Wikipedia:Reference desk/Science

Welcome to the science section
of the Wikipedia reference desk.

skip to bottom

Select a section:

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

Want a faster answer?

Main page: Help searching Wikipedia

   

How can I get my question answered?

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

Ready? Ask a new question!

How do I answer a question?

Main page: Wikipedia:Reference desk/Guidelines

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

See also:

• Teahouse
• Help desk
• Village pump
• Help manual

January 10

Relationship between sleep and seme* production/quality/maintenance

First, this question is serious and Wiki identified the post as "potentially unconstructive" so I hid some words but they're still deducible.

I noticed that whenever I'm deprived of sleep (less than 5 hours of sleep for 4 or days straight), my seme* becomes very fluid and more clear instead of gel-like and white. When I masturbat* in non-sleep-deprived state and then take some of it in my hand and try to let it drip down to the floor, all of it stays rigidly stuck onto my finger no matter how long I wait. But when I do the same while I'm sleep-deprived, the semen immediately drips down to the floor. Why would this be the case biologically? —Preceding unsigned comment added by Ysk1 (talk • contribs) 01:09, 10 January 2010 (UTC)

Seminal fluid viscosity is affected by several different endocrine processes, the most important being general hydration, which is certainly affected by sleep, although more so by intake and excretion patterns which are in turn also affected by sleep. 99.62.185.39 (talk) 01:44, 10 January 2010 (UTC)

WP:NOTCENSORED. Wikipedia has articles about Semen and Masturbation. Where was your post identified as "potentially unconstructive" ? Cuddlyable3 (talk) 00:03, 11 January 2010 (UTC)

Conversion efficiency.

We have a new puppy - Scott is about 10 weeks old and has been with us for 8 days. We've fed him pretty much exclusively on canned dog food - following the 1.5 cans per 10lbs of body weight that the manufacturers recommend. Scott has been eating ravenously...and the vet said today that he's doing fine - no worms nothing.

So here is the thing - in 8 days, he's gained about 4lbs. Now, the dog food can says 13 ounces per can...and he's eaten 12 cans in 8 days. That's 9.75 lbs of dog food...and it's added 4lbs of dog.

That seems like a SPECTACULARLY efficient rate of conversion of dog-food into dog. I guess some of that weight gain comes from the water he's been drinking - but I can testify that he's pooped an awful lot (I know - I've cleaned up most of it!).

Is this rate of conversion expected? What is the highest rate of conversion that's possible?

SteveBaker (talk) 02:03, 10 January 2010 (UTC)

Was he weighed at the same time of day both times? The difference is weight between different times of day can be quite significant (due to food and water being consumed and solid and liquid waste being excreted at different times and food being metabolised and breathed out gradually over time). --Tango (talk) 02:30, 10 January 2010 (UTC)

It wasn't at exactly the same time - but even so, his weight can't possibly vary by more than he eats & drinks. Conservation of mass applies even to cute black lab mix puppies. SteveBaker (talk) 06:17, 10 January 2010 (UTC)

A small mammal, like a dog, will convert the equivalent of about 2-3% of it's weight in glucose to CO2 and H2O per day in order to maintain its normal activity level. So for stasis a 10 lb dog would need about 4 ounces of bioavailable glucose-equivalent per day (which excludes the water content of the food and whatever portion is removed as poop). Protein and fat have a higher energy density than glucose and so the required weight would be less by up to about a factor of two assuming fatty dog food. Dragons flight (talk) 07:06, 10 January 2010 (UTC)

Ah - good info. So now I can crunch the numbers: so according to the label on the special puppy food (have you noticed how much better the labelling is on petfood than on human food?) it's 78% "moisture" 9% protein and 8% fat with the rest being mostly fiber, linoleic acid and calcium. So the 375g of can of food has 30 grams of fat and 34g of protein - which at 38kJ/g and 16.8kJ/g means that over 8 days he probably got 13.7MJ from fat and 6.8MJ from protein - around 20MJ altogether. So if 4.5kg of dog needs around 90 and 135g of glucose-equivelant for running round and chewing shoes, ethernet cables, etc, etc (and, sadly: more 'etc') - that would be between 11 and 17MJ...but he was about 30 to 40% heavier by the end of that time - so he's using a pretty good chunk of the energy in the food just for "normal" activity. Hyperactive puppy activity has to be pushing the high end of that limit!

Argh...NO SCOTT - STOP CHEWING THE ETHERNET CA@#$%^&*...<NO CARRIER> SteveBaker (talk) 15:08, 10 January 2010 (UTC)

Congrats on the new puppy! --Mr.98 (talk) 02:41, 10 January 2010 (UTC)

A 2:1 ratio across trophic levels doesn't seem remotely possible. However, aren't we all 80% water? That gets you up to 6:1, which is more reasonable. You might also check with the wife and kids to verify that 12 cans of dog food is really truly honestly all the food the little guy has been given or found himself. And ask that SteveBaker if he's been handing out treats too! :) Franamax (talk) 02:53, 10 January 2010 (UTC)

We're talking about canned puppy food - which is basically something that vaguely resembles fatty minced up meat - so isn't the canned food already 80% water itself? SteveBaker (talk) 06:17, 10 January 2010 (UTC)

Must resist demonic urge to burst into song... Clarityfiend (talk) 08:25, 10 January 2010 (UTC)

Gives in to temptation.Cuddlyable3 (talk) 10:00, 10 January 2010 (UTC)

Oh the humanity...Don't we have some kind of wikiRule against posting that kind of link here?  :-P SteveBaker (talk) 14:26, 10 January 2010 (UTC)

Steve, are you sure you are not also missing an unusual number of rats, small children, and rarely used body parts in the neighborhood? More seriously, you should probably keep a regular log and weigh him twice daily to get a feel for the natural variations. Maybe he was particularly hungry and somewhat dehydrated when you got him - that might make a pound or two of difference all by itself. --Stephan Schulz (talk) 15:25, 10 January 2010 (UTC)

Yep - we're gathering more data. We bought my Wife a 'Wii Fit' for Xmas - it has a super-high-precision weighing mechanism and there is a mode for tracking the weight of your pets and producing graphs, etc. We hadn't done a daily weighing until we took Scott to the Vet for his shots and he was weighed there. He was certainly incredibly hungry when we got him - but that hasn't waned after a solid week of shoving food into him at the recommended rate. But based on the calculations above - we're going to add more biscuit to his diet (aside from anything else, it's much cheaper than canned dog food).

I guess you could be right about a chunk of that weight being water - IF he was severely dehydrated when we got him. The animal rescue center had only had him for a few hours before we adopted him - so it's possible that his former owners had not looked after him well. I guess we'll know that if his weight gain levels off abruptly. We probably need to investigate the nutritional value of cat-6 Ethernet cable though - that seems to be a significant fraction of his diet. SteveBaker (talk) 03:24, 11 January 2010 (UTC)

The name of this flower?

Does anyone know the name of this flower? The picture was taken in Japan, and the photographer does not know its name either. --BorgQueen (talk) 03:25, 10 January 2010 (UTC)

Looks like a dogwood of some sort. Maybe Japanese cornel? --Jayron32 04:00, 10 January 2010 (UTC)

Alcohol hangover cause of insomnia?

I was drinking alcohol last night. I have been hung over all day and now I cannot sleep. Is there a link?--Sleep problems (talk) 04:08, 10 January 2010 (UTC)

Did you perhap drink lots of strong coffee to try to "cure" your hangover? Mitch Ames (talk) 08:54, 10 January 2010 (UTC)

Potentially, see Possible_long-term_effects_of_ethanol. LHS at the bottom. --220.101.28.25 (talk) 11:20, 10 January 2010 (UTC)

Those are long-term effects. Not the same thing at all. --Mr.98 (talk) 15:30, 10 January 2010 (UTC)

Might you have been dehydrated? Dauto (talk) 16:06, 10 January 2010 (UTC)

My understanding of insomnia is that one-off bouts can be caused by all sorts of things. If you were a regular drinker and had issues with sleep, there are definite connections there, but if it is a happened-once kind of thing, I'm not sure anyone can say one way or another whether it caused it or not. Alcohol, hydration, caffeine, stress — these can all affect insomnia. --Mr.98 (talk) 16:45, 10 January 2010 (UTC)

My understanding is that alcohol and other sedatives, such as benzodiazepines suppress some of the stages of normal sleep, particularly the REM stage, and in withdrawal you get a kind of rebound effect that produces a disturbed sleep pattern. Mattopaedia ^{Have a yarn} 05:10, 13 January 2010 (UTC)

biosynthesis of LSD-like compounds: how do tryptophan and asparagine end up fusing to share the same nitrogen atom?

Well if you ignore the substitutions on the amine like compounds, LSD looks like a strange fusion of asparagine and tryptophan, sharing the same alpha-amino group. If you look carefully, the chiral hydrogen appears to be on the site of where the alpha-carbon of tryptophan would be, but the methylene carbon next to the chiral amide group appears to be alpha-carbon of the asparagine motif, as though the COOH group has been decarboxylated. Does the ergot fungus somehow really condense tryptophan or asparagine together...? John Riemann Soong (talk) 08:37, 10 January 2010 (UTC)

I extracted this image from a lecture by Prof. Alan Spivey. He implicates that dimethylallyl pyrophosphate and S-adenosyl methionine are involved, not asparagine. (I'll upload the pdf if you're interested in biosynthesis of other alkaloids). --Mark PEA (talk) 13:29, 10 January 2010 (UTC)

environmentally friendly oxidation of aldehydes

What environmentally friendly oxidants are out there that will selectively oxidise aldehydes into carboxylic acids without being nasty (like Cr(VI)...

Can hydrogen peroxide or O2 in the right Zeolite or heterogeneous catalyst say, oxidise a carboxylic acid without say, touching other oxidant-sensitive groups (like aromatic rings, conjugated double bonds, amines...) John Riemann Soong (talk) 09:41, 10 January 2010 (UTC)

What about the ideas listed in the aldehyde article in the oxidation/reduction section? Googling for "oxidize aldehyde into carboxylic acid" was instructive too. Peroxides or halogen (either radical or in a positive oxidation state) could work but you'd need something nucleophilic (either the oxidant itself or a catalyst)...the mechanism of RCHO → RCO₂H is in standard orgo texts, explaining why you need to use dry conditions to stop RCH₂OH → RCHO without over-oxidation. Peroxide is pretty strong so you would need a very mild catalyst that can bleed off that excess reacitivity (H2O2 with various metal catalsts is a common way to oxidatively cleave alkenes). DMacks (talk) 23:29, 10 January 2010 (UTC)

LHC - cooling

I was researching the use of superconductors in the Large Hadron Collider, and the main benefit I saw was that since the LHC operates at 1.9K, the heat produced by resistance in conventional electromagnets would be prohibitive. But thinking through it, and rereading my sources, it was unclear which way round it is. Is the LHC at 1.9K in order to support the superconductors (i.e. to allow them to operate) or is there another reason why it operates at this temperature. Am I therefore correct in my analysis above? - Jarry1250 ^{[Humorous? Discuss.]} 16:33, 10 January 2010 (UTC)

Reading the LHC article again, this suggests that it is only at 1.9K to enable the superconductors to superconduct. Obviously, there are other reasons (electricity cost, for example) why you'd use superconductors, but is the non-production of heat itself one of them? - Jarry1250 ^{[Humorous? Discuss.]} 16:52, 10 January 2010 (UTC)

It is purely an engineering issue, the temperature of the cavern is of little influence on the experiment, given that the energies of it at 300K or 2K are both negligible compared the energy of the beam line. —Preceding unsigned comment added by 92.17.53.6 (talk) 17:27, 10 January 2010 (UTC)

(ec) To generate the intense magnetic fields needed, extraordinarily high currents are required: [1]. Your toaster draws, from the wall, somewhere between ten and fifteen amperes of current. The LHC's magnets, at full operating power, are circulating ten to fifteen thousand amps. Leaving aside the problems that would be caused by resistive heating (and the cost of all that electricity), there just isn't enough physical space around each beamline to fit in enough copper wire to do the job. The current carried by a thousand strands of household copper wire (picture the cord for your toaster, multiplied by a thousand times) is handled by woven niobium-titanium alloy about the size of your finger. TenOfAllTrades(talk) 17:33, 10 January 2010 (UTC)

In essence, then, it would be impractical to generate the 8.5 Teslas required through conventional means, based on space? - Jarry1250 ^{[Humorous? Discuss.]} 17:46, 10 January 2010 (UTC)

Generating the current is another reason superconducting magnets are great: you ramp up the power once, close the loop, then pull the plug, and the magnet then it stays at that field as long as you keep it cold. For a conventional electromagnet, you have to keep supplying that electric current forever from an external generator. With a good enough regulator to keep it constant to avoid magnetic fluctuations (these things need a large nonfluctuating, homogenous (or at least fixed and correctable) field, not just "large but not very stable"). And it would have to run stably at a huge voltage without arcing. Ohm's Law says that to push 15kA, even if the entire LHC only has a resistance of 100Ω, you need 15MV. If the resistance drops to zero... DMacks (talk) 23:15, 10 January 2010 (UTC)

There are superconductors working at temperatures a lot higher than 1.9K, why not use them instead? --131.188.3.20 (talk) 08:00, 11 January 2010 (UTC)

High temperature superconductors tend to be both expensive and fragile. By contrast the very low temperature superconductors tend to be simpler materials that are easy to work. In addition, superconductors break down at high magnetic field strength, but as you lower the temperature you can push towards higher field before the superconductor fails. Dragons flight (talk) 20:44, 11 January 2010 (UTC)

1,1-diacetoethylene

Basically a Michael acceptor with two carbonyls (on the same carbon) ... kinda like the acetoacetone except there's an ethylene group where the alpha-carbon should be.

Is it a common reagent used in industry? Are there any analogues in biology? (Maybe a carboxylic acid or an aldehyde version)? It's been really hard trying to find articles or the "proper name" for compounds with structural motifs I would think are common. John Riemann Soong (talk) 21:23, 10 January 2010 (UTC)

Help! What do I call it? 2-acetoacrylic acid? Isobutylene diketone? (Or isobutylene dicarboxylic acid for the acid version?) John Riemann Soong (talk) 21:37, 10 January 2010 (UTC)

Do you mean this or this? If neither of those, please draw. --Mark PEA (talk) 21:44, 10 January 2010 (UTC)

Yeah I mean either of those. Or the aldehyde version. Or an asymmetric "mixed" carbonyl (like ketone-acid, or acid-aldehyde, etc.) John Riemann Soong (talk) 23:11, 10 January 2010 (UTC)

January 11

Pace of CO₂ Capture

The OP apparently knows more about this subject than we do, so this section serves no purpose. --Tango (talk) 16:53, 11 January 2010 (UTC)

This begins a hidden part. Go to bottom for the part that is currently asking for a response.Julzes (talk) 02:23, 12 January 2010 (UTC)

This is a set of questions related to one I asked recently. It's about the pace at which a single device could remove Carbon Dioxide from the atmosphere.

Assume a device with an orifice a kilometer in diameter is placed at altitude one kilometer and pulls air through it at a rate of 100 kilometers per hour, transforming all of the Carbon Dioxide and some of the water vapor in it into a precipitable chemical (Just assume this part for now) before returning it. How long would it take before CO₂ levels would be at pre-industrial levels? Assume the atmosphere mixes perfectly.

What would be the power expended in the fan of such a device?

What would be the ideal chemical for precipitation, what would be the process chemically, and what would be the power expended in doing this at the same pace as the capture process?

Assuming that a fraction f of the sunlight is used from it, what size array of mirrors parallel to Earth in orbit would produce the power of the processes above?

I don't know if anyone can get the middle part involving the chemical process, but I'd like to see if the other parts have reasonable answers. —Preceding unsigned comment added by Julzes (talk • contribs) 18:36, January 10, 2010

According to Carbon dioxide#In the Earth's atmosphere, industrial activity has increased the amount of CO2 by 35%. That means you would need to process 26% of the atmosphere. The total mass of the atmosphere is about 5x10¹⁸ kg, so we need to process 1.30x10¹⁸ kg of air. At sea level air pressure, that corresponds to a volume of roughly 10¹⁸ m³. Your device processes 314 cubic kilometers an hour. That means it would take about 300 billion years to do the job (and that's ignoring further CO2 emissions). I think we need another plan! --Tango (talk) 22:51, 10 January 2010 (UTC)

Tango, I got about 2000 years. I'm not sure where you lost the thread but 300 billion is not reasonable. Dragons flight (talk) 22:59, 10 January 2010 (UTC)

Using Tango's volume for air, I got 1453 years [2]. Ariel. (talk) 23:20, 10 January 2010 (UTC)

Assuming T's numbers, 10^18/300.10^9/24/365 ~ 380 years for me William M. Connolley (talk) 23:21, 10 January 2010 (UTC)

Tango: He said diameter, not radius. So it's 78.5 cubic kilometers an hour, not 314. Ariel. (talk) 23:31, 10 January 2010 (UTC)

380 years doesn't work. (Even allowing for diameter/radius confusion.) That's the time it would take assuming that the "treated air" was somehow kept separate from the untreated air. Once the air you processed in year one mixes back into the atmosphere, the efficiency of the carbon removal in year two will be diminished. APL (talk) 00:27, 11 January 2010 (UTC)

True, but since we're only trying to remove 26% of the CO2 the diminishing returns won't be too significant. You might need to add about 10% on to the total time, but not much more. --Tango (talk) 01:11, 11 January 2010 (UTC)

Ok, so I don't know what a kilometre is... Nor a diameter... But otherwise, I did well, didn't I? ;) So, it ought to be 75 years (divide my initial answer by a billion to correct for the kilometre issue and by 4 to correct for the diameter issue). We now have 4 different people getting 4 completely different answers... Perhaps it is time to close the Ref Desk... --Tango (talk) 23:55, 10 January 2010 (UTC)

I still don't know what a diameter is. It's multiply by 4, not divide by 4, so I get 1500 years (with more precise calculations, I agree with Ariel). --Tango (talk) 00:00, 11 January 2010 (UTC)

About 25 gigawatts to run such a fan, assuming it draws from air at rest (which would be stupid, but gives you an idea). That's the power equivalent to 18 km² of sunlight in space at normal incidence (or probably an area 5-10 times larger with realistic efficiencies for solar based power collection). Dragons flight (talk) 23:14, 10 January 2010 (UTC)

As for as the chemical part of your question: There is no chemical that can do the job, not without a massive input of energy. And if you had such energy available, just use it and let plants take care of the CO2 in the air.

I know these questions are interesting, but trying to find a way remove CO2 from the air is not necessary. What's necessary is finding a source of energy that does not involve hydrocarbons. If we did that, plants would take care of the CO2 in the air for us. And of course we have such an energy source, but it's slightly more expensive than hydrocarbons. Ariel. (talk) 23:42, 10 January 2010 (UTC)

What is that slightly more expensive energy source?Cuddlyable3 (talk) 23:51, 10 January 2010 (UTC)

There are lots of them. Wind, tidal, solar, nuclear, hydro... --Tango (talk) 23:57, 10 January 2010 (UTC)

Okay, as a follow up, set the question at pre-WW2 levels, double that from 'diameter' to 'radius', assume re-forestation accompanies it so that as much land as is available is (small) forest in 40 years (This may be the hardest part to calculate), and refute the non-sensical claims on chemistry and what is needed by Ariel. Then what's the time period? And, by the way, the solar array is envisioned as being transported in thin pieces stacked like potato chips in a can and then robotically spread out and used for a massive solar furnace. Is the idea for a beam directed at effectively one small area (top of mount Chimborazo) manageable with what is known of high-temperature optics? Directing optics are needed using at least three satellites.Julzes (talk) 00:48, 11 January 2010 (UTC)

Make it a mile in diameter, half a mile altitude (Don't ignore the altitude, but do assume the outflow is at significant distance), and 80 miles per hour. This was the original set of conditions that I thought up. It is quite clear that pre-WW2 and re-forestation must be added to get close to a reasonable time. The conversion to a hydrocarbon of density sufficiently greater than air--is that endo- or exoergic?Julzes (talk) 01:03, 11 January 2010 (UTC)

You may also be interested in artificial trees. ~AH1^(TCU) 01:13, 11 January 2010 (UTC)

I'll take a look at that. Thanks, it may be a piece of the puzzle.Julzes (talk) 01:36, 11 January 2010 (UTC)

Your reforestation assumption is far too imprecise to even begin to calculate a timeframe. Ariel is right, though, if you have a massive solar array then you don't need to worry about removing CO2 from the atmosphere. The current levels aren't problematic, it's the future levels if we continue to emit as we are that will cause problems. If you have the means to build massive solar arrays then we can pretty much stop all emissions and there won't be any problem. --Tango (talk) 01:16, 11 January 2010 (UTC)

Thanks. I and plenty of other people disagree with your claims. Current levels are responsible for past changes already. See graph and the introduction at global warming. Make my preferred specific date of 1932, and assume a long-term leveling of what needs to be combatted at 2020 current projections (continued rise in emissions to a leveling). Assume for forestation that as many trees as were on Earth and have been lost since 1932 (suicides of Hitler's niece and Stalin's wife) are replaced and allowed to start growing in 2020, just as an average planting date, for both CO₂-level dates. Assume algae and the rest of the flora are also functioning at the same date's level (in addition, since small trees won't fit that).Julzes (talk) 01:32, 11 January 2010 (UTC)

There have been changes, yes, but no large scale problems (there has, perhaps, been an increase in the rate of natural disasters like hurricanes and major flooding, but I haven't seen any convincing evidence that the increase is statistically significant, if it even exists). --Tango (talk) 01:41, 11 January 2010 (UTC)

Actual warming lags behind CO₂ (and CH₄, which may all dump into the atmosphere from more than one source over a short time-period), and you haven't read through it all if that's what you think. I really must disagree.Julzes (talk) 01:51, 11 January 2010 (UTC)

Rule out the need for any energy to be used at all for separation of CO₂ and do or do not consider the idea of conversion to a precipitate as an alternative to sequestration, as you prefer. There is no energy required for separation, as whatever excess heat there is in the processes may be directed to a ground site (at the equator) for reaching 40-degrees Celsius (as per the reference given on artificial trees above).Julzes (talk) 02:03, 11 January 2010 (UTC)

How can you rule that out? There are no methods of turning CO2 into a precipitate without input of energy. The 40-degree method uses change in humidity as the energy source. It might work for a small (tiny actually) "tree", but not for something like what you want. You are ruling out so many things you might as well get a magic wand. You need an energy source to remove CO2. If you have an energy source, forget about using it to remove CO2, and just use it directly instead of adding more CO2 in the first place. You've been told this before, but it seems to be a blind spot for you. Ariel. (talk) 02:47, 11 January 2010 (UTC)

I think I've met you halfway on this, and you have been sounding consistently intellectually rude (and ill-informed on the subject of global warming) since my last post. At any rate, how do you yourself know that change in humidity cannot be used for this rather than a small tree? I'll grant it's true, if you will explain this, as I am genuinely interested in preventing the catastrophe that I know is imminent (in generational terms, neither hstorical nor next-year terms).Julzes (talk) 03:11, 11 January 2010 (UTC)

I'm all for the cleanest nuclear fission as well as all the others at the same time, by the way, but I am quite convinced we will need to and will be scrubbing the atmosphere as well. I've actually put a bit of thought (if not actual hard-headed research) into the question, and you haven't said a single thing that might enlighten me until this comment about humidity and scale.Julzes (talk) 03:22, 11 January 2010 (UTC)

Oh, I do appreciate your calculation, FWIW. I'll check up on the whole calculation as it proceeds here.Julzes (talk) 03:25, 11 January 2010 (UTC)

Never mind trying to explain that changes of humidity can't be used for something this scale. That's false or I'll eat my shorts.Julzes (talk) 03:34, 11 January 2010 (UTC)

Everybody keep in mind that using energy at the location at which it is generated is much much more efficient than building infrastructure for transmission and for transmission itself. That said, once this devoted device had fulfilled its initial purpose, it could be used for Latin American energy needs.Julzes (talk) 03:38, 11 January 2010 (UTC)

One thing I'm a little interested in that I don't know about as well is whether space-to-ground transmission would best be accomplished by something changing the spectrum of the Sun's light--microwave or something.Julzes (talk) 04:17, 11 January 2010 (UTC)

I'm also aware of research that shows that CO₂ passed over a certain heated catalyst be used to make gasoline. If, as I assume, transformation to a precipitable chemical is innately endoergic, I will have fully conceded that sequestration and/or passing the gas over flora or a more efficient converter (in the future) in an intelligently designed system should be given the higher attention.Julzes (talk) 04:17, 11 January 2010 (UTC)

If you're right then I can make a perpetual motion machine by turning gasoline into CO2 by burning it and extracting the energy - and then converting the CO2 back into gasoline using some of that energy. Since perpetual motion is most definitely impossible (several of the laws of thermodynamics are very clear on this point!) it follows that any device that could convert CO2 into gasoline would require considerably more energy to do so than you'd get by burning the gasoline in the first place. That's really the problem with getting rid of CO2 by means other than sequestration (which is highly dubious for a bazillion other reasons). CO2 is in a very low energy state - which is what you'd expect from stuff that is the byproduct of energy extraction. Converting it to something different puts it into a higher energy state - and that's going to cost you power...probably LOTS of power. Pretty much anything you could do to remove the CO2 we added into the atmosphere would require more energy than the total amount that humans have gotten by burning things since the dawn of time. I suppose if we found a really cheap source of abundant non-CO2-forming energy somewhere - then we could use some of it to power our civilisation - and the rest to reverse the CO2 damage. However, if we had any hope of getting such a thing in the immediate future, we wouldn't be in the mess we're currently in because we could use it to simply remove the need to make more CO2 right now - which would be enough to save the planet if we could do it SOON. It's no good hoping for fusion of helium-3 obtained from the moon because by the time we get it the polar bears will be extinct and removing the CO2 won't bring them back. SteveBaker (talk) 05:02, 11 January 2010 (UTC)

What part of what I said didn't you understand? Maybe the word 'heated', perhaps. At any rate, when I said 'familiar' I should have hedged a little bit and the purpose of the process was not to generate energy out of nothing. Last I saw, there were not 'several' laws of thermodynamics, and I could continue with this. You obviously didn't understand the word 'endoergic' (or at least the sentence containing it). You needn't have replied so strenuously, your statement about Carbon Dioxide seems quite the logic I would use, and we're both basically on the same page about how bad things are.Julzes (talk) 06:34, 11 January 2010 (UTC)

Hold on now, I'm not convinced about the logic on burning. The same logic says that obviously such an apparently weak process as photosynthesis shouldn't be able to make anything for life out of the Carbon. I imagine that CO₂ is near minimum energy for the constituent elements, but to consider it rock bottom even with access to other elements doesn't sound right, at least to me. It's really almost the only thing fueling life itself (not human needs) on this planet.Julzes (talk) 06:45, 11 January 2010 (UTC)

What we need to do is reproduce the Azolla event which removed much of the earth's carbon dioxide using azolla. Graeme Bartlett (talk) 07:33, 11 January 2010 (UTC)

I'll buy that if things go really badly.Julzes (talk) 08:03, 11 January 2010 (UTC)

The energetics of CO₂<--->C(graphite)+O₂ are such that the compound on the left is more apt to turn into the mixture on the right than the reverse, right?Julzes (talk) 08:09, 11 January 2010 (UTC)That's what it looks like to me if it takes something like chromic acid to oxidize graphite (allotropes of carbon).Julzes (talk) 08:29, 11 January 2010 (UTC)

You mean the reverse of what you said. The one on the right will turn into the one on the left. And not "more apt". Will ONLY, this is not a statistical process, this in a one way processes. And CO2 is pretty much rock bottom - even with access to other things (except maybe fluorine compounds), CO2 is not what fuels life - sunlight fuels life.

"The same logic says that obviously such an apparently weak process as photosynthesis shouldn't be able to make anything for life out of the Carbon." ???? Are you serious? What kind of logic is that? Is it a question? If so, then no, that's not correct.

I hate to break Ariel's post in two here, but this was a response to someone else's ridiculous response to me on something else. The same logic as that person's logic.Julzes (talk) 10:27, 11 January 2010 (UTC)

You can't turn CO2 into ANYTHING else without input of energy (endoergic to use your words). Exactly the same energy as was released in making it in the first place. Trying to remove CO2 directly from the air is 100% pointless. Except that you can store the CO2 as is if you want. But that's about it. Anything else you want to do needs a source of energy. If you had such a source just use it to power everything else, and plants will handle the CO2. (The change is humidity energy source is tiny, very tiny. You need to cover practically the entire earth to harvest enough energy from it. And if you did that, I'd rather build a windmill, or a solar concentrator.)

And the saddest thing is we HAVE those energy sources. We just don't use them.

BTW, I'm sorry if I sound rude. I edited this many times, but I could not find any other way of getting the point across. Ariel. (talk) 08:45, 11 January 2010 (UTC)

I'm sorry, but I just don't see any hydrogen here. What you seem to say is heating oxygen gas and graphite with nothing else present will produce Carbon Dioxide. I suggest you try lighting some graphite (or diamond since it is less stable) on fire. The word is 'endoergic' (or endothermic if you prefer). Leave this question permanently, please. You seem like you don't know what you are talking about. I won't ask you again.Julzes (talk) 09:06, 11 January 2010 (UTC)

That's right, 'endogenic' was the wrong word.Julzes (talk) 09:27, 11 January 2010 (UTC)

It looks like Ariel might be (a little) right here. The enthalpy of formation of CO₂ is the same sign as that of water, which definitely means that graphite will burn; so I've asked a question about that below. (I have to say s/he has hardly been helpful and doesn't understand the situation all that well, FWIW.)Julzes (talk) 10:00, 11 January 2010 (UTC)

Ariel is right, graphite + oxygen is exothermic and will burn to CO2 while emitting about 390 kJ/mol (a relatively low number compared to most fuels but definitely exothermic). The reaction has a large activation energy, and so it is not easy to get it started. You need to heat it to about 300 C to kick off a reaction, and because graphite is highly thermally conductive, you need to heat a large volume at once, otherwise the heat will be conducted away rather than sustaining a reaction. Hence matches tend to be ineffective at lighting graphite because the area affected is too small. As Ariel says, CO2 is a low energy state, and most reactions to change it into other compounds require energy input. Dragons flight (talk) 10:11, 11 January 2010 (UTC)

Thanks. Well, I can fully erase the question below, since your post is just about as close as one could get to a direct answer to that one.Julzes (talk) 10:19, 11 January 2010 (UTC)

One logical possibility is that the optimal solution involves the conversion of some of the air into fertilizer. At any rate, whatever the full solution is is not likely to be found here.Julzes (talk) 12:25, 11 January 2010 (UTC)

This is where the editing is split by a hidden part.Julzes (talk) 02:21, 12 January 2010 (UTC)

The question was reposed at the top. If anyone wants to answer or see what answer is given, that is the place to go. Leave the earlier part alone or fold it up on my request if you know how to do it properly.Julzes (talk) 01:42, 12 January 2010 (UTC)

I'm fine with closing up that long part that got off topic, as I asked it to be partially closed rather than fully (in the hidden part).Julzes (talk) 02:38, 12 January 2010 (UTC)

This end is unacceptable to me--a number of related questions were asked, differing from the original. Please calculate the time for CO₂ in the atmosphere to reach mid-1932 levels assuming 1) That trees and other flora are restored to the numbers of that date with an average new tree planted in 2020 (spread them uniformly over 2010-30); 2) Emissions of the gas double in their decline relative to what their increase was around 2020 projections; 3) a device can remove all of the gas from a part of the atmosphere equivalent to passing air at altitude 1/2 mile through an aperture of diameter 1 mile at velocity 80 miles per hour, and one of these devices is placed in operation every five years from 2020 onwards. We won't talk about what would be done with the gas immediately after capture, if it's all the same to the people here (Just assume the energy source is strong enough to get a precipitable compound from CO2 and other gases and the substance is spread through global circulation and falls to the ground in an inoccuous way). That should be a precise enough question to be answered.Julzes (talk) 01:30, 12 January 2010 (UTC)

Respond, if one can, below the three part exchange that follows.Julzes (talk) 09:49, 12 January 2010 (UTC)

I don't care if you find it acceptable or not. Your attitude towards volunteers that have been trying to help you has been unacceptable to me and I am not going to allow it to continue. If you wish to object to this decision, please do so at Wikipedia_talk:Reference desk. --Tango (talk) 02:02, 12 January 2010 (UTC)

Going off topic to avoid dealing with the likely need for geoengineering as well as all the other stuff that's slow to change is what I saw being done by the person in question (and others, like yourself). That said, I'll accept the calculation at about 1500 years for all the way back to the start of the industrial revolution with a single device with altitude treated as at sea-level and diameter 1km and speed 100km/hr as well done.Julzes (talk) 02:49, 12 January 2010 (UTC)

Now, no more posts about people here, please. This is not about me, Tango, or the one person I laid into a little bit (who laid into me first by expressing that my question was pointless and other somewhat irrelevant things).Julzes (talk) 02:16, 12 January 2010 (UTC)Anybody who wants to take a shot at the complications here, after this is the proper place. The part on emissions means that whatever the increase is expected to be in 2019, double that is the decline in 2021.Julzes (talk) 02:28, 12 January 2010 (UTC)

At WMC's talk space, I've thrown in another condition for calculation for comparison purposes that might get around the same teperature. It's more complicated still, but perhaps it can be done. Still get the time period under identical conditions but for 1979 as the date in place of 1932 and with cool roof (reflective) technology being uniformly brought to universality in 2030. So, two sets of conditions wanting the time period required and also whether this later set of conditions is as cool as 1932 conditions would be. The second set should be much faster and it also requires a less dubious condition on flora restoration.Julzes (talk) 17:36, 12 January 2010 (UTC)

I can understand this question not getting much attention at this point. What I cannot understand is why nobody knew or bothered to state that both Magnesium Carbonate and Calcium Carbonate creation releases energy from Carbon Dioxide. Hmph!! Julzes (talk) 14:27, 13 January 2010 (UTC)

...because it does not, or at least not with commonly available input material. It you have raw, elementary calcium or magnesium, then yes - but again, in that case you can just burn the metals for energy. But neither unoxidized calcium nor unoxidized magnesium are available in significant amounts in nature. --Stephan Schulz (talk) 14:47, 13 January 2010 (UTC)

Well a little elucidation of the whole question could have been a good thing. Anyway, the claim that CO₂ is pretty much rock bottom for Carbon was wrong. Now, combining anything naturally occurring with CO₂ to get a release of energy may be impossible on a large enough scale, but to treat that as obvious is a bit superficial.Julzes (talk) 17:21, 13 January 2010 (UTC)

"Well a little elucidation of the whole question could have been a good thing." Which was what Ariel, among others, tried to do. Look at how you reacted to that. Nobody else wants to be spat on for trying to help. 86.178.229.168 (talk) 16:27, 14 January 2010 (UTC)

You seem to me to be misinterpreting what Ariel was doing.Julzes (talk) 17:05, 14 January 2010 (UTC)

Human hair: stripes and dots?

I'm wondering if there has ever been a case of a human with hair (obviously head hair would be the best candidate here) that showed signs of being striped, dotted, or somehow patterned in the way other mammals (zebra, cheetah, panda) are, presumably due to the mutation of a certain gene/genes. If not in humans, perhaps in an animal that, like humans, is known for having single-tone fur (polar bear, squirrel?, lion?). I am of course referring to naturally occurring phenomenon, not like lion-zebra hybrids : D. 219.102.221.49 (talk) 02:18, 11 January 2010 (UTC)

Well, there are no spotted wolves - but there are plenty of spotted dogs - and dogs are descended from wolves. SteveBaker (talk) 02:42, 11 January 2010 (UTC)

Lion-zebra hybrids?!? Talk about "playing with your food"! APL (talk) 02:59, 11 January 2010 (UTC)

I think that a Chimera (genetics) might have two-toned fur or hair where you would expect a single-tone coat. APL (talk) 03:04, 11 January 2010 (UTC)

Cows and horses are also descended from animals of single tone fur. Many cows and horses are still of single tone, but many have also been bred for multi colour spots and patterns. The patterns were not "put" there by humans, the patterns were a naturally occurring phenomenon which has for thousands of years and probably hundreds of generations been selected for by humans. The thing you have to keep in mind is that no one would even claim that spots or stripes all of a sudden APPEARED in zebras or tigers after one generation, like your question implies you think it might. Those characteristics mostly evolve by very small increments, typically imperceptible from one generation to the next. There is absolutely NO reason to think spots must be present in the human population for spotty animals to have evolved, just as there is no reason to think some humans must have trunks for elephants to have evolved. Vespine (talk) 03:14, 11 January 2010 (UTC)

Darwin (in OoS) seemed to think that horses were partly or wholly evolved from a striped species, due to the occasional appearance of stripes in related hybrids and "monstrosities", but I don't know about cows. I'd like to think though, that the increments would be noticeable, though maybe only to a breeder with a good eye. On that point, I suppose it wouldn't be strange then if there were common mutations in the human genome producing striped/patterned hair that was merely too faint to be significant. 219.102.221.49 (talk) 03:47, 11 January 2010 (UTC)

Human hair is too long to be "spotty." Humans do occasionally display gradations of color throughout the head. It is not generally particularly pronounced. More commonly there are gradations of hair color on different parts of the scalp. The nape of the neck is sometimes different than the top of the head; similarly around the temples. But long hair might tend to disguise this. Bus stop (talk) 03:21, 11 January 2010 (UTC)

You may want to read Cat coat genetics for the mechanisms defining the (multi)color patterns of cat fur. It does not work the same way in humans, though. --Dr Dima (talk) 03:23, 11 January 2010 (UTC)

Thanks for the responses! 219.102.221.49 (talk) 03:47, 11 January 2010 (UTC)

I rather agree that the length of the hair makes a clear identification difficult. I have a very full beard - and as I age, parts are going grey - my chin is grey and I'm grey next to my ears but my cheeks are still brown. Technically, I have several grey "spots" (or maybe "stripes")...but nobody seems to think of it like that though. SteveBaker (talk) 04:37, 11 January 2010 (UTC)

That's odd -- I always thought of you as a 30ish whippersnapper. DRosenbach ^{(Talk | Contribs)} 18:29, 11 January 2010 (UTC)

"I am not getting old! I am simply turning into a gray dalmatian!" 219.102.221.49 (talk) 05:47, 11 January 2010 (UTC)

FRED: Your face is lined, your hair is grey

RUTH: It’s gradually got so.

-- W. S. Gilbert Cuddlyable3 (talk) 12:57, 11 January 2010 (UTC)

For what it's worth, Waardenburg syndrome is remarkable for a "white forelock" of hair, which helps to make it one of the more easily recognized genetic syndromes. Other terms used to describe this phenomenon are poliosis and piebaldism, which refer to depigmented patches of hair. In some cases, piebaldism is genetic, although it seems as though the genes affect hair pigment itself, not so much the patterning of pigmentation. --- Medical geneticist (talk) 19:09, 11 January 2010 (UTC)

I have heard the term "witch lock" or "witch's lock" for a natural streak of white or blond hair in an otherwise dark head of hair. But Google returns few uses of those terms. 75.41.110.200 (talk) 15:51, 12 January 2010 (UTC)

Mirrors and their color

I've been spending a lot of time thinking about mirrors lately (the normal, flat, glass-fronted, silver-backed kind), and I find the idea of a mirror's color to be very strange: While the mirror is reflecting a 100% accurate picture of me, I still know, without being told, that the mirror is also silver colored at the same time.

How is this possible? How is the mirror reflecting a complete image of me and my surroundings (and their completely non-silver colors) and I still have this niggling (almost subconscious) knowledge that the mirror is silver at the same time? ~fl 03:43, 11 January 2010 (UTC)

Could it be the other way around? I imagine silver is really just a grayish mirror, and though a true mirror has no color at all, your mind might register it as "close to silver", assigning by association the color "gray". Just wondering out loud : ) 219.102.221.49 (talk) 03:52, 11 January 2010 (UTC)

Keep in mind that no mirror truly reflects 100% of the light that hits it; reading our article, I see that even a high grade technical mirror only reflect abour 90-95% of the light, when new. I imagine that different wavelengths are absorbed in different amounts, which may give rise to a "silverish" mirror (pure spectulation on my part). There's probably also some psychological element too, given that you know that a mirror is glass that has been "silvered" (again, I'm just speculating). Buddy431 (talk) 04:11, 11 January 2010 (UTC)

(So does a white object...that's not a good answer!) SteveBaker (talk) 04:21, 11 January 2010 (UTC)

The problem is what we mean by "The color of an object". It's a typically human, imprecise, piece of terminology...one that gives computer graphics guys like me endless headaches when dealing with artists and designers.

Silver isn't really a color. Look at a spectrum - there is no frequency or combination of frequencies in the light that is "silver". You can't mix "silver" in Photoshop using just red, green and blue - yet those are all our eyes can see. The closest we can get is "grey". So where is "silver"? If you look at a photo of a "silver" car on your computer monitor - it's only made up of the same reds, greens and blues - so how come you can get silver in a computer photo - but not mix it yourself? What happens if you bring the photo into photoshop and grab a bit of the car with the eyedropper tool? You get grey.

The problem here is that our concept of "color" is a bit flakey.

When light hits a surface, three entirely different things happen:

1. Some percentage of the light (more or less regardless of frequency) is simply bounced off in a direction that's fairly close to the angle at which it came in (this is "specular reflection").
2. Some percentage of the light is absorbed by the surface (in some specific range of frequencies that depend on the chemistry of the material).
3. What's left is scattered off more or less uniformly in all directions (this is "lambertian reflection")

Those three things have to add up to 100% of the incoming light because all of the light has to go somewhere (well, except for objects that glow in their own light, translucent objects, etc - but let's ignore those for the sake of a simple explanation).

The thing we consider to be the "color" of the object is only the lambertian reflection part - the light that's scattered uniformly without being absorbed. We say that because that is the only set of frequencies that seems to be innate to the nature of the object - but that's not very scientific - which is why the concept breaks down for things like mirrors. In white light, a red plastic ball has a really bright white 'shiney spot' on it - but somehow that doesn't matter, we don't say that this is a "white" ball. We say that the ball is "red" - even though there is a ton of white light being specularly reflected in a certain small set of directions.

In the case of a mirror, close to 100% of the light is specularly reflected (90% or more) - leaving almost zero percent being either absorbed or lambertian-reflected. So if you had to use the same naming rule you used for the shiney red ball - you'd have to say that the mirror was "black"...which is the closest you're going to get to a good answer to your question! An object that has only 5 to 10% of lambertian reflection is either black or a very dark grey.

For some reason, we have no problem labelling a car with really shiney black paint as "black" - because in that case, even though there is not much lambertian reflection, a lot of the light shining onto the car is being absorbed - so far less than 100% is being specularly reflected. A black car doesn't look like a "silver" car.

The difference between "silver" (like the color of the unpolished metal) and "mirror" is the precision with which the specular light is reflected at PRECISELY the same angle as the light came in at. Mirrors (and highly polished metals like silver) do that reflection so precisely that a nice sharp image is formed. Unpolished silver reflects a similar amount of specular light to a smooth mirror - but it's not reflected at precisely the incoming angle - so a proper, sharp image doesn't form...although a softly blurry one might. What we're talking about now is not the "color" at all - but the "shininess", which is really a different concept. However, we know that the petal of a red flower, a red plastic ball and a shiney red car can all be the same "color" - even though the nature of the specular reflection is wildly different between the three of them.

SteveBaker (talk) 04:21, 11 January 2010 (UTC)

Paraphrasing Steve's coment above (But with much reduced wordyness): Silver ain't a color. Dauto (talk) 05:13, 11 January 2010 (UTC)

So who's going to delete the Wikipedia article, and update Wiktionary? We'd better let Oxford Press know that their dictionary is wrong as well. Mitch Ames (talk) 09:30, 11 January 2010 (UTC)

And then there's the Crayola corporation....

Just the same, in context, the claim is true; that sort of silver, at least, is not a color. --Trovatore (talk) 09:34, 11 January 2010 (UTC)

The OP did explicitly say "... a mirror's color ..." and "... the mirror is also silver colored ...". Mitch Ames (talk) 10:18, 11 January 2010 (UTC)

Right. That's precisely the sort of silver that isn't a color. There is a color called silver; it's sort of a light gray. But it has nothing to do with mirrors. --Trovatore (talk) 10:33, 11 January 2010 (UTC)

... and some "silver colours" combine the light grey with tiny reflective patches from which light is specularly reflected (like a mirror) to give a "shiny" or "metallic" silver. We tend to use the name "silver" for a range of reflective surfaces from a "proof" silver coin that is almost like a mirror, through matt silver that has some specular reflection, to just a shade of light grey with purely lambertian reflection. Dbfirs 10:45, 11 January 2010 (UTC)

See [3] and scroll down to the bottom two images. The bottom shows specular + Lambertian, the one above shows specular only (mirror) reflection. Cuddlyable3 (talk) 12:43, 11 January 2010 (UTC)

I'm not saying that people should stop saying that mirrors are silver or that they should stop thinking of silver as a "color". I'm merely trying to point out that the english language is imprecise (well, there's a shock!) and that in order to answer the question of what color a mirror really is, we have to understand why this is a question of linguistics and not a question of science. If you want a scientific answer then it is undoubtedly that silver isn't a "color" and that mirrors are really shiney black objects. If you only want a linguistic answer then (a) don't ask the science desk and (b) you already know that you want to call it "silver" so why bother asking?

So let me see if I understand Steve's answer correctly. Most of the light that hits a mirror (say 90%) is reflected at a similar angle that it came in at (called specular reflection). This is what makes a mirror usefull as a mirror. Of the remaining 10%, some (most?) is scattered in all directions (called lambertian reflectance), and this is what gives any object its "color" in a strict sense. The rest of the light is absorbed. In a mirror, the "color" caused by the lambertian reflection is a gray. When our minds see both this gray color, and a large amount of specular reflection, we say that a material is "silver".

I suppose that the same could be said for other metalic colors as well. When I say that a polished gold coin is "gold", what I really mean is that the lambertian reflection gives the coin a yellow or orange color, but the coin also reflects a large amount of light hitting it out at a similar angle to what came in. Buddy431 (talk) 15:37, 11 January 2010 (UTC)

Yes - I think you have that right. I don't honestly know how much of the light hitting a mirror that is not specularly reflected ends up being absorbed and how much becomes lambertian reflection. My guess is that for reasonably good mirrors and surfaces like chrome, almost everything that remains (after specular reflection has taken it's share of the incoming light) is absorbed...but for less good mirrors, perhaps there is still some lambertian reflection going on - I kinda doubt it. Hence, IMHO, mirrors are "black". SteveBaker (talk) 18:45, 11 January 2010 (UTC)

I would say that for a mirror, "silver" and "gold" come from the metallic elements. An ordinary mirror is silver in the sense that its reflectivity spectrum is roughly flat over visible wavelengths—silver, the element, has this property, but so does aluminum. Gold, on the other hand, reflects blue light poorly, giving a gold-coated mirror (as used on infrared telescopes, for example) its distinctive appearance. Reflectivity has a nice plot of reflectivity spectra. -- Coneslayer (talk) 14:35, 12 January 2010 (UTC)

Bathroom Bacteria Aerosol

Which lowers the spread of bacteria from a toilet flush? Putting the lid down or leaving it up? Does leaving it up directly expose its surroundings or does leaving it down incubate the aerosol after a flush?--99.11.199.76 (talk) 03:49, 11 January 2010 (UTC)

I can't answer your question - so I'm going to tell you why it's irrelevant instead! Countless studies (my favorite being two different tests from the Mythbusters) show that toilet seats are one of the cleanest places in the house. The hard, non-porous surfaces have zero nutrients - very little moisture and may be sprayed with urine (which is an antibacterial agent) and are frequently exposed to light - that's a very hostile place for bacteria to live. So don't worry about it. You should be much more concerned with (IIRC) the various sponges and pads used around your kitchen, your light switches and your computer keyboard. All of those are full of NASTY bacteria. You could quite safely eat lunch off of your toilet seat...but you should seriously consider washing your hands after using the computer and keeping food away from the keyboard area altogether. SteveBaker (talk) 04:02, 11 January 2010 (UTC)

Whilst I agree with SteveBaker (above), it must surely be true that putting the cover down before flushing must reduce the aerosol that travels to nearby porous, nutrient-rich surfaces. Has any research been done on this? The human body is adapted to cope with almost all normal bacteria, it is only the unexpected (and virulent) ones that cause illness, and they can be spread in so many other ways. Do most users never clean their computer keyboards? Dbfirs 08:17, 11 January 2010 (UTC)

In ~20 years of using computers I've never once cleaned a keyboard... ok, I did it ONCE, but that was only because I spilled 2 liters of coke across it and all the keys stuck... 218.25.32.210 (talk) 08:34, 11 January 2010 (UTC)

I agree - but humans are much less vulnerable to bacterial diseases than most of us think. It's widely believed that being overly clean is the reason that allergies and asthma are on the increase - and using antibacterial agents is guaranteed to cause them to become less effective over time as the bacteria evolve resistance. If we don't get regular exposure to the 'stuff' in our environment, our immune systems don't develop the necessary resistance to them. So NOT obsessively cleaning things that are not a realistic and serious threat is probably counter-productive in the longer term. Also, most keyboards are used predominantly by just one person at work - or by a few family members in the home - that means that whatever nastiness there is there was probably put there by you - so you're already exposed to whatever nastiness is there. Hence I would certainly consider cleaning a keyboard that a large number of strangers use - but not the ones I use at work and at home. Similar arguments apply to light switches. SteveBaker (talk) 14:46, 11 January 2010 (UTC)

Yes, I remember many years ago a large amount of coke being spilled into an Archimedes school computer where the keyboard is built-in. I took the machine apart and washed the keyboard under the hot tap, and it worked perfectly (better than the others) thereafter. Dbfirs 10:35, 11 January 2010 (UTC)

I wash mine, but not antibacterially. Mythbusters has also shown that the aerosol effects of flushing toilets are virtually nonexistent - a few dozen toothbrushes used for brushing teeth were virtually indistinguishable with regards to bacteria count, no matter where they were kept - near the toilet, other side of the room, even in a diferent room. Vimescarrot (talk) 10:55, 11 January 2010 (UTC)

If you watched their 'extra' material on their website, it turned out that the bacteria that was on the brushes came from the people using them - not from the bathroom environment they were kept in. SteveBaker (talk) 14:46, 11 January 2010 (UTC)

So there really is very little risk from the "aerosol" effect on flushing a toilet, and we might as well leave the cover up (as I always do anyway)? Why, then, do health authorities make such a fuss about the risk of "coliform" bacteria? Is there a much higher risk from hands? Dbfirs 08:25, 12 January 2010 (UTC)

Coliform bacteria are easy to spot, so they're used as a proxy for other, hard-to-spot hazards. --Carnildo (talk) 01:30, 13 January 2010 (UTC)

1,3,5 trihydroxyhexane

Does this compound exist? Or does it too easily convert to benzene? (I hate it when you google volatile compounds like that and they don't tell you why it doesn't exist.) John Riemann Soong (talk) 04:20, 11 January 2010 (UTC)

Are you thinking of 1,3,5 trihydroxycyclohexane? This is more likely to form benzene by eliminating water. Graeme Bartlett (talk) 07:24, 11 January 2010 (UTC)

Yeah that important cyclo description. Yes. What I'm thinking of not the synthesis of benzene itself, but the synthesis of substituted aromatic rings via substituted 1,3,5 trihydroxyhexanes (with aldol condensations and the like and reductions in the right places). Induce aromaticity, and boom! No need to worry about nasty Acyl-Crafts reactions. John Riemann Soong (talk) 07:32, 11 January 2010 (UTC)

"1,3,5 trihydroxyhexanes "...dude--you just said cyclo is important and that you are having trouble finding info because you don't know what terms to use...start by using something even close to chemically correct for your situation even if not best!

What's the basis for thinking these compounds are very volatile? Polyhydroxylation raises bp substantially (why?). None of the isomers (structural nor stereo) of trihydroxy-n-hexane nor of trihydroxycyclohexane are particularly volatile--bp are well over 100°C (sometimes up to several hundred at <1mmHg!). DMacks (talk) 07:44, 11 January 2010 (UTC)

Volatile as in "reactive" (layman's term), that is, it quickly forms something else a la carbamic acid. It's nice to have them above the BP of water since you can distill water all you want and not worry about your product evaporating. :) John Riemann Soong (talk) 08:03, 11 January 2010 (UTC)

Mass Difference of Chemical Bonds

What is the the average mass of a Carbon atom in graphite plus the mass of an Oxygen molecule minus the mass of a Carbon Dioxide molecule to as high a precision as known at present? I know that there is mass in the motions of the electrons and I'd like to know if the one-and-a-half single bonds plus whatever the other half bond of the floating electron is called in Graphite is heavier or lighter than one of the double bonds in CO₂ and by how much. A scaled up answer is fine. I can handle the basic stuff.Julzes (talk) 09:44, 11 January 2010 (UTC)

Better Question

Resolved

What temperature is required to burn transform Oxygen gas plus Graphite into Carbon Dioxide, as I now see it can be done from standard enthalpy of formation (and burning is the wrong word)? What is the activation energy?Julzes (talk) 10:12, 11 January 2010 (UTC)

It's easier if you start with the enthalpy of formation at room temperature and then scale based on specific heat capacity accordingly. (btw, if the mass contribution by electronic bond stabilisation is small... the fluctuations to the overall mass because of heat capacity is even smaller...)

In fact I'm sure it's already been done for you, so you actually don't need to do any work. For example the enthalpy of formation of say, CO2 or CO at 25C already has been compensated for, prolly by taking a reaction that might start at 200C and scaling based on heat capacity. John Riemann Soong (talk) 10:13, 11 January 2010 (UTC)

What does enthalpy of formation have to do either with temperature or with activation energy (which have more to do with each other)? If you look up that enthalpy and the heat capacities, you'll be able to tell what temperature difference results from the reaction, but I would interpret the question (especially with its activation energy component) as referring to the autoignition temperature of graphite (although that probably depends weakly on the concentration of oxygen, so you'd need to specify if it's normal air or oxygen at one atmosphere or what). That temperature is surely related to the activation energy via the Arrhenius equation: it should be very approximately $E_{a}/k_{B}$. --Tardis (talk) 15:28, 11 January 2010 (UTC)

Well, when I marked it resolved, it was answered well enough for me. I was mainly concerned with the practical issue of Carbon capture and sequestration, and it's been resolved for me that if I want to make an enormous fan and chemical reaction of CO₂ plus other substances in the air to a precipitable compound and then back into the atmosphere, then the chemical process is going to require rather than release energy because CO₂ is pretty much rock bottom (which I would have guessed originally, before this graphite thing entered my mind). Okay?Julzes (talk) 16:25, 11 January 2010 (UTC)

This status of CO₂ is incorrect. Calcium and Magnesium can be reacted with Carbon Dioxide with the release of energy.Julzes (talk) 14:33, 13 January 2010 (UTC)

OK: glad you're happy with it. I hope my further information is at least of some interest. I put the tag back. --20:30, 11 January 2010 (UTC)

Btw, carbon has no lone pairs in graphite. Graphite has a polyaromatic structure. John Riemann Soong (talk) 10:18, 11 January 2010 (UTC)

Really? I didn't know that.;-)Julzes (talk) 12:48, 11 January 2010 (UTC)

Dragon'sFlight gave plenty of detail on this just when I was asking it in the other question I asked. Thanks anyway.Julzes (talk) 10:17, 11 January 2010 (UTC)

F. B. H. Brown

I'm having trouble finding biographical information about Yale botanist F. B. H. Brown, also known as Forest Brown, sometimes as Forest B. H. Brown. There seems to be someone of the same name who worked for the USDA or some other government organization, but I'm not sure if it is him or his father, or a relative or someone else entirely. If anyone can point me in the right direction, that would be great. Viriditas (talk) 10:07, 11 January 2010 (UTC)

Found this reference in Google Books [4]. The Bernice P. Bishop Museum may be able to help. Alansplodge (talk) 11:46, 11 January 2010 (UTC)

I doubt they can help. I'm actually looking for information prior to and subsequent to his work with the Bishop Museum. Something on the order of this from Yale. Are there are any Yale archives available on their site? Viriditas (talk) 13:18, 11 January 2010 (UTC)

The one who went on the Bayard Dominick Expeditions? --BozMo talk 13:34, 11 January 2010 (UTC)

Yes, that's him. Viriditas (talk) 13:37, 11 January 2010 (UTC)

few mentions around the place like "Forest B. H. Brown, Botanist, returned to Honolulu on December 16, 1922, after a period of two years spent in the Marquesas and neighboring parts of the Pacific as a member of the Bayard Dominick Expedition. His work has resulted in filling a conspicuous gap in the knowledge of Pacific flora and should lead to the preparation of a standard treatise based on his collections, which comprise 9000 sheets of material and 395 photographs. During the year a paper by Mr. Brown on "The secondary xylem of Hawaiian trees" (Occasional Papers. Vol. VIII, No. 6) was issued by the Museum." --BozMo talk 13:40, 11 January 2010 (UTC)

I get the general impression there is quite a lot of stuff but you are handicapped by the fact he is called "Mr Brown" everywhere. Multi word searches keep turning up snippets. Any particular type of thing? --BozMo talk 13:42, 11 January 2010 (UTC)

Well, I've got that already here, but I'm looking for biographical information, such as birth, career highlights, and death because I want to create an article about him. JSTOR has several reviews, but very little bio info. I'm still curious if he's the same Brown who worked for the USDA. Viriditas (talk) 13:48, 11 January 2010 (UTC)

Ok, other ideas "Forest Buffen Harkness Brown" as a google search also turns up some stuff. Forest Buffen Harkness b 11 Dec 1873, Rushville, NY. AB, Univ Mich, 1902; AM, Univ Mich, 1903. Am Men Sei ed 3,4,5. etc--BozMo talk 13:51, 11 January 2010 (UTC)

That's interesting. I'll go from there. Thanks. Viriditas (talk) 13:54, 11 January 2010 (UTC)

explain the name of acetoacetaldehyde

Like, I'm actually trying to find what I thought would be a relatively simple compound, that is, 1,3-dioxobutane. Unfortunately, 1,3-dioxobutane doesn't seem to be used that often (either as the name or the chemical), so now I try some aldehyde nomenclature.

"If replacing the aldehyde group with a carboxyl group (-COOH) would yield a carboxylic acid with a trivial name, the aldehyde may be named by replacing the suffix -ic acid or -oic acid in this trivial name by -aldehyde. For example:"

So ooh, I could use acetoacetic acid, and then back-form acetoacetaldehyde, right?? Well, apparently googling this gives a KETONE, not an aldehyde. Someone please explain the insanity of this nomenclature. John Riemann Soong (talk) 15:26, 11 January 2010 (UTC)

There do appear to be two different chemicals that have "acetoacetaldehyde" as their name according to google. One is what you want, but it's not the first hit for that name. Great example of why simple web-searching always requires human sanity-checking to filter out hits that use a term in a way you don't mean. One reason the compound you want isn't easily found is that it doesn't actually exist in that form (except maybe as a transient intermediate in a reaction flask). DMacks (talk) 16:34, 11 January 2010 (UTC)

Wait ... do I get a conjugated enol ... ? H-bond + conjugation stabilisation, I guess? Btw, what's the thermodynamic difference between an enol and a ketone form usually? Before last year I didn't know it was that small as to be overcome by H-bond and conjugation which IIRC only provide max 5-15 kcal/mol of stabilisation. John Riemann Soong (talk) 01:18, 12 January 2010 (UTC)

Proton NMR

In the proton NMR spectrum for RuClH(CO)(PPh₃)₃ there is doublet of triplets (two sets of three peaks, with the peaks in the ratio 1:2:1) at about -7ppm. It is clear that this is the hydride ligand on the ruthenium, but I do not know why it has split in such a way. I understand that phosphorus will split the peak, but I cannot see how it is possible to end up with a doublet of triplets. Similarly, how would the splitting pattern be if there were two hydrides instead of the a hydride and a chloride? 188.221.55.165 (talk) 16:22, 11 January 2010 (UTC)

There must be two equivalent phosphorus atoms and one unique phosphorus - makes sense if the complex has this structure, as determined by XRD in this paper and others before it.

Ben (talk) 18:52, 11 January 2010 (UTC)

Derailed on the uses of trona

Watching a show on the train 7551 derailment, I got to wondering about the trona it was carrying. The NTSB says it's "used in the manufacture of fertilizer".[5] Our article just says that trona is a source of soda ash (sodium carbonate). Our sodium carbonate article mentions use for making glass, melting flesh off skulls, use in both bricks and food (comforting that) but nothing about fertilizer. Except one mention of a modification of the Solvay process (which trona mineral bypasses anyway) where the "byproduct" ammonium chloride can be used as a fertilizer. Our ammonium chloride article mentions use in oil wells, food, explosives - but not in fertilizer.

So what am I missing? How is trona used to make fertilizer? And how is ammonium chloride used to make fertilizer? Franamax (talk) 16:27, 11 January 2010 (UTC)

Trona is used for the Solvay process purely to create the ammonium chloride, which is a good source of nitrogen for fertilizers. See the ammonium chloride entry in the Fertilizer Encyclopaedia. Nanonic (talk) 17:33, 11 January 2010 (UTC)

Protein Shakes

Is there any unbiased scientific evidence that ingesting protein shakes while practicing an exercising regimen increases the amount of muscle tissue built up? By unbiased I mean studies not performed or funded by companies/parties with interest in protein shake sales. Something tells me all they do is fortify one's poop. 71.161.49.93 (talk) 23:44, 11 January 2010 (UTC)

Probably not much effect if the basic diet contains adequate protein -- see this article for a review of the science. Looie496 (talk) 00:11, 12 January 2010 (UTC)

It is physiologically true that ingesting high protein beyond that of daily values during adolescence (for growth and development) and rigorous body building increases muscle mass. An adult that ingests a high protein diet without regimented and prolonged exercise will not increase muscle fiber size. Wisdom89 _{(T / ^C)} 00:34, 12 January 2010 (UTC)

... --Jayron32 00:41, 12 January 2010 (UTC)

January 12

Thioglycolic acid depilatories in "sensitive" areas

According to the article, thioglycolic acid, which is used as a chemical depilatory breaks down disulfide bonds and breaks down the keratin in hair. Obviously this isn't the best solution as there is keratin in skin, which can become irritated by the acid. Most such creams caution against use in the genital areas, although I have seen at least one advertised for such a purpose, but I'm just curious as to why there would be a need for such a warning. They don't tell you not to put it in your eyes (though it does say that you should wash out with a lot of water if taken internally), so what are they protecting against? 219.102.221.49 (talk) 05:42, 12 January 2010 (UTC)

Product warnings protect a manufacturer from liability for what a user might be expected to do. If no reasonable person would want to put a substance in their eyes, eat it or feed it to their children then no such warnings are needed. Cuddlyable3 (talk) 13:41, 12 January 2010 (UTC)

cyclisation of tryptophan (C-4 self-acylation)

Is this reaction possible? Strong acidic conditions + PCl5 (or another acyl chloride generator), then self-acylate. I have a feeling C2-acylation will be the major product, but is there any way to get an intramolecular reaction at C4? (Is there anyway to "protect" an aromatic substitution site?) John Riemann Soong (talk) 09:06, 12 January 2010 (UTC)

speaker wires

Okay so I'm setting up a sound system ...

I'm wondering if speaker wires are worth the expense. What I'm thinking is going for speaker wire at the ends (near the amp and near the speakers) and running regular 12 gauge "primary" wire in between, and splicing the wires accordingly (and maybe sealing the splices with wire butts or something). I'm not really sure about the idea that using regular wire will result in diminished signal quality -- as long as I use a wire with a large enough cross-sectional area, right? I'm thinking of mainly using speaker wire for flexibility, at the terminals where I need to wrap the wire into speaker and into the amp. John Riemann Soong (talk) 09:39, 12 January 2010 (UTC)

There are lots of people who have very high cost HiFi systems that swear that extremely expensive speaker wire is worth every penny to make the best sound. Personally I'm sceptical. I simply use large gauge wire. Using thin gauge wire where you expect high volume would probably be a mistake, since high volumes can require 10s of amps, which would lead to significant voltage drop on thin gauge wire. However, in the final analysis there's only one way to tell. Try it and listen to the result. If you can't tell a difference, then it doesn't matter. --Phil Holmes (talk) 09:59, 12 January 2010 (UTC)

I use telephone wire, but the solid core is not flexible and it would be a bad idea for me to move my speakers around. SO stranded wire would be better. There is plenty of volume from my system. Amplification is cheap and speakers expensive. Put the money you save into better speakers, these are the weak point in the system. Graeme Bartlett (talk) 10:55, 12 January 2010 (UTC)

Ordinary stranded copper wire is good enough but make sure it has tight, preferably permanent, connections at each end. The issue that arises if wires are too long or thin is not loss of volume; it is loss of damping resulting in increased mechanical resonances in the speakers. Total resistance in wires and connections should be less than 1/10 of the nominal speaker impedance. Cuddlyable3 (talk) 13:33, 12 January 2010 (UTC)

What is the damping when cables of zero impedance are used? Infinity? No! --79.76.182.38 (talk) 00:34, 14 January 2010 (UTC)

Did you read High-end audio cables? --BozMo talk 13:38, 12 January 2010 (UTC)

are carboxylates still electron-withdrawing groups?

Can you straight-out hydrate acrylic acid with sodium hydroxide, and get 3-hydroxy propionic acid? I mean, a deprotonated COOH group is prolly not as electron-withdrawing as the protonated one, but I'm wondering if deprotonated acrylic acid is still a good Michael acceptor. John Riemann Soong (talk) 10:17, 12 January 2010 (UTC)

Also, what about the acid-catalysed hydration of Michael acceptors? First-semester orgo says that C2-hydration is favoured, but a secondary carbocation next to a carbonyl carbon may be worse than than a primary carbocation, yes? (Plus, there aren't even any hydrogen atoms on that carbonyl carbon to do any hyperconjugation...) Plus it seems that the enol mode would favour H attaching at the alpha carbon, not the beta-carbon. John Riemann Soong (talk) 10:21, 12 January 2010 (UTC)

Design for a wood shelf bracket

I want to make some simple bookshelves somewhat like this design http://www.made-in-china.com/image/2f0j00AMvQtimCrTlyM/Shelf-Support-Bracket.jpg but in wood, not metal. The shelf and the vertical part are no problem to make in wood. The wooden bracket will be a deeper right-angled triangle than that shown. The fundamental problem is to stop the bracket from rotating forward at its corner away from the vertical part, due to the leverage of the weight on the bookshelf. What would be the best and simplest way to firmly secure the wooden bracket to the vertical part? The top part of the bracket touching the vertical part will be under tension, not compression, which is more difficult to fix securely. I have a lot of books, the weight may be a lot. Thanks 89.242.107.166 (talk) 12:20, 12 January 2010 (UTC)

Although it's not obvious from the picture, the metal brackets in this design are secured to the uprights by downward pointing L-shaped flanges - there are 4 flanges on each bracket, and you slide a bracket into two pairs of slots in the hollow upright then push it down so that bottom edge of each slot fits into elbow of the L-shaped flange. I guess you could produce a similar design in wood, but you would have to make the flanges and slots thicker to prevent the flanges snapping off under tension - maybe you could make the flanges as wide as the bracket. Also, you will have to make the flanges a very precise fit to the slots, otherwise you will have a shelf that slopes from back to front. But if you are happy to have a permanent joint, rather than one that can be taken apart easily, then I imagine there are specific woodworking joints that are designed to be strong under this type of tension/rotation load. Gandalf61 (talk) 13:03, 12 January 2010 (UTC)

Screw. Cuddlyable3 (talk) 13:25, 12 January 2010 (UTC)

Where would you position the screw(s) please? 89.242.107.166 (talk) 17:42, 12 January 2010 (UTC)

                |   |
                |   |
                |   |
 _______________|   |
|_______________|   |
    |__         |   |
       \....    |   |
        \  ├+######>|
         \''    |   |
          \     |   |
           \    |   |
            \   |   |
             |__|   |
                |   |

Cuddlyable3 (talk) 22:18, 12 January 2010 (UTC)

I've usually seen wooden shelves supported with a diagonal truss support. Wood is a totally different material than metal - this is a no-brainer. But it has implications - wood's tensile strength and compressional strength mean that the appropriate joint shape is not a direct scaling from a joint that works in steel. As Gandalf has pointed out, there's a unique compression/rotation force going on in a bookshelf - and books can be heavy. A shelf acts as a lever arm against the joint, and so you may inadvertently be applying hundreds of pound-feet of torque on the joint. This can concentrate to thousands of psi on the load-bearing contact point. Steel may handle this gracefully, but you might want to reconsider and add a support truss to share the load for wood shelves. Here's building a bookcase from Bob Vila. The video demonstrates their preferred wood joins. The load is spread over an entire joint to avoid force concentration anywhere. Nimur (talk) 14:00, 12 January 2010 (UTC)

The problem is that cantilevering a shelf is going to require a tension joint somewhere. With wood, because of its grain it can quite easily shear. It is difficult to think up catilevered designs in wood that avoid these problems. 89.242.107.166 (talk) 15:00, 12 January 2010 (UTC)

If you want to be a purist and use a proper woodworking joint, then the wedged through-dovetail (picture) is probably the best one under tension. But you asked for the 'simplest' way, so this won't do. I would use a nut and bolt with suitable washers to prevent pulling-through. You could countersink the screw head and then hide it with filler. --Heron (talk) 19:53, 12 January 2010 (UTC)

Tea

What makes all these different types of tea taste different? I know you can scent them with an external flavour like mint, jasmine, ad nauseum; I know that the seven-odd 'colours' of tea must impart something like freshness or toasty flavours. But what makes two black, two green, two yellow teas so different from each other? Is it the location, surrounding vegetation, air and soil quality? Lady BlahDeBlah (talk) 13:18, 12 January 2010 (UTC)

In addition to Tea blending and additives, we also have Tea processing. The main tea article states: "A tea's type is determined by the processing which it undergoes. Leaves of Camellia sinensis soon begin to wilt and oxidize, if not dried quickly after picking. The leaves turn progressively darker as their chlorophyll breaks down and tannins are released. This process, enzymatic oxidation, is called fermentation in the tea industry, although it is not a true fermentation..." So, I would suggest that this is the first order effect on the tea's flavor. Regional climate and soil differences probably do have an effect, but probably to a lesser degree than the processing steps. I think this question has come up on Science Desk before and we found some academic research on tea flavor. I'll look in the archive. Nimur (talk) 13:52, 12 January 2010 (UTC)

Ooh, wonderful, I think I missed that first one... *opens new tab*...I do understand that the 'colour' (wilting + oxidising + fermentation) is the initial indicator of the expected flavour of the result, but I would like to know more on the method. Lady BlahDeBlah (talk) 13:57, 12 January 2010 (UTC)

"The seven-odd 'colours' of tea" - never heard of that before, what are they? Is that a North American marketing gimmick perhaps? In the UK we classify out teas according to location such as Darjeeling, Ceylon, Assam, China, and so on. And brands also. In addition to the various different production methods for black or green teas as mentioned above, I expect different sub-species are suited to the different climates and soils of the different locations. 89.242.107.166 (talk) 14:54, 12 January 2010 (UTC)

I'm English, my dear. I unno, tis something I made up based on what I've read on the Tea article. There's black, green, white, yellow, oolong, post-fermented and what was the other one? I forget. They all depend on what happens to the leaf after it's picked. But you've illustrated my question nicely: Darjeeling, Assam, Ceylon, all are black teas fromt he same species of plant treated in...approximately the same way after picking, right? So why do they taste different? Lady BlahDeBlah (talk) 15:01, 12 January 2010 (UTC)

They are probably different varieties of tea plant, treated differently, grown in different soils, and probably picked at different times of the year as well. I don't know why that's not a good enough explanation—the same sort of things accounts for the major differences you find between different wines and coffee, for example. --Mr.98 (talk) 16:22, 12 January 2010 (UTC)

The Stash Tea site gives a simple explanation of the various types of teas and how they are processed. They divide teas into four main categories on the basis of the degree and type of processing: black, green, oolong, and white. Take a look here [6]. Incidentally I order all my tea through Stash and have been very pleased with their tea. I like organic loose tea, and they have several different types. (I am not in any way affiliated with Stash!)--Eriastrum (talk) 20:07, 12 January 2010 (UTC)

Old weather data?

Hi, does anyone know where I can find weather data for, say, May 24 2008 in some town in Mongolia? Question is related to Winter_storms_of_2007–2008#May_26-27. Yaan (talk) 13:44, 12 January 2010 (UTC)

Try here [7].Accdude92 (talk to me!) (sign) 14:20, 12 January 2010 (UTC)

thanks a lot. Yaan (talk) 14:41, 12 January 2010 (UTC)

Synthetic Feather

Has anyone created the syntheic feather such as to use in costumes or such without buying the real thing? I referring to those giant feathers such as the one pictured here. --Reticuli88 (talk) 13:49, 12 January 2010 (UTC)

Well here's a patent: [8] and here's a manufacturer [9] --TammyMoet (talk) 18:13, 12 January 2010 (UTC)

are Zinc pills caustic?

i bought some from both gnc and the vitamin shop when i put them in my mouth they burned badly like i got lye in my mouth or something. it sems its like water activated like quicklime since they dont burn too much if you touch them with your hand. these are zinc only pills i got some with b6 in it that didnt burn but i didnt like those. whats the ph of these things? —Preceding unsigned comment added by 67.246.254.35 (talk) 14:05, 12 January 2010 (UTC)

I can't find the actual template but this sounds a lot like you're asking for medical advice? There are rules against us answering medical advice questions anyway, but I might hesetantly point you towards Zinc toxicity. Gunrun (talk) 14:48, 12 January 2010 (UTC)

I don't see this as a request for medical advice at all. The OP just wants to find out the ph of some zinc supplements. Regrettably, I could not find the information, but we do have an article on Dietary mineral which also lists some facts about zinc. 10draftsdeep (talk) 16:21, 12 January 2010 (UTC)

I'm a chemist, but I can't be 100% certain on my answer. Two parts: 1) Goodness knows whats in those pills, the FDA doesn't regulate supplements, for all you know they could in fact be lye (sodium hydroxide). 2) If the pill does in fact contain zinc, I suppose a particularly foolish manufacturer might simply make a highly concentrated (possibly even toxic at high enough doses....) zinc tablet without regard for the fact that zinc is in fact a Lewis acid and would cause such action. In a dry area like your hand you might not notice that, but if this were the case water would certainly have an effect as you describe. I would strongly suggest returning the pills to the place you purchased them regardless -- supplements, even shady ones, shouldn't hurt. 128.104.69.93 (talk) 19:25, 12 January 2010 (UTC)

Zinc chloride can be very irritating as it can form a strong solution, zinc sulfate will still have an astringent metallic taste, and the amino acid salts will be fairly benign. The idea is to swallow usually and not dissolve it in the mouth. Graeme Bartlett (talk) 20:58, 12 January 2010 (UTC)

If you have a bad reaction, don't take the pills. That said, lots of "dietary supplements" (which is the modern translation of the term snake oil) are entirely unregulated for either efficacy or quality, so major caveat emptor when dealing with such substances. Generally, if you are eating lots of "whole foods" from a wide variety of sources (meat, fish, dairy, fruits, vegetables, grains) it's entirely pointless to supplement your diet with anything. To the OP's original question, many homeopathic (read: quackery) zinc treatments like the now-pulled-from-the-market Zicam had high concentrations of sodium hydroxide which, it is supected, caused adverse reactions. Not knowing what zinc preparation you were using will make it impossible to know what else was in the pill, it could be literally anything at all, and since this market is unregulated, even if you knew the brand name of the pill, you may never know what you are really taking. If you are truly concerned, stop taking the supplements, and possibly see a qualified medical professional if you have serious questions about your health. --Jayron32 22:03, 12 January 2010 (UTC)

what exactly is a lewis acid? i read the article but it didnt help much? how is zinc a lewis acid?

I'd ask why the heck you think you need zinc supplement anyway? If you a meat-eater, you'll be getting plenty of zinc in your diet. If you are a vegan and eating a particularly poor vegan diet - then maybe you need zinc - but you can get it in a huge range of foods (cooked dried beans, sea vegetables, fortified cereals, soyfoods, nuts, peas, and seeds) - you don't need pills. These pills sound like you should be avoiding them like the plague! If you believe you have a zinc deficiency - then you should definitely see a doctor because you need to attack the cause of this strange and unusual problem and not just cover it up by taking pills. SteveBaker (talk) 05:15, 13 January 2010 (UTC)

Zn2+ has a positive charge, and is a good electrophile. It likes to bind to neutral water molecules. But when neutral water molecules do so, they acquire a positive charge, because they are donating electron density (solvating) to the Zinc. So it encourages protons to come off the water to form zinc hydroxide plus a proton (which is solvated by other water molecules). In reality, the proton is not very free, and there is an equilibrium involved, but Zn2+ still has corrosive properties.

Not all salts are neutral. NaCl is a neutral salt, but Na+ doesn't bind water as strongly -- sure water solvates it but it doesn't form very strong covalent bonds. MgCl2 forms covalent'ish bonds of a highly ionic nature with oxygen, so MgCl2 is slightly acidic. Zinc(II) chloride is a considerably more acidic salt, well, because zinc is a transition metal, a Zn-O covalent bond is more stable John Riemann Soong (talk) 05:16, 13 January 2010 (UTC)

Bacteria abundance

I am looking for references in the academic literature for:

1. The abundance of bacteria on human skin? (Both typical and max, if possible)
2. The abundance of bacteria on typical surfaces encountered in everyday life?

Any help appreciated, thanks. Dragons flight (talk) 14:13, 12 January 2010 (UTC)

This article doesn't provide the exact information you ask for, but might be a good starting point in your search. - Nunh-huh 00:47, 14 January 2010 (UTC)

first zero-net energy development of single family homes on the planet?

To whom it may concern-

I am the architect for Green Acres, a zero-net energy development of single family homes in New Paltz, NY, about 90 miles north of NYC. Construction began in summer 2008 and at this time 3 houses have been completed, purchased and occupied, and 4 more are under construction. I am trying to find out if Green Acres is the first zero-net energy development of single family homes on the planet. I know of an existing development of zero-net energy townhouses in Germany, but not much else that is already built in this or a similar category. Please contact me if you know of another development with proper claim to this title. You can find more information on Green Acres on my website. Thank you for your time.

       -Dave Toder, RA
        BOLDER Architecture
        (email removed per guidelines)  —Preceding unsigned comment added by 76.15.31.83 (talk) 15:31, 12 January 2010 (UTC) 

What about the Earthship community in Taos? 75.41.110.200 (talk) 15:35, 12 January 2010 (UTC)

Note: The question appears to be about Zero-energy buildings. Would a primitive community of tents or caves with no heat qualify? As for modern buildings, some are listed in the article. How many are required to make a "development?" A 10 unit development in Washington state, zhome, is listed in the article and claims to be the first such development, with completion expected by the end of 2009. Edison (talk) 15:43, 12 January 2010 (UTC)

(ec) This post runs dangerously close to WP:SPAM. It's against our policies to use Wikipedia for commercial advertising under the guise of legitimate activity. I hope I'm not misinterpreting your post, but the way it is worded sounds like an advertisement. As far as "zero-net-energy", I think that is a dubious claim. How do you define energy input to the house? Technically, even if nothing is happening and there is no human activity in the housing development, the laws of thermodynamics dictate that energy will be transferred either into or out of the development, in the form of radiant heat, unless the housing and the rest of the universe are in complete universe-wide equilibrium. It would be more scientific to say that you import no fossil fuels or utility electric power - if that describes the development - but to import no energy would require constraints on (for example) the diet of the human occupants, and the total quantity of metabolic activity they generate, and preclude them from listening to radio or telecommunications of any kind (which by definition are conveyed by waves of energy). And, to have a zero-net energy balance, all you need to do is produce extract energy on site - e.g. an oil rig. But this doesn't really create energy so much as harness it. I think in general it is safe to say that "zero net energy" is a marketing-ese buzz-word with little scientific merit. Nimur (talk) 15:46, 12 January 2010 (UTC)

Well, assuming you mean zero electrical input and no gas, no oil, etc - then I think we understand what you mean...although technically, Niumur is and Edison are correct in that the house does have energy inputs - (the sun's rays, for example) - but I'm sure everyone actualy understands what this is about - so let's try to be helpful and talk about that.

Anyway - you are FAR from the first to claim this. A very quick Google search turns up this for example...a builder in Dallas who is building "zero energy" homes. So I'm very sure you cannot lay claim to being the first of your kind in the US - let alone in the entire world. You're probably going to try to claim that this is the first zero energy home community - but you've only built three and three is not a "community" by any reasonable definition!

Also, there is a difference between "near-zero" and "actually, for real, definitely, zero". If your homes to not connected up to the electrical grid - then I might perhaps believe your claim for the latter...but if they are still 'on the grid' then your claim is only valid if the people who live in the house use it carefully. If they install a bunch of high-energy consumption gadgets and leave them turned on inappropriately - then I'm 100% sure they'll use more energy than your solar panels (or whatever) generate. If so, what you're building is merely energy-efficient homes and those are EVERYWHERE to some degree or another. For that reason alone, I very much doubt you can truthfully claim "ZERO" energy inputs from the grid - so the issue of whether you might be the first is moot.

Anyway - being the first is far from everything. Being the best on the other hand - that would be impressive. SteveBaker (talk) 19:57, 12 January 2010 (UTC)

A claim given on the web[10] is that "Using photovoltaic solar panels and geothermal heating and cooling, combined with super insulation (insulated concrete form walls, triple-pane glass) and heat recovery ventilation, these buildings consume less energy than they produce.." New Palz is surrounded by...the cultural mecca of Woodstock... I can believe the bit about Woodstock Festival. Cuddlyable3 (talk) 21:45, 12 January 2010 (UTC)

Yeah - but the problem with that claim is that they actually have no idea how much energy the buildings consume. If you have a large family with kids who habitually leave lights on - leave the doors open in the height of summer or the depths of winter - who leave the freezer door open or leave 4 TV's and 4 video games turned on all day and all night - lots of hot baths - many loads of laundry per week because of the baby - and a dishwasher which has to be run at least once a day...then the house is gonna consume a heck of a lot more than one that's occupied by a single person who works all day, eats out most evenings and has simple needs. You really can't claim literally zero energy consumption...not without a lot of explanations and caveats as to how the house will be lived in. SteveBaker (talk) 01:31, 13 January 2010 (UTC)

To be fair to the source, the claim wording continues "..than they produce (when occupied by an average family),.. Cuddlyable3 (talk) 02:36, 13 January 2010 (UTC)

physics

In a double-slit interference experiment, what actions cause the fringe spacing to increase? —Preceding unsigned comment added by 206.209.102.240 (talk) 15:56, 12 January 2010 (UTC)

Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misevaluation, but it is our policy here to not do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn how to solve such problems. Please attempt to solve the problem yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know. You may wish to start at Double-slit experiment. -- Coneslayer (talk) 16:20, 12 January 2010 (UTC)

radio waves and their structure

If a radio wave was passing through a vacuum why doesn't it loose its energy and how can it gain more energy? Also is there any way for radio waves to be held in one place —Preceding unsigned comment added by 82.38.102.58 (talk) 16:43, 12 January 2010 (UTC)

It doesn't lose energy in a vacuum because it doesn't -- that's a basic fact, not a derived fact. One way that it could gain energy is by interaction with gravity. And according to the Theory of Relativity there is no way for a radio wave to be held in one place. As a note of historical interest, Einstein said that his first motivation for developing Relativity was that he tried to imagine what an electromagnetic wave would look if it were held in one place, and decided that such a thing ought not to be possible. Looie496 (talk) 16:54, 12 January 2010 (UTC)

Where do you get the idea that a radio wave can "gain more energy?" It simply does not happen (without an amplifier of some sort). The opposite in fact occurs. The RF energy is the same but becomes dispersed over a greater area thus effectively weakening. --220.101.28.25 (talk) 17:16, 12 January 2010 (UTC)

A radio wave spreads out in a vacuum such that the new wave-front becomes a larger and larger sphere - but the total energy remains the same. This makes the radio waves harder and harder to detect as you get further away - but that's because you're intercepting an ever smaller fraction of the total expanding sphere of energy that the radio put out. The laws of thermodynamics apply to radio waves just as they do to any other form of energy - and one of those laws says that energy is neither created nor destroyed - it just changes from one form to another. If the radio waves "lost" energy somehow, that energy would have to turn into something else.

When you shine a light (or a radio wave) through the earth's atmosphere, it loses energy because the light/radio is being absorbed by atoms in the air - which means it more or less all ends up as heat - which is just another form of energy. The same thing happens with radio waves in the atmosphere. But out in the vacuum of space, there are almost zero atoms out there to absorb the energy and turn it into something else - so radio waves can travel across the entire width of the visible universe and still be detectable. This is also true of light and other forms of electromagnetic radiation.

Those same laws of thermodynamics also prevent the radio wave from gaining energy - because whatever energy it might hypothetically gain would have to come from somewhere...and in a good, hard vacuum - there is nowhere for the energy to come from.

SteveBaker (talk) 19:38, 12 January 2010 (UTC)

Regarding gaining energy, I see that I should have given a longer answer -- as our Gravitational redshift article points out, light (or radio, same thing) that passes into a a region of stronger gravity shows an increase in energy, and is said to be gravitationally blueshifted. Looie496 (talk) 20:06, 12 January 2010 (UTC)

Similarly it'll lose energy when it leaves a gravitational well. That works both ways of course. Rckrone (talk) 23:49, 12 January 2010 (UTC)

Alien Technology

In this video, do you have any examples of this technology being used/created today? --Reticuli88 (talk) 17:20, 12 January 2010 (UTC)

The video looks like crank-bait to me. The guy makes a lot of assertions with zero evidence. I wouldn't take it too seriously. Whether you want to believe that modern nanotech is the product of a long (and easily documentable) progress of Earth scientists, or whether it magically fell into our hands from the aliens in the 1940s, will determine whether you think there are examples of such technology being used today. --Mr.98 (talk) 17:45, 12 January 2010 (UTC)

As Mr.98 infers, this seems to be a load of crap synthesis and scientific gobbledy gook. A similar 'source' asserts we have velcro because it was found in the UFO that allegedly crashed at Roswell. Actually, can you be more specfic about which "examples of this technology being used/created today?" you actually mean, as there are several mentioned in the video. --220.101.28.25 (talk) 18:04, 12 January 2010 (UTC)

Oh the humanity...Stop this bullshit progress before it is too late! Cuddlyable3 (talk) 21:20, 12 January 2010 (UTC)

I fear it is way too late. Go Luddite! --220.101.28.25 (talk) 00:37, 13 January 2010 (UTC)

The way I know that the video is unscientific is because every chart and graph is displayed for just about 0.2 seconds. I have been through scientific and engineering lectures often enough to know that when a researcher displays a chart or graph in a presentation, they invariably spend about 20 minutes droning on about the axes, the labels, the scatter points that look like incoherent noise, and their elaborate curve-fitting regression algorithm which suggests strongly that their original hypothesis actually holds, even though the data may as well have been collected by Jackson Pollock. This video simply flashes up a series of "science pictures" without droning on in long, boring, incomprehensible fashion. No anomalous data was discussed which might discredit competing research groups' work that was published in 2002. Nobody mentioned that, while this technological innovation is all very well and good, Gauss and Euler both invented all of the fundamental analytic techniques for the meta-materials in the 18th century. These symptoms of actual scientific presentations are remarkably absent - the video belongs solidly in the crank bin - but kudos for creative science-fiction writing. While the vast majority of the explanations are jargon-slathered nonsense, it's mildly more accurate than your average generic sci-fi explanation. Nimur (talk) 15:54, 13 January 2010 (UTC)

Genius Offspring

What are the chances that the offspring of notable geniuses, like Einstein, will have children with the same natural gifts? --Reticuli88 (talk) 17:54, 12 January 2010 (UTC)

Just as rare as any other child. Most geniuses do not have children. Those that do will rarely have a genius as a child. Talent is passed from parent to child, but childhood is not. Whatever happened to a child to turn them from a talented baby into a genius adult is very likely to be missing from the genius' child's life. -- kainaw™ 18:01, 12 January 2010 (UTC)

See also regression to the mean. The child of a genius is likely to be more intelligent than average, but unlikely to be as intelligent as his or her dad (or mom). Similarily, Bush's kids aren't likely to be as big of douchebags as their father. Buddy431 (talk) 18:41, 12 January 2010 (UTC)

"Most geniuses do not have children." --Sean 20:28, 12 January 2010 (UTC)

For the google-impaired... [11] [12]

For anecdotal evidence (in no particular order): Michelangelo, Tesla, Leonardo, Newton, Kant, Beethoven, Galileo, Descartes, Spinoza, Florence Nitengale, Copernicus, Handel, Cavour, Flaubert, and Chateaubriand. -- kainaw™ 23:50, 12 January 2010 (UTC)

Well if you look at Albert Einstein's kids, 1 became a professor of I think some kind of engineering, one died very young, and the other had some kind of mental condition (Schizophrenia?) I do not know if the professor was a literal genius, but it is a fair bet that he was above average (as are most professors I would hope). Googlemeister (talk) 19:44, 13 January 2010 (UTC)

The question of hereditability of I.Q. is a controversial one. See Heritability of IQ. Most studies say that I.Q. is .75—meaning that about 3/4ths of ones I.Q. is determined by your genes. How that plays out in percentages of offspring, I don't know (it's been awhile since I took biology—but I don't think you can make that determination just based on the above information), but it is probably not as random as the above answers have suggested. There is more to it than just genes, of course, but genes do seem to play a non-trivial role (which is unsurprising). Whether a "genius" will be recognized as such is an entirely different question, though. In such a case, having a "genius" parent may or may not be helpful (it is easy to be overshadowed if your father in an Einstein, though on the other hand, you will have potentially great possibilities for training and networking.) --Mr.98 (talk) 18:53, 12 January 2010 (UTC)

I think my comment about regression to the norm still applies. Even with a hereditory aspect, a genius is a clear outlier in terms of intelligence, and it's still quite likely that any offspring will be closer to the average value than their parents. I suppose that a given genius is more likely than a given person of average intelligence to give birth to a genius, but the probability is still in favor of the dad being smarter than the kids.

That being said, there are some notable cases of very intelligent families. The Bohrs immediately come to mind. Both Niels and his son Aage won Nobel prizes in physics. And it's not like Niel's dad Christan and brother Harald had trouble tying their own shoes either. The Bernoulli family also seems to have a number of very smart members, though I'm not sure how many of them could be described as "geniuses" on the caliber of Einstein. Buddy431 (talk) 20:00, 12 January 2010 (UTC)

Yes, but none of this gets to the heart of the question: How much of this is "being born with smart genes" versus "being born in a smart environment" Your parents raise you, so one cannot discount the influence of having smart parents in the house in terms of heritability of intelligence (which is a dubious concept anyways!) So, what we need are studies of the intelligence of a) twins, b) seperated at birth, c) raised in different environments d) where their biological parents are known and also have had their intelligence testes and e) enough of these to have a meaningful sample size. I'm not saying such a study does or does not exist, but until I see it or one like it, I would be skeptical of any attempt to draw meaningful conclusions about genetic vs. environmental influences on intelligence. --Jayron32 21:55, 12 January 2010 (UTC)

Jayron, such studies do exist. Look at the article I linked to. People have been studying the heredity of I.Q. since the 19th century. Obviously it is still controversial, because splitting nature and nurture in such a complex trait is fairly impossible. Still, most of the studies point towards intelligence being fairly heredity. That doesn't mean that someone with "good genes" will do well despite their environment, or that someone without them will necessarily be dumb. The article is pretty good on explaining these sorts of caveats. The reason this is controversial (and hair color is not) is because once we start getting into questions of heredity and I.Q., people start seeing this either as a way to start thinking about making racial-superiority arguments (which the science does not support, in any case, even though I.Q. is determined a lot by genetics), and people recoil at the idea that something as fundamentally "individual" feeling as their own thinking ability is "locked in" by their genetics (which is not exactly true, though more true than the former). But assuming that all of us are, in good faith, just interested in the basic scientific question (and are not trying to enforce racial policies based on it), I think we can put out there that the most likely case is that intelligence should have a large genetic component, as do all human traits. --Mr.98 (talk) 14:21, 13 January 2010 (UTC)

I don't think the OP's question requires us to determine why a child of a genius is more likely to be a genius, but rather what the actual probability is. If we want to do that, we first need to pin down what a "notable genius" is, and what qualifies their kid as having "the same natural gifts". We could conduct a bit of OR here, and come up with a list of "notable geniuses", and then look at their kids, and determine who can be said to have these "natural gifts". Or, we could broaden the question, and look just at geniuses in general, and determine what the probability is that any one of their kids is also a genius. We should probably also look at the general population, and see what the probability that a kid born to anyone (with no more information) is a genius. The trouble is, our article doesn't list a clear cutoff point for what a genius is, giving anywhere from the top 1.2% to the top 0.005% in terms of IQ (and this doesn't even include people like Michael Jackson who are described as "geniuses" in a given field, but clearly don't have super high IQs). Let's peg our "genius" cutoff at the top 0.1% of the population (in terms of IQ), which would imply that over the whole population, the probability of any given child being a "genius" is 1/1000. Now, we need to find a source that tracks the IQs (or a suitible proxy; perhaps we could find enough SAT scores, or something like that) of parents and children, and that has enough people at the very high end, so that meaningful conclusions can be drawn for what the probability of a given child born to someone in the top 0.1% of the population also are in the top 0.1%. I have no clue where such a source will be found, and I suspect that the OP isn't going to get any sort of numeric answer to their question. Buddy431 (talk) 23:37, 12 January 2010 (UTC)

Incidentally, one of the first studies of the heredity of intelligence was none other that a study of the heredity of "genius", broadly defined. Francis Galton, Hereditary Genius (1869). Of course, it is not rigorous by modern standards, but it did make the strong argument (for the time) that talented people seem to have talented offspring. --Mr.98 (talk) 14:21, 13 January 2010 (UTC)

You don't need twins that have been separated at birth. You can do a standard twin study. You get lots of pairs of identical twins and lots of pairs of non-identical twins and give them all an IQ-test (or whatever other test of intelligence you choose). You then see if the identical twins are more likely that the non-identical twins to have similar results. If identical twins get similar results more often, then the characteristic in question is probably hereditary (by looking at the numbers very cleverly you can quantify how much of the characteristic is determined by genes). Since both identical and non-identical twins will have the same up-bringing as their twin, that factor cancels out leaving just genetics. You do need very large sample sizes to get a reliable result, though. --Tango (talk) 02:20, 13 January 2010 (UTC)

What's the sampling limit of human hearing?

At what sampling rate does the human ear distinguish continuous audio? Is there an upper limit (i.e. can someone tell the difference between 96KHz and 192KHz sampling on the same sound)? --70.167.58.6 (talk) 18:35, 12 January 2010 (UTC)

This isn't the exact answer to your question but will be close: I think you've confused the Kb rate of a music file with the KHz sampling rate. Our Hearing (sense) article says that humans can generally hear sounds from 20 Hz up to 20,000 Hz; and the Nyquist rate for 20,000 Hz is 40,000, or 40 KHz. That's presumably why compact discs use 16-bit samples at 44 KHz — there will be no aliasing of any sounds in the range detectable by humans, even the highest-pitched sounds. As for the difference between a data rate of 96 Kb versus 192 Kb, this depends on the sample size (16-bit samples? 8-bit samples? 1-bit samples?) and the sample rate, and on the lossy compression algorithm (like mp3 or AAC) that is being used — and so the actual answer to your question will have to come from a study where people are asked to evaluate their subjective perception of the music files. Comet Tuttle (talk) 19:03, 12 January 2010 (UTC)

I'd add to that great answer by mentioning that the upper limit varies dramatically with age. Younger people can hear significantly higher frequency sounds than older people. SteveBaker (talk) 19:26, 12 January 2010 (UTC)

SteveBaker said I wrote a "great answer" on the Science Desk! I get an Achievement! Actually I am uncomfortable with my lack of relating the 16-bit sample size to the Nyquist rate and perception. Comet Tuttle (talk) 19:41, 12 January 2010 (UTC)

Do Quantization error and Audio bit depth#Dynamic_range help? -- Coneslayer (talk) 20:07, 12 January 2010 (UTC)

They do, thanks. I'll use them next time. Comet Tuttle (talk) 20:17, 12 January 2010 (UTC)

For intelligible but poor "telephone quality" audio the sampling rate can be as low as 8kHz. If no compression is involved nor different distortions introduced by analog filters in A-to-D or D-to-A filters then the answer to the OP's 2nd question is No. Cuddlyable3 (talk) 20:55, 12 January 2010 (UTC)

(EC) I'm not so sure that the OP was confused although I suspect he/she didn't understand the meaning of the terms and how they relate to the audio. Since the OP mentioned a sample rate of 96kHz versus 192kHz not a data rate of 96 kb versus 192 kb I'll take this question at face value. Most ABX listening tests (and other reliable listening tests) I've seen from places like Hydrogenaudio (and published ones) show that with uncompressed samples, a decent bit depth (e.g. 16 bit), few people can tell the difference between 48kHz vs 96kHz even on very high end equipement. In fact, I can't recall if I've seen anyone shown to be able to tell the difference. Not surprisingly, few people bother to test 192kHz. This obviously agrees with the scientific understanding of audio sampling and the limits of human hearing. If the theory says one thing, the experiments reach the same conclusion, I think we can safely say both are correct unless some very strong evidence is presented to the contrary.

A bitrate of 24 bit however can be an improvement over 16 bit (i.e. detectable) by some listeners although I've seen it suggested 20 bit may be enough. A higher sampling rate could be useful for future mixing and for non human listeners or for scientific purposes. (A higher sample size/bit rate is generally important for future editing.) It's also possible a device capable of outputting 96 kHz may be better then one capable of only 48 kHz

The OP may wonder why Bluray and other such systems offer 192kHz if even 96kHz is useless. Well other then a few audiophile nuts, most be agree it's just fancy marketting. Note however that you can get a benefit from such formats in that in many cases the mastering is different and in particular may be less processed then the more mass market material like CDs which some listeners may prefer. And sometimes the options may be something like 44.1kHz/16bit (i.e. CD) vs 96kHz/24bit (or higher) and as I've mentioned there is a small chance you can detect the difference between 24bit and 16bit and it can especially be of benefit if you plan on editing.

You can easily perform such tests at home, get a bunch of 192 or 96kHz/24 bit samples and then using a very high quality algorithm convert them to 48kHz/16bit or whatever you want to test. Then use one of the various software programs that has the option of ABXing different samples to compare them and see if you can tell the difference. You can probably get some help at Hydrogenaudio if needed since this is a fairly common practice there. While convering the samples has the possibility to produce problems relating to the algorithm, it's the fairest method. In practice, I wouldn't bother particularly if you don't have very fancy equipement, I doubt you'd even be able to tell the difference between 24 bit and 16 bit.

Nil Einne (talk) 20:59, 12 January 2010 (UTC)

Actually looking at [13] I may have overestimated the number of people who can tell the difference between 24bit and 16bit Nil Einne (talk) 00:35, 13 January 2010 (UTC)

Thank you all. My original question is correctly stated. I'm not interested in music audio compression (which has been debated ad nauseum on infinite forum boards). Similar to persistence of vision, is there a persistence of hearing? What sampling rate can the human ear detect individual audio "frames"? And is there an upward limit where it's impossible to detect the difference between sampling rates (my previously mentioned comparison of 92KHz and 192KHz -- which are the upward limit of what current consumer audio technology is available) --68.103.143.23 (talk) 14:09, 13 January 2010 (UTC)

In terms of "persistence of vision"-type effects, audio doesn't really work like video. You could imagine "video" at a very low frame rate, like 0.1 fps (a slideshow where the image is changed every 10 seconds). It obviously wouldn't be smooth, but each individual frame would still be a perfectly good image. The framerate doesn't have anything to do with your ability to record and show an individual frame. Sounds is different; you need to sample at 20 kHz to be able to record and reproduce a 10 kHz sound. It doesn't matter whether that sound plays for just a few milliseconds or for hours, before changing to a different sound. Sound—even constant sound—is a wave, and you need to record all the peaks and troughs of that wave. So the high sampling frequency is necessary to record the sound in the first place... it's not related to how quickly your ears and brain can detect a change in the sound. Does that help? -- Coneslayer (talk) 16:42, 13 January 2010 (UTC)

Vision doesn't work in "frames" either - each rod and cone produces a continuous signal - not something that works via a sequence of snapshots like movie film or TV. However, our brains have adapted to cope well with 'interrupted' images. If you're a caveman chasing down a rabbit so you can chuck a large rock at it and eat it for lunch - then you need a visual system that can allow you to target the rabbit - even though it's running between trees or through tall grass. You need to maintain a mental model of where the rabbit is - even when it's out of sight for a tenth of a second. Hence we are able to mentally extrapolate the position of a moving object even though it's briefly invisible to us. As parts of the rabbit's body disappear and reappear behind blades of grass, we still "see" the entire rabbit - we aren't consciously trying to reassemble an image from little vertical strips that are changing all the time. This ability appears to be what produces that 'persistance' effect - and there are some rather subtle experiments you can do with computer graphics to demonstrate that. But the actual rods and cones are not snapping a sequence of still images like a movie camera - that's just not how our eyes work. We don't have 'persistance of hearing' because sounds can go around corners and are therefore not interrupted by the brief interposition of some small object between you and the sound source. We therefore have not evolved a tolerance for brief 'breaks' in an audio stream. SteveBaker (talk) 18:34, 13 January 2010 (UTC)

Right, I realize real life "analog" vision doesn't have frames. So my question was meant to focus on computer captured, sampled digital audio. My "persistence of vision" analogy was meant for captured images (film/video) which are "sampled" at so many times per second. Fall under that limit and your eye sees a series of still images and not continuous movement. Hearing has nothing similar -- a sound sampled so low that it sounds like chopped up samples? --70.167.58.6 (talk) 23:07, 13 January 2010 (UTC)

That's what I was trying to address above. If your sampling rate is too low, the sound doesn't become chopped up; instead, your recording can only reproduce lower and lower frequencies (pitches). A 1000 Hz (1 kHz) sampling frequency could only accurately reproduce tones of 500 Hz or lower (around Middle C). This is a fundamental limitation of signal processing, not our physiology. -- Coneslayer (talk) 23:32, 13 January 2010 (UTC)

Right - that failure to reproduce tones higher than the nyquist limit (twice the sampling rate) is called 'aliassing' - and the visual analog of that isn't slow frame rates - it's poor resolution. If you play a computer game at 320x200 pixel resolution - it has horrible stair-steps in the straight edges of objects. Run the same game at 1600x1200 pixels and the edges look MUCH smoother. That's essentially what's happening with the audio. Those smooth audio sine-waves - plotted as a graph - get more and more jagged looking as you reduce the sampling rate. This is a much better analog than the 'frame rate' and 'persistence of vision' phenomenon. SteveBaker (talk) 00:26, 14 January 2010 (UTC)

Magnetic Permeability of Free Space

I've got a decent grasp on E&M, quantum, and related physics, so feel free to give a fully technical answer to this question. My understanding is that magnetic permeability governs the strength of the response of a medium to a magnetic field traveling through that medium (classically, anyway). By that definition, why isn't the magnetic permeability of free space zero? It doesn't seem to me that the vacuum should be responding to the magnetic field, it should simply 'carry' it (I suppose 'allow its passage' would be a better way to phrase that). 128.104.69.93 (talk) 19:19, 12 January 2010 (UTC)

See the article Permeability (electromagnetism). Magnetic fields pass through a vacuum. The permeability of free space μ0 is an observed physical constant that is related to defined units by μ0 = 4π×10**−7 N·A**−2. Permeabilities of media are measured relative to μ0. Cuddlyable3 (talk) 20:47, 12 January 2010 (UTC)

Well, yeah. But that doesn't address why the vacuum responds to the magnetic field at all. It seems to me that if there is nothing there (again, classically) then there shouldn't be anything to propagate the magnetic field (since there is nothing to respond to it). A definition is not the same as a physical rationale. If this isn't explainable classically, by all means use relativity/quantum. 128.104.69.93 (talk) 21:03, 12 January 2010 (UTC)

Let me rephrase my last reply a different way: The definition of μ[sub]0[/sub] is equivalent to the observation that there is a magnetic permeability of free space. What is the origin of that magnetic permeability? What is responding to the magnetic field if there isn't any matter there? 128.104.69.93 (talk) 21:07, 12 January 2010 (UTC)

It can't be zero or else the magnetic field strength would be zero. Since we observe magnetic fields are not zero everywhere, μ0 must have some non-zero value. The actual value is arbitrary and merely acts as a way to convert between several convenient unit definitions. A better question might be why is the Fine-structure constant approximately 1/137. When you figure that one out make sure you send me some of the Nobel Prize money. Truthforitsownsake (talk) 21:19, 12 January 2010 (UTC)

This is, I believe, again equivalent to simply observing that the magnetic field propagates through vacuum and it has the same value everywhere. I don't really care what the particular value is, I just want to know why its not zero. 128.104.69.93 (talk) 21:21, 12 January 2010 (UTC)

I believe the real answer is that it is simply a historical accident of the way E&M developed. The vacuum doesn't respond to the field (not in a classical sense any way, which is all we need for this discussion since Maxwell's equations are purely classical). More explictly, the magnetization and magnetic susceptibility of the vacuum are zero always. Presumably one could recast E&M in terms of this other items in order to make the constancy of the vacuum explicit, but as it happens we historically chose to describe E&M in terms of a permeability instead. Dragons flight (talk) 21:27, 12 January 2010 (UTC)

Mu0 isn't a property of the vacuum or a measured physical constant. The article Vacuum permeability discusses this at length. Puzl bustr (talk) 21:32, 12 January 2010 (UTC)

Thank you! Question answered. 128.104.69.93 (talk) 18:40, 13 January 2010 (UTC) (OP)

The OP seems to be confusing permeability with susceptibility. Dauto (talk) 23:30, 12 January 2010 (UTC)

CYMK space models

Since the primary colors of printing computers is cyan, magenta, and yellow notice the cyan looks more azureish and magenta looks bringht pink is not the magenta they have from computer screen. Some secondary from CYMK is actually R, Green and the blue is not RGB blue it is indigo, then is there tertiary color on CYMK? turquoise is actually looks more tertiary in CYMK printing computer models.--209.129.85.4 (talk) 20:34, 12 January 2010 (UTC)

I'm sorry, what is your question? --Tango (talk) 21:18, 12 January 2010 (UTC)

natural tertiary color for CYMK, since cyan and magenta looks blue and pink when print on newspapaer. I don't know how else to clear this question up.--209.129.85.4 (talk) 21:21, 12 January 2010 (UTC)

Tertiary color refers to a process of mixing primaries and secondaries (did you look at the article?), so there is always tertiary color for any color system. I think the point you are getting at it is that since the definitions of the primaries vary from one system to another (or one physical implementation to another) the actual results will appear differently depending on the original colors. This is a pain in the ass for graphic artists but it doesn't change the fact that you mix some colors to get others. Dragons flight (talk) 21:38, 12 January 2010 (UTC)

Often RGB are taken as the secondary colors in CYM color schemes and vice versa (cyan is the absence of red, etc). In that sense, the tertiary colors in each scheme are very similar, since each tertiary color is between a primary and secondary color in the scheme. Rckrone (talk) 23:34, 12 January 2010 (UTC)

In printing, there are lots of subtleties that prevent tertiary colours having much meaning (though in some processes they can be reproduced). For example, printing, like mixing paints, is essentially a subtractive process, but halftoning can mimic an additive mixing (as for light). You might like to read our articles on CcMmYK color model, Hexachrome and color printing? Dbfirs 07:53, 13 January 2010 (UTC)

Gall stone disease urine dipstick results

If a person has gall stones present (and causing biliary colic), other than a raised bilirubin what findings might be present if a urine dipstick was performed?

Many thanks 188.220.144.215 (talk) 21:56, 12 January 2010 (UTC)

The best person to ask this of is your doctor. If you are concerned about the results of any medical test, you should contact a trusted medical professional. Wikipedia cannot interpret the results of any medical test. See Wikipedia:Medical disclaimer. --Jayron32 22:22, 12 January 2010 (UTC)

A urine dipstick test is common for checking for kidney stones. A blood test (for raised bilirubin and liver enzymes) is common for gallstones. It is not common to expect the results of a blood test to equate to the results of a urine test. -- kainaw™ 22:32, 12 January 2010 (UTC)

There are all kinds of urine dipsticks; some test only glucose, some only glucose & acetone; the more complete have tests for glucose, ketones, blood, protein, nitrite, pH, urobilinogen, bilirubin, leucocytes, and specific gravity. None of these are particularly useful for diagnosis of gallstones, though if complete biliary obstruction were present there might be decreased urinary urobilinogen. - Nunh-huh 04:55, 13 January 2010 (UTC)

With respect Nunh-huh I think that it is the other way round. If there is complete biliary obstruction then there will be a 'raised' urobilinogen level, together with pale faeces, because the serum bilirubin is raised leading to a raised renal excretion level. But the OP should go see a doctor if he has concerns about his/her health. Caesar's Daddy (talk) 08:25, 13 January 2010 (UTC)

"When jaundice is due to an obstruction in the flow of bile: (1) The patient's stools are pale. (2) His urine is dark, and contains little or no urobilinogen. (3) His skin itches." [14] - Nunh-huh 09:43, 13 January 2010 (UTC)

Yep, ISC. I confused it with urobilin. Caesar's Daddy (talk) 12:38, 13 January 2010 (UTC)

Vacuum energy level in heterojunctions

Hello,

I have a question about heterojunctions. As displayed in the figure of the article, the vacuum level can be chosen to be the zero-energy reference level before contact. If I am correct (because it is not displayed anymore) the vacuum level bends along with the other bands after the two materials have been brought in contact. It will thus be higher for the first material then for the second. An electron taken out from the junction to infinity distance has, in my view, zero potential energy left; but this 'zero' seems to differ for both materials now. Where is my mistake? Any help is highly appreciated --Gnorkel (talk) 22:27, 12 January 2010 (UTC)

Animal optical illusion

This?

What is the name of the optical illusion where looking below the animal, typically a horse or elephant, in a drawing it looks like the animal has more or less legs than it should in the way its been drawn? The legs appear, then appear as gaps between the other legs. Simply south (talk) 23:33, 12 January 2010 (UTC)

I distinctly remember a similar illusion (and one that I think predates and in fact initially inspired the elephant-leg modification) in which an object that appears similar to the head of a fork has tines that descend to the base of the fork's head only to be the space between the tines as they attach to the head. I always thought it was called a widget, but Wikipedia does not have an article on it (yet). DRosenbach ^{(Talk | Contribs)} 00:22, 13 January 2010 (UTC)

Ah...yes. Here it is. And you may be interested in the related Penrose triangle. DRosenbach ^{(Talk | Contribs)} 00:23, 13 January 2010 (UTC)

Thank you. The article was located under Blivet (and I'll create a link). I'll make a mention there that maybe the elephant could be featured. It looks like it is the same one. Simply south (talk) 00:56, 13 January 2010 (UTC)

Elements

Which elements does a person need to survive? --70.244.235.220 (talk) 23:51, 12 January 2010 (UTC)

Are we to assume that your hypothetical person already exists as an adult and that on some randomly chosen day, you want to know from now on which elements does he or she require for survival? I would say the basic organic elements (COHNS), as well as P for membranes, nucleic acids and the like. Then there's all the ions in solution that perform necessary functions, such as Na⁺, K⁺, Ca²⁺ and Cl^-. I think Mg and Li are necessary in trace amounts, as is I for thyroid function (at least). Then you have the necessary metal co-factors in various ion forms like Fe, Cu and Zn. (And as a dentist, I recommend a very small dose of F^- to help prevent tooth decay and Sr for tooth sensitivity.) There may be a few other necessary ones, though. DRosenbach ^{(Talk | Contribs)} 00:37, 13 January 2010 (UTC)

There's apparently a need for some Se for selenocysteine. DRosenbach ^{(Talk | Contribs)} 01:00, 13 January 2010 (UTC)

I meant all elements that the body uses in any quantity. --70.244.235.220 (talk) 01:03, 13 January 2010 (UTC)

Check out our human nutrition article. The minerals listed are: Calcium, Chlorine, Magnesium, Phosphorus, Potassium, Sodium, and Sulfur (greater than 200 mg/day), and Cobalt, Copper, Chromium, Iodine, Iron, Manganese, Molybdenum, Nickel, Selenium, Vanadium (speculative)and Zinc (less than 200 mg/day). Add in the Carbon, Oxygen, Nitrogen and Hydrogen found in organic molecules, and you should be good to go. Of course, some of these elements need to be in a specific form for us to use them (we need the essential amino acids already put together, phosphorus usually comes as a phosphate and would kill us in elemental form, etc.). Buddy431 (talk) 01:07, 13 January 2010 (UTC)

What foods contain those trace elements? I've never noticed most of them on nutrition labels. --70.244.235.220 (talk) 02:01, 13 January 2010 (UTC)

Most living things need the same elements, so most food will contain some of each, the issue will be is it enough for humans. The more famous ones for being deficient, such as iodine may not be found in land plants. Cobalt is needed in the form of cobalamin and the lack can cause vitamin B 12 deficiency. Graeme Bartlett (talk) 02:17, 13 January 2010 (UTC)

Composition of the human body would be a useful article to read. --Tango (talk) 02:33, 13 January 2010 (UTC)

A page that article links to, chemical makeup of the human body, shows that the human body contains more arsenic than some of the trace minerals, such as molybdenum. Why is it that trace amounts of those elements have an effect on the human body, but larger trace amounts of arsenic don't? --75.28.54.203 (talk) 03:06, 13 January 2010 (UTC)

Reading the Molybdenum article, I see that Molybdenum is necessary for the activation of certain enzymes. Enzymes merely catalyze reactions, and so there don't necessarily need to be a lot of them to be effective. Presumably, arsenic is not needed in any necessary reactions in the body. On the other hand, I'm not sure that we can definitively say that minute levels of aresenic don't have some effect on the body. I didn't read the articles on arsenic toxicity and arsenic poisoning, but they may have some information on how much arsenic is needed to cause ill effects. Buddy431 (talk) 03:34, 13 January 2010 (UTC)

January 13

Pain caused by discussion of pain or 'medical' issues

(Removed medical question)

I'm sorry but here on the Wikipedia reference desks, we're not allowed to give medical advice. If you are concerned - you should see a doctor. SteveBaker (talk) 00:52, 13 January 2010 (UTC)

I understand that, but I'm not asking for medical advice and I'm certainly not concerned. I just want to know what it is called. Thanks.--80.229.152.246 (talk) 21:21, 13 January 2010 (UTC)

We can't tell you what (if any) medical condition you might be suffering from without offering a diagnosis. If I said "The name of your condition is Antidisestablishmentarianism Histrionics" (I just made that up) then I'd be offering a diagnosis of your condition - implying that I've thought about the symptoms you explained and somehow concluded that you don't have "Supercalifragilisticexpialidocious Syndrome" (I made that up too). This is diagnosis of a condition - and it is STRICTLY prohibited for reference desk contributors - partly because it's dangerous to take medical advice from random individuals on the Internet - and partly because it's illegal to practice medicine without a license in the jurisdiction of most countries of the world. So even if we thought we could probably guess what your condition was - we're not allowed to say anything other than "If you are concerned - please seek medical attention from a qualified Doctor" (which I did). Since some less experienced ref desk contributors are ignorant of this rule, we tend to delete questions that clearly violate the guidelines listed at the top of this page in order to discourage those people from attempting an answer. Sorry - but them's the roolz. Please take any further debate to the "discussion" tab at the top of this page. SteveBaker (talk) 00:14, 14 January 2010 (UTC)

mirrors

if every human that owned a mirror were to place it outside for a day or so, would this reflect enough heat to make a difference in the temperature of the earth at all? Im just thinking that if everyone put out a mirror that is 1 m^2 then that would be 6.7 billion m^2 or 81km^2 ish of reflective surface. —Preceding unsigned comment added by 174.88.21.160 (talk) 03:30, 13 January 2010 (UTC)

There seem to be quite a bit out about "white roofs" (which accomplish pretty much the same thing as a mirror, though not to the same degree) as a way to fight global warming. The point is not so much to cool the whole Earth, but rather to reduce the amount of energy used to air condition buildings. Buddy431 (talk) 03:41, 13 January 2010 (UTC)

Well, let's suppose there are 6.8 billion people. Let's be generous and suppose that every one of us owns a 1 square meter full-length mirror (that can't remotely be true - but let's be generous). There are a million square meters in a square kilometer - so we're looking at a total area of 6,800 square kilometers of mirror (I don't know where you got your 81 square kilometer number from). The surface area of the earth is 510,000,000 square kilometers - so we'd be covering about one part in 100,000 of the earth's surface with our mirrors. Even if we all cunningly stand on the darkest part of the earth's surface and have perfectly shiney mirrors, we'll only increase the earth's albedo by something like a thousandth of a percent - from 0.367 to 0.368 or so. This would "make a difference" - and ought to reduce temperatures - but by a very, very tiny amount.

So you aren't going to solve global warming that way. We've lost close to 40% of the Arctic ice alone in the last 10 years. That's 40% of the 15,000,000 square kilometers turned from bright white shiney ice to dark ocean. The 6,800 square kilometers of mirror don't make even a tiny dent in that amount of albedo change...and that's not counting all of the glaciers, the antarctic and mountain-top ice & snow.

However, there might be other ways to do similar things. After the 9/11 disaster, the US shut down all air travel for a day or two. This resulted in there being no jet contrails in the sky. Since contrails are very white - and therefore reflect light back out into space (not as well as a mirror - but pretty good) - you'd expect there to have been a small increase in air temperatures over North America as a result...and it turns out that there was - and it was quite measurable. So it seems kinda possible that we could reduce global temperatures by spraying water droplets or something similar up into the atmosphere. That's maybe possible - and some scientists are actively discussing this possibility (it's generally known as "Plan B") - however, there are grave concerns that by tampering on such a large scale, we could inadvertently trigger some other major problem that we haven't yet thought of.

SteveBaker (talk) 04:59, 13 January 2010 (UTC)

Contrail#September 11, 2001 climate impact study -- Finlay McWalter • Talk 16:01, 13 January 2010 (UTC)

Fanuc Ac servomotor

How to calculate heat generation in fanuc AC servomotor? and what are the modes and parts of heat dissipitaion? Thanks - kushagra

Please see my response to your other FANUC question below. SteveBaker (talk) 00:03, 14 January 2010 (UTC)

time machine.

whats the latest development in research related to time machine? if a time machine is made will it be able to take us to the past??baba (talk) 10:43, 13 January 2010 (UTC)

See Time travel. Staecker (talk) 14:22, 13 January 2010 (UTC)

There are a few scientist who (mostly for the benefit of low-budget pop-sci programs on the Discovery channel) have toyed around with some fairly 'far out' concepts - typically involving wormholes (which really don't exist) and black holes (which do). These ideas are horribly speculative - and are in any case totally impractical. Aside from them, pretty much everyone agrees that time machines are impossible. Those few unlikely/impractical concepts that are out there almost all state that you'd never be able to go back in time to a point before the time machine was built...which means that nobody is travelling back to any point in our past. Broadly speaking, it's safe to say that time machines don't exist and we're pretty sure that they never will. That said - you could 'fast forward' time and effectively travel into the future merely by climbing into a spaceship and flying at somewhere close to the speed of light. Einstein's relativity theories will then allow you to (in effect) travel into the future...but with no possibility whatever of ever returning. SteveBaker (talk) 18:21, 13 January 2010 (UTC)

Long after I thought I had a grand idea of stating that since we don't have time machines that travel to the past now, we never will, I found that Stephen Hawking made the same statement in his Chronology protection conjecture. I'm writing up a paper on polynomial-time solutions to 3SAT now. So, I expect some famous guys published the same thing last month and everyone has already proven the whole P/NP thing. -- kainaw™ 00:53, 14 January 2010 (UTC)

Fanuc material

If you could please help with the materials used in making the magnets, bearings, front flange, windings, stator, brushes, motor, couplings, swap drives, gaskets, insulation and rotor shell of a fanuc ac servo motor, even non-fanuc would do. Also how do they impact the performance of such motors? Thanks-kushagra —Preceding unsigned comment added by 220.225.125.246 (talk) 10:57, 13 January 2010 (UTC)

I very much doubt that anyone here is going to be able to answer such a detailed question - FANUC motors are made by the Fuji Automatic NUmerical Control company - I suggest you ask at the service department of their web site here: http://www.fanuc.co.jp - however, I very much doubt they'll be willing to tell you such detailed information because end users of these motors generally do not wish to know that - and at best, they'd be passing on knowledge to a potential competitor. This is quite simply an unanswerable question. Sorry. SteveBaker (talk) 00:01, 14 January 2010 (UTC)

Flying Flat Bug

I live in the northeast US and there is a flying flat bug in our office. I can't take a pic of it cuz it won't stand still (divas). But it looks like the shape of a giant tick but with long legs and it looks like a wasp when it flies around. What is it? --Reticuli88 (talk) 17:05, 13 January 2010 (UTC)

Sounds like something in the Hippoboscidae family. --Mr.98 (talk) 17:09, 13 January 2010 (UTC)

Ok, someone killed it and here is the smashed version --Reticuli88 (talk) 17:19, 13 January 2010 (UTC)

It's a true bug. --Dr Dima (talk) 17:45, 13 January 2010 (UTC)

Average adult vitamin D status of the Maasai people of Kenya?

I am looking for the following epidemiological information:

Average adult vitamin D status of the Maasai people of Kenya? The answer will probably be in units of nmol/l or ng/ml. —Preceding unsigned comment added by 65.112.42.83 (talk) 17:51, 13 January 2010 (UTC)

I've looked all over the web - and I can't find any numbers for this. The biggest study of nutrition amongst the Maasai was evidently conducted by Dr. George V. Mann. Searches of his writings turn up all manner of other statistics - but no hard numbers about Vitamin D. Given that the Maasai live mostly out in the open, on the equator, wear fairly skimpy clothing (your skin makes Vitamin D when it's exposed to sunlight) and exist on a diet consisting of pretty much 100% meat, blood and milk (all great sources of Vitamin D) - it's pretty safe to assume that their Vitamin D numbers will be off the chart. Certainly more than adequate. Their problems come when these people move away from the equator, live indoors, switch to western-style clothing and a more typical "northern" human diet. Their very dark skin pigmentation then limits Vitamin D production and with less sunlight at more extreme latitudes, much less exposure to the sun - and a less meat/dairy-rich diet, they may well need Vitamin D supplements. SteveBaker (talk) 23:49, 13 January 2010 (UTC)

The "cc" rating of a car battery charger

I'm occasionally called upon to recharge the car batteries of hapless elderly relatives' cars. My current, ancient, charger has died, so I need to replace it. Looking on the website of large UK automotive-supplies retailer Halfords (just for example) they have a number of chargers, some of which they describe as "1200cc", some as "1800cc". But they don't say what that cc refers to - I guess it's supposed to be the size of the engine of the car engine? But the chargers are all 4A 12V. Do these "cc" values mean anything at all? 87.113.46.161 (talk) 19:27, 13 January 2010 (UTC)

The size of the battery. Car batteries are wet cell batteries, actually a lead-acid storage battery. The cc probably stands for cubic centimeter, aka "milliliter" and is probably the size of the battery itself, i.e. a 1200cc battery will have 1.2 liters of liquid inside. Just a guess, but that's my best guess. --Jayron32 20:52, 13 January 2010 (UTC)

No Jayron. Halfords say[15] "We sell specific chargers for smaller engine batteries: Up to 1200cc (181701). Up to 1800cc (181735)" i.e that the "cc" values do refer to the engine size. I think that is a silly way to market battery chargers. The data that matter are the maximum current and how the output voltage (nominally "12V") is controlled as the battery reaches full charge. Cuddlyable3 (talk) 21:00, 13 January 2010 (UTC)

Nm. So much for guessing. --Jayron32 21:25, 13 January 2010 (UTC)

I guess they are just trying to be helpful - Joe Public knows how many cc's his engine is - so he buys a charger to match. But it's rather silly - the only possible variable is how long the battery takes to charge. You could use an 1800cc charger to charge the battery in a 1200cc car - or vice versa. The voltage is the same - all that would change is how long it takes to charge and what strategy the electronics use to get the battery charged rapidly. In truth, the fastest way to charge a car battery is using a car. I have a couple of car chargers of various vintages - but the thing I use most is one of those "booster packs" that has a small 12v battery and a VERY slow trickle charger - you leave it plugged in all year long - and when you need it, you hook it up to the car like a set of jumper cables (only without needing another car) and that's enough to get the car started...then you drive around the block for 10 minutes in a low gear and your battery is charged. If the weather is unusually bad - or if your battery or your alternator is a bit 'iffy' then you can unplug it from the wall and toss it into the back of the car and it has enough charge to get you out of trouble a couple of times before it needs recharging. It's small enough and light enough that I can plug it in next to my desk at work and recharge the thing ready for the trip home. They aren't really designed for routine use - they are a "get you out of trouble" thing - but if your battery needs recharging a lot - there is something wrong with either the battery or the charging circuit/alternator in the car. In that case - fix the car rather than spending money on a charger. SteveBaker (talk) 23:21, 13 January 2010 (UTC)

I agree 100% with Steve Baker that the booster packs, sometimes marketed as "Portable Power Stations" (or similar) are very effective for helping out "hapless elderly relatives" (and for starting my own vehicle when I foolishly left the interior light on). They are also useful in the event of a household power failure, and can run a TV or other low-power appliance for a while using a solid-state invertor to generate household voltage. They are, however, significantly more expensive than a basic trickle-charger which can take up to 24 hours to fully charge a flat battery. Dbfirs 23:40, 13 January 2010 (UTC)

Mechanics of cancer death?

Pardon what may seem to be a very obvious question, but...how does cancer kill? Obviously the malignant cells spread throughout the body, but I've never quite understood how the spread of such cells causes death, and cancer doesn't seem to address the subject. Do they overload the circulatory system somehow? Nyttend (talk) 20:22, 13 January 2010 (UTC)

This question has been asked a couple of times before, see

• Cancer (Nov 10, 2006).
• Final cause of death in cancer (Dec 8, 2007).
• How does cancer kill people? (March 11, 2009).

--NorwegianBlue ^talk 20:44, 13 January 2010 (UTC)

Thanks very much; I forgot to look in the archives. Nyttend (talk) 22:20, 13 January 2010 (UTC)

Could you explain why all parrots seem to be able to communicate with each other?

With parrots, you can pretty much put any combination of species together in the same place, provided that they get on with each other as individuals and see that they're able to communicate and interact with each other pretty well. Even if they're species from different parts of the world. Put a macaw next to an African grey for example and they'll sit next to each other like friendly parrots do, preen each other, share food, etc. and understand each others body language perfectly well. Or a cockatoo and an amazon parrot, or a budgie and a lovebird. Sometimes they'll even pair up and try to breed with each other.

Why is it that (nearly?) all parrots have the capability to understand and be understood by all other parrots? —Preceding unsigned comment added by 95.148.104.164 (talk) 01:04, 14 January 2010 (UTC)

Would a spaceship travelling through a nebula leave vortices behind?

I posted this, initially, in the Fluid Dynamics discussion page and was referred here (after they took the time to give a partial answer anyway, which I thought was pretty nice of them):

Sorry if this is a bit lame, but this question has bothered me for a while, and I don't have the skill to answer it myself.

In the opening credits of Star Trek Voyager (I know, but try to keep reading anyway), there is a scene that shows the ship passing through, presumably, a nebula. YouTube has the opening credits if you want to look.

Anyway, the ship causes some nice vorteces, very similar to the Rayleigh–Taylor image in the article.

My question: would it really?

A nebula is, well, nebulous. Is it considered a fluid? I visualize it as sparse particles in a vacuum. At what point are there enough particle available that they interact and form those swirls. I think that you'd really see a perfect wake - a 'V' or cone spreading from the ship.

Where is the line between "dust particle scattered about in a near-vacuum" and "fluid"?

75.152.185.94 (talk) 01:54, 14 January 2010 (UTC)