphin (t) 01:33, 5 May 2010 (UTC)

That is what Dolphin51's link says. According to it, an aperiodic compass is a magnetic compass like a ship's compass, but with better damping to keep the needle from swinging erratically.

As for highly sophisticated jet aircraft having no magnetic compass and instead relying exclusively on R-NAV, personally I find it extremely disturbing -- what if there's a total electrical failure? Or if lightning strikes the plane and fries the electronics? On some aircraft, all electronics are powered by engine-driven generators without any battery backup worth the name, so if there's a double-engine failure then all the electronics fail too and the pilot has no way to determine his/her heading. Didn't the Air France disaster teach the designers anything? It's high time that the pilots got together and demanded more stand-by instruments in the cockpit as well as full manual backup for all the primary flight controls! 67.170.215.166 (talk) 02:00, 5 May 2010 (UTC)

When you talk about total electrical failure you aren't talking about Modern aircraft of the highly sophisticated jet-powered variety. Such aircraft have two or more electrical systems, all independent so that the probability of failure of all electrical systems during one flight is extremely small. Similarly their electrical systems must be designed and tested to withstand lightning strikes. In the unlikely event of double-engine failure these aircraft have ram air turbines to provide electrical and hydraulic power. Where national regulations specify a universal requirement for a magnetic compass these aircraft are equipped with same. The airworthiness certification standards don't specify a standby magnetic compass. If redundant navigational capability is provided by a couple of flux valves, IRS etc then manufacturers are happy to provide the aircraft without the magnetic compass. (I see Aspro has supplied an image of the flight deck of a Boeing 747-400. This is not really what I have in mind by a modern aircraft of the highly sophisticated jet-powered variety. I am thinking of Airbus 300-series aircraft and probably B777 and B787.) Dolphin (t) 12:03, 6 May 2010 (UTC)

Well then, how do you explain the total electrical failure on the Gimli Glider? And FYI, a ram air turbine is useless at low airspeed (e.g. when landing), so it should NEVER be considered a substitute for battery backup. The lesson of the Air France disaster is, you never rely entirely on any powered system, and you always make provision to limp home with all electrics and hydraulics completely gone, if need be. That, and nothing short of that, is what I call real fail-safe operation. 67.170.215.166 (talk) 08:47, 8 May 2010 (UTC)

Why do you say the Gimli Glider suffered total electrical failure? The crew was in contact with ATC by radio for position information. Gimli glider says that on approach the reduced power from the RAT made the aircraft difficult to control (but not impossible to control). I'm not aware of anything to suggest the RAT failed to provide electrical power at approach speed. I see what you mean by real fail-safe operation. I'm afraid no modern high-capacity airliner provides what you want. Please consider opening an account on Wikipedia - no cost but many benefits. Dolphin (t) 01:55, 10 May 2010 (UTC)

The magnetic compass on a 747

Relax. Of course modern aircraft have magnetic compasses -it part of the CIAA regulations. For instance: Smith's Industries used to make many of them and SIRS has taken over.[6]. Look on WC and you'll see them on other aircraft types. A peculiarity of the magnetic compass, that has not been mentioned yet, is acceleration error. Meaning: that when the compass is acceleratingly, the rose tilts up and towards the nearest pole. Decelerating the effect is reversed. Anyone who has a magnetic car compass will be very familiar with this. Reading a magnetic compass (on an aircraft) in unstable air to maintain a steady course can therefore be a trying exercise. --Aspro (talk) 09:14, 5 May 2010 (UTC)

Good, at least they're not totally oblivious to the need for low-tech backups for all them high-tech gadgets. Whew! As far as acceleration error, I'm actually perfectly aware of that -- it's prob'ly one of the big reasons why the DG is the primary heading reference and the magnetic compass is used only to reset the DG. Which leads me to my second question: would an aperiodic compass be less susceptible to acceleration error because of its heavier damping, or does it not make a significant difference? 67.170.215.166 (talk) 00:49, 6 May 2010 (UTC)

Personally, I would ignore the “over shoot whilst turning” remarks because a fixed wing aircraft and even dirigibles don't turn on sixpences (unless spiralling down to their doom). A turn would add more momentum to the kerosene fluid thus causing the overshoot rather than reducing it (if you don't believe me -compare the two types of compasses together). An aircraft however, is always changing speed (as far as a compass is concerned) because every change to the control surface increases or reduces induced drag, as well as being bounced around by the atmospheric conditions. The other very noticeable thing about early aircraft (and light aircraft today) is the amount of vibration (which one can describe as also periodic). This adds to the other problems and makes holding a course difficult. Military and orienteering compasses too are all fluid filled so that you can handhold them and read accurately with ease. In practical terms, I would think one needs to be able to quickly read a compass to within 5 degrees. With a wobbly pointer this is very trying and wears the patients. So, in short: the aperiodic compass would tend to cancel out the constant alternating acceleration / deceleration effects as well as cancel out the effects of vibration. However, under a uniform constant acceleration it would still eventually show exactly the same deviation. --Aspro (talk) 13:17, 6 May 2010 (UTC)

shadows, mirror images?

Are shadows mirror images? Are they superimposable? At times, i noticed the images of shadow and mirror being alike, for ex.: a word printed on a glass shows shadow (behind the glass)similar to that of the original (not reversed) and similar image is also seen when a mirror is placed behind the glass on which the word is written. Hope i am clear..- anandh, chennai. —Preceding unsigned comment added by 125.21.50.214 (talk) 05:15, 4 May 2010 (UTC)

No, shadows are caused by an object blocking light rays, while a mirror image is caused by light rays reflected from the object being reflected a second time by the mirror. FWiW 67.170.215.166 (talk) 05:36, 4 May 2010 (UTC)

Regarding your second question, shadows are not actual things. A shadow is a place where there is less light - but it isn't no light at all. There is still some light, but less. If you have a second shadow on top of the first, then you have even less light then before. Ariel. (talk) 06:17, 4 May 2010 (UTC)

If you're facing the writing on the same side as the light source, the shadow looks "normal" (i.e. you can read it easily). The mirror on the other side of the glass shows you the mirror image of the other side of the writing (i.e. the inverse of the inverse) so it looks the same as the shadow. This doesn't mean that the shadow is a mirror image - but in this case they are superimposable. Hope this helps. Zain Ebrahim (talk) 13:07, 4 May 2010 (UTC)

FORTRAN Programming (Lahey Compiler)

I am trying to run one old fortran program (1980's). I compiled it using Lahey Compiler and i removed all errors and warnings. It is not running properly, if i give some print or write commands at some particular locations in some subroutines, it starts running. I am not able to understand without making any change in the code how is it running just due to some print or write commands and the results are still some what away from expected.203.199.205.25 (talk) 07:12, 4 May 2010 (UTC)

You will probably find a more receptive audience at WP:Reference desk/Computing. I suggest you delete your message from the Science Reference Desk and paste it into the Computing Reference Desk. Dolphin (t) 08:16, 4 May 2010 (UTC)

Cross-posted at Computing desk. Nimur (talk) 12:14, 4 May 2010 (UTC)

is it HF that kills? or F-?

I'm a little confused by the articles. Is F- toxic because it can form HF, or is HF toxic because it can form F-? Ignoring acidity, which is the more toxic species here? Is it because F- is a potent nucleophile, or binds with Ca2+ to form calcium fluoride? John Riemann Soong (talk) 07:26, 4 May 2010 (UTC)

It looks like the F- reacts with the Ca++ to form CaF2, but the H+ in the HF seems to function as a carrier ion (it carries the acid into the skin); even though any F- (or fluorine gas) is toxic in itself. --Chemicalinterest (talk) 11:05, 4 May 2010 (UTC)

see Fluoride#Toxicology F- is 'mildy toxic' and poisonous by hypocalcemia at relativly high doses. Hydrogen fluoride causes burns - in addition to any toxicity caused by flouride present.

In both cases the 'solution' is Ca2+ ions (ie as calcium gluconate / hydroxide / chloride) to precipitate F- as CaF2.

HF is more toxic because it both burns and poisons.77.86.70.220 (talk) 11:35, 4 May 2010 (UTC)

Is fluoride really a potent nucleophile? It holds on to its electrons tightly, so I don't think it's very happy to donate them to electrophiles.

Ben (talk) 00:17, 5 May 2010 (UTC)

The peculiar thing about F- is that although it indeed holds on tightly to its electrons, it has a high charge/size ratio because of its small size, which causes it to bind irreversibly to both calcium and magnesium to form insoluble salts. Living cells can't function without either, so they die off. This is why HF can cause such deep burns -- it soaks into the skin due to the action of the H+ ion, and the F- ion then kills the cells by precipitating the calcium. (Which is why the folks at our alkylation unit have to wear neoprene coveralls at all times while on duty.) 67.170.215.166 (talk) 02:08, 5 May 2010 (UTC)

An additional effect is that HF isn't a strong acid, so it doesn't necessarily cause serious "acid burns" (only 1-2 pKa units stronger than acetic acid I think). But because it's not highly ionic, it would be more able to penetrate skin and other water-tight membranes. So the H+ assists getting the HF in, where F- then can do some serious damage. Glacial-acetic poured on your hand? Wash it off right away, will be red/itchy for a few hours. Dilute HF few drops on your hand? You're in for a world of hurt for a long time. DMacks (talk) 02:18, 5 May 2010 (UTC)

A few drops of dilute HF wouldn't cause a serious burn, provided that you wash it off promptly with soap and water. It's the concentrated stuff (such as what we use at the refinery) that can kill you or burn you to the bone (yes, even a few drops of concentrated HF can burn you down to the very bone, I'm not kidding). Not to mention that concentrated HF can also give off poison gas when exposed to moist air. 67.170.215.166 (talk) 04:39, 5 May 2010 (UTC)

Is it maybe a mix of effects? Someone said that you need high doses of Na+ F- to get poisoned. So why does a few drops of HF hurt so much? It looks that HF is a good skin-soluble acid, so after F- binds calcium or magnesium, maybe the remaining H+ protonates bicarbonate buffer to form carbon dioxide? I mean I've spilled 1M HCl solution on myself before ... it didn't burn at all, except for a mild sting(I washed it off within 10-15 seconds). I assume HF would be way less acidic. John Riemann Soong (talk) 04:47, 5 May 2010 (UTC)

It's the skin permeation and cellular toxicity that cause it to hurt so much. HCl just attacks your skin by acid-catalyzed protein hydrolysis, and human skin is pretty resistant to that (especially the skin of an amateur chemist). HF, on the other hand, soaks into the skin and kills the living cells underneath by calcium precipitation, and it is this destruction of living cells that causes deep, painful burns (sometimes even to the very bone, as I said before). It's all the difference between scraping your skin on rough concrete vs. falling on some punji stakes. In the first case (concrete/HCl) only the outer layer of skin is damaged, whereas in the second (spikes/HF) there's damage to the underlying tissue (which hurts a whole lot more). 67.170.215.166 (talk) 05:09, 5 May 2010 (UTC)

It seems that ingesting 1 mmol of NaF would be worse than spilling 1 mmol of HF on your skin. Apparently it's the other way round. But wouldn't 1 mmol F- have the same effect, regardless of counterion? John Riemann Soong (talk) 17:54, 5 May 2010 (UTC)

Yes. 1 mmol F- would have the same effect, but the H+ ion has certain properties, such as ability to penetrate skin and put the F- ion into your system. Na+ ion does not have any toxic effects generally. For example, HNO₃ is much more reactive than NaNO₃. One can oxidize copper quite easily, while the other one can only with difficulty (or not at all). The "carrier" ion has an effect on toxicity, too. --Chemicalinterest (talk) 18:22, 5 May 2010 (UTC)

Are Kepler's laws rigth?

Hi, I hope this is the rigth corner to open this discussion.So I copy-pasted my former talk from other wikicorners.I claim:

Planetary orbits are not elliptical,but spiraled,with the Sun at the barycenter.Newton's universal attraction force formula F=G*M*m/r^2 gives the masses a tangential velocity so that each masses have to orbit one around the other (attraction force=centrifugal force). This tangential velocity Vp is constant:Vpm for m and VpM for M until the masses reach to the barycenter.Kepler says the contrary. According Kepler the tangential velocities are variable and the areal velocities are constant.But,when you draw the polar graph of two bodies you find, according Newton's F*dt=m*dV,the motion's equation r=-a*t*(t-tmax) which shows no sign of ellipse.No ellipse,no focus,no aphelion,no perihelion,nor equality of swept out areas in equal interval of time.Consider Nasa's photos of the galaxies: you will see the spiraled orbits of celestial bodies.Newton does not confirm Kepler; except for period's law (P1/P2)^2=(r1/r2)^3 which is valid only and only for circular orbits.Does Kepler has changed his reasoning;(elliptical orbits in 1609 and circular orbits in 1618)? Yes.He wanted to say, the elliptical orbits will be transformed to circular orbits with time.How does a solid elliptical shape could be transformed to circular shape,unless the orbits are not elliptical? This is possible when the orbits are spiraled: expanding and then compressing, billions of spirals. TASDELEN (talk) 07:35, 4 May 2010 (UTC)

Think about conservation of energy and see how your proposal fits in. Graeme Bartlett (talk) 10:22, 4 May 2010 (UTC)

Kepler's laws are simplified, empirical observations that are valid to a certain level of accuracy for certain cases that are valid to describe planet-like orbits. I don't follow your description about spirals; but in any case, there are other types of orbit, including non-elliptical orbits (such as those of a non-returning comet, or the orbit of a ballistic missile, which intersects the planet it orbits). These cases require mathematical treatments using the more general laws of Newtonian gravitation (and eventually, general relativity's even more complete description of gravitation). Your polar-form equation of planetary motion is not correct in the general case - I'm not sure where you got that equation from, but it looks kind of like an equation for a parabolic orbit - only one of many possible paths. Kepler's laws are applicable only if the orbit is closed and unperturbed. Our articles are extraordinarily descriptive of all possible cases. Nimur (talk) 12:22, 4 May 2010 (UTC)

TASDELEN, you are mistaken. Kepler's laws are completely consistent with Newton's law's within the "two body problem" approximation - That is, provided any pertubations introduced by other planets are negligible. Dauto (talk) 14:40, 4 May 2010 (UTC)

Science can not prove that something is true. All that it can say is that is has not been disproved. Googlemeister (talk) 14:23, 5 May 2010 (UTC)

RE "Does Kepler has changed his reasoning;(elliptical orbits in 1609 and circular orbits in 1618)? Yes.He wanted to say, the elliptical orbits will be transformed to circular orbits with time." If Kepler said that, it was probably due to his Platonism. Ellipses are "imperfect" and circles are "perfect." Another example: Some of Kepler's insights derived from his false belief that planetary orbits were related directly to perfect poly-sided (polylateral?) geometric shapes. Similarly, Copernicus incorrectly retained a version of epicycles in his theory to preserve the "perfect" circle idea. 63.17.78.34 (talk) 04:36, 8 May 2010 (UTC)

Dears

Graeme Bartlett|talk]]) 10:22, 4 May 2010 (UTC)

When I consider energy conservation equation,I write

F*r*dt=m*r*dv (energy conservation equation), then I write

1/2*m*Vr^2+m*gr*r+1/2*I*w^2=m*r*dVr (total energy with g variable)

This is a differential equation

dr^2+K*dt^2=2*r*d(dr) (side's term analysis meter^2=meter^2)

with solution

r=-a*t*(t*tmax)+K where K=2*gr*r+I*w^2/m=-a^2*tmax^2/(1+4*a)

On Cartesian, the graph of (r) is a parabola.

On Polar, this graph is a cardioidal looking spiral: billions of spirals.

Expanding then after compressing; with a max.point, only one max.point.

Located on a paraboloid surface along the orbit of the Sun in its galaxy.(our Milky Way)

This is the shape of the orbits. No sign of ellipse, no sign of aphelion, no sign of perihelion.

See the spirals on Nasa’s galaxies photos. The barycenter is not at one focus of an ellipse.

(details on my TASDELEN (talk) 08:34, 6 May 2010 (UTC)

Nimur|talk]]) 12:22, 4 May 2010 (UTC

"Your polar-form equation of planetary motion is not correct in the general case - I'm not sure where you got that equation from, but it looks kind of like an equation for a parabolic orbit - only one of many possible paths. Kepler's laws are applicable only if the orbit..."

the equation r=-a*t*(t-tmax)+K is a derivation of Newton's F*dt=m*dv.It is similar to s=-1/2*g*t^2+Vy*t+s0. I would like to give a Polar design of this equation,but I don't know how to send it to Wiki.You may draw yourself this graph by considering (t as corresponding to angles degrees and r as corresponding to the distances from the pole).I can e-mail you this graph and if you believe you may add it to my talk.Even if you do not believe.So,you may help me.

Dauto|talk]]) 14:40, 4 May 2010 (UTC)

I would like to e-mail you my "2 body"-"3,5,.. body" graphical systeme solution,but I don't know how to upload them to Wiki.If you want to help me,I send the graphs to you,and you upload them to Wiki.Large article and graphs!

Googlemeister|talk]]) 14:23, 5 May 2010 (UTC)

"Science can not prove that something is true. All that it can say is that is has not been disproved".I like this.Don't you think that Kepler's laws are disproved,by these Newtonian mathematics.According me Newton do not confirmes Kepler,except for periods.

63.17.78.34|talk]]) 04:36, 8 May 2010 (UTC)

The derivation from Newton's [F*dt=m*dv] results to [r=-a*t*(t-tmax)+K].And the shape of the orbits for the whole universe is spiraled orbits.Conical sections should not be considered for material orbits.No ellipse,no parabola,no hyperbola.But only spirals;for our solar system,for other solar system of our Milky Way.Even our Milky Way is a material which should orbit together with other galaxies around a barycenter.Spiraled system,in spiraled system which are also in spiraled system.I can e-mail you a graph for "Sun-Earth-Moon= 3 body system" which shows spirals in spirals then again in spirals.I don't know how to upload such graphs to Wiki. TASDELEN (talk) 18:18, 9 May 2010 (UTC)

Coefficient of drag at hypersonic speeds

Hi,

I was wondering how C_D varies with Ma at hypersonic speeds? Must graphs of C_D I have seen only go up to Ma 2.0, I'd like to know how it varies up to Ma 20 (eg what the Falcon Hypersonic Technology Vehicle experiences). Thanks! --58.175.32.19 (talk) 08:36, 4 May 2010 (UTC)

At hypersonic speeds, the linear model described in drag coefficient is totally inapplicable, so there's no real need for these charts. The shape and geometry become significantly more important than the total effective surface area. This is why an aerospike reduces drag, even though it adds surface-area exposed to the fluid flow. Consider this paper, Numerical Solution of the Hypersonic Viscous Shock-Layer Equations (AIAA, 1970). Nimur (talk) 11:31, 4 May 2010 (UTC)

Newton's cradle question

I recently bought an inexpensive Newton's cradle. Much to my dismay, it is not operating as nicely as I had expected. When the outside ball hits the remaining four, the middle three do not stay perfectly still, they wiggle quite a lot - and very quickly start swinging back and forth. This causes the motion to deteriorate very quickly. If I start by putting two balls into motion, it is even worse. Are there any simple adjustments that can be done to improve it? Thanks, decltype (talk) 10:19, 4 May 2010 (UTC)

Make sure that the row of balls is precisely in a straight line. Should be able to adjust the supporting cords. Graeme Bartlett (talk) 10:24, 4 May 2010 (UTC)

Also make sure that the surface on which the cradle sits is completely level. caknuck _° needs to be running more often 05:15, 5 May 2010 (UTC)

Curvy tunnel

On Balfour Beatty's website there is a tunnel image http://www.balfourbeatty.com/bby/segments/business-intro/ - ( Image url ) can anyone identify what project this is from, and what the tunnel is for?

More importantly - can someone explain why the tunnel is so crazily curved - is this trick photography or real. Thanks. Sf5xeplus (talk) 10:59, 4 May 2010 (UTC)

Balfour Beatty's website gives a contact e-mail address. Have you tried asking them about the tunnel? Cuddlyable3 (talk) 12:05, 4 May 2010 (UTC)

No I haven't contacted them.Sf5xeplus (talk) 13:41, 4 May 2010 (UTC)

The convoluted nature, the lack of a flat foor, and the diameter, would suggest it was for carrying water. It looks like a pipe inside a hydroelectric power plant, or a pumped storage plant like Dinorwig Power Station. These typically feature wire-bore tunnels for water to pass through, either for power generation or as part of the overflow system (see these pictures for the Hoover Dam's overflow tunnels). That said, every tunnel of that nature I can find pictures of has a smooth surface (either concrete or stone). Balfour Beatty does just that kind of business, but then they do lots of large civils in general. -- Finlay McWalter • Talk 14:17, 4 May 2010 (UTC)

I was wondering about sewage (google images show some similar page 4 and 5 - but most are smooth) - The shape doesn't make a lot of sense - appears to be a S bend followed by a turn to the right - more suitable for a water slide - anyone think the image has been distorted? Sf5xeplus (talk) 15:03, 4 May 2010 (UTC)

I'd suggest that it's the pedestrian part of an underground railway station, without the floor. Bank Underground station has at least one tunnel which is essentially the shape shown, with a staircase on the bit that's not horizontal. AlexTiefling (talk) 00:13, 5 May 2010 (UTC)

Addendum: although I can't be certain, I'd suggest that it might be the new access tunnel leading to the Northern Line platforms at Kings Cross St Pancras. AlexTiefling (talk) 00:34, 5 May 2010 (UTC)

Thanks, a passenger access tunnel makes much more sense. Sf5xeplus (talk) 08:50, 5 May 2010 (UTC)

Actually, this is a Ventilation Shaft and Escape Tunnel on Jubilee Line of London Underground.Vromascanu (talk) 17:03, 15 October 2010 (UTC)

Gloria Allred

Question moved to Wikipedia:Reference_desk/Miscellaneous#Gloria_Allred

substitute for peanut butter

I initially became a big nutritional fan of peanut butter when I read that it had no cholesterol and twice the protein of calves liver. Boy was I excited - peanut butter the perfect food. Then I started gaining weight only to realize 40 lbs later that even though peanut butter had no cholesterol it had plenty of fat. Not only did it have fat but it had saturated fat but alas I could not stop eating the stuff because I also loved the taste. Now my doctor says stop eating peanut butter or die so I have to find a substitute. What tasty treats with unsaturated oil can I find that will take the place of squshed gubbers? 71.100.1.71 (talk) 15:52, 4 May 2010 (UTC)

ask your doctor. Dauto (talk) 15:56, 4 May 2010 (UTC)

I did and he said that for a longer list to consult the Wikipedia. —Preceding unsigned comment added by 71.100.1.71 (talk) 15:58, 4 May 2010 (UTC)

All right then. Here's my suggestion: Eat more fruits and vegetables andexercise more frequently. Dauto (talk) 16:17, 4 May 2010 (UTC)

While finding an unsaturated fat alternative is probably better, the real problem here is that consuming excessive fat whether it's unsaturated or saturated is likely to increase your weight, simply because fat's energy density is so much higher than protein/carbs. You need to find an alternative that's both lower in saturated fat and lower in calories! Exxolon (talk) 15:59, 4 May 2010 (UTC)

The calorie thing is under control by limiting myself to 11 grams of peanut butter per meal (3 meals per day) for a diet plan of 21% fat, 67% carbs and the rest protein. So what unsaturated substitutes do you suggest? 71.100.1.71 (talk) 16:12, 4 May 2010 (UTC)

Typing the words "peanut butter substitute" into Google returned this search result: [7]. There's lots of options. --Jayron32 16:18, 4 May 2010 (UTC)

LOL... I told my doctor that when I asked the Wikipedia they said to Google. 71.100.1.71 (talk) 17:19, 4 May 2010 (UTC)

I was surprised to find almost instantly a link to waht is being called "soynut butter". I guess this idea already took off due to peanut butter "allergy's". 71.100.1.71 (talk) 16:55, 4 May 2010 (UTC)

• However, in comparing the labels of great value brand peanut butter and peanut free soynut butter the soy actually fairs worse with 14% instead of only 10% saturated fat and 4 grams of sugar instead of only 3. 71.100.1.71 (talk) 17:12, 4 May 2010 (UTC)

Why the " " on "allergys"? 86.178.228.18 (talk) 21:20, 4 May 2010 (UTC)

clearly it's an attempt to excuse the misuse of an apostrophe --Psud (talk) 06:16, 6 May 2010 (UTC)

You eat peanut butter with every meal? One of the key features of a good diet is that it be varied, otherwise it is easy for it to be deficient in something (there are plenty of nutrients that you only need a small amount of but that aren't in all foods, eating lots of different foods means you will probably be eating at least one with each of the essential nutrients in it). --Tango (talk) 17:30, 4 May 2010 (UTC)

Ignoring the obvious problems involved with a diet high in any fat, I personally enjoy SunButter. It has multiple varieties, which are more or less similar in taste to a comparable type of peanut butter. That said, it still has saturated fat, about 2/3 the amount in peanut butter. And its overall fat content (saturated plus unsaturated) is close to peanut butter. —ShadowRanger ^(talk|stalk) 17:17, 4 May 2010 (UTC)

To be clear, there are a whole lot of varieties of SunButter, and the similarity to peanut butter varies. Natural Crunch is the only one I buy regularly (I like crunchy over creamy), and it's a very close match (a little sweeter and less oily to my taste). I can't say how close the other varieties are to their equivalent peanut butter. Also, if I didn't make it clear, the primary ingredient in SunButter is sunflower seeds plus some sugar. —ShadowRanger ^(talk|stalk) 17:20, 4 May 2010 (UTC)

I suggest you try either "organic" or "natural" peanut butter. In both cases they won't contain the added trans-fats, which make it creamy, and will have somewhat lower saturated fats, too. Without that it will separate and need stirring, but that's a small price to pay for avoiding trans-fats. You might wonder why the label says 0 trans fats on traditional creamy PB. They just keep the amount low enough that they are allowed to "round down" to zero. In the US, anything under 0.5 gram can thus be classified as 0, even though getting that much trans fat in every serving is unhealthy. Look for partially and/or fully hydrogenated vegetable oil in the ingredients, that means they added trans-fats. StuRat (talk) 17:33, 4 May 2010 (UTC)

As a side note yes I am aware of the round down problem which Congress can eliminate by requiring all nutrients be stated as grams per 1000 versus grams per serving and then let the customer do the serving math. 71.100.1.71 (talk) 18:54, 4 May 2010 (UTC)

Wouldn't it be simpler to require trans-fats be listed to the nearest tenth of a gram, or hundredth, or thousandth ? StuRat (talk) 22:13, 7 May 2010 (UTC)

Grams per thousand inherently indicates multiple servings whereas decimal grams inherently indicate a single serving. Because a kitchen scale is not accurate for a single gram a single serving measurement ends up getting rounded down as in the serving size system we use today. By forcing everyone to think initially in terms of an amount larger than a single serving we deny manufactures an opportunity to round up or down. 71.100.0.29 (talk) 17:00, 8 May 2010 (UTC)

Focusing on saturated fat for weight loss is simply wrong. It won't help in the slightest. Saturated far affects cardiovascular health, but not weight. And switching to unsaturated fat for cardiovascular health is also wrong. Because the ratio of the various types of unsaturated fat matters (the various Omega types) too. And cutting fat out entirely won't help either, because aside from being bad for you because you need essential fatty acids, carbohydrates can be converted into fat by the body. If you really do want to fix your health then for starters stop eating sweetened peanut butter, switch to unsweetened (it's harder to find though). Second stop eating a lot of any one food. There are some foods that historically have worked as the main source of calories (staples), but most are not suited for that. Ariel. (talk) 19:44, 4 May 2010 (UTC)

Even with lots of available variety, the problem of staples is taste. People have a tendency to eat over and over again only the tastes they like. 71.100.1.71 (talk) 20:20, 4 May 2010 (UTC)

My 2 roommates and I consumed 40 pounds of peanut butter one school year in college. So I consumed about 6 kilograms, or 40,000 calories, or 190 servings in 223 school days, and that seemed like a lot at the time, but we really never got tired of it. Peanut butter is the most caloric portion of a PBJ: 190 calories in a serving of peanut butter, 140 in 2 slices of white bread, and 50 in a serving of preserves, 380 total.Calories vary with variety and quantity of ingredients. Edison (talk) 19:28, 5 May 2010 (UTC)

I agree. I lived on PBJ and milk/old fashioned Coca-Cola all through high school. Its the most portable meal I know. Here, this site might be for you. 71.100.0.29 (talk) 17:08, 8 May 2010 (UTC)

Meteorological deposition of carbon dioxide snow or frost

Seeing as the coldest temperatures on earth (eg Vostok Station) are often well below the freezing point of carbon dioxide, do these areas see deposition of solid carbon dioxide from the atmosphere, such as CO2 snowfall or frost? If not, why not? —Preceding unsigned comment added by Btxtsf (talk • contribs) 16:39, 4 May 2010 (UTC)

The CO2 content of the atmosphere (around 0.05%) is so low that the snow probably would be unnoticeable. And the size of the miniscule amount of CO2 would decrease much more when solidified, since solids are generally smaller than gases. --Chemicalinterest (talk) 16:51, 4 May 2010 (UTC)

But, on the other hand, you get very little traditional snow there, due to the low water vapor content in the air, so any dry ice would therefore be a larger component of the total. An interesting Q, I wonder if you can easily tell the difference between the two. StuRat (talk) 17:45, 4 May 2010 (UTC)

An easy way to tell the difference: water snow feels wet in your hand, CO₂ snow doesn't. Clear skies to you 67.170.215.166 (talk) 02:13, 5 May 2010 (UTC)

I'm assuming the reason the massive block of CO₂ ice I touched felt wet was because of the condensation of the water vapour in the air nearby, then? Vimescarrot (talk) 06:00, 5 May 2010 (UTC)

Yeah, that's right. 67.170.215.166 (talk) 00:55, 6 May 2010 (UTC)

Another way to tell the difference between ordinary snow and CO₂ snow is to squeeze a handful in your glove -- water snow sticks together into a snowball, CO₂ snow doesn't, and also makes a whistling or shrieking sound when squeezed very hard. FWiW 67.170.215.166 (talk) 00:58, 6 May 2010 (UTC)

Like the sound you get when you crush Styrofoam peanuts ? StuRat (talk) 03:56, 8 May 2010 (UTC)

Yes, kinda like that -- it's caused by pressurized CO₂ escaping from the snowball. Ordinary snow doesn't ever make this sound, no matter how dry or how low its temperature. (Well, it could make kind of a squeaking sound if very cold and completely dry, but never this sort of screech that CO₂ snow makes). FWiW 67.170.215.166 (talk) 04:35, 8 May 2010 (UTC)

That would only work well with wet snow. Dry powdery snow will not form a snowball. Googlemeister (talk) 13:26, 6 May 2010 (UTC)

And, at temps low enough that you could have CO₂ ice, the water ice won't be wet. StuRat (talk) 03:56, 8 May 2010 (UTC)

Fill a Teflon sample bag with CO2 and seal it and the Vostokians may see some, but otherwise no. As to the 'why'. That has already been answered elsewhere, so I'll just link to it.[8]--Aspro (talk) 17:49, 4 May 2010 (UTC)

Vostok Station is over 11,000 feet above sea level, giving an atmospheric pressure only about 2/3 of the sea level value. That's enough of a difference to drop the sublimation temperature of CO2 by at least a few degrees, meaning that the sublimation point has never been reached in recorded data even there. Looie496 (talk) 00:49, 5 May 2010 (UTC)

Chemical element lists

I'd like lists for the following:

1) The state of matter (gas, liquid, solid) of each of the 118 chemical elements at STP.

2) The names from which the chemical symbols are derived, for those which are not derived from the English name. For example, W = Wolfram = Tungsten.

I could eventually figure them out by reading all 118 articles, but I hope lists are already available. StuRat (talk) 17:53, 4 May 2010 (UTC)

List of elements by name, List of elements by boiling point, List of elements by melting point might help.--Stone (talk) 18:02, 4 May 2010 (UTC)

List of chemical element name etymologies should help with 2 ? —Preceding unsigned comment added by 77.86.70.220 (talk) 19:49, 4 May 2010 (UTC)

Just to note, you are only going to find state-of-matter information for about 100 or so of the elements. Many of the largest elements have only existed briefly as a very small sample, sometimes of as little as a few hundred atoms; far too small a sample to say anything reliable about its "state". --Jayron32 19:55, 4 May 2010 (UTC)

Also, the heaviest elements are either named after famous scientists, or not named at all yet. Clear skies to you 67.170.215.166 (talk) 02:16, 5 May 2010 (UTC)

Mercury and bromine are liquids. Fluorine, chlorine, oxygen, nitrogen and the noble gases (with the possible exception of ununoctium) are gases. Rubidium, cesium, probably francium, and gallium are liquids near room temperature. The rest of the elements that can be observed are solids.--Chemicalinterest (talk) 15:16, 5 May 2010 (UTC)

Na-Latin natrium, K-latin kalium, W-german wolfram, Fe-latin ferrum, Cu-latin cuprum, Ag-latin argentum, Au-latin aurum, Hg-latin hydrargyrum, Pb-latin plumbum, Sb-latin stibium These are names of elements whose symbols do not correspond. --Chemicalinterest (talk) 15:46, 5 May 2010 (UTC)

Thanks, but that's not a complete list. And, as far as incomplete lists go, I just can't stannum. :-) StuRat (talk) 22:40, 7 May 2010 (UTC)

Hydrogen is a gas obviously as well. Googlemeister (talk) 13:24, 6 May 2010 (UTC)

PhD programs and mental health

Can a PhD program be harmful to your mental health?--Mr.K. (talk) 17:57, 4 May 2010 (UTC)

Most academics would deny it, while a lot of PhD students would say that they suffered mentally during their slave work like thesis.--Stone (talk) 18:04, 4 May 2010 (UTC)

I'm not sure that most academics would deny it. Most that I know (which is many) would say, "yes, of course." They might say it is worth it (they might not), they might say it weeds out the less fortified (but they might also think it weeds out the non-crazy, as well). Academics are surprisingly straightforward about how crappy their overall career system is, even if they at the same time are likely to be less straightforward about whether or not that implies that academia is not all it is cracked up to be. Just my anecdotal experience. --Mr.98 (talk) 21:44, 4 May 2010 (UTC)

Can anything be harmful to your mental health? Yes. It is hard to attribute it specifically to a PhD program. Consider my PhD experience. I worked full time as a software engineer. I was raising two babies. I had to teach up 80 students (including grading homework and exams). I had to write not only a thesis, but also a readiness paper. I was also pestered with attending one symposium after another. Basically, I had about 30 hours of responsibility each day for about 3 years. So, did the PhD program cause mental health issues or was it the kids or dealing with idiots as a software engineer or dealing with students who claim their grandmother died three times each semester or simply never getting more than 4 hours sleep per day (and not 4 hours of continuous sleep)? I don't think you can blame the PhD program itself. It is an entire lifestyle that easily contributes to poor mental health. -- kainaw™ 18:11, 4 May 2010 (UTC)

There has been suicides of graduate students ,for example Jason Altom. How closely this is connected to his supervisor was disputed and will never be known.--Stone (talk) 18:14, 4 May 2010 (UTC)

As an addendum, I thought it important to point out that I believe my experience of three months of boot camp in the Marines was far easier than any particular 3 month period of my PhD program. It doesn't take much to mindlessly follow orders. However, being able to mindlessly do tasks until they are done does help a great deal when you have something like 80 programs to grade, each submission about 20 pages of source code, and you would much rather be doing anything else other than read through tons and tons of code that doesn't compile, doesn't make sense, and looks like random snippets of code pasted from various websites. -- kainaw™ 18:16, 4 May 2010 (UTC)

The answer is of course yes, as can school, the army, work etc... PhD's are notorious for their stress-levels (not for everyone of course) - WP:OR and it's quite suprising the percentage of PhD students who express a hate for their supervisor, or a deep unhappiness with the process..

In particular the transistion from primarily taught courses to self propelled is a factor, as it will be also the first experience for many of truly individual responsibility for their actions.

There's some results under http://www.google.co.uk/search?hl=en&ei=gXvgS5C3KJuTsQauqYzoBA&sa=X&oi=spellfullpage&resnum=0&ct=result&cd=2&ved=0CAYQvwUoAQ&q=phd+student+stress&spell=1 —Preceding unsigned comment added by 77.86.70.220 (talk) 19:56, 4 May 2010 (UTC)

One possible form of stress release for suffering grad students is write a comic strip. 69.228.170.24 (talk) 20:27, 4 May 2010 (UTC)

Yes, that is generalizable. (rolls eyes) --Mr.98 (talk) 21:44, 4 May 2010 (UTC)

Being in a Ph.D. program can be stressful, and stress can "harm your mental health." Being up for tenure can be stressful, too. Trying to get admitted to a good college can be stressful, as can trying to "do more with less" in the deliberately stressful environment of a large (or small) business, where years invested in a career can suddenly go "poof" due to corp reorg. I would expect that being in a modern war or occupation zone is rather more stressful. Being unemployed or underemployed is pretty stressful. I would not rate a PhD program as being the highest stress level I have encountered. Edison (talk) 21:05, 4 May 2010 (UTC)

You have to consider your initial susceptibility, general stress level, and lifestyle choices. If you're already inclined to depression or anxiety, for example, even the stress of high school or undergraduate university work might be enough to induce a full-on crisis. A person who is trying to juggle single parenthood, a full-time job, and graduate work is probably going to have a harder time of it emotionally than someone who has no major responsibilities and nothing else to do but concentrate on academic work. Knowing how to manage your time and how to de-stress yourself is an important factor. And making the right lifestyle factors is crucial, especially if you're already susceptible or stressed in the first place. Eat good healthy meals, get plenty of sleep, exercise regularly, have a supportive social network, and try to find time for things you enjoy, and you'll give yourself the greatest chance to get through a Ph.D. program - or college admissions or unemployment or almost anything else - with your sanity intact. 71.104.119.240 (talk) 01:08, 5 May 2010 (UTC)

Stress in a PhD student depends on many things, though I would say it is more related to the competitiveness of a field, the funding resources available, and most importantly, the political environment of the lab. Your stress will be greatly compounded by the latter. Life can be hell if your lab-mates are leeches or backstabbers and your supervisors are abusive or incompetent. It is likely that more labs have split or died due to politics alone than any other factor. However, if you work well, know your research field, having funding, and work in a relatively tame lab environment the stress is not that bad. Sjschen (talk) 15:07, 5 May 2010 (UTC)

HTPB

Our article on Hydroxyl-terminated polybutadiene says it is a polymer of butadiene terminated at each end with a hydroxide radical. So does the reaction to make it go like this?

nC₄H₄(OH)₂ → nH₂O + (C₄H₄O)_n

Also, do the all the C₄H₄ have oxygen between them? Thanks, --The High Fin Sperm Whale 19:20, 4 May 2010 (UTC)

The Os are at the end only (if in between it would be a polyether).

One synthesis uses hydrogen peroxide [9] US patent 5159123

The link probably has much of the answers you want.

The wikipedia article Hydroxyl-terminated polybutadiene incorrectly described it as a polyol - I've corrected that. —Preceding unsigned comment added by 77.86.70.220 (talk) 19:47, 4 May 2010 (UTC)

So do you use C₄H₆ and H₂O₂? --The High Fin Sperm Whale 20:10, 4 May 2010 (UTC)

Any radical initiator should work to start the polymerization reaction. --Jayron32 21:30, 4 May 2010 (UTC)

It needs to be convertable to OH - hence why H2O2 is used.77.86.70.220 (talk) 23:02, 4 May 2010 (UTC)

So are the bonds C-C? --The High Fin Sperm Whale 00:57, 5 May 2010 (UTC)

Yes they are. 67.170.215.166 (talk) 02:17, 5 May 2010 (UTC)

Clarification: the bonds in polybutadiene are a mixture of C-C (single) and C=C (double) bonds; what I meant was they're carbon-carbon bonds as opposed to carbon-oxygen. Clear skies to you 67.170.215.166 (talk) 03:58, 5 May 2010 (UTC)

Gravity

Let's imagine I'm riding my bicycle in a frictionless world. Taking into account the following:

a) If I'm riding forwards on a completely flat road, I'll have to fight no gravity force at all (exactly 0 g), since gravity only hinders upward movement.

b) If I try to ride up a 90º wall, I'll have to fight all of the gravity force (exactly 1 g), since all my efforts will be directed towards movind upward.

Therefore, if I am riding up a 18º climb, I'll have to fight exactly 0.18 g, and if I am riding up a 23º climb, I'll have to fight exactly 0.23 g. Is that correct, or is my reasoning flawed? If so, what is the mistake? Thanks.

Leptictidium (mt) 19:32, 4 May 2010 (UTC)

The first mistake, surely, is that if 0º = 0g, and 90º = 1g, then 18º = 18/90 rather than 18/100. --Tagishsimon (talk) 19:34, 4 May 2010 (UTC)

I think force due to gravity = mgsinθ might be of use here. sin 90 = 1 and sin 0 = 0, but sin(18) degrees is not 0.18 (it's closer to 0.3, I think). - Jarry1250 ^{[Humorous? Discuss.]} 19:36, 4 May 2010 (UTC)

Not sure where this line of questioning is leading, but no, you can't even ride a bicycle on a flat road without friction. DMacks (talk) 19:38, 4 May 2010 (UTC)

What about a rocket powered bicycle? A kite attachment? A gun to fire backwards? - Jarry1250 ^{[Humorous? Discuss.]} 19:41, 4 May 2010 (UTC)

The OP is missing the necessary trigonometry to calculate the gravity force vector relative to the direction that he is traveling. I think Jarry1250 has it, you need to take the sine of the angle relative to the ground to get the portion of gravity you have to combat. --Jayron32 19:46, 4 May 2010 (UTC)

And, for completeness, you should consider the normal force of the incline. Without friction, you will experience a horizontal force, because the normal force is perpendicular to the incline, and only its vertical component is canceled by gravity. The remaining horizontal component will cause you to slide. Most often, that horizontal force is counterbalanced by static friction. Nimur (talk) 19:49, 4 May 2010 (UTC)

Sorry, yes, that was a lapsus and I was thinking along those lines. My question can be summarised as whether the force of gravity one must fight is directly proportional to the angle on which one is moving. Leptictidium (mt) 19:52, 4 May 2010 (UTC)

It is proportional to the angle in a sense. If you make a triangle such that the base is flat (zero degrees) and the angle you are riding is the hypotenuse, the height of the triangle is the amount of "upward travel" that will be fighting gravity in your example. You use trigonometry to calculate the length of the height based on the angle. Assuming that the hypotenuse is set to a length of 1, sine of the angle is the length of the height of the triangle - which is the amount of upward travel. -- kainaw™ 20:03, 4 May 2010 (UTC)

I've tried riding a bicycle on ice, which is a bit like the OP's problem statement. In a frictionless world, the driven wheel will spin without providing any forward motion whatsoever when you operate the pedals, so if stationary you will remain stationary, and if in motion you will remain in motion. You will not be able to accelerate or brake. Second, due to a lack of traction, the instant the center of mass is not directly over the center point of the line connecting the points of contact of the tires with the ground, the tires will slide sideways dumping you on the ground. Steering will not correct the condition, as it does in normal bike riding, even if you are moving forward. Any gyroscopic effect of the spinning tires is negligible (unless you get the the driven wheel spinning very fast indeed). The only ability to climb an incline would be due to the initial forward motion, since there is by definition no traction. Edison (talk) 20:53, 4 May 2010 (UTC)

"Can't Burn Your Skin"

i aw this

http://www.amazon.com/CERTOL-INTERNATIONAL-LLC-USA-128-1/dp/B000KKQ8LA

how can they say "Can't Burn Your Skin," —Preceding unsigned comment added by Tom12350 (talk • contribs) 20:46, 4 May 2010 (UTC)

That description isn't for the Muriatic acid (hydrochloric acid is the more formal name), its for something called "Acid magic" , which is described as buffered hydrochloric acid. See buffer solution for a description of what a buffer is and what it does. I can't find a full ingredients list anywhere; the best I can find is that its a "proprietary blend". Here is an FAQ about the product: [10]. --Jayron32 21:14, 4 May 2010 (UTC)

Here's a forum discussion on it http://www.troublefreepool.com/acid-magic-as-an-alternative-for-muriatic-acid-t16607.html it doesn't look like anyone has an answer. Ariel. (talk) 21:36, 4 May 2010 (UTC)

As the FAQ says to always use gloves and goggles when using it, and they also insist on good ventilation, it doesn't look like they have much confidence in their non-burning non-fuming claims. DuncanHill (talk) 01:52, 5 May 2010 (UTC)

The buffer is prob'ly a weak base such as ammonia or an amine of some sort. But c'mon, if the acid's supposed to be strong enough to do its job instead of HCl, it's gonna be strong enough to burn your skin -- that's just a fact of life, deal with it. 67.170.215.166 (talk) 02:21, 5 May 2010 (UTC)

Not necessarily. A sufficiently concentrated buffer of the appropriate pH could be very mild on the skin, and still be able to efficiently lower the pH of your swimming pool if it is too basic. Remember, the purpose of this stuff is to lower pH. There are lots of ways to do that using chemicals which aren't going to burn on contact. --Jayron32 03:12, 5 May 2010 (UTC)

Having spilled 1M HCl on myself before ... I should say H+ doesn't burn if you wash it off immediately. I take keratin is a pretty tough thing to hydrolyse. (I assume hydrolysis of skin is the main hazard of skin contact with HCl solution). You could buffer it with a very weak base like phosphate or biphosphate. This changes the dominant H+ species. HCl is a chemically mild acid... it's only hazard is H+. With H2SO4 or HNO3 on the other hand, you risk redox reactions, turning your skin a nice healthy black. Mmm, I love the smell of burnt skin and organic ash in the morning. John Riemann Soong (talk) 04:58, 5 May 2010 (UTC)

Actually, HNO₃ turns your skin yellow by oxidation (I know from personal experience). H₂SO₄ doesn't oxidize human tissue -- it dehydrates it, essentially turning it to charcoal (good thing it hadn't happened to me yet). 1M HCl wouldn't burn even if it stays on the skin a while; 3M HCl, however, will burn just a little bit (even if promptly washed away) and more concentrated HCl will burn a whole lot more. Buffering the HCl will reduce the effect by raising pH, but by the same token it will increase the amount needed to do the job required. FWiW 67.170.215.166 (talk) 05:26, 5 May 2010 (UTC)

You see the clever marketing ploy by the folks at Certol, don't you? By buffering plain ole HCl, they accomplish 3 things in 1 fell swoop: (1) they make a product that's almost as cheap as plain HCl, keeping their costs down; (2) they make something that allegedly "won't burn your skin" (but still requires rubber gloves, according to the fine print), thus justifying a higher price; and most brilliantly, (3) they also make this product less effective than ordinary HCl, so it will take more of this product to do the job than if you use plain HCl. Low production cost + higher price + greater quantity required = more moolah for the company. Good job, Certol, and may y'all rot in hell for swindling your customers! 67.170.215.166 (talk) 05:38, 5 May 2010 (UTC)

Again, not necessarily. The purpose of the stuff is to lower the pH of your swimming pool if the pH is too high due to excess chlorination. A highly concentrated buffer solution whose pKa was something close to the target pH of what you want your swimming pool to be, could sufficiently correct your pool's pH problems at volumes similar to what you would need if you tried to do the same with straight hydrochloric acid. It claims a one-to-one volume correspondance with straight conc. HCl, and also claims to be less harmful to skin and fumes much less. The only reasonable solution would be a highly-concentrated buffer system, which could in theory work exactly as described. Since the stuff does actually contain HCl (the MSDS confirms that much), then we'd need a weak base to serve as the other part of the buffer system. I with the above assessment that its like ammonia or another amine. --Jayron32 05:37, 5 May 2010 (UTC)

Yeah, they claim all this, but you don't really know unless you read the fine print on the bottle... 67.170.215.166 (talk) 05:42, 5 May 2010 (UTC)

Normally they use a weaker acid (or less concentrated) such as sodium bisulfate to prevent burns. The buffered HCl may be just a dilute solution. --Chemicalinterest (talk) 12:04, 5 May 2010 (UTC)

Um, the amine is certainly too strong a base to be a buffer for HCl. (You'd get NH4+ and not H+ as the dominant species). What you want I think is to create an acidic species with a pKa of around 0 or 1 (instead of say, -1.7). Much weaker bases like bisulfate and biphosphate come to mind. John Riemann Soong (talk) 14:28, 5 May 2010 (UTC)

I think you may be on the money - did you mean sulphate as a base? - the pkA of hydrogen sulphate is ~2 compare somewhere between -4 and -7 for hydrochloric acid - this means that an sulphate would be almost completely protonated to HSO4- (still a strong acid) - the FAQ for the product notes that it reduces the level of fuming (usually due to free HCl excaping as gas in concentrated hydrochloric acid) - in the presence of 1 mol equivalent of sodium sulphate this would almost certainly acchieve the "90% fume reduction" advertised.. whilst still having a low pH (easily 1) .. also sodium sulphate is dirt cheap. 77.86.70.220 (talk) 19:28, 5 May 2010 (UTC)

Sodium hydrogen sulfate, not sodium sulfate, which is not acidic. --Chemicalinterest (talk) 01:32, 6 May 2010 (UTC)

(outdent) Our sodium bisulfate article notes that it's easy to get solutions of this chemical are about as acidic as 1M HCl but it doesn't fume and it's used to adjust pool-water pH. "What ions are in this aqueous solution?" is a pretty straightforward analytical-chemistry question. Will have to see if any pool-supply stores near me have small amount for cheap. DMacks (talk) 13:40, 6 May 2010 (UTC)

Digestive Cycles

I've read on several websites that the human digestive process follows a specific cirdadian rhythm that has three distinct phases. The appropriation cycle begins around noon (in most people) and continues until 2000 (8 pm). During this time the body is naturally predisposed to dispense plenty of energy to the digestive tract, and a person is most likely to feel hungry (the body's way of indicating it's the right time to take in food). The assimiliation cycle lasts from 2000 to 0400 and during this time the body is most efficient at the later stages of the digestion process: the absorption of nutrients from the intestines and delivery to the cells. The elimination cycle lasts from 0400 to noon and is the time when the body is most efficient at removing from circulation the byproducts of the metabolic process. Eating during the assimilation or elimination cycles is not recommended, as the body is not prepared to devote its energy to digestion at that time, and if one forces one's body to divert energy from the intestines, liver and kidneys, and/or other parts of the body to the stomach, all processes are performed less efficiently and this can result in health problems, weight gain, restless sleep, etc. The exception is fruit, which can be consumed at any time because it doesn't take a great deal of energy to digest. (Water is another exception of course.) I may have described it a bit too simplistically and yet in rather too much detail, but what I want to know is, is any of this true? —Preceding unsigned comment added by 71.104.119.240 (talk) 21:42, 4 May 2010 (UTC)

The body will adjust to whatever food cycle it is given. If you always eat, exercise or do other events at the same time of day, that's what the body will expect. There is no fixed cycle. Ariel. (talk) 00:54, 5 May 2010 (UTC)

Food, drugs and other rewards can entrain the circadian clock in the absence of light cues (e.g. constant light / constant dark). If I remember my Circadian clocks class correctly, you can lesion the SCN in a mammal (under normal light conditions) and other cues will start to entrain the clock.

There have been circadian clock studies carried out with methamphetamine. For the purpose of circadian clock entrainment, meth is basically a more powerful version of a food cue. The clock period can be lengthened to as much as 38-44 hours (for both mice and humans), when allowed to "free run". (It also explains meth users' strange behaviours). You can also entrain the clock to shorter periods (i.e. by controlling when meth is administered).

I really disagree with the whole idea that eating/exercising during an elimination or absorption cycle results in you being less healthy. The whole "energy diversion" thing is crock. Digestion is energetically-intensive, but it doesn't consume a lot of oxygen. Blood sugar is easily produced from fat. I'd go so far to say that exercising after eating, provided you don't do anything stupid that would cause you to throw up, would increase blood sugar levels available to organs. Muscles tend to use glycogen stores (which are local) before drawing on blood sugar. There are clock effects, but they are with respect to entrainment/efficacy, etc. As a student, the thing I'm most concerned about is my alertness, i.e. studying at the optimum time.

You should be worried about efficacy when efficacy is of the utmost importance. You can administer botulism toxin via injection to mice at a time when livers are "optimised" to handle it -- generally at a time after eating. The mortality rate is around ~8%. Inject it 12 hours out of phase and the mortality rate skyrockets to 90+%. Regular food isn't like a toxin -- it doesn't hurt for its metabolism to wait. John Riemann Soong (talk) 18:08, 5 May 2010 (UTC)

Btw, "inefficient digestion" implying "worse health" sounds like a twist on colon cleansing crap. In general, slower digestion is better. Also, absorption is generally not that energetically-intensive -- it's mostly passive diffusion combined with maybe a few active transport pumps for certain ions or minerals. John Riemann Soong (talk) 18:17, 5 May 2010 (UTC)

Humans eating pet food

Is it possible to eat cat and/or dog food? What about other kinds of pet food? ScienceApe (talk) 22:25, 4 May 2010 (UTC)

Humans are potentially omnivores although vegetarians object. Cuddlyable3 (talk) 22:32, 4 May 2010 (UTC)

Chap I knew at college ate a tin of dog food for a bet once. Mind you, he also used to drink gin by the half-pint, so it is possible his judgement was somewhat impaired. DuncanHill (talk) 22:34, 4 May 2010 (UTC)

(ec)Generally, yes. We might not like them very much, having less taste for innards than dogs or cats do, but we could probably subsist on them reasonably well. It's possible to eat birdseed or fish food (it's possible to eat dirt, too) but it would be hard to derive much nutrition from them. Note, though, that dogs and cats make their own Vitamin C and we don't. There may be other such differences. So if you want to live on them, you might need some supplements. PhGustaf (talk) 22:40, 4 May 2010 (UTC)

Although pet food bags are generally labeled "Not For Human Consumption," there's nothing in cat or dog food that's really going to hurt the average person. Pranksters, mischievous older siblings, and pet-loving parents can all tell you stories of humans who ate dry pet food once or twice and lived to tell the story. It's also been reported in the past that some elderly or disabled individuals, struggling to get by on their government handouts, would eat canned wet dog food because it was cheaper than meat considered fit for human consumption. I would guess that dog food would be more nutritious for a human than cat food, because humans, like dogs, are omnivores (yes, even the vegetarians; being an omnivore is a fact of human biology and refers to what the body is equipped to chew and digest, whereas vegetarianism is a lifestyle choice), whereas cats are carnivores. Some columnist, I forget who, once said that if you could only eat one food for the rest of your life, dog food wouldn't be a bad choice - it's specially formulated to meet the complete nutritional needs of an omnivorous mammal. 71.104.119.240 (talk) 00:46, 5 May 2010 (UTC)

I've often thought there should be a "Purina People Chow", which meets all the nutritional reqs of people, just like their other products meet all the nutritional reqs of various animals. Instead we settle for packaged "food" which is completely at odds with our health. StuRat (talk) 13:57, 10 May 2010 (UTC)

The reason they say "Not For Human Consumption" is because the factories that make it don't follow the same food hygiene/food safety procedures as are required by law for food intended for human consumption. That means there is a slightly increased risk of food poisoning compared to eating human food, but that's about it (and given that dogs aren't always getting food poisoning, I think we can assume the risk is still minimal - it's probably just the paperwork they don't bother with rather than the actual hygiene). --Tango (talk) 01:08, 5 May 2010 (UTC)

But don't for get the Melamine Pet Food Recall of 2007 a lot of cats and dogs wound up in veterinary hospitals over that. APL (talk) 03:12, 5 May 2010 (UTC)

Not really comparable. That was a contamination issue. It doesn't prove anything about the healthfulness of pet food in general, any more than the occasional E. coli outbreak proves that human food is inherently unsafe. 71.104.119.240 (talk) 08:14, 5 May 2010 (UTC)

I've been told that the average dog or cat has a "hardier system" than the average human, which is why they can eat things that aren't labeled for human consumption. Whether or not this is true I can't say. You'd have to have a pretty hardy stomach to handle some of the things I've known dogs to gulp down their greedy gullets, but I don't know it would affect the average human to eat insects, burrs, and day-old things, so it's hard to say for sure whether dogs have some kind of systemic advantage. Humans are fussier than they used to be, so it's possible we can't handle some of what our pets consume, and our ancestors consumed, on a regular basis. 71.104.119.240 (talk) 01:15, 5 May 2010 (UTC)

I don't know that dogs really do have a "hardier system". Many of the things they gulp down happily do make them sick, they just aren't smart enough to avoid those foods, like we are. Then there's a range of foods we humans eat without trouble which seem to cause them problems, even death, like chocolate. My brother's dog died after eating a grilled cheese sandwich, which blocked it's intestines, caused a gas buildup, put pressure on it's lungs and heart, and then caused death. StuRat (talk) 14:05, 10 May 2010 (UTC)

It would be remiss not to mention Ann Hodgman. Her article on the subject is pretty funny. (Note that there are a lot of things that don't kill people but carry some kind of risk of long-term effects. I doubt that anyone has any interest in doing studies on the subject.) Paul (Stansifer) 02:04, 5 May 2010 (UTC)

Comedy Answer : The Monkey Chow Diaries] <-- Man decides to eat only monkey kibble for a week. APL (talk) 03:15, 5 May 2010 (UTC)

Record Maximum

link

How can the record max for Pond Inlet, NU, be 25.7C recorded in March when the temp has never reached that even in July? —Preceding unsigned comment added by 78.32.155.164 (talk) 23:50, 4 May 2010 (UTC)

Options include a) the weather event on 5 March 1993 was a freak b) the data is wrong c) you're imposing expectations on the data which are not entirely supported by the data. We had 22 degrees in July, but 21.5 in February. How much of a problem is 25.7 in March, given the February value? Sure, it's counter-intuitive, but non the worse for that. --Tagishsimon (talk) 00:01, 5 May 2010 (UTC)

Surely you've answered your own question? Nil Einne (talk) 00:10, 5 May 2010 (UTC)

May 5

Fucking Magnets!

HOW DO THEY WORK? —Preceding unsigned comment added by 69.180.172.142 (talk) 00:12, 5 May 2010 (UTC)

Are you asking how magnets fuck? Or are you just interested in magnetism? 71.104.119.240 (talk) 00:27, 5 May 2010 (UTC)

Both. —Preceding unsigned comment added by 69.180.172.142 (talk) 00:37, 5 May 2010 (UTC)

It has to do with all the electrons in the magnet being aligned a certain way so the subatomic forces don't cancel each other out. Why it is that the subatomic forces exist in the first place, I can't say. 71.104.119.240 (talk) 00:53, 5 May 2010 (UTC)

They exist because if they didn't we wouldn't be here to notice it. (See anthropic principle - it's the best answer to "why" questions we have. Science is good at "how" but it doesn't really do "why".) --Tango (talk) 01:09, 5 May 2010 (UTC)

Sure you're not just interested in ICP lameness? DMacks (talk) 01:22, 5 May 2010 (UTC)

For those not in on the joke, see Miracles (Insane Clown Posse song). Incidentally the New York Times had an amusing article on this meme. Regarding magnets:

VIOLENT J: I think we might have misused the word miracle. These things we mentioned in the song, they can all be explained. But what we’re doing is appreciating them. Even the infamous line “Magnets, how do they work?” I mean, yeah, we know how magnets work. But they’re still incredible. You can push something across the table without touching it.''

SHAGGY 2 DOPE: Come on, man. The North and South Pole makes a rock magnetic, and if you touch a piece of metal with it, that becomes magnetic? That’s crazy.''

I kind of agree, to be honest. I find magnetism pretty magical, scientific explanation be damned! --Mr.98 (talk) 01:54, 5 May 2010 (UTC)

The reason a magnet attracts iron/steel is basically because when you bring it toward an iron/steel object, it induces an electric current in the object, which interacts with the object's magnetic domains (if they're lined up right) such as to produce a magnetic field of the opposite polarity, which creates an attracting force. As for your question specifically about how fucking magnets work, I got no clue -- I'm pretty conventional in my love life, so I've never tried using magnets for it. Perhaps you could find out more on this use of magnets if you take a look at the article Sex toys...  :-D 67.170.215.166 (talk) 04:11, 5 May 2010 (UTC)

I thought only a moving magnetic field induces a current. When a magnet is motionless near a piece of iron, there is still the same attractive force present. DMacks (talk) 05:04, 5 May 2010 (UTC)

I think that's because the magnetic lines of force are a different density at different points in the metal object. But honestly, I'm not so sure about the induction part anymore... 67.170.215.166 (talk) 05:45, 5 May 2010 (UTC)

It's not usually induction (eg magnet/metal attraction). The Magnetic reluctance / Permeability (electromagnetism) are the factors in whether or not a material is attracted to a magnet (see below).Sf5xeplus (talk) 09:04, 5 May 2010 (UTC)

As for fucking magnets, I've checked out the article on sex toys -- there's no mention of magnets anywhere in it. I suppose you could put a pair of magnets on your cock for more female stimulation, but I don't think it would give much of an advantage vs. all those other toys, or simply improving your technique. FWiW 67.170.215.166 (talk) 05:52, 5 May 2010 (UTC)

Motors that are present in vibrators contain magnets. This would potentially make these magnets "fucking magnets" ;) Sjschen (talk) 15:45, 5 May 2010 (UTC)

Well, I've known more than a few guys who thought they were magnetically fuckable. And despite my asexuality, these losers seem to hit on me constantly. Subatomic forces aside, sometimes opposites just don't attract. 71.104.119.240 (talk) 08:11, 5 May 2010 (UTC)

One route to the explanation: Magnets in their interactions will move the position of lowest energy (like everything else - gravity, electric fields etc) - this explains both magnet-magnet and magnet-metal interactions - for 'part 2'; an explantion of how energy levels change with magnetism is required...Sf5xeplus (talk) 08:57, 5 May 2010 (UTC)

When two magnets meet at opposite poles, is their overall magnetic field lowered than when they were separated? John Riemann Soong (talk) 18:23, 5 May 2010 (UTC)

The easiest way to answer this is to treat the two magnets each as simple dipoles (assume an inverse square law if you wish) - what happens is that the shape of the field changes - along the axis there is some cancelling of field - yes. perpendicular to axis the field shape will be different from a single magnet - and slightly stronger along the center line.77.86.68.186 (talk) 18:08, 6 May 2010 (UTC)

Also I'm curious in the thermodynamics of how magnets reproduce, i.e. magnetise other materials. Generally delta-S is negative. How about delta-H? Do the calories expended in moving your arm provide the free energy required? John Riemann Soong (talk) 18:23, 5 May 2010 (UTC)

delta H is negative for magnetic attraction - energy levels are split into opposed and alligned states (eg for paramagnetic materials) - electrons will tend to drop from opposed states to alligned states (emmitting hv) and creating a net magnetic property.

As you note - delta S is negative - so thermal energy tends to demagnetise in general.77.86.70.220 (talk) 19:20, 5 May 2010 (UTC)

As a better attempt at a (simple) answer - a big strong magnet will magnetise a smaller weaker magnetic substance.. any energy required (from your hand/arm combination) will be to separate them afterwards..! 77.86.68.186 (talk) 20:18, 5 May 2010 (UTC)

Is delta-H negative for magnetic induction? And is delta-S still negative when two magnetic poles come together by attraction, without induction? John Riemann Soong (talk) 21:00, 5 May 2010 (UTC)

ok. So magnetic induction isn't a chemical process.. H=E+pV .. there's no pV change I can think of in induction so H=E for this. If you don't do any work in magnetic induction (ie no electrical load ) then delta H is zero. Maybe I'm missing something obvious? 77.86.68.186 (talk) 16:55, 6 May 2010 (UTC)

Surely there is some sort of ordering because of magnetisation though. Besides pV is just to describe work done by a gas, you can convert it to other forms. John Riemann Soong (talk) 17:19, 7 May 2010 (UTC)

It is interesting to hear Richard Feynman's take on the OP's question: Feynman argues [11] that the questions is currently unanswerable in terms of anything "simpler". (To be pedantic, his argument applies to magnetism rather than magnets, but leaving such cavils aside it's an interesting counter-intuitive viewpoint anyway). Abecedare (talk) 17:12, 6 May 2010 (UTC)

Gulf war oil spill

Is the claim that 36 billion gallons of oil was released in the Gulf War oil spill as ridiculous as it sounds to me? I'm ready to remove the quotation, reliable sources be damned, considering how silly it sounds. Thoughts? Magog the Ogre (talk) 01:04, 5 May 2010 (UTC)

As our article says, it is orders of magnitude bigger than all the other estimates we have. My guess is that the Times article is getting confused between the Gulf War oil spill and the Kuwaiti oil fires. The latter may well have burnt 36 billion gallons of oil, but I don't think that much has ever been spilt at sea. --Tango (talk) 01:15, 5 May 2010 (UTC)

For the record, it takes the entire US a month a half to consume that much oil. Magog the Ogre (talk) 01:22, 5 May 2010 (UTC)

Medical question

What is the name of the disease when the body has trouble keeping fat and storing it, and the sufferer is underweight as a result? I saw it describled on a medical TV show, but I didn't quite pick up the name. ```` —Preceding unsigned comment added by 76.229.150.6 (talk) 01:34, 5 May 2010 (UTC)

You may be thinking of Cachexia. Dauto (talk) 02:55, 5 May 2010 (UTC)

You might also be thinking of hyperthyroidism. Dismas|^(talk) 05:11, 5 May 2010 (UTC)

None of the above. You saw a description of lipodystrophy which occurs in both congenital and acquired forms, and both generalized and partial. Quite striking and in the severe forms associated with several other severe problems. alteripse (talk) 10:38, 5 May 2010 (UTC)

And to sign, use ~~~~ rather than ````. ~ is on the same key as `, SHIFT+` gives you ~ (on a US keyboard, at least) --Psud (talk) 06:58, 6 May 2010 (UTC)

Silver mineral

How does this type of silver form? 149.169.218.250 (talk) 01:49, 5 May 2010 (UTC)

By precipitation from hot sulfurous solution (such as in geysers, fumaroles, those kinds of places) due to the action of the dissolved hydrogen sulfide (generally upon cooling of the solution -- the stuff is slightly soluble in hot water, but completely insoluble in cold water). FWiW 67.170.215.166 (talk) 02:29, 5 May 2010 (UTC)

aka Hydrothermal synthesis 77.86.70.220 (talk) 15:58, 5 May 2010 (UTC)

as well as Ore_genesis#Hydrothermal_processes 77.86.70.220 (talk) 16:00, 5 May 2010 (UTC)

What is the current state of Computer text to speech compare to human readers?

Two question: is good/modern computer TTS system better reader then "average Joe" who is a human native speaker reading same text aloud? If yes, is computer TTS as good as professional announcer (TV, radio etc.)? 1) Sounds as good as human pro. 2) Very close. 3) Still far away, but better then average Joe.

As to give an example of good TTS, I generated mp3 on my computer from reading few paragraphs of introduction to Bird article. http://www.autohotkey.net/~TePe/BirdsIntro.mp3 TTS I used probably not the best one out there, but still quite good IMHO. And the reason I'm asking, I'm very curious, but ESL here, and computer sounds totally perfect for me. But my judgment could be clouded, plus once again, mine English is far from perfect. PS. Lets not go into acting and emotion, sure computer could mimic them, but there is too much room for good or bad taste opinions etc. Lets stick with reading informational articles like most on Wikipedia etc. 70.48.64.135 (talk) 01:52, 5 May 2010 (UTC)

It still sounds like a computer to me, regarding the tone. It still has something of a Stephen Hawking quality, and the timing of some words is off. Some of the words are a bit wrong to my ear (e.g. the second "i" in "fertilizer" is pronounced wrong), but it's not bad. What throws it off is the pitch at the end of words, and the timing between words, which is not very natural. It is definitely not as good as a professional announcer to a native English speaker. I have definitely heard better text to speech than that, though. --Mr.98 (talk) 02:29, 5 May 2010 (UTC)

I don't think the bird recording comes anywhere near to even an average native speaker in terms of quality. --99.237.234.104 (talk) 02:38, 5 May 2010 (UTC)

Thank you Mr.98! Much appreciated! Could you please point me to the system that sounds more natural then the one I choose as an example? Sure, if it is available online. Or, if that is not possible, make a recording of the same paragraphs for comparison. Thank you once again. 70.48.64.135 (talk) 03:26, 5 May 2010 (UTC)

I'm not a linguist, but I believe that getting the timing and emphasis perfect is AI-complete. Consider the sentence "Fruit flies like a banana.". To read that sentence aloud correctly requires recognizing that "fruit flies" is one noun phrase, and needs to be grouped tightly, so that it doesn't get parsed the same way as "Time flies like an arrow.", in which "flies" is the verb, not "like". (Time flies like an arrow; fruit flies like a banana) So, in order to get a sentence to sound just right, it's necessary to understand it. Paul (Stansifer) 02:50, 5 May 2010 (UTC)

The point is valid but the example is not a very good one. One of the reasons Chomsky chose "fruit flies like a banana" is that it actually sounds the same for both parsings, even though the meanings are completely different. Looie496 (talk) 03:00, 5 May 2010 (UTC)

I say the two parsings differently, although you would only notice if you were listening really carefully. The difference is in the pauses between the words "fruit" and "flies" and between "flies" and "like". --Tango (talk) 03:05, 5 May 2010 (UTC)

I'm with Tango. I say them they way he does. --Jayron32 03:08, 5 May 2010 (UTC)

They can be said the same if you're trying to make a point, but a normal human reading that line would emphasize it for clarity, depending on the intended meaning. APL (talk) 03:14, 5 May 2010 (UTC)

Interestingly, system I used got the phrase from |TTS article "My latest project is to learn how to better project my voice" right, but ""Time flies like an arrow. Fruit flies like a banana" was very unnatural. 70.48.64.135 (talk) 03:30, 5 May 2010 (UTC)

I just noticed that spellchecker highlighted the word "fertiliser" from bird article. The phrase is "Some species, particularly songbirds and parrots, are popular as pets. Other uses include the harvesting of guano (droppings) for use as a fertiliser." Could it be misspelled? When I have changed it to "fertilizer" TTS sounded much more natural :( 70.48.64.135 (talk) 03:39, 5 May 2010 (UTC)

You can pick even worse examples: "Green flies like a lettuce", for example is semantically reasonable spoken both ways. You need a much bigger context than that sentence. Since there are no such things as "Time flies", you'd at least have a chance at that one. SteveBaker (talk) 18:39, 5 May 2010 (UTC)

How does the colour green flying make any more sense than fruit flying? I would say it makes less sense - at least fruit is tangible. --Tango (talk) 20:21, 5 May 2010 (UTC)

See American_and_British_English_spelling_differences#-ise.2C_-ize_.28-isation.2C_-ization.29. The -ize/-ise are both equally acceptable spellings. Americans tend to exclusively use -ize endings, while the British tend to have a much more nuanced approach towards deciding when to use each of them. --Jayron32 03:55, 5 May 2010 (UTC)

(ec)Fertiliser is the British spelling and is just as correct, and is also consistent with the rest of the article (see the words specialise, characterise, categorise... in the same page). If your software can't read British-English spelling, it isn't very good. --Lgriot (talk) 04:02, 5 May 2010 (UTC)

So if a human make mistake while reading an article you will also claim that "humans are not very good"? Or just particular person? Have you tried to listen to WikiProject Spoken Wikipedia articles? Even on the project page they are talking about "incorrect pronunciation" in the problem section. And BTW, could you please point at better software? Thank you in advance. 70.48.64.135 (talk) 04:17, 5 May 2010 (UTC)

We've come a long way since the "Stephen Hawking" era of text-to-speech. He's been offered vastly better voice synths (some, even based on analysis of recordings of his own voice before he lost the ability to speak) - but he turns them down because he's become used to it. My Amazon Kindle has pretty good text to speech (the male voice seems superior to the female for some reason). There are a few words it gets wrong - but they are pretty rare and it seems to react to punctuation better than some that I've heard. Some of the best stuff I've heard is done by analysis of actual, specific people talking - and some of those are incredibly lifelike. But the limit comes (as others have observed) when the text doesn't contain enough information by itself to convey how it should be read. Since it would take a full-scale AI system with a vast knowledge of humanity and all of it's quirks to get that right. Figuring out when something should be read sarcastically - and when it's real requires a lot of smarts. The way you read "The dog was wearing pink and green spotted hat!" is quite different from "The man was wearing a pink and green spotted hat!" - my emphasis helps - but the reason that sentence is surprising is different because dogs don't often wear hats - but men do - and because pink and green spots would be remarkable on a man - but relatively unremarkable on a dog. The amount of culture, knowledge and so forth needed to artificially generate the highlighting I added to those sentences is incredible - way beyond the current ability of our best AI systems. SteveBaker (talk) 18:39, 5 May 2010 (UTC)

The example sounds like sampled speech (recorded speech) played back as a collection of phonemes, with rising and falling inflections added manually or by a clever program. It is better than early purely synthesized text-to-speech, which to Americans sounded a bit like a Russian reading from phonetically written Scottish English. It was full of unusual phonemes, and this sample is less so. Perhaps the earlier system sounded more natural to inhabitants of some other English speaking countries. Edison (talk) 19:04, 5 May 2010 (UTC)

File:Sirius A and B Hubble photo.jpg

On this File's description, it says "The cross-shaped diffraction spikes and concentric rings around Sirius A, and the small ring around Sirius B, are artifacts produced within the telescope's imaging system.".

Hadn't the mirror been replaced, and the battery replaced, by this time?174.3.123.220 (talk) 04:24, 5 May 2010 (UTC)

Diffraction spike has half your answer. Also, I don't think the mirror was actually replaced, our Hubble Space Telescope article describes what was done to correct the spherical aberration present in the original mirror. I suspect the concentric rings are also an artifact of part of the telescope's design, or limitation of the design, rather then a "fault" with some part of it. There is an example of a star imaged with the "uncorrected" mirror in the HST article, it looks a lot worse then the photo you link. Vespine (talk) 05:42, 5 May 2010 (UTC)

I think the other half of your answer might be Diffraction it self. Vespine (talk) 06:05, 5 May 2010 (UTC)

More specifically, see Airy disk. TenOfAllTrades(talk) 12:35, 5 May 2010 (UTC)

Using TNT or dynamite instead of smokeless powder in guns

According to this, http://en.wikipedia.org/wiki/Trinitrotoluene#Energy_content TNT and dynamite contain more energy per unit of mass than gunpowder. I don't know if the article means modern day smokeless powder or old day black powder. But why don't we use TNT or dynamite in smaller quantities (so energy content released is the same while mass used is reduced) instead of smokeless powder as propellant? Or maybe even gasoline?

Or perhaps to rephrase the question, what advantages does smokeless powder have over those other explosives when used in guns? Presumably reduced smoke is one. Is it possible to make guns using those propellants? ScienceApe (talk) 04:27, 5 May 2010 (UTC)

High explosives would blow the gun to bits and pieces instead of propelling the projectile. 67.170.215.166 (talk) 04:32, 5 May 2010 (UTC)

Smokeless powder deflagrates, while dynamite detonates. That is, the first goes "whoosh" while the second goes "bang". See USS Vesuvius (1888) for an unusual approach to keeping projectiles from going "bang" in the barrel. PhGustaf (talk) 04:40, 5 May 2010 (UTC)

TNT or any other higher explosives hav got a very high burning rate sometimes it being a few hundred meters per second! Now at such high speeds you have to provide small length barrels to maintain the pressures. just refer to this.. http://thefiringline.com/forums/showthread.php?p=2351433 Prady.. —Preceding unsigned comment added by 116.73.242.109 (talk) 05:16, 5 May 2010 (UTC)

Consistent, safe, controllable burning is important in a firearm. Modern smokeless powder can already easily produce the maximum allowable pressure (if desired) in any particular cartridge, so there is little advantage to a propellant with more power. Friday (talk) 15:14, 5 May 2010 (UTC)

Put another way: If you have an explosion then all of the explosive gets converted into gas pretty much instantly. The pressure in the barrel goes up insanely high and the bullet gets an extremely violent initial acceleration. As the bullet moves along the barrel, the space behind it gets bigger - and since no more gas is being produced, the pressure can only drop. The bullet is therefore no longer being accelerated as fast as it could be. For relatively slow burning propellants, the gas pressure builds up more slowly (although still pretty darned fast!) and the bullet gets a chance to start accelerating more slowly - and as the volume behind it increases, the propellant generates enough gas to fill it and keep the pressure up. So the bullet gets a more smooth and gradual acceleration down the barrel. For a given muzzle velocity, you need much lower pressures with a slow burning charge than with an explosive. So the gun doesn't have to be as strong - and can therefore be lighter and easier to handle. As far as the user of the gun is concerned, you can get the same muzzle velocity with a lighter weapon if you use a slower burning charge...or to put it another way - for the same pressure-resistance in the gun, you get a higher muzzle velocity with gunpowder than with dynamite - which gives you a longer range and better accuracy. A perfect charge would be one that produces exactly constant pressure from the moment it's triggered until precisely the moment when the bullet leaves the end of the barrel, and no more after that. Since the volume to be filled is at it's largest at the end, you ideally want a charge that gradually increases the amount of gas it produces until the bullet leaves the barrel...pretty much the opposite of an explosive. SteveBaker (talk) 18:18, 5 May 2010 (UTC)

An analogy might help. Think of a bow and arrow instead of a gun. The string of the bow accelerates the arrow over a distance of a foot or two. How hard would you have to hit the end of the arrow with a hammer to make it go as far? If I were to hit the end of the arrow as hard as I possibly could, it might go a few feet - but that would be it! But whacking the end of the arrow hard enough to make it go 100 feet would certainly smash it to bits! So a gentler (but more prolonged) force is better. SteveBaker (talk) 18:22, 5 May 2010 (UTC)

So even if the cannon or gun were invincible and wouldn't blow up, the gunpowder is still better to use? ScienceApe (talk) 00:00, 6 May 2010 (UTC)

The answer to that isn't very meaningful though. How much dynamite am I allowed to use versus how much gunpowder? Dynamite is an energetically more concentrated explosive than gunpowder - so if there is zero risk of harming the gun then stuff the barrel almost full of dynamite and get a really HUGE bang! But if you have a gun with a limited tolerance for pressure - then you can do better with gunpowder than dynamite. SteveBaker (talk) 03:35, 6 May 2010 (UTC)

Well the reason why I asked is because the example you gave seemed to indicate that no matter how hard you hit the arrow, it won't be as effective as the bow string. ScienceApe (talk) 05:29, 6 May 2010 (UTC)

Even if the gun barrel is strong enough to contain the initial pressure of the dynamite explosion, there is a limit to how much energy the explosion can impart to the bullet, because the bullet does not seal perfectly against the inside of the barrel. Some explosive gas will leak around the bullet. The leakage rate will be a function of the pressure difference from the back to the front of the bullet. Since the TNT will create a tremendously high pressure behind the bullet initially, before the bullet has time to get going, a lot of the combustion gas will leak around the bullet. In any case, it is possible to launch a projectile using high explosives without any barrel at all; see Project Orion (nuclear propulsion). If you adapted the same principle to firing a projectile out of a gun barrel, using high explosives, it would almost certainly be more effective to divide the explosive charge into multiple small charges that could detonate in sequence, for example by placing the charges in side chambers off the main barrel, each one exploding just when the bullet passes. See Supergun, Project Babylon, and V-3 cannon. However, even in supergun designs, the propellant is always gunpowder or cordite rather than a high explosive. Read the lead section of the cordite article for an explanation. I'd also guess that high explosives would not work well with gas-operated automatic firearms. And of course if the projectile contains an explosive warhead, using high explosive for the propellant might detonate the warhead too, by imparting too much shock to the projectile. Also see base bleed for another way to increase the range of a cannon-fired projectile. --Teratornis (talk) 00:24, 9 May 2010 (UTC)

Proximity of brain structures?

How close is the hypothalamus (especially the suprachiasmatic nucleus) to the hippocampus and amygdala? —Preceding unsigned comment added by 71.104.119.240 (talk) 10:02, 5 May 2010 (UTC)

Fairly close. There is a good schematic drawing on this page. --Dr Dima (talk) 10:31, 5 May 2010 (UTC)

Since the hypothalamus and hippocampus/amygdala don't actually touch, what is it exactly that's between them? 71.104.119.240 (talk) 19:34, 5 May 2010 (UTC)

Parts of hypothalamus are bounded by the third ventricle, optic tracts, and cerebral peduncles. Hypothalamus is fairly compact. Hippocampi, on the other hand, are fairly large, curving structures in the human brain. They go almost all the way around the thalamus, and join up in a fornix, adjacent to the third ventricle. The fornix projects down towards mamillary bodies, which are the part of the hypothalamus. So they do actually touch. --Dr Dima (talk) 23:19, 5 May 2010 (UTC)

Well, they are connected, but I wouldn't say that they touch. Looie496 (talk) 23:37, 5 May 2010 (UTC)

From Grey's anatomy (29th American edition), page 863: "The body of the fornix lies above the tela choroidea and ependymal roof of the third ventricle... Anteriorly, above the interventricular foramina, the body [of the fornix] divides again into the columns or anterior pillars of the fornix. They bend downward, forming an anterior boundary of the interventricular foramina, become buried behind the wall of the third ventricle and end in the mamillary bodies". So they do touch. --Dr Dima (talk) 01:15, 6 May 2010 (UTC)

Yes, the fornix touches the hypothalamus, but the fornix is not usually considered part of the hippocampus. It is a nerve bundle connecting the hippocampus to the hypothalamus and septum. Looie496 (talk) 03:51, 6 May 2010 (UTC)

Sleep before Exams

I feel more sleepy whenever I wish to avoid sleep the night before my exams. Why is that so? 'Interest' matters? - anandh, chennai —Preceding unsigned comment added by 125.21.50.214 (talk) 10:51, 5 May 2010 (UTC)

Perhaps this is because studying at night is more demanding for the brain than going out with your friends at night or watching a movie? Count Iblis (talk) 13:57, 5 May 2010 (UTC)

Wait, wait, waaaiiit! Staying up late the night before an exam is really seriously dumb! It's much more important that you are relaxed and well rested than that you cram facts into a sleep-deprived brain! You won't retain much of what you revise that late at night anyway - and being alert through the exam is critical to your performance. SteveBaker (talk) 18:06, 5 May 2010 (UTC)

Usually, yes. Although if you've just found that you only had access to half the course over the last couple of months, and the exam is in the morning, and you slept the night before, you might consider hours spent cramming outweighed hours sleeping. But usually, yes, it is much better to sleep than do last-minute revision. 86.178.228.18 (talk) 21:07, 5 May 2010 (UTC)

Well, We will speak about last minute preparation and not last minute revision! Why do i feel sleepy when i intend to avoid it? Not just in case of sleeplessness and exams but at many occasions, "I should not do that...Oops, I did that" happens. Something which I wish to avoid is mostly confronted. Why? —Preceding unsigned comment added by 125.21.50.214 (talk) 03:51, 6 May 2010 (UTC)

Inability to delay gratification? Sleep when you're tired is gratification, where as studying is not. If you figure out how to solve this problem, there are probably tens of millions of students who'd like to know it. --Mark PEA (talk) 21:05, 6 May 2010 (UTC)

Plastics & half-life periods

DO all entities have half-life periods? Why do they say that plastics are non-degradable (non-biodegradable)? - anandh, chennai —Preceding unsigned comment added by 125.21.50.214 (talk) 10:56, 5 May 2010 (UTC)

Theoretically, the entire universe has a "half life" in that it itself is degrading (see heat death of the universe). So yes, anything in the universe is, by definition, "temporary" and "degrading". If the half-life of a substance is, say, measured in the millions of years, its going to be here a while. Even though it may be "technically" degrading, on any scale reasonable for human life, it isn't. --Jayron32 13:23, 5 May 2010 (UTC)

Yeah...I once had a comb that said indestructible on it, and I made it my business to destroy it. In your case, perhaps it's supposed to be like a plastic bag in relation to, like, an apple core. The latter will be gone way before the former. DRosenbach ^{(Talk | Contribs)} 17:33, 5 May 2010 (UTC)

Plastics do degrade in sunlight, and you may find that some are slowly degraded by fungi or bacteria over thousands of years.. Also In theory proton decay could destroy all the matter you like. Graeme Bartlett (talk) 22:22, 5 May 2010 (UTC)

Right-hand writing & Left-leg tumbling

It is easy to write/draw (not with pen or pencil) using the right leg for a right-hander/right-hand-writer even though the one has never been exposed to practice for writing using legs. BUT, It is difficult for the same person to use the left leg for writing/drawing (not with pen or pencil). Does the left-brain hemisphere train the right-leg covertly when one practices to write using right-hand? - anandh, chennai. —Preceding unsigned comment added by 125.21.50.214 (talk) 11:08, 5 May 2010 (UTC)

I can't answer your question directly, but suggest that, to the extent that the left side of the brain does exercise preferential control over the opposite side of the body - bearing in mind (Ha!) that theories of brain lateralization have sometimes been exaggerated - the pre-existing brain functions for controlling the right hand to write and draw will be more easily applied to the novel use of the right leg for those tasks than to the left. A brief self-trial seems to indicate that this is true even for someone like myself who is naturally right-handed but also naturally left-footed. 87.81.230.195 (talk) 16:33, 5 May 2010 (UTC)

Can light be heard?

Can light be heard by any creature? What is the essential factors for an organism to 'hear' light? - anandh, chennai —Preceding unsigned comment added by 125.21.50.214 (talk) 11:56, 5 May 2010 (UTC)

Sound is caused by mechanical vibrations in the air, which is detected by an organ (usually in the ear) which is designed to detect those vibrations. See hearing. On the other hand, light is caused by electromagnetic radiation and does not cause mechanical vibrations, so no organ which can be described as a "hearing" organ would be able to detect it. See sight. --Jayron32 13:19, 5 May 2010 (UTC)

In certain ways, yes. When pulses of light at select frequenciecs strikes certain objects, the interaction may cause the object to emit sounds (photoacoustic effect). However you can't really "hear" the sound the the traditional sense of the word. Sjschen (talk) 14:42, 5 May 2010 (UTC)

Another "not really" answer... Some people with brain damage have a side effect of hearing noise when they see certain lights (or seeing light when they hear certain sounds). This is not hearing light. It is brain damage causing signals caused by perceiving light to trigger sensations in the part of the brain that should only be activated by hearing something. -- kainaw™ 14:46, 5 May 2010 (UTC)

Well...it both can and can't be heard...radio waves, microwaves, and I'm assuming visible light (as it's in the same spectrum) can be converted into sound, but cannot be heard outright. Also, some forms of synaesthesia may cause light to be heard, but this is, again, not hearing them in the true sense. Ks0stm ^(T•C•G) 15:11, 5 May 2010 (UTC)

You get on a slippery slope with some of these answers:

• Sound and light are very different things - organs designed to pick up vibrations in the air (our ears) can't pick up electromagnetic waves (which is what light is). So in truth, it's impossible to use an organ of hearing to detect light.
• However, light can sometimes cause sounds - which you could hear. If you attach a sensitive microphone to a tree - then as the sun rises and lights up the leaves, they will start to transpire water and you can hear the flow of that water up the trunk. Are you "hearing light"? Well, not really - you're hearing the consequences of the light.
• But then, our ears don't exactly transmit sound to the brain - they convert the sound waves into the vibration of little hairs which in turn create nerve impulses that are a combination of electrical signals and chemical reactions. In a sense, we aren't really "hearing" the sound - we're hearing the consequences of the sound hitting our ears.
• People who have synesthesia mistakenly interpret one sense as another - so they might get the sensation of sound from light - or vice-versa - but they aren't truly hearing the light. If you blindfold them, so their eyes can't see the light - but leave their ears wide open - then stop "hearing" the light immediately. So this doesn't count.
• There is a demonstration of sound being carried by a laser beam in the Dallas Science museum - but that's not really "hearing light" either because the light has to be converted back into sound by a bunch of electronics.

Short, direct answer: "No". SteveBaker (talk) 18:01, 5 May 2010 (UTC)

A few thoughts on this

• We don't know how bats and dolphins interpret their sonar.
• Some blind people report feeling an object in front of them brushing their face, before they actually touch it; it is believed that they hear the echos from their footfalls, see Human echolocation.
• There has been an experiment with a blind person. They wore a camera, connected to a computer. It scanned the image in horizontal lines, top to bottom. Pixels on each line were converted to a pure sine wave, low frequency to the left, high frequency to the right. The brightness of each pixel. controlled the intensity of each sine wave. Thus a thin vertical line gave a continuous pure tone, a thin horizontal line gave a short burst of white noise, a diagonal line gave either a rising or lowering tone. The subject could recognise simple shapes after a little practise. I'm not sure how successful the experiment was in the long run.

CS Miller (talk) 18:28, 5 May 2010 (UTC)

I'd be inclined to say the answer is just: no. I think it's a primarily semantic question. By definition, "hearing is the sense by which sound is perceived", I'd argue it doesn't matter if you do that with your eyes, visual cortex, or your backside; you hear sound, not light. Synaesthesia is a neurological condition which does "funny" things to perception, if EVERYONE was synesthetic, then our definitions of normal sight and hearing would be different. Vespine (talk) 22:50, 5 May 2010 (UTC)

See Environmental effects of wind power#Bats. Evidently bats are able to detect and avoid microwave transmitters. The mechanism is unknown.

• Aron, Jacob (2009-07-17). "Radar beams could protect bats from wind turbines". The Guardian. Retrieved 2009-07-17.
• Nicholls, Barry; Racey, Paul A. (2007). "Bats Avoid Radar Installations: Could Electromagnetic Fields Deter Bats from Colliding with Wind Turbines?". PLOS ONE. 2 (3): e297. Bibcode:2007PLoSO...2..297N. doi:10.1371/journal.pone.0000297. PMC 1808427. PMID 17372629. {{cite journal}}: Unknown parameter |lay-date= ignored (help); Unknown parameter |lay-source= ignored (help); Unknown parameter |laysummary= ignored (help)

--Teratornis (talk) 00:52, 9 May 2010 (UTC)

Chromate Reactions

The chromates I formed by the reaction of chromium hydroxide with sodium hypochlorite were yellow. When I reacted them with hydrogen peroxide (3%), they immediately turned dark purple-black. After a while, the hydrogen peroxide started sizzling (from catalytic decomposition), and the solution began lightening. It turned into a shade of yellow just darker than the previous one (more purple). I added more hydrogen peroxide and it repeated the reaction. The hydrogen peroxide was not finished up when it turned yellow again, because an addition of sodium hypochlorite made it fizz oxygen gas still. What is the purple-black substance. It is about as dark as solid potassium permanganate. --Chemicalinterest (talk) 11:59, 5 May 2010 (UTC)

Could it be something like or related to Potassium tetraperoxochromate(V) which is red-brown?77.86.70.220 (talk) 12:58, 5 May 2010 (UTC)

or Chromium#Chromium(VI) : "Chromium(VI) compounds in solution can be detected by adding an acidic hydrogen peroxide solution. The unstable dark blue chromium(VI) peroxide (CrO5) is formed, which can be stabilized as an ether adduct CrO5·OR2" 77.86.70.220 (talk) 13:05, 5 May 2010 (UTC)

It could be the chromium peroxide. It was dark blue and decomposed soon. --Chemicalinterest (talk) 13:44, 5 May 2010 (UTC) The formula would be CrO6 though, because the chromium is 6+ and 3 peroxide ions would be 3 O2(2-). --Chemicalinterest (talk) 14:37, 5 May 2010 (UTC)

I did some figuring and got these reactions.

Na₂CrO₄ + 3 H₂O₂ + 2 HCl → CrO₆ + 12 H₂O + 2 NaCl

CrO₆ + 6 NaCl + 2 H₂O → 4 NaOH + Na₂CrO₄ + 3 Cl₂

4 NaOH + 2 CrO₆ → 2 Na₂CrO₄ + 2 H₂O + 3 O₂

Overall reaction:

3 Na₂CrO₄ + 9 H₂O₂ + 6 HCl → 3 Na₂CrO₄ + 12 H₂O + 3 Cl₂ + 3 O₂

As you can see, the Na₂CrO₄ is not consumed. It is a slow acting catalyst for the reaction of H₂O₂ with HCl. They do not react normally. That is why the yellow color comes back after the reaction is over.

Thanks for the information on the chromium peroxide. It helped me figure out what I wrote here. --Chemicalinterest (talk) 14:37, 5 May 2010 (UTC)

What I mean by slow acting is that the intermediate states do not instantly decay, as in an ordinary catalyst. --Chemicalinterest (talk) 14:38, 5 May 2010 (UTC)

If it is CrO5 that would be 2 x O₂^2- (peroxide) and 1 x O^2- (oxide) - that's the often reported structure eg - explaining why it is two peroxide and not three is quite difficult.77.86.70.220 (talk) 15:33, 5 May 2010 (UTC)

So its not a pure peroxide, its chromium peroxide oxide? --Chemicalinterest (talk) 16:32, 5 May 2010 (UTC)

Then I have to refigure my reactions. --Chemicalinterest (talk) 16:33, 5 May 2010 (UTC)

Collagen-proline-triple helix

Might be an old question. Collagen is rich in proline. Collagen is triple helical for which the three strands should be 'tightly' wounded to each other, at the same time, proline distorts the structure (tertiary) of a protein. Paradoxical??? Are prolines present in the periphery of the helical structure? - anandh, chennai —Preceding unsigned comment added by 125.21.50.214 (talk) 12:09, 5 May 2010 (UTC)

The article collagen discusses this, and the picture in the article (unfortunately in French, so you'd have to translate it), this one [12], clearly shows the formation of crosslinking between collagen triple helices. Thus, coupled with the non-standard amino acids present in the chain probably explins the tertiary structure yoy note. --Jayron32 13:14, 5 May 2010 (UTC)

Proline does not disrupt the tertiary structure of a protein - on the contrary, the unique structural properties of prolines can be critical for a protein to fold into its final conformation. And it's not that prolines disrupt all secondary structure. For example a polyproline helix is actually remarkably stable. Proline is thought of as "secondary structure disrupting" because it does disrupt the two most common secondary structures (the alpha helix and the beta strand). -- 140.142.20.229 (talk) 22:48, 5 May 2010 (UTC)

What proline does is force the protein chain to adopt the right amount of twist, thus actually stabilizing the collagen triple helix. Note that the triple helix must also contain hydroxyproline to be adequately stabilized. BTW, the hydroxylation of proline requires vitamin C as a cofactor -- not having any vitamin C in your system weakens your collagen, which is responsible for the symptoms of scurvy. FWiW 67.170.215.166 (talk) 01:12, 6 May 2010 (UTC)

Space random movements vs planets

While every object in space moves in a random manner, how are planets and satellites moving in orbits? - anandh, chennai. —Preceding unsigned comment added by 125.21.50.214 (talk) 12:26, 5 May 2010 (UTC)

Macroscopic objects in space never move in a random manner. Perhaps you are thinking of thermal motion. Macroscopic objects (satellites, planets) are too massive to move in such a random manner, there is insufficient thermal energy available. 157.193.175.207 (talk) 12:37, 5 May 2010 (UTC)

You might want to read Formation and evolution of the Solar System. Dismas|^(talk) 12:55, 5 May 2010 (UTC)

The only force big enough to move large objects like this is gravity. Because gravity is an attraction force that acts as if the source is a point (at the "Center of gravity"), that forces nearby objects into elliptical orbits (strictly, they are conic sections). However, even gravity gets weak at intergalactic scales so you'd expect galaxies to have motion that's all over the place - except that at those colossal scales, the expansion of the universe starts to dominate motion and is seems like everything at those distances are moving directly away from wherever you happen to be. It's only at really small scales (around the size of dust grains, bacteria, stuff like that) where the forces involved are much more complex (electromagnetic, weak and strong nuclear forces) and truly random quantum effects come into play that the motion is truly random. Between those limits, there are some things (like winds and storms and stuff) that are not strictly random - but so complicated that they are "chaotic" (in the mathematical sense) and are therefore unpredictable beyond very short intervals of time...so they might as well be random for all practical purposes. SteveBaker (talk) 17:52, 5 May 2010 (UTC)

Gravity only acts as though from a point-source if the source is a shell (including spheres). At sufficient distance, any object is roughly spherical, so it is actually at large scales that you would expect elliptical (and other conic sectional) orbits. The reason you don't get that is because a conic section is the solution for the 2-body problem. At large distances you usually have to consider more than just two objects, which can result in very complicated motions. Within a cluster of galaxies, they do sometimes move in roughly elliptical orbits. At larger scales it can be difficult to determine the movement beyond current speed and direction (and even that isn't easy) - all paths are approximately straight on a small enough scale, and you don't need a very small scale when you are talking about clusters of galaxies. --Tango (talk) 20:34, 5 May 2010 (UTC)

Grass cuttings

I know stuff about slow and fast baterial decomposition of compost and the like but I have noticed that newly cut grass gets very warm very quick (e.g. in 15C ambient reaching 50C+ in the time it takes to finish mowing the lawn, so say an hour). Whether this cools off quick depends on the heap size, it can stay hotter for a few days. An hour seems very fast for bateria to multiply, is it possible that there is direct oxidation of some of the chemicals in the grass sap on that timescale? It is much more pronounced when (as at this time of year) the grass is fast growing and sappy. --BozMo talk 17:40, 5 May 2010 (UTC)

Are you sure its bacterial growth and not merely absorbing sunlight which is causing the additional heating? --Jayron32 18:25, 5 May 2010 (UTC)

Yes, sunlight causes much heat addition. Probably some oxidation is occurring, but there would need to be large quantities of a strong reducing agent in the phloem of the plant, which I don't hear of. --Chemicalinterest (talk) 18:38, 5 May 2010 (UTC)

There was no sun this afternoon. The grass was cut cold and went hot in a heap in about an hour, possibly two from the first blade cut. The pile of lawn cutting from cutting the lawn once must be at least 200 kg with an incident surface area in the pile of say 4 sq metres. So say 200 kg of grass contains what 100kg of water heated by 0.5C a minute I make about 20kW of heat. Also the heat is much more pronounced from about 10cm deep in the surface, the very surface is losing heat to air and feels about ambient. Not sun. Very fast fermentation of some sort or direct oxidation? --BozMo talk 18:50, 5 May 2010 (UTC)

Could be. Each blade of grass has a cut end and smashed cells of fatty acids, phospholipids, oils and enzymes splashed all over the place. Perhaps it could simply be due to the rapid oxidation of these volatile components taking place, multiplied millions of times. --Aspro (talk) 18:50, 5 May 2010 (UTC)

The O2 isn't present deep in the grass pile though, limiting the amount of oxidation and the heat. It would be used up very quickly (only a little can seep through the grass), limiting the heat output. --Chemicalinterest (talk) 18:59, 5 May 2010 (UTC)

Diffusion and the partial pressure of oxygen will insure will ensure there is no shortage (after all, an anaerobic heap would become black and stagnate -would it not).The smell of cut grass is due to a rapid chemical reaction [13]--Aspro (talk) 19:25, 5 May 2010 (UTC)

Nitrates and sulfates are other potential electron acceptors. You could culture the bacteria on an agar plate to see what type of species you get ... John Riemann Soong (talk) 19:01, 5 May 2010 (UTC)

Bit technical for me culturing something. And is it definitely a bateria not, say, a yeast? Only really smells grassy mind you. But certainly there will be a lot of nitrates. --BozMo talk 19:06, 5 May 2010 (UTC)

If it is oxidising something then I reckon it needs to release about 70MJ for my 200kg pile in an hour say which corresponds to oxidising a bit over a kg of sugar, or 1% of the total weight being an oxidisable mixture. S'pose thats vaguely plausible. --BozMo talk 19:10, 5 May 2010 (UTC)

If it's a yeast, you should see some of the colonies too. Why don't you smash up some of the cuttings and put it in a little bit of water in a test tube (or some sort of small see-through container). Cover the top of the solution with oil to prevent O2 entry. Or have two containers and cover one to see what oxygen presence does. (Seal both.) I'm a bit curious if any gas will evolve. (You could make a homemade gas test... basically any evolved N2, NO2, SO2, H2S etc. will bubble into an overturned glass dome inside the container and show up as a bubble.) John Riemann Soong (talk) 19:10, 5 May 2010 (UTC)

Getting dark here. Might have to wait until the next cut next week. Should I warm the crushed grass in water? Couple of centrimetres thickness of pestled grass? Presumably I don't need to use boiled water because disolved gas will be negligible? --BozMo talk 19:20, 5 May 2010 (UTC)

I don't think you have to warm it. Lukewarm water might do (25C - 37C), but plain tap water will work. I've never done a microbiological experiment in a drinking glass. Basically enough water to make a liquid suspension. We're being really unrigourous about the concentration and skipping buffering the solution, but I'm just curious what type of things will show up.

I wonder if you could also do a pH sample across time. Sample the pH of freshly cut grass, grass in a grass heap after 1h, 4h, 24h, etc. (Use a large sample of cuttings per time period to prevent sampling error). and use the same amount of liquid each time. John Riemann Soong (talk) 19:25, 5 May 2010 (UTC)

I don't think boiled water is necessary. The gas solubility for produced gases will be very low. On the other hand, dissolved O2 in water might retard the growth of any microbes causing the heat. You have a large sample of grass, I assume.

Some species causing the heat, e.g. Pseudomonas can turn a previously yellow/colourless culture a nice green. ;-) John Riemann Soong (talk) 19:27, 5 May 2010 (UTC)

Silage#Fermentation says fermentation takes 48 hours to establish. If that's true the heat might be respiration [14]. For some reason although I googled "grass" first googling "silage" did not immediately occur to me. But I have not found what "respiration" is beyond that it is immediate, heat releasing and uses carbohydrates. --BozMo talk 19:34, 5 May 2010 (UTC)

Note the reference refers to "a potential silo fire" from allowing too much respiration. This all sounds quite plausible now. --BozMo talk 19:37, 5 May 2010 (UTC)

The only issue is the oxygen. Maybe it's microbes using nitrates / sulfates. Fermentation might not be in full swing for 48 hours, but other forms of anaerobic respiration might be used before then. John Riemann Soong (talk) 19:59, 5 May 2010 (UTC)

Interesting. Hmm. I didn't know the browning reaction reduced the amount of available protein. I thought it just made proteins tastier by glycating them to sugars. John Riemann Soong (talk) 20:02, 5 May 2010 (UTC)

The initial heating may not be due to microbes at all but due to the living (about to die) grass. This is metabolising too, and it suddenly has a lot of repair work to do, so there will be a lot of activity in the damaged cells. Graeme Bartlett (talk) 22:13, 5 May 2010 (UTC)

I think there's too much thinking going on here. Did you cut the grass into a bag or was it all raked up afterwards? Given the relatively short amount of time you gave for cutting such a large amount of grass, I've got to think you used a bag. A bag held not too far away from a very hot electric motor or gasoline engine, which in fact probably got hotter and hotter the longer it was run. I'm thinking the grass is hot because the mower is hot; it's just retaining the heat well because the mass of cellulose is good insulator. Matt Deres (talk) 14:00, 6 May 2010 (UTC)

How often do you cut the grass? ;-) Grass in the collector/catcher has always been, as far as I can remember, nice and cool -regardless of the type of mower. By the next morning however, the grass heap is noticeably warm. I can't say I've noticed the same thing when harvesting rows of cauliflowers in the snow.--Aspro (talk) 16:13, 6 May 2010 (UTC)

Yep @Aspro Nope @ Matt. For the benefit of people who don't mow.. the dual fabric grass collection bags on a John Deere 54in mower hang in free air at the rear of the tractor whilst the (diesel) motor is at the front, with exhaust to one side. In between the motor and the bags there is a couple of metres plus a driver. On top of which when I lift off the heavy bags to empty them (say every 15 minutes) they are cool. An hour later the heap is hot. --BozMo talk 00:35, 7 May 2010 (UTC)

(←) I have a compost bin in my back yard made from four discarded wooden pallets tied together. It's roughly a cube five feet on a side. When I add fresh grass cuttings to the bin it gets noticeably hot, although I haven't paid attention to how fast it heats up. I notice the heat the following day when I dig down into the pile a bit to make a hole in which to dump kitchen scraps. Covering the putrescible material such as kitchen scraps with a thick layer of grass or leaves blocks odors and keeps the flies off. I can rule out other sources of heat because I mow with a human-powered reel mower, with no grass bag, and I rake the grass up. By the time I collect the grass, any heat it could have gained from the mowing itself would be dissipated. I also usually mow in the evening when there is little sun. The pile also gets noticeably hotter after a rain, which uniformly wets the upper layer of material that tends to dry out otherwise. Incidentally, Appropedia has some articles about using compost to heat domestic water, and a greenhouse. There is a lot of usable heat from biomass decay that currently gets wasted. If someone wanted to be systematic about this, a compost thermometer would be good to have. I have not bought one yet. I might buy one, if only to reassure myself that I am not risking a compost fire. That is, to check the pile for excessive internal temperature rise, particularly after I add a large amount of fresh material from the autumn leaf drop. --Teratornis (talk) 01:16, 9 May 2010 (UTC)

Copper oxidation

When copper metal is added to a solution of copper(II) nitrate, does the copper(II) nitrate oxidize the copper metal? The silver-potassium nitrate discussion in the reference desk archive is similar. If a small amount of HCl is added to it, does it oxidize it? Thanks. --Chemicalinterest (talk) 18:16, 5 May 2010 (UTC)

If it is of sufficiently low pH, then yes it will. See Standard electrode potential (data page) and find the half reaction for the reduction of nitrate. The reaction requires H⁺ ions, which means that at low enough pH, the nitrate ion will sufficiently oxidize additional copper metal. One could calculate the necessary concentration of H⁺ necessary to do so; converting the E^o for the overall reaction to an equilibrium constant is trivial, and from the equilibrium constant and the concentration of copper nitrate, you can calculate the concentration of H⁺ needed to oxidize additional copper. I suspect you will need a small amount of additional acid, either HCl or H₂SO₄ should be sufficient. You should see the brown NO₂ gas as a product; the counterion of the acid (either chloride or sulfate) effectively replaces the nitrate in the solution as the additonal copper is oxidized. --Jayron32 18:23, 5 May 2010 (UTC)

Does the counterion for the nitrate really matter for the oxidation to work? I assume that existing Cu(II) will tip the equilibrium slightly towards the reverse reaction. Unless the reaction is autocatalytic -- Cu2+ oxidises copper metal? (But two Cu(I) ions I recall, are less stable than Cu(0) and Cu(II). But maybe this represents a good intermediate...) John Riemann Soong (talk) 18:29, 5 May 2010 (UTC)

See above. The Cu(II) is irrelevent, excepting that it will lower the pH of the water by forming complex ions via lewis acid-base reactions. Basically, you will get some Cu(OH)₄^2- complexes in any solution with Cu(II) ions, and thus will also produce an excess of H⁺. I am not certain this excess H⁺ is of sufficient concentration to be useful in the nitrate reduction half-reaction, which is why you probably need a little bit of extra acid. --Jayron32 18:36, 5 May 2010 (UTC)

I don't have any nitrates, but I saw a demonstration of a Daniell cell using copper nitrate and copper electrodes, and I wondered if the copper got oxidized. --Chemicalinterest (talk) 18:41, 5 May 2010 (UTC)

Copper seems to need an acidic environment to oxidize. When copper metal is added to hydrogen peroxide, no black CuO is formed; but when HCl is added, green CuCl₂ solution is formed (green because of HCl prevalence). --Chemicalinterest (talk) 18:43, 5 May 2010 (UTC)

I'm wonder if it's out of a need to have a counterion more than anything. You're generating Cu2+ from Cu(0) -- you're generating OH-, which will accumulate unfavourably. What if you add a weak acid like ammonium chloride or acetic acid? John Riemann Soong (talk) 18:52, 5 May 2010 (UTC)

My possibly incorrect reaction on paper was: Cu(NO₃)₂ + Cu → 2 CuO + 2 NO₂. In this reaction, the OH- as O2- is precipitated from solution. --Chemicalinterest (talk) 18:57, 5 May 2010 (UTC)

I wonder if you can "guide" the reduction to other things, e.g. nitrogen, imines, amines... Also NO doesn't last long by itself in solution. In the presence of oxygen it becomes NO2. John Riemann Soong (talk) 18:59, 5 May 2010 (UTC)

In general yes - adding a reagent that will complex the oxidised copper helps - one v. good example from old A level course if the use of thiourea - it complexes Cu+ strongly enough to allow the reverse disproportionation reaction to happen. For Cu2+ - yes amines et al help - eg Copper and water - fairly non 'rusty' , but copper + water + ammonia - increase rate of corrosion.77.86.70.220 (talk) 19:45, 5 May 2010 (UTC)

I said before that I didn't complete this reaction, so it might not occur. --Chemicalinterest (talk) 19:04, 5 May 2010 (UTC)

No, your reaction is wrong. For the correct reaction, you need to use the correct half-reactions from Standard electrode potential (data page). The relevent half reactions are:

• Cathodic: NO₃⁻(aq) + 2 H⁺ + e⁻ ⇌ NO₂(g) + H₂O
• Anodic: Cu(s) ⇌ Cu²⁺ + 2 e⁻

Now, just balance the electrons by doubling the nitrate half reaction, and combine the two reactions, to get:

• 2 NO₃⁻(aq) + 4 H⁺ + Cu(s) ⇌ 2 NO₂(g) + 2 H₂O + Cu²⁺

Notice that the reaction equilibrium depends on the concentration of H⁺ on the reactant side, so you need a sufficiently low pH to drive the equilibrium to the product side. As I noted above, Cu²⁺ will generate some acid via lewis acid-base reactions with the water; however this is probably not sufficient to make the reaction extensive if you are just adding copper metal to copper nitrate solution. Remember, there is already Cu²⁺ ions present in the solution, so via the common ion effect, the equilibrium is unlikely to move forward. What you need to do is to overcome the common ion effect by adding something additional to the reactant side. Adding more copper metal does no good, since solids do not effect equilibrium, so you need to add either additional nitrate OR additional acid. The acid is easy enough to do, and you could easily figure out for yourself what the maximum pH is to have an extensive reaction by converting the total E^o for the above reaction to an equilibrium constant, and then using your initial concentration of copper(ii) nitrate. If doing that gives you trouble, I can help you with that too. --Jayron32 19:38, 5 May 2010 (UTC)

One of two things ie either Cu2+ or NO3- as the oxidant.

1.

Cu + Cu2+ >>> 2Cu+

This is called Symproportionation (opposite of Disproportionation)

This reaction doesn't happen in water - the reverse reaction does..

The overall reaction doesn't occur in major amounts in water ... but this is mainly due to hydration energy, right? But I wonder if Cu(I) can form intermediates. e.g. Cu + Cu2+ ---> 2 Cu(I) ---> 2 Cu(II). John Riemann Soong (talk) 19:56, 5 May 2010 (UTC)

2.

Cu + NO3- + H+ >>> yes ... products vary can be NO2 , N2 , N2O maybe others.

Jayron already covered this above - it only happens if you add acid (in general enough and strong enough to generate some free nitric acid).77.86.70.220 (talk) 19:45, 5 May 2010 (UTC)

Chromate reduction

What is a good chemical to reduce chromates to Cr₂O₃? --Chemicalinterest (talk) 19:03, 5 May 2010 (UTC)

Just about metal will do. Chromates have a very high standard reduction potential, see Standard electrode potential (data page), Cr₂O₇^2- has a reduction potential of +1.33 volts, more than sufficient to oxidize most any metal. The end product is Cr³⁺, which in a base will precipitate Cr(OH)₃. A hydroxide is just the hydrated oxide, If you heat a hydroxide in a crucible, you can drive off water and generate the oxide, in this case Cr₂O₃. --Jayron32 19:27, 5 May 2010 (UTC)

On the organic side, if you find metals a little expensive, you could try sugar, alcohols (vodka comes to mind), formaldehyde ... Organic reactions might be a little more chaotic though. If you don't care about the identity of what spread of sugar products you might get, e.g. you care only qualitatively about the production of Cr2O3 (or black/brown products from oxidation of sugar), then you're good. John Riemann Soong (talk) 19:35, 5 May 2010 (UTC)

endodermal cell solution

My biology question paper has the following multiple choice question: Four solutions, with different water potentials are listed. 1 endodermal cell solution 2 root hair cell solution 3 soil water solution 4 solution in a xylem vessel Which list has the solutions in order from the highest (least negative) water potential to the lowest (most negative) water potential? highest-----> lowest A 1 2 3 4 B 2 4 1 3 C 3 2 1 4 D 4 1 3 2

Link: http://www.xtremepapers.net/CIE/International%20A%20And%20AS%20Level/9700%20-%20Biology/9700_w08_qp_1.pdf Question no. 23 —Preceding unsigned comment added by 116.71.40.176 (talk) 20:20, 5 May 2010 (UTC)

I cant seem to find anything regarding the endodermal cell solution in either my textbook or the internet. What is it? And what would be the answer to the question? This is not a homework problem, and I have tried it. Thanks. --116.71.40.176 (talk) 20:18, 5 May 2010 (UTC)

heat capacity units and calculation

I find heat capacity units are confusing. (K = kilogram or K for Kelvin?. °K instead of °C.)

I would appreciate if someone would check if I have interpreted and calculated this correctly.

According to this table Heat capacity#Table of specific heat capacities, the heat capacity of water (under constant pressure) at 25 degrees C is 4.18 J/(g·K). Same at 100 degrees C.

Suppose I want to heat water from 25 to 75 °C, at atmospheric pressure

So to heat a gram of water takes 50 x 4.18 = 209 joules.

And to heat a kilogram of water takes 50 x 4.18 x 1000 = 209,000 joules.

And 1 kWh = 3.6 x 10**6 joules. So 1 kWh would heat 3.6 x 10**6 /209000 = about 17 kilograms of water. And 17 kilograms of water is 17 litres.

So to heat a 175 litre tank of water requires just over 10 kWh of energy.

Therefore a water tank that was one cubic meter in volume could be heated from 25 to 75 °C with 1000/175 = 57 kWh of energy. Please is this all correct?

Thank you, Wanderer57 (talk) 21:36, 5 May 2010 (UTC)

According to Google, your calculation is correct, (with a slight rounding error). [15]

Three points, the specific heat capacity of water is slightly dependant on the temperature, the units are normally 4.18 kJ/kg/K (kg is the base unit of mass, but its the same as J/g/K. Lastly K is kelvin, kg is kilogrammes. CS Miller (talk) 22:11, 5 May 2010 (UTC)

... and °K is just wrong. (While Celsius, Fahrenheit and Rankine get degree symbols, Kelvin does not.) -- 140.142.20.229 (talk) 22:42, 5 May 2010 (UTC)

It's wrong now, that is. The kelvin (no capital letter, symbol capital K) was previously called the degree Kelvin (with capital K, symbol °K) just like all the other "degrees" of temperature. It changed in 1968, but some people took a long time to notice. --Anonymous, 01:50 UTC, May 6, 2010.

(edit conflict) :The calculations seem correct, but how many liters (or litres) are in a 1 m³ tank? --Chemicalinterest (talk) 22:15, 5 May 2010 (UTC)

1 liter = 1 cubic decimeter. Since a decimeter is 1/10th of a meter, 1 liter is 1/10^3 = 1/1000 of a cubic meter. --Jayron32 22:25, 5 May 2010 (UTC)

Electric spacecraft drives

Why do Variable Specific Impulse Magnetoplasma Rocket drives have the ability to get spacecraft around the solar system better than Ion thrusters? The articles go on about the workings of each, but the main advantage claimed in the VASIMR article is less electrode erosion. Is that really the basis for the recent wild hype about VASIMR that it could get astronauts to Mars in 45 days? If they were both operated for the same burn duration in spacecraft of similar mass, would the VASIMR drive produce greater acceleration? Edison (talk) 23:45, 5 May 2010 (UTC)

Both Ion drives and VSIMR deliver varying amounts of force. So I can't answer your last question. Obviously if the force, mass, and burn duration are the same the two will do the same. But I think Ion drives have reached their limit for force, but VSIMR is just getting started. To increase the force on the ion drives lowers the lifespan of the electrode too much. But VSIMR can still be scaled up to even higher power levels. (i.e. ion drives topped out at 200Kw, while VSIMR started at 200Kw.) Ariel. (talk) 07:18, 6 May 2010 (UTC)

Ion drives I remember reading about had negligible thrust, .01 Newton or the weight of a sheet of paper on Earth, but could continue it for a very long time. The VASIMR article implies far more thrust, like 5 Newtons or more. Is the mass of the propulsion unit similar, or is it proportionately greater, mostly cancelling the advantage? Edison (talk) 19:17, 6 May 2010 (UTC)

Don't forget, in an ion drive the gas is ionized and accelerated using electrostatic feilds, in Vasimr it is ionized, super heated, then accelerated. The gas is much more energetic in a vasimr, boncing around much faster providing more power. —Preceding unsigned comment added by 74.67.89.61 (talk) 22:12, 7 May 2010 (UTC)

May 6

epson salts

how come the epson salts article dosent explain how it helps sore joints. —Preceding unsigned comment added by Tom12350 (talk • contribs) 00:57, 6 May 2010 (UTC)

It's sort of mentioned in the talk page... Maybe it's because no one can find a good reliable source to make it worth including? Vespine (talk) 06:20, 6 May 2010 (UTC)

Perhaps because it does not generally help sore joints. I know it's personal research but I have never heard that Epsom salts relieves sore joints. However if you have a reliable source for that claim then you might consider adding it to the article. Be bold! Caesar's Daddy (talk) 06:21, 6 May 2010 (UTC)

They're a fairly standard ingredient for many bath salts - which are the standard home remedy for sore joints. http://www.google.co.uk/search?q=epsom+salts+sore+joints&hl=en&start=0&sa=N

The epsom salt council suggests that it is magnesium that is effective. http://www.epsomsaltcouncil.org/about_better_health_through_soaking.htm 77.86.68.186 (talk) 17:01, 6 May 2010 (UTC)

Is that source to be trusted, though? I've read that it is not very effective. 67.243.7.245 (talk) 19:16, 6 May 2010 (UTC)

Could be a placebo effect - there's a vast amount of people claiming they are good though. Who knows? It's an unwanted product of the chemical industry.. Conspiracy theory perhaps??77.86.68.186 (talk) 21:03, 6 May 2010 (UTC)

I could certainly believe that soaking in warm water could help - relaxing the muscles - taking the weight off the joint and allow neutral bouyancy to support the limb, calming and mentally relaxing the patient because while in the bath they aren't being hassled by the perils of daily life. So it wouldn't surprise me if the whole business of using epsom salts had nothing whatever to do with it! If this hypothesis is correct then people will doubtless claim that soaking in an epsom salt bath helps their ailment - not realising that it's the bath - not the salts - that's really doing the job. Without a proper double-blind trial, I don't think we could say for sure...but the idea that magnesium salts migrate through our skins (which are pretty water-tight stuff!) through layers of fat and muscle to reach the knee - and then somehow acts to help the pain without all sorts of dangerous chemical imbalance side-effects - is one hell of a stretch! SteveBaker (talk) 01:59, 7 May 2010 (UTC)

There's a study here http://www.epsomsaltcouncil.org/articles/Report_on_Absorption_of_magnesium_sulfate.pdf

If you don't like the idea - how about a Magnesium salt lick , or just eat your greens :)

77.86.68.186 (talk) 11:01, 7 May 2010 (UTC)

That is one seriously flawed study!

1. It was funded by the "Epsom Salt Council" who are hardly an unbiassed source of information.
2. They only used 19 test subjects. That's not a good enough statistical sample.
3. Their test subjects were all young and healthy without joint problems. Is it not possible (if magnesium is indeed implicated in joint pain) that the entire reason older and less healthy individuals suffer joint pain is because whatever mechanism for magnesium uptake is responsible for the rises measured in this experiment is broken? That would completely invalidate the entire set of conclusions.
4. Their findings for one or two baths are less than their error bars and only after weeks of this treatment did they get an actual, measurable effect. An occasional bath in this stuff is useless - even by their own evidence. Do they tell people to bath in the stuff for weeks at a time? No.
5. They did no placebo controls and their "control" experiments are not explained. That's a huge "no-no".
6. The experiment was not done 'blind' - much less 'double-blind' - so some kind of placebo effect is a possibility here.
7. The amount of Epsom salts they needed to use to produce a measurable effect were over half a kilogram per bath! So two or three bottles of the pretty scented stuff you can buy in big glass jars or ten packets of the stuff you buy in a boring cardboard box at the supermarket in each bath - for weeks and weeks! Their main web page says to use two cupfulls per bath - which is below the level that this study says has any measurable effect! So one major conclusion should be "In normal amounts, Epsom salts have no measurable effect on magnesium levels in the blood of young, healthy individuals even after two weeks of use".
8. The "paper" hasn't been peer-reviewed, the experimental results have not been duplicated and no major scientific journal has published the study. They have not released the raw data for other people to analyse with their own statistical tools. So it's clearly not acceptable science yet.
9. Then we have to ask how long the stuff stays in the blood and whether increased magnesium levels in the blood is even any good for you in the first place! Their own article points out that the body normally carefully regulates magnesium levels in the blood - there is probably a very good reason our bodies do that!
10. They explain that the test subjects found bathing in the required high concentrations of epsom salts to be unpleasant. What happened to the "warm relaxing bath" thing?
11. They conclude "Bathing in Epsom salts is a safe and easy way to increase sulfate and magnesium levels in the body" - but none of those conclusions are actually found in the body of the paper. Where did they follow the subsequent health of these volunteers? Maybe they all dropped dead right after the study - or will have long-term health problems as a consequence.

This is a classic example of "junk science" and it should be ignored. SteveBaker (talk) 14:42, 7 May 2010 (UTC)

Curvature of the earth

Not a big deal, but I was wondering just now if it is known how much a certain area of earth's surface (assuming a perfectly flat area) is curved. Is there any measurable curvature within, say a mile? –Juliancolton | ^Talk 01:19, 6 May 2010 (UTC)

Divide the number of miles in the circumference, about 24000, into 360°. This will tell you how many miles it takes to produce one degree of curvature. --Chemicalinterest (talk) 01:29, 6 May 2010 (UTC)

That makes sense. Thanks! –Juliancolton | ^Talk 01:39, 6 May 2010 (UTC)

Not quite. That assumes the Earth is perfectly spherical, but it is actually a bit of a flattened sphere. Over a small distance like a mile, this imperfection can be discounted, but on a large scale it has to be considered. 76.199.153.83 (talk) 01:49, 6 May 2010 (UTC)

Not quite. If you wish to take flattening of the ellipsoid into account, then variations in distance per unit curvature as a function of latitude is as (or slightly more) noticeable for small distances then it is for large distances. 58.147.58.122 (talk) 15:50, 6 May 2010 (UTC)

Yes. The earth's diameter is about 24 miles bigger at the equator than from pole to pole because of centrifrugal force. --Chemicalinterest (talk) 15:40, 6 May 2010 (UTC)

Look at a map of one of the plains states in the US, like North Dakota or Nebraska, and you will see lots of places where a road, or a series of successive county boundaries, forms a straight north-south line that jogs to the west every so often as you go north. In Canada the boundary between Manitoba and Saskatchewan is an even better example, having the same sort of shape for hundreds of miles with no further irregularities. The reason for this is that both the Public Land Survey System in the US and the Dominion Land Survey System in Canada were based on dividing the land into squares with specific sizes -- squares whose boundaries run north-south and east-west. For example, a 1-mile square on this system was called a section.

But of course that's impossible on a curved planet. The way it was really done was that they made the shapes almost square, with true north-south sides, running north and/or south from an east-west baseline until they got too far from the desired size; then they jogged all the boundaries to one side (by an amount that depended on how far they were from a principal meridian) and continued north or south from there. So for example each of the stairstep points in the Saskatchewan-Manitoba border is the same distance west of a principal meridian that runs north and south more or less through Winnipeg. The jogs in this case are about 24 miles apart. Look at a map of Manitoba and you can see how much the curvature of the Earth affects things. --Anonymous, 02:15 UTC, May 6, 2010.

To really get a gut feel for it - imagine you're standing on the end of a long, straight, "flat" road (we have to put "flat" in quotes - because it follows the earth's curvature). Over the distance between where you're standing and where the horizon is - the difference between a 'flat earth' and the real curved earth is exactly the height of your eyes from the ground. Within a mile, this "curvature" distance is about 8 inches...which is quite measurable. It gets bigger fast though! Within 3 miles, it's about 6 feet of curvature...which is why (if you happen to be a little over 6' tall) the horizon is about 3 miles away on dead flat, level ground. SteveBaker (talk) 03:18, 6 May 2010 (UTC)

Pages 774-779 of an old science book from 1887 give an approchable understanding of the Earth's curvature. If the diameter is 8000 miles, then in 1 mile there is 8 inches of curvature. The "drop" increase more than 8 inches in the 2nd mile,to 32 inches, and to 72 inches at 3 miles, and 128 inches at 4 miles, 66 feet at 10 miles. Observers watching a ship see it go "hull down" with only the mast or superstructure visible, through a telescope, when it is several miles away. One old source claims "optical depression" of only 6 inches in the first mile at sea, with similar geometric increases in dip per mile. Only the top of a tall hill or mountain will be visible from a distance. If you note the setting of the sun from the ground floor of a skyscraper, then ride the elevator to the top floor, you might see it once again partly above the horizon. Edison (talk) 03:38, 6 May 2010 (UTC)

Another example of this effect is to look at a city skyline from across a wide body of water; if you're familiar with the relative heights of the different buildings, you can tell that their bottoms are missing. I have noticed this when riding toward Hamilton over the Garden City Skyway on a day when the air was clear, and observing the Toronto skyline across part of Lake Ontario. --Anonymous, 04:20 UTC, May 6, 2010.

Fascinating stuff. Please excuse my stupidity - why are the "drop" numbers not increasing at a constant rate? Steve said '"It gets bigger fast, though!"' -- why? 218.25.32.210 (talk) 05:46, 6 May 2010 (UTC)

Think of a ball. Put your finger on the center top. Move it sideways and watch as it also moves down. At the beginning it moves down slowly, but as you get closer to the edge it moves down faster and faster. Ariel. (talk) 07:10, 6 May 2010 (UTC)

Ahhh... most helpful! I see now that the constant rate drop I was expecting would mean I was standing on a planar surface - such as the hypotenuse of a triangle (if imagined in 2D). Thank you! 218.25.32.210 (talk) 07:54, 6 May 2010 (UTC)

Civil engineering surveyors also notice on very large man made structures such as the Humber Bridge ”The towers, although both vertical, are not parallel, being 36 millimetres (1.4 in) farther apart at the top than the bottom as a result of the curvature of the earth.”--Aspro (talk) 11:28, 6 May 2010 (UTC)

Thanks for the responses; Steve's explanation is particularly enlightening. –Juliancolton | ^Talk 18:41, 6 May 2010 (UTC)

Some of the old books say the curvature can be noted in the plains of the US, but when I am driving on a long straight highway and see things behind falling below the horizon, I always figure it could be due to rising and falling terrain. As a child I saw a book showing a man watching through a telescope as a ship sailed out of sight, gradually disappearing below the water, and wondered how he knew the ship was disappearing over the horizon and not simply sinking. Edison (talk) 19:13, 6 May 2010 (UTC)

Well, the idea is that you look for ships that are sailing towards you - then, when they reach land you can ask them whether they were miraculously recovered from sinking or merely hiding behind the planet! :-) The ocean (or, better still, a nice calm lake to avoid big waves getting in the way) is a better place for testing these ideas than on land because you can be sure that there aren't any hills worth mentioning! SteveBaker (talk) 01:50, 7 May 2010 (UTC)

"How do you know it's not sinking?" Maybe it is! When the Titanic was sinking, there was actually another ship within sight, the Californian, which had stopped for the night due to the ice hazard. Its radioman had already gone to bed when the Titanic hit the iceberg, but its crewmen saw the Titanic's distress rockets. However, its captain said, in effect, "Well, maybe they're not distress rockets," and decided to do nothing. When the Titanic could no longer be seen, they didn't know it had sunk, because it could have just sailed away. They found out what had happened when the radioman got up. (At least, this is the most widely accepted version of the story, but it certainly has been disputed. Wikipedia has something at RMS Titanic#SS Californian inquiry and SS Californian#Captain Stanley Lord and other places.) --Anonymous, 06:37 UTC, May 7, 2010.

can Blue cheese produce penicillin?

Just curious. If the cheese could produce penicillin then it might be bad to those that are allergic to penicillin. --121.54.2.188 (talk) 05:20, 6 May 2010 (UTC)

I'll leave it to a biologist rather than speculate, but I can link you to Penicillium roqueforti, the fungus used in the making of blue cheese; Penicillium, our article on the whole genus; and this Straight Dope column from 2004, which claims that "most cheeses contain relatively small levels of antibiotic mold relative to that found in concentrated pharmaceuticals". Comet Tuttle (talk) 06:47, 6 May 2010 (UTC)

Nobody has mentioned the traditional folk medical practice of using mouldy bread or grain in poultices. Bread supports some penicillium varieties. The practice of using mould has been recorded way back, including of course -mouldy cheese. Moulds in folk medicine--Aspro (talk) 17:30, 6 May 2010 (UTC)

inverse square law and electromagnetic force

If the distance between two positively charged nuclei is halved, the inverse square (of Newton's law of gravity) says that the gravitational force will increase (by a factor of four) (i.e. become more positive/stronger) and the inverse square (of Coulomb's law) says that the electrical force will decrease (also by a factor of four) (i.e. become more positive/weaker). Is this correct? I am having trouble with the semantics of saying that something (electrical force) which becomes more positive is actually decreasing in force/strength. This also doesn't seem to fit with my (fairly poor) understanding of magnets, whereby the force required to bring two repelling magnets together seems to increase (my numbers aren't bearing this out?).

The more I think about it, the more it appears illogical that a decrease in separation also equals a decrease in the net force. But my head gets so screwed up with these negative numbers. I've done the calculations for the original distance and the halved distance, and my net force has moved from a –x10^-27 to a –x10^-26. Can that be right?

Does this mean the electric force can eventually become a net positive? Why do I think this should all be working the other way around? Any tidbits, filling in the gaps, overviews, corrections, numbers, calculations, examples, etc very welcome. Thank you. Differentially (talk) 06:48, 6 May 2010 (UTC)

Thanks to Ariel for an answer, but I've just finally realised that –x10^-27 is a smaller repulsive force than –x10^-26. As soon as it's that way around, it makes sense! Differentially (talk) 08:19, 6 May 2010 (UTC)

Force is not positive or negative. Force is force, and it has a direction (it's a vector, not a scalar). A negative force is a positive force pointing in the other direction. Don't think of negative forces, just think of the direction of the force. Ariel. (talk) 07:08, 6 May 2010 (UTC)

Who's on first? ("Extraterrestrial life(forms)") (done)

Greetings Earthlings! The article Extraterrestrial life mentions people and schools who thought first about life beyond earth but there is no informationen who coined (used for the first time) the English expression "Extraterrestrial life(forms)". So - please no Greek, no other language - who (which book, which article) used this term first? I do not know the answer myself, but I have a bet going on, that it was rather a literary person than a person of science. Am I right? I appreciate any clues (going back in time). Grey Geezer 07:36, 6 May 2010 (UTC) —Preceding unsigned comment added by Grey Geezer (talk • contribs)

This would probably do better in the language reference desk, but I found this published 1870. And this in 1854. Yet this claims 1868, which is clearly wrong. I think you won't find a definitive answer. Google scanning books has actually caused a revolution in etymology finding much earlier uses that were currently known for many many words. Edit: Even earlier 1848 Ariel. (talk) 09:06, 6 May 2010 (UTC)

I searched GB before and got unsatisfactory results. It is the combination of life and extraterrestrial. I think I will move to "Languages". Thanks! Grey Geezer 12:03, 6 May 2010 (UTC)

Google Books is absolutely unreliable in their claimed publication dates, since their system may report the first date found in a work. If it is the 2010 volume from some organization founded in 1660, it usually cites the publication as being from 1660, so it is essential to page back to the title page or equivalent to determine the publication date. They do not even have a channel for reporting incorrect date attribution. Edison (talk) 19:21, 6 May 2010 (UTC)

Mathematics of Kepler's laws

Hi,

I have the following comments about the mathematics of Kepler's laws.In this concern the original paragraphs were edited as follows: Please let me appreciate your editing for this article.Thanks.

TASDELEN's arugments for why Kepler's Laws are wrong

Kepler’s laws are wrong. Kepler’s laws do not explain why the celestial bodies cycle around a barycenter, while Newton’s mechanical laws explain this cycling and give the shape of the orbits. General When two bodies are in the empty universe (even n-body in a system) m1*r1=m2*r2 where (r1+r2)=d F=G*m1*m2/d^2 means F*d^2=Ct (this is an hyperbola on Cartesian) Transporting the axes, we write: (f+f0)*(d^2+do^2)=Ct When f=0 dmax^2=(Ct/f0-d0^2) and then the attraction force=centrifugal force So, dmax has a limited, fixed value. Also the barycenter is fixed. First law: The orbits are not elliptical. Why the bodies cycle around a barycenter? Consider the velocities of the bodies in the attraction field V^2=Vp^2+Vr^2 where Vr is the radial velocity and Vp is the tangential (perpendicular) velocity Consider Newton’s law F=G*m1*m2/d^2.We write F=G*m1*m2/d^2=m1*Vp1^2/d=m2*Vp2^2/d then, m1*Vp1^2=m2*Vp2^2 where (d) is eliminated. For the equilibrium of the bodies in motion we see that: Vp1 and Vp2 should exist. This explains the cycling around a barycenter. How looks the shape of this cycling? Consider Newton’s F*dt=m*dv.This is, F*r*dt=m*r*dv (energy conservation equation), then we write 1/2*m*Vr^2+m*gr*r+1/2*I*w^2=m*r*dVr (total energy with g variable) This is a differential equation dr^2+K*dt^2=2*r*d(dr) with solution r=-a*t*(t*tmax)+K where K=2*gr*r+I*w^2/m=-a^2*tmax^2/(1+4*a) On Cartesian, the graph of (r) is a parabola. On Polar this graph is a cardioidal looking spiral: billions of spirals. Expanding then after compressing; with a max.point, only one max.point. Located on a paraboloid surface along the orbit of the Sun in its galaxy.(our Milky Way) This is the shape of the orbits. No sign of ellipse, no sign of aphelion, no sign of perihelion. See the spirals on Nasa’s galaxies photos. The barycenter is not at one focus of an ellipse. Second law: the areas swept out in equal time are not equal Kepler says the Vp velocities are variable, the areal velocities are constant. No.Vp velocities are constant since the existence of the body. This is an innate velocity. Consider the mass m1,and the velocities Vp11,Vp12,…Vp1n for different values of r1: From V^2=Vr^2+Vp^2 we write V11^2+Vp11^2+2*g11*r11=Ct (energy conservation). (I*w^2 is invariable, is innate) V11^2+Vp11^2+2*g11*r11=V1n^2+Vp1n^2+2*g1n*r1n=Ct In an attraction field, Vp doesn’t matter. So, Vr11^2+2*g11*r11=Vr1n^2+2*g1n*r1n (energy conservation, with g variable),therefore Vp11=Vp12=Vp13…..=Vp1n= Ct That is to say: Vp at dmax has the same value as at d0: invariable until the body reaches to the barycenter. Same reasoning for m2. Third law: periods (P1/P2)^2=(r1/r2)^3 is correct. In 1609 Kepler said, orbits are elliptical. Then in 1618 he gave the law of periods. But this last law is valid only and only when the orbits are circular. How Keplerian solid elliptical orbits could be transformed to circular orbit according this law of periods? Simply the orbits were not elliptical. Kepler himself has pronounced his orbital reasoning change with this period’s law: the actual orbits were not elliptical but another shape which could reach to circular orbits. These are spiraled orbits. Sun near the barycenter, no elliptical focus, no closest farthest point in one cycle of the body around the Sun, no aphelion, no perihelion, no equality of swept out areas.

TASDELEN (talk) 17:47, 8 May 2010 (UTC)=== Consequences: ===

As (r) is variable in the spiraled orbits theory:

P^2/r^2 =Ct is no more valid. It is variable

If today 1 year=365 days, billion years ago it was for example 15 days.

Light-year distance has no sense. Years have different quantity of days.

Light-day or 1000 LD has a meaning, since I*w^2 is constant, is innate.

Newton do not confirm Kepler as say the mathematicians.Etc,…TASDELEN (talk) 08:34, 6 May 2010 (UTC)

I've taken the liberty of reformatting your post and adding a collapse section so it doesn't take up a large portion of the page.

To be blunt, almost every bit of mathematics you try to derive above is wrong. Kepler's Laws are a strict mathematical consequence of Newton's Law of Gravitation when one has only two point masses. A complete derivation is given in the article at Kepler's laws#Derivation from Newton's laws, though I don't really expect that you will be able to follow it. Dragons flight (talk) 09:16, 6 May 2010 (UTC)

Without doubt, TASDELEN's mathematics are incorrect. Probably the first issue I spot is his first line, an equation for what appears to be a ... moment of inertia, or something ... but does not define distance from any particular location (presumably he meant to specify the center of mass, but critical steps are missing and/or rely on erroneous, unstated assumptions). The next line introduces a value, Ct, without explanation or justification. These sorts of skips and jumps are not permissible in a proper physics derivation. For a correct version of these derivations see our article on the two-body problem, specifically how to reduce it to a 1-body problem. Once you have mastered these equations, which are indisputably correct and have been verified by thousands of mathematicians and physicists during the last four centuries, you may be able to expand the theory; but the current work you have presented above is full of physics and mathematical error. Nimur (talk) 15:01, 6 May 2010 (UTC)

I agree - I'm sorry but what you've presented above is wrong - both physics-wise and mathematically. You can't just make stuff up - that's not how science works! If you attempted to add this to the article, it would be reverted instantly. Heck - I'll personally revert it if you did that!

But it doesn't actually matter whether your ideas are right or wrong. We simply don't write Wikipedia by having clever, original ideas and writing articles about them - that's just not how Wikipedia operates. In fact, we have a specific rule: No Original Research which actively prohibits you from writing about your own ideas...right or wrong. Instead, we have to write about things for which solid, reliable outside references can be found. Third party, peer-reviewed scientific papers, published in reputable journals are required for science articles like this one. So if you look at the bottom of the Kepler's laws article - you'll see all of the learned scientific papers that were referred to when writing that article.

So to get your ideas into Wikipedia - you'd first have to write this up as a formal scientific paper. Then you'd need to present your paper for publication at (let's say) "The Journal of Celestial Mechanics and Dynamical Astronomy" (that's a real journal by the way). They would examine your paper, have several other celestial mechanics experts read it - and only if they agreed with your findings and found the math plausible - would they allow it to be published. That's called "peer review" and it's a tough test to pass. If you did get published - then it would be appropriate to go to the talk page of the Kepler's Laws article and suggest a revision to include these new findings - along with a proper link to your article in the journal.

But the problem with doing that is that your math and science are hopelessly, naively, catastrophically wrong! (I'm sorry - but there is no polite way to express just how wrong it truly is!) Hence, the journal of celestial mechanics are going to write you a polite letter telling you in no uncertain terms that your paper is worthless and they won't publish it. That means that Wikipedians couldn't write about it - even if we agreed that the guys at that journal were clueless and you were the next Einstein (which we don't!).

So, no - there is no possibility whatever of your change being kept in the Kepler's laws article - or anyplace else in Wikipedia for that matter.

If you are unconvinced by what I say - please read WP:FRINGE - which covers how we handle these kinds of 'fringe theory'.

SteveBaker (talk) 15:19, 6 May 2010 (UTC)

Hi,

Many thanks for the comments.Dear commentors:

Dragons flight (talk) 09:16, 6 May 2010 (UTC)

Nimur (talk) 15:01, 6 May 2010 (UTC)

SteveBaker (talk) 15:19, 6 May 2010 (UTC)

“…almost every bit of mathematics you try to derive above is wrong. Kepler's Laws are a strict mathematical consequence of Newton's……”

If I say 2*2=7, then you say “No.You are wrong; 2*2=4”. So, you prove that I am wrong. Otherwise I must ask you “where is the wrong point ?”.Please, show me the wrong point of my mathematics.

“…Derivation from Newton's laws, though I don't really expect that you will be able to follow it.”

Thanks for the compliment. Really I am unable to follow this. This why, I have to repeat my Newton’s derivation so that you can point out the wrong expressions. I think you are mathematicians, dealing with physics, or astronomer. I am a mechanic, diesel engine repairer.

Newton’s F=G*M*m/d^2

is explaining,why the masses have to orbit around their barycenter. Vpm and VpM (the perpendicular velocities to the attraction direction) should EXIST for cycling. In fact F=G*M*m/d^2= m*Vpm^2/d= M*VpM^2/d, that is Attraction Force = Centrifugal force: m*Vpm^2=M*VpM^2, So the cycling is a MUST, due to these velocities.

Newton’s F*dt=m*dv gives

the shape of the orbits: Consider F*r*dt=m*r*dv

F*r*dt is the energy conservation expression’s left side .This is

F*r*dt=1/2*m*Vr^2+m*gr*r+1/2*I*w^2 (total energy, where Vr is the radial velocity).Then

1/2*m*Vr^2+m*gr*r+1/2*I*w^2=m*r*dv (we assume g variable,gr)

Vr=dr/dt and dVr= d(dr/dt)/dt

1/2*m*(dr/dt)^2+m*gr*r+1/2*I/w^2=m*r*d(dr/dt)/dt simplifiying

(dr)^2+ K*dt^2=2*r*d(dr) a differential equation, with solution

r=-a*t*(t*tmax)+K where K=2*gr*r+I*w^2/m=-a^2*tmax^2/(1+4*a)

On Cartesian, the graph of (r) is a parabola. On Polar, this graph is a cardioidal looking spiral: billions of spirals. No sign of ellipse! And this is due to Newton’s laws. Please edit and show the wrong points, before saying “…almost every bit of mathematics you try to derive above is wrong. Kepler's Laws are a strict mathematical consequence of Newton's……”

When speaking of areas

and considering the mass m, the total energy of the body is constant due to energy conservation law of Newton. That is:

Assuming V^2=Vr^2+Vp^2 (radial and perpendicular components of the velocity V)

1/2*m*Vr1^2+1/2*m*Vp1^2+m*g1*r1+1/2*I*w1^2=Constant=C1 (conservation)

1/2*m*Vrn^2+1/2*m*Vpn^2+m*gn*rn+1/2*I*wn^2=Constant=C1 (conservation)

1/2*I*w1^2=1/2*I*wn^2 ( as innate=nothing added to the mass,no modification of w)

In an attraction field a work is done ONLY in the direction of attraction. So,

1/2*m*Vr1^2+m*g1*r1=1/2*m*Vrn^2+m*gn*rn , then

Vp1=Vpn=Constant =C2

That is:

Vp perpendicular, to Vr, is constant at every level of the distance (r).Vr is variable.

When Vp is constant (that is the Vx in Cartesian) no equality of swept out areas in equal interval of time.So, what about Newton’s confirmation of the old mathematicians? Is this is a correct confirmation or a tricky confirmation? Have you controlled this confirmation yourself or just copy-pasted the confirmation of the old mathemeticians? Try it yourself.

“Once you have mastered these equations, which are indisputably correct and have been verified by thousands of mathematicians and physicists during the last four centuries, you may be able to expand the theory; but the current work you have presented above is full of physics and mathematical error.” Where are this errors?

I know it is difficult

to change the perception of the community with such contradictory arguments.And no one of the Keplerian religion will agree with these last Newtonian religion.

“Third party, peer-reviewed scientific papers, published in reputable journals are required for science articles like this one. So if you look at the bottom of the Kepler's laws article - you'll see all of the learned scientific papers that were referred to when writing that article.”

This is not

a scientific article.I do not know how to design a scientific article.I am sure Peer-reviewers will prefer to keep their position in Keplerian religion.But if you start to believe to my mathematics,then someone should help me write a scientific version of my evaluations.

Regards.TASDELEN (talk) 17:47, 8 May 2010 (UTC)

I did read much of your derivation, so I'll just point out the first couple of mistakes. First, you said that the gravitational attraction is equal to centripetal force (actually, you said centrifugal force, but you meant centripetal) - that is only true for circular orbits where d is constant. In general (and in reality) Keplerian orbits are non-circular ellipses. Second, you said "F*r*dt=1/2*m*Vr^2+m*gr*r+1/2*I*w^2". That equation has to be wrong because one side has a differential in it and the other doesn't - every term needs to be of the same order for it to make sense. You clearly don't understand differentials, so I suggest you avoid them. They are very confusing and completely unnecessary for this. Stick to derivatives (ie. don't say F*dt=m*dv, say F=m*dv/dt). --Tango (talk) 18:20, 8 May 2010 (UTC)

living species which appear to have stopped evolving

Is their a list of species such as sharks, crocodiles, palmetto bugs and ants which are not extinct but which appear to have evolving or which appear to have reached an apex of evolution, excluding my neighbor Billy Bob? :-} 71.100.0.29 (talk) 09:55, 6 May 2010 (UTC)

There is no such concept as "apex of evolution", evolution doesn't work that way. Living fossil may be of interest. How can you tell if an animal "stopped evolving" without being able to predict the future? Ariel. (talk) 09:59, 6 May 2010 (UTC)

Silly person. Because you do not need to predict the future to answer the question since the question only concerns itself with the present and the past. In fact even if you have a crystal ball I'm not interested in what it shows you. 11:45, 6 May 2010 (UTC) —Preceding unsigned comment added by 71.100.0.29 (talk)

The closest sensible version of the question might be: What species appear to have changed the least in the last 100 million years? Is that what you are asking? alteripse (talk) 10:33, 6 May 2010 (UTC)

It could simply be that they fill their ecological niche so well. Their present morphology is undoubtedly successful at preventing other species from taking over due to Competitive exclusion.--Aspro (talk) 10:41, 6 May 2010 (UTC)

Exactly. If the environment doesn't change, then the species won't change either. That's why Australian species have been preserved unchanged for so long: there were no changes in the enviromental condition, and there was no external influences that changed them (like new species that migrated from a different environment). Then the European arrived to Australia and introduced new species (rats and rabbits, among other), and existing species had to change or die. --Enric Naval (talk) 11:02, 6 May 2010 (UTC)

"That's why Australian species have been preserved unchanged for so long" . Who says they were unchanged? Do you have any evidence that the rate of speciation in Australia was markedly different than similar areas? Australian species are different because they evolved independently for a very long time, but on average they most definitely evolved. It just happened that evolution often took different paths than in other parts of the world. Even in the absence of migration the continent has still experienced large climate shifts (along with the rest of the globe) since it became an isolated island, and that is plenty of impetus for evolution. And even in the absence of external pressure genetic mutations still sometimes create new traits that are so successful they can disrupt established ecosystems anyway. Dragons flight (talk) 11:52, 6 May 2010 (UTC)

(edit conflict) Minor correction - it is probable that humans had a major impact on the Australian environment well before the arrival of Europeans - see our article on Australian megafauna. More significant correction - the engine room of evloution is random mutation, and there is no reason why this should stop or slow down just because a species has filled a comfortable niche in a stable environment. Even in a stable environment, species will tend to differentiate and specialise. Gandalf61 (talk) 11:57, 6 May 2010 (UTC)

100 million years is an exceptionally long time. Almost no species last that long. Either they die out entirely, or they evolve sufficiently new traits that they come to be labeled as a new species. The typical duration of a species level taxon is only a few million years. Higher level categories like families and classes are more robust, but individual species are usually ephemeral. Probably less than 1% of species would be expected to persist for 100 million years. Dragons flight (talk) 11:52, 6 May 2010 (UTC)

So if the environment is really changing then you are likely to see a reflection of those changes if species that have stopped evolving all of the sudden begen to change again. geez. 71.100.0.29 (talk) 11:49, 6 May 2010 (UTC)

You can't tell if a species stopped evolving, because you don't know what it will do in the future. Living fossil is probably the best answer available for your question. Ariel. (talk) 12:02, 6 May 2010 (UTC)

Reading some of the examples should also help. An example I like to use is the tuatara. As our article notes:

Tuatara have been referred to as living fossils,[2] which means their group retains many basal characteristics from around the time of the squamate - rhynchocephalian split (220 MYA).[19] However, taxonomic work[20] on Sphenodontia has shown that this group has undergone a variety of changes throughout the Mesozoic, and a recent molecular study showed that their rate of molecular evolution is faster than of any other animal so far examined.[21][22] Many of the niches occupied by lizards today were then held by sphenodontians. There was even a successful group of aquatic sphenodontians known as pleurosaurs, which differed markedly from living tuatara. Tuatara show cold weather adaptations that allow them to thrive on the islands of New Zealand; these adaptations may be unique to tuatara since their sphenodontian ancestors lived in the much warmer climates of the Mesozoic.

Although as a caveat to the rate of evolution I'll add [16] [17] [18] [19] [20].

Another interesting example is the case of the Wollemia (of which the location of the only known wild specimens is still being kept secret AFAIK [21], again the article helpful as are the references and external links e.g. [22]

Speaking more generally, if subject to a major environmental change, the rate of evolution may change (or more likely the species will just die off) but it doesn't mean that they ever 'stopped evolving'. That's primarily a simplistic and flawed creationist idea which doesn't get much consideration from evolutionary biologists.

Nil Einne (talk) 14:23, 6 May 2010 (UTC)

100 million years is really just a blink of the eye. Bus stop (talk) 14:28, 6 May 2010 (UTC)

No, it isn't. 100 million years is 100 millions years, which is a significant amount of time, even speaking geologically. The earth is about 4.5 billion years old, which makes 100 millions years a span of slightly more than 2% of the total - if each blink of your eyes took 2% of your life, you'd miss out on quite a bit, I think. And multicellular life is "only" about a billion years old - of which 100 million years would represent 10% of the span. It's important to emphasize the realities of deep time, but exaggerating it does no service. Matt Deres (talk) 16:37, 6 May 2010 (UTC)

Well, the age of the universe is 13.75 billion years. That's about 3 times older than the age of the Earth. Bus stop (talk) 17:04, 6 May 2010 (UTC)

True, but what's your point? The discussion at hand is about rates of evolution and speciation and so on, so the age of the universe is pretty much irrelevant. 100 million years is a very long time indeed and you're not doing anybody a service by telling them otherwise. Matt Deres (talk) 20:26, 6 May 2010 (UTC)

In a sense, these animals haven't stopped evolving at all. They will still be getting genetic change from mutation and the general genetic diversity within the species - but what is happening is that any changes that happen are having a negative effect - so the mutated animals are not surviving as well as the unmutated population.

What we need here is a good analogy - and the one I'm about to give is a classic. Imagine all possible sets of genes as being laid out on a large map with the similar gene makeups close to each other and the less similar ones further away - and imagine that the reproductive success/survival rate of a hypothetical animal with a particular genetic makeup to be represented by the elevation of this 'genetic terrain'. Then there will be hills and valleys all over the place on this map - with many of the hilltops being populated by particular species of real animals that have that particular makeup...but with other hilltops representing possible kinds of successful animals that don't happen to exist in the real world.

As particular animals mutate - their genes change which "moves them" to a slightly different location on the map...typically not far from their parents. Hence, individual animals appear that are a little way away from the others of their species - but because all of the members of the species share most of their genes, they come out as a small 'fuzzy' group of dots on this landscape. If some members of the species are positioned at a lower elevation (ie less reproductively successful) than the others higher up the hill - then they'll be out-bred and eventually die out leaving the ones on the higher elevations who survive. If the species is not quite at the top of the hill yet - then a random change could produce an animal that's higher up the hill (ie more successful at breeding and surviving) - and that animals' ancestors will come to dominate the population. Over many generations, you'd therefore see the members of the species gradually climbing to the top of the hills and then staying there because "when you're at the top, the only way is down".

So after enough time has passed, you'd see little groups of animals huddled together at the tops of their respective hills - having evolved to be there and all having genetic makeups that can't be improved upon.

Now, the nature of this process is that once on a 'hillside' the population will climb to the top of that hill. That doesn't mean that the hill is the highest one around. If there is a species in the same environment that's managed to get to the top of a higher hill - then the lesser species will be out-competed and die off - being unable to evolve to be any better without getting worse first.

It's also possible that there may be other hilltops nearby that are higher than the one they are currently sitting on. But they can't evolve over to that higher hill because any small genetic change just moves the animal off to lower ground where it gets out-bred by the ones higher up in the genetic landscape. A little further away, there will almost certainly be some higher mountains - sets of genes that are much better for survival than the present makeup of these animals. However, if those higher peaks are further away than a few generations of genetic change will reach - then the animals are effectively trapped with their present genes. Any small genetic change makes them worse off - but the huge genetic changes that would get them to a higher hill and allow them to evolve up that new slope are too far away.

If the slope of the local landscape is shallow enough - then it may be possible for a few generations of mutated animals to survive despite not being so great as the others and drift across that shallow genetic valley onto the slopes of the higher peak. When that happens, they'll rapidly climb that peak and suddenly you have a new species that's much better than the old one.

But if the slopes are steep then any animal that shifts it's genetic makeup far from the local peak will end up in a deep valley and will die off before it can get onto higher genetic terrain.

However, this is a statistical matter - it's possible that some really unlikely mutation could change the animal enough to transport it's genetic makeup to the slopes of a quite distant and much taller peak - and then you'd find a sudden shift in the population to a significantly different animal...probably a different species. But if it happens that these animals are on a really steep-sided hill in the middle of a vast plain - then it's possible that no 'reasonable' amount of genetic change will get them to a higher peak - and they will (in effect) have stopped evolving. That's evidently what's happened with these 'static' species. Any small genetic change in a crocodile makes a worse crocodile - and the necessary change to have six legs (or whatever it would take to be a better crocodile) is too large to happen in a single generation. So they are stuck on their little steep-sided hill - unable to evolve in any direction.

But the thing is that the world changes. If the environment changes (due to global warming, for example) - then that re-prints the map! Genetic positions that used to be hills could now become valleys, other genetic hills will get taller - and the animals will spontaneously start evolving to find the new hilltops. This sudden 'scrambling' to get to the higher genetic peaks is what drives these sudden bursts of new species that pop up after a major environmental change.

There are other places in this genetic landscape where there are relatively flat, high plateaus. In that case, there are lots of small changes that can happen to the species which are neither better nor worse than their present genes. The animals spread over the plateau because no place is particularly better than any other - and you see considerable diversity within the species. Humans are kinda like that - we have genes for different hair, eye and skin color - genes for lactose tolerance and intolerance - all sorts of variations - but none of those are having much of an impact on our survival rates - so you see people with all kinds of different skin/hair/eye colors surviving equally well.

If you take another situation, the dark skinned people of Africa had a problem with malaria - and a local 'peak' in the genetic landscape corresponded to having a particular gene that conferred protection against the problem...albeit at the cost of some individuals getting two copies of the gene and dying young with sickle-cell disease. However, this was a local peak and evolution took those people up to it. Now, transport those same people to a region where there is no malaria, or add medical treatment that makes the value of natural malaria immunity 'go away' - and the genetic landscape changes. The peak caused by the malaria problem goes away - revealing a valley due to the sickle-cell issue. Logic says that we should see this gene becoming less common over coming generations as those groups of people evolve back up the sides of that new valley to the top of whatever is the nearest local peak.

SteveBaker (talk) 14:54, 6 May 2010 (UTC)

For people who wish to do further research, does that classic analogy have a name? Does Wikipedia have an article about it?

-- Wavelength (talk) 15:38, 6 May 2010 (UTC)

That's a good analogy, but it would be better if you turned it upside-down. Better genes should be lower down. That reflects the fact that species will naturally move towards them, just as objects in real space naturally move downwards. They then reach the bottom of a local depression and are stuck there. Getting to a deeper depression would involve climbing over a ridge, which is difficult. --Tango (talk) 17:02, 6 May 2010 (UTC)

It sounds like something used in The Blind Watchmaker by Richard Dawkins, but with a bit of chemistry/physics thinking mixed in. The analogy lacks enough of a genetic drift element, to my mind. Even without the landscape changing, populations evolve through genetic drift. Not just a few places on the landscape having plateaus (and anyway, this gets a bit weird because we don't have enough dimensions to keep track of all the variables we're talking about), but almost all the places have plateaus for some parts of the genome. And this genetic drift can even alter the shape of the landscape without anything happening externally, leading to selection pressure on this species and others. This is why species continue to evolve, even when conditions don't change. 86.178.228.18 (talk) 19:29, 6 May 2010 (UTC)

You're close - it comes from Dawkins - but you got the wrong book: "Climbing Mount Improbable". But Dawkins isn't really the originator of this analogy. The general idea of mathematical optimisation is usually visualised that way - and optimising algorithms are sometimes called Hill climbing for that very reason. The way genes evolve is a lot like that mathematical process. When you do optimisation using 'hill climbing' math inside a computer program, you 'climb' a slope until you hit a local maxima...and you have the same problem that an evolving species has - that you may successfully reach a local maxima - yet miss a much better optimisation that's further away - but an overly rigorous algorithm might never be able to descend into the valley and cross the intervening space to find a higher peak. Computers can be programmed to do smarter things like "Shotgun hill climbing" and "Random restart hill climbing" - which involves occasionally injecting some randomness into the process to hopefully jump you over to somewhere on the map where you'll find a better hill. Real world species fail to do that - so it's interesting to note that evolution isn't the perfect algorithm that some people think it is...without the ability to somehow look for yet higher mountain on the other side of nearby valleys - you'll rarely hit upon the best possible solution. Genetics can't do that...computer programs can! SteveBaker (talk) 01:34, 7 May 2010 (UTC)

Okay, so we are talking about a landscape called an environment and organisms on that landscape. I mean this analogy seems to have paralleled the real world exactly. As for dimensions we have all sorts of things, temperature and light and moisture level and turbulence and you name it all of which can change, with the organisms themselves in this terrain representing the genetic code they contain. The mountains or valleys are just places where the environment comes closest to fulfilling the requirements of the genes and vice versa. So if the environment does not change and a change in the genes occurs that does not bring the organism closer to matching the environment then its numbers will decrease due to reproduction. It all makes sense that while a palmetto bug might do better outside due to temperature and rotten vegetation and dead worms, etc. except for spiders and birds and lizards it still comes inside to find enough hidden crud or crumbs to do well. What I'm looking for, however, even though genes will change and the environment will change is a list of organisms which have adapted to both through all kinds of changes and yet remains essentially the same as it always was. If I were designing a tank this is the tank I would want to design. One that is exposed to all sorts of change but is still functioning in the end due to the flexibility or stamina or shape, etc. of the initial design. I just need a list of organisms that are living today and the amount of time since their last notable change or origination as a new species. 71.100.0.29 (talk) 21:04, 6 May 2010 (UTC)

The original question was sensible, except that it should have used a term such as "local optimum" instead of "apex of evolution". There are a few species such as the cockroach, horseshoe crab, and coelecanth that appear to have changed very little over the last 100 million years, but I'm not aware of a list of such species. (Not that I would know, not being an evolutionary biologist.) Looie496 (talk) 21:39, 6 May 2010 (UTC)

I've wondered about this--so modern horseshoe crabs resemble fossils from hundreds of millions of years ago, so one could say their appearance has not changed much, right? But couldn't there have been all kinds of change that does not get fossilized? Our page says they use Hemocyanin in their blood to carry oxygen. Would one be able to tell, from fossils, when the use of Hemocyanin in horseshoe crabs began? Was it there all along? ..there must be all kinds of important stuff that is lost in the fossil record. Wouldn't it be impossible to make any claims about the actual genetics of fossils? Or when a new species evolved? Like, a modern horseshoe crab could breed with an ancient one from how long ago? Seems like the best that could be done is making statements about appearance, no? Pfly (talk) 02:17, 7 May 2010 (UTC)

The entire thread appears to be a tl;dr situation, although the above two posts try to give an answer. My two cents: Triops. 220 million years. ~ Amory (u • t • c) 03:43, 7 May 2010 (UTC)

Chemical explosive rail-gun-better than electric?

If a massive gun had a series of explosive chambers at right angles all the way along it's length, and after a projectile (a manned rocket perhaps) was set moving with an initial explosion at the start of the barrel, would a series of timed chemical explosions in the side chambers speed the projectile up even more, enough to escape Earth orbit without the G-force killing the astronaut, or could it be a more compact and powerful equivalent to an electric rail-gun for military use? Would the speed be higher than any other method? [Trevor Loughlin]80.1.80.12 (talk) 11:43, 6 May 2010 (UTC)

You are describing something very similar to the Nazi V3 weapon of WW2 [23]--Aspro (talk) 11:58, 6 May 2010 (UTC)

It's better than one large explosion, but not as good as electric. Electric is constant acceleration, this would be a series of jerks. Humans wouldn't like that. The force is lower for each explosion, but now you are shaking the person violently - this might actually damage them more than a single larger explosion. You could maybe add a buffer to stretch out the force for each explosion - a heavy pusher plate on a spring maybe, with the explosions carefully timed for when the pusher is just about to switch from compressing the spring to stretching it. But an explosion is not really the most efficient way to accelerate something, a constant fire would be better. Ariel. (talk) 12:08, 6 May 2010 (UTC)

We have, of course, an article at V-3 cannon. To escape from Earth, the projectile needs to reach the second cosmic velocity or escape velocity, which for Earth is 11.2 km/s (call it 10km/s). Assuming perfectly constant acceleration, at 1 g (call it 10m/s), you need to accelerate for roughly 1000 seconds to reach escape velocity. At 10 g, 100 seconds. In that time, your projectile will have traveled approximately 500 km. That's a mighty long barrel for a gun... --Stephan Schulz (talk) 12:16, 6 May 2010 (UTC)

The idea reminds me of Project Orion which was to be a spaceship powered by detonating atomic bombs behind a large 'pusher plate' behind the craft. The issue of peak versus average acceleration was handled by large shock-absorbers. In the case of our OP's idea, you could use a larger number of smaller charges to even out the acceleration still more - and even approximate continuous thrust that way. The difficulty (as others have pointed out) is that you effectively need the rail to be as long as distance travelled by a conventional rocket while under power - and that's going to be a very long 'rail'. Rail guns are a more practical proposition for unmanned launches where the g-forces can be higher...but their main advantage is re-use and the fact that they could be powered by electricity - making them feasible for things like doing mining operations out on the asteroids or on the moon where solar power is cheap but rocket fuel (or explosives) might be unobtainable - and the escape velocities are much lower. SteveBaker (talk) 14:02, 6 May 2010 (UTC)

Another problem with relying on a series of explosive chambers is the choice of propellant. The lower the molecular mass of the combustion products the faster it will expand (and push on the projectile). The railgun avoids this issue completely and can already achieve (so we are told) 3,600 meters per second (with a hydrogen filled barrel). Railgun#Tests. Faster speeds are theoretically possible to 7,000 m/s. Light gas guns can already achieve this using pure high pressure hydrogen -the lightest of the lot. Using multiple chambers on their own therefore, would not I think, ever be capable of beating this. So, I suppose the answer to the OP's question is no. --Aspro (talk) 15:00, 6 May 2010 (UTC)

Electrolysis of CuSO4

Is sulfate oxidized to SO4 when CuSO4 is electrolyzed? My chemistry teacher in 11th grade keeps saying that, but I don't think it does. Thanks. --Chemicalinterest (talk) 13:04, 6 May 2010 (UTC)

persulfate is a possibility SO₅²⁻. But SO₄ is not realistic. But I do not know if it is formed this way. Graeme Bartlett (talk) 13:21, 6 May 2010 (UTC)

I think that the reaction is: 2 CuSO₄ + 2 H₂O → 2 Cu + O₂ + 2 H₂SO₄ The sulfuric acid may react with additional copper sulfate to form copper bisulfate. They said that the reaction was: CuSO₄ → Cu + SO₄ --Chemicalinterest (talk) 13:36, 6 May 2010 (UTC)

Here is how you would figure this out. You have three species in the beaker: Cu²⁺, SO₄^2-, and H₂O. Figuring out the anodic and the cathodic reactions is actually very easy. Just look on any table of standard reduction potentials, like Standard electrode potential (data page) and then look up the potentials for each reaction. Possible cathodic reactions are:

• SO₄²⁻ + 4 H⁺ + 2 e⁻ ⇌ SO₂(aq) + 2 H₂O E^o = +.17
• Cu²⁺ + 2 e⁻ ⇌ Cu(s) E^o = +.340
• 2 H₂O + 2 e⁻ ⇌ H₂(g) + 2 OH⁻ E^o = -.8277

Possible anodic reaction are:

• 2 H₂O ⇌ O₂(g) + 4 H⁺ + 4 e⁻ E^o = -1.23
• 2 SO₄²⁻ ⇌ S₂O₈²⁻ + 2 e⁻ E^o = -2.010

You need to choose a reaction for each electrode. You always choose the one with the highest (most positive) electrode potential, that gives us a cathodic reaction of:

• Cu²⁺ + 2 e⁻ ⇌ Cu(s) E^o = +.340

and an anodic reaction of

• 2 H₂O ⇌ O₂(g) + 4 H⁺ + 4 e⁻ E^o = -1.23

So, we double the first, and combine to get an overall reaction.

• 2 Cu²⁺ + 2 H₂O ⇌ 2 Cu(s) + O₂(g) + 4 H⁺ E^o = -.89

Meaning that, assuming 1 molar concentrations you'd need a minimum of 0.89 V to make the electrolysis extensive. Where your teacher messed up is that they forgot that water was present; in any electrolysis, you need to consider whether or not water is more likely to electrolyze than your other reactants. At the anode, it turns out that the water is far more likely than the sulfate to electrolyze.

This assumes aqueous-phase electrolysis. You can also do liquid-phase electrolysis, but that requires liquid copper(II) sulfate, which isn't usually done in your high school chem lab. In that case, you'd need the liquid-phase electrode potential data; I don't have that at my finger tips, but the method is identical, except you don't have water present, so you'd need a liquid-phase half reaction for the oxidation of the sulfate ion into sulfur trioxide gas and oxygen gas. --Jayron32 15:40, 6 May 2010 (UTC)

CuSO4 decomposes before it melts into SO3 and CuO. Thanks. Another questionable reaction was that: Zinc and copper are placed in a sodium chloride solution. The sodium ions accept electrons to produce sodium, and the chloride ions give away electrons to produce chlorine. --Chemicalinterest (talk) 15:47, 6 May 2010 (UTC)

Bullshit. There's nothing you could do to an aqueous solution of sodium chloride to produce sodium metal or chlorine gas, especially not with Zinc metal or Copper metal. Sodium is far more active a metal than Zinc or Copper. You can compare the ionization energy for the metals, or you can look at the electrode potentials for either of them. Putting zinc metal in a salt solution will get you a wet, salty piece of zinc metal. There are corrosion reactions that can occur here, but these involve oxygen and water. Sodium ions can act as a catalyst for these reaction via ion exchange, but you never get sodium metal in the presence of water. It just doesn't happen. Oh, and I looked over your reaction; its pretty much the same as the one I came up with; just that sulfate is a spectator ion to the overall reaction, so I left it out of my analysis, and you kept it in yours. Either way, its correct and your teacher is incorrect. --Jayron32 15:53, 6 May 2010 (UTC)

Planets in Universe

why is it important to find out if there is anther planets in the universt ? —Preceding unsigned comment added by 90.149.184.157 (talk) 14:47, 6 May 2010 (UTC)

People like to see whether there is other life in space. See SETI. --Chemicalinterest (talk) 15:22, 6 May 2010 (UTC)

A lot of people consider understanding the universe to be important. There isn't necessarily any practical reason to do it, it's just human nature to want to understand things. Finding out about planets around other stars may help us understand our own solar system better (which may or may not be actually useful). --Tango (talk) 15:34, 6 May 2010 (UTC)

Pragmatism. The planet cannot sustain the current population growth levels of humans. At some point, either human population growth is going to have to level off (and the mechanisms for that will involve aggessive competition for resources, i.e. wars where lots of people are killed) OR we're going to have to find some other place to live. One of the things about finding life outside of the earth is it allows us to understand how to survive in other environments, either in our own solar system (like Mars) or, how life can be made to work in completely different environments. Furthermore, the prospect of finding a peaceful, but technologically advanced alien race would be quite helpful. Learning how to effectively travel interstellarly is something that seems impossible given our current understanding of the universe, but if another alien race has figured it out, we could too, and that would open up MANY possibilities for human colonization of the galaxy. Even if we were to figure out how to do that on our own, knowing what life, if any, existed outside of our solar system is a handy bit of knowledge. Trying to colonize a planet whose already intelligent inhabitants aren't interested in us doing so is something we'd want to know before we showed up. --Jayron32 15:58, 6 May 2010 (UTC)

I disagree with your parenthetical assertion. There seems to be a natural reduction in birthrate as standard of living increases (most of the developed world would be showing population decline if it weren't for immigration from the rest of the world). If we can increase the standard of living in the rest of the world, we may well find our population problems disappear. --Tango (talk) 16:53, 6 May 2010 (UTC)

Oh, yes, if we could raise the standard of living in the rest of the world, that would go a long way towards ameliorating overpopulation problems. How's that been going so far? --Jayron32 17:06, 6 May 2010 (UTC)

Well, we solved world hunger, then we solved global warming. What's next? Vimescarrot (talk) 18:30, 6 May 2010 (UTC)

Jayron, you laugh condescendingly at the idea of raising the standard of living in the third world, but you think colonizing other planets can solve overpopulation? -- BenRG (talk) 00:25, 7 May 2010 (UTC)

With any forseeable technology, of course, there is no way to send enough folks to another planet to make even a dent in population. What it is just barely conceivable that we might be able to do, though, is create a self-sustaining population somewhere else, in such a way that if worse comes to worst on this planet, the species will nevertheless survive.

But a flip side of that has occurred to me. It is possible that, on one planet, no one will deploy (or at least detonate) a weapon that would make the planet uninhabitable, because they themselves would have nowhere to go. With two planets, they could fire them at each other.... --Trovatore (talk) 00:31, 7 May 2010 (UTC)

No ecological catastrophe could make Earth nearly as uninhabitable as the Moon or Mars are already. Whatever technology might allow people to survive there long-term, you might as well just deploy it here. Put it underground or at the bottom of the ocean if you have to; that's still much, much easier than putting it on Mars. -- BenRG (talk) 03:48, 7 May 2010 (UTC)

Well, there's something to that argument, but I don't completely buy it. A sufficiently large body colliding with the Earth could indeed make it more uninhabitable, for one thing. Granted that impacts that large are pretty rare. But even in the case of a less-badly-wrecked Earth, one thing you could have here that you don't have there are the people who were left out of the ark. They might be tempted to attack it. --Trovatore (talk) 08:25, 7 May 2010 (UTC)

A large impact might make the Earth less inhabitable than the Moon for a short period of time (a few years, maybe) but after that time it would go back to being easier to inhabit. Really, the only thing that might be better about the Moon than the Earth is the absence of a dust cloud blocking out the sun making solar power impossible. As long as you have some other way of generating power, the Earth will probably be easier to inhabit within a couple of days of the impact (once the shockwaves have dissipated, for example), and generating power is easier on the Earth than the Moon (you can use geothermal energy, wind energy, tidal power, etc. on Earth, even after a big impact, but not on the Moon). --Tango (talk) 18:29, 8 May 2010 (UTC)

You won't live long enough to get to the time when the Earth is easier to inhabit. I'm talking about really big impacts, say of the sort that split the Moon off in the first place. --Trovatore (talk) 19:52, 8 May 2010 (UTC)

To understand our local solar system. We have a sample size of 1. This is not enough to know if our solar system is unique, unlikely, or common. So we look for others and try to get more information about solar systems. Ariel. (talk) 20:10, 6 May 2010 (UTC)

Incidentally, the wording of your question is a little hard to understand, but suggests that you may not realise that we have already found out if there are other planets in the universe (beyond the other 7 in our own Solar system); so far we have detected over 450 Extrasolar planets, and the number is climbing as fast as we can improve our instruments and methods. 87.81.230.195 (talk) 21:10, 6 May 2010 (UTC)

Do airlines use ground length measurements for their mile programs, or air length?

since airplanes travel at an altitude of somewhere near 30,000 feet, wouldn't that add a few miles to the length when compared from measuring from the ground? I know 30,000 feet is insignificant to the radius of the earth, and would only add a couple miles on really long trips, but i like to argue with airline companies. —Preceding unsigned comment added by 76.21.237.247 (talk) 16:05, 6 May 2010 (UTC)

They use "marketing-ese" to measure the mileage. I think they will tell you this in blunt terms, if you try to dispute a mileage number. They have a standard to determine how many "miles" a particular flight is worth to a frequent-flier program. Think of those as "points", not "miles" in the true sense. The pilots have much more accurate measures of the flight distance than the airline reports to you, the lowly customer; see air speed and ground speed. Integrating either air speed or ground speed will give you a different measure of the total trip-length; air-speed does account for the vertical distance, but is much more significantly affected by wind. Nimur (talk) 16:44, 6 May 2010 (UTC)

Back when I flew United constantly and obsessed over miles, I found that their FF mileages were extremely close to those from this great circle calculator. That would correspond to the shortest path, along the ground. But in terms of arguing with them, I agree with Nimur: They disclose how many miles the trip gets you, and that's it. They're more of an abstraction than an actual distance. -- Coneslayer (talk) 16:51, 6 May 2010 (UTC)

From the point of view of the customer, mileage should be calculated as shortest distance between points of departure and arival. The actual path taken, and height travelled, is somewhat irrelevent for your calculations since frequent flier miles are calculated by great-circle distances between airports. And for pilots, the air-mileage is also largely irrelevent. Far more important, for calculation of fuel consumption, is the intergrated air speed, as noted by Nimur. Fuel consumption will be directly related to integrated air speed, which is "virtual air miles travelled", basically the sum of the actual air miles traveled combined with the effect of headwinds or tailwinds. I doubt that anyone has any practical use for calculating the actual miles traveled through the air. It is trivial to calculate it, its just not very useful for either the customer or the airline to know it. --Jayron32 17:04, 6 May 2010 (UTC)

Here's the thing: Suppose you took a piece of string, long enough to stretch tightly all around the equator. If you then wanted to lift it up and put it on top of 10' poles all around the world - how much more string would you need? It sounds at first like it would be a lot - but in fact, it's pi times 10' - so it's just 31.4 feet extra. So for your airplane at 30,000 feet - the total extra distance if it flew all around the world would be pi times 30,000 feet - so 93,000 feet extra. That's a little over 17 miles. But if you're only flying (at most) halfway around - the difference is only around 8 miles - and for most flights the difference between "air distance" and "ground distance" is going to be just one or two miles. It's really completely irrelevent which they choose. When you consider that the plane is probably flying at between 300 and 400 mph - it's covering a mile every second ten seconds! You'd only have to be off-course by a few seconds half a minute to wipe out the error! SteveBaker (talk) 00:04, 7 May 2010 (UTC)

Steve, I think you need to re-check the number of seconds in an hour :-).

By the way, most commercial flights are traveling over 400 mph, and often as much as 600 mph, at cruising speed. --Trovatore (talk) 02:26, 7 May 2010 (UTC)

Oopsie! Thanks...fixed it. SteveBaker (talk) 03:35, 7 May 2010 (UTC)

Also, the height you give is added to the radius of the earth, not the diameter. Therefore, a plane flying at 30,000 ft would add 188,500 ft to an around the equator trip, for a total addition of 36 miles. 36 miles of 25,000 is still pretty much negligible for the purposes of the original inquiry, especially since the longest non-stop flight I know of is from LAX to Sydney, which is under 1/3 of the earth circumference, and would thus add less then 12 miles. Googlemeister (talk) 13:29, 7 May 2010 (UTC)

Snow accumulating in above-freezing temperatures?

A friend in Bethel, Alaska tells me that they had an accumulation of 5 inches (130 mm) of snow a few days ago, even though the temperature was above freezing. How is this possible? I understand that snow can fall when it's above freezing, but (1) how can it possibly accumulate so much when the air is above freezing, or (2) if enough is falling to accumulate this much snow, how doesn't the large amount of snow cool the air to a temperature below freezing? I should note that my friend is trustworthy; I have no reason to believe that she's making this up. Nyttend (talk) 17:10, 6 May 2010 (UTC)

It could simply be that the latent heat heat that the snow needed in order to melt was in sort supply due to the specific heat capacity of the air being so low (maybe it was dryish air too). The only other place the heat could come from is the ground and maybe that was very chilly as well. In other words the heat gradient was very small. Also, in the absence of wind there could very well be a laminar boundary layer of much colder dense air close to freezing - covering the snow. Just like the open top freezers in supermarkets.--Aspro (talk) 17:52, 6 May 2010 (UTC)

Additionally (expand above) if it had been very cold previously the ground itself could still be sub-zero - but the atmosphere above zero - which would delay melting, and cause the near ground temp to be lower..77.86.68.186 (talk) 19:26, 6 May 2010 (UTC)

Also, it is easy to overlook the amount of heat required to melt five inches of snow. It equals about half an inch of solid ice. To melt that, you need about the same number of calories as you need to bring half an inch of water up to boiling point. Being snow, it also reflects most infra-red heat and the air above it is an insulator. It is going to take time.--Aspro (talk) 19:48, 6 May 2010 (UTC)

The heat content of air is very small, but snow is wetter when it falls in warmer temperatures. It forms bigger flakes. --Chemicalinterest (talk) 20:44, 6 May 2010 (UTC)

Isn't snow stable up to about 4 °C, as long as it is kept out of direct sunlight? —Preceding unsigned comment added by Csmiller (talk • contribs) 21:29, 6 May 2010 (UTC)

If the frozen precipitation is heavy enough, it can accumulate when the surface temperature is well above freezing. Of course, lighter showers will melt at more than a few degrees above freezing. It doesn't surprise me that 5 inches fell, but it would be good to know how much above freezing the temperature was. –Juliancolton | ^Talk 02:32, 8 May 2010 (UTC)

If I remember rightly (can't access it anymore, since this was several days ago now), Weather.com said that it was in the high 30s °F. Nyttend (talk) 02:50, 8 May 2010 (UTC)

That's definitely possible, then. Snow can fall at temperatures exceeding 40° given the right conditions. –Juliancolton | ^Talk 03:20, 8 May 2010 (UTC)

metal differentiation

I am having some difficulties differentiating two metal samples. They have the same dimensions and density, though the metal alloys are quite different, with one sample containing nickel, and the other sample does not. Neither sample is magnetic. I can not damage the samples, so using chemicals that would react to nickel would not be feasible. For the same reason, I can not test the hardness or tensile strength of the alloys. I tried using a multimeter to determine if there is a difference in the resistance, however since both are metal, the multimeter gives only a very low Ω value which is lower then the multimeter can use. Are there any other ideas? Googlemeister (talk) 18:38, 6 May 2010 (UTC)

Have you considered X-ray fluorescence analysis?--Aspro (talk) 19:19, 6 May 2010 (UTC)

also Atomic_emission_spectroscopy#Spark_and_arc_atomic_emission_spectroscopy ? 77.86.68.186 (talk) 19:22, 6 May 2010 (UTC)

Have you got the composition of the two alloys and have to tell A from B, or is the only info you have is that one contains nickel.?

There are surface tests for nickel (specifically usually for jewelry for people are allergic) - this would not substantially damage the sample. ie you just wipe a swap on the surface...77.86.68.186 (talk) 19:20, 6 May 2010 (UTC)

Sadly, I do not have equipment for XRF available to me, though I would love such a device. Also, the surface test mentioned is not a good idea since even minor damage would be unacceptable. How about thermo effects on the material? Perhaps I could determine one sample heats faster then the other under the same circumstance, or one is a better conductor of heat? Googlemeister (talk) 19:31, 6 May 2010 (UTC)

I usually find that if I need a bit of equipment, somebody else has needed it so bad that they have actually purchased it. If they have already purchased it, I can always think of lots of reasons why they should allow me use it. So just because you can't afford one, is not what I consider a legitimate excuse ;-) Aspro (talk) 20:39, 6 May 2010 (UTC)

Sample A is 75% copper and 25% nickel, and sample B is 56% copper, 35% silver and the balance in Manganese. Googlemeister (talk) 19:33, 6 May 2010 (UTC)

You could measure the specific heat of the metals. Heat them both to identical temperatures, drop them into identical, insulated containers filled with the same amount of the same temperature water. Watch for the final temperature of the water. You wouldn't even need to calculate the final specific heat, since you know the identity of the two samples (but not which is which), you would just need to know which had the higher specific heat, and compare to the expected values. The one with the higher specific heat will heat the water to the higher temperature. --Jayron32 19:41, 6 May 2010 (UTC)

I would expect B to be yellow or yellowish in color - if one is more yellow/orange then that is definately B. (or maybe not): At the risk of appearing facetious it sounds like you are trying to tell apart nickel coins.. Nickel_(United_States_coin)#Wartime_nickels - if so - would the date on the coin be a give away? :) 77.86.68.186 (talk) 19:50, 6 May 2010 (UTC)

Technically - measuring compressive tensile strength is non destructive too... the silver allow should be weaker. or not.. really need a table of values for both.77.86.68.186 (talk) 19:46, 6 May 2010 (UTC)

Not if you suspect that they used the incorrect materials when they made the coin. Googlemeister (talk) 19:53, 6 May 2010 (UTC)

Are the coins 'as new'.. if not a photo would help - I claim to be able to spot silver patina at long range.77.86.68.186 (talk) 20:00, 6 May 2010 (UTC)

You said the density of both is the same, yet my simplistic calculation[24][25] shows sample A to have a density of 8.917 g/cm^3 and B is 9.339 g/cm^3. (Does alloying metal change the density, like dissolving salts does?) Ariel. (talk) 20:30, 6 May 2010 (UTC)

Not sure. All I know is that the weight is identical, and the external dimensions are identical. Googlemeister (talk) 20:33, 6 May 2010 (UTC)

If the weight is identical to the level of accuracy of the scales you've got, but isn't accurate enough to distinguish the above method ... you can use a simple balance (diy) - it's easy (use a knife edge as the pivot) - a 10cm arm will easily distinguish weight differences of 1mg. —Preceding unsigned comment added by 77.86.68.186 (talk) 20:51, 6 May 2010 (UTC)

If you've got an ideal material, you can find the Young's modulus non-destructively, but finding the yield strength and failure strength is a destructive process. In practice, most metals behave non-ideally, so even measuring the Young's modulus is a destructive test. (When I worked in a mechanical testing lab, our compressive test specimens would typically be 1/40" shorter after testing). --Carnildo (talk) 01:54, 7 May 2010 (UTC)

Alloys have density as a weighted average of the individual metals composing it. --Chemicalinterest (talk) 20:48, 6 May 2010 (UTC)

According to http://www.ukcoinpics.co.uk/metal.html the two allows also have similar electric resistances. I can't find any physical data for the Mn alloy - presumably because it was a one off.77.86.68.186 (talk)

The US national mint probably has the data - should be obtainable since USA has freedom of information acts. Not sure exactly where you would write to? 77.86.68.186 (talk) 21:36, 6 May 2010 (UTC)

What about microscopy - comparing them against known control samples?77.86.68.186 (talk) 20:52, 6 May 2010 (UTC)

I don't think density is a weighted average (by %composition) of the component densities unless the volumes literally add. But alloys aren't individual blocks of the components, more like a solution where atoms of one can fit in spaces between others in a packing different than either one alone (for example, nonideal Volume of mixing, so the volume of the alloy is not exactly the volume of the two pure metals being mixed). DMacks (talk) 21:59, 6 May 2010 (UTC)

Yes you may be able to discern crystal structure or corrosion products with a microscope. Another test is the speed of sound. This will change the pitch of the clink when you tap the sample, and if they are truly the same dimensions should differentiate. This can reveal the compressibility since you know the density. Graeme Bartlett (talk) 22:11, 6 May 2010 (UTC)

Besides specific heat, you can measure thermal conductivity. That should differ between different alloys. Electrical conductivity might also differ, but you need to be more creative than to just use a multimeter to measure resistance. Rather than just asserting "Neither sample is magnetic" you need to characterize their exact degree of Paramagnetism, Diamagnetism or Ferromagnetism. Copper and silver are diamagnetic, nickel is ferromagnetic, manganese is paramagnetic (no idea how alloys will come out). Such testing goes far beyond trying to pick them up with a magnet. A powerful electromagnetic field and sensitive measurements of effect are needed, but it should be a good test. Getting or making a known standard sample of one of the possible alloys would be very useful if that is possible. Edison (talk) 15:55, 7 May 2010 (UTC)

Cold, flu, etc season/s

Is there one cold, flu, allergy or etc for the whole world or 2 separate ones for all of them?

Basically, I always wonder about this.--Jessica A Bruno (talk) 22:14, 6 May 2010 (UTC)

I'm not sure I understand what you are asking? They are all 3 different medical conditions, with different causes, though their symptoms can overlap:

• The common cold is caused by a number of different viruses which usually infect the nose and upper respiratory tract, called rhinoviruses. Rhinovirus meaning "virus that infects your nose".
• The Flu, or Influenza, is caused by one of the group of influenza viruses, usually Influenza A or Influenza B. There are other medical conditions which get called flu (such as a "stomach flu") which are unrelated. Commonly (but not always) flu symptoms are more intense than cold symptoms (though sometimes a cold can be really bad, confusing the two). The other difference is that the Flu can be vaccinated against via the flu vaccine and there are antiviral drugs, like Tamiflu, which can fight the infection. The types of viruses that cause a cold are too varied for effective vaccination and treatment under current technology.
• Upper respiratory allergies, sometimes called "Hayfever", properly termed Allergic rhinitis, which is doctor speak for "allergy that causes stuffy nose", is caused by allergens (usually small little bits of dust or pollen) that iritate the nose and trigger a histamine response; such histamine responses usually cause similar symptoms to a cold or flu, however usually absent the fever.

Hope that helps. --Jayron32 21:12, 6 May 2010 (UTC)

The article Vitamin D and influenza suggests that there are two seasons, one for each hemisphere. Pollen allergy obviously oscillate between the two hemispheres. Colds? Pass! A submariner told me that for the first couple of weeks of a new tour, everyone has the sniffles. This can not be due to the lack of vitamin D as the body can store quite a bit and so it wont run out so suddenly. However, they are in a very enclosed space. The carbon/ electrostatic filtration system is obviously of little help in this regard. UV lamp sterilizers might help though.--Aspro (talk) 21:14, 6 May 2010 (UTC)

Thank you and interesting.--Jessica A Bruno (talk) 22:14, 6 May 2010 (UTC)

Night Vision

Is it possible to read a book in the dark with night vision goggles? —Preceding unsigned comment added by 71.104.119.240 (talk) 21:13, 6 May 2010 (UTC)

I don't know why it wouldn't be possible. --Chemicalinterest (talk) 21:16, 6 May 2010 (UTC)

The output of image intensifiers suffer from scintillation (speckling) , which may make it hard to make out fine details, which is needed for reading. However active IR night vision will probably work, as long as paper is IR reflective, and the ink absorbs IR. CS Miller (talk) 21:27, 6 May 2010 (UTC)

As above. Yes, if it is not active IR it will need some other light source (unless you have a generation 3½ device or something). --Aspro (talk) 21:33, 6 May 2010 (UTC)

IIRC, the first image intensifiers (in passive mode) need moonlight to work, the latest will work with starlight on a cloudless night. I'm not sure if the resolution of these devices is enough to read standard size print.

It goes with out saying that the body-heat night vision systems won't let you read a book. CS Miller (talk) 21:46, 6 May 2010 (UTC)

I've just tried out a class one device (i.e., cheap and cheerful) on a newspaper and I can easily read the news print. The thing I did notice, was that the optics are so poor that only the centre of the image was in sharp focus. This would make reading slow. Whilst it's possible to buy a reasonably good pair of binoculars for under a hundred dollars these days, if you want a good monocular night scope you might need to spend a thousand or so.--Aspro (talk) 21:57, 6 May 2010 (UTC)

Thank you, everyone - special thanks to Aspro for doing the experiment. Where do you go to buy them, anyway? I know they can be ordered online but it would be nice to try before I buy. 71.104.119.240 (talk) 22:45, 6 May 2010 (UTC)

I used a Tchibo nachtsichtgerät (night vision aid) tonight. This is a German company (the Nazis had nachtsichtgerät way back during the second world war) that buys job lots and markets them under its own brand. Good enough, if one wants to protect one's night adapted vision, (which would be washed out by the use of an electric lantern). Unfourtunatly, it does not respond fast enough to be able to follow bats and other critters that move quickly. They just don't show up! If you live in Virginia I don't know where you could try some out ( Norfolk Naval Base perhaps). I'd recommend getting one that has adaptations so that you can stick it on your SLR camera/ video camera. It is really nice to be able to record some of the things you see -just as you would, if they happened in daytime. Google around until you find an emporium that stocks them. If you have a specific use, then Google around for other people that would use them for the same thing. They will know which are the best ones to buy. Note: they are very sensitive to light, so it is not practical to try one out in a retail store. You will wreak it! If your just curious to try one out, buy a cheap one. A big benefit, that I have already mentioned is that you can still see ( it takes two hours for your eyes to become fully night adapted). Where as, using a torch to ensure you don't fall a*** over t** into the nearest ditch, would also alert any critters of you presents. Military scopes are great, but not worth the money IMHO for just exploring the back yard. --Aspro (talk) 00:11, 7 May 2010 (UTC)

Hmmm, if there is moonlight you can read a newspaper at night without any device (I would guess the Moon needs to be more than half full). Even on moonless skies, you can read newspaper headlines if there is significant light pollution, see here

Class 8: City sky. The sky glows whitish gray or orangish, and you can read newspaper headlines without difficulty.

Count Iblis (talk) 23:24, 6 May 2010 (UTC)

I too have read using one of these. There are really two problems - one is that they have a very narrow field of view - the other is that they are generally focussed out to infinity (or at least beyond a few tens of feet) - so it's hard to have things be in focus close-up. SteveBaker (talk) 23:54, 6 May 2010 (UTC)

Longevity of a species

Perhaps I failed to make my previous question clear so I apologize. Now what I am asking is where can I find a list of species and the amount of time the species existed or the age of the species. In other words if man is a species than how old the species of man is.

For example:

Man	1 million years
Palmetto Bug	350 million years

Thanks in advance. 71.100.0.29 (talk) 21:36, 6 May 2010 (UTC)

For old ones - Category:Living fossils (you'll need to get the dates yourself - and it's not exactly what you asked - but it's a start...) (misc. Anenomes are immortal).77.86.68.186 (talk) 21:44, 6 May 2010 (UTC)

Are you talking about the plants, the animals, the song or the actress? 71.100.0.29 (talk) 22:24, 6 May 2010 (UTC)

The rock pool animal.

For a overview (and earliest possible date for classes of species) Timeline of evolution is a good start.77.86.68.186 (talk) 22:39, 6 May 2010 (UTC)

It does not appear capable of surviving an oil spill. 71.100.0.29 (talk) 22:46, 6 May 2010 (UTC)

link ? 77.86.68.186 (talk) 23:10, 6 May 2010 (UTC)

Only if it could digest bunker c would I call it immortal. 71.100.0.29 (talk) 00:22, 7 May 2010 (UTC)

classification characteristics

Is there a table of characteristics which define Phylums within Kingdoms, Classes within Phylums, Orders within Classes, Families within orders, Genus within families, and Species within Genus such that one could determine by querying the table what sort of species they had in hand? 71.100.0.29 (talk) 22:21, 6 May 2010 (UTC)

For all species? Do you know how big that would be? 71.104.119.240 (talk) 22:42, 6 May 2010 (UTC)

Computers now-a-days should be able to handle not only the table but the queries. 71.100.0.29 (talk) 22:48, 6 May 2010 (UTC)

The key word is "taxonomic key" or "dichotomous key" or "identification key" - I've not seen one that goes all the way down in one book.

If there are 2 million species that would be about 22 questions in depth to get to a single species.77.86.68.186 (talk) 22:57, 6 May 2010 (UTC)

No problem. In fact it could probably be pre-programmed and made into a child's game here: http://www.20q.net/ 71.100.0.29 (talk) 23:02, 6 May 2010 (UTC)

Try the "Tree of Life Web Project" http://tolweb.org/tree/ - it has many keys for different groups - I don't know if it is complete.77.86.68.186 (talk) 23:04, 6 May 2010 (UTC)

I see the project and the structure, the names and the individuals that have been included... but alas, not the criteria or the characteristics. 71.100.0.29 (talk) 23:21, 6 May 2010 (UTC)

Another incomplete key here http://en.wikibooks.org/wiki/Dichotomous_Key/Start 77.86.68.186 (talk) 23:36, 6 May 2010 (UTC)

That's more like what I had in mind but I fear biological taxonomists will see it as a threat to the realm of biological taxonomy and as an act of biological taxonomic terror. 71.100.0.29 (talk) 00:04, 7 May 2010 (UTC)

I'm surprised that nobody mentioned our very own WikiSpecies over on http://species.wikimedia.org/wiki/Main_Page - it has the taxonomy for about a quarter million species. Of course that's really only a drop in the bucket. SteveBaker (talk) 00:36, 7 May 2010 (UTC)

Unfortunately the wikispecies project has the same problem as the tree of life web project. One must already be an expert to use it. Using characteristics you need not be an expert in the field but instead rely upon the expertise built into the system to which your job is to present measurements or observations. Why are these projects duplicating taxonomic systems only experts can use instead of making the system the expert that everyone can use? What unmitigated and self-serving hypocrisy I observe. 71.100.0.29 (talk) 01:45, 7 May 2010 (UTC)

I think that's a bit over-the-top. Bear in mind that Wikispecies is not a stand-alone project - like Wiktionary and other such projects, it's designed to complement Wikipedia. You can do formal navigation of the taxonomy tree using Wiktionary - and get to articles written in Wikipedia...or vice-versa. If you want to find an article about Giraffe - use Wikipedia - if you want to find where Giraffa camelopardalis rothschildi fits into the taxonomy tree - use Wikispecies. The reason it uses cold scientific latin terms throughout is that there are no language-specifiec Wikispecies branches as there are for Wikipedia. A German reader should be able to use WikiSpecies with little or no trouble. You can't traverse a modern taxonomy with 'characteristics' because there can be similar - or even identical features in unrelated species that happen to have evolved some similar characteristic. The characteristic: "Has simple eyes" would find the branch of the tree with fish and mammals in it - but it would also have to include cephalopods, annelids, crustacea and cubozoa - which all have eyes that evolved in completely separate ways. The most recent common ancestor of (say) humans and squid didn't have eyes at all. So there is no single point in a taxonomic tree where "has eyes" is a distinguishing characteristic. So a modern evolutionary-based tree can't be navigated that way. About the closest you could come to that would be to query genetic sequences - but that would be even tougher than the latin names! SteveBaker (talk) 02:18, 7 May 2010 (UTC)

The points you make support the need to ultimately replace the current taxonomic system with DNA sequence classification for animals and plants. (Show me a plant or animal that does not contain minerals or the non-existence of an animal which can photosynthesize.) Regardless, DNA sequences classification will still require classification of associated characteristics that can be measured, observed and described. To prepare for such a system we need to start now by developing a 30 characteristics based query system to permit identification by measurement, observation and description of what characteristics we have already observe. 71.100.0.29 (talk) 06:48, 7 May 2010 (UTC)

The taxonomic system (you mean 'shared characteristics' or Phenetics) is being replaced by cladistics or phylogenetic classification (as you request)..

Nevertheless it's still possible to create a decision tree system to result in a phylogenetic classification - in recent times species are being re-assessed to place them in the tree according to their evolutionary heritage (derived from DNA mostly) - more info Biological_classification#Modern_systems. 77.86.67.180 (talk) 11:16, 7 May 2010 (UTC)

I think there is a problem with attempting to make a single global decision tree for classification (which might still exist) - in that classification isn't a completely precise science - and that classifications are based on a number of factors per branch rather than a single binary decision (ie the decision tree isn't in itself the classification system..)- maybe that's why the biologists don't seem to have produced such a thing. 77.86.67.180 (talk) 11:53, 7 May 2010 (UTC)

I agree to the extent that:

1. query order be dynamic and use many-valued independent variables
2. emphasis be on keys which provide the greatest separatory value
3. multiple systems, each designed with respective users in mind
   1. Humans
   2. robotic probes

Biologist have had computer technology such as:

Wikibooks has a book on the topic of: Optimal Classification

available to them for only a (relatively) short period of time. 71.100.0.29 (talk) 12:43, 7 May 2010 (UTC)

How many humans a asteroid would be able to have?

How large an asteroid population would be able to be?

I tried to find this info on net but was not able to. —Preceding unsigned comment added by 187.116.80.68 (talk) 23:10, 6 May 2010 (UTC)

Zero. Except for Ceres, the largest known asteroid, none are large enough for humans to live on. Ceres appears to have enough mass that you won't drift off into space if you try to walk around, but its is leagues away the largest asteroid, so much so that some people have started characterizing it as a "dwarf planet" due to its size. For the "average" asteroid, most are no more than a kilometer or two across, and the simple act of walking on them would generate more than enough escape velocity to send you drifting off into space. --Jayron32 23:16, 6 May 2010 (UTC)

I think it depends on your imagination. Colonization of the asteroids covers this topic nicely. You might have a hard time living on the outside of one - but you could hollow a small one out, fill it full of air and spin it to make artificial gravity. A C-type asteroid would contain maybe 10% water, plus all sorts of useful organic compounds. It could be hollowed out while mining the ice for drinking water, oxygen for breathing and oxygen/hydrogen rocket fuel. You'd just need a heck of a lot of solar panels to make electricity to first melt the ice, then convert to oxygen & hydrogen for fuel and breathing. As you dig, you'd fill the resulting chamber with air and use the rocket fuel to start spinning it up to speed - a slow process, to be sure - but maybe you can have robots do that part for you and you can just move in when it's all ready. The rock and dirt that comes out of the 'dirty snowball' would be what you'd need for growing food in and for processing into silicon (or whatever) to make more solar panels and other things. The organic compounds would also be good for food production. It's doubtful that you could get one full 'g' of gravity by spinning it because it would fall apart - but something much less than that might be enough for comfortable living conditions. If you picked your target asteroid well, you might find several in similar orbits - the low gravity would make finding and mining other asteroids for metals and other useful substances attractive. When your population gets too big - you can just move to another one. I think asteroids make pretty good homes for technologically advanced humans. SteveBaker (talk) 23:43, 6 May 2010 (UTC)

Oh - yes...and actually answer the question! It's hard to estimate how many people you could house this way - it depends too much on the actual resource availability and the size of rock you pick. But hollowing out the asteroid into swiss-cheese-like holes with tunnels between them, the surface area of the interior (being three-dimensional) could be much larger than the surface area. But the sustainability issue becomes a problem with having to grow food using predominantly artificial light generated from solar power (or maybe nuclear power if you can find the right materials locally). The acreage of solar panels would have to be many times greater than the acreage of crops planted (because you're essentially condensing large areas of sunlight to account for the fact that the asteroid belt is so far from the sun. So the actual farmable space might be ten times less than the outside surface because of that. Asteroids come in all shapes and sizes - so it's tough to know which size you'd choose. I'd guess a thousand people on a reasonably sized (say 20 mile across) asteroid. SteveBaker (talk) 23:50, 6 May 2010 (UTC)

As for the solar panels, under the feeble gravity of an asteroid, they could be extended great distances into space, couldn't they ? If the asteroid is spinning, that might present more of a problem, but perhaps light energy could be beamed down to receiver stations on the asteroid, by solar panel satellites orbiting it. StuRat (talk) 21:50, 7 May 2010 (UTC)

If you imagine something like The Little Prince then it's fiction and doesn't work for a number of reasons. For one thing, there wouldn't be enough gravity to hold on to an atmosphere so you would need to keep air in a closed space like a spacesuit, a building or a hole inside the asteroid. If humans ever get on to an asteroid then it may be a very expensive science, mining or diversion operation relying on supplies from Earth, and not a permanent settlement. The number of people would likely be determined by the task and how many supplies you want to spend resources bringing in, and not on what the asteroid could theoretically support. PrimeHunter (talk) 00:19, 7 May 2010 (UTC)

The prime examples of fictional hollowed-out asteroids would be Fred Pohl's Gateway and Star Trek: The Original Series's "For the World Is Hollow and I Have Touched the Sky". Clarityfiend (talk) 00:45, 7 May 2010 (UTC)

Or for a total nut-job take on the idea, it's hard to beat Hollow Earth! SteveBaker (talk) 02:02, 7 May 2010 (UTC)

dinosaur o2 requirements versus mammals and others

In a previous question no one seemed to think that the extinction of the dinosaurs 65 million years ago was due to asphyxiation by carbon dioxide even owing to the deaths of animals and humans known to have died after collapsing within seconds of entering a ravine or other enclosure or depression where co2 has accumulated. Since the avail dinosaurs (birds) survived, however, I was wondering whether or not extinction of 65 million years ago may have been due not to a low-to-ground atmosphere of pure co2 but simply the absence of sufficient mixture of oxygen which the grounded dinosaurs could not overcome. Of course this idea might also account for the fact that some dinosaurs occupied mountainous areas high enough to escape the co2 but too high to provide enough o2. In other words a layer between the area too high in co2 and too low in o2 for a dinosaur to survive. Could then the lack of sufficient oxygen be the cause of mass dinosaur extinction whereas what was available was enough for avail dinosaurs, insects, mammals and the rest? 71.100.0.29 (talk) 23:56, 6 May 2010 (UTC)

I'm sure toxic gases played a role after the impact, but large levels of O₂ would have been required for the growth of the dinosaurs. In fact, high levels of diatomic oxygen gas are required for all of the fabulous processes of mammals, and while early mammals may have needed far less than we do now their requirements surely could be on par with current rodents. ~ Amory (u • t • c) 03:33, 7 May 2010 (UTC)

I think the extinction was more likely due to the impact sending huge amounts of water vapor and particulates into the air, causing worldwide nuclear winter: those creatures that could adapt to the cold temperatures survived, whereas dinosaurs, being essentially huge two-legged cold-blooded lizards, could not adapt (lizards need outside heat for their bodies to function, and dinosaurs need a lot of heat because of their size), so they died out. FWiW 67.170.215.166 (talk) 05:29, 8 May 2010 (UTC)

Actually the reverse is true. The amount of energy required to support a large animal's BMR is less: e=m^(3/4). 71.100.0.29 (talk) 20:21, 8 May 2010 (UTC)

May 7

humanure

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

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

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

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

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

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

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

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

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

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

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

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

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

Don't hold your breath

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

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

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

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

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

According to Static Apnea, the world record for breath-holding is eleven and a half minutes [26]. I had thought that it was around six! Man, sometimes I have a hard time going eleven and a half minutes between ginger snaps. (Note that the record was just eight minutes a decade ago, which suggests that being able to get anywhere close to that is highly unusual.) Paul (Stansifer) 03:23, 7 May 2010 (UTC)

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

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

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

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

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

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

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

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

What's a tumor like?

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

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

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

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

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

Reverse dial gauge/indicator alignment

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

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

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

archae biotech

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

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

How many slots on GEO are available for communication satellites?

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

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

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

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

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

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

Stars

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

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

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

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

In other words, they aren't alive, they aren't born, they don't die, and they don't "live different lives" as Whale said -- we just talk about them as if they do. It's a metaphor. People also speak of places and companies and lots of other non-living things as being born and dying, when we mean they start existing and stop existing. --Anonymous, 06:55 UTC, May 7, 2010. —Preceding unsigned comment added by 208.76.104.133 (talk) 06:55, 7 May 2010

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

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

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

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

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

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

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

Nitrogen in tyres

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

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

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

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

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

Four links for you: [27] [28] [29] [30] Ariel. (talk) 10:46, 7 May 2010 (UTC)

Using carbon dioxide will cause the tyres to get hotter. This gas is has a higher molecular mass, so the work done on it by the flexing tyre will heat it more than pure nitrogen and more the normal air. You did not say what type of vehicle you were considering this for. If you are a microbrewery, then it is not worth it, but if you have a fleet of commercial lorries, then you could save because you could have the same old tyres remoulded time, after time, after time. [31] As for nitrogenated beer -sacrilege! --Aspro (talk) 11:40, 7 May 2010 (UTC)

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

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

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

space objects on earth

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

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

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

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

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

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

Space materials-luminosity

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

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

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

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

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

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

Light & escape velocity

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

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

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

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

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

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

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

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

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

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

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

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

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

minimum oxygen requirements and carbon dioxide toxicity

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

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

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

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

wear earplugs 24 hours?

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

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

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

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

Hurricane gustav

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

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

Lung capacity vs. holding my breath

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

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

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

2) Your basal metabolic rate also affects oxygen consumption.

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

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

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

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

and according to Physical exercise,

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

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

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

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

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

I want to destroy a culture...

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

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

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

Crush, stir in, then ten or twenty minutes later stir again. I think it was done because we would then add pulped raw fruit (which also so treated). During the post-war austerity period, few people had refrigeration and we did not want it to start a different type fermentation that may have given it a less than pleasant tang. However, some asthmatics are sensitive to metabisulphites and so it might be easier in the long run just to heat it in a Bain-marie or something. According to page 2 of [32] heating in a hot water bath to 65 C and holding for 3 min should do the trick. --Aspro (talk) 11:15, 8 May 2010 (UTC)

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

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

Invasive surgery on small animals

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

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

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

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

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

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

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

Shell Oil Company

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

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

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

Reaction of metal hydrides from nickel-metal hydride cell

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

May 8

Reaction of chromates with acid

I am still analyzing chromates in my home lab. When hydrochloric acid is added to chromates, it turns black instantly. About 2 seconds later, it fizzes Cl2 furiously and turns green (the color of CrCl3) again. When sodium hypochlorite is added, it turns yellow again, showing the formation of chromates. My question is: What is the intermediate unstable (seems like strong oxidizer, produces Cl2) black substance? It looks similar to CrO5, chromium peroxide, but I didn't add any peroxide to the solution, just HCl. Thanks.--Chemicalinterest (talk) 00:41, 8 May 2010 (UTC)

Could you please give me the formula for the chromate you react HCl with? --The High Fin Sperm Whale 02:12, 8 May 2010 (UTC)

Na₂CrO₄ --Chemicalinterest (talk) 11:22, 8 May 2010 (UTC)

Could it be CrO₂Cl₂? Just an idea. 67.170.215.166 (talk) 05:10, 8 May 2010 (UTC)

Manganese dioxide

Manganese dioxide Graeme Bartlett (talk) 08:10, 8 May 2010 (UTC)

And where, may I ask, did the manganese come from? 67.170.215.166 (talk) 08:13, 8 May 2010 (UTC)

No Mn in the solution, just Na₂CrO₄ and NaCl with a very little H₂O₂, not enough to make the dark black color. --Chemicalinterest (talk) 11:25, 8 May 2010 (UTC)

In the chromyl chloride article it talks about reaction of potassium chromate with hydrochloric acid, followed by sulfuric acid as a desiccant. What happens if the sulfuric acid is not added, which is similar to what I did? --Chemicalinterest (talk) 11:52, 8 May 2010 (UTC)

A possible reaction to form CrO₂Cl₂ is: Na₂CrO₄ + 2 HCl → CrO₂Cl₂ + 2 NaOH --Chemicalinterest (talk) 11:55, 8 May 2010 (UTC)

Then: 2 CrO₂Cl₂ + 8 HCl → 2 CrCl₃ + 4 H₂O + 3 Cl₂ --Chemicalinterest (talk) 18:02, 8 May 2010 (UTC)

Is it possible to shoot a bear in the head?

Hello all, I'm a writer and I've recently completed a novel in which a weatherman gets attacked by a bear and the Civil Air Patrol has to drop a surgeon to him by parachute to save his life. Well anyway, in the opening scene the bear attacks the weatherman, whose own shotgun backfires in his face (I believe some of you might remember me asking about it under a different IP address), and the weatherman (having been partially, but not completely, blinded but still fully conscious) tries to fight off the bear with his bare hands and by hitting it with the gun butt until his partner arrives and shoots the bear in the head. So far, most of the folks who have read the novel seem to like the action, but many of them have also pointed out some bad details to me (mostly in the dialogues). One reviewer, however, objected to something entirely different: he told me that a bullet would not pierce a bear's skull because it's too thick and also sloped like the armor on a tank, so the bullet would just bounce off. Is it true, what he said? And if so, does it depend on the aspect angle of the hunter with respect to the bear (e.g. possible to shoot from the side but not from the front)? I'm not a hunter, so I'd really like to know. Thanks in advance! 67.170.215.166 (talk) 05:08, 8 May 2010 (UTC)

Well, if it's a brown bear (which I presume it is, since black bears don't attack people that way), the really implausible thing is that a person could put up meaningful resistance using bare hands and a rifle butt -- your weatherman better be one hell of an athlete. But that being said, whether a bullet would penetrate the skull depends a lot on the gun. Is is a pistol or a high-powered rifle? If it's a pistol, not only would the bullet probably not penetrate the skull, but the brain is so small compared to the head that you'd be likely to miss it in any case. Shooting for the heart is a much more viable proposition. Looie496 (talk) 05:50, 8 May 2010 (UTC)

The preferred way to take a bear is to shoot it in the shoulder, with a high-powered, fairly small-bore rifle (say, a .30-06 caliber). These rounds are small and fast, and can penetrate the thick skin and fur (and bone), and shatter the shoulder. This incapacitates the bear; it can then be approached and finished with a larger-caliber weapon, e.g. a pistol. Even a high-powered rifle round will (supposedly) bounce off the skull; at the very least, it is not considered fatal and is considered unnecessarily cruel and harmful to the bear (induces slow death). (I am not a hunter and don't really approve of taking bears for sport, but I know a bit about the subject. During radio-science field-work in the great Alaskan interior and Kodiak Island, I regularly stayed in hunting lodges, a few of which were operated by commercial bear hunt guides - there aren't always motels where you want to study radio signals!) Nimur (talk) 06:00, 8 May 2010 (UTC)

You probably have underestimated the power a gun can generate. It is nearly one mile per second! Yes, small bores like .22 or .25 or may be even a 9mm can not do much damage, but bores greater than that can really incapacitate a bear etc. in no time. A buckshot from a short-barrled 12 gauge will tear bear's skull apart. Anything larger, a 10-gauge if you can manage will blow the skull literally off. But the recoil may hurt even you (the shooter)People have killed elephants using big guns.Besides there are special revolvers made by Smith and Wesson to kill bears [[33]]  Jon Ascton  (talk) 07:50, 8 May 2010 (UTC)

For this discussion, assume Colt 45 automatic to the side of the head at point-blank range. And FYI, the bear is a polar bear. 67.170.215.166 (talk) 08:01, 8 May 2010 (UTC)

Oh, and did I say that the bullets are of the hollow-point type? 67.170.215.166 (talk) 08:09, 8 May 2010 (UTC)

Hilaire Belloc recommended platinum bullets. Gandalf61 (talk) 10:07, 8 May 2010 (UTC)

Even if the bullet didn't penetrate the bear's skull, it would have caused it a lot of pain. The sound produced by the gun would scare it. Both effects would hamper the bear's attack and may even cause it to run away122.169.221.144 (talk) 12:51, 8 May 2010 (UTC)

Break the details down into believable chunks. 1) Most guns carried into the wilderness -even if there are bears about- would I think - be light and practical ( I'm using 'light' in the relative sense). Therefore, his partner could have an ordinary and popular type firearm, which the reader may have well fired himself down a the local range. This takes the emphases away from the hardware and focuses it more on the action. I.e., instead of making the gun do all the hard-work, it makes his partner the brave hero instead. 2) Gun magazines for decades have been encouraging people to buy bigger guns by pointing out that rounds can be deflected by a bears scull. So don't go against popularly held beliefs -and in this case it does seem true in some cases. 3) Its bad form for a writer to let the any of the good guys kill with the first shot (unless the hero is down to his very last BB). So let the first round ricochet off into the blue yonder. 4) The suggestions posted above, give a good idea where to put the other slugs. If you look at the these polar bear and grizzly bear skulls one can easily believe the partner in a final act of desperation (perhaps the bear swipes his rifle from is hands) pulling out his grandfather's old Colt 36 and severing the spinal cord with a lucky shot in through the mouth. If the partner gets this close, don't forget to comment on weather this bear also has Halitosis . If the shot is at point blank, don't forget to consider the hot flash going out sideways and the smell of a bit of singed fur. Films and CSI aside, who really carries around a heavy Colt 45 ? Finally: Writer Cory Doctorow has discovered, he sells more books if he also releases them under a Creative Commons licence. HowTo Negotiate a Creative Commons License. --Aspro (talk) 12:55, 8 May 2010 (UTC)

Purely on your last point, Aspro, while that works well for Cory Doctorow who already has a doubly-established reputation, as a fiction writer, and as a champion of Creative Commons, it might not work so well for the (presumably as-yet unknown) OP. 87.81.230.195 (talk) 17:10, 8 May 2010 (UTC)

A writer's biggest problem is obscurity. Who is going to buy a book that they don't know exists, or a book from an author who is unknown to them? By distributing some work under a CC licence, they attract a wider audience. The same has happened, to people who thought of themselves as non writers but have been surprised with offers of book deals based on what the publisher has read on their blogs. Pop-stars understand this. You have to be 'seen' if you want to be noticed. So, this exposer could be even more valuable to any of the little know story tellers out there. --Aspro (talk) 18:54, 8 May 2010 (UTC)

A polar bear attacking an adult man is comparable to an adult man attacking a four year old child. In your case it would be a blind child waving a small stick. To make the story even halfway plausible you need something to slow down the bear. Why not give your guy some pepper spray? That wouldn't necessarily drive off the bear, but might slow it down enough to make the encounter last longer than 5 seconds. Youtube has a bunch of videos of bears attacking various things -- you might be able to write a more realistic account if you watched a few of them. Looie496 (talk) 22:07, 8 May 2010 (UTC)

Conventional Explosive v/s Plastic explosives

Conventional explosive like gunpowder cannot do damage if not held air-tightly. If we open a 12-gauge shot cartidge (NEVER, NEVER TRY IT AT HOME. I AM JUST GIVING EXAMPLE), and put all the smokless "powder", which is of course not plastic explosive, and set it light it will burn away with a SWOOSH and a very brillant flame, but there will not be any explosion. Even a fire-cracker has to be contained in something from which gases cannot escape without destroying it. But as far as plastic explosives are concerned, if I am not very much wrong, they do not need to be air-tightened. A piece of C-4 or semtex can explode in open when properly detonated (can't do it with fire, methinks). But is that also true about nitroglycine. Is it not necessery to hold nitroglycrine in a tight container to cause explosion ?  Jon Ascton  (talk) 08:51, 8 May 2010 (UTC)

I believe the difference is that gunpowder is a "low explosive" which, technically, deflagrates rather than detonates. This makes it suitable as a propellant in munitions and fireworks, but not damaging unless in a confined space. On the other hand, C-4, Semtex and nitroglycerin are all "high explosives", which undergo true detonation. Incidentally, you don't need always need fire to initiate detonation - some explosives are very sensitive and can be detonated by pressure, friction, electric shock, sound or even light. However, such sensitive explosives are usually used in only small amounts in detonators to trigger a larger quantity of more stable "seondary" explosive. See our article on explosive material for more details. Gandalf61 (talk) 10:01, 8 May 2010 (UTC)

Yeah, that is what I wanna know : Will a small quantity of nitroglycrine, let's say 1/10 litre - which is an oily liquid - when not in airtight position, that is lying in open, detonates cause a real explosion practically (like a bomb), or it will just burn with a SWOOSH sound....? Jon Ascton  (talk) 10:43, 8 May 2010 (UTC)

It depends on the speed of the shock wave caused by the suddenly expanding gases released by the explosive. --Chemicalinterest (talk) 11:26, 8 May 2010 (UTC)

Read the links. Nitroglycerin#Detonation says "... a self-sustained shock wave ... propagates through the explosive medium at some 30 times the speed of sound as a near-instantaneous pressure-induced decomposition of the fuel into a white hot gas. Detonation of nitroglycerin generates gases that would occupy more than 1,200 times the original volume at ordinary room temperature and pressure; moreover, the heat liberated raises the temperature to about 5,000 °C (9,030 °F)". That sounds like a "real explosion" to me. Gandalf61 (talk) 12:07, 8 May 2010 (UTC)

And 1/10 litre of Nitroglycerin is not "a small quantity". When we made it in school, we detonated microscopic amounts for a quite noticeable bang.--Stephan Schulz (talk) 15:03, 8 May 2010 (UTC)

For example, consider the iconic image of a stick of dynamite. It's essentially nitroglycerine and sand, wrapped in a cardboard (or paper) tube. The sand reduces the shock-sensitivity, but the paper tube isn't there to confine the blast - only to wrap the material conveniently. That stick of dynamite is still dangerous and can explode. Now, if you're performing road construction and want to remove rock from the highway, you might want to confine the blast to maximize the transfer of energy towards productive, useful purposes - so you might drill a borehole into a rock and use that confined space to harness the blast energy. But the explosive will detonate, confined or unconfined. As far a "plastic", the entire purpose of plasticizer is to reduce shock sensitivity - it has plays very little chemistry role, other than diluting the active ingredients. Nimur (talk) 16:11, 8 May 2010 (UTC)

Gosh, that's mixed up. It's not sand but diatomaceous earth that is the phlegmatizing agent in nitroglycerine. Second, plasticizer are added to make it 'plastic ' hence plastic explosive!--Aspro (talk) 16:31, 8 May 2010 (UTC)

It can be anything - sand, silt, mud, sawdust, ground up pieces of paper - it doesn't matter, as long as it's absorbent... The plasticizer replaces the role of this material, and as an added bonus allows the material to be molded. Nimur (talk) 17:02, 8 May 2010 (UTC)

Think you may be getting mixed up with Gelignite and even that article is inaccurate, as it does sweat – that's what old jelly is renowned for. Although the Dynamite article mentions sawdust, and Nobel used it for his early blasting sticks, Nobel's patent for Dynamite was for the absorption by dichotomous earth (which just happen to be mined close to him in Sweden). The reason why Dynamite was such an improvement on safety was that blasting sticks that used sawdust also 'sweated' - Dynamite didn't. By definition, a stick using anything else is not Dynamite. Just don't believe everything you read on Wikipedia.--Aspro (talk) 17:51, 8 May 2010 (UTC)

Like Kleenex, dynamite has become a genericized name; but you are absolutely correct. Nimur (talk) 17:54, 8 May 2010 (UTC)

Actually, dynamite is perfectly safe unless detonated. It can be thrown in a fire without exploding. --The High Fin Sperm Whale 22:09, 8 May 2010 (UTC)

irradiating an egg

What happens to an egg when it is irradiated? 71.100.0.29 (talk) 12:45, 8 May 2010 (UTC)

The bacteria are killed in it, but I don't think the egg itself is harmed. --Chemicalinterest (talk) 12:47, 8 May 2010 (UTC)

It depends mainly on how much irradiation they are subjected to In-shell irradiation of eggs . Here in Europe, health grounds tend to be considered before profit, therefore, this process is not permitted for most food stuffs -including eggs. I think this link covers most of the objections The Irradiation of Eggs: The Details.--Aspro (talk) 13:22, 8 May 2010 (UTC)

Let's be clear -- if there is a living embryo in the egg, it will be killed by irradiation. Most scientists think that the edibility of the egg would not be impaired. Looie496 (talk) 18:24, 8 May 2010 (UTC)

FWIW I've found a document that give the European position, which also gives examples of which food stuffs are sometimes irradiated over here. Commission adopts first EU report on irradiated food--Aspro (talk) 19:21, 8 May 2010 (UTC)

Insoluble chromate

Is there any insoluble hexavalent chromium compound? I reacted sodium hypochlorite with the product of the reaction of Nichrome with hydrochloric acid. It formed a dark orange-brown precipitate. What is that precipitate? It lightens when hydrogen peroxide is added to it, and dissolves in hydrochloric acid to turn yellow. --Chemicalinterest (talk) 14:43, 8 May 2010 (UTC)

Chromium and acid

Does chromium react with acids to form chromium(II) chloride or chromium(III) chloride? I have some information that may support the former. --Chemicalinterest (talk) 18:44, 8 May 2010 (UTC)

I think CrCl₂, because 2CrCl₃ + H₂ → 2CrCl₂ + 2HCl. However, I think in high concentrations of acids, CrCl₃ will from. --The High Fin Sperm Whale 20:45, 8 May 2010 (UTC)

Because the resulting solution reacts with ammonia to form an easily oxidized green precipitate. --Chemicalinterest (talk) 22:16, 8 May 2010 (UTC)

is it possible to have a defective sense of rhythm?

is it possible to have a defective sense of rhythm or no sense of rhythm? Thank youl. 84.153.199.22 (talk) 18:51, 8 May 2010 (UTC)

Yeah. I know quite a few drummers like that! —Preceding unsigned comment added by RampantFairy (talk • contribs) 19:04, 8 May 2010 (UTC)

See Amusia#Temporal relations. Qwfp (talk) 19:51, 8 May 2010 (UTC)

gas vent

can some1 explain how the monoxide vent to gas central heating works? its been cold in my basment and i hear wind gushing thru my ducts. i suspects the cap on the monoxide vent is missing or something. —Preceding unsigned comment added by Tom12350 (talk • contribs) 19:41, 8 May 2010 (UTC)

Get a technician. You'll want to find the carbon monoxide leak if there is one, it's very toxic and very unnoticeable by smell, sight or taste. Regards, --—Cyclonenim | Chat  00:34, 9 May 2010 (UTC)

Yellowjackets

Hoe many body lengths do they fly per minute? This just a curiosity question. —Preceding unsigned comment added by Unambiguous13 (talk • contribs) 21:01, 8 May 2010 (UTC) Find out how many miles per hour they fly. Divide it by sixty to get miles per minute. Multiply that by 5280 to get how many feet per minute. Find out how long a wasp's body is. Divide 1 foot into the length of the body in feet. Multiply that by the number of feet per minute it flies. That will give you the body lengths. PS: Sorry if you don't live in the US. --Chemicalinterest (talk) 23:18, 8 May 2010 (UTC)

(Edit Conflict) That would depend very much on whether they (generally called 'wasps' outside North America, by the way) were foraging amongst food sources, covering distance purposefully, escaping from danger, or attacking. Our article Yellow jacket gives a typical (worker) body length of ½"/12mm. This site quotes a (non-foraging) wasp flight speed of 0.094mph (in contrast to a foraging flight speed of 0.008mph), while this one gives a wasp flight speed of 2.5m/s (= 5.59mph). (Both sites found in the first half dozen Google hits from searching 'wasp flight speed'.) If my maths are correct, these two figures give body length per minute figures of about 198 and 11,806 (or more realistically 200 and 12,000) respectively. 87.81.230.195 (talk) 23:38, 8 May 2010 (UTC)

did people really have to stay quiet on submarines?

did people really have to stay quiet on submarines or is that just a movie thing? 85.181.146.182 (talk) 22:06, 8 May 2010 (UTC)

also: can you literally hear a high pitch "ping" if another ship or sub is acti ely sonarinf your position?

also, why in films do subs try to go very deep to become impervious cant ships see them there too or drop charges? 85.181.146.182 (talk) 22:49, 8 May 2010 (UTC)

Bird/crocodile grouping

Is there a taxonomic group that includes birds and crocodiles but excludes mammals? I remember reading that birds and crocodiles have similar lung structures, which suggests that they are more closely related than ether are to mammals, but the last common ancestors of the two I can find are Amniote and Tetrapod, which each include mammals. —Arctic Gnome (talk • contribs) 22:28, 8 May 2010 (UTC)

You are thinking of the clade Sauropsida (Goodrich, 1916), if I am not mistaken. Intelligentsium 22:45, 8 May 2010 (UTC)

The minimal group that includes birds and crocodiles is archosauria, I believe. The split between mammals and the others goes back to the very early split between diapsids (birds, crocodiles, reptiles) and synapsids (mammals and many extinct groups), which diverged well over 300 million years ago. Looie496 (talk) 23:56, 8 May 2010 (UTC)

Thanks. So is Archosaur a subgroup of Sauropsida? The relationship between the two groups isn't fully explained in either article. Also, the article on crocodilia seems to have merged the terms into Archosauromorpha. —Arctic Gnome (talk • contribs) 01:33, 9 May 2010 (UTC)

The tree diagrams in Sauropsida and archosauromorpha show the relationships -- archosauria is a subset of archosauromorpha; everything outside that subset is extinct, though. Looie496 (talk) 01:50, 9 May 2010 (UTC)

May 9

Neanderthal genes in modern humans

I read here that I may be partially Neanderthal. What I don't understand is how it is possible that you could only have a small nonzero Neanderthal contribution to the human genome. I mean, the scientists are surprised that it seems to be as large as 1% to 4% instead of a much lower number or zero. But how can any nonzero Neanderthal contribution to someone's DNA be less than an entire chromosome? Count Iblis (talk) 00:23, 9 May 2010 (UTC)

Chromosomes come in pairs, and the two members of a pair can swap parts via the process of chromosomal crossover. After a sufficient number of generations you get a very high level of mixing, even between parts of a single chromosome. Looie496 (talk) 00:35, 9 May 2010 (UTC)

(edit conflict)I think, emphasis on that, that they are referring to the original DNA that is left in your DNA. Clearly when the Neanderthal mated with a Homo sapien, they're contributing chromosomes, but over time this DNA is going be diluted with new DNA from other Homo sapiens. I think I explained that badly. In short, the 1% is the remaining original Neanderthal DNA. Regards, --—Cyclonenim | Chat  00:37, 9 May 2010 (UTC)

Yeah, Looie explains it better. Regards, --—Cyclonenim | Chat  00:37, 9 May 2010 (UTC)

Paintballing science

Where I went paintballing they sold pressurized CO₂ chambers, as well as more expensive pressurized N₂ chambers (used for firing the balls). Why would nitrogen be better than carbon dioxide? Isn't it just dependent on the pressure, which is independent of the gas used? Also, my facemask kept fogging up and I was wondering what could have been done to reduce that. But before that, I'm not too sure why it would fog up...my guess is that it fogs up because the moist air from our lungs (moist because it was raining?) hits the cold visor, causing the air to cool down which makes the water in the air condense. I'm not completely satisfied by this because the air cools down to the same temp as the surrounding air, which can hold its water without too much trouble. I was hopeing someone could help me out with this. But anyways, about preventing the fogging...I heard spitting on the visor helps, but why? Any other useful tips? Thanks. 173.179.59.66 (talk) 01:49, 9 May 2010 (UTC)

After looking at some paintball forums, it seems that the nitrogen is stored as a compressed gas, but the CO₂ is stored as a liquid. As a gas (nitrogen) expands, it gets slightly cooler, but as liquid CO₂ evaporates it gets very cold. Apparently this makes the gun cold and leads to less consistent shots. See [34].24.150.18.30 (talk) 02:27, 9 May 2010 (UTC)