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July 18

Nasal passages

Hi. This is not a request for medical advice. Let's say a person suffers a broken nose, leading to a nosebleed. Might the damage cause parts of the brain to be accessible from the nasal passages? The person subsequently develops a common cold. Could sneezing or nose blowing (No article?!) cause parts of the brain to be liquefied and excreted via the nose, or could 'sniffling' result in nasal mucus entering the brain? I am aware of the danger triangle of the face, but this mostly applies to surface cutaneous infections. Might an infection in the nasal cavity, under these circumstances, spread to the brain? Thanks. ~AH1^(TCU) 02:04, 18 July 2010 (UTC)

The brain is encased in a tough leathery membrane called the dura mater, and there's a large area of sinuses between nose and brain -- also the front part of the brain lies almost entirely above the level of the nose, in fact above the eyes. To expose the brain by hitting the nose, you'd pretty much have to smash the whole face in. Looie496 (talk) 02:33, 18 July 2010 (UTC)

Does the danger triangle also include infections of the upper wisdom teeth? Rimush (talk) 08:01, 18 July 2010 (UTC)

The danger triangle of the face relates to the very front of the face and relies heavily upon the anterior venous plexi (bilaterally) and ultimately the cavernous sinuses, bilaterally. Because maxillary posterior teeth exist inferior to the maxillary sinus, a spread of infection will either break into one of these sinuses, or more often, through the buccal plate of the alevolar ridge and into the soft tissue of the vestibule (area between teeth and cheek). Certainly, if an infection is allowed to remain untampered with for long enough, it can spread pretty much anywhere -- but there are also certain common pathways that are way more likely than others. Dental schools teach that abscesses of the maxillary anterior teeth (that would be incisors and canines) may lead to spread of infection into the danger triangle, but I'd say that even that is pretty uncommon. DRosenbach ^{(Talk | Contribs)} 13:54, 18 July 2010 (UTC)

So there is no danger of the passage between the brain and nose being broken and punctured like the ancient Egyptians did to their mummies to remove their brains? ~AH1^(TCU) 14:53, 18 July 2010 (UTC)

If you follow the Egyptians and you're doing it to someone already dead? No. If they're still alive, I'm not sure but I wouldn't worry about it, I'd worry more about the danger of removing their brain...

Sorry I couldn't resist Nil Einne (talk) 15:31, 18 July 2010 (UTC)

AH1 -- the diagram above may not be the best to use to visualize the relationship of the nose to the brain. I added another that may better suit you. The "nose" is not really what or where it seems and the term may be confusing. The nostrils become the nasal cavity as they ascend and it is split in the midsagittal line by the nasal septum. There is certainly a possiblity of the nasal cavity communicating with not only the inside of the braincase but even of cerebrospinal fluid leaking out of both the ears and the nose after serious trauma like a motor vehicle accident. But it's way more unlikely for a communication to form between the two areas from a broken nose related to a trip and fall. Then there are all of the various levels of trauma in between, such as getting smacked in the face by a baseball bat in full swing, etc. So there's no real way to determine the odds of such a thing happening, but it's certainly possible, as it's listed in BLS texts as a sign of potential brain damage (that is, the leaking of CSF from the ears/nose). DRosenbach ^{(Talk | Contribs)} 16:43, 18 July 2010 (UTC)

Reading anything about diseases and related stuff on Wikipedia makes it seem like everything is life-threatening and that we are in peril of dying from a number of problems every second. Scary. Rimush (talk) 17:15, 18 July 2010 (UTC)

Think of it as "Evolution in action" potential. 87.81.230.195 (talk) 17:25, 18 July 2010 (UTC)

Wikipedia does have an obsession over listing the most serious possible causes of any physical symptoms. ~AH1^(TCU) 23:59, 18 July 2010 (UTC)

Yes, I only meant to explain how difficult it would be for physical damage to the nose to get through to the brain, not to deny the possibility of interaction between sinuses and brain. As an additional note, there is a well-known case in the amnesia literature, of a patient called R.B. who had a fencing accident in which the point of the foil went up his nose and into his brain, causing damage localized to a small midbrain area which nevertheless produced a severe memory impairment. That's about the only way a blow to the nose can get through to the brain, as far as I can see -- short of a gunshot wound. Looie496 (talk) 17:34, 18 July 2010 (UTC)

A woman was killed in Italy by a pointy umbrella that went through her eye and into her brain (someone "stabbed" her on purpose). Rimush (talk) 18:17, 18 July 2010 (UTC)

Even without any mechanical trauma, an opening can spontaneously develop which allows cerebrospinal fluid to drain from the region outside the dura mater into the sinuses. I have known of such a case, which resulted in meningitis, and which was later closed by endoscopic microsurgery. Edison (talk) 18:48, 18 July 2010 (UTC)

Tippe top

http://www.xs4all.nl/~fabilsen/tippe-top.pdf I had a question about the explanation given here. It says that L has a constant orientation, but if there's a torque due to friction, then wouldn't L change direction? The only thing I can think of is that the torque due to friction traces a cone during one revolution, so the net torque will just be in the (opposite) direction of L. Is this right? 74.15.137.192 (talk) 03:31, 18 July 2010 (UTC)

I'm not familiar with the 'tippe-top' - but I think it's a variant of something called "Tesla's Egg". We had a detailed discussion about that a few months ago Spinning Tesla egg and stability - which I think applies to the tippe-top also. As I explained at the time - you can get the exact same effect by spinning a regular hard-boiled egg. Our article: Tesla's Egg of Columbus refers to some very complicated experiment with coils and a copper egg that winds up with the egg standing up on it's tip - but all of that fancy stuff just gets the egg to spin - the standing up on one end part is nothing to do with that (which you can prove by doing the same thing with a tippe-top or a hard boiled egg). SteveBaker (talk) 13:44, 18 July 2010 (UTC)

(We should really clean up this explanation and fix the Tesla's Egg of Columbus article to explain it properly). SteveBaker (talk) 13:52, 18 July 2010 (UTC)

A discussion of the tippe top is now archived at Wikipedia:Reference desk/Archives/Humanities/2010 June 27#What are these men doing?.

-- Wavelength (talk) 23:59, 18 July 2010 (UTC)

Is this cable modem fried from lightning or not? (2 pictures, Cisco EPC2607)

Two pictures: With flash, without flash (click "Visa i full storlek" to show full size, which is blurry 5 MP). It doesn't power up whatsoever. I can't check the transformer simply because the multimeter doesn't fit, and I can't try another transformer because the connector on the only other one I have won't fit into the modem (and also is 12V/1A when the modem wants 15V/1A).

Anyway... Is this the result of lightning or not? The connection went down at a time I was awake but still in bed, according to ping logs; local weather reports haven't reported any lightning nor have I heard any.

Oh, and the copper-colored spots in the pictures are a) located right around a ~5x5mm IC on the other side and b) extremely conductive. Also, everything on the other side looks brand-new - I haven't checked the two ICs that are on top in the pictures though; all three were shielded under metal casings, and I only removed the first (the one closest to the coax connector). -- Aeluwas (talk) 08:07, 18 July 2010 (UTC)

When lightning struck our network a few years ago, the router had a burn pattern like the twigs on a branch, so based on that I'd say no. --TammyMoet (talk) 08:16, 18 July 2010 (UTC)

Lightning can produce many different effects, but I agree with Tammy that component failure is a more likely cause. How far into the unit does your 15v supply reach, or is there no 15v coming in? Dbfirs 09:06, 18 July 2010 (UTC)

Those copper area don't look broken to me, they seem deliberate. In any case by far the most common failure is a loose or cracked solder joint caused by motion (for example where you plug something in, or where there is a button, or where there is a wire going to the outside world), or less often by heat. If you can find it you should be able to resolder it. If it's a high power connector you will often see burn marks. But for a signal line you won't, and you'll have to look for a cracks. Ariel. (talk) 13:42, 18 July 2010 (UTC)

Thanks everyone. As it turns out, the modem might not be broken after all. The power supply, on the other hand, definitely is. Y'know, the thing that's supposed to supply 15 volts... I measured it to 0.01 V, which is way within the margin of error of a cheap multimeter, so it's rather a question whether it simply died, or died and took the modem with it (e.g. due to lightning). Since I'll be getting a new modem (of a different make and model) anyhow, it doesn't really matter; the main reason I asked was to see if those copper areas are normal or not (for future reference :). Judging by the above responses, how pristine everything else looks and the shapes of those areas (no burns or such in the corners, or what have you), I can only assume they're supposed to be there. -- Aeluwas (talk) 14:44, 18 July 2010 (UTC)

Those bare areas may have been deliberately left that way in order that they may radiate heat better. Since you said that the components on the other side had metal covers over them - that seems quite plausible. If the problem happened during a storm, it's possible that a power spike induced by the nearby lightning took out the power supply without anything actually getting struck or damaged. If your cable had been struck by lightning, there would be all sorts of other signs - scorch marks on the case, damage to the cable itself, etc. SteveBaker (talk) 15:13, 18 July 2010 (UTC)

High-friction coating for bike rims to improve braking efficiency?

I'm going to try new brake pads for my caliper brakes, but I wondered whether the rims (apparently steel rims are poor braking surfaces) could also be coated with something to increase the coefficient of friction, ideally without unduly wearing-out the brake pads or quickly being destroyed in use? ----Seans Potato Business 11:24, 18 July 2010 (UTC)

Is this a pedal-powered bike or a motorbike? I'm guessing pedal-powered because of the rims. New brakes, or recently adjusted old brakes, will stop you very abruptly. This can be moderated by applying the brakes gently. High-friction rims would give you no choice in the matter, causing a stomach-wrenching halt every time, so I think it's a bad idea. 213.122.67.124 (talk) 12:14, 18 July 2010 (UTC)

Caliper breaks seems to indicate bicycle. It's probably possible to go with surface coating, but for modern (aluminium) rims and decent quality brake pads (I use CoolStop on my mountain bike with Shimano LX V Brakes, and Magura brake pads with the HS11 the on my commuting bike), there is no need. Both braking performance and brake pad lifetime are excellent in dry weather and plenty good enough if it rains. For more extreme needs, check out disk brakes. --Stephan Schulz (talk) 12:24, 18 July 2010 (UTC)

Steel rims are actually excellent. That's what cars use. For brakes you don't want too much sticktion - you want friction. It needs to be very smooth, and non sticky. Ariel. (talk) 13:46, 18 July 2010 (UTC)

Yes, exactly. You want to be able to use your brakes gradually to slow yourself down at a reasonable rate. Correctly set up bike brakes (even on a smooth steel rim) are more than able to throw you over the handlebars and/or lock up the wheels and put you into a skid. What you need is a controllable amount of friction that allows you to apply anything from the most gentle slowdown to a full-scale lock-up-the-wheels skid. Having an unnecessarily large amount of friction will make the bike harder to control because the slightest touch on the brakes could result in a skid or an over-the-handlebars event. Also (as Ariel points out), there is an important difference between 'sticktion' (static friction) and dynamic friction. If the material has a high coefficient of static friction then it's much easier to lock up the wheels. If all you needed for really good bike brakes was the maximum amount of friction - then you could just shove a stick between wheel spokes and frame! What you need is (a) good pads - which you must change when they wear down and (b) correct adjustment of the cable from the brake lever to the caliper so that the lever cannot be pulled all the way back to the end-stop, no matter how much force you apply. This second thing is the most common problem with bike brakes (especially the back ones) because the cables gradually stretch with use leading to a situation where the brakes would be perfectly able to stop you if only you could apply enough pressure to them without hitting the end-stop first. The back wheel brakes suffer the most from that because the cable is longer. SteveBaker (talk) 15:05, 18 July 2010 (UTC)

That's a little bit oversimplified. If you're riding downhill or at high speed, the main braking force should be applied to the rear wheel, to avoid flipping you over the front. In my experience, it's really hard to apply enough force to the rear brake to lock it up when you're going fast, even with new brakes. But I definitely agree that roughening the rim is a bad idea. If nothing else, it will grind away the rubber in the brake in no time. Looie496 (talk) 18:00, 18 July 2010 (UTC)

Well, no, I'm not so sure I agree about the rear-v-front thing. You have to keep the front braking light enough to avoid an endo, yes, that's true. But short of that, front braking pushes your front tire downwards into the roadway and improves your grip on the road. They tell me that the best balance is around 70-30 with the heavier braking in front.

Now I can't really claim experience on this, even though I bike a lot on hills, because I'm cautious and don't really let the bike get very close to losing traction (at least on the downhills). So if you have any pointers to studies on this, I'd be interested in seeing them. --Trovatore (talk) 21:19, 18 July 2010 (UTC)

The best thing to do would be to replace the rims with aluminium ones - an expensive proposition, but possibly worthwhile. Bicycling Science by D. G. Wilson quotes this paper from 1971: steel rims lost 90+% of braking power when wet. If your bike is anything like the ancient contraption I use at university, and you often ride in rain, I'd put serious thought into upgrading for safety reasons: if it rains during the course of a lecture, I have to use "sneaker brakes" on the way back. If your bike is newer, modern brake pads might have improved the situation, but it's up to you to judge. Brammers (talk/c) 20:48, 18 July 2010 (UTC)

Addendum after archiving: a company called Rigida (website) sell rims that have been coated with tungsten carbide. A review in the CTC's Cycle magazine says they are highly effective but will chew through anything but the hardest brake blocks. Brammers (talk/c) 11:16, 28 July 2010 (UTC)

Disc brakes — bikes

Why are the discs not a simple circular configuration? They follow a path that diverges from the plain circular form that one might expect. The divergence is regularly corrected, so that the overall configuration is circular. But why the periodic squiggles out of simple circularity? Click on the pic to enlarge it. It's a very nice photograph. Bus stop (talk) 15:25, 18 July 2010 (UTC)

Personally I think it's simply to make it look cool. Same for the holes. (If you are trying to save weight, there are better ways, like an internal grid, layered with thin smooth metal.) Ariel. (talk) 15:44, 18 July 2010 (UTC)

Agree about the form. As for the holes, they both safe weight and help dissipate heat, so I do think they have a function. --Stephan Schulz (talk) 15:50, 18 July 2010 (UTC)

The holes do not dissipate heat. They put them in cars not to dissipate heat but to release outgassing from the pads. Ariel. (talk) 15:52, 18 July 2010 (UTC)

Might it be to dislodge foreign matter like mud that might get splashed in there? I'm just guessing. Bus stop (talk) 16:10, 18 July 2010 (UTC)

See Disc brake#Discs, which mentions these ideas and could use some actual citations to support them. DMacks (talk) 17:31, 19 July 2010 (UTC)

A solid disk, I hypothesize, would be harder to get traction on than a disk with holes in it. And solid disk does have less heat dispersion than a holey one, but I doubt this really matters due to the fact that mountain bikes (unlike motorcycles, which have similar brake designs) don't usually weigh hundreds of pounds or go 100kph. The more important dispersion, I think, is of stress - a lot of circular saw blades have funky grooves in them to spread out mechanical stress from the workpiece, and this brake disk looks pretty thin so it probably needs all the strength it can get. But the most likely reason for the holes is that unlike a bulky frame (which only adds net weight), a bulky brake disk has to be spun around with the wheel, adding difficulty not only in net weight but in effort required to pedal the bike. So it's more important to save weight on the wheels than anywhere else. ZigSaw 14:33, 20 July 2010 (UTC)

Infrared thermometer

Is there a way to measure the room temperature / ambient temperature with an infrared thermometer? It seems that they must always measure the temperature of the surface of some object. --Yanwen (talk) 20:28, 18 July 2010 (UTC)

Infrared thermometer relies on the infrared being reflected back into the sensor, that's why you can't measure the actual temperature of the air, because it doesn't reflect. But depending on the situation, you can make some reasonable assumptions. In a room, most soft furnishings and other objects IN the room will be pretty close to the air temperature in the room. Stay away from windows and doors and anything that has been in or near direct sunlight.. Even if you can get just a piece of paper and let it rest in the room for a few minutes, I don't see why that wouldn't work.. Vespine (talk) 23:09, 18 July 2010 (UTC)

I'm afraid that is completely incorrect. It's not reflected IR that is used, it is emitted IR. It's the thermal radiation of the object (which, for objects at everyday temperatures, will be predominantly IR) that is being detected. Reflected light doesn't tell you anything about the temperature of the object, it just tells you about its colour and the colour of the light it is reflecting. The air does emit thermal radiation in exactly the same way as any other matter, however there really isn't very much air (about 1.2kg/m³, compared to around 1800kg/m³ for brick), which is why it doesn't emit a noticeable amount (this is also why the flame produced by complete combustion is almost invisible: red-hot air doesn't emit a significant amount of radiation, even though it is visible radiation, it is only when there are soot particles in the air that you get a visible flame, since the soot particles at the same temperature emit much more light, since there is much more matter there). --Tango (talk) 00:17, 19 July 2010 (UTC)

I admit you are right Tango however I don't think i'm "completely wrong". If anything i'm half wrong ;) . I'm wrong about how the IR thermometer worked, fair enough, but that's not even what the OP was actually asking, you didn't even address that. I think i still came to the right conclusions about that.. Vespine (talk) 01:21, 19 July 2010 (UTC)

Just to be clear, the little red light on the infrared thermometers is for targeting purposes only. The thermometer would work fine without it, but you wouldn't be able to accurately know what you were measuring the temperature of... Hense the little red laser to know where you are aiming. --Jayron32 03:30, 19 July 2010 (UTC)

Ok, your first sentence was completely wrong! The rest was ok. --Tango (talk) 13:33, 19 July 2010 (UTC)

July 19

corn fields

why is corn very small and scarce around the edges of corn fields?--Horseluv10 00:09, 19 July 2010 (UTC) —Preceding unsigned comment added by Horseluv10 (talk • contribs)

Huh? Do you mean in areas where it was not intentionally planted, or where the fertilizer missed?? Edison (talk) 02:11, 19 July 2010 (UTC)

The use of fertilizer is sometimes by purpose lower at the edge to meet the law that a undisturbed rim has to grow around the fields.--Stone (talk) 04:58, 19 July 2010 (UTC)

i mean where it is intentionally planted.--Horseluv10 12:04, 19 July 2010 (UTC) —Preceding unsigned comment added by Horseluv10 (talk • contribs)

You can think of lots of reasons - that the farmer didn't fertilize the edges of the field as well as the center because of the need to turn the tractor around...or maybe there are trees around the edges of the field that are sucking up the ground water...or if the field is irrigated, that the irrigation system doesn't extend all the way to the edges...or maybe that insecticides aren't being sprayed out to the edges (again, for the tractor-turning-around reason). Perhaps the plants in the center of the field are better shielded from the wind than the ones that only have neighbors on one side. It's hard to know which of those things it might be. I couldn't find any online information about such a phenomena. SteveBaker (talk) 14:54, 19 July 2010 (UTC)

The phenomenon is observed in this paper, but sadly it's behind a paywall so I can read anything but the abstract. The Google description says "For all crops, crop height was significantly greater in the field centre than in the sprayed edges", although the paper refers to pesticides and herbicides rather than fertiliser. SteveBaker's ideas sound good though. Brammers (talk/c) 15:45, 19 July 2010 (UTC)

Outlying plants are exposed more than sheltered plants to wind and possibly competition from other plant roots underground. Cuddlyable3 (talk) 22:51, 19 July 2010 (UTC)

I was also thinking that if some kind of flying pest arrived at random in or around the field, all of the plants in the center of the field would have about an equal chance of getting infested - but if a pest arrived just outside the boundary of the field, it would presumably make its way to the plants at the outer edge. That would make any given plant at the edge of the field much more likely to get pest infestations than one in the main part of the field.

Also, some plants exude chemicals that supress plants from other species from growing nearby - and again, this would benefit the plants in the center of the field to a greater extent than the ones at the edge because the combined contributions of greater numbers of plants would build up a higher concentration of the chemical. SteveBaker (talk) 22:57, 19 July 2010 (UTC)

Not to mention that "edges of corn fields" that us non-farmers are likely to see are the edges that face roads. Many plants are not happy growing immediately next to a road. APL (talk) 15:45, 20 July 2010 (UTC)

solar cells, photovoltaic, photosynthesis

I'd like some boffins to create a (short) entry that answers;

1. What are the best solar cells (for electricity) (then for heating). 1a. Explain why UV solar cells aren't worth producing. Doesn't the higher energy of UV make up for the lower frequency range (compared to visible light) [implied NOT in Solar Cell entry] 1b. Explain why IR solar cells aren't worth producing. Doesn't the much greater frequency range make up for the lower energy (compared to visible light) [also implied NOT in Solar Cell entry]

2. Why aren't countries - especially Japan and Australia - investing more in solar cell research than in oil exploration - when Australia has so much sun - and Japan is so dependent on oil, and so strong in technical stuff

3. Why can't plant photosynthesis be mimicked in an artificial photosynthesis, to produce a 100% efficient solar cell.

PS I hope the shift apostrophe is the "tilde"

````MGoold —Preceding unsigned comment added by 220.253.195.35 (talk) 02:27, 19 July 2010 (UTC)

No, the tilde is in the upper left corner of my keyboard. It shows a key with ` and ~ in it. Shift that key and it should work. or click the signature with pen button on the top of the edit window. --Chemicalinterest (talk) 11:01, 19 July 2010 (UTC)

This looks a bit homeworky but anyway on "Why aren't countries investing more in solar cell research than in oil exploration" obvious reasons include (1) because you cannot be granted "concessions" for research into areas of intellectual property whereas you can for oil fields (2) because oil exists and technology to improve solar cells may not exist (3) because of these reasons the rates of return on investment are lower in solar technology than in oil exploration. --BozMo talk 11:34, 19 July 2010 (UTC)

1: Best changes all the time, and by application, so just take a look at the solar cell article and this this image. For heating don't use any solar cell, use solar thermal.

1a, 1b: There isn't enough energy to make it worthwhile. The way it works is this: The higher the frequency you work with the more energy you gain from each photon - but this also means that all photons below the frequency are ignored, so you have less photons. If instead you use a lower frequency, you gain energy from more photons, but each photon gives you less energy, and the rest of the energy is wasted as heat. So there is a perfect frequency where multiplying energy*number of photons is maximized. (I could not immediately find what that number is for the sun.) There is also a Multijunction solar cell which layers the cells, each layer collects from a different frequency. But it's too expensive to be practical except is specialized applications.

2: I can't answer about countries, but solar cells are hard. We've been researching them for something like 40 years. There is another problem: Solar cells cost too much, and it's not just cost - there simply isn't enough rare earth elements on this earth for everyone to switch to solar cells. Unless someone comes up with a technology that uses more common elements solar cells will never be widespread for bulk power. Every time solar cells come out people make an estimate: Once oil goes up in price this much these cells will be cost effective, then you look at a graph of oil prices, predict when that will happen, and declare a date. But one thing is forgotten: When the price of oil goes up, the price of everything goes up right along with it - energy is the prime component of everything we build. If energy cost goes up the price of everything goes up - including those solar cells. So they never actually pass oil, they constantly stay tantalizingly just out of reach. Personally I do not favor photovoltaics for energy. I favor solar thermal. That we can build, and we can build it cheap. It's just not very exciting.

3: Why do you think plants are 100% efficient? They are not. According to the article on it (yes we have one) Photosynthetic efficiency is 11%. But anyway, why bother mimicking it?

Ariel. (talk) 11:35, 19 July 2010 (UTC)

In response to your second point, the prices have been declining for solar PV. A US government study found a decrease of an average 3.5% per year from 1998 to 2007. Mostly in non-panel costs[1]. Also solar PV replaces electricity, not oil unless you are one of the few using your panels to charge your electric car. Very little oil is used to produce electricity (except in a few island nations). Mostly it is a mix of coal, hydro, nuclear, and natural gas. Worldwide only about 6% of electricity is generated from oil but in the US and France for examples it is only around 2%[2] Rmhermen (talk) 16:50, 19 July 2010 (UTC)

Plasma weapon

Would a plasma weapon be feasible? --138.110.206.101 (talk) 03:01, 19 July 2010 (UTC)

Now or the future? =) --mboverload@ 03:21, 19 July 2010 (UTC)

In the future, but specifically handheld plasma weapons. It's obvious that vehicle-mounted plasma weapons will probably be developed somewhat soon. --138.110.206.101 (talk) 03:25, 19 July 2010 (UTC)

Do you mean a weapon that shoots a jet of plasma? That seems pretty impractical to me. The air would cool the jet very fast, limiting its range to less than ten feet. I don't think they will ever build one. --The High Fin Sperm Whale 04:51, 19 July 2010 (UTC)

Maybe the OP is thinking of some sort of Pulsed Energy Projectile as mentioned in Plasma weapon, like [3] [4]? Of course funding is no definative indication of success, it may turn out to be another Gay bomb Nil Einne (talk) 04:56, 19 July 2010 (UTC)

Do you have a source for it being "obvious" that "vehicle-mounted plasma weapons will probably be developed somewhat soon"? Vimescarrot (talk) 10:45, 19 July 2010 (UTC)

They wouldn't have the size constraints of handheld weapons. --138.110.206.101 (talk) 12:51, 19 July 2010 (UTC)

The laws of physics are the same at both sizes. If one is possible, then so is the other, it's just an engineering problem. I suspect neither is possible. What would prevent the jet of plasma from rapidly spreading out and cooling down? --Tango (talk) 13:49, 19 July 2010 (UTC)

Shoot it fast enough that it hits the target before spreading out too much. --138.110.206.101 (talk) 13:53, 19 July 2010 (UTC)

I don't think it works that way. I think it will spread out at roughly the same angle regardless of the speed. --Tango (talk) 15:14, 19 July 2010 (UTC)

The flamethrower has largely been replaced by the shoulder-mounted rocket-launcher as a heavy infantry weapon. The rocket is considered more accurate, more effective, more humane, safer to operate, and suitable in a wider array of tactical conditions, including anti-personnel, anti-vehicle, and anti-bunker. It seems unlikely that a plasma weapon serve a significantly different tactical role than a flame-thrower, except that it would be harder to construct, more complicated, more expensive, and more susceptible to environmental conditions. As such, I would not bet money that any plasma-weapons are going to be in use in the near future. Most plasma physics research is more related to the effects of nuclear weapon detonation; occasionally, by bureaucratic accident, some of that plasma-physics budget trickles into a tactical research group; but that doesn't mean that there is either a practical use or a real need to develop such weapons. Nimur (talk) 16:32, 19 July 2010 (UTC)

It depends alot on what you mean by plasma weapon, according to our plasma weapon article, a plasma weapon is any device that uses plasma as a weapon so there are many different devices that could fall under the catagory of plasma weapon. The pulsed energy projectile uses a laser that ablates part of the targets creating a burst of plasma strong enough to knock a person over or even kill them. This is currently being tested by the military. However, for a device that shoots out a beam of plasma like a flame thrower, the plasma woul most likely disipate and cool to quickly to cause damage.--74.67.89.61 (talk) 23:53, 19 July 2010 (UTC)

If you could somehow encapsulate a bolt of plasma in a magnetic field, you could potentially prevent the two biggest problems facing the use of ionized plasma as a weapon, namely blooming (The dissipation of a plasma when it interacts with other particles like air) and the cooling it would undergo, though I'm not sure such a targeted magnetic field is currently possible, so hypothetically plasma could only be used as a sort of flamethrower as the poster above mentions until such advancements are made. However, plasma could still be used with impunity in a hard vacuum like space, where there would be no blooming effect and cooling would happen at a slower rate as a sort of mid-range heavy assault weapon. —Preceding unsigned comment added by 174.88.50.154 (talk) 04:09, 20 July 2010 (UTC)

Would plasma cause electrocution in addition to burns?

--138.110.206.101 (talk) 03:06, 19 July 2010 (UTC)

At those conditions, I am not sure there'd be much of a distinction. --Jayron32 03:27, 19 July 2010 (UTC)

Plasma are locally neutral, so there wouldn't be any significant voltage differences over your body. But even a cold plasma could give a chemical-like burn via the free ions. --Tardis (talk) 04:09, 19 July 2010 (UTC)

A chemical burn? Not necessarily. Top layer of our skin -- stratum corneum -- is dead, and low-energy ions are extremely unlikely to penetrate it without being neutralized. --Dr Dima (talk) 05:35, 19 July 2010 (UTC)

The phrase "cold plasma" does not mean "plasma at room temperature". It is a measure of the average electron energy. It can only exist in vacuum conditions, or else recombination will neutralize the plasma. Bittencourt has a chapter on the cold plasma model: "This simple model encompasses only the equations of conservation of mass and of momentum." It says nothing about the thermodynamic temperature, nor the effects of sticking your hand into it. Again, for these cold-plasma considerations to be valid, it is almost always a requirement that the density are very low; e.g. such that the thermal velocities are much smaller than the electromagnetic wave speed (not the speed of light - the speed of the plasma oscillation). This is easier to accomplish by changing ionization rates and pressures than by changing the gas temperature. To address the original question: plasmas are often created by conditions (like highly ionizing incident electromagnetic radiation, and a sparse gas) that would be harmful to humans. With or without the ionization, those conditions would be harmful anyway. Direct effects attributable to the plasma would be enhanced chemical reactivity with the free radicals and ions. Everything else - the electromagnetic radiation, the temperature, the pressure, and so on - would be just as harmful as if there were no ionization present. Nimur (talk) 16:43, 19 July 2010 (UTC)

Silver + Phosphate

I've noticed that Wikipedia has no article on Silver phosphate. This leads me to wonder, does this compound exist? And if not, what reaction (if any) would be expected if a solution of Silver ion (like Silver nitrate) was mixed with a solution of Phosphate ion (like Sodium phosphate)? Would any insoluble products be formed? 67.172.250.173 (talk) 04:10, 19 July 2010 (UTC)

Most silver compounds (with the notable exception of the nitrate) are insoluble, so its likely that silver phosphate would be insoluble. If you have access to even a basic high school chemistry laboratory, they are usually stocked with both of those chemicals, so you could ask a teacher to do the experiment yourself. Silver phosphate undoubtedly exists, however not everything that exists merits a Wikipedia aticle. A compound that exists, but which has no practical applications would likely not merit one. --Jayron32 04:34, 19 July 2010 (UTC)

I would think that it is needed. I read in a science kit that one way to test for the aqueous phosphate ion would be to add silver ion, which would precipitate yellow silver phosphate. --Chemicalinterest (talk) 10:55, 19 July 2010 (UTC)

Created it (with redirects); feel free to expand with reliable sources. --Chemicalinterest (talk) 11:30, 19 July 2010 (UTC)

As it turns out Silver phosphate is notable due to its use in photography and analytical chemistry. It also seems to be a topic of current research too.77.86.59.77 (talk) 16:13, 19 July 2010 (UTC)

To answer the question - yes Silver phosphate is formed.77.86.59.77 (talk) 16:13, 19 July 2010 (UTC)

You can find details on the production of silver phosphate in this recently published paper - it's not free, but if you create an account, register an email address and use Special:EmailUser/Smartse, I can email you a copy. I've nominated the article to be in the "did you know" section on the main page, you can find the nomination here Smartse (talk) 14:30, 20 July 2010 (UTC)

Minimum air pressure for sound

What's the minimum air pressure required to carry sound at a detectable volume? Since outer space isn't a complete vacuum, would it be theoretically possible to create a microphone sensitive enough to pick up sound in space? NeonMerlin 04:54, 19 July 2010 (UTC)

That's a very good question. Sound is a pressure and density wave. My first guess would be therefore that for the sound wave to propagate, you need the mean free path of the air molecule, with respect to collisions with other air molecules, to be much shorter than the sound-wave wavelength. The mean free path increases as density decreases, so the longer is the sound wavelength the lower is the lowest air density at which it would still propagate adequately. So I think the wavelength (that is, the frequency) may be more important than the sound volume. Of course, the higher is the sound volume at the source the farther is the distance at which the sound is still detectable; that is also true. --Dr Dima (talk) 05:26, 19 July 2010 (UTC)

According to our Interstellar_space article there are only "a few hydrogen atoms per cubic meter". Far too little for a physical wave to transfer between this. However, this fascinating article has more information - it looks like they have detected "sound" in space, but nothing you would ever be able to hear. You'll need to read it to understand [5] --mboverload@ 05:32, 19 July 2010 (UTC)

More than mean free distance, you'd also need there to be enough collisions between particles to propagate the sound over noise level. As particles spread out, the signal-to-noise ratio grows significantly worse until no meaningful information can be propagated via sound waves. --Jayron32 05:44, 19 July 2010 (UTC)

Not quite what you asked, but density wave theory is relevant. It explains the formation and evolution of galactic spiral arms as a kind of sound wave propagating around the galaxy. The wave leads to episodes of local compression of the interstellar medium, which in turn triggers star formation and gives the appearance of concentrations of bright stars near and immediately after the compression maxima. This explains why the stars in these spiral bands don't actually move at the same apparent velocity as the spiral arms themselves, i.e. the individual stars in the arm that we observe today are only the current generation of stars created by a deeper process propagating through the interstellar medium. In this case the wavelength of the "sound" would be ~10-100 thousand light years. As Dima suggested above, if you make the wavelength long enough even the dilute medium of interstellar space can carry it. Of course, at this scale it isn't "sound" in any sense that humans would be able to directly measure or listen to. Dragons flight (talk) 07:04, 19 July 2010 (UTC)

So you're saying that in space, someone can hear you scream, if you scream at a low enough pitch and the other person's eardrums are really really big? --Trovatore (talk) 07:06, 19 July 2010 (UTC)

Pretty much, yes. Really big larynx and really, really big eardrums :) --Dr Dima (talk) 08:58, 19 July 2010 (UTC)

An analogy would be trying to transmit the details of a picture by a few bytes of information; the information is not enough to get the details. --Chemicalinterest (talk) 11:05, 19 July 2010 (UTC)

The commonly used "zero" reference sound pressure in air is 20 µPa RMS, which is usually considered the threshold of human hearing (at 1 kHz). Cuddlyable3 (talk) 13:59, 19 July 2010 (UTC)

And since we were talking about plasmas above, here: magneto-acoustic waves. Plasmas, being electrically conductive and therefore responsive to electromagnetic effects, can sustain acoustic longitudinal compression waves at much lower density, because ions can "collide" (interact electromagnetically) at greater distance than a neutral atom (which must only interact electrostatically). Naturally, there is a difference between ordinary sound waves and these effects; and it would be hard to put a regular acoustic transducer microphone to pick up the pressure fronts; but these are definitely compression waves at much lower gas density than ordinary sound. They are observed experimentally, usually by deducing the effective gas density from electromagnetic/radio signatures, and exist in the earth's magnetosphere, on the sun, and in the solar wind. Nimur (talk) 16:53, 19 July 2010 (UTC)

I should respond to Mboverload's linked article, as well as to responses to Dragons Flight. The linked article talks about sound (or intermolecular interaction) propagating in a very dense, relative to "empty space", cloud around a black hole. This sound wave emitted X-rays which are just ordinary light, and those are what we detected on Earth. So no, no sound went through normal 10-atoms-per-m^3 space, and in space no one will hear you scream ever because those molecules will not interact with each other on anything near that energy scale ever. Even the density waves Dragons talks about that generate spiral arms involve actual net motion of massive amounts of matter on the wavelength scale, which is very different from sound we hear every day in which matter actually moves net forward on a scale much much smaller than wavelength. SamuelRiv (talk) 08:22, 20 July 2010 (UTC)

Maps for streams

Where can I get maps for streams? I know Microsoft MapPoint, Google Maps, and Bing Maps do not like copying. Is there any other place to get maps? --Chemicalinterest (talk) 11:51, 19 July 2010 (UTC)

"...do not like copying." Copying to what end? Maps are basically always intended for use as maps; it's not a problem to print one off and use it as such. On the other hand, copying to resell is going to be breaking the copyright of virtually any map provider, not just online ones. Can you more clearly describe your purpose? — Lomn 12:25, 19 July 2010 (UTC)

The US government has lots of maps that are free (worldwide maps, not just US). Here are a few sites: [6] [7] [8] [9]. Ariel. (talk) 12:38, 19 July 2010 (UTC)

Articles for streams, such as the Shallow Brook and all other ones, are greatly enhanced by a map. I wanted to know where I could get maps for streams from. --Chemicalinterest (talk) 12:40, 19 July 2010 (UTC)

There might be something listed here which might help. --Tagishsimon (talk) 13:32, 19 July 2010 (UTC)

OpenStreetMap allows you to choose what data to export. Warofdreams talk 15:29, 19 July 2010 (UTC)

The other editors at WikiProject Rivers may have more ideas. Rmhermen (talk) 16:22, 19 July 2010 (UTC)

Used Seamless Maps on USGS. Resolved. --Chemicalinterest (talk) 23:04, 19 July 2010 (UTC)

Catnip and REM sleep

Is there a relationship between catnip exposure and increased REM sleep time in cats? Also, can anyone speculate as to what cats dream about? My cat refuses to respond to my questions but insists on being scratched behind the ears. Viriditas (talk) 12:07, 19 July 2010 (UTC)

I can't provide a source, but I do recall seeing a program on TV in Australia some time back in which a cat appeared to stalk prey while asleep. ("Asleep" as determined by measuring brainwave activity.) Presumably the cat was dreaming about stalking prey. Mitch Ames (talk) 13:46, 19 July 2010 (UTC)

I don't know about cats - but dogs certainly dream and I'm as sure as it's reasonably possible to be that they are dreaming of chasing and hunting and such. Dogs seem less able than humans to shut off the connection between brain and muscles when dreaming (Atony). Some people who suffer from Rapid eye movement behavior disorder have the same problem. In dogs, you can see their feet making small movements that start out sequenced alternately like they are walking, then switch to front-feet-together/back-feet-together like they are running. You can see their breathing speed up - sometimes you can hear tiny little barks. Then, suddenly you might see their jaws making little movements - one of my dogs would salivate at this point in the dream. It's hard to believe we aren't watching the dog dream of walking around in the park, seeing a squirrel, chasing it and probably catching and maybe eating it. If cats suffer the same lack of atonia that dogs do, then carefully watching your cat sleep might well give you some kind of insight as to what's going on in their furry little brains. SteveBaker (talk) 14:41, 19 July 2010 (UTC)

In my experience, cats do not engage in the same kind of thing, or at least don't do it as regularly. I've owned cats all my life and have only seen the occasional twitch or two - nothing like the drama Steve mentions above. Perhaps there's some kind of tie in to hunting styles; dogs chase down their prey, so it makes sense they dream about running. Perhaps my cat is dreaming intently about lying in ambush and I'm mistaken in thinking it's sleeping like a log (in much the same way my math teacher misinterpreted my attempts at afternoon meditation). Matt Deres (talk) 17:29, 19 July 2010 (UTC)

Yes, exactly. My experience is that cats just don't have REM as much as dogs. However, after leaving approximately 1 gram of dried, ground, organic catnip for my cat to play with every day for a month, I noticed that he began to have REM every day in the late evening, and I've never seen a cat do it that much, leading me to conclude that the catnip was influencing his dream state. His legs move as if he's running and jumping, his whiskers twitch like he's poking his face through a bush, etc. That's why I'm asking. Viriditas (talk) 18:27, 19 July 2010 (UTC)

Well, if you're going to dose your pet to the eyeballs with a strong (for a cat) hallucinogenic drug...you're bound to get some odd side-effects! What's strange about this is that in humans, the active ingredient in catnip is a mild sedative and an antispasmodic - which I'd naively imagine would help to dampen down atonia rather than enhance it...but then cats aren't humans...so all bets are off. SteveBaker (talk) 22:49, 19 July 2010 (UTC)

The cat "hunting" during REM sleep probably had surgery on locus coeruleus similar to experiments by Michel Jouvet #Cat dreams --Digrpat (talk) 18:24, 19 July 2010 (UTC)

Apparently the main active ingredient in catnip, nepetalactone, or its metabolic byproduct nepetalic acid, is a mild sedative and hallucinogen. However I haven't been able to spot any studies that discuss its neural mechanism of action, so I don't think it is possible to say anything about its effects on REM sleep. Looie496 (talk) 23:23, 19 July 2010 (UTC)

Alcubierre drive

Would an Alcubierre drive require large quantities of some sort of chemical compound (like the dilithium used in Star Trek's warp drives)? --138.110.206.101 (talk) 12:52, 19 July 2010 (UTC)

Our article on Alcubierre drives certainly seems to suggest so. Physchim62 (talk) 13:08, 19 July 2010 (UTC)

I meant, is there a single specific substance would be required in large quantities, which would play a role in the future similar to dilithium in Star Trek? --138.110.206.101 (talk) 13:12, 19 July 2010 (UTC)

Since this drive does not exist, there is no way to answer this. Ariel. (talk) 14:57, 19 July 2010 (UTC)

The article indicates it would require exotic matter. That's probably a good candidate for "dilithium" as anything else. --Mr.98 (talk) 15:32, 19 July 2010 (UTC)

Indeed, although I would guess (and guessing is all we can really do) that if exotic matter is possible then it would need to be made synthetically, rather than mined. --Tango (talk) 21:57, 19 July 2010 (UTC)

Scientific name of Clown Dorid

Hi, I am attempting to find the scientific name of the Clown Dorid so that I can make a mention of the Clown Dorid name in the appropriate wikipedia article, or make a new article if this animal doesn't have a page already. I found this picture which is described as a Clown Dorid in Victoria, B.C., Canada. At wikipedia, the closest picture I can find is the Triopha catalinae (sea clown Triopha). But the pictures don't look exactly the same, and I kind of doubt it is the same animal. Can you help me figure this out? Thanks. Fallendarling (talk) 14:22, 19 July 2010 (UTC)

According to this page, the Clown Dorid is Triopha catalinae. I think the 'sea clown' is the same thing - and the differences in those photos you link to are not significant. SteveBaker (talk) 22:35, 19 July 2010 (UTC)

scratching: survival benefits

Background:

The instinct to scratch is very strong and spreads through all of the mammal and apparently into at least some fish. Conventional medical advice is always that you must not scratch. However, behavior which is very widely distributed in the animal kingdom normally has some survival benefit. I am surprised to find no postings on the survival benefit of scratching.

With skin parasites such as tics and fleas, I can see that scratching would be a benefit, in that it has a real chance of physically eliminating the parasite. I would also suggest that scratching can help with mosquito bites and poison ivy etc., because causing the lymph and blood to leak from the skin would help purge locally concentrated toxins.

Searching the web shows lots of references to scratching being an indication of parasite infection but does not suggest that scratching helps it. I found nothing on the concept of eliminating locally concentrated toxins, as I mention above.

Question:

Can anybody give some informed comment on this?

Perhaps this could be a topic for a post-graduate biology student. Fixer Anderson (talk) 14:32, 19 July 2010 (UTC)

The usual theory, as you say, is that the reflex to scratch is intended to remove insects. Scratching at other times is probably just the body making a mistake. Evolution doesn't result in optimal solutions, just "good enough" solutions. The harm from scratching when you don't have an insect on you is minimal, so the evolutionary pressure to develop more refined itch sensations is very small. --Tango (talk) 15:51, 19 July 2010 (UTC)

Yup, I'd go with "mistake" because other situations produce same/similar sensation to the presumed evolutionarily-good trigger. If it's really conserved mechanistically across species, then it's gotta be something low-level like a reflex arc or something else that doesn't require substantial advanced sensing or processing (i.e., easy to trigger false-positive). But still, seems easy to co-opt existing sensory input (a certain level/location/size of touch?)...not sure what more specific sign one could have that didn't require substantially more/more-advanced sensing. DMacks (talk) 17:17, 19 July 2010 (UTC)

Did anyone else get itchy reading this question? Googlemeister (talk) 19:13, 19 July 2010 (UTC)

I'm pretty sure the general understanding is that scratching serves to remove irritants of every sort from the skin, including contaminants, skin damaged by sunburn, etc. If you Google around for "pruritis" (the medical term for itching), you should be able to get some leads into the literature. Looie496 (talk) 19:31, 19 July 2010 (UTC)

It's actually spelled pruritus, which might help with the Googling. It's not the -itis ending meaning "inflammation", but some different etymology. I think it's pronounced PROOR-it-us but I'm not sure of that.

Similarly for tinnitus (ringing in the ear), which again I think is pronounced TINN-it-us. --Trovatore (talk) 18:51, 21 July 2010 (UTC)

Dragons using chemicals to generate fire?

It seems to have become a trend now to describe fantasy dragons that use chemical compounds to create flames--as in the movie Reign Of Fire. Supposedly "if a beetle can do it a dragon can too", except that the bombardier beetle doesn't create sparks/flames, just boiling liquid. Are there really chemical mixtures an animal could use to create a flame, or is the whole concept just bunk? 75.200.39.63 (talk) 16:31, 19 July 2010 (UTC)

Sure. We have evidence that at least one animal can learn to use chemicals to produce fire. See also, fossil record of fire. Lots of chemical mixtures will work, so long as the mixture completes the fire triangle. I would think that any other animals that wanted to create flame would have to use similar approaches - naturally-occurring materials, like wood, sulfur, and phosphates, plus air, plus an ignition source. Nimur (talk) 16:58, 19 July 2010 (UTC)

see http://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Archives/Science/2010_May_22#Is_there_any_animal_that_can_.27emit.27_fire.3F

There are many chemical mixtures that catch fire when mixted eg potassium permanganate/glycerin - do animals produce such mixtures, or the components is sufficiently concentrated form - no. It's bunk.

The oft mentioned Bombardier beetle produces hydrogen peroxide at only 10% [10] that's nothing like enough to produce a fire .. if the concentration was high enough the beetle would have burned its ass off thousands of years ago in a spontaneous beetle combustion evolutionary dead end !

But real D&D Dragons aren't made of organic matter - so that doesn't matter.. 77.86.59.77 (talk) 17:06, 19 July 2010 (UTC)

Living organisms can produce hydrogen and methane, both of which are flammable - a mixture that is known to combust is flatus, as many videos on Youtube will testify. No doubt a bit of fantasy digestive tract re-plumbing could occur to make a fire-breathing dragon. Brammers (talk/c) 17:51, 19 July 2010 (UTC)

And an animal with the worst case of bad breath in the entire animal kingdom! SteveBaker (talk) 22:29, 19 July 2010 (UTC)

You'd still need an ignition system. After all, human fire breathers can blow dragon-like flames with an external source of ignition (and fuel, but the fuel is relatively easy from a biological point of view). Natural selection hasn't delivered us with fire-breathing dragons, probably because it's easier to use the required energy simply to grow bigger and/or cleverer. Physchim62 (talk) 22:41, 19 July 2010 (UTC)

In Anne McCaffrey's fantasy books the dragons produce phosphine which spontaneously ignites in air. I believe there are bacteria that can make this gas. Graeme Bartlett (talk) 02:46, 20 July 2010 (UTC)

Also because the advantage is not at all obvious, when compared to the downsides. Consider that soldiers only use flamethrowers in very specific situations—they are not very "general" weapons, unless you want to set your house on fire on a regular basis. --Mr.98 (talk) 18:58, 20 July 2010 (UTC)

Von Kossa Stain

Von Kossa Stain on the web makes no sense eg [11] the calcium is reduced by the strong light and replaced with silver deposits

The wikipedia article (here before I edited it) seems to make more sense - it says it is a test for bone phosphate. What's going on?77.86.59.77 (talk) 16:47, 19 July 2010 (UTC)

Is your question about calcium vs phosphate? Does this help? Ariel. (talk) 02:46, 20 July 2010 (UTC)

Yes - I was just trying to come to terms with the wrongness of many apparently reliable looking sources that clearly state it is an agent for calcium.87.102.13.208 (talk) 02:59, 20 July 2010 (UTC)

Info about the changing face of the Earth

It is about the GEOLOGICAL changes, how it is formed and its reasons. eg:1. Formation of mountains,rivers,valleys etc 2. Information about the tectonic plates. Please check about it in WIKEPEDIA or any other information giving websites188.135.2.50 (talk) 17:16, 19 July 2010 (UTC)

It appears that you copied a homework question here. We will not do your homework. The answers you seek are in the articles on Wikipedia. See mountain, river, and valley. You will also want erosion. The second question brings up tectonic plates. -- kainaw™ 18:42, 19 July 2010 (UTC)

And orogeny - learn the meaning of this word and impress your teacher! Personally, I've always been interested in comparative orogeny on extraterrestrial worlds, as it provides one of the best scientific justifications for planetary explanation of solid-surface planets and moons. It's very strange that mountains and valleys can develop on worlds that do not have seismic or tectonic activity, nor water or air to erode them. But, mountains and valleys do exist up there.... Nimur (talk) 23:41, 19 July 2010 (UTC)

Don't forget lakes too. Smartse (talk) 13:55, 20 July 2010 (UTC)

Teeth

Hello Why is it that teeth do not attempt to repair themselves? Surely in primitave man, broken damaged teeth would have been a threat to survival. This seems the only part of the body without the will to try and heal. Thanks Ossiee (talk) 17:21, 19 July 2010 (UTC)

We discussed a related question last April. The real issue is not so much why they don't repair themselves, as to why we only have two sets of teeth, rather than having a continuously replenishing number. Primates can't do this, but rodents can, but they sacrifice having teeth that fit well together, which humans kind of rely on. Keep in mind that this is not an evolutionary question limited to primitive man—this is a trait that evolved more generally with primates and probably even earlier than that. --Mr.98 (talk) 17:33, 19 July 2010 (UTC)

It's all part of the Grand Scheme by the Great Dentist in the Sky, looking after his chosen ones. Clarityfiend (talk) 22:33, 19 July 2010 (UTC)

We have this article: Hyperdontia. Bus stop (talk) 22:38, 19 July 2010 (UTC)

We grow one extra set of molars in our 20s, so primitive man had a few back-up teeth. 142.104.215.130 (talk) 22:47, 19 July 2010 (UTC)

Your premise is false -- teeth do not only attempt to but often succeed in repairing themselves. Sclerotic dentin is that dentin that has been exposed to noxious stimuli and has hardened in an attempt to block further insult (usually bacterial enzymatic toxins) and root canals become increasingly calcified when similarly exposed to bacterial insult. The fact that teeth cannot regenerate -- well, that is something entirely different. The majority of the human body cannot regenerate. Lost fingers, toes, eyes, ears, genitourinary structures, digestive tract structures, etc. are gone forever. It is only the very rare case that chordate organisms can completely regenerate lost limbs and or other minor body parts, such as amphibians, which can grow back appendages and then the famous (even) human liver that can regenerate. Peripheral nerves can also grow back, but my point is that teeth are far from the exception, so your query seems a bit misguided. DRosenbach <sup>(Talk | Contribs)</sup> 02:50, 20 July 2010 (UTC)

Indeed. My husband has a full set of perfect teeth because his filled teeth grew back and pushed the fillings out: he also has never lost a tooth. (It's nice to know it is a recognised medical phenomenon!) --TammyMoet (talk) 08:11, 20 July 2010 (UTC)

Dental repair only occurs on a level that it is barely-to-somewhat macroscopically recognizable -- chunks of missing tooth structure will not grow back, because that would be regeneration, not repair. The latter is resolution of bodily destruction with foreign or different tissue types, while the former is resolution with identical tissue types, perfectly restoring the wound or site of tissue destruction to its pre-damaged state. DRosenbach <sup>(Talk | Contribs)</sup> 17:49, 20 July 2010 (UTC)

Most mammals are diphyodonts, with two successive sets of teeth. However, there are at least two exceptions. Both elephants and manatees are polyphyodonts, with multiple replacement sets of molars - according to our article, an elephant has five or sometimes six sets of molars in its lifetime. Note that these are complete replacement teeth - this is different from rodents, whose incisors grow continually but are not replaced if lost. Gandalf61 (talk) 11:01, 20 July 2010 (UTC)

My grandmother had a third set of teeth and my own extra randomly-placed teeth were surgically removed when I was a young child. See super-numerary teeth. (which I now see is a redirect to the earlier mentioned Hyperdontia.) Rmhermen (talk) 18:07, 20 July 2010 (UTC)

How does your comment relate to the OP's question? DRosenbach <sup>(Talk | Contribs)</sup> 02:24, 21 July 2010 (UTC)

In the past, primitive man had a short life for all sorts of other reasons. It's only with modern medicine that man survives long enough for tooth loss to become a problem, and since modern dentistry makes sure this is not fatal, there is still no evolutionary pressure for such an adaption. Evolution only does enough to ensure survival to reproductive age-anything else is a luxury only to be changed (hopefully) with genetic engineering or regenerative medicine.[Trevor Loughlin]80.1.88.12 (talk) 13:11, 23 July 2010 (UTC)

Dextropropoxyphene

On the graph shown, where exactly does, the drug dextropropoxyphene stand. I, precisely, mean the red & grey capsule in the centre.

Thanks  Jon Ascton  (talk) 18:37, 19 July 2010 (UTC)

Probably mid way on the Y axis and pretty low on the X axis (depending on dose). As an opioid derivative it's going to be pretty addictive (at least in the long term) but, given it's wide availability as a drug to treat (and not to abuse), it's going to be fairly low on the physical harm side. Regards, --—Cyclonenim | Chat  19:07, 19 July 2010 (UTC)

That graph was put together by an expert following lots of research. We aren't experts and don't have the time or resources to do lots of research, so we can't work out where any other drugs would appear on that graph. --Tango (talk) 19:25, 19 July 2010 (UTC)

And in any case, as has been discussed here a few times, it's unclear how literally one should take that particular graph, as it doesn't account for the fact that numerous drugs come in different forms that have different propensities for harm and addictiveness (e.g. the difference between chewing coca leaf or smoking crack cocaine, both of which are technically the same drug). --Mr.98 (talk) 19:39, 19 July 2010 (UTC)

We can't work out exactly where a drug can go on that graph, but we can speculate based on it's properties that we do know. If a drug is an opiate, it's going to have a high risk of dependency. Regards, --—Cyclonenim | Chat  19:41, 19 July 2010 (UTC)

Note that the harm figure is an average of acute, chronic and injected harm - mostly chronic harm roughly mirrors dependance (with expceptions), also this means that drugs that are not injected score 2/3 of other similarly 'harmful drugs'. 178.78.65.223 (talk) 19:53, 19 July 2010 (UTC)

I mentioned this earlier. I object to using average as a measure of harm on this graph. I think they should have used max. Ariel. (talk) 21:23, 19 July 2010 (UTC)

The problem with using the maximum known harm is that one person could have reacted badly to a drug due to all sorts of reasons, even genetic defects. If a random drug kills one person because of a defect, but causes only mild harm in the others, do you use the maximum harm? Of course not. That's why you have to use averages. Regards, --—Cyclonenim | Chat  21:48, 19 July 2010 (UTC)

I don't mean maximum harm among various people, I mean maximum from the three types of harm listed in the accompanying table: Acute, Chronic, Intravenous Ariel. (talk) 22:14, 19 July 2010 (UTC)

Oh, sorry, completely misunderstood! I agree, e.g. Heroin should definitely have a harm of 2.8 if that's the acute harm value given but the rest are lower. Regards, --—Cyclonenim | Chat  23:40, 20 July 2010 (UTC)

Scrotal implosion

what is Scrotal implosion and why is it trending on twitter? —Preceding unsigned comment added by 86.159.8.157 (talk) 18:44, 19 July 2010 (UTC)

It's just nonsense hoping to become a meme. 178.78.65.223 (talk) 19:12, 19 July 2010 (UTC)

Check out http://www.whatthetrend.com/. It gives explanations of what all the things that are trending are and why they are trending. --Tango (talk) 19:21, 19 July 2010 (UTC)

Apparently, this one is a joke medication side effect from a recent episode of The Boondocks. --Tango (talk) 19:22, 19 July 2010 (UTC)

you can see the source here http://www.youtube.com/watch?v=vMvKIHw7bCI 178.78.65.223 (talk) 19:28, 19 July 2010 (UTC)

Two dimensional thrust vectoring

If you took an aircraft, such as the F-22, and remove the vertical stabilizers to make it more Stealthy, and replace them with yaw-controlling thrust vectoring nozzles, yet still maintain the agility of the fighter? I know of the X-36, but the article didn't say much about its performance. --The High Fin Sperm Whale 19:24, 19 July 2010 (UTC)

The article x-36 says The X-36 possessed high maneuverability that would be ideal for use as a fighter. I see no reason why not. 178.78.65.223 (talk) 19:37, 19 July 2010 (UTC)

There some more info here on the side effects of not having a 'rudder' - notably lack of or reduced yaw stabilty [12] 178.78.65.223 (talk) 19:40, 19 July 2010 (UTC)

See also Tailless aircraft 178.78.65.223 (talk) 19:45, 19 July 2010 (UTC)

The article on tailless aircraft is not much help. It is mostly about aircraft lacking horizontal stabilizers. AS for the first comment, I don't see how I could have missed that! Thanks anyways. --The High Fin Sperm Whale 20:32, 19 July 2010 (UTC)

At the expense of providing an unhelpful answer, "anything can be designed with any parameters you want." More importantly, if you made such a design, would the tradeoff involved be worth the effort? Removing a stabilizer can be done on any aircraft - the result is obviously a less stable aircraft. It will cost more money to design an active control system than a passive one with the same control characteristics and specs. You can look at the specs for a thrust-vectoring system to determine the force, velocity, and time-constant regimes that it can operate over - but I strongly suspect that complete removal of such a major, critical part of the stability and control system of the aircraft would render the airframe virtually uncontrollable. In fact, the advent of the vertical stabilizer is often credited as one of the crucial technologies that made the first heavier-than-air flight possible. Who would have thought that the most important "wing" on the aircraft was the one that didn't provide any lift! The Wright brothers' flyer is more a feat of control than of propulsion, lightweight materials, or any other characteristic - the majority of their innovation was that they could actually steer because they had rudders and wing-warping control. Since control is such an important part of design, it is heavily studied in the design of an airframe. MDATCOM is an aerodynamics program used to design these sorts of things and test them numerically before building models and running them through the wind tunnels. As you begin removing "pieces" from the airframe, you start approaching a missile-like aircraft; you can usually spin stabilize such airframes, but that would be unmanageable if you intended to put a human inside it. Needless to say, this is definitely an ongoing effort in modern defense research - efforts to replace 100% of our aircraft fleet with unmanned aerial vehicles are under way, because removing the human from the flight control equation results in relaxation of many other design constraints. (E.g., instead of a fighter, you could have a highly-maneuverable, spin-stabilized, steerable cruise missile for all of our air-to-air and air-to-ground combat needs). This would be cheaper to build, could operate more stealthily, could be more fuel-efficient/longer-range; could turn faster (without a pilot, there is virtually no restriction on turning radius, maximum G-force, and so on). Nimur (talk) 20:55, 19 July 2010 (UTC)

Also keep in mind that an aircraft which relies on thrust vectoring to control yaw requires thrust, so there would be no control without thrust. This situation could occur after engine failure, and would occur on every flight when the throttles are at idle during approach and landing. anonymous6494 21:54, 19 July 2010 (UTC)

For this reason, spacecraft (including the Space Shuttle orbiter, which is not very aerodynamic, despite its superficial "airplane" shape) have a primary propulsion system and a separate reaction control system. An RCS is easier to build and is more reliable than a vectored thrust nozzle; and it can be designed to provide 6-degree-of-freedom maneuverability. Nimur (talk) 23:44, 19 July 2010 (UTC)

Huh? The space shuttle can't use its primary propulsion after the external tank drops away. The RCS does orbital manuevers, but only orbital manuevers. Once it reaches aerodynamic altitudes on descent, the shuttle uses control surfaces like a plane. Rmhermen (talk) 05:01, 20 July 2010 (UTC)

I beg to differ - the Orbital Maneuvering System does orbital, and only orbital, maneuvering. But the RCS, a separate propulsion system on STS, is also used during descent for orientation and velocity control. Space Shuttle also has control surfaces, including a rudder and ailerons; but RCS is useful because it can provide independent, 6-DOF attitude and translation. See this NASA science brief: STS Reaction Control System: descent maneuvering is "...accomplished by using either control stick steering commands or automatic commands as inputs to the equations. The solution of these equations results in fire commands to the available RCS jets and/or appropriate orbiter aerosurfaces." Loosely speaking, STS has three different types of propulsion: primary propulsion (comprising the ET and SRBs, and the Space Shuttle Main Engine); the OMS (comprising the "jet pods" on the "tail"; and the RCS, comprising all the other small nozzles tucked neatly away throughout the rest of the Orbiter. Nimur (talk) 07:55, 20 July 2010 (UTC)

You are correct on the only-orbital part. From our article: "The aerodynamic shape is a compromise between the demands of radically different speeds and air pressures during re-entry, subsonic atmospheric flight, and hypersonic flight. As a result the orbiter has a high sink rate at low altitudes, and transitions from using RCS thrusters in low pressure to flight surfaces at low altitudes." That low altitude is minimum 45,000 feet when the last of the RCS shuts-off (the first part shuts-off at whatever altitude "dynamic pressure of 10 lbs/sq foot" corresponds to). However I can't find any point that the main engine and the RCS are functional at the same time. Flight control on ascent is managed with main engine gimbals, not the RCS or shuttle flight surfaces. Flight control on descent is managed by RCS until each flight surface becomes useful in thickening atmosphere. Flight control in space is handled by OMS and RCS but is non-aerodynamic. So the example fails to illustrate. Rmhermen (talk) 18:02, 20 July 2010 (UTC)

reply to anonymous6494 -- an interesting point. That means the plane would behave quite like a jetski - maneuverable only when powered. A very counter-intuitive situation for most people, especially when approaching a dangerous obstruction. 218.25.32.210 (talk) 07:44, 20 July 2010 (UTC)

Bates method

Are here any Bates method users? (I have read Wikipedia:Reference_desk/Guidelines/Medical_advice and I am not seeking medical advice). 83.31.74.163 (talk) 21:30, 19 July 2010 (UTC)

Currently? I'm sure some people are still trying it - but you are aware that studies have shown conclusively that it doesn't work...right? SteveBaker (talk) 22:23, 19 July 2010 (UTC)

It certainly has its fans. Its crazy, irrational, fans. If a popular blog makes a post about glasses or LASIK, there's a reasonable chance someone who's never posted a comment on that blog before will show up and post a diatribe about it. If you search Instructables you'll find many howtos covering simplified versions of the Bates method. I'm not sure why Instructables doesn't make an effort to remove such nonsense.

Another related bit of crazy is pinhole glasses. (Pin-hole glasses really do work as a primitive replacement for corrective lenses. But they're always sold as a cure-all that will magically fix your eyes. Which is proven to be nonsense.) APL (talk) 23:07, 19 July 2010 (UTC)

Take for example this: [13]. Comments by Andrei and ceanes say that this method is helpful. 83.31.89.30 (talk) 11:14, 20 July 2010 (UTC)

Exactly. You could post an article about any crazy, proven-not-to-work, doesn't-even-make-sense, folk cure you can think of, and you'd get a dozen internet comments from people who swear it works and that there is a global conspiracy to cover it up.

It's all so predictable, really. APL (talk) 14:42, 20 July 2010 (UTC)

What about Huxley? 83.31.96.69 (talk) 19:39, 20 July 2010 (UTC)

He made a lot of money selling books to suckers. If he did use the Bates method to improve his eyesight that wouldn't tell the rest of us anything useful, Huxley's vision was damaged by keratitis, not by a natural nearsightedness.

However, he didn't improve his visual acuity. From one of the sources in our article :

"It is often pointed out that Huxley's visual acuity has not improved in any extraordinary way. He admits that. The point is that he has learned how to use what he has to better advantage. It is not the primary retinal sensation that is improved; it is. the neglected, but vitally important, cerebral part of seeing that has been trained."

That is to say, it's all in his head and he admits as much. His eyes have not actually improved at all. (As Bates claims!) Huxley is only claiming that he has trained his BRAIN to make better use of his poor eyes.

It's flim-flam. When proponents of some great new technique start telling you that they can improve things, but not in a ways you can measure, then you know you're dealing with flim-flam. It's tough to tell if people like that are honestly self-deluded or if they're just scam artists, but either way you're better off steering clear. APL (talk) 19:59, 20 July 2010 (UTC)

Can probiotics develop antibiotic resistance?

After watching my toddler endure violent diarrhea resulting from his intestinal flora being completely wiped out by the amoxicillin he had to take for cellulitis, I began to wonder: Is it possible for probiotics to develop antibiotic resistance, so that when you need to take antibiotics, the beneficial organisms that normally live in your intestines won't be harmed?

I'm curious if there have ever been any studies conducted wherein healthy people take deliberately incomplete antibiotic doses, to kill off some of the beneficial bacteria, leaving the remainder to breed stronger. And if so, how long would the effect last? ~Amatulić (talk) 23:01, 19 July 2010 (UTC)

In principle I don't see anything against it. But I have a feeling it would not develop in humans. Harmful bacteria have a strong "motivation" to develop resistance - if they don't they are wiped out. The probiotic ones however, while they might be killed temporarily they will come back (from other people), so they don't really need resistance so badly. I bet it could be done in a lab though - grow cultures with low level doses of antibiotics. But it has a downside: bacteria are able to share genes (Horizontal gene transfer), so if the "good" bacteria had the genes for resistance, it's possible for "bad" ones to copy them. Ariel. (talk) 01:08, 20 July 2010 (UTC)

That seems logical. In that case there wouldn't be a real benefit in developing an antibiotic resistant strain of good bacteria in one's gut. ~Amatulić (talk) 05:09, 20 July 2010 (UTC)

Ariel's explanation does initially seem logical, but I would be very cautious about using the "motivation" argument Ariel proposes since natural selection acts at the level of the individual organism, not at the level of whole populations of bacteria. Consider the following case: a few good bacteria in a person have randomly acquired resistance, either by mutation or by horizontal gene transfer. Antibiotics are then used, which kill all of the sensitive good bacteria, but leave the resistant ones. The resistant ones are the only ones left, multiply and therefore almost all of the good bacteria are now resistant (of course this is simplified - individual antibiotics don't act on all types of bacteria or on all environments within the body). You now have a population of resistant bacteria. It doesn't matter whether or not they are going to be wiped out if they don't develop resistance, the bacteria don't "know" that. If there is a selective pressure and sufficient biological variation resistance will develop. Of course the resistant bacteria would often be less "fit" once the antibiotic is removed (e.g. if they waste energy producing enzymes which break down antibiotics) so may then be replaced by sensitive bacteria acquired from other people, or by a few sensitive bacteria who happened to survive. This sort of fluctuating resistance in "good"/neutral bacteria does actually occur [14] and can be a major problem, since, as Ariel mentions, harmful bacteria can acquire resistance from the good bacteria. This link has more explanation [15]. Equisetum (talk | email | contributions) 09:57, 20 July 2010 (UTC)

In addition, the concept of 'good' bacteria is a little simplistic. For starters, 'good' bacteria could obtain genes which make them pathogenic. More importantly perhaps, even without that in the right circumstances/conditions 'good' bacteria can cause problems. This is somewhat mentioned in the probiotics article although in reference to taking probiotics. In summary, purposely developing antibiotic resistance, even in healthy individuals with a very carefully controlled diet, sounds like a very bad idea. In fact, over prescribing of antibiotics, including to healthy and no so healthy people who won't benefit from them is a concern even when they finish the treatment. This link [16] may be of interest. Nil Einne (talk) 20:56, 20 July 2010 (UTC)

They already do - antibiotic resistance genes are (were) used to make genetically modified plants. Although people still debate the safety of this, the regulators decided that it was safe as the genes were already present in our gut flora (reference 1 reference 2). You might like to read this too - regarding what happens to when you take antibiotics. Smartse (talk) 13:47, 20 July 2010 (UTC)

July 20

Unidentified Insect

Hi. I was hoping for some help from anybody with knowledge of British entomology.

Earlier today, I had an insect fly into my house in Devon that I don’t believe I’ve ever seen before. It appeared bigger than a common wasp but rather smaller than a hornet. It had a round but, perhaps, slightly flat yellow body with two extremely well defined stripes circling the abdomen (this was the most immediately striking thing about it – the stripes were not blotchy and poorly defined as on most bees and wasps but perfectly defined, like you’d expect to see on a T-shirt and there were definitely only two stripes) and very big, bulbous grey eyes just above and either side of a bright yellow wasp-like mouthpart. Its thorax looked to be a dark brown colour (perhaps with a hint of red) and its legs (which seemed very long for a wasp) were most definitely reddish. It was so wasp-like that I assume it’s a member of hymenoptera but, given my lack of insect knowledge, I suppose it could conceivably be something else indulging in a bit of mimicry, although I doubt it. Any ideas?

Thanks Pantscat (talk) 00:54, 20 July 2010 (UTC)

Can you get a photograph of it?

See anthing similar in http://commons.wikimedia.org/wiki/Category:Wasps

Some mimic images here http://www.pbase.com/tmurray74/wasp_mimics&page=all

Hoverflys might have the flat abdomen - the eyes are distinctively 'flyish' though eg http://www.google.co.uk/images?q=hoverfly&um=1&ie=UTF-8&source=og&sa=N&hl=en&tab=wi&biw=1280&bih=937 178.78.65.223 (talk) 01:30, 20 July 2010 (UTC)

(edit conflict) I think that most "like a wasp but not a wasp" sightings turn out to be hoverflies, but there are so many different species of the critters that identifying the one that visited your house may be difficult. Do any of the ones pictured here look at all like your visitor? Deor (talk) 01:35, 20 July 2010 (UTC)

There's a list of common uk hoverflies here http://www.microscopy-uk.org.uk/mag/artmay07/cd-hoverflies.html I can't see your two stripe one, but your description of "big bulbous eyes" suggests a fly and not a wasp - which have big eyes - but I wouldn't call them bulbous.178.78.65.223 (talk) 01:40, 20 July 2010 (UTC)

I did get a photo of it but I'm not sure how good it was and am not at all sure how I would get it onto here even if it was a good one. I haven't yet found out what it was but I'm now reasonably confident that you guys are right and that it was a hoverfly (although I didn't realise they could be that size) as it looked similar (although not identical) to Epistrophe grossulariae. http://bugs.decemberized.com/images/Epistrophe_grossulariae_female.jpg

Must be a fairly close relative I would have thought. Pantscat (talk) 02:19, 20 July 2010 (UTC)

If you need more you can upload the image using the a button on the left hand margin - select "upload file" which should take you here http://en.wikipedia.org/wiki/Wikipedia:Upload - you'd need to give it a license since everything uploaded has to be shared. Uploading to commons is recommended http://commons.wikimedia.org/wiki/Commons:Upload , then just paste the link here...87.102.13.208 (talk) 02:41, 20 July 2010 (UTC)

How about this one - found nearish your region and has two yellow bands http://www.cornwalls.co.uk/photos/img2270.htm 87.102.13.208 (talk) 02:53, 20 July 2010 (UTC)

Yep, that's the fella. Looked just like that one and sounds about the right size. So I now have a name - Volucella zonaria or the Hornet Mimic Hoverfly.

Thanks, guys Pantscat (talk) 12:32, 20 July 2010 (UTC)

And we do have an article, with some other images. Deor (talk) 17:59, 20 July 2010 (UTC)

Elements in the human body

How many elements are necessary for human survival? So far I have listed:

• Hydrogen
• Oxygen
• Carbon
• Nitrogen
• Phosphorus
• Iron
• Calcium
• Sodium
• Magnesium
• Sulphur
• Potassium
• Iodine

Please list any more that I haven't named, and tell me if any of theses are not needed for humans. Thanks, --The High Fin Sperm Whale 01:38, 20 July 2010 (UTC)

Technically you need http://www.soils.wisc.edu/~barak/soilscience326/listofel.htm essential plant elements unless you want to starve. or Plant nutrition

See also Dietary mineral which I hope is a complete list.01:44, 20 July 2010 (UTC) —Preceding unsigned comment added by 178.78.65.223 (talk)

We need salt, and that has Chlorine in it. Maybe. I'm not a scientist, though. 142.104.215.130 (talk) 01:45, 20 July 2010 (UTC)

Both sodium and chlorine are in the list in dietary mineral.178.78.65.223 (talk) 01:47, 20 July 2010 (UTC)

You check out Composition of the human body yet? APL (talk) 01:50, 20 July 2010 (UTC)

Or better yet, Dietary mineral, which lists (in a convenient periodic table graphic) all of the elements typically in a human body (in reasonable amounts), and also what the different elements do. Buddy431 (talk) 03:22, 20 July 2010 (UTC)

That actually lists the minerals that people need to eat, which is an important distinction. Ariel. (talk) 13:54, 20 July 2010 (UTC)

I would be surprised if there were any reasonably common elements that we don't need for something. Either as a part of our bodies - or as a part of our food sources or some other subtle thing. Possibly the nobel gasses (helium, neon, etc) aren't necessary - but I wouldn't even want to bet on that. SteveBaker (talk) 04:26, 20 July 2010 (UTC)

Acording to the linked article: "An exception is aluminium, which is the third most common element in the Earth's crust (after oxygen and silicon), but seems to serve no function in living cells. Rather, it is harmful in large amounts." Rmhermen (talk) 04:46, 20 July 2010 (UTC)

Despite being linked to 3 (now 4) times the article Dietary mineral seems strangely inaccessible to some - to simplify I've copied the relevant data below:77.86.76.212 (talk) 20:35, 20 July 2010 (UTC)

H																		He
Li	Be												B	C	N	O	F	Ne
Na	Mg												Al	Si	P	S	Cl	Ar
K	Ca	Sc		Ti	V	Cr	Mn	Fe	Co	Ni	Cu	Zn	Ga	Ge	As	Se	Br	Kr
Rb	Sr	Y		Zr	Nb	Mo	Tc	Ru	Rh	Pd	Ag	Cd	In	Sn	Sb	Te	I	Xe
Cs	Ba	La	*	Hf	Ta	W	Re	Os	Ir	Pt	Au	Hg	Tl	Pb	Bi	Po	At	Rn
Fr	Ra	Ac	**	Rf	Db	Sg	Bh	Hs	Mt	Ds	Rg
			*	Ce	Pr	Nd	Pm	Sm	Eu	Gd	Tb	Dy	Ho	Er	Tm	Yb	Lu
			**	Th	Pa	U	Np	Pu	Am	Cm	Bk	Cf	Es	Fm	Md	No	Lr

The four organic basic elements

Quantity elements

Essential trace elements

Pervasive but no identified biological function in humans

Lemon Juice - alkaline or acidic?

I've heard that although lemon juice in its raw form (squeezed from the lemon) is acidic, once it enters your stomach it somehow becomes alkaline and has an alkaline affect on the pH of your stomach - is that true? And if so, by what process is the citric acid converted into an alkaline substance? —Preceding unsigned comment added by 118.139.32.234 (talk) 01:59, 20 July 2010 (UTC)

Once cells metabolise the citric acid to carbon dioxide and water, it will leave behind the alkaline components in the juice such as potassium ions. The carbon dioxide will equilibriate to bicarbonate ion in the body, which is mildly alkaline. The biochemistry that handles this is the citric acid cycle. Graeme Bartlett (talk) 02:40, 20 July 2010 (UTC)

... and, of course, even the most acidic lemon juice has a pH of about 2 which is similar to the average pH in the stomach. The pH of Gastric acid at the point of secretion can be as strong as 0.8. Dbfirs 08:23, 20 July 2010 (UTC)

Don't forget that the carbon dioxide equilibriates to bicarbonate and protons. --Chemicalinterest (talk) 10:49, 20 July 2010 (UTC)

I'm pretty sure that CO2 dissolved in blood is acidic. John Riemann Soong (talk) 18:57, 20 July 2010 (UTC)

It is. Protons are much more acidic than bicarbonate is basic. --Chemicalinterest (talk) 19:36, 20 July 2010 (UTC)

But that's only once the acid has diffused out of the stomach, so it won't have any effect on the pH of the stomach. Even before that lemon juice isnt really going to change to the pH of your stomach - pH is measured on a logarithmic scale - this means that to change the pH of the stomach from 1 > 2 would require diluting the acid with 10 times as much water. So no, lemon juice can't change the pH of your stomach. Smartse (talk) 00:08, 21 July 2010 (UTC)

But most of the CO2 is breathed out losing that acid producing carbonic acid and leaving behind the potassium bicarbonate. But this is not in the stomach, it is in the body cells. That CO2 goes on to acidify the oceans instead. Graeme Bartlett (talk) 06:11, 21 July 2010 (UTC)

Does not... The plants take it and produce O<sub>2</sub>, completing the cycle. If the CO<sub>2</sub> is breathed out, then the bicarbonate and carbonic acid are released because the equilibrium shifted. Why it is alkaline is because the K<sup>+</sup> ion is basic in comparison to gastric acid with its H<sup>+</sup> ion. --Chemicalinterest (talk) 14:44, 21 July 2010 (UTC)

Under normal conditions, the K+ ion is neither basic or acidic. It is ever so weakly Lewis acidic, even more than Na+. If you take the potassium salt of fluoroantimonic acid suddenly the normally stabilised K+ ion will become a strong Lewis acid indeed.

Also, breathing CO2 out does not leave behind bicarbonate. CO2 is breathed out by protonating bicarbonate. Blood near the lungs is more acidic than blood in the systemic capillaries. This does two things: diioxygen's affinity for haemoglobin increases, while bicarbonate is protonated and released from transporter complexes. All that is left behind is the water that the CO2 reacted with in the first place, at the actual site of metabolism. Bear in mind, blood pH is buffered by bicarbonate. John Riemann Soong (talk) 15:49, 21 July 2010 (UTC)

age

Can there is a medicine aur ane thing bye which the growth of child increse?? example like in movies now days actors age of about 15-17 look much younger than mormal .. —Preceding unsigned comment added by 115.248.45.13 (talk) 06:08, 20 July 2010 (UTC)

Nothing that would be remotely legal to administer to a child to alter their appearance for acting purposes. Film directors cast actors who look the right age for the part, and some people look older and some younger than the average, so an actor who looks young will be preferred (as they will have more acting experience than someone really that young), and such actors will specialise in such roles. Make-up also contributes, of course.

There are treatments to help the growth of people whose growth is less than it should be because of some medical problems, of which there are several. See, for example, Growth hormone. 87.81.230.195 (talk) 07:10, 20 July 2010 (UTC)

I'm confused why you want medicine to increase the growth of a child. Do you think actors age 15-17 need to be given it to look older? As 87 has said, this seems strange, actors who look young are generally preferred so there's no reason why anyone, either the director/s or the actor/s are going to want to take it. If you think actors age 15-17 have been given medicine to make them look young then logically it's medicine which reduces the growth of a child not increases. Nil Einne (talk) 20:48, 20 July 2010 (UTC)

Acting a part is more than just "being" the part. Early silent movie actress Lillian Gish said that director D.W. Griffith told his young adult actresses to hop and skip and jump around to look more like children. Today they just look like the are hyperactive or ate too much speed or sugar. Actors or comics today still use certain mannerisms when playing younger characters. Edison (talk) 19:58, 21 July 2010 (UTC)

Strange worms - Could anyone tell me what these are?

I've seen quite a few of these worms in covered areas (mostly on stored plush fabrics, boxes, bags, etc.) and have always wondered what they are. I most often find dead ones, but I've also noted a few live ones in some old carpets.

Most of the worms I've come across are about .3-.5cm in length, but, in the most extreme cases, I've seen them go up to 1cm.

Here is a picture of the one that I normally see: http://eepromeagle.dyndns.org/unknownbug/IMGP4319.JPG And a larger one: http://eepromeagle.dyndns.org/unknownbug/IMGP4322.JPG

EEPROM Eagle (talk) 06:35, 20 July 2010 (UTC)

It might help someone to make an identification if you tell us approximately where in the World you are, since insect species are very numerous and different continents and climates have markedly different populations. These look as if they may be the caterpillars of some kind of moth (so not a "worm" except in a very non-scientific sense), but beyond that we need geographical clues to narrow down the possibilities. 87.81.230.195 (talk) 06:57, 20 July 2010 (UTC)

Beetle larvae (not worms) - possibly Dermestidae Shyamal (talk) 07:01, 20 July 2010 (UTC)

Yes, it looks like the cast off shell of the larvae of the larder beetle. I get them in my flat, I wish I didn't. 213.122.7.114 (talk) 09:29, 20 July 2010 (UTC)

Heh, yes. I said worm just to say to what they kind of looked like to me. I was pretty sure they were larvae. To answer the above question, I'm in Massachusetts. Thanks for the information! EEPROM Eagle (talk) 22:01, 20 July 2010 (UTC)

would it be possible to duplicate, mechanically, the action of a modern CPU (obviously at up to minutes per clock cycle).

A modern latest CPU like the Intel i7 can have 8 megabytes of cache, which is 67 million bits (or a square array of 8185 by 8185 bit-representing elements). Then it has 731M transistors. That's a square array of 27038 x 27038 elements. However, they are constrained to work on a very, very small scale, as they must operate at close to or somewhat over 3 GHz. Now, in 3 GHz, light only travels 10 centimeters, so obviously the overall size can't be huge.

Our mechanical design has no such constraints: it's fine to be many feet by many feet (by many feet, since you can use vertical space more easily when assembling wooden parts by hand).

If "speed is no object", and it is fine to take as long as you want to go through one clock cycle, is it feasible to duplicate the action of this CPU mechanically, such that if you mechanically set the input of the "wooden processor-equivalent" it will churn and eventually give the same output as the actual Core i7?

Secondly, if you imagine this mechanical processor, what do you think the fastest spinning gear is, and how fast does it have to spin to complete one "clock cycle" in wood in, say, 30 seconds? Then, if we take that RPM and do simple multiplication, what RPM is the Intel i7 at 3 GHz equivalent to in wood and metal rpms? Say, 18 trillion RPM? Thanks. 84.153.247.76 (talk) 11:00, 20 July 2010 (UTC)

Charles Babbage nearly did something similar with his Difference engine and Analytical engine in Victorian times. 92.15.7.17 (talk) 11:18, 20 July 2010 (UTC)

(Well, he did make working 'designs' - but none of his designs were actually completed until the British Science Museum recreated one of them a couple of years ago). SteveBaker (talk) 11:54, 20 July 2010 (UTC)

Please read the third word in the sentence above. Incomplete parts of the machines were made under his supervision. 92.15.7.17 (talk) 12:49, 20 July 2010 (UTC)

I did read what you wrote - but "nearly" is a pretty weak explanation and I think it needs amplification. What Babbage achieved is widely misunderstood. He produced a complete design for the difference engine (which is NOT a computer - but more like a fancy printing calculator) and he made many partial designs for the analytical engine (which would have been, recognizably a "computer" - but for narrow technical reasons is not properly "Turing complete"). During his lifetime, only about 10% of the difference engine design was ever actually constructed - but it was fully completed recently by the science museum in London - and with a simple correction to the original drawings (where the orientation of some part was reversed) it was made fully functional. But the design for the analytical engine - which would have been "the world's first computer" is not complete enough to be constructed. What I think is most impressive is that the first ever computer program was written for the analytical engine (although there is some controversy about whether Babbage or Ada Lovelace actually wrote it). SteveBaker (talk) 00:18, 21 July 2010 (UTC)

You certainly wouldn't "duplicate" the way a modern CPU actually works. But it's certainly possible to build mechanical computers - and many people have done that. (I actually own one - you can see a photo I took of it in our Digi-Comp_I article). There is a mathematical law called the Church-Turing thesis that says that any computer that passes a certain minimal level of capability (a "Turing-complete" computer) is - in principle - capable of the same things as any other Turing-complete computer...providing you have enough time and memory to complete the calculation. So we could build a relatively small, fairly simple computer (like this one - which is made from Lego) and it could simulate an Intel i7 - eventually - and given enough memory...which is just a matter of being patient enough, and owning enough Lego! SteveBaker (talk) 11:54, 20 July 2010 (UTC)

you say "you certainly wouldn't "duplicate" the way a modern CPU actually works" (my emphasis). Why not? You say that it's not possible if the input, off the bus, is fed via braille, to get the same output as the i7, having taken the same intermediae processing steps??? Well why not... aren't all the little transistors basically just doing boolean logic? THere's nothing "magic" or analogue about an i7 that you couldn't do with another, logically equivalent, design: after all, before they ever built one, Intel surely modeled the i7 in software... 84.153.247.76 (talk) 12:30, 20 July 2010 (UTC)

I Imagine Steve's point is that although you could (in theory) duplicate the 731 million transistors of the i7 in a mechanical computer, that wouldn't be a rational way to design a mechanical computer. With a mechanical computer, costs of fabricating and maintaining individual components become significant, and factors such as friction increase with the number of components, so it would be better to go for a design that minimised the number of components, even though it did less in parallel and took more clock cycles to process each instruction than a mechanical i7 clone would. Gandalf61 (talk) 13:08, 20 July 2010 (UTC)

Well, I don't know what you guys think I might want with a mechanical computer, but it's nothing at all. I have absolutely no need for a mechanical computer, I am only interested in the Intel i7, and the only reason for asking about a mechanical computer is whether one could, theoretically, at great cost and impracticality, be created that was logically equivalent to it. If so, how long could we estimate it would take to "render" (or "virtualize" or in some way be equivalent to) one clock cycle on the i7? Going from that, how many RPM would it go at to, say do an i7 clock cycle in 30 seconds? Thanks. 84.153.247.76 (talk) 13:39, 20 July 2010 (UTC)

A mechanism that was "logically equivalent" to the i7 (i.e. gives equivalent outputs when presented with equivalent inputs) would not need to replicate the i7's internal design. So - do you really mean "logically equivalent", or do you mean a mechanical copy of the i7, where you could identify each i7 transistor with a specific mechanical widget ? Gandalf61 (talk) 14:10, 20 July 2010 (UTC)

There's no easy way to know this without actually spending the rest of our lives designing the machine. The mechanisms of an electronic chip (Transistors, etc.) do not exactly translate into mechanical constructions. Babbage's proposed computers used gears, but he was designing a new system from the ground up, taking full advantage of the parts he had available. It's not at all clear to me that an exact duplicate of the i7 could be built that way. In fact, pneumatic systems would be a closer analog to electronic circuits than gears would.

This is an important point because how that mechanism is crafted will be a large portion of what determines the speed that your machine runs at.

Not only that, mechanical linkages have problems that electronic ones don't. (Biggest issue : friction adding up over all those gears.) So something will have to change regardless for that to be fixed. APL (talk) 14:54, 20 July 2010 (UTC)

To be clear, there is no theoretical reason you couldn't build a mechanical copy of an i7. In practice, mechanical computers tend to work differently though because binary logic is not easily modeled with gears. (Think: What is the mechanical analog of a transistor, or an AND gate, etc.? Such things could be created, but the individual elements would tend to be more complex than is practical.) You'd also have to design so that the total friction in the system was manageable and the amount of force between individual gears was never so great that the gears would break. I would speculate that if you tried to follow i7 logic directly using wooden gears (as you suggest), then you'd probably fail both of these constraints. In practice, it would be much more reasonable to think about designing a system that takes i7 inputs and gives back i7 outputs, but was internally redesigned to operate mechanically. As Steve mentions, there are a wide variety of ways that could be accomplished. However, questions like "how fast is the fastest gear" and "what RPM" are largely pointless without considering a specific design and such values could be changed by orders of magnitude based on engineering choices that have no impact on overall performance. So I don't think there is any useful answer to those questions without considering a specific model. You could look at some of the historical mechanical calculators and try to figure out how much longer they take to operate than a modern CPU given the same operation, and that is perhaps the most useful comparison I could suggest. Dragons flight (talk) 13:48, 20 July 2010 (UTC)

It might be theoretically possible, but it would be an engineering wonder, and easily the most complicated machine ever constructed. Googlemeister (talk) 13:52, 20 July 2010 (UTC)

If the chip has 700 million transistors, and each one requires a few moving parts, you're talking billions of moving parts (compare to the Space Shuttle's 2-3 million mostly non-moving parts). I think it would be a statistical impossibility that they would all be functioning at the same time, even for a moment. --Sean 15:09, 20 July 2010 (UTC)

Let's think about this the way a computer-designer actually thinks about this. Every few years, a new VLSI process is introduced. Sometimes, they just make this year's process smaller; but sometimes they fundamentally change something - like the order that individual chemical layers get deposited. When those changes happen, the chip designers don't sit around thinking "darn, now we have to translate the i7 core, device by device, 731 million times." This is critical - a modern processor has 731 million pieces (or whatever) - so to build it, you must have another machine to macro-ize construction operations 731 million times. Instead, they just "recompile" their design for a new process, and then spend some effort "tuning" for performance. Here's how it works. First, you ask yourself how to build one transistor in the new process. And you come up with a transistor macro; and then you consider how you need to interconnect two transistors; and then after some time, you end up with a set of macros to represent a lookup table, a bit of a register, a multi-bit vector, and so on. Now, the i7 core is described somewhere deep in the vaults of Intel's research and development lab; and it is described in a language like verilog or VHDL (or more likely, some bizarre combination of both that gets woven together by incomprehensible perl scripts and passed down by an elite cabal of engineers and computer architects). Then it gets run through a different machine that maps each high-level interconnection description into a series of device-layer connections - called place and route or VLSI synthesis. So - let's get back to the horrifyingly huge wooden contraption. How do you build one transistor in mahogany and teak? Well, let's think about what a transistor actually is - and remember, we have the luxury that we really only care about digital logic, so we really just want a high-gain inverting transistor. This is a simple device that takes one input and produces an output at the opposite value of the input. So, let's think of your wooden device as some kind of lever or piston or something; it has to take a high- or low- input (maybe it gets poked by the position of another lever or piston, and then pokes the next lever with the opposite polarity). Of course friction has been brought up many times; transistors deal with this too, it is called the "static current draw" or the quiescent current. Even the best amplifiers waste some energy. If you look at a circuit schematic for a transistor, you will always see both a signal input and a power input. Thermodynamics requires that power be consumed. The difference is that one transistor is ridiculously close to the theoretically most-efficient system; whereas your wood/pneumatic piston is not. But oh well; nobody really worries about energy problems in modern computers anyway. Let's say you just attach an air-compressor to every piston, and power all the pneumatics using fossil fuels, (keeping the analogy to modern electronic computers). So we now have one wooden transistor, and we need to interconnect it to others to form basic building-block devices, like truth tables, clocks, registers, and arithmetic units. Then, we design the macros for each of these, and provide the list of available macros (and their description in terms of boolean logic) to the VHDL synthesizer software. That will crunch out our design for about 24 hours, and finally spit out a list of all 731 million wooden/pneumatic devices - including where to place them, and what to connect them. Now, you could require those placements to be exactly in the same location and connection pattern as an i7 core - but that would be stupidly inefficient. The i7 core has been optimized for the speed of propagation of 32-nm silicon CMOS. The number of cache-lines, and the number of bits per cache-line, for example, are directly determined based on real latency to main memory in the particular technology it was designed for. Much of the complexity comes about from these specialized hardware and process tuning. But, for the sake of exploration, let's say that your wooden memory timings are exactly scalable to those of a modern DRAM. Now you just need a way to fabricate 731 million pneumatic elements. In CMOS, this is easy - we call it photolithography - but you can probably find some way to easily obtain all the parts, lay them out, and operate on them in bulk. Don't forget to build redundancy into your design - because in 731 million wooden pistons, termites will bore out the innards in 1 in a million wooden pistons. So, at the wooden CPU factory, you need to be able to build everything - test everything - and then automatically reroute to a redundant piston any time a sub-unit doesn't work. Alternately, you can spend your whole life trying to de-termite your fabrication-process to obtain a 100% yield; but that is less efficient. So, in summary, yes it could be done. If the explanation above has served any purpose, it is to convince you why microfabrication and silicon are the only realistic ways to do processor design using reasonable quantities of time, resources, and engineering effort. VLSI is amazing stuff - it's got room for innovation - but it really is centuries ahead of any other mechanical manufacturing process. Nimur (talk) 16:02, 20 July 2010 (UTC)

Wait, I notice a couple of times the question-asker uses the phrase "logically equivilant". If all you want to do is mimick the inputs/outputs of the i7 then Steve's method above would work just fine. Any Turing compatible CPU can be made to mimic the inputs/outputs of any other Turing compatible CPU.

All you'd need is an additional mechanism to map certain parts of the mechanical Turing machine's 'memory' to the input/output pins, and run the 'memory' through that device at the end of every simulated cycle. APL (talk) 20:47, 20 July 2010 (UTC)

My first answer is still the right one. Let's refer to the actual wording of the question: "would it be possible to duplicate, mechanically, the action of a modern CPU". The "action" of a modern CPU can been seen at various levels. At the level of software - the Church Turing thesis says that, yes, any Turing machine could be programmed to accept a computer program for an Intel chip and produce the same numerical answers. At the level of voltages on pins of the ship, obviously a purely mechanical computer fails because it can't accept electrical signals without some kind of tiny low current/voltage motor.

The fuzzy answer of whether you could simulate an Intel chip by somehow simulating each of it's internal logic gates out of mechanical systems is tough...I don't think that's relevant to the original question though - you don't have to do a 1:1 simulation to fulfil the requirements to simulate that chip perfectly. For example - when the engineers at Intel are designing a new CPU, they don't draw out this vast circuit - then manufacture one - then see if it works. Turning a paper design into a chip costs millions of dollars - you don't do that until you have a known-working design. So they start out by simulating the new design - first at the level of registers and such - then at the level of gates, then at the level of transistors. Those simulations are 1:1 identical in function to that of the real chip - so that when they manufacture the chip, it should work the first time. Since that exact simulation of the chip is a computer program - the Church-Turing thesis says that we can precisely simulate the chip (right down to measuring the voltages at the inputs and outputs of transistors) on any sufficiently large Turing machine. We could even have our mechanical Turing machine have a mechanical display of some sort (imagine lots of multicolored cubes that rotate on rods to show different colored faces or something) - and display the interior logic of the Intel chip. So yeah - we can do a perfect simulation on any Turing machine.

Another branch of this discussion has been talking about the size and speed of a mechanical computer. But let's think out of the box here. A mechanical computer could be vastly faster than the fastest hardware we have today. Calculations on the possible speeds of a nanotechnological computer in which the mechanical parts were (let's say) 100 atom carbon chain push-rods, levers and cams suggest that it would be vastly faster than the fastest machine we could build out of electronics. The fastest transistors we have can switch at perhaps 100GHz - but moving 10 atoms a distance of just a few times the size of an atom can happen WAY faster than that. There is much debate about whether such machines are possible - but if they are, they will almost certainly be teeny-tiny mechanical turing machines.

SteveBaker (talk) 23:59, 20 July 2010 (UTC)

Did you mean to type "simulating each of ITS internal logic gates" ? Cuddlyable3 (talk) 15:44, 21 July 2010 (UTC)

It's an interesting idea and I certainly hope someone looks into it. But I'm not going to invest any money I can't afford to lose. Intuitively it seems to me the big problem is going to be reliability. How many of your enormous number of rods and cams and levers are going to get stretched, or squashed, or broken, in the course of a computation?

By the way I also think that's why your big version made out of wood probably won't work. Babbage never tried to represent a billion bits. At some point, changing one bit will require changing so many others, that the force you have to exert at the input level will simply break something along the way. But as I say, that's intuition; if you have a design that gets around the problem it would be interesting to see it. --Trovatore (talk) 00:32, 21 July 2010 (UTC)

That's why you need a wooden buffer amplifier - you must expend power in order to isolate each stage from the others. But this means that any individual wooden lever does not have to push a billion others - it just has to drive its own output. The friction of later stages is totally isolated. Each stage consumes power from an external power-supply, so that the signal input does not have to provide power input as well. Nimur (talk) 00:58, 21 July 2010 (UTC)

Hmm, might work. I'm still skeptical that it can be done reliably enough to simulate a modern computer. --Trovatore (talk) 01:15, 21 July 2010 (UTC)

Babbage had worked out some clever tricks to avoid the problem of changing one digit and thereby causing a whole bunch of gears to turn at once. The obvious worst case would be when if you added 0000000001 to 8999999999 - resulting in 9000000000 and the force of one tiny gear wheel changing would have to turn (in that case) 10 other wheels. Babbages difference engine used something like 30 decimal digits of precision (VASTLY more precise than a modern computer in full double-precision mode!) - so in his case, turning one wheel might cause 30 others to have to turn - which would have caused serious mechanical issues. Those kinds of problems had beset previous efforts at building mechanical calculators - resulting in them being restricted to low precision calculations and making them highly temperamental. He came up with a rather clever way to fix that problem so that the amount of force required to do a worst-case 'carry' was no different than for a simple non-carry addition. However, the way he did it in the Difference Engine was rather slow - basically, the turning of a result wheel from 9 to 0 tripped a little "carry" lever and didn't propagate the carry on to the next digit - then this little spiral gizmo went down the column of levers one at a time rotating the wheel by one unit whenever the previous wheel's carry lever was sticking out - resetting the carry lever and possibly tripping the next carry lever down the stack. If you watch the machine in the London Science Museum doing this while it's adding random numbers together, it's kinda hypnotic! The machine performs about one addition per second - so these things happen rather quickly! For his later "Analytical engine", he came up with an even more devious mechanism that avoided the mechanical force issues and didn't consume significant extra time by doing a kind of 'carry prediction' trick. The interesting thing about that was that it made the adding mechanism so freaking complicated that he gave up the idea of every stack of gears that represent a number having the "ADD" capability. Instead it would copy the numbers from a "memory register" into the "mill" where the addition would take place and the result copied back into the register. This is eerily similar to a modern CPU where numbers are stored in dumb memory and all of the math happens in one central unit rather than having full arithmetic capability at every single byte of RAM! SteveBaker (talk) 21:36, 21 July 2010 (UTC)

You could have small wooden balls to simulate electrons. It would then be the size of a skyscraper. 92.28.255.176 (talk) 08:59, 21 July 2010 (UTC)

For that you must have very small balls. Making DRAMs would be difficult. Cuddlyable3 (talk) 15:48, 21 July 2010 (UTC)

Skyscraper? No, it would be a few miles on a side at least. The i7 has a minimum feature size of 32nm. If you make the reasonable assumption that your wooden device will have a minimum feature size of half an inch, you wind up with a device roughly 400,000 times the original. APL (talk) 15:56, 21 July 2010 (UTC)

On early vacuum tube computers, the mean time between failure of the few thousand tubes (valves) was a practical limit on complexity (as was power consumption). What is the MTBF for a high speed wooden gear and pinion, or lever action? How many times can it repetitively click and clack at high speed before it wears or warps? There may be a practical limit on what fraction of a modern computer chip could be physically modelled in wood, and how many clock cycles it could complete before repairs/replacements/adjustments were necessary. As complicated wooden mechanism, various early automata, the Jacquard loom, the [Tracker action| tracker organ] and other musical instruments, and the wooden clock come to mind, so somewhat complex wooden gadgets can function thousands of times, or tens of thousands of times, with levers moving levers or gears turning pinions. A chip goes at many millions of operations per second and many seconds are required for some calculations or programs. It would be instructive to make a mechanical analog of an amplifier, an invertor, basic logic gates, or a flipflop. But I would not expect to see a wooden computer which would click and clack and invert a large matrix, say. Edison (talk) 19:40, 21 July 2010 (UTC)

A Pneumatic Transistor

Here's how to make a pneumatic (P) transistor (reverse the spring and gate for the N equivalent). You'll also need pneumatic "wires" (copper pipe will do the trick and give the whole thing an attractive old-world charm) and a few other simple device equivalents such as resistors (constricted pipes) etc. Once you've got the handful of fundamental devices, you can build and model a standard cell library, and enter it into your synthesis libraries. Run through the standard EDA flow as described above to get a fully mechanical pneumatic CPU.

The simulation part of the EDA flow will give you an estimate of the highest reliable clocking frequency as well as static and dynamic current (pressure) consumption. The MTBF of a pneumatic transistor is likely much lower than for a semiconductor one which will shorten your CPU's lifetime accordingly (perhaps to less than the time required for a single operation). David Carron (talk) 14:39, 22 July 2010 (UTC)

how did the Greeks discover the earth was round?

How did the Greeks discover the Earth was round? 84.153.247.76 (talk) 13:36, 20 July 2010 (UTC)

Well, the first guy who estimated the diameter was named Eratosthenes who did this around 250BC or so, but I think they knew it was round before that. Googlemeister (talk) 13:47, 20 July 2010 (UTC)

Because it looks round. My history of science tutor believes it was pretty obvious to any seafaring nation that the horizon was curved, and it was not a 'discovery' at all. The idea that it was flat wasn't one ever held by the Greeks, or by western civilisation at all, but found only in civilisations constrained to land (egypt, babylon, the western populace prior to civilization per se), where a smooth horizon is hard to come by, and so because the surface of a sphere locally approximates to euclidean, the ground appears flat. —Preceding unsigned comment added by 129.67.116.122 (talk) 13:58, 20 July 2010 (UTC)

I doubt the Greeks had Wikipedia back then, but we do now, and it has a page specifically about the issue: spherical earth. DMacks (talk) 14:15, 20 July 2010 (UTC)

Perhaps by considering the fact that the shadow at noon is not vertical in places to the north and south. But another explaination for that could be a flat earth and a nearby sun. 92.29.123.248 (talk) 13:00, 21 July 2010 (UTC)

Website which shows raincloud movement for the next few hours (in UK)?

In the Netherlands, there is a well known website that lets you see where rainclouds will be moving over the next few hours. It's pretty accurate, 'cause it's only predicting the next few hours based on radar data of cloud movements. Do we have such a website for the UK? ----Seans Potato Business 13:40, 20 July 2010 (UTC)

Have you tried the Met Office web site ? This app shows cloud cover forecasts in map form, and this one shows rainfall forecasts. Both show snapshots every 3 hours for next 24 hours, then two snapshots per day for following 3 days. Gandalf61 (talk) 13:50, 20 July 2010 (UTC)

You might also try http://news.bbc.co.uk/weather/ - click on the more uk weather link to access various interactive time-lapse displays of recent actual and future forecast rain etc, though unfortunately the scope and options of these seem to have been restricted quite recently. 87.81.230.195 (talk) 18:24, 20 July 2010 (UTC)

induction

would it be possible to induce a polar or overall charge on an incoming bullet usign static electricity or someother means and then using a high power magnetic field to deflect it away?--91.103.185.230 (talk) 14:01, 20 July 2010 (UTC)

In theory, yes. In practice, no. — Lomn 15:07, 20 July 2010 (UTC)

I agree. To elaborate, start by reading muzzle energy. A modern rifle round carries thousands of joules of kinetic energy. To "stop" this bullet, you need to dissipate that energy; to deflect it, you need to impart enough momentum to meaningfully change its trajectory. If you consider the energy involved, we have no machinery that can practically or safely deliver that amount of energy in a focused way to induce current or magnetic force on a bullet. An easier way to deflect such a bullet would be to detonate a large explosive in its trajectory. Alternately, you can dissipate bullet energy effectively by hiding behind a sandbag barrier. Because the bullet impacts inelastically with sand, sandbags are a better defense against rifle and machine-gun rounds than steel-plate armor. When you consider alternatives, you have to keep thinking about how much energy you need to dissipate, and/or how much momentum you need to null out or deflect. Nimur (talk) 16:26, 20 July 2010 (UTC)

It depends on what is meant by 'deflect'. I can conceive of a laboratory-demo-type experiment in which a bullet is fired, is given a static electric charge, and then passes through an intense magnetic or electric field and suffers a small deflection. In that situation, a shot aimed at a relatively distant target might be deflected by a few inches — enough to miss the person at whom it was aimed. Mind you, I can't think of a practical use for this sort of scheme; a small-angle deflection is only useful if it can be applied far, far from the target. TenOfAllTrades(talk) 18:26, 20 July 2010 (UTC)

(ec) If the bullet is linear dielectric it would be attracted to a point charge with a force that scales r<sup>-4</sup>. This would make it practically hard. —Preceding unsigned comment added by 92.8.29.89 (talk) 18:31, 20 July 2010 (UTC)

Suoermagnetman recommends using magnets to break the motion of metallic bullets (and so do I) ( http://www.youtube.com/watch?v=iABmUEH5s0k&NR=1&feature=fvwp )(see also Eddy current brake). The motion is close to critical damping, see Damping. 77.86.76.212 (talk) 19:33, 20 July 2010 (UTC)

You could do a calculation to determine how much momentum you need to impart to yield a 12-inch deflection on a round that is traveling at 900 m/s. If you begin applying an acceleration orthogonal to the round as it exist the muzzle, you have less than 1/3 of a second before it reaches its target (at maximum range). How much force is required to accelerate a 5 gram object so that it gets a 0.25 meter displacement in 0.3 seconds? This is elementary physics: I'm getting a force appoximately equal to 1 newton. Does anyone know a way to focus an electromagnetic or electrostatic field at a distance of 300 meters and impart a 1 newton force on a lead/copper bullet? As far as I know, there is no such technology capable of that. Take a look at our article on magnetic force. Electrostatic acceleration is just implausible; magnetic induction is equally unlikely (you must first produce eddy currents, and then subject the magnetized object to an additional external field to apply a force to it). The physics just is not on your side with this one. Even if you fired the round into a specially-constructed laboratory setup, some kind of tube or tunnel surrounded by magnetic coils... that's still a lot of force to produce strictly by induced magnetic interaction. The idea is fun to toy with in theory, but when you start looking quantitatively at feasibility, it is no surprise that today's best defense against bullets is still low-tech sandbags. The laws that govern energy and momentum are unchanged by our ability to harness electromagnetism. Nimur (talk) 20:13, 20 July 2010 (UTC)

Your life does get easier if you assume a muzzle velocity of 300 m/s (typical of a handgun) rather than 900 m/s (a supersonic rifle round). If we assume a 300-meter range, then the constant force over that distance to achieve a 0.25 meter deflection of a 5-gram object is just 0.0025 newton. If we apply a constant one newton force, then we only need to apply it over the first 0.5 meters (roughly) to generate a 0.25-meter displacement 300 meters downrange. TenOfAllTrades(talk) 21:00, 20 July 2010 (UTC)

TOAT, handguns at 300 yards? You must have watched different Westerns than I did! Physchim62 (talk) 23:03, 20 July 2010 (UTC)

I didn't say it was a good idea, just that a 'best-case' scenario for some sort of deflection device. I'll admit that expecting a handgun to be accurage within a foot at that distance is pretty unlikely. TenOfAllTrades(talk) 01:47, 21 July 2010 (UTC)

Unlikely? Try miraculous. Googlemeister (talk) 14:17, 21 July 2010 (UTC)

Some electromagnetic and electrostatic effects on projectiles could in principle make the difference between hitting or missing a target, but might require expensive equipment. A deflection applied near the muzzle, or over a large portion of the path, will have a larger deflection than one applied only near the target. How hard does the wind push on a bullet? Marksmen spend enough time adjusting for windage, which would otherwise deflect the bullet at distances rifles commonly shoot. A rubber comb, with a small static charge can deflect a falling stream of uncharged water dramatically. Static electricity should be able to deflect a bullet some if the bullet were charged. Electric guns firing ferrous projectiles illustrate how powerfully induction can accelerate a projectile longitudinally. A copper disc dropped between the poles of a strong magnet seems to stop in its descent before descending slowly due to induced currents. A charged round projectile like a BB would retain charge better than a bullet shaped one, and would follow a curving trajectory when it passed through a strong transverse magnetic field. As a thought experiment, if a BB gun were charged from a Van de Graaf to 100kv, then fired at a target, the aim could be made such that the drop due to gravity placed it in the bulls eye at some distance, like 10 meters. Now consider if the first meter it travels between vertical plates either side of the path, charged to plus and minus varying voltages, spaced just far enough apart they did not arc. How many cm of deflection could be achieved? It is like a mechanical analog of an oscilloscope. An uncharged steel bb could be similarly deflected by passing through a magnetic field. Edison (talk) 19:24, 21 July 2010 (UTC)

how do you tell if a plant cell has apoptosed?

I can see stuff through the cell wall (DIC microscopy) and it looks like a mess. However, it's not quite like the arrangement when animal cells die (they give off apoptosis "bubbles"), so I'm not sure. They are also onion cells, so I'm not sure if those are simply lots of storage vesicles clumped together. John Riemann Soong (talk) 16:31, 20 July 2010 (UTC)

Ok I used a 700 nm filter (for gold nanoparticles lol) and I can see distinct intact nuclei...wow I didn't think that reducing the light levels by 20 times would help me see inside the cell. Because I don't fully understand DIC -- I want to ask, is it because cellulose doesn't diffract 700 nm light very well? (I get lost when it comes to diffraction and polarisation and not simply absorption/emission). John Riemann Soong (talk) 16:45, 20 July 2010 (UTC)

odorless mineral spirits

How strong (harsh, corrosive) is odorless mineral spirits compared with 70% rubbing alcohol? I would like to use the spirits to clean off kitchen countertops, and formica kitchen table. —Preceding unsigned comment added by Tomjohnson357 (talk • contribs) 17:41, 20 July 2010 (UTC)

The article White spirit has some information about toxicity. It's not a good idea to wipe down counter-tops with white-spirits unless you are going to thoroughly wash them again straight afterwards (presumably you're asking because Formica doesn't work well with household Bleach]?). ny156uk (talk) 18:15, 20 July 2010 (UTC)

Is there something particularly horrible you're trying to clean off? White vinegar does a decent job of disinfecting surfaces and is obviously okay for food handling areas. I'd be leery of using anything as toxic as paint thinner on something I was going to leave food on. Matt Deres (talk) 18:53, 20 July 2010 (UTC)

Do any of these solvents contain OH groups? John Riemann Soong (talk) 18:54, 20 July 2010 (UTC)

will odorless mineral spirits damage the surfaces how strong is it —Preceding unsigned comment added by Tomjohnson357 (talk • contribs) 19:52, 20 July 2010 (UTC)

The strength of household white vinegar will vary from brand to brand, but you're typically going to find stuff that is around 5% to 8% acetic acid. As with any other acid, I would hesitate to use it on marble (which is essentially calcium carbonate), as it would eventually etch the surface. I use vinegar as my standard cleanser on glass, porcelain, chrome fixtures, and my countertops. I also use it to disinfect my plastic and wooden cutting boards (see here). I know a lot of people prefer diluted bleach for disinfecting surfaces, but I prefer the smell of vinegar and I like the convenience of not having to worry about getting the dilution correct - you just use it straight up. After applying vinegar, you need to wipe it off afterwards as it can leave a residue if you let it puddle. Matt Deres (talk) 23:46, 20 July 2010 (UTC)

Note: This follow-up question read "will it damage ..:" when Matt Deres responded. It was later changed to "will odorless mineral spirits damage ..."

Few countertops (worksurfaces in the UK) are made of marble in the strict sense, because it's not good to have a polished surface that you can easily etch with spilt lemon juice, vinegar etc. Most of them are some form of igneous rock (although very little of what's sold as granite is genuinely granite), which will probably survive most of the chemicals mentioned. Mikenorton (talk) 12:21, 21 July 2010 (UTC)

note the OP asked about a 'formica' worksurface. . OP - This link http://www.naturalhandyman.com/iip/infcountertop/infcleaningformica.html may be of use. ny156uk (talk) 17:41, 21 July 2010 (UTC)

Anything science still can't do?

Is there anything, after all these years, that science still can't do?

Any number of things; check out science fiction. — Lomn 21:02, 20 July 2010 (UTC)

It apparently can't make everyone know that there is no "end of science". See our Science article. Comet Tuttle (talk) 21:03, 20 July 2010 (UTC)

Well it depends what you mean 'science still can't do' since since isn't something that does stuff. But anyway at a guess at what you mean the answer is a arguably an unlimited number of things. We still haven't mastered nuclear fusion for electricity generation, we still haven't made spaceships capable of 0.1C... You could include things believed impossible like faster then light travel. Nil Einne (talk) 21:05, 20 July 2010 (UTC)

There are certainly things scientists can't do. APL (talk) 21:08, 20 July 2010 (UTC)

Science seems to find it difficult to explain why so many supposedly well educated people, totally willing to use the fruits of its discoveries, reject it publicly in favour of mystical explanations for many perfectly natural phenomena. HiLo48 (talk) 21:12, 20 July 2010 (UTC)

Science find it difficult to explain why so many supposedly well educated people, totally willing to use the fruits of its discoveries, reject it publicly in favor of unscientific random changes for many perfectly natural phenomena. --Chemicalinterest (talk) 21:48, 20 July 2010 (UTC)

Actually, human susceptibility to superstition seems to be reasonably well understood. APL (talk) 22:29, 20 July 2010 (UTC)

Try List of unsolved problems for starters.

Ben (talk) 21:15, 20 July 2010 (UTC)

BTW, thank you for that article / category; it is great. Comet Tuttle (talk) 23:48, 20 July 2010 (UTC)

I was expecting the link to economics' unsolved problems to just be a redirect to economics. :) Matt Deres (talk) 00:00, 21 July 2010 (UTC)

Go back in time. Otherwise, science could do whatever science CAN do at any time. Googlemeister (talk) 19:53, 21 July 2010 (UTC)

It's common to confuse science and technology. Although they're usually pretty closely linked, they're not the same thing. Dear OP, if you were you asking whether there's anything that science still doesn't understand, the answer is yes, and I sincerely hope that it always will be. Science doesn't ever end because most — if not all — any scientific advances let us ask more questions that we wouldn't have known to ask previously. For example, we couldn't begin to address the cure for cancer without first developing cell theory. – ClockworkSoul 22:00, 20 July 2010 (UTC)

Well, if you want a specific example, science can not explain why animals sleep. There is discussion on memory and stuff, but even flies sleep. Ariel. (talk) 22:36, 20 July 2010 (UTC)

Science will never explain why I love my partner, and I prefer it that way ;) everything thing in its right place! Physchim62 (talk) 22:59, 20 July 2010 (UTC)

It actually can probably give a variety of good accounts for that. --Mr.98 (talk) 23:54, 20 July 2010 (UTC)

I think that science actually can explain why animals sleep. To my mind the "synaptic homeostasis" theory of Giulio Tononi is very strong, and I have the impression that it's gradually gaining favor in the community. The basic idea behind the theory is that learning and memory produces increases in neural connection strength that destabilize brains, and it's necessary to have an off-line period in which memory is switched off so that the problem can be fixed. Flies need to sleep because flies have memory -- using mechanisms surprisingly similar to the ones in humans. Looie496 (talk) 04:13, 21 July 2010 (UTC)

The consequence of not sleeping, Fatal familial insomnia, can at least allow science to infer some things, e.g. that the brain has a critical need to rest periodically (as does the heart). ←Baseball Bugs <sup>What's up, Doc?</sup> carrots→ 04:29, 21 July 2010 (UTC)

"synaptic homeostasis" doesn't really answer the question though. You also need to explain why it's not possible to build a brain without this need. In an animal that must not sleep (dolphin), instead of changing the brain (as you might expect), the brain sleeps one half at a time. Ariel. (talk) 12:14, 21 July 2010 (UTC)

There are plenty of problems that are considered outside the purview of scientific practice. Of course, it has been a long struggle over the centuries as various problems considered "outside" of science have found their way into it. --Mr.98 (talk) 23:54, 20 July 2010 (UTC)

Ah, but were they considered outside science by scientists or by other people that wanted to keep control over them? --Tango (talk) 23:58, 20 July 2010 (UTC)

Both. But of course the lines are blurry a lot of the time. Nobody wants to control like the status quo. --Mr.98 (talk) 13:14, 21 July 2010 (UTC)

Mankind can put a man on the moon but forget about plugging a hole in the ground. Also explain the interactions of certain subatomic particles. Also brains in general... ZigSaw 13:11, 21 July 2010 (UTC)

For the record Ziggy, plugging an oil well a mile underwater is much more an engineering problem then a science problem (and last I heard it WAS plugged). Googlemeister (talk) 14:15, 21 July 2010 (UTC)

See Opinion: The Limitations of Science - TIME (Friday, May. 07, 1965).—Wavelength (talk) 01:44, 22 July 2010 (UTC)

Measuring temperatures in Ireland in the late 17th century

When I was a boy, I spent a summer in Northern Ireland; that year, 1995, had what we heard was an all-time high temperature for Belfast, at 86ºF. From what we were told, they'd kept records since the Glorious Revolution. Since the Fahrenheit scale was only proposed in 1724, how was temperature measured in Ireland before that time? Nyttend (talk) 21:58, 20 July 2010 (UTC)

Thermometer#Early_history "However, each inventor and each thermometer was unique—there was no standard scale. In 1665 Christiaan Huygens suggested using the melting and boiling points of water as standards, and in 1694 Carlo Renaldini proposed using them as fixed points on a universal scale. In 1701 Isaac Newton proposed a scale of 12 degrees between the melting point of ice and body temperature" and Category:Units of temperature (earliest about 1701)

I would guess that they had records of comparative but non-standardised temperatures. Galileo is reported to have had a type of thermometere [17] (not to be confused with the Galileo thermometer) and predates the glorious revolution - so maybe they used something like that.77.86.76.212 (talk) 22:54, 20 July 2010 (UTC)

This site is quite interesting http://www.mastco.net/home16.html in that it mentions alcohol in glass thermometers as early as 1641, and refers to one used by Robert Hooke in 1644. It's decribed in his micrographia [18] or [19] or [20] (different editions) It seems likely that they may have used Hooke's scale if they were associated in some way with the Royal Society .77.86.76.212 (talk) 23:09, 20 July 2010 (UTC)

By the way do you have any clues as to who had the records - eg Queen's University Belfast opened 1845, but Ireland was then politically one so maybe Trinity College, Dublin which dates back to 1592. Or perhaps it was some seafaring organisation or similar in Ireland that kept the records? or an amateur clergyman or gentry?? any clues? That might help find the answer. 77.86.76.212 (talk) 23:19, 20 July 2010 (UTC)

Sorry, no clue. As I said, I was just a boy; my parents told me that the all-time-record thing was from the Telegraph. Nyttend (talk) 17:00, 21 July 2010 (UTC)

July 21

A Shocking Experience ?

Can a car battery (12 volt) kill a person ?  Jon Ascton  (talk) 06:41, 21 July 2010 (UTC)

Absolutely, yes it can. The odds of a fatal event will vary greatly depending on the nature of the exposure, the current path through the body, and the availability of life saving efforts. Dragons flight (talk) 06:56, 21 July 2010 (UTC)

You mean, inspite of the fact that it's only 12 volts...

I agree with Dragons flight on the possibility, though you would need to go to very great lengths to kill someone using the car battery alone (except as a blunt object, or by extracting the acid!) . Under normal conditions, the resistance of human skin is sufficient to prevent any harm when handling 12 volts. Dbfirs 07:06, 21 July 2010 (UTC)

Yeah, that's the answer - theoretically it can. But practically there will be problems, like the skin's thickness etc.

A Darwin Award has been made in respect of a death by 9 volt battery. --Tagishsimon (talk) 10:23, 21 July 2010 (UTC)

This is at least the third time we have heard of the Snopes article and the claimed electrocution by ohmmeter. I doubt that it happened. But it is a fair cautionary note, since someone, somewhere might manage to pass enough current from a 9 volt battery through their bodies to stop the heart. If passing current from the 9 volt battery in my ohmmeter stopped my heart, I would be shocked, so to speak. Edison (talk) 19:01, 21 July 2010 (UTC)

If you just shock a vital area of your body, you will be dead; even if the voltage is so low. --Chemicalinterest (talk) 10:57, 21 July 2010 (UTC)

Uh, maybe because voltage has nothing to do with lethality? It's the amperage that kills you. A 12-volt battery can start a V8, a 20,000-volt taser can't. The former has amps, the latter doesn't. Vaguely related: don't put your finger on a spark plug and turn the ignition. It will hurt like hell. No amps, so not lethal, but Christ that stings ZigSaw 13:06, 21 July 2010 (UTC)

This is a silly, oft-repeated oversimplification. Amperage is a good way to measure lethality, but voltage has *everything* to do with how much amperage will be present given a circuit's resistance (even when a human body is that circuit). Given the same resistance (say, a human body) low voltage will *always* result in low amperage, where high voltage will result in high amperage. --144.191.148.3 (talk) 15:15, 21 July 2010 (UTC)

Yes, under normal circumstances, voltage determines whether a source is dangerous, but I have (in my younger and more foolish days) succeeded in giving myself quite a hefty shock (tens of milliamps) from a 12v battery. I won't tell you the method here in case anyone with a weak heart tries it and kills themselves. The probability of death is extremely low, but I cannot afford the law suit. Dbfirs 17:13, 21 July 2010 (UTC)

Actually, stopping the heart with a DC shock won't kill you: it will immediately start up again. AC is much more dangerous because the oscillations can set up a disrupted heart rhythm, leading to fibrillation. The only way a DC shock can produce death is if it has a timing and amplitude precisely balanced to disrupt the heart without fully resetting it. There was a man named George Ralph Mines who did pioneering work on heart rhythms, and apparently died that way as a result of experimenting on himslef, but it isn't clear what voltage levels he used. (See this paper for the story.) Looie496 (talk) 23:08, 21 July 2010 (UTC)

Yes, the body is sensitive to rate of change of current, so one would have to repeatedly connect and disconnect the DC voltage to produce a dangerous effect. Personally, I think the death by ohmmeter article is an urban myth but I presume that George Ralph Mines applied voltages direct to his heart muscle. Dbfirs 06:41, 22 July 2010 (UTC)

Why do we need oxygen?

After reading Alternative_biochemistry, i got wondering, could life exist in other types of atmosphere? The article mentions chlorine but doesn't really elaborate on why. So the question is what is so special about oxygen that we need it and theoretically could this be done by other gases? --90.210.25.177 (talk) 10:59, 21 July 2010 (UTC)

Both oxygen and chlorine are Oxidizers. See Redox for some of the details on what this is. There are lots of other things that can act as oxidizers but oxygen itself works very well, and has a few benefits: it's a very common element (astronomically speaking). When reacted with an even more common element (hydrogen) it produces the universal solvent called water. Chlorine would work as an oxidizer does doesn't do so well with hydrogen. (Hydrogen chloride). The group carbon-oxygen-hydrogen is really quite special in how versatile it is, and simultaneously how common those elements are. Ariel. (talk) 12:26, 21 July 2010 (UTC)

I was checking various hydrogen-oxidizer molecules, and oxygen is really quite the outlier amongst them. Also, in a world with a hydrogen chloride atmosphere or surface, water would be a very powerful corrosive. Ariel. (talk) 12:35, 21 July 2010 (UTC)

Does that mean that independently evolved space-aliens are likely to be oxygen breathers too? 92.29.123.248 (talk) 13:06, 21 July 2010 (UTC)

We don't use oxygen because it produces water. We use oxygen because it can be derived from water. Before the first cyanobacteria started splitting water, life used redox reactions like organosulfur chemistry, oxidiser like nitrates and Fe(III) and so forth. John Riemann Soong (talk) 15:18, 21 July 2010 (UTC)

Hmm, not quite. We use oxygen because you can get a hell of a lot of energy out of oxidizing carbohydrates to CO<sub>2</sub> and water; also because it's there! There's some plausible speculation that water-splitting photosynthesis actually evolved from H<sub>2</sub>S-splitting photosynthesis. Physchim62 (talk) 15:50, 21 July 2010 (UTC)

I really don't think that's why we use oxygen. I mean, if life really wanted to make energy-dense compounds, they'd make alkyne motifs all over the place. Much of the water on this planet was carried here by asteroids, probably because most of it boiled off in the initial formation of the Earth. Take the amount of energy not captured by cytochrome complexes in the electron transport chain -- that last jump from complex IV (cytochrome c oxidase) to oxygen is so energetic, the proton gradient it contributes to hardly compensates; most of it is wasted as heat. John Riemann Soong (talk) 16:05, 21 July 2010 (UTC)

Btw, all of this is lifetalk centric to bioorganic chemistry, which if you realise, is really unique to Earth's 1 atm and 1g. A hydrogen sulfide world based on row 3 elements or a mercury world could possibly evolve. Hell, why not a world strongly dependent on a eutectic-based mixture of liquid Fe and specific crystal structures of iron that can only exist at a narrow range of atmospheric pressures and temperatures? The crystal structure is just right to allow for the diffusion of many dislocations and other bulk defects, and atoms travelling in the "solution" can diffuse. Rather than forming cells or membranes, life and "genetic replication" is strongly dependent on crystal growth and chemical networking. The equivalent of cell division would proceed by crystal cleavage, and these microstructures are stabilised by protective network formations and other sophisticated structures based on host-guest chemistry.

There magnetic interactions are just as important as polar bonding, and a "detergent" particle would have both diamagnetic and paramagnetic ends. Rich chemistry can be derived from a mix of Cr(III), Cr(VI), Cu(I),Cu(II), F- and other fun ions. The primary energy source is the planet's ever-churning and changing magnetic field. John Riemann Soong (talk) 15:33, 21 July 2010 (UTC)

The Earth's oxygen was actually created by life, so it couldn't possibly be required for life to exist. (Well, CO2 is required; it isn't clear whether the question means to include this.) Looie496 (talk) 22:57, 21 July 2010 (UTC)

It's true that life started without oxygen, but life as we know it today has probably adapted to living off of oxygen. Therefore, if oxygen were taken away, every animal on Earth right now, with the exception of the most primitive life forms, would probably die. Primitive life forms wouldn't have, but we're not primitive life forms, are we? The Raptor <sup>Let's talk</sup>/<sub>My mistakes; I mean, er, contributions</sub> 23:02, 21 July 2010 (UTC)

Chemistry

Can i please get clear examples of sublimation and its opposite deposition? Is hail an example? why and/or why not? —Preceding unsigned comment added by 74.198.43.60 (talk) 14:56, 21 July 2010 (UTC)

There are a few good examples in Sublimation (phase transition), which you should definitely read if you haven't already. Hail can and does sublimate under the right conditions - ice held at temperatures significantly below its melting point does gradually sublimate to water vapour without melting - but dry ice is probably the easiest and most obvious example to use if you need one. ~ mazca <sup>talk</sup> 15:10, 21 July 2010 (UTC)

(edit conflict) Dry ice , Iodine and ammonium chloride are common examples of things that sublime - see Sublimation (phase transition)

According to Hail " hail forms in cumulonimbus clouds when supercooled water droplets freeze on contact with condensation nuclei" if that's true it's not sublimation since the water is in the form of droplets - which means it is liquid.77.86.76.212 (talk) 15:12, 21 July 2010 (UTC)

Indeed - the formation of hail (and indeed snow) definitely doesn't seem to be desublimation, rather a very fast freezing of liquid water. The appearance of frost on a very cold but non-foggy day is probably the best example of natural desublimation of water that I can think of. The other chemicals mentioned by 77 above are certainly easier examples to use for most things. ~ mazca <sup>talk</sup> 15:19, 21 July 2010 (UTC)

A possible household use is Dye-sublimation printer. Also the ice that forms in a freezer may be from sublimed ice in warmer parts of the freezer. 77.86.76.212 (talk) 15:35, 21 July 2010 (UTC)

You can get desublimation of CO<sub>2</sub> if you use a carbon dioxide fire extinguisher: as the pressurized gas comes out of the nozzle, it rapidly cools (this is the Joule–Thomson effect) and some of it solidifies as a fine white snow (it rapidly resublimes, but the effect is quite impressive). Physchim62 (talk) 15:27, 21 July 2010 (UTC)

Dry ice is the classic, but failing that, frost works too. If you look carefully, You'll notice that frost forms directly on surfaces without a liquid forming first (that's why it's lacy as opposed to being a solid film of ice) - that's deposition: a solid forming directly from a gas (water vapor). The opposite occurs with frost and snow too. In winter you may notice frost disappearing during the day or snowbanks shrinking, even though the temperature stays below freezing. This is because the frost and snow sublime (go directly to water vapor) in the dry air, without melting first. - 174.24.196.51 (talk) 16:46, 21 July 2010 (UTC)

Refrigerant leak?

The inside of both compartments of my refrigerator/freezer smells strongly of some organic solvent. It reminds me of 'model glue'. Does the refrigerant in a modern US refrigerator smell like that? If it is a refrigerant leak, is this generally a repairable problem or it on of those things where repair isn't practical? ike9898 (talk) 15:45, 21 July 2010 (UTC)

Assuming the fridge isn't brand new (in which case it could be the smell of glue used in the construction of it) - it may well be pentane which is a common refidgerant nowadays - in which case your fridge is leaking. It's possible that it could be fixed - but the important thing here would be not to use any naked flames, open all the windows, don't switch on any electrical items then call a fridge engineer from somewhere else and get them to come round - if your fridge is leaking pentane you have a very real explosion hazard.77.86.76.47 (talk) 15:53, 21 July 2010 (UTC)

On the other hand it may be an ozone-friendly fluorocarbon refrigerant with less flammability - it usually says on the fridge instructions or on the back of the fridge what type is used. Fixing a leak involves draining, finding the 'puncture', which may be brazed shut, and then refilling - however the fridge may not have been designed to be taken apart and put back together again (ie glue not screws) - making the repair problematic.77.86.76.47 (talk) 15:57, 21 July 2010 (UTC)

Also if it is leaking the gas may knock you out in sufficient concentrations - most refrigerants are heavier than air - which means they will settle lower down - important if the fridge is not on the ground floor or you have a basement where it can collect - in the worse case a fridge that is leaking is lethal. I would recommend getting it looked at.77.86.76.47 (talk) 16:01, 21 July 2010 (UTC)

Fluorocarbon refrigerants are usually fairly odorless, so yes, this sounds worryingly like a pentane leak. In theory, such a leak can be fixed but, for a domestic refridgerator, replacement may well be a cheaper option. You do need to get it looked at, though, because there is an explosion hazard from the light switch which operates when you open the fridge door... Physchim62 (talk) 16:06, 21 July 2010 (UTC)

Resolved

 – See this section for resolution.

Antibiotics

What kind of effect does a typical seven day course of antibiotics have on organisms that live in the human gut? —Preceding unsigned comment added by 129.67.119.150 (talk) 15:46, 21 July 2010 (UTC)

There are many hundreds of kinds of antibiotic preparations, so your question is too vague to give a definite answer. But "some antibiotics kill bacteria in the gut". You can read our Antibiotic article--I bet there is at least one section relevant to side-effects or somesuch. DMacks (talk) 16:22, 21 July 2010 (UTC)

See also gut flora#Effects of antibiotic use, as well as the individual on specific antibiotics (e.g. amoxicillin or ciprofloxacin). TenOfAllTrades(talk) 19:19, 21 July 2010 (UTC)

What do you call this sort of cytoplasmic channel?

Please help! Thanks, so I can search for it in the literature. I was observing a bunch of lung cancer cells (epithelial) under DIC microscopy. These cells had an initial connection of two tiny strands (nanotubules?) that later grew into an entire cytoplasmic channel. I saw a gold nanorod (25x73 nm) being transported across one of the stands as well as other vesicles crowding into the newly-formed channel. At the same time, I saw another cytoplasmic channel between the same cells being disassembled back into tububles; in time the tubules were even broken. The channel that formed remained strong though. What do you call these channels and tubules?

The particle being transported across the strand appeared not to be by free diffusion, but by actual binding (it stopped its flashy rotation behaviour while on the strand). I'm not sure if this is an actual microtubule or a complex of other types of polymers. Help! John Riemann Soong (talk) 16:38, 21 July 2010 (UTC)

Microtubules are part of the cytoskeleton and not actual "tubes" through which things are transported. Think of them as cables that motor proteins use to transport things around inside of a cell. There is no cellular component called a "nanotubule". You might be seeing a connection between two cellular protrusions, like filopodia, or the remnants of the cell membrane that sometimes happen after a cell divides but the daughter cells remain connected by retraction fibers (redlink? hmmm... might have to fix that). How close together were the two cells? Are your nanorods intracellular or extracellular? Can you post a photo? --- Medical geneticist (talk) 17:00, 21 July 2010 (UTC)

The cells (from memory) were separated by a distance about 2-5 micrometres apart. The nanorods were endocytosed and definitely intracellular. I was trying to witness an exocytosis event but the rods travelled across these strands instead. I don't know if the strands I saw were cables by which motor proteins were attached to, or actual very narrow channels. In time, membrane surrounded these strands and expanded to something like 10-20 times the strands' width (the strands were still the same width though). I took videos and photos which I may post soon, when I retrieve it from the lab hard disk. John Riemann Soong (talk) 17:18, 21 July 2010 (UTC)

How about membrane nanotubes? Maybe take a look at some figures in the references given in the article and see if they are similar. Smartse (talk) 20:18, 21 July 2010 (UTC)

I stand corrected! I would have used the term cytoneme but if people are calling those things "membrane nanotubes" these days it shows how long it's been since I learned cell biology! Back to the question... you probably are seeing some type of membranous tether between the cells. These things are sometimes hollow but often contain some type of structured cytoskeleton, usually actin and sometimes including microtubules, to allow for transport. When you see them expanding, I'd guess that's because they are filling up with cytoplasm. For what reason, I can't say. Still, sounds very interesting. --- Medical geneticist (talk) 21:56, 21 July 2010 (UTC)

Survival benefits of scratching

Deleted See July 19 for the same topic

Sheep breeding season

When exactly do sheep on farms (in temperate climates) tend to give birth? The domestic sheep article just says "in the autumn", which is not very specific. 86.143.231.207 (talk) 17:24, 21 July 2010 (UTC)

No, conception (tupping) is in the autumn. Lambs are born in spring. Dbfirs 18:07, 21 July 2010 (UTC)

Early spring, or technically late winter if memory serves. I think March is the most common month, but it might depend on where you are. Temperate climate is pretty broad. Googlemeister (talk) 19:48, 21 July 2010 (UTC)

Yes, where I live in the Pennines, sheep naturally lamb in April, but, for commercial reasons, many farmers (especially in milder climates) bring tupping forward to late summer and have lambs born indoors in January. Dbfirs 21:01, 21 July 2010 (UTC)

Note, however, that this technique is not known to have been practiced in 1st-century Judea :-). 87.81.230.195 (talk) 22:32, 21 July 2010 (UTC)

It is indeed thought that the true birthday of Jesus, assuming the biblical accounts about the shepherds are accurate, might well have been in the spring. The Romans choose the winter solstice as the time to celebrate Jesus' birth, as they already had spring covered by Easter. ←Baseball Bugs <sup>What's up, Doc?</sup> carrots→ 17:04, 22 July 2010 (UTC)

Wind Turbines on Cars

I was in the car with a couple of friends at the weekend, and one of them suggested putting a wind turbine on the roof in order to generate energy to subsidise the energy use of the car. I said that the turbine would create drag and would slow the car down, and so more fuel would need to be used to drive the same distance; meaning that net energy use would go up, and not down as desired. Even if the turbine converted energy perfectly, and without waste, the best that could be hoped for would be a constant net energy use.

One of my friends then suggested a turbine might be put behind the radiator grill of the car. Without the turbine, the air entering the radiator grill would be pushing against the car and impeding the car's progress. Putting a turbine behind the radiator grill would turn some of the stopping force of the wind into energy that could be used to propel the car.

Would the wind turbine still create drag, even though it was hidden away behind the radiator grill? The wind entering the radiator grill would otherwise just push against the car and slow the car. Would the turbine absorb some of this stopping energy, making the car slow less quickly, whilst at the same time generate energy to be used by the car? Are there any more comments and observations that you would like to make? I would really appreciate some input on this. •• Fly by Night (talk) 18:09, 21 July 2010 (UTC)

If I am not mistaken, the turbine would really not turn much, as the wind would pass through the turbine and stop on whatever is behind it, building up pressure, and trying to force itself back out. I could be wrong about how the turbine would behave, as I have never tried such an experiment, but laws of physics will tell you that you are not going to gain any energy by doing that. There are some things you can do to lose less energy, such as in a hybrid car (storing the stopping energy), but I don't think a wind turbine would help do anything on the car, except make it less efficient and heavier. Falconus<sup>p t c</sup> 18:17, 21 July 2010 (UTC)

The air would flow past the turbine and into the radiator proper; where it would be used to cool the engine. In fact, some cars even have a fan on the other side of the radiator, powered by the fan belt, which pulls the air through the radiator. So I don't think there would be any build-up of pressure. Having said that, if there is a constant stream of air passing through the grill and then the radiator, assisted by the a fan then there's steady stream of air. That wouldn't stop the car as I thought. And putting a turbine in that air would again cause drag and hence slow the car... Does that sound right? •• Fly by Night (talk) 18:53, 21 July 2010 (UTC)

The Mitsubishi i-MiEV Sport concept car had wind turbines behind the grille. I don't know whether the production i-MiEV does or not. Adding wind turbines can increase overall efficiency; this doesn't violate any conservation laws. There was a ref desk thread on this subject recently: 2010 June 11#Windmill on a car ?. -- BenRG (talk) 19:01, 21 July 2010 (UTC)

(after edit conflict) ::Yes, I agree with Falconus that this is not a practical option. When turbines were last discussed here (thanks for the link, Ben), it was suggested that, in theory, a wind turbine mounted on a car could generate electricity from the wind without (in theory) needing to draw energy from the engine of the car. The problem seems to be, as you correctly stated, that drag on the structure would drain a greater amount of energy than would be gained. Your suggestion might work with some clever aerodynamic design to prevent back-pressure, but then the energy to drive the turbine could come only from a true headwind (or from the car engine). It's a clever idea, but the amount of energy to be gained is probably not worth the effort. Car aerodynamics are fairly complex, and I'm not sure how the change in airflow would affect drag. If the air has to flow through for cooling anyway, and energy can be harvested as it passes, then this is gain even if the energy does come from the engine in the first place. Dbfirs 19:18, 21 July 2010 (UTC)

This is not the same thing at all, but still a remarkable piece of engineering. It is a wind-powered car that can travel downwind faster than the wind is blowing. Enjoy! TenOfAllTrades(talk) 19:25, 21 July 2010 (UTC)

(ec, five times!) BenRG, this is not correct. It does cost energy. The turbine acts as resistance to the air. Instead of just passing through, the air is blocked. This resistance costs energy. However, if your design of the car is such that you have friction resistance anyway, and switch it to turbine resistance then that is a benefit - but in that case you would be better off just removing the friction resistance and leaving out the turbine. Ariel. (talk) 19:26, 21 July 2010 (UTC)

Perhaps a small turbine strategically placed over the radiator, facing down and properly shielded from the wind caused by the car's motion would be able to provide benefit from the heat rising off of the radiator. Googlemeister (talk) 19:47, 21 July 2010 (UTC)

The car is in motion, so the air would not rise. It would be swept backwards into the engine. •• Fly by Night (talk) 19:51, 21 July 2010 (UTC)

Ariel, nothing that you said contradicts anything that I said. -- BenRG (talk) 23:57, 21 July 2010 (UTC)

You said "Adding wind turbines can increase overall efficiency; this doesn't violate any conservation laws." But that's not correct, adding a turbine will add friction. Unless you mean to harvest energy from external wind, but if so it wasn't obvious to me that that is what you meant. Ariel. (talk) 02:38, 22 July 2010 (UTC)

If the turbine is directly in the flow of air then it will create drag. It will push back on the air that pushes it. Also, if the airflow is used to cool the radiator (and in turn the engine) then surely by putting a turbine in the airflow you will decrease the wind speed and so decrease the cooling ability of the air. That means that the engine would run at higher temperatures. •• Fly by Night (talk) 19:51, 21 July 2010 (UTC)

Land yachts (and especially ice yachts) can got several times the wind speed, by sailing at about 45degrees into to apparent wind . 62.56.49.134 (talk) 20:21, 21 July 2010 (UTC)

Yes, this, and TenOfAllTrades' link, prove that energy can be harvested from the wind whilst travelling, but there are problems implementing this effectively in a motor vehicle. Efforts at present go into reducing drag and improving the efficiency of engines, where there are much larger gains to be made. Dbfirs 20:47, 21 July 2010 (UTC)

Follow up refrigerant leak question

I seem to have a refrigerant leak in refrigerator/freezer. Both compartments have a strong solvent smell. I have a service tech coming in the morning.

So now for the question... In the meantime, is the food stored in this refrigerator safe to eat? There is no liquid residue anywhere in either compartment. I'm just concerned about whether the food or beverages would have absorbed the vapor in concentrations great enough to matter. Would absorption be greater for fatty foods? ike9898 (talk) 19:59, 21 July 2010 (UTC)

Update: I spoke with the manufacturer's tech support. They said the refrigerant in my model is freon, and that freon doesn't smell like that. They didn't think anything in the refrigerator should cause that smell. ike9898 (talk) 20:28, 21 July 2010 (UTC)

Perhaps it's rotten meat? Or spoiled milk? Is there anything like that in the refrigerator? The Raptor <sup>Let's talk</sup>/<sub>My mistakes; I mean, er, contributions</sub> 20:44, 21 July 2010 (UTC)

Mmmmh. Could it be ripe fruit and veg - the cold temperatures mean than only the "high notes" of smells are volatile - these compounds are typically solvent like in smell and form eg small amounts of butane, butanal, acetaldehyde, ethylacetate.

Fridges do smell for this reason, even when cheese is removed - but I wouldn't say it is a strong smell.

Q. Is the smell 'alarming' - I'm not aware of this - but it seems likely/sensible for manufacturers to put a smelly compound in the freon in case of a leak.. 77.86.76.47 (talk) 20:48, 21 July 2010 (UTC)

When some plastics overheat, they can give off strange odours. Is anything getting hot? Dbfirs 20:49, 21 July 2010 (UTC)

A speculative suggestion, but partially consumed fruit juices (which on opening can be inoculated by wild yeast from the air much as in Lambic beer brewing) can if left long enough ferment and develop a noticeable alcoholic smell - it's happened in my own fridge! Could this be the source? 87.81.230.195 (talk) 22:28, 21 July 2010 (UTC)

To answer the original question, I don't think there would be any undue risk from eating the food in the fridge unless the food itself was smelly. If it a Freon leak, then Freon is notoriously non-toxic to mammals (except when it gets to the ozone layer, but that is not most people's definition of toxicity). In the case here, I would simply use my general judgement as to what to eat out of my fridge – if it looks or smells bad, don't eat it; if it looks and smells OK, eat it! Physchim62 (talk) 00:39, 22 July 2010 (UTC)

"Strong solvent smell" - could be ripe bananas. Have you tried removing everything from the fridge, cleaning it, and seeing if it still smells? 92.28.250.141 (talk) 10:00, 22 July 2010 (UTC)

Doesn't storing bananas in the fridge ruin them? Googlemeister (talk) 14:06, 22 July 2010 (UTC)

It makes the skin turn black and may negatively affect the texture but they definitely last longer (i.e. are edible/usable for longer) so it depends on what you mean by 'ruins' Nil Einne (talk) 15:16, 22 July 2010 (UTC)

Resolved

 – Original poster, ike9898 (talk)

I find this hard to believe, because it really, really didn't smell like rotten food, but it was. Some produce in the crisper drawer. The smell was actually strongest in the freezer; I suspect the freezer was acting as a condenser, and accumulating the volatiles. Thanks for all your help. ike9898 (talk) 14:28, 22 July 2010 (UTC)

For our own future reference (and current curiosity), are you able and willing to specify what the 'produce' was? 87.81.230.195 (talk) 17:04, 22 July 2010 (UTC)

I think it was carrots and celery (don't know if one or both were bad, we threw it all out). They were bad to the point that nasty liquid had drained off them and collected in the drawer. The funniest thing is that just smelling the drawer, the smell wasn't that bad. I hypothesize that the volatiles were getting concentrated in the freezer. ike9898 (talk) 17:43, 22 July 2010 (UTC)

Avro Vulcan

What is the carbon footprint of the Avro Vulcan?

Apart from the technical answer, can you please translate that into what that equates to compared to say, the Ford Fiesta, a London bus, Intercity 125, x flights to New York on a 747 or something we can more easily visualise!

Thanks. —Preceding unsigned comment added by EnglishNomad (talk • contribs) 20:47, 21 July 2010 (UTC)

It's not possible to answer your question as written. Are you asking about the fuel efficiency of this vs other vehicles? They hold different numbers of people, so do you want to take that into account? Why would you specify "to New York" - what different does the destination make? And you don't give the departure location (not that it matters if you just want fuel per mile - or do you?) All liquid hydrocarbon fuels generate more or less the same carbon dioxide, so just check the total fuel divided by maximum range for each of those. But it depends on the speed, basically this question is impossible to answer. Try: Fuel efficiency in transportation - it might have the answer to your question. Ariel. (talk) 20:56, 21 July 2010 (UTC)

An exact figure is truly impossible to estimate because we can't know how much went into manufacturing, servicing, etc. But simple fuel loads are easy - the thing carries 40,000 liters of fuel and it has a range of about 4,000km - so 0.1km/liter. A MkV Diesel Ford Fiesta does 30km/liter - so on a very rough estimate - the Vulcan is 300 times worse. SteveBaker (talk) 21:09, 21 July 2010 (UTC)

Keep in mind that unlike a car, an aircraft's fuel consumption rate can vary by orders of magnitude during a single flight. This is because of huge variation in the level of throttling, the immense change in mass as fuel is consumed (or combat payloads are deployed), climbing vs. cruising, and so on. Our article on jet aircraft range has some equations to calculate fuel consumption for an aircraft. Automobiles also have a "time-variation" in fuel consumption / mileage-per-gallon; but it usually doesn't vary by a factor of 100x over the course of a single drive outing, even accounting for things like acceleration and hills. Nimur (talk) 22:10, 21 July 2010 (UTC)

True, but a car's fuel consumption does vary by a factor of at least ten. (original research on local hills) Dbfirs 06:29, 22 July 2010 (UTC)

It has 4 rolls royce olympus engines - which have a fuel consumption to thrust ratio (see Thrust specific fuel consumption) of ~1.3 (imperial) - thrust is ~10,000ftlb each making the fuel consumption 40,000x1.3 = 52,000 lb/hr - in metric that's ~6.6kg/s of fuel in flight (2.2 pounds per kg, 3600 seconds per hour). Jet fuel has a calorific value of ~47MJ/kg (see Fuel_efficiency#Energy_content_of_fuel). So the machine is using 47x6.6 = 310MJ/s or 310MW (somebody should check these figures for mistakes)

That's approximately 100 Intercity 125's or 26 Eurostars , or 100,000 kettles. 77.86.76.47 (talk) 21:18, 21 July 2010 (UTC)

Assuming the thing does about 900km/hr at the above thrust (which is 0.25km/s) it does 0.25/310 = 0.0008km/MJ (or 1240MJ/km), but the crew is 5 so the figure for Megajoules per passenger kilometer is 1240/5 = 249 (which is about 100 times worse than using a bus) 77.86.76.47 (talk) 21:38, 21 July 2010 (UTC)

The Vulcan was not originally designed to be a passenger vehicle: if the question relates to the model of aircraft in general, one might wish to factor in the relative payloads of the vehicles being compared - a freight aircraft would arguably the 'fairest' comparison. On the other hand, the individual remaining airworthy Vulcan is used only for display and not to carry payloads (certainly not the specific ones it was designed for!) so perhaps comparison to passenger vehicles is more valid. Admittedly EnglishNomad did not actually ask for these nuances of interpretation. 87.81.230.195 (talk) 22:22, 21 July 2010 (UTC)

I multiplied force x velocity to determine power. The engines deliver around 13,000 lbf at around 925 km/hr, so 4 * 76 kN * 925 km/hr is around 100 megawatts of kinetic power. Assuming a ballpark thermodynamic efficiency of ~ 30%, 77.86's numbers seem to check out. Another way to look at it, 300 megawatts is about the instantaneous electricity consumption of a mid-sized city; so flying one combat bombing-run sortie of an Avro Vulcan to wipe one city off the map is tantamount to adding another city to the energy-economy, based on the aircraft's fuel-consumption alone. I suppose these things even out? Actually, on further reading, the Vulcan could carry two air-launched cruise-missiles, one under each wing pylon; so as usual, nuclear warfare does actually yield a net loss. Nimur (talk) 22:14, 21 July 2010 (UTC)

Colour-in 3D chick embryogenesis models/pictures?

I'm trying to study (as in reading, rather than experimenting) expression of a gene during in chick embryogenesis but it's difficult to keep a mental hold on the movements of the expression patterns. What would really aid me would be some 3D computer models of chick embryogenesis (HH stages in particular) to which I could colour in the locations of gene expression. 2D would be better than nothing, but would require two pictures to represent 3D patterns. Such blank pictures probably don't exist on the web for free, but I figured it's worth a shot. ----Seans Potato Business 21:01, 21 July 2010 (UTC)

Birds

is peanut butter bad for birds to eat? some books say it kills them and others say its a good treat for them.--Horseluv10 21:22, 21 July 2010 (UTC) —Preceding unsigned comment added by Horseluv10 (talk • contribs)

I would expect it depends on which birds you give it to. Different birds have different diets. --Tango (talk) 21:44, 21 July 2010 (UTC)

see http://birding.about.com/od/birdfeeders/tp/birdfeedingmyths.htm --Digrpat (talk) 21:48, 21 July 2010 (UTC)

Considering how much many birds love peanuts, I have a hard time believing they'd die from peanut butter without a really good reference. Matt Deres (talk) 21:58, 21 July 2010 (UTC)

My understanding with peanut butter is that it's lacking in some amino acids, so if an animal feeds on it exclusively they will suffer from a form of Kwashiorkor. Ariel. (talk) 22:36, 21 July 2010 (UTC)

Do you have any reason to suspect that would affect birds, though? - not all animals need to intake the same amino acids (see essential amino acid); organisms may synthesize different amino acids internally. Many birds also seem to get by on a whole variety of seemingly narrow diets (pine cone seeds, sunflower seeds, etc.). I'm not saying you're wrong, I'm just saying that my understanding of bird diet would make me suspicious of the various claims in this thread (peanut butter is bad, an exclusive diet of peanuts/peanut butter would fail to provide all a bird's required amino acids) without a really good reference. If a crossbill can be so intimately tied to a particular species of pine seed that it suffers when it has to switch to a different species in times of hardship, that makes me think that birds don't generally need the same kind of variety of diet that people do. Matt Deres (talk) 01:01, 22 July 2010 (UTC)

Your average crow, for example, eats rotting carcasses on the road, so I doubt peanut butter would bother it much, except it might be kinda gooey. ←Baseball Bugs <sup>What's up, Doc?</sup> carrots→ 17:00, 22 July 2010 (UTC)

Yosemite

hey all I am going to yosimite tomorrow and I want to know what the chance of me meeting/being attacked by a wild animal like a cougar or bear is and if there is anything I might do that would increase and anything that might decrease my chance of the same. Thnx. 76.199.166.85 (talk) 23:30, 21 July 2010 (UTC)

If you smear yourself with peanut butter and barbecue sauce and go walking naked through the woods at night, you'll increase your chances of being attacked by a bear. Basically the rule is, don't wave food in front of bears and you'll be okay. There are no other animals worth thinking about there. Looie496 (talk) 23:35, 21 July 2010 (UTC)

Here are Safety Tips, particularly as they pertain to bears and food storage. In truth, you have a greater chance of harm by falling off one of the waterfalls than by animal-attack. But, if you don't take proper precautions, especially if you are out of the valley, bears can be a real threat. Nimur (talk) 00:33, 22 July 2010 (UTC)

They are a threat to your food. Yosemite bears don't attack people unless the people try to take food away from them. Looie496 (talk) 00:52, 22 July 2010 (UTC)

Don't mess with any bear cubs (I mean don't get anywhere near them), or try to get a photo of you hugging the bear along with the above mentioned food advice and you should be ok. Googlemeister (talk) 13:22, 22 July 2010 (UTC)

The time-honored theory would be to bring along a friend that you're confident cannot run as fast as you can. ←Baseball Bugs <sup>What's up, Doc?</sup> carrots→ 16:58, 22 July 2010 (UTC)

July 22

Lily Flower Identification

I was wondering if anybody could help me identify this lily flower. It has six petals that are pink with purple spots towards the center of the flower. The stamens are full of brownish-yellow pollen and there is a large, yellow, three-lobed projection in the very middle. Here is a link to a photograph I took of this lily: Lily Flower. I took this photo on a property in Northern Wisconsin and I am assuming that this lily is not native to the area. I have looked online and in a flower identification book, but have had no luck. If anyone could help identify it, that would be great! Thanks! Stripey the crab (talk) 01:54, 22 July 2010 (UTC)

Telling the difference between free fall and micro-gravity

I am locked in a room with no windows in a future space ship. I am experiencing complete weightlessness. Is there a way for me to find out if I'm orbiting a planet in free-fall or if I'm actually between galaxies in micro-gravity? Looking for multiple methods if they exist.--mboverload@ 03:05, 22 July 2010 (UTC)

Einstein says no: Equivalence principle#The Einstein equivalence principle. TenOfAllTrades(talk) 03:10, 22 July 2010 (UTC)

If you were in orbit there would be tidal forces between two masses that are different distances from the center of the planet. These forces would be small but probably measurable. anonymous6494 03:16, 22 July 2010 (UTC)

I agree with TenOfAllTrades. As a side issue, in between galaxies you are in an environment of genuine weightlessness - weight is mass times local acceleration due to gravity, and local acceleration is close to zero. An astronaut orbiting the Earth, or a swimmer diving off a tower, or a trainee astronaut in a reduced gravity aircraft all claim to be weightless but of course they are not weightless because local gravity is significantly greater than zero. The reason they believe they are weightless is because the ground reaction force acting between them and their surroundings is zero.

So the original question could be re-worded to ask whether it is possible to distinguish between situations where the local acceleration due to gravity is close to zero, and where the ground reaction force is zero. Without being able to make a long-term observation of motion relative to the stars I don't believe it is possible to distinguish between these two situations. Dolphin (t) 05:32, 22 July 2010 (UTC)

While ToaT and Dolphin51 are I believe correct, note that the Principle of equivalence assumes that measurements are only made at one point (which is what "local" implies). If measurements are made at two points, even if (say) only a foot apart, there are sometimes ways of distinguishing between gravitational and accelerational effects. 87.81.230.195 (talk) 07:28, 22 July 2010 (UTC)

Tidal Forces

Take a look at the diagram showing two objects (your hands should do the trick) orbitting a big big blue planet (acceleration acting on the planet is not shown). The black arrows show acceleration due to gravity, The red arrows show the components of the acceleration toward the planet acting between the two objects (which a little bit of geometry shows is inversely proportional to the distance to the planet). If you feel more force pulling your hands together than you'd expect due to their usual mutual gravitational attraction, you're in orbit. David Carron (talk) 11:47, 22 July 2010 (UTC)

(Assuming I can remember my physics correctly...) A gyroscope will keep pointing in the same direction, relative to the rest of the universe. This can be used to tell if your spaceship is rotating. Accelerometers placed on the inside and outside edge of this rotation will indicate if the the ship is rotating around a point inside the ship, or an external point. In free movement, the centre-of-rotation will be the centre-of-mass. If you know where the centre-of-mass is you can tell if you are in orbit. If not, then a ship in orbit will tend to become tidally locked. During this process the ship's centre-of-rotation will move from outside the ship to the centre of the planet. Once the centre-of-rotation moves outside the ship, you can deduce that you are in orbit. A gradual movement of the centre-of-rotation is due to either tidal-locking or conservation of angular momentum due to objects inside the ship moving to, or away from, the centre-of-rotation, which will move the centre-of-rotation. CS Miller (talk) 11:39, 22 July 2010 (UTC)

Thinking about it more, until the ship is tidally locked, the reported acceleration will always have a component towards the centre of the planet, and thus will change over the course of each orbit (thanks David Carron, but the accelerometers are top and bottom, not front and back as in his diagram). So this can be used to deduce that you are in an orbit, without waiting for tidal locking to start. CS Miller (talk) 12:08, 22 July 2010 (UTC)

To expand slightly on my point, Einstein's statement of the equivalence principle (as described in the link I provided) does acknowledge that it only applies 'locally', and that the experiment needs to be 'small' with respect to variations in the ambient gravity field. That is, it doesn't work if your apparatus is sufficiently large and sufficiently sensitive to detect tidal effects across the length of your laboratory. Within the framework of the equivalence principle, I would argue that the rotation of the laboratory and the (eventual) establishment of a tidal lock constitutes such a 'non-local' experiment for our purposes. TenOfAllTrades(talk) 13:02, 22 July 2010 (UTC)

A gyroscope doesn't help at all, any more than noticing the local gravity inside a spinning spaceship would help. The circular motion of an orbit can be combined with any desired degree of rotation. --Tardis (talk) 14:53, 22 July 2010 (UTC)

Inertial navigation using gyroscopes is used for Apollo and the space shuttle. Gyroscopes are also used in the orbiting Hubble Space Telescope and its Rate Gyro Assembly can be seen here.Cuddlyable3 (talk) 15:18, 22 July 2010 (UTC)

Photocell experiment

A light of constant intensity was shone upon a photocell, and the potential difference was varied. When the potential difference is zero volts, a current is detected by the ammeter. Initially, as the potential difference increased, current increased rapidly. Then, to about 25 volts, current increased slowly as potential difference increased. After that, current increased rapidly when potential difference was increased again.

Basically I need to explain these four phenomena:
Why there is a current with a potential difference of zero.
Why the current initially increased rapidly when potential difference was increased.
Why, after that, the current increased slowly when potential difference was increased.
Finally why, after that, the current increased rapidly as potential difference was increased again.
Thanks for your help. ––115.178.29.142 (talk) 04:46, 22 July 2010 (UTC)

The device used is a phototube.––115.178.29.142 (talk) 04:46, 22 July 2010 (UTC)

(I'm assuming it's a gas filed phototube, not a vacuum phototube - the answer is slightly different) From the link in the phototube article The photocurrent initially saturates as in a vacuum phototube, but above 20 V it begins to increase, and may be multiplied by 7 at 80 V or so. At still higher voltages, a glow discharge begins, which does the tube no good, and is not useful. [21]

1. Why there is a current with a potential difference of zero. No idea - this seems wrong? This is due to electrons produced by the Photoelectric effect which happen to be emmitted in the direction of the anode and collide with the anode resulting in 'capture'

2. photoelectrons are produced at the cathode - increasing the potential so that they move towards the anode and are collected causes the first increase in current. Compared to 1 the electric field 'steers' photoelectrons towards the anode - causing increase in capture efficiency - ie up to the point where 99% of photoelectrons are hitting the anode.

3. further increases in potential do not cause increases in current since the current is limited by the number of electrons being produced by the photoelectric effect. (There's a small(?)effect whereby increasing the field strength will reduce the effective work function of the material - resulting in more emmisions from lower frequency light - I'm not sure how measurably relavant this is in your example) However accelerating the electrons in the higher field gives them greater energy which makes production of more charge species more likely on collisions.

4. At higher voltages glow discharge starts - this is the process mentioned in the last sentence of 3, plus the effect of having a high enough potential to cause ionisation of the gas in the tube. This is basically a form of arcing 77.86.76.47 (talk) 14:40, 22 July 2010 (UTC)

What do blind people see?

I closed my eyes the other day and paid close attention to the little colors and whatnot and it got me thinking: if I had no eyes, what would I see? Does someone without eyes see black like when I close my eyes? Or do they not "see" anything, as in their minds just don't have a visual perception? I know it's hard to explain to someone who can see, but what is it like? 69.207.132.170 (talk) 05:57, 22 July 2010 (UTC)

I believe it varies from one person to another. Of course if you had no eyes, you would not see anything, by definition. However, you might be interested to read up on closed-eye hallucination.--Shantavira|<sup>feed me</sup> 07:27, 22 July 2010 (UTC)

I get around 100000 Google hits on "What do blind people see?" A popular question! You may also be interested in Blind spot (vision). I once thought about using it to make an April Fool's joke claiming lots of people around the world were going blind for unknown reasons or a crazy reason like death rays from SN 1987A. The idea was to make a demonstration of the blind spot and claim it was just the start of gradually losing the whole field of view. However, I decided it was too cruel. PrimeHunter (talk) 14:29, 22 July 2010 (UTC)

Nothing. "Color" and "black" have no meaning to a person who is blind from birth. Cuddlyable3 (talk) 15:02, 22 July 2010 (UTC)

There has been a lot of research on this. My recollection from cog sci classes ages ago is that people born without sight generally don't have much of a concept of seeing at all and don't generally have a fully-developed visual cortex. People who become blind later in life—even after infancy—generally have a fully-developed visual cortex and describe their sight as black or white or gray or things of that nature. But this is a sketchy memory. "What made them blind" is important here, as well—people who are blind for defects in the eye probably have a different sense of it than those who are blind from defects in the brain. --Mr.98 (talk) 15:46, 22 July 2010 (UTC)

Ray Charles, who went blind when very young, said that he would dream about his mother's face. ←Baseball Bugs <sup>What's up, Doc?</sup> carrots→ 16:55, 22 July 2010 (UTC)

The colors and whatnot that you see when you close your eyes are discussed in our Phosphene article, and its "Electrical stimulation" section discusses electrically induced phosphenes in blind people. They weren't blind since birth. Seems like an easy question would be whether blind people see ordinary "pressure phosphenes" but I don't know. Comet Tuttle (talk) 16:31, 22 July 2010 (UTC)

I think it's also important to define what kind of blindness it is. I think if you are blind due the failure for reception of the visual signal (eye damage, optic nerve damage), it's going to be very different if there is damage in a perception portion of the brain (visual cortices). For the former I think it might be "black" with phosphenes, but for the latter I'll bet the person does not even realize that they are "missing" something. -- Sjschen (talk) 17:55, 22 July 2010 (UTC)

Soul

If my conscious is not the product of my immortal soul, but only an illusion created by the electric impulses in my neurons, could other electric impulses - for example, in a computer network - also create the illusion of consciousness?--Quest09 (talk) 10:09, 22 July 2010 (UTC)

Have a look at Artificial consciousness. It might not have to be be an illusion. Zain Ebrahim (talk) 11:10, 22 July 2010 (UTC)

Spider Identification Please

I live near Vancouver, British Columbia.

I have taken many pictures of this spider I captured.

Can you identify which spider this is?

I found (and killed - was too scared to attempt capture) bigger spiders than this, so I am wondering if this spider can grow bigger?

I have taken a very high resolution of the picture. It is 3.6 MB. So you can download and zoom in.

I have more pictures if required for different angles.

File:Better Picture Spider.JPG

--33rogers (talk) 10:26, 22 July 2010 (UTC)

Those pics are too blurry to see much of anything. You might post some better ones or perhaps look through here to see if you see your bug. --Sean 15:28, 22 July 2010 (UTC)

Qualia

Why do qualia exist? --138.110.206.102 (talk) 12:42, 22 July 2010 (UTC)

Not a very well-formed question. Do you mean, why do they exist rather than not exist? Or do you mean, why have we (and probably other creatures) evolved sense systems that operate the way they do? Depending how you define qualia, you'd get different answers for the latter (in some definitions it seems rather peculiarly human, in some it is just a term that applies to anything that 'experiences', probably even machines). For the former, there are no good answers, because it is not a particularly good question. --Mr.98 (talk) 13:12, 22 July 2010 (UTC)

Actually it is an excellent question to which Wikipedia cannot offer a better answer than the article on Qualia. Cuddlyable3 (talk) 14:57, 22 July 2010 (UTC)

No, it's bad question because it is exceptionally vague about what it is asking. It would need to be clarified for us to even presume to point him in the right direction. Asking why things exist when they don't have to exist is not a good question either, in my opinion—it presumes a lot of unstated things, wrapped in a wooly tissue of metaphysics. --Mr.98 (talk) 15:51, 22 July 2010 (UTC)

Our Hard problem of consciousness article specifies those exact four words as one of the formulations of the hard problem of consciousness. As the article states, the problem is unsolved. Comet Tuttle (talk) 18:30, 22 July 2010 (UTC)

Mouse

I had a mouse that used to eat fingernails. When I held her in my hand she would immediately go to the end of my finger and start nibbling the nails, and if I cut a bit off and gave it to her she would gleefully take it and eat it. Why? What is in my fingernails she would like? —Preceding unsigned comment added by Can u read my poker face (talk • contribs) 13:19, 22 July 2010 (UTC)

Fingernails are made of Keratin. Mice and all rodents also like to gnaw - since their teeth constantly grow and need to be worn down.77.86.76.47 (talk) 14:53, 22 July 2010 (UTC)

Negative energy?

Our article Dirac sea says this:

$E={\pm }mc^{2}.$

Here the negative solution is antimatter, discovered by Carl Anderson as the positron.

Whereas I was under the impression that the positron had a positive mass, and a positive energy (as positron would appear to confirm). Then, is the formula is identical for the positron not the same as it is for the electron? If we took E=-mc<sup>2</sup>, would we not arrive at a negative energy? Thanks, Grandiose (me, talk, contribs) 13:27, 22 July 2010 (UTC)

The positron has negative mass and there is mutual annihilation when it meets an electron. Cuddlyable3 (talk) 14:53, 22 July 2010 (UTC)

I don't believe that's correct. As noted at our exotic matter article, virtually every modern physicist suspects that antimatter has positive mass and should be affected by gravity just like normal matter and bubble chamber experiments are often cited as evidence that antiparticles have the same inertial mass as their normal counterparts. — Lomn 14:57, 22 July 2010 (UTC)

(edit conflict) That may not be right - the antiproton has the same magnitude of mass as the electron, and opposite charge. They do indeed annilate one another: this can be interpreted 2 ways:

The mass is negative - simplifying mass balance equations eg Electron–positron annihilation the 'reactants' have net mass 0

The mass is positive - but the object is labelled an 'antiparticle'

There's a reason for this - if the mass were negative an positron would be repelled by normal gravity assuming Newton's law of universal gravitation and similar are functions of 'vector mass' and not of 'absolute mass' ie |M| - see Gravitational interaction of antimatter - there may be an ongoing debate.77.86.76.47 (talk) 15:03, 22 July 2010 (UTC)

To answer the question - I recommend you read the linked essay from the article Dirac sea - it may actually help explain (or at least give context to) all this 'sweeping under the carpet' to do with negative mass and gravity and signs (hopefully).77.86.76.47 (talk) 15:19, 22 July 2010 (UTC)

Electrons that we observe have positive mass and negative charge. Positrons that we observe have positive mass and positive charge. The Dirac Sea is a way of interpreting the universe such that the natural (but unobservable) state of electrons is to have negative mass and positrons are an illusion created by the absence of electrons. The Dirac Sea conceives of the universe as being filled with an infinite number of negative mass energy "electrons". Sometimes, something comes along to kick one of these electrons out of the sea, across the mass gap, and into a state of positive energy. This positive mass electron then behaves as the electrons we know in ordinary life. In being excited, it leaves behind a hole in the sea. According to the Dirac Sea interpretation, a hole in the sea acts as though it has positive mass and the opposite charge as the electron that was excited. In other words, the hole acts as though it is positron, even though in the Dirac Sea model there are no such real particles as positrons. This interpretation of reality is rather counter-intuitive. It has some appeal because it resolves certain problems in understanding relativistic quantum mechanics. However, I would emphasize that the observable manifestations of the Dirac Sea are essentially identical to the traditional understanding of physics. In other words, it is mostly a way of interpreting reality (and giving different labels to the same phenomena), but it doesn't change the basic observations. Dragons flight (talk) 15:49, 22 July 2010 (UTC)

speeding up the cell cycle

I would like my human lung cancer cells to be encouraged to do mitosis while on my slide. What are some common techniques I can use? If it makes the cell skip some cell cycle checks it's OK -- as long as it doesn't cause any major nondisjunction events or make the cells kill themselves afterwards. Is mitosis inhibited at room temperature? John Riemann Soong (talk) 16:03, 22 July 2010 (UTC)

Just a quick point: if they're human lung cancer cells, haven't they already missed out some cell cycle checks? Regards, --—Cyclonenim | Chat  16:12, 22 July 2010 (UTC)

Or they could have some oncogenes, or suppressed p53. I don't really know -- I am just given them to work with. I think I catch a lot of cells with no (or a non-obvious) nucleus -- I thought they were apoptotic at first, but apparently a lot of them are just in prophase. But prophase takes waaaayyyy too long. (My time frame for observation is 3-6 hours.)

I suppose I could have them express fluorescent proteins (connected to cell cycle events) so I know which cells to look for or observe, but it might be a few months before I can do that. John Riemann Soong (talk) 16:18, 22 July 2010 (UTC)

Btw, when I incubate these cells at 37C in the presence of nanorods, I often see a few of them inside the nucleus (confirmed by focal plane checks). The only way this could have happened I see, is that the nucleus was dissolved during the incubation process and then reformed around some of the gold particles. Incubation takes 2.5 to 4 hours (usually ~3). Is it the temperature? John Riemann Soong (talk) 16:21, 22 July 2010 (UTC)

Why would the cells' nuclei dissolve during incubation at 37C? As I'm sure you're aware, that's body temperature and you don't catch nuclei dissolving in our bodies during cell division. I don't know why the gold particles are getting inside the nucleus, but I doubt it's because of the temperature. I can't really visualise how nuclei form during cell division very clearly. Do they form similar to the cells themselves and form from the division itself, or do the cells divide and then form new nuclei once separated? Either way, can't see why temperature would make gold nanorods appear in the nuclei.

On a less spectulative note, can't you just use a sort of rotation system with the cells you need to use? You mentioned that a lot of them were in prophase, but presumably not all of them. Can you just select the cells that are already undergoing mitosis/about to undergo mitosis and use those? Then, when you need more, go back and select the ones that have recently matured enough to undergo mitosis? Regards, --—Cyclonenim | Chat  17:20, 22 July 2010 (UTC)

The nucleus dissolves during prophase, doesn't it? Also, mu group is more chemical and microengineering than biological, so keeping track of lung cancer cell cycles would be rather new to them. But, it may be something I might do once I get back to my home institution. I meant to ask whether room temperature inhibits the onset or completion of prophase. John Riemann Soong (talk) 17:28, 22 July 2010 (UTC)

Speeding up the cell cycle is probably not what you want. You might be interested in cell synchronization. The easiest method would be to remove the serum (which contains all those tasty growth factors that cancer cells really love) by growing the cells in serum-free media for about 24 hours, which should arrest many/most of them in G1, then adding back serum-containing media to kick them back into growth phase. You might not necessarily have them exactly timed, but you'd probably be able to bias the population so that many of them would divide during the hours that you're observing them. --- Medical geneticist (talk) 19:03, 22 July 2010 (UTC)

Conservation laws and FTU

I have read that there were thought experiments with the constants to refute the concept of the fine-tuned universe, but what about the conservation laws? From what I know, if, say, the conservation of baryon number is violated, then the matter would become unstable and decays. Or if the conservation of linear momentum is violated, then, as the article suggests, the center of mass of any system of objects will always continue with the different velocity (which would yield quite harmful effects as I think). Looks quite strange for the randomly formed universe. Twilightchill t 18:43, 22 July 2010 (UTC)

redout

I looked at our article, but it was a bit short, so my question is, at what point would a person experience redout? Is it something that is rapid, or sustained? Would a -3g maneuver cause redout if it only lasted 15 seconds? Googlemeister (talk) 18:45, 22 July 2010 (UTC)

Here's a fun demo some web-searching turned up: Classroom demonstrations in aerospace physiology (1963). Build your own red-out simulator! I'm having a hard time finding exact numbers, but the higher the G-force, the shorter the exposure-time needed to cause redout or blackout. Nimur (talk) 19:09, 22 July 2010 (UTC)

Fall of the ant

Why does a small creature like ant does not die by falling ? Is it simply because of air-resistance ?  Jon Ascton  (talk) 18:50, 22 July 2010 (UTC)

I suspect gravity plays a part; ie small insects weight a lot less so don't hit the ground as hard when they fall. 82.43.90.93 (talk) 19:19, 22 July 2010 (UTC)