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August 14

Gull-proof sack?

MWAAAK?

How does this work, exactly? --Kurt Shaped Box (talk) 00:05, 14 August 2009 (UTC)

Looks like they have an embedded weave of fibers in there that makes it more difficult for gulls to peck a hole in the bag. 71.236.26.74 (talk) 00:12, 14 August 2009 (UTC)

Tyvek, possibly, or something similar. --Tagishsimon (talk) 00:15, 14 August 2009 (UTC)

Is the market for specifically-seagull-proof woven garbage bags really that large, or is this just a special printed label on an otherwise generic animal-resistant sturdy trash bag? Nimur (talk) 01:10, 14 August 2009 (UTC)

Good question. I wonder if large gulls (they being the ones who generally raid bin bags in towns) have more powerful bites than, say housecats or foxes? It's actually quite possible, considering that the jaw muscles are bringing all the pressure of the bite to bear on a much smaller surface area than you'd find in the mouth of a mammal. --Kurt Shaped Box (talk) 01:30, 14 August 2009 (UTC)

In many British localities, the problem of seagulls attacking garbage sacks pre-collection and spreading their contents all over the street is very considerable. I recently read a long blog entry touching on this problem in Edinburgh (though it was more about the misapplied monitoring of those who compounded the problem by putting their sacks out too early): not sure if it's netiquette/Wiki-appropriate to post a link here, though. 87.81.230.195 (talk) 01:32, 14 August 2009 (UTC)

I agree the scale of the problem, but note that Edinburgh has suffered a garbage collection strike in recent times which will have exacerbated the problem for them. --Tagishsimon (talk) 01:48, 14 August 2009 (UTC)

I don't know if this is the case in Edinburgh but I've heard that in some places, once the gulls have strewn the rubbish all over the street, the bin men are all like "Meh, it's not our problem now - it's not in a bag/wheelie bin" and they'll leave it there to rot. --Kurt Shaped Box (talk) 01:53, 14 August 2009 (UTC)

Haha, you read Language Log? John Riemann Soong (talk) 14:09, 14 August 2009 (UTC)

Well spotted, John! Both read and occasionally comment on. 87.81.230.195 (talk) 16:48, 14 August 2009 (UTC)

A couple of weblinks for reference: East Devon council, BBC News. It's a re-usable bag, so presumably there's a normal polythene bag within; they're for users who do not have access to a wheelie bin, and Devon, at least, is charging a fiver for them. --Tagishsimon (talk) 02:01, 14 August 2009 (UTC)

For a sack?! Time to go into business: Undercut them by 50% and you'll still be making a huge profit margin. Tempshill (talk) 03:04, 14 August 2009 (UTC)

Am I the only person who squinted at the photo and concluded it was some kind of a sack for reusable seagulls? It would parse SO much easier if it had been written:

             Reusable
          Seagull Proof
           Refuse Sack

Or maybe it's just time to get my eyeglasses upgraded :-)

--DaHorsesMouth (talk) 22:43, 14 August 2009 (UTC)

It just needs some punctuation: "seagull-proof" needs a hyphen and only the first word should have been capitalised. Although: "Reusable seagull? Proof! Refuse sack."...yeah, I'd refuse the sack alright. SteveBaker (talk) 02:30, 15 August 2009 (UTC)

I'd sincerely hope that you weren't intending on (re)using the seagull for evil. --Kurt Shaped Box (talk) 01:28, 17 August 2009 (UTC)

I'm having a hard time imagining a non-evil use for some kind of zombie re-used seagull - which (since they have proof) is the only reason I need to refuse the sack. I hope this clarifies the situation. SteveBaker (talk) 21:57, 17 August 2009 (UTC)

Sitting too close to a TV

Is it true that sitting too close to a TV is dangerous? And if so, then why is it ok to have a computer monitor so close to your face? ScienceApe (talk) 01:18, 14 August 2009 (UTC)

a) because it strains the muscles in your eyes

b) it's not okay to sit too close to the computer monitor for long periods of time, for the same reason.

Regards, --—Cyclonenim | Chat  01:44, 14 August 2009 (UTC)

No, it's not true. I've been sitting close to computer screens for close to 40 years - and aside from being a little astigmatic in one eye (requiring glasses for driving - but nothing else), I'm doing fine. I had my eyes tested just a few weeks ago - and my eyesight hasn't changed in the slightest over the last 30 years. Admittedly, I'm not a good statistical sample - but I've worked with an awful lot of people who also spend their entire waking hours glued to a screen - and I don't see any horrible eye injuries. There have been many studies about this kind of thing and no clear results have ever been attributed to computer use. Sure, you can get eyestrain - but that's not a permanent condition. You eye muscles are like most other muscles - they get tired - you rest them - they recover. It's a good idea to take a break from computer use for at least a few minutes in every 20 minutes (mostly so you get a change of posture and a break from typing) - and using that time to focus off into something in the distance will help to relax your eye muscles and avoid strain. Almost all of the problems relating to computer use relate to bad sitting posture, poorly adjusted work-stations, lack of exercise and repetitive strain issues due to too much rapid typing - or excessive mouse use. I'm pretty sure that the "Don't sit too close to the TV, you'll hurt your eyes." admonition that probably everyone's mother has delivered repeatedly has more to do with you blocking the adult's view rather than any evil deathrays emitting from the screen. SteveBaker (talk) 02:13, 14 August 2009 (UTC)

I think the best thing is to direct people to Myopia#Etiology and pathogenesis. SB's claim that 'many studies about this kind of thing and no clear results have ever been attributed to computer use' is not entirely accurate. As the article mentions, some studies have found evidence frequent near work (which includes computer use and sitting very close to the TV) may be a contributing factor, while others have not. In other words, it's a case of, we still can't be sure, rather the being definite either way (this doesn't exclude the possibility the evidence is far stronger in one direction). Edit: After some external discussions about this, I feel I should emphasise near work includes a lot of things besides normal computer use and sitting very close to a TV. It obviously includes stuff like reading a book. Also I've been wondering whether to mention this or it will just confuse things but I decided to go ahead. I believe one of the reasons why there is a fair amount of suspicion environmental factors may be at play is because of the greatly increasing apparent prevalence of myopia seen in some populations (especially East Asian I believe) that appear to be correlated to industrialisation and development. It's possible these are related to improved diagnosis and perhaps a greater demand for visual acuity but the trend appears to be quite strong and I believe several factors including some of the studies the article discusses suggest something else may be at play Nil Einne (talk) 04:22, 14 August 2009 (UTC)

Some screens emit radiations that can be harmful. —Preceding unsigned comment added by Quest09 (talk • contribs) 16:28, 14 August 2009 (UTC)

Can you point us to sources supporting your otherwise uncorroborated assertion? 87.81.230.195 (talk) 16:46, 14 August 2009 (UTC)

TVs do emit harmful "radiations," namely the horrible programming that rots the mind. But I think Quest09 is referring to radioactivity. I recall a study from the 1990's that did find detectable radiation from the face of CRTs, both computer monitors and TVs. The radiation was found to be from radon in the dust that accumulates on on the front of the class due to eletrostatic attraction induced by the charge buildup. The same effect probably occurs for plasma screens but not for LCDs. The correct mediation is to clean the screen, and of course to clean any other dust buildup in your house. -Arch dude (talk) 17:28, 14 August 2009 (UTC)

Found a ref: [1] -Arch dude (talk) 17:32, 14 August 2009 (UTC)

More about it: (...) most surveys of cathode ray tubes in the literature were made while the units were energized and indicated low-energy x-rays, (...) See [2] Moms were right after all, sitting too close to TV can harm you. --Quest09 (talk) 18:31, 14 August 2009 (UTC)

You might want to read that reference more carefully. That was not x-rays from the CTR beam. It was gamma radiation from the materials from which the tubes were manufactured. "Significalnly above background" is a term from the field of statistics, where "significant" means that the results are statistically higher than background, not "significant" as in harmful to health. Note that bricks, stones, and cinder blocks also emit radiation that is "significalntly above background," and fo the same reason: trace amounts of transuranics in the earth from which they are made. The radon/dust effect I mentioned above is a whole lot higher, at five times background, but is still not very unhealthy. -Arch dude (talk) 20:27, 14 August 2009 (UTC)

My reference is a reference about low energy x-ray radiation, even if its main topic is radioactivity in cathode ray tube. Quest09 (talk) 11:10, 17 August 2009 (UTC)

Mineralogy of the Black Stone

Muslim legends state that the Black Stone fell from the heavens. Has it ever been analyzed to determine whether it's a meteorite? NeonMerlin 05:58, 14 August 2009 (UTC)

As of 9 months ago, at least, the black stone had not actually been scientifically analyzed, although one geologist (Zaghloul al-Naggar) was wanting to take a sample to do so.[3] This page claims that “Western Scientists have confirmed that the black stone…is an outside meteorite object”, but the audio file that that claim links to, which is an interview with Zaghloul al-Naggar, does not actually support the claim that there has been an actual analysis of the stone. Note that although Zaghloul al-Naggar has a PhD in geology, he hasn’t published any peer-reviewed research, his web site is all about promoting islam, and he has called Jews “devils in human form”[4]. So it’s questionable as to how unbiased he would be able to be, even if he actually did an analysis of the black stone at some point. Red Act (talk) 07:31, 14 August 2009 (UTC)

P.S. This same web page also links to an audio file in which Zaghloul al-Naggar explains how through his careful interpretation of the quran, time descriptions in the quran can be shown to be consistent with the speed of light, accurate to three decimal places. With such a strong susceptibility to confirmation bias, and given that islamic tradition requires the stone to have fallen from heaven, it seems essentially impossible to me that Zaghloul al-Naggar would conclude that the black stone was anything other than a meteorite, if he ever does get his hands on a sample, regardless of what the black stone is actually made of. And I can’t find anything about anyone else with any scientific credentials hoping to get a sample and do an actual analysis. Red Act (talk) 08:15, 14 August 2009 (UTC)

I don't think anyone would be willing to do an actual analysis -- if he/she does and it turns out to be anything other than a meteorite, the Islamics would put a fatwa on his/her head (just as they did to Theo van Gogh (film director) for making an anti-Islamic documentary). Few scientists would be brave enough to risk that. 98.234.126.251 (talk) 00:16, 18 August 2009 (UTC)

I find it appaling that in the 21st century we are still in an age where practically the whole planet can be intimidated by the beliefs of people who worship a rock that fell from the sky.. Vespine (talk) 00:25, 21 August 2009 (UTC)

Direction of rotation of helicoptor blades

Which way do helicopter blades rotate? (i.e. clockwise or counterclockwise, when viewed from top) Is it standard? or does it vary across models? Is there any reason to prefer one way or the other? or is it arbitrary? --76.173.203.32 (talk) 06:07, 14 August 2009 (UTC)

American generally go counter-clockwise, the other type is French which go clockwise, other countries pick between the two. I believe clockwise is more common outside the US. It is pretty much arbitrary, like which side of the road you drive on. Vespine (talk) 06:17, 14 August 2009 (UTC)

From Helicopter rotor#Rotor configurations: “When viewed from above, the main rotors of helicopter designs from Germany, United Kingdom and the United States rotate counter-clockwise, all others rotate clockwise.” Of course, some helicopters have dual main rotors, in which case they rotate in opposite directions. Red Act (talk) 06:32, 14 August 2009 (UTC)

You can usually tell just by looking at the rotor blades - the blades are thicker on one side and taper down to a knife-edge on the other - just like the wing on an airplane. The fatter edge of the blade is the "leading" edge - it meets the on-coming air-flow. SteveBaker (talk) 12:39, 14 August 2009 (UTC)

On most helicopters it is easier to look at which side the tail rotor is, right side for clockwise and left side for counter-clockwise. MilborneOne (talk) 16:36, 14 August 2009 (UTC)

Unless it has fantail design, like the Eurocopter EC 135, then you are back to SB's method. Googlemeister (talk) 16:42, 14 August 2009 (UTC)

I was going to mention the tail rotor - but then it occurred to me that it shouldn't matter which side it's on...so it's possible that this isn't a hard-and-fast rule (although I agree it's common). The pitch of the tail rotor can be adjusted to direct its thrust in either direction - I can't see why it would need to be on a particular side of the tail. SteveBaker (talk) 02:24, 15 August 2009 (UTC)

Electric power stations

how does a electric power station pay for itself. The esolar 5MW station has me wondering. --207.229.169.245 (talk) 07:13, 14 August 2009 (UTC)

The owners of the power station sell the electricity produced in the Electricity market. Apparently California (where I think the station you're asking about is located) has a wholesale electricity market, where "competing generators offer their electricity output to retailers. The retailers then re-price the electricity and take it to market, in a classic example of the middle man scenario." AlmostReadytoFly (talk) 07:23, 14 August 2009 (UTC)

As for "how do they build it in the first place" - they get a loan, which they later repay with money from selling the electricity. Dcoetzee 07:54, 14 August 2009 (UTC)

Besides that, there are subsidies, depending on the type of power station and the country or state. Icek (talk) 11:42, 14 August 2009 (UTC)

By changing power suppliers, I recently changed from a standard residential rate of 11.34 cents per kwh to 8.50 cents per kwh. The power comes to me from the same grid and through the same pole transformer. There were no wiring changes at all. To add insult to injury, the original supplier (PennPower) still bills me, but passes the money to the new supplier (Dominion People Plus). No doubt PP gets a small fee for doing the billing. I live in NW Pennsylvania. —Preceding unsigned comment added by 98.21.108.45 (talk) 15:55, 14 August 2009 (UTC)

Why is consolidated billing an insult or an injury (i.e., does it really matter where you mail your check)? As you said, "The power comes to me from the same grid and through the same pole transformer. There were no wiring changes at all." That infrastructure probably has significant startup investment and ongoing maintenance costs. Even if you mailed Dominion directly for the actual poewr generation, you are still using services of PP to get the power, so you would expect Dominion to tack additional charges to be passed back to PP anyway. DMacks (talk) 19:58, 15 August 2009 (UTC)

Magnetism

Is molten iron still attracted by a magnetic field? I know that heat erases magnetic properties of a magnet, so molten iron can't be a magnet, but I don't know if it can be subject to external magnetism. --151.51.54.231 (talk) 10:16, 14 August 2009 (UTC)

Above the Curie temperature (the temperature at which you "erase magnetic properties"), iron no longer behaves ferromagnetically but paramagnetically. It is still attracted towards stronger magnetic fields, but the attraction is weaker - see Curie's law. There are also diamagnetic substances which are repelled by magnetic fields (but most only weakly so, except for superconductors). I don't know exactly how iron behaves in the molten state, but this article might be useful (if you have access to it). Icek (talk) 11:33, 14 August 2009 (UTC)

Positioning sound

I was having a dispute yesterday about the extent to which our perception of where sound comes from is based on what we see. It seems to me that with only 2 ears, you could only place the source of a sound on a plane - that is, you could not tell whether it is in front of, above, behind or below you. Is there any way of discerning these without rotating your head while listening, or would a blind person not be able to tell whether an instantaneous click sound was produced behind his head or in front of it? Insperatum (talk) 10:22, 14 August 2009 (UTC)

Sound localization is not only done by differences in the sounds from the 2 ears, but also by different dampening of frequencies at different angles by the pinna. This can in turn be used to create the illusion of 3D sound with speakers arranged in a plane. Icek (talk) 11:40, 14 August 2009 (UTC)

Yep - basically, we can do simple stereo localization by the obvious tricks of comparing the delay between the sound waves entering our two ears. But because our heads are not symmetrical - a sound coming from above passes through a different mass of bone and brain than one coming from below. That causes different delays, reflections and absorption of different frequencies in the sound. We're able to detect that change in the quality of the sound and use it to estimate that third dimension...albeit imperfectly. There is an audio recording system from a company called Sennheiser which uses a pair of microphones embedded into the ears of a fake plastic head which is designed to transmit, delay and reflect sound just like a real human head. If you listen to a sennheiser recording on a pair of in-ear headphones, then you can clearly hear that third dimension of sound. There was a while in the 1970's when you could buy sennheiser recordings of all sorts of music. Unfortunately, you have to listen to them on headphones - the effect is largely destroyed if you use loudspeakers. There are some computer software techniques that crudely simulate the effects of all of that 'stuff' that happens in your head and applies that to sounds used in computer games. The effect is moderately successful - but again, it only works well when you are using in-ear headphones. SteveBaker (talk) 12:27, 14 August 2009 (UTC)

I seem to recall that there's some debate about the mechanisms of 3D acoustic perception; it seems likely that the brain fuses in some visual cues into the mix, in addition to the stereo-ear-channel processing for delays and frequency-dependent amplitude variations. Nimur (talk) 14:44, 14 August 2009 (UTC)

How do ear muff-style headphones compare to in-ear style? --Sean 16:17, 14 August 2009 (UTC)

In this case, not well. You really need the speakers to be in roughly the same position in your ears as the microphones in the fake head. I believe there have been some successes at making synthetic 3D audio using cup-type headphones. SteveBaker (talk) 02:21, 15 August 2009 (UTC)

What if you had a 7 speaker home entertainment system? John Riemann Soong (talk) 15:11, 14 August 2009 (UTC)

Well - if they are positioned all around you (including above and below), I presume that suitable recordings could be made for them that would reproduce 3D moderately well. SteveBaker (talk) 02:21, 15 August 2009 (UTC)

"Visual capture" or the "ventriloquism effect"[5], [6] is the phenomenon of sight overruling auditory localization. When 16 mm movies were the common mode of audiovisual presentation, sometimes the speaker was on the projector, or was somewhere other than behind the projection screen. But during the movie, the audience was able to perceive the speech as coming from the actors' images on the screen. With only 2 ears, absent head movement such as tilting the head, we can localize sounds in the lateral dimension but not in the vertical dimension.[7] It would take 3 ears, not in a line, to truly localize in 3 dimensions. Edison (talk) 15:17, 14 August 2009 (UTC)

It is certainly possible to tell, with the eyes closed, and without head movement, whether natural sounds in the environment are coming from in front or behind. With binaural sound from earphones, this does not seem to be the case. This includes "binaural" recordings made with mics inside an artificial head. I did not note front/rear localization in listening to such a recording through earphones. Perhaps as stated elsewhere the influence on sound quality of the head aids in this for normal environmental sound. As for "visual capture," I can remember watching a movie, with the speaker behind me on the 16mm projector, when the projector lamp went out. The sound source location seemed to "fly" swiftly, but not instantaneously, from the movie screen, in front, to the projector, behind. Edison (talk) 22:20, 14 August 2009 (UTC)

One common reason for not hearing the 3D effect is if you have your earphones swapped into the wrong ears. I found the stennheiser recordings pretty convincing. SteveBaker (talk) 02:21, 15 August 2009 (UTC)

Off-topic, but the McGurk effect is an interesting case of sight overruling sound. --Sean 16:17, 14 August 2009 (UTC)

It seems to me that the need for visual queues is easily debunked. I know two blind people rather well. They are better at localizing a sound than I am. They have no visual queues. So, they are doing it strictly with two ears. -- kainaw™ 17:16, 14 August 2009 (UTC)

Not directly relevant to the question, but it may be interesting to know that barn owls localize sound in two dimensions by having one ear tilted up and the other tilted down -- this causes amplitude and time differences to carry indpendent information. Looie496 (talk) 17:34, 14 August 2009 (UTC)

It is difficult to locate the source of a single-frequency (sinewave) tone without moving the head. I have also observed that my cat snoozes contentedly while surrounded by all these household noises that it has become used to: radio, TV, traffic, door slams, kids yelling, etc. However a firework overhead upsets pussy greatly. It is clearly not the volume but the unexpected direction of the sound that causes alarm. Cuddlyable3 (talk) 18:25, 14 August 2009 (UTC)

That's not surprising though - the brain is relying on different transmission properties of different frequencies within a natural sound source. A simple, pure, sine wave wouldn't provide enough cues. You'd probably do better with 'white noise' or more natural sounds. SteveBaker (talk) 02:21, 15 August 2009 (UTC)

←Slightly off-topic, but holophonics may be of interest, as may this sound clip (use headphones). Fribbulus Xax (talk) 22:12, 14 August 2009 (UTC)

toxicity of crown ethers

Is it me or would a tiny amount of crown ether be potentially very toxic if ingested? I was wondering, because there aren't many mentions of safety precautions / MSDS stuff on our articles that cover them. John Riemann Soong (talk) 14:12, 14 August 2009 (UTC)

They are moderately toxic http://dohs.ors.od.nih.gov/pdf/Crown%20ethers%20REVISED.pdf page 5.

Long term effects are unknown.83.100.250.79 (talk) 14:19, 14 August 2009 (UTC)

John, it seems silly to even have to say this, but several of your previous questions seem to suggest that you plan to eat the results of your chemistry experiments. Please, don't do this. There's no way that the Reference Desk, or the publishers of the MSDS, or any other source, can know what is actually in your concoction. If you're so interested in food science, maybe you can consider interning in a lab or a company which specializes in chemistry for food applications. That way, you can play around with some expert supervision. Like many scientists, I'm sure you're excited about homebrew lab experiments, but whether you're working with chemicals, explosives, pressurized gases, (whatever) - the rules of lab safety don't disappear just because you're unsupervised. Nimur (talk) 14:51, 14 August 2009 (UTC)

While we're on the subject of crown ethers and toxicity, has anyone tried to use them as antidotes for mercury poisoning? I know they're good chelating agents, but would they work for chelating mercury out of a person's body? 98.234.126.251 (talk) 04:45, 16 August 2009 (UTC)

I don't know of any published info about that. Would be more likely with a crown thioether (sulfur seems to be a better ligand for mercury than oxygen is). Would want to put some sort of hydrophilic chain attached, since crown ethers are good for solubilizing ions in non-ionic solvents (compare structures of given treatements in the mercury-poisoning article), and the goal is to make the mercury excretable rather than stay in any lipophilic environment. Also, crown-ethers are good and specific chelating agents for cationic metals, but only work well if the metal atom fits inside the crown. For example, 12-crown-4 holds Li⁺, 15-Crown-5 holds Na⁺ and K⁺, and 18-crown-6 holds K⁺. Given the amount of such ions in the body, need something with a pretty high and specific affinity for mercury. Mercury is large, so would need a pretty large ring to get decent binding I would think. Although interestingly, our 15-Crown-5 article says that one has good selectivity for lead. DMacks (talk) 16:11, 16 August 2009 (UTC)

Water solubility increases with ring size, so that may also help solubility. John Riemann Soong (talk) 16:44, 16 August 2009 (UTC)

So, a hydrophilic-derivatized 15-crown-5-thioether could work for lead (and thus prob'ly for mercury too)? That's a good idea... where can I get the funding and the starting materials? DMacks, are you interested in this project? 98.234.126.251 (talk) 00:26, 17 August 2009 (UTC)

I just looked up the MSDS for 15-crown-5: it's got a health hazard rating of 2 and a REALLY big LD-50, so toxicity problems will likely be relatively minor (after all, the antidotes in use now, like British Anti-Lewisite are also moderately -- or in some cases not-so-moderately -- toxic). A bigger issue at this time is, will it work like we want it to? 98.234.126.251 (talk) 02:53, 17 August 2009 (UTC)

Guess we'd better start with lit-search. Turns out synthesis and use of crown-thioethers for chelation of mercury ions with apparently good selectivity is known. [8] among other refs don't even require advanced academic search engines to find. I didn't narrow down to physiological uses. DMacks (talk) 06:34, 17 August 2009 (UTC)

Great -- someone else has beat us to our idea AGAIN!!! It's hard to be an inventor these days, ain't it -- you come up with some great idea, and then you find out someone else has already put it on the market. Kinda sucks, don't it? Well, let's you and me keep coming up with more ideas till we come up with something nobody thought of yet. 98.234.126.251 (talk) 23:08, 17 August 2009 (UTC)

Thioethers have sharper bond angles, don't they? Won't that change the geometry a bit? John Riemann Soong (talk) 04:59, 17 August 2009 (UTC)

blood in the water

Some species of sharks are known to be able to detect blood in water at great distances. Are there any bony fishes that have this ability? Googlemeister (talk) 16:39, 14 August 2009 (UTC)

Sorry to nitpick and not answer, but it would be more precise to say sharks detect blood in water at very low concentrations. 152.16.15.144 (talk) 17:39, 14 August 2009 (UTC)

I don't quibble with the OP's words "detect blood at great distances" but if anyone can give a figure for a typical distance, can they say how long it takes for the blood to travel that distance? Cuddlyable3 (talk) 17:57, 14 August 2009 (UTC)

The diffusion rate of the blood would depend on the temperature of the water and local currents. My hunch is that the diffusion rate is going to not be uniform in all directions and vary significantly. The shark article gives the unsourced figure for sensitivity "as little as one part per million of blood in seawater". You can make a circular cow type approximation as to how far away the shark can sense blood while ignoring the time factor by assuming X amount of blood was spilt and assuming it is evenly mixed at the concentration of one part per million in a sphere of water. The radius of the sphere represents the distance the shark will sense blood. 1 mL of blood (several drops) mixed in 999,999 mLs of water gives 1ppm blood. 1 mL of anything is 1 cm³. 1,000,000 cm³ corresponds to a sphere with a radius of 62 cm. According to blood, "the average adult has a blood volume of roughly 5 liters" or 5000 cm³. Adding in the blood you get a volume of liquid of 5,000,000,000 cm³. That corresponds to a sphere with a radius of ~ 1060 cm or 10.6 meters. 152.16.15.144 (talk) 01:22, 15 August 2009 (UTC)

some predatory bony fish without the lateral line (the organ which sharks detect the struggles of fish and blood) they can detect it but in higher concentrations. around 10,000 p.p.m —Preceding unsigned comment added by The mophead (talk • contribs) 18:29, 14 August 2009 (UTC)

The lateral line detects motion (with little hairs, like your inner ears), and sometimes electrical impulses, but how could it detect blood in the water? --Sean 20:59, 14 August 2009 (UTC)

I'm fairly sure it can't. They taste/smell (the difference is minimal) the blood. --Tango (talk) 21:45, 14 August 2009 (UTC)

Catfish probably can although I'm not sure they would be looking for blood specifically. According to this book, catfish are very sensitive to amino acids. A channel catfish can sense alanine at 10^-9 to 10^-11 M. If I did my math right that corresponds to a minimum sensitivity of roughly 1 to 100 parts per trillion. 152.16.15.144 (talk) 01:45, 15 August 2009 (UTC)

Catfish thrive as bottom feeders in muddy rivers, so scent is a main means of finding prey. No visibility to see the food. Edison (talk) 19:15, 15 August 2009 (UTC)

acid question

If you place a gold alloy in acid that is not aqua regia (90% AU, 10% Cu) will the acid dissolve only the copper leaving you with a somewhat porous remainder? Googlemeister (talk) 16:49, 14 August 2009 (UTC)

The principle is known (see Raney Nickel), but only 10% copper will probably not provide a connected network of voids for this to happen, (try 20%) (also copper doesn't dissolve in many acids...)83.100.250.79 (talk) 17:56, 14 August 2009 (UTC)

Copper will dissolve fine in pure nitric acid while gold will not. That may work. Also, if you grind up the alloy into a fine powder, you may be able to get enough surface area to get more of the copper out. --Jayron32 04:57, 15 August 2009 (UTC)

chameleons: will they eat off your hand?

i have a pet yeman chameleon and im not sure if they will eat of my hand. or will it count my hand as competition for food? —Preceding unsigned comment added by The mophead (talk • contribs) 18:25, 14 August 2009 (UTC)

This thread says that they can and will bite, depending on the temperament of the animal. --Sean 20:34, 14 August 2009 (UTC)

Are you asking whether they will eat food out of your palm, or if they will devour your hand itself? The grammar of "eat off" is ambiguous. --98.217.14.211 (talk) 21:59, 14 August 2009 (UTC)

I have a bird that tries to eat off my fingers every time I put my hand in the cage, but it rarely breaks the skin. Edison (talk) 22:22, 14 August 2009 (UTC)

Is it a parrot of some denomination? They tend to do that. Unless the bird is obviously scared of your hand or annoyed by your presence, it's likely a substitute for the playful(ish) beak sparring that they engage in with others members of the same flock. --Kurt Shaped Box (talk) 00:01, 15 August 2009 (UTC)

I also enjoy the ambiguity of the hand competing with the chameleon and with the food.  :) --Sean 23:45, 14 August 2009 (UTC)

May I remind respondants that per Wikipedia:Reference_desk/guidelines we are specifically told: don't poke fun at a poorly-written question. SteveBaker (talk) 02:07, 15 August 2009 (UTC)

I'm honestly just confused about what they are asking. I'm not sure I understand what the bit about competition for food is meant to imply. --98.217.14.211 (talk) 04:31, 15 August 2009 (UTC)

There is a difference between "They eat off your hand" and "They eat your hand off"... Dauto (talk) 21:45, 15 August 2009 (UTC)

I had a pet chameleon when I was a kid, living in Kenya (I have no idea what kind of chameleon). It was a very small specimen - maybe just about an inch long with it's tail curled up. It would stand on the tip of my finger while I carried it around the room looking for flies and other insects for it to feed on. Because it had a 2" tongue (pretty remarkable for a 1" animal!) - you'd just have to get it within range of it's victim and it would do the rest! However, it only seemed interested in live insects - so "hand-feeding" in the conventional sense was impossible. It never bit me...but it was pretty tiny. SteveBaker (talk) 02:14, 15 August 2009 (UTC)

Calculating my daily calorie intake needed to lose weight

If I know my current weight and my height, what's the best way of estimating how many calories I should eat each day to stay at that weight? (The idea being that I then reduce that amount so that I gradually lose weight). Thanks 78.146.206.220 (talk) 18:46, 14 August 2009 (UTC)

There are numerous estimation calculators online, but you probably should not put a great deal of faith in them as metabolism (baseline calorie usage) can vary a great deal among different people who weigh the same. The US government usually assumes people eat 2,000 kcal a day when they provide nutrition values. Googlemeister (talk) 18:49, 14 August 2009 (UTC)

See Schofield equation and Harris-Benedict equation. For more in-depth information, see this. Red Act (talk) 19:14, 14 August 2009 (UTC)

There are calculators online that take in a lot of info about your height, weight, and activities, that try to give you an indication of what your baseline is. Google "Base metabolic rate". --98.217.14.211 (talk) 19:31, 14 August 2009 (UTC)

It's all a matter of having calories consumed greater than calories coming in. There are some estimations online of how much each activity uses, and you can calibrate that to yourself by, say, walking on a treadmill that you can calibrate. I would say the easiest way to lose weight is physical activity rather than dieting; just eat a healthy diet (veggies, fruit, some dairy, some protein, etc.) and spend a lot of time playing games outside, walking, etc. Awickert (talk) 04:36, 16 August 2009 (UTC)

Come to think of it, when I was more athletic, I used to burn ~6000 calories per day. Of course, that's a little on the intense end, but (since I enjoy food and exercise) I would say that more playing outside and working out is much easier (for me) than less eating. Awickert (talk) 04:47, 16 August 2009 (UTC)

The National Weight Control Registry consists of data about a set of people who have successfully lost a minimum of 30 pounds, and kept it off for a minimum of a year. Of the people in the NWCR, 98% modified their food intake in some way to lose weight, and 94% increased their physical activity.[9] So it is quite unusual to succeed at weight loss in the long term without both modifying food intake and increasing physical activity, but the data suggests that of the two, modifying food intake is the most crucial. Red Act (talk) 08:33, 16 August 2009 (UTC)

Gene Identification

Besides the "knockout" technique what other techniques are used to identify a gene's purpose i.e. genes such and such are for hair and genes xyz are for the color or texture? —Preceding unsigned comment added by 70.136.158.98 (talk) 21:26, 14 August 2009 (UTC)

Probably the most commonly used method is to analyze the gene's DNA sequence similarity to other genes whose functions are known. Looie496 (talk) 21:41, 14 August 2009 (UTC)

You're basically asking for the methods of genetics, molecular biology, biochemistry, cell biology, and physiology. It's a bit too much for one post, but here are some other examples: Genomics studies the organization of the gene and regulatory sequences (this is much easier now with the completion of various genome projects). In the good old days you would clone the cDNA from a gene expression library but this is rarely needed anymore, since most genes have been cloned at this point. Still, it can be interesting to clone alternative splice forms of the gene from different tissues. Gene expression analysis using northern blots, in situ hybridization, or DNA microarrays can show where the gene is expressed and give some idea of what tissues it is important in. Western bloting can be used to study the protein and whether it is post-translationally modified. Various biochemistry techniques are used to study protein-protein interactions. Immunohistochemistry can be used to detect the intracellular location of the protein, which gives some hints about what it does. Cell culture is used to study the gene in vitro. Depending on the initial clues about what the protein does, there will be more specialized methods specific to a given type of protein. People use comparative genetics and model organisms to see if the gene is conserved during evolution which would suggest a fundamental function. Often a gene's family member can be studied in a more simple organism before learning what it does in humans. Transgenic animals use gene overexpression to get information complementary to the knock-out. Ok, that should get you started. --- Medical geneticist (talk) 22:58, 14 August 2009 (UTC)

What about if we had an idea that the genes to make hair color like blonde for example if we knew that it was on chromosome 9, could they with any success study 1000 people who are natural blondes and look for genes that are the same (mostly) to try to uncover the genes involved in creating the blonde hair color? —Preceding unsigned comment added by 70.136.158.98 (talk) 04:31, 15 August 2009 (UTC)

Yes, you can do exactly that type of thing using families, with a technique called linkage analysis; or in larger groups of unrelated individuals using genome-wide association studies. However, one limitation is that although you may find a genomic location that is associated with a trait in a family or in a population, you would still need to do additional work to identify which gene in that area was responsible for the association, and then even more work to prove that the association represents a causal relationship between the gene and the disease/trait. Also, if a trait or disease is complex, the linkage or association studies may only reveal part of the story. --- Medical geneticist (talk) 17:08, 15 August 2009 (UTC)

August 15

Power of gull bites - any data?

Following on from the question above - are there actually any stats available for how much pressure various gull species can bring to bear with their beaks? I just had a quick look on Google but I couldn't find anything useful. --Kurt Shaped Box (talk) 00:20, 15 August 2009 (UTC)

I feel lazy but you can use the information in this paper which is based on finches but includes various data related to gulls to extrapolate. (M. A. A. van der Meij and R. G. Bout. "Scaling of jaw muscle size and maximal bite force in finches." The Journal of Experimental Biology. 207, 2745-2753. 18 May 2004) Also this person may know the answer if you want to contact him. 152.16.15.144 (talk) 02:07, 15 August 2009 (UTC)

executive chair that has a trigger

anyone having knowledge of such a chair please contact me at [email address removed]. I am 80 years of age and probably well never be able to find this site again.

I also do not buy whatever you may be selling so please do not fill my screen with offers.

the chair is constructed entirely of bentwood and steel by a master maker. when the trigger is touched it flies into peices with enough force to knock more than one person down.

I know the history since WWII and it has never been activated in all these years. after using it since 1995 I was walkig by and strcuk it with my walker. my left shouler was bruied very badly, something hit my right arm between the shouler and elbow with enough force to damage the radial nerve so much that I may never have use of my hand.

your will be appreciated. I —Preceding unsigned comment added by 65.34.15.65 (talk) 18:06, 14 August 2009 (UTC)

I copied this from WP:VPM. --Golbez (talk) 00:39, 15 August 2009 (UTC)

I have removed your email address to prevent you getting spammed. We don't respond by email, so hopefully you will manage to find this site again. --Tango (talk) 00:45, 15 August 2009 (UTC)

Could it have been a support spring that snapped, letting some material fly? Nimur (talk) 00:58, 15 August 2009 (UTC)

One-way rocking chair. Cuddlyable3 (talk) 18:27, 16 August 2009 (UTC)

How does evolution work where sexual selection is minimal?

I’m thinking of insects like bees and ants. The queens mate with a single drone which happens to be nearby. How do possibly beneficial mutations occurring in the colony propagate when sexual selection is minimal? With mayflies, there is a virtual orgy lasting a few hours at the end of their lives. How do beneficial mutations work when indiscriminate sexual activity is the norm? Myles325a (talk) 04:39, 15 August 2009 (UTC)

Through other kinds of natural selection? --Kjoonlee 05:10, 15 August 2009 (UTC)

I think you're thinking of the sort of sexual selection where mammals choose mates that appear healthy and fertile; but simple ability to survive and breed is surely a more fundamental driver of natural selection. Also, I'm no entomologist, but are you certain that the sexual activity you mentioned is truly indiscriminate? Tempshill (talk) 06:38, 15 August 2009 (UTC)

Sexual selection was never thought of as the primary mover of evolution; it was used by Darwin and others in order to explain certain things that don't fit well with natural selection. The case of the eusocial, colony insects doesn't fit into the sexual selection model all that well, but that isn't surprising—sexual selection does not always apply, it is a sub-set of natural selection. --98.217.14.211 (talk) 15:29, 15 August 2009 (UTC)

Kinship selection is at play in populations such as bees and termites in which most workers share the same genes. Imagine Reason (talk) 20:00, 15 August 2009 (UTC)

Remember : The total number of ants in a colony is a red herring. As is the lifespan of individual worker ants. Only the life-cycle of the queen is important, evolution-wise. Consider that ant colonies have "generations" shorter than human generations, and that most ant colonies are reproduced exclusively through sexual reproduction. So really, sex in ant colonies is not "minimal". They reproduce sexually just as much as we do.

(The queen mates with a male ('for life') then she gives birth to a few daughters and a few sons. The fact that she also gives birth to about a zillion sterile workers doesn't matter.) APL (talk) 05:41, 16 August 2009 (UTC)

Nobody said sex was minimal. They said sexual selection was minimal—competition between members of the same species for the right to reproduce. --98.217.14.211 (talk) 18:00, 16 August 2009 (UTC)

Why would it be any less? A queen ant leaves her parent colony to fly around searching for a suitable mate. Male ants similarly leave their parent colonies to fly around searching for a suitable mate. Why would you assume that there's less sexual selection here than with any other insect? APL (talk) 18:37, 16 August 2009 (UTC)

Multiple universe theory proves God exists?

If multiverse theory is true, and every possible universe exists, including many with completely different laws of physics to our own, does this mean that in at least one one of these universes an omnipotent entity (God) capable of moving between universes MUST exist? Incidentally I am an atheist, but I do find the idea of a multiverse plausible. —Preceding unsigned comment added by Trevor Loughlin (talk • contribs) 09:11, 15 August 2009 (UTC)

No. --194.197.235.43 (talk) 09:27, 15 August 2009 (UTC)

No is the correct answer. The existence of other universes is metaphysical speculation. It is completely untestable and therefore of zero interest either in explaining things or proving things. On top of which despite being a mainstream Christian (by European standards) I find the idea of God being an entity moving between universes (or moving around at all for that matter) completely absurd. Before you even think about God existing though I suggest you think long and hard about whether you exist and what on earth that means. --BozMo talk 10:54, 15 August 2009 (UTC)

If it is possible to move between them then they aren't really separate universes, in my opinion. But that is semantics, the answer is "no" regardless. I don't know of any multiverse theory (there are several) where different universes have completely different laws of physics, just different fundamental constants and/or different initial conditions and/or different results of random events. --Tango (talk) 11:25, 15 August 2009 (UTC)

And even if they have completely different physical laws, omnipotent concepts of god are logically impossible - as the old "can god make a stone so heavy he cannot lift it?" question illustrates --Stephan Schulz (talk) 11:29, 15 August 2009 (UTC)

Surely it's 'a stone that cannot be lifted by an omnipotent being' that's logically impossible? In any case, such debates have little to do with either physics or the everyday practice of religion. No-one expects their god to go around lifting infinitely heavy rocks, so no-one is bothered by this purely theoretical contradiction. AlexTiefling (talk) 11:39, 15 August 2009 (UTC)

Ex falso quodlibet. Logically, if you have any contradiction in your theory, its inconsistent. But indeed, few people really think about an "omnipotent" god. Usually, they imagine only a very very potent god. Which is why I wrote about "omnipotent concepts of god" (as the original question specified an omnipotent god), not "any god". --Stephan Schulz (talk) 12:22, 15 August 2009 (UTC)

I don't understand the distinction. "God" and "omnipotent being" sound pretty synonymous to me. --Tango (talk) 11:42, 15 August 2009 (UTC)

In a polytheistic context, they're certainly not synonymous. In a monotheistic context, it's substantially irrelevant whether or not they're synonymous. Religious people don't ask if God will create an unliftable rock. They ask 'Lord, will you now restore the Kingdom of Israel?', or 'Which of your Lord's blessings would you deny?'. The idea of interpreting the idea of God in terms of a strict definition of omnipotence has absolutely no resemblance to the idea of God entertained by the typical religious person. There are many criticisms of the 'unliftable rock' problem: If God is omnipotent, why can't he create logical contradictions? If the rock is heavy enough, won't it become a planet/a star/a black hole, such that 'lifting' is a useless concept? This problem no more invalidates the idea of God than the idea of 'the set of all sets that are not members of themselves' invalidates the idea of sets. It's just a juvenile thought-experiment. AlexTiefling (talk) 12:10, 15 August 2009 (UTC)

Sorry, I meant in the context of this discussion. Stephan said "omnipotent concepts of god", so I assumed we were using "god" in a vague Abrahamic sense. There are plenty of alternative definitions of the word. --Tango (talk) 12:27, 15 August 2009 (UTC)

FWIW I think the concept of technically omnipotent is fairly modern (I would hazard 300AD without getting any books down from the top shelf). Of course there are lots of poetic statements in the psalms etc but probably not by people with any concept of what that might mean, just as pre Herodotus the concept of historical statement was dubious. I think "could win any battle" rather than "can win every battle without casualties" or as Stephan put it "very potent" is probably the Abrahamic God. But as Alex has said most people these days are not really there. The question is whether the universe can be understood with reference to a greater being in the same way that a 41 year old lump of flesh can be understood with reference to a person called Stephan. --BozMo talk 15:50, 15 August 2009 (UTC)

AFAIK, Christian and generally Abrahamic theologists have predominantly considered God to be perfect, omniscient and omnipotent in a philosophical sense. The fact that everyday practitioners can't or won't see a problem does not make it disappear. If people have more "modest" requirements and only expect God to be omnipotent in those matters that concern them personally - well, it should at least be pointed out that even this is a very ambitious claim, and that acknowledging some fundamental principles to be independent of God and pre-God moves His image in the wrong direction - towards a giant, ingenious, invisible alien floating somewhere in intergalactic space, subject to the laws of physics and to the occasional headache. --91.148.159.4 (talk) 22:18, 16 August 2009 (UTC)

AFAIK no serious Christian Theologian since Thomas Aquinas has had the view you state is "predominant". Pretty much zip. Sorry. --BozMo talk 17:38, 17 August 2009 (UTC)

Well, you see, the problem is that in this respect, Thomas Aquinas was pretty much unchallenged until secularization in the 19/20th century; and no new view on this has really become predominant and "standard" since then. Sure, in the 20th century lots of theologists have been trying to "fix" these attributes in various ways (it's their job, after all), making some modifications to them in order to save the basic idea; some, such as Charles Hartshorne, have even dared dispute some of them. But, mutatis mutandis, the divine attributes remain mainstream and are normally "rescued" in some way or other, because they are essential to the whole business: a God that has defects and limited capabilities and knowledge is simply less competitive on the market. For "omnipotence" one can check, on Google Books, "Almighty God: a study of the doctrine of divine omnipotence" by Gijsbert van den Brink. For "omniscience" - "God, foreknowledge, and freedom" by John Martin Fischer. For "perfection" - "The untamed God: a philosophical exploration of divine perfection, simplicity and immutability" by Jay Wesley Richards. For all three you can see "The Christian God" by Richard Swinburne and "Philosophical foundations for a Christian worldview" by Moreland and Craig.--91.148.159.4 (talk) 21:25, 17 August 2009 (UTC)

In addition, here are a few specific citations for the divine attributes remaining mainstream: Christian sources - "Handbook of Christian apologetics: hundreds of answers to crucial questions" by Kreeft and Tacelli, p.72; "The God who risks: a theology of providence" by Sanders, p.194 "Reason for the hope within" by Murray, p.83); neutral sources - "A companion to philosophy of religion", by Quinn and Taliaferro, p.22,56, "Philosophical Inquiry: Classic and Contemporary Readings" by Adler and Elgin, p.877. --91.148.159.4 (talk) 22:12, 17 August 2009 (UTC)

I'm a Christian, and I also think the answer to this question is a resounding 'no'. Both the existence of one or more gods, and the existence of one or more alternate universes, are metaphysical speculation. These speculations are entirely independent, and can in principle be made to say whatever an individual speculator wants. Their levels of acceptance depend on their plausibility, and the idea that the one theory is linked to the other seems quite implausible, and certainly has a very low level of acceptance. Ideas of proof and determination don't come into play at all, and I'd question if this is really a 'science' question at all. AlexTiefling (talk) 11:39, 15 August 2009 (UTC)

Modern notions of a multiverse are not metaphysical speculation; they're much more credible than the pseudoscientific claims of religion. Other universes might not be observable, but if a theory like M-theory which predicts them is confirmed to be true, that would be indirect scientific evidence for the existence of a multiverse. Granted, it wouldn't be particularly good evidence and wouldn't convince most people, but any evidence at all places the multiverse hypothesis above the level of religion. --Bowlhover (talk) 15:15, 15 August 2009 (UTC)

What multiverses does M-theory predict? If you define "universe" as a collection of causally connected events (which I would) then, by definition, you cannot make any observations of other universes, so cannot directly demonstrate their existence. --Tango (talk) 16:51, 15 August 2009 (UTC)

IMHO you are right about that Tango. As said twice it is metaphysical speculation and multiple universes is generally an "of the gaps" type argument of varying disguise used to explain extraordinary coincidences in the universe (e.g. dynamics of the big bang was just right: bigger and we would have imploded smaller we would have expanded too fast for planets). A multiverse explains by saying there are zillions of completely isolated big bangs with universes but we can only observe the one which happened to work. Polkinghorne says evidence for a God, some say evidence for mulitverse and inflation offers another theory. But its a rare example in my view of Polkinghorne's logic being flawed (because metaphysical speculation about God's extra-universal role is still metaphysical speculation, we can only look at the observable universe and infer about it). --BozMo talk 18:18, 15 August 2009 (UTC)

A zillion-big-bangs theory is not comparable to the "God of the gaps". A zillion-big-bangs theory assumes that almost the same things that we have already observed may have occurred also in instances which we haven't been able to observe, but abiding largely by the same laws of physics we know. A God theory assumes that something the like of which we have never observed has occurred, abiding by laws that we, with the state of our present knowledge, can't possibly imagine.--91.148.159.4 (talk) 22:18, 16 August 2009 (UTC)

Ignoring Omnipotence beyond logical possibility, lets just settle for Q from Star Trek then?

• I think the conclusion to come to is that the idea of multiple universes can prove or disprove nothing. The "theory" is mostly philosophical postulation and moonbeam-fondling. However, if we wanted to forget about "proving" anything and just do some philosophising, I think it's worth looking to the theology. Many predominant monothesitic religions contend that Everything (note the capital 'E') is presided over by a being somewhat beyond our space, and Judeo-Christianity follows a God that is characterised as incomprehensible and above our reality. In speaking about a deity that is, in a sense, beyond reality, it seems less than meaningful to discuss how its (or His, in the Christian case) existence relates to multiple universes. —Anonymous Dissident^Talk 16:01, 15 August 2009 (UTC)

"Only Many Worlds can explain quantum superposition effects" 81.131.16.134 (talk) 19:52, 15 August 2009 (UTC)

Wrong type of multiverse. The Many Worlds interpretation of Quantum Mechanics is about different universes for every "choice" the universe has to make, the kind of multiverse we're talking about is where each universe has different physical laws/constants (and each of those universes could split into a multiverse of the first type). It's possible the two meanings could be combined if the physical laws/constants turn out to be a result of quantum fluctuations in the early universe, I suppose, but I don't believe any such theory has become mainstream. --Tango (talk) 23:47, 15 August 2009 (UTC)

Every possible universe cannot include impossible universes where laws of physics are violated or where every mystical notion is somewhere realized. The OP as a declared atheist seems to be confident about what cannot exist, so maybe the OPs question reflects a longing to find a God. Cuddlyable3 (talk) 18:09, 16 August 2009 (UTC)

Some responses in this thread seemed somewhat abrupt (apparently the OP was judged not to treat the sensitive issue of God with due seriousness, and his thought experiment was suspected of being irreverent or even blasphemous). The last post was probably the least helpful of all (maybe writing that the OPs question reflects a longing to find a God reflects a longing to find someone longing to find a God, and my writing the above reflects my longing to find someone longing to find someone longing... never mind). Also, I think it's obvious that the idea was - if multiverse theory were to be proven, would that prove the existence of God, too? So nobody is expected to dispute multiverse theory itself here. Even under these conditions, and with a risk of repetition, I concur with everybody else that the answer is "no". If multiverse A disallows an omnipotent God and multiverse B allows an omnipotent God, this God's omnipotence would still obtain only in multiverse B, so the one thing he could never do is move to multiverse A and exercize his omnipotence there. Of course, the whole way of posing the question is a little unfair to monotheism, because it presumes that the laws of the universe predate and restrict the divine person potentially operating in it. Monotheism is, in principle, based on the opposite causation: the person comes first. I think this is naturally and intuitively appealing to us humans, taking into account how we grow up and live. In the thought experiment, the God of Multiverse B is only omnipotent because Multiverse B allows him to; since there must be a general set of rules which determine how the parameters or features of any individual Multiverse determine its God-friendliness, it's obvious that there is a more general domain within which these rules hold true, let's call it the Super-Universe, or less reverently - Universe Universe (UU), and within UU Gods are not omnipotent. At all. To obtain an omnipotent God, we need to assume instead that God comes first, s/he is the first letter of the alphabet so to speak, and all sorts of laws, concepts, attributes etc are secondary. Hard to imagine, of course, but not necessarily impossible to accept - it depends on one's motivation.--91.148.159.4 (talk) 22:18, 16 August 2009 (UTC)

Well said. But the question itself is an excellent one and can be put in another form that has nothing to do with religion or even deities. One could ask that in a multi-verse system, with an infinite number of universes, where hypothetically anything could exist, including deities or omnipotent or omniscient phenomena, surely there would be scenarios where something from one universe could encroach on another universe? To contribute to the OP's question you could posit that even if a deity/god existed in another universe, surely that would not prove its existence in ours. It's an excellent question, and someone familiar with the philosophy of multi-verses can really answer it. Rfwoolf (talk) 23:24, 16 August 2009 (UTC)

The problem is in the 'kind' of multiverse we're talking about. The one that seems like it might be true (the multiple worlds interpretation of quantum theory) is the one where the laws of physics are the same in all of them. Ergo, no magic to make gods with. Infinitely powerful beings are simply not possible in our universe. If there are other universes with OTHER laws of physics - then indeed, all bets are off. However, if a universe with the right laws of physics to allow there to be gods in it were to exist (whatever that means) - then that's certainly no guarantee that these entities can cross into our universe - because here, our laws don't permit them to exist. But if ANYTHING could "cross" from one universe to another, that would kinda blow away the idea that they are separate universes. If things could cross - you'd think we'd see evidence of peculiar laws of physics showing up all over the place in our universe - and we don't. SteveBaker (talk) 23:34, 16 August 2009 (UTC)

Infinitely anything won't fit into the universe Steve.--BozMo talk 18:23, 17 August 2009 (UTC)

If God (or gods) exists then he must be part of the omniverse (a word I just coined only to discover we have an article on it! I think the definition in there is equivalent to what I mean - it contains everything that exists in the broadest possible sense), that omniverse must have some kind of rules governing it (whether they are rules we are capable of understanding is another matter entirely) and God is subject to those rules. The idea that "God comes first" doesn't make sense - the omniverse has to exist for God to exist. Of course, the omniverse doesn't necessarily has a concept of time (it certainly doesn't have our concept of time), so the ideas of "first" and "cause and effect" doesn't necessarily apply. --Tango (talk) 00:01, 17 August 2009 (UTC)

Ever take a look at Norse mythology? Well, according to Norse legend, the High God Odin is all-powerful -- but only as long as he keeps all his covenants with all his subjects; as soon as he willfully breaks even one covenant, all his power would vanish just like that. Seems just a little like what you're talking about here, as far as your statement that "God is subject to [the rules governing the omniverse]". (Of course, in Norse mythology, Odin and all the other gods are anthropomorphic, which is a very dubious notion to say the least...) 98.234.126.251 (talk) 00:44, 17 August 2009 (UTC)

Yes, that's not a bad example, although it isn't consistent with our theories of physics that isn't really a problem - we know our theories aren't perfect because we don't have a theory of everything. There are gaps (like Quantum Gravity) that we have yet to fill. Valhalla could fit into one of those gaps. (Unlikely, but not impossible.) --Tango (talk) 13:33, 17 August 2009 (UTC)

So Tango do you think YOU fit into one of the gaps, or conscious being with free will generally do--BozMo talk 18:23, 17 August 2009 (UTC)?

As a Christian, I wouldn't say specifically that "Valhalla could fit into one of the gaps", but well, some kind of afterlife could surely be consistent with our knowledge of the universe (and I'm sure that sooner or later, afterlife will be proven to exist beyond reasonable doubt). 98.234.126.251 (talk) 23:28, 17 August 2009 (UTC)

I'm not sure the bit about Odin is true in the original mythology (I've read the Prose Edda and much of the Poetic one, though I may have forgotten something); this reminds me more of the interpretation in Wagner's Ring Cycle, and/or G.B.Shaw's interpretation of that interpretation. Anyway, certainly the restriction to not breaking covenants means that he is not really omnipotent, he is restricted by at least this law, or perhaps even by an entity that imposes the law.

Re:"Odin and all the other gods are anthropomorphic, which is a very dubious notion to say the least". The word "anthropomorphic" is POV-laden, as it literally means (1) "described as being similar to humans to some extent", but in practice is used as (2) "described as being similar to humans to an unrealistic extent", and what is an "unrealistic extent" remains to be debated. I think it's obvious that any god is anthropomorphic in sense (1) - being similar to humans to some extent - and it can be argued that any god is anthropomorphic in sense (2) as well - being similar to humans to an unrealistic extent. —Preceding unsigned comment added by 91.148.159.4 (talk) 15:32, 17 August 2009 (UTC)

By "anthropomorphic" in this context, I meant specifically "so similar to humans as to be indistinguishable from them upon casual observation". This would be true in the case of Norse gods -- or indeed most of the gods from pagan mythology of the European nations -- but in the case of Jehovah, the Judeo-Christian God, this is not necessarily true (and indeed, He is most likely NOT anthropomorphic in this sense). Same with Allah, the Islamic god, according to the Koran he is not anthropomorphic but more like some kind of cosmic force (although I really have to wonder what kind of god would choose a child molester as his prophet, but that's a whole other topic altogether). 98.234.126.251 (talk) 23:47, 17 August 2009 (UTC)

An infinitely powerful god can be anthropomorphic if he/she/it feels like it. You could imagine how that would come in handy. Odin just needed a good lawyer. I'm sure he could find a way to repeal his pact with humanity without breaking the pact in the process. SteveBaker (talk) 21:52, 17 August 2009 (UTC)

Would Loge fit the bill as a "good lawyer"? He was infamous for giving crooked advice -- which is why the other gods didn't really trust him. ;-) 98.234.126.251 (talk) 23:19, 17 August 2009 (UTC)

Tango's argument was that "God comes first" doesn't make sense, because God is inevitably pre-conditioned by the Universe in which he exists. Well, one could argue that God was the Universe in its initial state, and then he created those parts of the Universe that are not strictly speaking part of himself, but still, in view of their origin (he had created them, and being omnipotent, he had created them perfectly in accordance with his purpose), he has retained absolute control of them. In the beginning was absolute Goodness&Wisdom, then It sort of budded or secreted from itself stuff like mathematics, logic, physics etc, so as to finally produce another thing with the potential for goodness and wisdom - namely us humans. I don't think this is logically impossible.

Another possibility is that physics and logic are not even a creation of God, but have been part of God from the start. In this case, the question often asked is: can he then can violate physics and hence his own nature? The answer would be the same as to the question whether he can do something evil: "Yes, he can in the sense of being capable, but he can't in the sense of being likely to do it - because he simply doesn't want to, because he is what he is." So I still stand by the "God comes first" option as the assumption best poised to lead to the desired conclusion. Cheers! --91.148.159.4 (talk) 15:17, 17 August 2009 (UTC)

91.148, you should be a theologist. :-) 98.234.126.251 (talk) 23:31, 17 August 2009 (UTC)

All possible paths don't lead to all possible outcomes.... Elocute (talk) 21:54, 17 August 2009 (UTC)

Species of monkey

Can anyone identify what species this monkey is?  Chzz  ►  13:55, 15 August 2009 (UTC)

Rhesus macaque? --82.21.25.109 (talk) 14:53, 15 August 2009 (UTC)

Crab eating macaque according to vervet.za.org --Muhammad(talk) 17:21, 15 August 2009 (UTC)

Sounds painful. Edison (talk) 19:12, 15 August 2009 (UTC)

That must be a big crab if it can eat a whole macaque. --Jayron32 01:48, 16 August 2009 (UTC)

One of those things that you really should know about the human body...

Hi! So, I have a question that you really should have learnt the answer to in high school, but it seems to me that no one did (I've asked five people this, and gotten five different answers). As we all know, men create sperm throughout their life inside their testicles, while women only have a limited number of ova that they get at birth and are stored inside their ovaries (I'm right so far, yes?). Here's my question: on average, how many eggs does a human female have? In total? I've heard everything from a few hundred to a few hundred thousand (which was what I thought, incidentally), with most people guessing at the lower range. Neither the ovum nor the ovary article would enlighten me on the subject.

I would be most thankful if you fine fellows could make up for the collective failure of me and my friends' human biology education and provide me with an answer. Cheers! 83.250.236.75 (talk) 17:43, 15 August 2009 (UTC)

It depends, and we may be wrong. Women do not have a store mature ova, but rather progenitor cells. The number of these decreases over time, but there are apparently several million of them. See Oogenesis#Number_of_primary_oocytes. In other words, women don't "run out of eggs" in menopause. --Stephan Schulz (talk) 18:02, 15 August 2009 (UTC)

The same article sited above also states

Recently, however, two publications have challenged the ovarian biology dogma that a finite number of oocytes are
et around the time of birth.[4][5] Renewal of ovarian follicles from germline stem cells (originating from bone
marrow and peripheral blood) was reported in the postnatal mouse ovary.
Due to the revolutionary nature of these claims, further experiments are required to examine the dynamics of small
follicle formation.

So may be the premiss of the question is incorrect. Dauto (talk) 21:40, 15 August 2009 (UTC)

Human presence detection technique

Hello! I'm presently working on a personal project which would require me to detect human presence in a room of 35'x20'x12'(l x b x h),as part of my objective. I've in mind PIR sensors but i'm afraid they might not respond accurately at ambient air temperatures over 40^oCelcius. Is there any alternative way of detecting human presence in a room other than PIR? P.S. Capacitive method is not viable as room houses multiple em radiating sources. And passive millimeter-wave (MMW) sensors are seemingly over my expertise grade it would seem.

A THANK YOU before hand to whoever might help me figure this problem out. —Preceding unsigned comment added by LONGBOW001 (talk • contribs) 20:29, 15 August 2009 (UTC)

Is a computer and webcam(s) an option to try? There already exists a program called motion (also in debian repositories) that lets you define commands to run when there's motion in video camera image. --194.197.235.43 (talk) 20:54, 15 August 2009 (UTC)

To properly solve this problem, you need to define some environmental conditions. You want to detect a human, but what other things are going to be present that you need to avoid detecting? If warm objects will be present, infrared or thermal detection will have an unacceptable false-positive rate. If other animals or pets will be present, you need to identify a human distinctly from, say, a cat - or whatever else is in there. If you want to identify a specific human, you might need facial recognition software or some other biometrics. If you are willing to have the human actively participate in the identification process, such as by wearing an RFID tag, this can simplify the process. Nimur (talk) 21:42, 15 August 2009 (UTC)

Have you considered using a petoscope? 98.234.126.251 (talk) 04:54, 16 August 2009 (UTC)

Pressure-sensitive mats. Cuddlyable3 (talk) 17:51, 16 August 2009 (UTC)

Candle pendulum

What is going on in this video? --Reticuli88 (talk) 20:42, 15 August 2009 (UTC)

The side of the candle that is lower will dump the hot wax. The side that is higher will hold the hot wax. Because the lower side dumped the hot wax, it is lighter. So, it rises. Then, the lower part dumps its wax. The higher part does not. So, the lower part becomes lighter and it rises. Another way to imagine this is a see-saw with a bucket on each end. If the bucket is lower, the water will dump out. Now, continually fill the buckets with water. The lower one will dump out the water while the higher one fills up with water. The higher one will lower and dump the water. You can also toss in a bit about one end of the candle getting shorter but I seriously doubt that has much effect compared to the loss of volume by dumping out the hot wax. -- kainaw™ 21:01, 15 August 2009 (UTC)

Unless that's a really volatile candle, I suspect we're also seeing some time lapse imagery - the burn rate and oscillations look like they're sped up somewhat. Nimur (talk) 21:46, 15 August 2009 (UTC)

Not just dripping either, (Most candle wax winds up in the air.) Notice how the flame cuts into the candle more on the downward side. I assume that wax is consumed faster on that side. APL (talk) 05:32, 16 August 2009 (UTC)

The right end is lit first and starts losing weight before the left is lit, so the candle initially tilts anticlockwise. The tilt then stabilises because the left flame is angled more towards the wax body and so melts it faster. Now both ends burn in an unusual sudeways mode. Note that the flames bend towards the center. We can't see the whole airflow but hot air must rise from the flames and be replaced by cool air from beneath. Two circulating airflows close together generate more friction than a single flow, therefore the former is not stable and there is turbulent combination of the flow modes. A slight imbalance in the turbulences tilts the candle. This has a regenerative effect at the physical resonant frequency of the see-saw where the air disturbance of the candle body adds to the thermal disturbances of the flames. The oscillation of the candle builds up so it becomes obvious that the two flames are alternately contributing to the same upward convection. Factors contributing to the oscillation are the flames alternately burning into or away from the candle body, and possibly (not visible) molten wax running down the gutter at the lower end and dropping off, making that end lighter.Cuddlyable3 (talk) 17:42, 16 August 2009 (UTC)

Thank you Cuddyable3--Reticuli88 (talk) 11:59, 19 August 2009 (UTC)

Faraday Cage

I've always thought that microwaves were Faraday cages. I saw a demonstration where they put a radio inside a Faraday cage (it wasn't a very good one but somewhat effective) and naturally the radio quality turned to shit. I was wondering why when I put my phone in the microwave oven and close the microwave door (naturally not turning on the microwave) my phone still could receive calls (I called it and it rang). I thought the whole point of a Faraday cage was to shield the objects inside. Thanks 66.133.202.209 (talk) 20:53, 15 August 2009 (UTC)

The mesh on the front panel of the microwave (that let you see in) are calibrated to be just the right size to keep the microwaves inside. Signals at different wavelength can pass through it, though. (Which is why you can see through it—visible light can pass through easily). I imagine that the cell phone wavelengths are more varied than the microwaves' and can make it through. --98.217.14.211 (talk) 21:05, 15 August 2009 (UTC)

We discussed this in December 2008. My excellent response was so fantastic that nobody else even needed to follow up on it! I will copy it here for your reading pleasure: Nimur (talk) 21:49, 15 August 2009 (UTC)

The question you are asking is, roughly restated, "does the microwave have a shield?" It should be more properly restated, to be very precise, as "What is the non-linear anisotropic attenuation-vs-frequency characteristic of the microwave casing, and what frequencies of attenuation overlap those frequencies used by the cellular phone?" First of all, let's clarify a few details:

• Microwaves and cell phones commonly do operate at the same or similar frequency band (for example, 2.45 GHz). But, maybe your microwave and cell phone operate at different frequencies... it depends on whether your phone uses GSM, where you bought your microwave, etc. You can check this with the marshmallow test, or if you're smart, just read the label on the back of the microwave oven.
• Microwaves commonly include a few features, such as a wave guide or horn to guide the microwave energy in a specific direction (towards the food)
• After the microwave energy is "in the oven", it bounces around, off the walls, maybe even setting up resonant waves. So, any "shielding" should really be surrounding the entire oven, with strongest protection at the places of strongest electromagnetic fields (typically, directly opposite the "horn" where the waves come in.
• Microwave ovens probably use a "crappy" but generally single-frequency tonal magnetron to create the electromagnetic waves. So, the shielding is quite probably a "notch filter" (isolating out that single frequency and preventing it from passing).
• By the second law of thermodynamics, any (passive) shielding should be bidirectional - that is, if the energy can't get out, then energy can't get in, either.
• Shielding is also not measured as "all or nothing" - it's measured as an attenuation. That means that the shield lowers the intensity of the radiation, but does not make the signal disappear completely. Now comes the non-linear part. The case in consideration compares two very very very different orders of magnitude - nearly one kilowatt of oven radiation, blasting from eight inches away, compared to a few milliwatts transmitted by the phone and maybe nanowatts (picowatts even!) received from the tower. (Depending on "details," your phone may need bi-directional communication to initiate the reception of a call; or it may just need to receive a single incoming message from the tower). So it may not be safe to say that the shielding materials attenuate by a fixed amount over this entire range of power levels. It's possible that very-low intensity signals, like those from the phone, are not attenuated much at all; while high-power signals are brought down to safe intensities (and no further)
• Cell phones use very complicated modulation to make sure that the data can be deciphered even when the signal is very very weak. This is what advertisers often mean when they say "fewer dropped calls" (though they might also be talking about density of towers). Specifically, some of the QAM spread-spectrum coding schemes are particularly insensitive to single-frequency interferers. So if the So even if the microwave shielding is "pretty good" at notching out (stopping) that single frequency that the oven operates at, the cell phone data may be fairly undeterred.
• And the anisotropic part makes a huge difference! The cell-phone probably has a crummy antenna, which may mean it has a weird angular reception pattern. And, the microwave oven shielding is probably not uniform either (presumably concentrated on blocking regions of highest radiation while cooking!) So, if you rotate the phone, you may get dramatically different reception patterns. And this is totally assuming that there is no resonant coupling between the 2.4-GHz resonant chamber of the oven, and the 2.4-GHz dipole antenna inside the phone. Who knows what may happen to the reception pattern if that effect is non-negligible! In summary, the orientation of the phone with respect to the oven, and the orientation of the oven with respect to the nearest tower, will dramatically change the results. (see Radiation pattern for more graphical explanation).

So, it can actually be fairly complicated to say whether a given microwave will "shield" a given cell-phone from a call. Irrespective of the result of that test, it is not really a good way to determine whether the oven casing effectively blocks out the microwave energy used during cooking. Nimur (talk) 17:00, 10 December 2008 (UTC)\

Thanks for that excellent response Nimur. As for the microwave blocking the microwave energy I sure hope so because alot of times I put my head next to the microwave to watch the food that I'm heating up so if the casing doesn't I'm screwed I guess... :) 66.133.202.209 (talk) 23:41, 15 August 2009 (UTC)

Thank you Nimur for the pleasure of reading your fantastically excellent response. But the marshmallow test won't tell anything about the cell phone operating frequency. And where does your hypothesis that the oven shielding is non-linear come from, when this implies there is some material change, ionisation or arcing somewhere? By spread-spectrum modulation I think you mean CDMA not QAM. If you want the OP to investigate the effects of orienting the phone and oven, the attention should be directed to the received signal strength indicator in the phone (if it has one) rather than just whether it receives a call. The OP may be reassured that the screening is adequate by checking whether a moist rag held close to the operating oven gets warm (it shouldn't). Cuddlyable3 (talk) 16:42, 16 August 2009 (UTC)

As far as the mobile phone operating frequency, the best way to check that is to look for a label. Inside my mobile phone, underneath the battery, is a bunch of FCC information, and I can see that my phone operates at either 900MHz or 1.8 GHz. You can also check this stuff on the web, this website applies to my phone model. As far as the non-linear attenuation, my assertion is that everything, including simple stuff like dielectric "constants," are inherently nonlinear, if you analyze them over a large enough experimental range. This Google Scholar search indicates active research into such material-dependent nonlinear attenuation; it seems I may be on the right track here. Though material-changes can be responsible for nonlinear behavior, they aren't the only reason why a measured value might deviate from a simple constant. A cursory glance through some research papers suggest that atomic structures and crystal lattices in the material may play a role. Regarding the phone's signal strength meter: I don't know about your microwaves, but mine doesn't have good visibility to the interior, so I doubt that I could read the phone's signal-strength indicator; anyway, it's hard to know exactly what that readout means (there can be time-averaging; digital post-processing, etc). Nimur (talk) 17:44, 16 August 2009 (UTC)

Nimur your Nokia mobile phone is a standard model for GSM which uses TDMA and FDMA (not spread spectrum). It has a received signal strength display that is averaged over 5 to 10.5 seconds (see RXLEV[10]). The display is in logarithmic steps (decibels) exactly defined in the ETSI GSM specifications. Microwave ovens are usually internally illuminated and your phone display should be legible in some positions looking through the door grille. As the OP says, microwave ovens are constructed as a Faraday cage of steel without "exotic" materials. Alleged non-linear attenuation by this cage would imply that a significant fraction of the heating power typically 600W is absorbed by something other than the food. Asserting that everything is nonlinear doesn't quantify anything here. Cuddlyable3 (talk) 20:25, 17 August 2009 (UTC)

FDMA is a spread-spectrum technique, is it not? Nimur (talk) 17:06, 18 August 2009 (UTC)

Thanks for the excellent GSM reference on receive levels, Cuddlyable - it's very relevant to the question (though it does highlight the complexity of cellphone communications as I was discussing in December). As far as the nonlinear dielectric constant, this does not only affect attenuation, but also the reflection coefficient (so my earlier statements should not be taken to imply that the steel shielding is dissipating energy by dielectric heating alone). The ability of the shield to direct energy back into the microwave interior will depend on its material properties. A nonlinear reflection coefficient may prefer reflecting strong signals while allowing weak signals to pass. (Electromagnetic oobleck?) According to conventional straightforward treatment, the reflectivity of a material should be constant; the next level of treatment is probably some refraction, like Snell's law, and finally a version of Snell's law that accounts for frequency variability; but the most rigorous treatment will actually consider all of the above, plus incident amplitude, plus incident polarization, etc. etc. etc. In reality, the ability of a "Faraday Cage" to reflect or shield electromagnetic signals depends on all of these parameters and more. We clearly have an experimental example of this - a microwave blocks kilowatt-scale energy (as you mentioned, a damp rag is not being heated outside the oven); but this same passive shield allows microwatt-scale energy at the same frequency band to pass freely. Evidently "faraday cage" is too simplistic of an approximation for this seemingly straightforward case. Nimur (talk) 17:19, 18 August 2009 (UTC)

Musical tastes and mental health diagnosis

Can musical tastes be a factor in diagnosing a mental illness or absence thereof? NeonMerlin 23:26, 15 August 2009 (UTC)

It looks like there has at least been some research in that area, yes. E.g., see the papers "Clinical diagnosis by the IPAT music preference test"[11] and "Can music preference indicate mental health status in young people?"[12] Red Act (talk) 07:57, 16 August 2009 (UTC)

I'd imagine so in many cases of anhedonia.Mo-Al (talk) 08:03, 16 August 2009 (UTC)

You may want to check Oliver Sacks´ book "Musicophilia: Tales of Music and the Brain". --Cookatoo.ergo.ZooM (talk) 08:11, 16 August 2009 (UTC)

Feeling tired when hiking, resting, then continuing

Why do humans need to rest? What good does it do? Why cannot the body just keep on supplying the energy at a constant rate without needing rest periods? And, when you are on a long hike or march, has anyone found out the optimum length and frequency of rest periods? 78.146.247.51 (talk) 23:49, 15 August 2009 (UTC)

There are two consumers of energy -- one is the nervous system (via the action potential), and the other is the ATP-driven motor that contracts the muscle fibres. The action potential is instantaneous, releasing electrochemical gradients a bit at a time to send signals -- but if you send a lot of signals you can deplete this potential. (Sometimes you need hours to restore the gradient to full strength again, because the gradient is restored by ion pumps that pump ions one ion at a time.)You can deplete the supply of ATP within cells while blood sugar is abundant, because it takes time for the cells to absorb the sugars, metabolise it via oxygen as a terminal electron acceptor, and make ATP with it. Also, fatigue is partially a safety mechanism. The body doesn't wait till cells are completely depleted of ATP -- you'd collapse, not to mention that cells need energy to stay alive (pump in certain ions/nutrients, repair damage to DNA, membrane holes and other materials) and running out of ATP would be bad. Imagine if the body simply allowed you to walk until your heart and lungs gave out? John Riemann Soong (talk) 01:20, 16 August 2009 (UTC)

As for your last question: back during the Civil War, Stonewall Jackson had his troops march for 1 hour, then rest for 10 minutes before continuing the march for another hour, and repeating this cycle until either the troops reached the objective, or had to stop for the night. This worked really well, so I'd say that 1 hour march / 10 minutes rest would be close to optimal. FWiW 98.234.126.251 (talk) 05:06, 16 August 2009 (UTC)

A lots of exercise routines use similar cycles. 20 minutes exercise and 1 minutes rest, repeated, for example. It does seem to be effective to have short breaks every so often - the important thing seems to be resting before you reach your limit. --Tango (talk) 16:19, 16 August 2009 (UTC)

The other thing that can cause a need for rest is running out of oxygen in the relevant muscles so they have to use anaerobic respiration and get a build up of lactic acid, your muscles will then start to hurt and you eventually have to stop. That should only happen for high intensity exercise, though, I doubt hiking would cause it. It is more of a problem for 400m runners, or something. --Tango (talk) 16:19, 16 August 2009 (UTC)

August 16

orbital

in niobium, what can be the possible orbital arrangement? i think it should be - 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d3

but in my book the last two are - 5s1 4d4

which one is correct and why (the half-filled orbital concept can't come here as d3 isn't half-filled)? —Preceding unsigned comment added by 122.50.129.193 (talk) 02:59, 16 August 2009 (UTC)

The huristic you have learned to fill electron orbitals in order is only an approximation, the actual filled orbitals will differ slightly. The "half filled" rule which applies to Chromium and Copper are an attempt to "justify" variations from the strict rules. Remember that the electron filling rules are a human invention, and that the elements themselves were not necessarily informed of the rules; even if they were they are not bound to follow them. If you are trying to get a homework problem right, you should probably just follow the rules and use the expected 5s2 4d3 configuration. The actual configuration has been experimentally confirmed to be 5s1 4d4 since it better explains niobium's +4 oxidation state (see Niobium); a state that would be unlikely to exist if the configuration were 5s2 4d3 (where you would ONLY expect the +3 and +5 states). Just remember that real, physical data will sometimes contradict the little games we invent to explain electron configuration. The standard orbital filling model works MOST of the time, with a few notable exceptions. The "half-filled" rule your teacher taught you is a kludge designed to explain away elements like chromium and copper; niobium cannot be explained away by anything except "the model does not work for that one". --Jayron32 03:51, 16 August 2009 (UTC)

The rules are a simple generalisation of the Schrodinger equation so you don't have to perform Hartree-Fock equations every time you want to estimate how orbitals are filled. John Riemann Soong (talk) 21:03, 16 August 2009 (UTC)

Chirping transformer

Why is the power adapter of my computer chirping like a bird, at a rate of roughly 1 chirp per second? Yes, I know it's malfunctioning; I just want to know how the malfunction is causing it to chirp. --99.237.234.104 (talk) 03:11, 16 August 2009 (UTC)

Does it have a built-in fan? (Most desktop power supplies do.) Probably the fan is wobbling slightly. That can produce very regular "chirping" noises. APL (talk) 05:33, 16 August 2009 (UTC)

No, this is a laptop adapter. I'm sure the sound is coming from the power adapter, not the laptop itself. --99.237.234.104 (talk) 06:09, 16 August 2009 (UTC)

Switched mode power supplies can make a noise ,probably due to varying forces on components (capacitors etc) as an input voltage is chopped to maintain output voltage.

Is it very loud?83.100.250.79 (talk) 12:16, 16 August 2009 (UTC)

I would suspect a capacitor is about to fail, or a capacitor has already failed, and there is a new resonant frequency in the supply. Not much should be happening at 1 Hz in an AC-DC power supply - low frequencies typically involve the large, front-end holding capacitors, but those usually are calibrated for kilohertz-ish time constants. Unfortunately it's very hard to diagnose; capacitor failure doesn't always leave any visible signs. Another possibility is that there is a short circuit somewhere in your load (on the computer motherboard) and the failsafe shutdown (if your PSU has one) is triggering at 1Hz and immediately restarting. Nimur (talk) 18:40, 16 August 2009 (UTC)

Capacitance and materials

I'm currently learning about capacitors, and trying to understand the concept of capacitance. Is it dependent upon the material which the capacitor's plates are made out of? Mo-Al (talk) 08:02, 16 August 2009 (UTC)

No but it depends hugely on the material between and around the plates and the area of the surface. --BozMo talk 08:06, 16 August 2009 (UTC)

Also the geometry(shape and size) of the capacitor.[[13]]--Leon (talk) 14:34, 16 August 2009 (UTC)

Capacitance. Cuddlyable3 (talk) 16:08, 16 August 2009 (UTC)

Well, of course the plates have to be made of something pretty highly conductive, e.g., a metal. And the number of free electrons has to be sufficient. But those are very minimal requirements. Looie496 (talk) 17:53, 16 August 2009 (UTC)

So does this mean that two capacitors that are of the same shape, and have the same dilectric, but whose plates are made of different (conductive) materials will have the same capacitance? Mo-Al (talk) 19:04, 16 August 2009 (UTC)

Sure, to within a reasonable accuracy. But when you try it in the lab in my experience if the dilectric is ionic it is difficult to eliminate battery effects as well and they are obviously dependent on the metal. So don't try and prove it as a school physics project unless you are incredibly careful--BozMo talk 19:41, 16 August 2009 (UTC)

A spelling error shall be stamped out with extreme prejudice before the infection spreads further. The word is DIELECTRIC. Cuddlyable3 (talk) 22:09, 16 August 2009 (UTC)

Cast iron stove paint

I am really after someone who know about paints. Sorry that the story is a bit long. I live in a cool climate (UK) with an (old) outdoor swimming pool. Since I have effectively unlimited free wood (I burn about 6 tonnes a year heating the house) I built a bonfire boiler out of scrap lying in the garden to heat the swimming pool. It cost around 50 USD to do and works pretty well (200 degree litres a minute) and over a few days makes an impact on the pool so I am keen to prolong its life. The top part of the boiler (hood and chimneys basically) is made from an old broken Victorian cast iron "Loughborough" boiler and weighs about 150kg. This cast iron has been outside in all weathers for at least a century (it was left under a tree in our garden along with a Victorian bathing hut and all sorts of nonsense) and is still mainly sound. This top piece sits above a steel pipe circulating heating fluid and is double skinned. Nonetheless to get good heat transfer I routed the fire vents through the skins on the way to the chimney and the outside surface of it gets pretty hot. Once I started using this boiler I noticed the rate of rusting of the cast iron had accelerated considerably presumably because the heat was stripping off protective layers. I tried cleaning it and putting two brands of "stove paint" on it but each only lasted one cycle of burn-rain-burn. So I tried "Hammerite" which weathers incredibly well on other iron/steel but had already discolored and I guess is degrading. Questions (1) is there some kind of enamel paint which would do better in rust-heat-rain (2) is it worth trying to cover the Hammerite with stove paint on the basis the degrading requires contact with air and the stove paint might well have failed because of a rusting process under the paint (3) do any primers survive this kind of heat? Hammerite and stove paint both say don't prime (4) Any other ideas? I could I guess cover the whole surface with fire cement but that would be a bit ugly and it is not clear to me if that would survive either. --BozMo talk 08:05, 16 August 2009 (UTC)

Please give the price in pounds. You are British, live in Britain, and many readers here are British. 78.147.255.120 (talk) 10:45, 16 August 2009 (UTC)

How is that of any relevance to the question? --antilived^{T | C | G} 10:48, 16 August 2009 (UTC)

It is relevant to the question because the OP is British, lives in Britain, and many readers here are British, yet strangely has not given the amount in British currency. 78.147.255.120 (talk) 13:05, 16 August 2009 (UTC)

More British people understand foreign currencies than the other way round. Say 30 guineas anyway. --BozMo talk 14:39, 16 August 2009 (UTC)

He can quote the cost in dollars as well as pounds to be polite to both our British and our American chums. I'm sure he did not pay the costs in dollars. 78.144.207.41 (talk) 17:00, 16 August 2009 (UTC)

He may quote prices in any currency he likes. Local or foreign, common or obscure. We do not need self-appointed culture police running around telling people to be true to their home currency. APL (talk) 18:32, 16 August 2009 (UTC)

1)Perhaps you can put a roof over the entire contraption to keep it dry? 2)You can also try to add a zinc sacrificial anode. 3)I have no idea if you could galvanize the thing. -Arch dude (talk) 11:15, 16 August 2009 (UTC)

(after research) take a look at Electroplating#Brush electroplating. -Arch dude (talk) 11:33, 16 August 2009 (UTC)

The problem with galvanizing I think it the heating. When I have had galvanized garden incinerators in the past the galvanization tends to strip as soon as they are in use. And in case our friend above protests about a Brit using US spelling unusually "z" in these words is correct usage in British English as always practiced by the Cambridge University Press (even though some Brits use s also). --BozMo talk 14:39, 16 August 2009 (UTC)

The OPs problem is similar to that of painting a car exhaust system. Look at [14]. Cuddlyable3 (talk) 16:03, 16 August 2009 (UTC)

You could try going to a car parts store and buying the stuff you use to paint car engine parts with. It's generally resistant to pretty high temperatures - check what it says on the can. SteveBaker (talk) 23:18, 16 August 2009 (UTC)

Another suggestion from the field: You need to get every last speck of rust off the original piece, and whatever you put on as the first coat over it has to "bond" to the bare iron. Inquire of a really old-time "plumbing and heating" contractor -- you're looking for guys who work on steam heating systems rather than "heating and air conditioning" guys, who are just sheet metal benders -- and ask who they subcontract (or hire out?) radiator refinishing to.

That said, however, it is possible that the temperatures at which your're working are just too high for any kind of paint. The same guys could probably advise you on that!

For the record, it doesn't matter at all whether the price is quoted in pounds or dollars or won :-)

--DaHorsesMouth (talk) 02:25, 17 August 2009 (UTC)

What is the conversion between pounds, bob, and guineas? U.S. hardware stores (iron mongers to Brits) sell high temp paints which seem to last better than what you report. They are intended for barbecues. I believe Rustoleum sells "Barbecue Black." Also look into paints used on steam locomotives. Edison (talk) 03:49, 17 August 2009 (UTC)

1 guinea = 1 pound + 1 bob

1 pound = 20 bob

1 bob = 1 shilling

--TammyMoet (talk) 13:35, 17 August 2009 (UTC)

Does exercise make people less drunk?

I alcohol can be used as a source of energy by humans. Does that mean you can " burn it away " by doing exercise? In other words: if I'm drunk will I be sober faster if I jog a few kilometers? (providing of course that I am still able to walk properly)PvT (talk) 11:01, 16 August 2009 (UTC)

Not really ... alcohol isn't like blood sugar, and it isn't a "preferred carbohydrate". See Ethanol metabolism#Thermodynamic_Considerations. Where the metabolism of sugars and the metabolism of alcohol merges is when they are converted into an acetyl group and bound as a thioester with coenzyme A to form acetyl-CoA. The first step of ethanol metabolism involves its conversion into acetaldehyde, and this *costs* energy (it's endergonic). Arguably, this is the "slow step" of the reaction, and why it takes so long to clear ethanol from the body. Unlike glycolysis, this first step doesn't give you any payoff, so less incentive for the body to use it. There's some minor payoff when acetaldehyde gets converted into acetic acid, but this is quite small compared to say, the decarboxylation step of pyruvic acid metabolism, in the oxidative metabolism of sugars (where a whole molecule of carbon dioxide is released).

The really big payoff of ethanol metabolism is when acetic acid is converted to acetyl-CoA and then the oxidised into water and carbon dioxide. But the sheer majority of ethanol never gets converted into an acetyl group on acetyl-CoA ... it gets converted to acetic acid which is then filtered out by your kidneys. Alcohol is treated as a toxin in your body. Unlike say, glucose, which enter the cell via special glucose channels, there are no special "alcohol channels" to allow ethanol molecules to pass through cell membranes ... say muscle cells. So what happens to alcohol in the bloodstream? It must be processed by liver cells who allow toxins to pass through them so enzymes can process them. (Liver cells get regularly killed by all this toxic waste handling of course, which is why your liver is one of those special organs that can grow back.) What will liver cells do with acetic acid? Probably nothing -- they aren't the ones doing the muscle work. They die, get recycled, the acetic acid ends up in your kidneys and it's passed out as urine (after you drink lots of water to allow renal excretion).

Note you really can't do anything to increase the rate of BAC removal ... you can do symptomatic things that make you feel somewhat better, but the only way to increase the rate of BAC removal is to increase the efficacy of your liver cells. (gene enhancement ... better enzymes ... more liver cells... etc.) And of course if you regularly poison your liver cells, your liver will slow down as well. Furthermore, alcohol is such a minor carbohydrate that even if muscle cells did metabolise alcohol, when you exercise you'd be mainly using sugar, and once in a while, every 100 ATP cycles or so, alcohol would be picked to be metabolised (if muscle cells would use alcohol at all). Alcohol metabolism evolved as a means of dealing with the alcohol toxins of bacteria, not for energy processing. It's probably very good that your muscles don't try to metabolise alcohol -- muscle cells don't grow back as easily as liver cells, you see. John Riemann Soong (talk) 13:46, 16 August 2009 (UTC)

See also Ethanol metabolism#Common_Misconceptions. "There is a common misconception that drinking alcohol leads to weight gain. This has never been proven in the literature and is the subject of ongoing debate among experts..." John Riemann Soong (talk) 13:47, 16 August 2009 (UTC)

On an episode of MythBusters, they concluded that is was plausible that exercise could help lessen the effects of alcohol: MythBusters_(2008_season)#Stone_Cold_Sober —Preceding unsigned comment added by 173.62.219.247 (talk) 13:53, 16 August 2009 (UTC)

I think the effect is purely symptomatic. Receiving vigourous nervous system input of course, would be a stimulatory effect that could potentially alleviate the neurodepressive effects of alcohol if the right stimulation is applied. Besides, breathalyser tests aren't really that reliable as blood tests. (The first can only be used as a reasonable warrant for an arrest. You need a blood test to secure a conviction.) I have no idea why getting slapped in the face will lower your BAC. John Riemann Soong (talk) 13:58, 16 August 2009 (UTC)

A simplistic guess would be: slap in face → anger / increased sympathetic activity → increased blood flow to liver → increased ethanol metabolism.

Did they definitely say that BAC lowered after being slapped in the face though? and was it statistically significant? --Mark PEA (talk) 15:46, 16 August 2009 (UTC)

It's a bit more complicated than that. Alcohol, along with benzodiazepine and barbiturate tranquilizers, has effects on the brain that are strongly arousal-dependent. The underlying causes are not fully understood, but the effect is so strong that a dose can be fatal if the subject falls asleep but survivable if the subject is kept awake by slapping, cold-showers, etc. The concentration of the drug in the blood doesn't change much, but the way the brain responds to it does. Looie496 (talk) 17:50, 16 August 2009 (UTC)

What I have taken away from this thread is that if I am ever stopped for suspected driving while intoxicated, after consuming a few beers, and told that after some period I will be tested for blood alcohol, my best strategy is to continuously slap myself in the face, while avoiding other forms of exercise. Has anyone tried this? Edison (talk) 03:44, 17 August 2009 (UTC)

Actually, you should do nothing at all, allow yourself to test positive, be convicted, and lose your licence. This is the smartest thing to suggest to anyone stupid enough to drive while intoxicated. On the other hand, when you show up black and blue from having slapped yourself repeatedly, you could create a diversion by claiming you were beaten by the cops, ;-) Maedin\^talk 11:59, 17 August 2009 (UTC)

That would be a utilitarian's opinion on what to do. Most people, however, care more about themselves than other people, so the prospect of having one's licence revoked, losing one's job, etc. is not favorable, therefore they will choose to slap themselves. --Mark PEA (talk) 16:25, 17 August 2009 (UTC)

Actually, "burning it away" is the only thing you won't achieve! If you do exercise, you will increase your breathing rate and thus increase the amount of alcohol that "evaporates" through your lungs (in normal circumstances, i.e. at rest, that is about 1 to 5 % of total alcohol disposal, and incidentally that is what gets measured in a Breathalyzer). In addition to the effect on your actual blood alcohol content, hyperventilation will give you a significantly lower reading on the breathalizer, while hypoventilation will give you a significantly higher reading (about 30% both ways). So, if you think you're borderline, at least don't hold your breath before taking the breathalyzer test!! :-)

Exercising will also lead you to "sweat it away" a little bit (about 0.5% at rest). The rest goes to kidneys and liver. If you decide to exercise, while you're at it you could drink water, which will lower you blood alcohol content, and consume fructose which will speed up metabolism. Stefano (talk) 22:31, 19 August 2009 (UTC)

The flip side is that vigorous exercise could lead to loss of water from the body, which can actually increase your BAC. So if you try to lower your BAC by exercising, make absolutely sure that you drink lots of water to prevent this tactic from backfiring. 98.234.126.251 (talk) 00:38, 20 August 2009 (UTC)

Does a compressed spring weigh more than an uncompressed one?

Einstein established an equivalence between mass and energy with E = mc^2. If energy and mass are thus equivalent, this means it makes sense to talk about the total "mass-energy" of a particular system, in that a body's mass is actually the total energy contained within.

Does this mean that a compressed spring, since it stores potential energy, will weigh more than an uncompressed (but otherwise identical) spring?

67.172.215.13 (talk) 12:44, 16 August 2009 (UTC)

Yes exactly, it has more mass. Dmcq (talk) 12:55, 16 August 2009 (UTC)

Really? Then does a rock have more mass when I hold it over my head than it does when on the ground? Wikiant (talk) 12:59, 16 August 2009 (UTC)

Ever so slightly. The energy of the rock is many times (many orders of magnitude) greater than the 10 J or so you gain by holding it over the ground. In a compressed spring, what you are doing is pushing atomic nuclei ever so slightly (this is elastic deformation)) beyond their optimal distances, and this stores energy in the form of greater electrostatic repulsion. In effect this makes the nuclei and the electrons ever slightly more massive, but the difference is so miniscule it cannot be measured reliably. John Riemann Soong (talk) 13:13, 16 August 2009 (UTC)

Hmmm. Are you sure about the rock? I can see the spring, easily. But the rock gains potential energy, and that energy is no really inherent in the rock, but depends on the gravitational field of the rock and the Earth. By Chuck-Norris-symmetry, if you lift the rock, the Earth should also gain mass. Does it gain more or less than the rock? Or the same? Or does this depend on the observer? --Stephan Schulz (talk) 14:32, 16 August 2009 (UTC)

I mean, I really should say the Earth-rock-lifter system. Separating masses attracted to each other is like separating attractive charges. I really don't know a lot about relativity, but my impression is that rest mass doesn't increase, so who gains the increased mass is indeed observer-dependent. John Riemann Soong (talk) 14:38, 16 August 2009 (UTC)

But that suggests that, as the rock moves an infinite distance away from the earth, the earth-rock system approaches infinite mass, no? Wikiant (talk) 15:47, 16 August 2009 (UTC)

You only need a finite amount of energy to reach escape velocity. Dmcq (talk) 16:27, 16 August 2009 (UTC)

And that's because of the inverse square law ... as masses separate the gravitational attraction between them rapidly decreases. John Riemann Soong (talk)

The compressed spring is used as an example in our article on mass–energy equivalence, which says "A spring's mass increases whenever it is put into compression or tension. Its added mass arises from the added potential energy stored within it, which is bound in the stretched chemical (electron) bonds linking the atoms within the spring". Chemical bonds are electrostatic, so the additional energy/mass is stored in the electromagnetic field. Similarly, when you lift a rock, the additional energy/mass is stored in the gravitational field. Gandalf61 (talk) 14:54, 16 August 2009 (UTC)

A field has mass? A spring weighs more when it is compressed? Cuddlyable3 (talk) 15:45, 16 August 2009 (UTC)

You've got it. Energy is put in to lift a rock. That energy has an associated mass and the gravitational field gains that amount of mass when the energy is used to lift the rock. So if the spring is used to lift the rock the spring loses mass but the whole system still has the same amount of mass. Dmcq (talk) 16:25, 16 August 2009 (UTC)

I'm sorry, but this isn't making sense. I've heard two contradictory statements: (1) increase the distance between rock and earth and the earth-rock system gains mass, and (2) as masses separate, gravitational attraction decreases (implying that the potential energy of the rock declines and therefore the mass of the earth-rock system decreases). It appears that, as the rock-earth distance approaches infinity, the mass of the system approaches infinity if (1) is true and zero if (2) is true. Which is it? Wikiant (talk) 18:39, 16 August 2009 (UTC)

The error is "gravitational attraction decreases, implying that the potential energy declines." The correct statement is that as they separate, the gravitation attraction decreases, therefore the potential energy increases more slowly. What you have to remember is that the potential energy you add to a rock by lifting it depends on the total work you did to lift it -- the higher you go, the more potential energy it has. That's why it does more damage if you drop it from 50 feet than if you drop it from 5 inches. If you lift it so high that gravity is noticeably weaker, that doesn't change the fact that you're still adding potential energy as you lift it further -- you just aren't doing it as fast. --Anonymous, 19:03 UTC, August 16, 2009.

And as for (1) vs. (2), neither one is true. The correct statement is that as the potential energy (and therefore the mass) increases more and more slowly, it asymptotically approaches a limiting value. Specifically, the most energy you can add to a rock (more precisely, to the Earth/rock system) by lifting the rock away from the Earth's surface (all the way to infinity) is GMm/r, where G is Newton's gravitational constant, M and m are the masses of the Earth and the rock, and r is the Earth's radius. (See under potential energy.) This corresponds to a mass increase of GMm/rc², which if I calculate correctly comes out to about something on the order of 1/1,000,000,000 of the rock's mass m. --Anonymous, 19:10 UTC, August 16, 2009.

Excellent! Thanks. Wikiant (talk) 20:09, 16 August 2009 (UTC)

But does this mean that if two linked springs were rotated around each other (in outer space),and one was compressed during half of the cycle, wouldn't the center of mass alter to allow a (very weak) reactionless drive to be created, in violation of Newtons third law of motion!?Trevor Loughlin (talk) 02:56, 17 August 2009 (UTC)

Please understand that a spring powered clock theoretically gains mass when you wind it, just as a grandfather clock with a weight to power it gains mass when you elevate the weight. If I accelerate my car to 125 miles per hour (200 km/h), as I did in my misspent youth, it also gains mass, but no practical scale could ever measure the mass increase. It would be many orders of magnitude smaller than the resolution of practical scales. In cyclotrons, the mass increase of the particles accelerated to an appreciable fraction of the speed of light has to be taken into account or the devices would not work. We can confirm relativistic mass increase, experimentally, in extreme cases, but we cannot observe it in everyday situations. Edison (talk) 03:39, 17 August 2009 (UTC)

As for what Trevor said if your spring setup is what I think it is (so that when one spring is compressed the other spring is stretched) to me it seems it wouldn't work because (besides the whole violating the 3rd law part) when you stretch a spring 1 m you store the same amount of energy as if you compressed it 1 m, so the center of mass wouldn't change. Also last month in Scientific American there was an article about moving yourself through space by flailing your arms and legs. From what I remember it works because of the curvature of space (and so is very neglible unless you are standing next to a black hole). Suppose you are standing on a curved surface (like the Earth). You walk in a straight line, after some miles turn 60 degrees, and repeat till you have walked three straight lines forming what would be a triangle. If you calculate the center of mass as the point connecting all the meridians of the sides, and then do it again as as the point 2/3 of the way down from one of the vertex's (which should bring the same point) you get different points. This difference (the fact your center of mass isn't precisely defined) allows you to move yourself (instead of just moving forward and coming back) —Preceding unsigned comment added by 66.133.202.209 (talk) 04:09, 17 August 2009 (UTC)

Listen guys, I have a big huge suspension spring in my basement, I stood on the bathroom scale and squeezed it. Nothing happened.</extreme intentional ignorance for the purpose of humor>ZS 11:49, 17 August 2009 (UTC)

Of course not. The energy that went into the spring, making it heavier, came from the chemical potential in your muscles. So the overall energy content of the system (you+spring) did not change. You need to weigh just the uncompressed spring, then compress it and re-weight. Alternatively, you can weigh yourself before and after the exercise, and subtract your body weight to cancel for the energy (and hence mass) you lost. --Stephan Schulz (talk) 12:10, 17 August 2009 (UTC)

Each spring is left to spring back to its normal state, not "stretched" during part of the cycle, but is compressed during the other part. But the power to weight of such a device (even if it worked ,which I don't know) would not have a practical application. But supposing you had two linked cyclotrons loaded with relativistic charged particles- protons for example swinging around each other, and switched one cyclotron off during part of the cycle? Would the centre of mass alter in a way sufficient for practical reactionless drive-or have I simply thought up a new version of "EM drive"-I don't know if this works either, though the Chinese are working on it now apparently. Also, if a spacecraft is ever constructed to achieve relativistic speeds, would the increase in mass cause the craft to collapse in on itself with gravitational effects?Trevor Loughlin (talk) 12:07, 17 August 2009 (UTC)

No. The rest mass doesn't change, and the spacecraft always perceives itself "at rest". — Lomn 13:04, 17 August 2009 (UTC)

If you turn off your cyclotron the protons travel in a straight line and crash into the sides of the tunnel. I'm not understanding your design... (either the springs one or the cyclotron one). Could you describe how one of them works in detail? What is causing this periodic compression and relaxation of the springs, for example? --Tango (talk) 13:14, 17 August 2009 (UTC)

On releasing trevor's spring all I can foresee is that simple harmonic motion ensues, with the energy that was potential, now oscillating to and fro from kinetic. Energy cannot be destroyed trevor, and so unless some sort of object leaves the system the mass of the system will remain the same. Elocute (talk) 21:47, 17 August 2009 (UTC)

The important thing is that the energy in the spring is conserved like any other mass. It isn't created when the spring is compressed, it flows from somewhere. Your perpetual motion device with compressed springs won't work for the same reason all those clever perpetual motion devices with shifting weights won't work. The same physical principles apply. -- BenRG (talk) 09:45, 18 August 2009 (UTC)

Toothpastes with two anti-bacterial ingredients

Which toothpastes, particularly those available in the UK, have two or more anti-bacterial ingredients please? Mentadent P is one, but few places stock it. 78.147.255.120 (talk) 13:01, 16 August 2009 (UTC)

Excuse my ignorance, but why does the number of such ingredients matter? Surely its their efficacy?--Leon (talk) 14:31, 16 August 2009 (UTC)

See here http://jac.oxfordjournals.org/cgi/content/full/45/2/153#SEC4 Note: I am not looking for a debate on the merits or otherwise of various toothpaste ingredients. Thanks. 78.144.207.41 (talk) 16:51, 16 August 2009 (UTC)

Is it possible for mouth bacteria to develop resistance against antibacterial ingredients? John Riemann Soong (talk) 14:47, 16 August 2009 (UTC)

Certainly, and the flora in the human mouth are legion both in number of species and number of organisms (even after brushing, flossing, and using mouthwash). Sterilization of the mouth is not feasible (perhaps not even desirable), so what's the point of using antibacterial toothpaste unless it has been demonstrated, in carefully-controlled studies, to reduce a major problem (e.g. caries and/or gingivitis) without causing short- or long-term problems? Without such evidence, this practice could cause much more harm than good. This is all general comment and is not meant to substitute for or diminish any advice you might be given by a health professional. --Scray (talk) 15:36, 16 August 2009 (UTC)

Is anyone going to answer the question asked please? 78.144.207.41 (talk) 16:41, 16 August 2009 (UTC)

Up till today I wasn't aware of a toothpaste with more than one antibacterial agent - unless you include fluoride, the only antibacterial agent I'm aware of in toothpaste (UK) is Triclosan. Perhaps there aren't any?83.100.250.79 (talk) 21:32, 16 August 2009 (UTC)

According to [15] (not the greatest of sources), it has triclosan and Zinc Citrate. I also came across this rather old study [16] which compares the activity levels. There also seem to be a lot of studies looking into the effects of the triclosan/zinc citrate combo [17] Nil Einne (talk) 22:50, 16 August 2009 (UTC)

This is a Science reference desk, so you're going to find it rather difficult to avoid discussion on which agents are truly "antibacterial" in anything other than the marketing literature. Many anitbacterials (antibiotics) have the perverse effect of actually promoting bacterial growth by eliminating beneficial (commensal) bacteria and promoting resistance in general when used in improper doses, so the focus here is rightly on whether the toothpastes in reality have a two-component action. Perhaps you would like to rephrase your question as "Which toothpastes claim to have two anti-bacterial ingredients?" - and then it becomes more of a RefMisc question than a RefScience question... Franamax (talk) 23:54, 16 August 2009 (UTC)

What sort of ridiculous people do you take us for? Do not use the science reference desk to ask questions that will be answered by those who answer by using Google to search for answers -- use Google yourself and spare us. DRosenbach ^{(Talk | Contribs)} 03:09, 17 August 2009 (UTC)

Please do not assume yourself to be ridiculous, or be emotive. It is impossible to predict beforehand if answers to questions asked will have answers from specialised knowledge, or just Google 'research' prompted by the question. Even with the latter, searchers may turn up information that the OP had not found despite spending some time previously searching, as happened in my case. 78.144.246.133 (talk) 12:48, 17 August 2009 (UTC)

Impossible to predict...quite presumtuous. DRosenbach ^{(Talk | Contribs)} 22:33, 17 August 2009 (UTC)

From a lead given above, I have found this http://www.ncbi.nlm.nih.gov/pubmed/9238875 which indicates that Crest Complete, Mentadent, and Colgate Total are such toothpastes. Crest Complete is said to be the most effective, while Colgate Total is not effective. However the study is open to question by apparantly being funded by the manufacturer of Crest Complete. 78.144.246.133 (talk) 12:48, 17 August 2009 (UTC)

De Havilland Dragon Rapide

What is the small propeller on the upper wing of this plane? —Preceding unsigned comment added by 217.30.185.1 (talk) 14:47, 16 August 2009 (UTC)

(Guessing) It looks unnecessarily large to be (only) an airspeed sensor. I think it is an air-powered electric generator. Cuddlyable3 (talk) 15:22, 16 August 2009 (UTC)

It is a wind-powered electric generator http://www.iaopa.eu/mediaServlet/storage/gamag/apr06/Rapide.pdf. MilborneOne (talk) 15:35, 16 August 2009 (UTC)

Fluorescent light comes on only after long, variable delay. Probable cause?

Here's a real-life puzzler: Fluorescent lights in a fixture would come on only after a long, variable delay (20 – 30 mins., sometimes longer). The fixture may have an electronic ballast (no starter is visible where it can be replaced easily). What might be the cause of the strange behavior? —Preceding unsigned comment added by 173.49.16.37 (talk) 15:31, 16 August 2009 (UTC)

Do the filaments at each end of the fluorescent tube glow during the start delay? If yes then try a new tube. If no then something is wrong with the starter (which is sometimes hard to see behind the tube). Cuddlyable3 (talk) 15:50, 16 August 2009 (UTC)

There's no visible glow during the delay. If you flip the switch to off before the light comes on, you'll see a brief flicker of light. Occasionally flipping the switch back and forth a few times would cause the light to come on without the delay, but that's not always successful. --173.49.16.37 (talk) 16:13, 16 August 2009 (UTC)

That is the symptom of a bad transformer in a "starterless" fixture. Replace the transformer. This is fairly cheap and easy to do (about like repairing a lamp or light fixture) but do not try it yourself unless you are comfortable with electricity. A dead transformer usually (but not always) has exuded some sticky melted tar: if you see tar, you know for sure it's bad. In my house, I gave up and refitted all of my tube flourescent fixtures to use compact flourescents. I removed the old transformers and wiring and added a bunch of screw-type scokets (four dual sockets) to each fixture. The compact flourescents are somewhat less efficient, but with tube flourescents I was always replacing either the bulbs or the transformers, and worrying that badd transformers were killing bulbs or vice versa. With the CFs, you just replace the bulb, the bulbs are each independent, and I can eventually shift to LEDs when they become economical. -Arch dude (talk) 20:14, 16 August 2009 (UTC)

Although LED fluorescent tube replacements seem more common (at least when I last looked) albeit perhaps can't be considered economical. E.g. [18] Nil Einne (talk) 23:01, 16 August 2009 (UTC)

I could understand a second, or a few seconds to reach full brightness, but 20 minutes is abnormal, and suggestive of some abnormality of the ballast, the starter, the bulb, or the wiring. Edison (talk) 03:30, 17 August 2009 (UTC)

A fluorescent light which is that slow to come on could have a problem with the grounding. There might not be a good ground connection to the case. There might also be a problem with the neutral connections. Edison (talk) 02:36, 18 August 2009 (UTC)

Did anyone else read the headline and think "No, that's not probable cause" ? —Tamfang (talk) 06:32, 6 December 2009 (UTC)

BLAST search always fruitless?

I have reason to believe that GCTGAGAGAGAGAAAAAAAAAAATCAG is part of the human genome but when I go here http://www.ncbi.nlm.nih.gov/genome/seq/BlastGen/BlastGen.cgi?taxid=9606, enter the sequence and click 'begin search', followed by 'view report', I get no matches. I also get the same result even with a simple string like CAT - what am I doing wrong? ----Seans Potato Business 16:39, 16 August 2009 (UTC)

I suspect that the presence of so-called low-complexity sequences (those highly-repetitive portions) are being automagically disregarded by the matching algorithm. Since the bulk of your sequence is low-complexity (highly-repetitive), all hits are getting filtered out. In the query screen that you've linked, look in the 'Optional parameters' box and change the 'Filter' setting from 'default' to 'none'. This will force BLAST to search using the entire sequence. Unfortunately, you're going to get a very large number of hits, as highly-repetitive regions tend to occur frequently by chance (due to gene slippage during copying). TenOfAllTrades(talk) 19:49, 16 August 2009 (UTC)

I'm not saying that slippage would generate the whole sequence spontaneously, only that it can extend the repetitive sections (the multiple GA and A repeats) in this sequence. TenOfAllTrades(talk) 21:35, 16 August 2009 (UTC)

The USCS genome browser places your sequence at chr14:51,714,964-51,714,983 using a BLAT algorithm. From what I understand, BLAT is better for looking for short, exact matches, than BLAST. It seems NCBI used to have an option to "search for short, nearly exact matches" but this is now part of the usual BLAST algorithm. FWIW I also got no hits using the NCBI version of BLAST, changing a couple of parameters. Weird... --- Medical geneticist (talk) 23:09, 16 August 2009 (UTC)

Artificial membrane

Hi, I would like to know if there are artificial membrane capable to separate CO2 and, at the same time, let the O2 and H2O molecules pass. If it is possible, I would like to know some commercial name. Thanks. —Preceding unsigned comment added by 94.163.134.160 (talk) 16:48, 16 August 2009 (UTC)

It sounds like you're looking for a Carbon dioxide scrubber, like you'd find on a Rebreather or a space ship, but they're more complicated than a simple membrane. APL (talk) 18:21, 16 August 2009 (UTC)

Most CO2 scrubbers work by absorption rather than membrane filtration. In the most commonly used type, CO2 is absorbed by metal oxide or hydroxide (often KOH or CaO, sometimes LiOH too) to form the corresponding carbonate, which is then regenerated back to the oxide / hydroxide by heating with the release of CO2 (into a different gas stream, of course). Absorption by amine solution is pretty commonly used too (the amine acts as a Lewis base). And for really thorough CO2 removal (for example, in coal liquefaction plants), physical absorption with refrigerated methanol (at -30 C) is often used -- it's expensive, but it removes CO2 to less than 100 parts per billion. Which method is best for you will of course depend on what you'll be using it for (and especially on the volume-flow of your gas stream, the CO2 partial pressure, and the maximum remaining CO2 level desired). So if you could tell me what is it you're trying to do, I could maybe point you in the right direction. 98.234.126.251 (talk) 01:13, 17 August 2009 (UTC)

Thanks to the both of you. 98.234.126.251, I would like to grow algae, so I need CO2 trapped in the internal side of the membrane (but not as carbonate), and I would like to let O2 and H2O (made from the algae) spread to the external side. —Preceding unsigned comment added by 94.162.2.225 (talk) 01:22, 17 August 2009 (UTC)

Oh -- I was assuming that you wanted to remove CO2 rather than concentrate it. (That's a natural assumption for me, cause most of my experience with CO2 scrubbing is in the context of a coal gasification plant.) Well, for your aquarium, I'd recommend passing the "product stream" (the mixture of O2/H2O/CO2 that comes out of the tank) through activated carbon, which will preferentially adsorb CO2 (but not O2), and then once the carbon is saturated with CO2, passing a stream of water (if the "product stream" is aqueous) or nitrogen (if the "product stream" is gaseous) through the CO2-saturated carbon and back into the tank. That will put the CO2 back into the tank while letting the O2 and H2O out -- essentially doing the same job as the membrane that you were asking about. 98.234.126.251 (talk) 03:20, 17 August 2009 (UTC)

I understand; the matter is that it would be a very large colture volume, so I can't use adsorbtion. It's not easy at all, but you were very kind. —Preceding unsigned comment added by 94.163.139.185 (talk) 12:25, 17 August 2009 (UTC)

Couldn't we use a principle similar to reverse osmosis? Just find membrane holes that will selectively allow oxygen and water, but not carbon dioxide. This seems possible, as CO2 contains 3 heteroatoms, oxygen only contains two, and water only contains one (and the hydrogen atoms should be small in comparison). On the other hand, it could be a problem if CO2 and O2 as linear molecules could slip in via the size of a single heteroatom. But CO2 is heavier than oxygen, so maybe that element could be combined too. How efficient would the CO2 filtration have to be? I mean if this only removes 50% of the CO2 with each pass, that might be good enough for some purposes. John Riemann Soong (talk) 13:23, 17 August 2009 (UTC)

Membranes:

• CO2 selective polymer membranes often contain amino groups -eg search "CO2 membrane selective amine"
• O2 selective membranes incorporate an oxygen carrier eg something like haemoglobin - see http://pubs.acs.org/doi/abs/10.1021/jp9816317
• water is a liquid.. I don't know any trade names. According to thermodyamics you'll have to supply energy to do the separation - probably as a pressure drop accross the membrane.83.100.250.79 (talk) 15:03, 17 August 2009 (UTC)

Zeolites are another possibility - CO2 and O2 are the same width, but CO2 is longer, it also has different chemical properties. Search "zeolite O2 CO2"83.100.250.79 (talk) 15:26, 17 August 2009 (UTC)

Don't you have to supply energy in reverse osmosis too? John Riemann Soong (talk) 20:57, 17 August 2009 (UTC)

Yes83.100.250.79 (talk) 10:38, 18 August 2009 (UTC)

Thanks, John Riemann Soong & 83.100.250.79. I agree, in theory it would be possible to make a membrane capable to saparate CO2 from O2 and H2O. The filtration should be very good, as the passing of the CO2 outside the membrane would result in pollution of the environment, but 50% could be a good start point. The problem is that I can't use any active system, just filtration, because every other method would make the tecnique too expensive, if compared to more classic way of colture: so I can't use matrix of amino groups or oxygen carrier, and neither zeolite, wich adsorbs. —Preceding unsigned comment added by 94.162.12.113 (talk) 12:26, 18 August 2009 (UTC)

I don't know if it's possible to do it any other way than actively (and I assume you mean "active" in the sense of activated carbon and not say, active transport requiring the supply of energy). I wonder if it's possible to borrow some principles of gas chromatography.... and selectively choose solvents which will dissolve CO2, O2, H2O, etc. We might turn water into a gas for this purpose ... but are you sure that an active method would be expensive? I mean, the capital cost would be high, but the maintenance would be low. Whereas if you're vaporising water to try to do the job, that might end up being more efficient in the long run. (You could also turn water into a gas via a vacuum environment of 0.001 atm -- but unless you had a superpowerful vacuum you might have to do this via tiny amounts of water at a time.) John Riemann Soong (talk) 14:37, 18 August 2009 (UTC)

I'd say 83.100 is on the right track -- a good option in the case of your seaweed plantation would be to pass the effluent through a membrane made of a polymer with lots of amino groups, which would selectively adsorb CO2 while letting O2 and H2O pass to the outside, and then when the membrane is saturated, use a reverse flow of water or nitrogen to desorb the CO2 and put it back into the tank. 98.234.126.251 (talk) 22:37, 18 August 2009 (UTC)

Ok, this way appears to be the best solution to the problem; the only real matter, unfortunately, is the same: energy. I will think about it in a deeper way, also starting from what you have written here. Thanks to all the partecipants, you really helped me! —Preceding unsigned comment added by 82.59.65.242 (talk) 16:21, 19 August 2009 (UTC)

Depending on where you're growing this algae -- couldn't you harness the tides or something? The tide going out brings out the H2O and O2, the tide going in restores the CO2... John Riemann Soong (talk) 16:42, 19 August 2009 (UTC)

Oh, that's interesting; the bounding should be weak in this case. This is not perfect yet, but it was such a good idea. If you want, you can leave me a contact; if this tecnique will be used, I would like to keep you name evident!

OK, seaweed grower, where can I leave you my contact info? I don't want to leave it here on the ref desk cause we might both get spammed; besides, this is against wiki policy. 98.234.126.251 (talk) 00:02, 21 August 2009 (UTC)

"Good" or "Bad" Firewood

We recently had a storm come through and damage two trees to the point we had to take them down and cut them into firewood. What level of MMBTU/Chord makes a type of wood a good firewood? Based on that, are the Mulberry and Ash trees we cut good firewood? Ks0stm ^(T•C) 17:46, 16 August 2009 (UTC)

This site [19] has a table listing the MBTU values of various trees. --Cookatoo.ergo.ZooM (talk) 18:46, 16 August 2009 (UTC)

But the critical thing for firewood is not MBTU but water content and how inclined to spit they are. Ash is generally rated as the best possible firewood. The very old rhyme we are all taught is fairly reliable except for Elm which burns fine (but superstition says don't do it)

Beechwood fires are bright and clear
If the logs are kept a year
Chestnut only good they say
If for long it's laid away
Make a fire of elder tree
Death within your house will be
But ash new or ash old
Is fit for a Queen with a crown of gold

Birch and Fir logs burn too fast
Blaze up bright and do not last
It is by the Irish said
Hawthorn bakes the sweetest bread
Elmwood burns like churchyard mould
Even the very flames are cold
But ash green or ash brown
Is fit for a Queen with a golden crown

Poplar gives a bitter smoke
Fills your eyes and makes you choke
Apple wood will scent your room
With an incense-like perfume
Oaken logs, if dry and old
Keep away the winters cold
But ash wet or ash dry
A king shall warm his slippers by.

or another version of the same poem:

Beechwood fires burn  bright and clear
If the logs are kept a year
Store your beech for Christmastide
With new holly laid beside
Chestnuts only good they say
If for years tis stayed away
Birch and firwood burn too fast
Blaze too bright and do not last
Flames from larch will shoot up high
Dangerously the sparks will fly
But Ashwood green and Ashwood brown
Are fit for a Queen with a golden crown

Oaken logs, if dry and old
Keep away the winters cold
Poplar gives a bitter smoke
Fills your eyes and makes you choke
Elmwood burns like churchyard mould
Even the very flames burn cold
Hawthorn bakes the sweetest bread
So it is in Ireland said
Applewood will scent the room
Pears wood smells like a flower in bloom
But Ashwood wet and Ashwood dry
A King may warm his slippers by.

--BozMo talk 19:05, 16 August 2009 (UTC)

DVD lasers

I've seen lots of speculation on the internet about taking the lasers out of DVD-R drives and putting them into flashlights, etc.e.g. These lasers are apparently powerful enough to pop balloons, burn retinas, and other not-very-safe things.

My question: how far can these project? How far are they dangerous? How much exposure would be necessary to, say, damage a human eye in a permanent way? What kind of eye-wear would be protective? The example above has a visibly red laser—what if one used the infrared laser from a CD-R drive? Or the violet laser of a bluray drive? How much of a threat is this, in the end?

I ask only because I am curious about the blinding-potential that exists out there in the world, were someone to be malicious about it, which is a disturbing thought. I thought one of you mad scientists could fill me in. --98.217.14.211 (talk) 18:16, 16 August 2009 (UTC)

This reference says that DVDs have Class 3B or Class 3R lasers. See Laser safety for precautions. -Arch dude (talk) 19:59, 16 August 2009 (UTC)

A class 3 laser is a fairly dangerous thing. Even a class 2 laser can damage your eye with just a quarter second of exposure. A class 3 laser can wreck your vision in less time than you can blink - so the scope for accidents while messing around with them is significant - it's easy to think you're pointing the laser across the room - then hit a mirror or a window or something and bounce the light back into your eyes. IR and UV lasers are doubly dangerous because you can't tell you're looking into one until you can't see clearly anymore. Even the little class 1 or class 1M lasers in laser pointers can damage your eyes with enough exposure. There really is no such thing as a "safe" laser - even the ones in green laser pointers rely on you looking away and blinking to save your sight.

As to how far they can project...that's the thing about lasers - they don't get dimmer with range (well, at least not very quickly). In theory a laser beam is a parallel beam - so all of the energy stays together instead of safely spreading out like 'ordinary' light. In practice, most lasers are not perfectly parallel - but still, it's kinda meaningless to talk about a "range".

SteveBaker (talk) 23:11, 16 August 2009 (UTC)

What I'm really trying to get at is: let's say there's a huge crowd of people at some kind of major event (let's say, the Superbowl). Could one guy with a CD writing drive laser (which is in the infrared, if I understand the optical drive page correctly, but is still in a wavelength that can do damage) plugged into a big mag-lite be able to secretly do major eye damage to lots of people there? --98.217.14.211 (talk) 00:45, 17 August 2009 (UTC)

OOH! Class 3a lasers can blind you in 1/4 second! Then why are they sold as pointers/cat toys? Could it be because the output is less than 5 milliwatts? How does that compare to the energy (per square mm) falling on the retina when I look at snow or a anything painted white under full sunlight? The BS alert just sounded full volume. Edison (talk) 03:27, 17 August 2009 (UTC)

Luckily for us Edison, we aren't talking about class III A lasers. True their output is less then 5 milliwats, which is why no one considers them dangerous. However a class III A laser isn't a class 3 B laser. Btw I can't remeber the name for the unit that measures the amount of energy from sunlight that falls on the ground. It has some really strange units (not Joules/square meter). Anyone remember? EDIT: I remember now: the unit I was thinking off was the langley (and it was in J/sq. m.

66.133.202.209 (talk) 04:52, 17 August 2009 (UTC)

Yeah - you have to be very careful. The OLD classification scheme used roman numerals and was based on some highly unsound science. The NEW classification uses arabic numerals and is a much more accurate description of the safety of lasers. So a class III laser is like a laser pointer or something - but a class 3 laser is able to blind you before you can blink. SteveBaker (talk) 21:36, 17 August 2009 (UTC)

A quarter of a second is a huge span of time if you're trying to blind someone from across a football stadium. Most people couldn't hit someone's pupil at that range with a rifle, let alone a laser pointer.

To do this you would have do construct a laser pointer with a tripod and a scope. Even then you'd still need tremendous skill and a lot of luck. It'd be a lot easier to just walk up to people and throw bleach in their face. APL (talk) 16:52, 17 August 2009 (UTC)

Right, except you'd get caught if you did that. If you had an infrared laser at some distance in a concealable case, nobody is going to know who did it. That's the issue I'm asking about, in the end. --98.217.14.211 (talk) 19:19, 17 August 2009 (UTC)

You'd either need to be so close to someone that it would be obvious that you were the one with the laser, or you'd need a super elaborate aiming contraption.

You'd never blend into the crowd with a laser-pointer that looks like a sniper-rifle on a tripod. The target you're trying to hit (and maintain contact with) is minuscule even at close range.

(If the laser is IR it's even MORE difficult to aim, because you don't have the red dot to use as reference.) APL (talk) 19:58, 17 August 2009 (UTC)

However, if the target is not one specific person, than it's easy to hit a lot of random people even from a great distance. --79.119.218.161 (talk) 07:49, 22 August 2009 (UTC)

What is the risk of brief laser exposure compared to briefly staring into the sun? Which (comparing the class of laser to a cloudless summer in England for example) would cause permanent damage the quickest? (I have NO plans to try this out!) Also, is staring into a shop laser scanner (out of curiosity at the scintillation effects) dangerous? My retinal scan shows no damage, though perhaps being short-sighted lessens the focus/damage? Trevor Loughlin (talk) 13:07, 17 August 2009 (UTC)

Shop scanners don't point at a single location, they flick rapidly back and forth across a path. So the damage would be less than their power output would imply. Vimescarrot (talk) 14:23, 17 August 2009 (UTC)

There seems to be some doubts up there whether the lasers can damage ones' eyes. I don't think there's ANY doubt that a strong laser can do that, and I imagine that a laser that can pop a balloon is strong enough to damage one's photoreceptors. If a stadium is rather too large to hit a small eye target (which I think is probably true), what about smaller distances? Or put another way—what's the minimum distance (estimated) that this would be a serious problem? (esp. if the one with a laser has both a scope of some sort, and some basic way to stabilize the laser). --98.217.14.211 (talk) 19:19, 17 August 2009 (UTC)

I don't think the lasers used in barcode scanners are class 3 - there is no reason for them to need to be that bright. They're probably class 1 - which are relatively safe. But as Vimescarrot points out - they are scanning so rapidly that the average brightness wouldn't be low enough to hurt you even if they were more powerful than that. The concern with such contraptions is what happens when the mechanism that oscillates the laser breaks...typically, everyone peers into the machine to see what broke! I bought a piece of a supermarket scanner mechanism on eBay for my 3D scanner project - and it doesn't move the laser at all. It has a holographic lens that stretches the laser spot out into a line - which it bounces off mirrors to make the criss-cross pattern. No moving parts...nothing to go wrong. SteveBaker (talk) 21:36, 17 August 2009 (UTC)

Using a scope to point the laser might not be such a good idea. If something reflective gets in the beam path, you have an excellent focussing mechanism pointing right at your own eye! Franamax (talk) 07:06, 18 August 2009 (UTC)

Oooh! I like it! Poetic justice. SteveBaker (talk) 12:32, 18 August 2009 (UTC)

August 17

Bell peppers

Are bell peppers true berries under the botanical definition? --✶♏‭ݣ 01:52, 17 August 2009 (UTC)

Yes, they are.CalamusFortis 01:58, 17 August 2009 (UTC)

Phases of matter -- all relative

Are all elements in gaseous form on the surface of the Sun? DRosenbach ^{(Talk | Contribs)} 03:38, 17 August 2009 (UTC)

I'm struggling to understand exactly what you mean by your question. Something that I think is relevant is that the Sun does not really have a "surface". There is giant ball of gas and it gets denser and hotter until it is opaque to electromagnetic radiation. That's what we see when we look at the sun. It's a gradient, not a absolute line. If you were to move towards the centre of the sun, there would be no specific point where you would say I was just above the surface and now I'm just below. Vespine (talk) 04:25, 17 August 2009 (UTC)

I think the answer to your question is yes. On what looks to be the surface of the sun, every substance we know of on the earth is a gas, it is too high for solids or liquids to exist. Graeme Bartlett (talk) 08:39, 17 August 2009 (UTC)

..or no, depending on how one reads the question. First, I'd suspects most elements are actually a plasma anywhere near the "surface" of the sun. A plasma is or is not a gas, depending on the ontology (if the 4 states of matter are disjoint, its not, from a thermodynamic POV it is). But secondly, are all elements on the surface of the sun? Probably not. I'd suspect that all naturally occurring ones are, though. --Stephan Schulz (talk) 09:10, 17 August 2009 (UTC)

I would suspect that the dense elements (Uranium, lead etc) would not be at the surface but in the center of the sun, but perhaps there are trace amounts at the surface. Googlemeister (talk) 14:16, 17 August 2009 (UTC)

My question may not have been my stated in the proverbial, but intention was to ask it in that way -- would all elements be in gaseous form at or near what appears to be the surface of the sun? DRosenbach ^{(Talk | Contribs)} 23:16, 17 August 2009 (UTC)

It is a little difficult to work out because boiling points depend on pressure. If we assume that at the surface the pressure is near to zero (which makes sense for the edge of the sun - there isn't much outside it) then you basically can't have liquids, they would boil instantly, so we're actually looking at the temperatures at which elements under low pressure sublime. Unfortunately we don't seem to have a List of elements by low pressure sublimation point (we have lots of other lists of elements, but not that one) article, so I'm drawing a blank! I'm also not sure about the pressure at the surface of the sun being near zero, the corona is usually considered to be outside the surface and it will cause some pressure, I'm just not sure if it is negligible or not. --Tango (talk) 00:28, 18 August 2009 (UTC)

Also our Sun does not contain "all" the naturally occuring elements, including lead and uranium. Those do not exist on the Sun as far as we know even in trace amounts. Only more massive stars have enough oomph to spit out heavier elements. Our sun is made up Hydrogen and Helium and of only about 10 other elements, none of which are heavier then iron or nickel.Vespine (talk) 00:50, 18 August 2009 (UTC)

If they are on Earth, then they will be in the Sun. The Earth formed out of the same nebula as the Sun. They are greater abundance on the Earth (proportionally speaking) because the Earth has lost most of its hydrogen and helium, but that doesn't change the absolute amounts. --Tango (talk) 00:54, 18 August 2009 (UTC)

According to Sun, the "effective surface temperature" of the sun is at 5778 degK. List of elements by boiling point says that Rhenium has the highest boiling point of all elements - and both it and Tungsten would just barely be liquid at 5778K (Tungsten boils at 5828K and Rhenium at 5869K). However, the sun's corona is at 5 million degrees and the core is at 16 million degrees...so this is a fairly 'careful' answering of our OP's question. SteveBaker (talk) 01:13, 18 August 2009 (UTC)

What is the meaning of effective surface temperature in relation to actual temperature? DRosenbach ^{(Talk | Contribs)} 02:10, 18 August 2009 (UTC)

"The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation." - Effective temperature. Stars are pretty good approximations to black bodies, so the actual temperature isn't far off the effective temperature, maybe a few hundred degrees difference. --Tango (talk) 02:39, 18 August 2009 (UTC)

Those temperatures are for standard atmospheric pressure. There is no reason to believe the surface of the Sun is at standard atmospheric pressure. --Tango (talk) 01:57, 18 August 2009 (UTC)

And getting a measurement for that pressure would be problematic since you are probably going to melt your equipment. Googlemeister (talk) 13:26, 18 August 2009 (UTC)

You can estimate pressure indirectly. Really, the problem is deciding where the surface is. --Tango (talk) 17:39, 18 August 2009 (UTC)

Squinting

Is it just me, or does looking at this make you want to squint, even though it's no brighter than a pure white screen? Is it like an optical illusion, because your brain thinks it's looking at the sun, so you squint by reflex? DRosenbach ^{(Talk | Contribs)} 04:14, 17 August 2009 (UTC)

I looked at it and the corners of my eyes tightened, and then I forced them back by telling myself that it was just a picture. But while looking at it, I felt nervous about something. So yes, I'm programmed to not look directly at the sun. Whew. Awickert (talk) 04:18, 17 August 2009 (UTC)

Me too. Very cool effect - I would not have expected this at all. --Stephan Schulz (talk) 13:13, 17 August 2009 (UTC)

Yes, same response here, I guess the eye tightening is a sort of acquired reflex. 86.4.181.14 (talk) 13:23, 17 August 2009 (UTC)

Could it be that it is simply a higher contrast image than a blank white screen? —Akrabbim^talk 13:56, 17 August 2009 (UTC)

I'm inclined to agree with Akkrabbim here, though I can't cite any studies to back it up. You're looking at this picture, and it appears that the figure in the middle is blown out by the 'bright' subject — so you squint to try to see missing detail that's been washed out. TenOfAllTrades(talk) 14:09, 17 August 2009 (UTC)

This (and many other) tricks are well-known to us evil computer game graphics geeks who seek to elicit real-world emotions from people staring at tiny, dim, flat screens! If you animate it to simulate the rate of change of light perception due to your irises rapidly shrinking to tiny little dots, it's even more effective. SteveBaker (talk) 20:21, 17 August 2009 (UTC)

Ah, so making the image darker, makes the viewer think they are looking at a very bright object. You are truly an evil genius :) 83.100.250.79 (talk) 20:28, 17 August 2009 (UTC)

A plain white filled circle would not cause the squinting reflex. The streaks and secondary images are characteristic of an "overloaded" eye lens + retina, to which sight the iris muscle is programmed to contract. Cuddlyable3 (talk) 21:27, 17 August 2009 (UTC)

It would be interesting to discover if people's irises actually do contract when viewing such images at the same brightness as a simple, white circle. I kinda suspect not...but anything is possible! SteveBaker (talk) 12:29, 18 August 2009 (UTC)

(undent) See here for a modified photograph -- i cut away a portion of the central circle of the sun and, in boxes of various shades, placed adjacent squares of eye-dropper copied central core (left) and cut away white background (right) to see if I could tell the difference. Granted the eye-dropper only works off one pixel and the central circle is likely not uniformly bright -- but perhaps it was so bright that all that could be captured digitally was a maximum, uniform whiteness. DRosenbach ^{(Talk | Contribs)} 13:57, 18 August 2009 (UTC)

Sleep deprivation and hallucinations

How long must sleep deprivation generally be maintained to achieve hallucinations? Is it always the safest method of doing so? NeonMerlin 04:35, 17 August 2009 (UTC)

Hallucinations are not a guaranteed side effect of sleep dep, they are a possible side effect. My record is staying awake for 4 days (over 80 hours) and I don't think I experienced any hallucinations, well nothing vivid or memorable anyway. I also do not believe intentional sleep deprivation is considered "safe". I am not aware of any safer and legal ways to more reliably achieve hallucinations, though there are several safer but illegal ways to do it, which I could not recommend in a public forum but for purely informative purposes you can start with the article on hallucinogen. Vespine (talk) 04:56, 17 August 2009 (UTC)

The definition of hallucination should also be taken into account. I believe sleep deprivation produces deliriant-like hallucinations, which is where one is unable to determine what is real or not (it is often compared to dreaming whilst being awake). The hallucinations produced by psychedelics can usually be distinguished from reality by those intoxicated, and they are generally stereotyped as things such as: colourful lines, streaks, shimmers, halos, etc.

We can't give medical advice on what is the safest way of achieving hallucinations. I suggest you read the articles that are wikilinked in this discussion. I should also mention that being delirious can lead to behaviour putting one's life into danger. The man in this article took nowhere near the lethal dose of diphenhydramine, but it sounds as though the delirium led him to fatally wound himself with an electric fan. --Mark PEA (talk) 16:08, 17 August 2009 (UTC)

I think sleep deprivation is reasonably safe if you avoid any sort of risky situation, but the level necessary to get hallucinations is so unpleasant that I can't imagine anybody doing it for that reason, especially considering that the hallucinations themselves are likely to be unpleasant. Looie496 (talk) 17:25, 17 August 2009 (UTC)

This is fun reading. (Unrelated, but fun reading.) Bus stop (talk) 20:41, 17 August 2009 (UTC)

I think it will depend on how you stay awake. If you just do it by willpower alone then you'll probably be fine - your body will force you to sleep before it becomes harmful, the human body is generally very good at stopping us from doing stupid things. If something happens to wake you up every time you start to drift off then you could reach dangerous levels of sleep deprivation. --Tango (talk) 01:01, 18 August 2009 (UTC)

Like Lindbergh during his transatlantic flight? 98.234.126.251 (talk) 01:41, 18 August 2009 (UTC)

That flight only took 33.5 hours, that doesn't really count as sleep deprivation. That's just an all-nighter, students do them the night before a deadline all the time! --Tango (talk) 02:44, 18 August 2009 (UTC)

He also didn't sleep much the night before, and toward the end of the flight he was getting kinda delirious, imagining he was seeing land where there was none. FWiW 98.234.126.251 (talk) 22:40, 18 August 2009 (UTC)

Press releases on research papers

Do any scientists regularly produce press releases on their own research papers to improve the accuracy of media coverage? NeonMerlin 07:06, 17 August 2009 (UTC)

See here for the scary truth. --Stephan Schulz (talk) 09:12, 17 August 2009 (UTC)

LOL! That is marvellous :) — QuantumEleven 15:11, 17 August 2009 (UTC)

We publish our results in as many places as we can. It's not the fault of the science community that the majority of the world prefers to consume media from secondary and tertiary sources - academic journals are widely available. Nimur (talk) 16:53, 17 August 2009 (UTC)

Indeed. In fact, most of the short pieces in science news magazines such as "New Scientist" are based on press releases. Sad to say, some scientists show much less discipline in writing press releases than in the journal articles they are based on, although the pressure for glitz from university press offices certainly comes into play. Looie496 (talk) 17:19, 17 August 2009 (UTC)

(ec) That comic is pretty accurate, and the next one too. Probably most of the science articles in a typical newspaper are adapted (or quoted verbatim) from a press release, but the press releases are not written to improve the accuracy of the reporting, they're written to make the sponsoring university look good so that they can attract more donors. Sometimes the researchers themselves write documents apparently intended to help reporters, like this one, but it's pretty uncommon. -- BenRG (talk) 17:21, 17 August 2009 (UTC)

At many universities there are people paid full time to figure out what researchers are up to and to try and publicize it. It's not a bad job, I hear, given the current state of journalism in general. --98.217.14.211 (talk) 19:11, 17 August 2009 (UTC)

No fish native to a river is poisonous?

I saw it on TV. True or false? I know that certain fishes, like the Candiru or Piranhas can seriously harm or kill you, but couldn't find any poisonous river fish.--Quest09 (talk) 11:28, 17 August 2009 (UTC)

Not sure - some catfish have spines (not teeth) that include a poisonous secretion http://www.google.co.uk/search?hl=en&q=catfish+spine+poison&meta=&aq=f&oq=

Perhaps it meant a posionous bite?83.100.250.79 (talk) 11:59, 17 August 2009 (UTC)

Then they meant "venomous" not "poisonous" (common mistake). --Tango (talk) 13:28, 17 August 2009 (UTC)

Or not? Catfish have venom- but not in the bite.83.100.250.79 (talk) 14:44, 17 August 2009 (UTC)

The flesh of all animals is edible (so says a survival handbook I once read). It is only the internal organs that could be poisonous, if you are careful to avoid them you should be fine. --Tango (talk) 13:28, 17 August 2009 (UTC)

The closest thing I can think of is the platypus which has poisonous/venomous/ouchy spurs. Aaadddaaammm (talk) 13:37, 17 August 2009 (UTC)

That depends on how broadly one interprets 'native' (and 'river'). (I'm also assuming, per Tango, that you're going for 'venomous' here.) There are a number of families of marine fish which have developed species adapted to river life. The stonefish, for instance, primarily occupy coastal waters of the Pacific, but a few species (like Notesthes robusta) have adapted to life in streams and tidal estuaries. Trichinus draco, the Greater weever, is now found in the Thames. There are a number of other 'edge cases' which rather blur the general rule you heard. TenOfAllTrades(talk) 14:02, 17 August 2009 (UTC)

The Greater weever doesn't seem to match Tango's description of venomous, there are plenty of venomous purely freshwater species that use venom as a defence.83.100.250.79 (talk) 14:44, 17 August 2009 (UTC)

I never gave a description of venomous, I just said that delivering a toxin by biting is venomous. Venom can be delivered by bites or stings. Poison has to be ingested. --Tango (talk) 17:49, 17 August 2009 (UTC)

You are right. Isn't venomous a subset of poisonous though?83.100.250.79 (talk) 18:52, 17 August 2009 (UTC)

Venomous = poisons things by attacking without dying, like a venomous snake. Poisonous = poisons things when those things eat it, like a poisonous fruit. Dcoetzee 21:02, 17 August 2009 (UTC)

Is catfish defensive spine venomous or poisonous or both?83.100.250.79 (talk) 21:12, 17 August 2009 (UTC)

Venomous, you don't get harmed by eating the spine, you get harmed by being stabbed by it. Of course, the venom glands (or whatever) of a venomous animal will presumably be poisonous. --Tango (talk) 01:02, 18 August 2009 (UTC)

This needn't be the case. Many venoms are protein-based and therefore would be destroyed in the stomach. Looie496 (talk) 17:47, 18 August 2009 (UTC)

Not a good idea to try drinking venom if you have an ulcer. Googlemeister (talk) 20:22, 18 August 2009 (UTC)

Good point. As Googlemeister says, there is a risk if the venom can reach your bloodstream when you eat it. --Tango (talk) 21:17, 18 August 2009 (UTC)

THERMODYNAMICS AND FLUID MACHINERY

1) In a stirling cycle,the volume varies between 0.03 and 0.06m3,the maximum pressure is 0.2MPa and the temperature varies between 540oC and 270oC.The working fluid is air. a)Find the efficiency and the workdone per cycle for the simple cycle. b)Find the efficiency and the workdone per cycle for the cycle with an ideal regenerator,and compare with the carnot cycle having the same isothermal heat supply process and the same temperature range.

referance:stirling  cycle.

2)A boat moved by a jet propulsion,discharge water through a jet of area 0.02m2,the water being drawn from inlet opening facing the direction of motion.The total drag is estimated to be 17.66u2Nm,where u is the speed of the boat in m/s.If the boat moves at 54km/h,determine:

          a)relative  velocity of jet;
          b)energy supplied by the jet and power of the motor required to work the  pumps;
          c)efficiency  of  propulsion.
Take the density of water 1020kg/m3 and efficiency of the  pump set 75%.
 referance :FLUID MACHINERY.  —Preceding unsigned comment added by 41.197.25.6 (talk) 11:41, 17 August 2009 (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. Thank you.

What lizard is this?

I was in Istanbul and saw this lizard. I was wondering if it could be used if there isn't a decent picture of this particular species of lizard. It was waiting for me to take its picture.

• 

  Spiderone (talk) 12:19, 17 August 2009 (UTC)

Personally, I'd place my bet on it being in the Lacertidae family, but I could never identify the genus, let alone the species. Perhaps someone at WP:WikiProject Amphibians and Reptiles would be more useful here.--91.148.159.4 (talk) 14:35, 17 August 2009 (UTC)

I was thinking of a variety of anole, Polychrotidae family. But I am not too confident on that one. --Jayron32 15:41, 17 August 2009 (UTC)

I would opine -- in fact, I do -- that it is not an anole. The body ornamentation + overall appearance of the skin folds of the neck/stockiness tell me that it is not an anole. I used to have anoles as pets. DRosenbach ^{(Talk | Contribs)} 02:12, 18 August 2009 (UTC)

Definitely not an anole, wrong continent for them anyway. Reminds me of a skink, but I really don't know anything about Old World lizards. I would second the recommendation to ask at the WikiProject. Guettarda (talk) 03:21, 18 August 2009 (UTC)

This certainly looks like a Lacertidae member. There are quite a few species found in Turkey: Lacerta anatolica, Lacerta cappadocica, Lacerta cyanisparsa, Darevskia parvula, Darevskia raddei, Podarcis sicula, etc... I can't identify the species of the one in the picture though. Sorry. --Dr Dima (talk) 05:29, 18 August 2009 (UTC)

Prion Terrorism

Could concentrated and extracted "Mad Cow" prions be a potential terrorist or state bio-weapon? Could they be distributed as a fine mist? —Preceding unsigned comment added by Trevor Loughlin (talk • contribs) 12:19, 17 August 2009 (UTC)

It wouldn't be very effective for terrorism. Even if it could be manufactured in sufficient quantities and distributed like you describe, most people wouldn't even be aware that they were 'infected' for many decades, or perhaps not until they were autopsied fifty years from now. Wouldn't give much terror bang for the buck. Much easier and more effective to blow something up. APL (talk) 12:58, 17 August 2009 (UTC)

With that being said, odds are if someone created a scare of prions, that cuuld cause high levels of panic and life alteration in a society. ~ Amory (user • talk • contribs) 15:07, 17 August 2009 (UTC)

It's not particularly useful as a state or military weapon; as APL notes the development of symptoms would take years, and infected individuals would be unlikely to transmit infection. (There's no point to using a weapon that doesn't have any effect until years after the war is over, unless you want to invite retribution by similar means.) As a terrorist weapon, it wouldn't have any immediate visible effect, so it's not going to kill people. It could be very effective as a scare tactic, however. A 'fine mist' would be difficult to use, and probably not an effective route of administration. Far more effective to spike food or beverages. Transmission in animals requires several milligrams of brain homogenate from an infected animal: [20]. The effective dose in humans is very uncertain. TenOfAllTrades(talk) 14:24, 17 August 2009 (UTC)

Quibble: Sure there could be a point to using a weapon with a really long "fuze". Suppose Country #1 wanted to wipe out the population of Small Country #2, and Country #1 had access to an effective, nonreversible sterility agent with a secret formula. Country #1 disperses it all throughout Small Country #2. Ten years later, nobody in Small Country #2 is having any kids, and in 50 years the population has crashed, or Small Country #2 is 90% immigrants and is pliable to new political suggestion from Country #1. Mission accomplished! That said, this speculation has nothing to do with prions. Tempshill (talk) 17:06, 17 August 2009 (UTC)

You've been watching Stargate. Vimescarrot (talk) 20:52, 17 August 2009 (UTC)

I dispute this! Cool, it works galactically, too. Tempshill (talk) 06:39, 18 August 2009 (UTC)

In general, bioterrorism in reality is a lot more difficult and a lot less effective than "security experts" would have you believe. Aum Shinrikyo learned this the hard way: they're one of the richest and most well-connected terrorist organizations in the world, and after several expensive, botched attempts at bioterrorism, they finally managed to kill a total of 12 people with sarin, which (unlike prions) is a highly lethal nerve agent. As APL succinctly put it, it's much easier and more effective to blow something up. --Ashenai (talk) 15:14, 17 August 2009 (UTC)

For a wonderful, short little history of how easy it is to blow something up, see Mike Davis, Buda's Wagon: A Brief History of the Car Bomb. --98.217.14.211 (talk) 21:40, 17 August 2009 (UTC)

Turbopumps on rockets

Turbopumps are used on liquid-fuelled rockets to pressurise the fuel and oxidiser before they reach the combustion chamber. What powers the turbopumps (turbochargers on cars use the car exhaust for power, what does a rocket turbopump use)? — QuantumEleven 14:56, 17 August 2009 (UTC)

The turbopumps are powered by a preburner, which burns a small amount of fuel and oxidizer to run the turbopumps. In the picutre, the preburner is number 6. The preburner provides hot gas to run the turbine (number 5), which drives the turbopumps (numbers 3 and 4). anonymous6494 15:25, 17 August 2009 (UTC)

(ec) There's a fairly extensive discussion in this page linked from our article. For cryogenic fuels and oxidizers (liquid oxygen, liquid hydrogen), some pumps can be driven simply by heating the liquid to ambient temperature or above and allowing the expanding gas produced to drive the turbine. With other fuels, a preburner can be used which combines fuel and oxidizer to generate a small amount of hot, pressurized gas. There are several variations on these themes, which offer different methods of preheating the fuels, and which vent the turbine exhaust in different ways. TenOfAllTrades(talk) 15:27, 17 August 2009 (UTC)

It depends on the design. Sometimes, the turbos are powered by a totally separate source (e.g. a battery or a small separate combustion engine). Other times, they tap off the main propulsion energy source, or use the decompression of a refrigerated fluid to power the pump. All of these scenarios have various advantages and disadvantages to the stability, robustness, and mass budget of the rocket. If mass and flight-time is not an issue, the probable best solution is an electric motor; but this requires a large battery (and suffers from scalability - large mass-flux rockets can't really work off an electric turbo pump) - so more often, the turbo either kicks in later or gets an electric start and eventually draws energy from the primary propulsion source. Nimur (talk) 16:56, 17 August 2009 (UTC)

color

What color is pure gold if there is no light shining on it? Is it possible to have color without having reflected light? Googlemeister (talk) 16:36, 17 August 2009 (UTC)

The same. What colour is blue paint in the dark? <rhetorical>83.100.250.79 (talk) 16:39, 17 August 2009 (UTC)

(EC with above)This sounds like "If a tree falls in the forest, and no one hears it, did it make a sound" sort of metaphysical discussion. How do you define color:

• As wavelength(s) of electromagnetic radiation
• As human perception of those wavelengths
• Is the potential to do something the same as actively doing it?

There's just way too many ways to interpret the question to answer it with a definative answer. --Jayron32 16:42, 17 August 2009 (UTC)

It is possible to have color without reflected light. I have a keychain that has a combination of tritium and phosphorus it appears pale green even in pitch blackness. This is because it emits a pale green light. Light has to be involved one way or the other. APL (talk) 16:45, 17 August 2009 (UTC)

Maybe the atomic absorption/emission spectrum of gold is relevant here. That's about as close to the "natural" inherent color of atomic gold as any definition can come. But because gold is a noble metal, and a transition metal, its valence electron behavior is a bit pathological - I'm not sure there's a very well-defined emission spectrum (at least, not as simple as, say the Hydrogen spectrum). Nimur (talk) 17:00, 17 August 2009 (UTC)

True, but then we get involved in the metaphysical discussion of whether or not something which normally has a color can be said to have a color even if it is not currently emitting/reflecting light. Is it enough to say that something has a color if we define a set of conditions where light could not possibly be involved? Its the "tree falling" discussion all over again... --Jayron32 16:59, 17 August 2009 (UTC)

Color, as most philosophers currently see it, is fundamentally a property of a material -- the color of an object defines the relationship between the light that strikes it and the light it emits. So it is completely proper to say that the color of gold is orange. What complicates things is that we perceive light itself as having a color, but these perceptions are tricky and paradoxical in some respects.

If the gold is hot enough, it will emit light, but the spectral distribution will vary with temperature. Edison (talk) 18:52, 17 August 2009 (UTC)

This is purely a linguistic thing. We use the word "color" for at least two phenomena: Firstly, the spectral characteristics of light coming from an object towards our eyes. Secondly, the inherent reflectivity-as-a-function-of-frequency (or transmissivity-as-a-function-of-frequency) of a material. So if you are talking about the color of gold in the first sense - then the answer depends on what color of light you're shining on it...or indeed if you are shining light on it at all. In this first sense of the word, the gold is black when there is no light shining on it. The second sense implies a property of gold (that it is golden) that is the same irrespective of whether there is light shining onto it or what color that light is. For some senses of the term, we actually use different descriptive words. We say that gold is "golden" - and not "orange" because we know that gold is highly reflective and "orange" somehow doesn't seem right. This problem is most clearly demonstrated when you ask what color a mirror is. Most people (if forced into giving an answer) would say "silvery" - implying something that reflects all frequencies equally - but "white" would be an acceptable answer. What gets difficult is when you have highly reflective surfaces that don't have these "special" names...a "green" car doesn't look at all green under an old-fashioned orange street-lamp. When this happens, we have to resort to circumloqutions like "That green car looks yellow!"...as is so often the case, language is a mess - but the science is quite clear. SteveBaker (talk) 20:13, 17 August 2009 (UTC)

Gold leaf can be beaten thin enough to become translucent. The transmitted light appears greenish blue, because gold strongly reflects yellow and red.<http://www.webexhibits.org/causesofcolor/9.html> Cuddlyable3 (talk) 21:04, 17 August 2009 (UTC)

(replying to Steve) It's even trickier than that, because our color perceptions are to a substantial degree illumination-invariant. This can lead to some weird effects. For example, suppose you are in a room with fluorescent lights, and looking at a piece of white paper next to an active computer monitor. Suppose you change from fluorescent to incandescent lighting (which is bluer) -- what you will perceive is that the image on the computer monitor shifts color while the piece of paper keeps the same color, exactly the opposite of what happens to the light they emit. Looie496 (talk) 21:19, 17 August 2009 (UTC)

Back when I was in Yeshiva University, I took 2 philosophy courses in order to fulfill my history requirements. In Philosophy 1, I wrote a proof paper on "Color does not exist," and in Philosophy 2, I wrote a proof paper that "Color does exist." The second was a much more difficult endeavor. In any event, it's not nearly as simple as the discussers above have made it seem -- there are apparently claims that only 1 family of bird (or no species) are actually green or blue in that they possess green or blue pigmentation. All other birds that appear green or blue merely do so because the air bubbles/pockets within the feather fibers are of a size that specifically absorbs non-blue/green light, thereby making it appear as though the feathers are blue or green, when in fact, they are not. But does that mean the feathers are not blue? If color is defined by pigment color? How do we know what the pigment color is...is it not only because we perceive it as being colorful? How then can we assert that something else absorbs and reflects light in a similar manner but is not that color? I think I remember the answer being that, microscopically, it was seen that these air pockets were hollow rather than filled with non-gaseous matter known as pigment by virtue of the fact that it causes us to perceive color. So it's sort of like a cyclical definition. I now notice that I've written a lot, perhaps without saying much...but now I'm done. DRosenbach ^{(Talk | Contribs)} 02:28, 18 August 2009 (UTC)

This is exactly the kind of thing that gets philosophers excited - and also the reason why philosophers are a waste of quarks! There really isn't any problem at all here. The science is clear and unambiguous - we understand exactly what's going on. Such difficulty as arises in the discussion is entirely due to imprecise use of language. If we use more precisely defined words like 'emissivity', 'reflectivity', 'transmissivity', 'pigmentation' and 'light-spectrum' and assiduously avoid this vague word 'color' then all of the complication falls away and such philosophical BS as "Color does/does-not exist" evaporates and can be replaced by the simple, true, and verifiable statement: "The word color is ambiguous". SteveBaker (talk) 12:25, 18 August 2009 (UTC)

See Elitzur–Vaidman bomb-tester. It should be possible to detect the wavelengths gold reflects without interacting with it by shining any photons at it. Dmcq (talk) 10:21, 18 August 2009 (UTC)

Indeed - but the OP wasn't asking about something so easy as what wavelengths it reflects - the question is about "color" - which is an ill-defined word in this context. SteveBaker (talk) 12:25, 18 August 2009 (UTC)

Ants sting instead of bite?

Am I the only person who assumed that ants bite with their mandibles instead of stinging with . . . something else? The ant in this photograph has scary-looking jaws, but apparently they are not responsible for the ant's painful "sting". Where exactly do they keep the sting? Do they spray or inject (the ant article mentions both as a possibility)? I've pulled up all of the information I can find on this species on the 'net, and they are consistently referred to as having a sting and not a bite, but no further details are given. Maedin\^talk 16:50, 17 August 2009 (UTC)

Our article on fire ants is informative. It states that most ants use a "bite and spit" combination to "sting"; while a fire ant uses an abdomen-mounted stinger, much like a bee, to do so. So the answer to your question is "it depends on the species of ant". --Jayron32 16:56, 17 August 2009 (UTC)

To elaborate, an ant clamps down with its mandibles, but the actual injury is sustained when it stings the target. Ants are related to bees and wasps.CalamusFortis 17:12, 17 August 2009 (UTC)

Didn't you see Them!? B00P (talk) 18:59, 17 August 2009 (UTC)

Obviously I didn't, ;-) Thanks a lot for your responses; it would still be nice to know whether Myrmecia esuriens stings with a stinger in its abdomen, or bites (or clamps) and spits. I don't see any specific mention of a physical stinger in any of the sources I could find, so I will have to assume that it's the latter method. Maedin\^talk 19:41, 17 August 2009 (UTC)

Recycled ants?

I crushed an ant on a window sill and left it there. A few minutes later I returned and found what appeared to be another ant carrying my first victim away. What is the purpose of this behavior? Do ants bury their dead? —Preceding unsigned comment added by 75.52.255.4 (talk) 17:18, 17 August 2009 (UTC)

More likely the first ant will be lunch. Googlemeister (talk) 17:46, 17 August 2009 (UTC)

Perhaps a ceremonial lunch in which the recently deceased will be remembered fondly for its contributions to ant culture. Bus stop (talk) 17:49, 17 August 2009 (UTC)

^†The decedant? DMacks (talk) 17:59, 17 August 2009 (UTC)

The ant's religious affinities are not known at this time. Bus stop (talk) 18:07, 17 August 2009 (UTC)

Protestant. DMacks (talk) 18:16, 17 August 2009 (UTC)

You've heard of "the Elephants' Graveyard," but, it seems, not "the Ants' Cemetary," Also the corpse is being studied by the ant equivalent of Gil Grissom to determine who the killer is. I'd leave town if I were you. B00P (talk) 19:15, 17 August 2009 (UTC)

I suppose the ant version of Grissom understands and is obsessed with humans? ~ Amory (user • talk • contribs) 19:18, 17 August 2009 (UTC)

I would think that, prior to deciding if the body should be carried off, they would determine the antecedant cause of death. StuRat (talk) 00:17, 18 August 2009 (UTC)

There was an interesting thing about this behavior on TV sometime ago. Evidently the dead ant gives off some kind of smell/pheremone that the other ants detect which kicks them into "Remove the body from the nest" behavior. The researcher (sorry - I forget his name) figured out what the chemical was and had a lot of fun smearing microscopic drops of it onto live ants - who would be grabbed and carried screaming and kicking from the nest by their former colleagues. As soon as they dumped the "corpse" outside the nest, it would immediately come scurrying back in - only to be grabbed and ejected again. Pretty funny actually. So evidently, the nest-mates don't eat the corpse (that would probably be a bad idea anyway because this could cause the spread of diseases through the nest). I have no idea what the smell causes them to do when they're outside the nest...but evidently there is still some behavior involved. SteveBaker (talk) 20:00, 17 August 2009 (UTC)

Maybe it was E. O. Wilson, who studies myrmecology. Bus stop (talk) 20:14, 17 August 2009 (UTC)

Wilson doesn't do stuff with chemicals... And I'm sure Steve would remember if it was E.O. Wilson! --98.217.14.211 (talk) 20:36, 17 August 2009 (UTC)

OK. I couldn't even think of E. O. Wilson's name. I had to search for ant man or some such search terms. Bus stop (talk) 20:44, 17 August 2009 (UTC)

Chemically-induced bullying... very funny, I'm sure, Steve. --Tango (talk) 20:04, 17 August 2009 (UTC)

Actually, this only applies to ants who are infected by a particular killer spore. Ants can tell normal dead ones from ones killed by a dangerous contagious disease. Dcoetzee 20:59, 17 August 2009 (UTC)

As to what Steve said there was some furthur thing with the ant pheromone and it didn't work precisly that way. I just can't remember how it was different. I'll post link if I can remember. EDIT: Here's the link from where I first heard the story Steve heard. Now if only I can find the later story that added some stuff to this one...66.133.202.209 (talk) 23:29, 17 August 2009 (UTC)

Yeah - that's the story I remembered (I can't believe I forgot that it was E.O.Wilson though...) - it's pretty funny. SteveBaker (talk) 01:45, 18 August 2009 (UTC)

Sounds like a standard EO error, I get them all the time. StuRat (talk) 01:10, 19 August 2009 (UTC)

Digital Electronics

What exactly is the differece between priority encoder and a priority decoder??

This FAQ may contain your answer. As I assume you know, a priority encoder gives a binary code telling you which is the highest-priority input (e.g. an interrupt) that is active. It seems that a priority decoder is just an ordinary decoder that converts the binary code from the priority encoder back to one of many outputs (e.g. interrupts again). In other words, a priority decoder is logically the same as an ordinary encoder, but it just has the word 'priority' added to indicate that it is being used in conjunction with a priority encoder. --Heron (talk) 20:10, 17 August 2009 (UTC)

This question was cross-posted on the Computing desk. I'm merging it to here. Nimur (talk) 20:47, 17 August 2009 (UTC)

What exactly is the differece between priority encoder and a priority decoder?? —Preceding unsigned comment added by Piyushbehera25 (talk • contribs) 18:41, 17 August 2009 (UTC)

Have you read Encoder and Decoder? An encoder reduces the number of bits, while a decoder increases the number of bits. Cascading the two devices, you can reconstruct the original signal (one device performs the adjoint operation to the other). Nimur (talk) 20:16, 17 August 2009 (UTC)

@Heron: thanks for your answer...but still i'm not quite clear...so you are saying that both the priority encoder and priority decoder are the same thing??I was also thinking the same but then why use 2 different names??

@nimur: yes i'v read those and know their functions...my question was what's the differece between priority encoder and priority decoder(if any)...please clarify if anyone knows —Preceding unsigned comment added by Piyushbehera25 (talk • contribs) 08:35, 18 August 2009 (UTC)

You clearly DON'T understand their functions or you'd know the difference! A priority encoder takes some number of input bits that are numbered from 0 to N. It finds the highest numbered input that contains a '1' bit and outputs the number of that bit in binary.

Hence, (if we number our bits with the highest bit on the left and bit zero on the right), a 4 bit priority encoder would work like this:

• 0001 ==> 00 (the highest numbered '1' bit is bit zero).
• 1101 ==> 11 (the highest numbered '1' bit is bit three).
• 1000 ==> 11 (the highest numbered '1' bit is bit three).
• 0110 ==> 10 (the highest numbered '1' bit is bit two).

...and so on.

A priority decoder is the opposite of this...but because information is lost in the priority encoder (we go from a 4 bit number down to a 2 bit number)...connecting a priority encoder to a priority decoder doesn't result in the same thing coming out as went in. eg:

• 00 ==> 0001 (generate a '1' bit on bit zero)
• 01 ==> 0010 (generate a '1' bit on bit one)
• 10 ==> 0100 (generate a '1' bit on bit two)
• 11 ==> 1000 (generate a '1' bit on bit three)

So if you connected the priority encoder in my first example to the priority decoder in my second, then you'd get:

• 0001 ==> 00 ==> 0001
• 1101 ==> 11 ==> 1000
• 1000 ==> 11 ==> 1000
• 0110 ==> 10 ==> 0100

...and so on.

You could imagine something like an elevator controller using this kind of circuit. In this building, the high up executives live in the upper floors of the building and the workers in the lower floors. The elevator is designed to pick up the managers first - even if multiple "call" buttons have been pressed. You might then connect all of the call buttons to the priority encoder. It would find the highest floor that is calling for the elevator and output the number of that floor. A priority decoder could then turn that into a single output bit representing the floor to which the elevator has been called. In a sense, the circuit has made a decision as to which call button has the highest priority and is ignoring all of the lower priority buttons. Once the call button on that floor is released, the priority encoder would then find the second highest floor with the call button pressed and send the elevator there. This is obviously a silly example - but it should give you the basic idea of what the priority encoder and decoder can do for you.

I hope this clarifies things a little. SteveBaker (talk) 12:10, 18 August 2009 (UTC)

Thanks that helped...that's exactly what I wanted to know...I was confused as to how the priority decoder will know the exact input when fed with the output of the priority encoder clearly it's impossible...so there's no such thing as a priority decoder,it's just a simple decoder(i.e the function and working of priority decoder and a normal decoder is the same)...Please correct me if i'm wrong...

thanks again —Preceding unsigned comment added by Piyushbehera25 (talk • contribs) 15:09, 18 August 2009 (UTC)

Correct - an encoder (especially a priority encoder) can be considered a hardware implementation of lossy compression. The exact signal cannot be reconstructed - only an approximation to it. The term "priority encoder" describes one method for deciding the scheme of that lossy compression. Any time that you take 4 bits and generate 2 bits, you have lost some information; the decoder will assume the simplest reconstructable signal and output that. Nimur (talk) 17:26, 18 August 2009 (UTC)

The name "Priority decoder" redirects[21][22] to Decoder where the name is not found. Perhaps another editor can break that redirection because it gives an incorrect impression that there exists some special kind of decoder called a "priority decoder". Cuddlyable3 (talk) 20:11, 18 August 2009 (UTC)

Certainly you don't often hear them called 'priority decoder's - the (approximate) inverse of a priority encoder is more often called a "single bit decoder". Many of the first few Google hits for the term are actually talking about a priority encoder instead! (This book on switching theory, for example has a page that starts with the heading "Priority Decoder" that has the logic table for what Wikipedia calls an encoder). It's a tough call. I think there should probably be a disambiguation page that says something like "The term 'priority decoder' can either refer to a priority encoder or to it's inverse - a 'single bit decoder'". SteveBaker (talk) 00:08, 19 August 2009 (UTC)

DNA ligation in vitro

I have a mix of standard d(N)₆ random DNA hexamers, and I want to ligate them to the 3' end of an arbitrary single-stranded DNA oligomer. Neither is currently modified in any way. Does anybody have any suggestions for a relatively cheap and easy way of going about this? – ClockworkSoul 18:42, 17 August 2009 (UTC)

Aha! This should do nicely. – ClockworkSoul 19:09, 17 August 2009 (UTC)

I misread the title as "DNA litigation in vitro". Gave rise to some interesting mental images! --Anonymous, 20:26 UTC, August 17, 2009.

suppository

what is the lube covering suppository for constipation. it looks like vasaline but i dont think its that —Preceding unsigned comment added by 74.65.3.30 (talk) 21:05, 17 August 2009 (UTC)

You'd have to tell us which brand of suppository you have to know for sure. Suppositories are often encased in a capsule of glycerin, which is itself a lubricant. Just the warmth of your finger (or other parts) can cause some melting so that the suppository is self-lubricating. It is very unlikely to be Vaseline or any other non-water-soluble lubricant, for a variety of reasons. --Sean 21:26, 17 August 2009 (UTC)

i dont know the brand it was it was in the 90s. there was lube all over it it was goopy like vasaline. they were not induvidulaly packaged. i think they were in a round tin. —Preceding unsigned comment added by 74.65.3.30 (talk) 22:39, 17 August 2009 (UTC)

Can't you check the packet? It should have a list of active and non active ingredients, or similar.

Could probably find ingredients-info in a PDR of that era. DMacks (talk) 15:08, 19 August 2009 (UTC)

Cant (road/rail)

I have taken issue with this article as it appears to be about two separate things. Camber and bank, the former being the raise in the middle of a road in both straight and curved sections that is there for drainage reasons, and secondly bank, the slope of a road on a curved sections to allow vehicles to pass at higher speed.

But before taking action I thought it best to agree with some people to which of these both cant and camber actually refer. Particularly as I have not heard of the term "cant" before. Thank you. Elocute (talk) 21:34, 17 August 2009 (UTC)

Cant (rail) is the same as superelevation (ie similar to a banked track)- ie the tilt of the track at right angles to the direction of travel. I don't know about roads.83.100.250.79 (talk) 11:48, 18 August 2009 (UTC)

Wiktionary provides this definition for "cant": slope, the angle at which something is set. Both camber and bank are examples of cant because both are reasons to apply slope to a road or railway track. I don't see anything wrong with our article. SteveBaker (talk) 11:51, 18 August 2009 (UTC)

Camber is not an overall slope but a curvature, and so has on average has no angle of deviation from the vertical. I see no real reason for you to fight me on this issue as they are clearly different things which serve different purposes. For example no railway has camber. Elocute (talk) 12:39, 18 August 2009 (UTC)

The definition of cant doesn't say anything about "average slope" - there is a slope on one side of the road and a roughly opposite slope on the other...there are undoubtedly slopes - so using the word 'cant' for each side of the road is perfectly acceptable. 'Cant' is really a synonym for 'slope'...not 'average slope'. If you're going to go around randomly averaging things - then I'll point out that if you take a long enough stretch of railroad track, the bank angles will very likely average out to roughly zero too. SteveBaker (talk) 23:51, 18 August 2009 (UTC)

I think 'camber' may require disambiguation. http://www.thefreedictionary.com/camber defines it as arch like, but it's clear that many regard it as being synonymous with cant/bank (possibly incorrectly).

Also if you are going to fix it please note that the section in Camber angle#Road camber should be moved too.83.100.250.79 (talk) 12:56, 18 August 2009 (UTC)

I don't think anyone is looking for a fight, Elocute; we're merely discussing how these words are used. As .79 says above, cant is a term commonly applied to railway tracks (in the UK at any rate) which means the same as superelevation or banking on a road (and in railway parlance, "elevation" and "banking" are used for two different and quite unrelated concepts, so might cause confusion if used in connection with the tilting sense). Your definition of road camber is strictly correct, but (again in the UK at any rate) "camber" is often used by laypersons (i.e. not civil engineers) more loosely to refer to banking, most often in the construction "reverse camber" when referring to a bend where the camber and banking combine sub-optimally to make negotiating the bend unexpectedly difficult. I suggest that recourse to a Civil Engineering textbook might help to compose a comprehensive and authoritative explanation of the terms that would take into account the common misuse of "camber." 87.81.230.195 (talk) 13:18, 18 August 2009 (UTC)

A romantic notion, but unfortunately I have neither the spare time or the academic resources to produce a conclusive treatise on this issue, I was merely trying to include the small amount information that I do have to offer into the article and make it more understandable. I shall see what I can put together in my userspace and invite you to comment before editing the articles. But on another note I fear you saw more aggression in my usage of the term "fight" than was intended, maybe "oppose" would have been a better choice of word. Elocute (talk) 18:54, 18 August 2009 (UTC)

The Ref Desk isn't the place to do that. You ask questions - we answer them. The place to discuss the appropriateness of a change to an article is in the article's own Talk: page. Also, if you're pretty sure that you're right - and the change isn't of earth-shattering importance to humanity - you should probably just "be bold" and alter the article. SteveBaker (talk) 18:55, 19 August 2009 (UTC)

Well in my experience no matter how benign an alteration one makes to an article, if it 'undoes' something someone else has done they usually get upset and the discourse degrades into pedantry followed by edit war. So all I was trying to do is find out if what I believed to be the case was actually correct or not before editing. Elocute (talk) 19:34, 19 August 2009 (UTC)

Suppositories - q for the medical people here

How common is it for patients to swallow prescribed suppositories by mistake? You hear stories about it but is it a particularly widespread error? --84.65.32.44 (talk) 21:55, 17 August 2009 (UTC)

I have been a nurse and involved with caring for people all my long life and I have never heard of a real case where this happened. I think it is rare. —Preceding unsigned comment added by 86.4.181.14 (talk) 07:01, 18 August 2009 (UTC)

Yes, they'd have to be a total butt-head with sh** for brains to do that. :-) StuRat (talk) 12:41, 18 August 2009 (UTC)

So, similar to the other apocryphal 'stupid patient' tales that medical staff like to swap with each other? Like the woman who goes to see her doctor complaining that she's still having heavy periods, despite swallowing a tampon every month - or the guy who says that he feels pain every time he touches his legs or his left arm, to which the doctor replies "your right hand is broken". Or the couple who claim to be having problems conceiving a child, despite 'sleeping together every night for two years' - and the doctor eventually discovers that *sleeping in the same bed every night* is *all* that they've been doing, both having failed to grasp the basic concepts of sexual reproduction... ;) --Kurt Shaped Box (talk) 17:10, 18 August 2009 (UTC)

What kind of effects would you expect if they did? Vimescarrot (talk) 11:08, 18 August 2009 (UTC)

Well, one reason for using a supository is that the drug is absorbed by the bowel/colon. Blood from here does not flow through the liver prior to entering the inferior vena cava. Some drugs are rapidly deactivated by the liver, so by bypassing the liver, the drug has a longer halflife in the body. Also, absorption through the colon has different kinetics than does absorption through the stomach/small intestine. There may also be a question of the drug being sensitive to the acidity of the stomach. I'm sure there are other reasons as well. In sum, I suspect less of the drug would enter the person's system and or that which does would do so more slowly if someone swallowed a suppository. A pharmacist may have more insight. -- Flyguy649 ^talk 16:23, 18 August 2009 (UTC)

Looking for a nutrition web site

No big deal, you say ? Well, I'm looking for a site which will list foods which are good for diabetics, those with high blood pressure, those with kidney failure, etc. Still no big deal ? Well, I want it to recommend foods for those with multiple medical conditions. (Note that I'm not asking anyone here to recommend any foods, just a site where I can look it up myself.) Ideally you should be able to weight the medical conditions, say if you only have slightly high blood pressure but have severe diabetes. In that case avoiding foods with a high glycemic index would be more important than avoiding salt. It should also list foods from best to worst, for the given medical conditions and weighting factors. So, does such a site exist, or must I create it myself ? StuRat (talk) 22:24, 17 August 2009 (UTC)

For advice that personalised I would suggest people get their doctor to refer them to a professional nutritionist. I think there are too many factors involved for a website to give reliable results. --Tango (talk) 01:05, 18 August 2009 (UTC)

I disagree. The Best Buy web site can do something similar with appliances right now. You give it some parameters, like the size of monitor, it's resolution, and cost range, and they give you a list of monitors that match. The same thing could easily be done with foods, where the parameters become low glycemic index, low salt, etc. The site nutritiondata.com already has this info, I just need it to be made "searchable" and "sortable". As for refering to a doctor, you tend to get doctors with various specialties each of whom only know the foods which are good or bad for those conditions, not for the overall health of the patient. I also tried the nutritionist approach, but she gave me several lists (one for each condition) and wanted me to to the work of cross-referencing it all. And the lists only had maybe 100 foods each (and they weren't even the same foods on each list), which meant there were only like 3 foods on the "good" list for all the conditions. If you started with more like 1000 foods you'd end up with a more respectable list of maybe 30 foods good for all conditions. And cross-referencing such a large number of foods manually is truly a daunting task which really should be automated. I can think of no better use for a computer than automating such drudgery for the benefit of mankind (well, ok, maybe distributing porn is a better use, :-) ). StuRat (talk) 12:12, 18 August 2009 (UTC)

A question from an answerer! Here are some contributions toward an answer and an explanation of why this is not so simple. Foods that are considered good for diabetes can be (a) foods that are healthy for everyone, since nearly all adults with diabetes need to eat less of some things (calories) and more of others even more than the rest of us; (b) those rare plants that might contribute to lowering blood glucose by various mechanisms, but plant names can be vague and overlapping and are rarely available as food (e.g., gymnema or cinnamon) and the hypoglycemic effect is small, and the efficacy claims often come from folk medicine sources and may be not well proven; (c) those things that might help if the person is deficient in a single nutrient (e.g., foods high in chromium); (d) foods that slow absorption of carbohydrates (e.g., high fiber and fat foods) can make it easier to match injected insulin with a meal; (e) carbohydrate foods that are more slowly digested and hence easier to dispose of by someone with limited insulin responses or on injected insulin (e.g., low glycemic index foods are better than high); and (f) dietary changes that would be helpful for the conditions often associated with adult diabetes (e.g., less calories for the overweight, less salt for the hypertensive, less fat for the hyperlipidemic, less potassium and protein for those with impaired kidney function). The really depressing answer for anyone developing type 2 diabetes with mildly high blood pressure and heart risk is that "eat a lot less of everything you like and have been eating for most of your life" is actually far more accurate and efficacious than attempting to add anything else from the list above. Good luck. alteripse (talk) 01:59, 20 August 2009 (UTC)

I both ask and answer questions all the time (hopefully not the same Q's.) The nutrition site could even bypass the possibly contentious issue of what is good and bad for various medical conditions by merely allowing you to sort foods by parameters you define, like low sodium, low glycemic index, etc. They would never need to ask your medical problems, in this way. As I mentioned, nutritiondata.com already lists these things about all foods, but looking through thousands of foods to find those which match my criteria is extremely time-consuming. StuRat (talk) 14:35, 20 August 2009 (UTC)

August 18

Harvestman

What can I feed a harvestman? Mac Davis (talk) 00:13, 18 August 2009 (UTC)

Have you read the article? I found plenty of relevant information at Harvestman#Behavior. Intelligentsium 00:33, 18 August 2009 (UTC)

Small insects and "all kinds of plant matter"? I was looking for something specific. Maybe they are just not very picky. Thanks! Mac Davis (talk) 01:01, 18 August 2009 (UTC)

In her book Broadsides from the Other Orders, Sue Hubbell describes capturing some of them and keeping them for observation (including breeding). Apparently the most critical thing for their survival is a supply of fresh water, which they need constantly. This she supplied in a "shallow jar cap" set into the sand and dead leaves with which she covered the bottom of their wire-mesh cage. Other than that, "they lived in apparent contentment … until the end of their lives, thriving on a diet of overripe persimmons, cornmeal, bacon fat, and an occasional dead fly." The whole of Chapter 4 may be of interest if you can dig up a copy of the book. Deor (talk) 02:57, 18 August 2009 (UTC)

The book seems to be widely available in libraries. -Arch dude (talk) 07:11, 18 August 2009 (UTC)

I've struck the reference to breeding. My memory had confused Hubbell's observations of harvestmen with her observations of captive camel crickets, described in Chapter 13. Deor (talk) 03:49, 18 August 2009 (UTC)

Wow! Thanks! Now I also get to read the article rhaphidophoridae, I find two in the room per day. Mac Davis (talk) 05:23, 18 August 2009 (UTC)

What is the opposite of a "Ploughman's lunch"?Edison (talk) 04:27, 19 August 2009 (UTC)

Fruit on an empty stomach

Hi All,

Got one of those forwarded emails, and I was intrigued at it's claim that fruits are best eaten on an empty stomach. It claims that though the fruit in question might be acidic (say a pineapple) in taste, the email claims that it turns basic once it interacts with digestive juices.

I do personally recall eating grapes on an empty stomach a few weeks ago and not really suffered anything, I was wondering if that was a fluke or does this claim have really have a scientific foundation? If its true what's the chemistry behind it? I (sucking at chemistry) would have assumed that acid + acid = more acid.

Please forgive my ignorance. :P Thanks in advance! PrinzPH (talk) 02:42, 18 August 2009 (UTC)

It sounds like nonsense to me. I eat fruit both on an empty stomach (for breakfast) and a full stomach (for desert) most days and don't have any problems. What did the email say would go wrong? --Tango (talk) 02:47, 18 August 2009 (UTC)

Well it claimed that eating food along with meats and other stuff would cause the other food to putrefy (is that the right term?) and cause gas. It also made claims that it (other food item) might absorb some of the nutrients that our body would have otherwise absorbed. PrinzPH (talk) 02:58, 18 August 2009 (UTC)

Gas varies from person to person and isn't usually harmful, so trial and error is the best approach there - if you find a combination of foods that gives you gas, you may want to stop eating that combination, otherwise don't worry about it. As for nutrients, it sounds unlikely - your body is going to absorb the other food as well, so at worst it will delay the absorption of the nutrients. I guess it is possible the nutrients will be absorbed by part of the other food that can't be digested and just goes straight through you, but it doesn't seem likely. Did the email give any kind of clue as to the source of this information? --Tango (talk) 03:04, 18 August 2009 (UTC)

It sounds like Fit for Life but I believe that there are other diets with similar ideas.Sjö (talk) 13:00, 18 August 2009 (UTC)

Sorry don't really recall too much (deleted it after giving it a once-over). Tango's explanation does make sense, I guess in the end it really boils down to individual reactions. I'm still curious though about how our digestive juices interact with food acids.. Anyone got an article to point me to? PrinzPH (talk) 18:05, 18 August 2009 (UTC)

There are two pretty good online sources at food combining. Livewireo (talk) 19:47, 18 August 2009 (UTC)

Transcendental Meditation and stress accumulation

My question is twofold:

1. A friend of mine started talking to me about how great transcendental meditation is and how it has changed him. From what he described it sounded like a cult (an immensely expensive one) and he insisted on telling me some anecdotal evidence which I dismissed. The Wikipedia article does sound like it has some benefits but some parts of it sound confusing- does TM have any real benefits, and if so are they greater from the benefits of say lying down or simply meditating normally? I tried looking for facts on the Internet but only found sources but only found sources by the TM company claiming some 500-600 studies done by 250 separate universities- is that true?? The number of studies sounds incredibly high! And all of the results I saw were way too good, and I couldn't help but thinking about bogus infomercials.
2. At some YouTube video discussing the awesome results of TM (uploaded by the TM company) John Hagelin said that the "that about 90% of diseases are caused or complicated by stress" and then said something about "stress accumulation". Is that "90%" part correct, and is there such a thing as accumulative stress (I've heard that term many times)? Stress isn't an object (as far as I know) but rather a state of mind- wouldn't you rather talk about some of the psychological and biological harm that a person suffers from too much stress?

Am I just a paranoid sceptic? At first I was going to mention how John Hagelin did not sound like a doctor at all (because he seemed way too certain and used too many absolutes) but he has a lot of credentials so I'm not too certain. I honestly don't know what to think, everything I hear about this screams cult and pseudo-science but yet it seems to check out.. --BiT (talk) 02:52, 18 August 2009 (UTC)

Oh and apparently the Ph.D. made an apperance in What the Bleep Do We Know!? which appears to be bullshit, but he was a researcher at CERN, a Professor of Physics and Director of the Institute of Science, Technology and Public Policy at Maharishi University of Management.. wait Maharishi University of Management was founded by Maharishi Mahesh Yogi, who introduced the Transcendental Meditation technique.

The plot thickens! --BiT (talk) 03:00, 18 August 2009 (UTC)

There is no thick plot and you are right, it is a cult and a pseudo-science. The only reason the plot appears thick is because the amount of money that is spent by TM on marketing. Do you think there are no people with "real and legit" credentials who would claim some rubbish for a high enough price? Or even if they aren't shilling, maybe there even are a few smart and well meaning people who do actually believe it, for some reason, that doesn't prove anything. If the claims were published in a peer reviewed journal, THEN is when I would start taking it seriously. And claims like "90% of diseases are caused or complicated by stress" mean nothing. Maybe 10% (purely for arguments sake) are caused mostly by stress and who would argue that excessive stress is a bad state to be in if you are sick already? The vast majority of the claims they make however are not so "ambiguous", they claim to influence world events with their "meditation", and that is definitely BS. Something funny I heard recently was when the Christian scientists at answering genesis came up with a petition of 300 scientists who "doubt evolution" (that list was found to be complete BS anyway). In response Project Steve was set up which gathered over ONE THOUSAND scientist with the given name Steve who support evolution. Without a context, those kind of claims made by TM mean absolutely nothing. And "what the bleep do we know" is complete rubbish, the whole thing was a promotion of the teachings of JZ Knight who under any rational definition is a complete loony and should have probably got medical help a long time ago. In any less libreal society she would have been thrown in a loony bin or burned at the stake for being a witch.. Not that I would condone the latter, but i'd probably not protest against the former. Vespine (talk) 04:32, 18 August 2009 (UTC)

Since "If the claims were published in a peer reviewed journal, THEN is when I would start taking it seriously", I have some shocking news to deliver: Transcendental_meditation#Research describes a number of studies published in genuine peer-reviewed journals concerning the physiological effects of transcendental meditation, some of which demonstrated significant results. Furthermore, it's high time that we end the practice of characterizing new religious movements as "pseudosciences": a pseudoscience necessarily involves a theory with pretensions towards science. Religions and spiritual theories aren't sciences, pseudo or otherwise. The existence of scientific studies regarding the effects of TM doesn't alter this basic framework, any more than studies of the physiological effects of Christian prayer would transform Christianity into a pseudoscience. Erik9 (talk) 05:05, 18 August 2009 (UTC)

The question of "cult" status is, perhaps, a more difficult one, discussed at Transcendental_Meditation#Cult_issues. Erik9 (talk) 05:18, 18 August 2009 (UTC)

Hang on what? I wasn't characterizing it as pseudoscience just because it was a new religion, it doesn't actually claim to be a religion. All of the apparently legit studies simply monitored the effects on things like blood pressure of the actual practitioners of TM, this isn't compared to studies of other types of meditation so I'd consider it completely useless as an indicator of anything. I guarantee there isn't an independent double blind study confirming a blood pressure difference in people who are in a room alone, where one group has TM people in the next room focusing their effort on them, and another control group has no one focusing "TM energy" on them. I guarantee such a claim would and could not be proved, but that is in effect what TM is trying to suggest with its pseudo-science claims such as this: http://www.tmprogram.com.au/charts/chart_51.html and this http://www.tmprogram.com.au/charts/chart_49.html complete garbage. Vespine (talk) 06:31, 18 August 2009 (UTC)

Ok I've actually read a bit more of the TM article because I'm actually interested in religions and science and and stuff like that. So there have been some studies which show some kind of positive effects of TM, ON THE PRACTITIONERS of TM. With respect to things like blood pressure, quitting smoking and even learning at school, but most of these studies are on people who already practiced TM or intended to study TM, so the motivation of these people can't be ruled out either (the control groups would have less motivation to do any better). But there are also many studies which show no effect, or very little effect, or effect comparable to that of other kinds of meditation. This is nothing surprising really. What there is none of, like I said above, is any kind of study showing that practitioners of TM have any kind of effect or influence on external things like the road toll, or war fatalities, which is exactly what TM claims to be capable of. They throw the bath water in with the baby, if I can reverse that saying, they attempt to use the scientific studies about "TM making you feel nice if you meditate" to validate their completely ridiculous claims of what else they can do. Pseudo-science through and through. Vespine (talk) 06:52, 18 August 2009 (UTC)

It's pretty obvious that stress is a major contributor to bad health of all kinds. It's also pretty clear that sitting down for a while, trying to forget your problems and generally relaxing is a way to (at least temporarily) relieve stress. So it's no stretch at all to believe that TM does indeed make you somewhat healthier, perhaps somewhat happier. However, the pseudo-science kicks in with all of the very tightly specified methods and attendant BS that comes with TM. What makes it a "pseudoscience" is that they use all of the trappings of science - but without any of the scientific methods. They started with a technique and then tried to justify it. In science, we study the problem and develop techniques to solve the problem. As our article points out, TM "experts" make all sorts of claims that are essentially unjustified - and it's pretty evident that simply relaxing, "going to your happy place", doing something to take your mind off of stress at work, etc, is what's doing you good. If you have to have all of the chanting and quasi-religious BS in order to do that - well, maybe it has some benefit. You could easily imagine the busy housewife with a handful of noisy, annoying, demanding kids running around the house gaining benefit from saying "Mommy is doing her TM now - that means you've all got to be quiet for half an hour and leave her alone." - compared to simply trying to relax amongst all of the chaos. Merely giving the technique a name may confer benefits that more obvious and informal relaxation cannot. However, the multiple days of (expensive) training and the mystique that's wrapped around TM is clearly just a means to extract money from gullible people. SteveBaker (talk) 11:43, 18 August 2009 (UTC)

I don't know about any spiritual claims, but I found the technique capable of completely blocking all pain from a tooth abscess when I was waiting for dental treament and had run out of (nowhere near as effective) painkilling drugs. I was even able to BITE on the absess-unthinkable even with painkillers. I had to maintain the lotus position to keep this self hypnosis up-deviating from it brought the pain back.Trevor Loughlin (talk) 12:42, 18 August 2009 (UTC)

At a minimum it could give a placebo effect. Googlemeister (talk) 14:41, 18 August 2009 (UTC)

So doing TM is tantamount to relaxing/taking a break? --BiT (talk) 15:11, 19 August 2009 (UTC)

And regarding the second part of my question- can stress accumulate? --BiT (talk) 15:11, 19 August 2009 (UTC)

Of course stress can accumulate. That is why some stressful jobs have such high turnover rates. Googlemeister (talk) 18:51, 19 August 2009 (UTC)

Trevor, you didn't even need a painkiller? Then you were able to transcend dental medication! Bunthorne (talk) 10:01, 20 August 2009 (UTC)

Fast acting diseases?

A staple of Sci-fi and other drama is the quick acting viral/bacterial infection, where the victim seem to go from first contact to death in a matter of minutes to seconds. Is that possible real life? If not, what would have to be different about the viruses and bacteria to make this possible?

Thanks in advance —Preceding unsigned comment added by 99.240.189.90 (talk) 06:21, 18 August 2009 (UTC)

The rate of growth of either a bacterial or a viral infection is limited by the rate at which cells can divide and then grow large enough to divide again. For bacteria it's the bacteria that do this; for viruses it's your own cells that the virus has taken over. Presumably the real-life diseases with the shortest incubation times, which I think are on the order of a day or two, represent the fastest that is possible in that regard. --Anonymous, 08:25 UTC, August 18, 2009.

Not sure how fast acting it is, but botulism is pretty quick (maybe on the order of hours?). That is a byproduct of certain bacteria, not the bacteria themselves. Googlemeister (talk) 13:12, 18 August 2009 (UTC)

I'd guess that diseases could kill in minutes or hours (but probably not seconds), but there's no evolutionary path there as killing your host quickly is a poor survival strategy for a virus or bacteria. Ideally they should keep the host alive for a long time so they spread the disease to others. If they even prevent the host from reproducing, then the host animals which are susceptible to the disease will be selected against, which will result in an immunity to the disease over time (as happened to Bubonic Plague, for example). However, some evil scientists doing genetic engineering might be able to come up with such a virus or bacteria. It would need some strategy for defeating the immune system of the host body, though, such as appearing to be normal cells. StuRat (talk) 13:24, 18 August 2009 (UTC)

Bacterial endotoxin released when the bacteria are lysed by the immune system, and bacterial exotoxin released by the bacteria themselves probably play a big role in the rapid decompensation (septic shock) that is sometimes seen in people with bacterial illnesses. However, in agreement with others, this process takes more than a few minutes, maybe on the order of hours to days depending on the severity of the infection, host's immune system, and other factors. In viral illnesses, you may sometimes see a cytokine storm that results from an overactive immune system and can be just as devastating as septicemia. --- Medical geneticist (talk) 13:55, 18 August 2009 (UTC)

I believe there are neurotoxins that can kill in absurdly small doses. If a bacteria produced one, it probably could kill someone that fast. Of course, then you might as well skip the bacteria and say that they got neurotoxin on them. — DanielLC 15:11, 18 August 2009 (UTC)

Prolly you could get a pathogen that triggered such a vigourous immune system response that their own immune system kills them. John Riemann Soong (talk) 16:02, 18 August 2009 (UTC)

Something that fast-acting would need to depend on something that is already present in the body. Consider a benign virus that somehow causes teh host to generate a precursor chemical that auocatalytically converts to a fast neurotoxin. Consider a second agent (a bacterium, perhaps) that propagates benignly until some envronmental condition causes it to emit a few molecules of the neurotoxin. The resulting autocatalytic cascade would flood the body in seconds. This would need to be engineered, as there is no reason such a system would arise as the result of natural selection. -Arch dude (talk) 16:34, 18 August 2009 (UTC)

I think a key question is whether this virus was naturally selected -- i.e. in accordance with selfish gene theory and zombies, or artficially selected by say, (controlled by an evil scientist). In a naturally-selected case of death within minutes, the pathogen's ideal host is probably a different species (say, an elephant) -- where it must act extremely virulently to avoid being suppressed by the elephant's immune system, but is too virulent in humans. The naturally-selected case is IMO the more frightening one (one good for a horror film) because the pathogen appears to have a will of its own ... and the best (most horrifying) timeframe would be death within a day, leaving time for the infected individuals to pass on their pathogen to other humans.

There are also not many mechanisms of death (besides just sheer violence) that would kill someone within minutes. A few things I can think of:

• Anaphylaxis
• Blood pH -- acidosis, alkalosis -- if key cells with a large influence over pH (kidneys, acid-releasing glands, etc. are compromised)
• Intercell apoptotic cascade in a few critical areas (suppose you got a small part of the stomach wall to suddenly undergo mass cell death, for instance...)

There's also a rather improbable mechanism, yet plausible enough for me to have suspension of disbelief during a sci-fi horror film. You basically have inactive proviruses stored within the genome ... lots of them. Now say there was one nicely embedded in a region that was shielded from DNA damage, or located next to some critical coding region, and maybe has an active DNA repair portion helping to keep the virus' integrity in check; if mutation in this region occurs, the cell undergoes apoptosis. Now, all you have to do is administer a little systemwide "signal" into the bloodstream that will trigger this provirus out of latency; cells everywhere in the body would suddenly activate viral replication ... John Riemann Soong (talk) 16:36, 18 August 2009 (UTC)

On second thought, we actually have a lot of active proviruses (active for our species, I mean, not in adults). They get activated during gestation (evolution has converted their virulent properties for other purposes, like preventing the mother's immune system from attacking developing young). As a result these proviruses are probably conserved. As a matter of fact, we have a lot of other "malicious" DNA as well (used for things like programmed cell death or phagocytosis); you could have a pathogen which would trigger such cascades. PCD and apoptosis by themselves evolved from "pathogens" as well -- we now see mitochondria and chloroplasts as "friendly" to the bigger eukaryotic cell of course, but once upon a time they were enemies. John Riemann Soong (talk) 16:50, 18 August 2009 (UTC)

Monitoring wireless

Can I monitor website visits by those who use my wireless? 173.54.205.131 (talk) 11:58, 18 August 2009 (UTC)

Yes, I believe you can use applications like Wireshark to monitor what websites computers that are using your wireless network are accessing.--droptone (talk) 12:21, 18 August 2009 (UTC)

Is there a way to block this? --Reticuli88 (talk) 12:27, 19 August 2009 (UTC)

You cannot truly prevent packet sniffing without preventing your own devices from communicating, but there are three practical ways to "block" it. The first is physical— it is to ensure that your broadcast area does not reach places you do not want it to through strategic placement of access points and physical barriers to signal. The second is to encrypt your communications so when the person watching your data picks it up, they can't actually understand it. The third is to prevent them from knowing your network exists in the at all, like making sure the SSID is not broadcast. Although only the physical security may stop a knowledgeable and determined person. Mac Davis (talk) 04:09, 20 August 2009 (UTC)

Photo diode question

is it posible an AVALANCHE PHOTODIODES to detect metals like cuper or gold?Sakis1964 (talk) 13:01, 18 August 2009 (UTC) Tank you very much

No. Is there any reason you thought it would? , or is it "shit and run" as usual?83.100.250.79 (talk) 17:29, 18 August 2009 (UTC)

Connecticut residence of Samuel Finley Breese Morse

Am attempting to track down specific dates (and any other related informtion) when Samuel F.B. Morse lived in Connecticut, specifically Saybrook, CT (probably when he was at Yale). Any information or references appreciated. 99.33.198.140 (talk) 13:40, 18 August 2009 (UTC)

KINEMATICS

This is my homework question. Please find where have I mistaken Here's the question:

A cylinder rolls without slipping over a horizontal plane. The radius of the cylinder is equal to r. Find the curvature radii of trajectories traced out by the points A & B. Point A is the topmost point(on the cylinder's circumference), whereas ,point B is at a distance r from the ground on the circumference of the cylinder.

What I did was, consider the cylinder to roll with velocity v. Then every particle on its circumference will have velocity v.

consider the trajectory of bottom-most point on the circumference. It willbe having constant velocity throughout.

consider downward acceleration to be a & along positive X axis to be b.

the maximum height is 2r & range is 2πr. Let the angle made by the projectile with X axis be Φ.

Solving , I got a=v²sin²Φ/(4r) & b=v²sin²Φ/(2πr) & (1-cosΦ)/sinΦ=b/a

From these three equations I got cosΦ=1 or cosΦ=(π²-4)/(π²+4) cosΦ=1 is neglected.

Now, at the topmost point of the trajectory, vertical forces are balanced. Therefore, mass*a=mass*v²/R° [Where R° is the radius of a very small arc near point A] Therefore , I get R°=4r*(π²+4)²/(16π²) But the answer is R°=4r & the radius at point B =2√2r which I am getting as R=4√2rπ/(2+π) Please tell me what is wrong in this method. —Preceding unsigned comment added by 121.245.182.159 (talk) 15:24, 18 August 2009 (UTC)

Unless I'm picturing the scenario incorrectly, some of your statements are false, especially "every particle on its circumference will have velocity v". The bottom point in particular always has an instantaneous velocity of zero, since the cylinder is rolling without slipping.

Cycloid. Cuddlyable3 (talk) 19:40, 18 August 2009 (UTC)

Eventhough this is homework, I think you seem to have put enough effort into it to deserve some help. The 'slick' way to do that problem is to move back and forth between two different reference frames. The first reference frame is the one where the ground is at rest and the cylinder moves with speed v henceforth RF1. The second reference frame would be the one where the cylinder is at rest and the ground is moving (back) with speed v henceforth RF2. The relative velocity between the two reference frames has magnitude v and you have to (vectorially) add (subtract) that velocity to a particle's velocity to go back and (forth) between the two reference frames. Your statement that all points on the circunference have the same speed is true in RF2: |VA2| = |VB2| = v. But that's not the case in RF1 because of the (vectorial) additions: VA1 = VA2 + Vrel and VB1 = VB2 + Vrel where Vrel is the relative velocity between the two reference frames. For the point A VA2 and Vrel are parallel and you get |VA1| = 2v. For the point B VB2 and Vrel are perpendicular and you get |VB1|= (√2)v. I will do the easy one (point A) for you and leave the hard one (point B) for you to do yourself. in RF2 we have the relationship between speed, radius of curvature, and centripetal acceleration: ac = |VA2|^2/R2 = v^2/r = . That acceleration is also perpendicular to motion in RF1 (that's not true for the point B and that's what makes that point harder. You will have to find the centripetal component of the acceleration to work out point B), so you also have the relation ac = |VA1|^2/R1 = (2v)^2/R1 = 4v^2/R1. R1 is the radius you are trying to find. Put the two expressions for ac together we have ac = v^2/r = 4v^2/R1 which simplifies to R1 = 4r as desired. Dauto (talk) 16:48, 19 August 2009 (UTC)

brain blood barrier

If you can remove some CSF with a lumber puncture why cant you add medication with the same method and bypass the brain blood barrier.D4n5er (talk) 16:35, 18 August 2009 (UTC)

Medications can indeed be given using lumbar puncture (called intrathecal injection), such as spinal anaesthesia and some chemotherapy drugs such as methotrexate. Axl ¤ [Talk] 17:03, 18 August 2009 (UTC)

But the method is generally too risky to use on a routine basis, besides being extremely painful. Any puncture of the membranes around the brain or spinal cord creates risks of infection or leakage, either of which can pretty easily lead to paralysis or even death. Looie496 (talk) 17:28, 18 August 2009 (UTC)

• "Extremely painful"? Done properly, it should not be extremely painful.
• "Any puncture of the membranes around the brain or spinal cord creates risks of infection or leakage." This is true, but again if done properly the risk is low. CSF leak is usually fairly easy to treat.
• "... either of which can pretty easily lead to paralysis or even death." This is certainly not true. Read this article.

Axl ¤ [Talk] 17:54, 18 August 2009 (UTC)

You can...but it would not nearly as easy a route as oral, subdermal, intramuscular or even intravenous administration. DRosenbach ^{(Talk | Contribs)} 02:49, 19 August 2009 (UTC)

Spherical coincidence

Can you visualize energy as the surface of a sphere having the diameter squared of the distance light travels in one second when mass is equal to pi? -- Taxa (talk) 16:51, 18 August 2009 (UTC)

No I can't - because parts of what you wrote seem meaningless - I got as far as a sphere. Can you clarify from "diameter squared" onwards.83.100.250.79 (talk) 17:28, 18 August 2009 (UTC)

I hate to say it, but I can actually make sense of this. Taxa is observing a parallel between $E=mc^{2}$ and $A=4\pi r^{2}=\pi d^{2}$. Of course, it should be the speed of light, not "the distance light travels in one second"; how would you pick "one second" out of all the possible lengths of time? Since Einstein's observation is that energy is proportional to mass (via the constant $c^{2}$), and the sphere formula gives area as proportional to diameter squared (via the constant $\pi$), I don't see any worthwhile correlation: the constant in one expression "corresponds to" the crucial variable in the other. --Tardis (talk) 17:39, 18 August 2009 (UTC)

Agreed, and for the purpose of developing an analog, the "squared" isn't so important as a constant is being squared, so I would be more simple-minded and use any old linear relationship to visualize. But yes, for a constant mass and a sphere with c diameter, the initial observation would work. Awickert (talk) 19:47, 18 August 2009 (UTC)

You can visualize anything you want - but this particular thought experiment seems to have no useful physical interpretation. In the case of mass-energy equivalence, there's not a relevant analog to "surface area of a sphere" - so I can't think of any reason to use such a geometric model. Did you have any particular reason or expected consequence for comparing that equation? There are plenty of other geometric equations which have a similar algebraic representation, but that doesn't mean they're in any way physically relevant. You might want to read about dimensional analysis for a better way to think about the units involved - you might actually come up with some more useful analogies by picking similar equations with similar units. Nimur (talk) 06:35, 19 August 2009 (UTC)

Blood pressure and emotions

Do blood pressure measurements vary based on a person's emotions such as when a person is sad, happy, angry or nervous? And if so, by how much at the most? Thank you. Clover345 (talk) 16:53, 18 August 2009 (UTC)

Yes, blood pressure does vary with emotion. Indeed there is a syndrome called "white coat hypertension" where blood pressure rises solely because of attendance at a doctor's clinic. Axl ¤ [Talk] 17:09, 18 August 2009 (UTC)

Have a look at this article.

Mean change in blood pressure with emotion-related imagery

Parameter	Happiness	Sadness	Anger	Fear	Control	Relaxation
Diastolic blood pressure	+3.6	+1.7	+6.9	+3.4	+1.5	-0.9
Systolic blood pressure	+5.0	+6.4	+7.3	+6.7	+0.5	+0.6

Axl ¤ [Talk] 17:25, 18 August 2009 (UTC)

Thanks. It says in one of your articles, that hypertension derived from emotions or "white coat hypertension" as its called can lead to actual hypertension. Is this as a direct result of blood pressure rising at such times or is it the emotions that cause blood pressure to rise in the long term? Surely if raised blood pressure dut to emotions can lead to actual raise blood pressure, then raised blood pressure as a result of physical activity can also have the same effect.Clover345 (talk) 17:38, 18 August 2009 (UTC)

I've also got to think that the sphygmomanometer itself must raise your BP, as it's about as pleasant as having a boa constrictor coiled around your arm and squeezing. StuRat (talk) 20:52, 18 August 2009 (UTC)

I had a look through the literature. I couldn't find any information on the progression of white coat hypertension. There's no clear evidence looking for the development of sustained hypertension. The potential benefit of treatment is controversial. See these articles: White-Coat Hypertension and Risk of Stroke & "White coat hypertension — should it be treated or not?". Axl ¤ [Talk] 21:03, 18 August 2009 (UTC)

To StuRat: the gold standard for blood pressure measurement is the arterial line. According to this article, "the direct [arterial line] and indirect [sphygmomanometer] methods yield similar measurements, but these are rarely identical because the direct method measures pressure and the indirect method is more indicative of flow. The indirect method is generally less accurate and less reproducible. Nevertheless, it is sufficiently accurate for many diagnostic and therapeutic studies." From this article: "Compared with direct intra-arterial measurement of blood pressure, the auscultatory technique using Korotkoff sounds tends to give systolic values that are slightly lower and diastolic values that are slightly higher than intra-arterial measurements." Axl ¤ [Talk] 21:24, 18 August 2009 (UTC)

I should think a painful arterial line would cause even more stress and thus higher BP. So how exactly do they know that it's more accurate ? StuRat (talk) 00:11, 19 August 2009 (UTC)

Arterial lines can be left in for days, during which time they are not constantly a source of discomfort, so they would not be expected to affect BP. One does have to be cautious about using arterial lines as a gold standard, because systematic measurement error can be introduced by phenomena like under-damping, which can cause artefactual elevation of systolic and depression of diastolic readings. --Scray (talk) 03:55, 19 August 2009 (UTC)

Also, exact blood pressure is not important. We are looking at comparison of blood pressure. Assume that the measuring device increases everyone's blood pressure by 10%. We would be comparing those with high blood pressure to those with normal blood pressure - with both values raised 10%. No problem. Further, if a person's blood pressure is raised abnormally by the measuring device, it is safe to assume that the person reacts similarly to other things. in other words, the person has repeated spikes in blood pressure throughout the day. This is intermittent hypertension and is very difficult to treat. If you control the spikes, blood pressure will be too low between the spikes. In the end, it isn't really a hypertension problem. It is an emotional problem that must be dealt with from a completely different expertise. -- kainaw™ 15:46, 19 August 2009 (UTC)

• "Assume that the measuring device increases everyone's blood pressure by 10%." This assumption is incorrect.
• "If a person's blood pressure is raised abnormally by the measuring device, it is safe to assume that the person reacts similarly to other things." Another inappropriate assumption.

Axl ¤ [Talk] 16:44, 19 August 2009 (UTC)

I had similar thoughts. Someone accustomed to medical procedures might not have any BP spike at all, while for someone else, who is normally calm, but with an absolute phobia of doctors, a sphygmomanometer or, God-forbid, an arterial line, may cause an all-out panic attack. StuRat (talk) 14:20, 20 August 2009 (UTC)

Airport Security & Philosophy

Why do airport security signs use the term "your person"? As in "Please remove all non-permitted materials from your person."

Has the Transportation Security Administration implicitly declared their adherence to the philosophy of Dualism? TheFutureAwaits (talk) 17:50, 18 August 2009 (UTC)

I believe the implication is that "your person" is broader and more encompassing than other terms such as "your body," "your clothing," or "your baggage." Saying "your person" is saying anything you feel is currently connected to you via ownership. ~ Amory (user • talk • contribs) 18:49, 18 August 2009 (UTC)

There's sort of a "formal language" which seems to be in use in law-enforcement-style communities (though the TSA is not a law enforcement agency properly - it's sort of similar in scope). I think it has to do with politeness, and treading delicately with words in what might otherwise have serious legal ramifications. (If the sign said "no contraband on your body" it's leaving a legal loophole for contraband in your pocket, for example). This legal liaison organization suggests that the use of such language has a sociological consequence of creating a power-imbalance between the citizen and the Officer - they claim that "verbal cues, which may include the use of technical jargon or a military-like formality in the use of language, contribute to perpetuating this power imbalance." Nimur (talk) 06:42, 19 August 2009 (UTC)

Why shouldn't there be a "power imbalance" between the citizens and the officers? They're in charge, they have the legal authority, why shouldnt they act like they're the boss? I mean, when a traffic cop gives you a ticket for speeding, do you complain that there's a "power imbalance" between you and the cop? That's just the way things are, get used to it. 98.234.126.251 (talk) 07:00, 19 August 2009 (UTC)

Nimur did not say that there should not be this power imbalance in such situations, he/she merely presented evidence that it exists. Try to vent your spleen towards the appropriate targets. 87.81.230.195 (talk) 11:28, 19 August 2009 (UTC)

Hmm, it seems like most of these answers skirt around my original question. What I'm getting at is when the signs state "your person" they are implicitly indicating that you own your person and that "you" are something different than your person. As in the ethereal consciousness of your being should be aware of the need to remove objects in the possession of your physical body.

Therefore, regardless of the formality of the term, the TSA is taking a stance on a philosophical issue by stating "you" are independent of your body (i.e. dualism). Is this position not logical? TheFutureAwaits (talk) 15:39, 19 August 2009 (UTC)

Not really. I doubt that the TSA has any such official philosophical stance for or against dualism. Their mission is not to debate the philosophy of mind; it's to "protects the Nation’s transportation systems to ensure freedom of movement for people and commerce." [23]. From the very few words on the sign, you're extrapolating quite a bit of philosophy. The word-choice on the sign is probably, as I mentioned above, more about legal formality than philosophical belief. If you're curious about the institutional philosophy and official positions of the TSA, reading signs in airports will be less instructive than reading their mission statement and self-descriptions, available here. And regarding the above comments - I endorsed no position; I merely found a description of the language from the web. I think the OP might appreciate the subtlety of word-choice in this context, because a warning sign at an airport is not really the same as a philosophical rumination.Nimur (talk) 15:53, 19 August 2009 (UTC)

Line

On particularly athletic bodies (I've only ever seen it on males but it could be on females as well) there is a line that curves upwards just by the kidneys, slightly above the waist. Could someone tell me the name of this line? Cheers. 92.3.166.124 (talk) 18:16, 18 August 2009 (UTC)

I've only ever heard them called "groin lines" in life, although I found a book that might help. The picture there (p. 24) lists some lines, and although it's not quite clear which exactly are which, it could be a combination of the femoral fosset and the Demicircular line. ~ Amory (user • talk • contribs) 19:00, 18 August 2009 (UTC)

I assume you are refering to Apollo's belt aka the iliac furrow that runs from the hips to the groin? --Jayron32 20:50, 18 August 2009 (UTC)

The OP is referring to a line above the waist and curving upward, this is not the iliac furrow which is below the waist and runs down from the waist. I think he is referring to the outside edge of the latissimus dorsi muscle, also visible in this diagram.[24]. I am not aware that this line has any special name. 86.4.181.14 (talk) 08:05, 19 August 2009 (UTC)

Extracting ricin from castor beans

A recent episode of Breaking Bad had Walter extracting Ricin from Castor beans. As a chemistry teacher, I know that he probably has the know-how to do that, but my question is, how easy is it for a layman to obtain Castor beans? He lives in New Mexico. Who then was a gentleman? (talk) 18:56, 18 August 2009 (UTC)

It is used as a decorative plant. It is not difficult to obtain, as you can just grow them. Now if you need 500 lbs of the beans to extract a small amount of the toxin, that is a different story, but if you just need a few beans, no difficulty at all if you live in a warm climate. Googlemeister (talk) 19:08, 18 August 2009 (UTC)

(ec) Too easy? The article says: "Ricin is easily purified from castor-oil manufacturing waste. The aqueous phase left over from the oil extraction process is called waste mash. It contains about 5-10% ricin by weight. Separation requires only simple chromatographic techniques." As to how easy one might actually find that, well, take a look at the patent (pdf). None of that is particularly complex or difficult to acquire, although high school or college level Chemistry courses (especially Organic chemistry) would make it a lot easier to understand, prepare, and follow. Still, it seems to be simply a matter of getting the reagents, glassware, and castor beans. ~ Amory (user • talk • contribs) 19:10, 18 August 2009 (UTC)

It's harder not to extract ricin than it is to extract it. When making castor oil you have to ensure that none of the ricin ends up in your oil. Just a few beans can kill you, so you shouldn't need too many. You don't even have to purify your extract. John Riemann Soong (talk) 19:25, 18 August 2009 (UTC)

Is somebody trying to manufacture chemical weapons here?! 98.234.126.251 (talk) 22:45, 18 August 2009 (UTC)

Ricin is not much of a chemical weapon; it is a poison. You could potentially take a LOT of it and drop it on people, but, as our article points out, it's not any more effective than dropping any old poison in quantities on people. It's more poisonous than, say, rat poison, but the same principle applies. The media gives it a lot of hype, but it's not necessarily all that worse from a security perspective than, say, arsenic, except for the fact that it is easy to get castor beans (though it's not hard to get rat poison, either). From a security perspective, it's a lot less worrying than, say, ANFO. --98.217.14.211 (talk) 01:15, 19 August 2009 (UTC)

Well what if some terrorist bastard decides to poison the water supplies with ricin, wouldn't that be chemical warfare too? 98.234.126.251 (talk) 07:02, 19 August 2009 (UTC)

Sure. But there's a ridiculous number of substances someone could use to poison water supplies. Ricin is by no means the most effective, or even the most readily available. Hell, you could just have all your terrorist friends empty their terrorist bowels into a huge plastic sack, let it fester for a while, and then dump the contents into the water supply, and you've got some homegrown chemical warfare right there. Super effective? Probably not, because the payload would end up very much diluted, but the same thing certainly applies to ricin as well. You'd have to get a lot of it for it to be effective -- or even noticeable, really. Poisoning the water supply isn't a very effective delivery method for all sorts of reasons. -- Captain Disdain (talk) 09:18, 19 August 2009 (UTC)

I saw a Musselman purchasing a dietary fiber supplement. Should I be worried? --Sean 16:11, 19 August 2009 (UTC)

With all due respect to Muslim terrorists, historically, the most significant ricin usage has been by "white people": Americans, Bulgarian communists, and Canadians - far more often than it has ever been used by Islamic terrorists. It's sort of worrisome that 98.234.126.251's kneejerk reaction is to suspect a particular religious community who (for all intents and purposes) have no association with this particular tactic. I think this is called racial profiling - and not very good profiling, either, as it fails to account for historical precedent. Nimur (talk) 16:45, 19 August 2009 (UTC)

With all due respect to Nimur, not all Muslims are Arabs. Iranians are caucassian. There are white people who adhere to Islam. Googlemeister (talk) 20:45, 19 August 2009 (UTC)

Have there been any significant instances of Islamic terrorism related to ricin? 98.234.126.251's link suggests he is concerned about motherless Muslims. Our article lists several cases of ricin-related incidents, and none of them appear at all related to Islamic terrorism or bastards. Maybe race, religion, family status, etc., have no correlation to ricin (I think that's a reasonable conclusion, no?). Nimur (talk) 21:50, 19 August 2009 (UTC)

Nimur -- how dare you accuse the American people of using ricin for criminal purposes without providing examples of non-Muslim Americans doing that? I challenge you to give me some examples of that; if you can't find any, then your comments are defamatory toward the Americans and you gotta take them back. 98.234.126.251 (talk) 00:47, 20 August 2009 (UTC)

Ok, there were a few examples, according to the article. I stand corrected on that count (but stand by my other statements). 98.234.126.251 (talk) 01:20, 20 August 2009 (UTC)

As for an example of Islamic terrorism related to ricin -- back in January 2003, six Arab muslims were arrested in London for trying to poison the water supply with ricin. Also, the article actually does mention several instances of islamics (Algerians, Kurds, Chickens, etc.) plotting to use ricin to murder people. Did you intentionally overlook these examples because they contradicted your pre-conceived notion that none of the ricin-related incidents were instigated by muslims? 98.234.126.251 (talk) 00:53, 20 August 2009 (UTC)

And BTW, when I said "bastards", I did not mean it in a literal sense -- so your assertion that I'm somehow insinuating a correlation between family status and a propensity toward terrorism is completely baseless. As for correlation between religion and terrorism, if you haven't noticed that the vast majority of terrorism is carried out by islamics then you've got your head buried in the sand (and that's putting it mildly). 98.234.126.251 (talk) 00:58, 20 August 2009 (UTC)

I hope you realize that the vast majority of acts of terrorism on American soil have been committed by Americans, though. Our category of Terrorist incidents in the United States, though by no means complete, should give you an idea. Not that I'm saying that islamic terrorism isn't a concern, but frankly, at this point you're blatantly soapboxing. -- Captain Disdain (talk) 06:04, 20 August 2009 (UTC)

What acts of terrorism are you talking about? I challenge you to give me some examples, and if you can't then you gotta take your statement back. 98.234.126.251 (talk) 09:18, 20 August 2009 (UTC)

I've just taken a look at the article History of terrorism -- the only American terrorist groups listed there are the Ku Klux Klan and the Weather Underground, while the Islamic terrorist groups (from the Assassins to Al-Qaida) are too numerous to count. 98.234.126.251 (talk) 09:39, 20 August 2009 (UTC)

Apologies: I did give some examples, but I screwed up the link. It's fixed now in my post above. The point is, domestic terrorism is no joke: white supremacists, non-Islamic religious fanatics and just plain old crazy people get around, and their actions have included murders, bombings, plane hijackings, and, yes, even ricin letters. Perhaps a part of the problem here is that these days, a lot of people think "terrorism" means "attack on America by Muslims", or "attack against another country", or "politically or religiously motivated attacks", or some variation thereof. But it doesn't. It just means doing something to scare the fuck out of people in order to get them to do what you want, or even just to make a statement. The 9/11 attacks where a horrible thing, absolutely, but they were really, really exceptional when compared to the "average" act of terror. Most acts of terror are fairly small, because generally, that's the point of engaging in terrorism: you do a relatively small thing, and you scare everyone who hears about it. Those Christians who bomb abortion clinics or murder doctors who perform abortions? They're terrorists, plain and simple. Terrorism is cheap, easy and efficient, because it's unpredictable and often very hard, if not impossible, to defend against. I mean, at its most extreme, there's pretty much nothing you can do to keep it from happening: if someone straps dynamite and nails to their midsection, you can probably keep them from boarding a plane, but you can't keep them from walking into the airport and exploding there before the security checkpoint, and they'll still accomplish precisely what they set out to do. It really isn't a problem you can solve by making more arrests or hitting the enemy harder (as evidenced by the situation with the IRA). It's most definitely not an Islamic thing by any means, and its often very easy to justify if you're the party committing it. It's hardly a very new observation to say that one man's terrorist is another man's freedom fighter. -- Captain Disdain (talk) 09:50, 20 August 2009 (UTC)

OK, I've checked out the link you gave -- it shows that there were actually about the same numbers (about 20 each) of major attacks by the Islamic terrorists as by the domestic terrorists (most of the latter either by left-wing radicals or by white supremacists); however, most of the terrorist attacks that happened in the last 40 years were, in fact, the work of Islamic terrorists, while many of the domestic terror attacks happened a long time ago (before WW2 for the most part). I'm not denying that domestic terrorism (especially the white-supremacist kind) is a serious concern, but right now Islamic terrorism is a much greater threat (especially since they got a worldwide network with a coherent agenda of waging jihad against the West, while the white supremacists are much less organized). As for "one man's terrorist is another man's freedom fighter", that's pure BS -- a terrorist is a terrorist is a terrorist, and ANYONE who says different is guilty of promoting terrorism! 98.234.126.251 (talk) 10:54, 20 August 2009 (UTC)

But like I said, it's not a complete list. It doesn't list every single act of terror, and it's also an example of systemic bias, which Wikipedia does suffer from: islamic acts of terror get a lot of press as terrorism, whereas man other actions do not. But the principle is the same. As for the freedom fighter thing, do you really think that the methods and goals of the French Resistance are fundamentally different from the roadside bombs you see in Iraq? Or that there's a huge moral difference between funding and arming al-Qaida, or funding and arming the Nicaraguans and Afghans (as the United States happily did back in the day)? The US didn't mind the terrorism these groups perpetrated at the time, because it was directed at people they considered enemies, even though the Contras in Nicaragua -- trained, funded and armed by the CIA -- kidnapped and raped civilians, among other things. Moral relativism is absolutely a major factor in how we view these things. And like I said, I'm not saying that islamic terror isn't a problem, because obviously it is. I'm just saying the issue isn't simple, and neither are the actual terrorists' motivations. It's not just that they're religious fanatics, just like Christian abortion clinic bombings aren't only motivated by Christian beliefs. (That said, people organizing these actions are certainly taking advantage of them -- using them to facilitate the actual acts of violence.) -- Captain Disdain (talk) 11:23, 20 August 2009 (UTC)

Thank you, Captain Disdain, for verbosely explaining the issue. My earlier objection might not have got the point across (and I admit I didn't really phrase it very well), but I hope we've managed to enlighten a few readers. Ricin is one of many scary things that are easily available and capable of large-scale harm; it is a worry to anyone who enjoys peace and security that such things exist. But the threats to public safety do not, categorically, come from a specific religious community - statistics do not even support that idea. Especially in the case of ricin, which was covered thoroughly in our article, the groups who have historically used this poison to spread fear are categorically not foreign terrorists. This does not mean foreign militants are non-existant, nor that they will never use ricin in the future - but without specific evidence, "idle speculation" is equivalent to racial profiling. Nimur (talk) 15:29, 20 August 2009 (UTC)

haircuts

While brushing my palm over my gelled hair I noticed a very sharp sensation along my palm. There was however no blood. So now I'm curious -- are there any documented cases of hair cutting people, in a manner not unlike a paper cut? John Riemann Soong (talk) 19:35, 18 August 2009 (UTC)

Hair is essentially 1d while paper is essentially 2d. That added dimension can allow the paper to be both thin and stiff in certain situations. Hair would only be thin. With the aid of gel, perhaps it could be both thin and stiff enough to cause a cut, but I am not aware of it causing cuts. I don't think that the medical community has gone to the effort of documenting such an unusual way to get a very minor injury, but it is possible. Googlemeister (talk) 19:45, 18 August 2009 (UTC)

Pilonidal sinus typically occurs in the natal cleft. However hairdressers are known to develop this on the hands. Axl ¤ [Talk] 20:02, 18 August 2009 (UTC)

Yes, a barber I know told me she can get painfully poked by freshly cut hair, especially that of Oriental men, who have thicker hair follicles than most of the rest of us. A recently shaved head or buzz-cut can also present hairs that are standing upright, in prime poking position. So, if you give hair-cuts to Asian Marines, you'd best wear some thick gloves. StuRat (talk) 20:39, 18 August 2009 (UTC)

Plus as any man who hasn't shaved for a day or two (or for some poor folks if they shaved in the morning) will attest - their wife/partner's complaints of their face being "prickly" and "scratchy" have a point. Certainly my facial-hair feels scratchy enough to graze (if not cut someone). 194.221.133.226 (talk) 09:06, 19 August 2009 (UTC)

Hair can definitely cut you, or at least cut into you. Facial hair tends to be thicker and sturdier than the hair on your head (mine certainly is!), but even the latter can be surprisingly sharp under the right circumstances, soft as it is! Here comes the anecdotal evidence: I generally cut my own hair with a hair trimmer, which obviously results in a lot of short little hairs since I do it pretty regularly to keep it neat. I generally do this in the shower (though not during a shower, for reason which I hope to be obvious!), and I usually just scoop the hair up from the bottom with a damp piece of tissue. Of course, I don't quite get all of it, but a few stray hairs aren't going to clog up the drain the way a huge clump of them might. As a result, it's not unusual for me to encounter a surprisingly sharp pain in a toe a day or two later: there'll be a single, thin piece of hair sticking up from it. It's no big deal; once I pluck it out, the pain's gone, but I was pretty surprised to see how deep those things can go, and how sharp the sensation can be even though it's just a single, very thin piece of hair I've managed to step on. There's never been any blood I could see, but I wouldn't be surprised to find some one day. -- Captain Disdain (talk) 12:52, 19 August 2009 (UTC)

Locked in syndrome

Can a person with Locked-in syndrome obtain an erection?????? —Preceding unsigned comment added by 79.146.163.233 (talk) 19:58, 18 August 2009 (UTC)

I don't see why not. An erection is largely an autonomic response and does not require conscious muscle control. --Jayron32 20:46, 18 August 2009 (UTC)

What is "Real" Speed of Electricity?

Ever since i've learnt first time about electricity; i've imagined electricity having speed similar to light. Recently i've come into contact of an wikipedia article about speed of electricity which states that electrons in a conductor flow very slowly. But this information contradicts with some practical observations; which i'll state below. In case of Lightning electron travels from its source(few km above ground) to the ground at a flash; which gives hints how fast electrons are. Someone may argue in this case the flow of electron is not continious rather than a single splash. To convince them i'll present my second observation. Consider the case of a TV or computer monitor; these electronic components show picture by directing electron beam towards a photosensative plate. Here electrons emitted from negative terminal struck to positive terminal(photosensative plate) very fast. To continue this flow of electron the electrons must have to flow quickly inside conductor of positive & negative terminals otherwise the potential difference between them will continue to rise. So is there any satisfactory explaination of slow speed of electron through conductor(as claimed in wikipedia article)? —Preceding unsigned comment added by Shamiul (talk • contribs) 21:08, 18 August 2009 (UTC)

In a wire the actual electrical principle is transferred by spin alignment in nearby electrons (this is a gross simplification and I expect to be told off for saying it) - eg similar to how bar magnets in a row would align. Thus the electron does not need to travel at all for electrical power to be transmitted. Let me set your mind at rest on that issue. The second part about experimental determination of electron drift speed I cannot answer.83.100.250.79 (talk) 21:40, 18 August 2009 (UTC)

Also note that in a cathode ray tube the electrons travel in a vacuum - which is different from a wire - also in this case they must travel through the medium since they cannot transmit the electrical signal by influencing nearby electrons (there are no nearby electrons in CRT), this is different from the case in the wire.83.100.250.79 (talk) 21:44, 18 August 2009 (UTC)

(more) Also it's worth noting that in lightning or a CRT the field strength is very high eg 1000V per meter - classically the force on a charged particle is proportional to the field strength - thus in these cases the electrons would be expected to accerelate (and by extension move) very quickly. However in a wire (of low resistance) the field strength is very low eg 1V/m -so the electrons would be expected to move much more slowly from a classical perspecctive. 83.100.250.79 (talk) 22:18, 18 August 2009 (UTC)

The speed of electrical energy and the speed of electrons are two different things. Electrons can move at any speed from zero to the speed of light, more or less. In matter they tend to move with a slow average speed, because they keep bouncing off atoms, but in a vacuum like that inside a cathode ray tube, they can move at close to the speed of light. Electrical energy, on the other hand, is transmitted by photons, which move at the speed of light, because they are light.

How can we prove that electrons move slowly in matter? I don't know of a direct experiment to prove this, but it follows from mathematics. A current is a flow of electrons. One ampere equals one coulomb of charge per second. We know how many electrons it takes to make one coulomb, and we know how many electrons are in a given volume of matter (like a piece of wire), so we can calculate how fast the electrons must be moving to carry that coulomb past a given point in one second. This speed turns out to be very slow.

The reason that an electrical signal moves faster than electrons is that the signal is carried by photons, not by electrons. All the electrons along the entire current path (such as a long wire) start moving at almost the same time, because the electric field that makes them move is carried by photons. -Heron (talk) 21:49, 18 August 2009 (UTC)

I think what you are referring to is the drift speed of electrons. This is far less then the speed of light.66.133.202.209 (talk) 22:50, 18 August 2009 (UTC)

According to drift velocity: In a 1mm wire, with a current of three amps - the electrons are moving at about one meter per hour.

The way to understand how this works is to imagine a 20 foot long, 2" diameter pipe, completely full of ping pong balls. If you take another ball and paint it red and push it into one end of the pipe, another ball will pop out of the far end almost instantly. The speed of "pingpong-current" is very fast indeed - if the balls were stiff enough, it could even get close to the speed of light! However, if you continue to shove more balls into the pipe, it'll be many minutes before the red ball pops out of the far end. The speed of a pingpong ball in this system is really slow!

When you flip on a light switch, you start (very slowly) pushing electrons down one of the wires - electrons start popping out of the other end almost instantly - but the time for a particular electron to get from one end of the wire to the other is measured in hours to days!

SteveBaker (talk) 23:32, 18 August 2009 (UTC)

Or with AC electricity they don't move at all.Dacium (talk) 00:18, 19 August 2009 (UTC)

There is an article Drift velocity which shows how the drift velocity (if it exists) can be estimated. To my knowledge calculations of this type have a primary function of testing higher grade schoolchildren's ability to apply maths to physically abstract problems, and as such the 'drift velocity of an electron' is a common topic in school physics textbooks. However in my electrical experience I've never encountered a situation where this derived quantity was useful or necessary to the solution of a real world problem.

However it is still of interest - particularily in extension to the calculation of the movement of ions in a solution - such as when doing electroplating. In this case the net drift velocity can be correlated to the extent of electroplating - in fact the mass change over time on an electroplated substrate can be used to derive/calculate the average velocity of the ions.83.100.250.79 (talk) 23:36, 18 August 2009 (UTC)

The electrons move slowly, but the transfer of energy happens extremely quickly (near the speed of light). Imagine a pipe filled with water, if you put some water in one end, some water will pop out the other end straight away. You can imagine the same thing with electrons, an electron goes in one end and another one is instantly forced out the other end, the propogation of this force is near the speed of light.

In A CRT a high voltage field accelerates electrons from a very slow speed to a very high speed, and they are only able to travel at high speed because they are essentially in a vaccum and not in a metal. Just because they are travelling fast in one part of the circuit does not mean the electrons are not flowing in a closed circuit - they are still flowing, slowly in the metal, then fast in the air, the net amount leaving/returning at any point is still the same. Remember also that in AC electricity, the electrons don't 'flow' at all, they just sit there and vibrate. Its the electroncs fields pushing on each other that is 'electricity' not the electrons themselves. Lighting is similair but again different. No electron from the top of the strike is likely to end up at earth, each electron pushes on the next one below it, some will get free of atoms and be under such high voltage fields that they will breifely fly at very high speeds between atoms, even large numbers of atoms, all this combined causes the lighting strike in a cascade effect.

Also, If you apply a voltage to piece of metal at one end only, a tiny amount of electrons will be pulled from it, but metals have such a huge amount of electrons that it would take millions of volts to pull all the electrons from even a tiny peice of metal, this is why metals are such good conductors, because you can't pull all the electrons off the metal, so if you let the metal pull electrons into itself (by connecting the other end of the metal to the other voltage) you can easily make electrons flow, but they do so extremely slowly.Dacium (talk) 00:18, 19 August 2009 (UTC)

(restore comment removed by vandal 83.100.250.79) "Electricity" can flow much faster than the electron drift. The electrons in the power cord of an AC appliance may move back and forth very slowly and a short distance, 50 or 60 times per second, Lightning ionizes the atoms of the gasses in the air. The lightning impulse travels from earth to cloud or from cloud to earth faster than the individual electrons. A CRT does have an electron beam. The voltage gradient might be 30 kv over a fraction of a meter. Edison (talk) 04:23, 19 August 2009 (UTC)

Genome Studies

Is linkage analysis or genome-wide association studies one of the better and efficient approaches to identifying genome expressions or is there a better technique? —Preceding unsigned comment added by 71.143.156.160 (talk) 21:15, 18 August 2009 (UTC)

You might want to clarify what you mean by "genome expressions". If you are referring to the transcriptional "expression" of genes, neither of these techniques would be particularly helpful. Linkage analysis and genome-wide association studies are usually for making causal inferences between genes and specific phenotypes (for example: gene "X" is involved in the regulation of phenotype "Y") but they don't give information about how, when, and why a gene is transcribed. Instead you'd want to look into a cDNA microarray used for gene expression profiling, which can tell you the genes that are expressed in a given biological sample under a particular set of conditions. --- Medical geneticist (talk) 01:02, 19 August 2009 (UTC)

Species population

Is there a species whose population is similar to humans (6.7 billion)? I have been reading articles on world's most endangered species and it would be interesting to create a list comparing species by world population. --Kvasir (talk) 21:18, 18 August 2009 (UTC)

Well, German cockroach population is prob'ly in the trillions or even quadrillions. Same for many other insect species I'm sure (like ants, termites, houseflies, moskeeters, lice, aphids, etc., etc.) Note also that many of those species are harmful to humans (but that's a whole different topic). 98.234.126.251 (talk) 09:41, 19 August 2009 (UTC)

The closest I know is the chicken. Six for every human according to QI; our article says 24 billion six years ago; it's still not on the same order of magnitude either way. Vimescarrot (talk) 10:25, 19 August 2009 (UTC)

There are estimated 1.3 billion cattle, so that is also same order of magnitude (though off in the other direction) Googlemeister (talk) 13:20, 19 August 2009 (UTC)

I actually wrote a response to this question a few days ago but did not post it because, after re-reading it, I found that it didn't answer the question. All of the above responses similarly do not answer the question -- what does the German cockroach have to do with this question? The majority of insect populations are in gross excess of 6.7 billion. And to respond with organism populations that merely possess calculable order of magnitudes, how does that answer this question? DRosenbach ^{(Talk | Contribs)} 15:34, 19 August 2009 (UTC)

Well, if I can provide an answer in the same order of magnitude, and no-one can come up with a closer match, then as far as our ability to answer goes, I've won the "most similar" contest. On that basis the chicken and cattle answers seem to be entirely apropos. --Tagishsimon (talk) 15:38, 19 August 2009 (UTC)

Let's put it this way then. Of the estimated 1 million + animal species on this planet, it is likely that there is one or more with a population similar to that of humans (how similar is similar?). Locating an exact species that fits this criteria would be time consuming (if it is indeed possible) so myself & VC have provided familiar species that are within an order of magnitude. Googlemeister (talk) 15:44, 19 August 2009 (UTC)

Realistically - chickens and cattle 'bracket' the human population numbers quite nicely. For tiny animals like insects, the numbers are either insanely too large (eg ants, roaches) - or if the insects are rare or endangered, far too small. Probably there is some relatively obscure insect with the right population - but finding it would be impossible. We just don't keep track of insect populations that closely. For larger animals, it's likely that rats and mice have us way outnumbered - for most other large species, they're not going to come close to our numbers unless they are domesticated...and even if they might be comparable (maybe rabbits or something) - those kinds of populations can't possibly be counted - we have to estimate them, and the error in that estimation could easily be a factor of 5 or 10 - which would make them no better as examples than chickens and cose. Which brings us back to things like cats and dogs, pigs, chickens and cows that we could probably estimate fairly accurately...maybe to within a factor or two or three. There actually aren't many species that we have domesticated in enough numbers - so the answer is never going to be all that close - an order of magnitude is actually pretty good, all things considered. I'm certain that there is no closer candidate that we know with as much certainty. IMHO, our best possible answer is "Cows". SteveBaker (talk) 18:48, 19 August 2009 (UTC)

Thank you all for attempting to answer this very difficult question. I just thought someone might have already did a survey like this. I would imagine a species on the IUCN Least Concern list would be a good place to start if there are domesticated animals there. The list usually post estimated population as part of the assessment. I think the order of magnitude would be a good place to aim at. I agree, domesticated animals is a good place to start and the IUCN's assessment would be a good authoritative population estimate. Thanks. --Kvasir (talk) 21:40, 19 August 2009 (UTC)

Then of course you have to ask yourself if "population of individuals" is actually the relevant factor here, I would consider a million humans to be less "endangered" then a million ants, ignoring our obvious self centeredness. Putting it another way, if there were only 6.7 billion ants in the world, they would probably be quite rare. Another method perhaps more relevant for measuring species "success of propagation" is Biomass_(ecology). In which case, as it turns out, cattle also turns out to be a decent match to humans (156 to 100 millions of tons respectively) , a bit better then chickens anyway (15 to 100) . ( Vespine (talk) 23:38, 19 August 2009 (UTC)

Tundra Climates

Does tundra climates places the latitudes lies obetween 70 and 90 shade in blue on map get warmer than 60 deg F on summer times? The summer is only short only few months.--69.229.39.33 (talk) 21:20, 18 August 2009 (UTC)

Well, from what I know, Murmansk can get warmer than 15 C in the summer on occasion, but then it's got a warm current warming it up quite a bit. (It's hard to believe, but it's warmer in Murmansk beyond the Arctic Circle than in Arkangel further south on the White Sea.) FWIW 98.234.126.251 (talk) 09:32, 19 August 2009 (UTC)

Some arctic and antarctic regions can get remarkably warm in the brief summer. Even though the Sun may be at a low angle, you can still get sunlight 24 hours a day, if above the arctic circle or below the antarctic circle. The Gulf stream and similar currents can warm coastal areas, and, conversely, hot air blown up from the south over a continent can bring warm air that way. So, there are two trends in the tundra, it is colder, on average, but also the range of temps is wider than in the tropics. The result is that it gets much colder in winter there, but can sometimes get almost as warm as temperate regions in the summer. If we plot the temp range for temperate climates as asterisks (*) and the temp range for the tundra as dots (.), you can see that both are sinusoidal, but the magnitude is higher in the tundra and the average is lower:

  ^
  |      ***         ***
T |    *  .  *     *  .  *
E | **  .   .  ***  .   .  *** <- temperate zone
M |    .     .     .     .
P |  .          .           .  <- tundra
  |
  +---------------------------->
     W    S     W     S      W
             SEASON

StuRat (talk) 13:34, 20 August 2009 (UTC)

Longitude per mile

If one degree is away from Greenwich then how many miles is 1 E or W? For latitude 1 away from equator is 69 miles.--69.229.39.33 (talk) 22:44, 18 August 2009 (UTC)

Miles per degree longitude depends on what latitude you’re at. Roughly,

Miles per degree longitude = 69 cos(latitude)

Red Act (talk) 22:58, 18 August 2009 (UTC)

So if you're talking a position 1° east or west of Greenwich, London, England, that's at about latitude 51.48°, so the answer is that it's aobut 43 miles away. --Anonymous, 00:18 UTC, August 19, 2009.

Are miles per degree of latitude dependent on your latitude, or is that constant? Googlemeister (talk) 13:16, 19 August 2009 (UTC)

There's just a small variation, about 1% between poles and equator, due to the Earth not being spherical. See Latitude#Degree length. --Anonymous, 15:05 UTC, August 19, 2009.

Hence why on flat maps, they get severely distorted when near the poles. Googlemeister (talk) 18:46, 19 August 2009 (UTC)

Actually, no. The inaccuracies of various map projections have nothing to do with the latitude discrepancy; rather, they usually stem from longitude's properties. — Lomn 20:10, 19 August 2009 (UTC)

Yes, to compare with the 1% variation due to the Earth not being round, there is also a 100% variation due to your latitude. That is, you move something like 67 miles by going 1° east or west at the equator, and move no distance at all by going 1° east or west at either pole. StuRat (talk) 13:10, 20 August 2009 (UTC)

What I mean is that while you only have a 1% change in the latitude scale over the 0-90 deg range, your longitude changes from 69 miles all the way down to 0, so when you get near the poles, you are getting distortions of 20 to 1 or even greater. Googlemeister (talk) 13:26, 20 August 2009 (UTC)

plate tectonics

Do all the plates move in same exact speed or some plates moves in a slower or faster speed? Do small plates moves faster or bigger plates moves faster.--69.229.39.33 (talk) 22:45, 18 August 2009 (UTC)

I don't think the plates all move at the exact same speed, but there are prob'ly many other factors besides size. FWiW 98.234.126.251 (talk) 22:50, 18 August 2009 (UTC)

That's wierd I thought I posted a reply to this question. Anyway according to this linkthey aren't. There are some tables down below. Remember the whole point of plate tectonics is that the plates are fractured and seperate so naturally they should move at different speeds (I'm assuming from the differential heating and cooling and the forces other plates exert on them (along plate boundaries)66.133.202.209 (talk) 23:41, 18 August 2009 (UTC)

The plates move at very different speeds. Plates attached to subducting slabs (subucting tectonic plates) typically move much faster than those surrounded by passive margins (like around the Mid-Atlantic Ridge). Where there is a slab, it is like holding a rug partway off a table: the weight of the portion of the rug off the table works to pull the rest of the rug forwards and off of the table. Where there isn't a slab, this very strong driving force is not available and the plates move more slowly. 66.133.202.209 above is partially right, but the guess isn't quite right. Interactions along plate boundaries are important, but much of plate motion comes from their coupling with the mantle.

Also, in representations of tectonic plate motions, some point must be set as the reference, so all velocities will be relative to that plate's velocity. But that's more of a data referencing issue than a science issue. Awickert (talk) 20:19, 19 August 2009 (UTC)

August 19

Paternal and maternal genes

Human cells have 46 chromosomes that can be divided into 23 homologous chromosome pairs ( a maternal and a paternal copy of each chromosome ). My question: is that means the maternal and paternal chromosomes are completely seperate from each other or is it mixed. For example if we assumed that both the eye color gene and the hair color gene are both on the chromosome pair number 5, is it always that the maternal copy of both genes are in one chromosome and the paternal copy in the other chromosome (i.e. seperate) or it is possible that one chromosome contain a paternal eye color gene and a maternal hair color gene (i.e. mixed). Dy yol (talk) 00:15, 19 August 2009 (UTC)

I don't think they can become mixed in regular cells (although I'm not 100% sure). I do know they can be mixed in gametes by chromosomal crossover, so (to use your example) your children may receive a combination of eye and hair colour genes from you that neither of your parents had, taking one gene from each of them. (Hair and eye colour involve more than one gene each, but it is only an example!) --Tango (talk) 00:21, 19 August 2009 (UTC)

I didn't think that eye color would be a sex-dependent trait. It shouldn't matter because you don't know whether, say, the father's gene comes from his father or mother (paternal grandpa or grandma). 98.14.222.41 (talk) 01:18, 19 August 2009 (UTC)

I don't think either I or the OP mentioned sex-dependent traits... --Tango (talk) 01:31, 19 August 2009 (UTC)

Chromosomes are independent entities, so what you get is what remains forever. Now that's not true for your offspring because, as brought up by Tango, crossing-over can and does occur -- but that's only on the metaphase plate during meiosis, not mitosis. Well...this was actually a question of mine during college, could crossing over occur during mitosis as well? Since homologous chromosomes do not line up together during mitosis, any crossing over between sister chromatids during mitosis would produce a genotypically and phenotypically identical result to what would have been had crossing over not occurred. Anyway, the only way for maternal and paternal chromosomes to swap would be when they are aligned, and that only occurs during meiosis -- so no, maternal and paternal copies cannot and do not mix. DRosenbach ^{(Talk | Contribs)} 02:32, 19 August 2009 (UTC)

I'm getting seriously confused. I post replies and they don't show up so I have to repost them. Anyway; some people think otherwise66.133.202.209 (talk) 03:30, 19 August 2009 (UTC)

DRosenbach is giving you the information that my high-school textbook has for crossing over: only in meiosis. But the truth is more complex: Mitotic crossing over for sure happens in mammalian cells, even if it is rare (and it's unnecessary, from an evolutionary point of view, because the genetic changes will not be inherited by the offspring, even if they are beneficial). Have a look at the NCBI page above that has an example with flies. The mechanism is not completely understood, but it seems that under some conditions, chromosomes (perhaps by chance) pair during mitosis and can then cross over. There are even some species of fungi that have lost meiosis in their evolution and use mitotic recombination as a way to increase the genetic diversity. But to put it into perspective: In humans, it is a very rare event, and in most cases it might not have phenotypic consequences (because it doesn't matter for most genes on what copy of the chromosome they are located, and/or because only few cells are affected). --TheMaster17 (talk) 08:43, 19 August 2009 (UTC)

To respond as a purist in a precisely absolute manner, I wouldn't say that maternal vs. paternal chromosome location does not matter. Genetic microdeletion disorders, such as in Prader-Willi and Angelman syndromes, occur as separate and distinct disorders, despite resulting from identical genetic disturbances -- the latter resulting from disturbance on the maternally-derived chromosome 15, whereas the former relates to the same on paternally-derived chromosome 15. DRosenbach ^{(Talk | Contribs)} 15:41, 19 August 2009 (UTC)

TheMaster17 did say "most". --Tango (talk) 17:44, 19 August 2009 (UTC)

And TheRosenbach was only responding as a purist :) DRosenbach ^{(Talk | Contribs)} 23:21, 19 August 2009 (UTC)

Only about 1% of genes are imprinted, so both "TheMaster" and "TheRosenbach" are technically correct. --- Medical geneticist (talk) 00:24, 20 August 2009 (UTC)

Oh, yes, I don't dispute either claims, it's the way DRosenbach presented the claims as if they contradicted TheMaster17's that I object to. It is a strawman argument. I would have preferred something like "Yes, that's true, but it is worth noting that for some genes it can make a very big difference which chromosome they are on. For example...". --Tango (talk) 01:41, 20 August 2009 (UTC)

(unindent)DRosenbach might be correct in saying that there are some genes for which it is important which copy(silent/expressed) is disrupted by a genetic event, but this was totally not the topic of my post or this question. We are talking about crossing over, which does not normally disrupt genes, just swaps them between sister chromosomes. And as epigenetic silencing by methylation (which imprinting is a special case of) of genes is inheritable through subsequent cell divisions, I cannot see how swapping the two copies would change anything in their imprinting pattern, as this would be swapped as well, together with the DNA. The special cases I was thinking of, where the exact chromosome would matter, were things like: Allele A on the maternal chromosome is controlled by promotor A and enhancers A,B,C. Allele a on the paternal chromosome is controlled by promotor a and enhancers a,b,c. A crossing over could now mix the different versions of alleles, promotors and enhancers (for example: maternal: Allele A, promotor A, enhancers A,b,c; paternal: Allele a, promotor a, enhancers a,B,C), leading to different expression levels of the different versions of the gene; more so, because promotors and enhancers do not always interact linearly. Or one of the promotors/enhancers could have a binding site for a transcription factor that the other doesn't have, totally changing the regulation of the alleles. But as I stated: these are very special cases (btw: it's the same reason why meiotic crossing over can change gene expression, but mostly leads to subtle changes), and they would only affect the daughter cells of the cell in which the mitotic crossing over happened, limiting the effect on the organism. There are special events in tumours which are supposed to involve mitotic crossing over, but I know of no direct phenotype caused by mitotic crossing over in humans. --TheMaster17 (talk) 08:36, 20 August 2009 (UTC)

Carbon sequestration by farming bamboo

Has there been any proposal for sequestering atmospheric carbon by planting (farming) bamboo? Bamboo being a fast growing plant, I wonder at what rate can carbon be removed from the atmosphere if the plant is farmed on a large scale. In the plan I have in mind, bamboo is cultivated artificially; harvested bamboo wood will be cut, compacted, and stored in underground mine caves. How well will this plan work? --98.114.146.89 (talk) 03:28, 19 August 2009 (UTC)

The google answer to your 1st question is yes. http://www.google.com/search?hl=en&q=Carbon+sequestration+bamboo&meta= Vespine (talk) 04:55, 19 August 2009 (UTC)

Why store the bamboo in underground mine caves? Why not use it, say, as a building material? I'm sure it would make a good reinforcing material for concrete, among other things. 98.234.126.251 (talk) 09:44, 19 August 2009 (UTC)

It's also now used, laminated, for wind mill rotors, or charred and used for soil improvement (see Biochar). But the problem is the sheer amount needed to counteract our CO2 emissions. We need to eliminate about 7 billion tons of Carbon per year to become Carbon-neutral. That's a lot of bamboo. --Stephan Schulz (talk) 12:29, 19 August 2009 (UTC)

As a point of comparison, only 784Million tons of corn and 600Million tons of rice are grown per year. (According to their WP articles.) APL (talk) 13:24, 19 August 2009 (UTC)

Quibble: Those numbers presumably only weigh the edible part (and the corncobs) and don't weigh all the rest, yes? Tempshill (talk) 17:08, 19 August 2009 (UTC)

I assume you are correct. But even if you multiply them by ten it's still a daunting comparison. APL (talk) 19:56, 19 August 2009 (UTC)

Why store it in underground mine caves? I know that bamboo is used for making furniture and as a flooring material. If it is widely accepted by consumers as an alternative to wood from trees, that'd be great. If not, you need to put a huge amount of it somewhere where it won't catch fire easily and turn back into atmospheric CO₂. Hence the idea. --98.114.146.89 (talk) 12:42, 19 August 2009 (UTC)

Couldn't you burn it underground without O2 and it would become charcoal and store the carbon that way? It would take less room and be more stable. Googlemeister (talk) 13:14, 19 August 2009 (UTC)

Burn without O2? How? Dauto (talk) 17:41, 19 August 2009 (UTC)

Well technically it isn't "burning". The process is called pyrolysis. You would need a heat source of course, but if your mine is really deep, you will get that for free. Googlemeister (talk) 18:13, 19 August 2009 (UTC)

100 years from now how much of that furniture would still be intact and not rotting in a landfill or used as firewood? 200 years? 1,000 years? Carbon sequestering has to be long-term or its not worth doing. APL (talk) 13:24, 19 August 2009 (UTC)

Removing millions of tons of carbon from the atmosphere for 200 years sounds worthwhile to me. You really don't think doing so for 1,000 years sounds worthwhile? (Aside from the bamboo proposal) Tempshill (talk) 17:08, 19 August 2009 (UTC)

Bamboo might not be the best plant for the purpose, at least not everywhere. It converts CO2 to biomass faster than any other plant, but it seems to be difficult to get it to grow vigorously in lots of climates. In lots of places growing trees and then burying them might work better; in other places growing weeds might be best. In any case, I personally believe this idea should get a lot more attention than it has so far. Currently the biggest difficulty is that even with massive economies of scale it's hard for the grow-plants-and-bury-them solution to reach prices below $100 per ton of carbon, but carbon credits trade on the exchanges at less than 1/10 that price. Looie496 (talk) 15:58, 19 August 2009 (UTC)

Bamboo gains height amazingly quickly - but having recently hacked down a minor forest of the stuff growing alongside the driveway of my house - I can tell you that it's mostly air! The stems are of course completely hollow and the leaves are pretty thin and skimpy. I doubt that they lock up as much mass as some plants that you'd think of as slower growing.

But in any case, to 'sequester' CO2, you have to harvest the bamboo and store it someplace where it won't ever decompose - if it's used for anything or burned or just left to rot, the CO2 will escape again.

If you form a mental picture of a 3 mile long coal train trundling into a power station (and they'll do that two or three times a DAY for a large power station) - and then imagine that same train trundling back out again, laden with freshly cut bamboo - you can tell that the acreage/manpower/machinery needed to keep those trains fully laden would be truly immense. The amount of energy required to cut and haul the stuff over all of that area and then to bury it somewhere (like in a coal mine) would be horrifying! Then realise that the amount of CO2 produced by a rail car full of coal is much heavier than the weight of the coal itself (because the coal is almost all carbon - and you're adding two oxygen atoms to every atom of carbon to turn it into CO2 and more atoms of hydrogen when you turn that into plant carbohydrates)...so for every trainload of coal you bring in - you need more than a trainload (by weight) of bamboo heading out again...and the volume of the bamboo (because it's full of air) is much MUCH bigger than the volume of coal...means that you need more bamboo trains than coal trains - and there isn't enough space in the coalmine to bury the stuff.

Suppose instead, you dispense with the coal train - and just cut the bamboo and feed it into the boilers of the power station. Now you have a closed loop system...all of the CO2 produced by the power station gets "recycled" into bamboo...which is burned by the power station...which produces CO2 that goes back into more bamboo. This is a fully sustainable model - you never run out of bamboo - you never run out of places to put the stuff. The ash from burning the bamboo should contain most of the minerals needed to fertilise the stuff. Furthermore, you have no more coal mines and no more coal trains...saving more pollution, energy, etc.

So why don't we have bamboo (or other plants) feeding power stations? Well, when you calculate the amount of land area you'd need to feed the USA's existing coal fired power stations with fast-growing-plant farms - the answer turns out to be about the area of the whole of North America! So this approach doesn't work either.

Bottom line is that using large plants of any kind to sequester the insane quantities of CO2 that we're generating simply won't work. The volume just isn't there. Even if there was, you'd be better off burning the plant material than the coal...but even that won't work. The reason we burn coal, oil and natural gas in the first place is because they are pure, concentrated biomass - they represent millions of years of carbon sequestration by plants. If you burn millions of years of sequestered carbon over a few hundred years - you can't expect plants to be able to reabsorb it all...you know it's got to take millions of years for that to happen.

SteveBaker (talk) 18:35, 19 August 2009 (UTC)

I have a picture in my head of an ancient human race burying huge quantities of trees saying, "This will solve the CO2 problem we have!" They die off and the pits with the trees in them turn into oil. Googlemeister (talk) 18:45, 19 August 2009 (UTC)

It was a trap! The dinosaurs intentionally sequestered all of this carbon knowing that it would form an irresistible fuel source to the civilization that would one day be built by the mammals that were even then starting to gain numbers. Now we're starting to turn the global climate back into a dinosaur friendly one, triggering a second age of dinosaurs. I tell you, those lizards had tremendous foresight. APL (talk) 19:22, 19 August 2009 (UTC)

History of atmospheric carbon dioxide concentrations as directly measured at Mauna Loa, Hawaii

We don't really need to take the carbon out of circulation forever -- if we can take it away for 100 years, we'll have enough time to get a handle on the problem. I've seen calculations showing that burying plant matter 10 feet underground is enough to accomplish that. If you look at the CO2 curve, you see a quite substantial yearly oscillation superimposed on the secular trend. That oscillation is believed to result from yearly plant growth and decay in the northern hemisphere. If we could remove just one or two percent of the annual plant growth from the system, it would go a long way toward solving our problem. Looie496 (talk) 19:18, 19 August 2009 (UTC)

I don't understand how that chart supports your contention that 100 year carbon sequestering would have a long-term impact. It seems to show that the annual variation is irrelevant to the overall trend, which I think is the opposite of what you were trying to say. Do you have a cite? APL (talk) 19:29, 19 August 2009 (UTC)

My apologies, I mixed two points in one paragraph, thereby violating the rules of good writing. The chart has no relation to 100 year sequestering, its point is just to show that the effects of plant growth on atmospheric CO2 levels are large enough to make it worthwhile trying to exploit them. My source for the point re 100 year sequestering is this paper, which drew some attention last year. Looie496 (talk) 21:51, 19 August 2009 (UTC)

What a 100 year sequestering would do would be to borrow from the future - and hand our grandkids a problem WAY harder than the one we're trying to solve. When those plants break down and return their CO2 to the atmosphere - it'll dump OUR CO2 into THEIR atmosphere. But a 1 or 2% change is hopeless - we need something like an 80% reduction. I don't see where this percentage gain comes from anyway - the graph you posted clearly shows that the annual variation in CO2 levels due to the absorption of CO2 by all of the plants across the entire planet is about the same as 3 years of human-induced atmospheric CO2 growth...that's easy to see - right? So to cut our emissions by 1%, we'd have to bury one third of one percent of all plantlife production across the entire planet! Do you have ANY conception of how many plants that is?! The idea of deforesting (and de-grassing and de-marine-planktoning) one third of a percent of the earth's surface...a third of the area of the USA...every single year...wow! SteveBaker (talk) 01:53, 20 August 2009 (UTC)

Borrowing from the future seems reasonable to me. We're still developing low-carbon technology and moving towards a low-carbon (I can't see us being sustainably carbon neutral, but that isn't really required) economy. In 100 years (if we get our acts together) we should have all those technologies and lifestyle changes and will be able to handle the stored CO2 being released then. The problem we face isn't really getting an 80% reduction, it is getting an 80% reduction quickly enough to minimise damage. That said, even if sequestering 1-2% of plant growth a year would be enough to make a big difference, that is an absolutely enormous amount of biomatter to store. If Steve's estimates (which I haven't checked) are correct and we need to store a third, it is definitely impossible - what would all the animals eat? We would have to increase plant growth by 1/3 and store that extra growth, and I can't see where we would grow those plants. Ocean algae might be an option, but I have no idea where you would store it. --Tango (talk) 02:11, 20 August 2009 (UTC)

Well, some in the oil industry inject CO2 into oil wells to facilitate better oil flow. Logically then, we should be able to inject a large amount of CO2 into empty natural gas caverns which we then cap? I don't know how many tons we could stash doing that, but it might be pretty significant. Googlemeister (talk) 13:22, 20 August 2009 (UTC)

You have to get the CO2 out of the atmosphere first. --Tango (talk) 13:43, 20 August 2009 (UTC)

parabola

Why does a jet of water under the influence of gravity adopt the shape of a parabola? I know why a single drop of water would, but a single drop of water is not the same thing as a continuous jet of water, where the centre of mass doesn't move. —Preceding unsigned comment added by 76.69.240.190 (talk) 04:04, 19 August 2009 (UTC)

Water in a stream is only "held together" by Surface tension which is fairly weak. Each "piece" of the water, whether a droplet or part of a stream will still be affected by gravity the same way. The only thing that makes it a stream is that there is enough water all travelling in a similar enough direction with a similar enough velocity so as the surface tension prevents it from flying apart. You can see this when a stream isn't "quite" enough in the same direction and it starts as a continuous stream but after a while breaks up, this can also be caused by turbulence and wind and anything else which moves the "droplets" enough apart for surface tension to be overcome. Vespine (talk) 04:12, 19 August 2009 (UTC)

When I watch streams of water from fountains they always seem to start breaking up almost exactly at the peak, any idea why that would be? --Tango (talk) 05:03, 19 August 2009 (UTC)

The slower the water is moving, the thicker the stream has to be to accommodate the same rate of water. As it reaches the peak and slows down, the water is basically running into itself a little bit which perturbs some bits of it from the uniform parabola trajectory. In addition, as the water speeds up again on the way down and the steam becomes less dense, the surface tension probably plays some role in pulling it into separate beads rather than stretching out into a narrower but continuous stream. Rckrone (talk) 05:41, 19 August 2009 (UTC)

I think the key word actually is "seem". If you photograph the rising jet of a fountain, you often find that what looked like a continuous stream of water actually consisted of drops close together. See this one, for example. It's breaking into drops very soon after leaving the jets. --Anonymous, 06:03 UTC, August 19, 2009.

There's a kind of fountain we have at our melbourne casino which is all fancy and computer controlled, it shoots powerful coherent and consistent streams of water into the air, which travel along a predictable path and land in the same spot every time. It's like a "water display" rather then a fountain. All the water in each stream is shot in a very controlled way at the same velocity and direction. This creates quite a striking effect since the water jet stops well before the leading edge of the water has hit the ground, o for a while you have what looks like a straight cable of water almost sailing trough the air. So it's at least possible to keep the water from breaking up noticably. I've tried a few googles and i can't find any pictures or what it might be called. Vespine (talk) 06:50, 19 August 2009 (UTC)

Those are the kind of fountains I'm talking about. [25] There are some. --Tango (talk) 18:05, 19 August 2009 (UTC)

(EC)Why does a jet of water not equal a stream of drops of water? Edison (talk) 04:13, 19 August 2009 (UTC)

The assertion that the "center of mass" doesn't move is completely wrong. There is a constant mass flux; and the center of mass must include the water which accumulates on the other end of the jet. The center of mass argument really doesn't even have anything to do with the effect of gravity though - consider a hanging rope - it takes a Catenary shape, even if the center of mass is truly stationary. Gravity is still present, and it exerts a force on each particle of water in the stream, whether that particle of water is moving or stationary. Nimur (talk) 06:50, 19 August 2009 (UTC)

By the way the fountains where the water looks like a pipe, that's called laminar flow and its use was pioneered by WET Design. Dmcq (talk) 09:05, 19 August 2009 (UTC)

The Mythbusters have tried on several occasions to get a jet of water to conduct electricity - which would require a continuous stream - and they've always had a hell of a hard time getting that to work. The reason being that very often, what LOOKS like a continuous stream is actually a broken up series of droplets. I think that what our senses tell us about "continuous" streams of liquid is very often wrong. SteveBaker (talk) 17:45, 19 August 2009 (UTC)

(outdent) Even if the stream is truly continuous, and not just a bunch of little droplets, there will be a parabola. This is because the viscosity of water and its surface tension are generally incapable of supporting its own weight. Because of this, the water is effectively detached from all of the adjoining water in the stream, and can move as a parabola as it wishes. A $2 experiment in how a high-viscosity fluid does not make a parabola would be to quickly squeeze a tube of toothpaste. The higher viscosity of the toothpaste will (at least for some time) allow it to be straighter than the jet of water. In this case, the cohesion due to the higher viscosity will create a shape whose solution requires not only the acceleration on the individual particle, but how that particle's weight affects the portions of the stream around it.

So the bottom line is that if it is low viscosity, it will move as an idealized stream of fluid with no significant interactions. If it is high viscosity, the parcels of fluid will interact, and this makes the calculation of the shape more complicated. Awickert (talk) 23:35, 19 August 2009 (UTC)

hi

someone answer my question —Preceding unsigned comment added by 74.65.3.30 (talk) 05:50, 19 August 2009 (UTC)

I presume you’re referring to your most recent question on the Science reference desk, the suppository question that you asked two days ago? It’s kind of a difficult question to answer, since it isn’t possible to go back to the 90’s and check out the various brands of suppositories that were available back then. The reference desk volunteers can’t always figure everything out for sure. It’s looking like the glycerin capsule hypothesis is likely to be the best guess that anyone here can come up with. In particular, maybe the tin of suppositories got hot, which melted the glycerin capsules? It’s just a guess, but guesses are likely to be the best that anyone here will be able to provide for you in this case. Sorry. Red Act (talk) 06:30, 19 August 2009 (UTC)

The people who answer questions here do it for fun. Treating us like servants takes all the fun out of it. Regards, Looie496 (talk) 15:49, 19 August 2009 (UTC)

Everyone who is likely to be able to answer your question has already read it - and (presumably) decided they don't know how to answer it. Generally, if you don't get an answer in a few days, you'll never get one - no matter how many times you re-ask it. Sorry - but this desk is manned by a bunch of enthusiasts - there are no guarantees. SteveBaker (talk) 17:38, 19 August 2009 (UTC)

Recording live concerts with microphones

Would widely spaced video cameras with a good quality microphones at a live rock concert come close in fidelity and stereo reproduction to directly "plugging in" to the microphones/instruments of the bands I want to film? And in the case of directly "plugging in", what sort of skills, equipment and general hassle/extra equipment setup time are involved, bearing in mind that I am not a professional recording technician (or camera man for that matter?)Trevor Loughlin (talk) 08:00, 19 August 2009 (UTC)

You don't want them so widely spaced that they pick up the audience more than the music. If I were to record it, I'd actually patch right into the band's microphones and pick-ups from electric guitars and other instruments. Then I'd also have some microphones placed near the audience. Record them all onto different tracks so you can mix them later. Sometimes crowd noise is nice, other times it ruins everything, like if one person has a coughing fit during the quiet parts of Stairway to Heaven. StuRat (talk) 11:47, 19 August 2009 (UTC)

If you had two video cameras and each recorded the sound on its own, you would get monophonic souns. It would not be simple (if even possible) to combine the two separate sound recordings to get stereo, since they would not be adequately synchronized. If you could record 2 sound tracks on one camera, via a long cord, with the mic from one camera and the line out from the other camera, or a mic cord from the other camera, it would be stereophonic, but people would trip over the cord unless it was taped down. Edison (talk) 13:42, 19 August 2009 (UTC)

Per Edison & Sturat, there are issues associated with recording from within the crowd. As to recording from the sound mixer ... synchronisation may be the major issue here. The sound desk has input channels for each of the microphones & direct inputs from the band; typically these'll be mixed down to a couple of channels, being a stereo left & right. For practical purposes, you'll be limited to taking a stereo feed from the desk. It'll be mixed for the speakers in the auditorium and may not be the best mix for playback; but will always tend to be better than a crowd recording since it lacks the hacking cough of the person behind you. The desk feed will tend to lack crowd noise; you need to decide whether you want such noise in your film. If you can capture the feed from the desk into your camera; no problem. If you cannot, then you have the problem of synching an audio soundtrack onto the video. How you go forward depends in part on how much you can influence the engineering of the gig - can you get a feed, can you get crowd noise mixed in, &c. There are more complex ways of doing the job (to do with timecoding recordings, and separate mixing desks for the recording, but your post indicates you have limited experience, so we'll leave those to one side for now. --Tagishsimon (talk)

Certainly, if you can get it, take the mix out of the back of the mixing desk. If you need the crowd for a more "live" feel - then point another microphone from the stage out towards the crowd, record that separately and mix it in later. That lets you fade the crowd down during the music and bring it back up in the gaps between the music...or whatever you want to do. SteveBaker (talk) 17:34, 19 August 2009 (UTC)

Audience recordings don't sound anything like board tapes, but they are very listenable and they have their aficionados. You can do pretty well with a single video camera or portable stereo recorder. If you want to do better (it gets outside of my range of experience) you need real microphones with mic stands, from what everyone tells me. www.taperssection.com is a good discussion forum for all aspects of this stuff. 70.90.174.101 (talk) 00:55, 20 August 2009 (UTC)

I read some years ago about removing the crowd noise using a number of microphones, I think it was from Qunitiq, the math was fairly advanced with tensors and suchlike but I'm sure there must be software for that sort of thing by now. However using the microphones on the stage is the obvious way to go rather than trying to patch up afterwards. Dmcq (talk) 09:03, 20 August 2009 (UTC)

Just occurred to me the same sort of thing is probably what's used in MIMO, wireless with multiple antennae. If it can be done there at those frequencies it's got tobe possible with sound. Dmcq (talk) 09:14, 20 August 2009 (UTC)

At least I've sorted the cable tripping problem! http://www.fencerecords.com/beefboard/viewtopic.php?t=16931 —Preceding unsigned comment added by Trevor Loughlin (talk • contribs) 10:37, 20 August 2009 (UTC)

Instrument landing

A question for all the professional pilots here: What is the minimum cloud ceiling and visibility for an NDB landing approach? Also, how are the NDB landing procedures different from, say, those for a VOR landing approach (in which I'm very well briefed)? Assume a 15-knot crosswind blowing directly (or almost directly) across the runway. Thanks in advance! 98.234.126.251 (talk) 09:20, 19 August 2009 (UTC)

Teen years

What are the key differences between the early teen years (appx.13-14), mid teen years (appx.15-16) and late teen years (appx.17-19). Early and mid teens seem very similar and late teens seem similar to early 20s but yet they're teens. 86.138.238.2 (talk) 10:36, 19 August 2009 (UTC)

The stage in their education, their closeness to 'adulthood', the legal allowances. See Age of consent, Adolesence and the many links/pages within. 194.221.133.226 (talk) 11:17, 19 August 2009 (UTC)

Sorry but you need to be more specific with regard to what you are asking. Are you asking about the biological/physiological transitions during the teen period, social (as 194.221.133.226 pointed out in age of consent, but there will be others such as age of voting, drinking alcohol, etc.) or physchological?

Well it's the science desk, not the humanties or social law desk - so I would assume biological.

Good point, but it's sometimes easy to speculate that it has been posted in the wrong section. This reads like a psychology question, not a biological one. Hence my query. I suppose you could take out the social point, though. In any case, the main biological changes are related to varying regulation in hormones in the body, changes in growth patterns and in physiological changes such as development of pubic hair etc. Adolescence has more information. —Preceding unsigned comment added by 157.203.42.175 (talk) 12:32, 19 August 2009 (UTC)

I consider developmental psychology as a science, not humanities. Edison (talk) 13:39, 19 August 2009 (UTC)

The difference is - they are progressively older, and so progressively more adult.83.100.250.79 (talk) 12:28, 19 August 2009 (UTC)

Thank you for that profound insight - without careful, knowledgeable researchers such as yourself, I have no idea how the ref desk could function. SteveBaker (talk) 17:24, 19 August 2009 (UTC)

Early and mid teens seem very similar and late teens seem similar to early 20s but yet they're teens. Well, yes. Someone who is 18 is a lot closer to 20 than 15 or 13. The reason they are called a "teen" is because of the number - thirteen, nineteen, etc., and so has nothing to do with actual maturity. At any rate, to completely and utterly generalize and stereotype, 13 and 14 year olds are just beginning to mature, likely starting puberty, and are gaining some independence. 15 and 16 year olds continue the trend, with more responsibilities, more maturity, and usually starting to finish their growth spurt. People 17, 18, and 19 years of age tend to look forward more, and usually try to act more adult and mature, in terms of independence and decision-making, which is helped by finishing high school and maybe looking toward college. These are all subject to radical changes based on nationality, culture, and so on, in addition to my earlier disclaimer. ~ Amory (user • talk • contribs) 12:49, 19 August 2009 (UTC)

So, what is it that makes 17-19 year olds not adults psychologically (putting legal factors aside). 86.138.6.31 (talk) 15:04, 19 August 2009 (UTC)

Third molars will generally not erupt earlier than 18, although they may take until 21 or later to erupt, if they ever do. This would work for determining the dental-age of a patient. There is also the skeletal age, mental age and probably many other "ages" that different practitioners utilize. There are also sexual changes that occur, but I'll leave that for the endocrinologists. DRosenbach ^{(Talk | Contribs)} 15:46, 19 August 2009 (UTC)

These classifications are problematic as the variance between individuals is such that a trained psychologist could not reliably determine whether an individual was 19 years old or 20 years old despite that they are classified separately. At best, he could give a probability estimate, but he could not definitively state as a fact that the person in question is 19 or 20 based solely on observation. Googlemeister (talk) 15:51, 19 August 2009 (UTC)

It's a good question, and it's rather difficult to defend the legal stances in most countries that have a specific cutoff date: After that date, you're an adult; and before that date, you're legally a child. The answer is ostensibly "experience" but there's nothing to guarantee that any particular 20 year old has more life experience than any particular 16 year old. Tempshill (talk) 17:03, 19 August 2009 (UTC)

Here's a quick test: Be 17. Then, a few years later, be 20. There is a world of difference, even if your actual world hasn't changed much. Any 20 year old can see they are a complete world apart from a high school kid, especially mentally. Despite the painfully early onset of age-related deterioration at 27-30, the body is still developing into the 20s, and often to a fair degree after. That's where one of the arguments for a drinking age of 21 comes from. I (amusingly) call it the Pokémon effect: At low levels/ages, a difference of a level/year or two makes a difference (Level 5 Pidgy will beat a Level 3 Pidgy) but when you level-up/get older, the difference doesn't matter as much (L50 Charizard can lose to a L40 one). ~ Amory (user • talk • contribs) 01:51, 20 August 2009 (UTC)

• 13-14: Happy (many sources of wonder and amazement)
• 15-16: Excitable (many exciting girls)
• 17-19: Manic-depressive and quite insane (damn, I think my soul is broken)

I can only speak for myself of course. Vranak (talk) 16:34, 19 August 2009 (UTC)

This question is not going to have a satisfactory answer. There are few groups more heterogeneous than an age group. Anyone who deals with adolescents of a given age -- or is an adolescent -- will tell you there are vast differences among people of the same age. Hopefully, a given person will be more mature and experienced at 20 than at 17 and moreso at 17 than at 14. But everyone matures at different rates. For example, some girls get their first period at age 9; others not until age 15. If such a basic physical trait can happen at such widely varying ages, no doubt the same could be said for aspects of mental or emotional maturity. And it's not as simple as saying that someone matures at a given age. There are many aspects to both emotional and physical maturity. In some ways, I demonstrated "adult" sensibility when I was 12 or 13; in other ways, I acted childlike even when 19 or 20. I get particularly frustrated when someone tries to attribute a characteristic to an adolescent age group. We often hear about how teen drivers (presumably 16-17) can be "reckless" and "think they're invincible." But when I was 16-17, I was so nervous about driving that I was afraid to change lanes! -- Mwalcoff (talk) 03:24, 20 August 2009 (UTC)

Actinidain

Where can I find out how many people are allergic to Actinidain? Googlemeister (talk) 16:45, 19 August 2009 (UTC)

I am going to make the assumption that you are interested in statistics pertaining to kiwifruit in general. According to the literature, the rates of allergies to kiwi and other foods vary by population. Another review paper of kiwifruit allergies didn't present any figures on the overall rate which suggests that by at least 2003 there hasn't been a comprehensive study on the rate of kiwifruit allergies in various populations. This paper only generally states that there has been an increase in the number of reported kiwifruit allergies. I found those papers by the way using google with the search term 'kiwifruit allergy rate.' Further examination for fruit allergy rates didn't lead to any hard numbers that included kiwifruit either. 152.16.15.144 (talk) 23:42, 19 August 2009 (UTC)

Wicca and mental health

My mother says she left Wicca partly because she felt too many of its members were paranoid or had other symptoms of mental illness. Are Wiccans less mentally healthy on average than members of other religions, and do they tend toward the same types of mental illness in the same relative proportions? NeonMerlin 19:12, 19 August 2009 (UTC)

That's an interesting question. Speaking purely from personal observation, I identify with certain subcultures more then the mainstream and I used to frequent alternative night clubs like goth and industrial clubs when I was younger. They sometimes get lumped together, goth/metal/industrial, because those kind of scenes do tend to attract certain similar fringes of society, people who don't "fit in" with the mainstream. So they are typically over represented with people who have alternate beliefs, odd personalities, unusually creative, more introvert or extrovert then "normal", that kind of thing. Within those groups I could confidently say there would also be an over representation of people with genuine mental "issues", (since a lot of mental issues make it harder to identify with the mainstream) and also people who believe/practice Wicca. How much those 2 groups overlap, I could not say but I would not find a correlation at all surprising. That is not to say there is a direct causal correlation, as in "it takes a person with mental problems to believe in Wicca", I don't believe that, but more plausibly that people with mental problems have a harder time fitting into a mainstream, therefore they may have a higher predisposition to be drawn to alternative views, like Wicca. Vespine (talk) 01:59, 20 August 2009 (UTC)

I think Vespine probably has it right: the general ethos of Wicca is non-judgemental, tolerant and welcoming to diverse and sometimes unusual belief clusters and personalities, so people with them tend to gravitate there. A not-dissimilar situation exists in the Science Fiction Fan community, which contains a higher than average proportion of people noticably on the Aspergers/Autism spectrum (both examples are based on my personal observations from within). However, I suspect that investigation of some non-Wiccan (or indeed non-neopagan) religious organisations/cults might reveal much higher proportions of those with dysfunctional mental states: I'm thinking of some Southern-USA schismatic Christian fundamentalist churches, and of Sc!ent0l0gy (excuse the hopefully search-engine baffling transliteration, they're notoriously litigious) which – as anyone who'se read their promotional literature and questionnaires will know - appear actively to target those with mental health issues.

A properly conducted scientific study of the broad question might be interesting, but I fear would be both highly contentious and open to misuse. 87.81.230.195 (talk) 04:54, 20 August 2009 (UTC)

Another possibility when comparing religious groups is that any relatively new religious group will have almost exclusively converts as members, while a well-established ecclesia will have mostly people who were born and raised in the religion. (Most people who are Lutherans today were raised Lutheran, while most people who are Wiccans today were not raised Wiccan.) This may have something to say about the level of tension that these people might have with their families or other social networks.

Here's how to test this hypothesis: examine Wiccans who were raised Wiccan, and converts to Lutheranism who had been raised in a religion that is hostile to Lutheranism. If the hypothesis is true, then raised-Wiccans will be less "crazy" than convert-Wiccans, and convert-Lutherans will be more "crazy" than raised-Lutherans. --FOo (talk) 09:54, 20 August 2009 (UTC)

I would think it would largely depend on how mental illnesses are defined. One old definition is "those who are mentally abnormal, that is, outside the norm". This would likely include just about all Wiccans, as well as homosexuals and many others. If you go with a more narrow definition, like "those who, due to their mental state, are a physical danger to themselves or others", then I doubt if Wiccans have a significantly higher rate than others. There could even be an argument that "letting yourself go" periodically, such as dancing naked and primal screams (do Wiccans do those things ?) might help relieve stress and thus make you healthier physically and mentally than in a typical repressive religion. StuRat (talk) 12:56, 20 August 2009 (UTC)

Nitrated Compounds

Why are highly nitrated compounds explosive?CalamusFortis 20:39, 19 August 2009 (UTC)

this website contains an excellent review of the thermochemistry of explosives like nitrates. The deal with nitrated compounds is that they are essentially "self-oxidizing"; its not that the combustion of a nitrated compound necessarily releases more energy, its that it releases that energy MUCH faster than a standard combustion because the oxidizer (the nitro group) is in the compound itself. The limiting factor in the speed of a standard combustion is the relative diffuse nature of the oxidizer; atmospheric oxygen is only about 20% of the atmosphere, and as a gas, it is also about 1/1000 the concentration of a liquid or solid. So your oxidizer in a standard open-air combustion is about 1/5000 as effective as it would be if you were dealing with pure, condensed oxygen, like liquid oxygen. With a nitrated organic compound, since the oxidizer is part of the molecule itself, it works essentially instantaneously, and there's enough of it around. --Jayron32 22:54, 19 August 2009 (UTC)

My Compost "Peters Out"

A few weeks back I made a composter out of an old plastic trash can. Following instructions, I cut a number of holes and duct taped them with plastic window screening. I then loaded it up with shredded paper and dried leaves (carbon rich "brown" waste) and old produce and grass clippings (nitrogen rich "green" waste). Per the instructions I found online, the ratio of green to brown by volume was approximately 1:4 or 1:6. The first week we had a dry spell and nothing seemed to happen. Apparently I wring out my sponges harder than most people do as my definition of a "wrung-out sponge" was too dry. Adding substantially more water and moving the composter into the shade helped and soon I felt the distinctive heat of decomposition when I turned the contents over.

After about a week, though, the heat went away and decomposition seems to have stopped. Dampening and aerating seem to do nothing. There is no unusual smell (i.e. ammonia) as indicated in various troubleshooting hints in the instructions. As of last night, the grass clippings seem to be mostly gone. I found other instructions (at http://www.ehow.com/how_16876_make-compost-bin.html which I can't link to because of a wikipedia link block) calling for a 1:1 ratio. The composting article indicates that my error was that by eyeballing volume I wound up with too low a ratio and that "mixing equal parts by volume approximates the ideal C:N range."

This weekend, I will mow my lawn and add more clippings to see how that works. In the meantime, though, I thought I'd post here to see if anyone can suggest other things I might need to look at if that doesn't work out. So, three questions:

• Does my diagnosis of too little green waste sound plausible?
• If the diagnosis is wrong and the grass clippings don't work, what should I do? (FYI, I'd really rather not dig out a pH meter or anything arcane like that)
• Also, should I count this last week as a "lost week" in my two to four week cycle before I can use the compost?

Thanks

--KNHaw ^(talk) 22:03, 19 August 2009 (UTC)

I looked at"Back to basics," (1981) by Readers' Digest. It is an excellent guide to lots of "back to the land" farming techniques. They say the optimum size for a compost pile is 4 feet, since a small pile loses heat too rapidly. They start with 2-3 inches of course material like cornstalks, twigs or straw, to promote ventilation. Only one such bottom layer is called for. They layer 3-6 inches of garden waste or dead leaves, 2-3 inches of manure (or a light sprinkling of synthetic fertilizer) to supply nitrogen, then a thin layer of garden soil. Repeat until the compost bin is full. Leave the top saucer shaped to hold water. Too little water and the breakdown comes to a halt. In dry weather, water it every few days. In rainy weather cover it with a tarp to prevent too much water. Turn it weekly. It is done when it no longer gives off heat and the material is "brown and crumbly." Compost does not have to look like dirt to be done. It can still be recognizable in form as leaves and grass, but should be dark or brown. They suggest the process can be complete in 2 weeks. So: was there an adequate nitrogen source? You might try adding manure or fertilizer. Was the volume large enough to hold heat? Did you add soil, so the needed microorganisms are plentiful? From my experience the manure or fertilizer and the layers of soil are important for speedy breakdown and heat. If it is not going to get hot, perhaps earthworms could do the composting for you. They crawl around, multiply, and turn old grass clippings into rich brown soil. Edison (talk) 01:21, 20 August 2009 (UTC)

OR: It may also be that your compost got too hot and was sterilized. Adding earthworms might work, but they don't like it too toasty either. Depending on what you use to treat your lawn and what type of grass you have, clippings may not be a good thing to put in your compost. Some grass types don't compost well and some lawn treatments can mess up the ecosystem in your compost. If you have oak trees then maybe your "leaf matter" is to blame. 71.236.26.74 (talk) 11:55, 20 August 2009 (UTC)

I agree that a very critical factor for composting is scale (it affects moisture level, temperature loss etc etc.). I think this is much more critical than composition. Most people seem to reckon a cubic metre is a minimum for general conditions so I wonder if your "plastic bin" is big enough? How much grass cutting do you get each time you mow the lawn? The first 48 hours with moist fresh cut grass is the hottest (50C is easy if you have a few cubic metres of squashed clippings each cut in my experience, in rough terms in the UK you get about a cubic metre per acre mown) and the steam which rises from the compost helps to moisten everything else. If you cannot get a cubic metre of compost together my advice would be to bury what you have in the soil and it will degrade there ok. --BozMo talk 12:37, 20 August 2009 (UTC)

I was also going to suggest earthworms. They put holes in the compost heap, allowing water and air to permeate it, and also directly break down the compost. I wouldn't be so focused on getting the composting done quickly, but just leave the worms enough time to work their magic. If you have to turn the compost heap periodically you may miss days or just get sick of it entirely, whereas the worms will never give up. I'd also compost in a hole you dig, rather than in a plastic bin, which could limit air and water flow. So, basically, let nature do the composting for you. StuRat (talk) 12:43, 20 August 2009 (UTC)

Looking at the instructions you linked to, my guess would be A) not enough material overall to keep heat up, and B) not enough aeration through the ventilation holes. You might want to take a look at this (pdf) link from NCSU's School of Agriculture, or this one from Cornell's Waste Management Institute. You sound like you've read up on this pretty well, so a lot of information may be things you already know, but I like the way the schools lay the information out, and you can trust that you're not reading something from someone who "swears to god they did thus-and-such, and got amazing results." Reading the forums on Gardenweb on the subject, every time you add new material to the container-type composters, you're starting the process over, in terms of week-count.

From personal experience with a stationary bin made of nailed-together pallets, I can tell you that I very quickly despaired of ever keeping it full enough for hot composting, because the pile shrinks as the material in it settles and breaks down. A bin full to the top with a mix of leaves (raked and pruned), chopped-up weeds (left in the sun for a couple days to kill the roots first), and kitchen scraps would in a week or so collapse to just a foot and a half to two feet of material in the bottom of the bin. I never even had a chance to worry about C:N ratios; I was just trying to find enough stuff to keep the bin full. So I gave up, and now I throw in what I have when I have it, and turn it every week or two, depending on whether I feel like it. I'm not churning out perfect batches of compost every couple of weeks, but I have a place for yard and kitchen waste to go, and it'll become something usable eventually. Good enough for me, but YMMV. Some jerk on the Internet (talk) 13:16, 20 August 2009 (UTC)

Names of the first 2009 influenza A H1N1 pandemic virus.

What is the difference between A/California/04/2009 and A/California/05/2009? Are these the old names of two samples, or two different names for the same strain? -- Jeandré (talk), 2009-08-19t22:15z

If you look at those pages, you'll notice some differences; specifically, the section called "Comment" always has some information on the sequence. The first appears to be from a 10 year old male, and the second from a nine year old female. The first was collected on April 1st, and the second on March 30th. Noticing they had the same protein product (PB2) and similar resistances, I BLASTed them against each other, which told me that out of 2280 nucleotides, they had all but two identical. The exact changes are at positions 1218, a guanine for an adenine, and at 1872, a cytosine for a thymine. Hence, they are not the exact same virus, which is why they have different names (the names are based on when they were discovered and published). They are, however, the same strain - a good hint (although by no means definite) is that they are both H1N1. ~ Amory (user • talk • contribs) 02:12, 20 August 2009 (UTC)

Blackheads

Did anyone out there try the methods mentioned for removal of blackheads in the article? Do they work well? Can I use masking or packing tape? What about something other than a loop, which I do not have? DRosenbach ^{(Talk | Contribs)} 23:23, 19 August 2009 (UTC)

It says "tape-like". The article is not recommending using actual tape. It is indicating that they are sometimes treated with an item similar to tape, but specifically designed for that purpose. APL (talk) 00:08, 20 August 2009 (UTC)

I really, really hate to have to say this, but we cannot give medical advice. Your question may not really be asking for medical advice, so this may not be applicable in this case. Nevertheless, lots of folks with blackheads and pimples end up at the doctor's office after a botched self-treatment. It is really better to go see the doctor first. 90% of the time, the doctor will be able to tell within one minute or less that your visit was unnecessary. It's the other 10% of the time we worry about. Basically, if you are worried enough to ask on this forum, you should go to the doctor so he can reassure you and keep you from doing something stupid. -Arch dude (talk) 01:02, 20 August 2009 (UTC)

Both of you are beyond intense. I know it said tape-like, I read the article. And I'm not asking how to take my gallbladder out -- take a chill pill! Man... DRosenbach ^{(Talk | Contribs)} 02:17, 20 August 2009 (UTC)

"Beyond intense"? That's a new one on me, when and where is that slang from? --Tango (talk) 03:30, 20 August 2009 (UTC)

I am Ultra Intense. APL (talk) 05:21, 20 August 2009 (UTC)

Is ultra intense beyond intense? Or just a subset? Or do put it a different way, are you disputing that you are beyoond intense of do we have a confession? To the OP if I'm reading your user page right, your a dentist? Do you encourage your patients to ask random strangers on the internet to find out whether using "3 parts baking soda (cleanser) thoroughly with 1 part salt (the abrasive)" or perhaps "with chalk, pulverized brick, or salt as ingredients" as a toothpaste subsitute or hydrogen peroxide as mouth wash is a good idea too? Nil Einne (talk) 10:08, 20 August 2009 (UTC)

DRosenbach, there is a chance you may harm yourself applying packing tape to your face. Be sure to avoid blocking respiratory orifices and do not put tape directly on the surface of your eyeball. Mac Davis (talk) 03:35, 20 August 2009 (UTC)

I. Similar to how severe could serve to classify a point on the severity spectrum, I was utilizing intense to refer to a point on the intensity spectrum -- thus, ultraintense, which likely exhibits greater frequency and perhaps lesser amplitude than intense, would be an example of "beyond intense," but would not define it, as beyond intense was meant as merely a relative label rather than a definition of another point along the spectrum. One could, of course, refer to a specific point as beyond intense, but that was not what I was doing.

II. I would encourage my patients to confirm my recommendations with their colleagues -- only one who is insecure and unconfident about his or her recommendations would restrict his or her patients access to other sources of information. Sort of like how China doesn't allow anti-Chinese sentiments to be expressed or disseminated among its masses.

III. I do not consider you all to be random strangers as much as I consider you all to be a fine subset of random strangers, heretofore entitled scientifically-drawn random strangers. I would, and as this case exemplifies, do ask scientific queries of scientifically-driven random stranger -- doesn't everyone else here do the same.

IV. So to summarize, I can use packing tape, as long as I avoid eyes, nose and mouth? DRosenbach ^{(Talk | Contribs)} 12:55, 20 August 2009 (UTC)

No. I'm fairly sure Mac Davis was being facetious. Use packing tape for your parcels and face cleaning tape for your face. The ref desk can't and won't give you advice on home-made alternatives. --Tango (talk) 13:05, 20 August 2009 (UTC)

Another one beyond. DRosenbach ^{(Talk | Contribs)} 13:07, 20 August 2009 (UTC)

Obviously, what we have here is an opportunity for a clinical trial. The Annals of Improbable Research would probably publish your results. APL (talk) 14:20, 20 August 2009 (UTC)

August 20

Motion, then no motion, in optical illusion

This link is to an optical illusion. When I look at it, I perceive a lot of motion in the image for around 3 seconds, by the end of which the motion has slowed down and stopped. If I continue to stare at the same place, there is no additional motion. If I move my eyes to a different location in the image, I see another 3 seconds of motion which then slows down and stops. Is there a writeup somewhere on why I am perceiving motion that then stops after a short, seemingly consistent, time? Our optical illusion article is disappointingly short. Tempshill (talk) 05:39, 20 August 2009 (UTC)

There is a large class of optical illusions that exploit the fact that our visual cortex is hard-wired to infer 3D structure of objects from illumination and shading. In this illusion, there exists a near order of light-and-shade directions, creating the illusory "direction of illumination" in each small part of the image. Thus, any small part looks like a valid "3D". However, the global 3D structure is invalid; thus shifting the gaze makes the perceived image distort and undulate for a while, until out visual cortex "gives up" finding a meaningful global 3D solution. This seems to take a few seconds, and repeats itself after each saccade or gaze shift. --Dr Dima (talk) 06:10, 20 August 2009 (UTC)

By the way, this very illusion picture is included in the Peripheral drift illusion article for some reason. However, I think that this is not a peripheral drift illusion at all. Indeed, there is no sawtooth intensity gradient in any of the ellipses, and the perceived direction of motion is not always the same. --Dr Dima (talk) 06:25, 20 August 2009 (UTC)

I get almost continual motion, also attempting to mimic the effect using random angular displacements (ie see the black.white circles hidden behind the blue) - gives a vague effect, but not as good.

random displacement pseudo code - works - but not very well

{{{2}}}

It looks like the angular displacements form some sort of orbit (ie some special Vector field ?)- for this to work well - maybe it would be a good idea to ask the creator how they did it, and where the idea came from?83.100.250.79 (talk) 11:27, 20 August 2009 (UTC)

how to get into research?

i am a medico.i am interested o become a biomedical scientist.how do i get into that?what should i do?like-projects to be done,etc. —Preceding unsigned comment added by 115.184.225.12 (talk) 06:52, 20 August 2009 (UTC)

What do you mean by "medico"? Medical student? To become a professional researcher you usually need to do a PhD. If you are a med student you will have tutors and lecturers that will be able to advise you on that. --Tango (talk) 06:56, 20 August 2009 (UTC)

"Medico" in Italian means "doctor", as does "médico" in Spanish. However, the IP address is in India, and I don’t know how the term is used there. Red Act (talk) 07:49, 20 August 2009 (UTC)

Either an MD or a PhD is capable of becoming a professional biomedical researcher, though it does vary somewhat depending on the field. Either way, you'll probably need to look into a post-doctoral research position, and it sounds as though you will have a lot of catching up to do in terms of reading science journals, developing expertise in your area of interest, etc. In academia, depending on your level of experience and success, it might take two post-docs before you've developed into an independent researcher with enough credentials to be hired by a university or other research institution. If you're not interested in establishing your own lab and would be just as happy as part of a larger team you might consider going into industry. Tango's advice is good -- try talking to other people at your institution who are doing research and find out how they got into the field. See if you can find a researcher willing to take an inexperienced trainee and show them how to get started, and go from there. Here are a few links to get you started: Science careers forum, "Career" area for the journal Science, "Jobs" area for the journal Nature. --- Medical geneticist (talk) 11:37, 20 August 2009 (UTC)

Time Machine and Law of conservation of energy.

There have been many debate regarding the possibility of constructing a time machine. I'm curious about the fact that wheather the use of time machine would violate the law of conservation of energy. Consider the whole universe as a single system at this moment; now if we send anything to the future(or past)then the system will lose energy(as matter is energy). Consider another scenerio ; if we use time machine to send something back at a time when even the big bang did'nt happened; then the balance of total matter in the universe would be disrupted. Does these scenerio contradicts with the law of conservation of energy?

In order to get any kind of time machine you need to use General Relativity (with some extra bits added in), and energy isn't really conserved in GR (there is a concept of conservation of energy, but it isn't very general). There is an explanation here, but it is a little technical (it was the first Google hit, someone else might know of a better explanation or be able to write one themselves). --Tango (talk) 13:01, 20 August 2009 (UTC)

Tango, You don't believe in the Cosmic censorship hypothesis? Wow! --BozMo talk 13:36, 20 August 2009 (UTC)

I never said that. The question only makes sense if we assume time travel is possible, so I answered based on that assumption. --Tango (talk) 13:46, 20 August 2009 (UTC)

I. Why would sending something back in time remove energy from the universe...you must thinking fourth dimensionally! If time is merely another axis on the space-time continuum graph, no energy is removed from the universe any more so than energy is removed from the universe when you travel from New York City to London -- the energy (and mass) is merely moved within the universe. So too are mass and energy conserved within the universe when time is the medium of travel.

II. Hmmm...if time began at the Big Bang, it would be impossible to travel to before the Big Bang -- it would be like trying to travel from the 86th floor of the Empire State Building in 2009 to the same location in January of 1930. Since construction of the building only began in late January of that year, one could not travel to that place because there was no that place at that time. DRosenbach ^{(Talk | Contribs)} 13:04, 20 August 2009 (UTC)

The law of conservation of energy states that there's a constant amount of energy in a closed system at all times. Not that if you add up all the energy in it ever, it would come to a total. That kind of goes without saying. — DanielLC 15:48, 20 August 2009 (UTC)

(stupid edit conflict) Conservation of energy is not a problem, that is why there is a law of conservation of energy, because it is always conserved. A bigger issue however would be the second law of thermodynamics, as going back in time would mean decreasing entropy (think: carbon dioxide + water -> hydrocarbon). Physics isn't my area however, so I'm certain someone will reply with an answer explaining how the second law isn't violated by travelling into the past. --Mark PEA (talk) 13:14, 20 August 2009 (UTC)

Without providing a full justification, bear in mind that the second law in no way prohibits the localized decrease of entropy (else Wikipedia wouldn't be here), provided that entropy generally increases. So long as the time machine consumes power, this one isn't a sticking point. — Lomn 13:38, 20 August 2009 (UTC)

Thanks, that explains it. Although it brings up new speculations of why a future generation would want to input such vast amounts of energy to get back in time. But that is way off topic. --Mark PEA (talk) 14:18, 20 August 2009 (UTC)

What if there was a drought one year and a really bad harvest? It would be great to be able to send some of next year's harvest back in time to tide you over. I can see plenty of benefits to time travel. --Tango (talk) 14:46, 20 August 2009 (UTC)

Actually, the past generations would need to input vast amounts of energy to receive the time-traveller. The future generations would be able to get (almost) as much energy as the past generations consume. — DanielLC 15:48, 20 August 2009 (UTC)

We can do that now. It's the reason financial markets exist. Wikiant (talk) 14:56, 20 August 2009 (UTC)

I think all these issues arise from trying to apply concepts that just don't apply if time travel is possible. Conservation requires the ability to take time-slices (and see that the quantity is the same in all of them) and the 2nd law of thermodynamics requires a nice simple linear time dimension where the concepts of "past" and "future" make sense. If spacetime is all wrapped around on itself so as to allow closed timelike curves (ie. time travel) then those things are simply impossible and the whole concepts cease to exist (at least globally, you might be able to manage locally). Energy is neither conserved or not conserved in such a universe because conservation makes no sense (which will really piss off the environmentalists! ;)). --Tango (talk) 14:43, 20 August 2009 (UTC)

Of course there are time machines. They will be invented circa 2750. However, while the inventors finally found a way to move material through time, they realized another problem they hadn't considered—moving material through space, instantaneously. The first experiment sent a chimp back in time one year. At first, they wondered why the chimp didn't appear in the lab one year earlier, then it hit them. The chimp arrived at the exact same place it was, but with the earth circling the sun, and the whole solar system moving, the chimp moved through time to a place in open space and promptly died. Next, they put the chimp in a spacesuit, but that simply left the chimp in space, thousands of miles away from the earth, to slowly die.

The problem of moving material through time was hard, but moving it through time to exactly coincide with a livable space at that same time proved insurmountable. You can look it up, it's the 310 millionth article in Wikipedia (or will be).--SPhilbrickT 16:02, 20 August 2009 (UTC)

Why soy wax?

Soy candles are made from partially hydrogenated soybean oil. But why is it just soybean oil that's so treated? Why isn't there canola/corn/olive/etc. wax from partially hydrogenated canola/corn/olive/etc. oils? Is there some physical property of soybean oil (fatty acid chain length or the like) which makes it ideally suited for wax making, or is it just an economic reason (soybean oil is cheaper/more readily available, or a soy="healthy alternative" association in the target market)? -- 128.104.112.102 (talk) 15:20, 20 August 2009 (UTC)

LED

What's the largest a single LED bulb can be?